WorldWideScience

Sample records for w stellarators

  1. Embedded Stellar Clusters in the W3/W4/W5 Molecular Cloud Complex

    CERN Document Server

    Carpenter, J M; Snell, R L; Carpenter, John M.; Heyer, Mark H.; Snell, Ronald L.

    2002-01-01

    We analyze the embedded stellar content in the vicinity of the W3/W4/W5 HII regions using the FCRAO Outer Galaxy 12CO(J=1-0) Survey, the IRAS Point Source Catalog, published radio continuum surveys, and new near-infrared and molecular line observations. Thirty-four IRAS Point Sources are identified that have far-infrared colors characteristic of embedded star forming regions, and we have obtained K' mosaics and 13CO(J=1-0) maps for 32 of them. Ten of the IRAS sources are associated with an OB star and 19 with a stellar cluster, although three OB stars are not identified with a cluster. Half of the embedded stellar population identified in the K' images is found in just the 5 richest clusters, and 61% is contained in IRAS sources associated with an embedded OB star. Thus rich clusters around OB stars contribute substantially to the stellar population currently forming in the W3/W4/W5 region. Approximately 39% of the cluster population is embedded in small clouds with an average mass of ~130 Mo that are located...

  2. Filterscope edge plasma diagnostic for the W7-X stellarator

    Science.gov (United States)

    Harris, Jeffrey; Unterberg, Ezekial; Lore, Jeremy; Stephey, Laurie; Schmitz, Oliver; Wurden, Glen; Biedermann, Christoph; Krychowiak, Maciej; Koenig, Ralf

    2015-11-01

    W7-X is a large (R = 5.5m, a = 0.5m, B 10 MW) superconducting stellarator at the Max-Planck Institut für Plasmaphysik in Greifswald, Germany, which will begin plasma operations in the last quarter of 2015. We describe here the first measurements with a 24-channel filterscope diagnostic [E. A. Unterberg et al., Rev. Sci. Instrum. 83, 10D722, (2012)] of edge plasma characteristics and spectral emission from impurities near the test limiters installed for initial plasma experiments. These measurements, together with high resolution IR thermography imaging of the limiter, will be used as inputs for edge transport modeling using the EMC3 code [J. D. Lore et al., Nucl. Fusion 52, 0540 (2012)]. This work is sponsored by DOE Contract No. DE-AC05- 00OR22725 with UT-Battelle.

  3. Simulation of neutron fluxes around the W7-X Stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Andersson, Jenny

    1999-12-01

    A new fusion experiment, the WENDELSTEIN 7-X Stellarator (W7-X), will be undertaken in Greifswald in Germany. Measurements of the neutron flux will provide information on fusion reaction rates and possibly also on ion temperatures as function of time. For this purpose moderating neutron counters will be designed, tested, calibrated and eventually used at W7-X. Extensive Monte-Carlo simulations have been performed in order to select the most suitable detector and moderator combination with a flat response function and highest achievable efficiency. Different detector configurations with different moderating materials have been tried out, showing that a 32 cm thick graphite moderating BF{sub 3} -counter gives the desired flat response and sufficient efficiency. Neutron spectra calculations have been made for different torus models and the influence of floor, walls and ceiling (i.e. reactor hall) have been investigated. Presented results suggest that a more detailed torus model significantly reduces the number of neutron counts at the detector. Calculations including the reactor hall indicate a tendency of shifting the neutron spectra towards the thermal region. The main part of the scattered neutrons are back-scattered from the floor. Finally, calculations on the graphite moderating BF{sub 3} -counter in the detailed torus environment were performed in order to assess the absolute response function under the influence of the reactor hall. The results show that the detector count rate will increase by only 5-7 % when the reactor hall is taken into account. With a stellarator generating 10{sup 12} to 10{sup 16} neutrons per second the detector count rate will be 2x10{sup 5} to 2x10{sup 9} neutrons per second.

  4. Star Formation & Young Stellar Content in the W3 GMC

    CERN Document Server

    Rivera-Ingraham, A; Polychroni, D; Moore, T J T

    2011-01-01

    In this work we have carried out an in-depth analysis of the young stellar content in the W3 GMC. The YSO population was identified and classified in the IRAC/MIPS color-magnitude space according to the `Class' scheme and compared to other classifications based on intrinsic properties. Class 0/I and II candidates were also compared to low/intermediate-mass pre-main-sequence stars selected through their colors and magnitudes in 2MASS. We find that a reliable color/magnitude selection of low-mass PMS stars in the infrared requires prior knowledge of the protostar population, while intermediate mass objects can be more reliably identified. By means of the MST algorithm and our YSO spatial distribution and age maps we investigated the YSO groups and the star formation history in W3. We find signatures of clustered and distributed star formation in both triggered and quiescent environments. The central/western parts of the GMC are dominated by large scale turbulence likely powered by isolated bursts of star format...

  5. The massive stellar population of W49: A spectroscopic survey

    Science.gov (United States)

    Wu, Shi-Wei; Bik, Arjan; Bestenlehner, Joachim M.; Henning, Thomas; Pasquali, Anna; Brandner, Wolfgang; Stolte, Andrea

    2016-05-01

    Context. Massive stars form on different scales that range from large, dispersed OB associations to compact, dense starburst clusters. The complex structure of regions of massive star formation and the involved short timescales provide a challenge for our understanding of their birth and early evolution. As one of the most massive and luminous star-forming region in our Galaxy, W49 is the ideal place to study the formation of the most massive stars. Aims: By classifying the massive young stars that are deeply embedded in the molecular cloud of W49, we aim to investigate and trace the star formation history of this region. Methods: We analyse near-infrared K-band spectroscopic observations of W49 from LBT/LUCI combined with JHK images obtained with NTT/SOFI and LBT/LUCI. Based on JHK-band photometry and K-band spectroscopy, the massive stars are placed in a Hertzsprung Russell diagram. By comparison with evolutionary models, their age and hence the star formation history of W49 can be investigated. Results: Fourteen O-type stars, as well as two young stellar objects (YSOs), are identified by our spectroscopic survey. Eleven O stars are main sequence stars with subtypes ranging from O3 to O9.5 and masses ranging from ~20 M⊙ to ~120 M⊙. Three of the O stars show strong wind features and are considered to be Of-type supergiants with masses beyond 100 M⊙. The two YSOs show CO emission, which is indicative of the presence of circumstellar disks in the central region of the massive cluster. The age of the cluster is estimated as ~1.5 Myr, with star formation continuing in different parts of the region. The ionising photons from the central massive stars have not yet cleared the molecular cocoon surrounding the cluster. W49 is comparable to extragalactic star-forming regions, and it provides us with a unique chance to study a starburst in detail. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among

  6. Star formation in W3 - AFGL333: Young stellar content, properties and roles of external feedback

    CERN Document Server

    Jose, Jessy; Herczeg, Gregory J; Samal, Manash R; Bieging, John H; Meyer, Michael R; Sherry, William H

    2016-01-01

    One of the key questions in the field of star formation is the role of stellar feedback on subsequent star formation process. The W3 giant molecular cloud complex at the western border of the W4 super bubble is thought to be influenced by the stellar winds of the massive stars in W4. AFGL333 is a ~10^4 Msun cloud within W3. This paper presents a study of the star formation activity within AFGL333 using deep JHKs photometry obtained from the NOAO Extremely Wide-Field Infrared Imager combined with Spitzer-IRAC-MIPS photometry. Based on the infrared excess, we identify 812 candidate young stellar objects in the complex, of which 99 are classified as Class I and 713 are classified as Class II sources. The stellar density analysis of young stellar objects reveals three major stellar aggregates within AFGL333, named here AFGL333-main, AFGL333-NW1 and AFGL333-NW2. The disk fraction within AFGL333 is estimated to be ~50-60%. We use the extinction map made from the H-Ks colors of the background stars to understand the...

  7. Overview video diagnostics for the W7-X stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Kocsis, G., E-mail: kocsis.gabor@wigner.mta.hu [Wigner RCP, RMI, Konkoly Thege 29-33, H-1121 Budapest (Hungary); Baross, T. [Wigner RCP, RMI, Konkoly Thege 29-33, H-1121 Budapest (Hungary); Biedermann, C. [Max-Planck-Institute for Plasma Physics, 17491 Greifswald (Germany); Bodnár, G.; Cseh, G.; Ilkei, T. [Wigner RCP, RMI, Konkoly Thege 29-33, H-1121 Budapest (Hungary); König, R.; Otte, M. [Max-Planck-Institute for Plasma Physics, 17491 Greifswald (Germany); Szabolics, T.; Szepesi, T.; Zoletnik, S. [Wigner RCP, RMI, Konkoly Thege 29-33, H-1121 Budapest (Hungary)

    2015-10-15

    Considering the requirements of the newly built Wendelstein 7-X stellarator a ten-channel overview video diagnostic system was developed and is presently under installation. The system covering the whole torus interior can be used not only to observe the plasma but also to detect irregular operational events which are dangerous for the stellarator itself and to send automatic warning for the machine safety. The ten tangential AEQ ports used by the diagnostic remain under atmospheric pressure, the vacuum/air interface is at the front window located at the plasma side of the AEQ port. The optical vacuum window is protected by a cooled pinhole. The Sensor Module (SM) of the intelligent camera (EDICAM) – developed especially for this purpose – is located directly behind the vacuum window. EDICAM is designed to simultaneously record several regions of interest of its CMOS sensor with different frame rate and to detect various predefined events in real time. The air cooled SM is fixed by a docking mechanism which can preserve the pointing of the view. EDICAM can withstand the magnetic field (∼3 T), the neutron and gamma fluxes expected in the AEQ port. In order to adopt the new features of the video diagnostics system both control and data acquisition and visualization and data processing softwares are developed.

  8. The Massive Stellar Population of W49: A Spectroscopic Survey

    CERN Document Server

    Wu, Shi-Wei; Bestenlehner, Joachim M; Henning, Thomas; Pasquali, Anna; Brandner, Wolfgang; Stolte, Andrea

    2016-01-01

    Massive stars form on different scales ranging from large, dispersed OB associations to compact, dense starburst clusters. The complex structure of regions of massive star formation, and the involved short timescales provide a challenge for our understanding of their birth and early evolution. As one of the most massive and luminous star-forming region in our Galaxy, W49 is the ideal place to study the formation of the most massive stars. By classifying the massive young stars deeply embedded into the molecular cloud of W49, we aim to investigate and trace the star formation history of this region. We analyse near-infrared $K$-band spectroscopic observations of W49 from LBT/LUCI combined with $JHK$ images obtained with NTT/SOFI and LBT/LUCI. Based on $JHK$-band photometry and K-band spectroscopy the massive stars are placed in a Hertzsprung Russell diagram. By comparison with evolutionary models, their age and hence the star formation history of W49 can be investigated. Fourteen O type stars as well as two yo...

  9. Optical design study for divertor observation at the stellarator W7-X

    NARCIS (Netherlands)

    König, R.; Hildebrandt, D.; Hübner, T.; Klinkhamer, J.F.F.; Moddemeijer, K.; Vliegenthart, W.A.

    2006-01-01

    The stellarator W7-X will be capable of running in a quasicontinuous operating mode with 10 MW of electron cyclotron heating (ECRH) heating for 30 min, the duration only being limited by the capacity of the available cooling reservoir. The integrated ten discrete water cooled divertor modules need t

  10. Optical design study for divertor observation at the stellarator W7-X

    NARCIS (Netherlands)

    König, R.; Hildebrandt, D.; Hübner, T.; Klinkhamer, J.F.F.; Moddemeijer, K.; Vliegenthart, W.A.

    2006-01-01

    The stellarator W7-X will be capable of running in a quasicontinuous operating mode with 10 MW of electron cyclotron heating (ECRH) heating for 30 min, the duration only being limited by the capacity of the available cooling reservoir. The integrated ten discrete water cooled divertor modules need

  11. STAR FORMATION AND YOUNG STELLAR CONTENT IN THE W3 GIANT MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Rivera-Ingraham, Alana [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Martin, Peter G. [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Polychroni, Danae [INAF-IFSI, via Fosso del Cavaliere 100, 00133 Roma (Italy); Moore, Toby J. T. [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)

    2011-12-10

    In this work, we have carried out an in-depth analysis of the young stellar content in the W3 giant molecular cloud (GMC). The young stellar object (YSO) population was identified and classified in the Infrared Array Camera/Multiband Imaging Photometer color-magnitude space according to the 'Class' scheme and compared to other classifications based on intrinsic properties. Class 0/I and II candidates were also compared to low-/intermediate-mass pre-main-sequence (PMS) stars selected through their colors and magnitudes in the Two Micron All Sky Survey. We find that a reliable color/magnitude selection of low-mass PMS stars in the infrared requires prior knowledge of the protostar population, while intermediate-mass objects can be more reliably identified. By means of the minimum spanning tree algorithm and our YSO spatial distribution and age maps, we investigated the YSO groups and the star formation history in W3. We find signatures of clustered and distributed star formation in both triggered and quiescent environments. The central/western parts of the GMC are dominated by large-scale turbulence likely powered by isolated bursts of star formation that triggered secondary star formation events. Star formation in the eastern high-density layer (HDL) also shows signs of quiescent and triggered stellar activity, as well as extended periods of star formation. While our findings support triggering as a key factor for inducing and enhancing some of the major star-forming activity in the HDL (e.g., W3 Main/W3(OH)), we argue that some degree of quiescent or spontaneous star formation is required to explain the observed YSO population. Our results also support previous studies claiming a spontaneous origin for the isolated massive star(s) powering KR 140.

  12. Remote-Steering Antennas for 140 GHz Electron Cyclotron Heating of the Stellarator W7-X

    Directory of Open Access Journals (Sweden)

    Lechte C.

    2017-01-01

    Full Text Available For electron cyclotron resonance heating of the stellarator W7-X at IPP Greifswald, a 140 GHz/10 MW cw millimeter wave system has been built. Two out of 12 launchers will employ a remote-steering design. This paper describes the overall design of the two launchers, and design issues like input coupling structures, manufacturing of corrugated waveguides, optimization of the steering range, integration of vacuum windows, mitrebends and vacuum valves into the launchers, as well as low power tests of the finished waveguides.

  13. 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

  14. Deep near-infrared imaging of W3 Main: constraints on stellar cluster formation

    Science.gov (United States)

    Bik, A.; Stolte, A.; Gennaro, M.; Brandner, W.; Gouliermis, D.; Hußmann, B.; Tognelli, E.; Rochau, B.; Henning, Th.; Adamo, A.; Beuther, H.; Pasquali, A.; Wang, Y.

    2014-01-01

    Context. Embedded clusters like W3 Main are complex and dynamically evolving systems that represent an important phase in the star formation process. Aims: We aim to characterize of the entire stellar content of W3 Main in a statistical sense, which will then identify possible differences in the evolutionary phase of the stellar populations and find clues about the formation mechanism of this massive embedded cluster. Methods: Deep JHKs imaging is used to derive the disk fraction, Ks-band luminosity functions, and mass functions for several subregions in W3 Main. A two-dimensional completeness analysis using artificial star experiments is applied as a crucial ingredient for assessing realistic completeness limits for our photometry. Results: We find an overall disk fraction of 7.7 ± 2.3%, radially varying from 9.4 ± 3.0% in the central 1 pc to 5.6 ± 2.2% in the outer parts of W3 Main. The mass functions derived for three subregions are consistent with a Kroupa and Chabrier mass function. The mass function of IRSN3 is complete down to 0.14 M⊙ and shows a break at M ~ 0.5 M⊙. Conclusions: We interpret the higher disk fraction in the center as evidence that the cluster center is younger. We find that the evolutionary sequence observed in the low-mass stellar population is consistent with the observed age spread among the massive stars. An analysis of the mass function variations does not show evidence of mass segregation. W3 Main is currently still actively forming stars, showing that the ionizing feedback of OB stars is confined to small areas (~0.5 pc). The FUV feedback might be influencing large regions of the cluster as suggested by the low overall disk fraction. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in Germany, Italy, and the United States. LBT Corporation partners are LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical

  15. 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.

  16. Star Formation in W3—AFGL 333: Young Stellar Content, Properties, and Roles of External Feedback

    Science.gov (United States)

    Jose, Jessy; Kim, Jinyoung S.; Herczeg, Gregory J.; Samal, Manash R.; Bieging, John H.; Meyer, Michael R.; Sherry, William H.

    2016-05-01

    One of the key questions in the field of star formation is the role of stellar feedback on the subsequent star formation process. The W3 giant molecular cloud complex at the western border of the W4 super bubble is thought to be influenced by the massive stars in W4. This paper presents a study of the star formation activity within AFGL 333, a ˜104 M ⊙ cloud within W3, using deep JHK s photometry obtained from the NOAO Extremely Wide Field Infrared Imager combined with Spitzer IRAC and MIPS photometry. Based on the infrared excess, we identify 812 candidate young stellar objects (YSOs) in the complex, of which 99 are Class I and 713 are Class II sources. The stellar density analysis of YSOs reveals three major stellar aggregates within AFGL 333, namely AFGL 333 Main, AFGL 333 NW1 and AFGL 333 NW2. The disk fraction within AFGL 333 is estimated to be ˜50%-60%. We use the extinction map made from the H-{K}s colors of the background stars and CO data to understand the cloud structure and to estimate the cloud mass. From the stellar and cloud mass associated with AFGL 333, we infer that the region is currently forming stars with an efficiency of ˜4.5% and at a rate of ˜2-3 M ⊙ Myr-1 pc-2. In general, the star formation activity within AFGL 333 is comparable to that of nearby low mass star-forming regions. We do not find any strong evidence to suggest that the stellar feedback from the massive stars of nearby W4 super bubble has affected the global star formation properties of the AFGL 333 region.

  17. Water Masers Outburst in the Massive Stellar Cluster W49A

    Science.gov (United States)

    Kramer, Busaba H.; Menten, Karl M.; Kamiński, Tomasz; Zhang, Bo; Patel, Nimesh A.; Kraus, Alex

    2017-03-01

    We report a multi-wavelength study of a recent major flare (~ 80,000 Jy at V LSR ~ -98.1 km s-1) of the 22-GHz water maser in W49A. In February 2014, we started monthly monitoring with the Effelsberg 100-m radio telescope. In May 2014, we carried out the nearly simultaneous observations of the 22-GHz transition with selected submillimeter water transitions using the IRAM 30-m telescope (at 183 GHz) and the Atacama Pathfinder Experiment (APEX) 12-m telescope (from 321 to 475 GHz). We have also performed interferometric observations using the NRAO Very Long Baseline Array (VLBA) at 22 GHz and the Submillimeter Array (SMA) at 321 and 325 GHz. One remarkable result is the detection of very high velocity emission features in several transitions. Our data also represent its first detection of the 475-GHz water transition in a star-forming region. Studying these multiple masing transitions in conjunction with theoretical modeling of their excitation not only places strong constraints on the physical conditions of the masing gas but also allows us to study their association with the embedded massive stellar cluster in W49A.

  18. Young Stellar Objects in the Massive Star Forming Region: W49

    CERN Document Server

    Saral, Gozde; Willis, Sarah E; Koenig, Xavier P; Gutermuth, Robert A; Saygac, A Talat

    2015-01-01

    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 to locate 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 (2MASS) 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 analysed 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 memb...

  19. Limiter heat loads during the first operation of the W7-X stellarator

    Science.gov (United States)

    Wurden, Glen; Niemann, Holger; Jakubowski, Marcin; Bozhenkov, Sergey; Biedermann, Christoph; Marsen, Stefan; Effenberg, Florian; Stephey, Laurie; Schmitz, Oliver; W7-X Team

    2016-10-01

    During the first operational phase (OP1.1) of the new W7-X stellarator, five poloidal graphite limiters served as the main boundary for the plasma. There was a dedicated set of diagnostics to observe the performance of the temporary poloidal limiters and infer basic transport behavior of the 3-D helical SOL plasma. We describe IR imaging of the limiters, which resulted in observations of 1) heat flux determination as a function of time and space, 2) total energy into the limiters, 3) high-frequency helical patterns of energy bursts onto the limiters, 4) changes in surface emissivity, and 5) detection of UFO's (small-to-large dusts). These measurements were made in 2 magnetic configuration discharges (differing iota), and in ones where the power loads to the limiters were systematically modified by the use of trim coils. Observed power fractions on the limiters ranged from 40% to 20% of the 0.6 to 4 MW ECRH input powers. Acknowledgement: Funded under DOE LANS Contract DE-AC5026NA25396 and DE-SC0014210, and within the EUROfusion Consortium under Euratom Grant 633053.

  20. Age Spread in W3 Main: Large Binocular Telescope/LUCI Near-infrared Spectroscopy of the Massive Stellar Content

    Science.gov (United States)

    Bik, A.; Henning, Th.; Stolte, A.; Brandner, W.; Gouliermis, D. A.; Gennaro, M.; Pasquali, A.; Rochau, B.; Beuther, H.; Ageorges, N.; Seifert, W.; Wang, Y.; Kudryavtseva, N.

    2012-01-01

    We present near-infrared multi-object spectroscopy and JHK s imaging of the massive stellar content of the Galactic star-forming region W3 Main, obtained with LUCI at the Large Binocular Telescope. We confirm 15 OB stars in W3 Main and derive spectral types between O5V and B4V from their absorption line spectra. Three massive young stellar objects are identified by their emission line spectra and near-infrared excess. The color-color diagram of the detected sources allows a detailed investigation of the slope of the near-infrared extinction law toward W3 Main. Analysis of the Hertzsprung-Russell diagram suggests that the Nishiyama extinction law fits the stellar population of W3 Main best (E(J - H)/E(H - K s) = 1.76 and R_{{K_s}} = 1.44). From our spectrophotometric analysis of the massive stars and the nature of their surrounding H II regions, we derive the evolutionary sequence of W3 Main and we find evidence of an age spread of at least 2-3 Myr. While the most massive star (IRS2) is already evolved, indications for high-mass pre-main-sequence evolution are found for another star (IRS N1), deeply embedded in an ultracompact H II (UCH II) region, in line with the different evolutionary phases observed in the corresponding H II regions. We derive a stellar mass of W3 Main of (4 ± 1) × 103 M ⊙ by extrapolating from the number of OB stars using a Kroupa initial mass function and correcting for our spectroscopic incompleteness. We have detected the photospheres of OB stars from the more evolved diffuse H II region to the much younger UCH II regions, suggesting that these stars have finished their formation and cleared away their circumstellar disks very fast. Only in the hyper-compact H II region (IRS5) do the early-type stars seem to be still surrounded by circumstellar material. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in Germany, Italy, and the United States. LBT Corporation

  1. Regrowth of stellar discs in mature galaxies: the two-component nature of NGC 7217 revisited with VIRUS-W

    Science.gov (United States)

    Fabricius, Maximilian H.; Coccato, Lodovico; Bender, Ralf; Drory, Niv; Gössl, Claus.; Landriau, Martin; Saglia, Roberto P.; Thomas, Jens; Williams, Michael J.

    2014-07-01

    Previous studies have reported the existence of two counter-rotating stellar discs in the early-type spiral galaxy NGC 7217. We have obtained high-resolution optical spectroscopic data (R ≈ 9000) with the new fibre-based Integral Field Unit instrument VIRUS-W at the 2.7-m telescope of the McDonald Observatory in Texas. Our analysis confirms the existence of two components. However, we find them to be corotating. The first component is the more luminous (≈77 per cent of the total light), has the higher velocity dispersion (≈170 km s-1) and rotates relatively slowly (projected vmax = 50 km s-1). The lower luminosity second component (≈23 per cent of the total light) has a low velocity dispersion (≈20 km s-1) and rotates quickly (projected vmax = 150 km s-1). The difference in the kinematics of the two stellar components allows us to perform a kinematic decomposition and to measure the strengths of their Mg and Fe Lick indices separately. The rotational velocities and dispersions of the less luminous and faster component are very similar to those of the interstellar gas as measured from the [O III] emission. Morphological evidence of active star formation in this component further suggests that NGC 7217 may be in the process of (re)growing a disc inside a more massive and higher dispersion stellar halo. The kinematically cold and regular structure of the gas disc in combination with the central almost dust-free morphology allows us to compare the dynamical mass inside of the central 500 pc with predictions from a stellar population analysis. We find agreement between the two if a Kroupa stellar initial mass function is assumed.

  2. The O- and B-Type Stellar Population in W3: Beyond the High-Density Layer

    CERN Document Server

    Kiminki, Megan M; Bagley, Micaela B; Sherry, William H; Rieke, George H

    2015-01-01

    We present the first results from our survey of the star-forming complex W3, combining VRI photometry with multiobject spectroscopy to identify and characterize the high-mass stellar population across the region. With 79 new spectral classifications, we bring the total number of spectroscopically-confirmed O- and B-type stars in W3 to 105. We find that the high-mass slope of the mass function in W3 is consistent with a Salpeter IMF, and that the extinction toward the region is best characterized by an Rv of approximately 3.6. B-type stars are found to be more widely dispersed across the W3 giant molecular cloud (GMC) than previously realized: they are not confined to the high-density layer (HDL) created by the expansion of the neighboring W4 HII region into the GMC. This broader B-type population suggests that star formation in W3 began spontaneously up to 8--10 Myr ago, although at a lower level than the more recent star formation episodes in the HDL. In addition, we describe a method of optimizing sky subtr...

  3. THE O- AND B-TYPE STELLAR POPULATION IN W3: BEYOND THE HIGH-DENSITY LAYER

    Energy Technology Data Exchange (ETDEWEB)

    Kiminki, Megan M.; Kim, Jinyoung Serena; Bagley, Micaela B.; Rieke, George H. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Sherry, William H., E-mail: mbagley@email.arizona.edu [National Optical Astronomy Observatories, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)

    2015-11-01

    We present the first results from our survey of the star-forming complex W3, combining VRI photometry with multiobject spectroscopy to identify and characterize the high-mass stellar population across the region. With 79 new spectral classifications, we bring the total number of spectroscopically confirmed O- and B-type stars in W3 to 105. We find that the high-mass slope of the mass function in W3 is consistent with a Salpeter IMF, and that the extinction toward the region is best characterized by an R{sub V} of approximately 3.6. B-type stars are found to be more widely dispersed across the W3 giant molecular cloud (GMC) than previously realized: they are not confined to the high-density layer (HDL) created by the expansion of the neighboring W4 H ii region into the GMC. This broader B-type population suggests that star formation in W3 began spontaneously up to 8–10 Myr ago, although at a lower level than the more recent star formation episodes in the HDL. In addition, we describe a method of optimizing sky subtraction for fiber spectra in regions of strong and spatially variable nebular emission.

  4. A Universal Portable Appliance for Stellarator W7-X Power Supply Controlling

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In the project Wendelstein 7-X (W7-X), the popular fieldbus Profibus has been determined as a uniform connection between the central control system and all the subordinate systems. A universal embedded control system has been developed for W7-X power supply con trolling. Siemens 80C167CR microcontroller is used as the central control unit of the system. With a user-defined printed circuit board (PCB) several control buses, i.e., Profibus, CAN, IEEE 488, RS485 and RS 232 have been connected to the microcontroller. The corresponding hardware interfaces for the control buses have been designed. A graphic liquid crystal display(LCD) and a user-defined keyboard are used as user interface. The control software will be developed with a C-like language, i.e., C166 for the controller.

  5. The circumstellar disk, envelope, and bi-polar outflow of the Massive Young Stellar Object W33A

    CERN Document Server

    Davies, Ben; Hoare, Melvin G; Oudmaijer, Rene D; de Wit, Willem-Jan

    2009-01-01

    The Young Stellar Object (YSO) W33A is one of the best known examples of a massive star still in the process of forming. Here we present Gemini North ALTAIR/NIFS laser-guide star adaptive-optics assisted K-band integral-field spectroscopy of W33A and its inner reflection nebula. In our data we make the first detections of a rotationally-flattened outer envelope and fast bi-polar jet of a massive YSO at near-infrared wavelengths. The predominant spectral features observed are Br-gamma, H_2, and a combination of emission and absorption from CO gas. We perform a 3-D spectro-astrometric analysis of the line emission, the first study of its kind. We find that the object's Br-gamma emission reveals evidence for a fast bi-polar jet on sub-milliarcsecond scales, which is aligned with the larger-scale outflow. The hybrid CO features can be explained as a combination of hot CO emission arising in a disk close to the central star, while cold CO absorption originates in the cooler outer envelope. Kinematic analysis of th...

  6. The Stellar Content of Obscured Galactic Giant HII Regions. VII. W3

    CERN Document Server

    Navarete, F; Damineli, A; Moisés, A P; Blum, R D; Conti, P S

    2011-01-01

    Spectrophotometric distances in the K band have been reported by different authors for a number of obscured Galactic HII regions. Almost 50% of them show large discrepancies compared to the classical method using radial velocities measured in the radio spectral region. In order to provide a crucial test of both methods, we selected a target which does not present particular difficulty for any method and which has been measured by as many techniques as possible. The W3 star forming complex, located in the Perseus arm, offers a splendid opportunity for such a task. We used the NIFS spectrograph on the Frederick C. Gillett Gemini North telescope to classify candidate "naked photosphere" OB stars based on 2MASS photometry. Two of the targets are revealed to be mid O-type main sequence stars leading to a distance of d = 2.20 kpc. This is in excellent agreement with the spectrophotometric distance derived in the optical band (d = 2.18 kpc, Humphreys 1978) and with a measurement of the W3 trigonometric parallax (d =...

  7. Massive young stellar object W42-MME: The discovery of an infrared jet using VLT/NACO near-infrared images

    CERN Document Server

    Dewangan, L K; Luna, A; Ojha, D K

    2015-01-01

    We report on the discovery of an infrared jet from a deeply embedded infrared counterpart of 6.7 GHz methanol maser emission (MME) in W42 (i.e. W42-MME). We also investigate that W42-MME drives a parsec-scale H2 outflow, with detection of bow shock feature at ~0.52 pc to the north. The inner ~0.4 pc part of the H2 outflow has a position angle of ~18 deg and the position angle of ~40 deg is found farther away on either side of outflow from W42-MME. W42-MME is detected at wavelengths longer than 2.2 microns and is a massive young stellar object, with the estimated stellar mass of 19+-4 Msun. We map the inner circumstellar environment of W42-MME using VLT/NACO adaptive optics Ks and L' observations at resolutions ~0.2 arcsec and ~0.1 arcsec, respectively. We discover a collimated jet in the inner 4500 AU using the L' band, which contains prominent Br alpha line emission. The jet is located inside an envelope/cavity (extent ~10640 AU) that is tapered at both ends and is oriented along the north-south direction. S...

  8. WFCAM, Spitzer-IRAC and SCUBA observations of the massive star forming region DR21/W75: II. Stellar content and star formation

    CERN Document Server

    Kumar, M S N; Grave, J M C; Froebrich, B F D

    2006-01-01

    Wide field near-infrared observations and Spitzer Space Telescope IRAC observations of the DR21/W75 star formation regions are presented. The photometric data are used to analyse the extinction, stellar content and clustering in the entire region by using standard methods. A young stellar population is identified all over the observed field, which is found to be distributed in embedded clusters that are surrounded by a distributed halo population extending over a larger projected area. The Spitzer/IRAC data are used to compute a spectral index value, "alpha", for each YSO in the field. We use these data to separate pure photospheres from disk excess sources. We find a small fraction of sources with "alpha" in excess of 2 to 3 (plus a handful with "alpha"~4), which is much higher than the values found in the low mass star forming region IC348 ("alpha" < 2). The sources with high values of "alpha" spatially coincide with the densest regions of the filaments and also with the sites of massive star formation. ...

  9. Re-growth of stellar disks in mature galaxies: The two component nature of NGC 7217 revisited with VIRUS-W

    CERN Document Server

    Fabricius, Maximilian H; Bender, Ralf; Drory, Niv; Goessl, Claus; Landriau, Martin; Saglia, Roberto P; Thomas, Jens; Williams, Michael J

    2014-01-01

    Previous studies have reported the existence of two counter-rotating stellar disks in the early-type spiral galaxy NGC7217. We have obtained high-resolution optical spectroscopic data (R ~ 9000) with the new fiber-based Integral Field Unit instrument VIRUS-W at the 2.7m telescope of the McDonald Observatory in Texas. Our analysis confirms the existence of two components. However, we find them to be co-rotating. The first component is the more luminous (~ 77% of the total light), has the higher velocity dispersion (~ 170 km/s) and rotates relatively slowly (projected $v_{max}$ = 50 km/s). The lower luminosity second component, (~ 23% of the total light), has a low velocity dispersion (~ 20 km/s) and rotates quickly (projected $v_{max}$ = 150 km/s). The difference in the kinematics of the two stellar components allows us to perform a kinematic decomposition and to measure the strengths of their Mg and Fe Lick indices separately. The rotational velocities and dispersions of the less luminous and faster component...

  10. From W7-X to a HELIAS fusion power plant: motivation and options for an intermediate-step burning-plasma stellarator

    Science.gov (United States)

    Warmer, F.; Beidler, C. D.; Dinklage, A.; Wolf, R.; The W7-X Team

    2016-07-01

    As a starting point for a more in-depth discussion of a research strategy leading from Wendelstein 7-X to a HELIAS power plant, the respective steps in physics and engineering are considered from different vantage points. The first approach discusses the direct extrapolation of selected physics and engineering parameters. This is followed by an examination of advancing the understanding of stellarator optimisation. Finally, combining a dimensionless parameter approach with an empirical energy confinement time scaling, the necessary development steps are highlighted. From this analysis it is concluded that an intermediate-step burning-plasma stellarator is the most prudent approach to bridge the gap between W7-X and a HELIAS power plant. Using a systems code approach in combination with transport simulations, a range of possible conceptual designs is analysed. This range is exemplified by two bounding cases, a fast-track, cost-efficient device with low magnetic field and without a blanket and a device similar to a demonstration power plant with blanket and net electricity power production.

  11. Physical properties and evolutionary status of the W-subtype contact binary V502 Oph with a stellar companion

    Science.gov (United States)

    Xiao, Zhou; Shengbang, Qian; Binghe, Huang; Hao, Li; Jia, Zhang

    2016-10-01

    Multi-color (B, V, Rc, Ic) CCD photometric light curves of the contact binary V502 Oph are analyzed using the Wilson-Devinney program. The solutions reveal that V502 Oph is a W-subtype contact (f = 35.3%) binary system. The temperature difference between its two components is 240 K and the more massive star has a lower surface temperature. A cool spot is added in our model to account for the light curves' asymmetry (O'Connell effect) and a third light is detected for the first time in the light curves' modeling. Combining the orbital inclination (i = 76.4°) with the published mass function of V502 Oph, the absolute physical parameters of the two components are determined, which are M1 = 0.46(±0.02) M⊙, M2 = 1.37(±0.02) M⊙, R1 = 0.94(±0.01) R⊙, R2 = 1.51(±0.01) R⊙, L1 = 1.13(±0.02) L⊙, and L2 = 2.49(±0.03) L⊙. The formation and the evolutionary status of V502 Oph are discussed. All photoelectric and CCD times of light minimum about V502 Oph are gathered and its orbital period variations are analyzed. The results show that the orbital period of V502 Oph is decreasing continuously at a rate of dP/dt = -1.69 × 10-7 d yr-1,which corresponds to a conservative mass transfer rate of dM2/dt = -3.01 × 10- 8 M⊙ yr-1. The light-travel time effect is due to the presence of a close-in tertiary component with a period of P3 = 18.7 yr and an amplitute of 0.00402 d. V502 Oph is an ideal target to test the formation and evolution theories of binary and multiple systems in which the light curves, the O - C curve and spectroscopic observations are comprehensively researched.

  12. Physical properties and evolutionary status of the W-subtype contact binary V502 Oph with a stellar companion

    Science.gov (United States)

    Xiao, Zhou; Shengbang, Qian; Binghe, Huang; Hao, Li; Jia, Zhang

    2016-12-01

    Multi-color (B, V, Rc, Ic) CCD photometric light curves of the contact binary V502 Oph are analyzed using the Wilson-Devinney program. The solutions reveal that V502 Oph is a W-subtype contact (f = 35.3%) binary system. The temperature difference between its two components is 240 K and the more massive star has a lower surface temperature. A cool spot is added in our model to account for the light curves' asymmetry (O'Connell effect) and a third light is detected for the first time in the light curves' modeling. Combining the orbital inclination (i = 76.4°) with the published mass function of V502 Oph, the absolute physical parameters of the two components are determined, which are M1 = 0.46(±0.02) M⊙, M2 = 1.37(±0.02) M⊙, R1 = 0.94(±0.01) R⊙, R2 = 1.51(±0.01) R⊙, L1 = 1.13(±0.02) L⊙, and L2 = 2.49(±0.03) L⊙. The formation and the evolutionary status of V502 Oph are discussed. All photoelectric and CCD times of light minimum about V502 Oph are gathered and its orbital period variations are analyzed. The results show that the orbital period of V502 Oph is decreasing continuously at a rate of dP/dt = -1.69 × 10-7 d yr-1,which corresponds to a conservative mass transfer rate of dM2/dt = -3.01 × 10- 8 M⊙ yr-1. The light-travel time effect is due to the presence of a close-in tertiary component with a period of P3 = 18.7 yr and an amplitute of 0.00402 d. V502 Oph is an ideal target to test the formation and evolution theories of binary and multiple systems in which the light curves, the O - C curve and spectroscopic observations are comprehensively researched.

  13. Stellar feedback efficiencies: supernovae versus stellar winds

    CERN Document Server

    Fierlinger, Katharina M; Ntormousi, Evangelia; Fierlinger, Peter; Schartmann, Marc; Ballone, Alessandro; Krause, Martin G H; Diehl, Roland

    2015-01-01

    Stellar winds and supernova (SN) explosions of massive stars ("stellar feedback") create bubbles in the interstellar medium (ISM) and insert newly produced heavy elements and kinetic energy into their surroundings, possibly driving turbulence. Most of this energy is thermalized and immediately removed from the ISM by radiative cooling. The rest is available for driving ISM dynamics. In this work we estimate the amount of feedback energy retained as kinetic energy when the bubble walls have decelerated to the sound speed of the ambient medium. We show that the feedback of the most massive star outweighs the feedback from less massive stars. For a giant molecular cloud (GMC) mass of 1e5 solar masses (as e.g. found in the Orion GMCs) and a star formation efficiency of 8% the initial mass function predicts a most massive star of approximately 60 solar masses. For this stellar evolution model we test the dependence of the retained kinetic energy of the cold GMC gas on the inclusion of stellar winds. In our model w...

  14. Stellar Populations

    NARCIS (Netherlands)

    Peletier, Reynier F.

    2013-01-01

    This is a summary of my lectures during the 2011 Canary Islands Winter School in Puerto de la Cruz. I give an introduction to the field of stellar populations in galaxies, and highlight some new results. Since the title of the Winter School is Secular Evolution in Galaxies I mostly concentrate on ne

  15. 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.

  16. Technical challenges of the WENDELSTEIN 7-X stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Wanner, M.; Erckmann, V.; Feist, J.H.; Sapper, J.; Schauer, F. [Association Euratom-Max-Planck-Institut fuer Plasmaphysik, Garching (Germany)

    1998-12-31

    WENDELSTEIN 7-X (W7-X) is an optimized advanced stellarator and continues the successful stellarator line of the IPP Garching. W7-X will be built at Greifswald and will exploit the inherent capability of the stellarator principle for stationary operation and aims to demonstrate its basic qualification as a power plant. The technical challenges of the major components of W7-X are being described in detail. (author)

  17. 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

  18. Stellar Opacity

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, F J; Iglesias, C A

    1999-11-07

    The monochromatic opacity, {kappa}{sub v}, quantifies the property of a material to remove energy of frequency v from a radiation field. A harmonic average of {kappa}{sub v}, known as the Rosseland mean, {kappa}{sub R}, is frequently used to simplify the calculation of energy transport in stars. The term ''opacity'' is commonly understood to refer to {kappa}{sub R}. Opacity plays an important role in stellar modeling because for most stars radiation is the primary mechanism for transporting energy from the nuclear burning region in the core to the surface. Depending on the mass, convection and electron thermal conduction can also be important modes of stellar energy transport. The efficiency of energy transport is related to the temperature gradient, which is directly proportional to the mean radiative opacity in radiation dominated regions. When the radiative opacity is large, convection can become the more efficient energy transport mechanism. Electron conductive opacity, the resistance of matter to thermal conduction, is inversely proportional to electron thermal conductivity. Thermal conduction becomes the dominant mode of energy transport at high density and low temperature.

  19. W43A: a Maverick Maser Source

    Science.gov (United States)

    Diamond, P. J.; Nyman, L. Å.

    The authors report on some preliminary results from a multi-epoch monitoring project of the OH and H2O masers in the source W43A. Their results suggest that W43A is a very young stellar object which has just entered a strong stellar wind stage.

  20. Fundamental stellar parameters

    CERN Document Server

    Wittkowski, M

    2004-01-01

    I present a discussion of fundamental stellar parameters and their observational determination in the context of interferometric measurements with current and future optical/infrared interferometric facilities. Stellar parameters and the importance of their determination for stellar physics are discussed. One of the primary uses of interferometry in the field of stellar physics is the measurement of the intensity profile across the stellar disk, both as a function of position angle and of wavelength. High-precision fundamental stellar parameters are also derived by characterizations of binary and multiple system using interferometric observations. This topic is discussed in detail elsewhere in these proceedings. Comparison of observed spectrally dispersed center-to-limb intensity variations with models of stellar atmospheres and stellar evolution may result in an improved understanding of key phenomena in stellar astrophysics such as the precise evolutionary effects on the main sequence, the evolution of meta...

  1. Advanced stellarator power plants

    Energy Technology Data Exchange (ETDEWEB)

    Miller, R.L.

    1994-07-01

    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.

  2. Advanced stellarator power plants

    Energy Technology Data Exchange (ETDEWEB)

    Miller, R.L.

    1994-07-01

    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.

  3. Stellarator status, 1989

    Energy Technology Data Exchange (ETDEWEB)

    Lyon, J.F. (Oak Ridge National Lab., TN (USA)); Grieger, G.; Rau, F. (Max-Planck-Institut fuer Plasmaphysik, Garching (Germany, F.R.)); Iiyoshi, A. (National Inst. for Fusion Science, Nagoya (Japan)); Navarro, A.P. (Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, Madrid (Spain)); Kovrizhnykh, L.M. (AN SSSR, Moscow (USSR). Inst. Obshchey Fiziki); Pavlichenko, O.S. (AN Ukrain

    1990-07-01

    The present status of stellarator experiments and recent progress in stellarator research (both experimental and theoretical) are reported by groups in the United States, the USSR, Japan, Australia, and the European Community (the Federal Republic of Germany and Spain). Experiments under construction and studies of large, next-generation stellarators are also described. 73 refs., 11 figs., 4 tabs.

  4. Stellar Astrophysics for the Local Group

    Science.gov (United States)

    Aparicio, A.; Herrero, A.; Sánchez, F.

    2011-06-01

    1. Fundamentals of stellar evolution theory: understanding the HRD C. Chiosi; 2. Observations of the most luminous stars in local group galaxies P. Massey; 3. Quantitative spectroscopy of the brightest blue supergiant stars in galaxies R. P. Kudritzki; 4. Calibration of the extragalactic distance scale B. F. Madore and W. L. Freedman; 5. Dwarf galaxies G. S. Da Costa; 6. Resolved stellar populations of the luminous galaxies in the local group M. Mateo; 7. Chemical evolution of the ISM in nearby galaxies E. D. Skillman; 8. Populations of massive stars and the interstellar medium C. Leitherer.

  5. Double-helix stellarator

    Energy Technology Data Exchange (ETDEWEB)

    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 {approx} 1--1.2. Other advantages include a high enclosed volume, appreciable rotational transform, and a possibility of extreme-high-{beta} 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.

  6. Trends of Stellar Entropy along Stellar Evolution

    CERN Document Server

    de Avellar, Marcio G B; Horvath, Jorge E

    2015-01-01

    This paper is devoted to discuss the difference in the thermodynamic entropy budget {\\it per baryon} in each type of stellar object found in Universe. We track and discuss the actual {\\it decrease} of the stored baryonic thermodynamic entropy from the most primitive molecular cloud up to the final fate of matter in the black holes, passing through evolved states of matter as found in white dwarfs and neutron stars. We then discuss the case of actual stars of different masses throughout their {\\it evolution}, clarifying the role of virial equilibrium condition for the decrease of the entropy and related issues. Finally, we discuss how gravity ultimately drives composition, hence structural changes along the stellar evolution all the way until the ultimate collapse to black holes, which may increase dramatically their entropy because of the gravitational contribution itself.

  7. Stellar ages from asteroseismology

    CERN Document Server

    Lebreton, Yveline

    2008-01-01

    Asteroseismology provides powerful means to probe stellar interiors. The oscillations frequencies are closely related to stellar interior properties via the density and sound speed profiles. Since these are tightly linked with the mass and evolutionary state, we can expect to determine the age and mass of a star from the comparison of its oscillation spectrum with predictions of stellar models. Such a comparison suffers both from the problems we face when modeling a particular star (as the uncertainties on global parameters and chemical composition) and from our misunderstanding of processes at work in stellar interiors (as the transport processes that may lead to core mixing and affect the model ages). For stars where observations have provided precise and numerous oscillation frequencies together with accurate global parameters and additional information (as the radius or the mass if the star is in a binary system, the interferometric radius or the mean density if the star is an exoplanet host), we can also...

  8. Stellar Chromospheric Activity

    Directory of Open Access Journals (Sweden)

    Hall Jeffrey C.

    2008-03-01

    Full Text Available The Sun, stars similar to it, and many rather dissimilar to it, have chromospheres, regions classically viewed as lying above the brilliant photosphere and characterized by a positive temperature gradient and a marked departure from radiative equilibrium. Stellar chromospheres exhibit a wide range of phenomena collectively called activity, stemming largely from the time evolution of their magnetic fields and the mass flux and transfer of radiation through the complex magnetic topology and the increasingly optically thin plasma of the outer stellar atmosphere. In this review, I will (1 outline the development of our understanding of chromospheric structure from 1960 to the present, (2 discuss the major observational programs and theoretical lines of inquiry, (3 review the origin and nature of both solar and stellar chromospheric activity and its relationship to, and effect on, stellar parameters including total energy output, and (4 summarize the outstanding problems today.

  9. Advanced Stellar Compass

    DEFF Research Database (Denmark)

    Madsen, Peter Buch; Jørgensen, John Leif; Thuesen, Gøsta;

    1997-01-01

    This document describes all interface properties for the Advanced Stellar Compass, developed for the German Research Satellite "CHAMP". Basic operations, modes, software protocol, calibration methods and closed loop test strategies are described.......This document describes all interface properties for the Advanced Stellar Compass, developed for the German Research Satellite "CHAMP". Basic operations, modes, software protocol, calibration methods and closed loop test strategies are described....

  10. Connection between dynamically derived IMF normalisation and stellar populations

    CERN Document Server

    McDermid, Richard M

    2015-01-01

    In this contributed talk I present recent results on the connection between stellar population properties and the normalisation of the stellar initial mass function (IMF) measured using stellar dynamics, based on a large sample of 260 early-type galaxies observed as part of the Atlas3D project. This measure of the IMF normalisation is found to vary non-uniformly with age- and metallicity-sensitive absorption line strengths. Applying single stellar population models, there are weak but measurable trends of the IMF with age and abundance ratio. Accounting for the dependence of stellar population parameters on velocity dispersion effectively removes these trends, but subsequently introduces a trend with metallicity, such that `heavy' IMFs favour lower metallicities. The correlations are weaker than those found from previous studies directly detecting low-mass stars, suggesting some degree of tension between the different approaches of measuring the IMF. Resolving these discrepancies will be the focus of future w...

  11. Merging W W and W W + jet with M inlo

    Science.gov (United States)

    Hamilton, Keith; Melia, Tom; Monni, Pier Francesco; Re, Emanuele; Zanderighi, Giulia

    2016-09-01

    We present a simulation program for the production of a pair of W bosons in association with a jet, that can be used in conjunction with general-purpose shower Monte Carlo generators, according to the Powheg method. We have further adapted and implemented the M inlo ' method on top of the NLO calculation underlying our W + W - + jet generator. Thus, the resulting simulation achieves NLO accuracy not only for inclusive distributions in W + W - + jet production but also W + W - production, i.e. when the associated jet is not resolved, without the introduction of any unphysical merging scale. This work represents the first extension of the M inlo ' method, in its original form, to the case of a genuine underlying 2 → 2 process, with non-trivial virtual corrections.

  12. 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

  13. Origins of Stellar Halos

    Science.gov (United States)

    Johnston, Kathryn V.

    2016-08-01

    This contribution reviews ideas about the origins of stellar halos. It includes discussion of the theoretical understanding of and observational evidence for stellar populations formed ``in situ'' (meaning formed in orbits close to their current ones), ``kicked-out'' (meaning formed in the inner galaxy in orbits unlike their current ones) and ``accreted'' (meaning formed in a dark matter halo other than the one they currently occupy). At this point there is general agreement that a significant fraction of any stellar halo population is likely ``accreted''. There is modest evidence for the presence of a ``kicked-out'' population around both the Milky Way and M31. Our theoretical understanding of and the observational evidence for an ``in situ'' population are less clear.

  14. Las Campanas Stellar Library

    Science.gov (United States)

    Chilingarian, Igor; Zolotukhin, Ivan; Beletsky, Yuri; Worthey, Guy

    2015-08-01

    Stellar libraries are fundamental tools required to understand stellar populations in star clusters and galaxies as well as properties of individual stars. Comprehensive libraries exist in the optical domain, but the near-infrared (NIR) domain stays a couple of decades behind. Here we present the Las Campanas Stellar Library project aiming at obtaining high signal-to-noise intermediate-resolution (R=8000) NIR spectra (0.83libraries, INDO-US and UVES-POP and followed up about 400 non-variable stars in the NIR in order to get complete optical-NIR coverage. Worth mentioning that our current sample includes about 80 AGB stars and a few dozens of bulge/LMC/SMC stars.

  15. 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.

  16. Sparse field stellar photometry.

    Science.gov (United States)

    Reid, N.

    The past few years have seen substantial developments in the capability of high speed measuring machines in the field of automated stellar photometry. In this review, after describing some of the limitations on photometric precision, empirical results are used to demonstrate the sort of accuracies that are possible with the UK Schmidt plate plus COSMOS/APM images-scan combination. The astronomical results obtained to date from these machines are discussed, and some consideration is given to the future role of measuring machines in stellar astronomy.

  17. Gravitational Lensing & Stellar Dynamics

    CERN Document Server

    Koopmans, L V E

    2005-01-01

    Strong gravitational lensing and stellar dynamics provide two complementary and orthogonal constraints on the density profiles of galaxies. Based on spherically symmetric, scale-free, mass models, it is shown that the combination of both techniques is powerful in breaking the mass-sheet and mass-anisotropy degeneracies. Second, observational results are presented from the Lenses Structure & Dynamics (LSD) Survey and the Sloan Lens ACS (SLACS) Survey collaborations to illustrate this new methodology in constraining the dark and stellar density profiles, and mass structure, of early-type galaxies to redshifts of unity.

  18. Energy confinement scaling from the international stellarator database

    Energy Technology Data Exchange (ETDEWEB)

    Stroth, U. [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany); Murakami, M.; Dory, R.A.; Yamada, H.; Okamura, S.; Sano, F.; Obiki, T.

    1995-09-01

    An international stellarator database on global energy confinement is presented comprising data from the ATF, CHS and Heliotron E heliotron/torsatrons and the W7-A and W7-AS shearless stellarators. Regression expressions for the energy confinement time are given for the individual devices and the combined dataset. A comparison with tokamak L mode confinement is discussed on the basis of various scaling expressions. In order to make this database available to interested colleagues, the structure of the database and the parameter list are explained in detail. More recent confinement results incorporating data from enhanced confinement regimes such as H mode are reported elsewhere. (author).

  19. Gravitational lensing & stellar dynamics

    NARCIS (Netherlands)

    Koopmans, L. V. E.; Mamon, GA; Combes, F; Deffayet, C; Fort, B

    2006-01-01

    Strong gravitational lensing and stellar dynamics provide two complementary and orthogonal constraints on the density profiles of galaxies. Based on spherically symmetric, scale-free, mass models, it is shown that the combination of both techniques is powerful in breaking the mass-sheet and mass-ani

  20. Few period quasisymmetric stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Isaev, M.Y.; Mikhailov, M.I.; Shafranov, V.D.; Subbotin, A.A. [Russian Research Centre `Kurchatov Institute`, Moscow (Russian Federation); Cooper, W.A. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); Medvedev, S.Y. [Keldysh Inst. of Applied Mathematics, Russian Academy of Sciences, Moscow (Russian Federation)

    1997-06-01

    The results of plasma equilibrium and local stability investigations in two and four-period quasisymmetric stellarators are presented. A near-axis approximation is used for 2-period systems and the 3D codes VMEC and TERPSICHORE are used for four-periods devices to optimise the configurations. (author) 4 figs., 8 refs.

  1. Gravitational lensing & stellar dynamics

    NARCIS (Netherlands)

    Koopmans, L. V. E.; Mamon, GA; Combes, F; Deffayet, C; Fort, B

    2006-01-01

    Strong gravitational lensing and stellar dynamics provide two complementary and orthogonal constraints on the density profiles of galaxies. Based on spherically symmetric, scale-free, mass models, it is shown that the combination of both techniques is powerful in breaking the mass-sheet and

  2. Stellar magnetic cycles

    Science.gov (United States)

    Baliunas, S. L.

    2004-05-01

    Is hope for understanding the solar magnetic cycle to be found in stars? Observations of stars with significant sub-surface convective zones -- masses smaller than about 1.5 solar masses on the lower main sequence and many types of cool, post-main-sequence stars -- indicate the presence of surface and atmospheric inhomogeneities analogous to solar magnetic features, making stellar magnetic activity a cosmically widespread phenomenon. Observations have been made primarily in visible wavelengths, and important information has also been derived from the ultraviolet and x-ray spectrum regions. Interannual to interdecadal variability of spectrum indicators of stellar magnetic features is common, and in some cases similar in appearance to the 11-year sunspot cycle. Successful models of the physical processes responsible for stellar magnetic cycles, typically cast as a magnetohydrodynamic dynamo, require advances in understanding not only convection but also the magnetic field's interaction with it. The observed facts that underpin the hope for models will be summarized. Properties of stellar magnetic cycles will be compared and contrasted with those of the sun, including inferences from paleo-environmental reservoirs that contain information on solar century- to millennial-scale magnetic variability. Partial support of this research came from NASA NAG5-7635, NRC COBASE, CRDF 322, MIT-MSG 5710001241, JPL 1236821, AF 49620-02-1-0194, Richard Lounsberry Foundation, Langley-Abbot, Rollins, Scholarly Studies and James Arthur Funds (Smithsonian Institution) and several generous individuals.

