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Sample records for selected young stellar

  1. The VISTA Carina Nebula Survey. II. Spatial distribution of the infrared-excess-selected young stellar population

    Science.gov (United States)

    Zeidler, P.; Preibisch, T.; Ratzka, T.; Roccatagliata, V.; Petr-Gotzens, M. G.

    2016-01-01

    We performed a deep wide-field (6.76 sq. deg) near-infrared survey with the VISTA telescope that covers the entire extent of the Carina nebula complex (CNC). The point-source catalog created from these data contains around four million individual objects down to masses of 0.1 M⊙. We present a statistical study of the large-scale spatial distribution and an investigation of the clustering properties of infrared-excesses objects, which are used to trace disk-bearing young stellar objects (YSOs). A selection based on a near-infrared (J-H) versus (H-Ks) color-color diagram shows an almost uniform distribution over the entire observed area. We interpret this as a result of the very high degree of background contamination that arises from the Carina Nebula's location close to the Galactic plane. Complementing the VISTA near-infrared catalog with Spitzer IRAC mid-infrared photometry improves the situation of the background contamination considerably. We find that a (J-H) versus (Ks- [4.5]) color-color diagram is well suited to tracing the population of YSO-candidates (cYSOs) by their infrared excess. We identify 8781 sources with strong infrared excess, which we consider as cYSOs. This sample is used to investigate the spatial distribution of the cYSOs with a nearest-neighbor analysis. The surface density distribution of cYSOs agrees well with the shape of the clouds as seen in our Herschel far-infrared survey. The strong decline in the surface density of excess sources outside the area of the clouds supports the hypothesis that our excess-selected sample consists predominantly of cYSOs with a low level of background contamination. This analysis allows us to identify 14 groups of cYSOs outside the central area.Our results suggest that the total population of cYSOs in the CNC comprises about 164 000 objects, with a substantial fraction (~35%) located in the northern, still not well studied parts. Our cluster analysis suggests that roughly half of the cYSOs constitute a

  2. Optical Monitoring of Young Stellar Objects

    Science.gov (United States)

    Kar, Aman; Jang-Condell, Hannah; Kasper, David; Findlay, Joseph; Kobulnicky, Henry A.

    2018-06-01

    Observing Young Stellar Objects (YSOs) for variability in different wavelengths enables us to understand the evolution and structure of the protoplanetary disks around stars. The stars observed in this project are known YSOs that show variability in the Infrared. Targets were selected from the Spitzer Space Telescope Young Stellar Object Variability (YSOVAR) Program, which monitored star-forming regions in the mid-infrared. The goal of our project is to investigate any correlation between the variability in the infrared versus the optical. Infrared variability of YSOs is associated with the heating of the protoplanetary disk while accretion signatures are observed in the H-alpha region. We used the University of Wyoming’s Red Buttes Observatory to monitor these stars for signs of accretion using an H-alpha narrowband filter and the Johnson-Cousins filter set, over the Summer of 2017. We perform relative photometry and inspect for an image-to-image variation by observing these targets for a period of four months every two to three nights. The study helps us better understand the link between accretion and H-alpha activity and establish a disk-star connection.

  3. Young and Exotic Stellar Zoo

    Science.gov (United States)

    2005-03-01

    Summary Super star clusters are groups of hundreds of thousands of very young stars packed into an unbelievably small volume. They represent the most extreme environments in which stars and planets can form. Until now, super star clusters were only known to exist very far away, mostly in pairs or groups of interacting galaxies. Now, however, a team of European astronomers [1] have used ESO's telescopes to uncover such a monster object within our own Galaxy, the Milky Way, almost, but not quite, in our own backyard! The newly found massive structure is hidden behind a large cloud of dust and gas and this is why it took so long to unveil its true nature. It is known as "Westerlund 1" and is a thousand times closer than any other super star cluster known so far. It is close enough that astronomers may now probe its structure in some detail. Westerlund 1 contains hundreds of very massive stars, some shining with a brilliance of almost one million suns and some two-thousand times larger than the Sun (as large as the orbit of Saturn)! Indeed, if the Sun were located at the heart of this remarkable cluster, our sky would be full of hundreds of stars as bright as the full Moon. Westerlund 1 is a most unique natural laboratory for the study of extreme stellar physics, helping astronomers to find out how the most massive stars in our Galaxy live and die. From their observations, the astronomers conclude that this extreme cluster most probably contains no less than 100,000 times the mass of the Sun, and all of its stars are located within a region less than 6 light-years across. Westerlund 1 thus appears to be the most massive compact young cluster yet identified in the Milky Way Galaxy. PR Photo 09a/05: The Super Star Cluster Westerlund 1 (2.2m MPG/ESO + WFI) PR Photo 09b/05: Properties of Young Massive Clusters Super Star Clusters Stars are generally born in small groups, mostly in so-called "open clusters" that typically contain a few hundred stars. From a wide range of

  4. YOUNG STELLAR CLUSTERS CONTAINING MASSIVE YOUNG STELLAR OBJECTS IN THE VVV SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Borissova, J.; Alegría, S. Ramírez; Kurtev, R.; Medina, N.; Navarro, C.; Kuhn, M.; Gromadzki, M.; Retamales, G.; Fernandez, M. A.; Agurto-Gangas, C.; Amigo, P. [Instituto de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Casilla 5030 (Chile); Alonso, J.; Decany, I. [Millennium Institute of Astrophysics (MAS), Santiago (Chile); Lucas, P. W.; Pena, C. Contreras; Thompson, M. A. [Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom); Chené, A.-N. [Gemini Observatory, Northern Operations Center, 670 N. A’ohoku Place, Hilo, HI 96720 (United States); Minniti, D. [Departamento de Ciencias Físicas, Universidad Andres Bello, Republica 220, Santiago (Chile); Catelan, M. [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22 (Chile); Morales, E. F. E., E-mail: jura.borissova@uv.cl [Max-Planck-Institute for Astronomy (Germany)

    2016-09-01

    The purpose of this research is to study the connections of the global properties of eight young stellar clusters projected in the Vista Variables in the Via Lactea (VVV) ESO Large Public Survey disk area and their young stellar object (YSO) populations. The analysis is based on the combination of spectroscopic parallax-based reddening and distance determinations with main-sequence and pre-main-sequence ishochrone fitting to determine the basic parameters (reddening, age, distance) of the sample clusters. The lower mass limit estimations show that all clusters are low or intermediate mass (between 110 and 1800  M {sub ⊙}), the slope Γ of the obtained present-day mass functions of the clusters is close to the Kroupa initial mass function. The YSOs in the cluster’s surrounding fields are classified using low resolution spectra, spectral energy distribution fits with theoretical predictions, and variability, taking advantage of multi-epoch VVV observations. All spectroscopically confirmed YSOs (except one) are found to be massive (more than 8 M {sub ⊙}). Using VVV and GLIMPSE color–color cuts we have selected a large number of new YSO candidates, which are checked for variability and 57% are found to show at least low-amplitude variations. In few cases it was possible to distinguish between YSO and AGB classifications on the basis of light curves.

  5. THE YOUNG STELLAR POPULATION OF LYNDS 1340. AN INFRARED VIEW

    International Nuclear Information System (INIS)

    Kun, M.; Moór, A.; Wolf-Chase, G.; Apai, D.; Balog, Z.; O’Linger-Luscusk, J.; Moriarty-Schieven, G. H.

    2016-01-01

    We present results of an infrared study of the molecular cloud Lynds 1340, forming three groups of low- and intermediate-mass stars. Our goals are to identify and characterize the young stellar population of the cloud, study the relationships between the properties of the cloud and the emergent stellar groups, and integrate L1340 into the picture of the star-forming activity of our Galactic environment. We selected candidate young stellar objects (YSOs) from the Spitzer and WISE databases using various published color criteria and classified them based on the slope of the spectral energy distribution (SED). We identified 170 Class II, 27 flat SED, and 45 Class 0/I sources. High angular resolution near-infrared observations of the RNO 7 cluster, embedded in L1340, revealed eight new young stars of near-infrared excess. The surface density distribution of YSOs shows three groups, associated with the three major molecular clumps of L1340, each consisting of ≲100 members, including both pre-main-sequence stars and embedded protostars. New Herbig–Haro objects were identified in the Spitzer images. Our results demonstrate that L1340 is a prolific star-forming region of our Galactic environment in which several specific properties of the intermediate-mass mode of star formation can be studied in detail.

  6. THE YOUNG STELLAR POPULATION OF LYNDS 1340. AN INFRARED VIEW

    Energy Technology Data Exchange (ETDEWEB)

    Kun, M.; Moór, A. [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege út 15-17 (Hungary); Wolf-Chase, G. [Astronomy Department, Adler Planetarium, 1300 South Lake Shore Drive, Chicago, IL 60605 (United States); Apai, D. [Steward Observatory, 933 N. Cherry Avenue, Tucson, AZ 85719 (United States); Balog, Z. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); O’Linger-Luscusk, J. [On leave from California Institute of Technology, 1200 E. California Avenue, Pasadena, CA 91125 (United States); Moriarty-Schieven, G. H., E-mail: kun@konkoly.hu [National Research Council—Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)

    2016-06-01

    We present results of an infrared study of the molecular cloud Lynds 1340, forming three groups of low- and intermediate-mass stars. Our goals are to identify and characterize the young stellar population of the cloud, study the relationships between the properties of the cloud and the emergent stellar groups, and integrate L1340 into the picture of the star-forming activity of our Galactic environment. We selected candidate young stellar objects (YSOs) from the Spitzer and WISE databases using various published color criteria and classified them based on the slope of the spectral energy distribution (SED). We identified 170 Class II, 27 flat SED, and 45 Class 0/I sources. High angular resolution near-infrared observations of the RNO 7 cluster, embedded in L1340, revealed eight new young stars of near-infrared excess. The surface density distribution of YSOs shows three groups, associated with the three major molecular clumps of L1340, each consisting of ≲100 members, including both pre-main-sequence stars and embedded protostars. New Herbig–Haro objects were identified in the Spitzer images. Our results demonstrate that L1340 is a prolific star-forming region of our Galactic environment in which several specific properties of the intermediate-mass mode of star formation can be studied in detail.

  7. Young Stellar Objects from Soft to Hard X-rays

    Science.gov (United States)

    Güdel, Manuel

    2009-05-01

    Magnetically active stars are the sites of efficient particle acceleration and plasma heating, processes that have been studied in detail in the solar corona. Investigation of such processes in young stellar objects is much more challenging due to various absorption processes. There is, however, evidence for violent magnetic energy release in very young stellar objects. The impact on young stellar environments (e.g., circumstellar disk heating and ionization, operation of chemical networks, photoevaporation) may be substantial. Hard X-ray devices like those carried on Simbol-X will establish a basis for detailed studies of these processes.

  8. YOUNG STELLAR OBJECTS IN THE GOULD BELT

    Energy Technology Data Exchange (ETDEWEB)

    Dunham, Michael M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, MA 02138 (United States); Allen, Lori E. [National Optical Astronomy Observatories, Tucson, AZ (United States); Evans II, Neal J.; Harvey, Paul M. [Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205 (United States); Broekhoven-Fiene, Hannah [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 3P6 (Canada); Cieza, Lucas A. [Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago (Chile); Di Francesco, James; Johnstone, Doug; Matthews, Brenda C. [National Research Council of Canada, Herzberg Astronomy and Astrophysics Programs, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada); Gutermuth, Robert A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Hatchell, Jennifer [Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Heiderman, Amanda [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States); Huard, Tracy L. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Kirk, Jason M. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE (United Kingdom); Miller, Jennifer F. [Gemini Observatory, 670 N. A’ohoku Place, Hilo, HI 96720 (United States); Peterson, Dawn E. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); Young, Kaisa E., E-mail: mdunham@cfa.harvard.edu [Department of Physical Sciences, Nicholls State University, P.O. Box 2022, Thibodaux, LA 70310 (United States)

    2015-09-15

    We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope “cores to disks” (c2d) and “Gould Belt” (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the GB. We compile extinction corrected spectral energy distributions for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0 + I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background Asymptotic Giant Branch stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40–0.78 Myr for Class 0 + I YSOs and 0.26–0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0 + I sample is classified as Class 0, leading to durations of 0.13–0.26 Myr (Class 0) and 0.27–0.52 Myr (Class I). We revisit infrared color–color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.

  9. YOUNG STELLAR OBJECTS IN THE GOULD BELT

    International Nuclear Information System (INIS)

    Dunham, Michael M.; Allen, Lori E.; Evans II, Neal J.; Harvey, Paul M.; Broekhoven-Fiene, Hannah; Cieza, Lucas A.; Di Francesco, James; Johnstone, Doug; Matthews, Brenda C.; Gutermuth, Robert A.; Hatchell, Jennifer; Heiderman, Amanda; Huard, Tracy L.; Kirk, Jason M.; Miller, Jennifer F.; Peterson, Dawn E.; Young, Kaisa E.

    2015-01-01

    We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope “cores to disks” (c2d) and “Gould Belt” (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the GB. We compile extinction corrected spectral energy distributions for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0 + I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background Asymptotic Giant Branch stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40–0.78 Myr for Class 0 + I YSOs and 0.26–0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0 + I sample is classified as Class 0, leading to durations of 0.13–0.26 Myr (Class 0) and 0.27–0.52 Myr (Class I). We revisit infrared color–color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs

  10. Warm gas towards young stellar objects in Corona Australis

    DEFF Research Database (Denmark)

    Lindberg, Johan; Jørgensen, Jes Kristian; D. Green, Joel

    2014-01-01

    The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an interm......The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated...... by an intermediate-mass young star. We study the effects on the warm gas and dust in a group of low-mass young stellar objects from the irradiation by the young luminous Herbig Be star R CrA. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented...... Be star R CrA. Our results show that a nearby luminous star does not increase the molecular excitation temperatures in the warm gas around a young stellar object (YSO). However, the emission from photodissociation products of H2O, such as OH and O, is enhanced in the warm gas associated...

  11. Radio continuum emission from young stellar objects in L1641

    International Nuclear Information System (INIS)

    Morgan, J.A.; Snell, R.L.; Strom, K.M.

    1990-01-01

    The results of a 6 and 20 cm radio continuum survey of young stellar objects in the L1641 region located south of the Orion Nebula are presented. Four are identified as low-luminosity young stellar objects in L1641 and three more as Herbig-Haro or Herbig-Haro-like objects. These objects have bolometric luminosities between 80 and 300 solar, and their 6-20 cm spectral index suggests optically thick, free-free emission. They are characterized by a rising spectrum between 2.2 and 25 microns, have no optical counterparts, and are associated with stellar wind activity. Thus, detectable radio continuum emission may be produced only by the youngest and most luminous objects in L1641. 34 refs

  12. Intracluster age gradients in numerous young stellar clusters

    Science.gov (United States)

    Getman, K. V.; Feigelson, E. D.; Kuhn, M. A.; Bate, M. R.; Broos, P. S.; Garmire, G. P.

    2018-05-01

    The pace and pattern of star formation leading to rich young stellar clusters is quite uncertain. In this context, we analyse the spatial distribution of ages within 19 young (median t ≲ 3 Myr on the Siess et al. time-scale), morphologically simple, isolated, and relatively rich stellar clusters. Our analysis is based on young stellar object (YSO) samples from the Massive Young Star-Forming Complex Study in Infrared and X-ray and Star Formation in Nearby Clouds surveys, and a new estimator of pre-main sequence (PMS) stellar ages, AgeJX, derived from X-ray and near-infrared photometric data. Median cluster ages are computed within four annular subregions of the clusters. We confirm and extend the earlier result of Getman et al. (2014): 80 per cent of the clusters show age trends where stars in cluster cores are younger than in outer regions. Our cluster stacking analyses establish the existence of an age gradient to high statistical significance in several ways. Time-scales vary with the choice of PMS evolutionary model; the inferred median age gradient across the studied clusters ranges from 0.75 to 1.5 Myr pc-1. The empirical finding reported in the present study - late or continuing formation of stars in the cores of star clusters with older stars dispersed in the outer regions - has a strong foundation with other observational studies and with the astrophysical models like the global hierarchical collapse model of Vázquez-Semadeni et al.

  13. The Effects of Stellar Dynamics on the Evolution of Young, Dense Stellar Systems

    Science.gov (United States)

    Belkus, H.; van Bever, J.; Vanbeveren, D.

    In this paper, we report on first results of a project in Brussels in which we study the effects of stellar dynamics on the evolution of young dense stellar systems using 3 decades of expertise in massive-star evolution and our population (number and spectral) synthesis code. We highlight an unconventionally formed object scenario (UFO-scenario) for Wolf Rayet binaries and study the effects of a luminous blue variable-type instability wind mass-loss formalism on the formation of intermediate-mass black holes.

  14. ASSESSMENT OF STELLAR STRATIFICATION IN THREE YOUNG STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Gouliermis, Dimitrios A.; Rochau, Boyke; Mackey, Dougal; Xin Yu

    2010-01-01

    We present a comprehensive study of stellar stratification in young star clusters in the Large Magellanic Cloud (LMC). We apply our recently developed effective radius method for the assessment of stellar stratification on imaging data obtained with the Advanced Camera for Surveys of three young LMC clusters to characterize the phenomenon and develop a comparative scheme for its assessment in such clusters. The clusters of our sample, NGC 1983, NGC 2002, and NGC 2010, are selected on the basis of their youthfulness, and their variety in appearance, structure, stellar content, and surrounding stellar ambient. Our photometry is complete for magnitudes down to m 814 ≅ 23 mag, allowing the calculation of the structural parameters of the clusters, the estimation of their ages, and the determination of their stellar content. Our study shows that each cluster in our sample demonstrates stellar stratification in a quite different manner and at different degree from the others. Specifically, NGC 1983 shows partial segregation, with the effective radius increasing with fainter magnitudes only for the faintest stars of the cluster. Our method on NGC 2002 provides evidence of strong stellar stratification for both bright and faint stars; the cluster demonstrates the phenomenon with the highest degree in the sample. Finally, NGC 2010 is not segregated, as its bright stellar content is not centrally concentrated, the relation of effective radius to magnitude for stars of intermediate brightness is rather flat, and we find no evidence of stratification for its faintest stars. For the parameterization of the phenomenon of stellar stratification and its quantitative comparison among these clusters, we propose the slope derived from the change in the effective radius over the corresponding magnitude range as indicative parameter of the degree of stratification in the clusters. A positive value of this slope indicates mass segregation in the cluster, while a negative or zero value

  15. Young Stellar Variability of GM Cephei by Circumstellar Dust Clumps

    Science.gov (United States)

    Huang, Po-Chieh; Chen, Wen-Ping; Hu, Chia-Ling; Burkhonov, Otabek; Ehgamberdiev, Shuhrat; Liu, Jinzhong; Naito, Hiroyuki; Pakstiene, Erika; Qvam, Jan Kare Trandem; Rätz, Stefanie; Semkov, Evgeni

    2018-04-01

    UX Orionis stars are a sub-type of Herbig Ae/be or T Tauri stars exhibiting sporadic extinction of stellar light due to circumstellar dust obscuration. GM Cep is such an UX Orionis star in the young (∼ 4 Myr) open cluster Trumpler 37 at ∼ 900 pc, showing a prominent infrared access, H-alpha emission, and flare activity. Our multi-color photometric monitoring from 2009 to 2016 showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) cyclic, but not strictly periodical, occultation events, each lasting for a couple months, with a probable recurrence time of about two years, (iii) normal dust reddening as the star became redder when dimmer, (iv) the unusual "blueing" phenomena near the brightness minima, during which the star appeared bluer when dimmer, and (v) a noticeable polarization, from 3 to 9 percent in g', r', and i' -bands. The occultation events may be caused by dust clumps, signifying the density inhomogeneity in a young stellar disk from grain coagulation to planetesimal formation. The level of polarization was anti-correlated with the brightness in the bright state, when the dust clump backscattered stellar light. We discussed two potential hypotheses: orbiting dust clumps versus dust clumps along a spiral arm structure.

  16. Mapping young stellar populations towards Orion with Gaia DR1

    Science.gov (United States)

    Zari, Eleonora; Brown, Anthony G. A.

    2018-04-01

    OB associations are prime sites for the study of star formation processes and of the interaction between young massive stars with the interstellar medium. Furthermore, the kinematics and structure of the nearest OB associations provide detailed insight into the properties and origin of the Gould Belt. In this context, the Orion complex has been extensively studied. However, the spatial distribution of the stellar population is still uncertain: in particular, the distances and ages of the various sub-groups composing the Orion OB association, and their connection to the surrounding interstellar medium, are not well determined. We used the first Gaia data release to characterize the stellar population in Orion, with the goal to obtain new distance and age estimates of the numerous stellar groups composing the Orion OB association. We found evidence of the existence of a young and rich population spread over the entire region, loosely clustered around some known groups. This newly discovered population of young stars provides a fresh view of the star formation history of the Orion region.

  17. SED Modeling of 20 Massive Young Stellar Objects

    Science.gov (United States)

    Tanti, Kamal Kumar

    In this paper, we present the spectral energy distributions (SEDs) modeling of twenty massive young stellar objects (MYSOs) and subsequently estimated different physical and structural/geometrical parameters for each of the twenty central YSO outflow candidates, along with their associated circumstellar disks and infalling envelopes. The SEDs for each of the MYSOs been reconstructed by using 2MASS, MSX, IRAS, IRAC & MIPS, SCUBA, WISE, SPIRE and IRAM data, with the help of a SED Fitting Tool, that uses a grid of 2D radiative transfer models. Using the detailed analysis of SEDs and subsequent estimation of physical and geometrical parameters for the central YSO sources along with its circumstellar disks and envelopes, the cumulative distribution of the stellar, disk and envelope parameters can be analyzed. This leads to a better understanding of massive star formation processes in their respective star forming regions in different molecular clouds.

  18. Circumstellar Disk Lifetimes In Numerous Galactic Young Stellar Clusters

    Science.gov (United States)

    Richert, A. J. W.; Getman, K. V.; Feigelson, E. D.; Kuhn, M. A.; Broos, P. S.; Povich, M. S.; Bate, M. R.; Garmire, G. P.

    2018-04-01

    Photometric detections of dust circumstellar disks around pre-main sequence (PMS) stars, coupled with estimates of stellar ages, provide constraints on the time available for planet formation. Most previous studies on disk longevity, starting with Haisch, Lada & Lada (2001), use star samples from PMS clusters but do not consider datasets with homogeneous photometric sensitivities and/or ages placed on a uniform timescale. Here we conduct the largest study to date of the longevity of inner dust disks using X-ray and 1-8 {μ m} infrared photometry from the MYStIX and SFiNCs projects for 69 young clusters in 32 nearby star-forming regions with ages t ≤ 5 Myr. Cluster ages are derived by combining the empirical AgeJX method with PMS evolutionary models, which treat dynamo-generated magnetic fields in different ways. Leveraging X-ray data to identify disk-free objects, we impose similar stellar mass sensitivity limits for disk-bearing and disk-free YSOs while extending the analysis to stellar masses as low as M ˜ 0.1 M⊙. We find that the disk longevity estimates are strongly affected by the choice of PMS evolutionary model. Assuming a disk fraction of 100% at zero age, the inferred disk half-life changes significantly, from t1/2 ˜ 1.3 - 2 Myr to t1/2 ˜ 3.5 Myr when switching from non-magnetic to magnetic PMS models. In addition, we find no statistically significant evidence that disk fraction varies with stellar mass within the first few Myr of life for stars with masses <2 M⊙, but our samples may not be complete for more massive stars. The effects of initial disk fraction and star-forming environment are also explored.

  19. EXPLOSIVE DISINTEGRATION OF A MASSIVE YOUNG STELLAR SYSTEM IN ORION

    International Nuclear Information System (INIS)

    Zapata, Luis A.; Schmid-Burgk, Johannes; Menten, Karl M.; Ho, Paul T. P.; Rodriguez, Luis F.

    2009-01-01

    Young massive stars in the center of crowded star clusters are expected to undergo close dynamical encounters that could lead to energetic, explosive events. However, there has so far never been clear observational evidence of such a remarkable phenomenon. We here report new interferometric observations that indicate the well-known enigmatic wide-angle outflow located in the Orion BN/KL star-forming region to have been produced by such a violent explosion during the disruption of a massive young stellar system, and that this was caused by a close dynamical interaction about 500 years ago. This outflow thus belongs to a totally different family of molecular flows that is not related to the classical bipolar flows that are generated by stars during their formation process. Our molecular data allow us to create a three-dimensional view of the debris flow and to link this directly to the well-known Orion H 2 'fingers' farther out.

  20. Explosive Disintegration of a Massive Young Stellar System in Orion

    Science.gov (United States)

    Zapata, Luis A.; Schmid-Burgk, Johannes; Ho, Paul T. P.; Rodríguez, Luis F.; Menten, Karl M.

    2009-10-01

    Young massive stars in the center of crowded star clusters are expected to undergo close dynamical encounters that could lead to energetic, explosive events. However, there has so far never been clear observational evidence of such a remarkable phenomenon. We here report new interferometric observations that indicate the well-known enigmatic wide-angle outflow located in the Orion BN/KL star-forming region to have been produced by such a violent explosion during the disruption of a massive young stellar system, and that this was caused by a close dynamical interaction about 500 years ago. This outflow thus belongs to a totally different family of molecular flows that is not related to the classical bipolar flows that are generated by stars during their formation process. Our molecular data allow us to create a three-dimensional view of the debris flow and to link this directly to the well-known Orion H2 "fingers" farther out.

  1. IRAS 20050+2720: ANATOMY OF A YOUNG STELLAR CLUSTER

    International Nuclear Information System (INIS)

    Günther, H. M.; Wolk, S. J.; Spitzbart, B.; Forbrich, J.; Wright, N. J.; Bourke, T. L.; Gutermuth, R. A.; Allen, L.; Megeath, S. T.; Pipher, J. L.

    2012-01-01

    IRAS 20050+2720 is young star-forming region at a distance of 700 pc without apparent high-mass stars. We present results of our multi-wavelength study of IRAS 20050+2720 which includes observations by Chandra and Spitzer, and Two Micron All Sky Survey and UBVRI photometry. In total, about 300 young stellar objects (YSOs) in different evolutionary stages are found. We characterize the distribution of YSOs in this region using a minimum spanning tree analysis. We newly identify a second cluster core, which consists mostly of class II objects, about 10' from the center of the cloud. YSOs of earlier evolutionary stages are more clustered than more evolved objects. The X-ray luminosity function (XLF) of IRAS 20050+2720 is roughly lognormal, but steeper than the XLF of the more massive Orion Nebula complex. IRAS 20050+2720 shows a lower N H /A K ratio compared with the diffuse interstellar medium.

  2. Hypervelocity stars from young stellar clusters in the Galactic Centre

    Science.gov (United States)

    Fragione, G.; Capuzzo-Dolcetta, R.; Kroupa, P.

    2017-05-01

    The enormous velocities of the so-called hypervelocity stars (HVSs) derive, likely, from close interactions with massive black holes, binary stars encounters or supernova explosions. In this paper, we investigate the origin of HVSs as consequence of the close interaction between the Milky Way central massive black hole and a passing-by young stellar cluster. We found that both single and binary HVSs may be generated in a burst-like event, as the cluster passes near the orbital pericentre. High-velocity stars will move close to the initial cluster orbital plane and in the direction of the cluster orbital motion at the pericentre. The binary fraction of these HVS jets depends on the primordial binary fraction in the young cluster. The level of initial mass segregation determines the value of the average mass of the ejected stars. Some binary stars will merge, continuing their travel across and out of the Galaxy as blue stragglers.

  3. Employing Machine-Learning Methods to Study Young Stellar Objects

    Science.gov (United States)

    Moore, Nicholas

    2018-01-01

    Vast amounts of data exist in the astronomical data archives, and yet a large number of sources remain unclassified. We developed a multi-wavelength pipeline to classify infrared sources. The pipeline uses supervised machine learning methods to classify objects into the appropriate categories. The program is fed data that is already classified to train it, and is then applied to unknown catalogues. The primary use for such a pipeline is the rapid classification and cataloging of data that would take a much longer time to classify otherwise. While our primary goal is to study young stellar objects (YSOs), the applications extend beyond the scope of this project. We present preliminary results from our analysis and discuss future applications.

  4. IRAS 20050+2720: ANATOMY OF A YOUNG STELLAR CLUSTER

    Energy Technology Data Exchange (ETDEWEB)

    Guenther, H. M.; Wolk, S. J.; Spitzbart, B.; Forbrich, J.; Wright, N. J.; Bourke, T. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Allen, L. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Megeath, S. T. [Department of Physics and Astronomy, MS-113, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606 (United States); Pipher, J. L., E-mail: hguenther@cfa.harvard.edu [Department of Physics and Astronomy, University of Rochester, 500 Wilson Boulevard, Rochester, NY 14627 (United States)

    2012-10-01

    IRAS 20050+2720 is young star-forming region at a distance of 700 pc without apparent high-mass stars. We present results of our multi-wavelength study of IRAS 20050+2720 which includes observations by Chandra and Spitzer, and Two Micron All Sky Survey and UBVRI photometry. In total, about 300 young stellar objects (YSOs) in different evolutionary stages are found. We characterize the distribution of YSOs in this region using a minimum spanning tree analysis. We newly identify a second cluster core, which consists mostly of class II objects, about 10' from the center of the cloud. YSOs of earlier evolutionary stages are more clustered than more evolved objects. The X-ray luminosity function (XLF) of IRAS 20050+2720 is roughly lognormal, but steeper than the XLF of the more massive Orion Nebula complex. IRAS 20050+2720 shows a lower N{sub H}/A{sub K} ratio compared with the diffuse interstellar medium.

  5. Activity cycles in members of young loose stellar associations

    Science.gov (United States)

    Distefano, E.; Lanzafame, A. C.; Lanza, A. F.; Messina, S.; Spada, F.

    2017-10-01

    Context. Magnetic cycles analogous to the solar cycle have been detected in tens of solar-like stars by analyzing long-term time series of different magnetic activity indexes. The relationship between the cycle properties and global stellar parameters is not fully understood yet. One reason for this is the lack of long-term time series for stars covering a wide range of stellar parameters. Aims: We searched for activity cycles in a sample of 90 young solar-like stars with ages between 4 and 95 Myr with the aim to investigate the properties of activity cycles in this age range. Methods: We measured the length Pcyc of a given cycle by analyzing the long-term time series of three different activity indexes: the period of rotational modulation, the amplitude of the rotational modulation and the median magnitude in the V band. For each star, we also computed the global magnetic activity index ⟨ IQR ⟩ that is proportional to the amplitude of the rotational modulation and can be regarded as a proxy of the mean level of the surface magnetic activity. Results: We detected activity cycles in 67 stars. Secondary cycles were also detected in 32 stars of the sample. The lack of correlation between Pcyc and Prot and the position of our targets in the Pcyc/Prot-Ro-1 diagram suggest that these stars belong to the so-called transitional branch and that the dynamo acting in these stars is different from the solar dynamo and from that acting in the older Mt. Wilson stars. This statement is also supported by the analysis of the butterfly diagrams whose patterns are very different from those seen in the solar case. We computed the Spearman correlation coefficient rS between Pcyc, ⟨ IQR ⟩ and various stellar parameters. We found that Pcyc in our sample is uncorrelated with all the investigated parameters. The ⟨ IQR ⟩ index is positively correlated with the convective turnover timescale, the magnetic diffusivity timescale τdiff, and the dynamo number DN, whereas it is anti

  6. Imaging Young Stellar Objects with VLTi/PIONIER

    Science.gov (United States)

    Kluska, J.; Malbet, F.; Berger, J.-P.; Benisty, M.; Lazareff, B.; Le Bouquin, J.-B.; Baron, F.; Dominik, C.; Isella, A.; Juhasz, A.; Kraus, S.; Lachaume, R.; Ménard, F.; Millan-Gabet, R.; Monnier, J.; Pinte, C.; Soulez, F.; Tallon, M.; Thi, W.-F.; Thiébaut, É.; Zins, G.

    2014-04-01

    Optical interferometry imaging is designed to help us to reveal complex astronomical sources without a prior model. Among these complex objects are the young stars and their environments, which have a typical morphology with a point-like source, surrounded by circumstellar material with unknown morphology. To image them, we have developed a numerical method that removes completely the stellar point source and reconstructs the rest of the image, using the differences in the spectral behavior between the star and its circumstellar material. We aim to reveal the first Astronomical Units of these objects where many physical phenomena could interplay: the dust sublimation causing a puffed-up inner rim, a dusty halo, a dusty wind or an inner gaseous component. To investigate more deeply these regions, we carried out the first Large Program survey of HAeBe stars with two main goals: statistics on the geometry of these objects at the first astronomical unit scale and imaging their very close environment. The images reveal the environment, which is not polluted by the star and allows us to derive the best fit for the flux ratio and the spectral slope. We present the first images from this survey and the application of the imaging method on other astronomical objects.

  7. Variability of Massive Young Stellar Objects in Cygnus-X

    Science.gov (United States)

    Thomas, Nancy H.; Hora, J. L.; Smith, H. A.

    2013-01-01

    Young stellar objects (YSOs) are stars in the process of formation. Several recent investigations have shown a high rate of photometric variability in YSOs at near- and mid-infrared wavelengths. Theoretical models for the formation of massive stars (1-10 solar masses) remain highly idealized, and little is known about the mechanisms that produce the variability. An ongoing Spitzer Space Telescope program is studying massive star formation in the Cygnus-X region. In conjunction with the Spitzer observations, we have conducted a ground-based near-infrared observing program of the Cygnus-X DR21 field using PAIRITEL, the automated infrared telescope at Whipple Observatory. Using the Stetson index for variability, we identified variable objects and a number of variable YSOs in our time-series PAIRITEL data of DR21. We have searched for periodicity among our variable objects using the Lomb-Scargle algorithm, and identified periodic variable objects with an average period of 8.07 days. Characterization of these variable and periodic objects will help constrain models of star formation present. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

  8. Modeling tracers of young stellar population age in star-forming galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Levesque, Emily M. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado 389-UCB, Boulder, CO 80309 (United States); Leitherer, Claus, E-mail: Emily.Levesque@colorado.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2013-12-20

    The young stellar population of a star-forming galaxy is the primary engine driving its radiative properties. As a result, the age of a galaxy's youngest generation of stars is critical for a detailed understanding of its star formation history, stellar content, and evolutionary state. Here we present predicted equivalent widths for the Hβ, Hα, and Brγ recombination lines as a function of stellar population age. The equivalent widths are produced by the latest generations of stellar evolutionary tracks and the Starburst99 stellar population synthesis code, and are the first to fully account for the combined effects of both nebular emission and continuum absorption produced by the synthetic stellar population. Our grid of model stellar populations spans six metallicities (0.001 < Z < 0.04), two treatments of star formation history (a 10{sup 6} M {sub ☉} instantaneous burst and a continuous star formation rate of 1 M {sub ☉} yr{sup –1}), and two different treatments of initial rotation rate (v {sub rot} = 0.0v {sub crit} and 0.4v {sub crit}). We also investigate the effects of varying the initial mass function. Given constraints on galaxy metallicity, our predicted equivalent widths can be applied to observations of star-forming galaxies to approximate the age of their young stellar populations.

  9. CO-ices in embedded Young Stellar Objects

    Science.gov (United States)

    Teixeira, Teresa Cláeira V. S.

    1998-09-01

    Stars are born in dense cores within molecular clouds, enshrouded in large cocoons of gas and dust which completely obscure the forming star. The large degree of obscuration towards the young stars is due to the presence of solid dust grains in their circumstellar envelopes, which efficiently absorb the radiation from the star at visual and ultraviolet wavelengths, reradiating that energy at far-infrared and submillimeter wavelengths. The composition and structure of the dust grains is not well known, but current studies point to grains having a refractory core and acquiring ice mantles in the cool, shielded conditions of molecular clouds. Such ice mantles are the subject of this thesis. Infrared spectroscopy is an important tool in the study of the complex ice mantles on interstellar grains. A variety of absorption features at these wavelengths, which have been identified as the vibrational transitions of the molecules in the ices, can provide important information on the composition, structure and evolution of the grains. The work reported in this thesis consists of an observational study of the composition of the ice mantles acquired by the dust grains in molecular clouds (with particular emphasis on the CO-ices in the material surrounding embedded Young Stellar Objects in nearby molecular clouds), what can be learned from that about the physical conditions in the regions where the ice mantles exist, and what may affect their survival and evolution. In this work, spectra of the 4.67 micron solid CO absorption feature are presented, mostly towards embedded objects in Taurus. The thesis starts with a brief overview of technical aspects of spectroscopic observations at thermal infrared wavelengths, where the CO stretch absorption feature is located. The observations and data reduction procedures are then reported and discussed in detail. The likely composition of the CO-bearing ices is analysed by fitting the observations with laboratory data. The statistical

  10. THE FORMATION OF SECONDARY STELLAR GENERATIONS IN MASSIVE YOUNG STAR CLUSTERS FROM RAPIDLY COOLING SHOCKED STELLAR WINDS

    Energy Technology Data Exchange (ETDEWEB)

    Wünsch, R.; Palouš, J.; Ehlerová, S. [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague (Czech Republic); Tenorio-Tagle, G. [Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla, México (Mexico)

    2017-01-20

    We study a model of rapidly cooling shocked stellar winds in young massive clusters and estimate the circumstances under which secondary star formation, out of the reinserted winds from a first stellar generation (1G), is possible. We have used two implementations of the model: a highly idealized, computationally inexpensive, spherically symmetric semi-analytic model, and a complex, three-dimensional radiation-hydrodynamic, simulation; they are in a good mutual agreement. The results confirm our previous findings that, in a cluster with 1G mass 10{sup 7} M {sub ⊙} and half-mass–radius 2.38 pc, the shocked stellar winds become thermally unstable, collapse into dense gaseous structures that partially accumulate inside the cluster, self-shield against ionizing stellar radiation, and form the second generation (2G) of stars. We have used the semi-analytic model to explore a subset of the parameter space covering a wide range of the observationally poorly constrained parameters: the heating efficiency, η {sub he}, and the mass loading, η {sub ml}. The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if η {sub he} ≲ 10%, which is suggested by the observations. Furthermore, for low η {sub he}, the model provides a self-consistent mechanism predicting 2G stars forming only in the central zones of the cluster. Finally, we have calculated the accumulated warm gas emission in the H30 α recombination line, analyzed its velocity profile, and estimated its intensity for super star clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas should be detectable with ALMA.

  11. Young stellar populations in early-type galaxies in the Sloan Digital Sky Survey

    Science.gov (United States)

    Nolan, Louisa A.; Raychaudhury, Somak; Kabán, Ata

    2007-02-01

    We use a purely data-driven rectified factor analysis to identify early-type galaxies with recent star formation in Data Release 4 of the Sloan Digital Sky Survey Spectroscopic Catalogue. We compare the spectra and environment of these galaxies with those of `normal' early-type galaxies, and a sample of independently selected E+A galaxies. We calculate the projected local galaxy surface density from the nearest five and 10 neighbours (Σ5 and Σ10) for each galaxy in our sample, and find that the dependence on projected local density, of the properties of E+A galaxies, is not significantly different from that of early-type galaxies with young stellar populations, dropping off rapidly towards denser environments, and flattening off at densities ~10 per cent of the stellar mass in these galaxies. This, together with the similarity of the environments in which this `E+F' population and the E+A galaxy sample are found, suggests that E+F galaxies used to be E+A galaxies, but have evolved by a further ~ one to a few Gyr. Our rectified factor analysis is sensitive enough to identify this hidden population, which allows us to study the global and intrinsic properties of early-type galaxies created in major mergers or interactions, and compare them with those early-types which have had the bulk of their stars in place since a much earlier epoch.

  12. Ionised Jets Associated With Massive Young Stellar Objects

    Science.gov (United States)

    Purser, Simon John Derek

    2017-09-01

    This thesis focuses on the phenomena of ionised jets associated with massive young stellar objects. Firstly a study was conducted with the aim to establish a statistical sample of such objects. Radio observations towards a sample of 49 MYSOs resulted in the detection of 28 objects classified as ionised jets. The jets’ radio luminosities scaled with their MYSOs’ bolometric luminosities in the same way as for low-mass examples. This infers that the jet launching and collimation mechanisms of high-mass jets are very similar to that in their low-mass counterparts and they are ejected for the last ≤65000 yr of the MYSO phase. Interestingly non-thermal emission was regularly detected towards spatially distinct radio lobes (associated with ˜50% of the jets), suggesting the presence of synchrotron emission and therefore, magnetic fields. With an average spectral index of ¯α=‑0. 55 (indicative of the 1st order Fermi acceleration mechanism) it is concluded these lobes are the result of shocks in the jets’ stream. My second science chapter is a study of radio variability, precession and proper motions towards a subset of objects from the first chapter. Over a two year time period, no significant variability and only one example of proper motion (1800±600 km s‑1) was detected. Precession was found to be commonplace however and if it arises as the result of binary interactions, we infer orbital radii between 30 and 1800 au for the binary companions. Lastly, high-resolution, VLA observations at C and Q-bands were analysed to extend the known sample of MYSOs harbouring ionised jets into the northern hemisphere. Only 3 radio sources were detected possessing jet-like characteristics towards the work’s sub-sample of 8 IRDCs containing 44 mm-cores (in our field of view), highlighting the radio-quiet (≳30μJy) nature of this early phase in massive star formation. Towards the RMS survey derived sample of 48 MYSOs, a total of 38 radio sources with jet

  13. Classifying the embedded young stellar population in Perseus and Taurus and the LOMASS database

    NARCIS (Netherlands)

    Carney, M.T.; Yıldız, U.; Mottram, J.C.; Dishoeck, van E.F.; Ramchandani, J.; Jørgensen, J.K.

    2016-01-01

    Context. The classification of young stellar objects (YSOs) is typically done using the infrared spectral slope or bolometric temperature, but either can result in contamination of samples. More accurate methods to determine the evolutionary stage of YSOs will improve the reliability of statistics

  14. Gas expulsion vs gas retention in young stellar clusters II: effects of cooling and mass segregation

    Science.gov (United States)

    Silich, Sergiy; Tenorio-Tagle, Guillermo

    2018-05-01

    Gas expulsion or gas retention is a central issue in most of the models for multiple stellar populations and light element anti-correlations in globular clusters. The success of the residual matter expulsion or its retention within young stellar clusters has also a fundamental importance in order to understand how star formation proceeds in present-day and ancient star-forming galaxies and if proto-globular clusters with multiple stellar populations are formed in the present epoch. It is usually suggested that either the residual gas is rapidly ejected from star-forming clouds by stellar winds and supernova explosions, or that the enrichment of the residual gas and the formation of the second stellar generation occur so rapidly, that the negative stellar feedback is not significant. Here we continue our study of the early development of star clusters in the extreme environments and discuss the restrictions that strong radiative cooling and stellar mass segregation provide on the gas expulsion from dense star-forming clouds. A large range of physical initial conditions in star-forming clouds which include the star-forming cloud mass, compactness, gas metallicity, star formation efficiency and effects of massive stars segregation are discussed. It is shown that in sufficiently massive and compact clusters hot shocked winds around individual massive stars may cool before merging with their neighbors. This dramatically reduces the negative stellar feedback, prevents the development of the global star cluster wind and expulsion of the residual and the processed matter into the ambient interstellar medium. The critical lines which separate the gas expulsion and the gas retention regimes are obtained.

  15. The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Grasha, K.; Calzetti, D. [Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States); Adamo, A.; Messa, M. [Dept. of Astronomy, The Oskar Klein Centre, Stockholm University, Stockholm (Sweden); Kim, H. [Gemini Observatory, La Serena (Chile); Elmegreen, B. G. [IBM Research Division, T.J. Watson Research Center, Yorktown Hts., NY (United States); Gouliermis, D. A. [Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Dale, D. A. [Dept. of Physics and Astronomy, University of Wyoming, Laramie, WY (United States); Fumagalli, M. [Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Durham University, Durham (United Kingdom); Grebel, E. K.; Shabani, F. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Johnson, K. E. [Dept. of Astronomy, University of Virginia, Charlottesville, VA (United States); Kahre, L. [Dept. of Astronomy, New Mexico State University, Las Cruces, NM (United States); Kennicutt, R. C. [Institute of Astronomy, University of Cambridge, Cambridge (United Kingdom); Pellerin, A. [Dept. of Physics and Astronomy, State University of New York at Geneseo, Geneseo NY (United States); Ryon, J. E.; Ubeda, L. [Space Telescope Science Institute, Baltimore, MD (United States); Smith, L. J. [European Space Agency/Space Telescope Science Institute, Baltimore, MD (United States); Thilker, D., E-mail: kgrasha@astro.umass.edu [Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD (United States)

    2017-05-10

    We present a study of the hierarchical clustering of the young stellar clusters in six local (3–15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ∼40–60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

  16. The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

    Science.gov (United States)

    Grasha, K.; Calzetti, D.; Adamo, A.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Dale, D. A.; Fumagalli, M.; Grebel, E. K.; Johnson, K. E.; Kahre, L.; Kennicutt, R. C.; Messa, M.; Pellerin, A.; Ryon, J. E.; Smith, L. J.; Shabani, F.; Thilker, D.; Ubeda, L.

    2017-05-01

    We present a study of the hierarchical clustering of the young stellar clusters in six local (3-15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ˜40-60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

  17. The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

    International Nuclear Information System (INIS)

    Grasha, K.; Calzetti, D.; Adamo, A.; Messa, M.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Dale, D. A.; Fumagalli, M.; Grebel, E. K.; Shabani, F.; Johnson, K. E.; Kahre, L.; Kennicutt, R. C.; Pellerin, A.; Ryon, J. E.; Ubeda, L.; Smith, L. J.; Thilker, D.

    2017-01-01

    We present a study of the hierarchical clustering of the young stellar clusters in six local (3–15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ∼40–60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

  18. A MODEL FOR (QUASI-)PERIODIC MULTIWAVELENGTH PHOTOMETRIC VARIABILITY IN YOUNG STELLAR OBJECTS

    Energy Technology Data Exchange (ETDEWEB)

    Kesseli, Aurora Y. [Boston University, 725 Commonwealth Ave, Boston, MA 02215 (United States); Petkova, Maya A.; Wood, Kenneth; Gregory, Scott G. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9AD (United Kingdom); Whitney, Barbara A. [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St, Madison, WI 53706 (United States); Hillenbrand, L. A. [Astronomy Department, California Institute of Technology, Pasadena, CA 91125 (United States); Stauffer, J. R.; Morales-Calderon, M.; Rebull, L. [Spitzer Science Center, California Institute of Technology, CA 91125 (United States); Alencar, S. H. P., E-mail: aurorak@bu.com [Departamento de Física—ICEx—UFMG, Av. Antônio Carlos, 6627, 30270-901, Belo Horizonte, MG (Brazil)

    2016-09-01

    We present radiation transfer models of rotating young stellar objects (YSOs) with hot spots in their atmospheres, inner disk warps, and other three-dimensional effects in the nearby circumstellar environment. Our models are based on the geometry expected from magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hot spots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project to determine if these processes can explain the variability observed at optical and mid-infrared wavelengths in young stars. We focus on those variables exhibiting “dipper” behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hot-spot size and temperature affects the optical and near-infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR light curve variations. Clumpy disk distributions with non-uniform fractal density structure produce more stochastic light curves. We conclude that magneto-accretion theory is consistent with certain aspects of the multiwavelength photometric variability exhibited by low-mass YSOs. More detailed modeling of individual sources can be used to better determine the stellar hot-spot and inner disk geometries of particular sources.

  19. Magnetic information affects the stellar orientation of young bird migrants

    Science.gov (United States)

    Weindler, Peter; Wiltschko, Roswitha; Wiltschko, Wolfgang

    1996-09-01

    WHEN young birds leave on their first migration, they are guided by innate information about their direction of migration. It is generally assumed that this direction is represented twice, namely with respect to celestial rotation and with respect to the Earth's magnetic field1,2. The interactions between the two cue systems have been analysed by exposing hand-raised young birds during the premigratory period to cue-conflict situations, in which celestial rotation and the magnetic field provided different information. Celestial rotation altered the course with respect to the magnetic field3-7, whereas conflicting magnetic information did not seem to affect the course with respect to the stars8,9. Celestial information thus seemed to dominate over magnetic information. Here we report that the interaction between the two cue systems is far more complex than this. Celestial rotation alone seems to provide only a tendency to move away from its centre (towards geographical south), which is then modified by information from the magnetic field to establish the distinctive, population-specific migratory direction.

  20. YOUNG STELLAR POPULATIONS IN MYStIX STAR-FORMING REGIONS: CANDIDATE PROTOSTARS

    Energy Technology Data Exchange (ETDEWEB)

    Romine, Gregory; Feigelson, Eric D.; Getman, Konstantin V. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Kuhn, Michael A. [Millennium Institute of Astrophysics, Camino El Observatorio 1515, Las Condes, Santiago (Chile); Povich, Matthew S., E-mail: edf@astro.psu.edu [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Ave., Pomona, CA 91768 (United States)

    2016-12-20

    The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog and Chandra -based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few “false positives” from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many “false negatives.” Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

  1. YOUNG STELLAR POPULATIONS IN MYStIX STAR-FORMING REGIONS: CANDIDATE PROTOSTARS

    International Nuclear Information System (INIS)

    Romine, Gregory; Feigelson, Eric D.; Getman, Konstantin V.; Kuhn, Michael A.; Povich, Matthew S.

    2016-01-01

    The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog and Chandra -based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few “false positives” from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many “false negatives.” Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

  2. Identification of Young Stellar Variables with KELT for K2 . I. Taurus Dippers and Rotators

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, Joseph E.; Cargile, Phillip A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ansdell, Megan [Institute for Astronomy, University of Hawaií at Manoa, Honolulu, HI 96822 (United States); Oelkers, Ryan J.; Somers, Garrett; Lund, Michael B.; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 (United States); Gaidos, Eric [Department of Geology and Geophysics, University of Hawaií at Manoa, Honolulu, HI 96822 (United States); Cody, Ann Marie [NASA Ames Research Center, Mountain View, CA 94035 (United States); Stevens, Daniel J.; Gaudi, B. Scott [Department of Astronomy, The Ohio State University, Columbus, OH 43210 (United States); James, David [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195 (United States); Beatty, Thomas G. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Siverd, Robert J. [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Santa Barbara, CA 93117 (United States); Kuhn, Rudolf B. [South African Astronomical Observatory, PO Box 9, Observatory 7935 (South Africa); Pepper, Joshua [Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, PA 18015 (United States)

    2017-10-20

    One of the most well-studied young stellar associations, Taurus–Auriga, was observed by the extended Kepler mission, K2 , in the spring of 2017. K2 Campaign 13 (C13) is a unique opportunity to study many stars in this young association at high photometric precision and cadence. Using observations from the Kilodegree Extremely Little Telescope (KELT) survey, we identify “dippers,” aperiodic and periodic variables among K2 C13 target stars. This release of the KELT data (light curve data in e-tables) provides the community with long-time baseline observations to assist in the understanding of the more exotic variables in the association. Transient-like phenomena on timescales of months to years are known characteristics in the light curves of young stellar objects, making contextual pre- and post- K2 observations critical to understanding their underlying processes. We are providing a comprehensive set of the KELT light curves for known Taurus–Auriga stars in K2 C13. The combined data sets from K2 and KELT should permit a broad array of investigations related to star formation, stellar variability, and protoplanetary environments.

  3. Identification of Young Stellar Variables with KELT for K2 . I. Taurus Dippers and Rotators

    International Nuclear Information System (INIS)

    Rodriguez, Joseph E.; Cargile, Phillip A.; Ansdell, Megan; Oelkers, Ryan J.; Somers, Garrett; Lund, Michael B.; Stassun, Keivan G.; Gaidos, Eric; Cody, Ann Marie; Stevens, Daniel J.; Gaudi, B. Scott; James, David; Beatty, Thomas G.; Siverd, Robert J.; Kuhn, Rudolf B.; Pepper, Joshua

    2017-01-01

    One of the most well-studied young stellar associations, Taurus–Auriga, was observed by the extended Kepler mission, K2 , in the spring of 2017. K2 Campaign 13 (C13) is a unique opportunity to study many stars in this young association at high photometric precision and cadence. Using observations from the Kilodegree Extremely Little Telescope (KELT) survey, we identify “dippers,” aperiodic and periodic variables among K2 C13 target stars. This release of the KELT data (light curve data in e-tables) provides the community with long-time baseline observations to assist in the understanding of the more exotic variables in the association. Transient-like phenomena on timescales of months to years are known characteristics in the light curves of young stellar objects, making contextual pre- and post- K2 observations critical to understanding their underlying processes. We are providing a comprehensive set of the KELT light curves for known Taurus–Auriga stars in K2 C13. The combined data sets from K2 and KELT should permit a broad array of investigations related to star formation, stellar variability, and protoplanetary environments.

  4. SPITZER OBSERVATIONS OF LONG-TERM INFRARED VARIABILITY AMONG YOUNG STELLAR OBJECTS IN CHAMAELEON I

    Energy Technology Data Exchange (ETDEWEB)

    Flaherty, Kevin M.; Herbst, William [Van Vleck Observatory, Astronomy Department, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States); DeMarchi, Lindsay [Department of Physics and Astronomy, Colgate University, 13 Oak Drive, Hamilton, NY 13346 (United States); Muzerolle, James [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Balog, Zoltan [Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117 Heidelberg (Germany); Megeath, S. Thomas [Ritter Astrophysical Research Center, Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States); Furlan, Elise [Infrared Processing and Analysis Center, California Institute of Technology, 770 S. Wilson Avenue, Pasadena, CA 91125 (United States); Gutermuth, Robert [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)

    2016-12-10

    Infrared variability is common among young stellar objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited to total baselines of about 1 month due to the orientation of the spacecraft. Here we present observations of the Chameleon I cluster, whose low declination makes it observable by the Spitzer Space Telescope over a 200-day period. We observe 30 young stellar objects with a daily cadence to better sample variability on timescales of months. We find that such variability is common, occurring in ∼80% of the detected cluster members. The change in [3.6]–[4.5] color over 200 days for many of the sources falls between that expected for extinction and fluctuations in disk emission. With our high cadence and long baseline we can derive power spectral density curves covering two orders of magnitude in frequency and find significant power at low frequencies, up to the boundaries of our 200-day survey. Such long timescales are difficult to explain with variations driven by the interaction between the disk and stellar magnetic field, which has a dynamical timescale of days to weeks. The most likely explanation is either structural or temperature fluctuations spread throughout the inner ∼0.5 au of the disk, suggesting that the intrinsic dust structure is highly dynamic.

  5. SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

    International Nuclear Information System (INIS)

    Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

    2012-01-01

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

  6. Selected Films for Young Adults, 1984.

    Science.gov (United States)

    Top of the News, 1984

    1984-01-01

    This 22-item filmography of 16mm films recommended for use in programs planned for young adults was compiled by the Selected Films for Young Adults Committee, Young Adult Services Division, American Library Association. Producers, directors, distributors, length, price, and brief annotations are provided. Addresses for 12 distributors are…

  7. Luminosity excesses in low-mass young stellar objects - a statistical study

    International Nuclear Information System (INIS)

    Strom, K.M.; Strom, S.E.; Kenyon, S.J.; Hartmann, L.

    1988-01-01

    This paper presents a statistical study in which the observed total luminosity is compared quantitatively with an estimate of the stellar luminosity for a sample of 59 low-mass young stellar objects (YSOs) in the Taurus-Auriga complex. In 13 of the analyzed YSOs, luminosity excesses greater than 0.20 are observed together with greater than 0.6 IR excesses, which typically contribute the bulk of the observed excess luminosity and are characterized by spectral energy distributions which are flat or rise toward long wavelengths. The analysis suggests that YSOs showing the largest luminosity excesses typically power optical jets and/or molecular outflows or have strong winds, as evidenced by the presence of O I emission, indicating a possible correlation between accretion and mass-outflow properties. 38 references

  8. Near-infrared spectroscopic observations of massive young stellar object candidates in the central molecular zone

    Science.gov (United States)

    Nandakumar, G.; Schultheis, M.; Feldmeier-Krause, A.; Schödel, R.; Neumayer, N.; Matteucci, F.; Ryde, N.; Rojas-Arriagada, A.; Tej, A.

    2018-01-01

    Context. The central molecular zone (CMZ) is a 200 pc region around the Galactic centre. The study of star formation in the central part of the Milky Way is of great interest as it provides a template for the closest galactic nuclei. Aims: We present a spectroscopic follow-up of photometrically selected young stellar object (YSO) candidates in the CMZ of the Galactic centre. Our goal is to quantify the contamination of this YSO sample by reddened giant stars with circumstellar envelopes and to determine the star formation rate (SFR) in the CMZ. Methods: We obtained KMOS low-resolution near-infrared spectra (R 4000) between 2.0 and 2.5 μm of sources, many of which have been previously identified by mid-infrared photometric criteria as massive YSOs in the Galactic centre. Our final sample consists of 91 stars with good signal-to-noise ratio. We separated YSOs from cool late-type stars based on spectral features of CO and Brγ at 2.3 μm and 2.16 μm, respectively. We made use of spectral energy distribution (SED) model fits to the observed photometric data points from 1.25 to 24 μm to estimate approximate masses for the YSOs. Results: Using the spectroscopically identified YSOs in our sample, we confirm that existing colour-colour diagrams and colour-magnitude diagrams are unable to efficiently separate YSOs and cool late-type stars. In addition, we define a new colour-colour criterion that separates YSOs from cool late-type stars in the H-KS vs. H -[8.0] diagram. We use this new criterion to identify YSO candidates in the |l| rate than predicted by various star forming models. Based on observations collected at the European Southern Observatory, Chile, programme number 097.C-0208(A).

  9. Massive Young Stellar Objects in the Galactic Center. 1; Spectroscopic Identification from Spitzer/IRS Observations

    Science.gov (United States)

    An, Deokkeun; Ramirez, Solange V.; Sellgren, Kris; Arendt, Richard G.; Boogert, A. C. Adwin; Robitaille, Thomas P.; Schultheis, Mathias; Cotera, Angela S.; Smith, Howard A.; Stolovy, Susan R.

    2011-01-01

    We present results from our spectroscopic study, using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, designed to identify massive young stellar objects (YSOs) in the Galactic Center (GC). Our sample of 107 YSO candidates was selected based on IRAC colors from the high spatial resolution, high sensitivity Spitzer/IRAC images in the Central Molecular Zone (CMZ), which spans the central approximately 300 pc region of the Milky Way Galaxy. We obtained IRS spectra over 5 micron to 35 micron using both high- and low-resolution IRS modules. We spectroscopically identify massive YSOs by the presence of a 15.4 micron shoulder on the absorption profile of 15 micron CO2 ice, suggestive of CO2 ice mixed with CH30H ice on grains. This 15.4 micron shoulder is clearly observed in 16 sources and possibly observed in an additional 19 sources. We show that 9 massive YSOs also reveal molecular gas-phase absorption from C02, C2H2, and/or HCN, which traces warm and dense gas in YSOs. Our results provide the first spectroscopic census of the massive YSO population in the GC. We fit YSO models to the observed spectral energy distributions and find YSO masses of 8 - 23 solar Mass, which generally agree with the masses derived from observed radio continuum emission. We find that about 50% of photometrically identified YSOs are confirmed with our spectroscopic study. This implies a preliminary star formation rate of approximately 0.07 solar mass/yr at the GC.

  10. Observations of Young Stellar Objects with Infrared Interferometry: Recent Results from PTI, KI and IOTA

    Science.gov (United States)

    Akeson, Rachel

    Young stellar objects have been one of the favorite targets of infrared interferometers for many years. In this contribution I will briefly review some of the first results and their contributions to the field and then describe some of the recent results from the Keck Interferometer (KI), the Palomar Testbed Interferometer (PTI) and the Infrared-Optical Telescope Array (IOTA). This conference also saw many exciting new results from the VLTI at both near and mid-infrared wavelengths that are covered by other contributions.

  11. RACE-OC Project: Rotation and variability in young stellar associations within 100 pc

    OpenAIRE

    Messina, S.; Desidera, S.; Turatto, M.; Lanzafame, A. C.; Guinan, E. F.

    2010-01-01

    Our goal is to determine the rotational and magnetic-related activity properties of stars at different stages of evolution. We have focussed our attention on 6 young loose stellar associations within 100 pc and ages in the range 8-70 Myr: TW Hydrae (~8 Myr), beta Pictoris (~10 Myr), Tucana/Horologium, Columba, Carina (~30 Myr), and AB Doradus (~70 Myr). Additional data on alpha Persei and the Pleiades from the literature is also considered. Rotational periods of stars showing rotational modul...

  12. Cosmic-Ray Propagation in Turbulent Spiral Magnetic Fields Associated with Young Stellar Objects

    Science.gov (United States)

    Fatuzzo, Marco; Adams, Fred C.

    2018-04-01

    External cosmic rays impinging upon circumstellar disks associated with young stellar objects provide an important source of ionization, and, as such, play an important role in disk evolution and planet formation. However, these incoming cosmic rays are affected by a variety of physical processes internal to stellar/disk systems, including modulation by turbulent magnetic fields. Globally, these fields naturally provide both a funneling effect, where cosmic rays from larger volumes are focused into the disk region, and a magnetic mirroring effect, where cosmic rays are repelled due to the increasing field strength. This paper considers cosmic-ray propagation in the presence of a turbulent spiral magnetic field, analogous to that produced by the solar wind. The interaction of this wind with the interstellar medium defines a transition radius, analogous to the heliopause, which provides the outer boundary to this problem. We construct a new coordinate system where one coordinate follows the spiral magnetic field lines and consider magnetic perturbations to the field in the perpendicular directions. The presence of magnetic turbulence replaces the mirroring points with a distribution of values and moves the mean location outward. Our results thus help quantify the degree to which cosmic-ray fluxes are reduced in circumstellar disks by the presence of magnetic field structures that are shaped by stellar winds. The new coordinate system constructed herein should also be useful in other astronomical applications.

  13. Formation of new stellar populations from gas accreted by massive young star clusters.

    Science.gov (United States)

    Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

    2016-01-28

    Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

  14. Accretion-induced variability links young stellar objects, white dwarfs, and black holes.

    Science.gov (United States)

    Scaringi, Simone; Maccarone, Thomas J; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R; Aranzana, Ester; Dhillon, Vikram S; Barros, Susana C C

    2015-10-01

    The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies.

  15. An Observational Study of Blended Young Stellar Clusters in the Galactic Plane - Do Massive Stars form First?

    Science.gov (United States)

    Martínez-Galarza, Rafael; Protopapas, Pavlos; Smith, Howard A.; Morales, Esteban

    2018-01-01

    From an observational point of view, the early life of massive stars is difficult to understand partly because star formation occurs in crowded clusters where individual stars often appear blended together in the beams of infrared telescopes. This renders the characterization of the physical properties of young embedded clusters via spectral energy distribution (SED) fitting a challenging task. Of particular relevance for the testing of star formation models is the question of whether the claimed universality of the IMF (references) is reflected in an equally universal integrated galactic initial mass function (IGIMF) of stars. In other words, is the set of all stellar masses in the galaxy sampled from a single universal IMF, or does the distribution of masses depend on the environment, making the IGIMF different from the canonical IMF? If the latter is true, how different are the two? We present a infrared SED analysis of ~70 Spitzer-selected, low mass ($facilities.

  16. Young stellar population and star formation history ofW4 HII region/Cluster Complex

    Science.gov (United States)

    Panwar, Neelam

    2018-04-01

    The HII region/cluster complex has been a subject of numerous investigations to study the feedback effect of massive stars on their surroundings. Massive stars not only alter the morphology of the parental molecular clouds, but also influence star formation, circumstellar disks and the mass function of low-mass stars in their vicinity. However, most of the studies of low-mass stellar content of the HII regions are limited only to the nearby regions. We study the star formation in the W4 HII region using deep optical observations obtained with the archival data from Canada - France - Hawaii Telescope, Two-Micron All Sky Survey, Spitzer, Herschel and Chandra. We investigate the spatial distribution of young stellar objects in the region, their association with the remnant molecular clouds, and search for the clustering to establish the sites of recent star formation. Our analysis suggests that the influence of massive stars on circumstellar disks is significant only to thei! r immediate neighborhood. The spatial correlation of the young stars with the distribution of gas and dust of the complex indicate that the clusters would have formed in a large filamentary cloud. The observing facilities at the 3.6-m Devasthal Optical Telescope (DOT), providing high-resolution spectral and imaging capabilities, will fulfill the major objectives in the study of HII regions.

  17. Dynamical evolution of stars and gas of young embedded stellar sub-clusters

    Science.gov (United States)

    Sills, Alison; Rieder, Steven; Scora, Jennifer; McCloskey, Jessica; Jaffa, Sarah

    2018-03-01

    We present simulations of the dynamical evolution of young embedded star clusters. Our initial conditions are directly derived from X-ray, infrared, and radio observations of local systems, and our models evolve both gas and stars simultaneously. Our regions begin with both clustered and extended distributions of stars, and a gas distribution which can include a filamentary structure in addition to gas surrounding the stellar subclusters. We find that the regions become spherical, monolithic, and smooth quite quickly, and that the dynamical evolution is dominated by the gravitational interactions between the stars. In the absence of stellar feedback, the gas moves gently out of the centre of our regions but does not have a significant impact on the motions of the stars at the earliest stages of cluster formation. Our models at later times are consistent with observations of similar regions in the local neighbourhood. We conclude that the evolution of young proto-star clusters is relatively insensitive to reasonable choices of initial conditions. Models with more realism, such as an initial population of binary and multiple stars and ongoing star formation, are the next step needed to confirm these findings.

  18. HIGH- AND INTERMEDIATE-MASS YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Gruendl, Robert A.; Chu, Y.-H.

    2009-01-01

    Archival Spitzer Infrared Array Camera (IRAC) and MIPS observations of the Large Magellanic Cloud (LMC) have been used to search for young stellar objects (YSOs). We have carried out independent aperture photometry of these data and merged the results from different passbands to produce a photometric catalog. To verify our methodology we have also analyzed the data from the SAGE and SWIRE Legacy programs; our photometric measurements are in general agreement with the photometry released by these programs. A detailed completeness analysis for our photometric catalog of the LMC shows that the 90% completeness limits are, on average, 16.0, 15.0, 14.3, 13.1, and 9.2 mag at 3.6, 4.5, 5.8, 8.0, and 24 μm, respectively. Using our mid-infrared photometric catalogs and two simple selection criteria, [4.5]-[8.0]>2.0 to exclude normal and evolved stars and [8.0]>14-([4.5]-[8.0]) to exclude background galaxies, we have identified a sample of 2910 sources in the LMC that could potentially be YSOs. We then used the Spitzer observations complemented by optical and near-infrared data to carefully assess the nature of each source. To do so we simultaneously considered multiwavelength images and photometry to assess the source morphology, spectral energy distribution (SED) from the optical through the mid-infrared wavelengths, and the surrounding interstellar environment to determine the most likely nature of each source. From this examination of the initial sample, we suggest that 1172 sources are most likely YSOs. We have also identified 1075 probable background galaxies, consistent with the expected number estimated from the SWIRE survey. Spitzer IRS observations of 269 of the brightest YSOs from our sample have confirmed that ∼>95% are indeed YSOs. An examination of color-color and color-magnitude diagrams shows no simple criteria in color-magnitude space that can unambiguously separate the LMC YSOs from all asymptotic giant branch (AGB)/post-AGB stars, planetary nebulae, and

  19. Dusty supernovae running the thermodynamics of the matter reinserted within young and massive super stellar clusters

    Energy Technology Data Exchange (ETDEWEB)

    Tenorio-Tagle, Guillermo; Silich, Sergiy; Martínez-González, Sergio [Instituto Nacional de Astrofísica Óptica y Electrónica, AP 51, 72000 Puebla (Mexico); Muñoz-Tuñón, Casiana [Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain); Palouš, Jan; Wünsch, Richard, E-mail: gtt@inaoep.mx, E-mail: cmt@ll.iac.es [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague (Czech Republic)

    2013-12-01

    Following the observational and theoretical evidence that points at core-collapse supernovae (SNe) as major producers of dust, here we calculate the hydrodynamics of the matter reinserted within young and massive super stellar clusters under the assumption of gas and dust radiative cooling. The large SN rate expected in massive clusters allows for a continuous replenishment of dust immersed in the high temperature thermalized reinserted matter and warrants a stationary presence of dust within the cluster volume during the type II SN era. We first show that such a balance determines the range of the dust-to-gas-mass ratio, and thus the dust cooling law. We then search for the critical line that separates stationary cluster winds from the bimodal cases in the cluster mechanical luminosity (or cluster mass) versus cluster size parameter space. In the latter, strong radiative cooling reduces considerably the cluster wind mechanical energy output and affects particularly the cluster central regions, leading to frequent thermal instabilities that diminish the pressure and inhibit the exit of the reinserted matter. Instead, matter accumulates there and is expected to eventually lead to gravitational instabilities and to further stellar formation with the matter reinserted by former massive stars. The main outcome of the calculations is that the critical line is almost two orders of magnitude or more, depending on the assumed value of V {sub A∞}, lower than when only gas radiative cooling is applied. And thus, many massive clusters are predicted to enter the bimodal regime.

  20. Detection of water masers toward young stellar objects in the Large Magellanic Cloud

    International Nuclear Information System (INIS)

    Johanson, A. K.; Migenes, V.; Breen, S. L.

