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Sample records for blue straggler stars

  1. Ecology of blue straggler stars

    CERN Document Server

    Carraro, Giovanni; Beccari, Giacomo

    2015-01-01

    The existence of blue straggler stars, which appear younger, hotter, and more massive than their siblings, is at odds with a simple picture of stellar evolution. Such stars should have exhausted their nuclear fuel and evolved long ago to become cooling white dwarfs. They are found to exist in globular clusters, open clusters, dwarf spheroidal galaxies of the Local Group, OB associations and as field stars. This book summarises the many advances in observational and theoretical work dedicated to blue straggler stars. Carefully edited extended contributions by well-known experts in the field cover all the relevant aspects of blue straggler stars research: Observations of blue straggler stars in their various environments; Binary stars and formation channels; Dynamics of globular clusters; Interpretation of observational data and comparison with models. The book also offers an introductory chapter on stellar evolution written by the editors of the book.

  2. Variable blue straggler stars in NGC 5466

    International Nuclear Information System (INIS)

    Harris, H.C.; Mateo, M.; Olszewski, E.W.; Nemec, J.M.

    1990-01-01

    Nine variable blue stragglers have been found in the globular cluster NGC 5466. The six dwarf Cepheids in this cluster coexist in the instability strip with other nonvariable stars. The three eclipsing binaries are among the hottest of the blue stragglers. The hypothesis is discussed that all blue stragglers in this cluster have undergone mass transfer in close binaries. Under this hypothesis, rotation and spin-down play important roles in controlling the evolution of blue stragglers in old clusters and in affecting some of their observational properties. 14 refs

  3. Spinning like a blue straggler: the population of fast rotating blue straggler stars in ω Centauri

    Energy Technology Data Exchange (ETDEWEB)

    Mucciarelli, A.; Lovisi, L.; Ferraro, F. R.; Dalessandro, E.; Lanzoni, B. [Dipartimento di Fisica and Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy); Monaco, L. [European Southern Observatory, Casilla 19001, Santiago (Chile)

    2014-12-10

    By using high-resolution spectra acquired with FLAMES-GIRAFFE at the ESO/VLT, we measured the radial and rotational velocities for 110 blue straggler stars (BSSs) in ω Centauri, the globular cluster-like stellar system harboring the largest known BSS population. According to their radial velocities, 109 BSSs are members of the system. The rotational velocity distribution is very broad, with the bulk of BSSs spinning at less than ∼40 km s{sup –1} (in agreement with the majority of such stars observed in other globular clusters) and a long tail reaching ∼200 km s{sup –1}. About 40% of the sample has v{sub e} sin i > 40 km s{sup –1} and about 20% has v{sub e} sin i > 70 km s{sup –1}. Such a large fraction is very similar to the percentage of fast rotating BSSs observed in M4. Thus, ω Centauri is the second stellar cluster, beyond M4, with a surprisingly high population of fast spinning BSSs. We found a hint of radial behavior for a fraction of fast rotating BSSs, with a mild peak within one core radius, and a possible rise in the external regions (beyond four core radii). This may suggest that recent formation episodes of mass transfer BSSs occurred preferentially in the outskirts of ω Centauri, or that braking mechanisms able to slow down these stars are least efficient in the lowest density environments.

  4. Blue straggler stars in the globular cluster NGC 5053

    International Nuclear Information System (INIS)

    Nemec, J.M.; Cohen, J.G.

    1989-01-01

    A study of the low central concentration globular cluster NGC 5053 based on photometry to 23 mag is reported. Deep C-M diagrams are presented, a mean metal abundance for the cluster is derived from the color of the RGB at the level of the horizontal branch, and theoretical isochrones are used to derive a distance modulus of (m - M0) = 16.05 + or - 0.14 mag and an age of 18 + or - 3 Gyr. A luminosity function based on subgiant and upper main-sequence stars is also constructed. A total of 24 blue stragglers in NGC 5053 are identified and their properties are studied. 65 references

  5. CHEMICAL AND KINEMATICAL PROPERTIES OF BLUE STRAGGLER STARS AND HORIZONTAL BRANCH STARS IN NGC 6397

    International Nuclear Information System (INIS)

    Lovisi, L.; Mucciarelli, A.; Lanzoni, B.; Ferraro, F. R.; Dalessandro, E.; Contreras Ramos, R.; Gratton, R.

    2012-01-01

    We used three sets of high-resolution spectra acquired with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to investigate the chemical and kinematical properties of a sample of 42 horizontal branch (HB) stars, 18 blue straggler stars (BSSs), and 86 main-sequence (MS) turnoff (TO) and sub-giant branch stars in the nearby globular cluster NGC 6397. We measured rotational velocities and Fe, O, and Mg abundances. All of the unevolved stars in our sample have low rotational velocites (vsin i –1 ), while the HB stars and BSSs show a broad distribution, with values ranging from 0 to ∼70 km s –1 . For HB stars with T 8200 K and T > 10,500 K, respectively) also show significant deviations in their iron abundance with respect to the cluster metallicity (as traced by the unevolved stars, [Fe/H] = –2.12). While similar chemical patterns have already been observed in other hot HB stars, this is the first evidence ever collected for BSSs. We interpret these abundance anomalies as due to the metal radiative levitation, occurring in stars with shallow or no convective envelopes.

  6. Estimation of spectral classifications for stars with interesting Stroemgren indices: population II field 'blue stragglers'

    International Nuclear Information System (INIS)

    Olsen, E.H.

    1979-01-01

    More than 17 years ago in Princeton at the Conference on Interstellar Matter, Stroemgren (1962) concluded the presentation of one of his papers by mentioning a program aimed at obtaining four-color photometry of all F8-G0 stars to apparent magnitude 8. The purpose was to perform a detailed analysis of the correlations between age, chemical composition, and kinematics, and thus gain new insight into the state of the interstellar matter at various times during the history of the Galaxy. The author considers one specific category of stars, 'blue stragglers'. (Auth.)

  7. The lithium abundance of M67 blue stragglers - A constraint on the blue straggler phenomenon

    International Nuclear Information System (INIS)

    Pritchet, C.J.; Glaspey, J.W.

    1991-01-01

    Upper limits have been placed on the line strength of the 6707 A Li I resonance doublet in seven blue stragglers in M67. The corresponding upper limits on abundances range from log N(Li) less than about 1.3 to less than about 2.3. This result is significantly below the level of log N(Li) about 3.1 + or - 0.1 found in field main-sequence stars of comparable temperature. It is concluded that some form of mixing has affected the outer envelopes of blue stragglers. (Such mixing has been proposed as the mechanism needed to prolong the lifetimes of blue stragglers relative to normal main-sequence stars at the same luminosity). Virtually all mechanisms for the production of blue stragglers other than mixing, binary mass transfer, or binary coalescence appear to be ruled out by the present observations. 45 refs

  8. Observationally Testing the Triple Origin of Blue Straggler Stars with Near-Infrared Spectroscopy

    Science.gov (United States)

    Kohler, Jacob P.; Gosnell, Natalie M.; Sokal, Kimberly R.; Mace, Gregory N.

    2018-01-01

    Presented are results to constrain blue straggler star (BSS) formation mechanisms in open cluster NGC 188 using data from the Immersion Grating INfrared Spectrometer (IGRINS) while at the Discovery Channel Telescope. The majority (at least 16 of 21) of NGC 188s BSSs are binaries, and, to date, seven white dwarf (WD) companions have been detected. This leaves at least nine undetected companion stars. Observations show a sharp peak of the BSSs companion mass distribution at 0.5 solar masses, highly suggestive of a WD or M-type main sequence (MS) star. Under our tested formation mechanism, the progenitors of BSSs are arranged in primordial hierarchical triple star systems that dynamically evolve through the Kozai-cycle tidal friction (KCTF) process into a binary composed of a BSS and, statistically, an M dwarf companion. We test for the presence of an M dwarf by cross-correlating a near-IR spectrum with both a BSS template and an M dwarf template. We present, for the first time, a preliminary detection of a 3800K, 0.5 solar mass M dwarf companion in each of the long period (log[P(d)]=3), single-lined binaries WOCS 451 and WOCS 5671 in NGC 188. To assess the possibility of a false M dwarf detection, we carry out Monte Carlo simulations cross-correlating an M dwarf template with a BSS-only spectrum with a signal-to-noise ratio matching our observations. Theoretical detection limits for various BSS-M dwarf pairs are reported. In the case of a non-detection, such as in WOCS 4970, we are able to place an upper limit on the mass, and thus temperature, of the companion star. Current and future research goals aim for further insight into the BSS formation mechanism frequencies of NGC 188.

  9. A Near-Infrared Surface Compositional Analysis of Blue Straggler Stars in Open Cluster M67

    Science.gov (United States)

    Seifert, Richard; Gosnell, Natalie M.; Sneden, Chris

    2017-06-01

    Blue straggler stars (BSSs) are stars whose evolutions have been directly impacted by binary system interactions. By obtaining additional mass from a companion, BSSs are able to live prolonged lives on the main sequence. BSSs bring confusions to studies that rely on a standard stellar evolutionary track when modeling stellar populations, since the presence of BSSs can make a population appear younger than it actually is. It is important to have a better understanding of the mechanisms that drive BSS formation so that BSSs may be correctly accounted for in future studies.Blue stagglers in clusters primarily form in one of two ways; either from a close binary system in which one star accretes mass from its companion star or from a hierarchical trinary system in which a close inner binary merges as a result of perturbations from a farther-orbiting third star. In order to investigate the nature of this mass transfer, We obtained IGRINS H-band high resolution spectra of 6 BSSs and 12 red giant stars in open cluster M67. Using a grid of synthetic spectra obtained from the line analysis code MOOG, we identified and fit abundances for absorption lines of iron, silicon, and carbon. Depending on the evolutionary stage of the donor star, the abundance of carbon in the resulting BSS can be affected by mixing during the mass transfer. By analyzing the abundance of carbon in our targets, we find that [Fe/H] ~= 0 and [C/H] ~= 0. We see no evidence of depletion of carbon from RGB-phase mass transfer or enhancement of carbon from AGB-phase mass transfer, implying that the mass transfer occured earlier in the donar star's evolution.Funding for this research comes from the John W. Cox endowment for the Advanced Studies in Astronomy. For support of this work we acknowledge NSF grants AST-1211585 and AST-1616040 to CS. The successful development of the IGRINS spectrograph has resulted from the combined efforts of teams at the University of Texas at Austin and the Korea Astronomy and

  10. Spectra and ages of blue stragglers

    International Nuclear Information System (INIS)

    Abt, H.A.

    1985-01-01

    A mechanism similar to Wheeler's quasi-homogeneous evolution and Finzi and Wolf's proposal for blue stragglers is proposed as the origin of the blue stragglers in intermediate-age clusters. Blue stragglers are stars whose positions in color-magnitude diagrams of open and globular clusters are significantly above the turn-off points and in the region of the (former) main sequence; they seem to represent a conflict with the general conclusion that all stars in a cluster originated at about the same time. It is concluded that there are at least two kinds of blue stragglers: (1) those stars of types about B3-A2 are primarily Ap stars and slow rotators, occur in the intermediate age clusters and remain in the main sequence region probably through magnetic mixing; and (2) the stars of type O6-B2 frequently have emission lines, are rapid rotators, occur in the young cluster, and remain in the main sequence region probably by rotational mixing. 30 references

  11. BD+43° 3654 - a blue straggler?

    Science.gov (United States)

    Gvaramadze, V. V.; Bomans, D. J.

    2008-07-01

    The astrometric data on the runaway star BD+43° 3654 are consistent with the origin of this O4If star in the center of the Cyg OB2 association, while BD+43° 3654 is younger than the association. To reconcile this discrepancy, we suggest that BD+43° 3654 is a blue straggler formed via a close encounter between two tight massive binaries in the core of Cyg OB2. A possible implication of this suggestion is that the very massive (and therefore apparently very young) stars in Cyg OB2 could be blue stragglers as well. We also suggest that the binary-binary encounter producing BD+43° 3654 might be responsible for ejection of two high-velocity stars (the stripped helium cores of massive stars) - the progenitors of the pulsars B2020+28 and B2021+51.

  12. INVESTIGATING THE MASS SEGREGATION PROCESS IN GLOBULAR CLUSTERS WITH BLUE STRAGGLER STARS: THE IMPACT OF DARK REMNANTS

    Energy Technology Data Exchange (ETDEWEB)

    Alessandrini, Emiliano; Lanzoni, Barbara; Ferraro, Francesco R.; Miocchi, Paolo [Dept. of Physics and Astronomy, University of Bologna, viale Berti Pichat, 6/2 (Italy); Vesperini, Enrico [Dept. of Astronomy, Indiana University, Bloomington, IN 47401 (United States)

    2016-12-20

    We present the results of a set of N -body simulations aimed at exploring how the process of mass segregation (as traced by the spatial distribution of blue straggler stars, BSSs) is affected by the presence of a population of heavy dark remnants (as neutron stars and black holes (BHs)). To this end, clusters characterized by different initial concentrations and different fractions of dark remnants have been modeled. We find that an increasing fraction of stellar-mass BHs significantly delay the mass segregation of BSSs and the visible stellar component. In order to trace the evolution of BSS segregation, we introduce a new parameter ( A {sup +}), which can be easily measured when the cumulative radial distribution of these stars and a reference population are available. Our simulations show that A {sup +} might also be used as an approximate indicator of the time remaining to the core collapse of the visible component.

  13. A binary origin for 'blue stragglers' in globular clusters.

    Science.gov (United States)

    Knigge, Christian; Leigh, Nathan; Sills, Alison

    2009-01-15

    Blue stragglers in globular clusters are abnormally massive stars that should have evolved off the stellar main sequence long ago. There are two known processes that can create these objects: direct stellar collisions and binary evolution. However, the relative importance of these processes has remained unclear. In particular, the total number of blue stragglers found in a given cluster does not seem to correlate with the predicted collision rate, providing indirect support for the binary-evolution model. Yet the radial distributions of blue stragglers in many clusters are bimodal, with a dominant central peak: this has been interpreted as an indication that collisions do dominate blue straggler production, at least in the high-density cluster cores. Here we report that there is a clear, but sublinear, correlation between the number of blue stragglers found in a cluster core and the total stellar mass contained within it. From this we conclude that most blue stragglers, even those found in cluster cores, come from binary systems. The parent binaries, however, may themselves have been affected by dynamical encounters. This may be the key to reconciling all of the seemingly conflicting results found to date.

  14. CCD time-series photometry of the globular cluster NGC 5053: RR Lyrae, Blue Stragglers and SX Phoenicis stars revisited

    Science.gov (United States)

    Arellano Ferro, A.; Giridhar, Sunetra; Bramich, D. M.

    2010-02-01

    We report the results of CCD V, r and I time-series photometry of the globular cluster NGC 5053. New times of maximum light are given for the eight known RR Lyrae stars in the field of our images, and their periods are revised. Their V light curves were Fourier decomposed to estimate their physical parameters. A discussion on the accuracy of the Fourier-based iron abundances, temperatures, masses and radii is given. New periods are found for the five known SX Phe stars, and a critical discussion of their secular period changes is offered. The mean iron abundance for the RR Lyrae stars is found to be [Fe/H] ~ -1.97 +/- 0.16 and lower values are not supported by the present analysis. The absolute magnitude calibrations of the RR Lyrae stars yield an average true distance modulus of 16.12 +/- 0.04 or a distance of 16.7 +/- 0.3 kpc. Comparison of the observational colour magnitude diagram (CMD) with theoretical isochrones indicates an age of 12.5 +/- 2.0 Gyr for the cluster. A careful identification of all reported blue stragglers (BS) and their V, I magnitudes leads to the conclusion that BS12, BS22, BS23 and BS24 are not BS. On the other hand, three new BS are reported. Variability was found in seven BS, very likely of the SX Phe type in five of them, and in one red giant star. The new SX Phe stars follow established Period-Luminosity relationships and indicate a distance in agreement with the distance from the RR Lyrae stars. Based on observations collected at the Indian Astrophysical Observatory, Hanle, India. E-mail: armando@astroscu.unam.mx (AAF); giridhar@iiap.res.in (SG); dan.bramich@hotmail.co.uk (DMB)

  15. THE BLUE STRAGGLER STAR POPULATION IN NGC 1261: EVIDENCE FOR A POST-CORE-COLLAPSE BOUNCE STATE

    International Nuclear Information System (INIS)

    Simunovic, Mirko; Puzia, Thomas H.; Sills, Alison

    2014-01-01

    We present a multi-passband photometric study of the Blue Straggler Star (BSS) population in the Galactic globular cluster (GC) NGC 1261, using available space- and ground-based survey data. The inner BSS population is found to have two distinct sequences in the color-magnitude diagram (CMD), similar to double BSS sequences detected in other GCs. These well defined sequences are presumably linked to single short-lived events such as core collapse, which are expected to boost the formation of BSSs. In agreement with this, we find a BSS sequence in NGC 1261 which can be well reproduced individually by a theoretical model prediction of a 2 Gyr old population of stellar collision products, which are expected to form in the denser inner regions during short-lived core contraction phases. Additionally, we report the occurrence of a group of BSSs with unusually blue colors in the CMD, which are consistent with a corresponding model of a 200 Myr old population of stellar collision products. The properties of the NGC 1261 BSS populations, including their spatial distributions, suggest an advanced dynamical evolutionary state of the cluster, but the core of this GC does not show the classical signatures of core collapse. We argue that these apparent contradictions provide evidence for a post-core-collapse bounce state seen in dynamical simulations of old GCs

  16. The Blue Straggler Star Population in NGC 1261: Evidence for a Post-core-collapse Bounce State

    Science.gov (United States)

    Simunovic, Mirko; Puzia, Thomas H.; Sills, Alison

    2014-11-01

    We present a multi-passband photometric study of the Blue Straggler Star (BSS) population in the Galactic globular cluster (GC) NGC 1261, using available space- and ground-based survey data. The inner BSS population is found to have two distinct sequences in the color-magnitude diagram (CMD), similar to double BSS sequences detected in other GCs. These well defined sequences are presumably linked to single short-lived events such as core collapse, which are expected to boost the formation of BSSs. In agreement with this, we find a BSS sequence in NGC 1261 which can be well reproduced individually by a theoretical model prediction of a 2 Gyr old population of stellar collision products, which are expected to form in the denser inner regions during short-lived core contraction phases. Additionally, we report the occurrence of a group of BSSs with unusually blue colors in the CMD, which are consistent with a corresponding model of a 200 Myr old population of stellar collision products. The properties of the NGC 1261 BSS populations, including their spatial distributions, suggest an advanced dynamical evolutionary state of the cluster, but the core of this GC does not show the classical signatures of core collapse. We argue that these apparent contradictions provide evidence for a post-core-collapse bounce state seen in dynamical simulations of old GCs.