  3. 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...

  4. Gravitational lensing & stellar dynamics

    NARCIS (Netherlands)

    Koopmans, L. V. E.; Mamon, GA; Combes, F; Deffayet, C; Fort, B

    2006-01-01

    Strong gravitational lensing and stellar dynamics provide two complementary and orthogonal constraints on the density profiles of galaxies. Based on spherically symmetric, scale-free, mass models, it is shown that the combination of both techniques is powerful in breaking the mass-sheet and mass-ani

  5. The W40 Cloud Complex

    CERN Document Server

    Rodney, Steven A

    2008-01-01

    The W40 complex is a nearby site of recent massive star formation composed of a dense molecular cloud adjacent to an HII region that contains an embedded OB star cluster. The HII region is beginning to blister out and break free from its envelope of molecular gas, but our line of sight to the central stars is largely obscured by intervening dust. Several bright OB stars in W40 - visible at optical, infrared, or cm wavelengths - are providing the ionizing flux that heats the HII region. The known stellar component of W40 is dominated by a small number of partly or fully embedded OB stars which have been studied at various wavelengths, but the lower mass stellar population remains largely unexamined. Despite its modest optical appearance, at 600pc W40 is one of the nearest massive star forming regions, and with a UV flux of about 1/10th of the Orion Nebula Cluster, this neglected region deserves detailed investigation.

  6. Stellar populations in star clusters

    CERN Document Server

    Li, Chengyuan; Deng, Licai

    2016-01-01

    Stellar populations contain the most important information about star clus- ter formation and evolution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar populations (SSPs). However, discoveries of multiple stellar populations in Galactic globular clusters have expanded our view on stellar populations in star clusters. They have simultaneously generated a number of controversies, particularly as to whether young star clusters may have the same origin as old globular clusters. In addition, extensive studies have revealed that the SSP scenario does not seem to hold for some intermediate-age and young star clusters either, thus making the origin of multiple stellar populations in star clusters even more complicated. Stellar population anomalies in numerous star clusters are well-documented, implying that the notion of star clusters as true SSPs faces serious challenges. In this review, we focus on stellar populations in massive clusters with different ...

  7. Microinstabilities in stellarator plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Rafiq, T.; Nasim, M.H.; Persson, M. [Department of Electromagnetics and Euratom/VR Association, Chalmers University of Technology, Goeteborg (Sweden)

    2003-07-01

    Linear stability and localization of ion temperature gradient modes in fully 3-dimensional stellarator plasmas is calculated in the electrostatic limit. A ballooning mode formalism with WKB assumption is applied to reduce the equations into ordinary differential equation along the field lines which are solved numerically for different plasma parameters. The results are correlated with the geometrical effects such as magnetic curvature, local magnetic shear and its integrated value along the field line and the effects of trapped electrons are also investigated. The eigenfunctions of the most unstable modes are found to be localized but the nodes in the amplitude of the eigenfunctions may be large depending upon the location on the magnetic surface. The results are compared and contrasted with calculations in tokamak geometry and the implications on future stellarator design is also discussed. (orig.)

  8. DOLPHOT: Stellar photometry

    Science.gov (United States)

    Dolphin, Andrew

    2016-08-01

    DOLPHOT is a stellar photometry package that was adapted from HSTphot for general use. It supports two modes; the first is a generic PSF-fitting package, which uses analytic PSF models and can be used for any camera. The second mode uses ACS PSFs and calibrations, and is effectively an ACS adaptation of HSTphot. A number of utility programs are also included with the DOLPHOT distribution, including basic image reduction routines.

  9. The DEMO Quasisymmetric Stellarator

    OpenAIRE

    McFadden, Geoffrey B.; Garabedian, Paul R.

    2010-01-01

    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, neo...

  10. Oscillations in stellar superflares

    CERN Document Server

    Balona, L A; Kosovichev, A; Nakariakov, V M; Pugh, C E; Van Doorsselaere, T

    2015-01-01

    Two different mechanisms may act to induce quasi-periodic pulsations (QPP) in whole-disk observations of stellar flares. One mechanism may be magneto-hydromagnetic (MHD) forces and other processes acting on flare loops as seen in the Sun. The other mechanism may be forced local acoustic oscillations due to the high-energy particle impulse generated by the flare (known as `sunquakes' in the Sun). We analyze short-cadence Kepler data of 257 flares in 75 stars to search for QPP in the flare decay branch or post-flare oscillations which may be attributed to either of these two mechanisms. About 18 percent of stellar flares show a distinct bump in the flare decay branch of unknown origin. The bump does not seem to be a highly-damped global oscillation because the periods of the bumps derived from wavelet analysis do not correlate with any stellar parameter. We detected damped oscillations covering several cycles (QPP), in seven flares on five stars. The periods of these oscillations also do not correlate with any ...

  11. Dissipative trapped electron modes in stellarator plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Nasim, M.H.; Rafiq, T.; Persson, M. [Department of Electromagnetics and Euratom/VR Association, Chalmers University of Technology, Gothenburg (Sweden)

    2003-07-01

    The objective of the present paper is to study the dissipative trapped electron modes in different stellarator and tokamak configurations with the purpose to contribute to the understanding of the geometrical effects on these instabilities. A three field periods heliac (H1-NF), a five field period helias (W7-X) and a circular tokamak are selected to study the effect of geometrical properties such as local magnetic shear, normal curvature, geodesic curvature and magnetic field, on the mode localisation. The VMEC code is used to obtain the 3-D equilibria. (orig.)

  12. The solar-stellar connection

    Science.gov (United States)

    Giampapa, Mark S.

    2016-07-01

    A review of some principal results achieved in the area of stellar astrophysics with its origins in solar physics - the Solar-Stellar Connection - is presented from the perspective of an observational astronomer. The historical origins of the Solar-Stellar Connection are discussed followed by a review of key results from observations of stellar cycles analogous to the solar cycle in terms of parameters relevant to dynamo theory. A review of facets of angular momentum evolution and irradiance variations, each of which is determined by emergent, dynamo-generated magnetic fields, is given. Recent considerations of the impacts of stellar magnetic activity on the ambient radiative and energetic particle environment of the habitable zone of exoplanet systems are summarized. Some anticipated directions of the Solar-Stellar Connection in the new era of astronomy as defined by the advent of transformative facilities are presented.

  13. 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...

  14. Stellar structure of magnetars

    Science.gov (United States)

    Dong, JianMin; Zuo, Wei; Gu, JianZhong; Shang, XinLe

    2016-04-01

    Magnetars are strong magnetized neutron stars which could emit quiescent X-ray, repeating burst of soft gamma ray, and even the giant flares. We investigate the effects of magnetic fields on the structure of isolated magnetars. The stellar structure together with the magnetic field configuration can be obtained at the same time within a self-consistent procedure. The magnetar mass and radius are found to be weakly enhanced by the strong magnetic fields. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars.

  15. 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.

  16. Stellar populations in star clusters

    Science.gov (United States)

    Li, Cheng-Yuan; de Grijs, Richard; Deng, Li-Cai

    2016-12-01

    Stellar populations contain the most important information about star cluster formation and evolution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar populations (SSPs). However, discoveries of multiple stellar populations in Galactic globular clusters have expanded our view on stellar populations in star clusters. They have simultaneously generated a number of controversies, particularly as to whether young star clusters may have the same origin as old globular clusters. In addition, extensive studies have revealed that the SSP scenario does not seem to hold for some intermediate-age and young star clusters either, thus making the origin of multiple stellar populations in star clusters even more complicated. Stellar population anomalies in numerous star clusters are well-documented, implying that the notion of star clusters as true SSPs faces serious challenges. In this review, we focus on stellar populations in massive clusters with different ages. We present the history and progress of research in this active field, as well as some of the most recent improvements, including observational results and scenarios that have been proposed to explain the observations. Although our current ability to determine the origin of multiple stellar populations in star clusters is unsatisfactory, we propose a number of promising projects that may contribute to a significantly improved understanding of this subject.

  17. Stellar Dymatics in 30 Doradus

    Directory of Open Access Journals (Sweden)

    Guillermo Bosch

    2001-01-01

    Full Text Available From multislit spectroscopy of 180 stars in the ionising cluster of 30 Doradus, we have obtained reliable stellar radial velocities for 58 stars. With these we calculated the stellar radial velocity dispersion and found it to be 35 km/s. If the cluster is dinamically relaxed the virial mass is ~ 1 × 107 Msolar

  18. 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.

  19. Alaska Athabascan stellar astronomy

    Science.gov (United States)

    Cannon, Christopher M.

    2014-01-01

    Stellar astronomy is a fundamental component of Alaska Athabascan cultures that facilitates time-reckoning, navigation, weather forecasting, and cosmology. Evidence from the linguistic record suggests that a group of stars corresponding to the Big Dipper is the only widely attested constellation across the Northern Athabascan languages. However, instruction from expert Athabascan consultants shows that the correlation of these names with the Big Dipper is only partial. In Alaska Gwich'in, Ahtna, and Upper Tanana languages the Big Dipper is identified as one part of a much larger circumpolar humanoid constellation that spans more than 133 degrees across the sky. The Big Dipper is identified as a tail, while the other remaining asterisms within the humanoid constellation are named using other body part terms. The concept of a whole-sky humanoid constellation provides a single unifying system for mapping the night sky, and the reliance on body-part metaphors renders the system highly mnemonic. By recognizing one part of the constellation the stargazer is immediately able to identify the remaining parts based on an existing mental map of the human body. The circumpolar position of a whole-sky constellation yields a highly functional system that facilitates both navigation and time-reckoning in the subarctic. Northern Athabascan astronomy is not only much richer than previously described; it also provides evidence for a completely novel and previously undocumented way of conceptualizing the sky---one that is unique to the subarctic and uniquely adapted to northern cultures. The concept of a large humanoid constellation may be widespread across the entire subarctic and have great antiquity. In addition, the use of cognate body part terms describing asterisms within humanoid constellations is similarly found in Navajo, suggesting a common ancestor from which Northern and Southern Athabascan stellar naming strategies derived.

  20. The Luminosity and Stellar Mass Functions of Red W1-W2 Galaxies

    CERN Document Server

    O'Connor, Jessica A; Satyapal, Shobita; Secrest, Nathan J

    2016-01-01

    We present a study of nearby galaxies as a function of their [3.4]-[4.6] colour. Galaxies that are red in their [3.4]-[4.6] colour contain heated dust and the reddest systems ([3.4]-[4.6] > 0.5) are classified as AGN by some selection criteria. The sample discussed here includes nearby galaxies selected from the Sloan Digital Sky Survey (SDSS) that are also in the Wide-field Infrared Survey Explorer (WISE) catalogue. We calculate the number density of galaxies, in the form of the luminosity and mass functions, using the V/Vmax method and a Stepwise Maximum Likelihood method that has been modified to account for the additional colour selection. The reddest galaxies which have [3.4]-[4.6] > 0.8 and are sometimes classified as AGN by their colour, make up 0.2% of nearby galaxies. However, the reddest galaxies are a rising fraction of the low mass galaxy population. Identifying the lowest mass (M 0.8) galaxies as AGN is surprising given that none are optical AGN or composites, in contrast with their more massive...

  1. Stellar Snowflake Cluster

    Science.gov (United States)

    2005-01-01

    [figure removed for brevity, see original site] Figure 1 Stellar Snowflake Cluster Combined Image [figure removed for brevity, see original site] Figure 2 Infrared Array CameraFigure 3 Multiband Imaging Photometer Newborn stars, hidden behind thick dust, are revealed in this image of a section of the Christmas Tree cluster from NASA's Spitzer Space Telescope, created in joint effort between Spitzer's infrared array camera and multiband imaging photometer instruments. The newly revealed infant stars appear as pink and red specks toward the center of the combined image (fig. 1). The stars appear to have formed in regularly spaced intervals along linear structures in a configuration that resembles the spokes of a wheel or the pattern of a snowflake. Hence, astronomers have nicknamed this the 'Snowflake' cluster. Star-forming clouds like this one are dynamic and evolving structures. Since the stars trace the straight line pattern of spokes of a wheel, scientists believe that these are newborn stars, or 'protostars.' At a mere 100,000 years old, these infant structures have yet to 'crawl' away from their location of birth. Over time, the natural drifting motions of each star will break this order, and the snowflake design will be no more. While most of the visible-light stars that give the Christmas Tree cluster its name and triangular shape do not shine brightly in Spitzer's infrared eyes, all of the stars forming from this dusty cloud are considered part of the cluster. Like a dusty cosmic finger pointing up to the newborn clusters, Spitzer also illuminates the optically dark and dense Cone nebula, the tip of which can be seen towards the bottom left corner of each image. This combined image shows the presence of organic molecules mixed with dust as wisps of green, which have been illuminated by nearby star formation. The larger yellowish dots neighboring the baby red stars in the Snowflake Cluster are massive stellar infants forming from the same cloud. The blue dots

  2. BOOK REVIEW: Stellarator and Heliotron Devices

    Science.gov (United States)

    Johnson, John L.

    1999-02-01

    Stellarators and tokamaks are the most advanced devices that have been developed for magnetic fusion applications. The two approaches have much in common; tokamaks have received the most attention because their axisymmetry justifies the use of simpler models and provides a more forgiving geometry. However, recent advances in treating more complicated three dimensional systems have made it possible to design stellarators that are not susceptible to disruptions and do not need plasma current control. This has excited interest recently. The two largest new magnetic experiments in the world are the LHD device, which commenced operation in Toki, Japan, in 1998 and W7-X, which should become operational in Greifswald, Germany, in 2004. Other recently commissioned stellarators, including H-1 in Canberra, Australia, TJ-II in Madrid, Spain, and IMS in Madison, Wisconsin, have joined these in rejuvenating the stellarator programme. Thus, it is most appropriate that the author has made the lecture material that he presents to his students in the Graduate School of Energy Science at Kyoto University available to everyone. Stellarator and Heliotron Devices provides an excellent treatment of stellarator theory. It is aimed at graduate students who have a good understanding of classical mechanics and mathematical techniques. It contains good descriptions and derivations of essentially every aspect of fusion theory. The author provides an excellent qualitative introduction to each subject, pointing out the strengths and weaknesses of the models that are being used and describing our present understanding. He judiciously uses simple models which illustrate the similarities and differences between stellarators and tokamaks. To some extent the treatment is uneven, rigorous derivations starting with basic principles being given in some cases and relations and equations taken from the original papers being used as a starting point in others. This technique provides an excellent training

  3. Resolved Near-Infrared Stellar Populations in Nearby Galaxies

    CERN Document Server

    Dalcanton, Julianne J; Melbourne, Jason L; Girardi, Léo; Dolphin, Andy; Rosenfield, Philip A; Boyer, Martha L; de Jong, Roelof S; Gilbert, Karoline; Marigo, Paola; Olsen, Knut; Seth, Anil C; Skillman, Evan

    2011-01-01

    We present near-infrared (NIR) color-magnitude diagrams (CMDs) for the resolved stellar populations within 26 fields of 23 nearby galaxies (<4 Mpc), based on F110W and F160W images from Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). The CMDs sample both old dormant and young star-forming populations. We match key NIR CMD features with their counterparts in optical CMDs, and identify the red core Helium burning (RHeB) sequence as a significant contributor to the NIR flux in stellar populations younger than a few 100 Myrs old, suggesting that star formation can drive surprisingly rapid variations in the NIR mass-to-light ratio. The NIR luminosity of star forming galaxies is therefore not necessarily proportional to the stellar mass. We note that these individual bright RHeB stars may be misidentified as old stellar clusters in low resolution imaging. We also discuss the CMD location of asymptotic giant branch (AGB) stars, and the separation of AGB sub-populations using a combination of optic...

  4. 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.

  5. Asteroseismic stellar activity relations

    CERN Document Server

    Bonanno, A; Karoff, C

    2014-01-01

    In asteroseismology an important diagnostic of the evolutionary status of a star is the small frequency separation which is sensitive to the gradient of the mean molecular weight in the stellar interior. It is thus interesting to discuss the classical age-activity relations in terms of this quantity. Moreover, as the photospheric magnetic field tends to suppress the amplitudes of acoustic oscillations, it is important to quantify the importance of this effect by considering various activity indicators. We propose a new class of age-activity relations that connects the Mt. Wilson $S$ index and the average scatter in the light curve with the small frequency separation and the amplitude of the p-mode oscillations. We used a Bayesian inference to compute the posterior probability of various empirical laws for a sample of 19 solar-like active stars observed by the Kepler telescope. We demonstrate the presence of a clear correlation between the Mt. Wilson $S$ index and the relative age of the stars as indicated by ...

  6. Stellar dynamics and black holes

    Indian Academy of Sciences (India)

    David Merritt

    2011-07-01

    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.

  7. Stellar activity and magnetic shielding

    CERN Document Server

    Grießmeier, J -M; Lammer, H; Grenfell, J L; Stadelmann, A; Motschmann, U; 10.1017/S1743921309992961

    2010-01-01

    Stellar activity has a particularly strong influence on planets at small orbital distances, such as close-in exoplanets. For such planets, we present two extreme cases of stellar variability, namely stellar coronal mass ejections and stellar wind, which both result in the planetary environment being variable on a timescale of billions of years. For both cases, direct interaction of the streaming plasma with the planetary atmosphere would entail servere consequences. In certain cases, however, the planetary atmosphere can be effectively shielded by a strong planetary magnetic field. The efficiency of this shielding is determined by the planetary magnetic dipole moment, which is difficult to constrain by either models or observations. We present different factors which influence the strength of the planetary magnetic dipole moment. Implications are discussed, including nonthermal atmospheric loss, atmospheric biomarkers, and planetary habitability.

  8. The Milky Way's Stellar Disk

    CERN Document Server

    Rix, Hans-Walter

    2013-01-01

    A suite of vast stellar surveys mapping the Milky Way, culminating in the Gaia mission, is revolutionizing the empirical information about the distribution and properties of stars in the Galactic stellar disk. We review and lay out what analysis and modeling machinery needs to be in place to test mechanisms of disk galaxy evolution and to stringently constrain the Galactic gravitational potential, using such Galactic star-by-star measurements. We stress the crucial role of stellar survey selection functions in any such modeling; and we advocate the utility of viewing the Galactic stellar disk as made up from `mono-abundance populations' (MAPs), both for dynamical modeling and for constraining the Milky Way's evolutionary processes. We review recent work on the spatial and kinematical distribution of MAPs, and lay out how further study of MAPs in the Gaia era should lead to a decisively clearer picture of the Milky Way's dark matter distribution and formation history.

  9. 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.

  10. Red supergiants and stellar evolution

    CERN Document Server

    Ekström, Sylvia; Meynet, Georges; Groh, Jose; Granada, Anahí

    2013-01-01

    We review the significant role played by red supergiants (RSGs) in stellar populations, and some challenges and questions they raise for theoretical stellar evolution. We present how metallicity and rotation modify the way stars go to the red part of the Hertzsprung- Russell diagram or come back from it, and how RSGs might keep a trace of their main-sequence evolution. We compare theoretical popu- lation ratios with observed ones.

  11. Advancing the understanding of plasma transport in mid-size stellarators

    Science.gov (United States)

    Hidalgo, Carlos; Talmadge, Joseph; Ramisch, Mirko; TJ-II, the; HXS; TJ-K Teams

    2017-01-01

    The tokamak and the stellarator are the two main candidate concepts for magnetically confining fusion plasmas. The flexibility of the mid-size stellarator devices together with their unique diagnostic capabilities make them ideally suited to study the relation between magnetic topology, electric fields and transport. This paper addresses advances in the understanding of plasma transport in mid-size stellarators with an emphasis on the physics of flows, transport control, impurity and particle transport and fast particles. The results described here emphasize an improved physics understanding of phenomena in stellarators that complements the empirical approach. Experiments in mid-size stellarators support the development of advanced plasma scenarios in Wendelstein 7-X (W7-X) and, in concert with better physics understanding in tokamaks, may ultimately lead to an advance in the prediction of burning plasma behaviour.

  12. Division G Commission 45: Stellar Classification

    Science.gov (United States)

    Gray, Richard; Soubiran, Caroline; Nordström, Birgitta; Burgasser, Adam; Gupta, Ranjan; Hanson, Margaret; Leggett, Sandy K.; Soubiran, Caroline; Singh, Harinder P.; Nordström, Birgitta

    2016-04-01

    Commission 45 is solidly anchored in the beginnings of the IAU. It evolved out of Commission 29, which was one of the original commissions and whose title and emphasis was the Spectral Classification of Stars (Transactions of the IAU, Volume I, 1922). C29 was formed with W.S. Adams (Pasadena) as president. Its first members were Miss Cannon, R.H. Curtiss, A. Fowler, A. de Gramont, M. Hamy, H.F. Newall, J.S. Plaskett, H.N. Russell, all very much part of the history of stellar spectroscopy. In the 1922 Transactions report it was recognized the Harvard System of spectral classification ``has already been adopted by international agreement. . .''

  13. 75 FR 10026 - Proposed Collection; Comment Request for Forms W-2, W-2c, W-2AS, W-2GU, W-2VI, W-3, W-3c, W-3cPR...

    Science.gov (United States)

    2010-03-04

    ... Internal Revenue Service Proposed Collection; Comment Request for Forms W-2, W-2c, W-2AS, W-2GU, W-2VI, W-3, W-3c, W-3cPR, W-3PR, and W-3SS AGENCY: Internal Revenue Service (IRS), Treasury. ACTION: Notice and... comments concerning Forms W-2, W-2c, W-2AS, W-2GU, W-2VI, W-3,......

  14. Compact Stellarator Path to DEMO

    Science.gov (United States)

    Lyon, J. F.

    2007-11-01

    Issues for a DEMO reactor are sustaining an ignited/high-Q plasma in steady state, avoiding disruptions and large variations in power flux to the wall, adequate confinement of thermal plasma and alpha-particles, control of a burning plasma, particle and power handling, etc. Compact stellarators have key advantages -- steady-state high-plasma-density operation without external current drive or disruptions, stability without a close conducting wall or active feedback systems, and low recirculating power -- in addition to moderate plasma aspect ratio, good confinement, and high-beta potential. The ARIES-CS study established that compact stellarators can be competitive with tokamaks as reactors. Many of the issues for a compact stellarator DEMO can be answered using results from large tokamaks, ITER D-T experiments and fusion materials, technology and component development programs, in addition to stellarators in operation, under construction or in development. However, a large next-generation stellarator will be needed to address some physics issues: size scaling and confinement at higher parameters, burning plasma issues, and operation with a strongly radiative divertor. Technology issues include simpler coils, structure, and divertor fabrication, and better cost information.

  15. 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...

  16. Accelerated Fitting of Stellar Spectra

    CERN Document Server

    Ting, Yuan-Sen; Rix, Hans-Walter

    2016-01-01

    Stellar spectra are often modeled and fit 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 parameters separately can introduce unknown systematics and do not produce correct error covariances in the derived labels. In this paper we present a new approach -- CHAT (Convex Hull Adaptive Tessellation) -- 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 datasets demonstrate that CHAT can reduce the number of required synthetic model calculations by...

  17. Seismological challenges for stellar structure

    CERN Document Server

    Christensen-Dalsgaard, J

    2010-01-01

    Helioseismology has provided very detailed information about the solar interior, and extensive data on a large number of stars, although at less detail, are promised by the ongoing and upcoming asteroseismic projects. In the solar case there remain serious challenges in understanding the inferred solar structure, particularly in the light of the revised determinations of the solar surface composition. Also, a secure understanding of the origins of solar rotation as inferred from helioseismology, both in the radiative interior and in the convection zone, is still missing. In the stellar case challenges are certain to appear as the data allow more detailed inferences of the properties of stellar cores. Large remaining uncertainties in modelling concerns the properties of convective cores and other processes that may cause mixing. As a result of developing asteroseismic signatures addressing these and other issues, we can look forward to a highly challenging, and hence exciting, era of stellar astrophysics.

  18. Antimicrobial screening of Mnium stellare

    Directory of Open Access Journals (Sweden)

    Kerem Canli

    2015-06-01

    Full Text Available Many plants contain active substances that are known to be effective in both enhancing the wound healing process and lowering the incidence of wound infections. Previous studies have shown that bryophytes produce a variety of secondary metabolites that present pharmaceutical activities including antimicrobial activity against various pathogenic bacteria and fungi. The aim of this study was to investigate the antimicrobial activity of Mnium stellare against 17 bacterial and 1 fungal strains. Our present study has shown that the ethanol extract of M. stellare has antimicrobial activity against several Gram positive and Gram negative microorganism tested, but its antimicrobial activity is notable especially against B. subtilis, S. typhimirium, S. aureus, S. carnosus, and S. epidermidis. These results are the very first report of the antimicrobial activity of M. stellare.

  19. TEM turbulence optimisation in stellarators

    CERN Document Server

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

    2015-01-01

    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 adressed 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 [C.D. Beidler $\\textit{et al}$ Fusion Technology $\\bf{17}$, 148 (1990)] 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 [D.A. Spong $\\textit{et al}$ Nucl. Fusion $\\bf{41}$, 711 (2001)] code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stella...

  20. Deriving stellar inclination of slow rotators using stellar activity

    CERN Document Server

    Dumusque, X

    2014-01-01

    Stellar inclination is an important parameter for many astrophysical studies. Although different techniques allow us to estimate stellar inclinationt for fast rotators, it becomes much more difficult when stars are rotating slower than $\\sim2$-2.5 \\kms. By using the new activity simulation SOAP 2.0 that can reproduce the photometric and spectroscopic variations induced by stellar activity, we are able to fit observations of solar-type stars and derive their inclination. For HD189733, we estimate the stellar inclination to be $i=84^{+6}_{-20}$ degrees, which implies a star-planet obliquity of $\\psi=4^{+18}_{-4}$ considering previous measurements of the spin-orbit angle. For $\\alpha$ Cen B, we derive an inclination of $i=45^{+9}_{-19}$, which implies that the rotational spin of the star is not aligned with the orbital spin of the $\\alpha$ Cen binary system. In addition, assuming that $\\alpha$ Cen Bb is aligned with its host star, no transit would occur. The inclination of $\\alpha$ Cen B can be measured using 40...

  1. Synthetic stellar mass-to-light ratios for stellar populations

    CERN Document Server

    Maraston, C

    1998-01-01

    Evolutionary synthesis models for stellar populations of various ages and chemical compositions are constructed with the approach described in Maraston (1998), in which the Fuel Consumption Theorem is used to evaluate the energetics of Post Main Sequence stars. We present here the synthetic `stellar' mass-to-light ratios (M*/L) in the U,B,V,R,I,J,H,K photometric bands, as functions of age and chemical composition, for single burst populations. Taking into account the contribution by stellar dead remnants, the computed M*/L ratios can be directly compared to those measured in early-type galaxies. The dependence of M*/L ratios on the IMF slope is also explored. The most interesting result is that the M*/L_B ratio of a 15 Gyr stellar population is found to increase by nearly a factor of three, when the chemical composition rises from [Fe/H] \\sim -0.5 to [Fe/H] \\sim +0.3. This impacts on the interpretation of the tilt of the Fundamental Plane of cluster ellipticals in the B band.

  2. Deriving stellar inclination of slow rotators using stellar activity

    Energy Technology Data Exchange (ETDEWEB)

    Dumusque, X., E-mail: xdumusque@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2014-12-01

    Stellar inclination is an important parameter for many astrophysical studies. Although different techniques allow us to estimate stellar inclination for fast rotators, it becomes much more difficult when stars are rotating slower than ∼2-2.5 km s{sup –1}. By using the new activity simulation SOAP 2.0 which can reproduce the photometric and spectroscopic variations induced by stellar activity, we are able to fit observations of solar-type stars and derive their inclination. For HD 189733, we estimate the stellar inclination to be i=84{sub −20}{sup +6} deg, which implies a star-planet obliquity of ψ=4{sub −4}{sup +18} considering previous measurements of the spin-orbit angle. For α Cen B, we derive an inclination of i=45{sub −19}{sup +9}, which implies that the rotational spin of the star is not aligned with the orbital spin of the α Cen binary system. In addition, assuming that α Cen Bb is aligned with its host star, no transit would occur. The inclination of α Cen B can be measured using 40 radial-velocity measurements, which is remarkable given that the projected rotational velocity of the star is smaller than 1.15 km s{sup –1}.

  3. How Lyman Alpha Emission Depends On Galaxy Stellar Mass

    CERN Document Server

    Oyarzún, Grecco A; González, Valentino; Mateo, Mario; Bailey, John I; Finkelstein, Steven L; Lira, Paulina; Crane, Jeffrey D; Olszewski, Edward W

    2016-01-01

    In this work, we show how the stellar mass (M) of galaxies affects the 3stellar mass bins. We find that, in all bins, the distribution is best represented by an exponential profile of the form dN(M)/dEW= A(M)exp(-EW/W0(M))/W0(M). Through a Bayesian analysis, we confirm that lower M galaxies have higher Ly-alpha EWs. We also find that the fraction A of galaxies featuring emission and the e-folding scale W0 of the distribution anti- correlate with M, recovering expressions of the forms A(M)= -0.26(.13) logM/Msun+3.01(1.2) and W0(M)= -15.6(3.5) logM/Msun +166(34). Th...

  4. Characterizing simulated galaxy stellar mass histories

    CERN Document Server

    Cohn, J D

    2014-01-01

    Galaxy formation simulations can now predict many galaxy properties and their evolution through time. To go beyond studying average stellar mass history properties, we classified ensembles of simulated stellar mass histories, holding fixed their z=0 stellar mass. We applied principal component analysis (PCA) to stellar mass histories from the dark matter plus semi-analytic Millennium simulation and the hydrodynamical OverWhelmingly Large Simulations (OWLS) project, finding that a large fraction of the total scatter around the average stellar mass history for each sample is due to only one PCA fluctuation. This fluctuation differs between some different models sharing the same z=0 stellar mass and between lower (<=3e10 M_o) and higher final stellar mass Millennium samples. We correlated the PCA characterization with several $z=0$ galaxy observables (in principle observable in a survey) and galaxy halo history properties. We also explored separating galaxy stellar mass histories into classes, using the large...

  5. The Supernova - A Stellar Spectacle.

    Science.gov (United States)

    Straka, W. C.

    This booklet is part of an American Astronomical Society curriculum project designed to provide teaching materials to teachers of secondary school chemistry, physics, and earth science. The following topics concerning supernovae are included: the outburst as observed and according to theory, the stellar remnant, the nebular remnant, and a summary…

  6. Mixing in massive stellar mergers

    NARCIS (Netherlands)

    Gaburov, E.; jr. Lombardi, J.C.; Portegies Zwart, S.

    2008-01-01

    The early evolution of dense star clusters is possibly dominated by close interactions between stars, and physical collisions between stars may occur quite frequently. Simulating a stellar collision event can be an intensive numerical task, as detailed calculations of this process require hydrodynam

  7. The Stellar Activity - Rotation Relationship

    CERN Document Server

    Wright, Nicholas J; Mamajek, Eric E; Henry, Gregory W

    2012-01-01

    Using a new catalog of 824 solar and late-type stars with X-ray luminosities and rotation periods we have studied the relationship between rotation and stellar activity. From an unbiased subset of this sample the power law slope of the unsaturated regime, $L_X/L_{bol}\\propto Ro^\\beta$, is fit as $\\beta=-2.70\\pm0.13$. This is inconsistent with the canonical $\\beta=-2$ slope to a confidence of 5$\\sigma$ and argues for an interface-type dynamo. Super-saturation is observed for the fastest rotators in our sample and its parametric dependencies are explored. Significant correlations are found with both the corotation radius and the excess polar updraft, the latter theory being supported by other observations. We also present a new X-ray population synthesis model of the mature stellar component of our Galaxy and use it to reproduce deep observations of a high Galactic latitude field. The model, XStar, can be used to test models of stellar spin-down and dynamo decay, as well as for estimating stellar X-ray contamin...

  8. 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)

  9. Fundamental stellar properties from asteroseismology

    DEFF Research Database (Denmark)

    Silva Aguirre, V.; Casagrande, L.; Miglio, A.

    2013-01-01

    Accurate characterization of stellar populations is of prime importance to correctly understand the formation and evolution process of our Galaxy. The field of asteroseismology has been particularly successful in such an endeavor providing fundamental parameters for large samples of stars in diff...

  10. Mixing in massive stellar mergers

    NARCIS (Netherlands)

    Gaburov, E.; jr. Lombardi, J.C.; Portegies Zwart, S.

    2008-01-01

    The early evolution of dense star clusters is possibly dominated by close interactions between stars, and physical collisions between stars may occur quite frequently. Simulating a stellar collision event can be an intensive numerical task, as detailed calculations of this process require

  11. Numerical methods for stellarator optimization

    Energy Technology Data Exchange (ETDEWEB)

    Morris, R.N.; Hedrick, C.L.; Hirshman, S.P.; Lyon, J.F.; Rome, J.A.

    1989-01-01

    A numerical optimization procedure utilizing an inverse 3-D equilibrium solver, a Mercier stability assessment, a deeply-trapped-particle loss assessment, and a nonlinear optimization package has been used to produce low aspect ratio (A = 4) stellarator designs. These designs combine good stability and improved transport with a compact configuration. 7 refs., 2 figs., 1 tab.

  12. W-O+W-A的GNS算法%GNS Algorithm for W-O+W-A

    Institute of Scientific and Technical Information of China (English)

    牛春平; 任哲平; 韩菊

    2009-01-01

    针对电路板线或和线与(W-O+W-A)共存的互连故障诊断问题,提出了针对W-O+W-A的GNS算法.该算法采用组同时具备W-O和W-A对角独立性移位序列、网络同时具备W-O和W-A对角独立性移位序列和转移网络同时具备W-O和W-A对角独立性移位序列组成W-O+W-A的GNS序列,重点对其故障诊断能力进行了讨论,并进行了算法的性能验证.

  13. The w-Socles of w-Modules%w-模的w-底座

    Institute of Scientific and Technical Information of China (English)

    张俊; 王芳贵

    2013-01-01

    引入了w-模的w-底座的概念,举例说明了w-底座与底座是不同的2个概念.借助w-底座,证明了设M是w-模,M是w-Artin模当且仅当若A是M的非零GV-无挠的商模,则w-soc(Aw)≠0且w-soc(Aw)是有限个w-单模的直和.

  14. 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.

  15. Theory of stellar convection - II. First stellar models

    Science.gov (United States)

    Pasetto, S.; Chiosi, C.; Chiosi, E.; Cropper, M.; Weiss, A.

    2016-07-01

    We present here the first stellar models on the Hertzsprung-Russell diagram, in which convection is treated according to the new scale-free convection theory (SFC theory) by Pasetto et al. The aim is to compare the results of the new theory with those from the classical, calibrated mixing-length (ML) theory to examine differences and similarities. We integrate the equations describing the structure of the atmosphere from the stellar surface down to a few per cent of the stellar mass using both ML theory and SFC theory. The key temperature over pressure gradients, the energy fluxes, and the extension of the convective zones are compared in both theories. The analysis is first made for the Sun and then extended to other stars of different mass and evolutionary stage. The results are adequate: the SFC theory yields convective zones, temperature gradients ∇ and ∇e, and energy fluxes that are very similar to those derived from the `calibrated' MT theory for main-sequence stars. We conclude that the old scale dependent ML theory can now be replaced with a self-consistent scale-free theory able to predict correct results, as it is more physically grounded than the ML theory. Fundamentally, the SFC theory offers a deeper insight of the underlying physics than numerical simulations.

  16. Theory of stellar convection II: first stellar models

    CERN Document Server

    Pasetto, S; Chiosi, E; Cropper, M; Weiss, A

    2015-01-01

    We present here the first stellar models on the Hertzsprung-Russell diagram (HRD), in which convection is treated according to the novel scale-free convection theory (SFC theory) by Pasetto et al. (2014). The aim is to compare the results of the new theory with those from the classical, calibrated mixing-length (ML) theory to examine differences and similarities. We integrate the equations describing the structure of the atmosphere from the stellar surface down to a few percent of the stellar mass using both ML theory and SFC theory. The key temperature over pressure gradients, the energy fluxes, and the extension of the convective zones are compared in both theories. The analysis is first made for the Sun and then extended to other stars of different mass and evolutionary stage. The results are adequate: the SFC theory yields convective zones, temperature gradients of the ambient and of the convective element, and energy fluxes that are very similar to those derived from the "calibrated" MT theory for main s...

  17. New light on the formation and evolution of bars - Trends in the stellar line-strength indices distribution inside the bar region

    NARCIS (Netherlands)

    Perez, I.; Sanchez-Blazquez, P.; Zurita, A.

    2007-01-01

    Aims. Our aim is to study the stellar content of the bar region to constrain its formation and evolution. Methods. Line-strength indices in the bar region of a sample of 6 barred galaxies were employed to derive age and metallicity gradients along the bars using stellar population models. Results. W

  18. W-symmetry

    CERN Document Server

    Bouwknegt, P G

    1995-01-01

    W-symmetry is an extension of conformal symmetry in two dimensions. Since its introduction in 1985, W-symmetry has become one of the central notions in the study of two-dimensional conformal field theory. The mathematical structures that underlie W-symmetry are so-called W-algebras, which are higher-spin extensions of the Virasoro algebra. This book contains a collection of papers on W-symmetry, covering the period from 1985 through 1993. Its main focus is the construction of W-algebras and their representation theory. A recurrent theme is the intimate connection between W-algebras and affine

  19. Electron heat transport in current carrying and currentless thermonuclear plasmas. Tokamaks and stellarators compared

    Energy Technology Data Exchange (ETDEWEB)

    Peters, M.

    1996-01-16

    In the first experiment the plasma current in the RTP tokamak is varied. Here the underlying idea was to check whether at a low plasma current, transport in the tokamak resembles transport in stellarators more than at higher currents. Secondly, experiments have been done to study the relation of the diffusivity {chi} to the temperature and its gradient in both W7-AS and RTP. In this case the underlying idea was to find the explanation for the phenomenon observed in both tokamaks and stellarators that the quality of the confinement degrades when more heating is applied. A possible explanation is that the diffusivity increases with the temperature or its gradient. Whereas in standard tokamak and stellarator experiments the temperature and its gradient are strongly correlated, a special capability of the plasma heating system of W7-AS and RTP can force them to decouple. (orig.).

  20. Stellar populations of ultraluminous infrared galaxies

    CERN Document Server

    Hou, L G; Kong, M Z; Xue-Bing, Wu

    2011-01-01

    Ultraluminous infrared galaxies (ULIRGs) have several types according to dominance of starburst or AGN component. We made stellar population analysis for a sample of 160 ULIRGs to study the evolution of ULIRGs. We found that the dominance of intermediate-age and old stellar populations increases along the sequence of HII-like ULIRGs, Seyfert-HII composite ULIRGs, and Seyfert 2 ULIRGs. Consequently the typical mean stellar age and the stellar mass increase along the sequence. Comparing the gas mass estimated from the CO measurements with the stellar mass estimated from the optical spectra, we found that gas fraction is anti-correlated with the stellar mass. HII-like ULIRGs with small stellar masses do not possess enough gas and the total mass, and therefore have no evolution connections with massive Seyfert 2 ULIRGs. Only massive ULIRGs may follow the evolution sequence toward AGNs, and massive HII-like ULIRGs are probably in an earlier stage of the sequence.

  1. Magnetohydrostatic modelling of stellar coronae

    CERN Document Server

    MacTaggart, David; Neukirch, Thomas; Donati, Jean-Francois

    2015-01-01

    We introduce to the stellar physics community a method of modelling stellar coronae that can be considered to be an extension of the potential field. In this approach, the magnetic field is coupled to the background atmosphere. The model is magnetohydrostatic (MHS) and is a balance between the Lorentz force, the pressure gradient and gravity. Analytical solutions are possible and we consider a particular class of equilibria in this paper. The model contains two free parameters and the effects of these on both the geometry and topology of the coronal magnetic field are investigated. A demonstration of the approach is given using a magnetogram derived from Zeeman-Doppler imaging of the 0.75 M$_{\\odot}$ M-dwarf star GJ 182.

  2. From stellar nebula to planetesimals

    CERN Document Server

    Marboeuf, Ulysse; Alibert, Yann; Cabral, Nahuel; Benz, Willy

    2014-01-01

    Solar and extrasolar comets and extrasolar planets are the subject of numerous studies in order to determine their chemical composition and internal structure. In the case of planetesimals, their compositions are important as they govern in part the composition of future planets. The present works aims at determining the chemical composition of icy planetesimals, believed to be similar to present day comets, formed in stellar systems of solar chemical composition. The main objective of this work is to provide valuable theoretical data on chemical composition for models of planetesimals and comets, and models of planet formation and evolution. We have developed a model that calculates the composition of ices formed during the cooling of the stellar nebula. Coupled with a model of refractory element formation, it allows us to determine the chemical composition and mass ratio of ices to rocks in icy planetesimals throughout in the protoplanetary disc. We provide relationships for ice line positions (for differen...

  3. Mixing in massive stellar mergers

    CERN Document Server

    Gaburov, E; Zwart, S Portegies

    2007-01-01

    The early evolution of dense star clusters is possibly dominated by close interactions between stars, and physical collisions between stars may occur quite frequently. Simulating a stellar collision event can be an intensive numerical task, as detailed calculations of this process require hydrodynamic simulations in three dimensions. We present a computationally inexpensive method in which we approximate the merger process, including shock heating, hydrodynamic mixing and mass loss, with a simple algorithm which is based on conservation laws and a basic qualitative understanding of the hydrodynamics of stellar mergers. The algorithm is based on Archimedes' principle, which dictates the distribution of the fluid in stable equilibrium situation. We calibrate and apply the method to mergers of massive stars, as these are expected to occur in young and dense star clusters. We find that mergers between spectral type B stars ($\\sim$10\\msun) result in substantial mixing, whereas mergers between stars of different sp...

  4. Investigating Exoplanets Within Stellar Clusters

    Science.gov (United States)

    Glaser, Joseph Paul; Reisinger, Tyler; Thornton, Jonathan; McMillan, Stephen L. W.

    2017-01-01

    Recent surveys exploring nearby open clusters have yielded noticeable differences in the planetary population from that seen in the Field. This is surprising, as it is widely accepted that a majority of stars form within clustered environments before dispersing throughout the galaxy. Though dynamical arguments have been used to explain this discrepancy in the past, previous surveys' observational statistics and detection biases can also be used to argue that the open cluster planet population is indistinguishable from the Field.Our group aims to explore the role of stellar close encounters and interplanetary interactions in producing the observed exoplanet populations for both open cluster stars and Field stars. We employ a variety of different computational techniques to investigate these effects, ranging from traditional Monte Carlo scattering experiments to multi-scale n-body simulations. We are interested in: the effects of stellar binaries; Hot Jupiter migrations; long-period ice giants; and the habitability history of terrestrial planets.

  5. Stellar models in Brane Worlds

    CERN Document Server

    Linares, Francisco X; Ureña-Lopez, L Arturo

    2015-01-01

    We consider here a full study of stellar dynamics from the brane-world point of view in the case of constant density and of a polytropic fluid. We start our study cataloguing the minimal requirements to obtain a compact object with a Schwarszchild exterior, highlighting the low and high energy limit, the boundary conditions, and the appropriate behavior of Weyl contributions inside and outside of the star. Under the previous requirements we show an extensive study of stellar behavior, starting with stars of constant density and its extended cases with the presence of nonlocal contributions. Finally, we focus our attention to more realistic stars with a polytropic equation of state, specially in the case of white dwarfs, and study their static configurations numerically. One of the main results is that the inclusion of the Weyl functions from braneworld models allow the existence of more compact configurations than within General Relativity.

  6. 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...

  7. Stellar Populations at the Center of IC 1613

    CERN Document Server

    Cole, A A; Gallagher, J S; Hössel, J G; Mould, J R; Holtzmann, J A; Saha, A; Ballester, G E; Burrows, C J; Clarke, J T; Crisp, D; Griffiths, R E; Grillmair, C J; Hester, J J; Krist, J E; Meadows, V; Scowen, P A; Stapelfeldt, K R; Trauger, J T; Watson, A M; Westphal, J R; Cole, Andrew A.; Tolstoy, Eline; Gallagher, John S.; Hoessel, John G.; Mould, Jeremy R.; Holtzman, Jon A.; Saha, Abhijit; Ballester, Gilda E.; Burrows, Christopher J.; Clarke, John T.; Crisp, David; Griffiths, Richard E.; Grillmair, Carl J.; Hester, Jeff J.; Krist, John E.; Meadows, Vikki; Scowen, Paul A.; Stapelfeldt, Karl R.; Trauger, John T.; Watson, Alan M.; Westphal, James R.

    1999-01-01

    We have observed the center of the Local Group dwarf irregular galaxy IC 1613 with WFPC2 aboard the Hubble Space Telescope in the F439W, F555W, and F814W filters. We find a dominant old stellar population (aged ~7 Gyr), identifiable by the strong red giant branch (RGB) and red clump populations. From the (V-I) color of the RGB, we estimate a mean metallicity of the intermediate-age stellar population [Fe/H] = -1.38 +/- 0.31. We confirm a distance of 715 +/- 40 kpc using the I-magnitude of the RGB tip. The main-sequence luminosity function down to I ~25 provides evidence for a roughly constant SFR of approximately 0.00035 solar masses per year across the WFPC2 field of view (0.22 square kpc) during the past 250-350 Myr. Structure in the blue loop luminosity function implies that the SFR was ~50% higher 400-900 Myr ago than today. The mean heavy element abundance of these young stars is 1/10th solar. The best explanation for a red spur on the main-sequence at I = 24.7 is the blue horizontal branch component of ...

  8. Gravitational waves from stellar encounters

    CERN Document Server

    Capozziello, Salvatore

    2008-01-01

    The emission of gravitational waves from a system of massive objects interacting on elliptical, hyperbolic and parabolic orbits is studied in the quadrupole approximation. Analytical expressions are then derived for the gravitational wave luminosity, the total energy output and gravitational radiation amplitude. A crude estimate of the expected number of events towards peculiar targets (i.e. globular clusters) is also given. In particular, the rate of events per year is obtained for the dense stellar cluster at the Galactic Center.

  9. Personage Column: W. -W. Hoepker

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    W.-W. Hoepker was born in July 1942 in Frankfurt/Main, Germany. He studied medicine and philosophy inHamburg and Heidelberg. In Mtinster/Westphalia he wasappointed to a professorship at the Institute of Pathologyin Heidelberg; Since 1987 he has been the Head of theInstitute of Pathology at Barmbek General Hospital, Ham-burg.

  10. Stellar Populations of Shell Galaxies

    CERN Document Server

    Carlsten, S; Zenteno, A

    2016-01-01

    We present a study of the inner (out to $\\sim$1 R$_{\\mathrm{eff}}$) stellar populations of 9 shell galaxies. We derive stellar population parameters from long slit spectra by both analyzing the Lick indices of the galaxies and by fitting Single Stellar Population model spectra to the full galaxy spectra. The results from the two methods agree reasonably well. Many of the shell galaxies in our sample appear to have lower central $\\mathrm{Mg}_{2}$ index values than non-shell galaxies of the same central velocity dispersion, which is likely due to a past interaction event. Our shell galaxy sample shows a relation between central metallicity and velocity dispersion that is consistent with previous samples of non-shell galaxies. Analyzing the metallicity gradients in our sample, we find an average metallicity gradient of -0.16$\\pm$0.10 dex per decade in radius. We compare this with formation models to constrain the merging history of shell galaxies. We argue that our galaxies likely have undergone major mergers in...

  11. Stellar Properties of Embedded Protostars

    CERN Document Server

    White, R J; Doppmann, G W; Covey, Kevin R; Hillenbrand, L A

    2006-01-01

    (Abridged) High dispersion spectrographs on large aperture telescopes have recently allowed observers to study the stellar and accretion properties of deeply embedded young stars, commonly referred to as Class I stars. We summarize these newly determined properties and compare them with observations of more optically revealed Class II (T Tauri) stars. Class I stars have spectral types and stellar luminosities similar to those of Class II stars, suggesting similar masses and ages. Estimates of stellar luminosity and age, however, are especially uncertain given the large extinctions, scattered light emission and continuum excesses typical of Class I stars. Several candidate Class I brown dwarfs are identified. Class I stars appear to rotate more rapidly than T Tauri stars, by roughly a factor of 2. Likewise, Class I disk accretion rates are only a factor of two larger than those of T Tauri stars, less than the mass infall rates predicted by envelope models by 1-2 orders of magnitude. In at least a few cases the...

  12. Stellar Echo Imaging of Exoplanets

    Science.gov (United States)

    Mann, Chris; Lerch, Kieran; Lucente, Mark; Meza-Galvan, Jesus; Mitchell, Dan; Ruedin, Josh; Williams, Spencer; Zollars, Byron

    2016-01-01

    All stars exhibit intensity fluctuations over several timescales, from nanoseconds to years. These intensity fluctuations echo off bodies and structures in the star system. We posit that it is possible to take advantage of these echoes to detect, and possibly image, Earth-scale exoplanets. Unlike direct imaging techniques, temporal measurements do not require fringe tracking, maintaining an optically-perfect baseline, or utilizing ultra-contrast coronagraphs. Unlike transit or radial velocity techniques, stellar echo detection is not constrained to any specific orbital inclination. Current results suggest that existing and emerging technology can already enable stellar echo techniques at flare stars, such as Proxima Centauri, including detection, spectroscopic interrogation, and possibly even continent-level imaging of exoplanets in a variety of orbits. Detection of Earth-like planets around Sun-like stars appears to be extremely challenging, but cannot be fully quantified without additional data on micro- and millisecond-scale intensity fluctuations of the Sun. We consider survey missions in the mold of Kepler and place preliminary constraints on the feasibility of producing 3D tomographic maps of other structures in star systems, such as accretion disks. In this report we discuss the theory, limitations, models, and future opportunities for stellar echo imaging.

  13. Embedded Star Clusters in the W51 Giant Molecular Cloud

    CERN Document Server

    Kumar, M S N; Davis, C J

    2004-01-01

    We present sub-arcsecond (0.35"-0.9"), near-infrared J,H,K band photometric observations of six fields along the W51 Giant Molecular Cloud (W51 GMC). Our observations reveal four new, embedded clusters and provide a new high-resolution (0.35") view of the W51IRS2 (G49.5-0.4) region. The cluster associated with G48.9-0.3 is found to be a double cluster enclosed in a nest of near-infrared nebulosity. We construct stellar surface density maps for four major clusters in the W51 GMC. These unveil the underlying hierarchical structure. Color-color and color-magnitude diagrams for each of these clusters show clear differences in the embedded stellar populations and indicate the relative ages of these clusters. In particular, the clusters associated with the HII regions G48.9-0.3 and G49.0-0.3 are found to have a high fraction of YSOs and are therefore considered the youngest of all the near-infrared clusters in the W51 GMC. The estimated masses of the individual clusters, when summed, yield a total stellar mass of ~...

  14. The Color and Stellar Mass Dependence of Small-scale Galaxy Clustering in SDSS-III BOSS

    Science.gov (United States)

    Law-Smith, Jamie; Eisenstein, Daniel J.

    2017-02-01

    We measure the color and stellar mass dependence of clustering in spectroscopic galaxies at 0.6 noise ratio. We find the ratio of the clustering amplitudes of red and blue massive galaxies to be {w}{red}/{w}{blue}=1.92+/- 0.11 in our smallest annulus of 75–125 kpc. At our largest radii (2–4 Mpc), we find {w}{red}/{w}{blue}=1.24+/- 0.05. Red galaxies therefore have denser environments than their blue counterparts at z ∼ 0.625, and this effect increases with decreasing radius. Irrespective of color, we find that w(R) does not obey a simple power-law relation with radius, showing a dip around 1 Mpc. Holding stellar mass fixed, we find a clear differentiation between clustering in red and blue galaxies, showing that clustering is not solely determined by stellar mass. Holding color fixed, we find that clustering increases with stellar mass, especially for red galaxies at small scales (more than a factor of 2 effect over 0.75 dex in stellar mass).

  15. The wind of W Hya as seen by Herschel. II. The molecular envelope of W Hya

    CERN Document Server

    Khouri, T; Decin, L; Waters, L B F M; Maercker, M; Lombaert, R; Alcolea, J; Blommaert, J A D L; Bujarrabal, V; Groenewegen, M A T; Justtanont, K; Kerschbaum, F; Matsuura, M; Menten, K M; Olofsson, H; Planesas, P; Royer, P; Schmidt, M R; Szczerba, R; Teyssier, D; Yates, J

    2014-01-01

    The evolution of low- and intermediate-mass stars on the asymptotic giant branch (AGB) is mainly controlled by the rate at which these stars lose mass in a stellar wind. Understanding the driving mechanism and strength of the stellar winds of AGB stars and the processes enriching their surfaces with products of nucleosynthesis are paramount to constraining AGB evolution and predicting the chemical evolution of galaxies. In a previous paper we have constrained the structure of the outflowing envelope of W Hya using spectral lines of the $^{12}$CO molecule. Here we broaden this study by modelling an extensive set of H$_{2}$O and $^{28}$SiO lines observed by the three instruments on board Herschel using a state-of-the-art molecular excitation and radiative transfer code. The oxygen isotopic ratios and the $^{28}$SiO abundance profile can be connected to the initial stellar mass and to crucial aspects of dust formation at the base of the stellar wind, respectively. The modelling of H$_{2}$O and $^{28}$SiO confirm...

  16. Photometric study of eclipsing binaries in the Large Magellanic Cloud - I. W UMa type binaries in the Large Magellanic Cloud

    Institute of Scientific and Technical Information of China (English)

    Devarapalli Shanti Priya; Kandulapati Sriram; Pasagada Vivekananda Rao

    2011-01-01

    Eclipsing binaries are among the most important sources of information on stellar parameters like radii, masses, luminosities, etc. We present the analysis of six W UMa systems discovered in the Large Magellanic Cloud using the WilsonDevinney method.

  17. $W^+ W^-$ + Jet: Compact Analytic Results

    Energy Technology Data Exchange (ETDEWEB)

    Campbell, John [Fermilab; Miller, David [Glasgow U.; Robens, Tania [Dresden, Tech. U.