    2014-01-01

    We present results from a search for water maser emission toward N4A, N190, and N206, three regions of massive star formation in the Large Magellanic Cloud (LMC). Four water masers were detected; two toward N4A, and two toward N190. In the latter region, no previously known maser emission has been reported. Future studies of maser proper motion to determine the galactic dynamics of the LMC will benefit from the independent data points the new masers in N190 provide. Two of these masers are associated with previously identified massive young stellar objects (YSOs), which strongly supports the authenticity of the classification. We argue that the other two masers identify previously unknown YSOs. No masers were detected toward N206, but it does host a newly discovered 22 GHz continuum source, also associated with a massive YSO. We suggest that future surveys for water maser emission in the LMC be targeted toward the more luminous, massive YSOs.

  1. Stellar Content of the Young Supershell GSH 305+01-24

    Science.gov (United States)

    Kaltcheva, N.; Golev, V.

    2013-06-01

    We combine several multi-wavelength surveys (Wisconsin Halpha Mapper Northern Sky Survey, MSX Mid-IR Galactic Plane Survey, WISE All-Sky Data Release, CO survey of the Milky Way, and the Southern Galactic Plane HI Survey) with intermediate-band uvby photometry to investigate the correlation between the young stars and various interstellar components related to the GSH 305+01-24 supershell seen toward Centaurus. The region shows striking similarities between the stellar distribution and Hα and HI emission morphologies. We identity 161 O-B9 stars at an average distance modulus 11.09 ± 0.71 (s.d.) mag located within the supershell and study their interaction with the surrounding interstellar material.

  2. Complex organic molecules in organic-poor massive young stellar objects

    DEFF Research Database (Denmark)

    Fayolle, Edith C.; Öberg, Karin I.; Garrod, Robin T.

    2015-01-01

    to search for complex organic molecules over 8-16 GHz in the 1 mm atmospheric window toward three MYSOs with known ice abundances, but without luminous molecular hot cores. Results. Complex molecules are detected toward all three sources at comparable abundances with respect to CH3OH to classical hot core......Context. Massive young stellar objects (MYSOs) with hot cores are classic sources of complex organic molecules. The origins of these molecules in such sources, as well as the small-and large-scale differentiation between nitrogen-and oxygen-bearing complex species, are poorly understood. Aims. We...... aim to use complex molecule abundances toward a chemically less explored class of MYSOs with weak hot organic emission lines to constrain the impact of hot molecular cores and initial ice conditions on the chemical composition toward MYSOs. Methods. We use the IRAM 30 m and the Submillimeter Array...

  3. THE PALOMAR TRANSIENT FACTORY ORION PROJECT: ECLIPSING BINARIES AND YOUNG STELLAR OBJECTS

    International Nuclear Information System (INIS)

    Van Eyken, Julian C.; Ciardi, David R.; Akeson, Rachel L.; Beichman, Charles A.; Von Braun, Kaspar; Gelino, Dawn M.; Kane, Stephen R.; Plavchan, Peter; RamIrez, Solange V.; Rebull, Luisa M.; Stauffer, John R.; Hoard, D. W.; Boden, Andrew F.; Howell, Steve B.; Bloom, Joshua S.; Cenko, S. Bradley; Kasliwal, Mansi M.; Kulkarni, Shrinivas R.; Law, Nicholas M.; Nugent, Peter E.

    2011-01-01

    The Palomar Transient Factory (PTF) Orion project is one of the experiments within the broader PTF survey, a systematic automated exploration of the sky for optical transients. Taking advantage of the wide (3. 0 5 x 2. 0 3) field of view available using the PTF camera installed at the Palomar 48 inch telescope, 40 nights were dedicated in 2009 December to 2010 January to perform continuous high-cadence differential photometry on a single field containing the young (7-10 Myr) 25 Ori association. Little is known empirically about the formation of planets at these young ages, and the primary motivation for the project is to search for planets around young stars in this region. The unique data set also provides for much ancillary science. In this first paper, we describe the survey and the data reduction pipeline, and present some initial results from an inspection of the most clearly varying stars relating to two of the ancillary science objectives: detection of eclipsing binaries and young stellar objects. We find 82 new eclipsing binary systems, 9 of which are good candidate 25 Ori or Orion OB1a association members. Of these, two are potential young W UMa type systems. We report on the possible low-mass (M-dwarf primary) eclipsing systems in the sample, which include six of the candidate young systems. Forty-five of the binary systems are close (mainly contact) systems, and one of these shows an orbital period among the shortest known for W UMa binaries, at 0.2156509 ± 0.0000071 days, with flat-bottomed primary eclipses, and a derived distance that appears consistent with membership in the general Orion association. One of the candidate young systems presents an unusual light curve, perhaps representing a semi-detached binary system with an inflated low-mass primary or a star with a warped disk, and may represent an additional young Orion member. Finally, we identify 14 probable new classical T-Tauri stars in our data, along with one previously known (CVSO 35) and

  4. A Search for Water Maser Emission from Brown Dwarfs and Low-luminosity Young Stellar Objects

    Energy Technology Data Exchange (ETDEWEB)

    Gómez, José F.; Manjarrez, Guillermo [Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Palau, Aina [Instituto de Radioastronomía y Astrofísica, UNAM, P.O. Box 3-72, 58090, Morelia, Michoacán, México (Mexico); Uscanga, Lucero [Departamento de Astronomía, Universidad de Guanajuato, A.P. 144, 36000 Guanajuato, Gto., México (Mexico); Barrado, David, E-mail: jfg@iaa.es [Centro de Astrobiología, INTA-CSIC, PO BOX 28692, ESAC Campus, E-208691 Villanueva de la Cañada, Madrid (Spain)

    2017-05-01

    We present a survey for water maser emission toward a sample of 44 low-luminosity young objects, comprising (proto-)brown dwarfs, first hydrostatic cores (FHCs), and other young stellar objects (YSOs) with bolometric luminosities lower than 0.4 L {sub ⊙}. Water maser emission is a good tracer of energetic processes, such as mass-loss and/or accretion, and is a useful tool to study these processes with very high angular resolution. This type of emission has been confirmed in objects with L {sub bol} ≳ 1 L {sub ⊙}. Objects with lower luminosities also undergo mass-loss and accretion, and thus, are prospective sites of maser emission. Our sensitive single-dish observations provided a single detection when pointing toward the FHC L1448 IRS 2E. However, follow-up interferometric observations showed water maser emission associated with the nearby YSO L1448 IRS 2 (a Class 0 protostar of L {sub bol} ≃ 3.6–5.3 L {sub ⊙}) and did not find any emission toward L1448 IRS 2E. The upper limits for water maser emission determined by our observations are one order of magnitude lower than expected from the correlation between water maser luminosities and bolometric luminosities found for YSOs. This suggests that this correlation does not hold at the lower end of the (sub)stellar mass spectrum. Possible reasons are that the slope of this correlation is steeper at L {sub bol} ≤ 1 L {sub ⊙} or that there is an absolute luminosity threshold below which water maser emission cannot be produced. Alternatively, if the correlation still stands at low luminosity, the detection rates of masers would be significantly lower than the values obtained in higher-luminosity Class 0 protostars.

  5. The Intermediate-mass Young Stellar Object 08576nr292: Discovery of A Disk-Jet System

    NARCIS (Netherlands)

    Ellerbroek, L.E.; Kaper, L.; Bik, A.; de Koter, A.; Horrobin, M.; Puga, E.; Sana, H.; Waters, L.B.F.M.

    2011-01-01

    We present observations of the embedded massive young stellar object (YSO) candidate 08576nr292, obtained with X-shooter and SINFONI on the ESO Very Large Telescope (VLT). The flux-calibrated, medium-resolution X-shooter spectrum (300–2500 nm) includes over 300 emission lines, but no (photospheric)

  6. RACE-OC project: Rotation and variability of young stellar associations within 100 pc

    Science.gov (United States)

    Messina, S.; Desidera, S.; Turatto, M.; Lanzafame, A. C.; Guinan, E. F.

    2010-09-01

    Context. Examining the angular momentum of stars and its interplay with their magnetic fields represent a promising way to probe the stellar internal structure and evolution of low-mass stars. Aims: We attempt to determine the rotational and magnetic-related activity properties of stars at different stages of evolution.We focused our attention primarily on members of clusters and young stellar associations of known ages. In this study, our targets are 6 young loose stellar associations within 100 pc and with ages in the range 8-70 Myr: TW Hydrae (~8 Myr), β Pictoris (~10 Myr), Tucana/Horologium, Columba, Carina (~30 Myr), and AB Doradus (~70 Myr). Additional rotational data for α Persei and the Pleiades from the literature are also considered. Methods: Rotational periods of stars exhibiting rotational modulation due to photospheric magnetic activity (i.e., starspots) were determined by applying the Lomb-Scargle periodogram technique to photometric time-series data obtained by the All Sky Automated Survey (ASAS). The magnetic activity level was derived from the amplitude of the V lightcurves. The statistical significance of the rotational evolution at different ages was inferred by applying a two-sided Kolmogorov-Smirnov test to subsequent age-bins. Results: We detected the rotational modulation and measured the rotation periods of 93 stars for the first time, and confirmed the periods of 41 stars already known from the literature. For an additional 10 stars, we revised the period determinations by other authors. The sample was augmented with periods of 21 additional stars retrieved from the literature. In this way, for the first time we were able to determine the largest set of rotation periods at ages of ~8, ~10 and ~30 Myr, as well as increase by 150% the number of known periodic members of AB Dor. Conclusions: The analysis of the rotation periods in young stellar associations, supplemented by Orion Nebula Cluster (ONC) and NGC 2264 data from the literature

  7. YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD STAR-FORMING REGION N206

    International Nuclear Information System (INIS)

    Romita, Krista Alexandra; Meixner, M.; Sewilo, M.; Shiao, B.; Carlson, Lynn Redding; Whitney, B.; Babler, B.; Meade, M.; Indebetouw, R.; Hora, J. L.

    2010-01-01

    We present analysis of the energetic star-forming region Henize 206 (N206) located near the southern edge of the Large Magellanic Cloud (LMC) based on photometric data from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE-LMC; IRAC 3.6, 4.5, 5.8, 8.0 μm and MIPS 24 μm), Infrared Survey Facility near-infrared survey (J, H, K s ), and the Magellanic Clouds Photometric Survey (MCPS UBVI) covering a wavelength range of 0.36-24 μm. Young stellar object (YSO) candidates are identified based upon their location in infrared color-magnitude space and classified by the shapes of their spectral energy distributions in comparison with a pre-computed grid of YSO models. We identify 116 YSO candidates: 102 are well characterized by the YSO models, predominately Stage I, and 14 may be multiple sources or young sources with transition disks. Careful examination of the individual sources and their surrounding environment allows us to identify a factor of ∼14.5 more YSO candidates than have already been identified. The total mass of these well-fit YSO candidates is ∼520 M sun . We calculate a current star formation rate of 0.27 x 10 -1 M sun yr -1 kpc -2 . The distribution of YSO candidates appears to follow shells of neutral material in the interstellar medium.

  8. YOUNG STELLAR OBJECTS IN THE MASSIVE STAR-FORMING REGION W49

    Energy Technology Data Exchange (ETDEWEB)

    Saral, G.; Hora, J. L.; Willis, S. E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Koenig, X. P. [Yale University, Department of Astronomy, 208101, New Haven, CT 06520-8101 (United States); Gutermuth, R. A. [University of Massachusetts, Department of Astronomy, Amherst, MA 01003 (United States); Saygac, A. T., E-mail: gsaral@cfa.harvard.edu [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

    2015-11-01

    We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the young stellar objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate objects using color–color and color–magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ≥7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.

  9. X-shooter spectroscopy of young stellar objects in Lupus. Atmospheric parameters, membership, and activity diagnostics

    Science.gov (United States)

    Frasca, A.; Biazzo, K.; Alcalá, J. M.; Manara, C. F.; Stelzer, B.; Covino, E.; Antoniucci, S.

    2017-06-01

    Aims: A homogeneous determination of basic stellar parameters of young stellar object (YSO) candidates is needed to confirm their pre-main sequence evolutionary stage and membership to star forming regions (SFRs), and to get reliable values of the quantities related to chromospheric activity and accretion. Methods: We used the code ROTFIT and synthetic BT-Settl spectra for the determination of the atmospheric parameters (Teff and log g), veiling (r), radial (RV), and projected rotational velocity (vsini) from X-shooter spectra of 102 YSO candidates (95 of infrared Class II and seven Class III) in the Lupus SFR. The spectral subtraction of inactive templates, rotationally broadened to match the vsini of the targets, enabled us to measure the line fluxes for several diagnostics of both chromospheric activity and accretion, such as Hα, Hβ, Ca II, and Na I lines. Results: We have shown that 13 candidates can be rejected as Lupus members based on their discrepant RV with respect to Lupus and/or the very low log g values. At least 11 of them are background giants, two of which turned out to be lithium-rich giants. Regarding the members, we found that all Class III sources have Hα fluxes that are compatible with a pure chromospheric activity, while objects with disks lie mostly above the boundary between chromospheres and accretion. Young stellar objects with transitional disks display both high and low Hα fluxes. We found that the line fluxes per unit surface are tightly correlated with the accretion luminosity (Lacc) derived from the Balmer continuum excess. This rules out that the relationships between Lacc and line luminosities found in previous works are simply due to calibration effects. We also found that the Ca II-IRT flux ratio, FCaII8542/FCaII8498, is always small, indicating an optically thick emission source. The latter can be identified with the accretion shock near the stellar photosphere. The Balmer decrement reaches instead, for several accretors, high

  10. Stellar-mass black holes in young massive and open stellar clusters and their role in gravitational-wave generation - II

    Science.gov (United States)

    Banerjee, Sambaran

    2018-01-01

    The study of stellar-remnant black holes (BH) in dense stellar clusters is now in the spotlight, especially due to their intrinsic ability to form binary black holes (BBH) through dynamical encounters, which potentially coalesce via gravitational-wave (GW) radiation. In this work, which is a continuation from a recent study (Paper I), additional models of compact stellar clusters with initial masses ≲ 105 M⊙ and also those with small fractions of primordial binaries (≲ 10 per cent) are evolved for long term, applying the direct N-body approach, assuming state-of-the-art stellar-wind and remnant-formation prescriptions. That way, a substantially broader range of computed models than that in Paper I is achieved. As in Paper I, the general-relativistic BBH mergers continue to be mostly mediated by triples that are bound to the clusters rather than happen among the ejected BBHs. In fact, the number of such in situ BBH mergers, per cluster, tends to increase significantly with the introduction of a small population of primordial binaries. Despite the presence of massive primordial binaries, the merging BBHs, especially the in situ ones, are found to be exclusively dynamically assembled and hence would be spin-orbit misaligned. The BBHs typically traverse through both the LISA's and the LIGO's detection bands, being audible to both instruments. The 'dynamical heating' of the BHs keeps the electron-capture-supernova (ECS) neutron stars (NS) from effectively mass segregating and participating in exchange interactions; the dynamically active BHs would also exchange into any NS binary within ≲1 Gyr. Such young massive and open clusters have the potential to contribute to the dynamical BBH merger detection rate to a similar extent as their more massive globular-cluster counterparts.

  11. Alma Survey of Circumstellar Disks in the Young Stellar Cluster IC 348

    Science.gov (United States)

    Ruíz-Rodríguez, D.; Cieza, L. A.; Williams, J. P.; Andrews, S. M.; Principe, D. A.; Caceres, C.; Canovas, H.; Casassus, S.; Schreiber, M. R.; Kastner, J. H.

    2018-05-01

    We present a 1.3 mm continuum survey of the young (2-3 Myr) stellar cluster IC 348, which lies at a distance of 310 pc, and is dominated by low-mass stars (M⋆ ˜ 0.1-0.6 M⊙). We observed 136 Class II sources (disks that are optically thick in the infrared) at 0.8″ (200 au) resolution with a 3σ sensitivity of ˜ 0.45 mJy (Mdust ˜ 1.3 M⊕). We detect 40 of the targets and construct a mm-continuum luminosity function. We compare the disk mass distribution in IC 348 to those of younger and older regions, taking into account the dependence on stellar mass. We find a clear evolution in disk masses from 1 to 5-10 Myr. The disk masses in IC 348 are significantly lower than those in Taurus (1-3 Myr) and Lupus (1-3 Myr), similar to those of Chamaleon I, (2-3 Myr) and σ Ori (3-5 Myr) and significantly higher than in Upper Scorpius (5-10 Myr). About 20 disks in our sample (˜5% of the cluster members) have estimated masses (dust + gas) >1 MJup and hence might be the precursors of giant planets in the cluster. Some of the most massive disks include transition objects with inner opacity holes based on their infrared SEDs. From a stacking analysis of the 96 non-detections, we find that these disks have a typical dust mass of just ≲ 0.4 M⊕, even though the vast majority of their infrared SEDs remain optically thick and show little signs of evolution. Such low-mass disks may be the precursors of the small rocky planets found by Kepler around M-type stars.

  12. The very young resolved stellar populations around stripped-envelope supernovae

    Science.gov (United States)

    Maund, Justyn R.

    2018-05-01

    The massive star origins for Type IIP supernovae (SNe) have been established through direct detection of their red supergiants progenitors in pre-explosion observations; however, there has been limited success in the detection of the progenitors of H-deficient SNe. The final fate of more massive stars, capable of undergoing a Wolf-Rayet phase, and the origins of Type Ibc SNe remain debated, including the relative importance of single massive star progenitors or lower mass stars stripped in binaries. We present an analysis of the ages and spatial distributions of massive stars around the sites of 23 stripped-envelope SNe, as observed with the Hubble Space Telescope, to probe the possible origins of the progenitors of these events. Using a Bayesian stellar populations analysis scheme, we find characteristic ages for the populations observed within 150 pc of the target Type IIb, Ib, and Ic SNe to be log (t) = 7.20, 7.05, and 6.57, respectively. The Type Ic SNe in the sample are nearly all observed within 100 pc of young, dense stellar populations. The environment around SN 2002ap is an important exception both in terms of age and spatial properties. These findings may support the hypothesis that stars with Minit > 30 M⊙ produce a relatively large proportion of Type Ibc SNe, and that these SN subtypes arise from progressively more massive progenitors. Significantly higher extinctions are derived towards the populations hosting these SNe than previously used in analysis of constraints from pre-explosion observations. The large initial masses inferred for the progenitors are in stark contrast with the low ejecta masses estimated from SN light curves.

  13. Young stellar population and ongoing star formation in the H II complex Sh2-252

    Science.gov (United States)

    Jose, Jessy; Pandey, A. K.; Samal, M. R.; Ojha, D. K.; Ogura, K.; Kim, J. S.; Kobayashi, N.; Goyal, A.; Chauhan, N.; Eswaraiah, C.

    2013-07-01

    In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken with an aim to explore its hidden young stellar population as well as to understand the structure and star formation history for the first time. This complex is composed of five prominent embedded clusters associated with the subregions A, C, E, NGC 2175s and Teu 136. We used Two Micron All Sky Survey-near-infrared and Spitzer-Infrared Array Camera, Multiband Imaging Photometer for Spitzer photometry to identify and classify the young stellar objects (YSOs) by their infrared (IR) excess emission. Using the IR colour-colour criteria, we identified 577 YSOs, of which, 163 are Class I, 400 are Class II and 14 are transition disc YSOs, suggesting a moderately rich number of YSOs in this complex. Spatial distribution of the candidate YSOs shows that they are mostly clustered around the subregions in the western half of the complex, suggesting enhanced star formation activity towards its west. Using the spectral energy distribution and optical colour-magnitude diagram-based age analyses, we derived probable evolutionary status of the subregions of Sh2-252. Our analysis shows that the region A is the youngest (˜0.5 Myr), the regions B, C and E are of similar evolutionary stage (˜1-2 Myr) and the clusters NGC 2175s and Teu 136 are slightly evolved (˜2-3 Myr). Morphology of the region in the 1.1 mm map shows a semicircular shaped molecular shell composed of several clumps and YSOs bordering the western ionization front of Sh2-252. Our analyses suggest that next generation star formation is currently under way along this border and that possibly fragmentation of the matter collected during the expansion of the H II region as one of the major processes is responsible for such stars. We observed the densest concentration of YSOs (mostly Class I, ˜0.5 Myr) at the western outskirts of the complex, within a molecular clump associated with water and methanol masers and we suggest that it

  14. Time monitoring of radio jets and magnetospheres in the nearby young stellar cluster R Coronae Australis

    International Nuclear Information System (INIS)

    Liu, Hauyu Baobab; Takami, Michihiro; Yan, Chi-Hung; Karr, Jennifer; Chou, Mei-Yin; Ho, Paul T.-P.; Galván-Madrid, Roberto; Costigan, Gráinne; Manara, Carlo Felice; Forbrich, Jan; Rodríguez, Luis F.; Zhang, Qizhou

    2014-01-01

    We report Karl G. Jansky Very Large Array 8-10 GHz (λ = 3.0-3.7 cm) monitoring observations toward the young stellar object (YSO) cluster R Coronae Australis (R CrA), taken from 2012 March 15 to 2012 September 12. These observations were planned to measure the radio flux variabilities in timescales from 0.5 hr to several days, to tens of days, and up to ∼200 days. We found that among the YSOs detectable in individual epochs, in general, the most reddened objects in the Spitzer observations show the highest mean 3.5 cm Stokes I emission, and the lowest fractional variabilities on <200 day timescales. The brightest radio flux emitters in our observations are the two reddest sources IRS7W and IRS7E. In addition, by comparing our observations with observations taken from 1996 to 1998 and 2005, we found that the radio fluxes of these two sources have increased by a factor of ∼1.5. The mean 3.5 cm fluxes of the three Class I/II sources, IRSI, IRS2, and IRS6, appear to be correlated with their accretion rates derived by a previous near-infrared line survey. The weakly accreting Class I/II YSOs, or those in later evolutionary stages, present radio flux variability on <0.5 hr timescales. Some YSOs were detected only during occasional flaring events. The source R CrA went below our detection limit during a few fading events.

  15. ABSENCE OF SIGNIFICANT COOL DISKS IN YOUNG STELLAR OBJECTS EXHIBITING REPETITIVE OPTICAL OUTBURSTS

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Hauyu Baobab; Hirano, Naomi; Takami, Michihiro; Dong, Ruobing [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan (China); Galván-Madrid, Roberto; Rodríguez, Luis F.; Carrasco-González, Carlos [Instituto de Radioastronomía y Astrofísica, UNAM, A.P. 3-72, Xangari, Morelia, 58089 (Mexico); Vorobyov, Eduard I. [Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, A-1180, Vienna (Austria); Kóspál, Ágnes [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O. Box 67, 1525 Budapest (Hungary); Dunham, Michael M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, MA 02138 (United States); Henning, Thomas [Max-Planck-Institut für Astronomie Königstuhl, 17 D-69117 Heidelberg (Germany); Hashimoto, Jun [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 Japan (Japan); Hasegawa, Yasuhiro, E-mail: baobabyoo@gmail.com [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

    2016-01-10

    We report Submillimeter Array 1.3 mm high angular resolution observations toward the four EXor-type outbursting young stellar objects VY Tau, V1118 Ori, V1143 Ori, and NY Ori. The data mostly show low dust masses M{sub dust} in the associated circumstellar disks. Among the sources, NY Ori possesses a relatively massive disk with M{sub dust} ∼ 9 × 10{sup −4}M{sub ⊙}. V1118 Ori has a marginal detection equivalent to M{sub dust} ∼ 6 × 10{sup −5}M{sub ⊙}. V1143 Ori has a non-detection also equivalent to M{sub dust} < 6 × 10{sup −5}M{sub ⊙}. For the nearest source, VY Tau, we get a surprising non-detection that provides a stringent upper limit M{sub dust} < 6 × 10{sup −6}M{sub ⊙}. We interpret our findings as suggesting that the gas and dust reservoirs that feed the short-duration, repetitive optical outbursts seen in some EXors may be limited to the small-scale, innermost region of their circumstellar disks. This hot dust may have escaped our detection limits. Follow-up, more sensitive millimeter observations are needed to improve our understanding of the triggering mechanisms of EXor-type outbursts.

  16. The Age of the Young Bulge-like Population in the Stellar System Terzan 5: Linking the Galactic Bulge to the High-z Universe

    NARCIS (Netherlands)

    Ferraro, F. R.; Massari, D.; Dalessandro, E.; Lanzoni, B.; Origlia, L.; Rich, R. M.; Mucciarelli, A.

    2016-01-01

    The Galactic bulge is dominated by an old, metal-rich stellar population. The possible presence and the amount of a young (a few gigayears old) minor component is one of the major issues debated in the literature. Recently, the bulge stellar system Terzan 5 was found to harbor three sub-populations

  17. X-shooter spectroscopy of young stellar objects in Lupus. Lithium, iron, and barium elemental abundances

    Science.gov (United States)

    Biazzo, K.; Frasca, A.; Alcalá, J. M.; Zusi, M.; Covino, E.; Randich, S.; Esposito, M.; Manara, C. F.; Antoniucci, S.; Nisini, B.; Rigliaco, E.; Getman, F.

    2017-09-01

    Aims: With the purpose of performing a homogeneous determination of elemental abundances for members of the Lupus T association, we analyzed three chemical elements: lithium, iron, and barium. The aims were: 1) to derive the lithium abundance for the almost complete sample ( 90%) of known class II stars in the Lupus I, II, III, and IV clouds; 2) to perform chemical tagging of a region where few iron abundance measurements have been obtained in the past, and no determination of the barium content has been done up to now. We also investigated possible barium enhancement at the very young age of the region, as this element has become increasingly interesting in the last few years following the evidence of barium over-abundance in young clusters, the origin of which is still unknown. Methods: Using the X-shooter spectrograph mounted on the Unit 2 (UT2) at the Very Large Telescope (VLT), we analyzed the spectra of 89 cluster members, both class II (82) and class III (7) stars. We measured the strength of the lithium line at λ6707.8 Å and derived the abundance of this element through equivalent width measurements and curves of growth. For six class II stars we also derived the iron and barium abundances using the spectral synthesis method and the code MOOG. The veiling contribution was taken into account in the abundance analysis for all three elements. Results: We find a dispersion in the strength of the lithium line at low effective temperatures and identify three targets with severe Li depletion. The nuclear age inferred for these highly lithium-depleted stars is around 15 Myr, which exceeds by an order of magnitude the isochronal one. We derive a nearly solar metallicity for the members whose spectra could be analyzed. We find that Ba is over-abundant by 0.7 dex with respect to the Sun. Since current theoretical models cannot reproduce this abundance pattern, we investigated whether this unusually large Ba content might be related to effects due to stellar

  18. A new spectroscopic and interferometric study of the young stellar object V645 Cygni

    Science.gov (United States)

    Miroshnichenko, A. S.; Hofmann, K.-H.; Schertl, D.; Weigelt, G.; Kraus, S.; Manset, N.; Albert, L.; Balega, Y. Y.; Klochkova, V. G.; Rudy, R. J.; Lynch, D. K.; Mazuk, S.; Venturini, C. C.; Russell, R. W.; Grankin, K. N.; Puetter, R. C.; Perry, R. B.

    2009-04-01

    Aims: We present the results of high-resolution optical spectroscopy, low-resolution near-IR spectroscopy and near-infrared speckle interferometry of the massive young stellar object candidate V645 Cyg, acquired to refine its fundamental parameters and the properties of its circumstellar envelope. Methods: Speckle interferometry in the H- and K-bands and an optical spectrum in the range 5200-6680 Å with a spectral resolving power of R = 60 000 were obtained at the 6 m telescope of the Russian Academy of Sciences. Another optical spectrum in the range 4300-10 500 Å with R = 79 000 was obtained at the 3.6 m CFHT. Low-resolution spectra in the ranges 0.46-1.4 μm and 1.4-2.5 μm with R ~ 800 and ~700, respectively, were obtained at the 3 m Shane telescope of the Lick Observatory. Results: Using a novel kinematical method based on the non-linear modeling of the neutral hydrogen density profile in the direction toward the object, we propose a distance of D = 4.2 ± 0.2 kpc. We also suggest a revised estimate of the star's effective temperature, T_eff ~ 25 000 K. We resolved the object in both H- and K-bands. Using a two-component ring fit, we derived a compact component size of 14 mas and 12 mas in the H- and K-band, respectively, which correspond to 29 and 26 AU at the revised distance. Analysis of our own and previously published data indicates a ~2 mag decrease in the near-infrared brightness of V645 Cyg at the beginning of the 1980's. At the same time, the cometary nebular condensation N1 appears to fade in this wavelength range with respect to the N0 object, representing the star with a nearly pole-on optically-thick disk and an optically-thin envelope. Conclusions: We conclude that V645 Cyg is a young, massive, main-sequence star, which recently emerged from its cocoon and has already experienced its protostellar accretion stage. The presence of accretion is not necessary to account for the high observed luminosity of (2-6) × 104 M⊙ yr-1. The receding part of

  19. The Cosmic Christmas Ghost - Two Stunning Pictures of Young Stellar Clusters

    Science.gov (United States)

    2005-12-01

    Just like Charles Dickens' Christmas Carol takes us on a journey into past, present and future in the time of only one Christmas Eve, two of ESO' s telescopes captured various stages in the life of a star in a single image. ESO PR Photo 42a/05 shows the area surrounding the stellar cluster NGC 2467, located in the southern constellation of Puppis (" The Stern" ). With an age of a few million years at most, it is a very active stellar nursery, where new stars are born continuously from large clouds of dust and gas. The image, looking like a colourful cosmic ghost or a gigantic celestial Mandrill [1] , contains the open clusters Haffner 18 (centre) and Haffner 19 (middle right: it is located inside the smaller pink region - the lower eye of the Mandrill), as well as vast areas of ionised gas. The bright star at the centre of the largest pink region on the bottom of the image is HD 64315, a massive young star that is helping shaping the structure of the whole nebular region. ESO PR Photo 42a/05 was taken with the Wide-Field Imager camera at the 2.2m MPG/ESO telescope located at La Silla, in Chile. Another image of the central part of this area is shown as ESO PR Photo 42b/05. It was obtained with the FORS2 instrument at ESO' s Very Large Telescope on Cerro Paranal, also in Chile. ESO PR Photo 42b/05 zooms in on the open stellar cluster Haffner 18, perfectly illustrating three different stages of this process of star formation: In the centre of the picture, Haffner 18, a group of mature stars that have already dispersed their birth nebulae, represents the completed product or immediate past of the star formation process. Located at the bottom left of this cluster, a very young star, just come into existence and, still surrounded by its birth cocoon of gas, provides insight into the very present of star birth. Finally, the dust clouds towards the right corner of the image are active stellar nurseries that will produce more new stars in the future. Haffner 18 contains

  20. QUASI-STELLAR OBJECT SELECTION ALGORITHM USING TIME VARIABILITY AND MACHINE LEARNING: SELECTION OF 1620 QUASI-STELLAR OBJECT CANDIDATES FROM MACHO LARGE MAGELLANIC CLOUD DATABASE

    International Nuclear Information System (INIS)

    Kim, Dae-Won; Protopapas, Pavlos; Alcock, Charles; Trichas, Markos; Byun, Yong-Ik; Khardon, Roni

    2011-01-01

    We present a new quasi-stellar object (QSO) selection algorithm using a Support Vector Machine, a supervised classification method, on a set of extracted time series features including period, amplitude, color, and autocorrelation value. We train a model that separates QSOs from variable stars, non-variable stars, and microlensing events using 58 known QSOs, 1629 variable stars, and 4288 non-variables in the MAssive Compact Halo Object (MACHO) database as a training set. To estimate the efficiency and the accuracy of the model, we perform a cross-validation test using the training set. The test shows that the model correctly identifies ∼80% of known QSOs with a 25% false-positive rate. The majority of the false positives are Be stars. We applied the trained model to the MACHO Large Magellanic Cloud (LMC) data set, which consists of 40 million light curves, and found 1620 QSO candidates. During the selection none of the 33,242 known MACHO variables were misclassified as QSO candidates. In order to estimate the true false-positive rate, we crossmatched the candidates with astronomical catalogs including the Spitzer Surveying the Agents of a Galaxy's Evolution LMC catalog and a few X-ray catalogs. The results further suggest that the majority of the candidates, more than 70%, are QSOs.

  1. Young Stellar Objects in the Massive Star-forming Regions W51 and W43

    Energy Technology Data Exchange (ETDEWEB)

    Saral, G.; Audard, M. [Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix (Switzerland); Hora, J. L.; Martínez-Galarza, J. R.; Smith, H. A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Koenig, X. P. [Yale University, Department of Astronomy, 208101, New Haven, CT 06520-8101 (United States); Motte, F. [Institut de Plantologie et d’Astrophysique de Grenoble, Univ. Grenoble Alpes—CNRS-INSU, BP 53, F-38041 Grenoble Cedex 9 (France); Nguyen-Luong, Q. [National Astronomical Observatory of Japan, Chile Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Saygac, A. T. [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

    2017-04-20

    We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color–magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions and, based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH ii regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H ii regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.

  2. Medium-resolution near-infrared spectroscopy of massive young stellar objects

    Science.gov (United States)

    Pomohaci, R.; Oudmaijer, R. D.; Lumsden, S. L.; Hoare, M. G.; Mendigutía, I.

    2017-12-01

    We present medium-resolution (R ∼ 7000) near-infrared echelle spectroscopic data for 36 massive young stellar objects (MYSOs) drawn from the Red MSX Source survey. This is the largest sample observed at this resolution at these wavelengths of MYSOs to date. The spectra are characterized mostly by emission from hydrogen recombination lines and accretion diagnostic lines. One MYSO shows photospheric H I absorption, a comparison with spectral standards indicates that the star is an A-type star with a low surface gravity, implying that the MYSOs are probably swollen, as also suggested by evolutionary calculations. An investigation of the Brγ line profiles shows that most are in pure emission, while 13 ± 5 per cent display P Cygni profiles, indicative of outflow, while less than 8 ± 4 per cent have inverse P Cygni profiles, indicative of infall. These values are comparable with investigations into the optically bright Herbig Be stars, but not with those of Herbig Ae and T Tauri stars, consistent with the notion that the more massive stars undergo accretion in a different fashion than lower mass objects that are undergoing magnetospheric accretion. Accretion luminosities and rates as derived from the Br γ line luminosities agree with results for lower mass sources, providing tentative evidence for massive star formation theories based on scaling of low-mass scenarios. We present Br γ/Br12 line profile ratios exploiting the fact that optical depth effects can be traced as a function of Doppler shift across the lines. These show that the winds of MYSOs in this sample are nearly equally split between constant, accelerating and decelerating velocity structures. There are no trends between the types of features we see and bolometric luminosities or near-infrared colours.

  3. A 1.3 mm SMA survey of 29 variable young stellar objects

    Science.gov (United States)

    Liu, Hauyu Baobab; Dunham, Michael M.; Pascucci, Ilaria; Bourke, Tyler L.; Hirano, Naomi; Longmore, Steven; Andrews, Sean; Carrasco-González, Carlos; Forbrich, Jan; Galván-Madrid, Roberto; Girart, Josep M.; Green, Joel D.; Juárez, Carmen; Kóspál, Ágnes; Manara, Carlo F.; Palau, Aina; Takami, Michihiro; Testi, Leonardo; Vorobyov, Eduard I.

    2018-04-01

    Context. Young stellar objects (YSOs) may undergo periods of active accretion (outbursts), during which the protostellar accretion rate is temporarily enhanced by a few orders of magnitude. Whether or not these accretion outburst YSOs possess similar dust and gas reservoirs to each other, and whether or not their dust and gas reservoirs are similar as quiescent YSOs, are issues yet to be clarified. Aims: The aim of this work is to characterize the millimeter thermal dust emission properties of a statistically significant sample of long and short duration accretion outburst YSOs (i.e., FUors and EXors) and the spectroscopically identified candidates of accretion outbursting YSOs (i.e., FUor-like objects). Methods: We have carried out extensive Submillimeter Array (SMA) observations mostly at 225 GHz (1.33 mm) and 272 GHz (1.10 mm), from 2008 to 2017. We covered accretion outburst YSOs located at database of 29 objects. We obtained 21 detections at >3σ significance. Detected sources except for the two cases of V883 Ori and NGC 2071 MM3 were observed with 1″ angular resolution. Overall our observed targets show a systematically higher millimeter luminosity distribution than those of the M* > 0.3 M⊙ Class II YSOs in the nearby (≲400 pc) low-mass star-forming molecular clouds (e.g., Taurus, Lupus, Upp Scorpio, and Chameleon I). In addition, at 1 mm our observed confirmed binaries or triple-system sources are systematically fainter than the rest of the sources even though their 1 mm fluxes are broadly distributed. We may have detected 30-60% millimeter flux variability from V2494 Cyg and V2495 Cyg, from the observations separated by approximately one year.

  4. NEAR-INFRARED VARIABILITY AMONG YOUNG STELLAR OBJECTS IN THE STAR FORMATION REGION CYGNUS OB7

    Energy Technology Data Exchange (ETDEWEB)

    Wolk, Scott J.; Rice, Thomas S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aspin, Colin [Institute for Astronomy, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720 (United States)

    2013-08-20

    We present an analysis of near-infrared time-series photometry in J, H, and K bands for about 100 epochs of a 1 Degree-Sign Multiplication-Sign 1 Degree-Sign region of the Lynds 1003/1004 dark cloud in the Cygnus OB7 region. Augmented by data from the Wide-field Infrared Survey Explorer, we identify 96 candidate disk bearing young stellar objects (YSOs) in the region. Of these, 30 are clearly Class I or earlier. Using the Wide-Field Imaging Camera on the United Kingdom Infrared Telescope, we were able to obtain photometry over three observing seasons, with photometric uncertainty better than 0.05 mag down to J Almost-Equal-To 17. We study detailed light curves and color trajectories of {approx}50 of the YSOs in the monitored field. We investigate the variability and periodicity of the YSOs and find the data are consistent with all YSOs being variable in these wavelengths on timescales of a few years. We divide the variability into four observational classes: (1) stars with periodic variability stable over long timescales, (2) variables which exhibit short-lived cyclic behavior, (3) long-duration variables, and (4) stochastic variables. Some YSO variability defies simple classification. We can explain much of the observed variability as being due to dynamic and rotational changes in the disk, including an asymmetric or changing blocking fraction, changes to the inner disk hole size, as well as changes to the accretion rate. Overall, we find that the Class I:Class II ratio of the cluster is consistent with an age of <1 Myr, with at least one individual, wildly varying source {approx}100, 000 yr old. We have also discovered a Class II eclipsing binary system with a period of 17.87 days.

  5. HUBBLE SPACE TELESCOPE NICMOS POLARIZATION OBSERVATIONS OF THREE EDGE-ON MASSIVE YOUNG STELLAR OBJECTS

    International Nuclear Information System (INIS)

    Simpson, Janet P.; Colgan, Sean W. J.; Erickson, Edwin F.; Burton, Michael G.; Cotera, Angela S.; Hines, Dean C.; Whitney, Barbara A.

    2009-01-01

    Massive young stellar objects (YSOs), like low-mass YSOs, appear to be surrounded by optically thick envelopes and/or disks and have regions, often bipolar, that are seen in polarized scattered light at near-infrared wavelengths. We are using the 0.''2 spatial resolution of the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) on Hubble Space Telescope to examine the structure of the disks and outflow regions of massive YSOs in star-forming regions within a few kpc of the Sun. Here we report on 2 μm polarimetry of NGC 6334 V and S255 IRS1. NGC 6334 V consists of a double-lobed bright reflection nebula seen against a dark region, probably an optically thick molecular cloud. Our polarization measurements show that the illuminating star lies ∼2'' south of the line connecting the two lobes; we do not detect this star at 2 μm, but there are a small radio source and a mid-infrared source at this location. S255 IRS1 consists of two YSOs (NIRS1 and NIRS3) with overlapping scattered light lobes and luminosities corresponding to early B stars. Included in IRS1 is a cluster of stars from whose polarization we determine the local magnetic field direction. Neither of the YSOs has its scattered light lobes aligned with this magnetic field. The line connecting the scattered light lobes of NIRS1 is twisted symmetrically around the star; the best explanation is that the star is part of a close binary and the outflow axis of NIRS1 is precessing as a result of non-coplanar disk and orbit. The star NIRS3 is also offset from the line connecting its two scattered light lobes. We suggest that all three YSOs show evidence of episodic ejection of material as they accrete from dense, optically thick envelopes.

  6. A Theoretical Model of X-Ray Jets from Young Stellar Objects

    Energy Technology Data Exchange (ETDEWEB)

    Takasao, Shinsuke; Suzuki, Takeru K. [Department of Physics, Nagoya University, Nagoya, Aichi 464-8602 (Japan); Shibata, Kazunari, E-mail: takasao@kwasan.kyoto-u.ac.jp [Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto 607-8471 (Japan)

    2017-09-20

    There is a subclass of X-ray jets from young stellar objects that are heated very close to the footpoint of the jets, particularly DG Tau jets. Previous models have attributed the strong heating to shocks in the jets. However, the mechanism that localizes the heating at the footpoint remains puzzling. We presented a different model of such X-ray jets, in which the disk atmosphere is magnetically heated. Our disk corona model is based on the so-called nanoflare model for the solar corona. We show that the magnetic heating near the disks can result in the formation of a hot corona with a temperature of ≳10{sup 6} K, even if the average field strength in the disk is moderately weak, ≳1 G. We determine the density and the temperature at the jet base by considering the energy balance between the heating and cooling. We derive the scaling relations of the mass-loss rate and terminal velocity of jets. Our model is applied to the DG Tau jets. The observed temperature and estimated mass-loss rate are consistent with the prediction of our model in the case of a disk magnetic field strength of ∼20 G and a heating region of <0.1 au. The derived scaling relation of the temperature of X-ray jets could be a useful tool for estimating the magnetic field strength. We also find that the jet X-ray can have a significant impact on the ionization degree near the disk surface and the dead zone size.

  7. Multi-Sensory Approach to Search for Young Stellar Objects in CG4

    Science.gov (United States)

    Hoette, Vivian L.; Rebull, L. M.; McCarron, K.; Johnson, C. H.; Gartner, C.; VanDerMolen, J.; Gamble, L.; Matche, L.; McCartney, A.; Doering, M.; Crump, R.; Laorr, A.; Mork, K.; Steinbergs, E.; Wigley, E.; Caruso, S.; Killingstad, N.; McCanna, T.

    2011-01-01

    Individuals with disabilities - specifically individuals who are deaf or hard of hearing (DHH) and/or blind and visually-impaired (BVI) - have traditionally been underrepresented in the fields of Science, Technology, Engineering, and Math (STEM). The low incidence rate of these populations, coupled with geographic isolation, creates limited opportunities for students to work with and receive mentoring by professionals who not only have specialty knowledge in disability areas but also work in STEM fields. Yerkes Observatory scientists, along with educators from the Wisconsin School for the Deaf, the Wisconsin Center for the Blind and Visually Impaired, Breck School, and Oak Park and River Forest High School, are engaged in active research with a Spitzer Science Center (SSC) scientist. Our ultimate goals are threefold; to engage DHH and BVI students with equal success as their sighted and hearing peers, to share our techniques to make astronomy more accessible to DHH and BVI youth, and to generate a life-long interest which will lead our students to STEM careers. This poster tracks our work with an SSC scientist during the spring, summer, and fall of 2010. The group coauthored another AAS poster on finding Young Stellar Objects (YSO) in the CG4 Nebula in Puppis. During the project, the students, scientists and teachers developed a number of techniques for learning the necessary science as well as doing the required data acquisition and analysis. Collaborations were formed between students with disabilities and their non-disabled peers to create multi-media projects. Ultimately, the projects created for our work with NITARP will be disseminated through our professional connections in order to ignite a passion for astronomy in all students - with and without disabilities. This research was made possible through the NASA/IPAC Teacher Archive Research Project (NITARP) and was funded by NASA Astrophysics Data Program and Archive Outreach funds.

  8. Near-infrared (JHK) spectroscopy of young stellar and substellar objects in orion

    International Nuclear Information System (INIS)

    Ingraham, P.; Albert, L.; Doyon, R.; Artigau, E.

    2014-01-01

    We performed low-resolution (R ∼ 40) near-infrared (0.9-2.4 μm) multi-object spectroscopy of 240 isolated point sources having apparent H-band magnitudes between 9 and 18 in the central 5' × 6' of the Orion Trapezium cluster. The observations were performed over four nights at the Canada-France-Hawaii Telescope using the visiting instrument SIMON, an infrared imager and multi-object spectrograph. We present the spectra of 104 objects with accurately derived spectral types including 7 new objects having masses below the hydrogen-burning limit, and 6 objects with masses below the deuterium-burning limit. The spectral classification is performed by fitting previously classified spectral templates of dwarf stars (K4-M3) and optically classified young stellar and substellar objects (M4-L0), to the entire 0.9-2.4 μm spectral energy distribution in order to assign a spectral type and visual extinction for each object. Of the 104 objects studied, 44 have been previously classified spectroscopically using various techniques. We perform a rigorous comparison between the previous classifications and our own and find them to be in good agreement. Using the dereddened H-band magnitudes, the classified objects are used to create an Hertzsprung-Russell diagram for the cluster. We find that the previous age estimates of ∼1 Myr to be consistent with our results. Consistent with previous studies, numerous objects are observed to have luminosities several magnitudes above the 1 Myr isochrone. Numerous objects exhibiting emission features in the J band are also reported

  9. The Red MSX Source Survey: The Massive Young Stellar Population of Our Galaxy

    Science.gov (United States)

    Lumsden, S. L.; Hoare, M. G.; Urquhart, J. S.; Oudmaijer, R. D.; Davies, B.; Mottram, J. C.; Cooper, H. D. B.; Moore, T. J. T.

    2013-09-01

    We present the Red MSX Source survey, the largest statistically selected catalog of young massive protostars and H II regions to date. We outline the construction of the catalog using mid- and near-infrared color selection. We also discuss the detailed follow up work at other wavelengths, including higher spatial resolution data in the infrared. We show that within the adopted selection bounds we are more than 90% complete for the massive protostellar population, with a positional accuracy of the exciting source of better than 2 arcsec. We briefly summarize some of the results that can be obtained from studying the properties of the objects in the catalog as a whole; we find evidence that the most massive stars form: (1) preferentially nearer the Galactic center than the anti-center; (2) in the most heavily reddened environments, suggestive of high accretion rates; and (3) from the most massive cloud cores.

  10. THE RED MSX SOURCE SURVEY: THE MASSIVE YOUNG STELLAR POPULATION OF OUR GALAXY

    International Nuclear Information System (INIS)

    Lumsden, S. L.; Hoare, M. G.; Oudmaijer, R. D.; Cooper, H. D. B.; Urquhart, J. S.; Davies, B.; Moore, T. J. T.; Mottram, J. C.

    2013-01-01

    We present the Red MSX Source survey, the largest statistically selected catalog of young massive protostars and H II regions to date. We outline the construction of the catalog using mid- and near-infrared color selection. We also discuss the detailed follow up work at other wavelengths, including higher spatial resolution data in the infrared. We show that within the adopted selection bounds we are more than 90% complete for the massive protostellar population, with a positional accuracy of the exciting source of better than 2 arcsec. We briefly summarize some of the results that can be obtained from studying the properties of the objects in the catalog as a whole; we find evidence that the most massive stars form: (1) preferentially nearer the Galactic center than the anti-center; (2) in the most heavily reddened environments, suggestive of high accretion rates; and (3) from the most massive cloud cores

  11. THE RED MSX SOURCE SURVEY: THE MASSIVE YOUNG STELLAR POPULATION OF OUR GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Lumsden, S. L.; Hoare, M. G.; Oudmaijer, R. D.; Cooper, H. D. B. [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Urquhart, J. S. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, Bonn (Germany); Davies, B.; Moore, T. J. T. [Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF (United Kingdom); Mottram, J. C. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)

    2013-09-01

    We present the Red MSX Source survey, the largest statistically selected catalog of young massive protostars and H II regions to date. We outline the construction of the catalog using mid- and near-infrared color selection. We also discuss the detailed follow up work at other wavelengths, including higher spatial resolution data in the infrared. We show that within the adopted selection bounds we are more than 90% complete for the massive protostellar population, with a positional accuracy of the exciting source of better than 2 arcsec. We briefly summarize some of the results that can be obtained from studying the properties of the objects in the catalog as a whole; we find evidence that the most massive stars form: (1) preferentially nearer the Galactic center than the anti-center; (2) in the most heavily reddened environments, suggestive of high accretion rates; and (3) from the most massive cloud cores.

  12. Herschel Observations of Protostellar and Young Stellar Objects in Nearby Molecular Clouds: The DIGIT Open Time Key Project

    Science.gov (United States)

    Green, Joel D.; DIGIT OTKP Team

    2010-01-01

    The DIGIT (Dust, Ice, and Gas In Time) Open Time Key Project utilizes the PACS spectrometer (57-210 um) onboard the Herschel Space Observatory to study the colder regions of young stellar objects and protostellar cores, complementary to recent observations from Spitzer and ground-based observatories. DIGIT focuses on 30 embedded sources and 64 disk sources, and includes supporting photometry from PACS and SPIRE, as well as spectroscopy from HIFI, selected from nearby molecular clouds. For the embedded sources, PACS spectroscopy will allow us to address the origin of [CI] and high-J CO lines observed with ISO-LWS. Our observations are sensitive to the presence of cold crystalline water ice, diopside, and carbonates. Additionally, PACS scans are 5x5 maps of the embedded sources and their outflows. Observations of more evolved disk sources will sample low and intermediate mass objects as well as a variety of spectral types from A to M. Many of these sources are extremely rich in mid-IR crystalline dust features, enabling us to test whether similar features can be detected at larger radii, via colder dust emission at longer wavelengths. If processed grains are present only in the inner disk (in the case of full disks) or from the emitting wall surface which marks the outer edge of the gap (in the case of transitional disks), there must be short timescales for dust processing; if processed grains are detected in the outer disk, radial transport must be rapid and efficient. Weak bands of forsterite and clino- and ortho-enstatite in the 60-75 um range provide information about the conditions under which these materials were formed. For the Science Demonstration Phase we are observing an embedded protostar (DK Cha) and a Herbig Ae/Be star (HD 100546), exemplars of the kind of science that DIGIT will achieve over the full program.

  13. A LARGE, MASSIVE, ROTATING DISK AROUND AN ISOLATED YOUNG STELLAR OBJECT

    International Nuclear Information System (INIS)

    Quanz, Sascha P.; Beuther, Henrik; Steinacker, Juergen; Linz, Hendrik; Krause, Oliver; Henning, Thomas; Birkmann, Stephan M.; Zhang Qizhou

    2010-01-01

    and the molecules' abundances are similar to those found in other circumstellar disks. We furthermore detected C 2 H toward the objects and discuss this finding in the context of star formation. Finally, we have performed radiative transfer modeling of the K-band scattered light image varying a disk plus outflow two-dimensional density profile and the stellar properties. The model approximately reproduces extent and location of the dark lane, and the basic appearance of the outflow. We discuss our findings in the context of circumstellar disks across all mass regimes and conclude that our discovery is an ideal laboratory to study the early phases in the evolution of massive circumstellar disks surrounding young stellar objects.

  14. PHOTOELECTRIC CHARGING OF DUST GRAINS IN THE ENVIRONMENT OF YOUNG STELLAR OBJECTS

    International Nuclear Information System (INIS)

    Pedersen, Andreas; Gomez de Castro, Ana I.

    2011-01-01

    The evolution of disks around young stellar objects (YSOs) is deeply affected by the YSOs' ultraviolet (UV) radiation field especially in the 500-1100 A spectral range. The two dominant processes are: the photodissociation of H 2 molecules in the Werner and Lyman bands, and the emission of photoelectrons from dust grains when high energy photons are absorbed. Photoelectrons are an important source of gas heating. In this paper, dust grain charging when exposed to various possible UV fields in the YSOs' environment is investigated. Numerical simulations of the evolution of photoelectrons in the electric field created by the charged dust grains are carried out to obtain the charging profile of dust grains. From the simulations it appears that the different spectra produce significant quantitative and qualitative differences in the charging processes. Both the UV background and the Ae-Herbig star radiation field produce a relatively slow charging of dust grains due to the low fraction of sufficiently energetic photons. The radiation field of T Tauri stars (TTSs) is harder due to the release of magnetic energy in the dense magnetospheric environment. These numerical results have been used to propose a new simple analytical model for grain charging in the atmosphere of protostellar disks around TTSs susceptible to be used in any disk modeling. It has been found that the yield decreases exponentially with the dust charge and that two populations of photoelectrons are produced: a low energy population with mean kinetic energy E = 2.5 eV and a high energy population with E = 5.5-6 eV; the energy dispersion within the populations is ∼1.3 eV (T ∼ 1.5 x 10 4 K). The high energy population is susceptible of dissociating the H 2 and ionizing some low ionization potential species, such as the Mg. These results add an additional role to dust on the chemistry of the layers just below the H 2 photoionization front. This photoelectic yield has been applied to a simple evaluation

  15. A Spectroscopic Study of Young Stellar Objects in the Serpens Cloud Core and NGC 1333

    Science.gov (United States)

    Winston, E.; Megeath, S. T.; Wolk, S. J.; Hernandez, J.; Gutermuth, R.; Muzerolle, J.; Hora, J. L.; Covey, K.; Allen, L. E.; Spitzbart, B.; Peterson, D.; Myers, P.; Fazio, G. G.

    2009-06-01

    We present spectral observations of 130 young stellar objects (YSOs) in the Serpens Cloud Core and NGC 1333 embedded clusters. The observations consist of near-IR spectra in the H and K bands from SpeX on the IRTF and far-red spectra (6000-9000 Å) from Hectospec on the Multi-Mirror Telescope. These YSOs were identified in previous Spitzer and Chandra observations, and the evolutionary classes of the YSOs were determined from the Spitzer mid-IR photometry. With these spectra we search for corroborating evidence for the pre-main-sequence nature of the objects, study the properties of the detected emission lines as a function of evolutionary class, and obtain spectral types for the observed YSOs. The temperatures implied by the spectral types are combined with luminosities determined from the near-IR photometry to construct Hertzsprung-Russell (H-R) diagrams for the clusters. By comparing the positions of the YSOs in the H-R diagrams with the pre-main-sequence tracks of Baraffe (1998), we determine the ages of the embedded sources and study the relative ages of the YSOs with and without optically thick circumstellar disks. The apparent isochronal ages of the YSOs in both clusters range from less than 1 Myr to 10 Myr, with most objects below 3 Myr. The observed distributions of ages for the Class II and Class III objects are statistically indistinguishable. We examine the spatial distribution and extinction of the YSOs as a function of their isochronal ages. We find the sources dispersed and are not deeply embedded. Nonetheless, the sources with isochronal ages >3 Myr show all the characteristics of YSOs in their spectra, their IR spectral energy distributions, and their X-ray emission; we find no evidence that they are contaminating background giants or foreground dwarfs. However, we find no corresponding decrease in the fraction of sources with infrared excess with isochronal age; this suggests that the older isochronal ages may not measure the true age of the >3

  16. Resolved 24.5 micron emission from massive young stellar objects

    Science.gov (United States)

    de Wit, W. J.; Hoare, M. G.; Fujiyoshi, T.; Oudmaijer, R. D.; Honda, M.; Kataza, H.; Miyata, T.; Okamoto, Y. K.; Onaka, T.; Sako, S.; Yamashita, T.

    2009-01-01

    Context: Massive young stellar objects (MYSO) are surrounded by massive dusty envelopes, whose physical structure and geometry are determined by the star formation process. Aims: Our principal aim is to establish the density structure of MYSO envelopes on scales of ~1000 AU. This constitutes an increase of a factor ~10 in angular resolution compared to similar studies performed in the (sub)mm. Methods: We have obtained diffraction-limited (0.6´´) 24.5 μm images (field of view of 40 arcsec×30 arcsec) of 14 well-known massive star formation regions with the COMICS instrument mounted on the 8.2 m Subaru telescope. We construct azimuthally averaged intensity profiles of the resolved MYSO envelopes and build spectral energy distributions (SEDs) from archival data and the COMICS 24.5 μm flux density. The SEDs range from near-infrared to millimeter wavelengths. Self-consistent 1-D radiative transfer models described by a density dependence of the form n(r) ∝ r-p are used to simultaneously compare the intensity profiles and SEDs to model predictions. Results: The images reveal the presence of discrete MYSO sources which are resolved on arcsecond scales, and, to first-order, the observed emission is circular on the sky. For many sources, the spherical models are capable of satisfactorily reproducing the 24.5 μm intensity profile, the 24.5 μm flux density, the 9.7 μm silicate absorption feature, and the submm emission. They are described by density distributions with p =1.0±0.25. Such distributions are shallower than those found on larger scales probed with single-dish (sub)mm studies. Other sources have density laws that are shallower/steeper than p=1.0 and there is evidence that these are viewed near edge-on or near face-on respectively. In these cases spherical models fail to provide good fits to the data. The images also reveal a diffuse component tracing somewhat larger scale structures, particularly visible in the regions S 140, AFGL 2136, IRAS 20126

  17. The Low-mass Population in the Young Cluster Stock 8: Stellar Properties and Initial Mass Function

    Energy Technology Data Exchange (ETDEWEB)

    Jose, Jessy; Herczeg, Gregory J.; Fang, Qiliang [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Haidian Qu, Beijing 100871 (China); Samal, Manash R. [Graduate Institute of Astronomy, National Central University 300, Jhongli City, Taoyuan County 32001, Taiwan (China); Panwar, Neelam, E-mail: jessyvjose1@gmail.com [Department of Physics and Astrophysics, University of Delhi, Delhi 110007 (India)

    2017-02-10

    The evolution of H ii regions/supershells can trigger a new generation of stars/clusters at their peripheries, with environmental conditions that may affect the initial mass function, disk evolution, and star formation efficiency. In this paper we study the stellar content and star formation processes in the young cluster Stock 8, which itself is thought to be formed during the expansion of a supershell. We present deep optical photometry along with JHK and 3.6 and 4.5 μ m photometry from UKIDSS and Spitzer -IRAC. We use multicolor criteria to identify the candidate young stellar objects in the region. Using evolutionary models, we obtain a median log(age) of ∼6.5 (∼3.0 Myr) with an observed age spread of ∼0.25 dex for the cluster. Monte Carlo simulations of the population of Stock 8, based on estimates for the photometric uncertainty, differential reddening, binarity, and variability, indicate that these uncertainties introduce an age spread of ∼0.15 dex. The intrinsic age spread in the cluster is ∼0.2 dex. The fraction of young stellar objects surrounded by disks is ∼35%. The K -band luminosity function of Stock 8 is similar to that of the Trapezium cluster. The initial mass function (IMF) of Stock 8 has a Salpeter-like slope at >0.5 M {sub ⊙} and flattens and peaks at ∼0.4 M {sub ⊙}, below which it declines into the substellar regime. Although Stock 8 is surrounded by several massive stars, there seems to be no severe environmental effect in the form of the IMF due to the proximity of massive stars around the cluster.

  18. Warm gas towards young stellar objects in Corona Australis. Herschel/PACS observations from the DIGIT key programme

    Science.gov (United States)

    Lindberg, Johan E.; Jørgensen, Jes K.; Green, Joel D.; Herczeg, Gregory J.; Dionatos, Odysseas; Evans, Neal J.; Karska, Agata; Wampfler, Susanne F.

    2014-05-01

    Context. The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an intermediate-mass young star. Aims: We study the effects of the irradiation coming from the young luminous Herbig Be star R CrA on the warm gas and dust in a group of low-mass young stellar objects. Methods: Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented. The distributions of CO, OH, H2O, [C ii], [O i], and continuum emission are investigated. We have developed a deconvolution algorithm which we use to deconvolve the maps, separating the point-source emission from the extended emission. We also construct rotational diagrams of the molecular species. Results: By deconvolution of the Herschel data, we find large-scale (several thousand AU) dust continuum and spectral line emission not associated with the point sources. Similar rotational temperatures are found for the warm CO (282 ± 4 K), hot CO (890 ± 84 K), OH (79 ± 4 K), and H2O (197 ± 7 K) emission in the point sources and the extended emission. The rotational temperatures are also similar to those found in other more isolated cores. The extended dust continuum emission is found in two ridges similar in extent and temperature to molecular millimetre emission, indicative of external heating from the Herbig Be star R CrA. Conclusions: Our results show that nearby luminous stars do not increase the molecular excitation temperatures of the warm gas around young stellar objects (YSOs). However, the emission from photodissociation products of H2O, such as OH and O, is enhanced in the warm gas associated with these protostars and their surroundings compared to similar objects not subjected to external irradiation. Table 9 and appendices are available in

  19. ECRH scenarios with selective heating of trapped/passing electrons in the W7-X Stellarator

    Directory of Open Access Journals (Sweden)

    Marushchenko N.B.

    2015-01-01

    Full Text Available Using specific features of the magnetic equilibrium in the W7-X stellarator, the ECRH scenarios with combined X2 and X3 modes are discussed. The RF beams for operation with X2 and X3 modes need to be launched from low- and, via the remote steering launcher, high-field-side, respectivaly, in the different crosssections of the device where the maximum and minimum of the magnetic field located. The aim is to explore the possibility of selective heating of the different classes of electrons, passing and trapped, by changing direction of the beam for X3 or switching between the beams for X2 and X3 launched from the different ports. The numerical predictions for this kind of experiments in W7-X are performed by coupled transport and ray tracing codes

  20. The Young Massive Stellar Cluster Sandage-96 after the Explosion of SN 2004DJ in NGC 2403

    Science.gov (United States)

    Vinko, J.; Sarneczky, K.; Balog, Z.; Immler, S.; Sugerman, B.; Brown, P. J.; Misselt, K.; Szabo, Gy. M.; Klagyivik, P.; Kun, M.; hide

    2008-01-01

    The bright supernova 2004dj occurred within the young massive stellar cluster Sandage-96 in a spiral arm of NGC 2403, close to other star-forming complexes. New multi-wavelength observations obtained with several ground-based- and space telescopes are combined to study the radiation from Sandage-96 after SN 2004dj faded away. The late-time light curves show that Sandage-96 started to dominate the flux in the optical bands after September, 2006 (+800 days after explosion). The optical fluxes are equal to the pre-explosion ones, suggesting that Sandage-96 has survived the explosion without significant changes in its stellar population. An optical Keck-spectrum obtained at +900 days after explosion shows the dominant blue continuum from the cluster stars shortward of 6000 A as well as strong SN nebular emission lines redward. The integrated SED of the cluster has been extended into the UV-region by archival XMM-Newton and new Swift observations, and compared with theoretical models. The outer parts of the cluster have been resolved by HST allowing the construction of a color-magnitude diagram. The fitting of the cluster SED with theoretical isochrones results in two possible solutions with ages being 9+/-1 Myr and 30+/-10 Myr, depending on the assumed metallicity and the theoretical model family. The isochrone fitting of the color-magnitude diagram indicates that the outer part of the cluster consists of stars having an age dispersion of 16 hypothesis that the outskirt of Sandage-96 is contaminated by stars captured from the field during cluster formation. The young age of Sandage-96 and the comparison of its pre- and post-explosion SEDs suggest a progenitor mass of 15 < or equal to M(sub prog) < 25 Stellar Mass.

  1. High Energy Emissions from Young Stellar Objects A. C. Das1 ...

    Indian Academy of Sciences (India)

    ... for the generation of emissions from a YSO on the basis of a simple interaction between the ... important role in generating intense radiation, bipolar flows, stellar winds and many ... Even in the case of a non-rotating compact object, the motion .... The change in energy of the particle due to this electric field is given by. 〈1.

  2. The reliability of age measurements for Young Stellar Objects from Hertzsprung-Russell or color-magnitude diagrams

    International Nuclear Information System (INIS)

    Preibisch, Thomas

    2012-01-01

    The possibility to estimate ages and masses of Young Stellar Objects (YSOs) from their location in the Hertzsprung-Russell diagram (HRD) or a color-magnitude diagram provides a very important tool for the investigation of fundamental questions related to the processes of star formation and early stellar evolution. Age estimates are essential for studies of the temporal evolution of circumstellar material around YSOs and the conditions for planet formation. The characterization of the age distribution of the YSOs in a star forming region allows researchers to reconstruct the star formation history and provides important information on the fundamental question of whether star formation is a slow or a fast process. However, the reliability of these age measurements and the ability to detect possible age spreads in the stellar population of star forming regions are fundamentally limited by several factors. The variability of YSOs, unresolved binary components, and uncertainties in the calibrations of the stellar parameters cause uncertainties in the derived luminosities that are usually much larger than the typical photometry errors. Furthermore, the pre-main sequence evolution track of a YSO depends to some degree on the initial conditions and the details of its individual accretion history. I discuss how these observational and model uncertainties affect the derived isochronal ages, and demonstrate how neglecting or underestimating these uncertainties can easily lead to severe misinterpretations, gross overestimates of the age spread, and ill-based conclusions about the star formation history. These effects are illustrated by means of Monte-Carlo simulations of observed star clusters with realistic observational uncertainties. The most important points are as follows. First, the observed scatter in the HRD must not be confused with a genuine age spread, but is always just an upper limit to the true age spread. Second, histograms of isochronal ages naturally show a

  3. Exploring the 13CO/C18O abundance ratio towards Galactic young stellar objects and HII regions

    Science.gov (United States)

    Areal, M. B.; Paron, S.; Celis Peña, M.; Ortega, M. E.

    2018-05-01

    Aims: Determining molecular abundance ratios is important not only for the study of Galactic chemistry, but also because they are useful to estimate physical parameters in a large variety of interstellar medium environments. One of the most important molecules for tracing the molecular gas in the interstellar medium is CO, and the 13CO/C18O abundance ratio is usually used to estimate molecular masses and densities of regions with moderate to high densities. Nowadays isotope ratios are in general indirectly derived from elemental abundances ratios. We present the first 13CO/C18O abundance ratio study performed from CO isotope observations towards a large sample of Galactic sources of different natures at different locations. Methods: To study the 13CO/C18O abundance ratio, we used 12CO J = 3 - 2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3 - 2 data from the 13CO/C18O (J = 3 - 2) Heterodyne Inner Milky Way Plane Survey, and some complementary data extracted from the James Clerk Maxwell Telescope database. We analyzed a sample of 198 sources composed of young stellar objects (YSOs), and HII and diffuse HII regions as catalogued in the Red MSX Source Survey in 27.°5 ≤ l ≤ 46.°5 and |b|0.°5. Results: Most of the analyzed sources are located in the galactocentric distance range 4.0-6.5 kpc. We found that YSOs have, on average, lower 13CO/C18O abundance ratios than HII and diffuse HII regions. Taking into account that the gas associated with YSOs should be less affected by the radiation than in the case of the others sources, selective far-UV photodissociation of C18O is confirmed. The 13CO/C18O abundance ratios obtained in this work are systematically lower than those predicted from the known elemental abundance relations. These results will be useful in future studies of molecular gas related to YSOs and HII regions based on the observation of these isotopes.

  4. X-ray sources associated with young stellar objects in the star formation region CMa R1

    Science.gov (United States)

    Santos-Silva, Thais; Gregorio-Hetem, Jane; Montmerle, Thierry

    2013-07-01

    In previous works we studied the star formation scenario in the molecular cloud Canis Major R1 (CMa R1), derived from the existence of young stellar population groups near the Be stars Z CMa and GU CMa. Using data from the ROSAT X-ray satellite, having a field-of-view of ~ 1° in diameter, Gregorio-Hetem et al. (2009) discovered in this region young stellar objects mainly grouped in two clusters of different ages, with others located in between. In order to investigate the nature of these objects and to test a possible scenario of sequential star formation in this region, four fields (each 30 arcmin diameter, with some overlap) have been observed with the XMM-Newton satellite, with a sensitivity about 10 times better than ROSAT. The XMM-Newton data are currently under analysis. Preliminary results indicate the presence of about 324 sources, most of them apparently having one or more near-infrared counterparts showing typical colors of young stars. The youth of the X-ray sources was also confirmed by X-ray hardness ratio diagrams (XHRD), in different energy bands, giving an estimate of their Lx/Lbol ratios. In addition to these results, we present a detailed study of the XMM field covering the cluster near Z CMa. Several of these sources were classified as T Tauri and Herbig Ae/Be stars, using optical spectroscopy obtained with Gemini telescopes, in order to validate the use of XHRD applied to the entire sample. This classification is also used to confirm the relation between the luminosities in the near-infrared and X-ray bands expected for the T Tauri stars in CMa R1. In the present work we show the results of the study based on the spectra of about 90 sources found nearby Z CMa. We checked that the X-ray spectra (0.3 to 10 keV) of young objects is different from that observed in field stars and extragalactic objects. Some of the candidates also have light curve showing flares that are typical of T Tauri stars, which confirms the young nature of these X

  5. Wide-field infrared survey explorer observations of young stellar objects in the Lynds 1509 dark cloud in Auriga

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wilson M.; McCollum, Bruce; Fajardo-Acosta, Sergio [Infrared Processing and Analysis Center, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Padgett, Deborah L. [National Aeronautics and Space Administration, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Terebey, Susan; Angione, John [Department of Physics and Astronomy, California State University, Los Angeles, CA 90032 (United States); Rebull, Luisa M. [Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States); Leisawitz, David, E-mail: wliu@ipac.caltech.edu [National Aeronautics and Space Administration, Goddard Space Flight Center, Code 605, Greenbelt, MD 20771 (United States)

    2014-06-01

    The Wide-Field Infrared Survey Explorer (WISE) has uncovered a striking cluster of young stellar object (YSO) candidates associated with the L1509 dark cloud in Auriga. The WISE observations, at 3.4 μm, 4.6 μm, 12 μm, and 22 μm, show a number of objects with colors consistent with YSOs, and their spectral energy distributions suggest the presence of circumstellar dust emission, including numerous Class I, flat spectrum, and Class II objects. In general, the YSOs in L1509 are much more tightly clustered than YSOs in other dark clouds in the Taurus-Auriga star forming region, with Class I and flat spectrum objects confined to the densest aggregates, and Class II objects more sparsely distributed. We estimate a most probable distance of 485-700 pc, and possibly as far as the previously estimated distance of 2 kpc.