  17. THE BLUE STRAGGLER STAR POPULATION IN NGC 1261: EVIDENCE FOR A POST-CORE-COLLAPSE BOUNCE STATE

    Energy Technology Data Exchange (ETDEWEB)

    Simunovic, Mirko; Puzia, Thomas H. [Institute of Astrophysics, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, 7820436 Macul, Santiago (Chile); Sills, Alison, E-mail: msimunov@astro.puc.cl, E-mail: tpuzia@astro.puc.cl, E-mail: asills@mcmaster.ca [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4M1 (Canada)

    2014-11-01

    We present a multi-passband photometric study of the Blue Straggler Star (BSS) population in the Galactic globular cluster (GC) NGC 1261, using available space- and ground-based survey data. The inner BSS population is found to have two distinct sequences in the color-magnitude diagram (CMD), similar to double BSS sequences detected in other GCs. These well defined sequences are presumably linked to single short-lived events such as core collapse, which are expected to boost the formation of BSSs. In agreement with this, we find a BSS sequence in NGC 1261 which can be well reproduced individually by a theoretical model prediction of a 2 Gyr old population of stellar collision products, which are expected to form in the denser inner regions during short-lived core contraction phases. Additionally, we report the occurrence of a group of BSSs with unusually blue colors in the CMD, which are consistent with a corresponding model of a 200 Myr old population of stellar collision products. The properties of the NGC 1261 BSS populations, including their spatial distributions, suggest an advanced dynamical evolutionary state of the cluster, but the core of this GC does not show the classical signatures of core collapse. We argue that these apparent contradictions provide evidence for a post-core-collapse bounce state seen in dynamical simulations of old GCs.

  18. Blue straggler stars beyond the Milky Way: a non-segregated population in the Large Magellanic Cloud cluster NGC 2213

    Science.gov (United States)

    Li, Chengyuan; Hong, Jongsuk

    2018-06-01

    Using the high-resolution observations obtained by the Hubble Space Telescope, we analysed the blue straggler stars (BSSs) in the Large Magellanic Cloud cluster NGC 2213. We found that the radial distribution of BSSs is consistent with that of the normal giant stars in NGC 2213, showing no evidence of mass segregation. However, an analytic calculation carried out for these BSSs shows that they are already dynamically old, because the estimated half-mass relaxation time for these BSSs is significantly shorter than the isochronal age of the cluster. We also performed direct N-body simulations for an NGC 2213-like cluster to understand the dynamical processes that lead to this non-segregated radial distribution of BSSs. Our numerical simulation shows that the presence of black hole subsystems inside the cluster centre can significantly affect the dynamical evolution of BSSs. The combined effects of the delayed segregation, binary disruption, and exchange interactions of BSS progenitor binaries may result in this non-segregated radial distribution of BSSs in NGC 2213.

  19. An unexpected detection of bifurcated blue straggler sequences in the young globular cluster NGC 2173

    OpenAIRE

    Li, Chengyuan; Deng, Licai; de Grijs, Richard; Jiang, Dengkai; Xin, Yu

    2018-01-01

    Bifurcated patterns of blue straggler stars in their color--magnitude diagrams have atracted significant attention. This type of special (but rare) pattern of two distinct blue straggler sequences is commonly interpreted as evidence of cluster core-collapse-driven stellar collisions as an efficient formation mechanism. Here, we report the detection of a bifurcated blue straggler distribution in a young Large MagellanicCloud cluster, NGC 2173. Because of the cluster's low central stellar numbe...

  20. Can physical stellar collisions explain the blue stragglers in the dwarf spheroidal galaxies?

    International Nuclear Information System (INIS)

    Leonard, P.J.T.

    1993-01-01

    The hypothesis that the blue stragglers in the dwarf spheroidal galaxie have a collisional origin is considered. If all of the dark matter in these galaxies is in the form of low-mass stars and the binary frequency is ≅ 50%, then it is quite possible that ≅ 10% to 20% of their blue stragglers have been produced by physical stellar collisions

  1. On the luminosity function, lifetimes, and origin of blue stragglers in globular clusters

    Science.gov (United States)

    Bailyn, Charles D.; Pinsonneault, Marc H.

    1995-01-01

    We compute theoretical evolutionary tracks of blue stragglers created by mergers. Two formation scenarios are considered: mergers of primordial binaries, and stellar collisions. These two scenarios predict strikingly different luminosity functions, which are potentially distinguishable observationally. Tabulated theoretical luminosity functions and lifetimes are presented for blue stragglers formed under a variety of input conditions. We compare our results with observations of the blue straggler sequences in 47 Tucanae and M3. In the case of 47 Tuc, the luminosity function and the formation rate are compatible with the hypothesis that the blue stragglers formed through the collision of single stars. Mergers of primordial binaries are only marginally cosistent with the data, and a significant enhancement of the collision cross section by binary-single-star encounters appears to be ruled out. In the case of M3, we find that the innermost blue stragglers have a luminosity function significantly different from that of the outer stragglers, thus confirming earlier suggestions that there are two distinct populations of blue stragglers in this cluster. The inner stragglers are preferentially brighter and bluer, as would be expected if they were made by collisions, but there are so many of them that the collision rate would need to be enhanced by interactions involving wide binaries. The luminosity function of the outer stragglers is almost identical to the predictions of mergers from primordial binaries and is inconsistent with the collision hypothesis.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-01-10

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

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

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

    Science.gov (United States)

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

    2014-01-01

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

  5. MOCK OBSERVATIONS OF BLUE STRAGGLERS IN GLOBULAR CLUSTER MODELS

    International Nuclear Information System (INIS)

    Sills, Alison; Glebbeek, Evert; Chatterjee, Sourav; Rasio, Frederic A.

    2013-01-01

    We created artificial color-magnitude diagrams of Monte Carlo dynamical models of globular clusters and then used observational methods to determine the number of blue stragglers in those clusters. We compared these blue stragglers to various cluster properties, mimicking work that has been done for blue stragglers in Milky Way globular clusters to determine the dominant formation mechanism(s) of this unusual stellar population. We find that a mass-based prescription for selecting blue stragglers will select approximately twice as many blue stragglers than a selection criterion that was developed for observations of real clusters. However, the two numbers of blue stragglers are well-correlated, so either selection criterion can be used to characterize the blue straggler population of a cluster. We confirm previous results that the simplified prescription for the evolution of a collision or merger product in the BSE code overestimates their lifetimes. We show that our model blue stragglers follow similar trends with cluster properties (core mass, binary fraction, total mass, collision rate) as the true Milky Way blue stragglers as long as we restrict ourselves to model clusters with an initial binary fraction higher than 5%. We also show that, in contrast to earlier work, the number of blue stragglers in the cluster core does have a weak dependence on the collisional parameter Γ in both our models and in Milky Way globular clusters

  6. DETECTION OF WHITE DWARF COMPANIONS TO BLUE STRAGGLERS IN THE OPEN CLUSTER NGC 188: DIRECT EVIDENCE FOR RECENT MASS TRANSFER

    Energy Technology Data Exchange (ETDEWEB)

    Gosnell, Natalie M.; Mathieu, Robert D. [Department of Astronomy, University of Wisconsin - Madison, 475 N. Charter St., Madison, WI 53706 (United States); Geller, Aaron M. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Rd, Evanston, IL 60208 (United States); Sills, Alison [Department of Physics and Astronomy, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4M1 (Canada); Leigh, Nathan [Department of Physics, University of Alberta, CCIS 4-183, Edmonton, AB T6G 2E1 (Canada); Knigge, Christian, E-mail: gosnell@astro.wisc.edu [School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 IBJ (United Kingdom)

    2014-03-01

    Several possible formation pathways for blue straggler stars have been developed recently, but no one pathway has yet been observationally confirmed for a specific blue straggler. Here we report the first findings from a Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel far-UV photometric program to search for white dwarf companions to blue straggler stars. We find three hot and young white dwarf companions to blue straggler stars in the 7 Gyr open cluster NGC 188, indicating that mass transfer in these systems ended less than 300 Myr ago. These companions are direct and secure observational evidence that these blue straggler stars were formed through mass transfer in binary stars. Their existence in a well-studied cluster environment allows for observational constraints of both the current binary system and the progenitor binary system, mapping the entire mass transfer history.

  7. Modeling blue stragglers in young clusters

    International Nuclear Information System (INIS)

    Lu Pin; Deng Licai; Zhang Xiaobin

    2011-01-01

    A grid of binary evolution models are calculated for the study of a blue straggler (BS) population in intermediate age (log Age = 7.85–8.95) star clusters. The BS formation via mass transfer and merging is studied systematically using our models. Both Case A and B close binary evolutionary tracks are calculated for a large range of parameters. The results show that BSs formed via Case B are generally bluer and even more luminous than those produced by Case A. Furthermore, the larger range in orbital separations of Case B models provides a probability of producing more BSs than in Case A. Based on the grid of models, several Monte-Carlo simulations of BS populations in the clusters in the age range are carried out. The results show that BSs formed via different channels populate different areas in the color magnitude diagram (CMD). The locations of BSs in CMD for a number of clusters are compared to our simulations as well. In order to investigate the influence of mass transfer efficiency in the models and simulations, a set of models is also calculated by implementing a constant mass transfer efficiency, β = 0.5, during Roche lobe overflow (Case A binary evolution excluded). The result shows BSs can be formed via mass transfer at any given age in both cases. However, the distributions of the BS populations on CMD are different.

  8. Anomalous Cepheids and population II blue stragglers

    Science.gov (United States)

    Nemec, James M.

    Recent studies of anomalous Cepheids (ACs) and population II blue stragglers (BSs), including photometrically variable BSs (VBSs), are reviewed. The VBSs represent about 25 percent of the BSs, the majority of which are SX Phe short-period variables in the Cepheid instability strip. Mass estimates derived using various techniques suggest that both ACs and BSs are relatively massive (about 1.0-1.6 solar mass). The recent discovery that two BSs in the globular cluster NGC 5466 are contact binaries, and the earlier discovery that one of the BSs in Omega Cen is an eclipsing binary, provide direct evidence that at least some BSs are binary systems.

  9. The “UV-route” to Search for Blue Straggler Stars in Globular Clusters: First Results from the HST UV Legacy Survey

    Energy Technology Data Exchange (ETDEWEB)

    Raso, S.; Ferraro, F. R.; Lanzoni, B. [Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat, 6/2, Bologna (Italy); Dalessandro, E. [INAF Osservatorio Astronomico di Bologna, Via Ranzani 1, Bologna (Italy); Nardiello, D. [Department of Physics and Astronomy Galileo Galilei, University of Padova, Vicolo dell’Osservatorio 3, I-35122 Padova (Italy); Bellini, A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Vesperini, E. [Department of Astronomy, Indiana University, Bloomington, IN, 47401 (United States)

    2017-04-10

    We used data from the Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters to select the Blue Straggler Star (BSS) population in four intermediate/high density systems (namely NGC 2808, NGC 6388, NGC 6541, and NGC 7078) through a “UV-guided search.” This procedure consists of using the F275W images in each cluster to construct the master list of detected sources, and then force it to the images acquired in the other filters. Such an approach optimizes the detection of relatively hot stars and allows the detection of a complete sample of BSSs even in the central region of high-density clusters, because the light from the bright cool giants, which dominates the optical emission in old stellar systems, is sensibly reduced at UV wavelengths. Our UV-guided selections of BSSs have been compared to the samples obtained in previous, optical-driven surveys, clearly demonstrating the efficiency of the UV approach. In each cluster we also measured the parameter A {sup +}, defined as the area enclosed between the cumulative radial distribution of BSSs and that of a reference population, which traces the level of BSS central segregation and the level of dynamical evolution suffered by the system. The values measured for the four clusters studied in this paper nicely fall along the dynamical sequence recently presented for a sample of 25 clusters.

  10. An Unexpected Detection of Bifurcated Blue Straggler Sequences in the Young Globular Cluster NGC 2173

    Science.gov (United States)

    Li, Chengyuan; Deng, Licai; de Grijs, Richard; Jiang, Dengkai; Xin, Yu

    2018-03-01

    The bifurcated patterns in the color–magnitude diagrams of blue straggler stars (BSSs) have attracted significant attention. This type of special (but rare) pattern of two distinct blue straggler sequences is commonly interpreted as evidence that cluster core-collapse-driven stellar collisions are an efficient formation mechanism. Here, we report the detection of a bifurcated blue straggler distribution in a young Large Magellanic Cloud cluster, NGC 2173. Because of the cluster’s low central stellar number density and its young age, dynamical analysis shows that stellar collisions alone cannot explain the observed BSSs. Therefore, binary evolution is instead the most viable explanation of the origin of these BSSs. However, the reason why binary evolution would render the color–magnitude distribution of BSSs bifurcated remains unclear. C. Li, L. Deng, and R. de Grijs jointly designed this project.

  11. FORMATION AND EVOLUTION OF BLUE STRAGGLERS IN 47 TUCANAE

    Energy Technology Data Exchange (ETDEWEB)

    Parada, Javiera; Richer, Harvey; Heyl, Jeremy; Goldsbury, Ryan [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1 (Canada); Kalirai, Jason, E-mail: jparada@phas.ubc.ca, E-mail: heyl@phas.ubc.ca, E-mail: richer@astro.ubc.ca, E-mail: jkalirai@stsci.edu [Space Telescope Science Institute, Baltimore, MD 21218 (United States)

    2016-10-20

    Blue stragglers (BSS) are stars whose position in the color–magnitude diagram (CMD) places them above the main sequence (MS) turn-off (TO) point of a star cluster. Using data from the core of 47 Tuc in the ultraviolet (UV), we have identified various stellar populations in the CMD, and used their radial distributions to study the evolution and origin of BSS, and obtain a dynamical estimate of the mass of BSS systems. When we separate the BSS into two samples by their magnitude, we find that the bright BSS show a much more centrally concentrated radial distribution and thus higher mass estimate (over twice the TO mass for these BSS systems), suggesting an origin involving triple or multiple stellar systems. In contrast, the faint BSS are less concentrated, with a radial distribution similar to the MS binaries, pointing to the MS binaries as the likely progenitors of these BSS. Putting our data together with available photometric data in the visible and using MESA evolutionary models, we calculate the expected number of stars in each evolutionary stage for the normal evolution of stars and the number of stars coming from the evolution of BSS. The results indicate that BSS have a post-MS evolution comparable to that of a normal star of the same mass and a MS BSS lifetime of about 200–300 Myr. We also find that the excess population of asymptotic giant branch stars in 47 Tuc is due to evolved BSS.

  12. A mass transfer origin for blue stragglers in NGC 188 as revealed by half-solar-mass companions.

    Science.gov (United States)

    Geller, Aaron M; Mathieu, Robert D

    2011-10-19

    In open star clusters, where all members formed at about the same time, blue straggler stars are typically observed to be brighter and bluer than hydrogen-burning main-sequence stars, and therefore should already have evolved into giant stars and stellar remnants. Correlations between blue straggler frequency and cluster binary star fraction, core mass and radial position suggest that mass transfer or mergers in binary stars dominates the production of blue stragglers in open clusters. Analytic models, detailed observations and sophisticated N-body simulations, however, argue in favour of stellar collisions. Here we report that the blue stragglers in long-period binaries in the old (7 × 10(9)-year) open cluster NGC 188 have companions with masses of about half a solar mass, with a surprisingly narrow mass distribution. This conclusively rules out a collisional origin, as the collision hypothesis predicts a companion mass distribution with significantly higher masses. Mergers in hierarchical triple stars are marginally permitted by the data, but the observations do not favour this hypothesis. The data are highly consistent with a mass transfer origin for the long-period blue straggler binaries in NGC 188, in which the companions would be white dwarfs of about half a solar mass.

  13. Using White Dwarf Companions of Blue Stragglers to Constrain Mass Transfer Physics

    Science.gov (United States)

    Gosnell, Natalie M.; Leiner, Emily; Geller, Aaron M.; Knigge, Christian; Mathieu, Robert D.; Sills, Alison; Leigh, Nathan

    2018-06-01

    Complete membership studies of old open clusters reveal that 25% of the evolved stars follow pathways in stellar evolution that are impacted by binary evolution. Recent studies show that the majority of blue straggler stars, traditionally defined to be stars brighter and bluer than the corresponding main sequence turnoff, are formed through mass transfer from a giant star onto a main sequence companion, resulting in a white dwarf in a binary system with a blue straggler. We will present constraints on the histories and mass transfer efficiencies for two blue straggler-white dwarf binaries in open cluster NGC 188. The constraints are a result of measuring white dwarf cooling temperatures and surface gravities with HST COS far-ultraviolet spectroscopy. This information sets both the timeline for mass transfer and the stellar masses in the pre-mass transfer binary, allowing us to constrain aspects of the mass transfer physics. One system is formed through Case C mass transfer, leaving a CO-core white dwarf, and provides an interesting test case for mass transfer from an asymptotic giant branch star in an eccentric system. The other system formed through Case B mass transfer, leaving a He-core white dwarf, and challenges our current understanding of the expected regimes for stable mass transfer from red giant branch stars.