    2016-01-14

    In the second run of the LHC, which started in April 2015, an accurate understanding of Standard Model processes is more crucial than ever. Processes including electroweak gauge bosons serve as standard candles for SM measurements, and equally constitute important background for BSM searches. We here present the NLO QCD virtual contributions to W+W- + jet in an analytic format obtained through unitarity methods and show results for the full process using an implementation into the Monte Carlo event generator MCFM. Phenomenologically, we investigate total as well as differential cross sections for the LHC with 14 TeV center-of-mass energy, as well as a future 100 TeV proton-proton machine. In the format presented here, the one-loop virtual contributions also serve as important ingredients in the calculation of W+W- pair production at NNLO.

  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. On plasma radiative properties in stellar conditions

    CERN Document Server

    Turck-Chièze, S; Gilles, D; Loisel, G; Piau, L; 10.1016/j.hedp.2009.06.007

    2012-01-01

    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 inte...

  20. Properties of stellar activity cycles

    CERN Document Server

    Korhonen, Heidi

    2015-01-01

    The current photometric datasets, that span decades, allow for studying long-term cycles on active stars. Complementary Ca H&K observations give information also on the cycles of normal solar-like stars, which have significantly smaller, and less easily detectable, spots. In the recent years, high precision space-based observations, for example from the Kepler satellite, have allowed also to study the sunspot-like spot sizes in other stars. Here I review what is known about the properties of the cyclic stellar activity in other stars than our Sun.

  1. Improvements on analytic modelling of stellar spots

    CERN Document Server

    Montalto, M; Oshagh, M; Boisse, I; Bruno, G; Santos, N C

    2014-01-01

    In this work we present the solution of the stellar spot problem using the Kelvin-Stokes theorem. Our result is applicable for any given location and dimension of the spots on the stellar surface. We present explicitely the result up to the second degree in the limb darkening law. This technique can be used to calculate very efficiently mutual photometric effects produced by eclipsing bodies occulting stellar spots and to construct complex spot shapes.

  2. Stellar Tools for High Resolution Population Synthesis

    Science.gov (United States)

    Chávez, M.; Bertone, E.; Rodríguez-Merino, L.; Buzzoni, A.

    2005-12-01

    We present preliminary results of the application of a new stellar library of high-resolution synthetic spectra (based upon ATLAS9 and SYNTHE codes developed by R. L. Kurucz) in the calculation of the ultraviolet-optical spectral energy distribution of simple stellar populations (SSPs). For this purpose, the library has been coupled with Buzzoni's population synthesis code. Part of this paper is also devoted to illustrate quantitatively the extent to which synthetic stellar libraries represent real stars.

  3. Artificial Neural Networks in Stellar Astronomy

    Directory of Open Access Journals (Sweden)

    R. K. Gulati

    2001-01-01

    Full Text Available Next generation of optical spectroscopic surveys, such as the Sloan Digital Sky Survey and the 2 degree field survey, will provide large stellar databases. New tools will be required to extract useful information from these. We show the applications of artificial neural networks to stellar databases. In another application of this method, we predict spectral and luminosity classes from the catalog of spectral indices. We assess the importance of such methods for stellar populations studies.

  4. Energetics of nearby stellar bow shocks

    CERN Document Server

    Benaglia, Paula

    2012-01-01

    The latest survey of stellar bow shocks (Peri et al. 2012) lists 28 candidates detected at IR wavelengths, associated with massive, early-type stars up to 3 kpc, along with the geometrical parameters of the structures found. I present here some considerations on the energetics involved, after the estimation of stellar wind power, infrared flux, stellar bolometric luminosity and radio flux limits for each source. The best candidates for relativistic particle acceleration are highlighted.

  5. Singularities around w=-1

    CERN Document Server

    Fernández-Jambrina, L

    2015-01-01

    In this talk we would like to analyse the appearance of singularities in FLRW cosmological models which evolve close to w=-1, where w is the barotropic index of the universe. We relate small terms in cosmological time around w=-1 with the correspondent scale factor of the universe and check for the formation of singularities.

  6. Overview of the PPPL International Experimental Stellarator Collaboration Activity

    Energy Technology Data Exchange (ETDEWEB)

    Gates, David [Princeton University

    2012-03-28

    PPPL has initiated and strengthened collaborative experimental programs aimed at developing the required toolsets and scientific knowledge for advancing stellarators as a viable fusion energy source. In particular, activities at LHD and W7-X, the two large superconducting helical confinement systems in the world, have been expanded. The focus at LHD has been on diagnostic development and data analysis, since the device is a mature research facility with more than 20MW of heating power available. High beta stability experiments, ion and electron temperature measurements using a recently installed imaging x-ray crystal spectrometer, and 3D equilibrium reconstructions will be described. The focus on W7-X has been to develop hardware capabilities for divertor heat flux control, including plasma-facing components, error field correction coils, and power supplies. Progress on these and other activities will be presented.

  7. New Age Indicators for Stellar Populations

    Institute of Scientific and Technical Information of China (English)

    KONG Xu; CHENG Fu-Zhen

    2000-01-01

    We apply the method of principal component analysis to a sample of simple stellar populations to select some age sensitive spectral indices. Besides the well-known age sensitive index Hβ, we also find some new age sensitive indices, G4300 and Fe4383, C24668, and Mgb. In addition, we find that these spectral indices sensitive to age depend on the metallicity of stellar population, Hβ and G4300 are more suitable to determine the age of loy metallicity stellar population, while C24668 and Mgb are more suitable to the high metallicity stellar population.

  8. Disks around young stellar objects

    Indian Academy of Sciences (India)

    H C Bhatt

    2011-07-01

    By 1939, when Chandrasekhar’s classic monograph on the theory of Stellar Structure was published, although the need for recent star formation was fully acknowledged, no one had yet recognized an object that could be called a star in the process of being born. Young stellar objects (YSOs), as pre-main-sequence stars, were discovered in the 1940s and 1950s. Infrared excess emission and intrinsic polarization observed in these objects in the 1960s and 1970s indicated that they are surrounded by flattened disks. The YSO disks were seen in direct imaging only in the 1980s. Since then, high-resolution optical imaging with HST, near-infrared adaptive optics on large groundbased telescopes, mm and radiowave interferometry have been used to image disks around a large number of YSOs revealing disk structure with ever-increasing detail and variety. The disks around YSOs are believed to be the sites of planet formation and a few such associations have now been confirmed. The observed properties of the disk structure and their evolution, that have very important consequences for the theory of star and planet formation, are discussed.

  9. Maximum stellar iron core mass

    Indian Academy of Sciences (India)

    F W Giacobbe

    2003-03-01

    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 different from a more typical Chandrasekhar mass limit approach. This technique produced a maximum stellar iron core mass value of 2.69 × 1030 kg (1.35 solar masses). This mass value is very near to the typical mass values found for neutron stars in a recent survey of actual neutron star masses. Although slightly lower and higher neutron star masses may also be found, lower mass neutron stars are believed to be formed as a result of enhanced iron core compression due to the weight of non-ferrous matter overlying the iron cores within large stars. And, higher mass neutron stars are likely to be formed as a result of fallback or accretion of additional matter after an initial collapse event involving an iron core having a mass no greater than 2.69 × 1030 kg.

  10. GIS w nauce

    OpenAIRE

    Jażdżewska, Iwona; Urbański, Jacek

    2013-01-01

    Artykuł prezentuje podejście świata nauki do roli, jaką odgrywa GIS w jej ramach. Przedstawia dyskusję, jaka miała miejsce w 1993 r. w ramach debaty GIS-L, jej najważniejsze wnioski zaprezentowane w pracy D.J. Wrighta, M.F. Goodchilda i J.D. Proctora (1997), a także przyszłość Systemów Informacji Geograficznej widzianą oczami M. Goodchilda (2010). Na tle tych rozważań autorzy przedstawili własne doś- wiadczenia związane z GIS w polskiej nauce oraz podejście do GIS jako nauki. ...

  11. A Tale of Two Tails: Exploring Stellar Populations in the Tidal Tails of NGC 3256

    CERN Document Server

    Rodruck, Michael; Knierman, Karen; Fedotov, Konstantin; Mullan, Brendan; Gallagher, Sarah; Gallagher, Sarah; Durrell, Patrick; Ciardullo, Robin; Gronwall, Caryl; Charlton, Jane

    2016-01-01

    We have developed an observing program using deep, multiband imaging to probe the chaotic regions of tidal tails in search of an underlying stellar population, using NGC 3256's 400 Myr twin tidal tails as a case study. These tails have different colours of $u - g = 1.05 \\pm 0.07$ and $r - i = 0.13 \\pm 0.07$ for NGC 3256W, and $u - g = 1.26 \\pm 0.07$ and $r - i = 0.26 \\pm 0.07$ for NGC 3256E, indicating different stellar populations. These colours correspond to simple stellar population ages of $288^{+11}_{-54}$ Myr and $841^{+125}_{-157}$ Myr for NGC 3256W and NGC 3256E, respectively, suggesting NGC 3256W's diffuse light is dominated by stars formed after the interaction, while light in NGC 3256E is primarily from stars that originated in the host galaxy. Using a mixed stellar population model, we break our diffuse light into two populations: one at 10 Gyr, representing stars pulled from the host galaxies, and a younger component, whose age is determined by fitting the model to the data. We find similar ages ...

  12. Constructing a small modular stellarator in Latin America

    Science.gov (United States)

    Vargas, V. I.; Mora, J.; Asenjo, J.; Zamora, E.; Otárola, C.; Barillas, L.; Carvajal-Godínez, J.; González-Gómez, J.; Soto-Soto, C.; Piedras, C.

    2015-03-01

    This paper aims at briefly describing the design and construction issues of the stellarator of Costa Rica 1 (SCR-1). The SCR-1 is a small modular stellarator for magnetic confinement of plasma developed by the Plasma Laboratory for Fusion Energy and Applications of the Instituto Tecnológico de Costa Rica (ITCR). SCR-1 will be a 2-field period small modular stellarator with an aspect ratio > 4.4; low shear configuration with core and edge rotational transform equal to 0.32 and 0.28; it will hold plasma in a 6061-T6 aluminum torus shaped vacuum vessel with an minor plasma radius 54.11 mm, a volume of 13.76 liters (0.01 m3), and major radius R = 238 mm. Plasma will be confined in the volume by on axis magnetic field 43.8 mT generated by 12 modular coils with 6 turns each, carrying a current of 767.8 A per turn providing a total toroidal field (TF) current of 4.6 kA-turn per coil. The coils will be supplied by a bank of cell batteries of 120 V. Typical length of the plasma pulse will be between 4 s to 10 s. The SCR-1 plasmas will be heated by ECH second harmonic at 2.45 GHz with a plasma density cut-off value of 7.45 × 1016 m-3. Two magnetrons with a maximum output power of 2 kW and 3 kW will be used.

  13. Rola leptyny w regulacji metabolizmu lipidów i węglowodanów

    Directory of Open Access Journals (Sweden)

    Patrycja Gogga*

    2011-01-01

    Full Text Available Leptyna jest białkiem wydzielanym głównie przez tkankę tłuszczową, a jej stężenie we krwi jest ściśle związane z ilością zapasów energetycznych zgromadzonych w adipocytach. Jako hormon leptyna ma niezwykle szeroki zakres działania. Białko to bezpośrednio lub za pośrednictwem układu współczulnego bierze udział w regulacji metabolizmu energetycznego. Leptyna hamuje biosyntezę triacylogliceroli w wątrobie i tkance tłuszczowej, a także w mięśniach szkieletowych, obniżając tym samym ilość odkładanych w nich lipidów. W adipocytach leptyna zmniejsza ekspresję genów kodujących syntazę kwasów tłuszczowych (FAS i karboksylazę acetylo-CoA (ACC – główne enzymy szlaku biosyntezy kwasów tłuszczowych. Zwiększa z kolei ekspresję genu kodującego lipazę zależną od hormonów (HSL, co stymuluje hydrolizę triacylogliceroli w tkance tłuszczowej. Ponadto leptyna wzmaga utlenianie kwasów tłuszczowych w adipocytach, mięśniach szkieletowych oraz w mięśniu sercowym, wywołując wzrost ekspresji genów kodujących podstawowe dla tego procesu enzymy, palmitoilotransferazę karnitynową 1 (CPT1 i dehydrogenazę acylo-CoA o średniej długości łańcucha (MCAD. Wykazano również, że hormon ten zwiększa wrażliwość tkanek na insulinę i poprawia tolerancję glukozy – pod wpływem leptyny wzrasta transport glukozy do komórek oraz intensywność glikolizy.Wiadomo, że leptyna bierze udział w długoterminowej regulacji pobierania pokarmu, jednak coraz więcej badań wskazuje, że ma ona również wpływ na przemiany substratów energetycznych w tkankach obwodowych. Leptyna może zatem kontrolować homeostaz�� energetyczną organizmu wywołując zmiany metabolizmu lipidów i węglowodanów, przede wszystkim w tkance tłuszczowej i w mięśniach.

  14. The Stellar IMF from turbulent fragmentation

    Science.gov (United States)

    Padoan, P.; Nordlund, A.

    2001-01-01

    In this paper they conclude that turbulent fragmentation is unavoidable in super-sonically turbulent molecular clouds, and given the success of the present model to predict the observed shape of the Stellar IMF, they conclude that turbulent fragmentation is essential to the origin of the stellar IMF.

  15. Stark broadening data for stellar plasma research.

    Science.gov (United States)

    Dimitrijević, M. S.

    Results of an effort to provide to astrophysicists and physicists an as much as possible complete set of Stark broadening parameters needed for stellar opacity calculations, stellar atmosphere modelling, abundance determinations and diagnostics of different plasmas in astrophysics, physics and plasma technology, are presented. Stark broadening has been considered within the semiclassical perturbation, and the modified semiempirical approaches.

  16. 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.

  17. The impact of companions on stellar evolution

    CERN Document Server

    De Marco, Orsola

    2016-01-01

    Stellar astrophysicists are increasingly taking into account the effects of orbiting companions on stellar evolution. New discoveries, many thanks to systematic time-domain surveys, have underlined the role of binary star interactions in a range of astrophysical events, including some that were previously interpreted as due uniquely to single stellar evolution. Here, we review classical binary phenomena such as type Ia supernovae, and discuss new phenomena such as intermediate luminosity transients, gravitational wave-producing double black holes, or the interaction between stars and their planets. Finally, we examine the reassessment of well-known phenomena in light of interpretations that include both single and binary stars, for example supernovae of type Ib and Ic or luminous blue variables. At the same time we contextualise the new discoveries within the framework and nomenclature of the corpus of knowledge on binary stellar evolution. The last decade has heralded an era of revival in stellar astrophysic...

  18. Plumes in stellar convection zones

    CERN Document Server

    Zahn, J P

    1999-01-01

    All numerical simulations of compressible convection reveal the presence of strong downwards directed flows. Thanks to helioseismology, such plumes have now been detected also at the top of the solar convection zone, on super- granular scales. Their properties may be crudely described by adopting Taylor's turbulent entrainment hypothesis, whose validity is well established under various conditions. Using this model, one finds that the strong density stratification does not prevent the plumes from traversing the whole convection zone, and that they carry upwards a net energy flux (Rieutord & Zahn 1995). They penetrate to some extent in the adjacent stable region, where they establish a nearly adiabatic stratification. These plumes have a strong impact on the dynamics of stellar convection zones, and they play probably a key role in the dynamo mechanism.

  19. Multiplicity in Early Stellar Evolution

    CERN Document Server

    Reipurth, Bo; Boss, Alan P; Goodwin, Simon P; Rodriguez, Luis Felipe; Stassun, Keivan G; Tokovinin, Andrei; Zinnecker, Hans

    2014-01-01

    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 mm 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 influenc...

  20. Collisionless Relaxation of Stellar Systems

    Science.gov (United States)

    Kandrup, Henry E.

    1999-08-01

    The objective of the work summarized here has been to exploit and extend ideas from plasma physics and accelerator dynamics to formulate a unified description of collisionless relaxation of stellar systems that views violent relaxation, Landau damping, and phase mixing as (manifestations of) a single phenomenon. This approach embraces the fact that the collisionless Boltzmann equation (CBE), the basic object of the theory, is an infinite-dimensional Hamiltonian system, with the distribution function f playing the role of the fundamental dynamical variable, and that, interpreted appropriately, an evolution described by the CBE is no different fundamentally from an evolution described by any other Hamiltonian system. Equilibrium solutions f0 correspond to extremal points of the Hamiltonian subject to the constraints associated with Liouville's Theorem. Stable equilibria correspond to energy minima. The evolution of a system out of equilibrium involves (in general nonlinear) phase space oscillations which may - or may not - interfere destructively so as to damp away.

  1. Hydrodynamic stability and stellar oscillations

    Indian Academy of Sciences (India)

    H M Antia

    2011-07-01

    Chandrasekhar’s monograph on Hydrodynamic and hydromagnetic stability, published in 1961, is a standard reference on linear stability theory. It gives a detailed account of stability of fluid flow in a variety of circumstances, including convection, stability of Couette flow, Rayleigh–Taylor instability, Kelvin–Helmholtz instability as well as the Jean’s instability for star formation. In most cases he has extended these studies to include effects of rotation and magnetic field. In a later paper he has given a variational formulation for equations of non-radial stellar oscillations. This forms the basis for helioseismic inversion techniques as well as extension to include the effect of rotation, magnetic field and other large-scale flows using a perturbation treatment.

  2. Stellar atmospheres, atmospheric extension and fundamental parameters: weighing stars using the stellar mass index

    CERN Document Server

    Neilson, Hilding R; Norris, Ryan; Kloppenborg, Brian; Lester, John B

    2016-01-01

    One of the great challenges in 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 stel...

  3. Stellar Interferometer Technology Experiment (SITE)

    Science.gov (United States)

    Crawley, Edward F.; Miller, David; Laskin, Robert; Shao, Michael

    1995-02-01

    The MIT Space Engineering Research Center and the Jet Propulsion Laboratory stand ready to advance science sensor technology for discrete-aperture astronomical instruments such as space-based optical interferometers. The objective of the Stellar Interferometer Technology Experiment (SITE) is to demonstrate system-level functionality of a space-based stellar interferometer through the use of enabling and enhancing Controlled-Structures Technologies (CST). SITE mounts to the Mission Peculiar Experiment Support System inside the Shuttle payload bay. Starlight, entering through two apertures, is steered to a combining plate where it is interferred. Interference requires 27 nanometer pathlength (phasing) and 0.29 archsecond wavefront-tilt (pointing) control. The resulting 15 milli-archsecond angular resolution exceeds that of current earth-orbiting telescopes while maintaining low cost by exploiting active optics and structural control technologies. With these technologies, unforeseen and time-varying disturbances can be rejected while relaxing reliance on ground alignment and calibration. SITE will reduce the risk and cost of advanced optical space systems by validating critical technologies in their operational environment. Moreover, these technologies are directly applicable to commercially driven applications such as precision matching, optical scanning, and vibration and noise control systems for the aerospace, medical, and automotive sectors. The SITE team consists of experienced university, government, and industry researchers, scientists, and engineers with extensive expertise in optical interferometry, nano-precision opto-mechanical control and spaceflight experimentation. The experience exists and the technology is mature. SITE will validate these technologies on a functioning interferometer science sensor in order to confirm definitely their readiness to be baselined for future science missions.

  4. Support system for the W7-X coil assembly

    Energy Technology Data Exchange (ETDEWEB)

    Jaksic, N.; Simon-Weidner, J.; Sapper, J. [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany)

    1998-07-01

    The WENDELSTEIN 7-X (W7-X) stellarator experiment is now in the state of its final design. The basic confinement system consists of 50 nonplanar and 20 planar superconducting coils. Meanwhile the geometrical data of the coils have been fixed. The changes with respect to the first design influenced the support concept taking into account needs on enlarged space for the different ports and nozzles. (author)

  5. Impact of galactic and intergalactic dust on the stellar EBL

    Science.gov (United States)

    Vavryčuk, V.

    2016-06-01

    Current theories assume that the low intensity of the stellar extragalactic background light (stellar EBL) is caused by finite age of the Universe because the finite-age factor limits the number of photons that have been pumped into the space by galaxies and thus the sky is dark in the night. We oppose this opinion and show that two main factors are responsible for the extremely low intensity of the observed stellar EBL. The first factor is a low mean surface brightness of galaxies, which causes a low luminosity density in the local Universe. The second factor is light extinction due to absorption by galactic and intergalactic dust. Dust produces a partial opacity of galaxies and of the Universe. The galactic opacity reduces the intensity of light from more distant background galaxies obscured by foreground galaxies. The inclination-averaged values of the effective extinction AV for light passing through a galaxy is about 0.2 mag. This causes that distant background galaxies become apparently faint and do not contribute to the EBL significantly. In addition, light of distant galaxies is dimmed due to absorption by intergalactic dust. Even a minute intergalactic opacity of 1 × 10^{-2} mag per Gpc is high enough to produce significant effects on the EBL. As a consequence, the EBL is comparable with or lower than the mean surface brightness of galaxies. Comparing both extinction effects, the impact of the intergalactic opacity on the EBL is more significant than the obscuration of distant galaxies by partially opaque foreground galaxies by factor of 10 or more. The absorbed starlight heats up the galactic and intergalactic dust and is further re-radiated at IR, FIR and micro-wave spectrum. Assuming static infinite universe with no galactic or intergalactic dust, the stellar EBL should be as high as the surface brightness of stars. However, if dust is considered, the predicted stellar EBL is about 290 nW m^{-2} sr^{-1}, which is only 5 times higher than the observed

  6. N = 2 W Supergravity

    NARCIS (Netherlands)

    Bergshoeff, E.; Roo, M. de

    1993-01-01

    We quantize the classical gauge theory of N = 2 w∞ supergravity and show how the underlying N = 2 super-w∞ algebra gets deformed into an N = 2 super-W∞ algebra. Both algebras contain the N = 2 super-Virasoro algebra as a subalgebra. We discuss how one can extract from these results information

  7. How elevated is the dynamical-to-stellar mass ratio of the ultra-compact dwarf S999?

    CERN Document Server

    Janz, Joachim; Norris, Mark A; Strader, Jay; Penny, Samantha J; Fagioli, Martina; Romanowsky, Aaron J

    2015-01-01

    Here we present new Keck ESI high-resolution spectroscopy and deep archival HST/ACS imaging for S999, an ultra-compact dwarf in the vicinity of M87, which was claimed to have an extremely high dynamical-to-stellar mass ratio. Our data increase the total integration times by a factor of 5 and 60 for spectroscopy and imaging, respectively. This allows us to constrain the stellar population parameters for the first time (simple stellar population equivalent age $=7.6^{+2.0}_{-1.6}$ Gyr; $[Z/\\textrm{H}]=-0.95^{+0.12}_{-0.10}$; $[\\alpha/\\textrm{Fe}]=0.34^{+0.10}_{-0.12}$). Assuming a Kroupa stellar initial mass function, the stellar population parameters and luminosity ($M_{F814W}=-12.13\\pm0.06$ mag) yield a stellar mass of $M_*=3.9^{+0.9}_{-0.6}\\times10^6 M_{\\odot}$, which we also find to be consistent with near-infrared data. Via mass modelling, with our new measurements of velocity dispersion ($\\sigma_{ap}=27\\pm2$ km s$^{-1}$) and size ($R_e=20.9\\pm1.0$ pc), we obtain an elevated dynamical-to-stellar mass ratio...

  8. Magnetic Modulation of Stellar Angular Momentum Loss

    CERN Document Server

    Garraffo, Cecilia; Cohen, Ofer

    2014-01-01

    Angular Momentum Loss is important for understanding astrophysical phenomena such as stellar rotation, magnetic activity, close binaries, and cataclysmic variables. Magnetic breaking is the dominant mechanism in the spin down of young late-type stars. We have studied angular momentum loss as a function of stellar magnetic activity. We argue that the complexity of the field and its latitudinal distribution are crucial for angular momentum loss rates. In this work we discuss how angular momentum is modulated by magnetic cycles, and how stellar spin down is not just a simple function of large scale magnetic field strength.

  9. Flow damping in stellarators close to quasisymmetry

    CERN Document Server

    Calvo, Ivan; Velasco, J L; Alonso, J Arturo

    2014-01-01

    Quasisymmetric stellarators are a type of optimized stellarators for which flows are undamped to lowest order in an expansion in the normalized Larmor radius. However, perfect quasisymmetry is impossible. Since large flows may be desirable as a means to reduce turbulent transport, it is important to know when a stellarator can be considered to be sufficiently close to quasisymmetry. The answer to this question depends strongly on the size of the spatial gradients of the deviation from quasisymmetry and on the collisionality regime. Recently, formal criteria for closeness to quasisymmetry have been derived in a variety of situations. In particular, the case of deviations with large gradients was solved in the $1/\

  10. Super-Eddington Stellar Winds Driven by Near-Surface Energy Deposition

    CERN Document Server

    Quataert, Eliot; Kasen, Daniel; Klion, Hannah; Paxton, Bill

    2015-01-01

    We develop analytic and numerical models of the properties of super-Eddington stellar winds, motivated by phases in stellar evolution when super-Eddington energy deposition (via, e.g., unstable fusion, wave heating, or a binary companion) heats a region near the stellar surface. This appears to occur in luminous blue variables (LBVs), Type IIn supernovae progenitors, classical novae, and X-ray bursts. We show that when the wind kinetic power exceeds Eddington, the photons are trapped and behave like a fluid. Convection does not play a significant role in the wind energy transport. The wind properties depend on the ratio of a characteristic speed in the problem vc ~ (Edot G)^{1/5} (where Edot is the heating rate) to the stellar escape speed near the heating region vesc(r_h). For vc > vesc(r_h) the wind kinetic power at large radii Edot_w ~ Edot. For vc < vesc(r_h), most of the energy is used to unbind the wind material and thus Edot_w < Edot. Multidimensional hydrodynamic simulations without radiation di...

  11. Stellarator Microinstability and Turbulence Simulations Using Gyrofluid (GryfX) and Gyrokinetic (GS2) Codes

    Science.gov (United States)

    Martin, Mike; Landreman, Matt; Mandell, Noah; Dorland, William

    2016-10-01

    GryfX is a delta-f code that evolves the gyrofluid set of equations using sophisticated nonlinear closures, with the option to evolve zonal flows (ky =0) kinetically. Since fluid models require less memory to store than a kinetic model, GryfX is ideally suited and thus written to run on a Graphics Processing Unit (GPU), yielding about a 1,200 times performance advantage over GS2. Here we present the first stellarator simulations using GryfX. Results compare linear growth rates of the Ion Temperature Gradient (ITG) mode between GryfX and the gyrokinetic code, GS2, using stellarator geometries from the National Compact Stellarator Experiment (NCSX) and Wendelstein 7-X (W7X). Strong agreement of <10% for maximum growth rates is observed between GS2 and GryfX for temperature gradients away from marginal stability for both NCSX and W7X geometries. Nonlinear stellarator results using GS2/GryfX are also presented.

  12. Extension of the SIESTA Equilibrium Code to Non-Stellarator Symmetry

    Science.gov (United States)

    Cianciosa, M. R.; Hirshman, S. P.; Seal, S. K.

    2016-10-01

    Resonant magnetic perturbation (RMP) fields applied for edge localized mode (ELM) mitigation, break the nested flux topology of nominally axisymmetric tokamaks. Understanding the implications of this, requires equilibrium codes that can account for non-nested surface topologies. SIESTA is a 3D equilibrium code that allows for islands and stochastic regions. With the assumption of stellarator symmetry, SIESTA has successfully solved island equilibria in RMP perturbed tokamaks (Hirshman et al. J. Plasma Phys. 2016). However, this assumption of stellarator symmetry limits the application of SIESTA to equilibria with up-down symmetry. Diverted tokamaks and the stellarator symmetry breaking trim coils of W7-X require an extension of SIESTA allowing for up-down asymmetry. We present an initial implementation of SIESTA without stellarator symmetry and study the effects of 3D asymmetry on DIII-D and W7-X plasmas. This work was supported by the U.S. D.O.E. contract DE-AC05-00OR22725.

  13. Recent Advances in Stellarator Optimization

    Science.gov (United States)

    Gates, David; Brown, T.; Breslau, J.; Landreman, M.; Lazerson, S. A.; Mynick, H.; Neilson, G. H.; Pomphrey, N.

    2016-10-01

    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. One criticism that has been levelled at this method of design is the complexity of the resultant field coils. Recently, a new coil optimization code, COILOPT + + , 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. 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. We have also explored possibilities for generating an experimental database that could check whether the reduction in turbulent transport that is predicted by GENE as a function of local shear would be consistent with experiments. To this end, a series of equilibria that can be made in the now latent QUASAR experiment have been identified. This work was supported by U.S. DoE Contract #DE-AC02-09CH11466.

  14. Stellar matter with pseudoscalar condensates

    Energy Technology Data Exchange (ETDEWEB)

    Andrianov, A.A. [Saint-Petersburg State University, St. Petersburg (Russian Federation); Universitat de Barcelona, Departament d' Estructura i Constituents de la Materia and Institut de Ciencies del Cosmos (ICCUB), Barcelona, Catalonia (Spain); Andrianov, V.A.; Kolevatov, S.S. [Saint-Petersburg State University, St. Petersburg (Russian Federation); Espriu, D. [Universitat de Barcelona, Departament d' Estructura i Constituents de la Materia and Institut de Ciencies del Cosmos (ICCUB), Barcelona, Catalonia (Spain)

    2016-03-15

    In this work we consider how the appearance of gradients of pseudoscalar condensates in dense systems may possibly influence the transport properties of photons in such a medium as well as other thermodynamic characteristics. We adopt the hypothesis that in regions where the pseudoscalar density gradient is large the properties of photons and fermions are governed by the usual lagrangian extended with a Chern-Simons interaction for photons and a constant axial field for fermions. We find that these new pieces in the lagrangian produce non-trivial reflection coefficients both for photons and fermions when entering or leaving a region where the pseudoscalar has a non-zero gradient. A varying pseudoscalar density may also lead to instability of some fermion and boson modes and modify some properties of the Fermi sea. We speculate that some of these modifications could influence the cooling rate of stellar matter (for instance in compact stars) and have other observable consequences. While quantitative results may depend on the precise astrophysical details most of the consequences are quite universal and consideration should be given to this possibility. (orig.)

  15. 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.

  16. W. W. "Mo" Cleland: a catalytic life.

    Science.gov (United States)

    Dunaway-Mariano, Debra; Holden, Hazel M; Raushel, Frank M

    2013-12-23

    Professor W. Wallace Cleland, the architect of modern steady-state enzyme kinetics, died on March 6, 2013, from injuries sustained in a fall outside of his home. He will be most remembered for giving the enzyme community Ping-Pong kinetics and the invention of dithiothreitol (DTT). He pioneered the utilization of heavy atom isotope effects for the elucidation of the chemical mechanisms of enzyme-catalyzed reactions. His favorite research journal was Biochemistry, in which he published more than 135 papers beginning in 1964 with the disclosure of DTT.

  17. The Stagnation of Contemporary Stellar Astronomy

    CERN Document Server

    Škoda, Petr

    2011-01-01

    The stellar astronomy has always been considered the fundamental source of knowledge about the basic building blocks of the universe - the stars. It has proved correctness of many physical theories - like e.g. the idea of nuclear fusion in stellar cores, the exchange of mass in interacting binaries or models of stellar evolution towards white dwarfs or neutron stars. Despite its well acknowledged importance it seems to be loosing its interestingness for students, for telescope allocation committees at large observatories, as well as for granting agencies. In the domain of big telescopes it has been gradually overtaken by the extra-galactic research and cosmology, surviving however at smaller observatories and among most advanced amateur astronomers. We try to analyse the main obstacles lowering the efficiency of research in contemporary stellar astronomy. We will shortly tackle several problems induced by paradigmatic changes in handling the extraordinary amount of data provided by current instruments as well...

  18. Diagnostics for the National Compact Stellarator Experiment

    Energy Technology Data Exchange (ETDEWEB)

    B.C. Stratton; D. Johnson; R. Feder; E. Fredrickson; H. Neilson; H. Takahashi; M. Zarnstorf; M. Cole; P. Goranson; E. Lazarus; B. Nelson

    2003-09-16

    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.

  19. CH in stellar atmospheres: an extensive linelist

    CERN Document Server

    Masseron, T; Van Eck, S; Colin, R; Daoutidis, I; Godefroid, M; Coheur, P F; Bernath, P; Jorissen, A; Christlieb, N

    2014-01-01

    The advent of high-resolution spectrographs and detailed stellar atmosphere modelling has strengthened the need for accurate molecular data. Carbon-enhanced metal-poor (CEMP) stars spectra are interesting objects with which to study transitions from the CH molecule. We combine programs for spectral analysis of molecules and stellar-radiative transfer codes to build an extensive CH linelist, including predissociation broadening as well as newly identified levels. We show examples of strong predissociation CH lines in CEMP stars, and we stress the important role played by the CH features in the Bond-Neff feature depressing the spectra of barium stars by as much as 0.2 magnitudes in the $\\lambda=$3000 -- 5500 \\AA\\ range. Because of the extreme thermodynamic conditions prevailing in stellar atmospheres (compared to the laboratory), molecular transitions with high energy levels can be observed. Stellar spectra can thus be used to constrain and improve molecular data.

  20. Stellar rotation effects in polarimetric microlensing

    CERN Document Server

    Sajadian, Sedighe

    2016-01-01

    It is well known that the polarization signal in microlensing events of hot stars is larger than that of main-sequence stars. Most hot stars rapidly rotate around their stellar axes. The stellar rotation makes ellipticity and gravity-darkening effects which break the spherical symmetry of the source shape and the circular symmetry of the source surface brightness respectively. Hence, it causes a net polarization signal for the source star. This polarization signal should be considered in polarimetry microlensing of fast rotating stars. For moderate rotating stars, lensing can magnify or even characterize small polarization signals due to the stellar rotation through polarimetry observations. The gravity-darkening effect due to a rotating source star makes asymmetric perturbations in polarimetry and photometry microlensing curves whose maximum happens when the lens trajectory crosses the projected position of the rotation pole on the sky plane. The stellar ellipticity makes a time shift (i) in the position of ...

  1. Estimating stellar mean density through seismic inversions

    CERN Document Server

    Reese, D R; Goupil, M J; Thompson, M J; Deheuvels, S

    2012-01-01

    Determining the mass of stars is crucial both to improving stellar evolution theory and to characterising exoplanetary systems. Asteroseismology offers a promising way to estimate stellar mean density. When combined with accurate radii determinations, such as is expected from GAIA, this yields accurate stellar masses. The main difficulty is finding the best way to extract the mean density from a set of observed frequencies. We seek to establish a new method for estimating stellar mean density, which combines the simplicity of a scaling law while providing the accuracy of an inversion technique. We provide a framework in which to construct and evaluate kernel-based linear inversions which yield directly the mean density of a star. We then describe three different inversion techniques (SOLA and two scaling laws) and apply them to the sun, several test cases and three stars. The SOLA approach and the scaling law based on the surface correcting technique described by Kjeldsen et al. (2008) yield comparable result...

  2. Bayesian isochrone fitting and stellar ages

    CERN Document Server

    Valls-Gabaud, D

    2016-01-01

    Stellar evolution theory has been extraordinarily successful at explaining the different phases under which stars form, evolve and die. While the strongest constraints have traditionally come from binary stars, the advent of asteroseismology is bringing unique measures in well-characterised stars. For stellar populations in general, however, only photometric measures are usually available, and the comparison with the predictions of stellar evolution theory have mostly been qualitative. For instance, the geometrical shapes of isochrones have been used to infer ages of coeval populations, but without any proper statistical basis. In this chapter we provide a pedagogical review on a Bayesian formalism to make quantitative inferences on the properties of single, binary and small ensembles of stars, including unresolved populations. As an example, we show how stellar evolution theory can be used in a rigorous way as a prior information to measure the ages of stars between the ZAMS and the Helium flash, and their u...

  3. F stars: A challenge to stellar evolution

    CERN Document Server

    Suchkov, A A

    2014-01-01

    Many main-sequence F and early G stars are too luminous for their effective temperature, surface gravity, and chemical composition. These {\\it overluminous stars} have two curious properties. First, their kinematics as a function of age from stellar evolution modeling (isochrone fitting) is very different from that of normal stars. Second, while X-ray luminosity of normal stars declines with age, the X-ray luminosity of overluminous F stars changes in the opposite direction, being on average higher for older stars. These properties imply that, in defiance of standard models of stellar evolution, F stars of a given mass and chemical composition can evolve very differently. Assuming that the models correctly describe normal stars, for overluminous F stars they predict too young age and the X-ray emission evolving in the direction opposite to the actually observed trend. This discrepancy between modeling results and observational data suggests that standard stellar evolution models and models of stellar activity...

  4. Convection in stellar envelopes a changing paradigm

    CERN Document Server

    Spruit, H C

    1996-01-01

    Progress in the theory of stellar convection over the past decade is reviewed. The similarities and differences between convection in stellar envelopes and laboratory convection at high Rayleigh numbers are discussed. Direct numerical simulation of the solar surface layers, with no other input than atomic physics, the equations of hydrodynamics and radiative transfer is now capable of reproducing the observed heat flux, convection velocities, granulation patterns and line profiles with remarkably accuracy. These results show that convection in stellar envelopes is an essentially non-local process, being driven by cooling at the surface. This differs distinctly from the traditional view of stellar convection in terms of local concepts such as cascades of eddies in a mean superadiabatic gradient. The consequences this has for our physical picture of processes in the convective envelope are illustrated with the problems of sunspot heat flux blocking, the eruption of magnetic flux from the base of the convection ...

  5. Chemical element transport in stellar evolution models

    Science.gov (United States)

    Cassisi, Santi

    2017-01-01

    Stellar evolution computations provide the foundation of several methods applied to study the evolutionary properties of stars and stellar populations, both Galactic and extragalactic. The accuracy of the results obtained with these techniques is linked to the accuracy of the stellar models, and in this context the correct treatment of the transport of chemical elements is crucial. Unfortunately, in many respects calculations of the evolution of the chemical abundance profiles in stars are still affected by sometimes sizable uncertainties. Here, we review the various mechanisms of element transport included in the current generation of stellar evolution calculations, how they are implemented, the free parameters and uncertainties involved, the impact on the models and the observational constraints.

  6. The K2-TESS Stellar Properties Catalog

    CERN Document Server

    Stassun, Keivan G; Paegert, Martin; De Lee, Nathan; Sanchis-Ojeda, Roberto

    2014-01-01

    We introduce a catalog of stellar properties for stars observed by the Kepler follow-on mission, K2. We base the catalog on a cross-match between the K2 Campaign target lists and the current working version of the NASA TESS target catalog. The resulting K2-TESS Stellar Properties Catalog includes value-added information from the TESS Target Catalog, including stellar colors, proper motions, and an estimated luminosity class (dwarf/subgiant versus giant) for each star based on a reduced-proper-motion criterion. Also included is the Guest Observer program identification number(s) associated with each K2 target. The K2-TESS Stellar Properties Catalog is available to the community as a freely accessible data portal on the Filtergraph system at: http://filtergraph.vanderbilt.edu/tess_k2campaigns .

  7. Collisionless microinstabilities in stellarators II - numerical simulations

    CERN Document Server

    Proll, Josefine Henriette Elise; Helander, Per

    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 (NCSX) 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 reduce...

  8. 29 CFR Appendix A to Subpart W to... - Figures W-14 through W-28

    Science.gov (United States)

    2010-07-01

    ... 29 Labor 8 2010-07-01 2010-07-01 false Figures W-14 through W-28 A Appendix A to Subpart W to part 1926 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION...; Overhead Protection Pt. 1926, Subpt. W, App. A Appendix A to Subpart W to part 1926—Figures W-14 through...

  9. The Zeeman effect in stellar spectra

    Science.gov (United States)

    Romanyuk, I. I.

    A short biography of Pieter Zeeman is presented. The main formulae for the normal, anomalous, quadratic Zeeman effects and Paschen-Back effect are given. Instrumentation for Zeeman effect measurements in stellar spectra is described, the most important scientific achievements in magnetic stars investigations with the world's largest telescopes for 50 years are demonstrated. The devices for magnetic measurements made at SAO and the main results of stellar magnetic observations obtained with the 6 m telescope are described in detail.

  10. 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.

  11. Does the Stellar Distribution Flare? A Comparison of Stellar Scale Heights with LAB H I Data

    Science.gov (United States)

    Kalberla, P. M. W.; Kerp, J.; Dedes, L.; Haud, U.

    2014-10-01

    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.

  12. Does the stellar distribution flare? A comparison of stellar scale heights with LAB HI data

    CERN Document Server

    Kalberla, P M W; Dedes, L; Haud, U

    2014-01-01

    The question, whether the stellar populations in the Milky Way take part in flaring of the scale heights as observed for the HI 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 that are incompatible with a constant scale height. We discuss recent observational evidence for stellar flaring and compare it with HI data from the Leiden/Argentine/Bonn (LAB) survey. Within the systemic and statistical uncertainties we find a good agreement between both.

  13. Proceedings of US-Japan heliotron-stellarator workshop: Volume 1

    Energy Technology Data Exchange (ETDEWEB)

    1987-01-01

    This paper is the first of four volumes on the US-Japan Heliotron-Stellarator workshop. It contains talks on the Heliotron E experiment, the compact helical system (CHS) program, the status of the ATF project, the status of the W VII-AS, the status of the TJ-II program, the ATF experimental plans, the ATF diagnostics, the compact Helical system, and the CHS experimental program and diagnostics. (LSP)

  14. Spatial distribution of turbulence in the Wendelstein 7-AS stellarator (invited paper)

    DEFF Research Database (Denmark)

    Basse, N.P.; Michelsen, Poul; Zoletnik, S.

    2002-01-01

    In this paper measurements of short wavelength electron density fluctuations using collective scattering of infrared light are presented. The Wendelstein 7-AS (W7-AS) stellarator (Renner H et al 1989 Plasma Phys. Control. Fusion 31 1579) and the diagnostic are briefly described. A series of plasma...... of the turbulence during both normal and degraded confinement. The found profiles display an increase of core turbulence for the reduced confinement state. The results are discussed and compared to similar tokamak measurements....

  15. Proceedings of US-Japan heliotron-stellarator workshop: Volume 1

    Energy Technology Data Exchange (ETDEWEB)

    1987-01-01

    This paper is the first of four volumes on the US-Japan Heliotron-Stellarator workshop. It contains talks on the Heliotron E experiment, the compact helical system (CHS) program, the status of the ATF project, the status of the W VII-AS, the status of the TJ-II program, the ATF experimental plans, the ATF diagnostics, the compact Helical system, and the CHS experimental program and diagnostics. (LSP)

  16. Featured Image: A Looping Stellar Stream

    Science.gov (United States)

    Kohler, Susanna

    2016-11-01

    This negative image of NGC 5907 (originally published inMartinez-Delgadoet al. 2008; click for the full view!) reveals the faint stellar stream that encircles the galaxy, forming loops around it a fossil of a recent merger. Mergers between galaxies come in several different flavors: major mergers, in which the merging galaxies are within a 1:5 ratio in stellar mass; satellite cannibalism, in which a large galaxy destroys a small satellite less than a 50th of its size; and the in-between case of minor mergers, in which the merging galaxieshave stellar mass ratios between 1:5 and 1:50. These minor mergers are thought to be relatively common, and they can have a significant effect on the dynamics and structure of the primary galaxy. A team of scientists led by Seppo Laine (Spitzer Science Center Caltech) has recently analyzed the metallicity and age of the stellar population in the stream around NGC 5907. By fitting these observations with a stellar population synthesis model, they conclude that this stream is an example of a massive minor merger, with a stellar mass ratio of at least 1:8. For more information, check out the paper below!CitationSeppo Laine et al 2016 AJ 152 72. doi:10.3847/0004-6256/152/3/72

  17. Ubiquitous time variability of integrated stellar populations.

    Science.gov (United States)

    Conroy, Charlie; van Dokkum, Pieter G; Choi, Jieun

    2015-11-26

    Long-period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to about 1,000 days and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long-period variables in a population is directly related to their lifetimes, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not previously been taken into account when modelling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long-period variable stars, and report the ubiquitous detection of this expected 'pixel shimmer' in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviours. The observed variation of 0.1 to 1 per cent is very well matched to the predictions of our models. The data provide a strong constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long-period variables in M87 is shorter by approximately 30 per cent compared to predictions from the latest stellar evolution models.

  18. The distribution of stellar populations within galaxies

    Science.gov (United States)

    Novais, P. M.; Sodré, L., Jr.

    2014-10-01

    The study of stellar populations in galaxies is particularly interesting, since they are a fossil record of several physical processes associated with the formation and evolution of galaxies. In this work we present the first results of our approach to study the spatial distribution of stellar populations inside galaxies. We are using ugriz magnitudes and principal component analysis (PCA) to obtain pixel-by-pixel proxies of the stellar populations and their distributions inside each galaxy. The distribution of these populations are then investigated with a variety of statistical tools, including Gini Indices and the Euler-Poincaré characteristic. Our approach aims to be a step forward with respect to the conventional profile fitting, allowing to obtain quantitative estimates on how the different stellar populations are distributed within a galaxy, bringing hints on how galaxies grow and evolve. The pixel-by-pixel analysis of a small sample of 15 galaxies of different types show that the stellar populations tend to evolve from inside to out in spiral and late spiral galaxies, while elliptical galaxies seem to have young stellar populations in the center. This first results show that this approach is effective and will be explored and improve in future works.

  19. Determination of the position angle of stellar spin axes

    CERN Document Server

    Lesage, Anna-Lea

    2014-01-01

    Measuring the stellar position angle provides valuable information on binary stellar formation or stellar spin axis evolution. We aim to develop a method for determining the absolute stellar position angle using spectro-astrometric analysis of high resolution long-slit spectra. The method has been designed in particular for slowly rotating stars. We investigate its applicability to existing dispersive long-slit spectrographs, identified here by their plate scale, and the size of the resulting stellar sample. The stellar rotation induces a tilt in the stellar lines whose angle depends on the stellar position angle and the orientation of the slit. We developed a rotation model to calculate and reproduce the effects of stellar rotation on unreduced high resolution stellar spectra. Then we retrieved the tilt amplitude using a spectro-astrometric extraction of the position of the photocentre of the spectrum. Finally we present two methods for analysing the position spectrum using either direct measurement of the t...

  20. Spitzer Reveals Stellar 'Family Tree'

    Science.gov (United States)

    2008-01-01

    [figure removed for brevity, see original site] High resolution poster version Generations of stars can be seen in this new infrared portrait from NASA's Spitzer Space Telescope. In this wispy star-forming region, called W5, the oldest stars can be seen as blue dots in the centers of the two hollow cavities (other blue dots are background and foreground stars not associated with the region). Younger stars line the rims of the cavities, and some can be seen as dots at the tips of the elephant-trunk-like pillars. The white knotty areas are where the youngest stars are forming. W5 spans an area of sky equivalent to four full moons and is about 6,500 light-years away in the constellation Cassiopeia. The Spitzer picture was taken over a period of 24 hours. Like other massive star-forming regions, such as Orion and Carina, W5 contains large cavities that were carved out by radiation and winds from the region's most massive stars. According to the theory of triggered star-formation, the carving out of these cavities pushes gas together, causing it to ignite into successive generations of new stars. This image contains some of the best evidence yet for the triggered star-formation theory. Scientists analyzing the photo have been able to show that the ages of the stars become progressively and systematically younger with distance from the center of the cavities. This picture was taken with Spitzer's infrared array camera. It is a four-color composite, in which light with a wavelength of 3.6 microns is blue; 4.5-micron light is green; 5.8-micron light is orange; and 8-micron light is red.

  1. Spitzer Reveals Stellar 'Family Tree'

    Science.gov (United States)

    2008-01-01

    [figure removed for brevity, see original site] High resolution poster version Generations of stars can be seen in this new infrared portrait from NASA's Spitzer Space Telescope. In this wispy star-forming region, called W5, the oldest stars can be seen as blue dots in the centers of the two hollow cavities (other blue dots are background and foreground stars not associated with the region). Younger stars line the rims of the cavities, and some can be seen as pink dots at the tips of the elephant-trunk-like pillars. The white knotty areas are where the youngest stars are forming. Red shows heated dust that pervades the region's cavities, while green highlights dense clouds. W5 spans an area of sky equivalent to four full moons and is about 6,500 light-years away in the constellation Cassiopeia. The Spitzer picture was taken over a period of 24 hours. Like other massive star-forming regions, such as Orion and Carina, W5 contains large cavities that were carved out by radiation and winds from the region's most massive stars. According to the theory of triggered star-formation, the carving out of these cavities pushes gas together, causing it to ignite into successive generations of new stars. This image contains some of the best evidence yet for the triggered star-formation theory. Scientists analyzing the photo have been able to show that the ages of the stars become progressively and systematically younger with distance from the center of the cavities. This is a three-color composite showing infrared observations from two Spitzer instruments. Blue represents 3.6-micron light and green shows light of 8 microns, both captured by Spitzer's infrared array camera. Red is 24-micron light detected by Spitzer's multiband imaging photometer.

  2. On the local stellar populations

    Science.gov (United States)

    Fuhrmann, Klaus; Chini, Rolf; Kaderhandt, Lena; Chen, Zhiwei

    2017-01-01

    We present a study of the local stellar populations from a volume-complete all-sky survey of the about 500 bright stars with distances less than 25 pc and down to main-sequence effective temperatures Teff ≥ 5300 K. The sample is dominated by a 93 per cent fraction of Population I stars, only 22 sources (5 per cent) are Population II stars, and 9 sources (2 per cent) are intermediate-disc stars. No source belongs to the halo. By following the mass of the stars instead of their light, the resulting subset of 136 long-lived stars distributes as 22 (16.2 per cent):6 (4.4 per cent):108 (79.4 per cent) for the Population II:intermediate disc:Population I, respectively. Along with the much larger scaleheight reached by Population II, this unbiased census of long-lived stars provides plain evidence for a starburst epoch in the early Milky Way, with the formation of a massive, rotationally supported, and dark Population II. The same conclusion arises from the substantial early chemical enrichment levels, exemplified here by the elements magnesium and iron, as it arises also from the local Population II white dwarfs. The kinematics, metallicity distribution functions, star formation rates, age-metallicity relations, the inventory of young stars, and the occurrence of blue straggler stars are discussed. A potentially new aspect of the survey is the possibility for substructure among the local Population II stars that may further subdivide into metal-poor and metal-rich sources.

  3. IUVS/MAVEN Stellar Occultations

    Science.gov (United States)

    Gröller, Hannes; Yelle, Roger; Montmessin, Franck; Lacombe, Gaetan; Schneider, Nicholas M.; Deighan, Justin; Jain, Sonal; Nakagawa, Hiromu; Jakosky, Bruce

    2016-10-01

    We present the latest results from stellar occultations observed with the Imaging Ultraviolet Spectrograph (IUVS) instrument on board of Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. So far 9 campaigns have been executed on average every two months since MAVEN began orbiting Mars. Approximately 50 occultations are recorded in each campaign. The IUVS instrument observes in two spectral regions, the far- and mid-UV. The FUV channel covers wavelengths from 110 to 190 nm and the MUV channel from 170 to 350 nm. By combining those two channels we cover the whole altitude range starting from around 30 km to 150 km. We present the geometric dependent CO2, O2, and O3 number densities from these occultations. The derived O2 mixing ratio varies between 1.5 × 10-3 and 5 × 10-3. In some of the MUV occultations we also can see aerosol extinction. In addition we present temperatures derived from the CO2 densities assuming hydrostatic equilibrium. We retrieved mean temperatures of around 180 K at lower altitudes, which decreasing with altitudes down to a mean of around 130 K at higher altitudes. We see a constantly cold layer with temperatures of 105 – 120 K at a pressure level at roughly 7 × 10-6 Pa, equivalent to an altitude of around 140 km. We also discuss possible wave structures with amplitudes between 5 and 15 K and wavelengths between 10 and 15 km in the obtained temperature profiles. The temperature profiles, retrieved with the IUVS instrument, are mostly in agreement with predicted values from the Mars Climate Database model, except where we see the cold layer around 140 km.

  4. Results from the first operation phase of W7-X

    Science.gov (United States)

    Pedersen, Thomas Sunn

    2016-10-01

    This talk will give a review of stellarator physics and the mission of Wendelstein 7-X (W7-X), and will summarize the most important results obtained during its first operation phase, OP1.1, which was completed in March 2016. The HELIAS reactor vision and open issues in stellarator research will also be discussed. The stellarator concept dates back to the 1950's. It has several intrinsic advantages, including being free of current-driven disruptions, and not needing current drive. However, the stellarator has been lagging behind the tokamak with respect to energy confinement. Recent advances in plasma theory and computational power have led to renewed interest in stellarators since they allow a complex but effective optimization of the confinement properties, one that should allow for tokamak-like confinement times. W7-X is the largest and most optimized stellarator in the world, and aims to show that the earlier weaknesses of the stellarator concept have been addressed successfully by optimization, and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant. It is built for steady-state operation, featuring 70 superconducting coils, and a confinement volume of about 30 m3. During OP1.1, it was operated at full field (B = 2.5 T on axis), with ECRH power up to 4.3 MW (later to be extended to 10 MW). Plasma operation was performed with helium and hydrogen, with deuterium planned for later phases. More than 2,000 discharges were created during the 10 operation weeks of OP1.1. Core Te 8 keV and Ti 2 keV were reached in discharge with densities in the low to mid 1019 range, and confinement times were on the order of 100-150 ms, within expectation. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement Number 633053.

  5. W mass measurement

    CERN Document Server

    Andari, Nansi; The ATLAS collaboration

    2017-01-01

    A first measurement of the W-boson mass at the LHC is presented based on about 4.6 fb^-1 of proton–proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector. The measured value is 80370±19 MeV, consistent with the Standard Model prediction, with the combined values measured at the LEP and Tevatron colliders, and with the world average. The ATLAS result equals in precision the previous best measurement of the W mass, performed by the CDF collaboration. The CMS results for the W-like measurement of the Z boson mass using dimuon events are also shown. An overview of the analyses is shown with a special emphasis on the evaluation of the experimental systematic uncertainties, as well as on the uncertainties due to the modelling of the vector boson production and decay.