  6. Growth of a Massive Young Stellar Object Fed by a Gas Flow from a Companion Gas Clump

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Xi; Shen, Zhiqiang [Shanghai Astronomical Observatories, Chinese Academy of Science, Nandan Rd. 80, Shanghai (China); Ren, Zhiyuan [National Astronomical Observatories, Chinese Academy of Science, Chaoyang District Datun Rd. A20, Beijing (China); Zhang, Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138 (United States); Qiu, Keping [School of Astronomy and Space Science, Nanjing University, 22 Hankou Rd., Nanjing, Jiangsu 210093 (China)

    2017-02-01

    We present a Submillimeter Array (SMA) observation toward the young massive double-core system G350.69-0.49. This system consists of a northeast (NE) diffuse gas bubble and a southwest (SW) massive young stellar object (MYSO), both clearly seen in the Spitzer images. The SMA observations reveal a gas flow between the NE bubble and the SW MYSO in a broad velocity range from 5 to 30 km s{sup −1} with respect to the system velocity. The gas flow is well confined within the interval between the two objects and traces a significant mass transfer from the NE gas bubble to the SW massive core. The transfer flow can supply the material accreted onto the SW MYSO at a rate of 4.2×10{sup −4} M{sub ⊙} yr{sup −1}. The whole system therefore suggests a mode for the mass growth in the MYSO from a gas transfer flow launched from its companion gas clump, despite the driving mechanism of the transfer flow not being fully determined from the current data.

  7. 2MASS J11151597+1937266: A Young, Dusty, Isolated, Planetary-mass Object with a Potential Wide Stellar Companion

    Science.gov (United States)

    Theissen, Christopher A.; Burgasser, Adam J.; Bardalez Gagliuffi, Daniella C.; Hardegree-Ullman, Kevin K.; Gagné, Jonathan; Schmidt, Sarah J.; West, Andrew A.

    2018-01-01

    We present 2MASS J11151597+1937266, a recently identified low-surface-gravity L dwarf, classified as an L2γ based on Sloan Digital Sky Survey optical spectroscopy. We confirm this spectral type with near-infrared spectroscopy, which provides further evidence that 2MASS J11151597+1937266 is a low-surface-gravity L dwarf. This object also shows significant excess mid-infrared flux, indicative of circumstellar material; and its strong Hα emission (EWHα = 560 ± 82 Å) is an indicator of enhanced magnetic activity or weak accretion. Comparison of its spectral energy distribution to model photospheres yields an effective temperature of {1724}-38+184 {{K}}. We also provide a revised distance estimate of 37 ± 6 pc using a spectral type–luminosity relationship for low-surface-gravity objects. The three-dimensional galactic velocities and positions of 2MASS J11151597+1937266 do not match any known young association or moving group. Assuming a probable age in the range of 5–45 Myr, the model-dependent estimated mass of this object is between 7 and 21 M Jup, making it a potentially isolated planetary-mass object. We also identify a candidate co-moving, young stellar companion, 2MASS J11131089+2110086.

  8. A SEARCH FOR X-RAY EMISSION FROM COLLIDING MAGNETOSPHERES IN YOUNG ECCENTRIC STELLAR BINARIES

    Energy Technology Data Exchange (ETDEWEB)

    Getman, Konstantin V.; Broos, Patrick S. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Kóspál, Ágnes [Konkoly Observatory, Research Center for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O. Box 67, 1525 Budapest (Hungary); Salter, Demerese M. [Department of Astronomy and Laboratory for Millimeter-Wave Astronomy, University of Maryland, College Park, MD 20742 (United States); Garmire, Gordon P. [Huntingdon Institute for X-ray Astronomy, LLC, 10677 Franks Road, Huntingdon, PA 16652 (United States)

    2016-12-01

    Among young binary stars whose magnetospheres are expected to collide, only two systems have been observed near periastron in the X-ray band: the low-mass DQ Tau and the older and more massive HD 152404. Both exhibit elevated levels of X-ray emission at periastron. Our goal is to determine whether colliding magnetospheres in young high-eccentricity binaries commonly produce elevated average levels of X-ray activity. This work is based on Chandra snapshots of multiple periastron and non-periastron passages in four nearby young eccentric binaries (Parenago 523, RX J1622.7-2325 Nw, UZ Tau E, and HD 152404). We find that for the merged sample of all four binaries the current X-ray data show an increasing average X-ray flux near periastron (at a ∼2.5-sigma level). Further comparison of these data with the X-ray properties of hundreds of young stars in the Orion Nebula Cluster, produced by the Chandra Orion Ultradeep Project (COUP), indicates that the X-ray emission from the merged sample of our binaries cannot be explained within the framework of the COUP-like X-ray activity. However, due to the inhomogeneities of the merged binary sample and the relatively low statistical significance of the detected flux increase, these findings are regarded as tentative only. More data are needed to prove that the flux increase is real and is related to the processes of colliding magnetospheres.

  9. A spectroscopic census in young stellar regions: the σ Orionis cluster

    Energy Technology Data Exchange (ETDEWEB)

    Hernández, Jesús; Perez, Alice; Hernan, Ramírez [Centro de Investigaciones de Astronomía, Apdo. Postal 264, Mérida 5101-A (Venezuela, Bolivarian Republic of); Calvet, Nuria; Hartmann, Lee [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Briceño, Cesar [Cerro Tololo Interamerican Observatory, Casilla 603, La Serena (Chile); Olguin, Lorenzo [Depto. de Investigación en Física, Universidad de Sonora, Sonora (Mexico); Contreras, Maria E. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, BC (Mexico); Allen, Lori [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Espaillat, Catherine, E-mail: hernandj@cida.ve [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)

    2014-10-10

    We present a spectroscopic survey of the stellar population of the σ Orionis cluster. We have obtained spectral types for 340 stars. Spectroscopic data for spectral typing come from several spectrographs with similar spectroscopic coverage and resolution. More than half of the stars in our sample are members confirmed by the presence of lithium in absorption, strong Hα in emission or weak gravity-sensitive features. In addition, we have obtained high-resolution (R ∼ 34,000) spectra in the Hα region for 169 stars in the region. Radial velocities were calculated from this data set. The radial velocity distribution for members of the cluster is in agreement with previous work. Analysis of the profile of the Hα line and infrared observations reveals two binary systems or fast rotators that mimic the Hα width expected in stars with accretion disks. On the other hand, there are stars with optically thick disks and narrow Hα profiles not expected in stars with accretion disks. This contribution constitutes the largest homogeneous spectroscopic data set of the σ Orionis cluster to date.

  10. BAYESIAN ANALYSIS TO IDENTIFY NEW STAR CANDIDATES IN NEARBY YOUNG STELLAR KINEMATIC GROUPS

    International Nuclear Information System (INIS)

    Malo, Lison; Doyon, René; Lafrenière, David; Artigau, Étienne; Gagné, Jonathan; Baron, Frédérique; Riedel, Adric

    2013-01-01

    We present a new method based on a Bayesian analysis to identify new members of nearby young kinematic groups. The analysis minimally takes into account the position, proper motion, magnitude, and color of a star, but other observables can be readily added (e.g., radial velocity, distance). We use this method to find new young low-mass stars in the β Pictoris and AB Doradus moving groups and in the TW Hydrae, Tucana-Horologium, Columba, Carina, and Argus associations. Starting from a sample of 758 mid-K to mid-M (K5V-M5V) stars showing youth indicators such as Hα and X-ray emission, our analysis yields 214 new highly probable low-mass members of the kinematic groups analyzed. One is in TW Hydrae, 37 in β Pictoris, 17 in Tucana-Horologium, 20 in Columba, 6 in Carina, 50 in Argus, 32 in AB Doradus, and the remaining 51 candidates are likely young but have an ambiguous membership to more than one association. The false alarm rate for new candidates is estimated to be 5% for β Pictoris and TW Hydrae, 10% for Tucana-Horologium, Columba, Carina, and Argus, and 14% for AB Doradus. Our analysis confirms the membership of 58 stars proposed in the literature. Firm membership confirmation of our new candidates will require measurement of their radial velocity (predicted by our analysis), parallax, and lithium 6708 Å equivalent width. We have initiated these follow-up observations for a number of candidates, and we have identified two stars (2MASSJ01112542+1526214, 2MASSJ05241914-1601153) as very strong candidate members of the β Pictoris moving group and one strong candidate member (2MASSJ05332558-5117131) of the Tucana-Horologium association; these three stars have radial velocity measurements confirming their membership and lithium detections consistent with young age.

  11. Exploring the Dynamics of Exoplanetary Systems in a Young Stellar Cluster

    Science.gov (United States)

    Thornton, Jonathan Daniel; Glaser, Joseph Paul; Wall, Joshua Edward

    2018-01-01

    I describe a dynamical simulation of planetary systems in a young star cluster. One rather arbitrary aspect of cluster simulations is the choice of initial conditions. These are typically chosen from some standard model, such as Plummer or King, or from a “fractal” distribution to try to model young clumpy systems. Here I adopt the approach of realizing an initial cluster model directly from a detailed magnetohydrodynamical model of cluster formation from a 1000-solar-mass interstellar gas cloud, with magnetic fields and radiative and wind feedback from massive stars included self-consistently. The N-body simulation of the stars and planets starts once star formation is largely over and feedback has cleared much of the gas from the region where the newborn stars reside. It continues until the cluster dissolves in the galactic field. Of particular interest is what would happen to the free-floating planets created in the gas cloud simulation. Are they captured by a star or are they ejected from the cluster? This method of building a dynamical cluster simulation directly from the results of a cluster formation model allows us to better understand the evolution of young star clusters and enriches our understanding of extrasolar planet development in them. These simulations were performed within the AMUSE simulation framework, and combine N-body, multiples and background potential code.

  12. Accretion-induced luminosity spreads in young clusters: evidence from stellar rotation

    Science.gov (United States)

    Littlefair, S. P.; Naylor, Tim; Mayne, N. J.; Saunders, Eric; Jeffries, R. D.

    2011-05-01

    We present an analysis of the rotation of young stars in the associations Cepheus OB3b, NGC 2264, 2362 and the Orion Nebula Cluster (ONC). We discover a correlation between rotation rate and position in a colour-magnitude diagram (CMD) such that stars which lie above an empirically determined median pre-main sequence rotate more rapidly than stars which lie below this sequence. The same correlation is seen, with a high degree of statistical significance, in each association studied here. If position within the CMD is interpreted as being due to genuine age spreads within a cluster, then the stars above the median pre-main sequence would be the youngest stars. This would in turn imply that the most rapidly rotating stars in an association are the youngest, and hence those with the largest moments of inertia and highest likelihood of ongoing accretion. Such a result does not fit naturally into the existing picture of angular momentum evolution in young stars, where the stars are braked effectively by their accretion discs until the disc disperses. Instead, we argue that, for a given association of young stars, position within the CMD is not primarily a function of age, but of accretion history. We show that this hypothesis could explain the correlation we observe between rotation rate and position within the CMD.

  13. Detached dust shell around Wolf-Rayet star WR60-6 in the young stellar cluster VVV CL036

    Energy Technology Data Exchange (ETDEWEB)

    Borissova, J.; Amigo, P.; Kurtev, R. [Departamento de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Casilla 5030 (Chile); Kumar, M. S. N. [Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Chené, A.-N. [Gemini Observatory, Northern Operations Center, 670 North A' ohoku Place Hilo, HI 96720 (United States); Minniti, D., E-mail: jura.borissova@uv.cl [Pontificia Universidad Católica de Chile, Facultad de Física, Departamento de Astronomía y Astrofísica, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile)

    2014-01-01

    The discovery of a detached dust shell around the Wolf-Rayet (WR) star WR60-6 in the young stellar cluster VVV CL036 is reported. This shell is uncovered through the Spitzer-MIPS 24 μm image, where it appears brightest, and it is invisible at shorter wavelengths. Using new APEX observations and other data available from the literature, we have estimated some of the shell parameters: the inner and outer radii of 0.15 and 0.90 pc, respectively; the overall systemic velocity of the molecular {sup 12}CO(3 → 2) emission of –45.7 ± 2.3 km s{sup –1}; an expansion velocity of the gas of 16.3 ± 1 km s{sup –1}; the dust temperature and opacity of 122 ± 12 K and 1.04, respectively; and an age of 2.8 × 10{sup 4} yr. The WR star displays some cyclic variability. The mass computed for the WR60-6 nebula indicates that the material was probably ejected during its previous stages of evolution. In addition, we have identified a bright spot very close to the shell, which can be associated with the Midcourse Space Experiment source G312.13+00.20.

  14. Extreme Radio Flares and Associated X-Ray Variability from Young Stellar Objects in the Orion Nebula Cluster

    Energy Technology Data Exchange (ETDEWEB)

    Forbrich, Jan [Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom); Reid, Mark J.; Wolk, Scott J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138 (United States); Menten, Karl M. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Rivilla, Victor M. [Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125, Firenze (Italy); Rau, Urvashi; Chandler, Claire J. [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States)

    2017-08-01

    Young stellar objects are known to exhibit strong radio variability on timescales of weeks to months, and a few reports have documented extreme radio flares with at least an order of magnitude change in flux density on timescales of hours to days. However, there have been few constraints on the occurrence rate of such radio flares or on the correlation with pre-main sequence X-ray flares, although such correlations are known for the Sun and nearby active stars. Here we report simultaneous deep VLA radio and Chandra X-ray observations of the Orion Nebula Cluster, targeting hundreds of sources to look for the occurrence rate of extreme radio variability and potential correlation with the most extreme X-ray variability. We identify 13 radio sources with extreme radio variability, with some showing an order of magnitude change in flux density in less than 30 minutes. All of these sources show X-ray emission and variability, but we find clear correlations with extreme radio flaring only on timescales <1 hr. Strong X-ray variability does not predict the extreme radio sources and vice versa. Radio flares thus provide us with a new perspective on high-energy processes in YSOs and the irradiation of their protoplanetary disks. Finally, our results highlight implications for interferometric imaging of sources violating the constant-sky assumption.

  15. BANYAN_Sigma: Bayesian classifier for members of young stellar associations

    Science.gov (United States)

    Gagné, Jonathan; Mamajek, Eric E.; Malo, Lison; Riedel, Adric; Rodriguez, David; Lafrenière, David; Faherty, Jacqueline K.; Roy-Loubier, Olivier; Pueyo, Laurent; Robin, Annie C.; Doyon, René

    2018-01-01

    BANYAN_Sigma calculates the membership probability that a given astrophysical object belongs to one of the currently known 27 young associations within 150 pc of the Sun, using Bayesian inference. This tool uses the sky position and proper motion measurements of an object, with optional radial velocity (RV) and distance (D) measurements, to derive a Bayesian membership probability. By default, the priors are adjusted such that a probability threshold of 90% will recover 50%, 68%, 82% or 90% of true association members depending on what observables are input (only sky position and proper motion, with RV, with D, with both RV and D, respectively). The algorithm is implemented in a Python package, in IDL, and is also implemented as an interactive web page.

  16. Variable Stellar and Circumstellar Properties of the Young Binary VV CrA

    Science.gov (United States)

    Avilez, Ian; Prato, Lisa A.; Allen, Thomas; Wright-Garba, Nuria Meilani Laure; Biddle, Lauren; Muzzio, Ryan

    2017-01-01

    VV CrA is a 2 arcsecond young binary system in the Corona Australis star forming region. The NE component, fainter in the near-infrared and invisible at optical wavelengths, dominates in the thermal infrared. The system has drawn attention because of its high degree of variability, significant cicrumstellar emission, and the mysterious nature of the infrared companion. Using high-resolution H- and K-band spectroscopy taken with the NIRSPEC spectrometer at the 10 m Keck II telescope, we have for the first time determined the spectral types of both components: the optically dominant primary is an M0 and the infrared compaion is an earlier K7 type star. Both components show significant and variable levels of H-band veiling, observed over 4 to 5 epochs during a period of 4 years; at times the veiling almost completely obscures the photospheric absorption lines. Hydrogen emission lines are observed at both H (Brackett 16) and K (Brackett gamma), consistent with the high rates of mass accretion described in previous studies. We determine values of Vsin(i), effective temperature, veiling, and radial velocity for both components and describe these results in the context of models of the nature and orientation of the system proposed by Smith et al. (2009) and Scicluna et al. (2016). The geometry of the VV CrA system may present a unique opportunity to study not only young star evolution in the binary environment but also to explore cirumstellar disk structure in high detail.Support for this research was provided by an REU supplement to NSF award AST-1313399.

  17. Adolescents and Young Adults Mates Selection

    Directory of Open Access Journals (Sweden)

    María Martina Casullo

    2016-02-01

    Full Text Available The study sought to identify the relation between gender and age on mate pre- ferences using an intentional sample drawn in Buenos Aires city and its suburban area. A questionnaire adapted from a previous study developed by D.Buss (1990 requested subjects to rank each of 19 characteristics on its desirability in a mate. Subjects for this study were 900 adolescents and young adults aging 13 to 30 years old. Means and standard deviations were calculated as well as Spearman ́s Rho coefficients. High correlations between gender, age, and ordering were found. Mutual attraction and love, kindness and understanding and trust are cho- sen as the most important criteria. Phisically attractive is important for younger males. Similar political and religious background as well as chastity are conside- red among the less important criteria. 

  18. CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS

    International Nuclear Information System (INIS)

    Craig, Jonathan; Krumholz, Mark R.

    2013-01-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  19. CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Craig, Jonathan; Krumholz, Mark R., E-mail: krumholz@ucolick.org [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2013-06-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  20. Close Stellar Encounters in Young, Substructured, Dissolving Star Clusters: Statistics and Effects on Planetary Systems

    Science.gov (United States)

    Craig, Jonathan; Krumholz, Mark R.

    2013-06-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  1. The age calibration of integrated ultraviolet colors and young stellar clusters in the Large Magellanic Cloud

    International Nuclear Information System (INIS)

    Barbero, J.; Brocato, E.; Cassatella, A.; Castellani, V.; Geyer, E.H.

    1990-01-01

    Integrated colors in selected far-UV bands are presented for a large sample of Large Magellanic Cloud (LMC) clusters. Theoretical calculations of these integrated colors are derived and discussed. The location in the two-color diagram C(18-28), C(15-31) is expected to be a sensitive but smooth function of cluster age for ages in the range 5 to 800 million yr. Theoretical results appear in very good agreement with the observed colors of LMC clusters. From this comparison, the gap in the observed colors is suggested to be caused by the lack of LMC clusters in the range of ages between 200 million to one billion yr. The two-color location of old globulars is discussed, also in connection with available data for the M31 clusters. 36 refs

  2. A GALEX-BASED SEARCH FOR THE SPARSE YOUNG STELLAR POPULATION IN THE TAURUS-AURIGAE STAR FORMING REGION

    International Nuclear Information System (INIS)

    Gómez de Castro, Ana I.; Lopez-Santiago, Javier; López-Martínez, Fatima; Sánchez, Néstor; Sestito, Paola; Gestoso, Javier Yañez; De Castro, Elisa; Cornide, Manuel

    2015-01-01

    In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region, using its ultraviolet excess as our baseline. The initial data set was defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands where TTSs show a prominent excess compared with main-sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as a fraction of the California Nebula and the Perseus complex; bright sources and dark clouds were avoided. The properties of TTSs in the ultraviolet (GALEX), optical (UCAC4), and infrared (2MASS) have been defined using the TTSs observed with the International Ultraviolet Explorer reference sample. The candidates were identified by means of a mixed ultraviolet-optical-infrared excess set of colors; we found that the FUV-NUV versus J–K color-color diagram is ideally suited for this purpose. From an initial sample of 163,313 bona fide NUV sources, a final list of 63 new candidates to TTSs in the region was produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, we show that the weak-lined TTSs are located in a well-defined stripe in the FUV-NUV versus J–K diagram. Moreover, in this work, we provide a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions

  3. A GALEX-BASED SEARCH FOR THE SPARSE YOUNG STELLAR POPULATION IN THE TAURUS-AURIGAE STAR FORMING REGION

    Energy Technology Data Exchange (ETDEWEB)

    Gómez de Castro, Ana I.; Lopez-Santiago, Javier; López-Martínez, Fatima; Sánchez, Néstor; Sestito, Paola; Gestoso, Javier Yañez [AEGORA Research Group, Universidad Complutense de Madrid, Plaza de Ciencias 3, E-28040 Madrid (Spain); De Castro, Elisa; Cornide, Manuel [Fac. de CC. Físicas, Universidad Complutense de Madrid, Plaza de Ciencias 1, E-28040 Madrid (Spain)

    2015-02-01

    In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region, using its ultraviolet excess as our baseline. The initial data set was defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands where TTSs show a prominent excess compared with main-sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as a fraction of the California Nebula and the Perseus complex; bright sources and dark clouds were avoided. The properties of TTSs in the ultraviolet (GALEX), optical (UCAC4), and infrared (2MASS) have been defined using the TTSs observed with the International Ultraviolet Explorer reference sample. The candidates were identified by means of a mixed ultraviolet-optical-infrared excess set of colors; we found that the FUV-NUV versus J–K color-color diagram is ideally suited for this purpose. From an initial sample of 163,313 bona fide NUV sources, a final list of 63 new candidates to TTSs in the region was produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, we show that the weak-lined TTSs are located in a well-defined stripe in the FUV-NUV versus J–K diagram. Moreover, in this work, we provide a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions.

  4. THE AGE OF THE YOUNG BULGE-LIKE POPULATION IN THE STELLAR SYSTEM TERZAN 5: LINKING THE GALACTIC BULGE TO THE HIGH- Z UNIVERSE

    Energy Technology Data Exchange (ETDEWEB)

    Ferraro, F. R.; Dalessandro, E.; Lanzoni, B.; Mucciarelli, A. [Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I–40127 Bologna (Italy); Massari, D. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani, 1, I-40127 Bologna (Italy); Origlia, L. [Kapteyn Astronomical Institute, University of Gröningen, Kapteyn Astron Institute, NL-9747 AD Gröningen (Netherlands); Rich, R. M. [Department of Physics and Astronomy, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States)

    2016-09-10

    The Galactic bulge is dominated by an old, metal-rich stellar population. The possible presence and the amount of a young (a few gigayears old) minor component is one of the major issues debated in the literature. Recently, the bulge stellar system Terzan 5 was found to harbor three sub-populations with iron content varying by more than one order of magnitude (from 0.2 up to two times the solar value), with chemical abundance patterns strikingly similar to those observed in bulge field stars. Here we report on the detection of two distinct main-sequence turnoff points in Terzan 5, providing the age of the two main stellar populations: 12 Gyr for the (dominant) sub-solar component and 4.5 Gyr for the component at super-solar metallicity. This discovery classifies Terzan 5 as a site in the Galactic bulge where multiple bursts of star formation occurred, thus suggesting a quite massive progenitor possibly resembling the giant clumps observed in star-forming galaxies at high redshifts. This connection opens a new route of investigation into the formation process and evolution of spheroids and their stellar content.

  5. The evolution of accretion in young stellar objects: Strong accretors at 3-10 Myr

    Energy Technology Data Exchange (ETDEWEB)

    Ingleby, Laura; Calvet, Nuria; Hartmann, Lee; Miller, Jon; McClure, Melissa [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Hernández, Jesus; Briceno, Cesar [Centro de Investigaciones de Astronomía (CIDA), Mérida, 5101-A (Venezuela, Bolivarian Republic of); Espaillat, Catherine, E-mail: lingleby@umich.edu, E-mail: ncalvet@umich.edu, E-mail: cce@bu.edu [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)

    2014-07-20

    While the rate of accretion onto T Tauri stars is predicted to decline with age, objects with strong accretion have been detected at ages of up to 10 Myr. We analyze a sample of these old accretors, identified by having a significant U band excess and infrared emission from a circumstellar disk. Objects were selected from the ∼3 Myr σ Ori, 4-6 Myr Orion OB1b, and 7-10 Myr Orion OB1a star forming associations. We use high-resolution spectra from the Magellan Inamori Kyocera Echelle to estimate the veiling of absorption lines and calculate extinction for our T Tauri sample. We also use observations obtained with the Magellan Echellette and, in a few cases, the SWIFT Ultraviolet and Optical Telescope to estimate the excess produced in the accretion shock, which is then fit with accretion shock models to estimate the accretion rate. We find that even objects as old as 10 Myr may have high accretion rates, up to ∼10{sup –8} M{sub ☉} yr{sup –1}. These objects cannot be explained by viscous evolution models, which would deplete the disk in shorter timescales unless the initial disk mass is very high, a situation that is unstable. We show that the infrared spectral energy distribution of one object, CVSO 206, does not reveal evidence of significant dust evolution, which would be expected during the 10 Myr lifetime. We compare this object to predictions from photoevaporation and planet formation models and suggest that neither of these processes have had a strong impact on the disk of CVSO 206.

  6. A UKIDSS-based search for low-mass stars and small stellar clumps in off-cloud parts of young star-forming regions* **

    Directory of Open Access Journals (Sweden)

    Barrado y Navascués D.

    2011-07-01

    Full Text Available The form and universality of the mass function of young and nearby star-forming regions is still under debate. Its relation to the stellar density, its mass peak and the dependency on most recent models shows significant differencies for the various regions and remains unclear up to date. We aim to get a more complete census of two of such regions. We investigate yet unexplored areas of Orion and Taurus-Auriga, observed by the UKIDSS survey. In the latter, we search for low-mass stars via photometric and proper motion criteria and signs for variability. In Orion, we search for small stellar clumps via nearest-neighbor methods. Highlights in Taurus would be the finding of the missing low-mass stars and the detection of a young cluster T dwarf. In Orion, we discovered small stellar associations of its OB1b and OB1c populations. Combined with what is known in literature, we will provide by this investigations a general picture of the results of the star-forming processes in large areas of Taurus and Orion and probe the most recent models.

  7. Flies selected for longevity retain a young gene expression profile

    DEFF Research Database (Denmark)

    Sarup, Pernille Merete; Sørensen, Peter; Loeschcke, Volker

    2011-01-01

      We investigated correlated responses in the transcriptomes of longevity-selected lines of Drosophila melanogaster to identify pathways that affect life span in metazoan systems. We evaluated the gene expression profile in young, middle-aged, and old male flies, finding that 530 genes were...

  8. Using photometrically selected metal-poor stars to study dwarf galaxies and the Galactic stellar halo

    Science.gov (United States)

    Youakim, Kris; Starkenburg, Else; Martin, Nicolas; Pristine Team

    2018-06-01

    The Pristine survey is a narrow-band photometric survey designed to efficiently search for extremely metal-poor (EMP) stars. In the first three years of the survey, it has demonstrated great efficiency at finding EMP stars, and also great promise for increasing the current, small sample of the most metal-poor stars. The present sky coverage is ~2500 square degrees in the Northern Galactic Halo, including several individual fields targeting dwarf galaxies. By efficiently identifying member stars in the outskirts of known faint dwarf galaxies, the dynamical histories and chemical abundance patterns of these systems can be understood in greater detail. Additionally, with reliable photometric metallicities over a large sky coverage it is possible to perform a large scale clustering analysis in the Milky Way halo, and investigate the characteristic scale of substructure at different metallicities. This can reveal important details about the process of building up the halo through dwarf galaxy accretion, and offer insight into the connection between dwarf galaxies and the Milky Way halo. In this talk I will outline our results on the search for the most pristine stars, with a focus on how we are using this information to advance our understanding of dwarf galaxies and their contribution to the formation of the Galactic stellar halo.

  9. OPTICAL/NEAR-INFRARED SELECTION OF RED QUASI-STELLAR OBJECTS: EVIDENCE FOR STEEP EXTINCTION CURVES TOWARD GALACTIC CENTERS?

    Energy Technology Data Exchange (ETDEWEB)

    Fynbo, J. P. U.; Krogager, J.-K.; Vestergaard, M.; Geier, S. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen O (Denmark); Venemans, B. [Max-Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Noterdaeme, P. [CNRS-UPMC, UMR7095, Institut d' Astrophysique de Paris, 98bis Bd. Arago, F-75014 Paris (France); Moller, P. [European Southern Observatory, Karl-Schwarzschildstrasse 2, D-85748 Garching bei Muenchen (Germany); Ledoux, C. [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19 (Chile)

    2013-01-15

    We present the results of a search for red QSOs using a selection based on optical imaging from the Sloan Digital Sky Survey (SDSS) and near-infrared imaging from UKIDSS. Our main goal with the selection is to search for QSOs reddened by foreground dusty absorber galaxies. For a sample of 58 candidates (including 20 objects fulfilling our selection criteria that already have spectra in the SDSS), 46 (79%) are confirmed to be QSOs. The QSOs are predominantly dust-reddened except for a handful at redshifts z {approx}> 3.5. However, the dust is most likely located in the QSO host galaxies (and for two, the reddening is primarily caused by Galactic dust) rather than in the intervening absorbers. More than half of the QSOs show evidence of associated absorption (BAL absorption). Four (7%) of the candidates turned out to be late-type stars, and another four (7%) are compact galaxies. We could not identify the remaining four objects. In terms of their optical spectra, these QSOs are similar to the QSOs selected in the FIRST-2MASS Red Quasar Survey except they are on average fainter, more distant, and only two are detected in the FIRST survey. As per the usual procedure, we estimate the amount of extinction using the SDSS QSO template reddened by Small-Magellanic-Cloud-(SMC) like dust. It is possible to get a good match to the observed (rest-frame ultraviolet) spectra, but it is not possible to match the observed near-IR photometry from UKIDSS for nearly all the reddened QSOs. The most likely reasons are that the SDSS QSO template is too red at optical wavelengths due to contaminating host galaxy light and because the assumed SMC extinction curve is too shallow. Three of the compact galaxies display old stellar populations with ages of several Gyr and masses of about 10{sup 10} M{sub Sun} (based on spectral energy distribution modeling). The inferred stellar densities in these galaxies exceed 10{sup 10} M{sub Sun} kpc{sup -2}, which is among the highest measured for early

  10. Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

    Energy Technology Data Exchange (ETDEWEB)

    Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B. [Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn (Germany); De Mink, S. E. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101 (United States); De Koter, A.; Sana, H. [Astronomical Institute " Anton Pannekoek" , Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands); Gvaramadze, V. V. [Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetskij Pr. 13, Moscow 119992 (Russian Federation); Liermann, A., E-mail: fschneid@astro.uni-bonn.de [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)

    2014-01-10

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M {sub ☉} limit and observations of four stars with initial masses of 165-320 M {sub ☉} in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M {sub ☉} star. Using the stellar population of R136, we revise the upper mass limit to values in the range

  11. Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

    International Nuclear Information System (INIS)

    Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B.; De Mink, S. E.; Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" data-affiliation=" (Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" >De Koter, A.; Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" data-affiliation=" (Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" >Sana, H.; Gvaramadze, V. V.; Liermann, A.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ☉ limit and observations of four stars with initial masses of 165-320 M ☉ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M ☉ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M ☉ .

  12. Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

    Science.gov (United States)

    Schneider, F. R. N.; Izzard, R. G.; de Mink, S. E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V. V.; Hußmann, B.; Liermann, A.; Sana, H.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ⊙ limit and observations of four stars with initial masses of 165-320 M ⊙ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M ⊙ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M ⊙.

  13. VLBA DETERMINATION OF THE DISTANCE TO NEARBY STAR-FORMING REGIONS. VI. THE DISTANCE TO THE YOUNG STELLAR OBJECT HW 9 IN CEPHEUS A

    International Nuclear Information System (INIS)

    Dzib, Sergio; Loinard, Laurent; RodrIguez, Luis F.; Mioduszewski, Amy J.; Torres, Rosa M.

    2011-01-01

    Using the Very Long Baseline Array (VLBA), we have observed the radio continuum emission from the young stellar object HW 9 in the Cepheus A star-forming region at 10 epochs between 2007 February and 2009 November. Due to its strong radio variability, the source was detected at only four of the ten epochs. From these observations, the trigonometric parallax of HW 9 was determined to be π = 1.43 ± 0.07 mas, in excellent agreement with a recent independent determination by Moscadelli et al. of the trigonometric parallax of a methanol maser associated with the nearby young stellar source HW 2 (π = 1.43 ± 0.08 mas). This concordance in results, obtained in one case from continuum and in the other from line observations, confirms the reliability of VLBA trigonometric parallax measurements. By combining the two results, we constrain the distance to Cepheus A to be 700 +31 - 28 pc, an uncertainty of 3.5%.

  14. A NEAR-INFRARED SPECTROSCOPIC SURVEY OF K-SELECTED GALAXIES AT z∼ 2.3: COMPARISON OF STELLAR POPULATION SYNTHESIS CODES AND CONSTRAINTS FROM THE REST-FRAME NIR

    International Nuclear Information System (INIS)

    Muzzin, Adam; Marchesini, Danilo; Van Dokkum, Pieter G.; Labbe, Ivo; Kriek, Mariska; Franx, Marijn

    2009-01-01

    We present spectral energy distribution (SED) modeling of a sample of 34 K-selected galaxies at z∼ 2.3. These galaxies have near-infrared (NIR) spectroscopy that samples the rest-frame Balmer/4000 A break as well as deep photometry in 13 broadband filters. New to our analysis is Infrared Array Camera (IRAC) data that extend the SEDs into the rest-frame NIR. Comparing parameters determined from SED fits with and without the IRAC data we find that the IRAC photometry significantly improves the confidence intervals of τ, A v , M star , and SFR for individual galaxies, but does not systematically alter the mean parameters of the sample. We use the IRAC data to assess how well current stellar population synthesis codes describe the rest-frame NIR SEDs of young galaxies where discrepancies between treatments of the thermally pulsating asymptotic giant branch phase of stellar evolution are most pronounced. The models of Bruzual and Charlot, Maraston, and Charlot and Bruzual all successfully reproduce the SEDs of our galaxies with ≤5% differences in the quality of fit; however, the best-fit masses from each code differ systematically by as much as a factor of 1.5, and other parameters vary more, up to factors of 2-3. A comparison of best-fit stellar population parameters from different stellar population synthesis (SPS) codes, dust laws, and metallicities shows that the choice of SPS code is the largest systematic uncertainty in most parameters, and that systematic uncertainties are typically larger than the formal random uncertainties. The SED fitting confirms our previous result that galaxies with strongly suppressed SF account for ∼50% of the K-bright population at z∼ 2.3; however, the uncertainty in this fraction is large due to systematic differences in the specific star formation rates derived from the three SPS models.

  15. Portion distortion: typical portion sizes selected by young adults.

    Science.gov (United States)

    Schwartz, Jaime; Byrd-Bredbenner, Carol

    2006-09-01

    The incidence of obesity has increased in parallel with increasing portion sizes of individually packaged and ready-to-eat prepared foods as well as foods served at restaurants. Portion distortion (perceiving large portion sizes as appropriate amounts to eat at a single eating occasion) may contribute to increasing energy intakes and expanding waistlines. The purpose of this study was to determine typical portion sizes that young adults select, how typical portion sizes compare with reference portion sizes (based in this study on the Nutrition Labeling and Education Act's quantities of food customarily eaten per eating occasion), and whether the size of typical portions has changed over time. Young adults (n=177, 75% female, age range 16 to 26 years) at a major northeastern university. Participants served themselves typical portion sizes of eight foods at breakfast (n=63) or six foods at lunch or dinner (n=62, n=52, respectively). Typical portion-size selections were unobtrusively weighed. A unit score was calculated by awarding 1 point for each food with a typical portion size that was within 25% larger or smaller than the reference portion; larger or smaller portions were given 0 points. Thus, each participant's unit score could range from 0 to 8 at breakfast or 0 to 6 at lunch and dinner. Analysis of variance or t tests were used to determine whether typical and reference portion sizes differed, and whether typical portion sizes changed over time. Mean unit scores (+/-standard deviation) were 3.63+/-1.27 and 1.89+/-1.14, for breakfast and lunch/dinner, respectively, indicating little agreement between typical and reference portion sizes. Typical portions sizes in this study tended to be significantly different from those selected by young adults in a similar study conducted 2 decades ago. Portion distortion seems to affect the portion sizes selected by young adults for some foods. This phenomenon has the potential to hinder weight loss, weight maintenance, and

  16. The Stellar Imager (SI)"Vision Mission"

    Science.gov (United States)

    Carpenter, Ken; Danchi, W.; Leitner, J.; Liu, A.; Lyon, R.; Mazzuca, L.; Moe, R.; Chenette, D.; Karovska, M.; Allen, R.

    2004-01-01

    The Stellar Imager (SI) is a "Vision" mission in the Sun-Earth Connection (SEC) Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar magnetic activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, at ultraviolet wavelengths, on the order of 100 micro-arcsec and thus baselines on the order of 0.5 km. These requirements call for a large, multi-spacecraft (less than 20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. SI's resolution will make it an invaluable resource for many other areas of astrophysics, including studies of AGN s, supernovae, cataclysmic variables, young stellar objects, QSO's, and stellar black holes. ongoing mission concept and technology development studies for SI. These studies are designed to refine the mission requirements for the science goals, define a Design Reference Mission, perform trade studies of selected major technical and architectural issues, improve the existing technology roadmap, and explore the details of deployment and operations, as well as the possible roles of astronauts and/or robots in construction and servicing of the facility.

  17. SUZAKU OBSERVATION OF STRONG FLUORESCENT IRON LINE EMISSION FROM THE YOUNG STELLAR OBJECT V1647 ORI DURING ITS NEW X-RAY OUTBURST

    International Nuclear Information System (INIS)

    Hamaguchi, Kenji; Grosso, Nicolas; Kastner, Joel H.; Richmond, Michael; Weintraub, David A.

    2010-01-01

    The Suzaku X-ray satellite observed the young stellar object (YSO) V1647 Ori on 2008 October 8 during the new mass accretion outburst reported in 2008 August. During the 87 ks observation with a net exposure of 40 ks, V1647 Ori showed a high level of X-ray emission with a gradual decrease in flux by a factor of 5 and then displayed an abrupt flux increase by an order of magnitude. Such enhanced X-ray variability was also seen in XMM-Newton observations in 2004 and 2005 during the 2003-2005 outburst, but has rarely been observed for other YSOs. The spectrum clearly displays emission from Helium-like iron, which is a signature of hot plasma (kT ∼ 5 keV). It also shows a fluorescent iron Kα line with a remarkably large equivalent width (EW) of ∼600 eV. Such a large EW suggests that a part of the incident X-ray emission that irradiates the circumstellar material and/or the stellar surface is hidden from our line of sight. XMM-Newton spectra during the 2003-2005 outburst did not show a strong fluorescent iron Kα line, so that the structure of the circumstellar gas very close to the stellar core that absorbs and re-emits X-ray emission from the central object may have changed in between 2005 and 2008. This phenomenon may be related to changes in the infrared morphology of McNeil's nebula between 2004 and 2008.

  18. Assessment of somatotype in young voleyball players: Validity as criteria to select young sports talents

    Directory of Open Access Journals (Sweden)

    Moisés de Hoyo Lora

    2008-07-01

    Full Text Available http://dx.doi.org/10.5007/1980-0037.2008v10n3p255 The anthropometric characteristics of athletes can determine their sporting performance. For this reason, we’ve defined the somatotype of young volleyball players in order to be able to control their sports training and to ensure their appropriate athletic development. In the present investigation 154 male and female volleyball players (aged from 12 to 14 years were analyzed. Data were collected according to the ISAK protocol. The results show an endomesomorphic profile for male and female volleyball players agreeing with the predominant profile at these ages. However, after comparing these data with results obtained in other studies, we observed a certain homogeneity in the male somatotype, invalidating the current trend of using this parameter as criteria to select young sports talent. However, somatotype could be a factor to take into account with female athletes, since their profile is much more heterogeneous.

  19. The slow ionized wind and rotating disklike system that are associated with the high-mass young stellar object G345.4938+01.4677

    Energy Technology Data Exchange (ETDEWEB)

    Guzmán, Andrés E.; Garay, Guido; Bronfman, Leonardo; Mardones, Diego [Departamento de Astronomía, Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago (Chile); Rodríguez, Luis F. [Centro de Radioastronomía y Astrofísica (UNAM), Morelia 58089 (Mexico); Moran, James [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA (United States); Brooks, Kate J. [CSIRO Astronomy and Space Science, P.O. Box 76, Epping, 1710 NSW (Australia); Nyman, Lars-Åke [Joint ALMA Observatory (JAO), Alonso de Córdova 3107, Vitacura, Santiago (Chile); Sanhueza, Patricio [Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States)

    2014-12-01

    We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40α, H42α, and H50β emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. This is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562–3959. The HRLs exhibit Voigt profiles, which is a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need for a high-velocity component. The Lorentzian line wings imply electron densities of 5 × 10{sup 7} cm{sup –3} on average. In addition, we detect SO and SO{sub 2} emission arising from a compact (∼3000 AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient that is perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind.

  20. PROPER MOTIONS OF YOUNG STELLAR OUTFLOWS IN THE MID-INFRARED WITH SPITZER (IRAC). I. THE NGC 1333 REGION

    International Nuclear Information System (INIS)

    Raga, A. C.; Noriega-Crespo, A.; Carey, S. J.; Arce, H. G.

    2013-01-01

    We use two 4.5 μm Spitzer (IRAC) maps of the NGC 1333 region taken over a ∼7 yr interval to determine proper motions of its associated outflows. This is a first successful attempt at obtaining proper motions of stellars' outflow from Spitzer observations. For the outflow formed by the Herbig-Haro objects HH7, 8, and 10, we find proper motions of ∼9-13 km s –1 , which are consistent with previously determined optical proper motions of these objects. We determine proper motions for a total of eight outflows, ranging from ∼10 to 100 km s –1 . The derived proper motions show that out of these eight outflows, three have tangential velocities ≤20 km s –1 . This result shows that a large fraction of the observed outflows have low intrinsic velocities and that the low proper motions are not merely a projection effect.

  1. Explaining the luminosity spread in young clusters: proto and pre-main sequence stellar evolution in a molecular cloud environment

    Science.gov (United States)

    Jensen, Sigurd S.; Haugbølle, Troels

    2018-02-01

    Hertzsprung-Russell diagrams of star-forming regions show a large luminosity spread. This is incompatible with well-defined isochrones based on classic non-accreting protostellar evolution models. Protostars do not evolve in isolation of their environment, but grow through accretion of gas. In addition, while an age can be defined for a star-forming region, the ages of individual stars in the region will vary. We show how the combined effect of a protostellar age spread, a consequence of sustained star formation in the molecular cloud, and time-varying protostellar accretion for individual protostars can explain the observed luminosity spread. We use a global magnetohydrodynamic simulation including a sub-scale sink particle model of a star-forming region to follow the accretion process of each star. The accretion profiles are used to compute stellar evolution models for each star, incorporating a model of how the accretion energy is distributed to the disc, radiated away at the accretion shock, or incorporated into the outer layers of the protostar. Using a modelled cluster age of 5 Myr, we naturally reproduce the luminosity spread and find good agreement with observations of the Collinder 69 cluster, and the Orion Nebular Cluster. It is shown how stars in binary and multiple systems can be externally forced creating recurrent episodic accretion events. We find that in a realistic global molecular cloud model massive stars build up mass over relatively long time-scales. This leads to an important conceptual change compared to the classic picture of non-accreting stellar evolution segmented into low-mass Hayashi tracks and high-mass Henyey tracks.

  2. FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME

    Energy Technology Data Exchange (ETDEWEB)

    Filippazzo, Joseph C.; Rice, Emily L. [Department of Engineering Science and Physics, College of Staten Island, City University of New York, 2800 Victory Blvd, Staten Island, NY 10314 (United States); Faherty, Jacqueline; Cruz, Kelle L. [Department of Astrophysics, American Museum of Natural History, New York, NY 10024 (United States); Van Gordon, Mollie M. [Department of Geography, University of California, Berkeley, CA 94720 (United States); Looper, Dagny L. [Tisch School of the Arts, New York University, New York, NY 10003 (United States)

    2015-09-10

    We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded spectral energy distributions for 145 field age (>500 Myr) and 53 young (lower age estimate <500 Myr) ultracool dwarfs (M6-T9). This range of spectral types includes very low mass stars, brown dwarfs, and planetary mass objects, providing fundamental parameters across both the hydrogen and deuterium burning minimum masses for the largest sample assembled to date. A subsample of 29 objects have well constrained ages as probable members of a nearby young moving group. We use 182 parallaxes and 16 kinematic distances to determine precise bolometric luminosities (L{sub bol}) and radius estimates from evolutionary models give semi-empirical effective temperatures (T{sub eff}) for the full range of young and field age late-M, L, and T dwarfs. We construct age-sensitive relationships of luminosity, temperature, and absolute magnitude as functions of spectral type and absolute magnitude to disentangle the effects of degenerate physical parameters such as T{sub eff}, surface gravity, and clouds on spectral morphology. We report bolometric corrections in J for both field age and young objects and find differences of up to a magnitude for late-L dwarfs. Our correction in Ks shows a larger dispersion but not necessarily a different relationship for young and field age sequences. We also characterize the NIR–MIR reddening of low gravity L dwarfs and identify a systematically cooler T{sub eff} of up to 300 K from field age objects of the same spectral type and 400 K cooler from field age objects of the same M{sub H} magnitude.

  3. Surveying the agents of galaxy evolution in the tidally stripped, low metallicity small Magellanic Cloud (SAGE-SMC). III. Young stellar objects

    International Nuclear Information System (INIS)

    Sewiło, M.; Carlson, L. R.; Seale, J. P.; Meixner, M.; Gordon, K.; Shiao, B.

    2013-01-01

    The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK s ) and optical (UBVI) data, we identified a population of ∼1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.

  4. Surveying the agents of galaxy evolution in the tidally stripped, low metallicity small Magellanic Cloud (SAGE-SMC). III. Young stellar objects

    Energy Technology Data Exchange (ETDEWEB)

    Sewiło, M. [The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Carlson, L. R. [Sterrewacht Leiden, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Seale, J. P.; Meixner, M.; Gordon, K.; Shiao, B., E-mail: mmsewilo@pha.jhu.edu, E-mail: carlson@strw.leidenuniv.nl, E-mail: seale@stsci.edu, E-mail: meixner@stsci.edu, E-mail: kgordon@stsci.edu, E-mail: shiao@stsci.edu [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); and others

    2013-11-20

    The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK {sub s}) and optical (UBVI) data, we identified a population of ∼1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.

  5. Solar and stellar oscillations

    International Nuclear Information System (INIS)

    Fossat, E.

    1981-01-01

    We try to explain in simple words what a stellar oscillation is, what kind of restoring forces and excitation mechanisms can be responsible for its occurence, what kind of questions the theoretician asks to the observer and what kind of tools the latter is using to look for the answers. A selected review of the most striking results obtained in the last few years in solar seismology and the present status of their consequences on solar models is presented. A brief discussion on the expected extension towards stellar seismology will end the paper. A selected bibliography on theory as well as observations and recent papers is also included. (orig.)

  6. THE VVV SURVEY REVEALS CLASSICAL CEPHEIDS TRACING A YOUNG AND THIN STELLAR DISK ACROSS THE GALAXY’S BULGE

    Energy Technology Data Exchange (ETDEWEB)

    Dékány, I. [Instituto Milenio de Astrofísica, Santiago (Chile); Minniti, D. [Departamento de Física, Facultad de Ciencias Exactas, Universidad Andres Bello, República 220, Santiago (Chile); Majaess, D. [Saint Mary’s University, Halifax, Nova Scotia (Canada); Zoccali, M.; Hajdu, G.; Catelan, M. [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago (Chile); Alonso-García, J. [Unidad de Astronomía, Fac. Cs. Básicas, Universidad de Antofagasta, Avda. U. de Antofagasta 02800, Antofagasta (Chile); Gieren, W. [Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Borissova, J., E-mail: idekany@astro.puc.cl [Instituto de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaso (Chile)

    2015-10-20

    Solid insight into the physics of the inner Milky Way is key to understanding our Galaxy’s evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the last 100 million years.

  7. On origin of stellar clusters

    International Nuclear Information System (INIS)

    Tovmasyan, G.M.

    1977-01-01

    The ratios of the gas component of the mass of young stellar clusters to their stellar mass are considered. They change by more than four orders from one cluster to another. The results are in direct contradiction with the hypothesis of formation of cluster stars from a preliminarily existing gas cloud by its condensation, and they favour the Ambartsumian hypothesis of the joint origin of stars and gas clouds from superdense protostellar matter

  8. THE SPITZER SPACE TELESCOPE SURVEY OF THE ORION A AND B MOLECULAR CLOUDS. II. THE SPATIAL DISTRIBUTION AND DEMOGRAPHICS OF DUSTY YOUNG STELLAR OBJECTS

    International Nuclear Information System (INIS)

    Megeath, S. T.; Kryukova, E.; Gutermuth, R.; Muzerolle, J.; Hora, J. L.; Myers, P. C.; Fazio, G. G.; Allen, L. E.; Flaherty, K.; Hartmann, L.; Pipher, J. L.; Stauffer, J.; Young, E. T.

    2016-01-01

    We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc −2 to over 10,000 pc −2 , with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities ≥10 pc −2 , we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ∼2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions

  9. A FIRST LOOK AT THE AURIGA-CALIFORNIA GIANT MOLECULAR CLOUD WITH HERSCHEL AND THE CSO: CENSUS OF THE YOUNG STELLAR OBJECTS AND THE DENSE GAS

    Energy Technology Data Exchange (ETDEWEB)

    Harvey, Paul M. [Astronomy Department, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259 (United States); Fallscheer, Cassandra [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2 (Canada); Ginsburg, Adam [Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309-0389 (United States); Terebey, Susan [Department of Physics and Astronomy PS315, 5151 State University Drive, California State University at Los Angeles, Los Angeles, CA 90032 (United States); Andre, Philippe; Koenyves, Vera [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service d' Astrophysique, CEA Saclay, F-91191 Gif-sur-Yvette (France); Bourke, Tyler L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Di Francesco, James; Matthews, Brenda C. [Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Peterson, Dawn E., E-mail: pmh@astro.as.utexas.edu, E-mail: Cassandra.Fallscheer@nrc-cnrc.gc.ca, E-mail: adam.ginsburg@colorado.edu, E-mail: sterebe@calstatela.edu, E-mail: pandre@cea.fr, E-mail: vera.konyves@cea.fr, E-mail: tbourke@cfa.harvard.edu, E-mail: James.DiFrancesco@nrc-cnrc.gc.ca, E-mail: Brenda.Matthews@nrc-cnrc.gc.ca, E-mail: dpeterson@spacescience.org [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80303 (United States)

    2013-02-20

    We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 {mu}m sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few Multiplication-Sign 10{sup 22} cm{sup -2} (N {sub H2}) and is distributed in a clear filamentary structure along which nearly all of the pre-main-sequence objects are found. We compare the young stellar object surface density to the gas column density and find a strong nonlinear correlation between them. The dust temperature in the densest parts of the filaments drops to {approx}10 K from values {approx}14-15 K in the low-density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud, which we compare with similar data on other star-forming clouds.

  10. A FIRST LOOK AT THE AURIGA-CALIFORNIA GIANT MOLECULAR CLOUD WITH HERSCHEL AND THE CSO: CENSUS OF THE YOUNG STELLAR OBJECTS AND THE DENSE GAS

    International Nuclear Information System (INIS)

    Harvey, Paul M.; Fallscheer, Cassandra; Ginsburg, Adam; Terebey, Susan; André, Philippe; Könyves, Vera; Bourke, Tyler L.; Di Francesco, James; Matthews, Brenda C.; Peterson, Dawn E.

    2013-01-01

    We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 μm sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few × 10 22 cm –2 (N H2 ) and is distributed in a clear filamentary structure along which nearly all of the pre-main-sequence objects are found. We compare the young stellar object surface density to the gas column density and find a strong nonlinear correlation between them. The dust temperature in the densest parts of the filaments drops to ∼10 K from values ∼14-15 K in the low-density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud, which we compare with similar data on other star-forming clouds.

  11. Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects

    Science.gov (United States)

    Ilee, J. D.; Oudmaijer, R. D.; Wheelwright, H. E.; Pomohaci, R.

    2018-04-01

    To date, there is no explanation as to why disc-tracing CO first overtone (or `bandhead') emission is not a ubiquitous feature in low- to medium-resolution spectra of massive young stellar objects, but instead is only detected toward approximately 25 per cent of their spectra. In this paper, we investigate the hypothesis that only certain mass accretion rates result in detectable bandhead emission in the near infrared spectra of MYSOs. Using an analytic disc model combined with an LTE model of the CO emission, we find that high accretion rates (≳ 10-4 M⊙yr-1) result in large dust sublimation radii, a larger contribution to the K-band continuum from hot dust at the dust sublimation radius, and therefore correspondingly lower CO emission with respect to the continuum. On the other hand, low accretion rates (≲ 10-6 M⊙yr-1) result in smaller dust sublimation radii, a correspondingly smaller emitting area of CO, and thus also lower CO emission with respect to the continuum. In general, moderate accretion rates produce the most prominent, and therefore detectable, CO first overtone emission. We compare our findings to a recent near-infrared spectroscopic survey of MYSOs, finding results consistent with our hypothesis. We conclude that the detection rate of CO bandhead emission in the spectra of MYSOs could be the result of MYSOs exhibiting a range of mass accretion rates, perhaps due to the variable accretion suggested by recent multi-epoch observations of these objects.

  12. SPECTRAL TYPING OF LATE-TYPE STELLAR COMPANIONS TO YOUNG STARS FROM LOW-DISPERSION NEAR-INFRARED INTEGRAL FIELD UNIT DATA

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, Lewis C.; Beichman, Charles A.; Burruss, Rick; Ligon, E. Robert; Lockhart, Thomas G.; Roberts, Jennifer E.; Shao, Michael [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Rice, Emily L.; Brenner, Douglas; Oppenheimer, Ben R. [American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Crepp, Justin R.; Dekany, Richard G.; Hillenbrand, Lynne A.; Hinkley, Sasha [California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); King, David; Parry, Ian R. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 OHA (United Kingdom); Metchev, Stanimir [Department of Physics and Astronomy, State University of New York, Stony Brook, NY 11794-3800 (United States); Pueyo, Laurent; Sivaramakrishnan, Anand; Soummer, Remi, E-mail: lewis.c.roberts@jpl.nasa.gov [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

    2012-07-15

    We used the Project 1640 near-infrared coronagraph and integral field spectrograph to observe 19 young solar-type stars. Five of these stars are known binary stars and we detected the late-type secondaries and were able to measure their JH spectra with a resolution of R {approx} 30. The reduced, extracted, and calibrated spectra were compared to template spectra from the IRTF spectral library. With this comparison, we test the accuracy and consistency of spectral-type determination with the low-resolution near-infrared spectra from P1640. Additionally, we determine effective temperature and surface gravity of the companions by fitting synthetic spectra calculated with the PHOENIX model atmosphere code. We also present several new epochs of astrometry of each of the systems. Together, these data increase our knowledge and understanding of the stellar make up of these systems. In addition to the astronomical results, the analysis presented helps validate the Project 1640 data reduction and spectral extraction processes and the utility of low-resolution, near-infrared spectra for characterizing late-type companions in multiple systems.

  13. Stellar formation

    CERN Document Server

    Reddish, V C

    1978-01-01

    Stellar Formation brings together knowledge about the formation of stars. In seeking to determine the conditions necessary for star formation, this book examines questions such as how, where, and why stars form, and at what rate and with what properties. This text also considers whether the formation of a star is an accident or an integral part of the physical properties of matter. This book consists of 13 chapters divided into two sections and begins with an overview of theories that explain star formation as well as the state of knowledge of star formation in comparison to stellar structure

  14. A CONSTRAINT ON BROWN DWARF FORMATION VIA EJECTION: RADIAL VARIATION OF THE STELLAR AND SUBSTELLAR MASS FUNCTION OF THE YOUNG OPEN CLUSTER IC 2391

    International Nuclear Information System (INIS)

    Boudreault, S.; Bailer-Jones, C. A. L.

    2009-01-01

    We present the stellar and substellar mass function (MF) of the open cluster IC 2391, plus its radial dependence, and use this to put constraints on the formation mechanism of brown dwarfs (BDs). Our multi-band optical and infrared photometric survey with spectroscopic follow-up covers 11 deg 2 , making it the largest survey of this cluster to date. We observe a radial variation in the MF over the range 0.072-0.3 M sun , but no significant variation in the MF below the substellar boundary at the three cluster radius intervals is analyzed. This lack of radial variation for low masses is what we would expect with the ejection scenario for BD formation, although considering that IC 2391 has an age about three times older than its crossing time, we expect that BDs with a velocity greater than the escape velocity have already escaped the cluster. Alternatively, the variation in the MF of the stellar objects could be an indication that they have undergone mass segregation via dynamical evolution. We also observe a significant variation across the cluster in the color of the (background) field star locus in color-magnitude diagrams and conclude that this is due to variable background extinction in the Galactic plane. From our preliminary spectroscopic follow-up, to confirm BD status and cluster membership, we find that all candidates are M dwarfs (in either the field or the cluster), demonstrating the efficiency of our photometric selection method in avoiding contaminants (e.g., red giants). About half of our photometric candidates for which we have spectra are spectroscopically confirmed as cluster members; two are new spectroscopically confirmed BD members of IC 2391.

  15. HOW DO YOUNG PEOPLE SELECT INFORMATION TO PLAN A TRIP

    Directory of Open Access Journals (Sweden)

    Oana ŢUGULEA

    2013-12-01

    Full Text Available The purpose of the research is to reveal the young tourists preferences in the process of planning a trip. Sources of information used, the utility of Internet/travel agencies in planning travel trip activities, preferred means of transportation and types of accommodation are investigated. As research methods, there used both qualitative and quantitative methods: focus group and survey. Internet is more used by young tourists in planning trips than travel agencies are. Internet is considered more useful in the documentation stage and when buying airline tickets. Young tourists are more influenced by friends when planning a trip. Young tourists prefer cars and planes as means of transportation for a trip and hotels and guesthouses as accommodation when traveling.

  16. Stellar remnants

    CERN Document Server

    Kawaler, S D; Srinivasan, G

    1997-01-01

    This volume examines the internal structure, origin and evolution of white dwarfs, neutron stars and black holes, all objects at the final stage of stellar evolution. It covers topics such as: pulsation of white dwarfs; millisecond pulsars; and the dynamics around black holes.

  17. Assessment of somatotype in young voleyball players: Validity as criteria to select young sports talents

    Directory of Open Access Journals (Sweden)

    Luís Carrasco Páez

    2008-06-01

    Full Text Available The anthropometric characteristics of athletes can determine their sporting performance. For this reason, we’ve defined the somatotype of young volleyball players in order to be able to control their sports training and to ensure their appropriate athletic development. In the present investigation 154 male and female volleyball players (aged from 12 to 14 years were analyzed. Data were collected according to the ISAK protocol. The results show an endomesomorphic profile for male and female volleyball players agreeing with the predominant profile at these ages. However, after comparing these data with results obtained in other studies, we observed a certain homogeneity in the male somatotype, invalidating the current trend of using this parameter as criteria to select young sports talent. However, somatotype could be a factor to take into account with female athletes, since their profile is much more heterogeneous. ResumoLas características antropométricas de los deportistas pueden determinar su rendimiento deportivo. Por esa razón se pretende conocer el somatotipo de jugadores infantiles de voleibol para poder así, controlar el entrenamiento y asegurar un adecuado desarrollo de los deportistas. En este estudio se analizaron 154 jugadores/as, con edades comprendidas entre 12 y 14 años. Los datos se extrajeron según las técnicas recomendadas por la ISAK (2001. Los resultados mostraron um perfil endomesomorfo tanto en chicos como en chicas, lo que concuerda con el perfil predominante en estas edades. Por otra parte, al comparar el somatotipo de estos jugadores con el de otros estudios observamos una cierta homogeneidad en el caso de los chicos, lo que invalidaría la tendencia actual de usar este parámetro como criterio para la selección de jóvenes talentos deportivos. Sin embargo, si podría ser un elemento a tener en cuenta en el caso de las chicas, ya que su perfil es mucho más heterogéneo.

  18. The low-mass stellar population in the young cluster Tr 37. Disk evolution, accretion, and environment

    Science.gov (United States)

    Sicilia-Aguilar, Aurora; Kim, Jinyoung Serena; Sobolev, Andrej; Getman, Konstantin; Henning, Thomas; Fang, Min

    2013-11-01

    Aims: We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr 37. With a well-studied solar-type population, Tr 37 is a benchmark for disk evolution. Methods: We used low-resolution spectroscopy to identify and classify 141 members (78 new ones) and 64 probable members, mostly M-type stars. Hα emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the spectral energy distributions (SEDs) and search for disks. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks. Results: Including the new members and the known solar-type stars, we confirm that a substantial fraction (~2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or as a more global evolution (with low small-dust masses, dust settling, and weak/absent accretion signatures). Accretion is strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, and dust-depleted disks have weak (or undetectable) accretion signatures, especially among M-type stars. Conclusions: The analysis of accretion and disk structure suggests a parallel evolution of dust and gas. We find several distinct classes of evolved disks, based on SED type and accretion status, pointing to different disk dispersal mechanisms and probably different evolutionary paths. Dust depletion and opening of inner holes appear to be independent processes: most transition disks are not dust-depleted, and most dust-depleted disks do not require inner holes. The differences in disk structure between M-type and solar-type stars in Tr 37 (4 Myr old) are not as remarkable as in the young, sparse, Coronet cluster (1-2 Myr old), suggesting that other factors, like the environment/interactions in each cluster, are likely to play an important role in the disk evolution and dispersal. Finally, we

  19. The Effect of Broadband Soft X-Rays in SO2-Containing Ices: Implications on the Photochemistry of Ices toward Young Stellar Objects

    Science.gov (United States)

    Pilling, S.; Bergantini, A.

    2015-10-01

    We investigate the effects produced mainly by broadband soft X-rays up to 2 keV (plus fast (˜keV) photoelectrons and low-energy (˜eV) induced secondary electrons) in the ice mixtures containing H2O:CO2:NH3:SO2 (10:1:1:1) at two different temperatures (50 and 90 K). The experiments are an attempt to simulate the photochemical processes induced by energetic photons in SO2-containing ices present in cold environments in the ices surrounding young stellar objects (YSO) and in molecular clouds in the vicinity of star-forming regions, which are largely illuminated by soft X-rays. The measurements were performed using a high-vacuum portable chamber from the Laboratório de Astroquímica e Astrobiologia (LASA/UNIVAP) coupled to the spherical grating monochromator beamline at the Brazilian Synchrotron Light Source (LNLS) in Campinas, Brazil. In situ analyses were performed by a Fourier transform infrared spectrometer. Sample processing revealed the formation of several organic molecules, including nitriles, acids, and other compounds such as H2O2, H3O+, SO3, CO, and OCN-. The dissociation cross section of parental species was on the order of (2-7) × 10-18 cm2. The ice temperature does not seem to affect the stability of SO2 in the presence of X-rays. Formation cross sections of new species produced were also determined. Molecular half-lives at ices toward YSOs due to the presence of incoming soft X-rays were estimated. The low values obtained employing two different models of the radiation field of YSOs (TW Hydra and typical T-Tauri star) reinforce that soft X-rays are indeed a very efficient source of molecular dissociation in such environments.

  20. [Fe II] 1.64 μm FEATURES OF JETS AND OUTFLOWS FROM YOUNG STELLAR OBJECTS IN THE CARINA NEBULA

    Energy Technology Data Exchange (ETDEWEB)

    Shinn, Jong-Ho; Lee, Jae-Joon; Chun, Moo-Young; Lyo, A.-Ran; Moon, Dae-Sik; Kyeong, Jaemann; Park, Byeong-Gon [Korea Astronomy and Space Science Institute, 776 Daeduk-daero, Yuseong-gu, Daejeon 305-348 (Korea, Republic of); Pyo, Tae-Soo [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A' ohōkū Place, Hilo, HI 96720 (United States); Lee, Ho-Gyu [Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Kim, Hyun-Jeong; Koo, Bon-Chul; Lee, Yong-Hyun [Department of Physics and Astronomy, Seoul National University, 599 Gwanangno, Gwanak-gu, Seoul 151-747 (Korea, Republic of); Sung, Hwankyung; Hur, Hyeonoh, E-mail: jhshinn@kasi.re.kr [Department of Astronomy and Space Science, Sejong University, 98 Kunja-dong, Kwangjin-gu, Seoul 143-747 (Korea, Republic of)

    2013-11-01

    We present [Fe II] 1.64 μm imaging observations for jets and outflows from young stellar objects (YSOs) over the northern part (∼24' × 45') of the Carina Nebula, a massive star-forming region. The observations were performed with IRIS2 of the Anglo-Australian Telescope and the seeing was ∼1.''5 ± 0.''5. Eleven jet and outflow features are detected at eight different regions and are termed ionized Fe objects (IFOs). One Herbig-Haro candidate that was missed in Hubble Space Telescope Hα observations is newly identified as HHc-16, referring to our [Fe II] images. IFOs have knotty or longish shapes, and the detection rate of IFOs against previously identified YSOs is 1.4%, which should be treated as a lower limit. Four IFOs show anti-correlated peak intensities in [Fe II] and Hα, where the ratio I([Fe II])/I(Hα) is higher for longish IFOs than for knotty IFOs. We estimate the outflow mass loss rate from the [Fe II] flux using two different methods. The jet-driving objects are identified for three IFOs (IFO-2, -4, and -7) for which we study the relations between the outflow mass loss rate and the YSO physical parameters from the radiative transfer model fitting. The ratios of the outflow mass loss rate over the disk accretion rate for IFO-4 and -7 are consistent with the previously reported values (10{sup –2}-10{sup +1}), while the ratio is higher for IFO-2. This excess may result from underestimating the disk accretion rate. The jet-driving objects are likely to be low- or intermediate-mass stars. Other YSO physical parameters, such as luminosity and age, show reasonable relations or trends.

  1. Modeling CO, CO2, and H2O Ice Abundances in the Envelopes of Young Stellar Objects in the Magellanic Clouds

    Science.gov (United States)

    Pauly, Tyler; Garrod, Robin T.

    2018-02-01

    Massive young stellar objects (MYSOs) in the Magellanic Clouds show infrared absorption features corresponding to significant abundances of CO, CO2, and H2O ice along the line of sight, with the relative abundances of these ices differing between the Magellanic Clouds and the Milky Way. CO ice is not detected toward sources in the Small Magellanic Cloud, and upper limits put its relative abundance well below sources in the Large Magellanic Cloud and the Milky Way. We use our gas-grain chemical code MAGICKAL, with multiple grain sizes and grain temperatures, and further expand it with a treatment for increased interstellar radiation field intensity to model the elevated dust temperatures observed in the MCs. We also adjust the elemental abundances used in the chemical models, guided by observations of H II regions in these metal-poor satellite galaxies. With a grid of models, we are able to reproduce the relative ice fractions observed in MC MYSOs, indicating that metal depletion and elevated grain temperature are important drivers of the MYSO envelope ice composition. Magellanic Cloud elemental abundances have a subgalactic C/O ratio, increasing H2O ice abundances relative to the other ices; elevated grain temperatures favor CO2 production over H2O and CO. The observed shortfall in CO in the Small Magellanic Cloud can be explained by a combination of reduced carbon abundance and increased grain temperatures. The models indicate that a large variation in radiation field strength is required to match the range of observed LMC abundances. CH3OH abundance is found to be enhanced in low-metallicity models, providing seed material for complex organic molecule formation in the Magellanic Clouds.

  2. THE EFFECT OF BROADBAND SOFT X-RAYS IN SO2-CONTAINING ICES: IMPLICATIONS ON THE PHOTOCHEMISTRY OF ICES TOWARD YOUNG STELLAR OBJECTS

    International Nuclear Information System (INIS)

    Pilling, S.; Bergantini, A.