  14. Blue stragglers in open clusters - a test of the binary hypothesis

    International Nuclear Information System (INIS)

    Manteiga, M.; Martinez, R.C.; Beckman, J.E.; Pickles, A.J.

    1987-01-01

    A search for binaries among 17 blue stragglers in five galactic clusters, NGC 7789, 6633, 6819, 6939, and M 67, has been performed using measurements of radial velocity variations. The spectra were obtained with the Intermediate Dispersion Spectrograph attached to the f/15 Cassegrain focus of the 2.5 m Isaac Newton Telescope at the Spanish Observatory of the Roque de los Muchachos. The wavelength coverage was 200 A, centered at 8510 A with a scale of 12.4 km/sec per pixel. All radial velocity determinations were made using cross-correlation techniques. A velocity resolution of about 3 km/sec/pixel was obtained for the standard radial velocity stars and the brighter program stars. For three of the blue stragglers variations in radial velocity greater than 30 km/sec are reported. 10 references

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

    NARCIS (Netherlands)

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

    2014-01-01

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

  16. HIP 10725: The first solar twin/analogue field blue straggler

    Science.gov (United States)

    Schirbel, Lucas; Meléndez, Jorge; Karakas, Amanda I.; Ramírez, Iván; Castro, Matthieu; Faria, Marcos A.; Lugaro, Maria; Asplund, Martin; Tucci Maia, Marcelo; Yong, David; Howes, Louise; do Nascimento, José D.

    2015-12-01

    Context. Blue stragglers are easy to identify in globular clusters, but are much harder to identify in the field. Here we present the serendipitous discovery of one field blue straggler, HIP 10725, that closely matches the Sun in mass and age, but with a metallicity slightly lower than solar. Aims: We characterise the solar twin/analogue HIP 10725 to assess whether this star is a blue straggler. Methods: We employed spectra with high resolution (R ~ 105) and high signal-to-noise ratio (330) obtained with UVES at the VLT to perform a differential abundance analysis of the solar analogue HIP 10725. Radial velocities obtained by other instruments were also used to check for binarity. We also studied its chromospheric activity, age, and rotational velocity. Results: HIP 10725 is severely depleted in beryllium ([ Be/H ] ≤ -1.2 dex) for its stellar parameters and age. The abundances relative to solar of the elements with Z ≤ 30 show a correlation with condensation temperature, and the neutron capture elements produced by the s-process are greatly enhanced, while the r-process elements seem normal. We found its projected rotational velocity (vsini = 3.3 ± 0.1 km s-1) to be significantly higher than solar and incompatible with its isochrone-derived age. Radial velocity monitoring shows that the star has a binary companion. Conclusions: Based on the high s-process element enhancements and low beryllium abundance, we suggest that HIP 10725 has been polluted by mass transfer from an AGB star that probably had an initial mass of about 2 M⊙. The radial velocity variations suggest the presence of an unseen binary companion, probably the remnant of a former AGB star. Isochrones predict a solar-age star, but this disagrees with the high projected rotational velocity and high chromospheric activity. We conclude that HIP 10725 is a field blue straggler, rejuvenated by the mass-transfer process of its former AGB companion. Based on observations obtained at the European

  17. Do the Pop II field blue stragglers have a collisional origin?

    International Nuclear Information System (INIS)

    Leonard, P.J.T.

    1993-01-01

    The hypothesis that the Pop II field blue stragglers have a collisional origin is considered. It appears unlikely that the majority of these stragglers were formed via collisions, but it is difficult to rule out the possibility that a small, but observable, fraction of them were

  18. Another non-segregated Blue Straggler population in a globular cluster: the case of NGC 2419.

    Science.gov (United States)

    Dalessandro, E.; Lanzoni, B.; Ferraro, F. R.; Vespe, F.; Bellazzini, M.; Rood, R. T.

    We have used a combination of ACS-HST high-resolution and wide-field SUBARU data in order to study the Blue Straggler Star (BSS) population over the entire extension of the remote Galactic globular cluster NGC 2419. The radial distribution of the selected BSS is the same as that of the other cluster stars. In this sense the BSS radial distribution is like that of omega Centauri and unlike that of all Galactic globular clusters studied to date, which have highly centrally segregated distributions and in most cases a pronounced upturn in the external regions. As in the case of omega Centauri, this evidence indicates that NGC 2419 is not yet relaxed even in the central regions. This observational fact is in agreement with estimated half-mass relaxation time, which is of the order of the cluster age.

  19. UV observations of blue stragglers and population 2 K dwarfs. Final Technical report, 1 July 1984-30 June 1986

    International Nuclear Information System (INIS)

    Carney, B.W.; Bond, H.E.

    1986-01-01

    Blue stragglers are stars, found usually in either open or globular clusters, that appear to lie on the main sequence, but are brighter and bluer than the cluster turn-off. Currently, two rival models are invoked to explain this apparently pathological behavior: internal mixing (so that fresh fuel is brought into the stellar core); and mass transfer (by which a normal main sequence star acquires mass from an evolving nearby companion and so moves up the main sequence). The latter model predicts that in the absence of complete mass transfer (i.e., coalescence), blue stragglers should be binary systems with the fainter star in a post-main sequence evolutionary state. It is important to ascertain the cause of this phenomenon since stellar evolution models of main sequence stars play such a vital role in astronomy. If mass transfer is involved, one may easily exclude binaries from age determinations of clusters, but if mixing is the cause, our age determinations will be much less accurate unless we can determine whether all stars or only some mix, and what causes the mixing to occur at all

  20. THE CENTRAL BLUE STRAGGLER POPULATION IN FOUR OUTER-HALO GLOBULAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Beccari, Giacomo; Luetzgendorf, Nora [European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Muenchen (Germany); Olczak, Christoph [Astronomisches Rechen-Institut (ARI), Zentrum fuer Astronomie Universitaet Heidelberg, Moenchhofstrasse 1214, 69120 Heidelberg (Germany); Ferraro, Francesco R.; Lanzoni, Barbara [Dipartimento di Astronomia, Universita degli Studi di Bologna, via Ranzani 1, I-40127 Bologna (Italy); Carraro, Giovanni; Boffin, Henri M. J. [European Southern Observatory, Alonso de Cordova 3107, Santiago de Chile (Chile); Stetson, Peter B. [National Research Council of Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Sollima, Antonio [INAF-Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, 35122 Padova (Italy)

    2012-08-01

    Using Hubble Space Telescope/Wide Field Planetary Camera 2 data, we have performed a comparative study of the Blue Straggler Star (BSS) populations in the central regions of the globular clusters (GCs) AM 1, Eridanus, Palomar 3, and Palomar 4. Located at distances R{sub GC} > 50 kpc from the Galactic center, these are (together with Palomar 14 and NGC 2419) the most distant clusters in the halo. We determine their color-magnitude diagrams and centers of gravity. The four clusters turn out to have similar ages (10.5-11 Gyr), significantly smaller than those of the inner-halo globulars, and similar metallicities. By exploiting wide-field ground-based data, we build the most extended radial density profiles from resolved star counts ever published for these systems. These are well reproduced by isotropic King models of relatively low concentration. BSSs appear to be significantly more centrally segregated than red giants in all GCs, in agreement with the estimated core and half-mass relaxation times which are smaller than the cluster ages. Assuming that this is a signature of mass segregation, we conclude that AM 1 and Eridanus are slightly dynamically more evolved than Pal 3 and Pal 4.

  1. Double blue straggler sequences in globular clusters: The case of NGC 362

    International Nuclear Information System (INIS)

    Dalessandro, E.; Ferraro, F. R.; Massari, D.; Lanzoni, B.; Miocchi, P.; Mucciarelli, A.; Lovisi, L.; Beccari, G.; Bellini, A.; Sills, A.; Sigurdsson, S.

    2013-01-01

    We used high-quality images acquired with the Wide Field Camera 3 on board the Hubble Space Telescope to probe the blue straggler star (BSS) population of the galactic globular cluster NGC 362. We have found two distinct sequences of BSSs: this is the second case, after M30, where such a feature has been observed. Indeed, the BSS location, their extension in magnitude and color, and their radial distribution within the cluster nicely resemble those observed in M30, thus suggesting that the same interpretative scenario can be applied: the red BSS sub-population is generated by mass-transfer binaries, the blue one by collisions. The discovery of four new W UMa stars, three of which lie along the red BSS sequence, further supports this scenario. We also found that the inner portion of the density profile deviates from a King model and is well reproduced by either a mild power law (α ∼ –0.2) or a double King profile. This feature supports the hypothesis that the cluster is currently undergoing the core-collapse phase. Moreover, the BSS radial distribution shows a central peak and monotonically decreases outward without any evidence of an external rising branch. This evidence is a further indication of the advanced dynamical age of NGC 362; in fact, together with M30, NGC 362 belongs to the family of dynamically old clusters (Family III) in the 'dynamical clock' classification proposed by Ferraro et al. The observational evidence presented here strengthens the possible connection between the existence of a double BSS sequence and a quite advanced dynamical status of the parent cluster.

  2. Using Blue Stragglers to Predict Retained Black Hole Population in Globular Clusters

    Science.gov (United States)

    Hermanek, Keith; Chatterjee, Sourav; Rasio, Frederic

    2018-01-01

    Large numbers of black holes (BHs) are expected to form in massive star clusters typical of the globular clusters (GCs). Sophisticated theoretical models suggest that many of these BHs can be retained in present-day GCs. Observations have also identified several BH candidates in Galactic and extragalactic GCs (e.g., Macarone et al. 2007; Irwin et al. 2010; Strader et al. 2012; Chomiuk et al. 2013; Miller-Jones et al. 2014). It has also been shown that high-mass and high-density clusters such as GCs are efficient factories of merging binary BHs similar to those observed by the LIGO observatories (Abbott et al. 2016a,b,c,d,e; Rodriguez et al. 2016). Understanding the formation rate and properties of binary BHs are dependent on a detailed understanding of how the BHs dynamically evolve within GCs. Nevertheless, directly detecting BHs in GCs is extremely challenging; BHs only in binaries with limited configurations can be directly detected by the detection of gravitational wave, X-ray, or radio emissions. We propose an indirect of inferring the number of undetected retained BHs in a GC by investigating the dynamical effects of a large number of BHs on the production of other tracer populations such as Blue Straggler Stars (BSS). Using a large grid of detailed GC models we show that there is a clear anti-correlation between the number of BSS in a cluster and the number of retained BHs. Being the most massive species, large numbers of retained BHs will dominate the core of the cluster as a result of mass-segregation driving away other low-mass species such as main-sequence stars from central high-density regions. BSS are expected to form from physical collisions between main-sequence (MS) stars mediated by binary encounters (e.g., Chatterjee et al. 2013) in cores of GCs. Production of BSS by collisions or mass transfer channels are suppressed if a large number of retained BHs in a cluster restrict the number of MS stars in the core. Extensive observational data exist on

  3. Photometry of faint blue stars

    International Nuclear Information System (INIS)

    Kilkenny, D.; Hill, P.W.; Brown, A.

    1977-01-01

    Photometry on the uvby system is given for 61 faint blue stars. The stars are classified by means of the Stromgren indices, using criteria described in a previous paper (Kilkenny and Hill (1975)). (author)

  4. Origin of faint blue stars

    International Nuclear Information System (INIS)

    Tutukov, A.; Iungelson, L.

    1987-01-01

    The origin of field faint blue stars that are placed in the HR diagram to the left of the main sequence is discussed. These include degenerate dwarfs and O and B subdwarfs. Degenerate dwarfs belong to two main populations with helium and carbon-oxygen cores. The majority of the hot subdwarfs most possibly are helium nondegenerate stars that are produced by mass exchange close binaries of moderate mass cores (3-15 solar masses). The theoretical estimates of the numbers of faint blue stars of different types brighter than certain stellar magnitudes agree with star counts based on the Palomar Green Survey. 28 references

  5. A HOT COMPANION TO A BLUE STRAGGLER IN NGC 188 AS REVEALED BY THE ULTRA-VIOLET IMAGING TELESCOPE (UVIT) ON ASTROSAT

    Energy Technology Data Exchange (ETDEWEB)

    Subramaniam, Annapurni; Sindhu, N.; Tandon, S. N.; Rao, N. Kameswara; George, K.; Mohan, R.; Murthy, J.; Sankarasubramanian, K.; Stalin, C. S.; Sutaria, F.; Mondal, C.; Sahu, S. [Indian Institute of Astrophysics, Koramangala II Block, Bangalore-560034 (India); Postma, J. [University of Calgary, Calgary, Alberta (Canada); Côté, Patrick; Hutchings, J. B. [National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Ghosh, S. K. [National Centre for Radio Astrophysics, Pune (India); Girish, V., E-mail: purni@iiap.res.in [ISRO Satellite Centre, HAL Airport Road, Bangalore 560017 (India)

    2016-12-20

    We present early results from the Ultra-Violet Imaging Telescope (UVIT) on board the ASTROSAT observatory. We report the discovery of a hot companion associated with one of the blue straggler stars (BSSs) in the old open cluster, NGC 188. Using fluxes measured in four filters in UVIT’s far-UV (FUV) channel, and two filters in the near-UV (NUV) channel, we have constructed the spectral energy distribution (SED) of the star WOCS-5885, after combining with flux measurements from GALEX , Ultraviolet Imaging Telescope, Ultraviolet Optical Telescope, SPITZER , WISE , and several ground-based facilities. The resulting SED spans a wavelength range of 0.15 μ m to 7.8 μ m. This object is found to be one of the brightest FUV sources in the cluster. An analysis of the SED reveals the presence of two components. The cooler component is found to have a temperature of 6000 ± 150 K, confirming that it is a BSS. Assuming it to be a main-sequence star, we estimate its mass to be ∼1.1–1.2 M {sub ⊙}. The hotter component, with an estimated temperature of 17,000 ± 500 K, has a radius of ∼ 0.6 R {sub ⊙} and L ∼30 L {sub ⊙}. Bigger and more luminous than a white dwarf, yet cooler than a sub-dwarf, we speculate that it is a post-AGB/HB star that has recently transferred its mass to the BSS, which is known to be a rapid rotator. This binary system, which is the first BSS with a post-AGB/HB companion identified in an open cluster, is an ideal laboratory to study the process of BSS formation via mass transfer.

  6. A HOT COMPANION TO A BLUE STRAGGLER IN NGC 188 AS REVEALED BY THE ULTRA-VIOLET IMAGING TELESCOPE (UVIT) ON ASTROSAT

    International Nuclear Information System (INIS)

    Subramaniam, Annapurni; Sindhu, N.; Tandon, S. N.; Rao, N. Kameswara; George, K.; Mohan, R.; Murthy, J.; Sankarasubramanian, K.; Stalin, C. S.; Sutaria, F.; Mondal, C.; Sahu, S.; Postma, J.; Côté, Patrick; Hutchings, J. B.; Ghosh, S. K.; Girish, V.

    2016-01-01

    We present early results from the Ultra-Violet Imaging Telescope (UVIT) on board the ASTROSAT observatory. We report the discovery of a hot companion associated with one of the blue straggler stars (BSSs) in the old open cluster, NGC 188. Using fluxes measured in four filters in UVIT’s far-UV (FUV) channel, and two filters in the near-UV (NUV) channel, we have constructed the spectral energy distribution (SED) of the star WOCS-5885, after combining with flux measurements from GALEX , Ultraviolet Imaging Telescope, Ultraviolet Optical Telescope, SPITZER , WISE , and several ground-based facilities. The resulting SED spans a wavelength range of 0.15 μ m to 7.8 μ m. This object is found to be one of the brightest FUV sources in the cluster. An analysis of the SED reveals the presence of two components. The cooler component is found to have a temperature of 6000 ± 150 K, confirming that it is a BSS. Assuming it to be a main-sequence star, we estimate its mass to be ∼1.1–1.2 M _⊙. The hotter component, with an estimated temperature of 17,000 ± 500 K, has a radius of ∼ 0.6 R _⊙ and L ∼30 L _⊙. Bigger and more luminous than a white dwarf, yet cooler than a sub-dwarf, we speculate that it is a post-AGB/HB star that has recently transferred its mass to the BSS, which is known to be a rapid rotator. This binary system, which is the first BSS with a post-AGB/HB companion identified in an open cluster, is an ideal laboratory to study the process of BSS formation via mass transfer.

  7. High-resolution spectroscopic observations of binary stars and yellow stragglers in three open clusters: NGC 2360, NGC 3680, and NGC 5822

    Energy Technology Data Exchange (ETDEWEB)

    Sales Silva, J. V.; Peña Suárez, V. J.; Katime Santrich, O. J.; Pereira, C. B.; Drake, N. A.; Roig, F., E-mail: joaovictor@on.br, E-mail: jearim@on.br, E-mail: osantrich@on.br, E-mail: claudio@on.br, E-mail: drake@on.br, E-mail: froig@on.br [Observatório Nacional/MCT, Rua Gen. José Cristino, 77, 20921-400 Rio de Janeiro (Brazil)

    2014-11-01

    Binary stars in open clusters are very useful targets in constraining the nucleosynthesis process. The luminosities of the stars are known because the distances of the clusters are also known, so chemical peculiarities can be linked directly to the evolutionary status of a star. In addition, binary stars offer the opportunity to verify a relationship between them and the straggler population in both globular and open clusters. We carried out a detailed spectroscopic analysis to derive the atmospheric parameters for 16 red giants in binary systems and the chemical composition of 11 of them in the open clusters NGC 2360, NGC 3680, and NGC 5822. We obtained abundances of C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employ the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. We found that the stars NGC 2360-92 and 96, NGC 3680-34, and NGC 5822-4 and 312 are yellow straggler stars. We show that the spectra of NGC 5822-4 and 312 present evidence of contamination by an A-type star as a secondary star. For the other yellow stragglers, evidence of contamination is given by the broad wings of the Hα. Detection of yellow straggler stars is important because the observed number can be compared with the number predicted by simulations of binary stellar evolution in open clusters. We also found that the other binary stars are not s-process enriched, which may suggest that in these binaries the secondary star is probably a faint main-sequence object. The lack of any s-process enrichment is very useful in setting constraints for the number of white dwarfs in the open cluster, a subject that is related to the birthrate of these kinds of stars in open clusters and also to the age of a

  8. High-resolution Spectroscopic Observations of Binary Stars and Yellow Stragglers in Three Open Clusters : NGC 2360, NGC 3680, and NGC 5822

    Science.gov (United States)

    Sales Silva, J. V.; Peña Suárez, V. J.; Katime Santrich, O. J.; Pereira, C. B.; Drake, N. A.; Roig, F.