  6. MESA Isochrones and Stellar Tracks (MIST) 0: Methods for the construction of stellar isochrones

    CERN Document Server

    Dotter, Aaron

    2016-01-01

    I describe a method to transform a set of stellar evolution tracks onto a uniform basis and then interpolate within that basis to construct stellar isochrones. The method accommodates a broad range of stellar types, from substellar objects to high-mass stars, and phases of evolution, from the pre-main sequence to the white dwarf cooling sequence. I discuss situations in which stellar physics leads to departures from the otherwise monotonic relation between initial stellar mass and lifetime and how these may be dealt with in isochrone construction. I close with convergence tests and recommendations for the number of points in the uniform basis and the mass between tracks in the original grid required in order to achieve a certain level of accuracy in the resulting isochrones. The programs that implement these methods are free and open-source; they may be obtained from the project webpage.

  7. Demeter-W

    Energy Technology Data Exchange (ETDEWEB)

    2017-09-27

    Demeter-W, an open-access software written in Python, consists of extensible module packages. It is developed with statistical downscaling algorithms, to spatially and temporally downscale water demand data into finer scale. The spatial resolution will be downscaled from region/basin scale to grid (0.5 geographic degree) scale and the temporal resolution will be downscaled from year to month. For better understanding of the driving forces and patterns for global water withdrawal, the researchers is able to utilize Demeter-W to reconstruct the data sets to examine the issues related to water withdrawals at fine spatial and temporal scales.

  8. On w-maximal groups

    CERN Document Server

    Gonzalez-Sanchez, Jon

    2010-01-01

    Let $w = w(x_1,..., x_n)$ be a word, i.e. an element of the free group $F =$ on $n$ generators $x_1,..., x_n$. The verbal subgroup $w(G)$ of a group $G$ is the subgroup generated by the set $\\{w (g_1,...,g_n)^{\\pm 1} | g_i \\in G, 1\\leq i\\leq n \\}$ of all $w$-values in $G$. We say that a (finite) group $G$ is $w$-maximal if $|G:w(G)|> |H:w(H)|$ for all proper subgroups $H$ of $G$ and that $G$ is hereditarily $w$-maximal if every subgroup of $G$ is $w$-maximal. In this text we study $w$-maximal and hereditarily $w$-maximal (finite) groups.

  9. Three quasi-stellar objects acting as strong gravitational lenses

    Science.gov (United States)

    Courbin, F.; Faure, C.; Djorgovski, S. G.; Rérat, F.; Tewes, M.; Meylan, G.; Stern, D.; Mahabal, A.; Boroson, T.; Dheeraj, R.; Sluse, D.

    2012-04-01

    We report the discovery of three new cases of quasi-stellar objects (QSOs) acting as strong gravitational lenses on background emission line galaxies: SDSS J0827+5224 (zQSO = 0.293, zs = 0.412), SDSS J0919+2720 (zQSO = 0.209, zs = 0.558), SDSS J1005+4016 (zQSO = 0.230, zs = 0.441). The selection was carried out using a sample of 22,298 SDSS spectra displaying at least four emission lines at a redshift beyond that of the foreground QSO. The lensing nature is confirmed from Keck imaging and spectroscopy, as well as from HST/WFC3 imaging in the F475W and F814W filters. Two of the QSOs have face-on spiral host galaxies and the third is a QSO+galaxy pair. The velocity dispersion of the host galaxies, inferred from simple lens modeling, is between σ = 210 and 285 km s-1, making these host galaxies comparable in mass with the SLACS sample of early-type strong lenses. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Also based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #GO12233.

  10. Kinetic properties of fractal stellar media

    Science.gov (United States)

    Chumak, O. V.; Rastorguev, A. S.

    2017-01-01

    Kinetic processes in fractal stellar media are analysed in terms of the approach developed in our earlier paper involving a generalization of the nearest neighbour and random force distributions to fractal media. Diffusion is investigated in the approximation of scale-dependent conditional density based on an analysis of the solutions of the corresponding Langevin equations. It is shown that kinetic parameters (time-scales, coefficients of dynamic friction, diffusion, etc.) for fractal stellar media can differ significantly both qualitatively and quantitatively from the corresponding parameters for a quasi-uniform random media with limited fluctuations. The most important difference is that in the fractal case, kinetic parameters depend on spatial scalelength and fractal dimension of the medium studied. A generalized kinetic equation for stellar media (fundamental equation of stellar dynamics) is derived in the Fokker-Planck approximation with the allowance for the fractal properties of the spatial stellar density distribution. Also derived are its limit forms that can be used to describe small departures of fractal gravitating medium from equilibrium.

  11. Stellarator Coil Design and Plasma Sensitivity

    Energy Technology Data Exchange (ETDEWEB)

    Long-Poe Ku and Allen H. Boozer

    2010-11-03

    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.

  12. Saturation of Stellar Winds from Young Suns

    CERN Document Server

    Suzuki, Takeru K; Kataoka, Ryuho; Kato, Yoshiaki; Matsumoto, Takuma; Miyahara, Hiroko; Tsuneta, Saku

    2013-01-01

    (Abridged)We investigate mass losses via stellar winds from sun-like main sequence stars with a wide range of activity levels. We perform forward-type magnetohydrodynamical numerical experiments for Alfven wave-driven stellar winds with a wide range of the input Poynting flux from the photosphere. Increasing the magnetic field strength and the turbulent velocity at the stellar photosphere from the current solar level, the mass loss rate rapidly increases at first owing to the suppression of the reflection of the Alfven waves. The surface materials are lifted up by the magnetic pressure associated with the Alfven waves, and the cool dense chromosphere is intermittently extended to 10-20% of the stellar radius. The densities of the corona and transition region above the chromosphere is also high, which leads to efficient radiative losses. Eventually most of the input Poynting energy from the stellar surface escapes by the radiation. As a result, there is no more sufficient energy remained for the kinetic energy...

  13. 78 FR 63570 - Proposed Collection; Comment Request for Forms W-8BEN, W-8BEN-E, W-8ECI, W-8EXP, and W-8IMY

    Science.gov (United States)

    2013-10-24

    ... Internal Revenue Service Proposed Collection; Comment Request for Forms W-8BEN, W-8BEN-E, W-8ECI, W-8EXP, and W-8IMY AGENCY: Internal Revenue Service (IRS), Treasury. ACTION: Notice and request for comments... Form W-8BEN, Certificate of Foreign Status of Beneficial Owner for United States Tax Withholding,...

  14. W-CDMA - Spread Spectrum

    DEFF Research Database (Denmark)

    Jakobsen, Kaj Bjarne

    1999-01-01

    Specifications, Direct Sequence, Frequency Hopping, Hybrid, W-CDMA, and Power Amplifier Linearisation.......Specifications, Direct Sequence, Frequency Hopping, Hybrid, W-CDMA, and Power Amplifier Linearisation....

  15. Electron capture cross sections for stellar nucleosynthesis

    CERN Document Server

    Giannaka, P G

    2015-01-01

    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 quasi-particle 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 above mentioned $e^-$-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 $^{66}Zn$ isotope, which belongs to the iron group nuclei and plays prominent role in stellar nucleosynthesis at core collapse supernovae environment.

  16. A method to deconvolve stellar rotational velocities

    CERN Document Server

    Cure, Michel; Cassetti, Julia; Christen, Alejandra

    2014-01-01

    Rotational speed is an important physical parameter of stars and knowing the distribution of stellar rotational velocities is essential for the understanding stellar evolution. However, it cannot be measured directly but the convolution of the rotational speed and the sine of the inclination angle, $v \\sin i$. We developed a method to deconvolve this inverse problem and obtain the cumulative distribution function (CDF) for stellar rotational velocities extending the work of Chandrasekhar & M\\"unch (1950). This method is applied a) to theoretical synthetic data recovering the original velocity distribution with very small error; b) to a sample of about 12.000 field main--sequence stars, corroborating that the velocity distribution function is non--Maxwellian, but is better described by distributions based on the concept of maximum entropy, such as Tsallis or Kaniadakis distribution functions. This is a very robust and novel method that deconvolve the rotational velocity cumulative distribution function fro...

  17. Magnetospheric outflows in young stellar objects

    Directory of Open Access Journals (Sweden)

    Zanni Claudio

    2014-01-01

    Full Text Available Different classes of outflows are associated with the magnetospheric activity of accreting T Tauri protostars. Stellar winds are accelerated along the open field lines anchored in the stellar surface; disk winds (extended or X-type can be launched along the open magnetic surfaces threading the accretion disk; another type of ejection can arise from the region of interaction of the closed magnetosphere with the accretion disk (magnetospheric ejections, conical winds, where the magnetic surfaces undergo quasiperiodic episodes of inflation and reconnection. In this chapter I will present the main dynamical properties of these different types of outflow. Two main issues will be addressed. First, I will try to understand if these ejection phenomena can account for the origin of the jets often observed in young forming stellar systems. Second, I will evaluate the impact of these outflows on the angular momentum evolution of the central protostar.

  18. A daylight experiment for teaching stellar interferometry

    Science.gov (United States)

    Illarramendi, M. A.; Hueso, R.; Zubia, J.; Aldabaldetreku, G.; Durana, G.; Sánchez-Lavega, A.

    2014-07-01

    We discuss the design of a simple experiment that reproduces the operation of the Michelson stellar interferometer. The emission of stellar sources has been simulated using light emerging from circular end-faces of step-index polymer optical fibers and from diffuse reflections of laser beams. Interference fringes have been acquired using a digital camera, coupled to a telescope obscured by a double aperture lid. The experiment is analogous to the classical determination of stellar sizes by Michelson and can be used during the day. Using this experimental set-up, we can determine the size of extended sources, located at a distance of about 75 m from our telescope, with errors less than 25%.

  19. Progress Toward Improved Compact Stellarator Designs

    Science.gov (United States)

    Neilson, G. H.; Brown, T.; Gates, D.; Ku, L. P.; Lazerson, S.; Pomphrey, N.; Reiman, A.; Zarnstorff, M.; Bromberg, L.; Boozer, A.; Harris, J.

    2010-11-01

    Stellarators offer robust physics solutions for MFE challenges-- steady-state operation, disruption elimination, and high-density operation-- but require design improvements to overcome technical risks in the construction and maintenance of future large-scale stellarators. Using the ARIES-CS design (aspect ratio 4.56) as a starting point, compact stellarator designs with improved maintenance characteristics have been developed. By making the outboard legs of the main magnetic field coils nearly straight and parallel, a sector maintenance scheme compatible with high availability becomes possible. Approaches that can allow the main coil requirements to be relaxed in this way are: 1) increase aspect ratio at the expense of compactness, 2) add local removable coils in the maintenance ports for plasma shaping, and 3) use passive conducting tiles made of bulk high-temperature superconducting material to help shape the magnetic field. Such tiles would be arranged on a shaped, segmented internal support structure behind the shield.

  20. 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.

  1. On stellar limb darkening and exoplanetary transits

    CERN Document Server

    Howarth, Ian D

    2011-01-01

    This paper examines how to compare stellar limb-darkening coefficients evaluated from model atmospheres with those estimated from photometry. Limb-darkening coefficients derived from light-curve analyses using approximate limb-darkening `laws' are shown to be dependent on system geometry, while different characterizations of a given model atmosphere can give quite different numerical results. These issues are examined in the context of exoplanetary transits, which offer significant advantages over traditional binary-star eclipsing systems in the investigation of stellar limb darkening. `Like for like' comparisons between light-curve analyses and new model-atmosphere results, mediated by synthetic photometry, are conducted for a small sample of stars. Agreement between the resulting synthetic-photometry/atmosphere-model (SPAM) limb-darkening coefficients and empirical values ranges from very good to quite poor, even though there is only a small dispersion in fundamental stellar parameters.

  2. Achieving continuity: a story of stellar magnitude

    Science.gov (United States)

    Evans, Michael S.

    2010-03-01

    Scientists tell a story of 2,000 years of stellar magnitude research that traces back to Hipparchus. This story of continuity in practices serves an important role in scientific education and outreach. STS scholars point out many ways that stories of continuity, like many narratives about science, are disconnected from practices. Yet the story of continuity in stellar magnitude is a powerful scientific achievement precisely because of its connection to practice. The historical development of star catalogues shows how specific recording practices connected past and present in a useful way. The narrative of continuity in stellar magnitude, however else it might be subject to STS critique of narrative, maintains its power because of its connection to practice. I suggest that more attention be paid to connections between practice and narrative in STS, and in particular to the ways that historical practices sustain narratives by connecting past and present.

  3. Simulation and optimisation of turbulence in stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Xanthopoulos, Pavlos; Helander, Per; Turkin, Yuriy; Plunk, Gabriel G.; Bird, Thomas; Proll, Josefine H.E. [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Wendelsteinstr. 1, 17491 Greifswald (Germany); Mynick, Harry [Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Jenko, Frank; Goerler, Tobias; Told, Daniel [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Boltzmannstr. 2, 85748 Garching (Germany)

    2014-07-01

    In tokamaks and stellarators - two leading types of devices used in fusion research - magnetic field lines trace out toroidal surfaces on which the plasma density and temperature are constant, but turbulent fluctuations carry energy across these surfaces to the wall, thus degrading the plasma confinement. Using petaflop-scale simulations, we calculate for the first time the pattern of turbulent structures forming on stellarator magnetic surfaces, and find striking differences relative to tokamaks. The observed sensitivity of the turbulence to the magnetic geometry suggests that there is room for further confinement improvement, in addition to measures already taken to minimise the laminar transport. With an eye towards fully optimised stellarators, we present a proof-of-principle configuration with substantially reduced turbulence compared to an existing design.

  4. Stellar Tidal Streams in External Galaxies

    CERN Document Server

    Carlin, Jeffrey L; Martinez-Delgado, David; Gabany, R Jay

    2016-01-01

    To place the highly substructured stellar halos of the Milky Way and M31 in a larger context of hierarchical galaxy formation, it is necessary to understand the prevalence and properties of tidal substructure around external galaxies. This chapter details the current state of our observational knowledge of streams in galaxies in and beyond the Local Group, which are studied both in resolved stellar populations and in integrated light. Modeling of individual streams in extragalactic systems is hampered by our inability to obtain resolved stellar kinematics in the streams, though many streams contain alternate luminous kinematic tracers, such as globular clusters or planetary nebulae. We compare the observed structures to the predictions of models of galactic halo formation, which provide insight in the number and properties of streams expected around Milky Way like galaxies. More specifically, we discuss the inferences that can be made about stream progenitors based only on observed morphologies. We expand our...

  5. The stellar atmosphere simulation code Bifrost

    CERN Document Server

    Gudiksen, Boris V; Hansteen, Viggo H; Hayek, Wolfgang; Leenaarts, Jorrit; Martínez-Sykora, Juan

    2011-01-01

    Context: Numerical simulations of stellar convection and photospheres have been developed to the point where detailed shapes of observed spectral lines can be explained. Stellar atmospheres are very complex, and very different physical regimes are present in the convection zone, photosphere, chromosphere, transition region and corona. To understand the details of the atmosphere it is necessary to simulate the whole atmosphere since the different layers interact strongly. These physical regimes are very diverse and it takes a highly efficient massively parallel numerical code to solve the associated equations. Aims: The design, implementation and validation of the massively parallel numerical code Bifrost for simulating stellar atmospheres from the convection zone to the corona. Methods: The code is subjected to a number of validation tests, among them the Sod shock tube test, the Orzag-Tang colliding shock test, boundary condition tests and tests of how the code treats magnetic field advection, chromospheric ...

  6. The Spitzer Atlas of Stellar Spectra

    CERN Document Server

    Ardila, David R; Makowiecki, Wojciech; Stauffer, John; Song, Inseok; Rho, Jeonghee; Fajardo-Acosta, Sergio; Hoard, D W; Wachter, Stefanie

    2010-01-01

    We present the Spitzer Atlas of Stellar Spectra (SASS), which includes 159 stellar spectra (5 to 32 mic; R~100) taken with the Infrared Spectrograph on the Spitzer Space Telescope. This Atlas gathers representative spectra of a broad section of the Hertzsprung-Russell diagram, intended to serve as a general stellar spectral reference in the mid-infrared. It includes stars from all luminosity classes, as well as Wolf-Rayet (WR) objects. Furthermore, it includes some objects of intrinsic interest, like blue stragglers and certain pulsating variables. All the spectra have been uniformly reduced, and all are available online. For dwarfs and giants, the spectra of early-type objects are relatively featureless, dominated by Hydrogen lines around A spectral types. Besides these, the most noticeable photospheric features correspond to water vapor and silicon monoxide in late-type objects and methane and ammonia features at the latest spectral types. Most supergiant spectra in the Atlas present evidence of circumstell...

  7. Neoclassical impurity transport in stellarator geometry

    CERN Document Server

    García-Regaña, J M; Beidler, C D; berg, H Maaß; Helander, P; Turkin, Y

    2012-01-01

    The impurity dynamics in stellarators has become an issue of moderate concern due to the, \\textit{a priori}, inherent tendency of the impurities to accumulate in the core when the neoclassical ambipolar radial electric field points radially inwards (ion root regime). This accumulation can lead to collapse of the plasma due to radiative losses, and thus limit high performance plasma discharges in non-axisymmetric devices. Theoretically, a quantitative description of the neoclassical impurity transport is complicated by the breakdown of the assumption of small $q \\tilde{\\Phi}/T$ for impurities, where $q$ is the electric charge, $T$ the temperature in energy units, and $\\tilde{\\Phi}$ the electrostatic potential variation within the flux surface. The present work describes quantitatively the particle transport of impurities in the frame of local neoclassical theory when $q\\tilde{\\Phi}/T=O(1)$ in the Large Helical Device (LHD) stellarator. %and the Wendelstein 7-X stellarators. The central numerical tool used is t...

  8. Stellar populations -- the next ten years

    CERN Document Server

    Bland-Hawthorn, J

    2007-01-01

    The study of stellar populations is a discipline that is highly dependent on both imaging and spectroscopy. I discuss techniques in different regimes of resolving power: broadband imaging (R~4), intermediate band imaging (R~16, 64), narrowband spectral imaging (R~256, 1024, 4096). In recent years, we have seen major advances in broadband all-sky surveys that are set to continue across optical and IR bands, with the added benefit of the time domain, higher sensitivity, and improved photometric accuracy. Tunable filters and integral field spectrographs are poised to make inroads into intermediate and narrowband imaging studies of stellar populations. Further advances will come from AO-assisted imaging and imaging spectroscopy, although photometric accuracy will be challenging. Integral field spectroscopy will continue to have a major impact on future stellar population studies, extending into the near infrared once the OH suppression problem is finally resolved. A sky rendered dark will allow a host of new idea...

  9. 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

  10. 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

  11. Spanning QTAIM topology phase diagrams of water isomers W4, W5 and W6.

    Science.gov (United States)

    Jenkins, Samantha; Restrepo, Albeiro; David, Jorge; Yin, Dulin; Kirk, Steven R

    2011-06-28

    Structural and chemical properties of the small water clusters W(4), W(5) and W(6) are investigated with the theory of atoms and molecules (QTAIM). For the W(4), W(5) and W(6) clusters, nine, fourteen and twenty-seven conformers, respectively, have been analyzed. For the W(4), W(5) and W(6) clusters one, two and three of these structures, respectively, have not been reported before. We then proceed to extend the W(4), W(5) and W(6) water cluster topology space using QTAIM; the Poincaré-Hopf topological sum rules are applied to create rules to identify the spanning set of conformer topologies, this includes finding three, ten and eight new distinct topologies that satisfy the Poincaré-Hopf relation for W(4), W(5) and W(6) respectively. The topological stability of degenerate solutions to the Poincaré-Hopf relation is compared by evaluating the proximity to rupturing of critical points of the gradient vector field of the charge density. We introduce a QTAIM topology space to replace the inconsistent use of Euclidean geometry to determine whether a cluster is 1-, 2- or 3-D. We show from the topology of the charge density that the conformers of the W(4), W(5) clusters are more energetically stable in less compact, planar forms, conversely the conformers of W(6) are more energetically stable with compact 3-D topologies. Quantifying the degree of covalent character in the hydrogen bonding for the W(4), W(5) and W(6) clusters independently verifies this finding. Differences in simple rules for the number of hydrogen bonds obeying the Bernal-Fowler ice rules between W(4), W(5) and W(6) reflect the transition from 2-D to 3-D structures being more energetically stable. In addition, we identify a new class of O-O bonding interactions that are up to 48% longer than the inter-nuclear separation and appear to be failed hydrogen bonds.

  12. 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.

  13. Approximate input physics for stellar modelling

    CERN Document Server

    Pols, O R; Eggleton, P P; Han, Z; Pols, O R; Tout, C A; Eggleton, P P; Han, Z

    1995-01-01

    We present a simple and efficient, yet reasonably accurate, equation of state, which at the moderately low temperatures and high densities found in the interiors of stars less massive than the Sun is substantially more accurate than its predecessor by Eggleton, Faulkner & Flannery. Along with the most recently available values in tabular form of opacities, neutrino loss rates, and nuclear reaction rates for a selection of the most important reactions, this provides a convenient package of input physics for stellar modelling. We briefly discuss a few results obtained with the updated stellar evolution code.

  14. Superconducting coil development for the Wendelstein 7-X stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Sapper, J. (Max-Planck-Inst. fuer Plasmaphysik, EURATOM Association, Garching (Germany)); W 7-X Technical Group

    1993-01-01

    At the Max-Planck-Institut fuer Plasmaphysik (IPP), Garching, the Wendelstein 7-X stellarator (W 7-X) is in the stage of the beginning R and D phase. The experiment will be a large modular machine with nonplanar coils, following the Garching development line. It fits into the range of next step devices. The main technical parameters are: Major radius: R[sub 0]=5.5 m, magnetic induction: B[sub 0]=3 T, stored magnetic energy: W[sub m]=600 MJ, average plasma radius: r[sub 0]=0.53 m. The expected plasma parameters are: Central temperatures: T[sub i](0), T[sub e](0)=2-5 keV, central electron density: n[sub e](0)=0.1-2x10[sup 20] m[sup -3], energy confinement time: [tau][sub E]=0.1-0.5 s, average beta value: <[beta]>[<=]0.05. The design has to allow steady-state plasma operation. Consequently the coil system is superconducting. An internally cooled cable-in-conduit conductor with copper stabilized NbTi strands will be used at 4 K (LHe). The paper presents an overview of the design features of the machine and describes in particular the conductor design, the coil arrangement with electrical, hydraulic and mechanical parameters as well as the sequence of prototype steps which are foreseen for establishing a well-developed series production of the magnet. (orig.).

  15. Circumstellar Dust, PAHs, and Stellar Populations in Early-Type Galaxies: Insights from GALEX and WISE

    CERN Document Server

    Simonian, Gregory V

    2016-01-01

    A majority of early-type galaxies contain interstellar dust, yet the origin of this dust, and why the dust sometimes exhibits unusual PAH ratios, remains a mystery. If the dust is internally produced, the most likely origin is the large number of AGB stars associated with the old stellar population. We present GALEX and WISE elliptical aperture photometry of $\\sim350$ early-type galaxies with Spitzer mid-infrared spectroscopy and/or ancillary data from ATLAS3D, to characterize their circumstellar dust and the shape of the radiation field that illuminates the interstellar PAHs. We find that circumstellar dust is ubiquitous in early-type galaxies, which indicates some tension between stellar population age estimates and models for circumstellar dust production in very old stellar populations. We also use dynamical masses from ATLAS3D to show that WISE W1 (3.4 $\\mu$m) mass-to-light ratios are inconsistent with model predictions for a single IMF, as found by previous work. While the stellar population differences...

  16. DELPHI: First W particles

    CERN Multimedia

    1996-01-01

    This track is an example of real data collected from the DELPHI detector on the Large Electron-Positron (LEP) collider at CERN, which ran between 1989 and 2000. These are the first pair of W particles produced at LEP2, the high energy upgrade of LEP that took place in 1996. Both Ws decay into a quark-antiquark pair, which are each seen as one of the four jets of hadrons in the detector.

  17. 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

  18. Estimation of distances to stars with stellar parameters from LAMOST

    CERN Document Server

    Carlin, Jeffrey L; Newberg, Heidi Jo; Beers, Timothy C; Chen, Li; Deng, Licai; Guhathakurta, Puragra; Hou, Jinliang; Hou, Yonghui; Lepine, Sebastien; Li, Guangwei; Luo, A-Li; Smith, Martin C; Wu, Yue; Yang, Ming; Yanny, Brian; Zhang, Haotong; Zheng, Zheng

    2015-01-01

    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-degree 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 ...

  19. The Stellar Observations Network Group - first results

    DEFF Research Database (Denmark)

    Antoci, Victoria; Grundahl, Frank; Christensen-Dalsgaard, Joergen

    SONG - the Stellar Observations Network Group is a Danish-led project set to design and build a global network of 1-m telescopes to carry out detailed studies of solar-like stars using asteroseismology and to discover and characterise exo-planets and their star system. Here we present more than 100...

  20. Stellar streams around the Magellanic Clouds

    CERN Document Server

    Belokurov, Vasily

    2015-01-01

    Using Blue Horizontal Branch stars identified in the Dark Energy Survey Year 1 data, we report the detection of an extended and lumpy stellar debris distribution around the Magellanic Clouds. At the heliocentric distance of the Clouds, overdensities of BHBs are seen to reach at least to ~30 degrees, and perhaps as far as ~50 degrees from the LMC. In 3D, the stellar halo is traceable to between 25 and 50 kpc from the LMC. We catalogue the most significant of the stellar sub-structures revealed, and announce the discovery of a number of narrow streams and diffuse debris clouds. Two narrow streams appear approximately aligned with the Magellanic Clouds' proper motion. Moreover, one of these overlaps with the gaseous Magellanic Stream on the sky. Curiously, two diffuse BHB agglomerations seem coincident with several of the recently discovered DES satellites. Given the enormous size and the conspicuous lumpiness of the LMC's stellar halo, we speculate that the dwarf could easily have been more massive than previou...

  1. The Stellar Structures around Disk Galaxies

    CERN Document Server

    Drozdovsky, I; Aparicio, A; Gallart, C; Monelli, M; Hidalgo, S; Bernard, E J; Galazutdinova, O

    2016-01-01

    We present a brief summary of our current results on the stellar distribution and population gradients of the resolved stars in the surroundings of ~50 nearby disk galaxies, observed with space- (Hubble & Spitzer) and ground-based telescopes (Subaru, VLT, BTA, Palomar, CFHT & INT). We examine the radial (in-plane) and vertical (extraplanar) distributions of resolved stars as a function of stellar age and metallicity by tracking changes in the color-magnitude diagram of face-on and edge-on galaxies. Our data show, that the scale length and height of a stellar population increases with age, with the oldest detected stellar populations identified at a large galactocentric radius or extraplanar height, out to typically a few kpc. In the most massive of the studied galaxies there is evidence for a break in number density and color gradients of evolved stars, which plausibly correspond to the thick disk and halo components of the galaxies. The ratio of intermediate-age to old stars in the outermost fields c...

  2. Accurate Stellar Parameters for Exoplanet Host Stars

    Science.gov (United States)

    Brewer, John Michael; Fischer, Debra; Basu, Sarbani; Valenti, Jeff A.

    2015-01-01

    A large impedement to our understanding of planet formation is obtaining a clear picture of planet radii and densities. Although determining precise ratios between planet and stellar host are relatively easy, determining accurate stellar parameters is still a difficult and costly undertaking. High resolution spectral analysis has traditionally yielded precise values for some stellar parameters but stars in common between catalogs from different authors or analyzed using different techniques often show offsets far in excess of their uncertainties. Most analyses now use some external constraint, when available, to break observed degeneracies between surface gravity, effective temperature, and metallicity which can otherwise lead to correlated errors in results. However, these external constraints are impossible to obtain for all stars and can require more costly observations than the initial high resolution spectra. We demonstrate that these discrepencies can be mitigated by use of a larger line list that has carefully tuned atomic line data. We use an iterative modeling technique that does not require external constraints. We compare the surface gravity obtained with our spectral synthesis modeling to asteroseismically determined values for 42 Kepler stars. Our analysis agrees well with only a 0.048 dex offset and an rms scatter of 0.05 dex. Such accurate stellar gravities can reduce the primary source of uncertainty in radii by almost an order of magnitude over unconstrained spectral analysis.

  3. Advanced Stellar Compass - Alenia Mars Express

    DEFF Research Database (Denmark)

    Kilsgaard, Søren; Betto, Maurizio; Jørgensen, John Leif;

    1998-01-01

    This document, submitted in reply to an Alenia R.f.P., is a proposal to implement the Advanced Stellar Compass (ASC) in the Mars Express mission.The Mars Express is an ESA dedicated mission to Mars scientific investigation.The ASC is a very advanced instrument designed by the Space Instrumentation...

  4. Summary of the Advanced Stellar Compass

    DEFF Research Database (Denmark)

    Jørgensen, John Leif

    1997-01-01

    The current version of the Advanced Stellar Compass (ASC) is an improved implementation of the instrument developed for the Danish Geomagnetic Research Satellite Ørsted. The Ørsted version was successfully tested in space on the NASA sounding rocket "Thunderstorm III", that was launched September 2...

  5. Evolution and seismic tools for stellar astrophysics

    CERN Document Server

    Monteiro, Mario JPFG

    2008-01-01

    A collection of articles published by the journal "Astrophysics and Space Science, Volume 316, Number 1-4", August 2008. This work covers 10 evolution codes and 9 oscillation codes. It is suitable for researchers and research students working on the modeling of stars and on the implementation of seismic test of stellar models.

  6. Benchmarking the Multidimensional Stellar Implicit Code MUSIC

    Science.gov (United States)

    Goffrey, T.; Pratt, J.; Viallet, M.; Baraffe, I.; Popov, M. V.; Walder, R.; Folini, D.; Geroux, C.; Constantino, T.

    2017-04-01

    We present the results of a numerical benchmark study for the MUltidimensional Stellar Implicit Code (MUSIC) based on widely applicable two- and three-dimensional compressible hydrodynamics problems relevant to stellar interiors. MUSIC is an implicit large eddy simulation code that uses implicit time integration, implemented as a Jacobian-free Newton Krylov method. A physics based preconditioning technique which can be adjusted to target varying physics is used to improve the performance of the solver. The problems used for this benchmark study include the Rayleigh-Taylor and Kelvin-Helmholtz instabilities, and the decay of the Taylor-Green vortex. Additionally we show a test of hydrostatic equilibrium, in a stellar environment which is dominated by radiative effects. In this setting the flexibility of the preconditioning technique is demonstrated. This work aims to bridge the gap between the hydrodynamic test problems typically used during development of numerical methods and the complex flows of stellar interiors. A series of multidimensional tests were performed and analysed. Each of these test cases was analysed with a simple, scalar diagnostic, with the aim of enabling direct code comparisons. As the tests performed do not have analytic solutions, we verify MUSIC by comparing it to established codes including ATHENA and the PENCIL code. MUSIC is able to both reproduce behaviour from established and widely-used codes as well as results expected from theoretical predictions. This benchmarking study concludes a series of papers describing the development of the MUSIC code and provides confidence in future applications.

  7. Light elements depletion in stellar environments.

    Science.gov (United States)

    Pizzone, R. G.; Lamia, L.; Romano, S.; Spitaleri, C.; Szanto de Toledo, A.; Blagus, S.; Bogovac, M.; Carlin, N.; Cherubini, S.; Crucillá, V.; Milin, M.; De Moura, M. M.; Gameiro Munhoz, M.; Gimenez del Santo, M.; Gulino, M.; La Cognata, M.; Liguori Neto, R.; Miljanić, D.; Puglia, S. M. R.; Rapisarda, G. G.; Sergi, M. L.; Soić, N.; Souza, F. A.; Suaide, A. A. P.; Szanto, E.; Tudisco, S.; Tumino, A.; Typel, S.

    Big efforts have been devoted in the last years to the study of light elements abundances. Definitively their importance is strongly related to cosmology as well as to stellar structure and evolution. In fact hints on the primordial nucleosynthesis can be achieved from Li, Be and B primordial abundances. Moreover these studies can be a precious tool for testing and understanding the inner stellar structure, especially for what regards the mixing processes in stellar envelopes \\citep{boesgard04}. In this framework the different nuclear processes which produce or destroy Li, Be and B must be studied in details and an accurate knowledge of the involved nuclear cross sections is necessary. In particular we will focus our attention on one of the main destruction channels for these elements in stellar environments, the (p,alpha ) reactions. In particular this work will review the last results achieved by the Trojan Horse Method (THM) for the 6Li(p,alpha )3He, 6Li(d,alpha )4He, 7Li(p,alpha )4He, 10B(p,alpha )7Be, 9Be(p,alpha )6Li and 11B(p,alpha )8Be.

  8. Stellar wind models of subluminous hot stars

    CERN Document Server

    Krticka, J; Krtickova, I

    2016-01-01

    Mass-loss rate is one of the most important stellar parameters. We aim to provide mass-loss rates as a function of subdwarf parameters and to apply the formula for individual subdwarfs, to predict the wind terminal velocities, to estimate the influence of the magnetic field and X-ray ionization on the stellar wind, and to study the interaction of subdwarf wind with mass loss from Be and cool companions. We used our kinetic equilibrium (NLTE) wind models with the radiative force determined from the radiative transfer equation in the comoving frame (CMF) to predict the wind structure of subluminous hot stars. Our models solve stationary hydrodynamical equations, that is the equation of continuity, equation of motion, and energy equation and predict basic wind parameters. We predicted the wind mass-loss rate as a function of stellar parameters, namely the stellar luminosity, effective temperature, and metallicity. The derived wind parameters (mass-loss rates and terminal velocities) agree with the values derived...

  9. The evolution of runaway stellar collision products

    CERN Document Server

    Glebbeek, E; de Mink, S E; Pols, O R; Zwart, S F Portegies

    2009-01-01

    In the cores of young dense star clusters repeated stellar collisions involving the same object can occur, which has been suggested to lead to the formation of an intermediate-mass black hole. In order to verify this scenario we compute the detailed evolution of the merger remnant of three sequences. We follow the evolution until the onset of carbon burning and estimate the final remnant mass to determine the ultimate fate of a runaway merger sequence. We use a detailed stellar evolution code to follow the evolution of the collision product. At each collision, we mix the two colliding stars, taking account of mass loss during the collision. During the stellar evolution we apply mass loss rates from the literature, as appropriate for the evolutionary stage of the merger remnant. We compute models for high ($Z=0.02$) and low ($Z=0.001$) metallicity to quantify metallicity effects. We find that the merger remnant becomes a Wolf-Rayet star before the end of core hydrogen burning. Mass loss from stellar winds domi...

  10. X-raying clumped stellar winds

    CERN Document Server

    Oskinova, L M; Feldmeier, A

    2008-01-01

    X-ray spectroscopy is a sensitive probe of stellar winds. X-rays originate from optically thin shock-heated plasma deep inside the wind and propagate outwards throughout absorbing cool material. Recent analyses of the line ratios from He-like ions in the X-ray spectra of O-stars highlighted problems with this general paradigm: the measured line ratios of highest ions are consistent with the location of the hottest X-ray emitting plasma very close to the base of the wind, perhaps indicating the presence of a corona, while measurements from lower ions conform with the wind-embedded shock model. Generally, to correctly model the emerging X-ray spectra, a detailed knowledge of the cool wind opacities based on stellar atmosphere models is prerequisite. A nearly grey stellar wind opacity for the X-rays is deduced from the analyses of high-resolution X-ray spectra. This indicates that the stellar winds are strongly clumped. Furthermore, the nearly symmetric shape of X-ray emission line profiles can be explained if t...

  11. Berkeley heterodyne interferometer. [for IR stellar observations

    Science.gov (United States)

    Betz, A.

    1975-01-01

    A prototype heterodyne stellar interferometer has been built in order to demonstrate the feasibility of heterodyne techniques in measuring angular diameters of bright infrared stars. The first system tests were performed in December 1972. Attention is given to investigations concerning the possibility that optical air turbulence within the structure of the solar telescope employed can possibly destroy the phase coherence of the fringe signals.

  12. Galactic stellar haloes in the CDM model

    NARCIS (Netherlands)

    Cooper, A. P.; Cole, S.; Frenk, C. S.; White, S. D. M.; Helly, J.; Benson, A. J.; De Lucia, G.; Helmi, A.; Jenkins, A.; Navarro, J. F.; Springel, V.; Wang, J.

    2010-01-01

    We present six simulations of galactic stellar haloes formed by the tidal disruption of accreted dwarf galaxies in a fully cosmological setting. Our model is based on the Aquarius project, a suite of high-resolution N-body simulations of individual dark matter haloes. We tag subsets of particles in

  13. Disentangling stellar activity and planetary signals

    CERN Document Server

    Boisse, I; Hebrard, G; Bonfils, X; Santos, N C; Vauclair, S

    2010-01-01

    Photospheric stellar activity might be an important source of noise and confusion in the radial-velocity measurements. RV planet search surveys as well as follow-up of photometric transit surveys require a deeper understanding and characterization of the effects of stellar activities to disentangle it from planetary signals. We simulate dark spots on a rotating stellar photosphere. The variations of the photometry, RV and spectral line shapes are characterized and analyzed according to the stellar inclination, the latitude and the number of spots. The Lomb-Scargle periodograms of the RV variations induced by activity present power at the rotational period Prot of the star and its two-first harmonics Prot/2 and Prot/3. Three adjusted sinusoids fixed at Prot and its two-first harmonics allow to remove about 90% of the RV jitter amplitude. We apply and validate our approach on four known active planet-host stars: HD189733, GJ674, CoRoT-7 and iHor. We succeed in fitting simultaneously activity and planetary signa...

  14. Exploring the Morphology of RAVE Stellar Spectra

    NARCIS (Netherlands)

    Matijevic, G.; Zwitter, T.; Bienayme, O.; Bland-Hawthorn, J.; Boeche, C.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Grebel, E. K.; Helmi, A.; Munari, U.; Navarro, J.; Parker, Q. A.; Reid, W.; Seabroke, G.; Siebert, A.; Siviero, A.; Steinmetz, M.; Watson, F. G.; Williams, M.; Wyse, R. F. G.

    The RAdial Velocity Experiment (RAVE) is a medium-resolution (R similar to 7500) spectroscopic survey of the Milky Way that has already obtained over half a million stellar spectra. They present a randomly selected magnitude-limited sample, so it is important to use a reliable and automated

  15. The Ancient stellar population of Leo A.

    NARCIS (Netherlands)

    Saha, Abhijit; Fiorentino, Giuliana; Tolstoy, Eline; Cole, Andrew

    2010-01-01

    The primary goal of our proposal is the characterisation of the oldest stellar populations in Leo A using the properties of ancient RR Lyrae variable stars as tracers. Well known and long established correlations exist between the periods and luminosities of RR Lyrae variable stars and their ages an

  16. The resolved stellar population of Leo A

    NARCIS (Netherlands)

    Tolstoy, E

    1996-01-01

    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 Ha filters are presented. Using the recent Cepheid variable star distance determination to Leo A by Hoessel et al., we are able to create an a

  17. Disentangling stellar activity and planetary signals

    Directory of Open Access Journals (Sweden)

    Santos N.C.

    2011-02-01

    Full Text Available Photospheric stellar activity (i.e. dark spots or bright plages might be an important source of noise and confusion in the radial-velocity (RV measurements. Radial-velocimetry planet search surveys as well as follow-up of photometric transit surveys require a deep understanding and precise characterization of the effects of stellar activity, in order to disentangle it from planetary signals. We simulate dark spots on a rotating stellar photosphere. The variations of the RV are characterized and analyzed according to the stellar inclination, the latitude and the number of spots. The Lomb-Scargle periodograms of the RV variations induced by activity present power at the rotational period Prot of the star and its two-first harmonics Prot/2 and Prot/3. Three adjusted sinusoids fixed at the fundamental period and its two-first harmonics allow to remove about 90% of the RV jitter amplitude. We apply and validate our approach on four known active planet-host stars: HD 189733, GJ 674, CoRoT-7 and ι Hor.

  18. The evolution of runaway stellar collision products

    NARCIS (Netherlands)

    Glebbeek, E.; Gaburov, E.; de Mink, S.E.; Pols, O.R.; Portegies Zwart, S.F.

    2009-01-01

    In the cores of young dense star clusters, repeated stellar collisions involving the same object can occur. It has been suggested that this leads to the formation of an intermediate-mass black hole. To verify this scenario we compute the detailed evolution of the merger remnant of three sequences, t

  19. The stellar halo of the Galaxy

    NARCIS (Netherlands)

    Helmi, Amina

    2008-01-01

    Stellar halos may hold some of the best preserved fossils of the formation history of galaxies. They are a natural product of the merging processes that probably take place during the assembly of a galaxy, and hence may well be the most ubiquitous component of galaxies, independently of their Hubble

  20. Division G Commission 35: Stellar Constitution

    Science.gov (United States)

    Limongi, Marco; Lattanzio, John C.; Charbonnel, Corinne; Dominguez, Inma; Isern, Jordi; Karakas, Amanda; Leitherer, Claus; Marconi, Marcella; Shaviv, Giora; van Loon, Jacco

    2016-04-01

    Commission 35 (C35), ``Stellar Constitution'', consists of members of the International Astronomical Union whose research spans many aspects of theoretical and observational stellar physics and it is mainly focused on the comprehension of the properties of stars, stellar populations and galaxies. The number of members of C35 increased progressively over the last ten years and currently C35 comprises about 400 members. C35 was part of Division IV (Stars) until 2014 and then became part of Division G (Stars and Stellar Physics), after the main IAU reorganisation in 2015. Four Working Groups have been created over the years under Division IV, initially, and Division G later: WG on Active B Stars, WG on Massive Stars, WG on Abundances in Red Giant and WG on Chemically Peculiar and Related Stars. In the last decade the Commission had 4 presidents, Wojciech Dziembowski (2003-2006), Francesca D'Antona (2006-2009), Corinne Charbonnel (2009-2012) and Marco Limongi (2012-2015), who were assisted by an Organizing Committee (OC), usually composed of about 10 members, all of them elected by the C35 members and holding their positions for three years. The C35 webpage (http://iau-c35.stsci.edu) has been designed and continuously maintained by Claus Leitherer from the Space Telescope Institute, who deserves our special thanks. In addition to the various general information on the Commission structure and activities, it contains links to various resources, of interest for the members, such as stellar models, evolutionary tracks and isochrones, synthetic stellar populations, stellar yields and input physics (equation of state, nuclear cross sections, opacity tables), provided by various groups. The main activity of the C35 OC is that of evaluating, ranking and eventually supporting the proposals for IAU sponsored meetings. In the last decade the Commission has supported several meetings focused on topics more or less relevant to C35. Since the primary aim of this document is to

  1. A Stellar Stream Surrounds the Whale Galaxy

    Science.gov (United States)

    Kohler, Susanna

    2015-10-01

    The -cold dark matter cosmological model predicts that galaxies are assembled through the disruption and absorption of small satellite dwarf galaxies by their larger hosts. A recent study argues that NGC 4631, otherwise known as the Whale galaxy, shows evidence of such a recent merger in the form of an enormous stellar stream extending from it.Stream SignaturesAccording to the -CDM model, stellar tidal streams should be a ubiquitous feature among galaxies. When satellite dwarf galaxies are torn apart, they spread out into such streams before ultimately feeding the host galaxy. Unfortunately, these streams are very faint, so were only recently starting to detect these features.Stellar tidal streams have been discovered around the Milky Way and Andromeda, providing evidence of these galaxies growth via recent (within the last 8 Gyr) mergers. But discovering stellar streams around other Milky Way-like galaxies would help us to determine if the model of hierarchical galaxy assembly applies generally.To this end, the Stellar Tidal Stream Survey, led by PI David Martnez-Delgado (Center for Astronomy of Heidelberg University), is carrying out the first systematic survey of stellar tidal streams. In a recent study, Martnez-Delgado and collaborators present their detection of a giant (85 kpc long!) stellar tidal stream extending into the halo of NGC 4631, the Whale galaxy.Modeling a SatelliteThe top image is a snapshot from an N-body simulation of a single dwarf satellite, 3.5 Gyr after it started interacting with the Whale galaxy. The satellite has been torn apart and spread into a stream that reproduces observations, which are shown in the lower image (scale is not the same). [Martnez-Delgado et al. 2015]The Whale galaxy is a nearby edge-on spiral galaxy interacting with a second spiral, NGC 4656. But the authors dont believe that the Whale galaxys giant tidal stellar stream is caused by its interactions with NGC 4656. Instead, based on their observations, they believe

  2. Habitability in Different Milky Way Stellar Environments: a Stellar Interaction Dynamical Approach

    CERN Document Server

    Jiménez-Torres, Juan J; Lake, George; Segura, Antígona

    2013-01-01

    Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the Solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the Solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the Solar neighborhood, however, is rather poor, and thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of star...

  3. PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code

    CERN Document Server

    Bressan, A; Girardi, L; Salasnich, B; Cero, C Dal; Rubele, S; Nanni, A

    2012-01-01

    We present the updated version of the code used to compute stellar evolutionary tracks in Padova. It is the result of a thorough revision of the major input physics, together with the inclusion of the pre-main sequence phase, not present in our previous releases of stellar models. Another innovative aspect is the possibility of promptly generating accurate opacity tables fully consistent with any selected initial chemical composition, by coupling the OPAL opacity data at high temperatures to the molecular opacities computed with our AESOPUS code (Marigo & Aringer 2009). In this work we present extended sets of stellar evolutionary models for various initial chemical compositions, while other sets with different metallicities and/or different distributions of heavy elements are being computed. For the present release of models we adopt the solar distribution of heavy elements from the recent revision by Caffau et al. (2011), corresponding to a Sun's metallicity Z=0.0152. From all computed sets of stellar t...

  4. The Dual Origin of Galactic Stellar Halos

    Science.gov (United States)

    Zolotov, Adi

    2011-01-01

    Accreted stellar halos are a natural consequence of galaxy formation in a Lambda-CDM Universe, and contain unique fossil records of hierarchical galaxy formation. The properties of local Milky Way halo stars, however, suggest that the Galaxy's halo is composed of at least two distinct stellar populations, each exhibiting different spatial distributions, orbits, and metallicities. This observed dichotomy is the result of the assembly history of the halo, which likely formed through a process more complex than pure hierarchical accretions. In this talk I will describe the formation of stellar halos surrounding Milky Way-massed disk galaxies simulated using high-resolution cosmological Smooth Particle Hydrodynamics + N-Body simulations. We find that two competing physical processes - accretion of dwarf galaxies and in situ star formation - contribute to the formation of every stellar halo. While the outer regions (r > 20 kpc) of the halos were assembled solely through the accretion and disruption of satellites, in situ star formation supplements accretion in the formation of inner halos. The relative contribution of each stellar population to a halo is shown to be a function of a galaxy's merging history. Galaxies with recent mergers, like M31, will host relatively few in situ stars, while galaxies with more quiescent recent histories, like the Milky Way, will likely have a larger population of such stars. We show how the chemical abundance trends ([Fe/H] vs. [alpha/Fe]) of accreted and in situ stars diverge at the high [Fe/H] end of the metallicity distribution function, and discuss how such trends can be used to study and identify the observable imprints of the Milky Way's formation history.

  5. Free-boundary ideal MHD stability of W7-X divertor equilibria

    Science.gov (United States)

    Nührenberg, C.

    2016-07-01

    Plasma configurations describing the stellarator experiment Wendelstein 7-X (W7-X) are computationally established taking into account the geometry of the test-divertor unit and the high-heat-flux divertor which will be installed in the vacuum chamber of the device (Gasparotto et al 2014 Fusion Eng. Des. 89 2121). These plasma equilibria are computationally studied for their global ideal magnetohydrodynamic (MHD) stability properties. Results from the ideal MHD stability code cas3d (Nührenberg 1996 Phys. Plasmas 3 2401), stability limits, spatial structures and growth rates are presented for free-boundary perturbations. The work focusses on the exploration of MHD unstable regions of the W7-X configuration space, thereby providing information for future experiments in W7-X aiming at an assessment of the role of ideal MHD in stellarator confinement.

  6. Targeted Optimization of Quasi-Symmetric Stellarators (Final Report)

    Energy Technology Data Exchange (ETDEWEB)

    Hegna, Chris [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.

  7. A short review of empirical stellar spectral libraries

    NARCIS (Netherlands)

    Trager, S. C.

    2012-01-01

    I present an overview of empirical stellar spectral libraries, their uses, and (briefly) their history. I focus primarily on their utility for understanding the stellar populations of composite stellar systems, but I show examples of their use for topics ranging from the determination of atmospheric

  8. Ripple transport in Helical-Axis Advanced Stellarators: A comparison with classical stellarator/torsatrons

    Energy Technology Data Exchange (ETDEWEB)

    Beidler, C.D. [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany); Hitchon, W.N.G. [Wisconsin Univ., Madison, WI (United States). Dept. of Electrical and Computer Engineering

    1995-07-01

    Calculations of the neoclassical transport rates due to particles trapped in the helical ripples of a stellarator`s magnetic field are carried out, based on solutions of the bounceaveraged kinetic equation. These calculations employ a model for the magnetic field strength, B, which is an accurate approximation to the actual B for a wide variety of stellarator-type devices, among which are Helical-Axis Advanced Stellarators (Helias) as well as conventional stellarators and torsatrons. Comparisons are carried out in which it is shown that the Helias concept leads to significant reductions in neoclassical transport rates throughout the entire long-mean-free-path regime, with the reduction being particularly dramatic in the {nu}{sup {minus}1} regime. These findings are confirmed by numerical simulations. Further, it is shown that the behavior of deeply trapped particles in Helias can be fundamentally different from that in classical stellarator/torsatrons; as a consequence, the beneficial effects of a radial electric field on the transport make themselves felt at lower collision frequency than is usual.

  9. Constraining the Stellar Mass Function in the Galactic Center via Mass Loss from Stellar Collisions

    Directory of Open Access Journals (Sweden)

    Douglas Rubin

    2011-01-01

    Full Text Available The dense concentration of stars and high-velocity dispersions in the Galactic center imply that stellar collisions frequently occur. Stellar collisions could therefore result in significant mass loss rates. We calculate the amount of stellar mass lost due to indirect and direct stellar collisions and find its dependence on the present-day mass function of stars. We find that the total mass loss rate in the Galactic center due to stellar collisions is sensitive to the present-day mass function adopted. We use the observed diffuse X-ray luminosity in the Galactic center to preclude any present-day mass functions that result in mass loss rates >10-5M⨀yr−1 in the vicinity of ~1″. For present-day mass functions of the form, dN/dM∝M-α, we constrain the present-day mass function to have a minimum stellar mass ≲7M⨀ and a power-law slope ≳1.25. We also use this result to constrain the initial mass function in the Galactic center by considering different star formation scenarios.

  10. A Mega-Grid of CMFGEN Model Atmospheres for Rapid Analysis of Stellar Spectra

    Science.gov (United States)

    Zsargo, J.; Arrieta, A.; Fierro, C.; Klapp, J.; Hillier, D. J.; Arias, L.; Mendoza, J.; Georgiev, L. N.

    2017-02-01

    CMFGEN (Hillier & Miller 1998) is a sophisticated and widely-used non-LTE stellar atmosphere code. It models the full spectrum, and has been used to model OB stars, W-R stars, luminous blue variables, and supernovae. However, it requires the user to have substantial knowledge and experience to run it, and even then a complete analysis of a star can be very difficult and time consuming. Computations and modeling with CMFGEN are greatly eased when suitable initial models are available. To expedite modeling, or to run a quick rudimentary analysis of the stellar spectra, we are undertaking a project to create a mega-grid of pre-calculated CMFGEN models which will be available to the general astronomical community via internet. Tools are also being developed to use this database for analysis.

  11. Super-Eddington stellar winds driven by near-surface energy deposition

    Science.gov (United States)

    Quataert, Eliot; Fernández, Rodrigo; Kasen, Daniel; Klion, Hannah; Paxton, Bill

    2016-05-01

    We develop analytic and numerical models of the properties of super-Eddington stellar winds, motivated by phases in stellar evolution when super-Eddington energy deposition (via, e.g. unstable fusion, wave heating, or a binary companion) heats a region near the stellar surface. This appears to occur in the giant eruptions of luminous blue variables (LBVs), Type IIn supernovae progenitors, classical novae, and X-ray bursts. We show that when the wind kinetic power exceeds Eddington, the photons are trapped and behave like a fluid. Convection does not play a significant role in the wind energy transport. The wind properties depend on the ratio of a characteristic speed in the problem v_crit˜ (dot{E} G)^{1/5} (where dot{E} is the heating rate) to the stellar escape speed near the heating region vesc(rh). For vcrit ≳ vesc(rh), the wind kinetic power at large radii dot{E}_w ˜ dot{E}. For vcrit ≲ vesc(rh), most of the energy is used to unbind the wind material and thus dot{E}_w ≲ dot{E}. Multidimensional hydrodynamic simulations without radiation diffusion using FLASH and one-dimensional hydrodynamic simulations with radiation diffusion using MESA are in good agreement with the analytic predictions. The photon luminosity from the wind is itself super-Eddington but in many cases the photon luminosity is likely dominated by `internal shocks' in the wind. We discuss the application of our models to eruptive mass-loss from massive stars and argue that the wind models described here can account for the broad properties of LBV outflows and the enhanced mass-loss in the years prior to Type IIn core-collapse supernovae.

  12. Constraining stellar physics from red-giant stars in binaries - stellar rotation, mixing processes and stellar activity

    CERN Document Server

    Beck, P G; Pavlovski, K; Palacios, A; Tkachenko, A; García, R A; Mathis, S; Corsaro, E; Johnston, C; Mosser, B; Ceillier, T; Nascimento, J -D do; Raskin, G

    2016-01-01

    The unparalleled photometric data obtained by NASA's Kepler Space Telescope has led to an improved understanding of stellar structure and evolution - in particular for solar-like oscillators in this context. Binary stars are fascinating objects. Because they were formed together, binary systems provide a set of two stars with very well constrained parameters. Those can be used to study properties and physical processes, such as the stellar rotation, dynamics and rotational mixing of elements and allows us to learn from the differences we find between the two components. In this work, we discussed a detailed study of the binary system KIC9163796, discovered through Kepler photometry. The ground-based follow-up spectroscopy showed that this system is a double-lined spectroscopic binary, with a mass ratio close to unity. However, the fundamental parameters of the components of this system as well as their lithium abundances differ substantially. Kepler photometry of this system allows to perform a detailed seism...