    2015-01-01

    We investigate the effects produced mainly by broadband soft X-rays up to 2 keV (plus fast (∼keV) photoelectrons and low-energy (∼eV) induced secondary electrons) in the ice mixtures containing H 2 O:CO 2 :NH 3 :SO 2 (10:1:1:1) at two different temperatures (50 and 90 K). The experiments are an attempt to simulate the photochemical processes induced by energetic photons in SO 2 -containing ices present in cold environments in the ices surrounding young stellar objects (YSO) and in molecular clouds in the vicinity of star-forming regions, which are largely illuminated by soft X-rays. The measurements were performed using a high-vacuum portable chamber from the Laboratório de Astroquímica e Astrobiologia (LASA/UNIVAP) coupled to the spherical grating monochromator beamline at the Brazilian Synchrotron Light Source (LNLS) in Campinas, Brazil. In situ analyses were performed by a Fourier transform infrared spectrometer. Sample processing revealed the formation of several organic molecules, including nitriles, acids, and other compounds such as H 2 O 2 , H 3 O + , SO 3 , CO, and OCN − . The dissociation cross section of parental species was on the order of (2–7) × 10 −18 cm 2 . The ice temperature does not seem to affect the stability of SO 2 in the presence of X-rays. Formation cross sections of new species  produced were also determined. Molecular half-lives at ices toward YSOs due to the presence of incoming soft X-rays were estimated. The low values obtained employing two different models of the radiation field of YSOs (TW Hydra and typical T-Tauri star) reinforce that soft X-rays are indeed a very efficient source of molecular dissociation in such environments

  3. Stellar winds

    International Nuclear Information System (INIS)

    Weymann, R.J.

    1978-01-01

    It is known that a steady outflow of material at comparable rates of mass loss but vastly different speeds is now known to be ubiquitous phenomenon among both the luminous hot stars and the luminous but cool red giants. The flows are probably massive enough in both cases to give rise to significant effects on stellar evolution and the mass balance between stars and the interstellar medium. The possible mechanisms for these phenomena as well as the methods of observation used are described. In particular, the mass-loss processes in stars other than the sun that also involve a steady flow of matter are considered. The evidence for their existence is described, and then the question of whether the process thought to produce the solar wind is also responsible for producing these stellar winds is explored

  4. Effects of genomic selection on genetic improvement, inbreeding, and merit of young versus proven bulls

    NARCIS (Netherlands)

    Roos, de A.P.W.; Schrooten, C.; Veerkamp, R.F.; Arendonk, van J.A.M.

    2011-01-01

    Genomic selection has the potential to revolutionize dairy cattle breeding because young animals can be accurately selected as parents, leading to a much shorter generation interval and higher rates of genetic gain. The aims of this study were to assess the effects of genomic selection and reduction

  5. Stellarator physics

    International Nuclear Information System (INIS)

    1990-07-01

    This document consists of the proceedings of the Seventh International Workshop on Stellarators, held in Oak Ridge, Tennessee, USA, 10-14 April, 1989. The document consists of a summary of presentations, an overview of experimental results, and papers presented at the workshop on transport, impurities and divertors, diagnostics, ECH confinement experiments, equilibrium and stability studies, RF heating, confinement, magnetic configurations, and new experiments. Refs, figs and tabs

  6. A COMPREHENSIVE SEARCH FOR STELLAR BOWSHOCK NEBULAE IN THE MILKY WAY: A CATALOG OF 709 MID-INFRARED SELECTED CANDIDATES

    Energy Technology Data Exchange (ETDEWEB)

    Kobulnicky, Henry A.; Chick, William T.; Schurhammer, Danielle P.; Andrews, Julian E.; Munari, Stephan A.; Olivier, Grace M.; Sorber, Rebecca L.; Wernke, Heather N.; Dale, Daniel A. [Dept. of Physics and Astronomy, University of Wyoming, Laramie, WY 82070 (United States); Povich, Matthew S.; Dixon, Don M. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States)

    2016-12-01

    We identify 709 arc-shaped mid-infrared nebula in 24 μ m Spitzer Space Telescope or 22 μ m Wide Field Infrared Explorer surveys of the Galactic Plane as probable dusty interstellar bowshocks powered by early-type stars. About 20% are visible at 8 μ m or at shorter mid-infrared wavelengths. The vast majority (660) have no previous identification in the literature. These extended infrared sources are strongly concentrated near the Galactic mid-plane, with an angular scale height of ∼0.°6. All host a symmetrically placed star implicated as the source of a stellar wind sweeping up interstellar material. These are candidate “runaway” stars potentially having high velocities in the reference frame of the local medium. Among the 286 objects with measured proper motions, we find an unambiguous excess with velocity vectors aligned with the infrared morphology—kinematic evidence that many of these are “runaway” stars with large peculiar motions responsible for the bowshock signature. We discuss a population of “in situ” bowshocks (∼103 objects) that face giant H ii regions where the relative motions between the star and ISM may be caused by bulk outflows from an overpressured bubble. We also identify ∼58 objects that face 8 μ m bright-rimmed clouds and apparently constitute a sub-class of in situ bowshocks where the stellar wind interacts with a photoevaporative flow (PEF) from an eroding molecular cloud interface (i.e., “PEF bowshocks”). Orientations of the arcuate nebulae exhibit a correlation over small angular scales, indicating that external influences such as H ii regions are responsible for producing some bowshock nebulae. However, the vast majority of the nebulae in this sample appear to be isolated (499 objects) from obvious external influences.

  7. Stellar evolution

    CERN Document Server

    Meadows, A J

    2013-01-01

    Stellar Evolution, Second Edition covers the significant advances in the understanding of birth, life, and death of stars.This book is divided into nine chapters and begins with a description of the characteristics of stars according to their brightness, distance, size, mass, age, and chemical composition. The next chapters deal with the families, structure, and birth of stars. These topics are followed by discussions of the chemical composition and the evolution of main-sequence stars. A chapter focuses on the unique features of the sun as a star, including its evolution, magnetic fields, act

  8. Ultraviolet photometry of stellar populations in galaxies

    International Nuclear Information System (INIS)

    Deharveng, J.M.

    1981-01-01

    The UV flux of stellar populations, which is essentially emitted by young stars, conveys information on the process of star formation and its recent history. However, the evaluation of the flux arising from the young stellar component may be difficult. In the case of late type galaxies it is hampered by the extinction and the effect of scattered stellar radiation. In the case of early type galaxies, the star formation, if any, has to be disentangled from the contribution of hot evolved stars and of a possible 'active' phenomenon. A review of observations and results relevant two cases is presented [fr

  9. THE c2d SPITZER SPECTROSCOPIC SURVEY OF ICES AROUND LOW-MASS YOUNG STELLAR OBJECTS. IV. NH3 AND CH3OH

    International Nuclear Information System (INIS)

    Bottinelli, Sandrine; Van Dishoeck, Ewine F.; Lahuis, Fred; Boogert, A. C. Adwin; Bouwman, Jordy; Beckwith, Martha; Oeberg, Karin I.; Linnartz, Harold; Pontoppidan, Klaus M.; Blake, Geoffrey A.; Evans, Neal J.

    2010-01-01

    NH 3 and CH 3 OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH 3 CN and CH 3 OCH 3 . Despite a number of recent studies, little is known about their abundances in the solid state. This is particularly the case for low-mass protostars, for which only the launch of the Spitzer Space Telescope has permitted high-sensitivity observations of the ices around these objects. In this work, we investigate the ∼8-10 μm region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass young stellar objects (YSOs). These data are part of a survey of interstellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10 μm silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH 3 - and CH 3 OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ∼9 μm in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH 3 ν 2 umbrella mode and derive abundances with respect to water between ∼2% and 15%. Simultaneously, we also revisited the case of CH 3 OH ice by studying the ν 4 C-O stretch mode of this molecule at ∼9.7 μm in 16 objects, yielding abundances consistent with those derived by Boogert et al. based on a simultaneous 9.75 and 3.53 μm data analysis. Our study indicates that NH 3 is present primarily in H 2 O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH 3 OH being in an almost pure methanol ice, or mixed mainly with CO or CO 2 , consistent with its formation through hydrogenation on grains. Finally, we use our derived NH 3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10%-20% of

  10. A FEATURE MOVIE OF SiO EMISSION 20-100 AU FROM THE MASSIVE YOUNG STELLAR OBJECT ORION SOURCE I

    International Nuclear Information System (INIS)

    Matthews, L. D.; Greenhill, L. J.; Goddi, C.; Humphreys, E. M. L.; Chandler, C. J.; Kunz, M. W.

    2010-01-01

    We present multi-epoch Very Long Baseline Array imaging of the 28 SiO v = 1 and v = 2, J = 1-0 maser emission toward the massive young stellar object (YSO) Orion Source I. Both SiO transitions were observed simultaneously with an angular resolution of ∼0.5 mas (∼0.2 AU for d = 414 pc) and a spectral resolution of ∼0.2 km s -1 . Here we explore the global properties and kinematics of the emission through two 19-epoch animated movies spanning 21 months (from 2001 March 19 to 2002 December 10). These movies provide the most detailed view to date of the dynamics and temporal evolution of molecular material within ∼20-100 AU of a massive (∼>8 M sun ) YSO. As in previous studies, we find that the bulk of the SiO masers surrounding Source I lie in an X-shaped locus; the emission in the south and east arms is predominantly blueshifted, and emission in the north and west is predominantly redshifted. In addition, bridges of intermediate-velocity emission are observed connecting the red and blue sides of the emission distribution. We have measured proper motions of over 1000 individual maser features and found that these motions are characterized by a combination of radially outward migrations along the four main maser-emitting arms and motions tangent to the intermediate-velocity bridges. We interpret the SiO masers as arising from a wide-angle bipolar wind emanating from a rotating, edge-on disk. The detection of maser features along extended, curved filaments suggests that magnetic fields may play a role in launching and/or shaping the wind. Our observations appear to support a picture in which stars with masses as high as at least 8 M sun form via disk-mediated accretion. However, we cannot yet rule out that the Source I disk may have been formed or altered following a recent close encounter.

  11. THE EFFECT OF BROADBAND SOFT X-RAYS IN SO{sub 2}-CONTAINING ICES: IMPLICATIONS ON THE PHOTOCHEMISTRY OF ICES TOWARD YOUNG STELLAR OBJECTS

    Energy Technology Data Exchange (ETDEWEB)

    Pilling, S.; Bergantini, A., E-mail: sergiopilling@pq.cnpq.br [Universidade do Vale do Paraíba (UNIVAP), Laboratório de Astroquímica e Astrobiologia (LASA), São José dos Campos, SP (Brazil)

    2015-10-01

    We investigate the effects produced mainly by broadband soft X-rays up to 2 keV (plus fast (∼keV) photoelectrons and low-energy (∼eV) induced secondary electrons) in the ice mixtures containing H{sub 2}O:CO{sub 2}:NH{sub 3}:SO{sub 2} (10:1:1:1) at two different temperatures (50 and 90 K). The experiments are an attempt to simulate the photochemical processes induced by energetic photons in SO{sub 2}-containing ices present in cold environments in the ices surrounding young stellar objects (YSO) and in molecular clouds in the vicinity of star-forming regions, which are largely illuminated by soft X-rays. The measurements were performed using a high-vacuum portable chamber from the Laboratório de Astroquímica e Astrobiologia (LASA/UNIVAP) coupled to the spherical grating monochromator beamline at the Brazilian Synchrotron Light Source (LNLS) in Campinas, Brazil. In situ analyses were performed by a Fourier transform infrared spectrometer. Sample processing revealed the formation of several organic molecules, including nitriles, acids, and other compounds such as H{sub 2}O{sub 2}, H{sub 3}O{sup +}, SO{sub 3}, CO, and OCN{sup −}. The dissociation cross section of parental species was on the order of (2–7) × 10{sup −18} cm{sup 2}. The ice temperature does not seem to affect the stability of SO{sub 2} in the presence of X-rays. Formation cross sections of new species  produced were also determined. Molecular half-lives at ices toward YSOs due to the presence of incoming soft X-rays were estimated. The low values obtained employing two different models of the radiation field of YSOs (TW Hydra and typical T-Tauri star) reinforce that soft X-rays are indeed a very efficient source of molecular dissociation in such environments.

  12. NEW YOUNG STAR CANDIDATES IN THE TAURUS-AURIGA REGION AS SELECTED FROM THE WIDE-FIELD INFRARED SURVEY EXPLORER

    International Nuclear Information System (INIS)

    Rebull, L. M.; Padgett, D. L.; Noriega-Crespo, A.

    2011-01-01

    The Taurus Molecular Cloud subtends a large solid angle on the sky, in excess of 250 deg 2 . The search for legitimate Taurus members to date has been limited by sky coverage as well as the challenge of distinguishing members from field interlopers. The Wide-field Infrared Survey Explorer has recently observed the entire sky, and we take advantage of the opportunity to search for young stellar object (YSO) candidate Taurus members from a ∼260 deg 2 region designed to encompass previously identified Taurus members. We use near- and mid-infrared colors to select objects with apparent infrared excesses and incorporate other catalogs of ancillary data to present a list of rediscovered Taurus YSOs with infrared excesses (taken to be due to circumstellar disks), a list of rejected YSO candidates (largely galaxies), and a list of 94 surviving candidate new YSO-like Taurus members. There is likely to be contamination lingering in this candidate list, and follow-up spectra are warranted.

  13. The search for multiple populations in Magellanic Cloud Clusters IV: Coeval multiple stellar populations in the young star cluster NGC 1978

    Science.gov (United States)

    Martocchia, S.; Niederhofer, F.; Dalessandro, E.; Bastian, N.; Kacharov, N.; Usher, C.; Cabrera-Ziri, I.; Lardo, C.; Cassisi, S.; Geisler, D.; Hilker, M.; Hollyhead, K.; Kozhurina-Platais, V.; Larsen, S.; Mackey, D.; Mucciarelli, A.; Platais, I.; Salaris, M.

    2018-04-01

    We have recently shown that the ˜2 Gyr old Large Magellanic Cloud star cluster NGC 1978 hosts multiple populations in terms of star-to-star abundance variations in [N/Fe]. These can be seen as a splitting or spread in the sub-giant and red giant branches (SGB and RGB) when certain photometric filter combinations are used. Due to its relative youth, NGC 1978 can be used to place stringent limits on whether multiple bursts of star-formation have taken place within the cluster, as predicted by some models for the origin of multiple populations. We carry out two distinct analyses to test whether multiple star-formation epochs have occurred within NGC 1978. First, we use UV CMDs to select stars from the first and second population along the SGB, and then compare their positions in optical CMDs, where the morphology is dominantly controlled by age as opposed to multiple population effects. We find that the two populations are indistinguishable, with age differences of 1 ± 20 Myr between them. This is in tension with predictions from the AGB scenario for the origin of multiple populations. Second, we estimate the broadness of the main sequence turnoff (MSTO) of NGC 1978 and we report that it is consistent with the observational errors. We find an upper limit of ˜65 Myr on the age spread in the MSTO of NGC 1978. This finding is in conflict with the age spread scenario as origin of the extendend MSTO in intermediate age clusters, while it fully supports predictions from the stellar rotation model.

  14. TWO-DIMENSIONAL MAPPING OF YOUNG STARS IN THE INNER 180 pc OF NGC 1068: CORRELATION WITH MOLECULAR GAS RING AND STELLAR KINEMATICS

    Energy Technology Data Exchange (ETDEWEB)

    Storchi-Bergmann, Thaisa; Riffel, Rogerio; Vale, Tiberio Borges [Departamento de Astronomia, Universidade Federal do Rio Grande do Sul, IF, CP 15051, 91501-970 Porto Alegre, RS (Brazil); Riffel, Rogemar A.; Diniz, Marlon R. [Departamento de Fisica, Centro de Ciencias Naturais e Exatas, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS (Brazil); McGregor, Peter J., E-mail: thaisa@ufrgs.br [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia)

    2012-08-20

    We report the first two-dimensional mapping of the stellar population and non-stellar continua within the inner 180 pc (radius) of NGC 1068 at a spatial resolution of 8 pc, using integral field spectroscopy in the near-infrared. We have applied the technique of spectral synthesis to data obtained with the instrument NIFS and the adaptive optics module ALTAIR at the Gemini North Telescope. Two episodes of recent star formation are found to dominate the stellar population contribution: the first occurred 300 Myr ago, extending over most of the nuclear region; the second occurred just 30 Myr ago, in a ring-like structure at Almost-Equal-To 100 pc from the nucleus, where it is coincident with an expanding ring of H{sub 2} emission. Inside the ring, where a decrease in the stellar velocity dispersion is observed, the stellar population is dominated by the 300 Myr age component. In the inner 35 pc, the oldest age component (age {>=} 2 Gyr) dominates the mass, while the flux is dominated by blackbody components with temperatures in the range 700 K {<=} T {<=} 800 K which we attribute to the dusty torus. We also find some contribution from blackbody and power-law components beyond the nucleus which we attribute to dust emission and scattered light.

  15. Suicide among young people in selected Brazilian State capitals

    Directory of Open Access Journals (Sweden)

    Souza Edinilsa Ramos de

    2002-01-01

    Full Text Available This study analyzes suicide among young Brazilians (15-24 years old in nine metropolitan areas. Mortality data for 1979-1998 were obtained from the Mortality Information System of the Ministry of Health. External causes are the main causes of death among youth, and suicide is the sixth most frequent of these causes. The distribution is heterogeneous, varying according to the social stratum, specific age group, sex, and means used to commit suicide. All cities analyzed showed increased suicide rates from 1979 to 1998 (from 3.5 to 5.0 per 100,000 inhabitants 15-24 years old. Salvador and Rio de Janeiro had the lowest suicide rates, while Porto Alegre and Curitiba had the highest. The principal means used by youth to commit suicide were hanging, strangling, and suffocation (Porto Alegre, followed by firearms and explosives (Belo Horizonte.

  16. Selecting patients with young-onset colorectal cancer for mismatch repair gene analysis

    DEFF Research Database (Denmark)

    Walker, M; O'Sullivan, B; Perakath, B

    2007-01-01

    BACKGROUND: Young patients with colorectal cancer are at increased risk of carrying a germline mutation in mismatch repair (MMR) genes. This study investigated the role of clinical criteria and immunohistochemistry for MMR proteins in selecting young patients for mutation testing. METHODS: A cohort...... of 56 consecutive patients with colorectal cancer aged less than 45 years were stratified into three groups based on clinical criteria: 'Amsterdam criteria', 'high risk' and 'young onset only'. Immunohistochemistry for four MMR proteins was carried out and the rate of compliance with clinical guidelines...

  17. Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

    NARCIS (Netherlands)

    Schneider, F.R.N.; Izzard, R.G.; de Mink, S.E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V.V.; Huβman, B.; Liermann, A.; Sana, H.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass

  18. THE HIGH A{sub V} Quasar Survey: Reddened Quasi-Stellar Objects selected from optical/near-infrared photometry. II

    Energy Technology Data Exchange (ETDEWEB)

    Krogager, J.-K.; Fynbo, J. P. U.; Vestergaard, M. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø (Denmark); Geier, S. [Instituto de Astrofísica de Canarias (IAC), E-38205 La Laguna, Tenerife (Spain); Venemans, B. P. [Max-Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Ledoux, C. [European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19 (Chile); Møller, P. [European Southern Observatory, Karl-Schwarzschildstrasse 2, D-85748 Garching bei München (Germany); Noterdaeme, P. [Institut d’Astrophysique de Paris, CNRS-UPMC, UMR7095, 98bis bd Arago, F-75014 Paris (France); Kangas, T.; Pursimo, T.; Smirnova, O. [Nordic Optical Telescope, Apartado 474, E-38700 Santa Cruz de La Palma (Spain); Saturni, F. G. [Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Väisäläntie 20, 21500 Piikkiö (Finland)

    2015-03-15

    Quasi-stellar objects (QSOs) whose spectral energy distributions (SEDs) are reddened by dust either in their host galaxies or in intervening absorber galaxies are to a large degree missed by optical color selection criteria like the ones used by the Sloan Digital Sky Survey (SDSS). To overcome this bias against red QSOs, we employ a combined optical and near-infrared (near-IR) color selection. In this paper, we present a spectroscopic follow-up campaign of a sample of red candidate QSOs which were selected from the SDSS and the UKIRT Infrared Deep Sky Survey (UKIDSS). The spectroscopic data and SDSS/UKIDSS photometry are supplemented by mid-infrared photometry from the Wide-field Infrared Survey Explorer. In our sample of 159 candidates, 154 (97%) are confirmed to be QSOs. We use a statistical algorithm to identify sightlines with plausible intervening absorption systems and identify nine such cases assuming dust in the absorber similar to Large Magellanic Cloud sightlines. We find absorption systems toward 30 QSOs, 2 of which are consistent with the best-fit absorber redshift from the statistical modeling. Furthermore, we observe a broad range in SED properties of the QSOs as probed by the rest-frame 2 μm flux. We find QSOs with a strong excess as well as QSOs with a large deficit at rest-frame 2 μm relative to a QSO template. Potential solutions to these discrepancies are discussed. Overall, our study demonstrates the high efficiency of the optical/near-IR selection of red QSOs.

  19. Stellar astrophysics

    International Nuclear Information System (INIS)

    1988-01-01

    Enhanced mass loss occurs at critical stages in the evolution of stars over a wide range of stellar mass. Observationally, these stages are difficult to identify because of their short duration and because the star is often obscured by dust which condenses in the ejecta. A study of a G-type star, of which only the outer envelope was directly visible, was undertaken by the South African Astronomical Observatory (SAAO). The star itself was obscured by dust clouds and its light was only feebly seen by reflection from some of these clouds. Other studies of the galaxy undertaken by the SAAO include observations of the following: the extreme carbon star IRAS 15194-5115; RV Tauri and T Tauri stars; pre-main sequence stars; the properties of circumstellar dust; rotational modulation and flares on RS CVn and BY Dra stars; heavy-element stars; hydrogen-deficient stars; the open cluster NGC6192; stars in Omega Centauri, and lunar occulations of stars. Simultaneous x-ray, radio and optical data of the flare star YZ CMi were also obtained. 1 fig

  20. Relative age effect and selection of young basketball players

    Directory of Open Access Journals (Sweden)

    Vučković Igor

    2013-01-01

    Full Text Available Purpose of the present study was to examine whether influence of relative age effect (RAE exists or not in the selected 13 year old basketball players. Subjects were 20 basketball players (HT=177.35cm±6.73, BW=61.42kg±8.98, average age 13 years and 7 months ±.28, average experience in basketball training 4 years and 6 months ±1.15. Sample was divided in two groups: 11 players born in first half of the year and 9 players born in the second half of the year. One-way ANOVA was used in order to analyze the differences between the two groups of players in set of anthropometric variables (body height, arm span, standing reach height, body weight and percentage of body fat, motor variables (velocity of neuromuscular reaction time, vertical jump, 5 meters sprint, 10 meters sprint, 20 meters sprint, T-test, Zig-zag test, ball throw from sitting position, Sit-ups for 30 seconds and standing forward bend and one functional variable (20-M shuttle run test. Subjects do not differ in applied set of parameters, except in on variable (sit-ups for 30 seconds, p=.040. It was concluded that RAE does not exist in this sample of examinees.

  1. Selected Health Status Indicators and Behaviors of Young Adults, United States-2003

    Science.gov (United States)

    Eaton, Danice K.; Kann, Laura; Okoro, Catherine A.; Collins, Janet

    2007-01-01

    This study examined the prevalence of selected clinical preventive health services, health status indicators, health risk behaviors, and health-promoting behaviors among adults aged 18 to 24 years in the general U.S. population. The study analyzed data from the 2003 Behavioral Risk Factor Surveillance System. Nearly 30% of young adults lacked…

  2. Galaxy And Mass Assembly (GAMA): the galaxy stellar mass function to z = 0.1 from the r-band selected equatorial regions

    Science.gov (United States)

    Wright, A. H.; Robotham, A. S. G.; Driver, S. P.; Alpaslan, M.; Andrews, S. K.; Baldry, I. K.; Bland-Hawthorn, J.; Brough, S.; Brown, M. J. I.; Colless, M.; da Cunha, E.; Davies, L. J. M.; Graham, Alister W.; Holwerda, B. W.; Hopkins, A. M.; Kafle, P. R.; Kelvin, L. S.; Loveday, J.; Maddox, S. J.; Meyer, M. J.; Moffett, A. J.; Norberg, P.; Phillipps, S.; Rowlands, K.; Taylor, E. N.; Wang, L.; Wilkins, S. M.

    2017-09-01

    We derive the low-redshift galaxy stellar mass function (GSMF), inclusive of dust corrections, for the equatorial Galaxy And Mass Assembly (GAMA) data set covering 180 deg2. We construct the mass function using a density-corrected maximum volume method, using masses corrected for the impact of optically thick and thin dust. We explore the galactic bivariate brightness plane (M⋆-μ), demonstrating that surface brightness effects do not systematically bias our mass function measurement above 107.5 M⊙. The galaxy distribution in the M-μ plane appears well bounded, indicating that no substantial population of massive but diffuse or highly compact galaxies are systematically missed due to the GAMA selection criteria. The GSMF is fitted with a double Schechter function, with M^\\star =10^{10.78± 0.01± 0.20} M_{⊙}, φ ^\\star _1=(2.93± 0.40)× 10^{-3} h_{70}^3 Mpc-3, α1 = -0.62 ± 0.03 ± 0.15, φ ^\\star _2=(0.63± 0.10)× 10^{-3} h_{70}^3 Mpc-3 and α2 = -1.50 ± 0.01 ± 0.15. We find the equivalent faint end slope as previously estimated using the GAMA-I sample, although we find a higher value of M^\\star. Using the full GAMA-II sample, we are able to fit the mass function to masses as low as 107.5 M⊙, and assess limits to 106.5 M⊙. Combining GAMA-II with data from G10-COSMOS, we are able to comment qualitatively on the shape of the GSMF down to masses as low as 106 M⊙. Beyond the well-known upturn seen in the GSMF at 109.5, the distribution appears to maintain a single power-law slope from 109 to 106.5. We calculate the stellar mass density parameter given our best-estimate GSMF, finding Ω _\\star = 1.66^{+0.24}_{-0.23}± 0.97 h^{-1}_{70} × 10^{-3}, inclusive of random and systematic uncertainties.

  3. A Foreground Masking Strategy for [C II] Intensity Mapping Experiments Using Galaxies Selected by Stellar Mass and Redshift

    Science.gov (United States)

    Sun, G.; Moncelsi, L.; Viero, M. P.; Silva, M. B.; Bock, J.; Bradford, C. M.; Chang, T.-C.; Cheng, Y.-T.; Cooray, A. R.; Crites, A.; Hailey-Dunsheath, S.; Uzgil, B.; Hunacek, J. R.; Zemcov, M.

    2018-04-01

    Intensity mapping provides a unique means to probe the epoch of reionization (EoR), when the neutral intergalactic medium was ionized by energetic photons emitted from the first galaxies. The [C II] 158 μm fine-structure line is typically one of the brightest emission lines of star-forming galaxies and thus a promising tracer of the global EoR star formation activity. However, [C II] intensity maps at 6 ≲ z ≲ 8 are contaminated by interloping CO rotational line emission (3 ≤ J upp ≤ 6) from lower-redshift galaxies. Here we present a strategy to remove the foreground contamination in upcoming [C II] intensity mapping experiments, guided by a model of CO emission from foreground galaxies. The model is based on empirical measurements of the mean and scatter of the total infrared luminosities of galaxies at z {10}8 {M}ȯ selected in the K-band from the COSMOS/UltraVISTA survey, which can be converted to CO line strengths. For a mock field of the Tomographic Ionized-carbon Mapping Experiment, we find that masking out the “voxels” (spectral–spatial elements) containing foreground galaxies identified using an optimized CO flux threshold results in a z-dependent criterion {m}{{K}}AB}≲ 22 (or {M}* ≳ {10}9 {M}ȯ ) at z cost of a moderate ≲8% loss of total survey volume.

  4. Stellar populations in the Carina region. The Galactic plane at l = 291°

    Science.gov (United States)

    Molina-Lera, J. A.; Baume, G.; Gamen, R.; Costa, E.; Carraro, G.

    2016-08-01

    Context. Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. However, in many cases, these studies only concentrated on the central region (Trumpler 14/16) or were not homogeneous. This latter aspect, in particular, is crucial because very different ages and distances for key clusters have been claimed in recent years. Aims: The aim of this work is to study in detail an area of the Galactic plane in Carina, eastward η Carina. We analyze the properties of different stellar populations and focus on a sample of open clusters and their population of young stellar objects and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction. Methods: We obtained deep and homogeneous photometric data (UBVIKC) for six young open clusters: NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11, and 12, located in Carina at l ~ 291°, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional information from the literature, which includes stellar spectral classifications and near-infrared photometry from 2MASS. We finally developed a numerical code that allowed us to perform a homogeneous and systematic analysis of the data. Our results provide more reliable estimates of distances, color excesses, masses, and ages of the stellar populations in this direction. Results: We estimate the basic parameters of the studied clusters and find that they identify two overdensities of young stellar populations located at about 1.8 kpc and 2.8 kpc, with EB - V ~ 0.1 - 0.6. We find evidence of pre-main-sequence populations inside them, with an apparent coeval stellar formation in the most conspicuous clusters. We also discuss apparent age and distance gradients in the direction NW-SE. We study the

  5. Stellar Metamorphosis:

    Science.gov (United States)

    2002-01-01

    [TOP LEFT AND RIGHT] The Hubble Space Telescope's Wide Field and Planetary Camera 2 has captured images of the birth of two planetary nebulae as they emerge from wrappings of gas and dust, like butterflies breaking out of their cocoons. These images highlight a fleeting phase in the stellar burnout process, occurring just before dying stars are transformed into planetary nebulae. The left-hand image is the Cotton Candy nebula, IRAS 17150-3224; the right-hand image, the Silkworm nebula, IRAS 17441-2411. Called proto-planetary nebulae, these dying stars have been caught in a transition phase between a red giant and a planetary nebula. This phase is only about 1,000 years long, very short in comparison to the 1 billion-year lifetime of a star. These images provide the earliest snapshots of the transition process. Studying images of proto-planetary nebulae is important to understanding the process of star death. A star begins to die when it has exhausted its thermonuclear fuel - hydrogen and helium. The star then becomes bright and cool (red giant phase) and swells to several tens of times its normal size. It begins puffing thin shells of gas off into space. These shells become the star's cocoon. In the Hubble images, the shells are the concentric rings seen around each nebula. But the images also reveal the nebulae breaking out from those shells. The butterfly-like wings of gas and dust are a common shape of planetary nebulae. Such butterfly shapes are created by the 'interacting winds' process, in which a more recent 'fast wind' - material propelled by radiation from the hot central star - punches a hole in the cocoon, allowing the nebula to emerge. (This 'interacting wind' theory was first proposed by Dr. Sun Kwok to explain the origin of planetary nebulae, and has been subsequently proven successful in explaining their shapes.) The nebulae are being illuminated by light from the invisible central star, which is then reflected toward us. We are viewing the nebulae

  6. LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

    Science.gov (United States)

    Lin, Ming-Yi; Davies, R. I.; Hicks, E. K. S.; Burtscher, L.; Contursi, A.; Genzel, R.; Koss, M.; Lutz, D.; Maciejewski, W.; Müller-Sánchez, F.; Orban de Xivry, G.; Ricci, C.; Riffel, R.; Riffel, R. A.; Rosario, D.; Schartmann, M.; Schnorr-Müller, A.; Shimizu, T.; Sternberg, A.; Sturm, E.; Storchi-Bergmann, T.; Tacconi, L.; Veilleux, S.

    2018-02-01

    In a complete sample of local 14-195 keV selected active galactic nuclei (AGNs) and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, eight AGNs and five inactive galaxies. The stellar velocity fields show a disc-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN, but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disc structure, which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies.

  7. Metacognition for strategy selection during arithmetic problem-solving in young and older adults.

    Science.gov (United States)

    Geurten, Marie; Lemaire, Patrick

    2018-04-19

    We examined participants' strategy choices and metacognitive judgments during arithmetic problem-solving. Metacognitive judgments were collected either prospectively or retrospectively. We tested whether metacognitive judgments are related to strategy choices on the current problems and on the immediately following problems, and age-related differences in relations between metacognition and strategy choices. Data showed that both young and older adults were able to make accurate retrospective, but not prospective, judgments. Moreover, the accuracy of retrospective judgments was comparable in young and older adults when participants had to select and execute the better strategy. Metacognitive accuracy was even higher in older adults when participants had to only select the better strategy. Finally, low-confidence judgments on current items were more frequently followed by better strategy selection on immediately succeeding items than high-confidence judgments in both young and older adults. Implications of these findings to further our understanding of age-related differences and similarities in adults' metacognitive monitoring and metacognitive regulation for strategy selection in the context of arithmetic problem solving are discussed.

  8. The BANANA Project. IV. Two Aligned Stellar Rotation Axes in the Young Eccentric Binary System EP Crucis: Primordial Orientation and Tidal Alignment

    Science.gov (United States)

    Albrecht, Simon; Setiawan, Johny; Torres, Guillermo; Fabrycky, Daniel C.; Winn, Joshua N.

    2013-04-01

    With observations of the EP Cru system, we continue our series of measurements of spin-orbit angles in eclipsing binary star systems, the BANANA project (Binaries Are Not Always Neatly Aligned). We find a close alignment between the sky projections of the rotational and orbital angular momentum vectors for both stars (βp = -1.°8 ± 1.°6 and |βs| < 17°). We also derive precise absolute dimensions and stellar ages for this system. The EP Cru and DI Her systems provide an interesting comparison: they have similar stellar types and orbital properties, but DI Her is younger and has major spin-orbit misalignments, raising the question of whether EP Cru also had a large misalignment at an earlier phase of evolution. We show that tidal dissipation is an unlikely explanation for the good alignment observed today, because realignment happens on the same timescale as spin-orbit synchronization, and the stars in EP Cru are far from synchronization (they are spinning nine times too quickly). Therefore it seems that some binaries form with aligned axes, while other superficially similar binaries are formed with misaligned axes. Based on observations made with ESOs 2.2 m Telescopes at the La Silla Paranal Observatory under program ID 084.C-1008 (12.5%) and under MPIA guaranteed time (87.5%).

  9. Influences on selection of assistive technology for young children in South Africa: perspectives from rehabilitation professionals.

    Science.gov (United States)

    van Niekerk, Karin; Dada, Shakila; Tönsing, Kerstin

    2017-12-20

    Selection of assistive technology for young children is a complex process. Within a context with limited resources, such as South Africa, research is needed to determine the factors influencing the assistive technology selection process, as these could ultimately either facilitate or hinder the availability and accessibility of affordable, adaptable, acceptable, and high quality assistive technology for this age group. Two asynchronous online focus groups were conducted with 16 rehabilitation professionals to identify the factors they perceived to influence the selection and provision of assistive technology to young children within the South African context. A process of deductive thematic analysis was followed by inductive analysis of the data. Components of the Assistive Technology Device Selection Framework were used as themes to guide the deductive analysis, followed by inductive analysis to create subthemes. The important role of the professional was highlighted in negotiating all the factors to consider in the assistive technology selection and provision process. Adaptation of the Assistive Technology Device Selection Framework is suggested in order to facilitate application to low resourced contexts, such as South Africa. Implications for rehabilitation Assistive technology selection is a complex process with factors pertaining to the users (child and family) of the assistive technology, as well as the rehabilitation professional recommending the assistive technology influencing the process. Although it may be an important factor, the availability of financial resources to purchase assistive technology is not the only determining factor in providing appropriate assistive technology to young children in contexts with limited resources. Formalized support, such as reflective supervision or mentorship programs should be facilitated and utilized by recommending professionals. Home and school visits during assessment ensure a good match between assistive

  10. 3D-HST WFC3-SELECTED PHOTOMETRIC CATALOGS IN THE FIVE CANDELS/3D-HST FIELDS: PHOTOMETRY, PHOTOMETRIC REDSHIFTS, AND STELLAR MASSES

    Energy Technology Data Exchange (ETDEWEB)

    Skelton, Rosalind E. [South African Astronomical Observatory, PO Box 9, Observatory, Cape Town 7935 (South Africa); Whitaker, Katherine E. [Astrophysics Science Division, Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Momcheva, Ivelina G.; Van Dokkum, Pieter G.; Bezanson, Rachel; Leja, Joel; Nelson, Erica J.; Oesch, Pascal [Department of Astronomy, Yale University, 260 Whitney Avenue, New Haven, CT 06511 (United States); Brammer, Gabriel B. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Labbé, Ivo; Franx, Marijn; Fumagalli, Mattia [Leiden Observatory, Leiden University, Leiden (Netherlands); Van der Wel, Arjen; Da Cunha, Elisabete; Maseda, Michael V. [Max Planck Institute for Astronomy (MPIA), Königstuhl 17, D-69117, Heidelberg (Germany); Förster Schreiber, Natascha [Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany); Kriek, Mariska [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Lundgren, Britt F. [Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706 (United States); Magee, Daniel [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA (United States); Marchesini, Danilo, E-mail: ros@saao.ac.za [Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States); and others

    2014-10-01

    The 3D-HST and CANDELS programs have provided WFC3 and ACS spectroscopy and photometry over ≈900 arcmin{sup 2} in five fields: AEGIS, COSMOS, GOODS-North, GOODS-South, and the UKIDSS UDS field. All these fields have a wealth of publicly available imaging data sets in addition to the Hubble Space Telescope (HST) data, which makes it possible to construct the spectral energy distributions (SEDs) of objects over a wide wavelength range. In this paper we describe a photometric analysis of the CANDELS and 3D-HST HST imaging and the ancillary imaging data at wavelengths 0.3-8 μm. Objects were selected in the WFC3 near-IR bands, and their SEDs were determined by carefully taking the effects of the point-spread function in each observation into account. A total of 147 distinct imaging data sets were used in the analysis. The photometry is made available in the form of six catalogs: one for each field, as well as a master catalog containing all objects in the entire survey. We also provide derived data products: photometric redshifts, determined with the EAZY code, and stellar population parameters determined with the FAST code. We make all the imaging data that were used in the analysis available, including our reductions of the WFC3 imaging in all five fields. 3D-HST is a spectroscopic survey with the WFC3 and ACS grisms, and the photometric catalogs presented here constitute a necessary first step in the analysis of these grism data. All the data presented in this paper are available through the 3D-HST Web site (http://3dhst.research.yale.edu)

  11. 3D-HST WFC3-selected Photometric Catalogs in the Five CANDELS/3D-HST Fields: Photometry, Photometric Redshifts, and Stellar Masses

    Science.gov (United States)

    Skelton, Rosalind E.; Whitaker, Katherine E.; Momcheva, Ivelina G.; Brammer, Gabriel B.; van Dokkum, Pieter G.; Labbé, Ivo; Franx, Marijn; van der Wel, Arjen; Bezanson, Rachel; Da Cunha, Elisabete; Fumagalli, Mattia; Förster Schreiber, Natascha; Kriek, Mariska; Leja, Joel; Lundgren, Britt F.; Magee, Daniel; Marchesini, Danilo; Maseda, Michael V.; Nelson, Erica J.; Oesch, Pascal; Pacifici, Camilla; Patel, Shannon G.; Price, Sedona; Rix, Hans-Walter; Tal, Tomer; Wake, David A.; Wuyts, Stijn

    2014-10-01

    The 3D-HST and CANDELS programs have provided WFC3 and ACS spectroscopy and photometry over ≈900 arcmin2 in five fields: AEGIS, COSMOS, GOODS-North, GOODS-South, and the UKIDSS UDS field. All these fields have a wealth of publicly available imaging data sets in addition to the Hubble Space Telescope (HST) data, which makes it possible to construct the spectral energy distributions (SEDs) of objects over a wide wavelength range. In this paper we describe a photometric analysis of the CANDELS and 3D-HST HST imaging and the ancillary imaging data at wavelengths 0.3-8 μm. Objects were selected in the WFC3 near-IR bands, and their SEDs were determined by carefully taking the effects of the point-spread function in each observation into account. A total of 147 distinct imaging data sets were used in the analysis. The photometry is made available in the form of six catalogs: one for each field, as well as a master catalog containing all objects in the entire survey. We also provide derived data products: photometric redshifts, determined with the EAZY code, and stellar population parameters determined with the FAST code. We make all the imaging data that were used in the analysis available, including our reductions of the WFC3 imaging in all five fields. 3D-HST is a spectroscopic survey with the WFC3 and ACS grisms, and the photometric catalogs presented here constitute a necessary first step in the analysis of these grism data. All the data presented in this paper are available through the 3D-HST Web site (http://3dhst.research.yale.edu).

  12. 3D-HST WFC3-SELECTED PHOTOMETRIC CATALOGS IN THE FIVE CANDELS/3D-HST FIELDS: PHOTOMETRY, PHOTOMETRIC REDSHIFTS, AND STELLAR MASSES

    International Nuclear Information System (INIS)

    Skelton, Rosalind E.; Whitaker, Katherine E.; Momcheva, Ivelina G.; Van Dokkum, Pieter G.; Bezanson, Rachel; Leja, Joel; Nelson, Erica J.; Oesch, Pascal; Brammer, Gabriel B.; Labbé, Ivo; Franx, Marijn; Fumagalli, Mattia; Van der Wel, Arjen; Da Cunha, Elisabete; Maseda, Michael V.; Förster Schreiber, Natascha; Kriek, Mariska; Lundgren, Britt F.; Magee, Daniel; Marchesini, Danilo

    2014-01-01

    The 3D-HST and CANDELS programs have provided WFC3 and ACS spectroscopy and photometry over ≈900 arcmin 2 in five fields: AEGIS, COSMOS, GOODS-North, GOODS-South, and the UKIDSS UDS field. All these fields have a wealth of publicly available imaging data sets in addition to the Hubble Space Telescope (HST) data, which makes it possible to construct the spectral energy distributions (SEDs) of objects over a wide wavelength range. In this paper we describe a photometric analysis of the CANDELS and 3D-HST HST imaging and the ancillary imaging data at wavelengths 0.3-8 μm. Objects were selected in the WFC3 near-IR bands, and their SEDs were determined by carefully taking the effects of the point-spread function in each observation into account. A total of 147 distinct imaging data sets were used in the analysis. The photometry is made available in the form of six catalogs: one for each field, as well as a master catalog containing all objects in the entire survey. We also provide derived data products: photometric redshifts, determined with the EAZY code, and stellar population parameters determined with the FAST code. We make all the imaging data that were used in the analysis available, including our reductions of the WFC3 imaging in all five fields. 3D-HST is a spectroscopic survey with the WFC3 and ACS grisms, and the photometric catalogs presented here constitute a necessary first step in the analysis of these grism data. All the data presented in this paper are available through the 3D-HST Web site (http://3dhst.research.yale.edu)

  13. Advanced stellarator power plants

    International Nuclear Information System (INIS)

    Miller, R.L.

    1994-01-01

    The stellarator is a class of helical/toroidal magnetic fusion devices. Recent international progress in stellarator power plant conceptual design is reviewed and comparisons in the areas of physics, engineering, and economics are made with recent tokamak design studies

  14. Selective attention affects conceptual object priming and recognition: A study with young and older adults

    OpenAIRE

    Soledad eBallesteros; Julia eMayas

    2015-01-01

    In the present study, we investigated the effects of selective attention at encoding on conceptual object priming (Experiment 1) and old–new recognition memory (Experiment 2) tasks in young and older adults. The procedures of both experiments included encoding and memory test phases separated by a short delay. At encoding, the picture outlines of two familiar objects, one in blue and the other in green, were presented to the left and to the right of fixation. In Experiment 1, participants wer...

  15. Ageing Drosophila selected for longevity retain a young gene expression profile

    DEFF Research Database (Denmark)

    Sarup, Pernille Merete

    and longevity selected lines. Among the latter genes we found a clear overrepresentation of genes involved in immune functions supporting the hypothesis of the life shortening effect of an overactive immune system (inflammaging). Eighty-four genes were differentially expressed at the same physiological age...... between control and longevity selected lines, and the overlap between the same chronological and physiological age gene lists counted 40 candidate genes for increased longevity. Among these were genes with functions in starvation resistance, a regulator of immune responses and several genes which have......  We have investigated how the gene-expression profile of longevity selected lines of Drosophila melanogaster differed from control lines in young, middle-aged and old male flies. 530 genes were differentially expressed between selected and control flies at the same chronological age. We used...

  16. Selection of performance-tested young bulls and indirect responses in commercial beef cattle herds on pasture and in feedlots

    OpenAIRE

    Raidan , Fernanda S. S.; Santos , Dalinne C. C.; Moraes , Mariana M.; Araújo , Andresa E. M.; Ventura , Henrique T.; Bergmann , José A. G.; Turra , Eduardo M.; Toral , Fabio L. B.

    2016-01-01

    International audience; AbstractBackgroundCentral testing is used to select young bulls which are likely to contribute to increased net income of the commercial beef cattle herd. We present genetic parameters for growth and reproductive traits on performance-tested young bulls and commercial animals that are raised on pasture and in feedlots.MethodsRecords on young bulls and heifers in performance tests or commercial herds were used. Genetic parameters for growth and reproductive traits were ...

  17. A STRING OF RADIO EMISSION ASSOCIATED WITH IRAS 16562-3959: A COLLIMATED JET EMANATING FROM A LUMINOUS MASSIVE YOUNG STELLAR OBJECT

    International Nuclear Information System (INIS)

    Guzman, Andres E.; Garay, Guido; Brooks, Kate J.

    2010-01-01

    We report the discovery, made using the Australia Telescope Compact Array, of a remarkable string of radio emission toward IRAS 16562-3959, a luminous infrared source with a bolometric luminosity of 7.0 x 10 4 L sun . The radio emission arises from a compact, bright central component, two inner lobes which are separated by about 7'' and symmetrically offset from the central source, and two outer lobes which are separated by about 45''. The emission from the central object has a spectral index between 1.4 and 8.6 GHz of 0.85 ± 0.15, consistent with free-free emission from a thermal jet. The radio emission from the lobes has spectral indices in the range characteristic of thermal emission. We suggest that the emission from the lobes arises in shocks resulting from the interaction of a collimated wind with the surrounding medium. The radio string is located within a massive dense molecular core, and is associated with extended green emission (Spitzer three-color), Herbig-Haro-type emission (2MASS K s band), and OH maser sites-all phenomena readily observed toward sites of massive star formation. We conclude that the massive core hosts a high-mass star in an early stage of evolution in which it is undergoing the ejection of a powerful collimated stellar wind, showing that jets found in the formation of low-mass stars are also produced in high-mass stars.

  18. DIFFERENCES BETWEEN YOUNG (13-14 YEARS OF AGE WATER POLO PLAYERS SELECTED AND NOT SELECTED TO THE NATIONAL TEAM

    Directory of Open Access Journals (Sweden)

    Igor Štirn

    2010-09-01

    Full Text Available Young water polo players at age 13 to 14 years were examined once a year in a four- year period using three morphological and eight specific skill tests: body height and mass, vital capacity, swimming at distances 5, 25 and 200 meters, swimming 4x5 meters with changing directions, ball dribbling, vertical jump and reach, vertical eggbeater kick and velocity of a throw at the goal. From the sum of 139 players tested, a group of 73 non-selected and of 66 selected players to the national team (U16, wider selection were formed and checked for differences. Differences in all observed variables (except body mass were found between the groups (P<0.05. One significant discriminant function was revealed (canonical R = 0.52 and the accounted variance was 100 %, P = 0.000. The variables that most differentiated the groups were swimming tests at distances of 25 and 200 meters, followed by vertical-egg beater kick and throwing velocity, while morphological variables differentiated the groups least.

  19. Stellar structure and evolution

    International Nuclear Information System (INIS)

    Kippernhahn, R.; Weigert, A.

    1990-01-01

    This book introduces the theory of the internal structure of stars and their evolution in time. It presents the basic physics of stellar interiors, methods for solving the underlying equations, and the most important results necessary for understanding the wide variety of stellar types and phenomena. The evolution of stars is discussed from their birth through normal evolution to possibly spectacular final stages. Chapters on stellar oscillations and rotation are included

  20. Selective attention affects conceptual object priming and recognition: a study with young and older adults.

    Science.gov (United States)

    Ballesteros, Soledad; Mayas, Julia

    2014-01-01

    In the present study, we investigated the effects of selective attention at encoding on conceptual object priming (Experiment 1) and old-new recognition memory (Experiment 2) tasks in young and older adults. The procedures of both experiments included encoding and memory test phases separated by a short delay. At encoding, the picture outlines of two familiar objects, one in blue and the other in green, were presented to the left and to the right of fixation. In Experiment 1, participants were instructed to attend to the picture outline of a certain color and to classify the object as natural or artificial. After a short delay, participants performed a natural/artificial speeded conceptual classification task with repeated attended, repeated unattended, and new pictures. In Experiment 2, participants at encoding memorized the attended pictures and classify them as natural or artificial. After the encoding phase, they performed an old-new recognition memory task. Consistent with previous findings with perceptual priming tasks, we found that conceptual object priming, like explicit memory, required attention at encoding. Significant priming was obtained in both age groups, but only for those pictures that were attended at encoding. Although older adults were slower than young adults, both groups showed facilitation for attended pictures. In line with previous studies, young adults had better recognition memory than older adults.

  1. Selective attention affects conceptual object priming and recognition: A study with young and older adults

    Directory of Open Access Journals (Sweden)

    Soledad eBallesteros

    2015-01-01

    Full Text Available In the present study, we investigated the effects of selective attention at encoding on conceptual object priming (Experiment 1 and old-new recognition memory (Experiment 2 tasks in young and older adults. The procedures of both experiments included encoding and memory test phases separated by a short delay. At encoding, the picture outlines of two familiar objects, one in blue and the other in green, were presented to the left and to the right of fixation. In Experiment 1, participants were instructed to attend to the picture outline of a certain color and to classify the object as natural or artificial. After a short delay, participants performed a natural/ artificial speeded conceptual classification task with repeated attended, repeated unattended and new pictures. In Experiment 2, participants at encoding memorized the attended pictures and classified them as natural or artificial. After the encoding phase, they performed an old-new recognition memory task. Consistent with previous findings with perceptual priming tasks, we found that conceptual object priming, like explicit memory, required attention at encoding. Significant priming was obtained in both age groups, but only for those pictures that were attended at encoding. Although older adults were slower than young adults, both groups showed facilitation for attended pictures. In line with previous studies, young adults had better recognition memory than older adults.

  2. Models for stellar flares

    International Nuclear Information System (INIS)

    Cram, L.E.; Woods, D.T.

    1982-01-01

    We study the response of certain spectral signatures of stellar flares (such as Balmer line profiles and the broad-band continuum) to changes in atmospheric structure which might result from physical processes akin to those thought to occur in solar flares. While each physical process does not have a unique signature, we can show that some of the observed properties of stellar flares can be explained by a model which involves increased pressures and temperatures in the flaring stellar chromosphere. We suggest that changes in stellar flare area, both with time and with depth in the atmosphere, may play an important role in producing the observed flare spectrum

  3. Stellar Physics 2: Stellar Evolution and Stability

    CERN Document Server

    Bisnovatyi-Kogan, Gennady S

    2011-01-01

    "Stellar Physics" is a an outstanding book in the growing body of literature on star formation and evolution. Not only does the author, a leading expert in the field, very thoroughly present the current state of knowledge on stellar physics, but he handles with equal care the many problems that this field of research still faces. A bibliography with well over 1000 entries makes this book an unparalleled reference source. "Stellar Evolution and Stability" is the second of two volumes and can be read, as can the first volume "Fundamental Concepts and Stellar Equilibrium," as a largely independent work. It traces in great detail the evolution of protostars towards the main sequence and beyond this to the last stage of stellar evolution, with the corresponding vast range from white dwarfs to supernovae explosions, gamma-ray bursts and black hole formation. The book concludes with special chapters on the dynamical, thermal and pulsing stability of stars. This second edition is carefully updated in the areas of pre...

  4. COMPARATIVE ANALYSIS OF BEHAVIOURS RELATED TO FUNCTIONAL FOODS AMONG SELECTED YOUNG CONSUMERS IN POLAND AND GERMANY

    Directory of Open Access Journals (Sweden)

    Magdalena Zegan

    2016-12-01

    Full Text Available Nutrition is one of the key factors infl uencing human health. Consuming foods that either naturally contain or have been enriched with bioactive substances may aid the organism’s proper development and functioning and, most importantly, be a vital element in the prophylaxis of many non-communicable diseases as well as improve general sense of well-being. The aim of the study was to compare behaviours related to functional foods among a selected group of young people. The survey was conducted among 153 purposively selected young consumers from Poland and Germany in March/April 2015. An original survey questionnaire was employed. IBM SPSS Statistics ver. 23 software was used for statistical analysis (chi-squared test p < 0.05. The term “functional foods” was largely unknown among the respondents. A defi nite majority of the survey participants reported having bought and consumed products that, in fact, belong to this group of foods. The main source of information on the topic of functional foods was the Internet. While buying these products, respondents from both countries chiefl y took into account the price, the quality and the list of ingredients. The results point to the need to popularize information about functional foods using trustworthy sources, in order to foster nutritional awareness. Consumer knowledge is the basis for the positive perception and acceptance of health-promoting foods and for making rational dietary choices. 

  5. Habitat selection and seasonal movements of young bearded seals (Erignathus barbatus in the Bering Sea.

    Directory of Open Access Journals (Sweden)

    Michael F Cameron

    Full Text Available The first year of life is typically the most critical to a pinniped's survival, especially for Arctic phocids which are weaned at only a few weeks of age and left to locate and capture prey on their own. Their seasonal movements and habitat selection are therefore important factors in their survival. During a cooperative effort between scientists and subsistence hunters in October 2004, 2005, and 2006, 13 female and 13 male young (i.e., age <2 bearded seals (Erignathus barbatus were tagged with satellite-linked dive recorders (SDRs in Kotzebue Sound, Alaska. Shortly after being released, most seals moved south with the advancing sea-ice through the Bering Strait and into the Bering Sea where they spent the winter and early spring. The SDRs of 17 (8 female and 9 male seals provided frequent high-quality positions in the Bering Sea; their data were used in our analysis. To investigate habitat selection, we simulated 20 tracks per seal by randomly selecting from the pooled distributions of the absolute bearings and swim speeds of the tagged seals. For each point in the observed and simulated tracks, we obtained the depth, sea-ice concentration, and the distances to sea-ice, open water, the shelf break and coastline. Using logistic regression with a stepwise model selection procedure, we compared the simulated tracks to those of the tagged seals and obtained a model for describing habitat selection. The regression coefficients indicated that the bearded seals in our study selected locations near the ice edge. In contrast, aerial surveys of the bearded seal population, predominantly composed of adults, indicated higher abundances in areas farther north and in heavier pack ice. We hypothesize that this discrepancy is the result of behavioral differences related to age. Ice concentration was also shown to be a statistically significant variable in our model. All else being equal, areas of higher ice concentration are selected for up to about 80%. The

  6. Stellar photometry and polarimetry

    International Nuclear Information System (INIS)

    Golay, M.; Serkowski, K.

    1976-01-01

    A critical review of progress made in stellar photometry and polarimetry over the period 1973-1975 is presented. Reports of photometric measurements from various observatories throughout the world are summarized. The summary of work on stellar polarimetry lists the review papers, the catalogues and lists of standard stars, and descriptions of new observing techniques. (B.R.H.)

  7. Compact stellarators as reactors

    International Nuclear Information System (INIS)

    Lyon, J.F.; Valanju, P.; Zarnstorff, M.C.; Hirshman, S.; Spong, D.A.; Strickler, D.; Williamson, D.E.; Ware, A.

    2001-01-01

    Two types of compact stellarators are examined as reactors: two- and three-field-period (M=2 and 3) quasi-axisymmetric devices with volume-average =4-5% and M=2 and 3 quasi-poloidal devices with =10-15%. These low-aspect-ratio stellarator-tokamak hybrids differ from conventional stellarators in their use of the plasma-generated bootstrap current to supplement the poloidal field from external coils. Using the ARIES-AT model with B max =12T on the coils gives Compact Stellarator reactors with R=7.3-8.2m, a factor of 2-3 smaller R than other stellarator reactors for the same assumptions, and neutron wall loadings up to 3.7MWm -2 . (author)

  8. Modular Stellarator Fusion Reactor concept

    International Nuclear Information System (INIS)

    Miller, R.L.; Krakowski, R.A.

    1981-08-01

    A preliminary conceptual study is made of the Modular Stellarator Reactor (MSR). A steady-state ignited, DT-fueled, magnetic fusion reactor is proposed for use as a central electric-power station. The MSR concept combines the physics of the classic stellarator confinement topology with an innovative, modular-coil design. Parametric tradeoff calculations are described, leading to the selection of an interim design point for a 4-GWt plant based on Alcator transport scaling and an average beta value of 0.04 in an l = 2 system with a plasma aspect ratio of 11. The physics basis of the design point is described together with supporting magnetics, coil-force, and stress computations. The approach and results presented herein will be modified in the course of ongoing work to form a firmer basis for a detailed conceptual design of the MSR

  9. You are what you choose to eat: factors influencing young adults' food selection behaviour.

    Science.gov (United States)

    Hebden, L; Chan, H N; Louie, J C; Rangan, A; Allman-Farinelli, M

    2015-08-01

    Young or 'emerging' adulthood (ages 18-24 years) is a life-stage characterised by rapid weight gain, particularly among those born in recent decades, when environments have become saturated with cheap, highly palatable, processed foods. Although intervening in the immediate food environments of emerging adults is indicated, little is known about the factors influencing their food selection. The present study aimed to: (i) measure the relative importance of different influences on foods selected by emerging adults for consumption from a tertiary education setting and (ii) examine whether these influences differ according to gender, adiposity status, perceived stress and dieting or physical activity behaviours. An online survey was administered with 112 emerging adults aged 19-24 years assessing demographics, perceived stress, dieting, physical activity and influences on food selection. Adiposity indicators (body mass index and waist circumference) were measured. Analyses compared the importance of influences on food selection by gender, adiposity, perceived stress, dieting and physical activity. Taste was the most important influence on food selection, followed by convenience (availability), cost, nutrition/health value, smell and stimulatory properties (alertness). Participants with an elevated waist circumference selected foods to help them cope with stress and control their weight. Those reporting a higher level of physical activity placed greater importance on nutritional/health value of foods but less importance on taste. Female dieters also placed less importance on taste and value for money. Health promotion strategies addressing tertiary education food environments of emerging adults should ensure the ready availability of tasty and nutritious foods at a low cost. © 2015 The British Dietetic Association Ltd.

  10. BANYAN. IV. Fundamental parameters of low-mass star candidates in nearby young stellar kinematic groups—isochronal age determination using magnetic evolutionary models

    Energy Technology Data Exchange (ETDEWEB)

    Malo, Lison; Doyon, René; Albert, Loïc; Lafrenière, David; Artigau, Étienne; Gagné, Jonathan [Département de physique and Observatoire du Mont-Mégantic, Université de Montréal, Montréal, QC H3C 3J7 (Canada); Feiden, Gregory A. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Riedel, Adric, E-mail: malo@cfht.hawaii.edu, E-mail: doyon@astro.umontreal.ca [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States)

    2014-09-01

    Based on high-resolution optical spectra obtained with ESPaDOnS at Canada-France-Hawaii Telescope, we determine fundamental parameters (T {sub eff}, R, L {sub bol}, log g, and metallicity) for 59 candidate members of nearby young kinematic groups. The candidates were identified through the BANYAN Bayesian inference method of Malo et al., which takes into account the position, proper motion, magnitude, color, radial velocity, and parallax (when available) to establish a membership probability. The derived parameters are compared to Dartmouth magnetic evolutionary models and field stars with the goal of constraining the age of our candidates. We find that, in general, low-mass stars in our sample are more luminous and have inflated radii compared to older stars, a trend expected for pre-main-sequence stars. The Dartmouth magnetic evolutionary models show a good fit to observations of field K and M stars, assuming a magnetic field strength of a few kG, as typically observed for cool stars. Using the low-mass members of the β Pictoris moving group, we have re-examined the age inconsistency problem between lithium depletion age and isochronal age (Hertzspring-Russell diagram). We find that the inclusion of the magnetic field in evolutionary models increases the isochronal age estimates for the K5V-M5V stars. Using these models and field strengths, we derive an average isochronal age between 15 and 28 Myr and we confirm a clear lithium depletion boundary from which an age of 26 ± 3 Myr is derived, consistent with previous age estimates based on this method.

  11. Dress Nicer = Know More? Young Children's Knowledge Attribution and Selective Learning Based on How Others Dress.

    Directory of Open Access Journals (Sweden)

    Kyla P McDonald

    Full Text Available This research explored whether children judge the knowledge state of others and selectively learn novel information from them based on how they dress. The results indicated that 4- and 6-year-olds identified a formally dressed individual as more knowledgeable about new things in general than a casually dressed one (Study 1. Moreover, children displayed an overall preference to seek help from a formally dressed individual rather than a casually dressed one when learning about novel objects and animals (Study 2. These findings are discussed in relation to the halo effect, and may have important implications for child educators regarding how instructor dress might influence young students' knowledge attribution and learning preferences.

  12. Stellarator-Spheromak

    International Nuclear Information System (INIS)

    Moroz, P.E.

    1997-03-01

    A novel concept for magnetic plasma confinement, Stellarator-Spheromak (SSP), is proposed. Numerical analysis with the classical-stellarator-type outboard stellarator windings demonstrates a number of potential advantages of SSP for controlled nuclear fusion. Among the main ones are: simple and compact magnet coil configuration, absence of material structures (e.g. magnet coils or conducting walls) in the center of the torus, high rotational transform, and a possibility of MHD equilibria with very high β (pressure/magnetic pressure) of the confined plasma

  13. Double-helix stellarator

    International Nuclear Information System (INIS)

    Moroz, P.E.

    1997-09-01

    A new stellarator configuration, the Double-Helix Stellarator (DHS), is introduced. This novel configuration features a double-helix center post as the only helical element of the stellarator coil system. The DHS configuration has many unique characteristics. One of them is the extreme low plasma aspect ratio, A ∼ 1--1.2. Other advantages include a high enclosed volume, appreciable rotational transform, and a possibility of extreme-high-β MHD equilibria. Moreover, the DHS features improved transport characteristics caused by the absence of the magnetic field ripple on the outboard of the torus. Compactness, simplicity and modularity of the coil system add to the DHS advantages for fusion applications

  14. Wimps and stellar structure

    International Nuclear Information System (INIS)

    Bouquet, A.; Salati, P.

    1988-01-01

    We present the results of an analytic approximation to compute the effects of WIMPs on stellar structures in a self-consistent way. We examine in particular the case of the Sun and of horizontal branch stars

  15. Principles of Stellar Interferometry

    CERN Document Server

    Glindemann, Andreas

    2011-01-01

    Over the last decade, stellar interferometry has developed from a specialist tool to a mainstream observing technique, attracting scientists whose research benefits from milliarcsecond angular resolution. Stellar interferometry has become part of the astronomer’s toolbox, complementing single-telescope observations by providing unique capabilities that will advance astronomical research. This carefully written book is intended to provide a solid understanding of the principles of stellar interferometry to students starting an astronomical research project in this field or to develop instruments and to astronomers using interferometry but who are not interferometrists per se. Illustrated by excellent drawings and calculated graphs the imaging process in stellar interferometers is explained starting from first principles on light propagation and diffraction wave propagation through turbulence is described in detail using Kolmogorov statistics the impact of turbulence on the imaging process is discussed both f...

  16. Convection and stellar oscillations

    DEFF Research Database (Denmark)

    Aarslev, Magnus Johan

    2017-01-01

    for asteroseismology, because of the challenges inherent in modelling turbulent convection in 1D stellar models. As a result of oversimplifying the physics near the surface, theoretical calculations systematically overestimate the oscillation frequencies. This has become known as the asteroseismic surface effect. Due...... to lacking better options, this frequency difference is typically corrected for with ad-hoc formulae. The topic of this thesis is the improvement of 1D stellar convection models and the effects this has on asteroseismic properties. The source of improvements is 3D simulations of radiation...... atmospheres to replace the outer layers of stellar models. The additional turbulent pressure and asymmetrical opacity effects in the atmosphere model, compared to convection in stellar evolution models, serve to expand the atmosphere. The enlarged acoustic cavity lowers the pulsation frequencies bringing them...

  17. STELLAR MASS DEPENDENT DISK DISPERSAL

    International Nuclear Information System (INIS)

    Kennedy, Grant M.; Kenyon, Scott J.

    2009-01-01

    We use published optical spectral and infrared (IR) excess data from nine young clusters and associations to study the stellar mass dependent dispersal of circumstellar disks. All clusters older than ∼3 Myr show a decrease in disk fraction with increasing stellar mass for solar to higher mass stars. This result is significant at about the 1σ level in each cluster. For the complete set of clusters we reject the null hypothesis-that solar and intermediate-mass stars lose their disks at the same rate-with 95%-99.9% confidence. To interpret this behavior, we investigate the impact of grain growth, binary companions, and photoevaporation on the evolution of disk signatures. Changes in grain growth timescales at fixed disk temperature may explain why early-type stars with IR excesses appear to evolve faster than their later-type counterparts. Little evidence that binary companions affect disk evolution suggests that photoevaporation is the more likely mechanism for disk dispersal. A simple photoevaporation model provides a good fit to the observed disk fractions for solar and intermediate-mass stars. Although the current mass-dependent disk dispersal signal is not strong, larger and more complete samples of clusters with ages of 3-5 Myr can improve the significance and provide better tests of theoretical models. In addition, the orbits of extra-solar planets can constrain models of disk dispersal and migration. We suggest that the signature of stellar mass dependent disk dispersal due to photoevaporation may be present in the orbits of observed extra-solar planets. Planets orbiting hosts more massive than ∼1.6 M sun may have larger orbits because the disks in which they formed were dispersed before they could migrate.

  18. Oscillations in stellar atmospheres

    International Nuclear Information System (INIS)

    Costa, A.; Ringuelet, A.E.; Fontenla, J.M.

    1989-01-01

    Atmospheric excitation and propagation of oscillations are analyzed for typical pulsating stars. The linear, plane-parallel approach for the pulsating atmosphere gives a local description of the phenomenon. From the local analysis of oscillations, the minimum frequencies are obtained for radially propagating waves. The comparison of the minimum frequencies obtained for a variety of stellar types is in good agreement with the observed periods of the oscillations. The role of the atmosphere in the globar stellar pulsations is thus emphasized. 7 refs

  19. Probing the Dusty Stellar Populations of the Local Volume Galaxies with JWST /MIRI

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Olivia C.; Meixner, Margaret [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States); Justtanont, Kay [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala (Sweden); Glasse, Alistair [UK Astronomy Technology Centre, Royal Observatory, Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)

    2017-05-20

    The Mid-Infrared Instrument (MIRI) for the James Webb Space Telescope ( JWST ) will revolutionize our understanding of infrared stellar populations in the Local Volume. Using the rich Spitzer -IRS spectroscopic data set and spectral classifications from the Surveying the Agents of Galaxy Evolution (SAGE)–Spectroscopic survey of more than 1000 objects in the Magellanic Clouds, the Grid of Red Supergiant and Asymptotic Giant Branch Star Model (grams), and the grid of YSO models by Robitaille et al., we calculate the expected flux densities and colors in the MIRI broadband filters for prominent infrared stellar populations. We use these fluxes to explore the JWST /MIRI colors and magnitudes for composite stellar population studies of Local Volume galaxies. MIRI color classification schemes are presented; these diagrams provide a powerful means of identifying young stellar objects, evolved stars, and extragalactic background galaxies in Local Volume galaxies with a high degree of confidence. Finally, we examine which filter combinations are best for selecting populations of sources based on their JWST colors.

  20. Anthropometric analysis and performance characteristics to predict selection in young male and female handball players

    Directory of Open Access Journals (Sweden)

    Juan J. Fernández-Romero

    Full Text Available Abstract The aim of this study was two-fold. The first aim was to determine if there were any anthropometric and physical performance differences (controlling for maturation between male and female handball players selected in training categories as well asthe relation of these differences with the performance level achieved. The second aim was to identify the discriminatory variables between the performance levels achieved. A total of 216 young handball players (125 men and 91 women participated in the study. The data were classified by selection level (regional n=154; national n=62, gender (men; women and age category (under-15; under-17. The use of MANCOVA analyses, controllingfor maturation, identified how gender could determine variables related to handball players' future competitive levels. The results revealed that anthropometric variables such as height, arm span, trochanter height, thigh girth, and leg girth were more influential in men than in women. In addition, the physical performance tests of vertical jump (squat jump and counter movement jump with/without arm and 10x5m shuttle run were determinants in both sexes. Discriminatory analysis predicted that a combination of five variables (counter movement jump with arm, body mass, 10x5m shuttle run, dominant hand length and trochanter height would successfully distinguish between regional and national players, with a predictive accuracy of 81.9% for all players.

  1. Galaxies in x-ray selected clusters and groups in Dark Energy Survey Data I: Stellar mass growth of bright central galaxies since Z similar to 1.2

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Y.; Miller, C.; McKay, T.; Rooney, P.; Evrard, A. E.; Romer, A. K.; Perfecto, R.; Song, J; Desai, S.; Mohr, J. J.; Vikram, V.

    2016-01-10

    Using the science verification data of the Dark Energy Survey for a new sample of 106 X-ray selected clusters and groups, we study the stellar mass growth of bright central galaxies (BCGs) since redshift z similar to 1.2. Compared with the expectation in a semi-analytical model applied to the Millennium Simulation, the observed BCGs become under-massive/under-luminous with decreasing redshift. We incorporate the uncertainties associated with cluster mass, redshift, and BCG stellar mass measurements into an analysis of a redshift-dependent BCG-cluster mass relation, m(*) proportional to (M-200/1.5 x 10(14)M(circle dot))(0.24 +/- 0.08)(1+z)(-0.19 +/- 0.34), and compare the observed relation to the model prediction. We estimate the average growth rate since z = 1.0 for BCGs hosted by clusters of M-200,M-z = 10(13.8)M(circle dot); at z = 1.0: m(*, BCG) appears to have grown by 0.13 +/- 0.11 dex, in tension at the similar to 2.5 sigma significance level with the 0.40 dex growth rate expected from the semi-analytic model. We show that the build-up of extended intracluster light after z = 1.0 may alleviate this tension in BCG growth rates.