    2014-11-01

    Binary stars in open clusters are very useful targets in constraining the nucleosynthesis process. The luminosities of the stars are known because the distances of the clusters are also known, so chemical peculiarities can be linked directly to the evolutionary status of a star. In addition, binary stars offer the opportunity to verify a relationship between them and the straggler population in both globular and open clusters. We carried out a detailed spectroscopic analysis to derive the atmospheric parameters for 16 red giants in binary systems and the chemical composition of 11 of them in the open clusters NGC 2360, NGC 3680, and NGC 5822. We obtained abundances of C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employ the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. We found that the stars NGC 2360-92 and 96, NGC 3680-34, and NGC 5822-4 and 312 are yellow straggler stars. We show that the spectra of NGC 5822-4 and 312 present evidence of contamination by an A-type star as a secondary star. For the other yellow stragglers, evidence of contamination is given by the broad wings of the Hα. Detection of yellow straggler stars is important because the observed number can be compared with the number predicted by simulations of binary stellar evolution in open clusters. We also found that the other binary stars are not s-process enriched, which may suggest that in these binaries the secondary star is probably a faint main-sequence object. The lack of any s-process enrichment is very useful in setting constraints for the number of white dwarfs in the open cluster, a subject that is related to the birthrate of these kinds of stars in open clusters and also to the age of a

  9. A new interpretation of luminous blue stars

    International Nuclear Information System (INIS)

    Stothers, R.

    1976-01-01

    A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's new radiative opacities are adopted in stellar models. Unlike earlier opacities, the new opacities exhibit a large ''bump'' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot, diffuse stellar envelopes (typically those in which L/M>10 3 solar units). Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. Thus, the new stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures (which are yet to be observationally confirmed) for O stars, and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than approx.20 M/sub sun/, beginning at M/sub v/=-4.5 and Sp=B1. They also predict slower surface rotations for O stars compared with B stars; and, in binary systems, slower apsidal motions, closer rotational-revolutional synchronism, and smaller orbital eccentricities. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Radial pulsations of the models have been calculated by employing linearized nonadiabatic pulsation theory. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The new models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars. Ultrashort-period variability, observed in many classes of hot luminous stars, may be due, in part, to high radial overtone pulsations (or, possibly, to nonradial pulsation or convective modes)

  10. Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123

    Science.gov (United States)

    Takada-Hidai, Masahide; Kurtz, Donald W.; Shibahashi, Hiromoto; Murphy, Simon J.; Takata, Masao; Saio, Hideyuki; Sekii, Takashi

    2017-10-01

    A spectroscopic analysis was carried out to clarify the properties of KIC 11145123 - the first main-sequence star with a directly measured core-to-surface rotation profile - based on spectra observed with the High Dispersion Spectrograph (HDS) of the Subaru telescope. The atmospheric parameters (Teff = 7600 K, log g = 4.2, ξ = 3.1 km s-1 and [Fe/H] = -0.71 dex), the radial and rotation velocities, and elemental abundances were obtained by analysing line strengths and fitting line profiles, which were calculated with a 1D LTE model atmosphere. The main properties of KIC 11145123 are: (1) a low [Fe/H] = -0.71 ± 0.11 dex and a high radial velocity of -135.4 ± 0.2 km s-1. These are remarkable among late-A stars. Our best asteroseismic models with this low [Fe/H] have slightly high helium abundance and low masses of 1.4 M⊙. All of these results strongly suggest that KIC 11145123 is a Population II blue straggler; (2) the projected rotation velocity confirms the asteroseismically predicted slow rotation of the star; (3) comparisons of abundance patterns between KIC 11145123 and Am, Ap, and blue stragglers show that KIC 11145123 is neither an Am star nor an Ap star, but has abundances consistent with a blue straggler. We conclude that the remarkably long 100-d rotation period of this star is a consequence of it being a blue straggler, but both pathways for the formation of blue stragglers - merger and mass loss in a binary system - pose difficulties for our understanding of the exceedingly slow rotation. In particular, we show that there is no evidence of any secondary companion star, and we put stringent limits on the possible mass of any such purported companion through the phase modulation technique.

  11. MK classification of evolved blue stars in the halo

    International Nuclear Information System (INIS)

    Garrison, R.F.

    1987-01-01

    The problem of the masses and origin of the evolved blue stars is very complex. No single approach can give all the answers unambiguously; it would be naive to suppose otherwise. The MK process and the MK system give a perspective which complements photometric, kinematic, high dispersion and other quantitative data. It is useful to know which stars are similar (or not) in spectral morphology, so that interesting candidates can be selected for further study. In many cases, the gross physical characteristics can be fairly well determined by use of the MK System. 8 references

  12. IDENTIFYING BLUE HORIZONTAL BRANCH STARS USING THE z FILTER

    International Nuclear Information System (INIS)

    Vickers, John J.; Grebel, Eva K.; Huxor, Avon P.

    2012-01-01

    In this paper we present a new method for selecting blue horizontal branch (BHB) candidates based on color-color photometry. We make use of the Sloan Digital Sky Survey z band as a surface gravity indicator and show its value for selecting BHB stars from quasars, white dwarfs, and main-sequence A-type stars. Using the g, r, i, and z bands, we demonstrate that extraction accuracies on a par with more traditional u, g, and r photometric selection methods may be achieved. We also show that the completeness necessary to probe major Galactic structure may be maintained. Our new method allows us to efficiently select BHB stars from photometric sky surveys that do not include a u-band filter such as the Panoramic Survey Telescope and Rapid Response System.

  13. Stroemgren and BV photometry of potential halo blue horizontal branch field stars

    Energy Technology Data Exchange (ETDEWEB)

    Flynn, C; Sommer-Larsen, J

    1988-11-01

    Stroemgren four-colour and broadband BV photoelectric photometry has been obtained for a sample of potential halo blue horizontal branch stars in two high galactic latitude fields. The large majority of the stars observed are classified as blue horizontal branch stars on the basis of two different surface gravity indicators. Measurements of Ca K-line equivalent widths from medium-dispersion spectra of the stars confirm that most are Population II objects. No metal-rich A-stars were found beyond a few kpc from the galactic disc in the study of faint blue stars.

  14. The Search for New Luminous Blue Variable Stars: Near-Infrared Spectroscopy of Stars With 24 micron Shells

    Science.gov (United States)

    Stringfellow, Guy; Gvaramadze, Vasilii

    2010-02-01

    Luminous Blue Variable (LBV) stars represent an extremely rare class of very luminous and massive stars. Only about a dozen confirmed Galactic LBV stars are known to date, which precludes us from determining a solid evolutionary connection between LBV and other intermediate (e.g. Ofpe/WN9, WNL) phases in the life of very massive stars. The known LBV stars each have their own unique properties, so new discoveries add insight into the properties and evolutionary status of LBVs and massive stars; even one new discovery of objects of this type could provide break-through results in the understanding of the intermediate stages of massive star evolution. We have culled a prime sample of possible LBV candidates from the Spitzer 24 (micron) archival data. All have circumstellar nebulae, rings, and shells (typical of LBVs and related stars) surrounding reddened central stars. Spectroscopic followup of about two dozen optically visible central stars associated with the shells from this sample showed that they are either candidate LBVs, late WN-type Wolf-Rayet stars or blue supergiants. We propose infrared spectroscopic observations of the central stars for a large fraction (23 stars) of our northern sample to determine their nature and discover additional LBV candidates. These stars have no plausible optical counterparts, so infrared spectra are needed. This program requires two nights of Hale time using TripleSpec.

  15. Low-Metallicity Blue Compact Dwarfs as Templates for Primordial Star Formation

    OpenAIRE

    Hunt, L. K.; Hirashita, H.; Thuan, T. X.; Izotov, Y. I.; Vanzi, L.

    2003-01-01

    Understanding how galaxies formed their first stars is a vital cosmological question, but the study of high-redshift objects, caught in the act of forming their first stars, is difficult. Here we argue that two extremely low-metallicity Blue Compact Dwarf galaxies (BCDs), IZw18 and SBS0335-052, could be local templates for primordial star formation, since both lack evolved ($> $1 Gyr) stellar populations; but they form stars differently.

  16. The different star formation histories of blue and red spiral and elliptical galaxies

    Science.gov (United States)

    Tojeiro, Rita; Masters, Karen L.; Richards, Joshua; Percival, Will J.; Bamford, Steven P.; Maraston, Claudia; Nichol, Robert C.; Skibba, Ramin; Thomas, Daniel

    2013-06-01

    We study the spectral properties of intermediate mass galaxies (M* ˜ 1010.7 M⊙) as a function of colour and morphology. We use Galaxy Zoo to define three morphological classes of galaxies, namely early types (ellipticals), late-type (disc-dominated) face-on spirals and early-type (bulge-dominated) face-on spirals. We classify these galaxies as blue or red according to their Sloan Digital Sky Survey (SDSS) g - r colour and use the spectral fitting code Versatile Spectral Analyses to calculate time-resolved star formation histories, metallicity and total starlight dust extinction from their SDSS fibre spectra. We find that red late-type spirals show less star formation in the last 500 Myr than blue late-type spirals by up to a factor of 3, but share similar star formation histories at earlier times. This decline in recent star formation explains their redder colour: their chemical and dust content are the same. We postulate that red late-type spirals are recent descendants of blue late-type spirals, with their star formation curtailed in the last 500 Myr. The red late-type spirals are however still forming stars ≃17 times faster than red ellipticals over the same period. Red early-type spirals lie between red late-type spirals and red ellipticals in terms of recent-to-intermediate star formation and dust content. Therefore, it is plausible that these galaxies represent an evolutionary link between these two populations. They are more likely to evolve directly into red ellipticals than red late-type spirals, which show star formation histories and dust content closer to blue late-type spirals. Blue ellipticals show similar star formation histories as blue spirals (regardless of type), except that they have formed less stars in the last 100 Myr. However, blue ellipticals have different dust content, which peaks at lower extinction values than all spiral galaxies. Therefore, many blue ellipticals are unlikely to be descendants of blue spirals, suggesting there may

  17. New Galactic Candidate Luminous Blue Variables and Wolf-Rayet Stars

    Science.gov (United States)

    Stringfellow, Guy S.; Gvaramadze, Vasilii V.; Beletsky, Yuri; Kniazev, Alexei Y.

    2012-04-01

    We have undertaken a near-infrared spectral survey of stars associated with compact mid-IR shells recently revealed by the MIPSGAL (24 μm) and GLIMPSE (8 μm) Spitzer surveys, whose morphologies are typical of circumstellar shells produced by massive evolved stars. Through spectral similarity with known Luminous Blue Variable (LBV) and Wolf-Rayet (WR) stars, a large population of candidate LBVs (cLBVs) and a smaller number of new WR stars are being discovered. This significantly increases the Galactic cLBV population and confirms that nebulae are inherent to most (if not all) objects of this class.

  18. Evolution of a blue supergiant with a neutron star companion immersed in its envelope

    International Nuclear Information System (INIS)

    Delgado, A.J.

    1980-01-01

    The evolution of a binary system consisting of 1 Msub(sun) neutron star and a 25 Msub(sun) blue supergiant through a phase of common envelope is investigated. We include the effects of an additional energy source on the supergiant's envelope, due to the presence of the neutron star, and variable mass loss from the system, taken as proportional to the total luminosity. The results indicate that, independently of the initial period, the system loses its whole envelope as a consequence of the common envelope phase, the final product of this being a detached system, consisting of a neutron star and a helium star. (orig.)

  19. FAKE STAR FORMATION BURSTS: BLUE HORIZONTAL BRANCH STARS MASQUERADE AS YOUNG MASSIVE STARS IN OPTICAL INTEGRATED LIGHT SPECTROSCOPY

    International Nuclear Information System (INIS)

    Ocvirk, P.

    2010-01-01

    Model color-magnitude diagrams of low-metallicity globular clusters (GCs) usually show a deficit of hot evolved stars with respect to observations. We investigate quantitatively the impact of such modeling inaccuracies on the significance of star formation history reconstructions obtained from optical integrated spectra. To do so, we analyze the sample of spectra of galactic globular clusters of Schiavon et al. with STECKMAP (Ocvirk et al.), and the stellar population models of Vazdekis et al. and Bruzual and Charlot, and focus on the reconstructed stellar age distributions. First, we show that background/foreground contamination correlates with E(B - V), which allows us to define a clean subsample of uncontaminated GCs, on the basis of an E(B - V) filtering. We then identify a 'confusion zone' where fake young bursts of star formation pop up in the star formation history although the observed population is genuinely old. These artifacts appear for 70%-100% of cases depending on the population model used, and contribute up to 12% of the light in the optical. Their correlation with the horizontal branch (HB) ratio indicates that the confusion is driven by HB morphology: red HB clusters are well fitted by old stellar population models while those with a blue HB require an additional hot component. The confusion zone extends over [Fe/H] = [ - 2, - 1.2], although we lack the data to probe extreme high and low metallicity regimes. As a consequence, any young starburst superimposed on an old stellar population in this metallicity range could be regarded as a modeling artifact, if it weighs less than 12% of the optical light, and if no emission lines typical of an H II region are present. This work also provides a practical method for constraining HB morphology from high signal to noise integrated light spectroscopy in the optical. This will allow post-asymptotic giant branch evolution studies in a range of environments and at distances where resolving stellar populations

  20. Pulsar-irradiated stars in dense globular clusters

    Science.gov (United States)

    Tavani, Marco

    1992-01-01

    We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

  1. The nature of the nebula associated with the luminous blue variable star WRA 751

    OpenAIRE

    Hutsemekers, Damien; van Drom, E.

    1991-01-01

    Narrow-band filter imagery as well as medium to high resolution spectroscopy of the nebula surrounding the luminous blue variable (LBV) star WRA 751 are presented. The nebula appears as a slowly expanding H II region of low excitation characterized by a significant N/O overabundance which may be due to the presence in the nebula of nuclear processed material ejected by the star. With the recent discovery of a nebula around HR Car, all but one known galactic LBVs are now shown to be associated...

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

    Science.gov (United States)

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

    2017-05-01

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

  3. Constraining the Stellar Populations and Star Formation Histories of Blue Compact Dwarf Galaxies with SED Fits

    Energy Technology Data Exchange (ETDEWEB)

    Janowiecki, Steven [International Center for Radio Astronomy Research, M468, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009 (Australia); Salzer, John J.; Zee, Liese van [Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405 (United States); Rosenberg, Jessica L. [Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030 (United States); Skillman, Evan, E-mail: steven.janowiecki@uwa.edu.au [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street, SE Minneapolis, MN, 55455 (United States)

    2017-02-10

    We discuss and test possible evolutionary connections between blue compact dwarf galaxies (BCDs) and other types of dwarf galaxies. BCDs provide ideal laboratories to study intense star formation episodes in low-mass dwarf galaxies, and have sometimes been considered a short-lived evolutionary stage between types of dwarf galaxies. To test these connections, we consider a sample of BCDs as well as a comparison sample of nearby galaxies from the Local Volume Legacy (LVL) survey for context. We fit the multi-wavelength spectral energy distributions (SED, far-ultra-violet to far-infrared) of each galaxy with a grid of theoretical models to determine their stellar masses and star formation properties. We compare our results for BCDs with the LVL galaxies to put BCDs in the context of normal galaxy evolution. The SED fits demonstrate that the star formation events currently underway in BCDs are at the extreme of the continuum of normal dwarf galaxies, both in terms of the relative mass involved and in the relative increase over previous star formation rates. Today’s BCDs are distinctive objects in a state of extreme star formation that is rapidly transforming them. This study also suggests ways to identify former BCDs whose star formation episodes have since faded.

  4. FROM BLUE STAR-FORMING TO RED PASSIVE: GALAXIES IN TRANSITION IN DIFFERENT ENVIRONMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Vulcani, Benedetta [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, the University of Tokyo, Kashiwa 277-8582 (Japan); Poggianti, Bianca M.; Fasano, Giovanni; Moretti, Alessia [INAF-Astronomical Observatory of Padova, I-35122 Padova (Italy); Fritz, Jacopo [Sterrenkundig Observatorium Vakgroep Fysica en Sterrenkunde Universiteit Gent, Krijgslaan 281, S9 B-9000 Gent (Belgium); Calvi, Rosa; Paccagnella, Angela [Dipartimento di Fisica e Astronomia, Universitá degli Studi di Padova, vicolo Osservatorio 2, I-35122 Padova (Italy)

    2015-01-01

    Exploiting a mass-complete (M {sub *} > 10{sup 10.25} M {sub ☉}) sample at 0.03 star-formation activity and/or morphology: green galaxies, red passive late types, and blue star-forming early types. Color fractions depend on mass and only for M {sub *} < 10{sup 10.7} M {sub ☉} on environment. The incidence of red galaxies increases with increasing mass, and, for M {sub *} < 10{sup 10.7} M {sub ☉}, decreases toward the group outskirts and in binary and single galaxies. The relative abundance of green and blue galaxies is independent of environment and increases monotonically with galaxy mass. We also inspect galaxy structural parameters, star-formation properties, histories, and ages and propose an evolutionary scenario for the different subpopulations. Color transformations are due to a reduction and suppression of the star-formation rate in both bulges and disks that does not noticeably affect galaxy structure. Morphological transitions are linked to an enhanced bulge-to-disk ratio that is due to the removal of the disk, not to an increase of the bulge. Our modeling suggests that green colors might be due to star-formation histories declining with long timescales, as an alternative scenario to the classical ''quenching'' processes. Our results suggest that galaxy transformations in star-formation activity and morphology depend neither on the environment nor on being a satellite or the most massive galaxy of a halo. The only environmental dependence we find is the higher fast quenching efficiency in groups giving origin to poststarburst signatures.