  13. eSTOMP-W

    Energy Technology Data Exchange (ETDEWEB)

    2017-02-17

    STOMP is a numerical simulator, developed by PNNL, for solving problems involving multi-fluid coupled flow and reactive transport in geologic media. The code has been under development at PNNL for more than twenty-five years. This release of STOMP will allow users to directly access the software, and will be limited to selected operational modes. The initial release will include STOMP-W. Additional operational modes will be released depending on market trends and user needs.The STOMP simulator has been available to parties outside of PNNL via license agreements. A new trend in projects supported by the U.S. government is that software be available as open source. This release of the STOMP software will meet that need. The initial target operational mode, STOMP-W, is one that solves isothermal problems involving variably saturated geologic systems with nonreactive solutes and reactive species. The capabilities of this simulator are often applied to environmental stewardship and restoration problems, such as those at the Hanford Site.

  14. QUANTIZATION DEFORMS W-INFINITY TO W-INFINITY GRAVITY

    NARCIS (Netherlands)

    BERGSHOEFF, E; HOWE, PS; POPE, CN; SEZGIN, E; SHEN, [No Value; STELLE, KS

    1991-01-01

    Quantising a classical theory of w infinity gravity requires the introduction of an infinite number of counterterms in order to remove matter-dependent anomalies. We show that these counterterms correspond precisely to a renormalisation of the classical w infinity currents to quantum W(x) currents.

  15. The Search for Stellar Coronal Mass Ejections

    Science.gov (United States)

    Villadsen, Jacqueline Rose

    2017-05-01

    Coronal mass ejections (CMEs) may dramatically impact habitability and atmospheric composition of planets around magnetically active stars, including young solar analogs and many M dwarfs. Theoretical predictions of such effects are limited by the lack of observations of stellar CMEs. This thesis addresses this gap through a search for the spectral and spatial radio signatures of CMEs on active M dwarfs. Solar CMEs produce radio bursts with a distinctive spectral signature, narrow-band plasma emission that drifts to lower frequency as a CME expands outward. To search for analogous events on nearby stars, I worked on system design, software, and commissioning for the Starburst project, a wideband single-baseline radio interferometry backend dedicated to stellar observations. In addition, I led a survey of nearby active M dwarfs with the Karl G. Jansky Very Large Array (VLA), detecting coherent radio bursts in 13 out of 23 epochs, over a total of 58 hours. This survey's ultra-wide bandwidth (0.23-6.0 GHz) dynamic spectroscopy, unprecedented for stellar observations, revealed diverse behavior in the time-frequency plane. Flare star UV Ceti produced complex, luminous events reminiscent of brown dwarf aurorae; AD Leo sustained long-duration, intense, narrow-band "storms"; and YZ CMi emitted a burst with substructure with rapid frequency drift, resembling solar Type III bursts, which are attributed to electrons moving at speeds of order 10% of the speed of light. To search for the spatial signature of CMEs, I led 8.5-GHz observations with the Very Long Baseline Array simultaneous to 24 hours of the VLA survey. This program detected non-thermal continuum emission from the stars in all epochs, as well as continuum flares on AD Leo and coherent bursts on UV Ceti, enabling measurement of the spatial offset between flaring and quiescent emission. These observations demonstrate the diversity of stellar transients that can be expected in time-domain radio surveys, especially

  16. The Search for Stellar Coronal Mass Ejections

    Science.gov (United States)

    Villadsen, Jacqueline; Hallinan, Gregg; Monroe, Ryan; Bourke, Stephen; Starburst Program Team

    2017-01-01

    Coronal mass ejections (CMEs) may dramatically impact habitability and atmospheric composition of planets around magnetically active stars, including young solar analogs and many M dwarfs. Theoretical predictions of such effects are limited by the lack of observations of stellar CMEs. My thesis addresses this gap through a search for the spectral and spatial radio signatures of CMEs on active M dwarfs.Solar CMEs produce radio bursts with a distinctive spectral signature, narrow-band plasma emission that drifts to lower frequency as a CME expands outward. To search for analogous events on nearby stars, I worked on system design, software, and commissioning for the Starburst project, a wideband single-baseline radio interferometry backend dedicated to stellar observations. In addition, I led a survey of nearby active M dwarfs with the Karl G. Jansky Very Large Array (JVLA), detecting 12 bright (>10 mJy) radio bursts in 58 hours. This survey’s ultra-wide bandwidth (0.23-6.0 GHz) dynamic spectroscopy, unprecedented for stellar observations, revealed diverse behavior in the time-frequency plane. Flare star UV Ceti produced complex, luminous events reminiscent of brown dwarf aurorae; AD Leo sustained long-duration, intense, narrow-band "storms"; and YZ CMi emitted a burst with substructure with rapid frequency drift, resembling solar Type III bursts, which are attributed to electrons moving at speeds of order 10% of the speed of light.To search for the spatial signature of CMEs, I led 8.5-GHz observations with the Very Long Baseline Array simultaneous to 24 hours of the JVLA survey. This program detected non-thermal continuum emission from the stars in all epochs, as well as continuum flares on AD Leo and coherent bursts on UV Ceti, enabling measurement of the spatial offset between flaring and quiescent emission.These observations demonstrate the diversity of stellar transients that can be expected in time-domain radio surveys, especially with the advent of large low

  17. BONNSAI: correlated stellar observables in Bayesian methods

    Science.gov (United States)

    Schneider, F. R. N.; Castro, N.; Fossati, L.; Langer, N.; de Koter, A.

    2017-02-01

    In an era of large spectroscopic surveys of stars and big data, sophisticated statistical methods become more and more important in order to infer fundamental stellar parameters such as mass and age. Bayesian techniques are powerful methods because they can match all available observables simultaneously to stellar models while taking prior knowledge properly into account. However, in most cases it is assumed that observables are uncorrelated which is generally not the case. Here, we include correlations in the Bayesian code Bonnsai by incorporating the covariance matrix in the likelihood function. We derive a parametrisation of the covariance matrix that, in addition to classical uncertainties, only requires the specification of a correlation parameter that describes how observables co-vary. Our correlation parameter depends purely on the method with which observables have been determined and can be analytically derived in some cases. This approach therefore has the advantage that correlations can be accounted for even if information for them are not available in specific cases but are known in general. Because the new likelihood model is a better approximation of the data, the reliability and robustness of the inferred parameters are improved. We find that neglecting correlations biases the most likely values of inferred stellar parameters and affects the precision with which these parameters can be determined. The importance of these biases depends on the strength of the correlations and the uncertainties. For example, we apply our technique to massive OB stars, but emphasise that it is valid for any type of stars. For effective temperatures and surface gravities determined from atmosphere modelling, we find that masses can be underestimated on average by 0.5σ and mass uncertainties overestimated by a factor of about 2 when neglecting correlations. At the same time, the age precisions are underestimated over a wide range of stellar parameters. We conclude that

  18. 3D Maxwell-Vlasov boundary value problem solution in stellarator geometry in ion cyclotron frequency range. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Vdovin, V.; Watari, T.; Fukuyama, A.

    1996-12-01

    We develop the theory for the wave excitation, propagation and absorption in 3-dimensional (3D) stellarator equilibrium high beta plasma in ion cyclotron frequency range (ICRF). This theory forms a basis for a 3D code creation, urgently needed for the ICRF heating scenarios development for the constructed LHD and projected W7-X stellarators and for the stellarators being at operation (like CHS, W7-AS, etc.). The theory solves the 3D Maxwell-Vlasov antenna-plasma-conducting shell boundary value problem in the non - orthogonal flux coordinates ({psi}, {theta}, {phi}), {psi} being magnetic flux function, {theta} and {phi} being the poloidal and toroidal angles, respectively. All basic physics, like wave refraction, reflection and diffraction are firstly self consistently included, along with the fundamental ion and ion minority cyclotron resonances, two ion hybrid resonance, electron Landau and TTMP absorption. Antenna reactive impedance and loading resistance are also calculated and urgently needed for an antenna -generator matching. This is accomplished in a real confining magnetic field being varying in a plasma major radius direction, in toroidal and poloidal directions, through making use of the hot dense plasma dielectric kinetic tensor. The theory is developed in a manner that includes tokamaks and magnetic mirrors as the particular cases through general metric tensor (provided by an equilibrium solver) treatment of the wave equations. We describe the structure of newly developed stellarator ICRF 3D full wave code STELION, based on theory described in this report. (J.P.N.)

  19. Welding Development W87 Baseline

    Energy Technology Data Exchange (ETDEWEB)

    A. Newman; G. Gibbs; G. K. Hicken

    1998-11-01

    This report covers the development activities used to qualify the Gas Tungsten Arc (FTA) girth weld and the resistance stem attachments on the W87 Base Line (W87BL). Design of experiments was used throughout the development activities.

  20. Designs of Langmuir probes for W7-X

    Energy Technology Data Exchange (ETDEWEB)

    Laube, Ralph, E-mail: ralph.laube@ipp.mpg.de [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Teilinstitut Greifswald, Wendelsteinstr. 1, D-17491 Greifswald (Germany); Laux, Michael; Ye, Min You [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Teilinstitut Greifswald, Wendelsteinstr. 1, D-17491 Greifswald (Germany); Greuner, Henri; Lindig, Stefan [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Boltzmannstr. 2, D-85748 Garching (Germany)

    2011-10-15

    Several designs of Langmuir probes for the stellarator Wendelstein 7-X (W7-X) are described. Different types of probes are proposed for the different divertors to be used during different operational phases of W7-X. Comb-like arrays of stiff probes, arrays of flexible probes, and fixed inlay probes are reviewed. For the initial phase of W7-X it was decided to install arrays of fixed inlay probes. Two mockups were manufactured and one of them was tested with success in the high heat flux test facility GLADIS. For long-pulse operation of W7-X different conceptual designs are proposed and are still developed further. This paper summarizes the different design constrains for the Langmuir probes in the different divertor surroundings, describes the design of the array of inlay probes for the initial phase and the result of the GLADIS test, and gives a preview of the conceptual designs of probes for the long-pulse operational phase of W7-X.

  1. Radial Velocity Planet Detection Biases at the Stellar Rotational Period

    CERN Document Server

    Vanderburg, Andrew; Johnson, John Asher; Ciardi, David R; Swift, Jonathan; Kane, Stephen R

    2016-01-01

    Future generations of precise radial velocity (RV) surveys aim to achieve sensitivity sufficient to detect Earth mass planets orbiting in their stars' habitable zones. A major obstacle to this goal is astrophysical radial velocity noise caused by active areas moving across the stellar limb as a star rotates. In this paper, we quantify how stellar activity impacts exoplanet detection with radial velocities as a function of orbital and stellar rotational periods. We perform data-driven simulations of how stellar rotation affects planet detectability and compile and present relations for the typical timescale and amplitude of stellar radial velocity noise as a function of stellar mass. We show that the characteristic timescales of quasi-periodic radial velocity jitter from stellar rotational modulations coincides with the orbital period of habitable zone exoplanets around early M-dwarfs. These coincident periods underscore the importance of monitoring the targets of RV habitable zone planet surveys through simul...

  2. Accretion disks in luminous young stellar objects

    CERN Document Server

    Beltran, M T

    2015-01-01

    An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and therefore predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates.

  3. Probabilistic Catalogs for Crowded Stellar Fields

    CERN Document Server

    Brewer, Brendon J; Hogg, David W

    2012-01-01

    We introduce a probabilistic (Bayesian) method for producing catalogs from images of crowded stellar fields. The method is capable of inferring the number of sources (N) in the image and can also handle the challenges introduced by overlapping sources. The luminosity function of the stars can also be inferred even when the precise luminosity of each star is uncertain. This is in contrast with standard techniques which produce a single catalog, potentially underestimating the uncertainties in any study of the stellar population and discarding information about sources at or below the detection limit. The method is implemented using advanced Markov Chain Monte Carlo (MCMC) techniques including Reversible Jump and Nested Sampling. The computational feasibility of the method is demonstrated on simulated data where the luminosity function of the stars is a broken power-law. The parameters of the luminosity function can be recovered with moderate uncertainties. We compare the results obtained from our method with t...

  4. Stellar evolution as seen by mixed modes

    Directory of Open Access Journals (Sweden)

    Mosser Benoît

    2015-01-01

    Full Text Available The detection of mixed modes in subgiants and red giants allows us to monitor stellar evolution from the main sequence to the asymptotic giant branch and draw seismic evolutionary tracks. Quantified asteroseismic definitions that characterize the change in the evolutionary stages have been defined. This seismic information can now be used for stellar modelling, especially for studying the energy transport in the helium burning core or for specifying the inner properties of stars all along their evolution. Modelling will also allow us to study stars identified in the helium subflash stage, high-mass stars either arriving or quitting the secondary clump, or stars that could be in the blue-loop stage.

  5. Physics of stellar evolution and cosmology

    Science.gov (United States)

    Goldberg, H. S.; Scadron, M. D.

    Astrophysical phenomena are examined on a fundamental level, stressing basic physical laws, in a textbook suitable for a one-semester intermediate course. The ideal gas law, the meaning of temperature, black-body radiation, discrete spectra, and the Doppler effect are introduced and used to study such features of the interstellar medium as 21-cm radiation, nebulae and dust, and the galactic magnetic field. The phases of stellar evolution are discussed, including stellar collapse, quasi-hydrostatic equilibrium, the main sequence, red giants, white dwarves, neutron stars, supernovae, pulsars, and black holes. Among the cosmological topics covered are the implications of Hubble's constant, the red-shift curve, the steady-state universe, the evolution of the big bang (thermal equilibrium, hadron era, lepton era, primordial nucleosynthesis, hydrogen recombination, galaxy formation, and the cosmic fireball), and the future (cold end or big crunch).

  6. Preferred longitudes in solar and stellar activity

    Science.gov (United States)

    Berdyugina, S. V.

    An analysis of the distribution of starspots on the surfaces of very active stars, such as RS CVn- FK Com-type stars as well as young solar analogs, reveals preferred longitudes of spot formation and their quasi-periodic oscillations, i.e. flip-flop cycles. A non-linear migration of the preferred longitudes suggests the presence of the differential rotation and variations of mean spot latitudes. It enables recovering stellar butterfly diagrams. Such phenomena are found to persist in the sunspot activity as well. A comparison of the observed properties of preferred longitudes on the Sun with those detected on more active stars leads to the conclusion that we can learn fine details of the stellar dynamo by studying the Sun, while its global parameters on the evolutionary time scale are provided by a sample of active stars.

  7. Resolved Host Studies of Stellar Explosions

    CERN Document Server

    Levesque, Emily M

    2016-01-01

    The host galaxies of nearby (z<0.3) core-collapse supernovae and long-duration gamma-ray bursts offer an excellent means of probing the environments and populations that produce these events' varied massive progenitors. These same young stellar progenitors make LGRBs and SNe valuable and potentially powerful tracers of star formation, metallicity, the IMF, and the end phases of stellar evolution. However, properly utilizing these progenitors as tools requires a thorough understanding of their formation and, consequently, the physical properties of their parent host environments. This review looks at some of the recent work on LGRB and SN hosts with resolved environments that allows us to probe the precise explosion sites and surrounding environments of these events in incredible detail.

  8. Onion-peeling inversion of stellarator images

    Science.gov (United States)

    Hammond, K. C.; Diaz-Pacheco, R. R.; Kornbluth, Y.; Volpe, F. A.; Wei, Y.

    2016-11-01

    An onion-peeling technique is developed for inferring the emissivity profile of a stellarator plasma from a two-dimensional image acquired through a CCD or CMOS camera. Each pixel in the image is treated as an integral of emission along a particular line-of-sight. Additionally, the flux surfaces in the plasma are partitioned into discrete layers, each of which is assumed to have uniform emissivity. If the topology of the flux surfaces is known, this construction permits the development of a system of linear equations that can be solved for the emissivity of each layer. We present initial results of this method applied to wide-angle visible images of the Columbia Neutral Torus (CNT) stellarator plasma.

  9. Onion-peeling inversion of stellarator images

    CERN Document Server

    Hammond, K C; Kornbluth, Y; Volpe, F A; Wei, Y

    2016-01-01

    An onion-peeling technique is developed for inferring the emissivity profile of a stellarator plasma from a two-dimensional image acquired through a CCD or CMOS camera. Each pixel in the image is treated as an integral of emission along a particular line-of-sight. Additionally, the flux surfaces in the plasma are partitioned into discrete layers, each of which is assumed to have uniform emissivity. If the topology of the flux surfaces is known, this construction permits the development of a system of linear equations that can be solved for the emissivity of each layer. We present initial results of this method applied to wide-angle visible images of the CNT stellarator plasma.

  10. Star Formation & Stellar Evolution: Future Surveys & Instrumentation

    CERN Document Server

    Evans, C J

    2015-01-01

    The next generation of multi-object spectrographs (MOS) will deliver comprehensive surveys of the Galaxy, Magellanic Clouds and nearby dwarfs. These will provide us with the vast samples, spanning the full extent of the Hertzsprung-Russell diagram, that are needed to explore the chemistry, history and dynamics of their host systems. Further ahead, the Extremely Large Telescopes (ELTs) will have sufficient sensitivity and angular resolution to extend stellar spectroscopy well beyond the Local Group, opening-up studies of the chemical evolution of galaxies across a broad range of galaxy types and environments. In this contribution I briefly reflect on current and future studies of stellar populations, and introduce plans for the MOSAIC instrument for the European ELT.

  11. ASteCA - Automated Stellar Cluster Analysis

    CERN Document Server

    Perren, Gabriel I; Piatti, Andrés E

    2014-01-01

    We present ASteCA (Automated Stellar Cluster Analysis), a suit of tools designed to fully automatize the standard tests applied on stellar clusters to determine their basic parameters. The set of functions included in the code make use of positional and photometric data to obtain precise and objective values for a given cluster's center coordinates, radius, luminosity function and integrated color magnitude, as well as characterizing through a statistical estimator its probability of being a true physical cluster rather than a random overdensity of field stars. ASteCA incorporates a Bayesian field star decontamination algorithm capable of assigning membership probabilities using photometric data alone. An isochrone fitting process based on the generation of synthetic clusters from theoretical isochrones and selection of the best fit through a genetic algorithm is also present, which allows ASteCA to provide accurate estimates for a cluster's metallicity, age, extinction and distance values along with its unce...

  12. Simulating Stellar Cluster Formation and Early Evolution

    Science.gov (United States)

    Wall, Joshua; McMillan, Stephen L. W.; Mac Low, Mordecai-Mark; Ibañez-Mejia, Juan; Portegies Zwart, Simon; Pellegrino, Andrew

    2017-01-01

    We present our current development of a model of stellar cluster formation and evolution in the presence of stellar feedback. We have integrated the MHD code Flash into the Astrophysical Multi-Use Software Environment (AMUSE) and coupled the gas dynamics to an N-body code using a Fujii gravity bridge. Further we have integrated feedback from radiation using the FERVENT module for Flash, supernovae by thermal and kinetic energy injection, and winds by kinetic energy injection. Finally we have developed a method of implementing star formation using the Jeans criterion of the gas. We present initial results from our cluster formation model in a cloud using self-consistent boundary conditions drawn from a model of supernova-driven interstellar turbulence.

  13. Numerical simulations of stellar winds polytropic models

    CERN Document Server

    Keppens, R

    1999-01-01

    We discuss steady-state transonic outflows obtained by direct numerical solution of the hydrodynamic and magnetohydrodynamic equations. We make use of the Versatile Advection Code, a software package for solving systems of (hyperbolic) partial differential equations. We proceed stepwise from a spherically symmetric, isothermal, unmagnetized, non-rotating Parker wind to arrive at axisymmetric, polytropic, magnetized, rotating models. These represent 2D generalisations of the analytical 1D Weber-Davis wind solution, which we obtain in the process. Axisymmetric wind solutions containing both a `wind' and a `dead' zone are presented. Since we are solving for steady-state solutions, we efficiently exploit fully implicit time stepping. The method allows us to model thermally and/or magneto-centrifugally driven stellar outflows. We particularly emphasize the boundary conditions imposed at the stellar surface. For these axisymmetric, steady-state solutions, we can use the knowledge of the flux functions to verify the...

  14. Stellar Wind Erosion of Protoplanetary Discs

    CERN Document Server

    Schnepf, Neesha R; Romanova, Marina

    2014-01-01

    An analytic model is developed for the erosion of protoplanetary gas discs by high velocity magnetized stellar winds. The winds are centrifugally driven from the surface of rapidly rotating, strongly magnetized young stars. The presence of the magnetic field in the wind leads to Reynolds numbers sufficiently large to cause a strongly turbulent wind/disk boundary layer which entrains and carries away the disc gas. The model uses the conservation of mass and momentum in the turbulent boundary layer. The time-scale for significant erosion depends on the disc accretion speed, accretion rate and on the wind mass loss rate. The time-scale is estimated to be ~2E6 yr. The stellar wind erosion may act in conjunction with photo-evaporation of the discs.

  15. The Doubling of Stellar Black Hole Nuclei

    CERN Document Server

    Kazandjian, Mher V

    2012-01-01

    It is strongly believed that Andromeda's double nucleus signals a disk of stars revolving around its central super-massive black hole on eccentric Keplerian orbits with nearly aligned apsides. A self-consistent stellar dynamical origin for such apparently long-lived alignment has so far been lacking, with indications that cluster self-gravity is capable of sustaining such lopsided configurations if and when stimulated by external perturbations. Here, we present results of N-body simulations which show unstable counter-rotating stellar clusters around super-massive black holes saturating into uniformly precessing lopsided nuclei. The double nucleus in our featured experiment decomposes naturally into a thick eccentric disk of apo-apse aligned stars which is embedded in a lighter triaxial cluster. The eccentric disk reproduces key features of Keplerian disk models of Andromeda's double nucleus; the triaxial cluster has a distinctive kinematic signature which is evident in HST observations of Andromeda's double ...

  16. BONNSAI: correlated stellar observables in Bayesian methods

    CERN Document Server

    Schneider, F R N; Fossati, L; Langer, N; de Koter, A

    2016-01-01

    In an era of large spectroscopic surveys of stars and big data, sophisticated statistical methods become more and more important in order to infer fundamental stellar parameters such as mass and age. Bayesian techniques are powerful methods because they can match all available observables simultaneously to stellar models while taking prior knowledge properly into account. However, in most cases it is assumed that observables are uncorrelated which is generally not the case. Here, we include correlations in the Bayesian code BONNSAI by incorporating the covariance matrix in the likelihood function. We derive a parametrisation of the covariance matrix that, in addition to classical uncertainties, only requires the specification of a correlation parameter that describes how observables co-vary. Our correlation parameter depends purely on the method with which observables have been determined and can be analytically derived in some cases. This approach therefore has the advantage that correlations can be accounte...

  17. Neoclassical Viscosities and Anomalous Flows in Stellarators

    Science.gov (United States)

    Ware, A. S.; Spong, D. A.; Breyfogle, M.; Marine, T.

    2009-05-01

    We present initial work to use neoclassical viscosities calculated with the PENTA code [1] in a transport model that includes Reynolds stress generation of flows [2]. The PENTA code uses a drift kinetic equation solver to calculate neoclassical viscosities and flows in general three-dimensional geometries over a range of collisionalities. The predicted neoclassical viscosities predicted by PENTA can be flux-surfaced average and applied in a 1-D transport model that includes anomalous flow generation. This combination of codes can be used to test the impact of stellarator geometry on anomalous flow generation. As a test case, we apply the code to modeling flows in the HSX stellarator. Due to variations in the neoclassical viscosities, HSX can have strong neoclassical flows in the core region. In turn, these neoclassical flows can provide a seed for anomalous flow generation. [1] D. A. Spong, Phys. Plasmas 12, 056114 (2005). [2] D. E. Newman, et al., Phys. Plasmas 5, 938 (1998).

  18. Measuring stellar granulation during planet transits

    CERN Document Server

    Chiavassa, A; Selsis, F; Leconte, J; Von Paris, P; Bordé, P; Magic, Z; Collet, R; Asplund, M

    2016-01-01

    Stellar activity and convection-related surface structures might cause bias in planet detection and characterization that use these transits. Surface convection simulations help to quantify the granulation signal. We used realistic three-dimensional radiative hydrodynamical simulations from the Stagger grid and synthetic images computed with the radiative transfer code Optim3D to model the transits of three prototype planets: a hot Jupiter, a hot Neptune, and a terrestrial planet. We computed intensity maps from RHD simulations of the Sun and a K-dwarf star at different wavelength bands from optical to far-infrared. We modeled the transit using synthetic stellar-disk images and emulated the temporal variation of the granulation intensity. We identified two types of granulation noise that act simultaneously during the planet transit: (i) the intrinsic change in the granulation pattern with timescales smaller than the usual planet transit, and (ii) the fact that the transiting planet occults isolated regions of...

  19. Star clusters as simple stellar populations

    CERN Document Server

    Bruzual, A Gustavo

    2009-01-01

    In this paper, I review to what extent we can understand the photometric properties of star clusters, and of low-mass, unresolved galaxies, in terms of population synthesis models designed to describe `simple stellar populations' (SSPs), i.e., groups of stars born at the same time, in the same volume of space, and from a gas cloud of homogeneous chemical composition. The photometric properties predicted by these models do not readily match the observations of most star clusters, unless we properly take into account the expected variation in the number of stars occupying sparsely populated evolutionary stages, due to stochastic fluctuations in the stellar initial mass function. In this case, population synthesis models reproduce remarkably well the full ranges of observed integrated colours and absolute magnitudes of star clusters of various ages and metallicities. The disagreement between the model predictions and observations of cluster colours and magnitudes may indicate problems with or deficiencies in the...

  20. Stellar Variability Effects on Transit Spectroscopy

    Science.gov (United States)

    Zellem, Robert Thomas; Swain, Mark R.; Shkolnik, Evgenya; Line, Michael R.; Llama, Joe

    2016-10-01

    Stellar variability caused by surface magnetic activity poses a great challenge to accurately and precisely characterize the atmospheres of transiting exoplanets. We present a preliminary analysis of the effects of unocculted star spots at IR wavelengths on planetary transmission and emission spectra. We will explore how stellar variability changes the derived exoplanet atmospheric parameters inferred through retrievals for a group of exoplanetary hosts stars. Our study includes stars ranging in activity levels from an inactive sun to a very active late-type star, and a range of planetary masses from super-Earths to Jupiters. These effects will be especially important for the high precision measurements (TESS orbiting nearby M dwarfs, which are more active than solar-type stars.

  1. Disc formation from stellar tidal disruptions

    CERN Document Server

    Bonnerot, Clément; Lodato, Giuseppe; Price, Daniel J

    2015-01-01

    The potential of tidal disruption of stars to probe otherwise quiescent supermassive black holes cannot be exploited, if their dynamics is not fully understood. So far, the observational appearance of these events has been commonly derived from analytical extrapolations of the debris dynamical properties just after the stellar disruption. In this paper, we perform hydrodynamical simulations of stars in highly eccentric orbits, that follow the stellar debris after disruption and investigate their ultimate fate. We demonstrate that gas debris circularize on an orbital timescale because relativistic apsidal precession causes the stream to self-cross. The higher the eccentricity and/or the deeper the encounter, the faster is the circularization. If the internal energy deposited by shocks during stream self-interaction is readily radiated, the gas forms a narrow ring at the circularization radius. It will then proceed to accrete viscously at a super-Eddington rate, puffing up under radiation pressure. If instead c...

  2. Modular stellarator reactor: a fusion power plant

    Energy Technology Data Exchange (ETDEWEB)

    Miller, R.L.; Bathke, C.G.; Krakowski, R.A.; Heck, F.M.; Green, L.; Karbowski, J.S.; Murphy, J.H.; Tupper, R.B.; DeLuca, R.A.; Moazed, A.

    1983-07-01

    A comparative analysis of the modular stellarator and the torsatron concepts is made based upon a steady-state ignited, DT-fueled, reactor embodiment of each concept for use as a central electric-power station. Parametric tradeoff calculations lead to the selection of four design points for an approx. 4-GWt plant based upon Alcator transport scaling in l = 2 systems of moderate aspect ratio. The four design points represent high-aspect ratio. The four design points represent high-(0.08) and low-(0.04) beta versions of the modular stellarator and torsatron concepts. The physics basis of each design point is described together with supporting engineering and economic analyses. The primary intent of this study is the elucidation of key physics and engineering tradeoffs, constraints, and uncertainties with respect to the ultimate power reactor embodiment.

  3. Stellar model atmospheres with magnetic line blanketing

    CERN Document Server

    Kochukhov, O; Shulyak, D

    2004-01-01

    Model atmospheres of A and B stars are computed taking into account magnetic line blanketing. These calculations are based on the new stellar model atmosphere code LLModels which implements direct treatment of the opacities due to the bound-bound transitions and ensures an accurate and detailed description of the line absorption. The anomalous Zeeman effect was calculated for the field strengths between 1 and 40 kG and a field vector perpendicular to the line of sight. The model structure, high-resolution energy distribution, photometric colors, metallic line spectra and the hydrogen Balmer line profiles are computed for magnetic stars with different metallicities and are discussed with respect to those of non-magnetic reference models. The magnetically enhanced line blanketing changes the atmospheric structure and leads to a redistribution of energy in the stellar spectrum. The most noticeable feature in the optical region is the appearance of the 5200 A depression. However, this effect is prominent only in ...

  4. Survey of stellar associations using proper motions

    Directory of Open Access Journals (Sweden)

    C. Abad

    2001-01-01

    Full Text Available Stellar Proper Motions can be represented as great circles over the Celestial Sphere. This point of view creates a geometry over the sphere where the study of parallelism of the motions is possible in an easy form. Calculus of intersections between circles can detect convergence point of motions. This means parallel spatial motion. The model can be carried out to open stars clusters, identifying convergence points as apex, in order to get membership probabilities or, in a general form, to stars of our galaxy to detect big stellar structures and to infer some details about their kinematics. We present here a short description of the model and some examples using stars of the Hipparcos catalogue.

  5. Nitrogen abundances and multiple stellar populations in the globular clusters of the Fornax dSph

    CERN Document Server

    Larsen, S S; Grundahl, F; Strader, J

    2014-01-01

    We use measurements of nitrogen abundances in red giants to search for multiple stellar populations in the four most metal-poor globular clusters (GCs) in the Fornax dwarf spheroidal galaxy (Fornax 1, 2, 3, and 5). New imaging in the F343N filter, obtained with the Wide Field Camera 3 on the Hubble Space Telescope, is combined with archival F555W and F814W observations to determine the strength of the NH band near 3370 AA. After accounting for observational errors, the spread in the F343N-F555W colors of red giants in the Fornax GCs is similar to that in M15 and corresponds to an abundance range of Delta([N/Fe])=2 dex, as observed also in several Galactic GCs. The spread in F555W-F814W is, instead, fully accounted for by observational errors. The stars with the reddest F343N-F555W colors (indicative of N-enhanced composition) have more centrally concentrated radial distributions in all four clusters, although the difference is not highly statistically significant within any individual cluster. From double-Gau...

  6. Design of a remote steering antenna for ECRH heating in the stellarator Wendelstein 7-X

    Energy Technology Data Exchange (ETDEWEB)

    Plaum, B., E-mail: plaum@igvp.uni-stuttgart.de [Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie (IGVP), Univ. Stuttgart, Pfaffenwaldring 31, D-70569 Stuttgart (Germany); Lechte, C.; Kasparek, W.; Gaiser, S.; Zeitler, A. [Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie (IGVP), Univ. Stuttgart, Pfaffenwaldring 31, D-70569 Stuttgart (Germany); Erckmann, V. [Max-Planck-Institut für Plasmaphysik, EURATOM-IPP, D-17491 Greifswald (Germany); Weißgerber, M. [Max-Planck-Institut für Plasmaphysik, EURATOM-IPP, D-85748 Garching (Germany); Bechtold, A. [NTG Neue Technologie GmbH & Co KG, D-63571 Gelnhausen (Germany); Busch, M.; Szcepaniak, B. [Galvano-T electroplating-electroforming GmbH, D-51570 Windeck-Rosbach (Germany)

    2015-10-15

    Highlights: • We report about the design activities for the remote steering antennas for the stellarator W7-X. • The integration into the W7-X system and the manufacturing procedure are described. • Simulations and loss measurements for the waveguide walls were done and are in good agreement. • A method for extending the steering range is presented. • A mechanical deformation analysis showed that the deformation is not critical for the beam quality. - Abstract: For the ECRH heating system of the stellarator Wendelstein 7-X, two remote steering antennas are developed and manufactured. The principle of remote steering antennas is based on the imaging characteristics of corrugated rectangular waveguides, which is well understood and can accurately be simulated. Several details, however, require deeper investigation. The antenna needs a miter-bend and a 24 mm gap. The positions of these elements need to be chosen carefully to reduce losses and stray radiation. The antennas are manufactured from copper by electroforming. This allows to integrate all components, including the corrugated inner walls and the cooling channels, in one vacuum-tight piece. This paper reviews the design process of the remote steering antennas for W7-X as well as technological issues and experimental results from test pieces.

  7. Ekspansja muzeów w Europie Środkowej?

    Directory of Open Access Journals (Sweden)

    Jagodzińska, Katarzyna

    2015-06-01

    Full Text Available Przedmiotem artykułu są rozważania na temat specyfiki Europy Środkowej w zakresie kolekcji i muzeów sztuki współczesnej oraz możliwość stworzenia alternatywy regionalnej dla krajów zachodnich. Kontekstem dla tych rozważań jest ekspansjonistyczna polityka współczesnych muzeów, która w związku z licznymi nowymi inwestycjami – w szczególności Luwru, Fundacji Guggenheima, Ermitażu – budzi w świecie muzeologicznym różnorakie dylematy. Autorka omawia światowe "marki muzealne" inwestujące w Europie Środkowej, zastanawia się nad skutkami ekspansji tych "koncernów" dla kultury w regionie, wskazuje też na potencjał regionu, który można wykorzystać bez posiłkowania się nazwiskami światowych kolekcjonerów.

  8. Solar Twins and Stellar Maunder Minima

    Science.gov (United States)

    Hall, Jeffrey C.

    2012-05-01

    In 1966, Olin C. Wilson undertook an answer to the question “Does the chromospheric activity of main-sequence stars vary with time, and if so, how?”, initiating the so-called HK Project at Mount Wilson Observatory, which resulted in a magnificent 43-year data set and which has spawned a number of complementary synoptic programs in both hemispheres. Subsequent developments, in particular the realization that activity controls angular momentum evolution in the stars and Sun, that solar activity modulates irradiance, and that there was a pronounced response of terrestrial climate to the Maunder Minimum, spurred efforts to identify solar twins, stars that Giusa Cayrel de Strobel required to possess “fundamental physical parameters very similar, if not identical to those of the Sun.” Non-cycling states appear to occur in the Mount Wilson stars and in other synoptic data with about the same frequency that the Sun’s grand minima occur in the long-term proxy record, suggesting that stellar analogs of the Maunder Minimum may be used to guide understanding of the Sun’s state in the late seventeenth century and, as appears possible given the extended Cycle 23/24 minimum, in the near future. However, the magnitude limits of the existing surveys have kept the sample of solar twins small and long-term monitoring programs have only recently begun to accumulate good time-domain data beyond the canonical HK-index. Addressing these and other issues toward understanding prolonged stellar minima is therefore a key area of inquiry in solar-stellar connection work for the next decade. I will summarize the state of the field and the most promising lines of work for the immediate future. I and my colleagues Wes Lockwood and Brian Skiff sincerely appreciate the National Science Foundation’s long-time support of stellar cycles work at Lowell Observatory.

  9. Stellar Spectral Synthesis with OpenGL

    Science.gov (United States)

    Hill, Nicholas R.; Townsend, R.

    2011-01-01

    Given an appropriate model atmosphere, synthesizing the spectrum of a star is a relatively straightforward task -- *if* the star is spherical and homogeneous across its surface. Many astronomically interesting objects do not, however, fall into this category. Examples include single stars that are spotted, rapidly rotating or pulsating, and binary stars in eclipsing or ellipsoidal-variable configurations. To synthesize a spectrum in such cases, it is necessary to construct a 3-D model of the stellar surface; determine which regions of the surface are visible to an external observer; and then calculate the observer-directed radiation from these regions. The Open Graphics Library (OpenGL), a cross-platform application programming interface for creation of 2-D and 3-D graphics, already includes much of the functionality required to implement these steps. We describe a new approach to stellar spectral synthesis that leverages this functionality. A 3-D mesh is constructed to represent the (possibly non-spherical) geometry of the stellar surface (or surfaces, in the case of binary or multiple systems). Textures are laid over this mesh to represent the run of physical attributes such as temperature, gravity, velocity, etc. The textured mesh is then rendered by OpenGL into a framebuffer, a step which naturally takes care of projection and occultation effects. The attributes of each framebuffer pixel are used to look up an appropriate spectrum in pre-calculated tables of specific intensities; and finally, summing the spectra from all pixels gives the disk-integrated synthetic flux spectrum of the star. The advantage of this approach lies in its efficiency (many OpenGL features are hardware-implemented), flexibility and manifest simplicity. Possible applications include binary light-curve modeling, mode identification in pulsating stars, and stellar population synthesis.

  10. Molecular clouds. [significance in stellar evolution

    Science.gov (United States)

    Thaddeus, P.

    1977-01-01

    An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.

  11. Fundamental Stellar Properties from Optical Interferometry

    CERN Document Server

    van Belle, Gerard T; Boyajian, Tabetha; Harper, Graham; Hummel, Christian; Pedretti, Ettore; Baines, Ellyn; White, Russel; Ravi, Vikram; Ridgway, Steve

    2010-01-01

    High-resolution observations by visible and near-infrared interferometers of both single stars and binaries have made significant contributions to the foundations that underpin many aspects of our knowledge of stellar structure and evolution for cool stars. The CS16 splinter on this topic reviewed contributions of optical interferometry to date, examined highlights of current research, and identified areas for contributions with new observational constraints in the near future.

  12. Compact stellar object: the formation and structure

    Energy Technology Data Exchange (ETDEWEB)

    Duarte, S.B. [Centro Brasileiro de Pesquisas Fisicas (CBPF/MCT), Rio de Janeiro, RJ (Brazil)

    2012-07-01

    Full text: The formation of compact objects is viewed at the final stages of stellar evolution. The supernova explosion events are then focalized to explain the formation of pulsars, hybrid neutron star and the limit case of the latter, the quark stars. We discuss the stability and structure of these objects in connection with the properties of the hadron and quark-gluon plasma equation of state. The hadron-quark phase transition in deep interior of these objects is discussed taking into account the implications on the density distribution of matter along the radial direction. The role of neutrinos confinement in the ultradense stellar medium in the early stages of pulsar formation is another interesting aspect to be mentioned in this presentation. Recent results for maximum mass of compact stellar objects for different forms of equations of state will be shown, presenting some theoretical predictions for maximum mass of neutron stars allowed by different equations of state assigned to dense stellar medium. Although a density greater than few times the nuclear equilibrium density appears in deep interior of the core, at the crust the density decreases by several orders of magnitude where a variety of hadronic states appears, the 'pasta'-states of hadrons. More externally, a lattice of nuclei can be formed permeated not only by electrons but also by a large amount of free neutrons and protons. These are possible structure of neutron star crust to have the density and pressures with null values at the neutron star surface. The ultimate goal of this talk is to give a short view of the compact star area for students and those who are introducing in this subject. (author)

  13. Uncertainties in stellar evolution models: convective overshoot

    CERN Document Server

    Bressan, Alessandro; Marigo, Paola; Rosenfield, Philip; Tang, Jing

    2014-01-01

    In spite of the great effort made in the last decades to improve our understanding of stellar evolution, significant uncertainties remain due to our poor knowledge of some complex physical processes that require an empirical calibration, such as the efficiency of the interior mixing related to convective overshoot. Here we review the impact of convective overshoot on the evolution of stars during the main Hydrogen and Helium burning phases.

  14. Uncertainties in Stellar Evolution Models: Convective Overshoot

    Science.gov (United States)

    Bressan, Alessandro; Girardi, Léo; Marigo, Paola; Rosenfield, Philip; Tang, Jing

    In spite of the great effort made in the last decades to improve our understanding of stellar evolution, significant uncertainties remain due to our poor knowledge of some complex physical processes that require an empirical calibration, such as the efficiency of the interior mixing related to convective overshoot. Here we review the impact of convective overshoot on the evolution of stars during the main Hydrogen and Helium burning phases.

  15. Memorial W.Gentner

    CERN Multimedia

    Schopper,H

    1981-01-01

    Le DG H.Schopper fait une introduction pour la commémoration et cérémonie de la vie et du travail du Prof.Wolfgang Gentner. W. Gentner, physicien allemand, né en 1906 à Francfort et mort en septembre 1980 à Heidelberg, était directeur au Cern de 1955 à 1960, président du "scientific policy commitee" de 1968 à 1971 et président du Conseil du Cern de 1972 à 1974. Il était un des fondateurs du Cern et 4 personnes qui l'ont bien connu lui rendent hommage, entre autres un de ses élèves, ainsi que Mme ?, J.B.Adams et O.Sheffard(?)

  16. Trevor W. Robbins: Award for Distinguished Scientific Contributions.

    Science.gov (United States)

    2011-11-01

    Presents Trevor W. Robbins, the 2011 winner of the American Psychological Association Award for Distinguished Scientific Contributions."For distinguished theoretical and empirical contributions to basic research in experimental psychology and neuroscience. Trevor W. Robbins has made innovative and landmark contributions to understanding monoaminergic and glutamatergic regulation of cortico-striatal-limbic function and its involvement in psychological processes and pathological states such as addiction, depression, schizophrenia, and attention-deficit/hyperactivity disorder. His pioneering accomplishments have included the development of methodologies for parallel sophisticated behavioral assessments in humans, rodents, and monkeys combined with psychopharmacological and imaging studies across species. His vigor and dedication to research, exemplary leadership, scholarship, and stellar productivity have advanced our knowledge of brain function and inspired several generations of cognitive neuroscientists." (PsycINFO Database Record (c) 2011 APA, all rights reserved). 2011 APA, all rights reserved

  17. Determining the Stellar Spin Axis Orientation

    Science.gov (United States)

    Lesage, Anna-Lea; Wiedemann, Gunter

    2015-01-01

    We present an observing method that permits the determination of the absolute stellar spin axis position angle based on spectro-astrometric observations for slowly-rotating late-type stars. This method is complementary to current interferometric observations that determine the orientation of stellar spin axis for early-type fast-rotating stars. Spectro-astrometry enables us to study phenomena below the diffraction limit, at the milli-arcsecond scale. It relies on the wavelength dependent variations of the centroid position of a structured source in a long-slit spectrum. A rotating star has a slight tilt in its spectral lines, which induces a displacement of the photocentre's position. By monitoring the amplitude of the displacement for varying slit orientations, we can infer the absolute position angle of the stellar spin axis. Finally, we present first observational results on Aldebaran obtained with the Thüringer Landesternwarte high resolution spectrograph. We were able to retrieve Aldebaran's position angle with less than 10° errors.

  18. Galactic stellar populations with APOGEE and Kepler

    Science.gov (United States)

    Johnson, J. A.; APOKASC Collaboration

    2016-09-01

    Understanding the history of baryons is key to understanding galaxy formation, as galaxies with very similar stellar mass and/or dark matter halo mass can have markedly different morphologies in their stellar light. Stars are a useful way to study this history, because properties such as their composition, age, and orbital motion can map galaxy formation and evolution. Lightcurves from the Kepler mission, both original and extended, provide asteroseismic parameters, such as Δ ν and ν_max, and rotation periods. The high-resolution near-infrared APOGEE spectroscopic survey is observing an extensive sample of red giants and cool dwarfs in both the Kepler and K2 fields to provide composition and effective temperature measurements. These spectroscopic and seismic parameters can be combined to yield ages, important for dissecting the history of the Milky Way. Results based on this combination have already been published in the first APOKASC catalog. Among the interesting results about stellar populations so far are the presence of a large metallicity spread in the young secondary red clump population at the solar circle, the identification of young, yet α-rich stars, and the detection of a field blue straggler descendant. The K2 fields along the ecliptic will extend the possibilities of these techniques to new lines of sight in the Galaxy and provide a much more representative sample of Galactic populations with seismic and spectroscopic information.

  19. STELLAR: fast and exact local alignments

    Directory of Open Access Journals (Sweden)

    Weese David

    2011-10-01

    Full Text Available Abstract Background Large-scale comparison of genomic sequences requires reliable tools for the search of local alignments. Practical local aligners are in general fast, but heuristic, and hence sometimes miss significant matches. Results We present here the local pairwise aligner STELLAR that has full sensitivity for ε-alignments, i.e. guarantees to report all local alignments of a given minimal length and maximal error rate. The aligner is composed of two steps, filtering and verification. We apply the SWIFT algorithm for lossless filtering, and have developed a new verification strategy that we prove to be exact. Our results on simulated and real genomic data confirm and quantify the conjecture that heuristic tools like BLAST or BLAT miss a large percentage of significant local alignments. Conclusions STELLAR is very practical and fast on very long sequences which makes it a suitable new tool for finding local alignments between genomic sequences under the edit distance model. Binaries are freely available for Linux, Windows, and Mac OS X at http://www.seqan.de/projects/stellar. The source code is freely distributed with the SeqAn C++ library version 1.3 and later at http://www.seqan.de.

  20. The relativistic inverse stellar structure problem

    Energy Technology Data Exchange (ETDEWEB)

    Lindblom, Lee [Theoretical Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)

    2014-01-14

    The observable macroscopic properties of relativistic stars (whose equations of state are known) can be predicted by solving the stellar structure equations that follow from Einstein’s equation. For neutron stars, however, our knowledge of the equation of state is poor, so the direct stellar structure problem can not be solved without modeling the highest density part of the equation of state in some way. This talk will describe recent work on developing a model independent approach to determining the high-density neutron-star equation of state by solving an inverse stellar structure problem. This method uses the fact that Einstein’s equation provides a deterministic relationship between the equation of state and the macroscopic observables of the stars which are composed of that material. This talk illustrates how this method will be able to determine the high-density part of the neutron-star equation of state with few percent accuracy when high quality measurements of the masses and radii of just two or three neutron stars become available. This talk will also show that this method can be used with measurements of other macroscopic observables, like the masses and tidal deformabilities, which can (in principle) be measured by gravitational wave observations of binary neutron-star mergers.

  1. Intrinsic Turbulence Stabilization in a Stellarator

    Directory of Open Access Journals (Sweden)

    P. Xanthopoulos

    2016-06-01

    Full Text Available The magnetic surfaces of modern stellarators are characterized by complex, carefully optimized shaping and exhibit locally compressed regions of strong turbulence drive. Massively parallel computer simulations of plasma turbulence reveal, however, that stellarators also possess two intrinsic mechanisms to mitigate the effect of this drive. In the regime where the length scale of the turbulence is very small compared to the equilibrium scale set by the variation of the magnetic field, the strongest fluctuations form narrow bandlike structures on the magnetic surfaces. Thanks to this localization, the average transport through the surface is significantly smaller than that predicted at locations of peak turbulence. This feature results in a numerically observed upshift of the onset of turbulence on the surface towards higher ion temperature gradients as compared with the prediction from the most unstable regions. In a second regime lacking scale separation, the localization is lost and the fluctuations spread out on the magnetic surface. Nonetheless, stabilization persists through the suppression of the large eddies (relative to the equilibrium scale, leading to a reduced stiffness for the heat flux dependence on the ion temperature gradient. These fundamental differences with tokamak turbulence are exemplified for the QUASAR stellarator [G. H. Neilson et al., IEEE Trans. Plasma Sci. 42, 489 (2014].

  2. The formation of stellar black holes

    Science.gov (United States)

    Mirabel, Félix

    2017-08-01

    It is believed that stellar black holes (BHs) can be formed in two different ways: Either a massive star collapses directly into a BH without a supernova (SN) explosion, or an explosion occurs in a proto-neutron star, but the energy is too low to completely unbind the stellar envelope, and a large fraction of it falls back onto the short-lived neutron star (NS), leading to the delayed formation of a BH. Theoretical models set progenitor masses for BH formation by implosion, namely, by complete or almost complete collapse, but observational evidences have been elusive. Here are reviewed the observational insights on BHs formed by implosion without large natal kicks from: (1) the kinematics in three dimensions of space of five Galactic BH X-ray binaries (BH-XRBs), (2) the diversity of optical and infrared observations of massive stars that collapse in the dark, with no luminous SN explosions, possibly leading to the formation of BHs, and (3) the sources of gravitational waves (GWs) produced by mergers of stellar BHs so far detected with LIGO. Multiple indications of BH formation without ejection of a significant amount of matter and with no natal kicks obtained from these different areas of observational astrophysics, and the recent observational confirmation of the expected dependence of BH formation on metallicity and redshift, are qualitatively consistent with the high merger rates of binary black holes (BBHs) inferred from the first detections with LIGO.

  3. POLLUX : a database of synthetic stellar spectra

    CERN Document Server

    Palacios, A; Josselin, E; Martins, F; Plez, B; Belmas, M; Lebre, A

    2010-01-01

    Synthetic spectra are needed to determine fundamental stellar and wind parameters of all types of stars. They are also used for the construction of theoretical spectral libraries helpful for stellar population synthesis. Therefore, a database of theoretical spectra is required to allow rapid and quantitative comparisons to spectroscopic data. We provide such a database offering an unprecedented coverage of the entire Hertzsprung-Russell diagram. We present the POLLUX database of synthetic stellar spectra. For objects with Teff 25 000 K). Their spectra are computed with CMF_FLUX. Both high resolution (R>150 000) optical spectra in the range 3 000 to 12 000 A and spectral energy distributions extending from the UV to near--IR ranges are presented. These spectra cover the HR diagram at solar metallicity. We propose a wide variety of synthetic spectra for various types of stars in a format that is compliant with the Virtual Observatory standards. A user--friendly web interface allows an easy selection of spectra...

  4. The Stellar Imager (SI) Vision Mission

    CERN Document Server

    Carpenter, K G; Karovska, M; SI Vision Mission Team; Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita; Team, SI Vision Mission

    2006-01-01

    The Stellar Imager (SI) is a UV-Optical, Space-Based Interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general and asteroseismic imaging of stellar interiors. SI is identified as a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap (May, 2005). SI will revolutionize our view of many dynamic astrophysical processes: its resolution will transform point sources into extended sources, and snapshots into 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. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant p...

  5. Resilient non-resonant divertors for stellarators

    Science.gov (United States)

    Bader, A.; Boozer, A. H.; Hegna, C. C.; Lazerson, S. A.

    2016-10-01

    In this work, we investigate whether resilient non-resonant divertor solutions exist for optimized stellarators. Resiliency is measured by the consistency of performance over a broad range of operational states, such as through bootstrap current and modified plasma pressures. A non-resonant configuration is one where the crucial topological feature is the existence and sharpness of ridges along the last closed flux surface. We develop a modified field-line following method for testing the resiliency of stellarator divertors and apply it to altered HSX configurations generated by varying external coil currents, wall positioning, and internal plasma currents. We compare a magnetic diffusion calculation with a ``zero-diffusion'' calculation that endeavors to measure the first escaping flux tubes. The results from these calculations are corroborated with a more complete edge simulation with EMC3-EIRENE. The EMC3-EIRENE simulations show resilient helical stripes that are consistent with the simpler field line following methods. The goal of the study is to find a metric for edge/divertor optimization of stellarators, a crucial piece that is missing from current optimization schemes. Work supported by DE-SC0006103 and DE-FG02-93ER54222,.

  6. The Relativistic Inverse Stellar Structure Problem

    CERN Document Server

    Lindblom, Lee

    2014-01-01

    The observable macroscopic properties of relativistic stars (whose equations of state are known) can be predicted by solving the stellar structure equations that follow from Einstein's equation. For neutron stars, however, our knowledge of the equation of state is poor, so the direct stellar structure problem can not be solved without modeling the highest density part of the equation of state in some way. This talk will describe recent work on developing a model independent approach to determining the high-density neutron-star equation of state by solving an inverse stellar structure problem. This method uses the fact that Einstein's equation provides a deterministic relationship between the equation of state and the macroscopic observables of the stars which are composed of that material. This talk illustrates how this method will be able to determine the high-density part of the neutron-star equation of state with few percent accuracy when high quality measurements of the masses and radii of just two or thr...

  7. Intrinsic Turbulence Stabilization in a Stellarator

    Science.gov (United States)

    Xanthopoulos, P.; Plunk, G. G.; Zocco, A.; Helander, P.

    2016-04-01

    The magnetic surfaces of modern stellarators are characterized by complex, carefully optimized shaping and exhibit locally compressed regions of strong turbulence drive. Massively parallel computer simulations of plasma turbulence reveal, however, that stellarators also possess two intrinsic mechanisms to mitigate the effect of this drive. In the regime where the length scale of the turbulence is very small compared to the equilibrium scale set by the variation of the magnetic field, the strongest fluctuations form narrow bandlike structures on the magnetic surfaces. Thanks to this localization, the average transport through the surface is significantly smaller than that predicted at locations of peak turbulence. This feature results in a numerically observed upshift of the onset of turbulence on the surface towards higher ion temperature gradients as compared with the prediction from the most unstable regions. In a second regime lacking scale separation, the localization is lost and the fluctuations spread out on the magnetic surface. Nonetheless, stabilization persists through the suppression of the large eddies (relative to the equilibrium scale), leading to a reduced stiffness for the heat flux dependence on the ion temperature gradient. These fundamental differences with tokamak turbulence are exemplified for the QUASAR stellarator [G. H. Neilson et al., IEEE Trans. Plasma Sci. 42, 489 (2014)].

  8. Stellar photometry with Multi Conjugate Adaptive Optics

    CERN Document Server

    Fiorentino, Giuliana; McConnachie, Alan; Stetson, Peter B; Bono, Giuseppe; Turri, Paolo; Andersen, David; Veran, Jean-Pierre; Diolaiti, Emiliano; Schreiber, Laura; Ciliegi, Paolo; Bellazzini, Michele; Tolstoy, Eline; Monelli, Matteo; Iannicola, Giacinto; Ferraro, Ivan; Testa, Vincenzo

    2016-01-01

    We overview the current status of photometric analyses of images collected with Multi Conjugate Adaptive Optics (MCAO) at 8-10m class telescopes that operated, or are operating, on sky. Particular attention will be payed to resolved stellar population studies. Stars in crowded stellar systems, such as globular clusters or in nearby galaxies, are ideal test particles to test AO performance. We will focus the discussion on photometric precision and accuracy reached nowadays. We briefly describe our project on stellar photometry and astrometry of Galactic globular clusters using images taken with GeMS at the Gemini South telescope. We also present the photometry performed with DAOPHOT suite of programs into the crowded regions of these globulars reaching very faint limiting magnitudes Ks ~21.5 mag on moderately large fields of view (~1.5 arcmin squared). We highlight the need for new algorithms to improve the modeling of the complex variation of the Point Spread Function across the ?eld of view. Finally, we outl...