  2. Effect of Ramadan intermittent fasting on selective fitness profile parameters in young untrained Muslim men.

    Science.gov (United States)

    Roy, Anindita Singha; Bandyopadhyay, Amit

    2015-01-01

    The present study was aimed at investigating the effects of sleep deprivation and dietary irregularities during Ramadan intermittent fasting (RIF) on selective fitness profile parameters in young untrained male Muslim individuals. 77 untrained Muslim men were recruited in the study. They were divided into the experimental group (EG; n=37, age: 22.62±1.77 years) and the control group (CG; n=40, age: 23.00±1.48 years). EG was undergoing RIF while CG abstained. Aerobic fitness, anaerobic capacity or high-intensity efforts (HIEs), agility, flexibility, vertical jump height and handgrip strength were measured on 8 separate occasions-15 days before RIF, 7 days before RIF, 1st day of RIF, 7th day of RIF, 15th day of RIF, 21st day of RIF, last day of RIF and 15 days after RIF. Aerobic fitness and HIE showed a significant difference (p<0.05) during RIF in EG. Agility and flexibility score showed a significant decrease in EG during RIF, whereas changes in the vertical jump score (VJT) and handgrip strength were statistically insignificant. Studied parameters showed an insignificant variation in CG during RIF. Aerobic fitness, HIEs, agility and flexibility showed a significant intergroup variation during different experimental trials. The present investigation revealed that RIF had adverse effects on aerobic fitness, HIEs, agility and flexibility of young untrained Muslims of Kolkata, India. VJT, waist-hip ratio and handgrip strength were not affected by RIF in the studied population. Mild but statistically insignificant reduction in body mass was also reflected after the mid-Ramadan week.

  3. PREFACE: A Stellar Journey A Stellar Journey

    Science.gov (United States)

    Asplund, M.

    2008-10-01

    The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor at Stockholm University and two years as director of the Sigtuna foundation, Bengt has forged his illustrious professional career at Uppsala University. The symposium venue was Museum Gustavianum, once the main building of the oldest university in Scandinavia. The title of the symposium is a paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in English: Cosmic Journey) written in the early eighties. I think this aptly symbolizes his career that has been an astronomical voyage from near to far, from the distant past to the present. The original book title was modified slightly to reflect that most of his work to date has dealt with stars in one way or another. In addition it also gives credit to Bengt's important role as a guiding light for a very large number of students, colleagues and collaborators, indeed for several generations of astronomers. For me personally, the book Kosmisk Resa bears particular significance as it has shaped my life rather profoundly. Although I had already decided to become an astronomer, when I first read the book as a 14-year-old I made up my mind then and there that I would study under Bengt Gustafsson and work on stars. Indeed I have remained true to this somewhat audacious resolution. I suspect that a great number of us have similar stories how Bengt has had a major influence on our lives, whether on the professional or personal level. Perhaps Bengt's most outstanding characteristic is his enthralling enthusiasm. This is equally true whether he is pondering some scientific conundrum, supervising students or performing in front of an audience, be it an

  4. Stellar magnetic activity

    International Nuclear Information System (INIS)

    Schrijver, C.J.

    1986-01-01

    The stellar emission in the chromospheric Ca II H+K lines is compared with the coronal soft X-ray emission, measuring the effects of non-radiative heating in the outer atmosphere at temperatures differing two orders of magnitude. The comparison of stellar flux densities in Ca II H+K and X-rays is extended to fluxes from the transition-region and the high-temperature chromosphere. The stellar magnetic field is probably generated in the differentially rotating convective envelope. The relation between rotation rate and the stellar level of activity measured in chromospheric, transition-region, and coronal radiative diagnostics is discovered. X-ray observations of the binary λ Andromedae are discussed. The departure of M-type dwarfs from the main relations, and the implications for the structure of the chromospheres of these stars are discussed. Variations of the average surface flux densities of the Sun during the 11-year activity cycle agree with flux-flux relations derived for other cool stars, suggesting that the interpretation of the stellar relations may be furthered by studying the solar analogue in more detail. (Auth.)

  5. Selection of performance-tested young bulls and indirect responses in commercial beef cattle herds on pasture and in feedlots.

    Science.gov (United States)

    Raidan, Fernanda S S; Santos, Dalinne C C; Moraes, Mariana M; Araújo, Andresa E M; Ventura, Henrique T; Bergmann, José A G; Turra, Eduardo M; Toral, Fabio L B

    2016-11-09

    Central testing is used to select young bulls which are likely to contribute to increased net income of the commercial beef cattle herd. We present genetic parameters for growth and reproductive traits on performance-tested young bulls and commercial animals that are raised on pasture and in feedlots. Records on young bulls and heifers in performance tests or commercial herds were used. Genetic parameters for growth and reproductive traits were estimated. Correlated responses for commercial animals when selection was applied on performance-tested young bulls were computed. The 90% highest posterior density (HPD90) intervals for heritabilities of final weight (FW), average daily gain (ADG) and scrotal circumference (SC) ranged from 0.41 to 0.49, 0.23 to 0.30 and 0.47 to 0.57, respectively, for performance-tested young bulls on pasture, from 0.45 to 0.60, 0.20 to 0.32 and 0.56 to 0.70, respectively, for performance-tested young bulls in feedlots, from 0.29 to 0.33, 0.14 to 0.18 and 0.35 to 0.45, respectively, for commercial animals on pasture, and from 0.24 to 0.44, 0.13 to 0.24 and 0.35 to 0.57 respectively, for commercial animals in feedlots. The HPD90 intervals for genetic correlations of FW, ADG and SC in performance-tested young bulls on pasture (feedlots) with FW, ADG and SC in commercial animals on pasture (feedlots) ranged from 0.86 to 0.96 (0.83 to 0.94), 0.78 to 0.90 (0.40 to 0.79) and from 0.92 to 0.97 (0.50 to 0.83), respectively. Age at first calving was genetically related to ADG (HPD90 interval = -0.48 to -0.06) and SC (HPD90 interval = -0.41 to -0.05) for performance-tested young bulls on pasture, however it was not related to ADG (HPD90 interval = -0.29 to 0.10) and SC (HPD90 interval = -0.35 to 0.13) for performance-tested young bulls in feedlots. Heritabilities for growth and SC are higher for performance-tested young bulls than for commercial animals. Evaluating and selecting for increased growth and SC on performance-tested young bulls is

  6. Introduction to stellar structure

    CERN Document Server

    Maciel, Walter J

    2016-01-01

    In the first part of this book, the author presents the basic properties of the stellar interior and describes them thoroughly, along with deriving the main stellar structure equations of temperature, density, pressure and luminosity, among others. The process and application of solving these equations is explained, as well as linking these results with actual observations.  The second part of the text describes what happens to a star over time, and how to determine this by solving the same equations at different points during a star’s lifetime. The fate of various stars is quite different depending on their masses, and this is described in the final parts of the book. This text can be used for an upper level undergraduate course or an introductory graduate course on stellar physics.

  7. The Galactic stellar disc

    International Nuclear Information System (INIS)

    Feltzing, S; Bensby, T

    2008-01-01

    The study of the Milky Way stellar discs in the context of galaxy formation is discussed. In particular, we explore the properties of the Milky Way disc using a new sample of about 550 dwarf stars for which we have recently obtained elemental abundances and ages based on high-resolution spectroscopy. For all the stars we also have full kinematic information as well as information about their stellar orbits. We confirm results from previous studies that the thin and the thick discs have distinct abundance patterns. But we also explore a larger range of orbital parameters than what has been possible in our previous studies. Several new results are presented. We find that stars that reach high above the Galactic plane and have eccentric orbits show remarkably tight abundance trends. This implies that these stars formed out of well-mixed gas that had been homogenized over large volumes. We find some evidence that suggest that the event that most likely caused the heating of this stellar population happened a few billion years ago. Through a simple, kinematic exploration of stars with super-solar [Fe/H], we show that the solar neighbourhood contains metal-rich, high velocity stars that are very likely associated with the thick disc. Additionally, the HR1614 moving group and the Hercules and Arcturus stellar streams are discussed and it is concluded that, probably, a large fraction of the groups and streams so far identified in the disc are the result of evolution and interactions within the stellar disc rather than being dissolved stellar clusters or engulfed dwarf galaxies.

  8. Transport in stellarators

    International Nuclear Information System (INIS)

    Maassberg, H.; Brakel, R.; Burhenn, R.; Gasparino, U.; Grigull, P.; Kick, M.; Kuehner, G.; Ringler, H.; Sardei, F.; Stroth, U.; Weller, A.

    1993-01-01

    The local electron and ion heat transport as well as the particle and impurity transport properties in stellarators are reviewed. In this context, neoclassical theory is used as a guideline for the comparison of the experimental results of the quite different confinement concepts. At sufficiently high temperatures depending on the specific magnetic configuration, neoclassical predictions are confirmed by experimental findings. The confinement properties in the LMFP collisionality regime are discussed with respect to the next stellarator generation, for which at higher temperatures the neoclassical transport is expected to become more important. (orig.)

  9. Exploring Marine Citizenship among Young People in Select Urban and Rural Villages in the Philippines

    Science.gov (United States)

    Jabar, Melvin A.; Regadio, Crisanto Q., Jr.; Collado, Zaldy C.

    2018-01-01

    This article explores the understanding of marine citizenship among young people from two villages (urban and rural) in the Philippines. The purpose of the article is to examine the differences and similarities of their attitudes toward and engagement in marine environment conservation in rural and urban contexts. Young Focus Group Discussion…

  10. ESTIMATION OF DISTANCES TO STARS WITH STELLAR PARAMETERS FROM LAMOST

    Energy Technology Data Exchange (ETDEWEB)

    Carlin, Jeffrey L.; Newberg, Heidi Jo [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Liu, Chao; Deng, Licai; Li, Guangwei; Luo, A-Li; Wu, Yue; Yang, Ming; Zhang, Haotong [Key Lab of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Beers, Timothy C. [Department of Physics and JINA: Joint Institute for Nuclear Astrophysics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Chen, Li; Hou, Jinliang; Smith, Martin C. [Shanghai Astronomical Observatory, 80 Nandan Road, Shanghai 200030 (China); Guhathakurta, Puragra [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Hou, Yonghui [Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042 (China); Lépine, Sébastien [Department of Physics and Astronomy, Georgia State University, 25 Park Place, Suite 605, Atlanta, GA 30303 (United States); Yanny, Brian [Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States); Zheng, Zheng, E-mail: jeffreylcarlin@gmail.com [Department of Physics and Astronomy, University of Utah, UT 84112 (United States)

    2015-07-15

    We present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star’s absolute magnitude. This technique is tailored specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ∼5° diameter “plate” that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and target selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ∼20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ∼40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.

  11. ON THE ORIGIN OF STELLAR MASSES

    International Nuclear Information System (INIS)

    Krumholz, Mark R.

    2011-01-01

    It has been a longstanding problem to determine, as far as possible, the characteristic masses of stars in terms of fundamental constants; the almost complete invariance of this mass as a function of the star-forming environment suggests that this should be possible. Here I provide such a calculation. The typical stellar mass is set by the characteristic fragment mass in a star-forming cloud, which depends on the cloud's density and temperature structure. Except in the very early universe, the latter is determined mainly by the radiation released as matter falls onto seed protostars. The energy yield from this process is ultimately set by the properties of deuterium burning in protostellar cores, which determines the stars' radii. I show that it is possible to combine these considerations to compute a characteristic stellar mass almost entirely in terms of fundamental constants, with an extremely weak residual dependence on the interstellar pressure and metallicity. This result not only explains the invariance of stellar masses, it resolves a second mystery: why fragmentation of a cold, low-density interstellar cloud, a process with no obvious dependence on the properties of nuclear reactions, happens to select a stellar mass scale such that stellar cores can ignite hydrogen. Finally, the weak residual dependence on the interstellar pressure and metallicity may explain recent observational hints of a smaller characteristic mass in the high-pressure, high-metallicity cores of giant elliptical galaxies.

  12. The fundamentals of stellar astrophysics

    International Nuclear Information System (INIS)

    Collins, G.W. II.

    1989-01-01

    A broad overview of theoretical stellar astrophysics is presented in a textbook intended for graduate students. Chapters are devoted to fundamental principles, assumptions, theorems, and polytropes; energy sources and sinks; the flow of energy through the star and the construction of stellar models; the theory of stellar evolution; relativistic stellar structure; the structure of distorted stars; stellar pulsation and oscillation. Also discussed are the flow of radiation through the stellar atmosphere, the solution of the radiative-transfer equation, the environment of the radiation field, the construction of a stellar model atmosphere, the formation and shape of spectral lines, LTE breakdown, illuminated and extended stellar atmospheres, and the transfer of polarized radiation. Diagrams, graphs, and sample problems are provided. 164 refs

  13. Spanish normative studies in young adults (NEURONORMA young adults project): norms for the Rey-Osterrieth Complex Figure (copy and memory) and Free and Cued Selective Reminding Test.

    Science.gov (United States)

    Palomo, R; Casals-Coll, M; Sánchez-Benavides, G; Quintana, M; Manero, R M; Rognoni, T; Calvo, L; Aranciva, F; Tamayo, F; Peña-Casanova, J

    2013-05-01

    The Rey-Osterrieth Complex Figure (ROCF) and the Free and Cued Selective Reminding Test (FCSRT) are widely used in clinical practice. The ROCF assesses visual perception, constructional praxis, and visuo-spatial memory. The FCSRT assesses verbal learning and memory. In this study, as part of the Spanish normative studies project in young adults (NEURONORMA young adults), we present age- and education-adjusted normative data for both tests obtained by using linear regression techniques. The sample consisted of 179 healthy participants ranging in age from 18 to 49 years. We provide tables for converting raw scores to scaled scores in addition to tables with scores adjusted by socio-demographic factors. The results showed that education affects scores for some of the memory tests and the figure-copying task. Age was only found to have an effect on the performance of visuo-spatial memory tests, and the effect of sex was negligible. The normative data obtained will be extremely useful in the clinical neuropsychological evaluation of young Spanish adults. Copyright © 2011 Sociedad Española de Neurología. Published by Elsevier Espana. All rights reserved.

  14. Progress Toward Attractive Stellarators

    International Nuclear Information System (INIS)

    Neilson, G.H.; Bromberg, L.; Brown, T.G.; Gates, D.A.; Ku, L.P.; Zarnstorff, M.C.; Boozer, A.H.; Harris, J.H.; Meneghini, O.; Mynick, H.E.; Pomphrey, N.; Reiman, A.H.; Xanthopoulos, P.

    2011-01-01

    The quasi-axisymmetric stellarator (QAS) concept offers a promising path to a more compact stellarator reactor, closer in linear dimensions to tokamak reactors than previous stellarator designs. Concept improvements are needed, however, to make it more maintainable and more compatible with high plant availability. Using the ARIES-CS design as a starting point, compact stellarator designs with improved maintenance characteristics have been developed. While the ARIES-CS features a through-the-port maintenance scheme, we have investigated configuration changes to enable a sector-maintenance approach, as envisioned for example in ARIES AT. Three approaches are reported. The first is to make tradeoffs within the QAS design space, giving greater emphasis to maintainability criteria. The second approach is to improve the optimization tools to more accurately and efficiently target the physics properties of importance. The third is to employ a hybrid coil topology, so that the plasma shaping functions of the main coils are shared more optimally, either with passive conductors made of high-temperature superconductor or with local compensation coils, allowing the main coils to become simpler. Optimization tools are being improved to test these approaches.

  15. Stellar population synthesis

    International Nuclear Information System (INIS)

    Pickles, A.J.

    1989-01-01

    The techniques used to derive astrophysically useful information from observations of the integrated light of composite stellar systems are briefly reviewed. A synthesis technique, designed to separate and describe on a standard system the competing effects of age and metallicity variations is introduced, and illustrated by its application to the study of the history of star formation in bright elliptical galaxies in clusters. (author)

  16. Relativistic stellar dynamics

    International Nuclear Information System (INIS)

    Contopoulos, G.

    1983-01-01

    In this paper, three main areas of relativistic stellar dynamics are reviewed: (a) The dynamics of clusters, or nuclei of galaxies, of very high density; (b) The dynamics of systems containing a massive black hole; and (c) The dynamics of particles (and photons) in an expanding Universe. The emphasis is on the use of orbit perturbations. (Auth.)

  17. Compact stellarator coils

    International Nuclear Information System (INIS)

    Pomphrey, N.; Berry, L.A.; Boozer, A.H.

    2001-01-01

    Experimental devices to study the physics of high-beta (β>∼4%), low aspect ratio (A<∼4.5) stellarator plasmas require coils that will produce plasmas satisfying a set of physics goals, provide experimental flexibility, and be practical to construct. In the course of designing a flexible coil set for the National Compact Stellarator Experiment, we have made several innovations that may be useful in future stellarator design efforts. These include: the use of Singular Value Decomposition methods for obtaining families of smooth current potentials on distant coil winding surfaces from which low current density solutions may be identified; the use of a Control Matrix Method for identifying which few of the many detailed elements of the stellarator boundary must be targeted if a coil set is to provide fields to control the essential physics of the plasma; the use of Genetic Algorithms for choosing an optimal set of discrete coils from a continuum of potential contours; the evaluation of alternate coil topologies for balancing the tradeoff between physics objective and engineering constraints; the development of a new coil optimization code for designing modular coils, and the identification of a 'natural' basis for describing current sheet distributions. (author)

  18. Stellar Structure and Evolution

    CERN Document Server

    Kippenhahn, Rudolf; Weiss, Achim

    2013-01-01

    This long-awaited second edition of the classical textbook on Stellar Structure and Evolution by Kippenhahn and Weigert is a thoroughly revised version of the original text. Taking into account modern observational constraints as well as additional physical effects such as mass loss and diffusion, Achim Weiss and Rudolf Kippenhahn have succeeded in bringing the book up to the state-of-the-art with respect to both the presentation of stellar physics and the presentation and interpretation of current sophisticated stellar models. The well-received and proven pedagogical approach of the first edition has been retained. The book provides a comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The models developed to explain the stability, dynamics and evolution of the stars are presented and great care is taken to detail the various stages in a star’s life. Just as the first edition, which remained a standard work for more than 20 years after its...

  19. 8. stellarator workshop

    International Nuclear Information System (INIS)

    1991-07-01

    The technical reports in this collection of papers were presented at the 8th International Workshop on Stellarators, and International Atomic Energy Agency Technical Committee Meeting. They include presentations on transport, magnetic configurations, fluctuations, equilibrium, stability, edge plasma and wall aspects, heating, diagnostics, new concepts and reactor studies. Refs, figs and tabs

  20. A SPITZER SURVEY OF PROTOPLANETARY DISK DUST IN THE YOUNG SERPENS CLOUD : HOW DO DUST CHARACTERISTICS EVOLVE WITH TIME?

    NARCIS (Netherlands)

    Oliveira, Isa; Pontoppidan, Klaus M.; Merin, Bruno; van Dishoeck, Ewine F.; Lahuis, Fred; Geers, Vincent C.; Jorgensen, Jes K.; Olofsson, Johan; Augereau, Jean-Charles; Brown, Joanna M.

    2010-01-01

    We present Spitzer InfraRed Spectrograph (IRS) mid-infrared (5-35 mu m) spectra of a complete flux-limited sample (>= 3 mJy at 8 mu m) of young stellar object (YSO) candidates selected on the basis of their infrared colors in the Serpens Molecular Cloud. Spectra of 147 sources are presented and

  1. Stellar wind theory

    International Nuclear Information System (INIS)

    Summers, D.

    1980-01-01

    The theory of stellar winds as given by the equations of classical fluid dynamics is considered. The equations of momentum and energy describing a steady, spherically symmetric, heat-conducting, viscous stellar wind are cast in a dimensionless form which involves a thermal conduction parameter E and a viscosity parameter γ. An asymptotic analysis is carried out, for fixed γ, in the cases E→O and E→infinity (corresponding to small and large thermal conductivity, respectively), and it is found that it is possible to construct critical solutions for the wind velocity and temperature over the entire flow. The E→O solution represents a wind which emanates from the star at low, subsonic speeds, accelerates through a sonic point, and then approaches a constant asymptotic speed, with its temperature varying as r/sup -4/3/ at large distances r from the star; the E→infinity solution represents a wind which, after reaching an approximately constant speed, with temperature varying as r/sup -2/7/, decelerates through a diffuse shock and approaches a finite pressure at infinity. A categorization is made of all critical stellar wind solutions for given values of γ and E, and actual numerical examples are given. Numerical solutions are obtained by integrating upstream 'from infinity' from initial values of the flow parameters given by appropriate asymptotic expansions. The role of viscosity in stellar wind theory is discussed, viscous and inviscid stellar wind solutions are compared, and it is suggested that with certain limitations, the theory presented may be useful in analyzing winds from solar-type stars

  2. Recent advances in stellarator optimization

    Science.gov (United States)

    Gates, D. A.; Boozer, A. H.; Brown, T.; Breslau, J.; Curreli, D.; Landreman, M.; Lazerson, S. A.; Lore, J.; Mynick, H.; Neilson, G. H.; Pomphrey, N.; Xanthopoulos, P.; Zolfaghari, A.

    2017-12-01

    Computational optimization has revolutionized the field of stellarator design. To date, optimizations have focused primarily on optimization of neoclassical confinement and ideal MHD stability, although limited optimization of other parameters has also been performed. The purpose of this paper is to outline a select set of new concepts for stellarator optimization that, when taken as a group, present a significant step forward in the stellarator concept. One of the criticisms that has been leveled at existing methods of design is the complexity of the resultant field coils. Recently, a new coil optimization code—COILOPT++, which uses a spline instead of a Fourier representation of the coils,—was written and included in the STELLOPT suite of codes. The advantage of this method is that it allows the addition of real space constraints on the locations of the coils. The code has been tested by generating coil designs for optimized quasi-axisymmetric stellarator plasma configurations of different aspect ratios. As an initial exercise, a constraint that the windings be vertical was placed on large major radius half of the non-planar coils. Further constraints were also imposed that guaranteed that sector blanket modules could be removed from between the coils, enabling a sector maintenance scheme. Results of this exercise will be presented. New ideas on methods for the optimization of turbulent transport have garnered much attention since these methods have led to design concepts that are calculated to have reduced turbulent heat loss. We have explored possibilities for generating an experimental database to test whether the reduction in transport that is predicted is consistent with experimental observations. To this end, a series of equilibria that can be made in the now latent QUASAR experiment have been identified that will test the predicted transport scalings. Fast particle confinement studies aimed at developing a generalized optimization algorithm are also

  3. SDP_golofs01_3: Stellar Disk Evolution

    Science.gov (United States)

    Olofsson, G.

    2010-03-01

    n a collaboration between the HSC, P. Harvey (Mission Scientist) and the three instrument consortia we propose to apply the full power of Herschel to investigate the properties of circum-stellar disks. The versatility of Herschel allows us to address several key questions: How do the disks evolve with time? Planets clearly form out of circum-stellar disks and there is growing evidence that the time scale is short, 1 - 10 Myr, for the main accretion phase. During this time period, the stellar radiation and stellar winds clean the disks from most of their dust and gas, eventually making them transparent. However, collisions and evaporation from comet- like bodies will continue to produce dust and gas. This activity declines with time, and we will pursue this scenario by observing a sample of IR excess stars of known age, ranging from a few million years to the age of the sun. Are there analogues to our Kuiper belt around nearby stars? The Kuiper belt is a dust belt surrounding the Sun, located outside the orbit of Neptune, which has a key role in stabilizing orbits of the KE-objects and this dynamical aspect makes it particularly interesting to search for stars that may host KE-belt analogues. Herschel offers a unique sensitivity beyond 100 m and we propose an extensive survey of nearby stars seeking cold dust emission. What will a closer IR look at the "Fabulous Four" (and some other resolved disks) reveal? Several nearby MS stars with IR excesses have circumstellar dust structures that can be resolved by Herschel. Imaging these structures in the six PACS+SPIRE bands will enable us to explore the dust properties, notably the size distribution and albedo.. What is the composition of young disks? We propose a detailed spectroscopic investigation of four bright disks, including a full spectral scan with PACS, an FTS scan at full resolution and HIFI observations of selected frequencies. The aim is to constrain the properties of both the dust and gas components.

  4. KINEMATICS OF CLASSICAL CEPHEIDS IN THE NUCLEAR STELLAR DISK

    International Nuclear Information System (INIS)

    Matsunaga, Noriyuki; Fukue, Kei; Yamamoto, Ryo; Kobayashi, Naoto; Hamano, Satoshi; Inno, Laura; Genovali, Katia; Bono, Giuseppe; Baba, Junichi; Fujii, Michiko S.; Aoki, Wako; Tsujimoto, Takuji; Kondo, Sohei; Ikeda, Yuji; Nishiyama, Shogo; Nagata, Tetsuya

    2015-01-01

    Classical Cepheids are useful tracers of the Galactic young stellar population because their distances and ages can be determined from their period-luminosity and period-age relations. In addition, the radial velocities and chemical abundance of the Cepheids can be derived from spectroscopic observations, providing further insights into the structure and evolution of the Galaxy. Here, we report the radial velocities of classical Cepheids near the Galactic center, three of which were reported in 2011 and a fourth being reported for the first time. The velocities of these Cepheids suggest that the stars orbit within the nuclear stellar disk, a group of stars and interstellar matter occupying a region of ∼200 pc around the center, although the three-dimensional velocities cannot be determined until the proper motions are known. According to our simulation, these four Cepheids formed within the nuclear stellar disk like younger stars and stellar clusters therein

  5. A new study of stellar substructures in the Fornax dwarf spheroidal galaxy

    NARCIS (Netherlands)

    de Boer, T. J. L.; Tolstoy, E.; Saha, A.; Olszewski, E. W.

    Using deep V, B - V wide-field photometry, we have conducted a new study of stellar over-densities in the Fornax dwarf spheroidal galaxy by determining detailed star formation histories from colour-magnitude diagram analysis. We have concentrated on the relatively young stellar component ( We have

  6. A descriptive study on selected growth parameters and growth hormone receptor gene in healthy young adults from the American Midwest.

    Science.gov (United States)

    Hartin, Samantha N; Hossain, Waheeda A; Manzardo, Ann M; Brown, Shaquanna; Fite, Paula J; Bortolato, Marco; Butler, Merlin G

    2018-02-12

    The first study of growth hormone receptor (GHR) genotypes in healthy young adults in the United States attending a Midwestern university and impact on selected growth parameters. To describe the frequency of GHR genotypes in a sample of healthy young adults from the United States attending a university in the Midwest and analyze the relationship between GHR genotypes and selected growth parameters. Saliva was collected from 459 healthy young adults (237 females, 222 males; age range = 18-25 y) and DNA isolated for genotyping of GHR alleles (fl/fl, fl/d3, or d3/d3). Selected growth parameters were collected and GHR genotype data examined for previously reported associations (e.g., height, weight or bone mass density) or novel findings (e.g., % body water and index finger length). We found 219 participants (48%) homozygous for fl/fl, 203 (44%), heterozygous fl/d3 and 37 (8%) homozygous d3/d3. The distribution of GHR genotypes in our participants was consistent with previous reports of non-US populations. Several anthropometric measures differed by sex. The distribution of GHR genotypes did not significantly differ by sex, weight, or other anthropometric measures. However, the fl/d3 genotype was more common among African-Americans. Our study of growth and anthropometric parameters in relationship to GHR genotypes found no association with height, weight, right index finger length, BMI, bone mass density, % body fat or % body water in healthy young adults. We did identify sex differences with increased body fat, decreased bone density, body water and index finger length in females. Copyright © 2018 Elsevier Ltd. All rights reserved.

  7. Ion transport in stellarators

    International Nuclear Information System (INIS)

    Ho, D.D.M.; Kulsrud, R.M.

    1985-09-01

    Stellarator ion transport in the low-collisionality regime with a radial electric field is calculated by a systematic expansion of the drift-Boltzmann equation. The shape of the helical well is taken into account in this calculation. It is found that the barely trapped ions with three to four times the thermal energy give the dominant contribution to the diffusion. Expressions for the ion particle and energy fluxes are derived

  8. Status of stellarator research

    International Nuclear Information System (INIS)

    Wobig, H.

    1985-01-01

    In recent years main activities in stellarator research were focussed on production and investigation of currentless plasmas. Several heating methods have been applied: electron cyclotron heating, ion cyclotron heating and neutral beam injection. The parameters achieved in HELIOTRON E and W VII-A are: antin 20 m 3 , Tsub(i) <= 1 keV. The confinement is improved as compared with ohmically heated discharges. By ECRH (P = 200 kW) it is possible to heat electrons up to 1.4 keV, confinement in this regime is dominated already by trapped particle effects. Toroidal currents up to 2 kA - either bootstrap currents or externally driven currents - were observed. High β-values (antiβ = 2%) have been obtained in HELIOTRON E, in this regime already pressure driven MHD-modes were observed. Future experiments (ATF-1 and W VII-AS) will extend the parameter regime to temperatures of several keV. These experiments will give important information about critical problems of the stellarator line (β-limit, neoclassical confinement impurity transport). A few reactor studies of stellarators exist, attention is mainly concentrated on technical problems of the modular coil system

  9. Selection, Inclusion, Evaluation and Defense of Transgender-Inclusive Fiction for Young Adults: A Resource Guide

    Science.gov (United States)

    Rockefeller, Elsworth I.

    2009-01-01

    An increasingly visible youth transgender population is emerging and the number of transgender-inclusive fiction texts for young adults is growing. Adults serving teens in schools, libraries, and community agencies must begin actively pursuing, utilizing, and incorporating these texts into resource collections. This article provides an overview of…

  10. Testing Selected Behaviors to Reduce Indoor Air Pollution Exposure in Young Children

    Science.gov (United States)

    Barnes, B. R.; Mathee, A.; Krieger, L.; Shafritz, L.; Favin, M.; Sherburne, L.

    2004-01-01

    Indoor air pollution is responsible for the deaths and illness of millions of young children in developing countries. This study investigated the acceptability (willingness to try) and feasibility (ability to perform) of four indoor air pollution reduction behaviors (improve stove maintenance practices, child location practices, ventilation…

  11. Interactive versus passive distraction for acute pain management in young children: the role of selective attention and development.

    Science.gov (United States)

    Wohlheiter, Karen A; Dahlquist, Lynnda M

    2013-03-01

    To examine whether age and developmental differences in selective attention influence young children's differential responses to interactive and passive distraction. 65 3- to 6-year-old children underwent three cold-pressor trials while receiving no intervention, playing a video game (interactive distraction), or watching a video game (passive distraction). In addition, children completed a test of selective attention, and parents completed ratings of attention. Consistent with neurocognitive models of pain, children benefited more from interactive distraction than from passive distraction. Although older children demonstrated superior pain tolerance overall, age and selective attention skills did not moderate children's responses to the distraction intervention. These findings suggest that younger preschoolers can benefit from interactive distraction to manage acute pain, provided that the distraction activity is developmentally appropriate. Research is needed to determine whether developmental issues are more important moderators of children's responses to distraction when faced with more challenging task demands.

  12. Effects of selective bile duct ligation on liver parenchyma in young animals: histologic and molecular evaluations.

    Science.gov (United States)

    Tannuri, Ana Cristina A; Coelho, Maria Cecília M; de Oliveira Gonçalves, Josiane; Santos, Maria Mercês; Ferraz da Silva, Luiz Fernando; Bendit, Israel; Tannuri, Uenis

    2012-03-01

    The mechanisms of increased collagen production and liver parenchyma fibrosis are poorly understood. These phenomena are observed mainly in children with biliary obstruction (BO), and in a great number of patients, the evolution to biliary cirrhosis and hepatic failure leads to the need for liver transplantation before adolescence. However, pediatric liver transplantation presents with biliary complications in 20% to 30% of cases in the postoperative period. Intra- or extrahepatic stenosis of bile ducts is frequent and may lead to secondary biliary cirrhosis and the need for retransplantation. It is unknown whether biliary stenosis involving isolated segments or lobes may affect the adjacent nonobstructed lobes by paracrine or endocrine means, leading to fibrosis in this parenchyma. Therefore, the present study aimed to create an experimental model of selective biliary duct ligation in young animals with a subsequent evaluation of the histologic and molecular alterations in liver parenchyma of the obstructed and nonobstructed lobes. After a pilot study to standardize the surgical procedures, weaning rats underwent ligation of the bile ducts of the median, left lateral, and caudate liver lobes. The bile duct of the right lateral lobe was kept intact. To avoid intrahepatic biliary duct collaterals neoformation, the parenchymal connection between the right lateral and median lobes was clamped. The animals were divided into groups according to the time of death: 1, 2, 3, 4, and 8 weeks after surgical procedure. After death, the median and left lateral lobes (with BO) and the right lateral lobe (without BO [NBO]) were harvested separately. A group of 8 healthy nonoperated on animals served as controls. Liver tissues were subjected to histologic evaluation and quantification of the ductular proliferation and of the portal fibrosis. The expressions of smooth muscle α-actin (α-SMA), desmin, and transforming growth factor β1 genes were studied by molecular analyses

  13. The Resolved Stellar Population of Leo A

    Science.gov (United States)

    Tolstoy, Eline

    1996-05-01

    New observations of the resolved stellar population of the extremely metal-poor Magellanic dwarf irregular galaxy Leo A in Thuan-Gunn r, g, i, and narrowband Hα filters are presented. Using the recent Cepheid variable star distance determination to Leo A by Hoessel et al., we are able to create an accurate color-magnitude diagram (CMD). We have used the Bavesian inference method described by Tolstoy & Saha to calculate the likelihood of a Monte Carlo simulation of the stellar population of Leo A being a good match to the data within the well understood errors in the data. The magnitude limits on our data are sensitive enough to look back at ~1 Gyr of star formation history at the distance of Leo A. To explain the observed ratio of red to blue stars in the observed CMD, it is necessary to invoke either a steadily decreasing star formation rate toward the present time or gaps in the star formation history. We also compare the properties of the observed stellar population with the known spatial distribution of the H I gas and H II regions to support the conclusions from CMD modeling. We consider the possibility that currently there is a period of diminished star formation in Leo A, as evidenced by the lack of very young stars in the CMD and the faint H II regions. How the chaotic H I distribution, with no observable rotation, fits into our picture of the evolution of Leo A is as yet unclear.

  14. THE ADVANCED STELLAR COMPASS

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Liebe, Carl Christian

    1997-01-01

    The science objective of the Danish Geomagnetic Research Satellite "Ørsted" is to map the magnetic field of the Earth, with a vector precision of a fraction of a nanotesla. This necessitates an attitude reference instrument with a precision of a few arcseconds onboard the satellite. To meet...... this demand the Advanced Stellar Compass (ASC), a fully autonomous miniature star tracker, was developed. This ASC is capable of both solving the "lost in space" problem and determine the attitude with arcseconds precision. The development, principles of operation and instrument autonomy of the ASC...

  15. Physics of Stellar Convection

    Science.gov (United States)

    Arnett, W. David

    2009-05-01

    We review recent progress using numerical simulations as a testbed for development of a theory of stellar convection, much as envisaged by John von Newmann. Necessary features of the theory, non-locality and fluctuations, are illustrated by computer movies. It is found that the common approximation of convection as a diffusive process presents the wrong physical picture, and improvements are suggested. New observational results discussed at the conference are gratifying in their validation of some of our theoretical ideas, especially the idea that SNIb and SNIc events are related to the explosion of massive star cores which have been stripped by mass loss and binary interactions [1

  16. Engaging in Security Work: Selective Disclosure in Friendships of Korean and Mexican Undocumented Young Adults

    OpenAIRE

    Cho, Esther Y

    2017-01-01

    While much of the literature on undocumented immigrants has focused on employment and education outcomes, we know little about the effects of their precarious legal status on interpersonal relationships. Based on interviews with 50 Korean and Mexican undocumented young adults, I find that, regardless of ethnoracial background, undocumented immigrants approach relationships cautiously, engaging in "security work" to protect themselves and their loved ones. Security work is a negotiated process...

  17. Young Adults’ Selection and Use of Dependent Coverage under the Affordable Care Act

    Directory of Open Access Journals (Sweden)

    Weiwei Chen

    2018-01-01

    Full Text Available The dependent coverage expansion under the Affordable Care Act (ACA required health insurance policies that cover dependents to offer coverage for policyholder’ children up to age 26. It has been well documented that the provision successfully reduced the uninsured rate among the young adults. However, less is known about whether dependent coverage crowded out other insurance types and whether young adults used dependent coverage as a fill-in-the-gap short-term option. Using data from the Survey of Income and Program Participation 2008 Panel, the paper assesses dependent coverage uptake and duration before and after the ACA provision among young adults aged 19–26 versus those aged 27–30. Regressions for additional coverage outcomes were also performed to estimate the crowd-out rate. It was found that the ACA provision had a significant positive impact on dependent coverage uptake and duration. The estimated crowd-out rate ranges from 27 to 42%, depending on the definition. Most dependent coverage enrollees used the coverage for 1 or 2 years. Differences in dependent coverage uptake and duration remained among racial groups. Less healthy individuals were also less likely to make use of dependent coverage.

  18. New Classes of Quasi-helically Symmetric Stellarators

    International Nuclear Information System (INIS)

    Ku, L.P.; Boozer, A.H.

    2010-01-01

    New classes of quasi-helically symmetric stellarators with aspect ratios (le) 10 have been found which are stable to the perturbation of magnetohydrodynamic modes at plasma pressures of practical interest. These configurations have large rotational transform and good quality of flux surfaces. Characteristics of some selected examples are discussed in detail. The feasibility of using modular coils for these stellarators has been investigated. It is shown that practical designs for modular coils can be achieved.

  19. Stellar axion models

    Energy Technology Data Exchange (ETDEWEB)

    Nowakowski, Daniel; Kuster, Markus; Meister, Claudia V.; Fuelbert, Florian; Hoffmann, Dieter H.H. [TU Darmstadt (Germany). Institut fuer Kernphysik; Weiss, Achim [Max-Planck-Institut fuer Astrophysik, Garching (Germany)

    2010-07-01

    An axion helioscope is typically operated to observe the sun as an axion source. Additional pointings at celestial sources, e.g. stars in other galaxies, result in possible detections of axions from distant galactic objects. For the observation of supplementary axion sources we therefore calculate the thereotical axion flux from distant stars by extending axionic flux models for the axion Primakoff effect in the sun to other main sequence stars. The main sequence star models used for our calculations are based on full stellar structure calculations. To deduce the effective axion flux of stellar objects incident on the Earth the All-Sky catalogue was used to obtain the spectral class and distance of the stars treated. Our calculations of the axion flux in the galactic plane show that for a zero age main sequence star an maximum axion flux of {phi}{sub a}=303.43 cm{sup -2}s{sup -1} could be expected. Furthermore we present estimates of axion fluxes from time-evolved stars.

  20. The DEMO Quasisymmetric Stellarator

    Directory of Open Access Journals (Sweden)

    Geoffrey B. McFadden

    2010-02-01

    Full Text Available The NSTAB nonlinear stability code solves differential equations in conservation form, and the TRAN Monte Carlo test particle code tracks guiding center orbits in a fixed background, to provide simulations of equilibrium, stability, and transport in tokamaks and stellarators. These codes are well correlated with experimental observations and have been validated by convergence studies. Bifurcated 3D solutions of the 2D tokamak problem have been calculated that model persistent disruptions, neoclassical tearing modes (NTMs and edge localized modes (ELMs occurring in the International Thermonuclear Experimental Reactor (ITER, which does not pass the NSTAB simulation test for nonlinear stability. So we have designed a quasiaxially symmetric (QAS stellarator with similar proportions as a candidate for the demonstration (DEMO fusion reactor that does pass the test [1]. The configuration has two field periods and an exceptionally accurate 2D symmetry that furnishes excellent thermal confinement and good control of the prompt loss of alpha particles. Robust coils are found from a filtered form of the Biot-Savart law based on a distribution of current over a control surface for the coils and the current in the plasma defined by the equilibrium calculation. Computational science has addressed the issues of equilibrium, stability, and transport, so it remains to develop an effective plan to construct the coils and build a diverter.

  1. SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Wuyts, Stijn; Foerster Schreiber, Natascha M.; Genzel, Reinhard; Lutz, Dieter [Max-Planck-Institut fuer extraterrestrische Physik, Postfach 1312, Giessenbachstr., D-85741 Garching (Germany); Guo Yicheng; Giavalisco, Mauro [Astronomy Department, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States); Barro, Guillermo; Faber, Sandra M.; Kocevski, Dale D.; Koo, David C.; McGrath, Elizabeth [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Dekel, Avishai [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Ferguson, Henry C.; Grogin, Norman A.; Koekemoer, Anton M.; Lotz, Jennifer [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Hathi, Nimish P. [Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States); Huang, Kuang-Han [Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Newman, Jeffrey A. [Department of Physics and Astronomy, University of Pittsburgh, 3941 O' Hara Street, Pittsburgh, PA 15260 (United States); and others

    2012-07-10

    We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies (SFGs) at 0.5 < z < 1.5 and 326 SFGs at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of GOODS-South. Galaxies were selected to be more massive than 10{sup 10} M{sub Sun} and have specific star formation rates (SFRs) above 1/t{sub H} . We model the seven-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible in the inferred stellar mass distributions. Off-center clumps contribute up to {approx}20% to the integrated SFR, but only 7% or less to the integrated mass of all massive SFGs at z {approx} 1 and z {approx} 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100-200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.

  2. Estimating young Australian adults' risk of hearing damage from selected leisure activities.

    Science.gov (United States)

    Beach, Elizabeth; Williams, Warwick; Gilliver, Megan

    2013-01-01

    Several previous studies have attempted to estimate the risk of noise-induced hearing loss from loud leisure noise. Some of these studies may have overestimated the risk because they used noise estimates taken from the higher end of reported levels. The aim of the present study was to provide a realistic estimate of the number of young Australian adults who may be at risk of hearing damage and eventual hearing loss from leisure-noise exposure. Average noise levels at five high-noise leisure activities, (1) nightclubs; (2) pubs, bars, and registered clubs; (3) fitness classes; (4) live sporting events; (5) concerts and live music venues, were calculated using 108 measurements taken from a large database of leisure noise measurements. In addition, an online survey was administered to a convenience sample of 1000 young adults aged 18 to 35 years, who reported the time spent at these leisure activities and the frequency with which they undertook the activities. They also answered questions about tinnitus and their perceived risk of hearing damage. Although the survey data cannot be considered representative of the population of young Australian adults, it was weighted to this population in respect of age, gender, education, and location. The survey data and the average noise levels were used to estimate each individual's annual noise exposure, and in turn, estimate those at risk of hearing damage from leisure-noise exposure. For the majority of participants (n = 868), the accumulated leisure noise level was within the acceptable workplace limit. However, 132 participants or 14.1% (population weighted) were exposed to an annual noise dose greater than the acceptable workplace noise limit. By far, the main source of high-risk leisure noise was from nightclubs. Those with more leisure-noise exposure experienced more tinnitus and perceived themselves to be more at risk than those with lower noise exposures. It is recommended that nightclub operators reduce noise levels

  3. Nuclear challenges and progress in designing stellarator fusion power plants

    International Nuclear Information System (INIS)

    El-Guebaly, L.A.; Wilson, P.; Henderson, D.; Sawan, M.; Sviatoslavsky, G.; Tautges, T.; Slaybaugh, R.; Kiedrowski, B.; Ibrahim, A.

    2008-01-01

    Over the past 5-6 decades, stellarator power plants have been studied in the US, Europe, and Japan as an alternate to the mainline magnetic fusion tokamaks, offering steady-state operation and eliminating the risk of plasma disruptions. The earlier 1980s studies suggested large-scale stellarator power plants with an average major radius exceeding 20 m. The most recent development of the compact stellarator concept delivered ARIES-CS - a compact stellarator with 7.75 m average major radius, approaching that of tokamaks. For stellarators, the most important engineering parameter that determines the machine size and cost is the minimum distance between the plasma boundary and mid-coil. Accommodating the breeding blanket and necessary shield within this distance to protect the ARIES-CS superconducting magnet represents a challenging task. Selecting the ARIES-CS nuclear and engineering parameters to produce an economic optimum, modeling the complex geometry for 3D nuclear analysis to confirm the key parameters, and minimizing the radwaste stream received considerable attention during the design process. These engineering design elements combined with advanced physics helped enable the compact stellarator to be a viable concept. This paper provides a brief historical overview of the progress in designing stellarator power plants and a perspective on the successful integration of the nuclear activity into the final ARIES-CS configuration

  4. A catalog of stellar spectrophotometry

    Science.gov (United States)

    Adelman, S. J.; Pyper, D. M.; Shore, S. N.; White, R. E.; Warren, W. H., Jr.

    1989-01-01

    A machine-readable catalog of stellar spectrophotometric measurements made with rotating grating scanner is introduced. Consideration is given to the processes by which the stellar data were collected and calibrated with the fluxes of Vega (Hayes and Latham, 1975). A sample page from the spectrophotometric catalog is presented.

  5. Variability in HOMA-IR, lipoprotein profile and selected hormones in young active men.

    Science.gov (United States)

    Keska, Anna; Lutoslawska, Grazyna; Czajkowska, Anna; Tkaczyk, Joanna; Mazurek, Krzysztof

    2013-01-01

    Resistance to insulin actions is contributing to many metabolic disturbances. Such factors as age, sex, nutrition, body fat, and physical activity determine body insulin resistance. Present study attempted to asses insulin resistance and its metabolic effects with respect to energy intake in young, lean, and active men. A total of 87 men aged 18-23 participated in the study. Plasma levels of glucose, insulin, lipoproteins, cortisol, and TSH were determined. Insulin resistance was expressed as Homeostasis Model Assessment for Insulin Resistance (HOMA-IR) and calculated using homeostatic model. The median value of HOMA-IR (1.344) was used to divide subjects into two groups. Men did not differ in anthropometric parameters, daily physical activity, and plasma TSH and cortisol levels. However, in men with higher HOMA-IR significantly lower daily energy intake was observed concomitantly with higher TG, TC, and HDL-C concentrations in plasma versus their counterparts with lower HOMA-IR. Exclusively in subjects with higher HOMA-IR significant and positive correlation was noted between HOMA-IR and TC and LDL-C. We concluded that despite a normal body weight and physical activity, a subset of young men displayed unfavorable changes in insulin sensitivity and lipid profile, probably due to insufficient energy intake.

  6. Quasisymmetry equations for conventional stellarators

    International Nuclear Information System (INIS)

    Pustovitov, V.D.

    1994-11-01

    General quasisymmetry condition, which demands the independence of B 2 on one of the angular Boozer coordinates, is reduced to two equations containing only geometrical characteristics and helical field of a stellarator. The analysis is performed for conventional stellarators with a planar circular axis using standard stellarator expansion. As a basis, the invariant quasisymmetry condition is used. The quasisymmetry equations for stellarators are obtained from this condition also in an invariant form. Simplified analogs of these equations are given for the case when averaged magnetic surfaces are circular shifted torii. It is shown that quasisymmetry condition can be satisfied, in principle, in a conventional stellarator by a proper choice of two satellite harmonics of the helical field in addition to the main harmonic. Besides, there appears a restriction on the shift of magnetic surfaces. Thus, in general, the problem is closely related with that of self-consistent description of a configuration. (author)

  7. Young children can be taught basic natural selection using a picture-storybook intervention.

    Science.gov (United States)

    Kelemen, Deborah; Emmons, Natalie A; Seston Schillaci, Rebecca; Ganea, Patricia A

    2014-04-01

    Adaptation by natural selection is a core mechanism of evolution. It is also one of the most widely misunderstood scientific processes. Misconceptions are rooted in cognitive biases found in preschoolers, yet concerns about complexity mean that adaptation by natural selection is generally not comprehensively taught until adolescence. This is long after untutored theoretical misunderstandings are likely to have become entrenched. In a novel approach, we explored 5- to 8-year-olds' capacities to learn a basic but theoretically coherent mechanistic explanation of adaptation through a custom storybook intervention. Experiment 1 showed that children understood the population-based logic of natural selection and also generalized it. Furthermore, learning endured 3 months later. Experiment 2 replicated these results and showed that children understood and applied an even more nuanced mechanistic causal explanation. The findings demonstrate that, contrary to conventional educational wisdom, basic natural selection is teachable in early childhood. Theory-driven interventions using picture storybooks with rich explanatory structure are beneficial.

  8. Nucleosynthesis in stellar explosions

    Energy Technology Data Exchange (ETDEWEB)

    Woosley, S.E.; Axelrod, T.S.; Weaver, T.A.

    1983-01-01

    The final evolution and explosion of stars from 10 M/sub solar/ to 10/sup 6/ M/sub solar/ are reviewed with emphasis on factors affecting the expected nucleosynthesis. We order our paper in a sequence of decreasing mass. If, as many suspect, the stellar birth function was peaked towards larger masses at earlier times (see e.g., Silk 1977; but also see Palla, Salpeter, and Stahler 1983), this sequence of masses might also be regarded as a temporal sequence. At each stage of Galactic chemical evolution stars form from the ashes of preceding generations which typically had greater mass. A wide variety of Type I supernova models, most based upon accreting white dwarf stars, are also explored using the expected light curves, spectra, and nucleosynthesis as diagnostics. No clearly favored Type I model emerges that is capable of simultaneously satisfying all three constraints.

  9. Nucleosynthesis in stellar explosions

    International Nuclear Information System (INIS)

    Woosley, S.E.; Axelrod, T.S.; Weaver, T.A.

    1983-01-01

    The final evolution and explosion of stars from 10 M/sub solar/ to 10 6 M/sub solar/ are reviewed with emphasis on factors affecting the expected nucleosynthesis. We order our paper in a sequence of decreasing mass. If, as many suspect, the stellar birth function was peaked towards larger masses at earlier times (see e.g., Silk 1977; but also see Palla, Salpeter, and Stahler 1983), this sequence of masses might also be regarded as a temporal sequence. At each stage of Galactic chemical evolution stars form from the ashes of preceding generations which typically had greater mass. A wide variety of Type I supernova models, most based upon accreting white dwarf stars, are also explored using the expected light curves, spectra, and nucleosynthesis as diagnostics. No clearly favored Type I model emerges that is capable of simultaneously satisfying all three constraints

  10. Remarks on stellar clusters

    International Nuclear Information System (INIS)

    Teller, E.

    1985-01-01

    In the following, a few simple remarks on the evolution and properties of stellar clusters will be collected. In particular, globular clusters will be considered. Though details of such clusters are often not known, a few questions can be clarified with the help of primitive arguments. These are:- why are spherical clusters spherical, why do they have high densities, why do they consist of approximately a million stars, how may a black hole of great mass form within them, may they be the origin of gamma-ray bursts, may their invisible remnants account for the missing mass of our galaxy. The available data do not warrant a detailed evaluation. However, it is remarkable that exceedingly simple models can shed some light on the questions enumerated above. (author)

  11. L = ± 1 stellarator

    International Nuclear Information System (INIS)

    Kikuchi, T.; Shiina, S.; Saito, K.; Gesso, H.; Aizawa, M.; Kawakami, I.

    1985-01-01

    We report the magnetic field configuration of helical magnetic axis stellarator. The magnetic field configuration is composed of large l=1 field and small l=-1 and l=0(bumpy) fields. The large l=1 field (combined with the small l=-1 field) is used to form helical magnetic axis with the helical curvature much larger than the toroidal curvature, which provides the high limiting values of β. The small l=-1 field, furthermore, as well as the large l=1 field reduces the Pfirsch-Schlueter currents by combining with l=0 field. Therefore, the large l=1 field and the combination of three field components may be favourable for the increase of limiting β value

  12. Modular Stellarator Fusion Reactor (MSR) concept

    International Nuclear Information System (INIS)

    Miller, R.L.; Krakowski, R.A.

    1981-01-01

    A preliminary conceptual study has been made of the Modulator Stellarator Reactor (MSR) as a stedy-state, ignited, DT-fueled, magnetic fusion reactor. The MSR concept combines the physics of classic stellarator confinement with an innovative, modular-coil design. Parametric tradeoff calculations are described, leading to the selection of an interim design point for a 4.8-GWt plant based on Alcator transport scaling and an average beta value of 0.04 in an l = 2 system with a plasma aspect ratio of 11. Neither an economic analysis nor a detailed conceptual engineering design is presented here, as the primary intent of this scoping study is the elucidation of key physics tradeoffs, constraints, and uncertainties for the ultimate power-reactor embodiment

  13. Stellar physics with the ALHAMBRA photometric system

    International Nuclear Information System (INIS)

    Villegas, T Aparicio; Alfaro, E J; Moles, M; Benítez, N; Perea, J; Olmo, A del; Cristóbal-Hornillos, D; Cervio, M; Delgado, R M González; Márquez, I; Masegosa, J; Prada, F; Cabrera-Caño, J; Fernández-Soto, A; Aguerri, J A L; Cepa, J; Broadhurst, T; Castander, F J; Infante, L; Martínez, V J

    2011-01-01

    The ALHAMBRA photometric system was specifically designed to perform a tomography of the Universe in some selected areas. Although mainly designed for extragalactic purposes, its 20 contiguous, equal-width, medium-band photometric system in the optical wavelength range, shows a great capacity for stellar classification. In this contribution we propose a methodology for stellar classification and physical parameter estimation (T eff , log g, [Fe/H], and color excess E(B – V)) based on 18 independent reddening-free Q-values from the ALHAMBRA photometry. Based on the theoretical Spectral library BaSeL 2.2, and applied to 288 stars from the Next Generation spectral Library (NGSL), we discuss the reliability of the method and its dependence on the extinction law used.

  14. Exercise tolerance and selected motor skills in young females with idiopathic scoliosis treated with different physiotherapeutic methods.

    Science.gov (United States)

    Fabian, Krzysztof Marek; Rożek-Piechura, Krystyna

    2014-01-01

    Scoliosis is a disorder that leads to dysfunction of a number of systems in the body, especially in young females. Physical capacity is one of the most important elements of good health as well as ofbiological development. Adolescence is a time when physical capacity develops intensively, and the condition of the respiratory system is one of many factors that have an impact on the level of physical capacity. This paper aims to evaluate a short-term application of two methods of physiotherapy and their influence on the level of exercise tolerance in young females suffering from idiopathic scoliosis. The study involved a group of 49 young females aged 14-15 years diagnosed with (2040°) thoracic and lumbar scoliosis who were in-patients at the rehabilitation ward of the Regional Paediatric Rehabilitation Hospital in Jastrzębie Zdrój. The group was divided into two subgroups depending on the method of rehabilitation employed: the first subgroup received asymmetric breathing exercise therapy by Dobosiewicz and the second subgroup practised symmetric remedial exercises. Cobb's angle, the degree of skeletal maturity, i.e. the Risser sign and the degree trunk rotation of the apex of the curvature by means of Raimondi's coefficient were determined once in an x-ray image. Basic somatic features, maximal voluntary ventilation (MVV parameter), selected motor skills and exercise tolerance were assessed on two occasions (before beginning and after completion of the rehabilitation treatment). 1. Young females suffering from (20-40°) thoracic and lumbar scoliosis demonstrate respiratory dysfunction, as shown by decreased maximal voluntary ventilation (MVV) in the two subgroups in the present study. Exercises according to Dobosiewicz's method brought about a significantly higher degree of improvement in this parameter. 2. The physiotherapeutic regimen administered to the young girls with scoliosis significantly improved their strength motor skills and exercise tolerance. A

  15. Older partner selection in young African-American men who have sex with men.

    Science.gov (United States)

    Arrington-Sanders, Renata; Leonard, Lori; Brooks, Durryle; Celentano, David; Ellen, Jonathan

    2013-06-01

    Young African-American (AA) men who have sex with men (YAAMSM) have experienced the greatest proportional increase in new HIV cases compared with other groups. Bridging sexual partnerships between YAAMSM and older aged cohorts with higher rates of primary HIV infection has emerged as an important independent risk factor for the development of HIV. We explored reasons young AAMSM cite for being attracted to and seeking an older partner and the interpersonal needs met within older sexual partnerships. Seventeen in-depth semistructured qualitative interviews were conducted in YAAMSM residing in a midsized urban city with high HIV prevalence. Two coders independently evaluated transcribed data to identify/collapse codes that emerged. We analyzed data using categorical and contextualizing analytic methods. Two themes emerged from the text for seeking an older sexual partner: the emotional maturity the older partner represented and the ability of the older partner to expose the younger partner to more life experiences. In addition, two themes emerged around attraction: support and physical attractiveness of the older partner. Few men described seeking age-discordant relationships for the sole purpose of exchange sex. Older partners during first same-sex experience helped younger partners sort through sexual position and how to perform in relationships. These interviews suggest that YAAMSM may be seeking older partners to fulfill desires to be in a stable, emotionally mature relationship and for exposure in the larger community. Prevention strategies aimed at targeting adolescent MSM age-discordant relationships will need to address the interpersonal needs met within older sexual partnerships. Copyright © 2013 Society for Adolescent Health and Medicine. Published by Elsevier Inc. All rights reserved.

  16. Target Selection for the SDSS-IV APOGEE-2 Survey

    Energy Technology Data Exchange (ETDEWEB)

    Zasowski, G. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Cohen, R. E.; Carlberg, J. K.; Fleming, Scott W. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Chojnowski, S. D.; Holtzman, J. [Department of Astronomy, New Mexico State University, Las Cruces, NM 88001 (United States); Santana, F. [Departamento de Astronomía, Universidad de Chile, Santiago (Chile); Oelkers, R. J.; Bird, J. C. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Andrews, B. [PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Beaton, R. L. [The Observatories of the Carnegie Institution for Science, Pasadena, CA 91101 (United States); Bender, C.; Cunha, K. [Steward Observatory, The University of Arizona, Tucson, AZ 85719 (United States); Bovy, J. [Department of Astronomy and Astrophysics and Dunlap Institute for Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4 (Canada); Covey, K. [Department of Physics and Astronomy, Western Washington University, Bellingham, WA 98225 (United States); Dell’Agli, F.; García-Hernández, D. A. [Departamento de Astrofísica, Universidad de La Laguna, and Instituto de Astrofísica de Canarias, La Laguna, Tenerife (Spain); Frinchaboy, P. M. [Department of Physics and Astronomy, Texas Christian University, Fort Worth, TX 76129 (United States); Harding, P. [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106 (United States); Johnson, J. A., E-mail: gail.zasowski@gmail.com [Department of Astronomy, The Ohio State University, Columbus, OH 43210 (United States); and others

    2017-11-01

    APOGEE-2 is a high-resolution, near-infrared spectroscopic survey observing ∼3 × 10{sup 5} stars across the entire sky. It is the successor to APOGEE and is part of the Sloan Digital Sky Survey IV (SDSS-IV). APOGEE-2 is expanding on APOGEE’s goals of addressing critical questions of stellar astrophysics, stellar populations, and Galactic chemodynamical evolution using (1) an enhanced set of target types and (2) a second spectrograph at Las Campanas Observatory in Chile. APOGEE-2 is targeting red giant branch and red clump stars, RR Lyrae, low-mass dwarf stars, young stellar objects, and numerous other Milky Way and Local Group sources across the entire sky from both hemispheres. In this paper, we describe the APOGEE-2 observational design, target selection catalogs and algorithms, and the targeting-related documentation included in the SDSS data releases.

  17. Target Selection for the SDSS-IV APOGEE-2 Survey

    International Nuclear Information System (INIS)

    Zasowski, G.; Cohen, R. E.; Carlberg, J. K.; Fleming, Scott W.; Chojnowski, S. D.; Holtzman, J.; Santana, F.; Oelkers, R. J.; Bird, J. C.; Andrews, B.; Beaton, R. L.; Bender, C.; Cunha, K.; Bovy, J.; Covey, K.; Dell’Agli, F.; García-Hernández, D. A.; Frinchaboy, P. M.; Harding, P.; Johnson, J. A.

    2017-01-01

    APOGEE-2 is a high-resolution, near-infrared spectroscopic survey observing ∼3 × 10 5 stars across the entire sky. It is the successor to APOGEE and is part of the Sloan Digital Sky Survey IV (SDSS-IV). APOGEE-2 is expanding on APOGEE’s goals of addressing critical questions of stellar astrophysics, stellar populations, and Galactic chemodynamical evolution using (1) an enhanced set of target types and (2) a second spectrograph at Las Campanas Observatory in Chile. APOGEE-2 is targeting red giant branch and red clump stars, RR Lyrae, low-mass dwarf stars, young stellar objects, and numerous other Milky Way and Local Group sources across the entire sky from both hemispheres. In this paper, we describe the APOGEE-2 observational design, target selection catalogs and algorithms, and the targeting-related documentation included in the SDSS data releases.

  18. Changing Minds with the Story of Adaptation: Strategies for Teaching Young Children about Natural Selection

    Science.gov (United States)

    Emmons, Natalie; Smith, Hayley; Kelemen, Deborah

    2016-01-01

    Research Findings: Educational guidelines recommend a delayed, piecemeal approach to instruction on adaptation by natural selection. This approach is questionable given suggestions that older students' pervasive misunderstandings about adaptation are rooted in cognitive biases that develop early. In response to this, Kelemen et al. (2014) recently…

  19. Action-Selection Perseveration in Young Children : Advances of a Dynamic Model

    NARCIS (Netherlands)

    Cox, R.F.A

    2008-01-01

    This study presents an empirical test and dynamic model of perseverative limb selection in children of 14-, 24-, and 36-months old (N = 66 in total). In the experiment children repeatedly grasped a spoon with a single hand. In 2 separate conditions, the spoon was presented either 4 times on their

  20. Recruiting Young Volunteers in an Area of Selective Education: A Qualitative Case Study

    Science.gov (United States)

    Dean, Jon

    2016-01-01

    This article presents findings from a small qualitative case study of a youth volunteering brokerage organisation in England, operating in an area of selective state education. Data show how brokerage workers felt grammar schools managed their students in a concerted way to improve students' chances of attending university. Conversely, workers…

  1. Interaction effects on galaxy pairs with Gemini/GMOS- III: stellar population synthesis

    Science.gov (United States)

    Krabbe, A. C.; Rosa, D. A.; Pastoriza, M. G.; Hägele, G. F.; Cardaci, M. V.; Dors, O. L., Jr.; Winge, C.

    2017-05-01

    We present an observational study of the impacts of interactions on the stellar population in a sample of galaxy pairs. Long-slit spectra in the wavelength range 3440-7300 Å obtained with the Gemini Multi-Object Spectrograph (GMOS) at Gemini South for 15 galaxies in nine close pairs were used. The spatial distributions of the stellar population contributions were obtained using the stellar population synthesis code starlight. Taking into account the different contributions to the emitted light, we found that most of the galaxies in our sample are dominated by young/intermediate stellar populations. This result differs from the one derived for isolated galaxies, where the old stellar population dominates the disc surface brightness. We interpreted such different behaviour as being due to the effect of gas inflows along the discs of interacting galaxies on the star formation over a time-scale of the order of about 2 Gyr. We also found that, in general, the secondary galaxy of a pair has a higher contribution from the young stellar population than the primary one. We compared the estimated values of stellar and nebular extinction derived from the synthesis method and the Hα/Hβ emission-line ratio, finding that nebular extinctions are systematically higher than stellar ones by about a factor of 2. We did not find any correlation between nebular and stellar metallicities. Neither did we find a correlation between stellar metallicities and ages, while a positive correlation between nebular metallicities and stellar ages was obtained, with older regions being the most metal-rich.

  2. Selection of core animals in the Algorithm for Proven and Young using a simulation model.

    Science.gov (United States)

    Bradford, H L; Pocrnić, I; Fragomeni, B O; Lourenco, D A L; Misztal, I

    2017-12-01

    The Algorithm for Proven and Young (APY) enables the implementation of single-step genomic BLUP (ssGBLUP) in large, genotyped populations by separating genotyped animals into core and non-core subsets and creating a computationally efficient inverse for the genomic relationship matrix (G). As APY became the choice for large-scale genomic evaluations in BLUP-based methods, a common question is how to choose the animals in the core subset. We compared several core definitions to answer this question. Simulations comprised a moderately heritable trait for 95,010 animals and 50,000 genotypes for animals across five generations. Genotypes consisted of 25,500 SNP distributed across 15 chromosomes. Genotyping errors and missing pedigree were also mimicked. Core animals were defined based on individual generations, equal representation across generations, and at random. For a sufficiently large core size, core definitions had the same accuracies and biases, even if the core animals had imperfect genotypes. When genotyped animals had unknown parents, accuracy and bias were significantly better (p ≤ .05) for random and across generation core definitions. © 2017 The Authors. Journal of Animal Breeding and Genetics Published by Blackwell Verlag GmbH.

  3. The evaluation of selected insomnia predictors in adolescents and young adults with cystic fibrosis.

    Science.gov (United States)

    Tomaszek, Lucyna; Cepuch, Grazyna; Pawlik, Lidia

    2018-03-21

    The purpose of the study was to assess the incidence of insomnia in adolescents and young adults with cystic fibrosis and its impact on the quality of life, and to examine whether demographic and clinical factors and negative emotional states are predictors of insomnia in these patients. The study was conducted among 95 cystic fibrosis patients aged 14-25 years. The study used a personal questionnaire survey, the Athens Insomnia Scale, the Cystic Fibrosis Quality of Life Questionnaire, the Hospital Anxiety and Depression Scale, and the Numeric Rating Scale. Insomnia was diagnosed in 38% of cystic fibrosis patients. In patients with insomnia, the level of anxiety (Me: 10 vs. 4; P=0.000) and depression (Me: 6.5 vs. 2; P=0.000) was significantly higher than in the good sleep quality group. The risk of insomnia increases as anxiety (OR: 4.31; 95% CI: 2.20 to 8.41) and depressive symptoms exacerbate (OR: 4.98; 95% CI: 1.84 to 13.43). Insomnia significantly worsens the quality of life in cystic fibrosis patients (ß =-0.5, P=0.000). Insomnia affects a large percentage of cystic fibrosis patients, and anxiety and depression are factors that increase the risk of insomnia. Insomnia decreases the quality of life in cystic fibrosis patients.

  4. SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES

    International Nuclear Information System (INIS)

    Wuyts, Stijn; Förster Schreiber, Natascha M.; Genzel, Reinhard; Lutz, Dieter; Guo Yicheng; Giavalisco, Mauro; Barro, Guillermo; Faber, Sandra M.; Kocevski, Dale D.; Koo, David C.; McGrath, Elizabeth; Bell, Eric F.; Dekel, Avishai; Ferguson, Henry C.; Grogin, Norman A.; Koekemoer, Anton M.; Lotz, Jennifer; Hathi, Nimish P.; Huang, Kuang-Han; Newman, Jeffrey A.

    2012-01-01

    We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies (SFGs) at 0.5 10 M ☉ and have specific star formation rates (SFRs) above 1/t H . We model the seven-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible in the inferred stellar mass distributions. Off-center clumps contribute up to ∼20% to the integrated SFR, but only 7% or less to the integrated mass of all massive SFGs at z ∼ 1 and z ∼ 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100-200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.

  5. Walking, cycling and the urban form: A Heckman selection model of active travel mode and distance by young adolescents

    DEFF Research Database (Denmark)

    Kaplan, Sigal; Nielsen, Thomas Alexander Sick; Prato, Carlo Giacomo

    2016-01-01

    Physical inactivity of children and adolescents is a major public health challenge of the modern era but, when adequately promoted and nurtured, active travel offers immediate health benefits and forms future sustainable and healthy travel habits. This study explores jointly the choice...... and the extent of active travel of young adolescents while considering walking and cycling as distinct travel forms, controlling for objective urban form measures, and taking both a "street-buffer" looking at the immediate home surroundings and a "transport-zone" looking at wider neighborhoods. A Heckman...... selection model represents the distance covered while cycling (walking) given the mode choice being bicycle (walk) for a representative sample of 10-15 year-olds from the Capital Region of Denmark extracted from the Danish national travel survey. Results illustrate the necessity of different urban...

  6. Dress Nicer = Know More? Young Children’s Knowledge Attribution and Selective Learning Based on How Others Dress

    Science.gov (United States)

    McDonald, Kyla P.; Ma, Lili

    2015-01-01

    This research explored whether children judge the knowledge state of others and selectively learn novel information from them based on how they dress. The results indicated that 4- and 6-year-olds identified a formally dressed individual as more knowledgeable about new things in general than a casually dressed one (Study 1). Moreover, children displayed an overall preference to seek help from a formally dressed individual rather than a casually dressed one when learning about novel objects and animals (Study 2). These findings are discussed in relation to the halo effect, and may have important implications for child educators regarding how instructor dress might influence young students’ knowledge attribution and learning preferences. PMID:26636980

  7. Selective REM-sleep deprivation does not diminish emotional memory consolidation in young healthy subjects.

    Science.gov (United States)

    Morgenthaler, Jarste; Wiesner, Christian D; Hinze, Karoline; Abels, Lena C; Prehn-Kristensen, Alexander; Göder, Robert

    2014-01-01

    Sleep enhances memory consolidation and it has been hypothesized that rapid eye movement (REM) sleep in particular facilitates the consolidation of emotional memory. The aim of this study was to investigate this hypothesis using selective REM-sleep deprivation. We used a recognition memory task in which participants were shown negative and neutral pictures. Participants (N=29 healthy medical students) were separated into two groups (undisturbed sleep and selective REM-sleep deprived). Both groups also worked on the memory task in a wake condition. Recognition accuracy was significantly better for negative than for neutral stimuli and better after the sleep than the wake condition. There was, however, no difference in the recognition accuracy (neutral and emotional) between the groups. In summary, our data suggest that REM-sleep deprivation was successful and that the resulting reduction of REM-sleep had no influence on memory consolidation whatsoever.