  5. Tidal interaction, star formation and chemical evolution in blue compact dwarf galaxy Mrk 22

    Science.gov (United States)

    Paswan, A.; Omar, A.; Jaiswal, S.

    2018-02-01

    The optical spectroscopic and radio interferometric H I 21 cm-line observations of the blue compact dwarf galaxy Mrk 22 are presented. The Wolf-Rayet (WR) emission-line features corresponding to high ionization lines of He II λ4686 and C IV λ5808 from young massive stars are detected. The ages of two prominent star-forming regions in the galaxy are estimated as ∼10 and ∼ 4 Myr. The galaxy has non-thermal radio deficiency, which also indicates a young starburst and lack of supernovae events from the current star formation activities, consistent with the detection of WR emission-line features. A significant N/O enrichment is seen in the fainter star-forming region. The gas-phase metallicities [12 + log(O/H)] for the bright and faint regions are estimated as 7.98±0.07 and 7.46±0.09, respectively. The galaxy has a large diffuse H I envelop. The H I images reveal disturbed gas kinematics and H I clouds outside the optical extent of the galaxy, indicating recent tidal interaction or merger in the system. The results strongly indicate that Mrk 22 is undergoing a chemical and morphological evolution due to ongoing star formation, most likely triggered by a merger.

  6. EFFECTS OF ROTATIONALLY INDUCED MIXING IN COMPACT BINARY SYSTEMS WITH LOW-MASS SECONDARIES AND IN SINGLE SOLAR-TYPE STARS

    International Nuclear Information System (INIS)

    Chatzopoulos, E.; Robinson, Edward L.; Wheeler, J. Craig

    2012-01-01

    Many population synthesis and stellar evolution studies have addressed the evolution of close binary systems in which the primary is a compact remnant and the secondary is filling its Roche lobe, thus triggering mass transfer. Although tidal locking is expected in such systems, most studies have neglected the rotationally induced mixing that may occur. Here we study the possible effects of mixing in mass-losing stars for a range of secondary star masses and metallicities. We find that tidal locking can induce rotational mixing prior to contact and thus affect the evolution of the secondary star if the effects of the Spruit-Tayler dynamo are included both for angular momentum and chemical transport. Once contact is made, the effect of mass transfer tends to be more rapid than the evolutionary timescale, so the effects of mixing are no longer directly important, but the mass-transfer strips matter to inner layers that may have been affected by the mixing. These effects are enhanced for secondaries of 1-1.2 M ☉ and for lower metallicities. We discuss the possible implications for the paucity of carbon in the secondaries of the cataclysmic variable SS Cyg and the black hole candidate XTE J1118+480 and for the progenitor evolution of Type Ia supernovae. We also address the issue of the origin of blue straggler stars in globular and open clusters. We find that for models that include rotation consistent with that observed for some blue straggler stars, evolution is chemically homogeneous. This leads to tracks in the H-R diagram that are brighter and bluer than the non-rotating main-sequence turn-off point. Rotational mixing could thus be one of the factors that contribute to the formation of blue stragglers.

  7. SEARCH FOR BLUE COMPACT DWARF GALAXIES DURING QUIESCENCE. II. METALLICITIES OF GAS AND STARS, AGES, AND STAR FORMATION RATES

    International Nuclear Information System (INIS)

    Sanchez Almeida, J.; Aguerri, J. A. L.; Munoz-Tunon, C.; Vazdekis, A.

    2009-01-01

    We examine the metallicity and age of a large set of Sloan Digital Sky Survey/Data Release 6 galaxies that may be blue compact dwarf (BCD) galaxies during quiescence (QBCDs). The individual spectra are first classified and then averaged to reduce noise. The metallicity inferred from emission lines (tracing ionized gas) exceeds by ∼0.35 dex the metallicity inferred from absorption lines (tracing stars). Such a small difference is significant according to our error budget estimate. The same procedure was applied to a reference sample of BCDs, and in this case the two metallicities agree, being also consistent with the stellar metallicity in QBCDs. Chemical evolution models indicate that the gas metallicity of QBCDs is too high to be representative of the galaxy as a whole, but it can represent a small fraction of the galactic gas, self-enriched by previous starbursts. The luminosity-weighted stellar age of QBCDs spans the whole range between 1 and 10 Gyr, whereas it is always smaller than 1 Gyr for BCDs. Our stellar ages and metallicities rely on a single stellar population spectrum fitting procedure, which we have specifically developed for this work using the stellar library MILES.

  8. The Rise and Fall of Star Formation Histories of Blue Galaxies at Redshifts 0.2 < z < 1.4

    Science.gov (United States)

    Pacifici, Camilla; Kassin, Susan A.; Weiner, Benjamin; Charlot, Stephane; Gardner, Jonathan P.

    2012-01-01

    Popular cosmological scenarios predict that galaxies form hierarchically from the merger of many progenitor, each with their own unique star formation history (SFH). We use the approach recently developed by Pacifici et al. to constrain the SFHs of 4517 blue (presumably star-forming) galaxies with spectroscopic redshifts in the range O.2 galaxies rise and fall in a roughly symmetric bell-shaped manner, while those of low-mass galaxies rise progressively in time, consistent with the typically stronger activity of star formation in low-mass compared to high-mass galaxies. For galaxies of all masses, the star formation activity rises more rapidly at high than at low redshift. These findings imply that the standard approximation of exponentially declining SFHs wIdely used to interpret observed galaxy spectral energy distributions is not appropriate to constrain the physical parameters of star-forming galaxies at intermediate redshifts.

  9. DISCOVERY OF A POSSIBLY SINGLE BLUE SUPERGIANT STAR IN THE INTRA-CLUSTER REGION OF VIRGO CLUSTER OF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Ohyama, Youichi; Hota, Ananda [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan (China)

    2013-04-20

    IC 3418 is a dwarf irregular galaxy falling into the Virgo cluster, and a 17 kpc long trail is seen behind the galaxy, which is considered to have formed due to ram pressure stripping. The trail contains compact knots and diffuse blobs of ultraviolet and blue optical emission and, thus, it is a clear site of recent star formation but in an unusual environment, surrounded by a million degree intra-cluster medium. We report on our optical spectroscopy of a compact source in the trail, SDSS J122952.66+112227.8, and show that the optical spectrum is dominated by emission from a massive blue supergiant star. If confirmed, our report would mark the farthest star with spectroscopic observation. We interpret that a massive O-type star formed in situ in the trail has evolved recently out of the main sequence into this blue supergiant phase, and now lacks any detectable spectral sign of its associated H II region. We argue that turbulence within the ram pressure striped gaseous trail may play a dominant role for the star formation within such trails.

  10. DISCOVERY OF A POSSIBLY SINGLE BLUE SUPERGIANT STAR IN THE INTRA-CLUSTER REGION OF VIRGO CLUSTER OF GALAXIES

    International Nuclear Information System (INIS)

    Ohyama, Youichi; Hota, Ananda

    2013-01-01

    IC 3418 is a dwarf irregular galaxy falling into the Virgo cluster, and a 17 kpc long trail is seen behind the galaxy, which is considered to have formed due to ram pressure stripping. The trail contains compact knots and diffuse blobs of ultraviolet and blue optical emission and, thus, it is a clear site of recent star formation but in an unusual environment, surrounded by a million degree intra-cluster medium. We report on our optical spectroscopy of a compact source in the trail, SDSS J122952.66+112227.8, and show that the optical spectrum is dominated by emission from a massive blue supergiant star. If confirmed, our report would mark the farthest star with spectroscopic observation. We interpret that a massive O-type star formed in situ in the trail has evolved recently out of the main sequence into this blue supergiant phase, and now lacks any detectable spectral sign of its associated H II region. We argue that turbulence within the ram pressure striped gaseous trail may play a dominant role for the star formation within such trails.

  11. IDENTIFYING STAR STREAMS IN THE MILKY WAY HALO

    Energy Technology Data Exchange (ETDEWEB)

    King, Charles III; Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J., E-mail: cking@cfa.harvard.edu, E-mail: wbrown@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)

    2012-05-01

    We develop statistical methods for identifying star streams in the halo of the Milky Way that exploit observed spatial and radial velocity distributions. Within a great circle, departures of the observed spatial distribution from random provide a measure of the likelihood of a potential star stream. Comparisons between the radial velocity distribution within a great circle and the radial velocity distribution of the entire sample also measure the statistical significance of potential streams. The radial velocities enable construction of a more powerful joint statistical test for identifying star streams in the Milky Way halo. Applying our method to halo stars in the Hypervelocity Star (HVS) survey, we detect the Sagittarius stream at high significance. Great circle counts and comparisons with theoretical models suggest that the Sagittarius stream comprises 10%-17% of the halo stars in the HVS sample. The population of blue stragglers and blue horizontal branch stars varies along the stream and is a potential probe of the distribution of stellar populations in the Sagittarius dwarf galaxy prior to disruption.

  12. IDENTIFYING STAR STREAMS IN THE MILKY WAY HALO

    International Nuclear Information System (INIS)

    King, Charles III; Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.

    2012-01-01

    We develop statistical methods for identifying star streams in the halo of the Milky Way that exploit observed spatial and radial velocity distributions. Within a great circle, departures of the observed spatial distribution from random provide a measure of the likelihood of a potential star stream. Comparisons between the radial velocity distribution within a great circle and the radial velocity distribution of the entire sample also measure the statistical significance of potential streams. The radial velocities enable construction of a more powerful joint statistical test for identifying star streams in the Milky Way halo. Applying our method to halo stars in the Hypervelocity Star (HVS) survey, we detect the Sagittarius stream at high significance. Great circle counts and comparisons with theoretical models suggest that the Sagittarius stream comprises 10%-17% of the halo stars in the HVS sample. The population of blue stragglers and blue horizontal branch stars varies along the stream and is a potential probe of the distribution of stellar populations in the Sagittarius dwarf galaxy prior to disruption.

  13. Red giants and yellow stragglers in the young open cluster NGC 2447

    Science.gov (United States)

    da Silveira, M. D.; Pereira, C. B.; Drake, N. A.

    2018-06-01

    In this work we analysed, using high-resolution spectroscopy, a sample of 12 single and 4 spectroscopic binary stars of the open cluster NGC 2447. For the single stars, we obtained atmospheric parameters and chemical abundances of Li, C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, Nd, Eu. Rotational velocities were obtained for all the stars. The abundances of the light elements and Eu and the rotational velocities were derived using spectral synthesis technique. We obtained a mean metallicity of [Fe/H] = -0.17 ± 0.05. We found that the abundances of all elements are similar to field giants and/or giants of open clusters, even for the s-process elements, which are enhanced as in other young open clusters. We show that the spectroscopic binaries NGC 2447-26, 38, and 42 are yellow-straggler stars, of which the primary is a giant star and the secondary a main-sequence A-type star.

  14. Evolution of massive stars in very young clusters and associations

    International Nuclear Information System (INIS)

    Stothers, R.B.

    1985-01-01

    The stellar content of very young galactic clusters and associations with well-determined ages has been analyzed statistically to derive information about stellar evolution at high masses. The adopted approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram, together with the stars' apparent magnitudes. Cluster distance moduli are not used. Only the most basic elements of stellar evolution theory are required as input. For stellar aggregates with main-sequence turnups at spectral types between O9 and B2, the following conclusions have emerged: (1) O-type main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most of the O-type blue stragglers are newly formed massive stars, burning core hydrogen; (3) supergiants lying redward of the turnup, as well as most, or all, of the Wolf-Rayet stars, are burning core helium; (4) Wolf-Rayet stars originally had masses greater than 30--40 M/sub sun/, while known M-type supergiants evolved from star less massive than approx.30 M/sub sun/; (5) phases of evolution following core helium burning are unobservably rapid, presumably on account of copious neutrino emission; and (6) formation of stars of high mass continues vigorously in most young clusters and association for approx.8 x 10 6 yr. The important result concerning the evolutionary status of the supergiants depends only on the total number of these stars and not on how they are distributed between blue and red types; the result, however, may be sensitive to the assumed amount of convective core overshooting. Conclusions in the present work refer chiefly to luminous stars in the mass range 10--40 M/sub sun/, belonging to aggregates in the age range (6--25) x 10 6 yr

  15. An ultraviolet study of B[e] stars: evidence for pulsations, luminous blue variable type variations and processes in envelopes

    Science.gov (United States)

    Krtičková, I.; Krtička, J.

    2018-06-01

    Stars that exhibit a B[e] phenomenon comprise a very diverse group of objects in a different evolutionary status. These objects show common spectral characteristics, including the presence of Balmer lines in emission, forbidden lines and strong infrared excess due to dust. Observations of emission lines indicate illumination by an ultraviolet ionizing source, which is key to understanding the elusive nature of these objects. We study the ultraviolet variability of many B[e] stars to specify the geometry of the circumstellar environment and its variability. We analyse massive hot B[e] stars from our Galaxy and from the Magellanic Clouds. We study the ultraviolet broad-band variability derived from the flux-calibrated data. We determine variations of individual lines and the correlation with the total flux variability. We detected variability of the spectral energy distribution and of the line profiles. The variability has several sources of origin, including light absorption by the disc, pulsations, luminous blue variable type variations, and eclipses in the case of binaries. The stellar radiation of most of B[e] stars is heavily obscured by circumstellar material. This suggests that the circumstellar material is present not only in the disc but also above its plane. The flux and line variability is consistent with a two-component model of a circumstellar environment composed of a dense disc and an ionized envelope. Observations of B[e] supergiants show that many of these stars have nearly the same luminosity, about 1.9 × 105 L⊙, and similar effective temperatures.

  16. A SPECTROSCOPIC STUDY OF BLUE SUPERGIANT STARS IN THE SCULPTOR GALAXY NGC 55: CHEMICAL EVOLUTION AND DISTANCE

    Energy Technology Data Exchange (ETDEWEB)

    Kudritzki, R. P.; Ho, I.-T.; Bresolin, F. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Castro, N. [Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109 (United States); Urbaneja, M. A.; Przybilla, N. [Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstr. 25/8, A-6020 Innsbruck (Austria); Gieren, W.; Pietrzyński, G. [Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción (Chile)

    2016-10-01

    Low-resolution (4.5–5 Å) spectra of 58 blue supergiant stars distributed over the disk of the Magellanic spiral galaxy NGC 55 in the Sculptor group are analyzed by means of non-LTE techniques to determine stellar temperatures, gravities, and metallicities (from iron peak and α -elements). A metallicity gradient of −0.22 ± 0.06 dex/ R {sub 25} is detected. The central metallicity on a logarithmic scale relative to the Sun is [ Z ] = −0.37 ± 0.03. A chemical evolution model using the observed distribution of column densities of the stellar and interstellar medium gas mass reproduces the observed metallicity distribution well and reveals a recent history of strong galactic mass accretion and wind outflows with accretion and mass-loss rates of the order of the star formation rate. There is an indication of spatial inhomogeneity in metallicity. In addition, the relatively high central metallicity of the disk confirms that two extraplanar metal-poor H ii regions detected in previous work 1.13 to 2.22 kpc above the galactic plane are ionized by massive stars formed in situ outside the disk. For a subsample of supergiants, for which Hubble Space Telescope photometry is available, the flux-weighted gravity–luminosity relationship is used to determine a distance modulus of 26.85 ± 0.10 mag.

  17. COMBINED EFFECTS OF BINARIES AND STELLAR ROTATION ON THE COLOR-MAGNITUDE DIAGRAMS OF INTERMEDIATE-AGE STAR CLUSTERS

    International Nuclear Information System (INIS)

    Li Zhongmu; Mao Caiyan; Chen Li; Zhang Qian

    2012-01-01

    About 70% of intermediate-age star clusters in the Large Magellanic Clouds have been confirmed to have broad main sequence, multiple or extended turnoffs, and dual red giant clumps. The observed result seems to be at odds with the classical idea that such clusters are simple stellar populations. Although many models have been used to explain the results via factors such as prolonged star formation history, metallicity spread, differential reddening, selection effect, observational uncertainty, stellar rotation, and binary interaction, the reason for the special color-magnitude diagrams is still uncertain. We revisit this question via the combination of stellar rotation and binary effects. As a result, it shows 'golf club' color-magnitude diagrams with broad or multiple turnoffs, dual red clumps, blue stragglers, red stragglers, and extended main sequences. Because both binaries and massive rotators are common, our result suggests that most color-magnitude diagrams, including extended turnoff or multiple turnoffs, can be explained using simple stellar populations including both binary and stellar rotation effects, or composite populations with two components.