  9. The Yale–Potsdam Stellar Isochrones

    Science.gov (United States)

    Spada, F.; Demarque, P.; Kim, Y.-C.; Boyajian, T. S.; Brewer, J. M.

    2017-04-01

    We introduce the Yale–Potsdam Stellar Isochrones (YaPSI), a new grid of stellar evolution tracks and isochrones of solar-scaled composition. In an effort to improve the Yonsei–Yale database, special emphasis is placed on the construction of accurate low-mass models ({M}* up to the tip of the red giant branch. The isochrones, with ages between 1 Myr and 20 Gyr, provide UBVRI colors in the Johnson–Cousins system, and JHK colors in the homogenized Bessell & Brett system, derived from two different semi-empirical {T}{eff}–color calibrations from the literature. We also provide utility codes, such as an isochrone interpolator, in age, metallicity, and helium content, and an interface of the tracks with an open-source Monte Carlo Markov-Chain tool for the analysis of individual stars. Finally, we present comparisons of the YaPSI models with the best empirical mass–luminosity and mass–radius relations available to date, as well as isochrone fitting of well-studied stellar clusters.

  10. Stellar parametrization from Gaia RVS spectra

    CERN Document Server

    Recio-Blanco, A; Prieto, C Allende; Fustes, D; Manteiga, M; Arcay, B; Bijaoui, A; Dafonte, C; Ordenovic, C; Blanco, D Ordoñez

    2016-01-01

    Among the myriad of data collected by the ESA Gaia satellite, about 150 million spectra will be delivered by the Radial Velocity Spectrometer (RVS) for stars as faint as G_RVS~16. A specific stellar parametrization will be performed for most of these RVS spectra. Some individual chemical abundances will also be estimated for the brightest targets. We describe the different parametrization codes that have been specifically developed or adapted for RVS spectra within the GSP-spec working group of the analysis consortium. The tested codes are based on optimization (FERRE and GAUGUIN), projection (MATISSE) or pattern recognition methods (Artificial Neural Networks). We present and discuss their expected performances in the recovered stellar atmospheric parameters (Teff, log(g), [M/H]) for B- to K- type stars. The performances for the determinations of [alpha/Fe] ratios are also presented for cool stars. For all the considered stellar types, stars brighter than G_RVS~12.5 will be very efficiently parametrized by t...

  11. 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.

  12. Accretion-Powered Stellar Winds II: Numerical Solutions for Stellar Wind Torques

    CERN Document Server

    Matt, Sean

    2008-01-01

    [Abridged] In order to explain the slow rotation observed in a large fraction of accreting pre-main-sequence stars (CTTSs), we explore the role of stellar winds in torquing down the stars. For this mechanism to be effective, the stellar winds need to have relatively high outflow rates, and thus would likely be powered by the accretion process itself. Here, we use numerical magnetohydrodynamical simulations to compute detailed 2-dimensional (axisymmetric) stellar wind solutions, in order to determine the spin down torque on the star. We explore a range of parameters relevant for CTTSs, including variations in the stellar mass, radius, spin rate, surface magnetic field strength, the mass loss rate, and wind acceleration rate. We also consider both dipole and quadrupole magnetic field geometries. Our simulations indicate that the stellar wind torque is of sufficient magnitude to be important for spinning down a ``typical'' CTTS, for a mass loss rate of $\\sim 10^{-9} M_\\odot$ yr$^{-1}$. The winds are wide-angle, ...

  13. Geometry and W-Gravity

    OpenAIRE

    Hull, C. M.

    1993-01-01

    The higher-spin geometries of $W_\\infty$-gravity and $W_N$-gravity are analysed and used to derive the complete non-linear structure of the coupling to matter and its symmetries. The symmetry group is a subgroup of the symplectic diffeomorphisms of the cotangent bundle of the world-sheet, and the $W_N$ geometry is obtained from a non-linear truncation of the $W_\\infty$ geometry. Quantum W-gravity is briefly discussed. (Talk given at {\\it Pathways to Fundamental Interactions}, the 16th John Ho...

  14. Geometry and W-Gravity

    CERN Document Server

    Hull, C M

    1993-01-01

    The higher-spin geometries of $W_\\infty$-gravity and $W_N$-gravity are analysed and used to derive the complete non-linear structure of the coupling to matter and its symmetries. The symmetry group is a subgroup of the symplectic diffeomorphisms of the cotangent bundle of the world-sheet, and the $W_N$ geometry is obtained from a non-linear truncation of the $W_\\infty$ geometry. Quantum W-gravity is briefly discussed. (Talk given at {\\it Pathways to Fundamental Interactions}, the 16th John Hopkins Workshop on Current Problems in Particle Theory, Gothenborg, 1992.)

  15. Simulation studies of the power supply and the protection system for the Wendelstein 7-X Stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Wieczorek, A. [Max-Planck-Inst. fuer Plasmaphysik, EURATOM Association, Garching (Germany); Sapper, J. [Max-Planck-Inst. fuer Plasmaphysik, EURATOM Association, Garching (Germany)

    1995-12-31

    The magnet system of the Wendelstein 7-X Stellarator comprises seven superconducting coil groups, each of them consisting of ten coils connected electrically in series. For experimental flexibility reasons all these groups must be powered independently. The electrical circuits of the W7-X coil systems have been modelled to enable the choice of the type of converter and its modifications prior to installation. A safety system protects the coils in case of faults. The computer models make it possible to simulate the different kinds of faults that may occur in the system. (orig.).

  16. Stellar classification from single-band imaging using machine learning

    Science.gov (United States)

    Kuntzer, T.; Tewes, M.; Courbin, F.

    2016-06-01

    Information on the spectral types of stars is of great interest in view of the exploitation of space-based imaging surveys. In this article, we investigate the classification of stars into spectral types using only the shape of their diffraction pattern in a single broad-band image. We propose a supervised machine learning approach to this endeavour, based on principal component analysis (PCA) for dimensionality reduction, followed by artificial neural networks (ANNs) estimating the spectral type. Our analysis is performed with image simulations mimicking the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) in the F606W and F814W bands, as well as the Euclid VIS imager. We first demonstrate this classification in a simple context, assuming perfect knowledge of the point spread function (PSF) model and the possibility of accurately generating mock training data for the machine learning. We then analyse its performance in a fully data-driven situation, in which the training would be performed with a limited subset of bright stars from a survey, and an unknown PSF with spatial variations across the detector. We use simulations of main-sequence stars with flat distributions in spectral type and in signal-to-noise ratio, and classify these stars into 13 spectral subclasses, from O5 to M5. Under these conditions, the algorithm achieves a high success rate both for Euclid and HST images, with typical errors of half a spectral class. Although more detailed simulations would be needed to assess the performance of the algorithm on a specific survey, this shows that stellar classification from single-band images is well possible.

  17. Young Stellar Clusters Containing Massive Young Stellar Objects in the VVV Survey

    CERN Document Server

    Borissova, J; Alonso, J; Lucas, P W; Kurtev, R; Medina, N; Navarro, C; Kuhn, M; Gromadzki, M; Retamales, G; Fernandez, M A; Agurto-Gangas, C; Chené, A -N; Minniti, D; Peña, C Contreras; Catelan, M; Decany, I; Thompson, M A; Morales, E F E; Amigo, P

    2016-01-01

    The purpose of this research is to study the connection of 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 population. The analysis in 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 Mo), the slope Gamma of the obtained present-day mass functions of the clusters is close to the Kroupa initial mass function. On the other hand, the young stellar objects in the surrounding cluster's fields are classified by low resolution spectra, spectral energy distribution fit with theoretical predictions, and variability, taking advantage of multi-epoch VVV observations. All spectroscopically confirmed young s...

  18. Starspots, stellar cycles and stellar flares: Lessons from solar dynamo models

    Science.gov (United States)

    Choudhuri, Arnab Rai

    2017-01-01

    In this review, we discuss whether the present solar dynamo models can be extrapolated to explain various aspects of stellar activity. We begin with a summary of the following kinds of data for solar-like stars: (i) data pertaining to stellar cycles from Ca H/K emission over many years; (ii) X-ray data indicating hot coronal activity; (iii) starspot data (especially about giant polar spots); and (iv) data pertaining to stellar superflares. Then we describe the current status of solar dynamo modelling—giving an introduction to the flux transport dynamo model, the currently favoured model for the solar cycle. While an extrapolation of this model to solar-like stars can explain some aspects of observational data, some other aspects of the data still remain to be theoretically explained. It is not clear right now whether we need a different kind of dynamo mechanism for stars having giant starspots or producing very strong superflares.

  19. A new method for deriving the stellar birth function of resolved stellar populations

    CERN Document Server

    Gennaro, Mario; Brown, Tom; Gordon, Karl

    2015-01-01

    We present a new method for deriving the stellar birth function (SBF) of resolved stellar populations. The SBF (stars born per unit mass, time, and metallicity) is the combination of the initial mass function (IMF), the star-formation history (SFH), and the metallicity distribution function (MDF). The framework of our analysis is that of Poisson Point Processes (PPPs), a class of statistical models suitable when dealing with points (stars) in a multidimensional space (the measurement space of multiple photometric bands). The theory of PPPs easily accommodates the modeling of measurement errors as well as that of incompleteness. Compared to most of the tools used to study resolved stellar populations, our method avoids binning stars in the color-magnitude diagram and uses the entirety of the information (i.e., the whole likelihood function) for each data point; the proper combination of the individual likelihoods allows the computation of the posterior probability for the global population parameters. This inc...

  20. The stellar kinematics in the solar neighborhood from LAMOST data

    CERN Document Server

    Tian, Hai-Jun; Carlin, Jeffrey L; Zhao, Yong-Heng; Chen, Xue-Lei; Wu, Yue; Li, Guang-Wei; Hou, Yong-Hui; Zhang, Yong

    2015-01-01

    We use about 200,000 FGK type main-sequence stars from the LAMOST DR1 data to map the local stellar kinematics. With the velocity de-projection technique, we are able to derive the averaged 3 dimensional velocity and velocity ellipsoids using only the line-of-sight velocity for the stars with various effective temperatures within $100 6000$K show a net asymmetric motion of $\\sim3 km\\,s^{-1}$ in $\\langle W\\rangle$ compared to the stars with ${T}_{\\rm eff}<6000$K. And their azimuthal velocity increases when $|z|$ increases. This peculiar motion in the warmer stars is likely because they are young and not completely relaxed, although other reasons, such as the resonance induced by the central rotating bar or the spiral structures, and the perturbation of the merging dwarf galaxies, can not be ruled out. The derived velocity dispersions and cross terms for the data are approximately consistent with previous studies. We also find that the vertical gradients of $\\sigma_{U}$ and $\\sigma_V$ are larger than that of...

  1. Determination of the position angle of stellar spin axes

    Science.gov (United States)

    Lesage, A.-L.; Wiedemann, G.

    2014-03-01

    Context. Measuring the stellar position angle provides valuable information on binary stellar formation or stellar spin axis evolution. Aims: We aim to develop a method for determining the absolute stellar position angle using spectro-astrometric analysis of high resolution long-slit spectra. The method has been designed in particular for slowly rotating stars. We investigate its applicability to existing dispersive long-slit spectrographs, identified here by their plate scale, and the size of the resulting stellar sample. Methods: The stellar rotation induces a tilt in the stellar lines whose angle depends on the stellar position angle and the orientation of the slit. We developed a rotation model to calculate and reproduce the effects of stellar rotation on unreduced high resolution stellar spectra. Then we retrieved the tilt amplitude using a spectro-astrometric extraction of the position of the photocentre of the spectrum. Finally we present two methods for analysing the position spectrum using either direct measurement of the tilt or a cross-correlation analysis. Results: For stars with large apparent diameter and using a spectrograph with a small plate scale, we show that it is possible to determine the stellar position angle directly within 10° with a signal-to-noise ratio of the order of 6. Under less favourable conditions, i.e. larger plate scale or smaller stellar diameter, the cross-correlation method yields comparable results. Conclusions: We show that with the currently existing instruments, it is possible to determine the stellar position angle of at least 50 stars precisely, mostly K-type giants with apparent diameter down to 5 milliarcseconds. If we consider errors of around 10° still acceptable, we may include stars with apparent diameter down to 2 mas in the sample that then comprises also some main sequence stars.

  2. 3D Maxwell-Vlasov boundary value problem solution in stellarator geometry in ion cyclotron frequency range

    Energy Technology Data Exchange (ETDEWEB)

    Vdovin, V.; Watari, T. [National Inst. for Fusion Science, Nagoya (Japan); Fukuyama, A.

    1997-12-31

    In the work we formulate the basic equations to solve the above ICRF problem in flux coordinates on different equilibria. The kinetic effects like cyclotron and Cherenkov absorptions, along with excitation of kinetic Alfven waves and finite Larmor radius effects are included. The ICRF plasma heating ({omega} {approx} {omega}{sub ci}) methods are prepared for the newly constructed LHD and projected W7-X stellarators or are conducted on operating machines like W7-AS, CHS, etc. For their adequate ICRH modelling and antenna development it is needed to create more complicated in compare with tokamaks ICRF code accounting for non axis symmetrical plasmas in complicated geometry. (author)

  3. Spatially resolved spectroscopy across stellar surfaces. I. Using exoplanet transits to analyze 3D stellar atmospheres

    Science.gov (United States)

    Dravins, Dainis; Ludwig, Hans-Günter; Dahlén, Erik; Pazira, Hiva

    2017-09-01

    Context. High-precision stellar analyses require hydrodynamic modeling to interpret chemical abundances or oscillation modes. Exoplanet atmosphere studies require stellar background spectra to be known along the transit path while detection of Earth analogs require stellar microvariability to be understood. Hydrodynamic 3D models can be computed for widely different stars but have been tested in detail only for the Sun with its resolved surface features. Model predictions include spectral line shapes, asymmetries, and wavelength shifts, and their center-to-limb changes across stellar disks. Aims: We observe high-resolution spectral line profiles across spatially highly resolved stellar surfaces, which are free from the effects of spatial smearing and rotational broadening present in full-disk spectra, enabling comparisons to synthetic profiles from 3D models. Methods: During exoplanet transits, successive stellar surface portions become hidden and differential spectroscopy between various transit phases provides spectra of small surface segments temporarily hidden behind the planet. Planets cover no more than 1% of any main-sequence star, enabling high spatial resolution but demanding very precise observations. Realistically measurable quantities are identified through simulated observations of synthetic spectral lines. Results: In normal stars, line profile ratios between various transit phases may vary by 0.5%, requiring S/N ≳ 5000 for meaningful spectral reconstruction. While not yet realistic for individual spectral lines, this is achievable for cool stars by averaging over numerous lines with similar parameters. Conclusions: For bright host stars of large transiting planets, spatially resolved spectroscopy is currently practical. More observable targets are likely to be found in the near future by ongoing photometric searches.

  4. 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.

  5. 改进的W-A、W-O+W-A自适应互连诊断算法%Modified W -A . W -O +W -A adaptive interconnect diagnosis algorithm

    Institute of Scientific and Technical Information of China (English)

    牛春平; 任哲平; 任锐; 杨月婷

    2009-01-01

    针对电路板线与(W-A)以及线或和线与(W-O+W-A)共存的互连故障诊断问题,提出了针对W-A和W-O+W-A的改进的边界扫描自适应互连诊断算法.借鉴改进的W-O自适应算法研究经验,由改进的W-A抗误判算法+移位"O"序列得到改进的w-A自适应算法;采用同时具备W-O和W-A对角独立性的测试序列得到W-O+W-A的改进的自适应算法.%To study the diagnostic problem of W-A and W-O+W-A interconnect fault of PCB (Printed Circuit Board),moclifiod boundary scan interconnect diagnosis algorithms for W-A and W-O+W-A are put forward.These algorithms take the research experience of modified W-O adaptive algorithm as example,apply modified W-A anti-aliasing algorithm and walking zero sequence,test sequence with both W-O and W-A diagonal independence,modified adaptive algorithms W-A and W-O+W-A are gained.

  6. Autocorrelations of stellar light and mass at z~0 and ~1: From SDSS to DEEP2

    CERN Document Server

    Li, Cheng; Chen, Yanmei; Coil, Alison L; Davis, Marc; De Lucia, Gabriella; Guo, Qi; Jing, Y P; Kauffmann, Guinevere; Willmer, Christopher N A; Zhang, Wei

    2011-01-01

    We present measurements of projected autocorrelation functions w_p(r_p) for the stellar mass of galaxies and for their light in the U, B and V bands, using data from the third data release of the DEEP2 Galaxy Redshift Survey and the final data release of the Sloan Digital Sky Survey (SDSS). We investigate the clustering bias of stellar mass and light by comparing these to projected autocorrelations of dark matter estimated from the Millennium Simulations (MS) at z=1 and 0.07, the median redshifts of our galaxy samples. All of the autocorrelation and bias functions show systematic trends with spatial scale and waveband which are impressively similar at the two redshifts. This shows that the well-established environmental dependence of stellar populations in the local Universe is already in place at z=1. The recent MS-based galaxy formation simulation of Guo et al. (2011) reproduces the scale-dependent clustering of luminosity to an accuracy better than 30% in all bands and at both redshifts, but substantially ...

  7. Three-dimensional simulations of stellar core collapse in full general relativity: Nonaxisymmetric dynamical instabilities

    CERN Document Server

    Shibata, M; Shibata, Masaru; Sekiguchi, Yu-ichirou

    2005-01-01

    We perform fully general relativistic simulations of rotating stellar core collapse in three spatial dimension. A parametric equation of state is adopted following Dimmelmeier et al. The early stage of the collapse is followed by an axisymmetric code. When the stellar core becomes compact enough, we start a 3-dimensional simulation adding a bar-mode nonaxisymmetric density perturbation. In the axisymmetric simulations, it is clarified that the maximum value of $\\beta \\equiv T/W$ achieved during the stellar collapse and depends sensitively on the velocity profile and total mass of the initial core, and equations of state. It is also found that for all the models with high degree of differential rotation, a funnel structure is formed around the rotational axis after the formation of neutron stars. For selected models in which the maximum value of $\\beta$ is larger than $\\sim 0.27$, 3-dimensional simulations are performed. It is found that the bar-mode dynamical instability sets in for the case that the followin...

  8. Measuring stellar granulation during planet transits

    Science.gov (United States)

    Chiavassa, A.; Caldas, A.; Selsis, F.; Leconte, J.; Von Paris, P.; Bordé, P.; Magic, Z.; Collet, R.; Asplund, M.

    2017-01-01

    Context. Stellar activity and convection-related surface structures might cause bias in planet detection and characterization that use these transits. Surface convection simulations help to quantify the granulation signal. Aims: We used realistic three-dimensional (3D) radiative hydrodynamical (RHD) simulations from the Stagger grid and synthetic images computed with the radiative transfer code Optim3D to model the transits of three prototype planets: a hot Jupiter, a hot Neptune, and a terrestrial planet. Methods: We computed intensity maps from RHD simulations of the Sun and a K-dwarf star at different wavelength bands from optical to far-infrared that cover the range of several ground- and space-based telescopes which observe exoplanet transits. We modeled the transit using synthetic stellar-disk images obtained with a spherical-tile imaging method and emulated the temporal variation of the granulation intensity generating random images covering a granulation time-series of 13.3 h. We measured the contribution of the stellar granulation on the light curves during the planet transit. Results: We identified two types of granulation noise that act simultaneously during the planet transit: (i) the intrinsic change in the granulation pattern with timescale (e.g., 10 min for solar-type stars assumed in this work) is smaller than the usual planet transit ( hours as in our prototype cases); and (ii) the fact that the transiting planet occults isolated regions of the photosphere that differ in local surface brightness as a result of convective-related surface structures. First, we showed that our modeling approach returns granulation timescale fluctuations that are comparable with what has been observed for the Sun. Then, our statistical approach shows that the granulation pattern of solar and K-dwarf-type stars have a non-negligible effect of the light curve depth during the transit, and, consequentially on the determination of the planet transit parameters such as the

  9. Stellar Activity and Coronal Heating: an overview of recent results

    CERN Document Server

    Testa, Paola; Drake, Jeremy

    2015-01-01

    Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars.

  10. Near-term directions in the world stellarator program

    Energy Technology Data Exchange (ETDEWEB)

    Lyon, J.F.

    1989-10-01

    Interest in stellarators has increased because of the progress being made in the development of this concept and the inherent advantages of stellarators as candidates for an attractive, steady-state fusion reactor. Three new stellarator experiments started operation in 1988, and three more are scheduled to start in the next few years. In addition, design studies have started on large next-generation stellarator experiments for the mid-1990s. These devices are designed to test four basic approaches to stellarator configuration optimization. This report describes how these devices complement each other in exploring the potential of the stellarator concept and what main issues they will address during the next decade. 31 refs., 9 figs., 4 tabs.

  11. Stellar activity and coronal heating: an overview of recent results

    Science.gov (United States)

    Testa, Paola; Saar, Steven H.; Drake, Jeremy J.

    2015-01-01

    Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars. PMID:25897087

  12. The W Boson Mass Measurement

    Science.gov (United States)

    Kotwal, Ashutosh V.

    2016-10-01

    The measurement of the W boson mass has been growing in importance as its precision has improved, along with the precision of other electroweak observables and the top quark mass. Over the last decade, the measurement of the W boson mass has been led at hadron colliders. Combined with the precise measurement of the top quark mass at hadron colliders, the W boson mass helped to pin down the mass of the Standard Model Higgs boson through its induced radiative correction on the W boson mass. With the discovery of the Higgs boson and the measurement of its mass, the electroweak sector of the Standard Model is over-constrained. Increasing the precision of the W boson mass probes new physics at the TeV-scale. We summarize an extensive Tevatron (1984-2011) program to measure the W boson mass at the CDF and Dø experiments. We highlight the recent Tevatron measurements and prospects for the final Tevatron measurements.

  13. The W Boson Mass Measurement

    CERN Document Server

    Kotwal, Ashutosh V

    2016-01-01

    The measurement of the W boson mass has been growing in importance as its precision has improved, along with the precision of other electroweak observables and the top quark mass. Over the last decade, the measurement of the W boson mass has been led at hadron colliders. Combined with the precise measurement of the top quark mass at hadron colliders, the W boson mass helped to pin down the mass of the Standard Model Higgs boson through its induced radiative correction on the W boson mass. With the discovery of the Higgs boson and the measurement of its mass, the electroweak sector of the Standard Model is over-constrained. Increasing the precision of the W boson mass probes new physics at the TeV-scale. We summarize an extensive Tevatron (1984–2011) program to measure the W boson mass at the CDF and Dø experiments. We highlight the recent Tevatron measurements and prospects for the final Tevatron measurements.

  14. Advances In Understanding Solar And Stellar Flares

    Science.gov (United States)

    Kowalski, Adam F.

    2016-07-01

    Flares result from the sudden reconnection and relaxation of magnetic fields in the coronae of stellar atmospheres. The highly dynamic atmospheric response produces radiation across the electromagnetic spectrum, from the radio to X-rays, on a range of timescales, from seconds to days. New high resolution data of solar flares have revealed the intrinsic spatial properties of the flaring chromosphere, which is thought to be where the majority of the flare energy is released as radiation in the optical and near-UV continua and emission lines. New data of stellar flares have revealed the detailed properties of the broadband (white-light) continuum emission, which provides straightforward constraints for models of the transformation of stored magnetic energy in the corona into thermal energy of the lower atmosphere. In this talk, we discuss the physical processes that produce several important spectral phenomena in the near-ultraviolet and optical as revealed from new radiative-hydrodynamic models of flares on the Sun and low mass stars. We present recent progress with high-flux nonthermal electron beams in reproducing the observed optical continuum color temperature of T 10,000 K and the Balmer jump properties in the near-ultraviolet. These beams produce dense, heated chromospheric condensations, which can explain the shape and strength of the continuum emission in M dwarf flares and the red-wing asymmetries in the chromospheric emission lines in recent observations of solar flares from the Interface Region Imaging Spectrograph. Current theoretical challenges and future modeling directions will be discussed, as well as observational synergies between solar and stellar flares.

  15. Parameterizing Stellar Spectra Using Deep Neural Networks

    Science.gov (United States)

    Li, Xiang-Ru; Pan, Ru-Yang; Duan, Fu-Qing

    2017-03-01

    Large-scale sky surveys are observing massive amounts of stellar spectra. The large number of stellar spectra makes it necessary to automatically parameterize spectral data, which in turn helps in statistically exploring properties related to the atmospheric parameters. This work focuses on designing an automatic scheme to estimate effective temperature ({T}{eff}), surface gravity ({log}g) and metallicity [Fe/H] from stellar spectra. A scheme based on three deep neural networks (DNNs) is proposed. This scheme consists of the following three procedures: first, the configuration of a DNN is initialized using a series of autoencoder neural networks; second, the DNN is fine-tuned using a gradient descent scheme; third, three atmospheric parameters {T}{eff}, {log}g and [Fe/H] are estimated using the computed DNNs. The constructed DNN is a neural network with six layers (one input layer, one output layer and four hidden layers), for which the number of nodes in the six layers are 3821, 1000, 500, 100, 30 and 1, respectively. This proposed scheme was tested on both real spectra and theoretical spectra from Kurucz’s new opacity distribution function models. Test errors are measured with mean absolute errors (MAEs). The errors on real spectra from the Sloan Digital Sky Survey (SDSS) are 0.1477, 0.0048 and 0.1129 dex for {log}g, {log}{T}{eff} and [Fe/H] (64.85 K for {T}{eff}), respectively. Regarding theoretical spectra from Kurucz’s new opacity distribution function models, the MAE of the test errors are 0.0182, 0.0011 and 0.0112 dex for {log}g, {log}{T}{eff} and [Fe/H] (14.90 K for {T}{eff}), respectively.

  16. Multiboson production in W' decays

    CERN Document Server

    Aguilar-Saavedra, J A

    2015-01-01

    In models with an extra $\\text{SU}(2)_R$ gauge group and an extended scalar sector, the cascade decays of the $W'$ boson can provide various multiboson signals. In particular, diboson decays $W' \\to WZ$ can be suppressed while $W' \\to WZX$, with $X$ one of the scalars present in the model, can reach branching ratios around 4%. We discuss these multiboson signals focusing on possible interpretations of the ATLAS excess in fat jet pair production.

  17. Measuring stellar rotation periods with Kepler

    CERN Document Server

    Nielsen, M B; Schunker, H; Karoff, C

    2015-01-01

    We measure rotation periods for 12151 stars in the Kepler field, based on the photometric variability caused by stellar activity. Our analysis returns stable rotation periods over at least six out of eight quarters of Kepler data. This large sample of stars enables us to study the rotation periods as a function of spectral type. We find good agreement with previous studies and vsini measurements for F, G and K stars. Combining rotation periods, B-V color, and gyrochronology relations, we find that the cool stars in our sample are predominantly younger than ~1Gyr.

  18. Collisional Drift Waves in Stellarator Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    J.L.V. Lewandowski

    2003-10-07

    A computational study of resistive drift waves in the edge plasma of a stellarator with an helical magnetic axis is presented. Three coupled field equations, describing the collisional drift wave dynamics in the linear approximation, are solved as an initial-value problem along the magnetic field line. The magnetohydrodynamic equilibrium is obtained from a three-dimensional local equilibrium model. The use of a local magnetohydrodynamic equilibrium model allows for a computationally efficient systematic study of the impact of the magnetic field structure on drift wave stability.

  19. MHD stability of the MHH2 stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Garabedian, P.R. [New York Univ., NY (United States). Courant Inst. of Mathematical Sciences

    1998-12-31

    The NSTAB code provides a computer implementation of the variational principle of magnetohydrodynamics. Excellent resolution is obtained by combining a spectral representation in the toroidal and poloidal angles with a low order, but exceptionally accurate, finite difference scheme in the radial direction. Conservation form of the magnetostatics equations is used to capture islands and current sheets effectively on crude grids. This method enables one to discuss global stability by analyzing bifurcated solutions of the equilibrium problem. The author applies it to investigate the physics of the MHH2 stellarator, whose magnetic structure has a remarkable property of quasi-axial symmetry.

  20. The Stellar Observations Network Group - first results

    DEFF Research Database (Denmark)

    Antoci, Victoria; Grundahl, Frank; Christensen-Dalsgaard, Joergen

    SONG - the Stellar Observations Network Group is a Danish-led project set to design and build a global network of 1-m telescopes to carry out detailed studies of solar-like stars using asteroseismology and to discover and characterise exo-planets and their star system. Here we present more than 100...... nights of high-precision radial velocity measurements from 2014 of the subgiant mu Herculis. Preliminary analyses of the largest ground-based data set ever obtained for such as star clearly show the detection of stochastically excited pressure modes. The high quality of our data allows unique extraction...

  1. The Advanced Stellar Compass, Development and Operations

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Liebe, Carl Christian

    1996-01-01

    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...

  2. Biological effects of stellar collapse neutrinos

    CERN Document Server

    Collar, J I

    1996-01-01

    Massive stars in their final stages of collapse radiate most of their binding energy in the form of MeV neutrinos. The recoil atoms that they produce in elastic scattering off nuclei in organic tissue create a radiation damage which is highly effective in the production of irreparable DNA harm, leading to cellular mutation, neoplasia and oncogenesis. Using a conventional model of the galaxy and of the collapse mechanism, the periodicity of nearby stellar collapses and the radiation dose are calculated. The possible contribution of this process to the paleontological record of mass extinctions is examined.

  3. Colour and stellar population gradients in galaxies

    CERN Document Server

    Tortora, C; Cardone, V F; Capaccioli, M; Jetzer, P; Molinaro, R

    2010-01-01

    We discuss the colour, age and metallicity gradients in a wide sample of local SDSS early- and late-type galaxies. From the fitting of stellar population models we find that metallicity is the main driver of colour gradients and the age in the central regions is a dominant parameter which rules the scatter in both metallicity and age gradients. We find a consistency with independent observations and a set of simulations. From the comparison with simulations and theoretical considerations we are able to depict a general picture of a formation scenario.

  4. Synthetic Stellar Clusters for Pop III

    CERN Document Server

    Raimondo, G; Cassisi, S; Castellani, V

    1999-01-01

    We present preliminary results of an incoming theoretical work concerning the integrated properties of the Population III clusters of stars. On the basis of synthetic Color-Magnitude Diagrams, we provide a grid of optical and near-IR colors of Simple Stellar Populations with very low metallicity (Z=10$^{-10}$ and Z=10$^{-6}$) and age which spans from 10 Myr to 15 Gyr. A comparison with higher metallicities up to 0.006 is also shown, disclosing sizable differences in the CMD morphology, integrated colors and Spectral Energy Distribution (SED).

  5. Influence of Rotation on Stellar Evolution

    CERN Document Server

    Palacios, A

    2013-01-01

    The Sun has been known to rotate for more than 4 centuries, and evidence is also available through direct measurements, that almost all stars rotate. In this lecture, I will propose a review of the different physical processes associated to rotation that are expected to impact the evolution of stars. I will describe in detail the way these physical processes are introduced in 1D stellar evolution codes and how their introduction in the modelling has impacted our understanding of the internal structure, nucleosynthesis and global evolution of stars.

  6. Colour and stellar population gradients in galaxies

    Science.gov (United States)

    Tortora, C.; Napolitano, N. R.; Cardone, V. F.; Capaccioli, M.; Jetzer, P.; Molinaro, R.

    We discuss the colour, age and metallicity gradients in a wide sample of local SDSS early- and late-type galaxies. From the fitting of stellar population models we find that metallicity is the main driver of colour gradients and the age in the central regions is a dominant parameter which rules the scatter in both metallicity and age gradients. We find a consistency with independent observations and a set of simulations. From the comparison with simulations and theoretical considerations we are able to depict a general picture of a formation scenario.

  7. A Grid of Synthetic Stellar UV Fluxes

    CERN Document Server

    Rodríguez-Merino, L H; Buzzoni, A; Bertone, E; Rodriguez-Merino, Lino H.; Chavez, Miguel; Buzzoni, Alberto; Bertone, Emanuele

    2001-01-01

    We present preliminary results of a large project aimed at creating an extended theoretical and observational database of stellar spectra in the ultraviolet wavelength range. This library will consist of IUE spectra at low and high resolution, and a set of LTE and NLTE theoretical fluxes. A first grid of 50 model fluxes with solar metallicity, in the wavelength interval 1000 - 4400 AA, is reported here. Calculations are based on the Kurucz (1993) SYNTHE code. The models span effective temperatures between 10,000 K and 50,000 K, and a surface gravity in the range 2.5 <= log g <= 5.0 dex.

  8. The Advanced Stellar Compass, Development and Operations

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Liebe, Carl Christian

    1996-01-01

    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...

  9. WSO-UV Project for Stellar Astrophysics

    Science.gov (United States)

    Sachkov, M.; Shustov, B.; Gómez de Castro, A. I.; Kanev, E.; Klochkova, V.; Panchuk, V.; Savanov, I.; Sichevskij, S.; Shugarov, A.

    2017-06-01

    The WSO-UV (World Space Observatory - Ultraviolet) project is intended to built and operate an international space observatory designed for observations in the UV (115-310 nm) spectral range. In this spectral domain many stellar astrophysical processes can be efficiently studied. The project is the solution to the problem of future access to the UV spectroscopy. Dedicated to spectroscopic and imaging observations of the ultraviolet sky, the World Space Observatory - Ultraviolet mission is a Russian-Spanish collaboration with potential Mexican minor contribution. This paper provides a state of art of the project and pays a special attention to the key scientific drivers of the mission.

  10. The Stellar parametrization using Artificial Neural Network

    CERN Document Server

    Giridhar, Sunetra; Kunder, Andrea; Muneer, S; Kumar, G Selva

    2012-01-01

    An update on recent methods for automated stellar parametrization is given. We present preliminary results of the ongoing program for rapid parametrization of field stars using medium resolution spectra obtained using Vainu Bappu Telescope at VBO, Kavalur, India. We have used Artificial Neural Network for estimating temperature, gravity, metallicity and absolute magnitude of the field stars. The network for each parameter is trained independently using a large number of calibrating stars. The trained network is used for estimating atmospheric parameters of unexplored field stars.

  11. Advanced Stellar Compass, SAC-C, Interface Control Document

    DEFF Research Database (Denmark)

    Madsen, Peter Buch; Betto, Maurizio; Riis, Troels;

    Interface Control Document for the Advanced Stellar Compass for the SAC-C satellite. The SAC-C is Argentine, Danish and NASA satellite. On the SAC-C satellite there are a simplified version of the Ørsted instrumentation platform. The Advanced Stellar Compass is a improved version of the Ørsted Star...... Imager. This document descibes the interface between the Advanced Stellar Compass and OBDH, the size of the DPU and the Camera etc....

  12. Radial velocity planet detection biases at the stellar rotational period

    OpenAIRE

    2016-01-01

    Future generations of precise radial velocity (RV) surveys aim to achieve sensitivity sufficient to detect Earth mass planets orbiting in their stars' habitable zones. A major obstacle to this goal is astrophysical radial velocity noise caused by active areas moving across the stellar limb as a star rotates. In this paper, we quantify how stellar activity impacts exoplanet detection with radial velocities as a function of orbital and stellar rotational periods. We perform data-driven simulati...

  13. Testing Density Wave Theory with Resolved Stellar Populations around Spiral Arms in M81

    CERN Document Server

    Choi, Yumi; Williams, Benjamin F; Weisz, Daniel R; Skillman, Evan D; Fouesneau, Morgan; Dolphin, Andrew E

    2015-01-01

    Stationary density waves rotating at a constant pattern speed $\\Omega_{\\rm P}$ would produce age gradients across spiral arms. We test whether such age gradients are present in M81 by deriving the recent star formation histories (SFHs) of 20 regions around one of M81's grand-design spiral arms. For each region, we use resolved stellar populations to determine the SFH by modeling the observed color-magnitude diagram (CMD) constructed from archival Hubble Space Telescope (HST) F435W and F606W imaging. Although we should be able to detect systematic time delays in our spatially-resolved SFHs, we find no evidence of star formation propagation across the spiral arm. Our data therefore provide no convincing evidence for a stationary density wave with a single pattern speed in M81, and instead favor the scenario of kinematic spiral patterns that are likely driven by tidal interactions with the companion galaxies M82 and NGC 3077.

  14. Scrap of gloveboxes No. 801-W and No. 802-W

    CERN Document Server

    Ohuchi, S; Kurosawa, M; Okane, S; Usui, T

    2002-01-01

    Both gloveboxes No. 801-W for measuring samples of uranium or plutonium and No. 802-W for analyzing the quantity of uranium or plutonium are established at twenty five years ago in the analyzing room No. 108 of Plutonium Fuel Research Facility. It was planned to scrap the gloveboxes and to establish new gloveboxes. This report describes the technical view of the scrapping works.

  15. An updated MILES stellar library and stellar population models (Research Note)

    NARCIS (Netherlands)

    Falcon-Barroso, J.; Sanchez-Blazquez, P.; Vazdekis, A.; Ricciardelli, E.; Cardiel, N.; Cenarro, A. J.; Gorgas, J.; Peletier, R. F.

    Aims: We present a number of improvements to the MILES library and stellar population models. We correct some small errors in the radial velocities of the stars, measure the spectral resolution of the library and models more accurately, and give a better absolute flux calibration of the models.

  16. Single stellar populations in the near-infrared. I. Preparation of the IRTF spectral stellar library

    NARCIS (Netherlands)

    Meneses-Goytia, S.; Peletier, R. F.; Trager, S. C.; Falcón-Barroso, J.; Koleva, M.; Vazdekis, A.

    2015-01-01

    We present a detailed study of the stars of the NASA InfraRed Telescope Facility (IRTF) spectral library to understand its full extent and reliability for use with stellar population (SP) modeling. The library consist of 210 stars, with a total of 292 spectra, covering the wavelength range of 0.94 t

  17. THE STEADY-STATE WIND MODEL FOR YOUNG STELLAR CLUSTERS WITH AN EXPONENTIAL STELLAR DENSITY DISTRIBUTION

    Energy Technology Data Exchange (ETDEWEB)

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Martinez-Gonzalez, Sergio [Instituto Nacional de Astrofisica Optica y Electronica, AP 51, 72000 Puebla (Mexico); Bisnovatyi-Kogan, Gennadiy, E-mail: silich@inaoep.mx, E-mail: gkogan@iki.rssi.ru [Space Research Institute, 84/32 Profsoyuznaya, Moscow 117810 (Russian Federation)

    2011-12-20

    A hydrodynamic model for steady-state, spherically symmetric winds driven by young stellar clusters with an exponential stellar density distribution is presented. Unlike in most previous calculations, the position of the singular point R{sub sp}, which separates the inner subsonic zone from the outer supersonic flow, is not associated with the star cluster edge, but calculated self-consistently. When the radiative losses of energy are negligible, the transition from the subsonic to the supersonic flow occurs always at R{sub sp} Almost-Equal-To 4R{sub c} , where R{sub c} is the characteristic scale for the stellar density distribution, irrespective of other star cluster parameters. This is not the case in the catastrophic cooling regime, when the temperature drops abruptly at a short distance from the star cluster center, and the transition from the subsonic to the supersonic regime occurs at a much smaller distance from the star cluster center. The impact from the major star cluster parameters to the wind inner structure is thoroughly discussed. Particular attention is paid to the effects which radiative cooling provides to the flow. The results of the calculations for a set of input parameters, which lead to different hydrodynamic regimes, are presented and compared to the results from non-radiative one-dimensional numerical simulations and to those from calculations with a homogeneous stellar mass distribution.

  18. The AIMSS Project III: The Stellar Populations of Compact Stellar Systems

    CERN Document Server

    Janz, Joachim; Forbes, Duncan A; Huxor, Avon; Romanowsky, Aaron J; Frank, Matthias J; Escudero, Carlos G; Faifer, Favio R; Forte, Juan Carlos; Kannappan, Sheila J; Maraston, Claudia; Brodie, Jean P; Strader, Jay; Thompson, Bradley R

    2015-01-01

    In recent years, a growing zoo of compact stellar systems (CSSs) have been found whose physical properties (mass, size, velocity dispersion) place them between classical globular clusters (GCs) and true galaxies, leading to debates about their nature. Here we present results using a so far underutilised discriminant, their stellar population properties. Based on new spectroscopy from 8-10m telescopes, we derive ages, metallicities, and [\\alpha/Fe] of 29 CSSs. These range from GCs with sizes of merely a few parsec to compact ellipticals larger than M32. Together with a literature compilation, this provides a panoramic view of the stellar population characteristics of early-type systems. We find that the CSSs are predominantly more metal rich than typical galaxies at the same stellar mass. At high mass, the compact ellipticals (cEs) depart from the mass-metallicity relation of massive early-type galaxies, which forms a continuous sequence with dwarf galaxies. At lower mass, the metallicity distribution of ultra...

  19. The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

    Science.gov (United States)

    Christensen-Dalsgaard, Jorgen; Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

    2012-01-01

    The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled processes in the Universe. SI is a "LandmarklDiscovery Mission" in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission

  20. A Novel Approach to Constraining Uncertain Stellar Evolution Models

    Science.gov (United States)

    Rosenfield, Philip; Girardi, Leo; Dalcanton, Julianne; Johnson, L. C.; Williams, Benjamin F.; Weisz, Daniel R.; Bressan, Alessandro; Fouesneau, Morgan

    2017-01-01

    Stellar evolution models are fundamental to nearly all studies in astrophysics. They are used to interpret spectral energy distributions of distant galaxies, to derive the star formation histories of nearby galaxies, and to understand fundamental parameters of exoplanets. Despite the success in using stellar evolution models, some important aspects of stellar evolution remain poorly constrained and their uncertainties rarely addressed. We present results using archival Hubble Space Telescope observations of 10 stellar clusters in the Magellanic Clouds to simultaneously constrain the values and uncertainties of the strength of core convective overshooting, metallicity, interstellar extinction, cluster distance, binary fraction, and age.

  1. CP violating observables in e$^{-}$e$^{+}$ --> W$^{-}$W$^{+}$

    CERN Document Server

    Chang, D; Phillips, I

    1993-01-01

    We consider various integrated lepton charge-energy asymmetries and azimuthal asymmetries as tests of CP violation in the process $e^-e^+ \\to W^-W^+$. These asymmetries are sensitive to different linear combinations of the CP violating form factors in the three gauge boson $W^-W^+$ production vertex, and can distinguish dispersive and absorptive parts of the form factors. It makes use of purely hadronic and purely leptonic modes of $W$'s decays as well as the mixed modes. The techniques of using the kinematics of jets or missing momentum to construct CP--odd observables are also employed. These CP violating observables are illustrated in the generalized Left-Right Model and the Charged Higgs Model.

  2. Circumstellar dust, PAHs and stellar populations in early-type galaxies: insights from GALEX and WISE

    Science.gov (United States)

    Simonian, Gregory V.; Martini, Paul

    2017-02-01

    A majority of early-type galaxies contain interstellar dust, yet the origin of this dust, and why the dust sometimes exhibits unusual polycyclic aromatic hydrocarbon (PAH) ratios, remains a mystery. If the dust is internally produced, it likely originates from the large number of asymptotic giant branch stars associated with the old stellar population. We present GALEX and WISE elliptical aperture photometry of ˜310 early-type galaxies with Spitzer mid-infrared spectroscopy and/or ancillary data from ATLAS3D, to characterize their circumstellar dust and the shape of the radiation field that illuminates the interstellar PAHs. We find that circumstellar dust is ubiquitous in early-type galaxies, which indicates some tension between stellar population age estimates and models for circumstellar dust production in very old stellar populations. We also use dynamical masses from ATLAS3D to show that WISE W1 (3.4 μm) mass-to-light ratios are consistent with the initial mass function variation found by previous work. While the stellar population differences in early-type galaxies correspond to a range of radiation field shapes incident upon the diffuse dust, the ratio of the ionization-sensitive 7.7 μm/11.3 μm PAH feature does not correlate with the shape of the radiation field, nor to variations with the size-sensitive 11.3 μm/17 μm ratio. The 7.7 μm/11.3 μm PAH ratio does tend to be smaller in galaxies with proportionally greater H2 emission, which is evidence that processing of primarily smaller grains by shocks is responsible for the unusual ratios, rather than substantial differences in the overall PAH size or ionization distribution.

  3. Modelling accretion disc and stellar wind interactions: the case of Sgr A*

    Science.gov (United States)

    Christie, I. M.; Petropoulou, M.; Mimica, P.; Giannios, D.

    2016-07-01

    Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the S-cluster. When a star intercepts the accretion disc, the ram and thermal pressures of the disc terminate the stellar wind leading to the formation of a bow shock structure. Here, a semi-analytical model is constructed which describes the geometry of the termination shock formed in the wind. With the employment of numerical hydrodynamic simulations, this model is both verified and extended to a region prone to Kelvin-Helmholtz instabilities. Because the characteristic wind and stellar velocities are in ˜108 cm s-1 range, the shocked wind may produce detectable X-rays via thermal bremsstrahlung emission. The application of this model to the pericentre passage of S2, the brightest member of the S-cluster, shows that the shocked wind produces roughly a month long X-ray flare with a peak luminosity of L ≈ 4 × 1033 erg s-1 for a stellar mass-loss rate, disc number density, and thermal pressure strength of dot{M}_w= 10^{-7} M_{⊙} yr^{-1}, nd = 105 cm-3, and α = 0.1, respectively. This peak luminosity is comparable to the quiescent X-ray emission detected from Sgr A* and is within the detection capabilities of current X-ray observatories. Its detection could constrain the density and thickness of the disc at a distance of ˜3000 gravitational radii from the supermassive black hole.

  4. Stellar Differential Rotation and Coronal Timescales

    CERN Document Server

    Gibb, G P S; Mackay, D H

    2014-01-01

    We investigate the timescales of evolution of stellar coronae in response to surface differential rotation and diffusion. To quantify this we study both the formation time and lifetime of a magnetic flux rope in a decaying bipolar active region. We apply a magnetic flux transport model to prescribe the evolution of the stellar photospheric field, and use this to drive the evolution of the coronal magnetic field via a magnetofrictional technique. Increasing the differential rotation (i.e. decreasing the equator-pole lap time) decreases the flux rope formation time. We find that the formation time is dependent upon the geometric mean of the lap time and the surface diffusion timescale. In contrast, the lifetime of flux ropes are proportional to the lap time. With this, flux ropes on stars with a differential rotation of more than eight times the solar value have a lifetime of less than two days. As a consequence, we propose that features such as solar-like quiescent prominences may not be easily observable on s...

  5. Intergalactic stellar populations in intermediate redshift clusters

    CERN Document Server

    Melnick, J; Toledo, I; Selman, F J; Quintana, H

    2012-01-01

    A substantial fraction of the total stellar mass in rich clusters of galaxies resides in a diffuse intergalactic component usually referred to as the Intra-Cluster 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 onto the cluster. The models make predictions about the age distribution of the ICL stars, which may provide additional observational constraints. However, these models also over-predict the fraction of stellar mass in the ICL by a substantial margin. Here we present population synthesis models for the ICL of a dumb-bell dominated intermediate redshift (z=0.29) X-ray cluster for which we have deep MOS data obtained with the FORS2 instrument. In a previous paper we have proposed that the dumbell galaxy act as a grinding machine tearing to pieces t...

  6. Stellar Nucleosynthesis in the Hyades Open Cluster

    CERN Document Server

    Schuler, S C; The, L -S

    2009-01-01

    We report a comprehensive light element (Li, C, N, O, Na, Mg, and Al) abundance analysis of three solar-type main sequence (MS) dwarfs and three red giant branch (RGB) clump stars in the Hyades open cluster using high-resolution and high signal-to-noise spectroscopy. For each group (MS or RGB), the CNO abundances are found to be in excellent star-to-star agreement. Our results confirm that the giants have undergone the first dredge-up and that material processed by the CN cycle has been mixed to the surface layers. The observed abundances are compared to predictions of a standard stellar model based on the Clemson-American University of Beirut (CAUB) stellar evolution code. The model reproduces the observed evolution of the N and O abundances, as well as the previously derived 12C/13C ratio, but it fails to predict by a factor of 1.5 the observed level of 12C depletion. Li abundances are derived to determine if non-canonical extra mixing has occurred in the Hyades giants. The Li abundance of the giant gamma T...

  7. Il desiderio stellare del Principe di Salina

    Directory of Open Access Journals (Sweden)

    Rosalba Galvagno

    2013-05-01

    Full Text Available If desire originates from the stars –de sideribus- and, if we agree with this etymology, the Subject’s desire coincides with the Other’s desire, Tomasi di Lampedusa’s Il Gattopardo shows one of the most fascinating and enigmatic literary figures of stellar desire, as it can be read, furthermore, in the explicit of the seventh part of the novel: «Giunta faccia a faccia con lui sollevò il velo e così, pudica ma pronto ad esser posseduta, gli apparve più bella di come mai l’avesse intravista negli spazi stellari».            Why does this female figure descending from the stellar spaces in order to yield to Don Fabrizio who has reached the final stage of his journey, embody the object of a possessive desire which, paradoxically, corresponds to death? Indeed, death marks the entire novel since its memorable incipit: «”Nunc et in hora mortis nostrae. Amen”». What kind of desire is it precisely about? What is our unexpectedly Hamlet-like hero troubled by? The cues which the novel shows for the interpretation of this desire are few but meaningful. However we could appeal to Ricordi d’Infanzia which lead to the writer’s laboratory at the time of the Gattopardo, and, perhaps, let us know the “cause” of the prince of Salina’s desire.

  8. The energy budget of stellar magnetic fields

    Science.gov (United States)

    See, V.; Jardine, M.; Vidotto, A. A.; Donati, J.-F.; Folsom, C. P.; Boro Saikia, S.; Bouvier, J.; Fares, R.; Gregory, S. G.; Hussain, G.; Jeffers, S. V.; Marsden, S. C.; Morin, J.; Moutou, C.; do Nascimento, J. D.; Petit, P.; Rosén, L.; Waite, I. A.

    2015-11-01

    Spectropolarimetric observations have been used to map stellar magnetic fields, many of which display strong bands of azimuthal fields that are toroidal. A number of explanations have been proposed to explain how such fields might be generated though none are definitive. In this paper, we examine the toroidal fields of a sample of 55 stars with magnetic maps, with masses in the range 0.1-1.5 M⊙. We find that the energy contained in toroidal fields has a power-law dependence on the energy contained in poloidal fields. However the power index is not constant across our sample, with stars less and more massive than 0.5 M⊙ having power indices of 0.72 ± 0.08 and 1.25 ± 0.06, respectively. There is some evidence that these two power laws correspond to stars in the saturated and unsaturated regimes of the rotation-activity relation. Additionally, our sample shows that strong toroidal fields must be generated axisymmetrically. The latitudes at which these bands appear depend on the stellar rotation period with fast rotators displaying higher latitude bands than slow rotators. The results in this paper present new constraints for future dynamo studies.

  9. Inferring information about rotation from stellar oscillations

    CERN Document Server

    Goupil, M J; Lochard, J; Dziembowski, W A; Pamyatnykh, A A

    2003-01-01

    The first part of this paper aims at illustrating the intense scientific activity in the field of stellar rotation although, for sake of shortness, we cannot be exhaustive nor give any details. The second part is devoted to the rotation as a pertubation effect upon oscillation frequencies. The discussion focuses on one specific example: the p-modes frequency small separation which provides information about properties of the stellar inner layers. It is shown that the small separation can be affected by rotation at the level of 0.1-0.2 microHz for a 1.4 Mo model rotating with an equatorial velocity of 20 km/s at the surface. This is of the same order of magnitude as the expected precision on frequencies with a 3 months observation and must therefore be taken into account. We show however that it is possible to recover the small separation free of these contaminating effects of rotation, provided enough high quality data are available as will be with space seismic missions such as Eddington.

  10. A Search for Extremely Young Stellar Objects

    Institute of Scientific and Technical Information of China (English)

    吴月芳; 王均智; 吴京文

    2003-01-01

    We have observed 22 sources in 13CO and C18O J = 1 - 0 lines with a 13.7-m telescope at Qinghai station of PMO, NAOC. The samples were chosen with new criteria so that the sources are much redder and fainter than those chosen before. All the 22 sources were detected with the pair lines of 13CO and C18O and are suitable for analysing star formation except one multiple emission source IRAS 20300+3909. Physical parameters were derived from the local thermodynamic equilibrium assumption. The excitation temperature and column density of C18O are 13K and 1.5 × 1015 cm-2, respectively, on the average. 11 sources in the samples have line widths larger than 3 km/s. The IRAS colour indices are larger than those of class-O objects. The intermediate and farinfrared energy distributions show that the emission peaks of the samples fall in far infrared or longer wavelengths except IRAS 20149+3955, indicating that they may be very young stellar objects. Analyses of line widths and bolometric luminosity show that seven of those sources may be extremely young high or intermediate mass stellar objects.

  11. Pycnonuclear reactions in dense stellar matter

    CERN Document Server

    Yakovlev, D G; Gnedin, O Y

    2005-01-01

    We discuss pycnonuclear burning of highly exotic atomic nuclei in deep crusts of neutron stars, at densities up to 1e13 g/cc. As an application, we consider pycnonuclear burning of matter accreted on a neutron star in a soft X-ray transient (SXT, a compact binary containing a neutron star and a low-mass companion). The energy released in this burning, while the matter sinks into the stellar crust under the weight of newly accreted material, is sufficient to warm up the star and initiate neutrino emission in its core. The surface thermal radiation of the star in quiescent states becomes dependent of poorly known equation of state (EOS) of supranuclear matter in the stellar core, which gives a method to explore this EOS. Four qualitatively different model EOSs are tested against observations of SXTs. They imply different levels of the enhancement of neutrino emission in massive neutron stars by (1) the direct Urca process in nucleon/hyperon matter; (2) pion condensates; (3) kaon condensates; (4) Cooper pairing ...

  12. INTERRUPTED STELLAR ENCOUNTERS IN STAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Geller, Aaron M. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Leigh, Nathan W. C., E-mail: a-geller@northwestern.edu, E-mail: nleigh@amnh.org [Department of Astrophysics, American Museum of Natural History, Central Park West and 79th Street, New York, NY 10024 (United States)

    2015-07-20

    Strong encounters between single stars and binaries play a pivotal role in the evolution of star clusters. Such encounters can also dramatically modify the orbital parameters of binaries, exchange partners in and out of binaries, and are a primary contributor to the rate of physical stellar collisions in star clusters. Often, these encounters are studied under the approximation that they happen quickly enough and within a small enough volume to be considered isolated from the rest of the cluster. In this paper, we study the validity of this assumption through the analysis of a large grid of single–binary and binary–binary scattering experiments. For each encounter we evaluate the encounter duration, and compare this with the expected time until another single or binary star will join the encounter. We find that for lower-mass clusters, similar to typical open clusters in our Galaxy, the percent of encounters that will be “interrupted” by an interloping star or binary may be 20%–40% (or higher) in the core, though for typical globular clusters we expect ≲1% of encounters to be interrupted. Thus, the assumption that strong encounters occur in relative isolation breaks down for certain clusters. Instead, many strong encounters develop into more complex “mini-clusters,” which must be accounted for in studying, for example, the internal dynamics of star clusters, and the physical stellar collision rate.