  8. The relationship between bilingualism and selective attention in young adults: Evidence from an ambiguous figures task.

    Science.gov (United States)

    Chung-Fat-Yim, Ashley; Sorge, Geoff B; Bialystok, Ellen

    2017-03-01

    Previous research has shown that bilinguals outperform monolinguals on a variety of tasks that have been described as involving executive functioning, but the precise mechanism for those effects or a clear definition for "executive function" is unknown. This uncertainty has led to a number of studies for which no performance difference between monolingual and bilingual adults has been detected. One approach to clarifying these issues comes from research with children showing that bilinguals were more able than their monolingual peers to perceive both interpretations of an ambiguous figure, an ability that is more tied to a conception of selective attention than to specific components of executive function. The present study extends this notion to adults by assessing their ability to see the alternative image in an ambiguous figure. Bilinguals performed this task more efficiently than monolinguals by requiring fewer cues to identify the second image. This finding has implications for the role of selective attention in performance differences between monolinguals and bilinguals.

  9. Stellar Atmospheric Modelling for the ACCESS Program

    Science.gov (United States)

    Morris, Matthew; Kaiser, Mary Elizabeth; Bohlin, Ralph; Kurucz, Robert; ACCESS Team

    2018-01-01

    A goal of the ACCESS program (Absolute Color Calibration Experiment for Standard Stars) is to enable greater discrimination between theoretical astrophysical models and observations, where the comparison is limited by systematic errors associated with the relative flux calibration of the targets. To achieve these goals, ACCESS has been designed as a sub-orbital rocket borne payload and ground calibration program, to establish absolute flux calibration of stellar targets at flight candidates, as well as a selection of A and G stars from the CALSPEC database. Stellar atmosphere models were generated using Atlas 9 and Atlas 12 Kurucz stellar atmosphere software. The effective temperature, log(g), metallicity, and redenning were varied and the chi-squared statistic was minimized to obtain a best-fit model. A comparison of these models and the results from interpolation between grids of existing models will be presented. The impact of the flexibility of the Atlas 12 input parameters (e.g. solar metallicity fraction, abundances, microturbulent velocity) is being explored.

  10. Stellar Wind Retention and Expulsion in Massive Star Clusters

    Science.gov (United States)

    Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

    2018-05-01

    Mass and energy injection throughout the lifetime of a star cluster contributes to the gas reservoir available for subsequent episodes of star formation and the feedback energy budget responsible for ejecting material from the cluster. In addition, mass processed in stellar interiors and ejected as winds has the potential to augment the abundance ratios of currently forming stars, or stars which form at a later time from a retained gas reservoir. Here we present hydrodynamical simulations that explore a wide range of cluster masses, compactnesses, metallicities and stellar population age combinations in order to determine the range of parameter space conducive to stellar wind retention or wind powered gas expulsion in star clusters. We discuss the effects of the stellar wind prescription on retention and expulsion effectiveness, using MESA stellar evolutionary models as a test bed for exploring how the amounts of wind retention/expulsion depend upon the amount of mixing between the winds from stars of different masses and ages. We conclude by summarizing some implications for gas retention and expulsion in a variety of compact (σv ≳ 20 kms-1) star clusters including young massive star clusters (105 ≲ M/M⊙ ≲ 107, age ≲ 500 Myrs), intermediate age clusters (105 ≲ M/M⊙ ≲ 107, age ≈ 1 - 4 Gyrs), and globular clusters (105 ≲ M/M⊙ ≲ 107, age ≳ 10 Gyrs).

  11. Evolution of stellar systems

    International Nuclear Information System (INIS)

    Vader, P.

    1981-01-01

    The stellar systems of which the evolution will be considered in this thesis, are either galaxies, which contain about 10 11 stars, or binary systems, which consist of only two stars. It is seen that binary systems can give us some insight into the relative age of the nucleus of M31. The positive correlation between the metal content of a galaxy and its mass, first noted for elliptical galaxies, seems to be a general property of galaxies of all types. The observed increase of metallicity with galaxy mass is too large to be accounted for by differences in the evolutionary stage of galaxies. To explain the observed correlation it is proposed that a relatively larger proportion of massive stars is formed in more massive galaxies. The physical basis is that the formation of massive stars seems to be tied to the enhanced gas-dynamical activity in more massive galaxies. A specific aspect of the production of heavy elements by massive stars is investigated in some detail. In 1979 a cluster of 18 point X-ray sources within 400 pc of the centre of M31 was detected with the Einstein satellite. This is a remarkable result since no equivalent of this cluster has been observed in the nucleus of our own Galaxy, which otherwise is very similar to that of M31. An explanation for this phenomenon is proposed, suggesting that X-ray binaries are the products of the long-term evolution of nova systems. (Auth.)

  12. Stellar extreme ultraviolet astronomy

    International Nuclear Information System (INIS)

    Cash, W.C. Jr.

    1978-01-01

    The design, calibration, and launch of a rocket-borne imaging telescope for extreme ultraviolet astronomy are described. The telescope, which employed diamond-turned grazing incidence optics and a ranicon detector, was launched November 19, 1976, from the White Sands Missile Range. The telescope performed well and returned data on several potential stellar sources of extreme ultraviolet radiation. Upper limits ten to twenty times more sensitive than previously available were obtained for the extreme ultraviolet flux from the white dwarf Sirius B. These limits fall a factor of seven below the flux predicted for the star and demonstrate that the temperature of Sirius B is not 32,000 K as previously measured, but is below 30,000 K. The new upper limits also rule out the photosphere of the white dwarf as the source of the recently reported soft x-rays from Sirius. Two other white dwarf stars, Feige 24 and G191-B2B, were observed. Upper limits on the flux at 300 A were interpreted as lower limits on the interstellar hydrogen column densities to these stars. The lower limits indicate interstellar hydrogen densitites of greater than .02 cm -3 . Four nearby stars (Sirius, Procyon, Capella, and Mirzam) were observed in a search for intense low temperature coronae or extended chromospheres. No extreme ultraviolet radiation from these stars was detected, and upper limits to their coronal emisson measures are derived

  13. Mapping stellar surface features

    International Nuclear Information System (INIS)

    Noah, P.V.

    1987-01-01

    New photometric and spectroscopic observations of the RS Canum Venaticorum binaries Sigma Geminorum and UX Arietis are reported along with details of the Doppler-imaging program SPOTPROF. The observations suggest that the starspot activity on Sigma Gem has decreased to 0.05 magnitude in two years. A photometric spot model for September 1984 to January 1985 found that a single spot covering 2% of the surface and 1000 K cooler than the surrounding photosphere could model the light variations. Equivalent-width observations contemporaneous with the photometric observations did not show any significant variations. Line-profile models from SPOTPROF predict that the variation of the equivalent width of the 6393 A Fe I line should be ∼ 1mA. Photometric observations of UX Ari from January 1984 to March 1985 show an 0.3 magnitude variation indicating a large spot group must cover the surface. Contemporaneous spectroscopic observations show asymmetric line profiles. The Doppler imaging and the photometric light-curve models were used in an iterative method to describe the stellar surface-spot distribution and successfully model both the photometric and the spectroscopic variations

  14. SI: The Stellar Imager

    Science.gov (United States)

    Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

    2006-01-01

    The ultra-sharp images of the Stellar Imager (SI) will revolutionize our view of many dynamic astrophysical processes: The 0.1 milliarcsec resolution of this deep-space telescope will transform point sources into extended sources, and simple snapshots into spellbinding evolving views. SI s science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI s prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era by imaging a sample of magnetically active stars with enough resolution to map their evolving dynamo patterns and their internal flows. By exploring the Universe at ultra-high resolution, SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled structures and processes in the Universe.

  15. Stellar Presentations (Abstract)

    Science.gov (United States)

    Young, D.

    2015-12-01

    (Abstract only) The AAVSO is in the process of expanding its education, outreach and speakers bureau program. powerpoint presentations prepared for specific target audiences such as AAVSO members, educators, students, the general public, and Science Olympiad teams, coaches, event supervisors, and state directors will be available online for members to use. The presentations range from specific and general content relating to stellar evolution and variable stars to specific activities for a workshop environment. A presentation—even with a general topic—that works for high school students will not work for educators, Science Olympiad teams, or the general public. Each audience is unique and requires a different approach. The current environment necessitates presentations that are captivating for a younger generation that is embedded in a highly visual and sound-bite world of social media, twitter and U-Tube, and mobile devices. For educators, presentations and workshops for themselves and their students must support the Next Generation Science Standards (NGSS), the Common Core Content Standards, and the Science Technology, Engineering and Mathematics (STEM) initiative. Current best practices for developing relevant and engaging powerpoint presentations to deliver information to a variety of targeted audiences will be presented along with several examples.

  16. Testosterone may increase selective attention to threat in young male macaques.

    Science.gov (United States)

    Lacreuse, Agnès; King, Hanna M; Kurdziel, Laura B; Partan, Sarah R; Caldwell, Kaelyn M; Chiavetta, Margaret R; Millette, Matthew M; Meyer, Jerrold S; Grow, Daniel R

    2010-11-01

    Animal studies indicate that sex hormones have widespread effects on the brain, cognition and emotion, but findings in humans are inconsistent. Well-controlled studies in nonhuman primates are crucial to resolve these discrepancies. In this study, we examined the effects of testosterone (T) on emotion in male rhesus monkeys. Six young adult males were tested on two emotional tasks during three hormonal conditions in a crossover design: when intact at baseline and when pharmacologically hypogonadal with add-back of T or placebo. The emotional tasks were the Approach-Avoidance task, which tested behavioral responses to three categories of objects (familiar, novel, and negative) and a Social Playback task which tested behavioral responses to scenes of unfamiliar conspecifics engaged in three types of social activities (neutral, positive, or negative). Following a 4-week baseline period, monkeys were treated with Depot Lupron, 200μg/kg before being randomly assigned to one of two treatment groups: Depot Lupron+Testosterone Enanthate (TE, 20mg/kg) or Depot Lupron+oil vehicle. In each treatment group, monkeys received one injection of Lupron and one injection of TE or one injection of Lupron and one injection of oil at the onset of a 4-week testing period, before crossing over to the alternate treatment for an additional 4weeks of testing. TE treatment had no effect on behavioral measures in the Approach-Avoidance task. For the Social Playback task, however, TE significantly increased watching time of video clips which depicted fights between unfamiliar conspecifics. The enhancing effect of T on watching time for negative social scenes is consistent with human data suggesting that T decreases aversion or facilitates approach to threatening social stimuli. Further studies are needed to understand the mechanisms by which T may mediate responsiveness to social threat in male primates. Copyright © 2010 Elsevier Inc. All rights reserved.

  17. HIGH-PRECISION C17O, C18O, AND C16O MEASUREMENTS IN YOUNG STELLAR OBJECTS: ANALOGUES FOR CO SELF-SHIELDING IN THE EARLY SOLAR SYSTEM

    International Nuclear Information System (INIS)

    Smith, Rachel L.; Young, Edward D.; Pontoppidan, Klaus M.; Morris, Mark R.; Van Dishoeck, Ewine F.

    2009-01-01

    Using very high resolution (λ/Δλ ∼ 95 000) 4.7 μm fundamental and 2.3 μm overtone rovibrational CO absorption spectra obtained with the Cryogenic Infrared Echelle Spectrograph infrared spectrometer on the Very Large Telescope (VLT), we report detections of four CO isotopologues-C 16 O, 13 CO, C 18 O, and the rare species, C 17 O-in the circumstellar environment of two young protostars: VV CrA, a binary T Tauri star in the Corona Australis molecular cloud, and Reipurth 50, an intermediate-mass FU Ori star in the Orion Molecular Cloud. We argue that the observed CO absorption lines probe a protoplanetary disk in VV CrA, and a protostellar envelope in Reipurth 50. All CO line profiles are spectrally resolved, with intrinsic line widths of ∼3-4 km s -1 (FWHM), permitting direct calculation of CO oxygen isotopologue ratios with 5%-10% accuracy. The rovibrational level populations for all species can be reproduced by assuming that CO absorption arises in two temperature regimes. In the higher temperature regime, in which the column densities are best determined, the derived oxygen isotope ratios in VV CrA are: [C 16 O]/[C 18 O] =690 ± 30; [C 16 O]/[C 17 O] =2800 ± 300, and [C 18 O]/[C 17 O]=4.1 ± 0.4. For Reipurth 50, we find [C 16 O]/[C 18 O] =490 ± 30; [C 16 O]/[C 17 O] =2200 ± 150, [C 18 O]/[C 17 O] = 4.4 ± 0.2. For both objects, 12 C/ 13 C are on the order of 100, nearly twice the expected interstellar medium (ISM) ratio. The derived oxygen abundance ratios for the VV CrA disk show a significant mass-independent deficit of C 17 O and C 18 O relative to C 16 O compared to ISM baseline abundances. The Reipurth 50 envelope shows no clear differences in oxygen CO isotopologue ratios compared with the local ISM. A mass-independent fractionation can be interpreted as being due to selective photodissociation of CO in the disk surface due to self-shielding. The deficits in C 17 O and C 18 O in the VV CrA protoplanetary disk are consistent with an analogous

  18. "I Don't Shag Dirty Girls": Marginalized Masculinities and the Use of Partner Selection as a Sexual Health Risk Reduction Strategy in Heterosexual Young Men.

    Science.gov (United States)

    Limmer, Mark

    2016-03-01

    Understanding and addressing the sexual risk taking of young men remains a key research, policy, and practice concern in attempts to improve the emotional and physical sexual health of young men and their sexual partners. This article explores one of the ways in which young men attempt to mitigate sexual risk through the assigning of labels to particular young women and using these as a basis for their decisions in relation to sexual activity, contraception, and condom use. The article uses the lens of hegemonic masculinities theory to increase understanding of the role played by the construction and performance of marginalized masculinities and how these in turn are influenced by social exclusionary processes. The article draws on focus group and interview data from 46 young men aged 15 to 17 years living in the northwest of England, purposively selected on the basis of the prevailing policy definitions of social inclusion and exclusion. The article describes a form of marginalized masculinity pertaining to socially excluded young men, which as a result of limited access to other tenets of hegemonic masculinity, is disproportionately reliant on sexual expertise and voracity alongside overt demonstrations of their superiority over women. It is in this context that young women are assigned the labels of "dirty" or "clean" on the basis of a selection of arbitrary judgments relating to dress, demeanor, area of residence, and perceived sexual activities. The motivations of the young men, the impact on young women, and the policy and practice implications are all discussed. © The Author(s) 2014.

  19. Clustering in the stellar abundance space

    Science.gov (United States)

    Boesso, R.; Rocha-Pinto, H. J.

    2018-03-01

    We have studied the chemical enrichment history of the interstellar medium through an analysis of the n-dimensional stellar abundance space. This work is a non-parametric analysis of the stellar chemical abundance space. The main goal is to study the stars from their organization within this abundance space. Within this space, we seek to find clusters (in a statistical sense), that is, stars likely to share similar chemo-evolutionary history, using two methods: the hierarchical clustering and the principal component analysis. We analysed some selected abundance surveys available in the literature. For each sample, we labelled the group of stars according to its average abundance curve. In all samples, we identify the existence of a main enrichment pattern of the stars, which we call chemical enrichment flow. This flow is set by the structured and well-defined mean rate at which the abundances of the interstellar medium increase, resulting from the mixture of the material ejected from the stars and stellar mass-loss and interstellar medium gas. One of the main results of our analysis is the identification of subgroups of stars with peculiar chemistry. These stars are situated in regions outside of the enrichment flow in the abundance space. These peculiar stars show a mismatch in the enrichment rate of a few elements, such as Mg, Si, Sc and V, when compared to the mean enrichment rate of the other elements of the same stars. We believe that the existence of these groups of stars with peculiar chemistry may be related to the accretion of planetary material on to stellar surfaces or may be due to production of the same chemical element by different nucleosynthetic sites.

  20. Turbulence optimisation in stellarator experiments

    Energy Technology Data Exchange (ETDEWEB)

    Proll, Josefine H.E. [Max-Planck/Princeton Center for Plasma Physics (Germany); Max-Planck-Institut fuer Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald (Germany); Faber, Benjamin J. [HSX Plasma Laboratory, University of Wisconsin-Madison, Madison, WI 53706 (United States); Helander, Per; Xanthopoulos, Pavlos [Max-Planck/Princeton Center for Plasma Physics (Germany); Lazerson, Samuel A.; Mynick, Harry E. [Plasma Physics Laboratory, Princeton University, P.O. Box 451 Princeton, New Jersey 08543-0451 (United States)

    2015-05-01

    Stellarators, the twisted siblings of the axisymmetric fusion experiments called tokamaks, have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of stellarators in which the laminar transport is reduced to levels below that of tokamaks by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. Recent analytical theory suggests that the large configuration space of stellarators allows for an additional optimisation of the magnetic field to also reduce the turbulent transport. In this talk, the idea behind the turbulence optimisation is explained. We also present how an optimised equilibrium is obtained and how it might differ from the equilibrium field of an already existing device, and we compare experimental turbulence measurements in different configurations of the HSX stellarator in order to test the optimisation procedure.

  1. Optimizing Stellarators for Turbulent Transport

    International Nuclear Information System (INIS)

    Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.

    2010-01-01

    Up to now, the term 'transport-optimized' stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.

  2. Stellar magnetic activity and exoplanets

    Directory of Open Access Journals (Sweden)

    Vidotto A.A.

    2017-01-01

    Full Text Available It has been proposed that magnetic activity could be enhanced due to interactions between close-in massive planets and their host stars. In this article, I present a brief overview of the connection between stellar magnetic activity and exoplanets. Stellar activity can be probed in chromospheric lines, coronal emission, surface spot coverage, etc. Since these are manifestations of stellar magnetism, these measurements are often used as proxies for the magnetic field of stars. Here, instead of focusing on the magnetic proxies, I overview some recent results of magnetic field measurements using spectropolarimetric observations. Firstly, I discuss the general trends found between large-scale magnetism, stellar rotation, and coronal emission and show that magnetism seems to be correlated to the internal structure of the star. Secondly, I overview some works that show evidence that exoplanets could (or not act as to enhance the activity of their host stars.

  3. Superbanana orbits in stellarator geometries

    International Nuclear Information System (INIS)

    Derr, J.A.; Shohet, J.L.

    1979-04-01

    The presence of superbanana orbit types localized to either the interior or the exterior of stellarators and torsatrons is numerically investigated for 3.5 MeV alpha particles. The absence of the interior superbanana in both geometries is found to be due to non-conservation of the action. Exterior superbananas are found in the stellarator only, as a consequence of the existence of closed helical magnetic wells. No superbananas of either type are found in the torsatron

  4. The galaxy population of Abell 1367: the stellar mass-metallicity relation

    Science.gov (United States)

    Mouhcine, M.; Kriwattanawong, W.; James, P. A.

    2011-04-01

    Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galaxies traces a sequence of varying metallicity at a narrow range of luminosity-weighted stellar ages. Lenticular galaxies in the red sequence, however, exhibit a substantial spread of luminosity-weighted stellar metallicities and ages. For red-sequence lenticular galaxies and blue cloud galaxies, low-mass galaxies tend to be on average dominated by stellar populations of younger luminosity-weighted ages. Sample galaxies exhibit a strong correlation between integrated stellar mass and luminosity-weighted stellar metallicity. Galaxies with signs of morphological disturbance and ongoing star formation activity, tend to be underabundant with respect to passive galaxies in the red sequence of comparable stellar masses. We argue that this could be due to tidally driven gas flows towards the star-forming regions, carrying less enriched gas and diluting the pre-existing gas to produce younger stellar populations with lower metallicities than would be obtained prior to the interaction. Finally, we find no statistically significant evidence for changes in the luminosity-weighted ages and metallicities for either red-sequence or blue-cloud galaxies, at fixed stellar mass, with location within the cluster. We dedicate this work to the memory of our friend and colleague C. Moss who died suddenly recently.

  5. Stellar-to-halo mass relation of cluster galaxies

    International Nuclear Information System (INIS)

    Niemiec, Anna; Jullo, Eric; Limousin, Marceau; Giocoli, Carlo

    2017-01-01

    In the formation of galaxy groups and clusters, the dark matter haloes containing satellite galaxies are expected to be tidally stripped in gravitational interactions with the host. We use galaxy-galaxy weak lensing to measure the average mass of dark matter haloes of satellite galaxies as a function of projected distance to the centre of the host, since stripping is expected to be greater for satellites closer to the centre of the cluster. We further classify the satellites according to their stellar mass: assuming that the stellar component of the galaxy is less disrupted by tidal stripping, stellar mass can be used as a proxy of the infall mass. We study the stellar to halo mass relation of satellites as a function of the cluster-centric distance to measure tidal stripping. We use the shear catalogues of the DES science veri cation archive, the CFHTLenS and the CFHT Stripe 82 surveys, and we select satellites from the redMaPPer catalogue of clusters. For galaxies located in the outskirts of clusters, we nd a stellar to halo mass relation in good agreement with the theoretical expectations from Moster, Naab & White (2013) for central galaxies. In the centre of the cluster, we nd that this relation is shifted to smaller halo mass for a given stellar mass. We interpret this nding as further evidence for tidal stripping of dark matter haloes in high density environments.

  6. Stellar population in star formation regions of galaxies

    Science.gov (United States)

    Gusev, Alexander S.; Shimanovskaya, Elena V.; Shatsky, Nikolai I.; Sakhibov, Firouz; Piskunov, Anatoly E.; Kharchenko, Nina V.

    2018-05-01

    We developed techniques for searching young unresolved star groupings (clusters, associations, and their complexes) and of estimating their physical parameters. Our study is based on spectroscopic, spectrophotometric, and UBVRI photometric observations of 19 spiral galaxies. In the studied galaxies, we found 1510 objects younger than 10 Myr and present their catalogue. Having combined photometric and spectroscopic data, we derived extinctions, chemical abundances, sizes, ages, and masses of these groupings. We discuss separately the specific cases, when the gas extinction does not agree with the interstellar one. We assume that this is due to spatial offset of Hii clouds with respect to the related stellar population.We developed a method to estimate age of stellar population of the studied complexes using their morphology and the relation with associated H emission region. In result we obtained the estimates of chemical abundances for 80, masses for 63, and ages for 57 young objects observed in seven galaxies.

  7. Auditory measures of selective and divided attention in young and older adults using single-talker competition.

    Science.gov (United States)

    Humes, Larry E; Lee, Jae Hee; Coughlin, Maureen P

    2006-11-01

    In this study, two experiments were conducted on auditory selective and divided attention in which the listening task involved the identification of words in sentences spoken by one talker while a second talker produced a very similar competing sentence. Ten young normal-hearing (YNH) and 13 elderly hearing-impaired (EHI) listeners participated in each experiment. The type of attention cue used was the main difference between experiments. Across both experiments, several consistent trends were observed. First, in eight of the nine divided-attention tasks across both experiments, the EHI subjects performed significantly worse than the YNH subjects. By comparison, significant differences in performance between age groups were only observed on three of the nine selective-attention tasks. Finally, there were consistent individual differences in performance across both experiments. Correlational analyses performed on the data from the 13 older adults suggested that the individual differences in performance were associated with individual differences in memory (digit span). Among the elderly, differences in age or differences in hearing loss did not contribute to the individual differences observed in either experiment.

  8. On the dynamics of non-stationary binary stellar systems

    International Nuclear Information System (INIS)

    Bekov, A. A.; Bejsekov, A.N.; Aldibaeva, L.T.

    2005-01-01

    The motion of test body in the external gravitational field of the binary stellar system with slowly variable some physical parameters of radiating components is considered on the base of restricted non-stationary photo-gravitational three and two bodies problem. The family of polar and coplanar solutions are obtained. These solutions give the possibility of the dynamical and structure interpretation of the binary young evolving stars and galaxies. (author)

  9. A Toolbox for Imaging Stellar Surfaces

    Science.gov (United States)

    Young, John

    2018-04-01

    In this talk I will review the available algorithms for synthesis imaging at visible and infrared wavelengths, including both gray and polychromatic methods. I will explain state-of-the-art approaches to constraining the ill-posed image reconstruction problem, and selecting an appropriate regularisation function and strength of regularisation. The reconstruction biases that can follow from non-optimal choices will be discussed, including their potential impact on the physical interpretation of the results. This discussion will be illustrated with example stellar surface imaging results from real VLTI and COAST datasets.

  10. Ecstasy use and serotonin syndrome: a neglected danger to adolescents and young adults prescribed selective serotonin reuptake inhibitors.

    Science.gov (United States)

    Dobry, Yuriy; Rice, Timothy; Sher, Leo

    2013-01-01

    At present, there are scarce clinical and basic lab data concerning the risk of acute serotonin toxicity from selective serotonin reuptake inhibitors (SSRIs) and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) co-administration. The health care community can strongly benefit from efforts to address the high risks associated with serotonin syndrome from this specific drug combination. The aim of this work is to review the risk of serotonin syndrome in adolescents and young adults prescribed with SSRIs and are concurrently using ecstasy. An electronic search of the major behavioral science bibliographic databases (Pubmed, PsycINFO, Medline) was conducted to retrieve peer-reviewed articles, which detail the clinical characteristics, biological mechanisms and social implications of SSRIs, MDMA, and their potential synergism in causing serotonin syndrome in the pediatric and young adult population. Search terms included "serotonin syndrome", "ecstasy", "MDMA", "pediatric", and "SSRI". Additional references were incorporated from the bibliographies of these retrieved articles. MDMA, in combination with the widely-prescribed SSRI antidepressant class, can lead to rapid, synergistic rise of serotonin (5-HT) concentration in the central nervous system, leading to the acute medical emergency known as serotonin syndrome. This review addresses such complication through an exploration of the theoretical mechanisms and clinical manifestations of this life-threatening pharmacological interaction. The increasing incidences of recreational ecstasy use and SSRI pharmacotherapy among multiple psychiatric disorders in the adolescent population have made this an overlooked yet increasingly relevant danger, which poses a threat to public health. This can be curbed through further research, as well as greater health care provision and attention from a regulatory body owing.

  11. The young, the weak and the sick: evidence of natural selection by predation.

    Directory of Open Access Journals (Sweden)

    Meritxell Genovart

    2010-03-01

    Full Text Available It is assumed that predators mainly prey on substandard individuals, but even though some studies partially support this idea, evidence with large sample sizes, exhaustive analysis of prey and robust analysis is lacking. We gathered data from a culling program of yellow-legged gulls killed by two methods: by the use of raptors or by shooting at random. We compared both data sets to assess whether birds of prey killed randomly or by relying on specific individual features of the prey. We carried out a meticulous post-mortem examination of individuals, and analysing multiple prey characteristics simultaneously we show that raptors did not hunt randomly, but rather preferentially predate on juveniles, sick gulls, and individuals with poor muscle condition. Strikingly, gulls with an unusually good muscle condition were also predated more than expected, supporting the mass-dependent predation risk theory. This article provides a reliable example of how natural selection may operate in the wild and proves that predators mainly prey on substandard individuals.

  12. Stellar Interlopers Caught Speeding Through Space

    Science.gov (United States)

    2009-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 1 Figure 2 Figure 3 Figure 4 Click on individual image for larger view Resembling comets streaking across the sky, these four speedy stars are plowing through regions of dense interstellar gas and creating brilliant arrowhead structures and trailing tails of glowing gas. These bright arrowheads, or bow shocks, can be seen in these four images taken with NASA's Hubble Space Telescope. The bow shocks form when the stars' powerful stellar winds, streams of matter flowing from the stars, slam into surrounding dense gas. The phenomenon is similar to that seen when a speeding boat pushes through water on a lake. The stars in these images are among 13 runaway stars spotted by Hubble's Advanced Camera for Surveys. The stars appear to be young, just millions of years old. Their ages are based on their colors and the presence of strong stellar winds, a signature of youthful stars. Depending on their distance from Earth, the bullet-nosed bow shocks could be 100 billion to a trillion miles wide (the equivalent of 17 to 170 solar system diameters, measured out to Neptune's orbit). The bow shocks indicate that the stars are moving fast, more than 180,000 kilometers an hour (more than 112,000 miles an hour) with respect to the dense gas they are plowing through. They are traveling roughly five times faster than typical young stars, relative to their surroundings. The high-speed stars have traveled far from their birth places. Assuming their youthful phase lasts only a million years and they are moving at roughly 180,000 kilometers an hour, the stars have journeyed 160 light-years. The Hubble observations were taken between October 2005 and July 2006.

  13. Investigation into the Effects of Eight Weeks of Step Aerobic Dance Practice on Static Balance, Flexibility and Selected Basketball Skills in Young Basketball Players

    Science.gov (United States)

    Bavli, Özhan

    2016-01-01

    The aim of this study was to investigate the effects of eight weeks of step aerobic exercises on static balance, flexibility and selected basketball skills in young basketball players. A total of 20 basketball players (average age 16.1 ± 0.7 years and average sporting age 4.1 ± 0.7 years) voluntarily joined the study. Participants were randomly…

  14. Engineering aspects of compact stellarators

    International Nuclear Information System (INIS)

    Nelson, B.E.; Benson, R.D.; Brooks, A.

    2003-01-01

    Compact stellarators could combine the good confinement and high beta of a tokamak with the inherently steady state, disruption-free characteristics of a stellarator. Two U.S. compact stellarator facilities are now in the conceptual design phase: the National Compact Stellarator Experiment (NCSX) and the Quasi- Poloidal Stellarator (QPS). NCSX has a major radius of 1.4 m and a toroidal field up to 2 T. The primary feature of both NCSX and QPS is the set of modular coils that provide the basic magnetic configuration. These coils represent a major engineering challenge due to the complex shape, precise geometric accuracy, and high current density of the windings. The winding geometry is too complex for conventional hollow copper conductor construction. Instead, the modular coils will be wound with flexible, multi strand cable conductor that has been compacted to a 75% copper packing fraction. Inside the NCSX coil set and surrounding the plasma is a highly contoured vacuum vessel. The vessel consists of three identical, 120 deg. segments that are bolted together at double sealed joints. The QPS device has a major radius of 0.9 m, a toroidal field of 1 T, and an aspect ratio of only 2.7. Instead of an internal vacuum vessel, the QPS modular coils will operate in an external vacuum tank. (author)

  15. Stellar Oxygen Abundances

    Science.gov (United States)

    King, Jeremy

    1994-04-01

    This dissertation addresses several issues concerning stellar oxygen abundances. The 7774 {\\AA} O I triplet equivalent widths of Abia & Rebolo [1989, AJ, 347, 186] for metal-poor dwarfs are found to be systematically too high. I also argue that current effective temperatures used in halo star abundance studies may be ~150 K too low. New color-Teff relations are derived for metal-poor stars. Using the revised Teff values and improved equivalent widths for the 7774A O I triplet, the mean [O/Fe] ratio for a handful of halo stars is found to be +0.52 with no dependence on Teff or [Fe/H]. Possible cosmological implications of the hotter Teff scale are discussed along with additional evidence supporting the need for a higher temperature scale for metal-poor stars. Our Teff scale leads to a Spite Li plateau value of N(Li)=2.28 +/- 0.09. A conservative minimal primordial value of N(Li)=2.35 is inferred. If errors in the observations and models are considered, consistency with standard models of Big Bang nucleosynthesis is still achieved with this larger Li abundance. The revised Teff scale raises the observed B/Be ratio of HD 140283 from 10 to 12, making its value more comfortably consistent with the production of the observed B and Be by ordinary spallation. Our Teff values are found to be in good agreement with values predicted from both the Victoria and Yale isochrone color-Teff relations. Thus, it appears likely that no changes in globular cluster ages would result. Next, we examine the location of the break in the [O/Fe] versus [Fe/H] plane in a quantitative fashion. Analysis of a relatively homogeneous data set does not favor any unique break point in the range -1.7 /= -3), in agreement with the new results for halo dwarfs. We find that the gap in the observed [O/H] distribution, noted by Wheeler et al. [1989, ARAA, 27, 279], persists despite the addition of more O data and may betray the occurrence of a hiatus in star formation between the end of halo formation and

  16. LMC clusters: young

    International Nuclear Information System (INIS)

    Freeman, K.C.

    1980-01-01

    The young globular clusters of the LMC have ages of 10 7 -10 8 y. Their masses and structure are similar to those of the smaller galactic globular clusters. Their stellar mass functions (in the mass range 6 solar masses to 1.2 solar masses) vary greatly from cluster to cluster, although the clusters are similar in total mass, age, structure and chemical composition. It would be very interesting to know why these clusters are forming now in the LMC and not in the Galaxy. The author considers the 'young globular' or 'blue populous' clusters of the LMC. The ages of these objects are 10 7 to 10 8 y, and their masses are 10 4 to 10 5 solar masses, so they are populous enough to be really useful for studying the evolution of massive stars. The author concentrates on the structure and stellar content of these young clusters. (Auth.)

  17. Planets, stars and stellar systems

    CERN Document Server

    Bond, Howard; McLean, Ian; Barstow, Martin; Gilmore, Gerard; Keel, William; French, Linda

    2013-01-01

    This is volume 3 of Planets, Stars and Stellar Systems, a six-volume compendium of modern astronomical research covering subjects of key interest to the main fields of contemporary astronomy. This volume on “Solar and Stellar Planetary Systems” edited by Linda French and Paul Kalas presents accessible review chapters From Disks to Planets, Dynamical Evolution of Planetary Systems, The Terrestrial Planets, Gas and Ice Giant Interiors, Atmospheres of Jovian Planets, Planetary Magnetospheres, Planetary Rings, An Overview of the Asteroids and Meteorites, Dusty Planetary Systems and Exoplanet Detection Methods. All chapters of the handbook were written by practicing professionals. They include sufficient background material and references to the current literature to allow readers to learn enough about a specialty within astronomy, astrophysics and cosmology to get started on their own practical research projects. In the spirit of the series Stars and Stellar Systems published by Chicago University Press in...

  18. The relationships of coping, negative thinking, life satisfaction, social support, and selected demographics with anxiety of young adult college students.

    Science.gov (United States)

    Mahmoud, Jihan S R; Staten, Ruth Topsy; Lennie, Terry A; Hall, Lynne A

    2015-05-01

    Understanding young adults' anxiety requires applying a multidimensional approach to assess the psychosocial, behavioral, and cognitive aspects of this phenomenon. A hypothesized model of the relationships among coping style, thinking style, life satisfaction, social support, and selected demographics and anxiety among college students was tested using path analysis. A total of 257 undergraduate students aged 18-24 years completed an online survey. The independent variables were measured using the Multidimensional Scale of Perceived Social Support, the Brief Students' Multidimensional Life Satisfaction Scale, the Brief COPE Inventory, the Positive Automatic Thoughts Questionnaire, and the Cognition Checklist-Anxiety. The outcome, anxiety, was measured using the Anxiety subscale of the 21-item Depression Anxiety and Stress Scale. Only negative thinking and maladaptive coping had a direct relationship with anxiety. Negative thinking was the strongest predictor of both maladaptive coping and anxiety. These findings suggest that helping undergraduates manage their anxiety by reducing their negative thinking is critical. Designing and testing interventions to decrease negative thinking in college students is recommended for future research. © 2015 Wiley Periodicals, Inc.

  19. Infrared Extinction and Stellar Populations in the Milky Way Midplane

    Science.gov (United States)

    Zasowski, Gail; Majewski, S. R.; Benjamin, R. A.; Nidever, D. L.; Skrutskie, M. F.; Indebetouw, R.; Patterson, R. J.; Meade, M. R.; Whitney, B. A.; Babler, B.; Churchwell, E.; Watson, C.

    2012-01-01

    The primary laboratory for developing and testing models of galaxy formation, structure, and evolution is our own Milky Way, the closest large galaxy and the only one in which we can resolve large numbers of individual stars. The recent availability of extensive stellar surveys, particularly infrared ones, has enabled precise, contiguous measurement of large-scale Galactic properties, a major improvement over inferences based on selected, but scattered, sightlines. However, our ability to fully exploit the Milky Way as a galactic laboratory is severely hampered by the fact that its midplane and central bulge -- where most of the Galactic stellar mass lies -- is heavily obscured by interstellar dust. Therefore, proper consideration of the interstellar extinction is crucial. This thesis describes a new extinction-correction method (the RJCE method) that measures the foreground extinction towards each star and, in many cases, enables recovery of its intrinsic stellar type. We have demonstrated the RJCE Method's validity and used it to produce new, reliable extinction maps of the heavily-reddened Galactic midplane. Taking advantage of the recovered stellar type information, we have generated maps probing the extinction at different heliocentric distances, thus yielding information on the elusive three-dimensional distribution of the interstellar dust. We also performed a study of the interstellar extinction law itself which revealed variations previously undetected in the diffuse ISM and established constraints on models of ISM grain formation and evolution. Furthermore, we undertook a study of large-scale stellar structure in the inner Galaxy -- the bar(s), bulge(s), and inner spiral arms. We used observed and extinction-corrected infrared photometry to map the coherent stellar features in these heavily-obscured parts of the Galaxy, placing constraints on models of the central stellar mass distribution.

  20. Stellar CME candidates: towards a stellar CME-flare relation

    Science.gov (United States)

    Paraskevi Moschou, Sofia; Drake, Jeremy J.; Cohen, Ofer; Alvarado-Gomez, Julian D.; Garraffo, Cecilia

    2018-06-01

    For decades the Sun has been the only star that allowed for direct CME observations. Recently, with the discovery of multiple extrasolar systems, it has become imperative that the role of stellar CMEs be assessed in the context of exoplanetary habitability. Solar CMEs and flares show a higher association with increasing flaring energy, with strong flares corresponding to large and fast CMEs. As argued in earlier studies, extrasolar environments around active stars are potentially dominated by CMEs, as a result of their extreme flaring activity. This has strong implications for the energy budget of the system and the atmospheric erosion of orbiting planets.Nevertheless, with current instrumentation we are unable to directly observe CMEs in even the closest stars, and thus we have to look for indirect techniques and observational evidence and signatures for the eruption of stellar CMEs. There are three major observational techniques for tracing CME signatures in other stellar systems, namely measuring Type II radio bursts, Doppler shifts in UV/optical lines or transient absorption in the X-ray spectrum. We present observations of the most probable stellar CME candidates captured so far and examine the different observational techniques used together with their levels of uncertainty. Assuming that they were CMEs, we try to asses their kinematic and energetic characteristics and place them in an extension of the well-established solar CME-flare energy scaling law. We finish by discussing future observations for direct measurements.

  1. STELLAR, GAS, AND DARK MATTER CONTENT OF BARRED GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Cervantes Sodi, Bernardo, E-mail: b.cervantes@crya.unam.mx [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Campus Morelia, A.P. 3-72, C.P. 58089 Michoacán, México (Mexico)

    2017-01-20

    We select a sample of galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) where galaxies are classified, through visual inspection, as hosting strong bars, weak bars, or as unbarred galaxies, and make use of H i mass and kinematic information from the Arecibo Legacy Fast ALFA survey catalog, to study the stellar, atomic gas, and dark matter content of barred disk galaxies. We find, in agreement with previous studies, that the bar fraction increases with increasing stellar mass. A similar trend is found with total baryonic mass, although the dependence is not as strong as with stellar mass, due to the contribution of gas. The bar fraction shows a decrease with increasing gas mass fraction. This anticorrelation between the likelihood of a galaxy hosting a bar with the gas richness of the galaxy results from the inhibiting effect the gas has in the formation of bars. We also find that for massive galaxies with stellar masses larger than 10{sup 10} M {sub ⊙}, at fixed stellar mass, the bar fraction decreases with increasing global halo mass (i.e., halo mass measured up to a radius of the order of the H i disk extent).

  2. Associations among Selected Motor Skills and Health-Related Fitness: Indirect Evidence for Seefeldt's Proficiency Barrier in Young Adults?

    Science.gov (United States)

    Stodden, David F.; True, Larissa K.; Langendorfer, Stephen J.; Gao, Zan

    2013-01-01

    Purpose: This exploratory study examined the notion of Seefeldt's (1980) hypothesized motor skill "proficiency barrier" related to composite levels of health-related physical fitness (HRF) in young adults. Method: A motor skill competence (MSC) index composed of maximum throwing and kicking speed and jumping distance in 187 young adults…

  3. Science with Synthetic Stellar Surveys

    Science.gov (United States)

    Sanderson, Robyn Ellyn

    2018-04-01

    A new generation of observational projects is poised to revolutionize our understanding of the resolved stellar populations of Milky-Way-like galaxies at an unprecedented level of detail, ushering in an era of precision studies of galaxy formation. In the Milky Way itself, astrometric, spectroscopic and photometric surveys will measure three-dimensional positions and velocities and numerous chemical abundances for stars from the disk to the halo, as well as for many satellite dwarf galaxies. In the Local Group and beyond, HST, JWST and eventually WFIRST will deliver pristine views of resolved stars. The groundbreaking scale and dimensionality of this new view of resolved stellar populations in galaxies challenge us to develop new theoretical tools to robustly compare these surveys to simulated galaxies, in order to take full advantage of our new ability to make detailed predictions for stellar populations within a cosmological context. I will describe a framework for generating realistic synthetic star catalogs and mock surveys from state-of-the-art cosmological-hydrodynamical simulations, and present several early scientific results from, and predictions for, resolved stellar surveys of our Galaxy and its neighbors.

  4. Maximum stellar iron core mass

    Indian Academy of Sciences (India)

    An analytical method of estimating the mass of a stellar iron core, just prior to core collapse, is described in this paper. The method employed depends, in part, upon an estimate of the true relativistic mass increase experienced by electrons within a highly compressed iron core, just prior to core collapse, and is significantly ...

  5. Maximum stellar iron core mass

    Indian Academy of Sciences (India)

    60, No. 3. — journal of. March 2003 physics pp. 415–422. Maximum stellar iron core mass. F W GIACOBBE. Chicago Research Center/American Air Liquide ... iron core compression due to the weight of non-ferrous matter overlying the iron cores within large .... thermal equilibrium velocities will tend to be non-relativistic.

  6. Integrated Circuit Stellar Magnitude Simulator

    Science.gov (United States)

    Blackburn, James A.

    1978-01-01

    Describes an electronic circuit which can be used to demonstrate the stellar magnitude scale. Six rectangular light-emitting diodes with independently adjustable duty cycles represent stars of magnitudes 1 through 6. Experimentally verifies the logarithmic response of the eye. (Author/GA)

  7. Stellar dynamics and black holes

    Indian Academy of Sciences (India)

    Chandrasekhar's most important contribution to stellar dynamics was the concept of dynamical friction. I briefly review that work, then discuss some implications of Chandrasekhar's theory of gravitational encounters for motion in galactic nuclei. Author Affiliations. David Merritt1. Department of Physics, Rochester Institute ...

  8. TEM turbulence optimisation in stellarators

    Science.gov (United States)

    Proll, J. H. E.; Mynick, H. E.; Xanthopoulos, P.; Lazerson, S. A.; Faber, B. J.

    2016-01-01

    With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has been achieved via shaping of the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence is addressed in the present paper. Recent analytical and numerical findings suggest TEMs are stabilised when a large fraction of trapped particles experiences favourable bounce-averaged curvature. This is the case for example in Wendelstein 7-X (Beidler et al 1990 Fusion Technol. 17 148) and other Helias-type stellarators. Using this knowledge, a proxy function was designed to estimate the TEM dynamics, allowing optimal configurations for TEM stability to be determined with the STELLOPT (Spong et al 2001 Nucl. Fusion 41 711) code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stellarator experiment HSX (Anderson et al 1995 Fusion Technol. 27 273) is presented for which a reduction of the linear growth rates is achieved over a broad range of the operational parameter space. As an important consequence of this property, the turbulent heat flux levels are reduced compared with the initial configuration.

  9. Stellar Parameters for Trappist-1

    Science.gov (United States)

    Van Grootel, Valérie; Fernandes, Catarina S.; Gillon, Michael; Jehin, Emmanuel; Manfroid, Jean; Scuflaire, Richard; Burgasser, Adam J.; Barkaoui, Khalid; Benkhaldoun, Zouhair; Burdanov, Artem; Delrez, Laetitia; Demory, Brice-Olivier; de Wit, Julien; Queloz, Didier; Triaud, Amaury H. M. J.

    2018-01-01

    TRAPPIST-1 is an ultracool dwarf star transited by seven Earth-sized planets, for which thorough characterization of atmospheric properties, surface conditions encompassing habitability, and internal compositions is possible with current and next-generation telescopes. Accurate modeling of the star is essential to achieve this goal. We aim to obtain updated stellar parameters for TRAPPIST-1 based on new measurements and evolutionary models, compared to those used in discovery studies. We present a new measurement for the parallax of TRAPPIST-1, 82.4 ± 0.8 mas, based on 188 epochs of observations with the TRAPPIST and Liverpool Telescopes from 2013 to 2016. This revised parallax yields an updated luminosity of {L}* =(5.22+/- 0.19)× {10}-4 {L}ȯ , which is very close to the previous estimate but almost two times more precise. We next present an updated estimate for TRAPPIST-1 stellar mass, based on two approaches: mass from stellar evolution modeling, and empirical mass derived from dynamical masses of equivalently classified ultracool dwarfs in astrometric binaries. We combine them using a Monte-Carlo approach to derive a semi-empirical estimate for the mass of TRAPPIST-1. We also derive estimate for the radius by combining this mass with stellar density inferred from transits, as well as an estimate for the effective temperature from our revised luminosity and radius. Our final results are {M}* =0.089+/- 0.006 {M}ȯ , {R}* =0.121+/- 0.003 {R}ȯ , and {T}{eff} = 2516 ± 41 K. Considering the degree to which the TRAPPIST-1 system will be scrutinized in coming years, these revised and more precise stellar parameters should be considered when assessing the properties of TRAPPIST-1 planets.

  10. Targeted Optimization of Quasi-Symmetric Stellarators

    International Nuclear Information System (INIS)

    Hegna, Chris C.; Talmadge, J. N.

    2016-01-01

    The proposed research focuses on targeted areas of plasma physics dedicated to improving the stellarator concept. Research was pursued in the technical areas of edge/divertor physics in 3D configurations, magnetic island physics in stellarators, the role of 3D shaping on microinstabilities and turbulent transport and energetic ion confinement in stellarators.

  11. Targeted Optimization of Quasi-Symmetric Stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Hegna, Chris C. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics; Anderson, D. T. [Univ. of Wisconsin, Madison, WI (United States); Talmadge, J. N. [Univ. of Wisconsin, Madison, WI (United States)

    2016-10-06

    The proposed research focuses on targeted areas of plasma physics dedicated to improving the stellarator concept. Research was pursued in the technical areas of edge/divertor physics in 3D configurations, magnetic island physics in stellarators, the role of 3D shaping on microinstabilities and turbulent transport and energetic ion confinement in stellarators.

  12. UARS Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) Level 3BS V001

    Data.gov (United States)

    National Aeronautics and Space Administration — The Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) Level 3BS data product consists of daily, 1 nm resolution, solar spectral irradiances and selected...

  13. Students Excited by Stellar Discovery

    Science.gov (United States)

    2011-02-01

    In the constellation of Ophiuchus, above the disk of our Milky Way Galaxy, there lurks a stellar corpse spinning 30 times per second -- an exotic star known as a radio pulsar. This object was unknown until it was discovered last week by three high school students. These students are part of the Pulsar Search Collaboratory (PSC) project, run by the National Radio Astronomy Observatory (NRAO) in Green Bank, WV, and West Virginia University (WVU). The pulsar, which may be a rare kind of neutron star called a recycled pulsar, was discovered independently by Virginia students Alexander Snider and Casey Thompson, on January 20, and a day later by Kentucky student Hannah Mabry. "Every day, I told myself, 'I have to find a pulsar. I better find a pulsar before this class ends,'" said Mabry. When she actually made the discovery, she could barely contain her excitement. "I started screaming and jumping up and down." Thompson was similarly expressive. "After three years of searching, I hadn't found a single thing," he said, "but when I did, I threw my hands up in the air and said, 'Yes!'." Snider said, "It actually feels really neat to be the first person to ever see something like that. It's an uplifting feeling." As part of the PSC, the students analyze real data from NRAO's Robert C. Byrd Green Bank Telescope (GBT) to find pulsars. The students' teachers -- Debra Edwards of Sherando High School, Leah Lorton of James River High School, and Jennifer Carter of Rowan County Senior High School -- all introduced the PSC in their classes, and interested students formed teams to continue the work. Even before the discovery, Mabry simply enjoyed the search. "It just feels like you're actually doing something," she said. "It's a good feeling." Once the pulsar candidate was reported to NRAO, Project Director Rachel Rosen took a look and agreed with the young scientists. A followup observing session was scheduled on the GBT. Snider and Mabry traveled to West Virginia to assist in the

  14. EXPERIENCE OF USING A NON-SELECTIVE BETA-BLOCKER IN COMPLEX THERAPY OF REPOLARIZATION DISORDERS IN YOUNG ATHLETES

    Directory of Open Access Journals (Sweden)

    A. Yu. Tikhomirov

    2017-01-01

    Full Text Available Purpose. To study the effectiveness of various schemes of correction of repolarization disorder syndrome, including with the use of beta-blockers, in young athletes of the initial training group.Materials and methods. At the first stage, 410 children involved in sports sections were examined. The average age of the examined was 12.22 ± 3.11 years. At the second stage, the athletes (boys of the initial training group were selected from the surveyed contingent, engaged in martial arts. The groups were formed: A – people with violation of myocardial repolarization processes (72 patients, the average age 10,50 ± 0,35 years, the control group – people without changes in an electrocardiogram (33 people, the average age 10.36 ± 0, 62 years old. All underwent an electrocardiographic study at rest and after physical activity on the Innomed HS80GL apparatus with analysis of the main indicators. The vegetative status and the state of adaptation were estimated by Kerdo index and adaptive potential by Baevsky. After the examination, the subgroup A1 (40 people was prescribed metabolic and antioxidant drugs. Additionally, in the subgroup A2 (32 people, a non-selective beta-blocker was included in the treatment regimen. The course of treatment is 10 days. The analysis of indicators was carried out in 10 days and in a month after the initiation treatment. Statistical processing was carried out in the program Statistica.Results. An earlier disappearance of cardialgia was determined in the subgroup A2 (p < 0.05, whereas in the subgroup A1, 5% of patients had complaints not only at the end of the course, but also a month later after the initiation treatment. The more rapid positive dynamics of the electrocardiographic pattern with a more stable result was observed with the prescription of a beta-blocker.Conclusion. It was proved the advisability of prescribing of beta-blockers in the treatment of beginning athletes with violation of myocardial repolarization

  15. Investigating stellar surface rotation using observations of starspots

    DEFF Research Database (Denmark)

    Korhonen, Heidi Helena

    2011-01-01

    Rapid rotation enhances the dynamo operating in stars, and thus also introduces significantly stronger magnetic activity than is seen in slower rotators. Many young cool stars still have the rapid, primordial rotation rates induced by the interstellar molecular cloud from which they were formed....... Also older stars in close binary systems are often rapid rotators. These types of stars can show strong magnetic activity and large starspots. In the case of large starspots which cause observable changes in the brightness of the star, and even in the shapes of the spectral line profiles, one can get...... information on the rotation of the star. At times even information on the spot rotation at different stellar latitudes can be obtained, similarly to the solar surface differential rotation measurements using magnetic features as tracers. Here, I will review investigations of stellar rotation based...

  16. A classification scheme for young stellar objects using the wide-field infrared survey explorer AllWISE catalog: revealing low-density star formation in the outer galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Koenig, X. P. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Leisawitz, D. T. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2014-08-20

    We present an assessment of the performance of WISE and the AllWISE data release for a section of the Galactic Plane. We lay out an approach to increasing the reliability of point-source photometry extracted from the AllWISE catalog in Galactic Plane regions using parameters provided in the catalog. We use the resulting catalog to construct a new, revised young star detection and classification scheme combining WISE and 2MASS near- and mid-infrared colors and magnitudes and test it in a section of the outer Milky Way. The clustering properties of the candidate Class I and II stars using a nearest neighbor density calculation and the two-point correlation function suggest that the majority of stars do form in massive star-forming regions, and any isolated mode of star formation is at most a small fraction of the total star forming output of the Galaxy. We also show that the isolated component may be very small and could represent the tail end of a single mechanism of star formation in line with models of molecular cloud collapse with supersonic turbulence and not a separate mode all to itself.

  17. The Resilience of Kepler Systems to Stellar Obliquity

    Science.gov (United States)

    Spalding, Christopher; Marx, Noah W.; Batygin, Konstantin

    2018-04-01

    The Kepler mission and its successor K2 have brought forth a cascade of transiting planets. Many of these planetary systems exhibit multiple members, but a large fraction possess only a single transiting example. This overabundance of singles has led to the suggestion that up to half of Kepler systems might possess significant mutual inclinations between orbits, reducing the transiting number (the so-called “Kepler Dichotomy”). In a recent paper, Spalding & Batygin demonstrated that the quadrupole moment arising from a young, oblate star is capable of misaligning the constituent orbits of a close-in planetary system enough to reduce their transit number, provided that the stellar spin axis is sufficiently misaligned with respect to the planetary orbital plane. Moreover, tightly packed planetary systems were shown to be susceptible to becoming destabilized during this process. Here, we investigate the ubiquity of the stellar obliquity-driven instability within systems with a range of multiplicities. We find that most planetary systems analyzed, including those possessing only two planets, underwent instability for stellar spin periods below ∼3 days and stellar tilts of order 30°. Moreover, we are able to place upper limits on the stellar obliquity in systems such as K2-38 (obliquity ≲20°), where other methods of measuring the spin–orbit misalignment are not currently available. Given the known parameters of T-Tauri stars, we predict that up to one-half of super-Earth-mass systems may encounter the instability, in general agreement with the fraction typically proposed to explain the observed abundance of single-transiting systems.

  18. THE DYNAMICAL EVOLUTION OF STELLAR BLACK HOLES IN GLOBULAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Morscher, Meagan; Pattabiraman, Bharath; Rodriguez, Carl; Rasio, Frederic A.; Umbreit, Stefan, E-mail: m.morscher@u.northwestern.edu [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, Evanston, IL (United States)

    2015-02-10

    Our current understanding of the stellar initial mass function and massive star evolution suggests that young globular clusters (GCs) may have formed hundreds to thousands of stellar-mass black holes (BHs), the remnants of stars with initial masses from ∼20-100 M {sub ☉}. Birth kicks from supernova explosions may eject some BHs from their birth clusters, but most should be retained. Using a Monte Carlo method we investigate the long-term dynamical evolution of GCs containing large numbers of stellar BHs. We describe numerical results for 42 models, covering a broad range of realistic initial conditions, including up to 1.6 × 10{sup 6} stars. In almost all models we find that significant numbers of BHs (up to ∼10{sup 3}) are retained all the way to the present. This is in contrast to previous theoretical expectations that most BHs should be ejected dynamically within a few gigayears The main reason for this difference is that core collapse driven by BHs (through the Spitzer {sup m}ass segregation instability{sup )} is easily reverted through three-body processes, and involves only a small number of the most massive BHs, while lower-mass BHs remain well-mixed with ordinary stars far from the central cusp. Thus the rapid segregation of stellar BHs does not lead to a long-term physical separation of most BHs into a dynamically decoupled inner core, as often assumed previously. Combined with the recent detections of several BH X-ray binary candidates in Galactic GCs, our results suggest that stellar BHs could still be present in large numbers in many GCs today, and that they may play a significant role in shaping the long-term dynamical evolution and the present-day dynamical structure of many clusters.

  19. A new analysis of the momentum and mass-loss rates of stellar jets

    International Nuclear Information System (INIS)

    Raga, A.C.

    1991-01-01

    A very important question in the theory of bipolar outflows from young stars is posed by the still not understood relation between molecular outflows and optical outflows (i.e., stellar jets and Herbig-Haro objects). In some past studies, estimates of mass and momentum rates associated with these outflows indicated that stellar jets have approximately 2 orders of magnitude smaller values for these parameters than the molecular outflows associated with the same sources. However, a reanalysis of observations of stellar jets in the light of new theoretical jet models yields values of mass and momentum rates comparable to the ones of molecular outflows. From this result it can be tentatively speculated that stellar jets (or Herbig-Haro objects) and molecular outflows might be different manifestations of basically the same flow. 21 refs

  20. The Environments of High-Redshift Quasi-Stellar Objects

    Science.gov (United States)

    Kim, Soyoung; Stiavelli, Massimo; Trenti, M.; Pavlovsky, C. M.; Djorgovski, S. G.; Scarlata, C.; Stern, D.; Mahabal, A.; Thompson, D.; Dickinson, M.; Panagia, N.; Meylan, G.

    2009-04-01

    We present a sample of i 775-dropout candidates identified in five Hubble Advanced Camera for Surveys (ACS) fields centered on Sloan Digital Sky Survey quasi-stellar objects (QSOs) at redshift z ~ 6. Our fields are as deep as the GOODS ACS images, which are used as a reference field sample. We find them to be overdense in two fields, underdense in two fields, and as dense as the average density of GOODS in one field. The two excess fields show significantly different color distributions from that of GOODS at the 99% confidence level, strengthening the idea that the excess objects are indeed associated with the QSO. The distribution of i 775-dropout counts in the five fields is broader than that derived from GOODS at the 80%-96% confidence level, depending on which selection criteria were adopted to identify i 775-dropouts; its width cannot be explained by cosmic variance alone. Thus, QSOs seem to affect their environments in complex ways. We suggest the picture where the highest redshift QSOs are located in very massive overdensities and are therefore surrounded by an overdensity of lower mass halos. Radiative feedback by the QSO can in some cases prevent halos from becoming galaxies, thereby generating in extreme cases an underdensity of galaxies. The presence of both enhancement and suppression is compatible with the expected differences between lines of sight at the end of reionization as the presence of residual diffuse neutral hydrogen would provide young galaxies with shielding from the radiative effects of the QSO. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities of Research in Astronomy, Inc., under NASA contract NAS5-26555.

  1. THE ENVIRONMENTS OF HIGH-REDSHIFT QUASI-STELLAR OBJECTS

    International Nuclear Information System (INIS)

    Kim, Soyoung; Stiavelli, Massimo; Trenti, M.; Pavlovsky, C. M.; Djorgovski, S. G.; Scarlata, C.; Stern, D.; Mahabal, A.; Thompson, D.; Panagia, N.; Dickinson, M.; Meylan, G.

    2009-01-01

    We present a sample of i 775 -dropout candidates identified in five Hubble Advanced Camera for Surveys (ACS) fields centered on Sloan Digital Sky Survey quasi-stellar objects (QSOs) at redshift z ∼ 6. Our fields are as deep as the GOODS ACS images, which are used as a reference field sample. We find them to be overdense in two fields, underdense in two fields, and as dense as the average density of GOODS in one field. The two excess fields show significantly different color distributions from that of GOODS at the 99% confidence level, strengthening the idea that the excess objects are indeed associated with the QSO. The distribution of i 775 -dropout counts in the five fields is broader than that derived from GOODS at the 80%-96% confidence level, depending on which selection criteria were adopted to identify i 775 -dropouts; its width cannot be explained by cosmic variance alone. Thus, QSOs seem to affect their environments in complex ways. We suggest the picture where the highest redshift QSOs are located in very massive overdensities and are therefore surrounded by an overdensity of lower mass halos. Radiative feedback by the QSO can in some cases prevent halos from becoming galaxies, thereby generating in extreme cases an underdensity of galaxies. The presence of both enhancement and suppression is compatible with the expected differences between lines of sight at the end of reionization as the presence of residual diffuse neutral hydrogen would provide young galaxies with shielding from the radiative effects of the QSO.

  2. Ambitious Survey Spots Stellar Nurseries

    Science.gov (United States)

    2010-08-01

    -dimensional geometry of the Magellanic system. Chris Evans from the VMC team adds: "The VISTA images will allow us to extend our studies beyond the inner regions of the Tarantula into the multitude of smaller stellar nurseries nearby, which also harbour a rich population of young and massive stars. Armed with the new, exquisite infrared images, we will be able to probe the cocoons in which massive stars are still forming today, while also looking at their interaction with older stars in the wider region." The wide-field image shows a host of different objects. The bright area above the centre is the Tarantula Nebula itself, with the RMC 136 cluster of massive stars in its core. To the left is the NGC 2100 star cluster. To the right is the tiny remnant of the supernova SN1987A (eso1032). Below the centre are a series of star-forming regions including NGC 2080 - nicknamed the "Ghost Head Nebula" - and the NGC 2083 star cluster. The VISTA Magellanic Cloud Survey is one of six huge near-infrared surveys of the southern sky that will take up most of the first five years of operations of VISTA. Notes [1] VISTA ― the Visible and Infrared Survey Telescope for Astronomy ― is the newest telescope at ESO's Paranal Observatory in northern Chile. VISTA is a survey telescope working at near-infrared wavelengths and is the world's largest survey telescope. Its large mirror, wide field of view and very sensitive detectors will reveal a completely new view of the southern sky. The telescope is housed on the peak adjacent to the one hosting ESO's Very Large Telescope (VLT) and shares the same exceptional observing conditions. VISTA has a main mirror that is 4.1 m across. In photographic terms it can be thought of as a 67-megapixel digital camera with a 13 000 mm f/3.25 mirror lens. More information ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries

  3. CHARACTERIZING ULTRAVIOLET AND INFRARED OBSERVATIONAL PROPERTIES FOR GALAXIES. I. INFLUENCES OF DUST ATTENUATION AND STELLAR POPULATION AGE

    International Nuclear Information System (INIS)

    Mao Yewei; Kong Xu; Kennicutt, Robert C. Jr.; Hao, Cai-Na; Zhou Xu

    2012-01-01

    The correlation between infrared-to-ultraviolet luminosity ratio and ultraviolet color (or ultraviolet spectral slope), i.e., the IRX-UV (or IRX-β) relation, found in studies of starburst galaxies is a prevalent recipe for correcting extragalactic dust attenuation. Considerable dispersion in this relation discovered for normal galaxies, however, complicates its usability. In order to investigate the cause of the dispersion and to have a better understanding of the nature of the IRX-UV relation, in this paper, we select five nearby spiral galaxies, and perform spatially resolved studies on each of the galaxies, with a combination of ultraviolet and infrared imaging data. We measure all positions within each galaxy and divide the extracted regions into young and evolved stellar populations. By means of this approach, we attempt to discover separate effects of dust attenuation and stellar population age on the IRX-UV relation for individual galaxies. In this work, in addition to dust attenuation, stellar population age is interpreted to be another parameter in the IRX-UV function, and the diversity of star formation histories is suggested to disperse the age effects. At the same time, strong evidence shows the need for more parameters in the interpretation of observational data, such as variations in attenuation/extinction law. Fractional contributions of different components to the integrated luminosities of the galaxies suggest that the integrated measurements of these galaxies, which comprise different populations, would weaken the effect of the age parameter on IRX-UV diagrams. The dependence of the IRX-UV relation on luminosity and radial distance in galaxies presents weak trends, which offers an implication of selective effects. The two-dimensional maps of the UV color and the infrared-to-ultraviolet ratio are displayed and show a disparity in the spatial distributions between the two galaxy parameters, which offers a spatial interpretation of the scatter in

  4. Intergalactic stellar populations in intermediate redshift clusters

    Science.gov (United States)

    Melnick, J.; Giraud, E.; Toledo, I.; Selman, F.; Quintana, H.

    2012-11-01

    A substantial fraction of the total stellar mass in rich clusters of galaxies resides in a diffuse intergalactic component usually referred to as the intracluster light (ICL). Theoretical models indicate that these intergalactic stars originate mostly from the tidal interaction of the cluster galaxies during the assembly history of the cluster, and that a significant fraction of these stars could have formed in situ from the late infall of cold metal-poor gas clouds on to the cluster. However, these models also overpredict the fraction of stellar mass in the ICL by a substantial margin, something that is still not well understood. The models also make predictions about the age distribution of the ICL stars, which may provide additional observational constraints. Here we present population synthesis models for the ICL of an intermediate redshift (z = 0.29) X-ray cluster that we have extensively studied in previous papers. The advantage of observing intermediate redshift clusters rather than nearby ones is that the former fit the field of view of multi-object spectrographs in 8-m telescopes and therefore permit us to encompass most of the ICL with only a few well-placed slits. In this paper we show that by stacking spectra at different locations within the ICL it is possible to reach sufficiently high signal-to-noise ratios to fit population synthesis models and derive meaningful results. The models provide ages and metallicities for the dominant populations at several different locations within the ICL and the brightest cluster galaxies (BCG) halo, as well as measures of the kinematics of the stars as a function of distance from the BCG. We thus find that the ICL in our cluster is dominated by old metal-rich stars, at odds with what has been found in nearby clusters where the stars that dominate the ICL are old and metal poor. While we see weak evidence of a young, metal-poor component, if real, these young stars would amount to less than 1 per cent of the total ICL

  5. Characterizing stellar and exoplanetary environments

    CERN Document Server

    Khodachenko, Maxim

    2015-01-01

    In this book an international group of specialists discusses studies of exoplanets subjected to extreme stellar radiation and plasma conditions. It is shown that such studies will help us to understand how terrestrial planets and their atmospheres, including the early Venus, Earth and Mars, evolved during the host star’s active early phase. The book presents an analysis of findings from Hubble Space Telescope observations of transiting exoplanets, as well as applications of advanced numerical models for characterizing the upper atmosphere structure and stellar environments of exoplanets. The authors also address detections of atoms and molecules in the atmosphere of “hot Jupiters” by NASA’s Spitzer telescope. The observational and theoretical investigations and discoveries presented are both timely and important in the context of the next generation of space telescopes. 
 The book is divided into four main parts, grouping chapters on exoplanet host star radiation and plasma environments, exoplanet u...

  6. Hydromagnetic instability in a stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Kruskal, M D; Gottlieb, M B; Johnson, J L; Goldman, L M [Project Matterhorn, Princeton University, Princeton, NJ (United States)

    1958-07-01

    It was noted that when there is a uniform externally imposed longitudinal field much larger than the field of the discharge current, one should expect instabilities in the form of a lateral displacement of the plasma column into a helix of large pitch. At the wavelength of fastest growth the e-folding time approximates the time it takes a sound wave in the plasma to traverse the radius of the plasma column. This problem has been re-examines under the conditions which might be expected to occur in the stellarator during ohmic heating, including the presence of external conductors. The theory is applied to the stellarator; and it is shown that the external conductors are in fact unimportant. The important effects due to the finite length of the Machine are discussed and the effects of more general current distributions are considered. The results from the experiments are given.

  7. Age gradients in the stellar populations of massive star forming regions based on a new stellar chronometer

    Energy Technology Data Exchange (ETDEWEB)

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.; Broos, Patrick S.; Townsley, Leisa K.; Luhman, Kevin L. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Naylor, Tim [School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Povich, Matthew S. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States); Garmire, Gordon P. [Huntingdon Institute for X-ray Astronomy, LLC, 10677 Franks Road, Huntingdon, PA 16652 (United States)

    2014-06-01

    A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, Age {sub JX} . Stellar masses are derived from X-ray luminosities using the L{sub X} -M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. Age {sub JX} is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The Age {sub JX} method has been applied to 5525 out of 31,784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The Age {sub JX} ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J – H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters.

  8. ACCELERATED FITTING OF STELLAR SPECTRA

    Energy Technology Data Exchange (ETDEWEB)

    Ting, Yuan-Sen; Conroy, Charlie [Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Rix, Hans-Walter [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)

    2016-07-20

    Stellar spectra are often modeled and fitted by interpolating within a rectilinear grid of synthetic spectra to derive the stars’ labels: stellar parameters and elemental abundances. However, the number of synthetic spectra needed for a rectilinear grid grows exponentially with the label space dimensions, precluding the simultaneous and self-consistent fitting of more than a few elemental abundances. Shortcuts such as fitting subsets of labels separately can introduce unknown systematics and do not produce correct error covariances in the derived labels. In this paper we present a new approach—Convex Hull Adaptive Tessellation (chat)—which includes several new ideas for inexpensively generating a sufficient stellar synthetic library, using linear algebra and the concept of an adaptive, data-driven grid. A convex hull approximates the region where the data lie in the label space. A variety of tests with mock data sets demonstrate that chat can reduce the number of required synthetic model calculations by three orders of magnitude in an eight-dimensional label space. The reduction will be even larger for higher dimensional label spaces. In chat the computational effort increases only linearly with the number of labels that are fit simultaneously. Around each of these grid points in the label space an approximate synthetic spectrum can be generated through linear expansion using a set of “gradient spectra” that represent flux derivatives at every wavelength point with respect to all labels. These techniques provide new opportunities to fit the full stellar spectra from large surveys with 15–30 labels simultaneously.