  18. The swift UVOT stars survey. I. Methods and test clusters

    Energy Technology Data Exchange (ETDEWEB)

    Siegel, Michael H.; Porterfield, Blair L.; Linevsky, Jacquelyn S.; Bond, Howard E.; Hoversten, Erik A.; Berrier, Joshua L.; Gronwall, Caryl A. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Holland, Stephen T. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Breeveld, Alice A. [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom); Brown, Peter J., E-mail: siegel@astro.psu.edu, E-mail: blp14@psu.edu, E-mail: heb11@psu.edu, E-mail: caryl@astro.psu.edu, E-mail: sholland@stsci.edu, E-mail: aab@mssl.ucl.ac.uk, E-mail: grbpeter@yahoo.com [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A. and M. University, Department of Physics and Astronomy, 4242 TAMU, College Station, TX 77843 (United States)

    2014-12-01

    We describe the motivations and background of a large survey of nearby stellar populations using the Ultraviolet Optical Telescope (UVOT) on board the Swift Gamma-Ray Burst Mission. UVOT, with its wide field, near-UV sensitivity, and 2.″3 spatial resolution, is uniquely suited to studying nearby stellar populations and providing insight into the near-UV properties of hot stars and the contribution of those stars to the integrated light of more distant stellar populations. We review the state of UV stellar photometry, outline the survey, and address problems specific to wide- and crowded-field UVOT photometry. We present color–magnitude diagrams of the nearby open clusters M67, NGC 188, and NGC 2539, and the globular cluster M79. We demonstrate that UVOT can easily discern the young- and intermediate-age main sequences, blue stragglers, and hot white dwarfs, producing results consistent with previous studies. We also find that it characterizes the blue horizontal branch of M79 and easily identifies a known post-asymptotic giant branch star.

  19. The swift UVOT stars survey. I. Methods and test clusters

    International Nuclear Information System (INIS)

    Siegel, Michael H.; Porterfield, Blair L.; Linevsky, Jacquelyn S.; Bond, Howard E.; Hoversten, Erik A.; Berrier, Joshua L.; Gronwall, Caryl A.; Holland, Stephen T.; Breeveld, Alice A.; Brown, Peter J.

    2014-01-01

    We describe the motivations and background of a large survey of nearby stellar populations using the Ultraviolet Optical Telescope (UVOT) on board the Swift Gamma-Ray Burst Mission. UVOT, with its wide field, near-UV sensitivity, and 2.″3 spatial resolution, is uniquely suited to studying nearby stellar populations and providing insight into the near-UV properties of hot stars and the contribution of those stars to the integrated light of more distant stellar populations. We review the state of UV stellar photometry, outline the survey, and address problems specific to wide- and crowded-field UVOT photometry. We present color–magnitude diagrams of the nearby open clusters M67, NGC 188, and NGC 2539, and the globular cluster M79. We demonstrate that UVOT can easily discern the young- and intermediate-age main sequences, blue stragglers, and hot white dwarfs, producing results consistent with previous studies. We also find that it characterizes the blue horizontal branch of M79 and easily identifies a known post-asymptotic giant branch star.

  20. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta

    Energy Technology Data Exchange (ETDEWEB)

    Nicholl, M.; Berger, E.; Kasen, D.; Metzger, B. D.; Elias, J.; Briceño, C.; Alexander, K. D.; Blanchard, P. K.; Chornock, R.; Cowperthwaite, P. S.; Eftekhari, T.; Fong, W.; Margutti, R.; Villar, V. A.; Williams, P. K. G.; Brown, W.; Annis, J.; Bahramian, A.; Brout, D.; Brown, D. A.; Chen, H. -Y.; Clemens, J. C.; Dennihy, E.; Dunlap, B.; Holz, D. E.; Marchesini, E.; Massaro, F.; Moskowitz, N.; Pelisoli, I.; Rest, A.; Ricci, F.; Sako, M.; Soares-Santos, M.; Strader, J.

    2017-10-16

    We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the SOAR and Magellan telescopes; the UV spectrum was obtained with the \\textit{Hubble Space Telescope} at 5.5 days. Our data reveal a rapidly-fading blue component ($T\\approx5500$ K at 1.5 days) that quickly reddens; spectra later than $\\gtrsim 4.5$ days peak beyond the optical regime. The spectra are mostly featureless, although we identify a possible weak emission line at $\\sim 7900$ \\AA\\ at $t\\lesssim 4.5$ days. The colours, rapid evolution and featureless spectrum are consistent with a "blue" kilonova from polar ejecta comprised mainly of light $r$-process nuclei with atomic mass number $A\\lesssim 140$. This indicates a sight-line within $\\theta_{\\rm obs}\\lesssim 45^{\\circ}$ of the orbital axis. Comparison to models suggests $\\sim0.03$ M$_\\odot$ of blue ejecta, with a velocity of $\\sim 0.3c$. The required lanthanide fraction is $\\sim 10^{-4}$, but this drops to $<10^{-5}$ in the outermost ejecta. The large velocities point to a dynamical origin, rather than a disk wind, for this blue component, suggesting that both binary constituents are neutron stars (as opposed to a binary consisting of a neutron star and a black hole). For dynamical ejecta, the high mass favors a small neutron star radius of $\\lesssim 12$ km. This mass also supports the idea that neutron star mergers are a major contributor to $r$-process nucleosynthesis.

  1. Surface brightness and color distributions in blue compact dwarf galaxies. I. Haro 2, an extreme example of a star-forming young elliptical galaxy

    International Nuclear Information System (INIS)

    Loose, H.H.; Thuan, T.X.; Virginia Univ., Charlottesville, VA)

    1986-01-01

    The first results of a large-scale program to study the morphology and structure of blue compact dwarf galaxies from CCD observations are presented. The observations and reduction procedures are described, and surface brightness and color profiles are shown. The results are used to discuss the morphological type of Haro 2 and its stellar populations. It is found that Haro 2 appears to be an extreme example of an elliptical galaxy undergoing intense star formation in its central regions, and that the oldest stars it contains were made only about four million yr ago. The missing mass problem of Haro 2 is also discussed. 28 references

  2. The Frequency of Binary Stars in the Globular Cluster M71

    Science.gov (United States)

    Barden, S. C.; Armandroff, T. E.; Pryor, C. P.

    1994-12-01

    The frequency of binary stars is a fundamental property of a stellar population. A comparison of the frequency of binaries in globular clusters with those in the field halo and disk populations tests the similarity of star formation in those environments. Binary stars in globular clusters also act as an energy source which ``heats" the cluster through super-elastic encounters with other stars and binaries. Such encounters can not only profoundly affect the dynamical evolution of the cluster, they can disrupt the widely separated binaries and catalyze the formation of exotic objects such as blue stragglers, x-ray binaries, and milli-second pulsars. We have used the KPNO 4-m and the multi-fiber instruments Nessie and Hydra to measure radial velocities at 4 epochs over two years for a sample of 126 stars in the globular cluster M71. Velocity errors are under 1 km s(-1) for the brighter stars and under 2 km s(-1) for the majority of our data set. These velocities will be valuable for studying the kinematics of M71, but here we focus on searching for binaries. The faintest stars are at V=17, or just above the main sequence turnoff. Our sample is thus deeper than any published globular cluster binary search utilizing spectroscopic techniques. By observing smaller stars, we double the number of decades of binary periods sampled compared to previous studies and come within a factor of 4 of the shortest possible periods for turnoff stars. This wider period window has produced the largest known sample of binaries in a globular cluster. Four stars show velocity ranges larger than 20 km s(-1) , nine have ranges larger than 10 km s(-1) , and others are clearly variable. We will compare the radial distribution of these stars to that predicted by theory and derive the main-sequence binary fraction.

  3. Fluctuations at the blue edge of saturated wind lines in IUE spectra of O-type stars

    Science.gov (United States)

    Owocki, Stanley P.; Fullerton, Alex

    1993-01-01

    We examine basic issues involved in synthesizing resonance-line profiles from 1-D, dynamical models of highly structured hot-star winds. Although these models exhibit extensive variations in density as well as velocity, the density scale length is still typically much greater than the Sobolev length. The line transfer is thus treated using a Sobolev approach, as generalized by Rybicki & Hummer (1978) to take proper account of the multiple Sobolev resonances arising from the nonmonotonic velocity field. The resulting reduced-Lambda-matrix equation describing nonlocal coupling of the source function is solved by iteration, and line profiles and then derived from formal solution integration using this source function. The more appropriate methods that instead use either a stationary or a structured, local source function yield qualitatively similar line-profiles, but are found to violate photon conservation by 10 percent or more. The full results suggest that such models may indeed be able to reproduce naturally some of the qualitative properties long noted in observed UV line profiles, such as discrete absorption components in unsaturated lines, or the blue-edge variability in saturated lines. However, these particular models do not yet produce the black absorption troughs commonly observed in saturated lines, and it seems that this and other important discrepancies (e.g., in acceleration time scale of absorption components) may require development of more complete models that include rotation and other 2-D and/or 3-D effects.

  4. Tidal breakup of triple stars in the Galactic Centre

    Science.gov (United States)

    Fragione, Giacomo; Gualandris, Alessia

    2018-04-01

    The last decade has seen the detection of fast moving stars in the Galactic halo, the so-called hypervelocity stars (HVSs). While the bulk of this population is likely the result of a close encounter between a stellar binary and the supermassive black hole (MBH) in the Galactic Centre (GC), other mechanims may contribute fast stars to the sample. Few observed HVSs show apparent ages, which are shorter than the flight time from the GC, thereby making the binary disruption scenario unlikely. These stars may be the result of the breakup of a stellar triple in the GC, which led to the ejection of a hypervelocity binary (HVB). If such binary evolves into a blue straggler star due to internal processes after ejection, a rejuvenation is possible that make the star appear younger once detected in the halo. A triple disruption may also be responsible for the presence of HVBs, of which one candidate has now been observed. We present a numerical study of triple disruptions by the MBH in the GC and find that the most likely outcomes are the production of single HVSs and single/binary stars bound to the MBH, while the production of HVBs has a probability ≲ 1 per cent regardless of the initial parameters. Assuming a triple fraction of ≈ 10 per cent results in an ejection rate of ≲ 1 Gyr - 1, insufficient to explain the sample of HVSs with lifetimes shorter than their flight time. We conclude that alternative mechanisms are responsible for the origin of such objects and HVBs in general.

  5. STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF THE SEXTANS DWARF SPHEROIDAL GALAXY

    International Nuclear Information System (INIS)

    Lee, Myung Gyoon; Yuk, In-Soo; Park, Hong Soo; Harris, Jason; Zaritsky, Dennis

    2009-01-01

    We present the star formation history (SFH) and chemical evolution of the Sextans dSph galaxy as a function of a galactocentric distance. We derive these from the VI photometry of stars in the 42' x 28' field using the SMART model developed by Yuk and Lee and adopting a closed-box model for chemical evolution. For the adopted age of Sextans 15 Gyr, we find that >84% of the stars formed prior to 11 Gyr ago, significant star formation extends from 15 to 11 Gyr ago (∼ 65% of the stars formed 13-15 Gyr ago, while ∼ 25% formed 11-13 Gyr ago), detectable star formation continued to at least 8 Gyr ago, the SFH is more extended in the central regions than the outskirts, and the difference in star formation rates between the central and outer regions is most marked 11-13 Gyr ago. Whether blue straggler stars are interpreted as intermediate-age main-sequence stars affects conclusions regarding the SFH for times 4-8 Gyr ago, but this is at most only a trace population. We find that the metallicity of the stars increased rapidly up to [Fe/H] = -1.6 in the central region and to [Fe/H] = -1.8 in the outer region within the first Gyr, and has varied slowly since then. The abundance ratios of several elements derived in this study are in good agreement with the observational data based on the high-resolution spectroscopy in the literature. We conclude that the primary driver for the radial gradient of the stellar population in this galaxy is the SFH, which self-consistently drives the chemical enrichment history.

  6. Structure of the Milky Way stellar halo out to its outer boundary with blue horizontal-branch stars

    Science.gov (United States)

    Fukushima, Tetsuya; Chiba, Masashi; Homma, Daisuke; Okamoto, Sakurako; Komiyama, Yutaka; Tanaka, Masayuki; Tanaka, Mikito; Arimoto, Nobuo; Matsuno, Tadafumi

    2018-06-01

    We present the structure of the Milky Way stellar halo beyond Galactocentric distances of r = 50 kpc traced by blue horizontal-branch (BHB) stars, which are extracted from the survey data in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We select BHB candidates based on (g, r, i, z) photometry, where the z-band is on the Paschen series and the colors that involve the z-band are sensitive to surface gravity. About 450 BHB candidates are identified between r = 50 kpc and 300 kpc, most of which are beyond the reach of previous large surveys, including the Sloan Digital Sky Survey. We find that the global structure of the stellar halo in this range has substructures, which are especially remarkable in the GAMA15H and XMM-LSS fields in the HSC-SSP. We find that the stellar halo can be fitted to a single power-law density profile with an index of α ≃ 3.3 (3.5) with (without) these fields and its global axial ratio is q ≃ 2.2 (1.3). Thus, the stellar halo may be significantly disturbed and be made in a prolate form by halo substructures, perhaps associated with the Sagittarius stream in its extension beyond r ˜ 100 kpc. For a broken power-law model allowing different power-law indices inside/outside a break radius, we obtain a steep power-law slope of α ≃ 5 outside a break radius of ˜100 kpc (200 kpc) for the case with (without) GAMA15H and XMM-LSS. This radius of 200 kpc might be as close as a halo boundary if there is any, although a larger BHB sample is required from further HSC-SSP surveys to increase its statistical significance.

  7. THE RISE AND FALL OF THE STAR FORMATION HISTORIES OF BLUE GALAXIES AT REDSHIFTS 0.2 < z < 1.4

    International Nuclear Information System (INIS)

    Pacifici, Camilla; Kassin, Susan A.; Gardner, Jonathan P.; Weiner, Benjamin; Charlot, Stéphane

    2013-01-01

    Popular cosmological scenarios predict that galaxies form hierarchically from the merger of many progenitors, each with their own unique star formation history (SFH). We use a sophisticated approach to constrain the SFHs of 4517 blue (presumably star-forming) galaxies with spectroscopic redshifts in the range 0.2 s bands and rest-frame optical emission-line luminosities with those of one million model spectral energy distributions. We explore the dependence of the resulting SFHs on galaxy stellar mass and redshift. We find that the average SFHs of high-mass galaxies rise and fall in a roughly symmetric bell-shaped manner, while those of low-mass galaxies rise progressively in time, consistent with the typically stronger activity of star formation in low-mass compared to high-mass galaxies. For galaxies of all masses, the star formation activity rises more rapidly at high than at low redshift. These findings imply that the standard approximation of exponentially declining SFHs widely used to interpret observed galaxy spectral energy distributions may not be appropriate to constrain the physical parameters of star-forming galaxies at intermediate redshifts.

  8. THE STAR FORMATION HISTORY OF THE VERY METAL-POOR BLUE COMPACT DWARF I Zw 18 FROM HST/ACS DATA

    Energy Technology Data Exchange (ETDEWEB)

    Annibali, F.; Cignoni, M.; Tosi, M.; Clementini, G.; Contreras Ramos, R.; Fiorentino, G. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Van der Marel, R. P.; Aloisi, A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Marconi, M.; Musella, I., E-mail: francesca.annibali@oabo.inaf.it [INAF-Osservatorio Astronomico di Capodimonte, via Moiariello 16, I-80131 Napoli (Italy)

    2013-12-01

    We have derived the star formation history (SFH) of the blue compact dwarf galaxy I Zw 18 through comparison of deep HST/ACS data with synthetic color-magnitude diagrams (CMDs). A statistical analysis was implemented for the identification of the best-fit SFH and relative uncertainties. We confirm that I Zw 18 is not a truly young galaxy, having started forming stars earlier than ∼1 Gyr ago, and possibly at epochs as old as a Hubble time. In I Zw 18's main body we infer a lower limit of ≈2 × 10{sup 6} M {sub ☉} for the mass locked up in old stars. I Zw 18's main body has been forming stars very actively during the last ∼10 Myr, with an average star formation rate (SFR) as high as ≈1 M {sub ☉} yr{sup –1} (or ≈2 × 10{sup –5} M {sub ☉} yr{sup –1} pc{sup –2}). On the other hand, the secondary body was much less active at these epochs, in agreement with the absence of significant nebular emission. The high current SFR can explain the very blue colors and the high ionized gas content in I Zw 18, resembling primeval galaxies in the early universe. Detailed chemical evolution models are required to quantitatively check whether the SFH from the synthetic CMDs can explain the low measured element abundances, or if galactic winds with loss of metals are needed.

  9. The barium-to-iron enrichment versus age relation of ancient disc stars

    Science.gov (United States)

    Fuhrmann, K.; Chini, R.; Kaderhandt, L.; Chen, Z.; Lachaume, R.

    2017-11-01

    We report an intrinsically precise relation of the barium-to-iron enrichment as a function of age for a local, volume-complete (N = 30) sample of ancient Population II (τ ≥ 12 Gyr) and intermediate-disc stars (τ ≃ 10 Gyr), which suggests a common, r-process-dominated nucleosynthesis site for both elements in the early stages of the Milky Way. Deviants from this empirical relation are to a large extent identified as formerly known or new blue straggler stars. We report in particular the striking case of the Population II star HD 159062, whose barium overabundance is difficult to explain without wind accretion of s-process material from a former asymptotic giant branch (AGB) primary that very likely survived as a white dwarf companion. The weak but significant barium enhancement that we measure for HR 3578 and 104 Tau also suggests that both may be accompanied by faint degenerate companions. If confirmed through precision astrometry or direct imaging observations, this would mean a very efficient method to uncover ancient stellar remnant companions around solar-type stars.

  10. Probing star formation and feedback in dwarf galaxies. Integral field view of the blue compact galaxy Tololo 1937-423

    Science.gov (United States)

    Cairós, L. M.; González-Pérez, J. N.