  13. Stochastic microhertz gravitational radiation from stellar convection

    CERN Document Server

    Bennett, M F

    2014-01-01

    High-Reynolds-number turbulence driven by stellar convection in main-sequence stars generates stochastic gravitational radiation. We calculate the wave-strain power spectral density as a function of the zero-age main-sequence mass for an individual star and for an isotropic, universal stellar population described by the Salpeter initial mass function and redshift-dependent Hopkins-Beacom star formation rate. The spectrum is a broken power law, which peaks near the turnover frequency of the largest turbulent eddies. The signal from the Sun dominates the universal background. For the Sun, the far-zone power spectral density peaks at $S(f_\\mathrm{peak}) = 5.2 \\times 10^{-52}$ Hz$^{-1}$ at frequency $f_\\mathrm{peak} = 2.3 \\times 10^{-7}$ Hz. However, at low observing frequencies $f < 3 \\times 10^{-4}$ Hz, the Earth lies inside the Sun's near zone and the signal is amplified to $S_\\mathrm{near}(f_\\mathrm{peak}) = 4.1 \\times 10^{-27}$ Hz$^{-1}$ because the wave strain scales more steeply with distance ($\\propto ...

  14. A new type of stellar explosion

    CERN Document Server

    Perets, H B; Mazzali, P; Arnett, D; Kagan, D; Filippenko, A V; Li, W; Cenko, S B; Fox, D B; Leonard, D C; Moon, D -S; Sand, D J; Soderberg, A M; Foley, R J; Ganeshalingam, M; Anderson, J P; James, P A; Ofek, E O; Bildsten, L; Nelemans, G; Shen, K J; Weinberg, N N; Metzger, B D; Piro, A L; Quataert, E; Kiewe, M; Poznanski, D

    2009-01-01

    The explosive deaths of stars (supernovae; SNe) are generally explained by two physical processes. Young massive stars (more than eight solar masses, M_Sun) undergo gravitational core-collapse and appear as type Ib/c and II SNe. Type Ia SNe result from thermonuclear explosions of older, Chandrasekhar-mass carbon-oxygen white dwarfs (WDs). Even the most underluminous SNe Ia eject ~1 M_Sun of C/O burning products. Here we report our discovery of the faint type Ib SN 2005E in the halo of the nearby isolated galaxy, NGC 1032. The lack of any trace of recent star formation near the SN location, and the very low ejected mass we find (~0.3 M_Sun) argues strongly against a core-collapse origin of this event. Our spectroscopic observations and the derived nucleosynthetic output show that the SN ejecta is dominated by helium-burning products, indicating that SN 2005E was neither a subluminous nor a regular SNe Ia. We have therefore found a new type of stellar explosion, arising from a low-mass, old stellar system. The ...

  15. Electromagnetic simulations of tokamaks and stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Cole, Michael; Mishchenko, Alexey [Max-Planck-Institut fuer Plasmaphysik, EURATOM-Assoziation, Wendelsteinstrasse 1, 17491 Greifswald (Germany)

    2014-07-01

    A practical fusion reactor will require a plasma β of around 5%. In this range Alfvenic effects become important. Since a practical reactor will also produce energetic alpha particles, the interaction between Alfvenic instabilities and fast ions is of particular interest. We have developed a fluid electron, kinetic ion hybrid model that can be used to study this problem. Compared to fully gyrokinetic electromagnetic codes, hybrid codes offer faster running times and greater flexibility, at the cost of reduced completeness. The model has been successfully verified against the worldwide ITPA Toroidal Alfven Eigenmode (TAE) benchmark, and the ideal MHD code CKA for the internal kink mode in a tokamak. Use of the model can now be turned toward cases of practical relevance. Current work focuses on simulating fishbones in a tokamak geometry, which may be of relevance to ITER, and producing the first non-perturbative self-consistent simulations of TAE in a stellarator, which may be of relevance both to Wendelstein 7-X and any future stellarator reactor. Preliminary results of these studies are presented.

  16. Observing stellar mass and supermassive black holes

    Science.gov (United States)

    Cherepashchuk, A. M.

    2016-07-01

    During the last 50 years, great progress has been made in observing stellar-mass black holes (BHs) in binary systems and supermassive BHs in galactic nuclei. In 1964, Zeldovich and Salpeter showed that in the case of nonspherical accretion of matter onto a BH, huge energy releases occur. The theory of disk accretion of matter onto BHs was developed in 1972-1973 by Shakura and Sunyaev, Pringle and Rees, and Novikov and Thorne. Up to now, 100 years after the creation of Albert Einstein's General Theory of Relativity, which predicts the existence of BHs, the masses of tens of stellar-mass BHs ( M_BH=(4-35) M_⊙) and many hundreds of supermassive BHs ( M_BH=(10^6-1010) M_⊙) have been determined. A new field of astrophysics, so-called BH demography, is developing. The recent discovery of gravitational waves from BH mergers in binary systems opens a new era in BH studies.

  17. Synthetic polarimetric spectra from stellar prominences

    Science.gov (United States)

    Felipe, T.; Martínez González, M. J.; Asensio Ramos, A.

    2017-02-01

    Stellar prominences detected in rapidly rotating stars serve as probes of the magnetism in the corona of cool stars. We have synthesized the temporal evolution of the Stokes profiles generated in the He I 10 830 and 5876 Å triplets during the rotation of a prominence around a star. The synthesis was performed with the HAZEL code using a cloud model in which the prominence is characterized by a slab located at a fixed latitude and height. It accounts for the scattering polarization and Zeeman and Hanle effects. Several cases with different prominence magnetic field strengths and orientations have been analysed. The results show an emission feature that drifts across the profile while the prominence is out of the stellar disc. When the prominence eclipses the star, the intensity profile shows an absorption. The scattering induced by the prominence generates linear polarization signals in Stokes Q and U profiles, which are modified by the Hanle effect when a magnetic field is present. Due to the Zeeman effect, Stokes V profiles show a signal with very low amplitude when the magnetic field along the line of sight is different from zero. The estimated linear polarization signals could potentially be detected with the future spectropolarimeter Mid-resolution InfRAreD Astronomical Spectrograph, to be attached to Gran Telescopio Canarias telescope.

  18. Synthetic polarimetric spectra from stellar prominences

    CERN Document Server

    Felipe, T; Ramos, A Asensio

    2016-01-01

    Stellar prominences detected in rapidly rotating stars serve as probes of the magnetism in the corona of cool stars. We have synthesized the temporal evolution of the Stokes profiles generated in the He I 10830 and 5876 A triplets during the rotation of a prominence around a star. The synthesis was performed with the HAZEL code using a cloud model in which the prominence is characterized by a slab located at a fixed latitude and height. It accounts for the scattering polarization and Zeeman and Hanle effects. Several cases with different prominence magnetic field strengths and orientations have been analyzed. The results show an emission feature that drifts across the profile while the prominence is out of the stellar disk. When the prominence eclipses the star, the intensity profile shows an absorption. The scattering induced by the prominence generates linear polarization signals in Stokes Q and U profiles, which are modified by the Hanle effect when a magnetic field is present. Due to the Zeeman effect, St...

  19. Galaxy bimodality versus stellar mass and environment

    CERN Document Server

    Baldry, I; Bower, R; Glazebrook, K; Nichol, R; Bamford, S; Budavari, T

    2006-01-01

    We analyse a z<0.1 galaxy sample from the Sloan Digital Sky Survey focusing on the variation of the galaxy colour bimodality with stellar mass and projected neighbour density Sigma, and on measurements of the galaxy stellar mass functions. The characteristic mass increases with environmental density from about 10^10.6 Msun to 10^10.9 Msun (Kroupa IMF, H_0=70) for Sigma in the range 0.1--10 per Mpc^2. The galaxy population naturally divides into a red and blue sequence with the locus of the sequences in colour-mass and colour-concentration index not varying strongly with environment. The fraction of galaxies on the red sequence is determined in bins of 0.2 in log Sigma and log mass (12 x 13 bins). The red fraction f_r generally increases continuously in both Sigma and mass such that there is a unified relation: f_r = F(Sigma,mass). Two simple functions are proposed which provide good fits to the data. These data are compared with analogous quantities in semi-analytical models based on the Millennium N-body ...

  20. The Kepler Catalog of Stellar Flares

    Science.gov (United States)

    Davenport, James R. A.

    2016-09-01

    A homogeneous search for stellar flares has been performed using every available Kepler light curve. An iterative light curve de-trending approach was used to filter out both astrophysical and systematic variability to detect flares. The flare recovery completeness has also been computed throughout each light curve using artificial flare injection tests, and the tools for this work have been made publicly available. The final sample contains 851,168 candidate flare events recovered above the 68% completeness threshold, which were detected from 4041 stars, or 1.9% of the stars in the Kepler database. The average flare energy detected is ˜1035 erg. The net fraction of flare stars increases with g - i color, or decreasing stellar mass. For stars in this sample with previously measured rotation periods, the total relative flare luminosity is compared to the Rossby number. A tentative detection of flare activity saturation for low-mass stars with rapid rotation below a Rossby number of ˜0.03 is found. A power-law decay in flare activity with Rossby number is found with a slope of -1, shallower than typical measurements for X-ray activity decay with Rossby number.

  1. Investigating stellar-mass black hole kicks

    CERN Document Server

    Repetto, Serena; Sigurdsson, Steinn

    2012-01-01

    We investigate whether stellar-mass black holes have to receive natal kicks in order to explain the observed distribution of low-mass X-ray binaries containing black holes within our Galaxy. Such binaries are the product of binary evolution, where the massive primary has exploded forming a stellar-mass black hole, probably after a common envelope phase where the system contracted down to separations of order 10-30 Rsun. We perform population synthesis calculations of these binaries, applying both kicks due to supernova mass-loss and natal kicks to the newly-formed black hole. We then integrate the trajectories of the binary systems within the Galactic potential. We find that natal kicks are in fact necessary to reach the large distances above the Galactic plane achieved by some binaries. Further, we find that the distribution of natal kicks would seem to be similar to that of neutron stars, rather than one where the kick velocities are reduced by the ratio of black hole to neutron-star mass (i.e. where the ki...

  2. Probing Stellar Dynamics With Space Photometry

    Science.gov (United States)

    García, Rafael A.; Salabert, D.; Ballot, J.; Beck, P. G.; Bigot, L.; Corsaro, E.; Creevey, O.; Egeland, R.; Jiménez, A.; Mathur, S.; Metcalfe, T.; do Nascimento, J.; Pallé, P. L.; Pérez Hernández, F.; Regulo, C.

    2016-08-01

    The surface magnetic field has substantial influence on various stellar properties that can be probed through various techniques. With the advent of new space-borne facilities such as CoRoT and Kepler, uninterrupted long high-precision photometry is available for hundred of thousand of stars. This number will substantially grow through the forthcoming TESS and PLATO missions. The unique Kepler observations -covering up to 4 years with a 30-min cadence- allows studying stellar variability with different origins such as pulsations, convection, surface rotation, or magnetism at several time scales from hours to years. We study the photospheric magnetic activity of solar-like stars by means of the variability induced in the observed signal by starspots crossing the visible disk. We constructed a solar photometric magnetic activity proxy, Sph from SPM/VIRGO/SoHO, as if the Sun was a distant star and we compare it with several solar well-known magnetic proxies. The results validate this approach. Thus, we compute the Sph proxy for a set of CoRoT and Kepler solar-like stars for which pulsations were already detected. After characterizing the rotation and the magnetic properties of 300 solar-like stars, we use their seismic properties to characterize 18 solar analogs for which we study their magnetism. This allows us to put the Sun into context of its siblings.

  3. The Kepler Catalog of Stellar Flares

    CERN Document Server

    Davenport, James R A

    2016-01-01

    A homogeneous search for stellar flares has been performed using every available Kepler light curve. An iterative light curve de-trending approach was used to filter out both astrophysical and systematic variability to detect flares. The flare recovery completeness has also been computed throughout each light curve using artificial flare injection tests, and the tools for this work have been made publicly available. The final sample contains 851,168 candidate flare events recovered above the 68% completeness threshold, which were detected from 4041 stars, or 1.9% of the stars in the Kepler database. The average flare energy detected is ~$10^{35}$ erg. The net fraction of flare stars increases with $g-i$ color, or decreasing stellar mass. For stars in this sample with previously measured rotation periods, the total relative flare luminosity is compared to the Rossby number. A tentative detection of flare activity saturation for low-mass stars with rapid rotation below a Rossby number of ~0.03 is found. A power...

  4. Stellar subsystems of the galaxy NGC 1313

    Science.gov (United States)

    Tikhonov, N. A.; Galazutdinova, O. A.

    2016-07-01

    Based on archival Hubble Space Telescope (HST) ACS/WFC images, we have performed stellar photometry for eight fields of the spiral galaxy NGC 1313 and its satellite, the low-mass Sph/Irr galaxy AM0319-662. Stars of various ages have been identified on the constructed Hertzsprung-Russell diagrams: young supergiants, middle-aged stars, and old stars (red giants); their apparent distributions over the body of the galaxy are presented. The red supergiants and giants have been divided into groups with larger and smaller color indices, corresponding to a difference in stellar metallicity. These groups of stars are shown to have different spatial distributions and to belong to two galaxies, NGC1313 itself and the disrupted satellite. We have determined the distance to NGC 1313, D = 3.88 ± 0.07 Mpc, by the TRGB method from six fields. Our photometry of 2014 HST images has revealed an emerged charge transfer inefficiency on the ACS/WFC CCDs, which manifests itself as a dependence of the photometry of stars on their coordinates on the CCD.

  5. CHARAKTERYSTYKA HELIOSTATÓW I ICH ZASTOSOWANIE W HELIOELEKTROWNIACH

    Directory of Open Access Journals (Sweden)

    Paweł WAJSS

    Full Text Available Rozwój energetyki słonecznej związany jest z powstawaniem coraz to nowych konstrukcji maksymalizującej wykorzystanie promieniowania słonecznego. Jednym z kierunków jest wysokotemperaturowa konwersja promieniowania na ciepło. Wtedy, z termodynamicznego punktu widzenia otwierają się nam możliwości np. na generację energii elektrycznej. Konwersja wysokotemperaturowa wymaga jednak koncentracji promieniowania słonecznego. Sposobów koncentracji jest wiele, jednak w artykule skupiono się na koncentracji w układzie pole heliostatów- wieża słoneczna. System taki ma szereg zalet w porównaniu do pojedynczych układów koncentrujących, m.in. możliwe jest budowanie pojedynczej elektrowni. Zasadniczym elementem jest tutaj heliostat. Artykuł definiuje pojęcie heliostatu, przedstawia zasadę jego działania oraz przeznaczenie w helioelektrowniach typu wieżowego. Dokonany został podział urządzeń na podgrupy w zależności od technologii w nich zastosowanych. Zaprezentowane zostały poszczególne elementy budowy heliostatów oraz czynniki, które pośrednio lub bezpośrednio wpływają na ich typ, wielkość oraz cenę. Przedstawiono problematykę rentowności przed jaką stoi dziś rynek helioelektrowni oraz stopień istotności jaki stanowi pole heliostatów dla budżetu całej inwestycji. Wymieniono szczegółowe parametry jakie winny spełniać tego typu urządzenia, z wyodrębnieniem trzech grup: wymagania operacyjne, optyczne oraz wytrzymałościowe. Zaprezentowano szczegółowo trzy przykładowe, znacząco różniące co do zasady działania oraz skali, rozwiązania i sparametryzowano je w formie tabelarycznej.

  6. Astrostatistical Analysis in Solar and Stellar Physics

    Science.gov (United States)

    Stenning, David Craig

    This dissertation focuses on developing statistical models and methods to address data-analytic challenges in astrostatistics---a growing interdisciplinary field fostering collaborations between statisticians and astrophysicists. The astrostatistics projects we tackle can be divided into two main categories: modeling solar activity and Bayesian analysis of stellar evolution. These categories from Part I and Part II of this dissertation, respectively. The first line of research we pursue involves classification and modeling of evolving solar features. Advances in space-based observatories are increasing both the quality and quantity of solar data, primarily in the form of high-resolution images. To analyze massive streams of solar image data, we develop a science-driven dimension reduction methodology to extract scientifically meaningful features from images. This methodology utilizes mathematical morphology to produce a concise numerical summary of the magnetic flux distribution in solar "active regions'' that (i) is far easier to work with than the source images, (ii) encapsulates scientifically relevant information in a more informative manner than existing schemes (i.e., manual classification schemes), and (iii) is amenable to sophisticated statistical analyses. In a related line of research, we perform a Bayesian analysis of the solar cycle using multiple proxy variables, such as sunspot numbers. We take advantage of patterns and correlations among the proxy variables to model solar activity using data from proxies that have become available more recently, while also taking advantage of the long history of observations of sunspot numbers. This model is an extension of the Yu et al. (2012) Bayesian hierarchical model for the solar cycle that used the sunspot numbers alone. Since proxies have different temporal coverage, we devise a multiple imputation scheme to account for missing data. We find that incorporating multiple proxies reveals important features of

  7. Equilibrium Reconstructions with V3FIT and Current Evolution Modeling for 3-D Stellarator Plasmas

    Science.gov (United States)

    Schmitt, J. C.; Cianciosa, M.; Geiger, J.; Lazerson, S.

    2016-10-01

    V3FIT is a powerful equilibrium reconstruction tool for magnetic confinement fusion experiments which are inherently 3-D in nature (i.e. stellarators) or have 3-D components (tokamaks with 3-D shaping, reversed field pinches with helical states, etc). Here, we present details of the diagnostic modeling, constraints and the user interface for reconstructions of W7-X plasmas. For typical discharges during the OP1.1 run campaign of W7-X, the net toroidal current and current density profile do not reach steady-state. When modeling the current evolution in 3-D plasmas, both poloidal and toroidal currents are linked with both poloidal and toroidal fluxes. In contrast, in toroidally axisymmetric plasmas, the poloidal flux is linked only with the toroidal current and the toroidal current is linked only with the poloidal flux. Compared to an equivalently-sized axisymmetric configuration, the current diffusion in 3-D plasmas is enhanced, leading to a faster relaxation of the current profile to its steady-state. Implications for the time-evolution of the current and rotational transform profiles in stellarator plasmas are discussed. This work is supported by DoE Grant DE-SC00014529.

  8. Calculation of continuum damping of Alfvén eigenmodes in tokamak and stellarator equilibria

    Energy Technology Data Exchange (ETDEWEB)

    Bowden, G. W.; Hole, M. J. [Plasma Theory and Modelling, Research School of Physics and Engineering, Australian National University, Acton 2601, Australian Capital Territory (Australia); Könies, A. [Max-Planck-Institut für Plasmaphysik, EURATOM-Association, D-17491 Greifswald (Germany)

    2015-09-15

    In an ideal magnetohydrodynamic (MHD) plasma, shear Alfvén eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfvén continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfvén eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. Such an approach can be implemented in three-dimensional ideal MHD codes which use the Galerkin method. Analytic functions can be fitted to numerical data for equilibrium quantities in order to determine the value of these quantities along the complex contour. This approach requires less resolution than the established technique of calculating damping as resistivity vanishes and is thus more computationally efficient. The complex contour method has been applied to the three-dimensional finite element ideal MHD Code for Kinetic Alfvén waves. In this paper, we discuss the application of the complex contour technique to calculate the continuum damping of global modes in tokamak as well as torsatron, W7-X and H-1NF stellarator cases. To the authors' knowledge, these stellarator calculations represent the first calculation of continuum damping for eigenmodes in fully three-dimensional equilibria. The continuum damping of global modes in W7-X and H-1NF stellarator configurations investigated is found to depend sensitively on coupling to numerous poloidal and toroidal harmonics.

  9. Regrowth of stellar disks in mature galaxies: The two component nature of NGC 7217 revisited with VIRUS-W† ⋄

    Science.gov (United States)

    Fabricius, Maximilian H.; Coccato, Lodovico; Bender, Ralf; Drory, Niv; Gössl, Claus; Landriau, Martin; Saglia, Roberto P.; Thomas, Jens; Williams, Michael J.

    2015-02-01

    We have obtained high spectral resolution (R ~ 9000), integral field observations of the three spiral galaxies NGC 3521, NGC 7217 and NGC 7331 using the new fiber-based Integral Field Unit instrument VIRUS-W at the 2.7 m telescope of the McDonald Observatory in Texas. Our data allow us to revisit previous claims of counter rotation in these objects. A detailed kinematic decomposition of NGC 7217 shows that no counter rotating stellar component is present. We find that NGC 7217 hosts a low dispersion, rotating disk that is embedded in a high velocity dispersion stellar halo or bulge that is co-rotating with the disk. Due to the very different velocity dispersions (~ 20 km s-1 vs. 150 km s-1) , we are further able to perform a Lick index analysis on both components separately which indicates that the two stellar populations are clearly separated in (Mgb,) space. The velocities and dispersions of the faster component are very similar to those of the interstellar gas as measured from the [O iii] emission. Morphological evidence of active star formation in this component further suggests that NGC 7217 may be in the process of (re)growing a disk inside a more massive and higher dispersion stellar halo.

  10. The Resolved Stellar Population in 50 Regions of M83 from HST/WFC3 Early Release Science Observations

    CERN Document Server

    Kim, Hwihyun; Chandar, Rupali; Saha, Abhijit; Kaleida, Catherine C; Mutchler, Max; Cohen, Seth H; Calzetti, Daniela; O'Connell, Robert W; Windhorst, Rogier A; Balick, Bruce; Bond, Howard E; Carollo, C Marcella; Disney, Michael J; Dopita, Michael A; Frogel, Jay A; Hall, Donald N B; Holtzman, Jon A; Kimble, Randy A; McCarthy, Patrick J; Paresce, Francesco; Silk, Joe I; Trauger, John T; Walker, Alistair R; Young, Erick T

    2012-01-01

    We present a multi-wavelength photometric study of ~15,000 resolved stars in the nearby spiral galaxy M83 (NGC5236, D=4.61Mpc) 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 towards 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...

  11. The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations

    CERN Document Server

    Milone, A P; Renzini, A; Marino, A F; Bedin, L R; Vesperini, E; D'Antona, F; Nardiello, D; Anderson, J; King, I R; Yong, D; Bellini, A; Aparicio, A; Barbuy, B; Brown, T M; Cassisi, S; Ortolani, S; Salaris, M; Sarajedini, A; van der Marel, R P

    2016-01-01

    We use high-precision photometry of red-giant-branch (RGB) stars in 57 Galactic globular clusters (GCs), mostly from the `Hubble Space Telescope (HST) UV Legacy Survey of Galactic globular clusters', to identify and characterize their multiple stellar populations. For each cluster the pseudo two-color diagram (or `chromosome map') is presented, built with a suitable combination of stellar magnitudes in the F275W, F336W, F438W and F814W filters that maximizes the separation between multiple populations. In the chromosome map of most GCs (Type I clusters), stars separate in two distinct groups that we identify with the first (1G) and the second generation (2G). This identification is further supported by noticing that 1G stars have primordial (oxygen-rich, sodium-poor) chemical composition, whereas 2G stars are enhanced in sodium and depleted in oxygen. This 1G-2G separation is not possible for a few GCs where the two sequences have apparently merged into an extended, continuous sequence. In some GCs (Type II c...

  12. 75 FR 38179 - Proposed Collection; Comment Request for Forms W-8BEN, W-8ECI, W-8EXP, and W-8IMY

    Science.gov (United States)

    2010-07-01

    ... Internal Revenue Service Proposed Collection; Comment Request for Forms W-8BEN, W-8ECI, W- 8EXP, and W-8IMY... 104-13 (44 U.S.C. 3506(c)(2)(A)). Currently, the IRS is soliciting comments concerning Form W-8BEN, Certificate of Foreign Status of Beneficial Owner for United States Tax Withholding, Form W-8ECI,...

  13. White Dwarf Pulsational Constraints on Stellar Evolution

    Science.gov (United States)

    Dunlap, Bart H.; Clemens, J. Christopher; O'Brien, Patrick C.; Hermes, J. J.; Fuchs, Joshua T.

    2017-01-01

    The complex processes that convert a protostellar cloud into a carbon/oxygen-core white dwarf star are distilled and modeled in state of the art stellar evolution codes. Many of these processes are well-constrained, but several are uncertain or must be parameterized in the models because a complete treatment would be computationally prohibitive—turbulent motions such as convective overshoot cannot, for example, be modeled in 1D. Various free parameters in the models must therefore be calibrated. We will discuss how white dwarf pulsations can inform such calibrations. The results of all prior evolution are cemented into the interiors of white dwarf stars and, so, hidden from view. However, during certain phases of their cooling, pulsations translate the star's evolutionary history into observable surface phenomena. Because the periods of a pulsating white dwarf star depend on an internal structure assembled as it evolved to its final state, white dwarf pulsation periods can be viewed as observable endpoints of stellar evolution. For example, the thickness of the helium layer in a white dwarf directly affects its pulsations; the observed periods are, therefore, a function of the number of thermal pulses during which the star converts helium into core material on the asymptotic giant branch. Because they are also a function of several other significant evolutionary processes, several pulsation modes are necessary to tease all of these apart. Unfortunately, white dwarf pulsators typically do not display enough oscillation modes to constrain stellar evolution. To avoid this limitation, we consider the pulsations of the entire collection of hot pulsating hydrogen-atmosphere white dwarf stars (DAVs). Though any one star may not have sufficient information to place interesting constraints on its evolutionary history, taken together, the stars show a pattern of modes that allows us to test evolutionary models. For an example set of published evolutionary models, we show a

  14. Polarized radiation diagnostics of stellar magnetic fields

    Science.gov (United States)

    Mathys, Gautier

    The main techniques used to diagnose magnetic fields in stars from polarimetric observations are presented. First, a summary of the physics of spectral line formation in the presence of a magnetic field is given. Departures from the simple case of linear Zeeman effect are briefly considered: partial Paschen-Back effect, contribution of hyperfine structure, and combined Stark and Zeeman effects. Important approximate solutions of the equation of transfer of polarized light in spectral lines are introduced. The procedure for disk-integration of emergent Stokes profiles, which is central to stellar magnetic field studies, is described, with special attention to the treatment of stellar rotation. This formalism is used to discuss the determination of the mean longitudinal magnetic field (through the photographic technique and through Balmer line photopolarimetry). This is done within the specific framework of Ap stars, which, with their unique large-scale organized magnetic fields, are an ideal laboratory for studies of stellar magnetism. Special attention is paid to those Ap stars whose magnetically split line components are resolved in high-dispersion Stokes I spectra, and to the determination of their mean magnetic field modulus. Various techniques of exploitation of the information contained in polarized spectral line profiles are reviewed: the moment technique (in particular, the determination of the crossover and of the mean quadratic field), Zeeman-Doppler imaging, and least-squares deconvolution. The prospects that these methods open for linear polarization studies are sketched. The way in which linear polarization diagnostics complement their Stokes I and V counterparts is emphasized by consideration of the results of broad band linear polarization measurements. Illustrations of the use of various diagnostics to derive properties of the magnetic fields of Ap stars are given. This is used to show the interest of deriving more physically realistic models of the

  15. THE ORIGIN OF THE VIRGO STELLAR SUBSTRUCTURE

    Energy Technology Data Exchange (ETDEWEB)

    Carlin, Jeffrey L.; Yam, William; Willett, Benjamin A.; Newberg, Heidi J. [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180 (United States); Casetti-Dinescu, Dana I.; Girard, Terrence M. [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Majewski, Steven R., E-mail: carlij@rpi.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)

    2012-07-10

    We present three-dimensional space velocities of stars selected to be consistent with membership in the Virgo stellar substructure. Candidates were selected from SA 103, a single 40' Multiplication-Sign 40' field from our proper-motion (PM) survey in Kapteyn's Selected Areas (SAs), based on the PMs, Sloan Digital Sky Survey (SDSS) photometry, and follow-up spectroscopy of 215 stars. The signature of the Virgo substructure is clear in the SDSS color-magnitude diagram (CMD) centered on SA 103, and 16 stars are identified that have high Galactocentric-frame radial velocities (V{sub GSR} > 50 km s{sup -1}) and lie near the CMD locus of Virgo. The implied distance to the Virgo substructure from the candidates is 14 {+-} 3 kpc. We derive mean kinematics from these 16 stars, finding a radial velocity V{sub GSR} = 153 {+-} 22 km s{sup -1} and proper motions ({mu}{sub {alpha}}cos {delta}, {mu}{sub {delta}}) = (- 5.24, -0.91) {+-} (0.43, 0.46) mas yr{sup -1}. From the mean kinematics of these members, we determine that the Virgo progenitor was on an eccentric (e {approx} 0.8) orbit that recently passed near the Galactic center (pericentric distance R{sub p} {approx} 6 kpc). This destructive orbit is consistent with the idea that the substructure(s) in Virgo originated in the tidal disruption of a Milky Way satellite. N-body simulations suggest that the entire cloud-like Virgo substructure (encompassing the 'Virgo Overdensity' and the 'Virgo Stellar Stream') is likely the tidal debris remnant from a recently disrupted massive ({approx}10{sup 9} M{sub Sun }) dwarf galaxy. The model also suggests that some other known stellar overdensities in the Milky Way halo (e.g., the Pisces Overdensity and debris near NGC 2419 and SEGUE 1) are explained by the disruption of the Virgo progenitor.

  16. Fuel Efficient Galaxies: Sustaining Star Formation with Stellar Mass Loss

    CERN Document Server

    Leitner, Samuel N

    2010-01-01

    We examine the importance of secular stellar mass loss for fueling ongoing star formation in disk galaxies during the late stages of their evolution. For a galaxy of a given stellar mass, we calculate the total mass loss rate of its entire stellar population using star formation histories derived from the observed evolution of the M*-star formation rate relation, along with the predictions of standard stellar evolution models for stellar mass loss for a variety of initial stellar mass functions. Using cosmological simulations of galaxy formation, we test a prescription for modeling the rate at which gas that was returned by stars to interstellar medium will be consumed by star formation. Our model shows that recycled gas from stellar mass loss can provide most or all of the fuel required to sustain the current level of star formation in late type galaxies. Stellar mass loss can therefore remove the tension between the low gas infall rates that are derived from observations and the relatively rapid star format...

  17. Binary Populations and Stellar Dynamics in Young Clusters

    Science.gov (United States)

    Vanbeveren, D.; Belkus, H.; Van Bever, J.; Mennekens, N.

    2008-06-01

    We first summarize work that has been done on the effects of binaries on theoretical population synthesis of stars and stellar phenomena. Next, we highlight the influence of stellar dynamics in young clusters by discussing a few candidate UFOs (unconventionally formed objects) like intermediate mass black holes, η Car, ζ Pup, γ2 Velorum and WR 140.

  18. A Stellar Reference Unit Design Study for SIRTF

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Liebe, Carl Christian

    1996-01-01

    A design study for a stellar reference unit, or star tracker, for SIRTF was conducted in FY96 in conjunction with the Tracking Sensors Group of the Avionic Equipment Section of JPL. The resulting design was derived from the Oersted, autonomous, Advanced Stellar Compass, star tracker. The projecte...... of star tracker integration with the cryogenic telescope structure....

  19. Proton Testing of Advanced Stellar Compass Digital Processing Unit

    DEFF Research Database (Denmark)

    Thuesen, Gøsta; Denver, Troelz; Jørgensen, Finn E

    1999-01-01

    The Advanced Stellar Compass Digital Processing Unit was radiation tested with 300 MeV protons at Proton Irradiation Facility (PIF), Paul Scherrer Institute, Switzerland.......The Advanced Stellar Compass Digital Processing Unit was radiation tested with 300 MeV protons at Proton Irradiation Facility (PIF), Paul Scherrer Institute, Switzerland....

  20. Advanced Stellar Compass Summary for the Auroral Lites mission

    DEFF Research Database (Denmark)

    Jørgensen, John Leif

    1998-01-01

    This document provides technical and managerial information about the Advanced Stellar Compass and its possible use in the Auroral Lites Project.The Auroral Lites is a NASA project.......This document provides technical and managerial information about the Advanced Stellar Compass and its possible use in the Auroral Lites Project.The Auroral Lites is a NASA project....

  1. Advanced Stellar Compass - Adeos II - Interface Control Document

    DEFF Research Database (Denmark)

    Betto, Maurizio; Jørgensen, John Leif; Kilsgaard, Søren;

    This document describes the Advanced Stellar Compass (ASC) and defines the interfaces between the instrument and the ADEOS II satellite. The ASC is a highly advanced and autonomous Stellar Reference Unit designed, developed and produced by the Space Instrumentation Group of the Department...

  2. Advanced Stellar Compass - Proposal for the LunARSat project

    DEFF Research Database (Denmark)

    Betto, Maurizio; Jørgensen, John Leif; Kilsgaard, Søren;

    1998-01-01

    request for proposal (r.f.p.) for the LunARSat star tracker.The Advanced Stellar Compass (ASC) is a highly advanced and autonomous Stellar Reference Unit designed, developed and produced by the Space Instrumentation Group of the Department of Automation of the Technical University of Denmark.The document...

  3. The stellar atmosphere simulation code Bifrost. Code description and validation

    NARCIS (Netherlands)

    Gudiksen, B.V.; Carlsson, M.; Hansteen, V.H.; Hayek, W.; Leenaarts, J.|info:eu-repo/dai/nl/304837946; Martínez-Sykora, J.

    2011-01-01

    Context. Numerical simulations of stellar convection and photospheres have been developed to the point where detailed shapes of observed spectral lines can be explained. Stellar atmospheres are very complex, and very different physical regimes are present in the convection zone, photosphere,

  4. Binary populations and stellar dynamics in young clusters

    CERN Document Server

    Vanbeveren, D; Van Bever, J; Mennekens, N

    2008-01-01

    We first summarize work that has been done on the effects of binaries on theoretical population synthesis of stars and stellar phenomena. Next, we highlight the influence of stellar dynamics in young clusters by discussing a few candidate UFOs (unconventionally formed objects) like intermediate mass black holes, Eta Carinae, Zeta Puppis, Gamma Velorum and WR 140.

  5. Operations of a non-stellar object tracker in space

    DEFF Research Database (Denmark)

    Riis, Troels; Jørgensen, John Leif; Betto, Maurizio

    1999-01-01

    The ability to detect and track non-stellar objects by utilizing a star tracker may seem rather straight forward, as any bright object, not recognized as a star by the system is a non stellar object. However, several pitfalls and errors exist, if a reliable and robust detection is required. To te...

  6. Variation of galactic cold gas reservoirs with stellar mass

    CERN Document Server

    Maddox, Natasha; Obreschkow, Danail; Jarvis, M J; Blyth, S -L

    2014-01-01

    The stellar and neutral hydrogen (HI) mass functions at z~0 are fundamental benchmarks for current models of galaxy evolution. A natural extension of these benchmarks is the two-dimensional distribution of galaxies in the plane spanned by stellar and HI mass, which provides a more stringent test of simulations, as it requires the HI to be located in galaxies of the correct stellar mass. Combining HI data from the ALFALFA survey, with optical data from SDSS, we find a distinct envelope in the HI-to-stellar mass distribution, corresponding to an upper limit in the HI fraction that varies monotonically over five orders of magnitude in stellar mass. This upper envelope in HI fraction does not favour the existence of a significant population of dark galaxies with large amounts of gas but no corresponding stellar population. The envelope shows a break at a stellar mass of ~10^9 Msun, which is not reproduced by modern models of galaxy populations tracing both stellar and gas masses. The discrepancy between observati...

  7. Keeping the options open: concept improvements and stellarator physics

    Science.gov (United States)

    Sanchez, J.; Tribaldos, V.

    2005-12-01

    The roadmap to a feasible fusion reactor based on the tokamak line is already established. However, options for further improvement are very desirable in order to be ready to meet the future requirements of the energy market. In this respect, stellarators have a significant role to play as candidates for steady state operation reactors. Like tokamaks, stellarators are toroidal confining devices but they show two fundamental differences: the fact that the confining magnetic field is generated by external coils; and the lack of toroidal symmetry. The history of tokamaks shows that from the original concept, solutions have converged into a given range of configurations, and, in fact, all large tokamak are relatively similar. On the other hand most of the stellarators are apparently very different (coil structure, plasma shape, size, ...). The advantage of the higher dimensionality of stellarators has been perceived as a shortcoming, but recent developments, both theoretical and computational, have permitted us to develop improved concepts and design new stellarators with outstanding physics properties. Moreover, most of the devices presently under construction are stellarators. This work is devoted to discuss, firstly, the present role of stellarators in the understanding of basic physical processes in fusion devices, secondly the role of future devices, based on different concept improvements, which will significantly expand the stellarator plasma parameter range, and finally, the potential of the concept as a fusion reactor.

  8. Theoretical Mid-UV Spectroscopic Indices for Evolved Stellar Populations

    Science.gov (United States)

    Bertone, E.; Buzzoni, A.; Chavez, M.; Rodriguez-Merino, L. H.

    2007-12-01

    Aiming at picking up suitable theoretical tools to break the age-metallicity degeneracy in simple stellar populations (SSPs), we explore here the properties of a set of 17 synthetic mid-UV spectroscopic indices relying on the Uvblue synthetic stellar library and the Buzzoni population synthesis code.

  9. Variation of galactic cold gas reservoirs with stellar mass

    NARCIS (Netherlands)

    Maddox, Natasha; Hess, Kelley M.; Obreschkow, Danail; Blyth, S.-L.; Jarvis, Matt J.

    The stellar and neutral hydrogen (H I) mass functions at z ˜ 0 are fundamental benchmarks for current models of galaxy evolution. A natural extension of these benchmarks is the two-dimensional distribution of galaxies in the plane spanned by stellar and H I mass, which provides a more stringent test

  10. A Stellar Reference Unit Design Study for SIRTF

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Liebe, Carl Christian

    1996-01-01

    A design study for a stellar reference unit, or star tracker, for SIRTF was conducted in FY96 in conjunction with the Tracking Sensors Group of the Avionic Equipment Section of JPL. The resulting design was derived from the Oersted, autonomous, Advanced Stellar Compass, star tracker. The projected...

  11. Substructure in the Stellar Halos of the Aquarius Simulations

    NARCIS (Netherlands)

    Helmi, Amina; Cooper, A. P.; White, S. D. M.; Cole, S.; Frenk, C. S.; Navarro, J. F.

    2011-01-01

    We characterize the substructure in the simulated stellar halos of Cooper et al. which were formed by the disruption of satellite galaxies within the cosmological N-body simulations of galactic halos of the Aquarius project. These stellar halos exhibit a wealth of tidal features: broad overdensities

  12. The Advanced Stellar Compass onboard the Oersted satellite

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Eisenman, Allan R.; Liebe, Carl Christian;

    1997-01-01

    In 1997 the first Danish satellite will be launched. The primarily scientific objective of the satellite is to map the magnetic field of the Earth. The attitude of the satellite is determined by an advanced stellar compass (star tracker). An advanced stellar compass consists of a CCD camera conne...

  13. Interstellar extinction and the distribution of stellar populations in the direction of the ultra-deep Chandra Galactic field

    CERN Document Server

    Revnivtsev, M; Burenin, R; Grindlay, J E; Karasev, D; Forman, W

    2010-01-01

    We studied the stellar population in the central 6.6x6.6arcmin,region of the ultra-deep (1Msec) Chandra Galactic field - the "Chandra bulge field" (CBF) approximately 1.5 degrees away from the Galactic Center - using the Hubble Space Telescope ACS/WFC blue (F435W) and red (F625W) images. We mainly focus on the behavior of red clump giants - a distinct stellar population, which is known to have an essentially constant intrinsic luminosity and color. By studying the variation in the position of the red clump giants on a spatially resolved color-magnitude diagram, we confirm the anomalous total-to-selective extinction ratio, as reported in previous work for other Galactic bulge fields. We show that the interstellar extinction in this area is = 4 on average, but varies significantly between ~3-5 on angular scales as small as 1 arcminute. Using the distribution of red clump giants in an extinction-corrected color-magnitude diagram, we constrain the shape of a stellar-mass distribution model in the direction of thi...

  14. Spatially Resolved Colors and Stellar Population Properties in Early-Type Galaxies at z ~ 1.5

    CERN Document Server

    Gargiulo, A; Longhetti, M; La Barbera, F; Tamburri, S

    2012-01-01

    We present F850LP-F160W color gradients for 11 early-type galaxies (ETGs) at 1.0R_e we have found that the fraction of high-z ETGs with negative F850LP-F160W color gradients rises up to 100%. For each galaxy, we investigate the origin of the radial color variation with a technique based on the matching of both the spatially resolved color and the global spectral energy distribution (SED) to predictions of composite stellar population models. In fact, we find that the age of the stellar populations is the only parameter whose radial variation alone can fully account for the observed color gradients and global SEDs for half of the galaxies in our sample (6 ETGs), without the need of radial variation of any other stellar population property. For four out of these six ETGs, a pure metallicity variation can also reproduce the detected color gradients. Nonetheless, a minor contribution to the observed color gradients from radial variation of star-formation time scale, abundance of low-to-high mass stars and dust ca...

  15. Modelling of advanced three-ion ICRF heating and fast ion generation scheme for tokamaks and stellarators

    Science.gov (United States)

    Faustin, J. M.; Graves, J. P.; Cooper, W. A.; Lanthaler, S.; Villard, L.; Pfefferlé, D.; Geiger, J.; Kazakov, Ye O.; Van Eester, D.

    2017-08-01

    Absorption of ion-cyclotron range of frequencies waves at the fundamental resonance is an efficient source of plasma heating and fast ion generation in tokamaks and stellarators. This heating method is planned to be exploited as a fast ion source in the Wendelstein 7-X stellarator. The work presented here assesses the possibility of using the newly developed three-ion species scheme (Kazakov et al (2015) Nucl. Fusion 55 032001) in tokamak and stellarator plasmas, which could offer the capability of generating more energetic ions than the traditional minority heating scheme with moderate input power. Using the SCENIC code, it is found that fast ions in the MeV range of energy can be produced in JET-like plasmas. The RF-induced particle pinch is seen to strongly impact the fast ion pressure profile in particular. Our results show that in typical high-density W7-X plasmas, the three-ion species scheme generates more energetic ions than the more traditional minority heating scheme, which makes three-ion scenario promising for fast-ion confinement studies in W7-X.

  16. A Critical Assessment of Stellar Mass Measurement Methods

    CERN Document Server

    Mobasher, Bahram; Ferguson, Henry C; Acquaviva, Viviana; Barro, Guillermo; Finkelstein, Steven L; Fontana, Adriano; Gruetzbauch, Ruth; Johnson, Seth; Lu, Yu; Papovich, Casey J; Pforr, Janine; Salvato, Mara; Somerville, Rachel S; Wiklind, Tommy; Wuyts, Stijn; Ashby, Matthew L N; Bell, Eric; Conselice, Christopher J; Dickinson, Mark E; Faber, Sandra M; Fazio, Giovanni; Finlator, Kristian; Galametz, Audrey; Gawiser, Eric; Giavalisco, Mauro; Grazian, Andrea; Grogin, Norman A; Guo, Yicheng; Hathi, Nimish; Kocevski, Dale; Koekemoer, Anton M; Koo, David C; Newman, Jeffrey A; Reddy, Naveen; Santini, Paola; Wechsler, Risa H

    2015-01-01

    In this paper we perform a comprehensive study of the main sources of random and systematic errors in stellar mass measurement for galaxies using their Spectral Energy Distributions (SEDs). We use mock galaxy catalogs with simulated multi-waveband photometry (from U-band to mid-infrared) and known redshift, stellar mass, age and extinction for individual galaxies. Given different parameters affecting stellar mass measurement (photometric S/N ratios, SED fitting errors, systematic effects, the inherent degeneracies and correlated errors), we formulated different simulated galaxy catalogs to quantify these effects individually. We studied the sensitivity of stellar mass estimates to the codes/methods used, population synthesis models, star formation histories, nebular emission line contributions, photometric uncertainties, extinction and age. For each simulated galaxy, the difference between the input stellar masses and those estimated using different simulation catalogs, $\\Delta\\log(M)$, was calculated and use...

  17. The stellar populations of massive galaxies in the local Universe

    CERN Document Server

    McDermid, Richard M

    2012-01-01

    I present a brief review of the stellar population properties of massive galaxies, focusing on early-type galaxies in particular, with emphasis on recent results from the ATLAS3D Survey. I discuss the occurrence of young stellar ages, cold gas, and ongoing star formation in early-type galaxies, the presence of which gives important clues to the evolutionary path of these galaxies. Consideration of empirical star formation histories gives a meaningful picture of galaxy stellar population properties, and allows accurate comparison of mass estimates from populations and dynamics. This has recently provided strong evidence of a non-universal IMF, as supported by other recent evidences. Spatially-resolved studies of stellar populations are also crucial to connect distinct components within galaxies to spatial structures seen in other wavelengths or parameters. Stellar populations in the faint outer envelopes of early-type galaxies are a formidable frontier for observers, but promise to put constraints on the ratio...

  18. IMF shape constraints from stellar populations and dynamics from CALIFA

    CERN Document Server

    Lyubenova, M; van de Ven, G; Falcón-Barroso, J; Galbany, L; Gallazzi, A; García-Benito, R; Delgado, R González; Husemann, B; La Barbera, F; Marino, R A; Mast, D; Mendez-Abreu, J; Peletier, R F P; Sánchez-Blázquez, P; Sánchez, S F; Trager, S C; Bosch, R C E van den; Vazdekis, A; Walcher, C J; Zhu, L; Zibetti, S; Ziegler, B; Bland-Hawthorn, J

    2016-01-01

    In this letter we describe how we use stellar dynamics information to constrain the shape of the stellar IMF in a sample of 27 early-type galaxies from the CALIFA survey. We obtain dynamical and stellar mass-to-light ratios, $\\Upsilon_\\mathrm{dyn}$ and $\\Upsilon_{\\ast}$, over a homogenous aperture of 0.5~$R_{e}$. We use the constraint $\\Upsilon_\\mathrm{dyn} \\ge \\Upsilon_{\\ast}$ to test two IMF shapes within the framework of the extended MILES stellar population models. We rule out a single power law IMF shape for 75% of the galaxies in our sample. Conversely, we find that a double power law IMF shape with a varying high-mass end slope is compatible (within 1$\\sigma$) with 95% of the galaxies. We also show that dynamical and stellar IMF mismatch factors give consistent results for the systematic variation of the IMF in these galaxies.

  19. Particle tagging and its implications for stellar population dynamics

    Science.gov (United States)

    Le Bret, Theo; Pontzen, Andrew; Cooper, Andrew P.; Frenk, Carlos; Zolotov, Adi; Brooks, Alyson M.; Governato, Fabio; Parry, Owen H.

    2017-07-01

    We establish a controlled comparison between the properties of galactic stellar haloes obtained with hydrodynamical simulations and with 'particle tagging'. Tagging is a fast way to obtain stellar population dynamics: instead of tracking gas and star formation, it 'paints' stars directly on to a suitably defined subset of dark matter particles in a collisionless, dark-matter-only simulation. Our study shows that 'live' particle tagging schemes, where stellar masses are painted on to the dark matter particles dynamically throughout the simulation, can generate good fits to the hydrodynamical stellar density profiles of a central Milky Way-like galaxy and its most prominent substructure. Energy diffusion processes are crucial to reshaping the distribution of stars in infalling spheroidal systems and hence the final stellar halo. We conclude that the success of any particular tagging scheme hinges on this diffusion being taken into account, and discuss the role of different subgrid feedback prescriptions in driving this diffusion.

  20. Improving 1D Stellar Models with 3D Atmospheres

    CERN Document Server

    Mosumgaard, Jakob Rørsted; Weiss, Achim; Christensen-Dalsgaard, Jørgen; Trampedach, Regner

    2016-01-01

    Stellar evolution codes play a major role in present-day astrophysics, yet they share common issues. In this work we seek to remedy some of those by the use of results from realistic and highly detailed 3D hydrodynamical simulations of stellar atmospheres. We have implemented a new temperature stratification extracted directly from the 3D simulations into the Garching Stellar Evolution Code to replace the simplified atmosphere normally used. Secondly, we have implemented the use of a variable mixing-length parameter, which changes as a function of the stellar surface gravity and temperature -- also derived from the 3D simulations. Furthermore, to make our models consistent, we have calculated new opacity tables to match the atmospheric simulations. Here, we present the modified code and initial results on stellar evolution using it.

  1. Stellar ages and metallicities of nearby elliptical galaxies

    Institute of Scientific and Technical Information of China (English)

    Bai-Tian Tang; Qiu-Sheng Gu; Song Huang

    2009-01-01

    Stellar ages and metallicities are crucial for understanding the formation and evolution of elliptical galaxies.However,due to the age-metallicity degeneracy,it is hard to measure these two parameters accurately with broad-hand photometry.In this paper,we observed high-resolution spectra for a sample of 20 nearby elliptical galaxies (EGs) with the NAOC 2.16 m telescope,and determined stellar ages and metallicities by using the empirical population synthesis and Lick/IDS index system methods.We found that stellar ages from these two methods are consistent with each other for purely old EGs; however,stellar metallicities show a zeropoint offset of 0.5 Z_⊙.Our results confirm that stellar populations in low-density environment galaxies are more diverse compared to their high-density counterparts.We also investigated the element abundance-galaxy mass relation for nearby elliptical galaxies.

  2. Metallicity dependence of turbulent pressure and macroturbulence in stellar envelopes

    CERN Document Server

    Grassitelli, Luca; Langer, Norbert; Simon-Diaz, Sergio; Castro, Norberto; Sanyal, Debashis

    2016-01-01

    Macroturbulence, introduced as a fudge to reproduce the width and shape of stellar absorption lines, reflects gas motions in stellar atmospheres. While in cool stars, it is thought to be caused by convection zones immediately beneath the stellar surface, the origin of macroturbulence in hot stars is still under discussion. Recent works established a correlation between the turbulent-to-total pressure ratio inside the envelope of stellar models and the macroturbulent velocities observed in corresponding Galactic stars. To probe this connection further, we evaluated the turbulent pressure that arises in the envelope convective zones of stellar models in the mass range 1-125 Msun based on the mixing-length theory and computed for metallicities of the Large and Small Magellanic Cloud. We find that the turbulent pressure contributions in models with these metallicities located in the hot high-luminosity part of the Hertzsprung-Russel (HR) diagram is lower than in similar models with solar metallicity, whereas the ...

  3. Star clusters as laboratories for stellar and dynamical evolution

    CERN Document Server

    Kalirai, Jason S

    2009-01-01

    Open and globular star clusters have served as benchmarks for the study of stellar evolution due to their supposed nature as simple stellar populations of the same age and metallicity. After a brief review of some of the pioneering work that established the importance of imaging stars in these systems, we focus on several recent studies that have challenged our fundamental picture of star clusters. These new studies indicate that star clusters can very well harbour multiple stellar populations, possibly formed through self-enrichment processes from the first-generation stars that evolved through post-main-sequence evolutionary phases. Correctly interpreting stellar evolution in such systems is tied to our understanding of both chemical-enrichment mechanisms, including stellar mass loss along the giant branches, and the dynamical state of the cluster. We illustrate recent imaging, spectroscopic and theoretical studies that have begun to shed new light on the evolutionary processes that occur within star cluste...

  4. Towards the Intensity Interferometry Stellar Imaging System

    CERN Document Server

    Daniel, M; Dravins, D; Kieda, D; Le Bohec, S; Núñez, P; Ribak, E

    2009-01-01

    The imminent availability of large arrays of large light collectors deployed to exploit atmospheric Cherenkov radiation for gamma-ray astronomy at more than 100GeV, motivates the growing interest in application of intensity interferometry in astronomy. Indeed, planned arrays numbering up to one hundred telescopes will offer close to 5,000 baselines, ranging from less than 50m to more than 1000m. Recent and continuing signal processing technology developments reinforce this interest. Revisiting Stellar Intensity Interferometry for imaging is well motivated scientifically. It will fill the short wavelength (B/V bands) and high angular resolution (< 0.1mas) gap left open by amplitude interferometers. It would also constitute a first and important step toward exploiting quantum optics for astronomical observations, thus leading the way for future observatories. In this paper we outline science cases, technical approaches and schedule for an intensity interferometer to be constructed and operated in the visible...

  5. Fractal Reconnection in Solar and Stellar Environments

    CERN Document Server

    Shibata, Kazunari

    2016-01-01

    Recent space based observations of the Sun revealed that magnetic reconnection is ubiquitous in the solar atmosphere, ranging from small scale reconnection (observed as nanoflares) to large scale one (observed as long duration flares or giant arcades). Often the magnetic reconnection events are associated with mass ejections or jets, which seem to be closely related to multiple plasmoid ejections from fractal current sheet. The bursty radio and hard X-ray emissions from flares also suggest the fractal reconnection and associated particle acceleration. We shall discuss recent observations and theories related to the plasmoid-induced-reconnection and the fractal reconnection in solar flares, and their implication to reconnection physics and particle acceleration. Recent findings of many superflares on solar type stars that has extended the applicability of the fractal reconnection model of solar flares to much a wider parameter space suitable for stellar flares are also discussed.

  6. Stellar mixing length theory with entropy rain

    CERN Document Server

    Brandenburg, Axel

    2015-01-01

    Stellar mixing length theory is modified to include the effects of a nongradient term that originates from the motion of convective elements with entropy perturbations of either sign. It is argued that such a term, first studied by Deardorff in the meteorological context, represents the effects of thin intense downdrafts caused by the rapid cooling in the granulation layer at the top of the convection zone. They transport heat nonlocally, as originally anticipated by Spruit in the 1990s, who describes the convection in the strongly stratified simulations of Stein & Nordlund as entropy rain. Although our model has ill-determined free parameters, it demonstrates that solutions can be found that look similar to the original ones, except that the deeper layers are now Schwarzschild stable, so no giant cells are produced and the typical convective scale is that of granules even at larger depth. Consequences for modeling solar differential, the global dynamo, and sunspots are briefly discussed.