  9. Grigori Kuzmin and Stellar Dynamics

    Directory of Open Access Journals (Sweden)

    Zeeuw P. Tim de

    2011-06-01

    Full Text Available Grigori Kuzmin was a very gifted dynamicist and one of the towering figures in the distinguished history of the Tartu Observatory. He obtained a number of important results in relative isolation which were later rediscovered in the West. This work laid the foundation for further advances in the theory of stellar systems in dynamical equilibrium, thereby substantially increasing our understanding of galaxy dynamics.

  10. Geometry Dependence of Stellarator Turbulence

    International Nuclear Information System (INIS)

    Mynick, H.E.; Xanthopoulos, P.; Boozer, A.H.

    2009-01-01

    Using the nonlinear gyrokinetic code package GENE/GIST, we study the turbulent transport in a broad family of stellarator designs, to understand the geometry-dependence of the microturbulence. By using a set of flux tubes on a given flux surface, we construct a picture of the 2D structure of the microturbulence over that surface, and relate this to relevant geometric quantities, such as the curvature, local shear, and effective potential in the Schrodinger-like equation governing linear drift modes

  11. Models of hot stellar systems

    International Nuclear Information System (INIS)

    Van Albada, T.S.

    1986-01-01

    Elliptical galaxies consist almost entirely of stars. Sites of recent star formation are rare, and most stars are believed to be several billion years old, perhaps as old as the Universe itself (--10/sup 10/ yrs). Stellar motions in ellipticals show a modest amount of circulation about the center of the system, but most support against the force of gravity is provided by random motions; for this reason ellipticals are called 'hot' stellar systems. Spiral galaxies usually also contain an appreciable amount of gas (--10%, mainly atomic hydrogen) and new stars are continually being formed out of this gas, especially in the spiral arms. In contrast to ellipticals, support against gravity in spiral galaxies comes almost entirely from rotation; random motions of the stars with respect to rotation are small. Consequently, spiral galaxies are called 'cold' stellar systems. Other than in hot systems, in cold systems the collective response of stars to variations in the force field is an essential part of the dynamics. The present overview is limited to mathematical models of hot systems. Computational methods are also discussed

  12. Characterizing Extragalactic Star Formation with GALEX Legacy Photometric Analysis of UV-Bright Stellar Complexes

    Science.gov (United States)

    Thilker, David

    At the close of nearly a decade of observing, GALEX has accumulated an unprecedented archive of ultraviolet (UV) images revealing both the scope and intricacy of star formation (SF) in many thousands of galaxies inhabiting the local universe. If the observed hierarchical SF morphology can be quantified systematically, and physically interpreted with multi-wavelength ancillary data and modeling, then the low redshift GALEX legacy will approach completion. However, the GALEX GR6 pipeline database contains a highly incomplete census of young stellar complexes even for very well-studied galaxies. We propose to apply a dedicated photometry algorithm that has been optimized for measuring the properties of irregularly shaped sources in crowded galaxy images containing spatially variant, diffuse intra-clump emission. Structures will be selected in the UV, but we will compile UV-visible-MIR SEDs for each detection utilizing Pan-STARRS1+SDSS and WISE data. These SEDs will then be fit using population-synthesis models to derive estimated stellar mass, age, and extinction. Processing will be completed for the entire diameter-limited GALEX Large Galaxy Atlas (GLGA) sample of 20,000+ galaxies, at a variety of standardized spatial resolutions. Although the precise categorization of the cataloged substructures will depend on galaxy distance, the outcome of our analysis will be a catalog similar to the stellar association surveys of past decades for very nearby galaxies based on resolved stars (e.g. van den Bergh 1964, Hodge 1986, Efremov et al. 1987), except that our investigation will probe a galaxy sample of dramatically larger size using the integrated UV light from such groupings of young stars. Our algorithm is multi-scale in nature and will thus preserve the hierarchical properties of the stellar distribution, by linking sub-clumps to their larger-scale parent feature(s). The resulting database will be a fundamental resource for follow-up multi-wavelength studies probing SF

  13. Results of Compact Stellarator Engineering Trade Studies

    International Nuclear Information System (INIS)

    Brown, Tom; Bromberg, L.; Cole, M.

    2009-01-01

    A number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study

  14. Results of Compact Stellarator Engineering Trade Studies

    International Nuclear Information System (INIS)

    Brown, T.; Bromberg, L.; Cole, M.

    2009-01-01

    A number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study.

  15. Stellar configurations in f(R) theories of gravity

    International Nuclear Information System (INIS)

    Henttunen, K.; Multamaeki, T.; Vilja, I.

    2008-01-01

    We study stellar configurations and the space-time around them in metric f(R) theories of gravity. In particular, we focus on the polytropic model of the Sun in two specific cases: the f(R)=R-μ 4 /R model and a model with a stabilizing higher order term f(R)=R-μ 4 /R+βR 3 /(3μ 4 ). We show how the stellar configuration in the f(R) theory can, by appropriate initial conditions, be selected to be equal to that described by the Lane-Emden equation and how a simple scaling relation exists between the solutions. We also derive the correct solution analytically near the center of the star in f(R) theory. Previous analytical and numerical results are confirmed, indicating that the space-time around the Sun is incompatible with solar system constraints in the f(R)=R-μ 4 /R model. Numerical work shows that stellar configurations, with a regular metric at the center, lead to γ PPN ≅1/2 outside the star for both models, i.e., the Schwarzschild-de Sitter space-time is not the correct vacuum solution for such configurations. This shows that even when one fine-tunes the initial conditions inside a star such that the mass of the effective scalar in the equivalent scalar-tensor theory is large, γ PPN is still 1/2 outside the star. Conversely, by selecting the Schwarzschild-de Sitter metric as the outside solution, or equivalently setting the mass of the effective scalar to be large outside the star, we find that the stellar configuration is unchanged but the metric is irregular at the center. The possibility of constructing a f(R) theory compatible with the solar system experiments and possible new constraints arising from the radius-mass relation of stellar objects is discussed

  16. Picturing Success: Young Femininities and the (Im)Possibilities of Academic Achievement in Selective, Single-Sex Education

    Science.gov (United States)

    Allan, Alexandra

    2010-01-01

    Over the last decade it is young women who have come to be widely understood as the bearers of educational qualifications. It is girls who are now seen to have "the world at their feet" and to be able to attain the glittering prizes of academic success associated with elite universities and top occupations. And it is upper-middle-class…

  17. Stellarator fusion neutronics research in Australia

    International Nuclear Information System (INIS)

    Zimin, S.; Cross, R.C.

    1997-01-01

    The new status of the H-INF Heliac Stellaralor as a National Facility and the signed international Implementing Agreement on 'Collaboration in the Development of the Stellarator Concept' represents a significant encouragement for further fusion research in Australia. In this report the future of fusion research in Australia is discussed with special attention being paid to the importance of Stellarator power plant studies and in particular stellarator fusion neutronics. The main differences between tokamak and stellarator neutronics analyses are identified, namely the neutron wall loading, geometrical modelling and total heating in in-vessel reactor components including toroidal field (TF) coils. Due to the more complicated nature of stellarator neutronics analyses, simplified approaches to fusion neutronics already developed for tokamaks are expected to be even more important and widely used for designing a Conceptual Stellarator Power Plant

  18. On the universal stellar law

    Science.gov (United States)

    Krot, Alexander

    In this work, we consider a statistical theory of gravitating spheroidal bodies to derive and develop the universal stellar law for extrasolar systems. Previously, the statistical theory for a cosmogonic body forming (so-called spheroidal body)has been proposed [1-3]. This theory starts from the conception for forming a spheroidal body inside a gas-dust protoplanetary nebula; it permits us to derive the form of distribution functions, mass density, gravitational potentials and strengths both for immovable and rotating spheroidal bodies as well as to find the distribution function of specific angular momentum[1-3]. If we start from the conception for forming a spheroidal body as a protostar (in particular, proto-Sun) inside a prestellar (presolar) nebula then the derived distribution functions of particle (as well as the mass density of an immovable spheroidal body) characterizes the first stage of evolution: from a prestellar molecular cloud (the presolar nebula) to the forming core of protostar (the proto-Sun) together with its shell as a stellar nebula (the solar nebula). This work derives the equation of state of an ideal stellar substance based on conception of gravitating spheroidal body. Using this equation, we obtain the universal stellar law (USL) for the planetary systems connecting temperature, size and mass of each of stars. This work also considers the Solar corona in the connection with USL. Then it is accounting under calculation of the ratio of temperature of the Solar corona to effective temperature of the Sun’ surfaceand modification of USL. To test justice of the modified USLfor different types of stars, the temperature of stellar corona is estimated. The prediction of parameters of stars is carrying out by means of the modified USL,as well as the Hertzsprung-Russell’s dependence [5-7]is derivedby means of USL directly. This paper also shows that knowledge of some characteristics for multi-planet extrasolar systems refines own parameters of

  19. Extragalactic stellar astronomy with the brightest stars in the universe

    Energy Technology Data Exchange (ETDEWEB)

    Kudritzki, R P; Urbaneja, M A; Bresolin, F [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Przybilla, N [Dr Remeis-Sternwarte Bamberg, Erlangen University, Sternwartstr. 7, D-96049 Bamberg (Germany)], E-mail: kud@ifa.hawaii.edu

    2008-12-15

    Supergiants are objects in transition from the blue to the red (and vice versa) in the uppermost HRD. They are the intrinsically brightest 'normal' stars at visual light with absolute visual magnitudes up to -9. They are ideal to study young stellar populations in galaxies beyond the Local Group to determine chemical composition and evolution, interstellar extinction, reddening laws and distances. We discuss the most recent results on the quantitative spectral analysis of such objects in galaxies beyond the Local Group based on medium and low-resolution spectra obtained with the ESO VLT and Keck. We describe the analysis method including the determination of metallicity and metallicity gradients. A new method to measure extragalactic distances accurately based on stellar gravities and effective temperatures is presented, the flux-weighted gravity-luminosity relationship (FGLR). The FGLR is a purely spectroscopic method that overcomes the uncertainties, introduced by interstellar extinction and variations of metallicity, which plague all methods of photometric stellar distance determination. We discuss the perspectives of future work using the giant ground-based telescopes of the next generation such as the TMT, the GMT and the E-ELT.

  20. Multiplicity in Early Stellar Evolution

    Science.gov (United States)

    Reipurth, B.; Clarke, C. J.; Boss, A. P.; Goodwin, S. P.; Rodríguez, L. F.; Stassun, K. G.; Tokovinin, A.; Zinnecker, H.

    Observations from optical to centimeter wavelengths have demonstrated that multiple systems of two or more bodies is the norm at all stellar evolutionary stages. Multiple systems are widely agreed to result from the collapse and fragmentation of cloud cores, despite the inhibiting influence of magnetic fields. Surveys of class 0 protostars with millimeter interferometers have revealed a very high multiplicity frequency of about 2/3, even though there are observational difficulties in resolving close protobinaries, thus supporting the possibility that all stars could be born in multiple systems. Near-infrared adaptive optics observations of class I protostars show a lower binary frequency relative to the class 0 phase, a declining trend that continues through the class II/III stages to the field population. This loss of companions is a natural consequence of dynamical interplay in small multiple systems, leading to ejection of members. We discuss observational consequences of this dynamical evolution, and its influence on circumstellar disks, and we review the evolution of circumbinary disks and their role in defining binary mass ratios. Special attention is paid to eclipsing PMS binaries, which allow for observational tests of evolutionary models of early stellar evolution. Many stars are born in clusters and small groups, and we discuss how interactions in dense stellar environments can significantly alter the distribution of binary separations through dissolution of wider binaries. The binaries and multiples we find in the field are the survivors of these internal and external destructive processes, and we provide a detailed overview of the multiplicity statistics of the field, which form a boundary condition for all models of binary evolution. Finally, we discuss various formation mechanisms for massive binaries, and the properties of massive trapezia.

  1. Physics of Compact Advanced Stellarators

    International Nuclear Information System (INIS)

    Zarnstorff, M.C.; Berry, L.A.; Brooks, A.; Fredrickson, E.; Fu, G.-Y.; Hirshman, S.; Hudson, S.; Ku, L.-P.; Lazarus, E.; Mikkelsen, D.; Monticello, D.; Neilson, G.H.; Pomphrey, N.; Reiman, A.; Spong, D.; Strickler, D.; Boozer, A.; Cooper, W.A.; Goldston, R.; Hatcher, R.; Isaev, M.; Kessel, C.; Lewandowski, J.; Lyon, J.; Merkel, P.; Mynick, H.; Nelson, B.E.; Nuehrenberg, C.; Redi, M.; Reiersen, W.; Rutherford, P.; Sanchez, R.; Schmidt, J.; White, R.B.

    2001-01-01

    Compact optimized stellarators offer novel solutions for confining high-beta plasmas and developing magnetic confinement fusion. The 3-D plasma shape can be designed to enhance the MHD stability without feedback or nearby conducting structures and provide drift-orbit confinement similar to tokamaks. These configurations offer the possibility of combining the steady-state low-recirculating power, external control, and disruption resilience of previous stellarators with the low-aspect ratio, high beta-limit, and good confinement of advanced tokamaks. Quasi-axisymmetric equilibria have been developed for the proposed National Compact Stellarator Experiment (NCSX) with average aspect ratio 4-4.4 and average elongation of approximately 1.8. Even with bootstrap-current consistent profiles, they are passively stable to the ballooning, kink, vertical, Mercier, and neoclassical-tearing modes for beta > 4%, without the need for external feedback or conducting walls. The bootstrap current generates only 1/4 of the magnetic rotational transform at beta = 4% (the rest is from the coils), thus the equilibrium is much less nonlinear and is more controllable than similar advanced tokamaks. The enhanced stability is a result of ''reversed'' global shear, the spatial distribution of local shear, and the large fraction of externally generated transform. Transport simulations show adequate fast-ion confinement and thermal neoclassical transport similar to equivalent tokamaks. Modular coils have been designed which reproduce the physics properties, provide good flux surfaces, and allow flexible variation of the plasma shape to control the predicted MHD stability and transport properties

  2. Radiation transfer and stellar atmospheres

    Science.gov (United States)

    Swihart, T. L.

    This is a revised and expanded version of the author's Basic Physics of Stellar Atmospheres, published in 1971. The equation of transfer is considered, taking into account the intensity and derived quantities, the absorption coefficient, the emission coefficient, the source function, and special integrals for plane media. The gray atmosphere is discussed along with the nongray atmosphere, and aspects of line formation. Topics related to polarization are explored, giving attention to pure polarized radiation, general polarized radiation, transfer in a magnetic plasma, and Rayleigh scattering and the sunlit sky. Physical and astronomical constants, and a number of problems related to the subjects of the book are presented in an appendix.

  3. Drift waves in a stellarator

    International Nuclear Information System (INIS)

    Bhattacharjee, A.; Sedlak, J.E.; Similon, P.L.; Rosenbluth, M.N.; Ross, D.W.

    1982-11-01

    We investigate the eigenmode structure of drift waves in a straight stellarator using the ballooning mode formalism. The electrons are assumed to be adiabatic and the ions constitute a cold, magnetized fluid. The effective potential has an overall parabolic envelope but is modulated strongly by helical ripples along B. We have found two classes of solutions: those that are strongly localized in local helical wells, and those that are weakly localized and have broad spatial extent. The weakly localized modes decay spatially due to the existence of Mathieu resonances between the periods of the eigenfunction and the effective potential

  4. Helical axis stellarator equilibrium model

    International Nuclear Information System (INIS)

    Koniges, A.E.; Johnson, J.L.

    1985-02-01

    An asymptotic model is developed to study MHD equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two-dimensional generalized partial differential equation of the Grad-Shafranov type. A stellarator-expansion free-boundary equilibrium code is modified to solve the helical-axis equations. The expansion model is used to predict the equilibrium properties of Asperators NP-3 and NP-4. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift

  5. Neutrino transport in stellar matter

    International Nuclear Information System (INIS)

    Basdevant, J.L.

    1985-09-01

    We reconsider the neutrino transport problem in dense stellar matter which has a variety of applications among which the participation of neutrinos to the dynamics of type II supernova explosions. We describe the position of the problem and make some critiscism of previously used approximation methods. We then propose a method which is capable of handling simultaneously the optically thick, optically thin, and intermediate regimes, which is of crucial importance in such problems. The method consists in a simulation of the transport process and can be considered exact within numerical accuracy. We, finally exhibit some sample calculations which show the efficiency of the method, and present interesting qualitative physical features

  6. Characterizing Convection in Stellar Atmospheres

    International Nuclear Information System (INIS)

    Tanner, Joel; Basu, Sarbani; Demarque, Pierre; Robinson, Frank

    2011-01-01

    We perform 3D radiative hydrodynamic simulations to study the properties of convection in the superadiabatic layer of stars. The simulations show differences in both the stratification and turbulent quantities for different types of stars. We extract turbulent pressure and eddy sizes, as well as the T-τ relation for different stars and find that they are sensitive to the energy flux and gravity. We also show that contrary to what is usually assumed in the field of stellar atmospheres, the structure and gas dynamics of simulations of turbulent atmospheres cannot be parameterized with T eff and log(g) alone.

  7. On modular stellarator reactor coils

    International Nuclear Information System (INIS)

    Rau, F.; Harmeyer, E.; Kisslinger, J.; Wobig, H.

    1985-01-01

    Modular twisted coils are discussed which produce magnetic fields of the Advanced Stellarator WENDELSTEIN VII-AS type. Reducing the number coils/FP offers advantage for maintenance of coils, but increases the magnetic ripple and B m /B o . Computation of force densities within the coils of ASR and ASB yield local maximum values of about 80 and 180 MN/m 3 , respectively. A system of mutual coil support is being developed. Twisted coils in helical arrangement provide a reactor-sized HELIAC system. In order to reduce the magnetic ripple, a large number of 14 coils/FP in special arrangement is used

  8. Stellar orbits around Sgr A*

    International Nuclear Information System (INIS)

    Trippe, S; Gillessen, S; Ott, T; Eisenhauer, F; Paumard, T; Martins, F; Genzel, R; Schoedel, R; Eckart, A; Alexander, T

    2006-01-01

    In this article we present and discuss the latest results from the observations of stars (''S-stars'') orbiting Sgr A* . With improving data quality the number of observed S-stars has increased substantially in the last years. The combination of radial velocity and proper motion information allows an ever more precise determination of orbital parameters and of the mass of and the distance to the supermassive black hole in the centre of the Milky Way. Additionally, the orbital solutions allow us to verify an agreement between the NIR source Sgr A* and the dynamical centre of the stellar orbits to within 2 mas

  9. The stellar metallicity gradients in galaxy discs in a cosmological scenario

    Science.gov (United States)

    Tissera, Patricia B.; Machado, Rubens E. G.; Sanchez-Blazquez, Patricia; Pedrosa, Susana E.; Sánchez, Sebastián F.; Snaith, Owain; Vilchez, Jose

    2016-08-01

    Context. The stellar metallicity gradients of disc galaxies provide information on disc assembly, star formation processes, and chemical evolution. They also might store information on dynamical processes that could affect the distribution of chemical elements in the gas phase and the stellar components. Understanding their joint effects within a hierarchical clustering scenario is of paramount importance. Aims: We studied the stellar metallicity gradients of simulated discs in a cosmological simulation. We explored the dependence of the stellar metallicity gradients on stellar age and on the size and mass of the stellar discs. Methods: We used a catalogue of galaxies with disc components selected from a cosmological hydrodynamical simulation performed including a physically motivated supernova feedback and chemical evolution. Disc components were defined based on angular momentum and binding energy criteria. The metallicity profiles were estimated for stars with different ages. We confront our numerical findings with results from the Calar Alto Legacy Integral Field Area (CALIFA) Survey. Results: The simulated stellar discs are found to have metallicity profiles with slopes in global agreement with observations. Low stellar mass galaxies tend to have a larger variety of metallicity slopes. When normalized by the half-mass radius, the stellar metallicity gradients do not show any dependence and the dispersion increases significantly, regardless of the galaxy mass. Galaxies with stellar masses o f around 1010M⊙ show steeper negative metallicity gradients. The stellar metallicity gradients correlate with the half-mass radius. However, the correlation signal is not present when they are normalized by the half-mass radius. Stellar discs with positive age gradients are detected to have negative and positive metallicity gradients, depending on the relative importance of recent star formation activity in the central regions. Conclusions: Our results suggest that inside

  10. Introduction to stellar astrophysics. V. 1

    International Nuclear Information System (INIS)

    Boehm-Vitense, E.

    1989-01-01

    This textbook introduces basic elements of fundamental astronomy and astrophysics which serve as a foundation for understanding the structure, evolution, and observed properties of stars. The first half of the book explains how stellar motions, distances, luminosities, colours, radii, masses and temperatures are measured or derived. The author then shows how data of these sorts can be arranged to classify stars through their spectra. Stellar rotation and stellar magnetic fields are introduced. Stars with peculiar spectra and pulsating stars also merit special attention. The endpoints of stellar evolutions are briefly described. There is a separate chapter on the Sun and a final one on interstellar absorption. (author)

  11. Diversification of the economic profile and selected aspects of market activity in age groups of young consumers

    Directory of Open Access Journals (Sweden)

    Grażyna Adamczyk

    2010-01-01

    Full Text Available In the article an influence of the age of young consumers on chosen economic aspects of their market activity was described. It is stated that with the age of young consumers their purchasing fund and sources of its recruiting were increasing. Teenagers (secondary-school people more often demonstrate also a tendency to save money to concrete objectives, e.g. holidays, travels, training, but their current expenses are concentrating mainly around different active or passive forms of spending free time. Older teenagers are also more critical in relation to advertisements, and price and different instruments of sales promotion are factors which are exerting a significant influence on their purchase decisions. With the growth of importance of goods in the hierarchy of satisfying needs, role of determinants of choice besides the price, also a brand of the product are assumed.

  12. A tidally stripped stellar component of the Magellanic bridge

    Energy Technology Data Exchange (ETDEWEB)

    Nidever, David L.; Monachesi, Antonela; Bell, Eric F. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48104 (United States); Majewski, Steven R.; Beaton, Rachael L. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Muñoz, Ricardo R., E-mail: dnidever@umich.edu, E-mail: rmunoz@das.uchile.cl [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile)

    2013-12-20

    Deep photometry of the Small Magellanic Cloud (SMC) stellar periphery (R = 4°, 4.2 kpc) is used to study its line-of-sight depth with red clump (RC) stars. The RC luminosity function is affected little by young (≲1 Gyr) blue-loop stars in these regions because their main-sequence counterparts are not observed in the color-magnitude diagrams. The SMCs eastern side is found to have a large line-of-sight depth (∼23 kpc) while the western side has a much shallower depth (∼10 kpc), consistent with previous photographic plate photometry results. We use a model SMC RC luminosity function to deconvolve the observed RC magnitudes and construct the density function in distance for our fields. Three of the eastern fields show a distance bimodality with one component at the 'systemic' ∼67 kpc SMC distance and a second component at ∼55 kpc. Our data are not reproduced well by the various extant Magellanic Cloud and Stream simulations. However, the models predict that the known H I Magellanic Bridge (stretching from the SMC eastward toward the Large Magellanic Cloud, LMC) has a decreasing distance with angle from the SMC and should be seen in both the gaseous and stellar components. From comparison with these models, we conclude that the most likely explanation for our newly identified ∼55 kpc stellar structure in the eastern SMC is a stellar counterpart of the H I Magellanic Bridge that was tidally stripped from the SMC ∼200 Myr ago during a close encounter with the LMC. This discovery has important implications for microlensing surveys of the SMC.

  13. The Relationship between Selected Anthropometric Indices and Cardiorespiratory Fitness in Apparently Healthy Young Adults in a Nigerian Community

    OpenAIRE

    C. N. Ofiaeli; A. V. Egwuonwu; M. J. Nwankwo; Y. E. Ihegihu; U. P. Okonkwo

    2017-01-01

    Background and Aim: Cardiorespiratory fitness (CRF) is a useful tool for establishment of baseline fitness status and monitoring of physical activity level. Therefore, it may by extension serve as health risk index. However, studies that have determined the correlation between anthropometric indices and CRF in apparently healthy young adults is difficult to find in other to preempt preventive actions before pathology develops. Materials and Methods: Using a descriptive correlational resea...

  14. Magnetohydrodynamic instabilities in a stellarator

    International Nuclear Information System (INIS)

    Matsuoka, K.; Miyamoto, K.; Ohasa, K.; Wakatani, M.

    1977-05-01

    Numerical studies of stability on kink and resistive tearing modes in a linear stellarator are presented for various current profiles and helical fields. In the case of an l = 2 helical field, a magnetic shear vanishes and the stability diagram is given by the straight lines with iota sup(σ) + iota sup(delta) = const., where iota sup(σ) is a rotational transform due to the plasma current and iota sup(delta) is due to the helical field. In the l = 2 stellarator with chi sup(delta) > 0.5, the m.h.d. stability against kink and tearing modes is improved compared with that in tokamaks. While an l = 3 helical component exists, the magnetic shear plays an important role in the stability properties. The stability diagrams become fairly complex; however, they can be explained by properties of the Euler equation. It should be noted that the internal kink modes become more unstable than in tokamaks by the l = 3 helical field. (auth.)

  15. Neoclassical transport simulations for stellarators

    International Nuclear Information System (INIS)

    Turkin, Y.; Beidler, C. D.; Maassberg, H.; Murakami, S.; Wakasa, A.; Tribaldos, V.

    2011-01-01

    The benchmarking of the thermal neoclassical transport coefficients is described using examples of the Large Helical Device (LHD) and TJ-II stellarators. The thermal coefficients are evaluated by energy convolution of the monoenergetic coefficients obtained by direct interpolation or neural network techniques from the databases precalculated by different codes. The temperature profiles are calculated by a predictive transport code from the energy balance equations with the ambipolar radial electric field estimated from a diffusion equation to guarantee a unique and smooth solution, although several solutions of the ambipolarity condition may exist when root-finding is invoked; the density profiles are fixed. The thermal transport coefficients as well as the ambipolar radial electric field are compared and very reasonable agreement is found for both configurations. Together with an additional W7-X case, these configurations represent very different degrees of neoclassical confinement at low collisionalities. The impact of the neoclassical optimization on the energy confinement time is evaluated and the confinement times for different devices predicted by transport modeling are compared with the standard scaling for stellarators. Finally, all configurations are scaled to the same volume for a direct comparison of the volume-averaged pressure and the neoclassical degree of optimization.

  16. THE MASS DEPENDENCE BETWEEN PROTOPLANETARY DISKS AND THEIR STELLAR HOSTS

    International Nuclear Information System (INIS)

    Andrews, Sean M.; Rosenfeld, Katherine A.; Kraus, Adam L.; Wilner, David J.

    2013-01-01

    We present a substantial extension of the millimeter (mm) wave continuum photometry catalog for circumstellar dust disks in the Taurus star-forming region, based on a new ''snapshot'' λ = 1.3 mm survey with the Submillimeter Array. Combining these new data with measurements in the literature, we construct a mm-wave luminosity distribution, f(L mm ), for Class II disks that is statistically complete for stellar hosts with spectral types earlier than M8.5 and has a 3σ depth of roughly 3 mJy. The resulting census eliminates a longstanding selection bias against disks with late-type hosts, and thereby demonstrates that there is a strong correlation between L mm and the host spectral type. By translating the locations of individual stars in the Hertzsprung-Russell diagram into masses and ages, and adopting a simple conversion between L mm and the disk mass, M d , we confirm that this correlation corresponds to a statistically robust relationship between the masses of dust disks and the stars that host them. A Bayesian regression technique is used to characterize these relationships in the presence of measurement errors, data censoring, and significant intrinsic scatter: the best-fit results indicate a typical 1.3 mm flux density of ∼25 mJy for 1 M ☉ hosts and a power-law scaling L mm ∝M * 1.5-2.0 . We suggest that a reasonable treatment of dust temperature in the conversion from L mm to M d favors an inherently linear M d ∝M * scaling, with a typical disk-to-star mass ratio of ∼0.2%-0.6%. The measured rms dispersion around this regression curve is ±0.7 dex, suggesting that the combined effects of diverse evolutionary states, dust opacities, and temperatures in these disks imprint a full width at half-maximum range of a factor of ∼40 on the inferred M d (or L mm ) at any given host mass. We argue that this relationship between M d and M * likely represents the origin of the inferred correlation between giant planet frequency and host star mass in the

  17. The Mass Dependence between Protoplanetary Disks and their Stellar Hosts

    Science.gov (United States)

    Andrews, Sean M.; Rosenfeld, Katherine A.; Kraus, Adam L.; Wilner, David J.

    2013-07-01

    We present a substantial extension of the millimeter (mm) wave continuum photometry catalog for circumstellar dust disks in the Taurus star-forming region, based on a new "snapshot" λ = 1.3 mm survey with the Submillimeter Array. Combining these new data with measurements in the literature, we construct a mm-wave luminosity distribution, f(L mm), for Class II disks that is statistically complete for stellar hosts with spectral types earlier than M8.5 and has a 3σ depth of roughly 3 mJy. The resulting census eliminates a longstanding selection bias against disks with late-type hosts, and thereby demonstrates that there is a strong correlation between L mm and the host spectral type. By translating the locations of individual stars in the Hertzsprung-Russell diagram into masses and ages, and adopting a simple conversion between L mm and the disk mass, Md , we confirm that this correlation corresponds to a statistically robust relationship between the masses of dust disks and the stars that host them. A Bayesian regression technique is used to characterize these relationships in the presence of measurement errors, data censoring, and significant intrinsic scatter: the best-fit results indicate a typical 1.3 mm flux density of ~25 mJy for 1 M ⊙ hosts and a power-law scaling L_mm ∝ M_{\\ast}^{1.5-2.0}. We suggest that a reasonable treatment of dust temperature in the conversion from L mm to Md favors an inherently linear Md vpropM * scaling, with a typical disk-to-star mass ratio of ~0.2%-0.6%. The measured rms dispersion around this regression curve is ±0.7 dex, suggesting that the combined effects of diverse evolutionary states, dust opacities, and temperatures in these disks imprint a full width at half-maximum range of a factor of ~40 on the inferred Md (or L mm) at any given host mass. We argue that this relationship between Md and M * likely represents the origin of the inferred correlation between giant planet frequency and host star mass in the exoplanet

  18. STELLAR MASSES FROM THE CANDELS SURVEY: THE GOODS-SOUTH AND UDS FIELDS

    International Nuclear Information System (INIS)

    Santini, P.; Fontana, A.; Castellano, M.; Grazian, A.; Amorin, R.; Ferguson, H. C.; Mobasher, B.; Barro, G.; Finkelstein, S. L.; Hsu, L. T.; Salvato, M.; Wuyts, S.; Galametz, A.; Lee, B.; Lee, S.-K.; Pforr, J.; Wiklind, T.; Almaini, O.; Cooper, M. C.; Weiner, B.

    2015-01-01

    We present the public release of the stellar mass catalogs for the GOODS-S and UDS fields obtained using some of the deepest near-IR images available, achieved as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey project. We combine the effort from 10 different teams, who computed the stellar masses using the same photometry and the same redshifts. Each team adopted their preferred fitting code, assumptions, priors, and parameter grid. The combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. Thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. The choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). On the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. The inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ∼80% of the sample). Nevertheless, the stellar mass for the subsample of young galaxies (age <100 Myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for <20 Myr sources) if nebular contribution is ignored

  19. STELLAR MASSES FROM THE CANDELS SURVEY: THE GOODS-SOUTH AND UDS FIELDS

    Energy Technology Data Exchange (ETDEWEB)

    Santini, P.; Fontana, A.; Castellano, M.; Grazian, A.; Amorin, R. [INAF-Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monte Porzio Catone, Roma (Italy); Ferguson, H. C. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Mobasher, B. [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Barro, G. [UCO/Lick Observatory and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Finkelstein, S. L. [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States); Hsu, L. T.; Salvato, M.; Wuyts, S.; Galametz, A. [Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312, D-85741 Garching (Germany); Lee, B. [Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States); Lee, S.-K. [Center for the Exploration of the Origin of the Universe, Department of Physics and Astronomy, Seoul National University, Seoul (Korea, Republic of); Pforr, J. [National Optical Astronomy Observatories, 950 N Cherry Avenue, Tucson, AZ 85719 (United States); Wiklind, T. [Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile); Almaini, O. [University of Nottingham, School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Cooper, M. C. [Center for Galaxy Evolution, Department of Physics and Astronomy, University of California, Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); Weiner, B., E-mail: paola.santini@oa-roma.inaf.it [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); and others

    2015-03-10

    We present the public release of the stellar mass catalogs for the GOODS-S and UDS fields obtained using some of the deepest near-IR images available, achieved as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey project. We combine the effort from 10 different teams, who computed the stellar masses using the same photometry and the same redshifts. Each team adopted their preferred fitting code, assumptions, priors, and parameter grid. The combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. Thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. The choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). On the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. The inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ∼80% of the sample). Nevertheless, the stellar mass for the subsample of young galaxies (age <100 Myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for <20 Myr sources) if nebular contribution is ignored.

  20. A Bayesian method for detecting stellar flares

    Science.gov (United States)

    Pitkin, M.; Williams, D.; Fletcher, L.; Grant, S. D. T.

    2014-12-01

    We present a Bayesian-odds-ratio-based algorithm for detecting stellar flares in light-curve data. We assume flares are described by a model in which there is a rapid rise with a half-Gaussian profile, followed by an exponential decay. Our signal model also contains a polynomial background model required to fit underlying light-curve variations in the data, which could otherwise partially mimic a flare. We characterize the false alarm probability and efficiency of this method under the assumption that any unmodelled noise in the data is Gaussian, and compare it with a simpler thresholding method based on that used in Walkowicz et al. We find our method has a significant increase in detection efficiency for low signal-to-noise ratio (S/N) flares. For a conservative false alarm probability our method can detect 95 per cent of flares with S/N less than 20, as compared to S/N of 25 for the simpler method. We also test how well the assumption of Gaussian noise holds by applying the method to a selection of `quiet' Kepler stars. As an example we have applied our method to a selection of stars in Kepler Quarter 1 data. The method finds 687 flaring stars with a total of 1873 flares after vetos have been applied. For these flares we have made preliminary characterizations of their durations and and S/N.

  1. Stellar Spectral Classification with Locality Preserving Projections ...

    Indian Academy of Sciences (India)

    With the help of computer tools and algorithms, automatic stellar spectral classification has become an area of current interest. The process of stellar spectral classification mainly includes two steps: dimension reduction and classification. As a popular dimensionality reduction technique, Principal Component Analysis (PCA) ...

  2. Enhanced-confinement class of stellarators

    International Nuclear Information System (INIS)

    Mynick, H.E.; Chu, T.K.; Boozer, A.H.

    1981-08-01

    A class of stellarators has been found in which the transport is reduced by an order of magnitude from transport in conventional stellarators, by localizing the helical ripple to the inside of the torus. The reduction is observed in numerical experiments and explained theoretically

  3. Theories for convection in stellar atmospheres

    International Nuclear Information System (INIS)

    Nordlund, Aa.

    1976-02-01

    A discussion of the fundamental differences between laboratory convection in a stellar atmosphere is presented. The shortcomings of laterally homogeneous model atmospheres are analysed, and the extent to which these shortcoming are avoided in the two-component representation is discussed. Finally a qualitative discussion on the scaling properties of stellar granulation is presented. (Auth.)

  4. The SPECT tracer [123I]ADAM binds selectively to serotonin transporters: a double-blind, placebo-controlled study in healthy young men

    International Nuclear Information System (INIS)

    Giessen, Elsmarieke van de; Booij, Jan

    2010-01-01

    The tracer 123 I-2-([2-({dimethylamino}methyl)phenyl]thio)-5-iodophenylamine ([ 123 I]ADAM) has been developed to image serotonin transporters (SERTs) with SPECT. Preclinical studies have shown that [ 123 I]ADAM binds selectively to SERTs. Moreover, initial human studies have shown that [ 123 I]ADAM binding could be blocked by selective serotonin reuptake inhibitors (SSRIs). However, in humans it has not been proven that [ 123 I]ADAM binds selectively to SERTs. We examined the in vivo availability of SERTs in 12 healthy young volunteers 5 h after bolus injection of [ 123 I]ADAM. To evaluate the selectivity of binding, four participants were pretreated (double-blinded design) with placebo, four with paroxetine (20 mg) and four with the dopamine/norepinephrine blocker methylphenidate (20 mg). SPECT studies were performed on a brain-dedicated system (Neurofocus), and the SPECT images were coregistered with individual MR scans of the brain. ADAM binding in SERT-rich brain areas and cerebellar cortex (representing non-specific binding) was assessed by drawing regions of interest (ROIs) on the individual MR images. Specific to non-specific ratios were used as the outcome measure. We found that specific to non-specific ratios were statistically significantly lower in paroxetine-pretreated participants than in placebo- or methylphenidate-pretreated participants. No such difference was found between groups pretreated with placebo or methylphenidate. Our preliminary findings suggest that [ 123 I]ADAM binds selectively to SERTs in human brain. (orig.)

  5. Structure of stellar hydroxyl masers

    International Nuclear Information System (INIS)

    Reid, M.J.; Muhleman, D.O.; Moran, J.M.; Johnston, K.J.; Schwartz, P.R.

    1977-01-01

    This paper presents the results of two spectral-line very long baseline (VLB) interferometric experiments on stellar OH masers. These masers are usually associated with long-period variable stars, and exhibit a characteristic double-peaked 1612 MHz OH spectrum. The sources IRC +10011, R Aql, and U Ori were carefully studied in order to determine the spatial structure of their masers. Maser components in these sources exhibited a complex structure which can be interpreted in terms of ''core-halo'' models. For these sources, the emission at any velocity appears to originate from a small (approximately-less-than0.''03) region of brightness approximately-greater-than10 9 K, and from a large (approximately-greater-than0.''5) region of brightness approximately-less-than10 8 K. In IRC+10011, ''core'' components in the two OH peaks probably are separated by less than the apparent size of the ''halos.'' A map of the low-velocity emission of U Ori with a resolution of 0.''01 indicates that the ''cores'' are distributed over a region of only 0.''2. This region is smaller than the apparent sizes of the ''halos.'' Other sources surveyed to determine apparent maser sizes include IRC+50137, OH 1821--12, OH 1837--05, OH 26.5+0.6, W43 A, and VX Sgr at 1612 MHz; and W Hya, R Aql, and IRC--10529 at 1667 MHz. The results of all VLB observations of 1612 MHz stellar OH masers are summarized.The apparent sizes of the strongest components (''halos'') of stellar OH masers typically are approximately-greater-than0.''5, corresponding to linear dimensions of approximately-greater-than3 x 10 15 cm. These surprisingly large sizes imply brightness temperatures much lower than those observed in most other types of astronomical masers. The large sizes rule out models of the 1612 MHz OH masers that require contracting or rotating circumstellar envelopes to explain the double-peaked OH spectra, or that try to explain the apparent maser sizes in terms of interstellar or interplanetary scattering

  6. The warped young stellar disc in the Galactic centre

    Czech Academy of Sciences Publication Activity Database

    Šubr, Ladislav; Schovancová, J.; Kroupa, P.

    2009-01-01

    Roč. 496, č. 3 (2009), s. 695-699 ISSN 0004-6361 R&D Projects: GA ČR GA205/07/0052 Institutional research plan: CEZ:AV0Z10030501 Keywords : black holes * galactic centre Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.179, year: 2009

  7. Warping the young stellar disc in the galactic centre

    Czech Academy of Sciences Publication Activity Database

    Šubr, Ladislav; Schovancová, J.

    2008-01-01

    Roč. 131, - (2008), s. 1-7 ISSN 1742-6588. [Universe under the microscope - astrophysics at high angular resolution. Bad Honnef, 21.04.2008-25.04.2008] R&D Projects: GA ČR GA205/07/0052 Institutional research plan: CEZ:AV0Z10030501 Keywords : circum-nuclear disc * zoung stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  8. Nuclear challenges and progress in designing stellarator power plants

    International Nuclear Information System (INIS)

    El-Guebaly, L.

    2007-01-01

    , such as recycling (within the nuclear industry) and clearance (or unconditional release to the commercial market). The ARIES-CS bioshield, cryostat, and individual magnet constituents qualify for clearance, representing ∼80% of the total waste volume. We developed a recycling approach for the non-clearable, in-vessel components using a combination of conventional and advanced remote handling equipment that can handle high doses of 3000 Sv/h or more. Several additional nuclear-related tasks received considerable attention during the ARIES-CS design process. These include the radial build definition, the well-optimized in-vessel components that satisfy the top-level requirements, the carefully selected nuclear and engineering parameters to produce an economic optimum, and the overarching safety constraints to deliver a safe and reliable power plant. This paper provides a brief historical overview of the progress in designing stellarator power plants and a perspective to the successful integration of the nuclear activity into the final ARIES-CS design

  9. Wisconsin torsatron/stellarator program, FY 1989

    International Nuclear Information System (INIS)

    Shohet, J.L.; Anderson, D.T.; Anderson, F.S.B.; Talmadge, J.N.

    1988-07-01

    This proposal documents recent activities within the University of Wisconsin-Madison Torsatron/Stellarator Laboratory and presents plans for future research activities for a three year period. Research efforts have focused on fundamental stellarator physics issues through experimental investigations on the Interchangeable Module Stellarator (IMS) and the Proto-Cleo Stellarator. Theoretical activities and studies of new configurations are being undertaken to support and broaden the experimental program. Experimental research at the Torsatron Stellarator Laboratory has been primarily concerned with effects induced through electron-cyclotron resonant frequency plasma production and heating in the IMS device. Plasma electric fields have been shown to play a major role in particle transport and confinement in IMS. ECRF heating at 6 kG has produced electron tail populations in agreement with Monte-Carlo models. Electric and magnetic fields have been shown to alter the particle flows to the IMS modular divertors. 48 refs

  10. Astrospheres and Solar-like Stellar Winds

    Directory of Open Access Journals (Sweden)

    Wood Brian E.

    2004-07-01

    Full Text Available Stellar analogs for the solar wind have proven to be frustratingly difficult to detect directly. However, these stellar winds can be studied indirectly by observing the interaction regions carved out by the collisions between these winds and the interstellar medium (ISM. These interaction regions are called "astrospheres", analogous to the "heliosphere" surrounding the Sun. The heliosphere and astrospheres contain a population of hydrogen heated by charge exchange processes that can produce enough H I Ly alpha absorption to be detectable in UV spectra of nearby stars from the Hubble Space Telescope (HST. The amount of astrospheric absorption is a diagnostic for the strength of the stellar wind, so these observations have provided the first measurements of solar-like stellar winds. Results from these stellar wind studies and their implications for our understanding of the solar wind are reviewed here. Of particular interest are results concerning the past history of the solar wind and its impact on planetary atmospheres.

  11. Stellarmak a hybrid stellarator: Spheromak

    International Nuclear Information System (INIS)

    Hartman, C.W.

    1980-01-01

    This paper discusses hybridization of modified Stellarator-like transform windings (T-windings) with a Spheromak or Field-Reversed-Mirror configuration. This configuration, Stellarmak, retains the important topological advantage of the Spheromak or FRM of having no plasma linking conductors or blankets. The T-windings provide rotational transformation in toroidal angle of the outer poloidal field lines, in effect creating a reversed B/sub Toroidal/ Spheromak or adding average B/sub T/ to the FRM producing higher shear, increased limiting β, and possibly greater stability to kinks and tilt. The presence of field ripple in the toroidal direction may be sufficient to inhibit cancellation of directed ion current by electron drag to allow steady state operation with the toroidal as well as poloidal current maintained by neutral beams

  12. Stellar Equilibrium in Semiclassical Gravity.

    Science.gov (United States)

    Carballo-Rubio, Raúl

    2018-02-09

    The phenomenon of quantum vacuum polarization in the presence of a gravitational field is well understood and is expected to have a physical reality, but studies of its backreaction on the dynamics of spacetime are practically nonexistent outside of the specific context of homogeneous cosmologies. Building on previous results of quantum field theory in curved spacetimes, in this Letter we first derive the semiclassical equations of stellar equilibrium in the s-wave Polyakov approximation. It is highlighted that incorporating the polarization of the quantum vacuum leads to a generalization of the classical Tolman-Oppenheimer-Volkoff equation. Despite the complexity of the resulting field equations, it is possible to find exact solutions. Aside from being the first known exact solutions that describe relativistic stars including the nonperturbative backreaction of semiclassical effects, these are identified as a nontrivial combination of the black star and gravastar proposals.

  13. On rapid rotation in stellarators

    International Nuclear Information System (INIS)

    Helander, Per

    2008-01-01

    The conditions under which rapid plasma rotation may occur in a three-dimensional magnetic field, such as that of a stellarator, are investigated. Rotation velocities comparable to the ion thermal speed are found to be attainable only in magnetic fields which are approximately isometric. In an isometric magnetic field the dependence of the magnetic field strength B on the arc length l along the field is the same for all field lines on each flux surface ψ. Only in fields where the departure from exact isometry, B=B(ψ,l), is of the order of the ion gyroradius divided by the macroscopic length scale are rotation speeds comparable to the ion thermal speed possible. Moreover, it is shown that the rotation must be in the direction of the vector ∇ψx∇B. (author)

  14. Magnetohydodynamics stability of compact stellarators

    International Nuclear Information System (INIS)

    Fu, G.Y.; Ku, L.P.; Cooper, W.A.; Hirshman, S.H.

    2000-01-01

    Recent stability results of external kink modes and vertical modes in compact stellarators are presented. The vertical mode is found to be stabilized by externally generated poloidal flux. A simple stability criterion is derived in the limit of large aspect ratio and constant current density. For a wall at infinite distance from the plasma, the amount of external flux needed for stabilization is given by Fi = (k2 minus k)=(k2 + 1), where k is the axisymmetric elongation and Fi is the fraction of the external rotational transform. A systematic parameter study shows that the external kink mode in QAS can be stabilized at high beta (approximately 5%) without a conducting wall by magnetic shear via 3D shaping. It is found that external kinks are driven by both parallel current and pressure gradient. The pressure contributes significantly to the overall drive through the curvature term and the Pfirsch-Schluter current

  15. NEMO: A Stellar Dynamics Toolbox

    Science.gov (United States)

    Barnes, Joshua; Hut, Piet; Teuben, Peter

    2010-10-01

    NEMO is an extendible Stellar Dynamics Toolbox, following an Open-Source Software model. It has various programs to create, integrate, analyze and visualize N-body and SPH like systems, following the pipe and filter architecture. In addition there are various tools to operate on images, tables and orbits, including FITS files to export/import to/from other astronomical data reduction packages. A large growing fraction of NEMO has been contributed by a growing list of authors. The source code consist of a little over 4000 files and a little under 1,000,000 lines of code and documentation, mostly C, and some C++ and Fortran. NEMO development started in 1986 in Princeton (USA) by Barnes, Hut and Teuben. See also ZENO (ascl:1102.027) for the version that Barnes maintains.

  16. Time-scales of stellar rotational variability and starspot diagnostics

    Science.gov (United States)

    Arkhypov, Oleksiy V.; Khodachenko, Maxim L.; Lammer, Helmut; Güdel, Manuel; Lüftinger, Teresa; Johnstone, Colin P.

    2018-01-01

    The difference in stability of starspot distribution on the global and hemispherical scales is studied in the rotational spot variability of 1998 main-sequence stars observed by Kepler mission. It is found that the largest patterns are much more stable than smaller ones for cool, slow rotators, whereas the difference is less pronounced for hotter stars and/or faster rotators. This distinction is interpreted in terms of two mechanisms: (1) the diffusive decay of long-living spots in activity complexes of stars with saturated magnetic dynamos, and (2) the spot emergence, which is modulated by gigantic turbulent flows in convection zones of stars with a weaker magnetism. This opens a way for investigation of stellar deep convection, which is yet inaccessible for asteroseismology. Moreover, a subdiffusion in stellar photospheres was revealed from observations for the first time. A diagnostic diagram was proposed that allows differentiation and selection of stars for more detailed studies of these phenomena.

  17. Realistic limitations of detecting planets around young active stars

    Directory of Open Access Journals (Sweden)

    Pinfield D.

    2013-04-01

    Full Text Available Current planet hunting methods using the radial velocity method are limited to observing middle-aged main-sequence stars where the signatures of stellar activity are much less than on young stars that have just arrived on the main-sequence. In this work we apply our knowledge from the surface imaging of these young stars to place realistic limitations on the possibility of detecting orbiting planets. In general we find that the magnitude of the stellar jitter is directly proportional to the stellar vsini. For G and K dwarfs, we find that it is possible, for models with high stellar activity and low stellar vsini, to be able to detect a 1 MJupiter mass planet within 50 epochs of observations and for the M dwarfs it is possible to detect a habitable zone Earth-like planet in 10s of observational epochs.

  18. Non-parametric cell-based photometric proxies for galaxy morphology: methodology and application to the morphologically defined star formation-stellar mass relation of spiral galaxies in the local universe

    Science.gov (United States)

    Grootes, M. W.; Tuffs, R. J.; Popescu, C. C.; Robotham, A. S. G.; Seibert, M.; Kelvin, L. S.

    2014-02-01

    We present a non-parametric cell-based method of selecting highly pure and largely complete samples of spiral galaxies using photometric and structural parameters as provided by standard photometric pipelines and simple shape fitting algorithms. The performance of the method is quantified for different parameter combinations, using purely human-based classifications as a benchmark. The discretization of the parameter space allows a markedly superior selection than commonly used proxies relying on a fixed curve or surface of separation. Moreover, we find structural parameters derived using passbands longwards of the g band and linked to older stellar populations, especially the stellar mass surface density μ* and the r-band effective radius re, to perform at least equally well as parameters more traditionally linked to the identification of spirals by means of their young stellar populations, e.g. UV/optical colours. In particular, the distinct bimodality in the parameter μ*, consistent with expectations of different evolutionary paths for spirals and ellipticals, represents an often overlooked yet powerful parameter in differentiating between spiral and non-spiral/elliptical galaxies. We use the cell-based method for the optical parameter set including re in combination with the Sérsic index n and the i-band magnitude to investigate the intrinsic specific star formation rate-stellar mass relation (ψ*-M*) for a morphologically defined volume-limited sample of local Universe spiral galaxies. The relation is found to be well described by ψ _* ∝ M_*^{-0.5} over the range of 109.5 ≤ M* ≤ 1011 M⊙ with a mean interquartile range of 0.4 dex. This is somewhat steeper than previous determinations based on colour-selected samples of star-forming galaxies, primarily due to the inclusion in the sample of red quiescent discs.

  19. Neoclassical transport in stellarators - a comparison of conventional stellarator/torsatrons with the advanced stellarator, Wendelstein 7X

    Energy Technology Data Exchange (ETDEWEB)

    Beidler, C D [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany)

    1991-01-01

    A general expression for the magnitude of a stellarator's magnetic field, in terms of a Fourier decomposition, is too complicated to lend itself easily to analytic transport calculations. The great majority of stellarator-type devices, however, may be accurately described if one retains only those harmonics with m=0 and m=1. In the long-mean-free-path regime an analytical approximation to the particle's bounce-averaged kinetic equation can then be found. Using a numerical solution of this equation, it is possible to calculate the particle and heat fluxes due to helical-ripple transport in stellarators throughout the entire long-mean-free-path regime. 3 figs.

  20. Gemini Spectroscopic Survey of Young Intermediate-Mass Star-Forming Regions

    Science.gov (United States)

    Lundquist, Michael; Kobulnicky, Henry

    2018-01-01

    The majority of stars form in embedded clusters. Current research into star formation has focused on either high-mass star-forming regions or low-mass star-forming regions. We present the results from a Gemini spectroscopic survey of young intermediate-mass star-forming regions. These are star forming regions selected to produce stars up to but not exceeding 8 solar masses. We obtained spectra of these regions with GNIRS on Gemini North and Flamingos-2 on Gemini South. We also combine this with near-infrared imaging from 2MASS, UKIDSS, and VVV to study the stellar content.

  1. Selection of the optimum font type and size interface for on screen continuous reading by young adults: an ergonomic approach.

    Science.gov (United States)

    Banerjee, Jayeeta; Bhattacharyya, Moushum

    2011-12-01

    There is a rapid shifting of media: from printed paper to computer screens. This transition is modifying the process of how we read and understand text. The efficiency of reading is dependent on how ergonomically the visual information is presented. Font types and size characteristics have been shown to affect reading. A detailed investigation of the effect of the font type and size on reading on computer screens has been carried out by using subjective, objective and physiological evaluation methods on young adults. A group of young participants volunteered for this study. Two types of fonts were used: Serif fonts (Times New Roman, Georgia, Courier New) and Sans serif fonts (Verdana, Arial, Tahoma). All fonts were presented in 10, 12 and 14 point sizes. This study used a 6 X 3 (font type X size) design matrix. Participants read 18 passages of approximately the same length and reading level on a computer monitor. Reading time, ranking and overall mental workload were measured. Eye movements were recorded by a binocular eye movement recorder. Reading time was minimum for Courier New l4 point. The participants' ranking was highest and mental workload was least for Verdana 14 point. The pupil diameter, fixation duration and gaze duration were least for Courier New 14 point. The present study recommends using 14 point sized fonts for reading on computer screen. Courier New is recommended for fast reading while for on screen presentation Verdana is recommended. The outcome of this study will help as a guideline to all the PC users, software developers, web page designers and computer industry as a whole.

  2. Hydrodynamics and stellar winds an introduction

    CERN Document Server

    Maciel, Walter J

    2014-01-01

    Stellar winds are a common phenomenon in the life of stars, from the dwarfs like the Sun to the red giants and hot supergiants, constituting one of the basic aspects of modern astrophysics. Stellar winds are a hydrodynamic phenomenon in which circumstellar gases expand towards the interstellar medium. This book presents an elementary introduction to the fundamentals of hydrodynamics with an application to the study of stellar winds. The principles of hydrodynamics have many other applications, so that the book can be used as an introduction to hydrodynamics for students of physics, astrophysics and other related areas.

  3. Helical post stellarator. Part 1: Vacuum configuration

    International Nuclear Information System (INIS)

    Moroz, P.E.

    1997-08-01

    Results on a novel type of stellarator configuration, the Helical Post Stellarator (HPS), are presented. This configuration is different significantly from all previously known stellarators due to its unique geometrical characteristics and unique physical properties. Among those are: the magnetic field has only one toroidal period (M = 1), the plasma has an extremely low aspect ratio, A ∼ 1, and the variation of the magnetic field, B, along field lines features a helical ripple on the inside of the torus. Among the main advantages of a HPS for a fusion program are extremely compact, modular, and simple design compatible with significant rotational transform, large plasma volume, and improved particle transport characteristics

  4. STELLAR ACTIVITY IN THE BROADBAND ULTRAVIOLET

    International Nuclear Information System (INIS)

    Findeisen, K.; Hillenbrand, L.; Soderblom, D.

    2011-01-01

    The completion of the GALEX All-Sky Survey in the ultraviolet allows activity measurements to be acquired for many more stars than is possible with the limited sensitivity of ROSAT or the limited sky coverage of Chandra, XMM, or spectroscopic surveys for line emission in the optical or ultraviolet. We have explored the use of GALEX photometry as an activity indicator, using stars within 50 pc as a calibration sample representing the field and in selected nearby associations representing the youngest stages of stellar evolution. We present preliminary relations between UV flux and the optical activity indicator R' HK and between UV flux and age. We demonstrate that far-UV (FUV, 1350-1780 A) excess flux is roughly proportional to R' HK . We also detect a correlation between near-UV (NUV, 1780-2830 A) flux and activity or age, but the effect is much more subtle, particularly for stars older than ∼0.5-1 Gyr. Both the FUV and NUV relations show large scatter, ∼0.2 mag when predicting UV flux, ∼0.18 dex when predicting R' HK , and ∼0.4 dex when predicting age. This scatter appears to be evenly split between observational errors in current state-of-the-art data and long-term activity variability in the sample stars.

  5. Effects of Combined Stellar Feedback on Star Formation in Stellar Clusters

    Science.gov (United States)

    Wall, Joshua Edward; McMillan, Stephen; Pellegrino, Andrew; Mac Low, Mordecai; Klessen, Ralf; Portegies Zwart, Simon

    2018-01-01

    We present results of hybrid MHD+N-body simulations of star cluster formation and evolution including self consistent feedback from the stars in the form of radiation, winds, and supernovae from all stars more massive than 7 solar masses. The MHD is modeled with the adaptive mesh refinement code FLASH, while the N-body computations are done with a direct algorithm. Radiation is modeled using ray tracing along long characteristics in directions distributed using the HEALPIX algorithm, and causes ionization and momentum deposition, while winds and supernova conserve momentum and energy during injection. Stellar evolution is followed using power-law fits to evolution models in SeBa. We use a gravity bridge within the AMUSE framework to couple the N-body dynamics of the stars to the gas dynamics in FLASH. Feedback from the massive stars alters the structure of young clusters as gas ejection occurs. We diagnose this behavior by distinguishing between fractal distribution and central clustering using a Q parameter computed from the minimum spanning tree of each model cluster. Global effects of feedback in our simulations will also be discussed.

  6. Young Children's Near and Far Transfer of the Basic Theory of Natural Selection: An Analogical Storybook Intervention

    Science.gov (United States)

    Emmons, Natalie; Lees, Kristin; Kelemen, Deborah

    2018-01-01

    Misconceptions about adaptation by natural selection are widespread among adults and likely stem, in part, from cognitive biases and intuitive theories observable in early childhood. Current educational guidelines that recommend delaying comprehensive instruction on the topic of adaptation until adolescence, therefore, raise concerns because…

  7. Antisocial Peer Affiliation and Externalizing Disorders in the Transition from Adolescence to Young Adulthood: Selection versus Socialization Effects

    Science.gov (United States)

    Samek, Diana R.; Goodman, Rebecca J.; Erath, Stephen A.; McGue, Matt; Iacono, William G.

    2016-01-01

    Prior research has demonstrated both socialization and selection effects for the relationship between antisocial peer affiliation and externalizing problems in adolescence. Less research has evaluated such effects postadolescence. In this study, a cross-lagged panel analysis was used to evaluate the extent of "socialization" (i.e., the…

  8. Early Neurological Outcome of Young Infants Exposed to Selective Serotonin Reuptake Inhibitors during Pregnancy : Results from the Observational SMOK Study

    NARCIS (Netherlands)

    de Vries, N.K.S.; van der Veere, C.N.; Reijneveld, S.A.; Bos, A.F.

    2013-01-01

    Background: Use of selective serotonin reuptake inhibitors (SSRI) during pregnancy is common while the effect on the infant's neurological outcome is unknown. Our objective was to determine the effects of prenatal SSRI-exposure on the infants' neurological functioning, adjusted for maternal mental

  9. Parent-Implemented Procedural Modification of Escape Extinction in the Treatment of Food Selectivity in a Young Child with Autism

    Science.gov (United States)

    Tarbox, Jonathan; Schiff, Averil; Najdowski, Adel C.

    2010-01-01

    Fool selectivity is characterized by the consumption of an inadequate variety of foods. The effectiveness of behavioral treatment procedures, particularly nonremoval of the spoon, is well validated by research. The role of parents in the treatment of feeding disorders and the feasibility of behavioral procedures for parent implementation in the…

  10. “If it Feels Good…”: Research on School Selection Process Motives Among Parents of Young Children

    NARCIS (Netherlands)

    ter Avest, I.; Bertram-Troost, G.D.; Miedema, S.

    2015-01-01

    From (inter)national research we know about parents’ priorities in the school selection process. In this research the authors focus on parents’ motivations underpinning these priorities. The question is: “What motivates parents to send their child to a Christian primary school?” In the Dutch plural

  11. The Safety, Pharmacokinetics, and Effects of LGD-4033, a Novel Nonsteroidal Oral, Selective Androgen Receptor Modulator, in Healthy Young Men

    Science.gov (United States)

    Basaria, Shehzad; Collins, Lauren; Dillon, E. Lichar; Orwoll, Katie; Storer, Thomas W.; Miciek, Renee; Ulloor, Jagadish; Zhang, Anqi; Eder, Richard; Zientek, Heather; Gordon, Gilad; Kazmi, Syed; Sheffield-Moore, Melinda

    2013-01-01

    Background. Concerns about potential adverse effects of testosterone on prostate have motivated the development of selective androgen receptor modulators that display tissue-selective activation of androgenic signaling. LGD-4033, a novel nonsteroidal, oral selective androgen receptor modulator, binds androgen receptor with high affinity and selectivity. Objectives. To evaluate the safety, tolerability, pharmacokinetics, and effects of ascending doses of LGD-4033 administered daily for 21 days on lean body mass, muscle strength, stair-climbing power, and sex hormones. Methods. In this placebo-controlled study, 76 healthy men (21–50 years) were randomized to placebo or 0.1, 0.3, or 1.0 mg LGD-4033 daily for 21 days. Blood counts, chemistries, lipids, prostate-specific antigen, electrocardiogram, hormones, lean and fat mass, and muscle strength were measured during and for 5 weeks after intervention. Results. LGD-4033 was well tolerated. There were no drug-related serious adverse events. Frequency of adverse events was similar between active and placebo groups. Hemoglobin, prostate-specific antigen, aspartate aminotransferase, alanine aminotransferase, or QT intervals did not change significantly at any dose. LGD-4033 had a long elimination half-life and dose-proportional accumulation upon multiple dosing. LGD-4033 administration was associated with dose-dependent suppression of total testosterone, sex hormone–binding globulin, high density lipoprotein cholesterol, and triglyceride levels. follicle-stimulating hormone and free testosterone showed significant suppression at 1.0-mg dose only. Lean body mass increased dose dependently, but fat mass did not change significantly. Hormone levels and lipids returned to baseline after treatment discontinuation. Conclusions. LGD-4033 was safe, had favorable pharmacokinetic profile, and increased lean body mass even during this short period without change in prostate-specific antigen. Longer randomized trials should

  12. Spiral structure and star formation. II. Stellar lifetimes and cloud kinematics

    International Nuclear Information System (INIS)

    Hausman, M.A.; Roberts, W.W. Jr.

    1984-01-01

    We present further results of our model, introduced in Paper I, of star formation and star-gas interactions in the cloud-dominated ISMs of spiral density wave galaxies. The global density distribution and velocity field of the gas clouds are virtually independent of stellar parameters and even of mean free path for the wide range of values studied, but local density variations are found which superficially resemble cloud complexes. Increasing the average life span of ''spiral tracer'' stellar associations beyond about 20 Myr washes out the spiral pattern which younger associations show. Allowing clouds to form several successive associations (sequential star formation) slightly increases the frequency of interarm, young-star spurs and substantially increases the average star formation rate. The mean velocity field of clouds shows tipped oval streamlines, similar to both continuum gas dynamical models and stellar-kinematic models of spiral density waves. These streamlines are almost ballistic orbits except close to the spiral arms. Newly formed stellar associations leave the spiral density peak with initial tangential velocitie shigher than ''postshock'' values and do not fall back into the ''preshock'' region. By varying our stellar parametes within physically reasonable limits, we may reproduce spiral galaxies with a wide range of morphological appearaces

  13. Stellar X-Ray Polarimetry

    Science.gov (United States)

    Swank, J.

    2011-01-01

    Most of the stellar end-state black holes, pulsars, and white dwarfs that are X-ray sources should have polarized X-ray fluxes. The degree will depend on the relative contributions of the unresolved structures. Fluxes from accretion disks and accretion disk corona may be polarized by scattering. Beams and jets may have contributions of polarized emission in strong magnetic fields. The Gravity and Extreme Magnetism Small Explorer (GEMS) will study the effects on polarization of strong gravity of black holes and strong magnetism of neutron stars. Some part of the flux from compact stars accreting from companion stars has been reflected from the companion, its wind, or accretion streams. Polarization of this component is a potential tool for studying the structure of the gas in these binary systems. Polarization due to scattering can also be present in X-ray emission from white dwarf binaries and binary normal stars such as RS CVn stars and colliding wind sources like Eta Car. Normal late type stars may have polarized flux from coronal flares. But X-ray polarization sensitivity is not at the level needed for single early type stars.

  14. Stellar recipes for axion hunters

    Energy Technology Data Exchange (ETDEWEB)

    Giannotti, Maurizio [Physical Sciences, Barry University, 11300 NE 2nd Ave., Miami Shores, FL 33161 (United States); Irastorza, Igor G.; Redondo, Javier [Departamento de Física Teórica, Universidad de Zaragoza, Pedro Cerbuna 12, E-50009, Zaragoza (Spain); Ringwald, Andreas; Saikawa, Ken' ichi, E-mail: mgiannotti@barry.edu, E-mail: igor.irastorza@cern.ch, E-mail: jredondo@unizar.es, E-mail: andreas.ringwald@desy.de, E-mail: kenichi.saikawa@desy.de [Theory Group, Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg (Germany)

    2017-10-01

    There are a number of observational hints from astrophysics which point to the existence of stellar energy losses beyond the ones accounted for by neutrino emission. These excessive energy losses may be explained by the existence of a new sub-keV mass pseudoscalar Nambu-Goldstone boson with tiny couplings to photons, electrons, and nucleons. An attractive possibility is to identify this particle with the axion—the hypothetical pseudo Nambu-Goldstone boson predicted by the Peccei-Quinn solution to the strong CP problem. We explore this possibility in terms of a DFSZ-type axion and of a KSVZ-type axion/majoron, respectively. Both models allow a good global fit to the data, prefering an axion mass around 10 meV. We show that future axion experiments—the fifth force experiment ARIADNE and the helioscope IAXO—can attack the preferred mass range from the lower and higher end, respectively. An axion in this mass range can also be the main constituent of dark matter.

  15. Stellar recipes for axion hunters

    Energy Technology Data Exchange (ETDEWEB)

    Giannotti, Maurizio [Barry Univ., Miami Shores, FL (United States). Physical Sciences; Irastorza, Igor G. [Zaragoza Univ. (Spain). Dept. de Fisica Teorica; Redondo, Javier [Zaragoza Univ. (Spain). Dept. de Fisica Teorica; Max-Planck-Institut fuer Physik, Muenchen (Germany); Ringwald, Andreas; Saikawa, Ken' ichi [DESY, Hamburg (Germany). Theory Group

    2017-08-15

    There are a number of observational hints from astrophysics which point to the existence of stellar energy losses beyond the ones accounted for by neutrino emission. These excessive energy losses may be explained by the existence of a new sub-keV mass pseudoscalar Nambu-Goldstone boson with tiny couplings to photons, electrons, and nucleons. An attractive possibility is to identify this particle with the axion - the hypothetical pseudo Nambu-Goldstone boson predicted by the Peccei-Quinn solution to the strong CP problem. We explore this possibility in terms of a DFSZ-type axion and of a KSVZ-type axion/majoron, respectively. Both models allow a good global fit to the data, prefering an axion mass around 10 meV. We show that future axion experiments - the fifth force experiment ARIADNE and the helioscope IAXO - can attack the preferred mass range from the lower and higher end, respectively. An axion in this mass range can also be the main constituent of dark matter.

  16. Stellar recipes for axion hunters

    International Nuclear Information System (INIS)

    Giannotti, Maurizio; Ringwald, Andreas; Saikawa, Ken'ichi

    2017-08-01

    There are a number of observational hints from astrophysics which point to the existence of stellar energy losses beyond the ones accounted for by neutrino emission. These excessive energy losses may be explained by the existence of a new sub-keV mass pseudoscalar Nambu-Goldstone boson with tiny couplings to photons, electrons, and nucleons. An attractive possibility is to identify this particle with the axion - the hypothetical pseudo Nambu-Goldstone boson predicted by the Peccei-Quinn solution to the strong CP problem. We explore this possibility in terms of a DFSZ-type axion and of a KSVZ-type axion/majoron, respectively. Both models allow a good global fit to the data, prefering an axion mass around 10 meV. We show that future axion experiments - the fifth force experiment ARIADNE and the helioscope IAXO - can attack the preferred mass range from the lower and higher end, respectively. An axion in this mass range can also be the main constituent of dark matter.

  17. Stellar core collapse and supernova

    International Nuclear Information System (INIS)

    Wilson, J.R.; Mayle, R.; Woosley, S.E.; Weaver, T.

    1985-04-01

    Massive stars that end their stable evolution as their iron cores collapse to a neutron star or black hole long been considered good candidates for producing Type II supernovae. For many years the outward propagation of the shock wave produced by the bounce of these iron cores has been studied as a possible mechanism for the explosion. For the most part, the results of these studies have not been particularly encouraging, except, perhaps, in the case of very low mass iron cores or very soft nuclear equations of state. The shock stalls, overwhelmed by photodisintegration and neutrino losses, and the star does not explode. More recently, slow late time heating of the envelope of the incipient neutron star has been found to be capable of rejuvenating the stalled shock and producing an explosion after all. The present paper discusses this late time heating and presents results from numerical calculations of the evolution, core collapse, and subsequent explosion of a number of recent stellar models. For the first time they all, except perhaps the most massive, explode with reasonable choices of input physics. 39 refs., 17 figs., 1 tab

  18. Stellar convection and dynamo theory

    Energy Technology Data Exchange (ETDEWEB)

    Jennings, R L

    1989-10-01

    In considering the large scale stellar convection problem the outer layers of a star are modelled as two co-rotating plane layers coupled at a fluid/fluid interface. Heating from below causes only the upper fluid to convect, although this convection can penetrate into the lower fluid. Stability analysis is then used to find the most unstable mode of convection. With parameters appropriate to the Sun the most unstable mode is steady convection in thin cells (aspect ratio {approx equal} 0.2) filling the convection zone. There is negligible vertical motion in the lower fluid, but considerable thermal penetration, and a large jump in helicity at the interface, which has implications for dynamo theory. An {alpha}{omega} dynamo is investigated in isolation from the convection problem. Complexity is included by allowing both latitudinal and time dependence in the magnetic fields. The nonlinear dynamics of the resulting partial differential equations are analysed in considerable detail. On varying the main control parameter D (the dynamo number), many transitions of behaviour are found involving many forms of time dependence, but not chaos. Further, solutions which break equatorial symmetry are common and provide a theoretical explanation of solar observations which have this symmetry. Overall the behaviour was more complicated than expected. In particular, there were multiple stable solutions at fixed D, meaning that similar stars can have very different magnetic patterns, depending upon their history. (author).