    2017-12-01

    Context. Blue compact galaxies (BCG) are gas-rich, low-mass, small systems that form stars at unusually high rates. This makes them excellent laboratories for investigating the process of star-formation (SF) at galactic scales and the effects of massive stellar feedback on the interstellar (and intergalactic) medium. Aims: We analyzed the BCG Tololo 1937-423 using optical integral field spectroscopy to probe its morphology, stellar content, nebular excitation and ionization properties, and the kinematics of its warm ionized gas. Methods: Tololo 1937-423 was observed with the Visible Multi-Object Spectrograph at the Very Large Telescope. We took data in the wavelength range 4150-7400 Å, covering a field of view of 27″× 27″ on the sky with a spatial sampling of 0.̋67. From these data we built maps in the continuum and brighter emission lines, diagnostic line ratio maps, and velocity dispersion fields. We also generated the integrated spectrum of the main H II regions and young stellar clusters to determine reliable physical parameters and oxygen abundances. Results: We found that Tololo 1937-423 is currently undergoing an extended starburst. In the Hα maps we identified nine major clumps, aligned mostly northeast-southwest, and stretching to galactocentric distances ≥2 kpc. The galaxy presents a single continuum peak that is not cospatial with any knot in emission lines, indicating at least two relatively recent episodes of SF. The inhomogeneous dust distribution reachs its maximum (E(B-V) 0.97) roughly at the position of the continuum peak. We found shocked regions in the galaxy outer regions and at the edges of the SF knots. The oxygen abundance, 12 + log(O/H) 8.20 ± 0.1, is similar in all the SF regions, suggesting a chemically homogeneous ionized interstellar medium over spatial scales of several kpc. The ionized gas kinematics displays an overall regular rotation around a northwest-southeast axis, with a maximum velocity of 70 ± 7 km s-1. Conclusions

  11. THE RISE AND FALL OF THE STAR FORMATION HISTORIES OF BLUE GALAXIES AT REDSHIFTS 0.2 < z < 1.4

    Energy Technology Data Exchange (ETDEWEB)

    Pacifici, Camilla [Yonsei University Observatory, Yonsei University, Seoul 120-749 (Korea, Republic of); Kassin, Susan A.; Gardner, Jonathan P. [Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Weiner, Benjamin [Steward Observatory, 933 North Cherry Street, University of Arizona, Tucson, AZ 85721 (United States); Charlot, Stephane [UPMC-CNRS, UMR7095, Institut d' Astrophysique de Paris, F-75014 Paris (France)

    2013-01-01

    Popular cosmological scenarios predict that galaxies form hierarchically from the merger of many progenitors, each with their own unique star formation history (SFH). We use a sophisticated approach to constrain the SFHs of 4517 blue (presumably star-forming) galaxies with spectroscopic redshifts in the range 0.2 < z < 1.4 from the All-Wavelength Extended Groth Strip International Survey. This consists in the Bayesian analysis of the observed galaxy spectral energy distributions with a comprehensive library of synthetic spectra assembled using realistic, hierarchical star formation, and chemical enrichment histories from cosmological simulations. We constrain the SFH of each galaxy in our sample by comparing the observed fluxes in the B, R, I, and K{sub s} bands and rest-frame optical emission-line luminosities with those of one million model spectral energy distributions. We explore the dependence of the resulting SFHs on galaxy stellar mass and redshift. We find that the average SFHs of high-mass galaxies rise and fall in a roughly symmetric bell-shaped manner, while those of low-mass galaxies rise progressively in time, consistent with the typically stronger activity of star formation in low-mass compared to high-mass galaxies. For galaxies of all masses, the star formation activity rises more rapidly at high than at low redshift. These findings imply that the standard approximation of exponentially declining SFHs widely used to interpret observed galaxy spectral energy distributions may not be appropriate to constrain the physical parameters of star-forming galaxies at intermediate redshifts.

  12. Outflow-Induced Dynamical and Radiative Instability in Stellar Envelopes with an Application to Luminous Blue Variables and Wolf-Rayet Stars

    Science.gov (United States)

    Stothers, Richard B.; Hansen, James E. (Technical Monitor)

    2002-01-01

    Theoretical models of the remnants of massive stars in a very hot, post-red-supergiant phase display no obvious instability if standard assumptions are made. However, the brightest observed classical luminous blue variables (LBVs) may well belong to such a phase. A simple time-dependent theory of moving stellar envelopes is developed in order to treat deep hydrodynamical disturbances caused by surface mass loss and to test the moving envelopes for dynamical instability. In the case of steady-state outflow, the theory reduces to the equivalent of the Castor, Abbott, and Klein formulation for optically thick winds at distances well above the sonic point. The time-dependent version indicates that the brightest and hottest LBVs are both dynamically and radiatively unstable, as a result of the substantial lowering of the generalized Eddington luminosity limit by the mass-loss acceleration. It is suggested that dynamical instability, by triggering secular cycles of mass loss, is primarily what differentiates LBVs from the purely radiatively unstable Wolf-Rayet stars. Furthermore, when accurate main-sequence mass-loss rates are used to calculate the evolutionary tracks, the predicted surface hydrogen and nitrogen abundances of the blue remnants agree much better with observations of the brightest LBVs than before.

  13. THE GALACTIC O-STAR SPECTROSCOPIC SURVEY. I. CLASSIFICATION SYSTEM AND BRIGHT NORTHERN STARS IN THE BLUE-VIOLET AT R ∼ 2500

    International Nuclear Information System (INIS)

    Sota, A.; Maiz Apellaniz, J.; Alfaro, E. J.; Walborn, N. R.; Barba, R. H.; Morrell, N. I.; Gamen, R. C.; Arias, J. I.

    2011-01-01

    We present the first installment of a massive spectroscopic survey of Galactic O stars, based on new, high signal-to-noise ratio, R ∼ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog of MaIz Apellaniz et al. and Sota et al. The spectral classification system is rediscussed and a new atlas is presented, which supersedes previous versions. Extensive sequences of exceptional objects are given, including types Ofc, ON/OC, Onfp, Of?p, Oe, and double-lined spectroscopic binaries. The remaining normal spectra bring this first sample to 184 stars, which is close to complete to B = 8 and north of δ = -20 0 and includes all of the northern objects in MaIz Apellaniz et al. that are still classified as O stars. The systematic and random accuracies of these classifications are substantially higher than previously attainable, because of the quality, quantity, and homogeneity of the data and analysis procedures. These results will enhance subsequent investigations in Galactic astronomy and stellar astrophysics. In the future, we will publish the rest of the survey, beginning with a second paper that will include most of the southern stars in MaIz Apellaniz et al.

  14. The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-violet at R ~ 2500

    Science.gov (United States)

    Sota, A.; Maíz Apellániz, J.; Walborn, N. R.; Alfaro, E. J.; Barbá, R. H.; Morrell, N. I.; Gamen, R. C.; Arias, J. I.

    2011-04-01

    We present the first installment of a massive spectroscopic survey of Galactic O stars, based on new, high signal-to-noise ratio, R ~ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog of Maíz Apellániz et al. and Sota et al. The spectral classification system is rediscussed and a new atlas is presented, which supersedes previous versions. Extensive sequences of exceptional objects are given, including types Ofc, ON/OC, Onfp, Of?p, Oe, and double-lined spectroscopic binaries. The remaining normal spectra bring this first sample to 184 stars, which is close to complete to B = 8 and north of δ = -20° and includes all of the northern objects in Maíz Apellániz et al. that are still classified as O stars. The systematic and random accuracies of these classifications are substantially higher than previously attainable, because of the quality, quantity, and homogeneity of the data and analysis procedures. These results will enhance subsequent investigations in Galactic astronomy and stellar astrophysics. In the future, we will publish the rest of the survey, beginning with a second paper that will include most of the southern stars in Maíz Apellániz et al. The spectroscopic data in this article were gathered with three facilities: the 1.5 m telescope at the Observatorio de Sierra Nevada (OSN), the 3.5 m telescope at Calar Alto Observatory (CAHA), and the du Pont 2.5 m telescope at Las Campanas Observatory (LCO). Some of the supporting imaging data were obtained with the 2.2 m telescope at CAHA and the NASA/ESA Hubble Space Telescope (HST). The rest were retrieved from the DSS2 and Two Micron All Sky Survey (2MASS) surveys. The HST data were 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.

  15. A GMOS-N IFU study of the central H II region in the blue compact dwarf galaxy NGC 4449: kinematics, nebular metallicity and star formation

    Science.gov (United States)

    Kumari, Nimisha; James, Bethan L.; Irwin, Mike J.

    2017-10-01

    We use integral field spectroscopic (IFS) observations from the Gemini Multi-Object Spectrograph North (GMOS-N) to study the central H II region in a nearby blue compact dwarf (BCD) galaxy NGC 4449. The IFS data enable us to explore the variation of physical and chemical conditions of the star-forming region and the surrounding gas on spatial scales as small as 5.5 pc. Our kinematical analysis shows possible signatures of shock ionization and shell structures in the surroundings of the star-forming region. The metallicity maps of the region, created using direct Te and indirect strong line methods (R23, O3N2 and N2), do not show any chemical variation. From the integrated spectrum of the central H II region, we find a metallicity of 12 + log(O/H) = 7.88 ± 0.14 ({˜ }0.15^{+0.06}_{-0.04} Z⊙) using the direct method. Comparing the central H II region metallicity derived here with those of H II regions throughout this galaxy from previous studies, we find evidence of increasing metallicity with distance from the central nucleus. Such chemical inhomogeneities can be due to several mechanisms, including gas loss via supernova blowout, galactic winds or metal-poor gas accretion. However, we find that the localized area of decreased metallicity aligns spatially with the peak of star-forming activity in the galaxy, suggesting that gas accretion may be at play here. Spatially resolved IFS data for the entire galaxy are required to confirm the metallicity inhomogeneity found in this study and determine its possible cause.

  16. Open clusters. III. Fundamental parameters of B stars in NGC 6087, NGC 6250, NGC 6383, and NGC 6530 B-type stars with circumstellar envelopes

    Science.gov (United States)

    Aidelman, Y.; Cidale, L. S.; Zorec, J.; Panei, J. A.

    2018-02-01

    Context. Stellar physical properties of star clusters are poorly known and the cluster parameters are often very uncertain. Methods: Our goals are to perform a spectrophotometric study of the B star population in open clusters to derive accurate stellar parameters, search for the presence of circumstellar envelopes, and discuss the characteristics of these stars. The BCD spectrophotometric system is a powerful method to obtain stellar fundamental parameters from direct measurements of the Balmer discontinuity. To this end, we wrote the interactive code MIDE3700. The BCD parameters can also be used to infer the main properties of open clusters: distance modulus, color excess, and age. Furthermore, we inspected the Balmer discontinuity to provide evidence for the presence of circumstellar disks and identify Be star candidates. We used an additional set of high-resolution spectra in the Hα region to confirm the Be nature of these stars. Results: We provide Teff, log g, Mv, Mbol, and spectral types for a sample of 68 stars in the field of the open clusters NGC 6087, NGC 6250, NGC 6383, and NGC 6530, as well as the cluster distances, ages, and reddening. Then, based on a sample of 230 B stars in the direction of the 11 open clusters studied along this series of three papers, we report 6 new Be stars, 4 blue straggler candidates, and 15 B-type stars (called Bdd) with a double Balmer discontinuity, which indicates the presence of circumstellar envelopes. We discuss the distribution of the fraction of B, Be, and Bdd star cluster members per spectral subtype. The majority of the Be stars are dwarfs and present a maximum at the spectral type B2-B4 in young and intermediate-age open clusters (operating under agreement of CONICET and the Universities of La Plata, Córdoba, and San Juan, Argentina.Tables 1, 2, 9-16 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A30

  17. The MAVERIC Survey: A Red Straggler Binary with an Invisible Companion in the Galactic Globular Cluster M10

    Science.gov (United States)

    Shishkovsky, Laura; Strader, Jay; Chomiuk, Laura; Bahramian, Arash; Tremou, Evangelia; Li, Kwan-Lok; Salinas, Ricardo; Tudor, Vlad; Miller-Jones, James C. A.; Maccarone, Thomas J.; Heinke, Craig O.; Sivakoff, Gregory R.

    2018-03-01

    We present the discovery and characterization of a radio-bright binary in the Galactic globular cluster M10. First identified in deep radio continuum data from the Karl G. Jansky Very Large Array, M10-VLA1 has a flux density of 27 ± 4 μJy at 7.4 GHz and a flat-to-inverted radio spectrum. Chandra imaging shows an X-ray source with L X ≈ 1031 erg s‑1 matching the location of the radio source. This places M10-VLA1 within the scatter of the radio-X-ray luminosity correlation for quiescent stellar-mass black holes, and a black hole X-ray binary is a viable explanation for this system. The radio and X-ray properties of the source disfavor, but do not rule out, identification as an accreting neutron star or white dwarf system. Optical imaging from the Hubble Space Telescope and spectroscopy from the SOAR telescope show that the system has an orbital period of 3.339 days and an unusual “red straggler” component: an evolved star found redward of the M10 red giant branch. These data also show UV/optical variability and double-peaked Hα emission characteristic of an accretion disk. However, SOAR spectroscopic monitoring reveals that the velocity semi-amplitude of the red straggler is low. We conclude that M10-VLA1 is most likely either a quiescent black hole X-ray binary with a rather face-on (i orientation or an unusual flaring RS Canum Venaticorum variable-type active binary, and discuss future observations that could distinguish between these possibilities.

  18. The Cluster AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster M22

    Science.gov (United States)

    Rozyczka, M.; Thompson, I. B.; Pych, W.; Narloch, W.; Poleski, R.; Schwarzenberg-Czerny, A.

    2017-09-01

    The field of the globular cluster M22 (NGC 6656) was monitored between 2000 and 2008 in a search for variable stars. BV light curves were obtained for 359 periodic, likely periodic, and long-term variables, 238 of which are new detections. 39 newly detected variables, and 63 previously known ones are members or likely members of the cluster, including 20 SX Phe, 10 RRab and 16 RRc type pulsators, one BL Her type pulsator, 21 contact binaries, and 9 detached or semi-detached eclipsing binaries. The most interesting among the identified objects are V112 - a bright multimode SX Phe pulsator, V125 - a β Lyr type binary on the blue horizontal branch, V129 - a blue/yellow straggler with a W UMa-like light curve, located halfway between the extreme horizontal branch and red giant branch, and V134 - an extreme horizontal branch object with P=2.33 d and a nearly sinusoidal light curve. All four of them are proper motion members of the cluster. Among nonmembers, a P=2.83 d detached eclipsing binary hosting a δ Sct type pulsator was found, and a peculiar P=0.93 d binary with ellipsoidal modulation and narrow minimum in the middle of one of the descending shoulders of the sinusoid. We also collected substantial new data for previously known variables. In particular we revise the statistics of the occurrence of the Blazhko effect in RR Lyr type variables of M22.

  19. Starbursts in Blue compact dwarf galaxies

    International Nuclear Information System (INIS)

    Thuan, T.X.

    1987-01-01

    We summarize all the arguments for a bursting mode of star formation in blue compact dwarf galaxies. We show in particular how spectral synthesis of far ultraviolet spectra of Blue compact dwarf galaxy constitutes a powerful way for studying the star formation history in these galaxies. Blue compact dwarf galaxy luminosity functions show jumps and discontinuities. These jumps act like fossil records of the star-forming bursts, helping us to count and date the bursts

  20. VARIABLE STARS IN THE GLOBULAR CLUSTER NGC 2808

    International Nuclear Information System (INIS)

    Kunder, Andrea; Walker, Alistair R.; Stetson, Peter B.; Catelan, Márcio; Amigo, Pía

    2013-01-01

    The first calibrated broadband BVI time-series photometry is presented for the variable stars in NGC 2808, with observations spanning a range of 28 years. We have also redetermined the variability types and periods for the variable stars identified previously by Corwin et al., revising the number of probable fundamental-mode RR Lyrae variables (RR0) to 11 and the number of first-overtone variables (RR1) to five. Our observations were insufficient to discern the nature of the previously identified RR1 star, V24, and the tentatively identified RR1 star, V13. These two variables are ∼0.8 mag brighter than the RR Lyrae variables, appear to have somewhat erratic period and/or luminosity changes, and lie inside the RR Lyrae instability strip. Curiously, all but one of the RR Lyrae stars studied in this relatively metal-rich cluster exhibit the Blazhko phenomenon, an effect thought to occur with higher frequency in metal-poor environments. The mean periods of the RR0 and RR1 variables are (P) RR0 = 0.56 ± 0.01 d and RR1 = 0.30 ± 0.02 d, respectively, supporting an Oosterhoff I classification of the cluster. On the other hand, the number ratio of RR1-to-RR0-type variables is high, though not unprecedented, for an Oosterhoff I cluster. The RR Lyrae variables have no period shifts at a given amplitude compared to the M3 variables, making it unlikely that these variables are He enhanced. Using the recent recalibration of the RR Lyrae luminosity scale by Catelan and Cortés, a mean distance modulus of (m – M) V = 15.57 ± 0.13 mag for NGC 2808 is obtained, in good agreement with that determined here from its type II Cepheid and SX Phoenicis population. Our data have also allowed the discovery of two new candidate SX Phoenicis stars and an eclipsing binary in the blue straggler region of the NGC 2808 color-magnitude diagram.

  1. Luminous and Variable Stars in M31 and M33. IV. Luminous Blue Variables, Candidate LBVs, B[e] Supergiants, and the Warm Hypergiants: How to Tell Them Apart

    Energy Technology Data Exchange (ETDEWEB)

    Humphreys, Roberta M.; Gordon, Michael S.; Hahn, David [Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota, Minneapolis, MN 55455 (United States); Martin, John C. [University of Illinois Springfield, Springfield, IL 62703 (United States); Weis, Kerstin, E-mail: roberta@umn.edu [Astronomical Institute, Ruhr-Universitaet Bochum (Germany)

    2017-02-10

    In this series of papers we have presented the results of a spectroscopic survey of luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission-line spectra, including luminous blue variables (LBVs) and candidate LBVs, Fe ii emission line stars, the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. We examine their similarities and differences and propose the following guidelines that can be used to help distinguish these stars in future work. (1) The B[e] supergiants have emission lines of [O i] and [Fe ii] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their spectral energy distributions (SEDs). (2) Confirmed LBVs do not have the [O i] emission lines in their spectra. Some LBVs have [Fe ii] emission lines, but not all. Their SEDs show free–free emission in the near-infrared but no evidence for warm dust . Their most important and defining characteristic is the S Dor-type variability. (3) The warm hypergiants spectroscopically resemble the LBVs in their dense wind state and the B[e] supergiants. However, they are very dusty. Some have [Fe ii] and [O i] emission in their spectra like the sgB[e] stars, but are distinguished by their A- and F-type absorption-line spectra. In contrast, the B[e] supergiant spectra have strong continua and few if any apparent absorption lines. Candidate LBVs should share the spectral characteristics of the confirmed LBVs with low outflow velocities and the lack of warm circumstellar dust.