  7. Cool WISPs for stellar cooling excesses

    Energy Technology Data Exchange (ETDEWEB)

    Giannotti, Maurizio [Barry Univ., Miami Shores, FL (United States). Physical Sciences; Irastorza, Igor [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 [DESY Hamburg (Germany). Theory Group

    2015-12-15

    Several stellar systems (white dwarfs, red giants, horizontal branch stars and possibly the neutron star in the supernova remnant Cassiopeia A) show a preference for a mild non-standard cooling mechanism when compared with theoretical models. This exotic cooling could be provided by Weakly Interacting Slim Particles (WISPs), produced in the hot cores and abandoning the star unimpeded, contributing directly to the energy loss. Taken individually, these excesses do not show a strong statistical weight. However, if one mechanism could consistently explain several of them, the hint could be significant. We analyze the hints in terms of neutrino anomalous magnetic moments, minicharged particles, hidden photons and axion-like particles (ALPs). Among them, the ALP represents the best solution. Interestingly, the hinted ALP parameter space is accessible to the next generation proposed ALP searches, such as ALPS II and IAXO.

  8. Stellar Pulsations in Beyond Horndeski Gravity Theories

    CERN Document Server

    Sakstein, Jeremy; Koyama, Kazuya

    2016-01-01

    Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify the best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.

  9. The LARI Experience - Young Stellar Light Curves

    Science.gov (United States)

    Cook, Michael J.; Coveyl, Kevin; Heiland, Leo; Steffens, Gary W.

    2015-05-01

    The Lowell Observatory has had a long and rich history of professional-amateur (Pro-Am) collaborations beginning with the observatory's founder, Percival Lowell. The Lowell Amateur Research Initiative (LARI) was launched in 2012 to formally involve amateur astronomers in scientific research by bringing them to the attention of and helping professional astronomers with their research endeavours. One of the LARI projects is the BVRI photometric monitoring of Young Stellar Objects (YSOs), wherein amateurs obtain observations to search for new outburst events and characterize the colour evolution of previously identified outbursters. We summarize the scientific and organizational aspects of this LARI program, including its goals and science motivation, the process for getting involved with the project, the current team members and their equipment, our unique methods of collaboration, programme stars, preliminary findings, and lessons learned.

  10. Stellar feedback during the reionization with EMMA

    Science.gov (United States)

    Deparis, N.; Aubert, D.; Ocvirk, P.

    2016-12-01

    Stellar feedback during the epoch of reionization is a complex problem that is far to be fully understood. The apparition of first stars in the Universe involves highly nonlinear processes that are studied using numerical simulations. We present here a model of star formation, radiation and supernovae feedback, implemented in a new AMR code with fully coupled radiative-hydrodynamic named EMMA. We present a preliminary study concerning the flow of matter and radiation passing through the virial sphere of each halos. We found a class of low-mass halo (less than 10^9 M_⊙) getting at the same time gas outflow and radiative inflow, suggesting a photo-heating effect.

  11. Evolution of Binaries in Dense Stellar Systems

    CERN Document Server

    Ivanova, Natalia

    2011-01-01

    In contrast to the field, the binaries in dense stellar systems are frequently not primordial, and could be either dynamically formed or significantly altered from their primordial states. Destruction and formation of binaries occur in parallel all the time. The destruction, which constantly removes soft binaries from a binary pool, works as an energy sink and could be a reason for cluster entering the binary-burning phase. The true binary fraction is greater than observed, as a result, the observable binary fraction evolves differently from the predictions. Combined measurements of binary fractions in globular clusters suggest that most of the clusters are still core-contracting. The formation, on other hand, affects most the more evolutionary advanced stars, which significantly enhances the population of X-ray sources in globular clusters. The formation of binaries with a compact objects proceeds mainly through physical collisions, binary-binary and single-binary encounters; however, it is the dynamical for...

  12. Retrieving Cirrus Microphysical Properties from Stellar Aureoles

    CERN Document Server

    DeVore, John G; Rappaport, Saul

    2013-01-01

    The aureoles around stars caused by thin cirrus limit nighttime measurement opportunities for ground-based astronomy but can provide information on high-altitude ice crystals for climate research. In this paper we attempt to demonstrate quantitatively how this works. Aureole profiles can be followed out to ~0.2 degrees from stars and ~0.5 degrees from Jupiter. Interpretation of diffracted starlight is similar to that for sunlight, but emphasizes larger particles. Stellar diffraction profiles are very distinctive, typically being approximately flat out to a critical angle followed by gradually steepening power-law falloff with slope less steep than -3. Using the relationship between the phase function for diffraction and the average Fourier transform of the projected area of complex ice crystals we show that defining particle size in terms of average projected area normal to the propagation direction of the starlight leads to a simple, analytic approximation representing large-particle diffraction that is near...

  13. Cool WISPs for stellar cooling excesses

    CERN Document Server

    Giannotti, Maurizio; Redondo, Javier; Ringwald, Andreas

    2015-01-01

    Several stellar systems (white dwarfs, red giants, horizontal branch stars and possibly the neutron star in the supernova remnant Cassiopeia A) show a preference for a mild non-standard cooling mechanism when compared with theoretical models. This exotic cooling could be provided by Weakly Interacting Slim Particles (WISPs), produced in the hot cores and abandoning the star unimpeded, contributing directly to the energy loss. Taken individually, these excesses do not show a strong statistical weight. However, if one mechanism could consistently explain several of them, the hint could be significant. We analyze the hints in terms of neutrino anomalous magnetic moments, minicharged particles, hidden photons and axion-like particles (ALPs). Among them, the ALP represents the best solution. Interestingly, the hinted ALP parameter space is accessible to the next generation proposed ALP searches, such as ALPS II and IAXO.

  14. Self-consistent stellar dynamical tori

    CERN Document Server

    Ciotti, L; Londrillo, P

    2003-01-01

    We present preliminary results on a new family of distribution functions that are able to generate axisymmetric, truncated (i.e., finite size) stellar dynamical models characterized by toroidal shapes. The relevant distribution functions generalize those that are known to describe polytropic spheres, for which all the dynamical and structural properties of the system can be expressed in explicit form as elementary functions of the system gravitational potential. The model construction is then completed by a numerical study of the associated Poisson equation. We note that our axisymmetric models can also include the presence of an external gravitational field, such as that produced by a massive disk or by a central mass concentration (e.g., a supermassive black hole).

  15. Probing Stellar Dynamics in Galactic Nuclei

    CERN Document Server

    Miller, M Coleman; Amaro-Seoane, Pau; Barth, Aaron J; Cutler, Curt; Gair, Jonathan R; Hopman, Clovis; Merritt, David; Phinney, E Sterl; Richstone, Douglas O

    2009-01-01

    Electromagnetic observations over the last 15 years have yielded a growing appreciation for the importance of supermassive black holes (SMBH) to the evolution of galaxies, and for the intricacies of dynamical interactions in our own Galactic center. Here we show that future low-frequency gravitational wave observations, alone or in combination with electromagnetic data, will open up unique windows to these processes. In particular, gravitational wave detections in the 10^{-5}-10^{-1} Hz range will yield SMBH masses and spins to unprecedented precision and will provide clues to the properties of the otherwise undetectable stellar remnants expected to populate the centers of galaxies. Such observations are therefore keys to understanding the interplay between SMBHs and their environments.

  16. PROBABILISTIC CATALOGS FOR CROWDED STELLAR FIELDS

    Energy Technology Data Exchange (ETDEWEB)

    Brewer, Brendon J. [Department of Statistics, University of Auckland, Private Bag 92019, Auckland 1142 (New Zealand); Foreman-Mackey, Daniel; Hogg, David W., E-mail: bj.brewer@auckland.ac.nz [Center for Cosmology and Particle Physics, Department of Physics, New York University, Washington Place, New York, NY 10003 (United States)

    2013-07-01

    We present and implement a probabilistic (Bayesian) method for producing catalogs from images of stellar fields. The method is capable of inferring the number of sources N in the image and can also handle the challenges introduced by noise, overlapping sources, and an unknown point-spread function. The luminosity function of the stars can also be inferred, even when the precise luminosity of each star is uncertain, via the use of a hierarchical Bayesian model. The computational feasibility of the method is demonstrated on two simulated images with different numbers of stars. We find that our method successfully recovers the input parameter values along with principled uncertainties even when the field is crowded. We also compare our results with those obtained from the SExtractor software. While the two approaches largely agree about the fluxes of the bright stars, the Bayesian approach provides more accurate inferences about the faint stars and the number of stars, particularly in the crowded case.

  17. The Stellar Extreme-Ultraviolet Radiation Field

    Science.gov (United States)

    Vallerga, John

    1998-04-01

    The local extreme ultraviolet (EUV) radiation field from stellar sources has been determined by combining the EUV spectra of 54 stars, taken with the spectrometers aboard the Extreme Ultraviolet Explorer satellite. The resultant spectrum over the range 70-730 Å is estimated to be 95% complete above 400 Å and 90% complete above 200 Å. The flux contributed by two B stars and three hot white dwarfs dominate the spectrum except at the shortest wavelengths, where an assortment of EUV source types contribute. The high electron densities measured toward nearby stars can be accounted for by photoionization from this radiation field, but the spectrum is too soft to explain the overionization of helium with respect to hydrogen recently measure in the Local Cloud.

  18. Studying stellar populations at high spectral resolution

    CERN Document Server

    Bruzual, Gustavo A

    2007-01-01

    I describe very briefly the new libraries of empirical spectra of stars covering wide ranges of values of the atmospheric parameters Teff, log g, [Fe/H], as well as spectral type, that have become available in the recent past, among them the HNGSL, MILES, UVES-POP, ELODIE, and the IndoUS libraries. I show the results of using the IndoUS and the HNGSL libraries, as well as an atlas of theoretical model atmospheres, to build population synthesis models. These libraries are complementary in spectral resolution and wavelength coverage, and will prove extremely useful to describe spectral features expected in galaxy spectra from the NUV to the NIR. The fits to observed galaxy spectra using simple and composite stellar population models are discussed.

  19. KEPLER ECLIPSING BINARIES WITH STELLAR COMPANIONS

    Energy Technology Data Exchange (ETDEWEB)

    Gies, D. R.; Matson, R. A.; Guo, Z.; Lester, K. V. [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 5060, Atlanta, GA 30302-5060 (United States); Orosz, J. A. [Department of Astronomy, San Diego State University, San Diego, CA 92182-1221 (United States); Peters, G. J., E-mail: gies@chara.gsu.edu, E-mail: rmatson@chara.gsu.edu, E-mail: guo@chara.gsu.edu, E-mail: lester@chara.gsu.edu, E-mail: jorosz@mail.sdsu.edu, E-mail: gjpeters@mucen.usc.edu [Space Sciences Center and Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089-1341 (United States)

    2015-12-15

    Many short-period binary stars have distant orbiting companions that have played a role in driving the binary components into close separation. Indirect detection of a tertiary star is possible by measuring apparent changes in eclipse times of eclipsing binaries as the binary orbits the common center of mass. Here we present an analysis of the eclipse timings of 41 eclipsing binaries observed throughout the NASA Kepler mission of long duration and precise photometry. This subset of binaries is characterized by relatively deep and frequent eclipses of both stellar components. We present preliminary orbital elements for seven probable triple stars among this sample, and we discuss apparent period changes in seven additional eclipsing binaries that may be related to motion about a tertiary in a long period orbit. The results will be used in ongoing investigations of the spectra and light curves of these binaries for further evidence of the presence of third stars.

  20. SKIRT: Stellar Kinematics Including Radiative Transfer

    Science.gov (United States)

    Baes, Maarten; Dejonghe, Herwig; Davies, Jonathan

    2011-09-01

    SKIRT is a radiative transfer code based on the Monte Carlo technique. The name SKIRT, acronym for Stellar Kinematics Including Radiative Transfer, reflects the original motivation for its creation: it has been developed to study the effects of dust absorption and scattering on the observed kinematics of dusty galaxies. In a second stage, the SKIRT code was extended with a module to self-consistently calculate the dust emission spectrum under the assumption of local thermal equilibrium. This LTE version of SKIRT has been used to model the dust extinction and emission of various types of galaxies, as well as circumstellar discs and clumpy tori around active galactic nuclei. A new, extended version of SKIRT code can perform efficient 3D radiative transfer calculations including a self-consistent calculation of the dust temperature distribution and the associated FIR/submm emission with a full incorporation of the emission of transiently heated grains and PAH molecules.

  1. Stellar pulsations in beyond Horndeski gravity theories

    Science.gov (United States)

    Sakstein, Jeremy; Kenna-Allison, Michael; Koyama, Kazuya

    2017-03-01

    Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify the best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.

  2. Presupernova neutrinos: realistic emissivities from stellar evolution

    Science.gov (United States)

    Patton, Kelly; Lunardini, Cecilia; Farmer, Rob; Timmes, Frank

    2017-01-01

    We present a calculation of neutrino emissivities and energy spectra from a presupernova, a massive star going through the advanced stages of nuclear burning before becoming a supernova. Neutrinos produced from beta decay and electron capture, as well as pair annihilation, plasmon decay, and the photoneutrino process are included. We use the state of the art stellar evolution code MESA to obtain realistic conditions for temperature, density, electron fraction, and nuclear isotopic composition. We have found that beta processes contribute significantly to the neutrino flux at potentially detectable energies of a few MeV. Estimates for the number of events at several current and future detectors are presented for the last few hours before collapse.

  3. Presupernova neutrinos: realistic emissivities from stellar evolution

    CERN Document Server

    Patton, Kelly M

    2015-01-01

    We present a new calculation of neutrino emissivities and energy spectra from a presupernova, a massive star going through the advanced stages of nuclear burning in the months before becoming a supernova. The contributions from beta decay and electron capture, pair annihilation, plasmon decay, and the photoneutrino process are modeled in detail, using updated tabulated nuclear rates. We also use realistic conditions of temperature, density, electron fraction and nuclear isotopic composition of the star from the state of the art stellar evolution code MESA. It is found that beta processes contribute substantially to the neutrino flux above realistic detection thresholds of few MeV, at selected positions and times in the evolution of the star.

  4. Numerical aspects of 3D stellar winds

    CERN Document Server

    Strugarek, A; Matt, S P; Reville, V

    2014-01-01

    This paper explores and compares the pitfalls of modelling the three-dimensional wind of a spherical star with a cartesian grid. Several numerical methods are compared, using either uniform and stretched grid or adaptative mesh refinement (AMR). An additional numerical complication is added, when an orbiting planet is considered. In this case a rotating frame is added to the model such that the orbiting planet is at rest in the frame of work. The three-dimensional simulations are systematically compared to an equivalent two-dimensional, axisymmetric simulation. The comparative study presented here suggests to limit the rotation rate of the rotating frame below the rotating frame of the star and provides guidelines for further three-dimensional modelling of stellar winds in the context of close-in star-planet interactions.

  5. Stellar parametrization from Gaia RVS spectra

    Science.gov (United States)

    Recio-Blanco, A.; de Laverny, P.; Allende Prieto, C.; Fustes, D.; Manteiga, M.; Arcay, B.; Bijaoui, A.; Dafonte, C.; Ordenovic, C.; Ordoñez Blanco, D.

    2016-01-01

    Context. Among the myriad of data collected by the ESA Gaia satellite, about 150 million spectra will be delivered by the Radial Velocity Spectrometer (RVS) for stars as faint as GRVS~ 16. A specific stellar parametrization will be performed on most of these RVS spectra, i.e. those with enough high signal-to-noise ratio (S/N), which should correspond to single stars that have a magnitude in the RVS band brighter than ~14.5. Some individual chemical abundances will also be estimated for the brightest targets. Aims: We describe the different parametrization codes that have been specifically developed or adapted for RVS spectra within the GSP-Spec working group of the analysis consortium. The tested codes are based on optimisation (FERRE and GAUGUIN), projection (MATISSE), or pattern-recognition methods (Artificial Neural Networks). We present and discuss each of their expected performances in the recovered stellar atmospheric parameters (effective temperature, surface gravity, overall metallicity) for B- to K-type stars. The performances for determining of [α/Fe] ratios are also presented for cool stars. Methods: Each code has been homogeneously tested with a large grid of RVS simulated synthetic spectra of BAFGK-spectral types (dwarfs and giants), with metallicities varying from 10-2.5 to 10+ 0.5 the solar metallicity, and taking variations of ±0.4 dex in the composition of the α-elements into consideration. The tests were performed for S/N ranging from ten to 350. Results: For all the stellar types we considered, stars brighter than GRVS~ 12.5 are very efficiently parametrized by the GSP-Spec pipeline, including reliable estimations of [α/Fe]. Typical internal errors for FGK metal-rich and metal-intermediate stars are around 40 K in Teff, 0.10 dex in log(g), 0.04 dex in [M/H], and 0.03 dex in [α/Fe] at GRVS = 10.3. They degrade to 155 K in Teff, 0.15 dex in log(g), 0.10 dex in [M/H], and 0.1 dex in [α/Fe] at GRVS~ 12. Similar accuracies in Teff and [M/H] are

  6. Precision Stellar Astrophysics in the Kepler Era

    CERN Document Server

    Huber, Daniel

    2016-01-01

    The study of fundamental properties (such as temperatures, radii, masses, and ages) and interior processes (such as convection and angular momentum transport) of stars has implications on various topics in astrophysics, ranging from the evolution of galaxies to understanding exoplanets. In this contribution I will review the basic principles of two key observational methods for constraining fundamental and interior properties of single field stars: the study stellar oscillations (asteroseismology) and optical long-baseline interferometry. I will highlight recent breakthrough discoveries in asteroseismology such as the measurement of core rotation rates in red giants and the characterization of exoplanet systems. I will furthermore comment on the reliability of interferometry as a tool to calibrate indirect methods to estimate fundamental properties, and present a new angular diameter measurement for the exoplanet host star HD219134 which demonstrates that diameters for stars which are relatively well resolved...

  7. Summary of the Advanced Stellar Compass

    DEFF Research Database (Denmark)

    Jørgensen, John Leif

    1997-01-01

    during several real-sky tests. The new version of the instrument was developed in order to further miniaturize the system, improve the update rate, the accuracy and the robustness. Currently, this version has been successfully integrated into two spacecraft; the Swedish micro satellite "Astrid II......The current version of the Advanced Stellar Compass (ASC) is an improved implementation of the instrument developed for the Danish Geomagnetic Research Satellite Ørsted. The Ørsted version was successfully tested in space on the NASA sounding rocket "Thunderstorm III", that was launched September 2....... 1995. During the flight, an attitude accuracy of 15-20 arcseconds was achieved, in spite of the rotation speed of the payload of 6 deg/sec being 5 times higher than the design limit. The instrument, now ready for flight and integrated in the Ørsted satellite, has an accuracy of 3" absolute, proven...

  8. New determination of abundances and stellar parameters for a set of weak G-band stars

    CERN Document Server

    Palacios, A; Masseron, T; Thévenin, F; Itam-Pasquet, J; Parthasarathy, M

    2015-01-01

    Weak G-band (wGb) stars are very peculiar red giants almost devoided of carbon and often mildly enriched in lithium. Despite their very puzzling abundance patterns, very few detailed spectroscopic studies existed up to a few years ago, preventing any clear understanding of the wGb phenomenon. We recently proposed the first consistent analysis of published data for 28 wGb stars and identified them as descendants of early A-type to late B-type stars, without being able to conclude on their evolutionary status or the origin of their peculiar abundance pattern. We used newly obtained high-resolution and high SNR spectra for 19 wGb stars in the southern and northern hemisphere to homogeneously derive their fundamental parameters, metallicities, as well as the spectroscopic abundances for Li, C, N, O, Na, Sr, and Ba. We also computed dedicated stellar evolution models that we used to determine the masses and to investigate the evolutionary status and chemical history of the stars in our sample. We confirm that the ...

  9. Stellar oscillations induced by the passage of a fast stellar object

    Science.gov (United States)

    Bertulani, C. A.; Naizer, M.; Newton, W.

    2014-09-01

    In this paper, we investigate induced oscillations by the gravitational field of a fast stellar object, such as a neutron star or a black-hole in a near miss collision with another star. Nonadiabatic collision conditions may lead to large amplitude oscillations in the star. We show that for a solar-type star a resonant condition can be achieved by a fast moving stellar object with velocity in the range of 100 to 1000 km/s, passing at a distance of a few multiples of the star radius. Although such collisions are rare, they are more frequent than head-on collisions, and their effects could be observed through a visible change of the star luminosity occurring within a few hours.

  10. Stellar oscillations induced by the passage of a fast stellar object

    CERN Document Server

    Bertulani, C A; Newton, W

    2014-01-01

    We investigate induced oscillations by the gravitational field of a fast stellar object, such as a neutron star or a black-hole in a near miss collision with another star. Non-adiabatic collision conditions may lead to large amplitude oscillations in the star. We show that for a solar-type star a resonant condition can be achieved by a fast moving stellar object with velocity in the range of 100 km/s to 1000 km/s, passing at a distance of a few multiples of the star radius. Although such collisions are rare, they are more frequent than head-on collisions, and their effects could be observed through a visible change of the star luminosity occurring within a few hours.

  11. The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies

    CERN Document Server

    Kirby, Evan N; Guhathakurta, Puragra; Cheng, Lucy; Bullock, James S; Gallazzi, Anna

    2013-01-01

    We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass-metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z_* ~ M_*^(0.30 +/- 0.02). The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M_* = 10^12 M_sun. Although the average metallicities of dwarf galaxies depend only on stellar mass, the shapes of their metallicity distributions depend on galaxy type. The metallicity distributions of dIrrs resemble simple, leaky box chemical evolution models, whereas dSphs require an additional parameter, such as gas accretion, to explain the shapes of their metallicity distributions. Furthermore, the metallicity distributions of the more luminous dSphs have sharp, metal-rich cut-offs that are consistent with the s...

  12. The Spatial Structure of Young Stellar Clusters. II. Total Young Stellar Populations

    CERN Document Server

    Kuhn, Michael A; Feigelson, Eric D

    2015-01-01

    We investigate the intrinsic stellar populations (estimated total numbers of OB and pre-main-sequence stars down to 0.1 Mo) that are present in 17 massive star-forming regions (MSFRs) surveyed by the MYStIX project. The study is based on the catalog of >31,000 MYStIX Probable Complex Members with both disk-bearing and disk-free populations, compensating for extinction, nebulosity, and crowding effects. Correction for observational sensitivities is made using the X-ray Luminosity Function (XLF) and the near-infrared Initial Mass Function (IMF)--a correction that is often not made by infrared surveys of young stars. The resulting maps of the projected structure of the young stellar populations, in units of intrinsic stellar surface density, allow direct comparison between different regions. Several regions have multiple dense clumps, similar in size and density to the Orion Nebula Cluster. The highest projected density of ~34,000 stars/pc^2 is found in the core of the RCW38 cluster. Histograms of surface densit...

  13. The stellar and sub-stellar IMF of simple and composite populations

    CERN Document Server

    Kroupa, Pavel; Pflamm-Altenburg, Jan; Thies, Ingo; Dabringhausen, Joerg; Marks, Michael; Maschberger, Thomas

    2011-01-01

    The current knowledge on the stellar IMF is documented. It is usually described as being invariant, but evidence to the contrary has emerged: it appears to become top-heavy when the star-formation rate density surpasses about 0.1 Msun/(yr pc^3) on a pc scale and it may become increasingly bottom-heavy with increasing metallicity. It ends quite abruptly below about 0.1 Msun with brown dwarfs (BDs) and very low mass stars having their own IMFs. The most massive star of mass mmax formed in an embedded cluster with stellar mass Mecl correlates strongly with Mecl being a result of gravitation-driven but resource limited growth and fragmentation induced starvation. There is no convincing evidence whatsoever that massive stars do form in isolation. Massive stars form above a density threshold in embedded clusters which become saturated when mmax = mmax\\star \\approx 150Msun which appears to be the canonical physical upper mass limit of stars. Super-canonical massive stars arise naturally due to stellar mergers induce...

  14. The Steady State Wind Model for Young Stellar Clusters with an Exponential Stellar Density Distribution

    CERN Document Server

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Martinez-Gonzalez, Sergio

    2011-01-01

    A hydrodynamic model for steady state, spherically-symmetric winds driven by young stellar clusters with an exponential stellar density distribution is presented. Unlike in most previous calculations, the position of the singular point R_sp, which separates the inner subsonic zone from the outer supersonic flow, is not associated with the star cluster edge, but calculated self-consistently. When the radiative losses of energy are negligible, the transition from the subsonic to the supersonic flow occurs always at R_sp ~ 4 R_c, where R_c is the characteristic scale for the stellar density distribution, irrespective of other star cluster parameters. This is not the case in the catastrophic cooling regime, when the temperature drops abruptly at a short distance from the star cluster center and the transition from the subsonic to the supersonic regime occurs at a much smaller distance from the star cluster center. The impact from the major star cluster parameters to the wind inner structure is thoroughly discusse...

  15. Better Stars, Better Planets: Using Stellar Rotation to Refine Estimates of Stellar Parameters

    Science.gov (United States)

    Van Saders, Jennifer

    2014-01-01

    Rotation is a fundamental property of all stars. Rotation periods are a strong function of age, evolutionary state, and mass for single stars on the main sequence (MS) and subgiant branch (SGB). These rates may differ by up to an order of magnitude when comparing hot or or young stars to cool or evolved stars. Because rotation depends sensitively on underlying stellar parameters that are challenging to measure, namely mass and age, measurements of rotation can be used to constrain and complement stellar parameters inferred through other means. This is particularly crucial in the case of transiting exoplanet host stars. We have produced models of stars with realistic angular momentum loss laws, both on the MS and SGB. Two important features of the rotation distribution are apparent: on the subgiant branch itself, rotation periods can differ by an order of magnitude between stars born above the Kraft break (6250 K) and those born below it. This allows one to infer both masses and radii on the SGB based on rotation. Secondly, subgiants born above the Kraft break can be rapidly rotating and masquerade as young stars in samples in which the luminosity or gravities are not well known. Therefore, when realistic populations of stars are considered, one cannot simply assume that rapid rotation is always an indication of youth. We provide examples with data from Kepler, among other sources, in which the addition of rotation information our understanding of the underlying stellar (and therefore planetary) distribution substantially. Implications for planet demographics are also discussed.

  16. Measurements of W Charge Asymmetry

    Energy Technology Data Exchange (ETDEWEB)

    Holzbauer, J. L. [Mississippi U.

    2015-10-06

    We discuss W boson and lepton charge asymmetry measurements from W decays in the electron channel, which were made using 9.7 fb$^{-1}$ of RunII data collected by the D0 detector at the Fermilab Tevatron Collider. The electron charge asymmetry is presented as a function of pseudo-rapidity out to |$\\eta$| $\\le$ 3.2, in five symmetric and asymmetric kinematic bins of electron transverse momentum and the missing transverse energy of the event. We also give the W charge asymmetry as a function of W boson rapidity. The asymmetries are compared with next-to-leading order perturbative quantum chromodynamics calculations. These charge asymmetry measurements will allow more accurate determinations of the proton parton distribution functions and are the most precise to date.

  17. W and Z precision physics

    Directory of Open Access Journals (Sweden)

    Isabel Josa M.

    2013-11-01

    Full Text Available Recent results on W and Z physics from LHC experiments are presented. Measurements reviewed include total W and Z cross sections, W lepton charge asymmetry, and Z differential cross sections. Production of Z bosons is studied as a function of rapidity, transverse momentum and angular variables. The Drell-Yan differential distribution with the dilepton mass and the double differential distribution with the dilepton mass and rapidity are shown. Finally, measurements of several electroweak observables, the forward-backward Drell-Yan asymmetry and the sin θW are also presented. The measurements are compared with theoretical predictions using the most accurate theoretical predictions and modern part on distribution functions. A general agreement is observed.

  18. Polski nacjonalizm w szerokiej perspektywie

    Directory of Open Access Journals (Sweden)

    Krzysztof Karczewski

    2015-12-01

    Full Text Available On Polish nationalism in wide perspective In this book review of “Dylematy polskiego nacjonalizmu” by B. Grott the author argues that B. Grott based on an interdisciplinary comparative shows not only the shape of selected Polish nationalist political doctrines in the two factions: the Catholic faction that is characterized by traditionalism, and the modernizing faction, that is characterized by facing the challenges of modernity, but also shows the compounds between them and their values and practice of life of the nation and its historical success.   Polski nacjonalizm w szerokiej perspektywie W niniejszej recenzji książki B. Grotta pt. Dylematy polskiego nacjonalizmu… autor przekonuje, iż B. Grott w oparciu o metodę interdyscyplinarną i porównawczą przedstawia nie tylko kształt wybranych polskich nacjonalistycznych doktryn politycznych w dwóch odłamach: w katolickim odłamie, o charakterze na wskroś tradycjonalistycznym i w modernizacyjnym odłamie, zwróconym frontem do wyzwań nowoczesności, ale także ukazuje związki pomiędzy nimi i lansowanymi tam wartościami a praktyką życia narodu i jego powodzenia dziejowego.

  19. A High-resolution Multiband Survey of Westerlund 2 with the Hubble Space Telescope. III. The Present-day Stellar Mass Function

    Science.gov (United States)

    Zeidler, Peter; Nota, Antonella; Grebel, Eva K.; Sabbi, Elena; Pasquali, Anna; Tosi, Monica; Christian, Carol

    2017-03-01

    We present a detailed analysis of the spatial distribution of the stellar population and the present-day mass function (PDMF) of the Westerlund 2 (Wd2) region using the data from our high-resolution multiband survey with the Hubble Space Telescope. We used state-of-the-art artificial star tests to determine spatially resolved completeness maps for each of the broadband filters. We reach a level of completeness of 50% down to F555W=24.8 mag (0.7 {M}ȯ ) and F814W=23.3 mag (0.2 {M}ȯ ) in the optical and F125W=20.2 mag and F160W=19.4 mag (both 0.12 {M}ȯ ) in the infrared throughout the field of view. We had previously reported that the core of Wd2 consists of two clumps: namely the main cluster and the northern clump. From the spatial distribution of the completeness-corrected population, we find that their stellar surface densities are 1114 {stars} {{pc}}-2 and 555 {stars} {{pc}}-2, respectively, down to F814W=21.8 mag. We find that the PDMF of Wd2 has a slope of {{Γ }}=-1.46+/- 0.06, which translates to a total stellar cluster mass of (3.6+/- 0.3)\\cdot {10}4 {M}ȯ . The spatial analysis of the PDMF reveals that the cluster population is mass-segregated and most likely primordial. In addition, we report the detection of a stellar population of spatially uniformly distributed low-mass (< 0.15 {M}ȯ ) stars, extending into the gas ridges of the surrounding gas and dust cloud, as well as a confined region of reddened stars, likely caused by a foreground CO cloud. We find hints that a cloud–cloud collision might be the origin of the formation of Wd2.

  20. Simulating the effects of stellarator geometry on gyrokinetic drift-wave turbulence

    Science.gov (United States)

    Baumgaertel, Jessica Ann

    Nuclear fusion is a clean, safe form of energy with abundant fuel. In magnetic fusion energy (MFE) experiments, the plasma fuel is confined by magnetic fields at very high temperatures and densities. One fusion reactor design is the non-axisymmetric, torus-shaped stellarator. Its fully-3D fields have advantages over the simpler, better-understood axisymmetric tokamak, including the ability to optimize magnetic configurations for desired properties, such as lower transport (longer confinement time). Turbulence in the plasma can break MFE confinement. While turbulent transport is known to cause a significant amount of heat loss in tokamaks, it is a new area of research in stellarators. Gyrokinetics is a good mathematical model of the drift-wave instabilities that cause turbulence. Multiple gyrokinetic turbulence codes that had great success comparing to tokamak experiments are being converted for use with stellarator geometry. This thesis describes such adaptations of the gyrokinetic turbulence code, GS2. Herein a new computational grid generator and upgrades to GS2 itself are described, tested, and benchmarked against three other gyrokinetic codes. Using GS2, detailed linear studies using the National Compact Stellarator Experiment (NCSX) geometry were conducted. The first compares stability in two equilibria with different β=(plasma pressure)/(magnetic pressure). Overall, the higher β case was more stable than the lower β case. As high β is important for MFE experiments, this is encouraging. The second compares NCSX linear stability to a tokamak case. NCSX was more stable with a 20% higher critical temperature gradient normalized by the minor radius, suggesting that the fusion power might be enhanced by ˜ 50%. In addition, the first nonlinear, non-axisymmetric GS2 simulations are presented. Finally, linear stability of two locations in a W7-AS plasma were compared. The experimentally-measured parameters used were from a W7-AS shot in which measured heat fluxes

  1. Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile

    Science.gov (United States)

    Gilbert, Karoline M.; Guhathakurta, Puragra; Beaton, Rachael L.; Bullock, James; Geha, Marla C.; Kalirai, Jason S.; Kirby, Evan N.; Majewski, Steven R.; Ostheimer, James C.; Patterson, Richard J.; Tollerud, Erik J.; Tanaka, Mikito; Chiba, Masashi

    2012-11-01

    We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power law with index -2.2 ± 0.2 and extends to a projected distance of at least ~175 kpc (~2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a = 0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates that a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features cannot be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California

  2. Formation and stellar spin-orbit misalignment of hot Jupiters from Lidov-Kozai oscillations in stellar binaries

    Science.gov (United States)

    Anderson, Kassandra R.; Storch, Natalia I.; Lai, Dong

    2016-03-01

    Observed hot Jupiter (HJ) systems exhibit a wide range of stellar spin-orbit misalignment angles. This paper investigates the inward migration of giant planets due to Lidov-Kozai (LK) oscillations induced by a distant stellar companion. We conduct a large population synthesis study, including the octupole gravitational potential from the stellar companion, mutual precession of the host stellar spin axis and planet orbital axis, tidal dissipation in the planet and stellar spin-down in the host star due to magnetic braking. We consider a range of planet masses (0.3-5 MJ) and initial semimajor axes (1-5 au), different properties for the host star, and varying tidal dissipation strengths. The fraction of systems that result in HJs depends on planet mass and stellar type, with fHJ = 1-4 per cent (depending on tidal dissipation strength) for Mp = 1 MJ, and larger (up to 8 per cent) for more massive planets. The production efficiency of `hot Saturns' (Mp = 0.3MJ) is much lower, because most migrating planets are tidally disrupted. We find that the fraction of systems that result in either HJ formation or tidal disruption, fmig ≃ 11-14 per cent is roughly constant, having little variation with planet mass, stellar type and tidal dissipation strength. The distribution of final HJ stellar obliquities exhibits a complex dependence on the planet mass and stellar type. For Mp = (1-3)MJ, the distribution is always bimodal, with peaks around 30° and 130°. The distribution for 5MJ planets depends on host stellar type, with a preference for low obliquities for solar-type stars, and higher obliquities for more massive (1.4 M⊙) stars.

  3. Historia Afroeuropejczyków

    Directory of Open Access Journals (Sweden)

    Judyta Krawczyk-Onyibe

    2016-01-01

    Full Text Available History of Afro-Germans The purpose of article History of Afro-Germans is to shad more light on the history of Afro-Germans of the last eight decades. I raise here issues like: social inclusion and exclusion, national affiliation, acceptance, self-identification and social categorization, stigmatization, discrimination based on racial background. I describe how this group has been perceived by the White majority of Germans, and activities of Afro-Germans that influenced change of their status and image in Germany. Based on a theoretical analysis, the following results reflect an incremental development in the recognition of Afro-Germans in Germany. Whereas the first generation of the 1940’s had been labelled as “occupation kids” not recognized by the majority of German society as member of it, rather as unwanted souvenir of Allies soldiers, the youngest generation in the meantime enjoys almost all rights included in being a German citizen.   Historia Afroeuropejczyków Historia Afroeuropejczyków to artykuł, którego celem jest rzucić światło na historię Afroniemców na przestrzeni ostatnich ośmiu dekad. Poruszam w nim takie zagadnienia, jak: inkluzja i ekskluzja społeczna, przynależność narodowa, akceptacja, autoidentyfikacja i kategoryzacja społeczna oraz stygmatyzacja i dyskryminacja na tle rasowym. Opisuję sposób postrzegania Afroniemców przez białą większość Niemców, jak i działania samej mniejszości wpływające na zmianę jej statusu i wizerunku w Niemczech. Na podstawie teoretycznej analizy dostępnych materiałów stwierdzam, iż doszło do stopniowego postępu w kwestii akceptacji Afroniemców. Mam na uwadze, że pierwsza generacja nazywana „dziećmi okupacji” nie była uznawana za część społeczeństwa niemieckiego, raczej za niechcianą „pamiątkę” po alianckich żołnierzach, tymczasem najmłodsza generacja cieszy się prawie pełnią praw, jakie przysługują niemieckiemu obywatelowi.

  4. Theory of stellar convection: Removing the Mixing-Length Parameter

    CERN Document Server

    Pasetto, S; Cropper, M; Grebel, E K

    2014-01-01

    Stellar convection is customarily described by Mixing-Length Theory, which makes use of the mixing-length scale to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is taken to be proportional to the local pressure scale height, and the proportionality factor (the mixing-length parameter) must be determined by comparing the stellar models to some calibrator, usually the Sun. No strong arguments exist to suggest that the mixing-length parameter is the same in all stars and at all evolutionary phases. Because of this, all stellar models in literature are hampered by this basic uncertainty. The aim of this study is to present a new theory of stellar convection that does not require the mixing length parameter. We present a self-consistent analytical formulation of stellar convection that determines the properties of stellar convection as a function of the physical behaviour of the convective elements themselves and the surround...

  5. Automatic stellar spectral classification via sparse representations and dictionary learning

    Science.gov (United States)

    Díaz-Hernández, R.; Peregrina-Barreto, H.; Altamirano-Robles, L.; González-Bernal, J. A.; Ortiz-Esquivel, A. E.

    2014-11-01

    Stellar classification is an important topic in astronomical tasks such as the study of stellar populations. However, stellar classification of a region of the sky is a time-consuming process due to the large amount of objects present in an image. Therefore, automatic techniques to speed up the process are required. In this work, we study the application of a sparse representation and a dictionary learning for automatic spectral stellar classification. Our dataset consist of 529 calibrated stellar spectra of classes B to K, belonging to the Pulkovo Spectrophotometric catalog, in the 3400-5500Å range. These stellar spectra are used for both training and testing of the proposed methodology. The sparse technique is applied by using the greedy algorithm OMP (Orthogonal Matching Pursuit) for finding an approximated solution, and the K-SVD (K-Singular Value Decomposition) for the dictionary learning step. Thus, sparse classification is based on the recognition of the common characteristics of a particular stellar type through the construction of a trained basis. In this work, we propose a classification criterion that evaluates the results of the sparse representation techniques and determines the final classification of the spectra. This methodology demonstrates its ability to achieve levels of classification comparable with automatic methodologies previously reported such as the Maximum Correlation Coefficient (MCC) and Artificial Neural Networks (ANN).

  6. The Massive End of the Stellar Mass Function

    CERN Document Server

    D'Souza, R; Kauffmann, G

    2015-01-01

    We derive average flux corrections to the \\texttt{Model} magnitudes of the Sloan Digital Sky Survey (SDSS) galaxies by stacking together mosaics of similar galaxies in bins of stellar mass and concentration. Extra flux is detected in the outer low surface brightness part of the galaxies, leading to corrections ranging from 0.05 to 0.32 mag for the highest stellar mass galaxies. We apply these corrections to the MPA-JHU (Max-Planck Institute for Astrophysics - John Hopkins University) stellar masses for a complete sample of half a million galaxies from the SDSS survey to derive a corrected galaxy stellar mass function at $z=0.1$ in the stellar mass range $9.5<\\log(M_\\ast/M_\\odot)<12.0$. We find that the flux corrections and the use of the MPA-JHU stellar masses have a significant impact on the massive end of the stellar mass function, making the slope significantly shallower than that estimated by Li \\& White (2009), but steeper than derived by Bernardi et al. (2013). This corresponds to a mean comov...

  7. The Decay of Stellar Dynamos and X-ray Activity

    CERN Document Server

    Wright, Nicholas J; Civano, Francesca

    2010-01-01

    Existing stellar X-ray surveys suggest major problems in our understanding of the evolution of stellar magnetic activity in solar and late-type stars, reaching conflicting conclusions over the rate of decay of X-ray activity and the spectral types responsible. We are confronting these discrepancies with a new model of the expected stellar X-ray luminosity distribution, combining a Galactic population synthesis model with current theories for rotational spin- down and the rotation - activity relation for the stellar magnetic dynamo. Here we test our model using new observations of the stellar content of the Chandra COSMOS survey, for which 60 new stellar X-ray sources are identified from the thin disk and Galactic halo populations. Our model is in approximate agreement with the observed X-ray luminosity distribution and the distribution of spectral types responsible. However, slight differences in the form of the X-ray luminosity distribution exist that may hint at problems in our understanding of stellar X-ra...

  8. The Dark Energy Survey: Prospects for Resolved Stellar Populations

    CERN Document Server

    Rossetto, B M; Girardi, L; Camargo, J I B; Balbinot, E; da Costa, L N; Yanny, B; Maia, M A G; Makler, M; Ogando, R L C; Pellegrini, P S; Ramos, B; de Simoni, F; Armstrong, R; Bertin, E; Desai, S; Kuropatkin, N; Lin, H; Mohr, J J; Tucker, D L

    2011-01-01

    Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2x10^8 stars will be sampled in DES grizY filters. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy. DES will probe low-mass stellar and sub-stellar objects at depths from 3 to 8 times larger than SDSS. The faint end of the main-sequence will be densely sampled beyond 10 kpc. The slope of the low mass end of the stellar IMF will be constrained to within a few hundredth dex, even in the thick disk and halo. In the sub-stellar mass regime, the IMF slope will be potentially constrained to within dlog \\phi(m) / dlog m ~ 0.1$. About 3x10^4 brown dwarf and at least 7.6x10...

  9. A vista of research in astronomy: stars and stellar systems

    Science.gov (United States)

    Hu, Jing-Yao; Dong, Guo-Xuan; Chen, Dong-Ping

    2004-09-01

    Based on the statistics of the paper on stars and stellar systems published in domestic and international journals, it is found that between 1981 and 2000, the progress of these two fields developed more rapidly in Chinese astronomical community than those in abroad, which reflected the fast progress in Chinese scientific researches after the reformation. Some branch fields in stars and stellar systems had made more significant progress based on their active research groups, such as supernovae and their remnants, interstellar media and star formation regions as well as stellar chemical abundances. The binary systems, which is one of the key fields in stellar systems, had synchronously with international progress, while the research on the Galaxy was relatively poorer in China. In these 20 years, the fraction of total number of the paper on stars and stellar sytems published by Chinese astronomers was only 1.3% in the world, and it shows an obvious increasing in the recent 5 years with the fraction about 2.0%, which is stll less than the fraction of international IAU members in China. Due to the development of deep-sky and high energy observing instruments, the progress in stellar research is relatively slowed down compared to the other fields in astronomy. Besides analyzing the field of stars and stellar systems, we also need to analyze the other major branches in astronomy so that a feasible development plan can be made for Chinese astronomy in the future.

  10. Multiple stellar populations in Magellanic Cloud clusters - V. The split main sequence of the young cluster NGC 1866

    Science.gov (United States)

    Milone, A. P.; Marino, A. F.; D'Antona, F.; Bedin, L. R.; Piotto, G.; Jerjen, H.; Anderson, J.; Dotter, A.; Criscienzo, M. Di; Lagioia, E. P.

    2017-03-01

    One of the most unexpected results in the field of stellar populations of the last few years is the discovery that some Magellanic Cloud globular clusters younger than ∼400 Myr exhibit bimodal main sequences (MSs) in their colour-magnitude diagrams (CMDs). Moreover, these young clusters host an extended main-sequence turn-off (eMSTO) in close analogy with what is observed in most ∼1-2 Gyr old clusters of both Magellanic Clouds. We use high-precision Hubble Space Telescope photometry to study the young star cluster NGC 1866 in the Large Magellanic Cloud. We discover an eMSTO and a split MS. The analysis of the CMD reveals that (i) the blue MS is the less populous one, hosting about one-third of the total number of MS stars; (ii) red MS stars are more centrally concentrated than blue MS stars; (iii) the fraction of blue MS stars with respect to the total number of MS stars drops by a factor of ∼2 in the upper MS with mF814W ≲ 19.7. The comparison between the observed CMDs and stellar models reveals that the observations are consistent with ∼200 Myr old highly rotating stars on the red MS, with rotation close to critical value, plus a non-rotating stellar population spanning an age interval between ∼140 and 220 Myr, on the blue MS. Noticeable, neither stellar populations with different ages only, nor coeval stellar models with different rotation rates, properly reproduce the observed split MS and eMSTO. We discuss these results in the context of the eMSTO and multiple MS phenomenon.

  11. Zastosowanie sztucznych sieci neuronowych podczas rozmieszczania towar?w w magazynie sztukowym

    OpenAIRE

    Kudelska, ?.

    2016-01-01

    Efektywno?? procesu magazynowania wp?ywa na przep?yw materia?owy w przedsi?biorstwie jak r?wnie? na funkcjonowanie ca?ego ?a?cucha dostaw. Jednym z czynnik?w utrudniaj?cych podejmowanie decyzji w sferze magazynowania jest alokacja towar?w w strefie sk?adowania. Dlatego te? celem niniejszego badania jest opisanie zastosowania sztucznej sieci neuronowej w podejmowaniu decyzji rozmieszczenia towar?w w magazynie. Przedmiotem niniejszego badania jest rozmieszczenie towaru w magazynie. Zastosowano ...

  12. Investigation of the Spherical Stellarator Concept - Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Moroz, P.E.

    2000-10-15

    This document is a final report of the U.S. DOE grant entitled ''Investigation of the Spherical Stellarator Concept'' which supported theoretical and numerical investigation of a novel fusion concept, the ultra-low-aspect-ratio stellarator system called Spherical Stellarator (SS). The research was concentrated on (a) search for principally different types of SS configurations, (b) optimization of SS configurations by varying the parameters of the coil systems, (c) finite beta and finite plasma current (including bootstrap current) equilibria in the SS, and (d) Monte Carlo particle transport simulations for the SS.

  13. Photometric entropy of stellar populations and related diagnostic tools

    CERN Document Server

    Buzzoni, A

    2005-01-01

    We discuss, from a statistical point of view, some leading issues that deal with the study of stellar populations in fully or partially unresolved aggregates, like globular clusters and distant galaxies. A confident assessment of the effective number and luminosity of stellar contributors can provide, in this regard, a very useful interpretative tool to properly assess the observational bias coming from crowding conditions or surface brightness fluctuations. These arguments have led us to introduce a new concept of "photometric entropy" of a stellar population, whose impact on different astrophysical aspects of cluster diagnostic has been reviewed here.

  14. Stellar Population Analysis of Galaxies based on Genetic Algorithms

    Institute of Scientific and Technical Information of China (English)

    Abdel-Fattah Attia; H.A.Ismail; I.M.Selim; A.M.Osman; I.A.Isaa; M.A.Marie; A.A.Shaker

    2005-01-01

    We present a new method for determining the age and relative contribution of different stellar populations in galaxies based on the genetic algorithm.We apply this method to the barred spiral galaxy NGC 3384, using CCD images in U, B, V, R and I bands. This analysis indicates that the galaxy NGC 3384 is mainly inhabited by old stellar population (age > 109 yr). Some problems were encountered when numerical simulations are used for determining the contribution of different stellar populations in the integrated color of a galaxy. The results show that the proposed genetic algorithm can search efficiently through the very large space of the possible ages.

  15. The Dark Energy Survey: Prospects for resolved stellar populations

    Energy Technology Data Exchange (ETDEWEB)

    Rossetto, Bruno M. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Santiago, Basílio X. [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); Girardi, Léo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Osservatorio Astronomica di Padova-INAF, Padova (Italy); Camargo, Julio I. B. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Balbinot, Eduardo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); da Costa, Luiz N. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Yanny, Brian [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Maia, Marcio A. G. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Makler, Martin [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro (Brazil); Ogando, Ricardo L. C. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Pellegrini, Paulo S. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Ramos, Beatriz [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); de Simoni, Fernando [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Armstrong, R. [Univ. of Illinois, Urbana, IL (United States); Bertin, E. [Univ. Pierre et Marie Curie, Paris (France); Desai, S. [Univ. of Illinois, Urbana, IL (United States); Kuropatkin, N. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lin, H. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Mohr, J. J. [Max-Planck-Institut fur extraterrestrische Physik, Garching (Germany); Tucker, D. L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

    2011-05-06

    Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 x 108 stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy.

  16. Scattering and extinction: interpreting hazes in stellar occultation data

    Science.gov (United States)

    Bosh, Amanda S.; Levine, Stephen; Sickafoose, Amanda A.; Person, Michael J.

    2016-10-01

    There has been debate concerning interpretation of stellar occultation data and whether those data contain evidence for hazes within Pluto's atmosphere. Multiple layers of haze have been imaged in at Pluto with the New Horizons spacecraft; color-dependent differences in minimum flux from stellar occultations also suggests haze. We look at a purely geometric approach, to evaluate whether it is valid to sidestep details of atmospheric temperature structure and, in an approximate manner, conduct an analysis of the 2015 stellar occultation data that is consistent with the New Horizons imaging results. Support for this work was provided by NASA SSO grant NNX15AJ82G to Lowell Observatory.

  17. STELLAR FEEDBACK AND THE EVOLUTION OF YOUNG EMBEDDED STAR CLUSTERS

    Directory of Open Access Journals (Sweden)

    C. Weidner

    2009-01-01

    Full Text Available In this contribution we present the rst results of an theoretical attempt to address the question of the evacuation time-scale but also the star-formation efficiency and the in uence of feedback on the most-massive star in a star cluster. With the use of stellar evolution models, known descriptions for the evolution of an ionised sphere around a star and further models to describe stellar winds, the e ects of young stellar populations of di erent sizes are studied.

  18. Extreme high-velocity H/sub 2/O maser features in W49N, W51, and Sagittarius B2

    Energy Technology Data Exchange (ETDEWEB)

    Morris, M.

    1976-11-15

    Extreme high-velocity 1.3 cm emission features of water vapor were found and studied in W49N, W51, and Sgr B2, extending the total ranges covered by H/sub 2/O emission in these objects to 530, 180, and 150 km s/sup -1/, respectively. Variations in the extreme high-velocity emission in W49N were monitored over a 9 month interval. Also, a spatial map of the maser sources in Sgr B2 has been made.Various models for the W49N maser source are examined in the light of the new observations, and it is concluded that the most plausible hypothesis is that an intense stellar wind from an O star has accelerated the maser clouds to their observed velocities. The W51 maser sources appears to be physically similar to W49N. Sgr B2, on the other hand, appears to be a different type of maser source. We advance the hypothesis that it is a bound cluster of discrete protostellar condensations. (AIP)

  19. Bibliografia w cyfrowej przestrzeni informacyjnej

    Directory of Open Access Journals (Sweden)

    Jadwiga Woźniak-­Kasperek

    2014-12-01

    Full Text Available Bibliography in a digital information environment The dynamically changing area of the digital, including web, information interacts with the bibliographic universe, bringing new opportunities as well as new problems for both the bibliographers and the users. The article analyzes the following issues: 1 The aim of bibliography. Bibliographies serve utilitarian purposes, they allow, or at the very least facilitate, the access to relevant publications; they connect the information with its potential recipient. But bibliographies fulfil more tasks. They are treasuries of memory, images of a widely understood culture in a certain time and place; documents of archival value meant to be preserved for future generations. 2 Bibliography and library catalogue. The dangers of identifying bibliography as library catalogue. 3 The form of bibliography. The advantages and disadvantages of the paper (printed and the digital forms. Full­-text resource as the target standard of bibliographic services and an opportunity of computer-­aided indexing. The possibilities and advantages of using Web 2.0 tools in bibliographies. 4 Searching tools. Arrangements and indexes.   Bibliografia w cyfrowej przestrzeni informacyjnej Dynamicznie zmieniająca się przestrzeń informacji cyfrowej, w tym sieciowej, oddziałuje na uniwersum bibliograficzne, stając się źródłem zarówno nowych możliwości, jak i trudności, z którymi muszą się zmagać i bibliografowie, i użytkownicy. W artykule poddano analizie cztery grupy zagadnień: 1 Cele i zadania bibliografii. Bibliografie służą celom utylitarnym, umożliwiają, lub co najmniej ułatwiają, osobom zainteresowanym dotarcie do właściwych publikacji. Bibliografie mają też inne zadania. Są skarbnicami pamięci, obrazem stanu szeroko rozumianej kultury w określonym czasie i miejscu, dokumentem, który ma znamiona dokumentu archiwalnego, przeznaczonego do zachowania dla przyszłych pokoleń. 2 Bibliografia a

  20. Absence of evidence is not evidence of absence: the colour-density relation at fixed stellar mass persists to z ~ 1

    Science.gov (United States)

    Cooper, Michael C.; Coil, Alison L.; Gerke, Brian F.; Newman, Jeffrey A.; Bundy, Kevin; Conselice, Christopher J.; Croton, Darren J.; Davis, Marc; Faber, S. M.; Guhathakurta, Puragra; Koo, David C.; Lin, Lihwai; Weiner, Benjamin J.; Willmer, Christopher N. A.; Yan, Renbin

    2010-11-01

    We use data drawn from the DEEP2 Galaxy Redshift Survey to investigate the relationship between local galaxy density, stellar mass and rest-frame galaxy colour. At z ~ 0.9, we find that the shape of the stellar mass function at the high-mass [ log 10(M*/h-2 Msolar) > 10.1] end depends on the local environment, with high-density regions favouring more massive systems. Accounting for this stellar mass-environment relation (i.e. working at fixed stellar mass), we find a significant colour-density relation for galaxies with 10.6 1. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation. E-mail: cooper@as.arizona.edu (MCC); cnaw@as.arizona.edu (CNAW); bjw@as.arizona.edu (BJW); bgerke@slac.stanford.edu (BFG); janewman@pitt.edu (JAN); kbundy@astro.berkeley.edu (KB); marc@astro.berkeley.edu (MD); conselice@nottingham.ac.uk (CJC); dcroton@astro.swin.edu.au (DJC); faber@ucolick.org (SMF); koo@ucolick.org (DCK); raja@ucolick.org (PG); lihwailin@asiaa.sinica.edu.tw (LL); yan@astro.utoronto.ca (RY) ‡ Spitzer Fellow. ¶ Alfred P. Sloan Foundation Fellow. § Hubble Fellow.