  19. Collapsing stellar cores and supernovae

    Energy Technology Data Exchange (ETDEWEB)

    Epstein, R J [Nordisk Inst. for Teoretisk Atomfysik, Copenhagen (Denmark); Noorgaard, H [Nordisk Inst. for Teoretisk Atomfysik, Copenhagen (Denmark); Chicago Univ., IL (USA). Enrico Fermi Inst.); Bond, J R [Niels Bohr Institutet, Copenhagen (Denmark); California Inst. of Tech., Pasadena (USA). W.K. Kellogg Radiation Lab.)

    1979-05-01

    The evolution of a stellar core is studied during its final quasi-hydrostatic contraction. The core structure and the (poorly known) properties of neutron rich matter are parametrized to include most plausible cases. It is found that the density-temperature trajectory of the material in the central part of the core (the core-center) is insensitive to nearly all reasonable parameter variations. The central density at the onset of the dynamic phase of the collapse (when the core-center begins to fall away from the rest of the star) and the fraction of the emitted neutrinos which are trapped in the collapsing core-center depend quite sensitively on the properties of neutron rich matter. We estimate that the amount of energy Ecm which is imparted to the core-mantle by the neutrinos which escape from the imploded core-center can span a large range of values. For plausible choices of nuclear and model parameters Ecm can be large enough to yield a supernova event.

  20. The SPECT tracer [{sup 123}I]ADAM binds selectively to serotonin transporters: a double-blind, placebo-controlled study in healthy young men

    Energy Technology Data Exchange (ETDEWEB)

    Giessen, Elsmarieke van de [University of Amsterdam, Academic Medical Center, Graduate School Neurosciences Amsterdam, Department of Nuclear Medicine, Amsterdam (Netherlands); Booij, Jan [University of Amsterdam, Academic Medical Center, Graduate School Neurosciences Amsterdam, Department of Nuclear Medicine, Amsterdam (Netherlands); University of Amsterdam, Academic Medical Center, Department of Nuclear Medicine, F2-236, Amsterdam (Netherlands)

    2010-08-15

    The tracer {sup 123}I-2-([2-({l_brace}dimethylamino{r_brace}methyl)phenyl]thio)-5-iodophenylamine ([{sup 123}I]ADAM) has been developed to image serotonin transporters (SERTs) with SPECT. Preclinical studies have shown that [{sup 123}I]ADAM binds selectively to SERTs. Moreover, initial human studies have shown that [{sup 123}I]ADAM binding could be blocked by selective serotonin reuptake inhibitors (SSRIs). However, in humans it has not been proven that [{sup 123}I]ADAM binds selectively to SERTs. We examined the in vivo availability of SERTs in 12 healthy young volunteers 5 h after bolus injection of [{sup 123}I]ADAM. To evaluate the selectivity of binding, four participants were pretreated (double-blinded design) with placebo, four with paroxetine (20 mg) and four with the dopamine/norepinephrine blocker methylphenidate (20 mg). SPECT studies were performed on a brain-dedicated system (Neurofocus), and the SPECT images were coregistered with individual MR scans of the brain. ADAM binding in SERT-rich brain areas and cerebellar cortex (representing non-specific binding) was assessed by drawing regions of interest (ROIs) on the individual MR images. Specific to non-specific ratios were used as the outcome measure. We found that specific to non-specific ratios were statistically significantly lower in paroxetine-pretreated participants than in placebo- or methylphenidate-pretreated participants. No such difference was found between groups pretreated with placebo or methylphenidate. Our preliminary findings suggest that [{sup 123}I]ADAM binds selectively to SERTs in human brain. (orig.)

  1. Diagnostics for the National Compact Stellarator Experiment

    International Nuclear Information System (INIS)

    Stratton, B.C.; Johnson, D.; Feder, R.; Fredrickson, E.; Neilson, H.; Takahashi, H.; Zarnstorf, M.; Cole, M.; Goranson, P.; Lazarus, E.; Nelson, B.

    2003-01-01

    The status of planning of the National Compact Stellarator Experiment (NCSX) diagnostics is presented, with the emphasis on resolution of diagnostics access issues and on diagnostics required for the early phases of operation

  2. Stellar Spectral Classification with Locality Preserving Projections ...

    Indian Academy of Sciences (India)

    School of Computer and Control Engineering, North University of China,. Taiyuan 030051 ... (2013) was used to mine the association rules of a stellar ... of the graph, we then compute a transformation matrix which maps the data points to.

  3. The relation between stellar evolution and cosmology

    International Nuclear Information System (INIS)

    Tayler, R.J.

    1984-01-01

    Observations of star clusters combined with the theory of stellar evolution enable us to estimate the ages of stars while cosmological observations and theories give us a value for the age of the Universe. This is the most important interaction between cosmology and stellar evolution because it is clearly necessary that stars are younger than the Universe. Stellar evolution also plays an important role in relating the present chemical composition of the Universe to its original composition. The author restricts the review to a discussion of the relation between stellar evolution and the big bang cosmological theory because there is such a good qualitative agreement between the hot big bang theory and observations. (Auth.)

  4. Evaluating Stellarator Divertor Designs with EMC3

    Science.gov (United States)

    Bader, Aaron; Anderson, D. T.; Feng, Y.; Hegna, C. C.; Talmadge, J. N.

    2013-10-01

    In this paper various improvements of stellarator divertor design are explored. Next step stellarator devices require innovative divertor solutions to handle heat flux loads and impurity control. One avenue is to enhance magnetic flux expansion near strike points, somewhat akin to the X-Divertor concept in Tokamaks. The effect of judiciously placed external coils on flux deposition is calculated for configurations based on the HSX stellarator. In addition, we attempt to optimize divertor plate location to facilitate the external coil placement. Alternate areas of focus involve altering edge island size to elucidate the driving physics in the edge. The 3-D nature of stellarators complicates design and necessitates analysis of new divertor structures with appropriate simulation tools. We evaluate the various configurations with the coupled codes EMC3-EIRENE, allowing us to benchmark configurations based on target heat flux, impurity behavior, radiated power, and transitions to high recycling and detached regimes. Work supported by DOE-SC0006103.

  5. Development of the stellarator/heliotron research

    International Nuclear Information System (INIS)

    Iiyoshi, A.

    1991-05-01

    The author reviewed the history of the development of the stellarator/heliotron system, and pointed out the important role of the radial electric field in plasma transport in helical devices. (J.P.N.)

  6. Radiative otacity tables for 40 stellar mixtures

    International Nuclear Information System (INIS)

    Cox, A.N.; Tabor, J.E.

    1976-01-01

    Using improved methods, radiative opacities for 40 mixtures of elements are given for use in calculations of stellar structure, stellar evolution, and stellar pulsation. The major improvements over previous Los Alamos data are increased iron abundance in the composition, better allowance for the continuum depression for bound electrons, and corrections in some bound-electron energy levels. These opacities have already been widely used, and represent a relatively homogeneous set of data for stellar structures. Further improvements to include more bound-bound (line) transitions by a smearing technique and to include molecular absorptions are becoming available, and in a few years these tables, as well as all previous tables, will be outdated. At high densities the conduction of energy will dominate radiation flow, and this effect must be added separately

  7. The metastable dynamo model of stellar rotational evolution

    International Nuclear Information System (INIS)

    Brown, Timothy M.

    2014-01-01

    This paper introduces a new empirical model for the rotational evolution of Sun-like stars—those with surface convection zones and non-convective interior regions. Previous models do not match the morphology of observed (rotation period)-color diagrams, notably the existence of a relatively long-lived 'C-sequence' of fast rotators first identified by Barnes. This failure motivates the Metastable Dynamo Model (MDM) described here. The MDM posits that stars are born with their magnetic dynamos operating in a mode that couples very weakly to the stellar wind, so their (initially very short) rotation periods at first change little with time. At some point, this mode spontaneously and randomly changes to a strongly coupled mode, the transition occurring with a mass-dependent lifetime that is of the order of 100 Myr. I show that with this assumption, one can obtain good fits to observations of young clusters, particularly for ages of 150-200 Myr. Previous models and the MDM both give qualitative agreement with the morphology of the slower-rotating 'I-sequence' stars, but none of them have been shown to accurately reproduce the stellar-mass-dependent evolution of the I-sequence stars, especially for clusters older than a few hundred million years. I discuss observational experiments that can test aspects of the MDM, and speculate that the physics underlying the MDM may be related to other situations described in the literature, in which stellar dynamos may have a multi-modal character.

  8. STELLAR ATMOSPHERES, ATMOSPHERIC EXTENSION, AND FUNDAMENTAL PARAMETERS: WEIGHING STARS USING THE STELLAR MASS INDEX

    Energy Technology Data Exchange (ETDEWEB)

    Neilson, Hilding R.; Lester, John B. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, M5S 3H4 (Canada); Baron, Fabien; Norris, Ryan; Kloppenborg, Brian, E-mail: neilson@astro.utoronto.ca [Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, Georgia State University, P.O. Box 5060, Atlanta, GA 30302-5060 (United States)

    2016-10-20

    One of the great challenges of understanding stars is measuring their masses. The best methods for measuring stellar masses include binary interaction, asteroseismology, and stellar evolution models, but these methods are not ideal for red giant and supergiant stars. In this work, we propose a novel method for inferring stellar masses of evolved red giant and supergiant stars using interferometric and spectrophotometric observations combined with spherical model stellar atmospheres to measure what we call the stellar mass index, defined as the ratio between the stellar radius and mass. The method is based on the correlation between different measurements of angular diameter, used as a proxy for atmospheric extension, and fundamental stellar parameters. For a given star, spectrophotometry measures the Rosseland angular diameter while interferometric observations generally probe a larger limb-darkened angular diameter. The ratio of these two angular diameters is proportional to the relative extension of the stellar atmosphere, which is strongly correlated to the star’s effective temperature, radius, and mass. We show that these correlations are strong and can lead to precise measurements of stellar masses.

  9. Does the stellar distribution flare? A comparison of stellar scale heights with LAB H I data

    Energy Technology Data Exchange (ETDEWEB)

    Kalberla, P. M. W.; Kerp, J.; Dedes, L. [Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn (Germany); Haud, U., E-mail: pkalberla@astro.uni-bonn.de [Tartu Observatory, 61602 Tõravere (Estonia)

    2014-10-10

    The question of whether the stellar populations in the Milky Way take part in the flaring of scale heights as observed for the H I gas is a matter of debate. Standard mass models for the Milky Way assume a constant scale height for each of the different stellar distributions. However, there is mounting evidence that at least some of the stellar distributions reach, at large galactocentric distances, high altitudes, which are incompatible with a constant scale height. We discuss recent observational evidence for stellar flaring and compare it with H I data from the Leiden/Argentine/Bonn survey. Within the systemic and statistical uncertainties we find a good agreement between both.

  10. The WEGA Stellarator: Results and Prospects

    International Nuclear Information System (INIS)

    Otte, M.; Andruczyk, D.; Koenig, R.; Laqua, H. P.; Lischtschenko, O.; Marsen, S.; Schacht, J.; Podoba, Y. Y.; Wagner, F.; Warr, G. B.; Holzhauer, E.; Howard, J.; Krupnik, L.; Zhezhera, A.; Urban, J.; Preinhalter, J.

    2008-01-01

    In this article an overview is given on results from magnetic flux surface measurements, applied ECR heating scenarios for 2.45 GHz and 28 GHz, fluctuation and transport studies and plasma edge biasing experiments performed in the WEGA stellarator. Examples for the development of new diagnostics and the machine control system are given that will be used at Wendelstein 7-X stellarator, which is currently under construction in Greifswald

  11. Cosmic abundances: The impact of stellar duplicity

    OpenAIRE

    Jorissen, A.; Van Eck, S.

    2004-01-01

    The mass-transfer scenario links chemical peculiarities with stellar duplicity for an increasing number of stellar classes (classical and dwarf barium stars, subgiant and giant CH stars, S stars without technetium, yellow symbiotic stars, WIRRING stars, Abell-35-like nuclei of planetary nebulae...). Despite these successes, the mass-transfer scenario still faces several problems: What is the mass-transfer mode? Why orbital elements of dwarf barium stars do not fully match those of the classic...

  12. The Stellar-Dynamical Oeuvre James Binney

    Indian Academy of Sciences (India)

    tribpo

    of the eigenvalues of M. The variation of the stellar density from point to point .... of Σ,(ΔΕ)2 , where ∆ Ε is the change in energy that a star suffers during a binary ... could use these results to calculate the relaxation time in a stellar system if he .... the region of enhanced density that tails behind it like a wake behind a ship. By.

  13. Weakly interacting massive particles and stellar structure

    International Nuclear Information System (INIS)

    Bouquet, A.

    1988-01-01

    The existence of weakly interacting massive particles (WIMPs) may solve both the dark matter problem and the solar neutrino problem. Such particles affect the energy transport in the stellar cores and change the stellar structure. We present the results of an analytic approximation to compute these effects in a self-consistent way. These results can be applied to many different stars, but we focus on the decrease of the 8 B neutrino flux in the case of the Sun

  14. Close stellar encounters in globular clusters

    International Nuclear Information System (INIS)

    Bailyn, C.D.

    1989-01-01

    Stellar encounters are expected to produce a variety of interesting objects in the cores of globular clusters, either through the formation of binaries by tidal capture, or direct collisions. Here, I describe several attempts to observe the products of stellar encounters. In particular, the use of color maps has demonstrated the existence of a color gradient in the core of M15, which seems to be caused by a population of faint blue objects concentrated towards the cluster center. (author)

  15. Stellar aspects of habitability--characterizing target stars for terrestrial planet-finding missions.

    Science.gov (United States)

    Kaltenegger, Lisa; Eiroa, Carlos; Ribas, Ignasi; Paresce, Francesco; Leitzinger, Martin; Odert, Petra; Hanslmeier, Arnold; Fridlund, Malcolm; Lammer, Helmut; Beichman, Charles; Danchi, William; Henning, Thomas; Herbst, Tom; Léger, Alain; Liseau, René; Lunine, Jonathan; Penny, Alan; Quirrenbach, Andreas; Röttgering, Huub; Selsis, Frank; Schneider, Jean; Stam, Daphne; Tinetti, Giovanna; White, Glenn J

    2010-01-01

    We present and discuss the criteria for selecting potential target stars suitable for the search for Earth-like planets, with a special emphasis on the stellar aspects of habitability. Missions that search for terrestrial exoplanets will explore the presence and habitability of Earth-like exoplanets around several hundred nearby stars, mainly F, G, K, and M stars. The evaluation of the list of potential target systems is essential in order to develop mission concepts for a search for terrestrial exoplanets. Using the Darwin All Sky Star Catalogue (DASSC), we discuss the selection criteria, configuration-dependent subcatalogues, and the implication of stellar activity for habitability.

  16. Uncertainties and Systematic Effects on the estimate of stellar masses in high z galaxies

    Science.gov (United States)

    Salimbeni, S.; Fontana, A.; Giallongo, E.; Grazian, A.; Menci, N.; Pentericci, L.; Santini, P.

    2009-05-01

    We discuss the uncertainties and the systematic effects that exist in the estimates of the stellar masses of high redshift galaxies, using broad band photometry, and how they affect the deduced galaxy stellar mass function. We use at this purpose the latest version of the GOODS-MUSIC catalog. In particular, we discuss the impact of different synthetic models, of the assumed initial mass function and of the selection band. Using Chariot & Bruzual 2007 and Maraston 2005 models we find masses lower than those obtained from Bruzual & Chariot 2003 models. In addition, we find a slight trend as a function of the mass itself comparing these two mass determinations with that from Bruzual & Chariot 2003 models. As consequence, the derived galaxy stellar mass functions show diverse shapes, and their slope depends on the assumed models. Despite these differences, the overall results and scenario is observed in all these cases. The masses obtained with the assumption of the Chabrier initial mass function are in average 0.24 dex lower than those from the Salpeter assumption, at all redshifts, causing a shift of galaxy stellar mass function of the same amount. Finally, using a 4.5 μm-selected sample instead of a Ks-selected one, we add a new population of highly absorbed, dusty galaxies at z~=2-3 of relatively low masses, yielding stronger constraints on the slope of the galaxy stellar mass function at lower masses.

  17. On plasma radiative properties in stellar conditions

    International Nuclear Information System (INIS)

    Turck-Chieze, S.; Delahaye, F.; Gilles, D.; Loisel, G.; Piau, L.; Loisel, G.

    2009-01-01

    The knowledge of stellar evolution is evolving quickly thanks to an increased number of opportunities to scrutinize the stellar internal plasma properties by stellar seismology and by 1D and 3D simulations. These new tools help us to introduce the internal dynamical phenomena in stellar modeling. A proper inclusion of these processes supposes a real confidence in the microscopic physics used, partly checked by solar or stellar acoustic modes. In the present paper we first recall which fundamental physics has been recently verified by helioseismology. Then we recall that opacity is an important ingredient of the secular evolution of stars and we point out why it is necessary to measure absorption coefficients and degrees of ionization in the laboratory for some well identified astrophysical conditions. We examine two specific experimental conditions which are accessible to large laser facilities and are suitable to solve some interesting questions of the stellar community: are the solar internal radiative interactions properly estimated and what is the proper role of the opacity in the excitation of the non-radial modes in the envelop of the β Cepheids and the Be stars? At the end of the paper we point out the difficulties of the experimental approach that we need to overcome. (authors)

  18. Comparative studies of stellarator and tokamak transport

    Energy Technology Data Exchange (ETDEWEB)

    Stroth, U; Burhenn, R; Geiger, J; Giannone, L.; Hartfuss, H J; Kuehner, G; Ledl, L; Simmet, E E; Walter, H [Max-Planck-Inst. fuer Plasmaphysik, IPP-Euratom Association, Garching (Germany); ECRH Team; W7-AS Team

    1997-09-01

    Transport properties in the W7-AS stellarator and in tokamaks are compared. The parameter dependences and the absolute values of the energy confinement time are similar. Indications are found that the density dependence, which is usually observed in stellarator confinement, can vanish above a critical density. The density dependence in stellarators seems to be similar to that in the linear ohmic confinement regime, which, in small tokamaks, extends to high density values, too. Because of the similarity in the gross confinement properties, transport in stellarators and tokamaks should not be dominated by the parameters which are very different in the two concepts, i.e. magnetic shear, major rational values of the rotational transform and plasma current. A difference in confinement is that there exists evidence for pinches in the particle and, possibly, energy transport channels in tokamaks whereas in stellarators no pinches have been observed, so far. In order to study the effect of plasma current and toroidal electric fields, stellarator discharges were carried out with an increasing amount of plasma current. From these experiments, no clear evidence of a connection of pinches with these parameters is found. The transient response in W7-AS plasmas can be described in terms of a non-local model. As in tokamaks, also cold pulse experiments in W7-AS indicate the importance of non-local transport. (author). 8 refs, 5 figs.

  19. Runaways and weathervanes: The shape of stellar bow shocks

    Science.gov (United States)

    Henney, W. J.; Tarango-Yong, J. A.

    2017-11-01

    Stellar bow shocks are the result of the supersonic interaction between a stellar wind and its environment. Some of these are "runaways": high-velocity stars that have been ejected from a star cluster. Others are "weather vanes", where it is the local interstellar medium itself that is moving, perhaps as the result of a champagne flow of ionized gas from a nearby HII region. We propose a new two-dimensional classification scheme for bow shapes, which is based on dimensionless geometric ratios that can be estimated from observational images. The two ratios are related to the flatness of the bow’s apex, which we term "planitude" and the openness of its wings, which we term "alatude". We calculate the inclination-dependent tracks on the planitude-alatude plane that are predicted by simple models for the bow shock shape. We also measure the shapes of bow shocks from three different observational datasets: mid-infrared arcs around hot main-sequence stars, far-infrared arcs around luminous cool stars, and emission-line arcs around proplyds and other young stars in the Orion Nebula. Clear differences are found between the different datasets in their distributions on the planitude-alatude plane, which can be used to constrain the physics of the bow shock interaction and emission mechanisms in the different classes of object.

  20. On the dynamics of non-stationary binary stellar system with non-isotropic mass flow

    International Nuclear Information System (INIS)

    Bekov, A.A.; Bejsekov, A.N.; Aldibaeva, L.T.

    2006-01-01

    The motion of test body in the external gravitational field of the binary stellar systems with slowly variable some physical parameters of radiating components is considered on the base of restricted nonstationary photo-gravitational three and two bodies problem with non-isotropic mass flow. The family of polar and coplanar solutions are obtained. The solutions give the possibility of the dynamical and structure interpretation of binary young evolving stars and galaxies. (author)

  1. Synthetic H-R diagrams as an observational test of stellar evolution theory

    International Nuclear Information System (INIS)

    Mathews, G.J.; Becker, S.A.; Brunish, W.M.

    1983-07-01

    Synthetic H-R diagrams are constructed from a grid of stellar models. These are compared directly with observations of young clusters in the LMC and SMC as a test of the models and as a means to determine the age, age dispersion, and composition of the clusters. Significant discrepancies between the observed and model H-R diagrams indicate the possible influences of convective overshoot, large AGB mass-loss rates, and the best value for the mixing length parameter

  2. Suicide among young people in selected Brazilian State capitals Suicídio de jovens nas principais capitais do Brasil

    Directory of Open Access Journals (Sweden)

    Edinilsa Ramos de Souza

    2002-06-01

    Full Text Available This study analyzes suicide among young Brazilians (15-24 years old in nine metropolitan areas. Mortality data for 1979-1998 were obtained from the Mortality Information System of the Ministry of Health. External causes are the main causes of death among youth, and suicide is the sixth most frequent of these causes. The distribution is heterogeneous, varying according to the social stratum, specific age group, sex, and means used to commit suicide. All cities analyzed showed increased suicide rates from 1979 to 1998 (from 3.5 to 5.0 per 100,000 inhabitants 15-24 years old. Salvador and Rio de Janeiro had the lowest suicide rates, while Porto Alegre and Curitiba had the highest. The principal means used by youth to commit suicide were hanging, strangling, and suffocation (Porto Alegre, followed by firearms and explosives (Belo Horizonte.O presente estudo analisa o comportamento dos suicídios de jovens nas capitais das nove Regiões Metropolitanas brasileiras. Utiliza os dados do Sistema de Informação sobre Mortalidade (SIM do Ministério da Saúde, na faixa etária de 15 a 24 anos, no período de 1979 a 1998. As externas são as principais causes de óbito de jovens e entre elas o suicídio ocupa a 6ª posição, com uma distribuição heterogênea. Sua incidência varia em função dos diferentes espaços sociais, das faixas etárias específicas, do sexo e dos meios utilizados. Para o conjunto das capitais observou-se uma certa elevação das taxas de suicídios nos anos analisados, correspondendo a 3,5 (em 1979, 3,4 (1985, 4,0 (1990 e a 5,0 (em 1998 por 100.000 habitantes de 15 a 24 anos. Salvador e Rio de Janeiro tiveram as menores taxas de suicídio; em contrapartida, Porto Alegre e Curitiba apresentaram as maiores taxas. Os principais meios utilizados para perpetrar tais mortes foram o enforcamento, estrangulamento e sufocação, sobretudo em Porto Alegre, e a utilização de armas de fogo e explosivos, ressaltando-se sua utilização em

  3. Aripiprazole Selectively Reduces Motor Tics in a Young Animal Model for Tourette’s Syndrome and Comorbid Attention Deficit and Hyperactivity Disorder

    Directory of Open Access Journals (Sweden)

    Francesca Rizzo

    2018-02-01

    Full Text Available Tourette’s syndrome (TS is a neurodevelopmental disorder characterized primarily by motor and vocal tics. Comorbidities such as attention deficit and hyperactivity disorder (ADHD are observed in over 50% of TS patients. We applied aripiprazole in a juvenile rat model that displays motor tics and hyperactivity. We additionally assessed the amount of ultrasonic vocalizations (USVs as an indicator for the presence of vocal tics and evaluated the changes in the striatal neurometabolism using in vivo proton magnetic resonance spectroscopy (1H-MRS at 11.7T. Thirty-one juvenile spontaneously hypertensive rats (SHRs underwent bicuculline striatal microinjection and treatment with either aripiprazole or vehicle. Control groups were sham operated and sham injected. Behavior, USVs, and striatal neurochemical profile were analyzed at early, middle, and late adolescence (postnatal days 35 to 50. Bicuculline microinjections in the dorsolateral striatum induced motor tics in SHR juvenile rats. Acute aripiprazole administration selectively reduced both tic frequency and latency, whereas stereotypies, USVs, and hyperactivity remained unaltered. The striatal neurochemical profile was only moderately altered after tic-induction and was not affected by systemic drug treatment. When applied to a young rat model that provides high degrees of construct, face, and predictive validity for TS and comorbid ADHD, aripiprazole selectively reduces motor tics, revealing that tics and stereotypies are distinct phenomena in line with clinical treatment of patients. Finally, our 1H-MRS results suggest a critical revision of the striatal role in the hypothesized cortico-striatal dysregulation in TS pathophysiology.

  4. Use of the stellarator expansion to investigate plasma equilibrium in modular stellarators

    International Nuclear Information System (INIS)

    Anania, G.; Johnson, J.L.; Weimer, K.E.

    1982-11-01

    A numerical code utilizing a large-aspect ratio, small-helical-distortion expansion is developed and used to investigate the effect of plasma currents on stellarator equilibrium. Application to modular stellarator configurations shows that a large rotational transform, and hence large coil deformation, is needed to achieve high-beta equilibria

  5. The evolution of the stellar mass functions of star-forming and quiescent galaxies to z = 4 from the COSMOS/ultraVISTA survey

    DEFF Research Database (Denmark)

    Muzzin, Adam; Marchesini, Danilo; Stefano, Mauro

    2013-01-01

    We present measurements of the stellar mass functions (SMFs) of star-forming and quiescent galaxies to z = 4 using a sample of 95,675 Ks -selected galaxies in the COSMOS/UltraVISTA field. The SMFs of the combined population are in good agreement with previous measurements and show that the stellar...

  6. Stellar Firework in a Whirlwind

    Science.gov (United States)

    2007-09-01

    VLT Image of Supernova in Beautiful Spiral Galaxy NGC 1288 Stars do not like to be alone. Indeed, most stars are members of a binary system, in which two stars circle around each other in an apparently never-ending cosmic ballet. But sometimes, things can go wrong. When the dancing stars are too close to each other, one of them can start devouring its partner. If the vampire star is a white dwarf - a burned-out star that was once like our Sun - this greed can lead to a cosmic catastrophe: the white dwarf explodes as a Type Ia supernova. In July 2006, ESO's Very Large Telescope took images of such a stellar firework in the galaxy NGC 1288. The supernova - designated SN 2006dr - was at its peak brightness, shining as bright as the entire galaxy itself, bearing witness to the amount of energy released. ESO PR Photo 39/07 ESO PR Photo 39/07 SN 2006dr in NGC 1288 NGC 1288 is a rather spectacular spiral galaxy, seen almost face-on and showing multiple spiral arms pirouetting around the centre. Bearing a strong resemblance to the beautiful spiral galaxy NGC 1232, it is located 200 million light-years away from our home Galaxy, the Milky Way. Two main arms emerge from the central regions and then progressively split into other arms when moving further away. A small bar of stars and gas runs across the centre of the galaxy. The first images of NGC 1288, obtained during the commissioning period of the FORS instrument on ESO's VLT in 1998, were of such high quality that they have allowed astronomers [1] to carry out a quantitative analysis of the morphology of the galaxy. They found that NGC 1288 is most probably surrounded by a large dark matter halo. The appearance and number of spiral arms are indeed directly related to the amount of dark matter in the galaxy's halo. The supernova was first spotted by amateur astronomer Berto Monard. On the night of 17 July 2006, Monard used his 30-cm telescope in the suburbs of Pretoria in South Africa and discovered the supernova as an

  7. Comparison of the effect of selected muscle groups fatigue on postural control during bipedal stance in healthy young women.

    Science.gov (United States)

    Shirazi, Zahra Rojhani; Jahromi, Fatemeh Nikhalat

    2013-09-01

    The maintenance of balance is an essential requirement for the performance of daily tasks and sporting activities and muscular fatigue is a factor to impair postural control, so this study was done to compare the effect of selected muscle groups fatigue on postural control during bipedal stance in healthy subjects. Fifteen healthy female students (24.3 ± 2.6 years) completed three testing session with a break period of at least 2 days. During each session, postural control was assessed during two 30-s trials of bipedal stance with eyes close before and after the fatigue protocol. Fatigue protocols were performed by 60% of their unfatigued Maximum Voluntary Contraction of unilateral ankle plantar flexors, bilateral lumbar extensors and bilateral neck extensors. One of the three fatigue protocols was performed on each session. The result showed that fatigue had a significant effect on COP velocity and it increase COP velocity but there was not found any difference in postural sway between muscle groups. Localized muscle fatigue caused deficits in postural control regardless of the location of fatigue. Authors suggest the possibility of the contributions of central mechanisms to postural deficits due to fatigue and it seems that difference was not between muscle groups due to central fatigue.

  8. sunstardb: A Database for the Study of Stellar Magnetism and the Solar-stellar Connection

    Science.gov (United States)

    Egeland, Ricky

    2018-05-01

    The “solar-stellar connection” began as a relatively small field of research focused on understanding the processes that generate magnetic fields in stars and sometimes lead to a cyclic pattern of long-term variability in activity, as demonstrated by our Sun. This area of study has recently become more broadly pertinent to questions of exoplanet habitability and exo-space weather, as well as stellar evolution. In contrast to other areas of stellar research, individual stars in the solar-stellar connection often have a distinct identity and character in the literature, due primarily to the rarity of the decades-long time-series that are necessary for studying stellar activity cycles. Furthermore, the underlying stellar dynamo is not well understood theoretically, and is thought to be sensitive to several stellar properties, e.g., luminosity, differential rotation, and the depth of the convection zone, which in turn are often parameterized by other more readily available properties. Relevant observations are scattered throughout the literature and existing stellar databases, and consolidating information for new studies is a tedious and laborious exercise. To accelerate research in this area I developed sunstardb, a relational database of stellar properties and magnetic activity proxy time-series keyed by individual named stars. The organization of the data eliminates the need for the problematic catalog cross-matching operations inherent when building an analysis data set from heterogeneous sources. In this article I describe the principles behind sunstardb, the data structures and programming interfaces, as well as use cases from solar-stellar connection research.

  9. Indicators of Mass in Spherical Stellar Atmospheres

    Science.gov (United States)

    Lester, John B.; Dinshaw, Rayomond; Neilson, Hilding R.

    2013-04-01

    Mass is the most important stellar parameter, but it is not directly observable for a single star. Spherical model stellar atmospheres are explicitly characterized by their luminosity ( L⋆), mass ( M⋆), and radius ( R⋆), and observations can now determine directly L⋆ and R⋆. We computed spherical model atmospheres for red giants and for red supergiants holding L⋆ and R⋆ constant at characteristic values for each type of star but varying M⋆, and we searched the predicted flux spectra and surface-brightness distributions for features that changed with mass. For both stellar classes we found similar signatures of the stars’ mass in both the surface-brightness distribution and the flux spectrum. The spectral features have been use previously to determine log 10(g), and now that the luminosity and radius of a non-binary red giant or red supergiant can be observed, spherical model stellar atmospheres can be used to determine a star’s mass from currently achievable spectroscopy. The surface-brightness variations of mass are slightly smaller than can be resolved by current stellar imaging, but they offer the advantage of being less sensitive to the detailed chemical composition of the atmosphere.

  10. Stellarator Coil Design and Plasma Sensitivity

    International Nuclear Information System (INIS)

    Ku, Long-Poe; Boozer, Allen H.

    2010-01-01

    The rich information contained in the plasma response to external magnetic perturbations can be used to help design stellarator coils more effectively. We demonstrate the feasibility by first devel oping a simple, direct method to study perturbations in stellarators that do not break stellarator symmetry and periodicity. The method applies a small perturbation to the plasma boundary and evaluates the resulting perturbed free-boundary equilibrium to build up a sensitivity matrix for the important physics attributes of the underlying configuration. Using this sensitivity information, design methods for better stellarator coils are then developed. The procedure and a proof-of-principle application are given that (1) determine the spatial distributions of external normal magnetic field at the location of the unperturbed plasma boundary to which the plasma properties are most sen- sitive, (2) determine the distributions of external normal magnetic field that can be produced most efficiently by distant coils, (3) choose the ratios of the magnitudes of the the efficiently produced magnetic distributions so the sensitive plasma properties can be controlled. Using these methods, sets of modular coils are found for the National Compact Stellarator Experiment (NCSX) that are either smoother or can be located much farther from the plasma boundary than those of the present design.

  11. Development of code PRETOR for stellarator simulation

    International Nuclear Information System (INIS)

    Dies, J.; Fontanet, J.; Fontdecaba, J.M.; Castejon, F.; Alejandre, C.

    1998-01-01

    The Department de Fisica i Enginyeria Nuclear (DFEN) of the UPC has some experience in the development of the transport code PRETOR. This code has been validated with shots of DIII-D, JET and TFTR, it has also been used in the simulation of operational scenarios of ITER fast burnt termination. Recently, the association EURATOM-CIEMAT has started the operation of the TJ-II stellarator. Due to the need of validating the results given by others transport codes applied to stellarators and because all of them made some approximations, as a averaging magnitudes in each magnetic surface, it was thought suitable to adapt the PRETOR code to devices without axial symmetry, like stellarators, which is very suitable for the specific needs of the study of TJ-II. Several modifications are required in PRETOR; the main concerns to the models of: magnetic equilibrium, geometry and transport of energy and particles. In order to solve the complex magnetic equilibrium geometry the powerful numerical code VMEC has been used. This code gives the magnetic surface shape as a Fourier series in terms of the harmonics (m,n). Most of the geometric magnitudes are also obtained from the VMEC results file. The energy and particle transport models will be replaced by other phenomenological models that are better adapted to stellarator simulation. Using the proposed models, it is pretended to reproduce experimental data available from present stellarators, given especial attention to the TJ-II of the association EURATOM-CIEMAT. (Author)

  12. Collisionless microinstabilities in stellarators. II. Numerical simulations

    International Nuclear Information System (INIS)

    Proll, J. H. E.; Xanthopoulos, P.; Helander, P.

    2013-01-01

    Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-J geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here, the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes, and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-J configurations

  13. Review of stellarator research world wide

    International Nuclear Information System (INIS)

    Shonet, J.L.

    1987-01-01

    The world-wide effort in stellarators has evolved considerably during the past few years. Stellarator facilities are located in the Australia, Federal Republic of Germany, Japan, the Soviet Union, Spain, the United Kingdom and the United States. Dimensions of stellarators range from less than 20 centimeters in major radius to more than 2 meters, and magnetic field values between 0.2 Tesla to more than 3.0 Tesla. Stellarators are made in a variety of magnetic configurations with wide ranges of toroidal aspect ratios and methods of generating the stellarator magnetic surfaces. In particular, continuous helical coils, twisted modular coils, or twisted vacuum chambers all provide different means to generate nested toroidal magnetic surfaces without the need for currents flowing in the plasma. The goal of present day experiments is to accumulate a physics data base. This is being done by increasing electron and ion temperatures with non-ohmic heating, by transport and scaling studies considering neoclassical scaling, global scaling, effects of electric fields, the bootstrap current and magnetic islands. Higher betas are being attempted by designing suitable magnetic configurations, pellet injection and/or minimizing transport losses. Plasma-wall interactions and particle control are being examined by divertor, pumped-limiter and carbonization experiments

  14. Geometric phase modulation for stellar interferometry

    International Nuclear Information System (INIS)

    Roy, M.; Boschung, B.; Tango, W.J.; Davis, J.

    2002-01-01

    Full text: In a long baseline optical interferometer, the fringe visibility is normally measured by modulation of the optical path difference between the two arms of the instruments. To obtain accurate measurements, the spectral bandwidth must be narrow, limiting the sensitivity of the technique. The application of geometric phase modulation technique to stellar interferometry has been proposed by Tango and Davis. Modulation of the geometric phase has the potential for improving the sensitivity of optical interferometers, and specially the Sydney University Stellar Interferometer (SUSI), by allowing broad band modulation of the light signals. This is because a modulator that changes the geometric phase of the signal is, in principle, achromatic. Another advantage of using such a phase modulator is that it can be placed in the common path traversed by the two orthogonally polarized beams emerging from the beam combiner in a stellar interferometer. Thus the optical components of the modulator do not have to be interferometric quality and could be relatively easily introduced into SUSI. We have investigated the proposed application in a laboratory-based experiment using a Mach-Zehnder interferometer with white-light source. This can be seen as a small model of an amplitude stellar interferometer where the light source takes the place of the distant star and two corner mirrors replaces the entrance pupils of the stellar interferometer

  15. The effects of selected dietary bioflavonoid supplementation on dental caries in young rats fed a high-sucrose diet.

    Science.gov (United States)

    Wood, Nelson

    2007-12-01

    Recent evidence suggests that certain bioflavonoids reduce dental caries and cariogenic bacteria incidence. The present study evaluates two separate, but related, dietary trials -- trial 1, 0.09%, 0.18%, 0.36%, and 0.72% dietary naringenin (NAR) supplementation; and trial 2, 0.57% dietary rutin (R), quercetin (Q), and naringin (N) supplementation-on dental caries formation in 40 different male albino rats, at the expense of dextrose, for periods of 42 days. All rats were fed 40% sucrose. In dietary trial 1, rats were evaluated for dental caries, dental plaque accumulation, and saliva flow rates using oneway analysis of variance, post hoc Tukey's test, Kruskal-Wallis test, and Spearman's correlations. In dietary trial 2, rats were evaluated for occlusal dental caries only using a Kruskal-Wallis H test and analysis of variance. A 5% level of statistical significance was adopted throughout. In dietary trial 1, NAR showed a statistically significant effect on dental caries, plaque, and saliva flow rate reduction compared with the control group (P < .05-.01). An inverse dose-dependent relationship was established among the NAR experimental groups and control group. Dietary NAR supplementation significantly reduced dental caries formation, possibly because of reduced dental plaque accumulation. In dietary trial 2, statistically significant reductions in occlusal caries were observed for R, Q, and N in the maxillary molars and for Q and N in the mandibular molars compared with the control group (P < .05). Significant associations were observed among the experimental groups and maxillary (P < .05) and mandibular (P < .01) occlusal dental caries. Hence, selected bioflavonoids may show promise as an alternative means of reducing dental caries.

  16. INSIGHTS ON THE STELLAR MASS-METALLICITY RELATION FROM THE CALIFA SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    González Delgado, R. M.; García-Benito, R.; Pérez, E.; Cortijo-Ferrero, C.; López Fernández, R.; Sánchez, S. F. [Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Cid Fernandes, R.; De Amorim, A. L.; Lacerda, E. A. D.; Vale Asari, N. [Departamento de Física, Universidade Federal de Santa Catarina, P.O. Box 476, 88040-900 Florianópolis, SC (Brazil); Alves, J. [University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna (Austria); Bland-Hawthorn, J. [Sydney Institute for Astronomy, The University of Sydney, NSW 2006 (Australia); Galbany, L. [Millennium Institute of Astrophysics and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Gallazzi, A. [INAF—Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze (Italy); Husemann, B. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching b. München (Germany); Bekeraite, S. [Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany); Jungwiert, B. [Astronomical Institute of the Academy of Sciences of the Czech Republic, v.v.i., Bocni II 1401, 14131 Prague (Czech Republic); López-Sánchez, A. R. [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia); De Lorenzo-Cáceres, A. [School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, KY16 9SS (United Kingdom); Marino, R. A. [CEI Campus Moncloa, UCM-UPM, Departamento de Astrofísica y CC. de la Atmósfera, Facultad de CC. Físicas, Universidad Complutense de Madrid, Avda. Complutense s/n, E-28040 Madrid (Spain); Collaboration: CALIFA collaboration920; and others

    2014-08-10

    We use spatially and temporally resolved maps of stellar population properties of 300 galaxies from the CALIFA integral field survey to investigate how the stellar metallicity (Z {sub *}) relates to the total stellar mass (M {sub *}) and the local mass surface density (μ{sub *}) in both spheroidal- and disk-dominated galaxies. The galaxies are shown to follow a clear stellar mass-metallicity relation (MZR) over the whole 10{sup 9}-10{sup 12} M {sub ☉} range. This relation is steeper than the one derived from nebular abundances, which is similar to the flatter stellar MZR derived when we consider only young stars. We also find a strong relation between the local values of μ{sub *} and Z {sub *} (the μZR), betraying the influence of local factors in determining Z {sub *}. This shows that both local (μ{sub *}-driven) and global (M {sub *}-driven) processes are important in determining metallicity in galaxies. We find that the overall balance between local and global effects varies with the location within a galaxy. In disks, μ{sub *} regulates Z {sub *}, producing a strong μZR whose amplitude is modulated by M {sub *}. In spheroids it is M {sub *} that dominates the physics of star formation and chemical enrichment, with μ{sub *} playing a minor, secondary role. These findings agree with our previous analysis of the star formation histories of CALIFA galaxies, which showed that mean stellar ages are mainly governed by surface density in galaxy disks and by total mass in spheroids.

  17. An infrared view of (candidate accretion) disks around massive young stars

    NARCIS (Netherlands)

    Bik, A.; Lenorzer, A.; Thi, W.F.; Puga Antolín, E.; Waters, L.B.F.M.; Kaper, L.; Martín-Hernández, L.N.

    2008-01-01

    Near-infrared surveys of high-mass star-forming regions start to shed light onto their stellar content. A particular class of objects found in these regions, the so-called massive Young Stellar Objects (YSOs) are surrounded by dense circumstellar material. Several near- and mid-infrared diagnostic

  18. Stellar Wakes from Dark Matter Subhalos.

    Science.gov (United States)

    Buschmann, Malte; Kopp, Joachim; Safdi, Benjamin R; Wu, Chih-Liang

    2018-05-25

    We propose a novel method utilizing stellar kinematic data to detect low-mass substructure in the Milky Way's dark matter halo. By probing characteristic wakes that a passing dark matter subhalo leaves in the phase-space distribution of ambient halo stars, we estimate sensitivities down to subhalo masses of ∼10^{7}  M_{⊙} or below. The detection of such subhalos would have implications for dark matter and cosmological models that predict modifications to the halo-mass function at low halo masses. We develop an analytic formalism for describing the perturbed stellar phase-space distributions, and we demonstrate through idealized simulations the ability to detect subhalos using the phase-space model and a likelihood framework. Our method complements existing methods for low-mass subhalo searches, such as searches for gaps in stellar streams, in that we can localize the positions and velocities of the subhalos today.

  19. Stellar Wakes from Dark Matter Subhalos

    Science.gov (United States)

    Buschmann, Malte; Kopp, Joachim; Safdi, Benjamin R.; Wu, Chih-Liang

    2018-05-01

    We propose a novel method utilizing stellar kinematic data to detect low-mass substructure in the Milky Way's dark matter halo. By probing characteristic wakes that a passing dark matter subhalo leaves in the phase-space distribution of ambient halo stars, we estimate sensitivities down to subhalo masses of ˜107 M⊙ or below. The detection of such subhalos would have implications for dark matter and cosmological models that predict modifications to the halo-mass function at low halo masses. We develop an analytic formalism for describing the perturbed stellar phase-space distributions, and we demonstrate through idealized simulations the ability to detect subhalos using the phase-space model and a likelihood framework. Our method complements existing methods for low-mass subhalo searches, such as searches for gaps in stellar streams, in that we can localize the positions and velocities of the subhalos today.

  20. Effect of finite β on stellarator transport

    International Nuclear Information System (INIS)

    Mynick, H.E.

    1984-04-01

    A theory of the modification of stellarator transport due to the presence of finite plasma pressure is developed, and applied to a range of stellarator configurations. For many configurations of interest, plasma transport can change by more than an order of magnitude in the progression from zero pressure to the equilibrium β limit of the device. Thus, a stellarator with transport-optimized vacuum fields can have poor confinement at the desired operating β. Without an external compensating field, increasing β tends to degrade confinement, unless the initial field structure is very carefully chosen. The theory permits one to correctly determine this vacuum structure, in terms of the desired structure of the field at a prescribed operating β. With a compensating external field, the deleterious effect of finite β on transport can be partially eliminated

  1. Recent advances in modeling stellar interiors (u)

    Energy Technology Data Exchange (ETDEWEB)

    Guzik, Joyce Ann [Los Alamos National Laboratory

    2010-01-01

    Advances in stellar interior modeling are being driven by new data from large-scale surveys and high-precision photometric and spectroscopic observations. Here we focus on single stars in normal evolutionary phases; we will not discuss the many advances in modeling star formation, interacting binaries, supernovae, or neutron stars. We review briefly: (1) updates to input physics of stellar models; (2) progress in two and three-dimensional evolution and hydrodynamic models; (3) insights from oscillation data used to infer stellar interior structure and validate model predictions (asteroseismology). We close by highlighting a few outstanding problems, e.g., the driving mechanisms for hybrid {gamma} Dor/{delta} Sct star pulsations, the cause of giant eruptions seen in luminous blue variables such as {eta} Car and P Cyg, and the solar abundance problem.

  2. Electron Capture Cross Sections for Stellar Nucleosynthesis

    Directory of Open Access Journals (Sweden)

    P. G. Giannaka

    2015-01-01

    Full Text Available In the first stage of this work, we perform detailed calculations for the cross sections of the electron capture on nuclei under laboratory conditions. Towards this aim we exploit the advantages of a refined version of the proton-neutron quasiparticle random-phase approximation (pn-QRPA and carry out state-by-state evaluations of the rates of exclusive processes that lead to any of the accessible transitions within the chosen model space. In the second stage of our present study, we translate the abovementioned e--capture cross sections to the stellar environment ones by inserting the temperature dependence through a Maxwell-Boltzmann distribution describing the stellar electron gas. As a concrete nuclear target we use the 66Zn isotope, which belongs to the iron group nuclei and plays prominent role in stellar nucleosynthesis at core collapse supernovae environment.

  3. Equilibrium reconstruction in stellarators: V3FIT

    Energy Technology Data Exchange (ETDEWEB)

    Hanson, J.D.; Knowlton, S.F. [Physics Department, Auburn University, Auburn, AL (United States); Hirshman, S.P.; Lazarus, E.A. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Lao, L.L. [General Atomics, San Diego, CA (United States)

    2003-07-01

    The first section describes a general response function formalism for computing stellarator magnetic diagnostic signals, which is the first step in developing a reconstruction capability. The approach parallels that used in the EFIT two-dimensional (2-D) equilibrium reconstruction code. The second section describes the two codes we have written, V3RFUN and V3POST. V3RFUN computes the response functions for a specified magnetic diagnostic coil, and V3POST uses the response functions calculated by V3RFUN, along with the plasma current information supplied by the equilibrium code VMEC, to compute the expected magnetic diagnostic signals. These two codes are currently being used to design magnetic diagnostic for the NCSX stellarator (at PPPL) and the CTH toroidal hybrid stellarator (at Auburn University). The last section of the paper describes plans for the V3FIT code. (orig.)

  4. The low-luminosity stellar mass function

    International Nuclear Information System (INIS)

    Kroupa, Pavel; Tout, C.A.; Gilmore, Gerard

    1990-01-01

    The stellar mass function for low-mass stars is constrained using the stellar luminosity function and the slope of the mass-luminosity relation. We investigate the range of mass functions for stars with absolute visual magnitude fainter than M V ≅ +5 which are consistent with both the local luminosity function and the rather poorly determined mass-absolute visual magnitude relation. Points of inflexion in the mass-luminosity relation exist because of the effects of H - , H 2 and of other molecules on the opacity and equation of state. The first two of these correspond to absolute magnitudes M V ≅ +7 and M V ≅ +12, respectively, at which structure is evident in the stellar luminosity function (a flattening and a maximum, respectively). Combining the mass-luminosity relation which shows these inflexion points with a peaked luminosity function, we test smooth mass functions in the mass range 0.9-0.1 the solar mass. (author)

  5. OGLE-ing the Magellanic system: stellar populations in the Magellanic Bridge

    International Nuclear Information System (INIS)

    Skowron, D. M.; Jacyszyn, A. M.; Udalski, A.; Szymański, M. K.; Skowron, J.; Poleski, R.; Kozłowski, S.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Mróz, P.; Pietrukowicz, P.; Ulaczyk, K.; Wyrzykowski, Ł.

    2014-01-01

    We report the discovery of a young stellar bridge that forms a continuous connection between the Magellanic Clouds. This finding is based on number density maps for stellar populations found in data gathered by OGLE-IV that fully cover over 270 deg 2 of the sky in the Magellanic Bridge area. This is the most extensive optical survey of this region to date. We find that the young population is present mainly in the western half of the MBR, which, together with the newly discovered young population in the eastern Bridge, form a continuous stream of stars connecting both galaxies along δ ∼ –73.5 deg. The young population distribution is clumped, with one of the major densities close to the SMC and the other fairly isolated and located approximately mid-way between the Clouds, which we call the OGLE island. These overdensities are well matched by H I surface density contours, although the newly found young population in the eastern Bridge is offset by ∼2 deg north from the highest H I density contour. We observe a continuity of red clump stars between the Magellanic Clouds which represent an intermediate-age population. Red clump stars are present mainly in the southern and central parts of the Magellanic Bridge, below its gaseous part, and their presence is reflected by a strong deviation from the radial density profiles of the two galaxies. This may indicate either a tidal stream of stars, or that the stellar halos of the two galaxies overlap. On the other hand, we do not observe such an overlap within an intermediate-age population represented by the top of the red giant branch and the asymptotic giant branch stars. We also see only minor mixing of the old populations of the Clouds in the southern part of the Bridge, represented by the lowest part of the red giant branch.

  6. OGLE-ing the Magellanic system: stellar populations in the Magellanic Bridge

    Energy Technology Data Exchange (ETDEWEB)

    Skowron, D. M.; Jacyszyn, A. M.; Udalski, A.; Szymański, M. K.; Skowron, J.; Poleski, R.; Kozłowski, S.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Mróz, P.; Pietrukowicz, P.; Ulaczyk, K.; Wyrzykowski, Ł., E-mail: dszczyg@astrouw.edu.pl [Warsaw University Astronomical Observatory, Aleje Ujazdowskie 4, 00-478 Warszawa (Poland)

    2014-11-10

    We report the discovery of a young stellar bridge that forms a continuous connection between the Magellanic Clouds. This finding is based on number density maps for stellar populations found in data gathered by OGLE-IV that fully cover over 270 deg{sup 2} of the sky in the Magellanic Bridge area. This is the most extensive optical survey of this region to date. We find that the young population is present mainly in the western half of the MBR, which, together with the newly discovered young population in the eastern Bridge, form a continuous stream of stars connecting both galaxies along δ ∼ –73.5 deg. The young population distribution is clumped, with one of the major densities close to the SMC and the other fairly isolated and located approximately mid-way between the Clouds, which we call the OGLE island. These overdensities are well matched by H I surface density contours, although the newly found young population in the eastern Bridge is offset by ∼2 deg north from the highest H I density contour. We observe a continuity of red clump stars between the Magellanic Clouds which represent an intermediate-age population. Red clump stars are present mainly in the southern and central parts of the Magellanic Bridge, below its gaseous part, and their presence is reflected by a strong deviation from the radial density profiles of the two galaxies. This may indicate either a tidal stream of stars, or that the stellar halos of the two galaxies overlap. On the other hand, we do not observe such an overlap within an intermediate-age population represented by the top of the red giant branch and the asymptotic giant branch stars. We also see only minor mixing of the old populations of the Clouds in the southern part of the Bridge, represented by the lowest part of the red giant branch.

  7. MASSCLEANage-STELLAR CLUSTER AGES FROM INTEGRATED COLORS

    International Nuclear Information System (INIS)

    Popescu, Bogdan; Hanson, M. M.

    2010-01-01

    We present the recently updated and expanded MASSCLEANcolors, a database of 70 million Monte Carlo models selected to match the properties (metallicity, ages, and masses) of stellar clusters found in the Large Magellanic Cloud (LMC). This database shows the rather extreme and non-Gaussian distribution of integrated colors and magnitudes expected with different cluster age and mass and the enormous age degeneracy of integrated colors when mass is unknown. This degeneracy could lead to catastrophic failures in estimating age with standard simple stellar population models, particularly if most of the clusters are of intermediate or low mass, like in the LMC. Utilizing the MASSCLEANcolors database, we have developed MASSCLEANage, a statistical inference package which assigns the most likely age and mass (solved simultaneously) to a cluster based only on its integrated broadband photometric properties. Finally, we use MASSCLEANage to derive the age and mass of LMC clusters based on integrated photometry alone. First, we compare our cluster ages against those obtained for the same seven clusters using more accurate integrated spectroscopy. We find improved agreement with the integrated spectroscopy ages over the original photometric ages. A close examination of our results demonstrates the necessity of solving simultaneously for mass and age to reduce degeneracies in the cluster ages derived via integrated colors. We then selected an additional subset of 30 photometric clusters with previously well-constrained ages and independently derive their age using the MASSCLEANage with the same photometry with very good agreement. The MASSCLEANage program is freely available under GNU General Public License.

  8. THE RESOLVED STELLAR POPULATION IN 50 REGIONS OF M83 FROM HST/WFC3 EARLY RELEASE SCIENCE OBSERVATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hwihyun; Cohen, Seth H.; Windhorst, Rogier A. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404 (United States); Whitmore, Bradley C.; Mutchler, Max; Bond, Howard E. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Chandar, Rupali [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States); Saha, Abhijit [National Optical Astronomy Observatories, Tucson, AZ 85726-6732 (United States); Kaleida, Catherine C. [Cerro Tololo Inter-American Observatory, La Serena (Chile); Calzetti, Daniela [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); O' Connell, Robert W. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Balick, Bruce [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States); Carollo, Marcella [Department of Physics, ETH-Zurich, Zurich 8093 (Switzerland); Disney, Michael J. [School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA (United Kingdom); Dopita, Michael A. [Mount Stromlo and Siding Spring Observatories, Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia); Frogel, Jay A. [Galaxies Unlimited, 1 Tremblant Court, Lutherville, MD 21093 (United States); Hall, Donald N. B. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Holtzman, Jon A. [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); Kimble, Randy A. [NASA-Goddard Space Flight Center, Greenbelt, MD 20771 (United States); McCarthy, Patrick J., E-mail: hwihyun.kim@asu.edu [Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101-1292 (United States); and others

    2012-07-01

    We present a multi-wavelength photometric study of {approx}15,000 resolved stars in the nearby spiral galaxy M83 (NGC 5236, D = 4.61 Mpc) based on Hubble Space Telescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83 and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction toward each individual star by comparing its colors with predictions from stellar isochrones. We compare the resulting luminosity-weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations of Wolf-Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected.

  9. The Resolved Stellar Population in 50 Regions of M83 from HST/WFC3 Early Release Science Observations

    Science.gov (United States)

    Kim, Hwihyun; Whitmore, Bradley C.; Chandar, Rupali; Saha, Abhijit; Kaleida, Catherine C.; Mutchler, Max; Cohen, Seth H.; Calzetti, Daniela; O’Connell, Robert W.; Windhorst, Rogier A.; hide

    2012-01-01

    We present a multi-wavelength photometric study of approximately 15,000 resolved stars in the nearby spiral galaxy M83 (NGC 5236, D = 4.61 Mpc) based on Hubble Space Telescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83 and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction toward each individual star by comparing its colors with predictions from stellar isochrones.We compare the resulting luminosity-weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations ofWolf-Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected.

  10. THE RESOLVED STELLAR POPULATION IN 50 REGIONS OF M83 FROM HST/WFC3 EARLY RELEASE SCIENCE OBSERVATIONS

    International Nuclear Information System (INIS)

    Kim, Hwihyun; Cohen, Seth H.; Windhorst, Rogier A.; Whitmore, Bradley C.; Mutchler, Max; Bond, Howard E.; Chandar, Rupali; Saha, Abhijit; Kaleida, Catherine C.; Calzetti, Daniela; O'Connell, Robert W.; Balick, Bruce; Carollo, Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.

    2012-01-01

    We present a multi-wavelength photometric study of ∼15,000 resolved stars in the nearby spiral galaxy M83 (NGC 5236, D = 4.61 Mpc) based on Hubble Space Telescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83 and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction toward each individual star by comparing its colors with predictions from stellar isochrones. We compare the resulting luminosity-weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations of Wolf-Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected.

  11. The Stellar IMF from Isothermal MHD Turbulence

    Science.gov (United States)

    Haugbølle, Troels; Padoan, Paolo; Nordlund, Åke

    2018-02-01

    We address the turbulent fragmentation scenario for the origin of the stellar initial mass function (IMF), using a large set of numerical simulations of randomly driven supersonic MHD turbulence. The turbulent fragmentation model successfully predicts the main features of the observed stellar IMF assuming an isothermal equation of state without any stellar feedback. As a test of the model, we focus on the case of a magnetized isothermal gas, neglecting stellar feedback, while pursuing a large dynamic range in both space and timescales covering the full spectrum of stellar masses from brown dwarfs to massive stars. Our simulations represent a generic 4 pc region within a typical Galactic molecular cloud, with a mass of 3000 M ⊙ and an rms velocity 10 times the isothermal sound speed and 5 times the average Alfvén velocity, in agreement with observations. We achieve a maximum resolution of 50 au and a maximum duration of star formation of 4.0 Myr, forming up to a thousand sink particles whose mass distribution closely matches the observed stellar IMF. A large set of medium-size simulations is used to test the sink particle algorithm, while larger simulations are used to test the numerical convergence of the IMF and the dependence of the IMF turnover on physical parameters predicted by the turbulent fragmentation model. We find a clear trend toward numerical convergence and strong support for the model predictions, including the initial time evolution of the IMF. We conclude that the physics of isothermal MHD turbulence is sufficient to explain the origin of the IMF.

  12. Near-Field Cosmology with Resolved Stellar Populations Around Local Volume LMC Stellar-Mass Galaxies

    Science.gov (United States)

    Carlin, Jeffrey L.; Sand, David J.; Willman, Beth; Brodie, Jean P.; Crnojevic, Denija; Forbes, Duncan; Hargis, Jonathan R.; Peter, Annika; Pucha, Ragadeepika; Romanowsky, Aaron J.; Spekkens, Kristine; Strader, Jay

    2018-06-01

    We discuss our ongoing observational program to comprehensively map the entire virial volumes of roughly LMC stellar mass galaxies at distances of ~2-4 Mpc. The MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos) survey will deliver the first census of the dwarf satellite populations and stellar halo properties within LMC-like environments in the Local Volume. Our results will inform our understanding of the recent DES discoveries of dwarf satellites tentatively affiliated with the LMC/SMC system. This program has already yielded the discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep Subaru+HyperSuprimeCam imaging reaching ~2 magnitudes below its TRGB, and at least two additional candidate satellites. We will summarize the survey results and status to date, highlighting some challenges encountered and lessons learned as we process the data for this program through a prototype LSST pipeline. Our program will examine whether LMC stellar mass dwarfs have extended stellar halos, allowing us to assess the relative contributions of in-situ stars vs. merger debris to their stellar populations and halo density profiles. We outline the constraints on galaxy formation models that will be provided by our observations of low-mass galaxy halos and their satellites.

  13. A study of the stellar population in the Lynds 1641 dark cloud. I. The IRAS catalog sources

    International Nuclear Information System (INIS)

    Strom, K.M.; Newton, G.; Strom, S.E.; Seaman, R.L.; Carrasco, L.

    1989-01-01

    The character of the sources identified in the IRAS Point Source Catalog and located within the boundaries of the nearest giant molecular cloud, Lynds 1641 is discussed. New optical and near-infrared photometry are combined to provide spectral energy distributions (SEDs) for these objects divided into three classes: class I objects with flat or rising spectra, class II objects with spectra intermediate in slope between a flat and blackbody spectrum, and class III objects with spectra similar to those of blackbodies. It is found that L1641 contains a much larger percentage of class I sources than does the nearby Taurus-Auriga star-forming complex. Spectral energy distributions for the IRAS-selected sample are examined and compared with SEDs for young stellar objects (YSOs) located in Taurus-Auriga. The IRAS-selected sources having optical counterparts in the H-R diagram are identified and discussed along with the distribution of masses and ages for these YSOs. 86 refs

  14. Optimisation of stellarator systems: Possible ways

    International Nuclear Information System (INIS)

    Cooper, W.A.; Isaev, M.; Leneva, A.E.; Mikhailov, M.; Shafranov, V.D.; Subbotin, A.A.

    2001-01-01

    The results of our search for advanced helical (stellarator) systems with a small number of field periods over the last five years are presented. The comparison of stellarator systems with toroidal (helical or axial) and poloidal directions of the contours with B = constant on the magnetic surface as well as systems with Helias and Heliac-like orientation of the magnetic surfaces cross-sections with respect to the principal normal to the magnetic axis is undertaken. Particular attention is paid to some attractive features of the systems with constant B-lines in the poloidal direction. (author)

  15. Optimisation of stellarator systems: Possible ways

    International Nuclear Information System (INIS)

    Cooper, W.A.; Isaev, M.Yu.; Leneva, A.E.; Mikhailov, M.I.; Sharfranov, V.D.; Subbotin, A.A.

    1999-01-01

    The results of our search for advanced helical (stellarator) systems with a small number of field periods over the last five years are presented. The comparison of stellarator systems with toroidal (helical or axial) and poloidal directions of the contours with B = constant on the magnetic surface as well as systems with Helias and Heliac-like orientation of the magnetic surfaces cross-sections with respect to the principal normal to the magnetic axis is undertaken. Particular attention is paid to some attractive features of the systems with constant B-lines in the poloidal direction. (author)

  16. 3D radiative transfer in stellar atmospheres

    International Nuclear Information System (INIS)

    Carlsson, M

    2008-01-01

    Three-dimensional (3D) radiative transfer in stellar atmospheres is reviewed with special emphasis on the atmospheres of cool stars and applications. A short review of methods in 3D radiative transfer shows that mature methods exist, both for taking into account radiation as an energy transport mechanism in 3D (magneto-) hydrodynamical simulations of stellar atmospheres and for the diagnostic problem of calculating the emergent spectrum in more detail from such models, both assuming local thermodynamic equilibrium (LTE) and in non-LTE. Such methods have been implemented in several codes, and examples of applications are given.

  17. Stellar compass for the Clementine Mission

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, B. [Lawrence Livermore National Lab., CA (United States)

    1994-11-15

    A CCD sensor with 42 x 28 degrees FOV and 576 x 384 pixels was built by the Advanced Technology Program (ATP) in the Physics Department at LLNL. That sensor, called the StarTracker camera, is used on the Clementine Lunar Mapping mission between January and May, 1994. Together with the Stellar Compass software, the StarTracker camera provided a way of identifying its orientation to within about 150 microradians in camera body pitch and yaw. This presentation will be an overview of basically how the Stellar Compass software works, along with showing some of its performance results.

  18. Overdense Plasma Operation in the WEGA Stellarator

    Czech Academy of Sciences Publication Activity Database

    Otte, M.; Laqua, H.P.; Marsen, S.; Podoba, Y.; Preinhaelter, Josef; Stange, T.; Urban, Jakub; Wagner, F.; Zhang, D.

    2010-01-01

    Roč. 50, č. 8 (2010), s. 785-789 ISSN 0863-1042. [International Stellarator/Heliotron Workshop/17th./. Princeton, 12.10.2009-16.10.2009] R&D Projects: GA ČR GA202/08/0419; GA MŠk 7G09042 Institutional research plan: CEZ:AV0Z20430508 Keywords : Stellarator * Bernstein waves * overdense plasma * supra -thermal electrons Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.006, year: 2010 http://dx.doi.org/10.1002/ctpp.200900053

  19. 176Lu: Cosmic clock or stellar thermometer

    International Nuclear Information System (INIS)

    Ward, R.A.; Beer, H.; Kaeppeler, F.; Wisshak, K.

    1980-12-01

    We quantitatively examine the various experimental and theoretical aspects of the stellar synthesis of the long-lived ground state of 176 Lu (3.6 x 10 10 y). We discuss the various regimes of stellar temperature and free-neutron density in which either: (i) the internal electromagnetic couplings between 176 Lusup(o) and 176 Lusup(m) (3.68 hours) are sufficiently slow that they may be treated as separate nuclei, or (ii) the internal couplings are rapidly able to establish thermal equilibrium between 176 Lusup(o) and 176 Lusup(m). (orig.)

  20. On the construction of a new stellar classification template library for the LAMOST spectral analysis pipeline

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Peng; Luo, Ali; Li, Yinbi; Tu, Liangping; Wang, Fengfei; Zhang, Jiannan; Chen, Xiaoyan; Hou, Wen; Kong, Xiao; Wu, Yue; Zuo, Fang; Yi, Zhenping; Zhao, Yongheng; Chen, Jianjun; Du, Bing; Guo, Yanxin; Ren, Juanjuan [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Pan, Jingchang; Jiang, Bin; Liu, Jie, E-mail: lal@nao.cas.cn, E-mail: weipeng@nao.cas.cn [School of Mechanical, Electrical, and Information Engineering, Shandong University, Weihai 264209 (China); and others

    2014-05-01

    The LAMOST spectral analysis pipeline, called the 1D pipeline, aims to classify and measure the spectra observed in the LAMOST survey. Through this pipeline, the observed stellar spectra are classified into different subclasses by matching with template spectra. Consequently, the performance of the stellar classification greatly depends on the quality of the template spectra. In this paper, we construct a new LAMOST stellar spectral classification template library, which is supposed to improve the precision and credibility of the present LAMOST stellar classification. About one million spectra are selected from LAMOST Data Release One to construct the new stellar templates, and they are gathered in 233 groups by two criteria: (1) pseudo g – r colors obtained by convolving the LAMOST spectra with the Sloan Digital Sky Survey ugriz filter response curve, and (2) the stellar subclass given by the LAMOST pipeline. In each group, the template spectra are constructed using three steps. (1) Outliers are excluded using the Local Outlier Probabilities algorithm, and then the principal component analysis method is applied to the remaining spectra of each group. About 5% of the one million spectra are ruled out as outliers. (2) All remaining spectra are reconstructed using the first principal components of each group. (3) The weighted average spectrum is used as the template spectrum in each group. Using the previous 3 steps, we initially obtain 216 stellar template spectra. We visually inspect all template spectra, and 29 spectra are abandoned due to low spectral quality. Furthermore, the MK classification for the remaining 187 template spectra is manually determined by comparing with 3 template libraries. Meanwhile, 10 template spectra whose subclass is difficult to determine are abandoned. Finally, we obtain a new template library containing 183 LAMOST template spectra with 61 different MK classes by combining it with the current library.

  1. TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Agertz, Oscar; Kravtsov, Andrey V.; Leitner, Samuel N.; Gnedin, Nickolay Y.

    2013-05-21

    We investigate the momentum and energy budget of stellar feedback during different stages of stellar evolution, and study its impact on the interstellar medium (ISM) using simulations of local star-forming regions and galactic disks at the resolution affordable in modern cosmological zoom-in simulations. In particular, we present a novel subgrid model for the momentum injection due to radiation pressure and stellar winds from massive stars during early, pre-supernova (pre-SN) evolutionary stages of young star clusters. Early injection of momentum acts to clear out dense gas in star-forming regions, hence limiting star formation. The reduced gas density mitigates radiative losses of thermal feedback energy from subsequent SN explosions. The detailed impact of stellar feedback depends sensitively on the implementation and choice of parameters. Somewhat encouragingly, we find that implementations in which feedback is efficient lead to approximate self-regulation of the global star formation efficiency. We compare simulation results using our feedback implementation to other phenomenological feedback methods, where thermal feedback energy is allowed to dissipate over timescales longer than the formal gas cooling time. We find that simulations with maximal momentum injection suppress star formation to a similar degree as is found in simulations adopting adiabatic thermal feedback. However, different feedback schemes are found to produce significant differences in the density and thermodynamic structure of the ISM, and are hence expected to have a qualitatively different impact on galaxy evolution.

  2. TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS

    International Nuclear Information System (INIS)

    Agertz, Oscar; Kravtsov, Andrey V.; Leitner, Samuel N.; Gnedin, Nickolay Y.

    2013-01-01

    We investigate the momentum and energy budget of stellar feedback during different stages of stellar evolution, and study its impact on the interstellar medium (ISM) using simulations of local star-forming regions and galactic disks at the resolution affordable in modern cosmological zoom-in simulations. In particular, we present a novel subgrid model for the momentum injection due to radiation pressure and stellar winds from massive stars during early, pre-supernova (pre-SN) evolutionary stages of young star clusters. Early injection of momentum acts to clear out dense gas in star-forming regions, hence limiting star formation. The reduced