  2. The K2 M67 Study: A Curiously Young Star in an Eclipsing Binary in an Old Open Cluster

    Science.gov (United States)

    Sandquist, Eric L.; Mathieu, Robert D.; Quinn, Samuel N.; Pollack, Maxwell L.; Latham, David W.; Brown, Timothy M.; Esselstein, Rebecca; Aigrain, Suzanne; Parviainen, Hannu; Vanderburg, Andrew; Stello, Dennis; Somers, Garrett; Pinsonneault, Marc H.; Tayar, Jamie; Orosz, Jerome A.; Bedin, Luigi R.; Libralato, Mattia; Malavolta, Luca; Nardiello, Domenico

    2018-04-01

    We present an analysis of a slightly eccentric (e = 0.05), partially eclipsing, long-period (P = 69.73 days) main-sequence binary system (WOCS 12009, Sanders 1247) in the benchmark old open cluster M67. Using Kepler K2 and ground-based photometry, along with a large set of new and reanalyzed spectra, we derived highly precise masses (1.111 ± 0.015 and 0.748 ± 0.005 M ⊙) and radii (1.071 ± 0.008 ± 0.003 and 0.713 ± 0.019 ± 0.026 R ⊙, with statistical and systematic error estimates) for the stars. The radius of the secondary star is in agreement with theory. The primary, however, is approximately 15% smaller than reasonable isochrones for the cluster predict. Our best explanation is that the primary star was produced from the merger of two stars, as this can also account for the nondetection of photospheric lithium and its higher temperature relative to other cluster main-sequence stars at the same V magnitude. To understand the dynamical characteristics (low measured rotational line broadening of the primary star and low eccentricity of the current binary orbit), we believe that the most probable (but not the only) explanation is the tidal evolution of a close binary within a primordial triple system (possibly after a period of Kozai–Lidov oscillations), leading to merger approximately 1 Gyr ago. This star appears to be a future blue straggler that is being revealed as the cluster ages and the most massive main-sequence stars die out. Based on observations made at Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation; with the Tillinghast Reflector Echelle Spectrograph (TRES) on the 1.5 m Tillinghast telescope, located at the Smithsonian Astrophysical Observatory’s Fred L. Whipple Observatory on Mt. Hopkins in Arizona; the HARPS-N spectrograph on the Italian Telescopio Nazionale

  3. Constraining cosmic scatter in the Galactic halo through a differential analysis of metal-poor stars

    Science.gov (United States)

    Reggiani, Henrique; Meléndez, Jorge; Kobayashi, Chiaki; Karakas, Amanda; Placco, Vinicius

    2017-12-01

    find two blue straggler stars, based on their very depleted Li abundances. One of them shows intriguing abundance anomalies, including a possible zinc enhancement, suggesting that zinc may have been also produced by a former AGB companion. Tables A.1-A.6 are also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/608/A46

  4. IONIZED GAS KINEMATICS AT HIGH RESOLUTION. V. [Ne ii], MULTIPLE CLUSTERS, HIGH EFFICIENCY STAR FORMATION, AND BLUE FLOWS IN HE 2–10

    International Nuclear Information System (INIS)

    Beck, Sara; Turner, Jean; Lacy, John; Greathouse, Thomas

    2015-01-01

    We measured the 12.8 μm [Ne ii] line in the dwarf starburst galaxy He 2–10 with the high-resolution spectrometer TEXES on the NASA IRTF. The data cube has a diffraction-limited spatial resolution of ∼1″ and a total velocity resolution, including thermal broadening, of ∼5 km s −1 . This makes it possible to compare the kinematics of individual star-forming clumps and molecular clouds in the three dimensions of space and velocity, and allows us to determine star formation efficiencies. The kinematics of the ionized gas confirm that the starburst contains multiple dense clusters. From the M/R of the clusters and the ≃30%–40% star formation efficiencies, the clusters are likely to be bound and long lived, like globulars. Non-gravitational features in the line profiles show how the ionized gas flows through the ambient molecular material, as well as a narrow velocity feature, which we identify with the interface of the H ii region and a cold dense clump. These data offer an unprecedented view of the interaction of embedded H ii regions with their environment

  5. AGE DETERMINATION OF SIX INTERMEDIATE-AGE SMALL MAGELLANIC CLOUD STAR CLUSTERS WITH HST/ACS

    International Nuclear Information System (INIS)

    Glatt, Katharina; Kayser, Andrea; Grebel, Eva K.; Sabbi, Elena; Gallagher, John S. III; Harbeck, Daniel; Nota, Antonella; Sirianni, Marco; Clementini, Gisella; Tosi, Monica; Koch, Andreas; Da Costa, Gary

    2008-01-01

    We present a photometric analysis of the star clusters Lindsay 1, Kron 3, NGC 339, NGC 416, Lindsay 38, and NGC 419 in the Small Magellanic Cloud (SMC), observed with the Hubble Space Telescope Advanced Camera for Surveys (ACS) in the F555W and F814W filters. Our color-magnitude diagrams (CMDs) extend ∼3.5 mag deeper than the main-sequence turnoff points, deeper than any previous data. Cluster ages were derived using three different isochrone models: Padova, Teramo, and Dartmouth, which are all available in the ACS photometric system. Fitting observed ridgelines for each cluster, we provide a homogeneous and unique set of low-metallicity, single-age fiducial isochrones. The cluster CMDs are best approximated by the Dartmouth isochrones for all clusters, except for NGC 419 where the Padova isochrones provided the best fit. Using Dartmouth isochrones we derive ages of 7.5 ± 0.5 Gyr (Lindsay 1), 6.5 ± 0.5 Gyr (Kron 3), 6 ± 0.5 Gyr (NGC 339), 6 ± 0.5 Gyr (NGC 416), and 6.5 ± 0.5 Gyr (Lindsay 38). The CMD of NGC 419 shows several main-sequence turnoffs, which belong to the cluster and to the SMC field. We thus derive an age range of 1.2-1.6 Gyr for NGC 419. We confirm that the SMC contains several intermediate-age populous star clusters with ages unlike those of the Large Magellanic Cloud and the Milky Way. Interestingly, our intermediate-age star clusters have a metallicity spread of ∼0.6 dex, which demonstrates that the SMC does not have a smooth, monotonic age-metallicity relation. We find an indication for centrally-concentrated blue straggler star candidates in NGC 416, while these are not present for the other clusters. Using the red clump magnitudes, we find that the closest cluster, NGC 419 (∼50 kpc), and the farthest cluster, Lindsay 38 (∼67 kpc), have a relative distance of ∼17 kpc, which confirms the large depth of the SMC. The three oldest SMC clusters (NGC 121, Lindsay 1, and Kron 3) lie in the northwestern part of the SMC, while the youngest

  6. On the Origin of Sub-subgiant Stars. I. Demographics

    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 60201 (United States); Leiner, Emily M.; Mathieu, Robert D. [Department of Astronomy, University of Wisconsin–Madison, 475 North Charter Street, Madison, WI 53706 (United States); Bellini, Andrea; Watkins, Laura L. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Gleisinger, Robert; Haggard, Daryl [Department of Physics, McGill University, McGill Space Institute, 3550 University Street, Montreal, QC H3A 2A7 (Canada); Kamann, Sebastian [Institut für Astrophysik, Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen (Germany); Leigh, Nathan W. C.; Zurek, David [Department of Astrophysics, American Museum of Natural History, Central Park West and 79th Street, New York, NY 10024 (United States); Sills, Alison, E-mail: a-geller@northwestern.edu [Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada)

    2017-05-10

    Sub-subgiants are stars that are observed to be redder than normal main-sequence stars and fainter than normal subgiant (and giant) stars in an optical color–magnitude diagram (CMD). The red straggler stars, which lie redward of the red giant branch, may be related and are often grouped together with the sub-subgiants in the literature. These stars defy our standard theory of single-star evolution and are important tests for binary evolution and stellar collision models. In total, we identify 65 sub-subgiants (SSG) and red stragglers (RS) in 16 open and globular star clusters from the literature; 50 of these, including 43 sub-subgiants, pass our strict membership selection criteria (though the remaining sources may also be cluster members). In addition to their unique location on the CMD, we find that at least 58% (25/43) of sub-subgiants in this sample are X-ray sources with typical 0.5–2.5 keV luminosities of order 10{sup 30}–10{sup 31} erg s{sup −1}. Their X-ray luminosities and optical–to–X-ray flux ratios are similar to those of RS CVn active binaries. At least 65% (28/43) of the sub-subgiants in our sample are variables, 21 of which are known to be radial-velocity binaries. Typical variability periods are ≲15 days. At least 33% (14/43) of the sub-subgiants are H α emitters. These observational demographics provide strong evidence that binarity is important for sub-subgiant formation. Finally, we find that the number of sub-subgiants per unit mass increases toward lower-mass clusters, such that the open clusters in our sample have the highest specific frequencies of sub-subgiants.

  7. The Blue Compact Dwarf Galaxy IZw18

    NARCIS (Netherlands)

    Musella, I.; Marconi, M.; Fiorentino, G.; Clementini, G.; Aloisi, A.; Annibali, F.; Contreras, R.; Saha, A.; Tosi, M.; van der Marel, R. P.

    2012-01-01

    We present the results obtained for the Blue compact galaxy IZw18 on the basis of ACS HST data obtained from our group. In particular, we discuss the stellar population and the variable stars content of this galaxy to get information about its star formation history and distance.

  8. SN2015bh: NGC2770's 4th supernova or a luminous blue variable on its way to a Wolf-Rayet star?

    DEFF Research Database (Denmark)

    Thone, C. C.; de Ugarte Postigo, A.; Leloudas, G.

    2017-01-01

    yr that experienced a possible terminal explosion as type IIn SN in 2015, named SN 2015bh. This possible SN (or " main event") had a precursor peaking similar to 40 days before maximum. The total energy release of the main event ;is similar to 1.8 X 10(49) erg, consistent with a ... 2015bh lies within a spiral arm of NGC2770 next to several small star-forming regions with a metallicity of similar to 0.5 solar and a stellar population age of 7-10 Myr. SN 2015bh shares many similarities with SN 2009ip and may form a new class of objects that exhibit outbursts a few decades prior...

  9. Inter-Division IV/V WG on Active OB Stars

    NARCIS (Netherlands)

    Owocki, S.; Aerts, C.; Fabregat, J.; Gies, D.; Henrichs, H.F.; McDavid, D.; Porter, J.; Rivinius, T.; Peters, G.; Stefl, S.

    2007-01-01

    Our group studies active early-type (OB) stars, with historical focus on classical Be stars, but extending in recent years to include Slowly Pulsating B-stars (SPB), Beta-Cephei stars, the strongly magnetic Bp stars, Luminous Blue Vairiable (LBV) stars, and B[e] stars. An overall goal is to

  10. Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds. III. X-ray emission from wind-embedded shocks

    Science.gov (United States)

    Carneiro, L. P.; Puls, J.; Sundqvist, J. O.; Hoffmann, T. L.

    2016-05-01

    Context. Extreme ultraviolet (EUV) and X-ray radiation emitted from wind-embedded shocks in hot, massive stars can affect the ionization balance in their outer atmospheres and can be the mechanism responsible for producing highly ionized atomic species detected in stellar wind UV spectra. Aims: To allow for these processes in the context of spectral analysis, we have implemented the emission from wind-embedded shocks and related physics into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. Methods: The shock structure and corresponding emission is calculated as a function of user-supplied parameters (volume filling factor, radial stratification of shock strength, and radial onset of emission). We account for a temperature and density stratification inside the postshock cooling zones, calculated for radiative and adiabatic cooling in the inner and outer wind, respectively. The high-energy absorption of the cool wind is considered by adding important K-shell opacities, and corresponding Auger ionization rates have been included in the NLTE network. To test our implementation and to check the resulting effects, we calculated a comprehensive model grid with a variety of X-ray emission parameters. Results: We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from shock emission for important ions from He, C, N, O, Si, and P. Surprisingly, dielectronic recombination turned out to play an essential role for the ionization balance of O iv/O v (particularly in dwarfs with Teff~ 45 000 K). Finally, we investigated the frequency dependence and radial behavior of the mass absorption coefficient, κν(r), which is important in the context of X-ray line formation in massive star winds. Conclusions: In almost all of the cases considered, direct ionization is of major influence because of the enhanced EUV radiation field, and Auger ionization only affects N vi

  11. A mathematical model of star formation in the Galaxy

    Directory of Open Access Journals (Sweden)

    M.A. Sharaf

    2012-06-01

    Full Text Available This paper is generally concerned with star formation in the Galaxy, especially blue stars. Blue stars are the most luminous, massive and the largest in radius. A simple mathematical model of the formation of the stars is established and put in computational algorithm. This algorithm enables us to know more about the formation of the star. Some real and artificial examples had been used to justify this model.

  12. Neutron stars

    International Nuclear Information System (INIS)

    Irvine, J.M.

    1978-01-01

    The subject is covered in chapters entitled: introduction (resume of stellar evolution, gross characteristics of neutron stars); pulsars (pulsar characteristics, pulsars as neutron stars); neutron star temperatures (neutron star cooling, superfluidity and superconductivity in neutron stars); the exterior of neutron stars (the magnetosphere, the neutron star 'atmosphere', pulses); neutron star structure; neutron star equations of state. (U.K.)

  13. Blue gods, blue oil, and blue people.

    Science.gov (United States)

    Fairbanks, V F

    1994-09-01

    Studies of the composition of coal tar, which began in Prussia in 1834, profoundly affected the economies of Germany, Great Britain, India, and the rest of the world, as well as medicine and surgery. Such effects include the collapse of the profits of the British indigo monopoly, the growth in economic power of Germany based on coal tar chemistry, and an economic crisis in India that led to more humane tax laws and, ultimately, the independence of India and the end of the British Empire. Additional consequences were the development of antiseptic surgery and the synthesis of a wide variety of useful drugs that have eradicated infections and alleviated pain. Many of these drugs, particularly the commonly used analgesics, sulfonamides, sulfones, and local anesthetics, are derivatives of aniline, originally called "blue oil" or "kyanol." Some of these aniline derivatives, however, have also caused aplastic anemia, agranulocytosis, and methemoglobinemia (that is, "blue people"). Exposure to aniline drugs, particularly when two or three aniline drugs are taken concurrently, seems to be the commonest cause of methemoglobinemia today.

  14. Posthuman blues

    CERN Document Server

    Tonnies, Mac

    2013-01-01

    Posthuman Blues, Vol. I is first volume of the edited version of the popular weblog maintained by author Mac Tonnies from 2003 until his tragic death in 2009. Tonnies' blog was a pastiche of his original fiction, reflections on his day-to-day life, trenchant observations of current events, and thoughts on an eclectic range of material he culled from the Internet. What resulted was a remarkably broad portrait of a thoughtful man and the complex times in which he lived, rendered with intellige...

  15. Star formation histories of irregular galaxies

    International Nuclear Information System (INIS)

    Gallagher, J.S. III; Hunter, D.A.; Tutukov, A.V.

    1984-01-01

    We explore the star formation histories of a selection of irregular and spiral galaxies by using three parameters that sample the star formation rate (SFR) at different epochs: (1) the mass of a galaxy in the form of stars measures the SFR integrated over a galaxy's lifetime; (2) the blue luminosity is dominated primarily by stars formed over the past few billion years; and (3) Lyman continuum photon fluxes derived from Hα luminosities give the current ( 8 yr) SFR

  16. Symbiotic stars

    International Nuclear Information System (INIS)

    Boyarchuk, A.A.

    1975-01-01

    There are some arguments that the symbiotic stars are binary, where one component is a red giant and the other component is a small hot star which is exciting a nebula. The symbiotic stars belong to the old disc population. Probably, symbiotic stars are just such an evolutionary stage for double stars as planetary nebulae for single stars. (Auth.)

  17. Spectrophotometry of carbon stars

    International Nuclear Information System (INIS)

    Gow, C.E.

    1975-01-01

    Observations of over one hundred carbon stars have been made with the Indiana rapid spectral scanner in the red and, when possible, in the visual and blue regions of the spectrum. Five distinct subtypes of carbon stars (Barium, CH, R, N, and hydrogen deficient) are represented in the list of observed stars, although the emphasis was placed on the N stars when the observations were made. The rapid scanner was operated in the continuous sweep mode with the exit slit set at twenty angstroms, however, seeing fluctuations and guiding errors smear the spectrum to an effective resolution of approximately thirty angstroms. Nightly observations of Hayes standard stars yielded corrections for atmospheric extinction and instrumental response. The reduction scheme rests on two assumptions, that thin clouds are gray absorbers and the wavelength dependence of the sky transparency does not change during the course of the night. Several stars have been observed in the blue region of the spectrum with the Indiana SIT vidicon spectrometer at two angstroms resolution. It is possible to derive a color temperature for the yellow--red spectral region by fitting a black-body curve through two chosen continuum points. Photometric indices were calculated relative to the blackbody curve to measure the C 2 Swan band strength, the shape of the CN red (6,1) band to provide a measure of the 12 C/ 13 C isotope ratio, and in the hot carbon stars (Barium, CH, and R stars) the strength of an unidentified feature centered at 400 angstroms. An extensive abundance grid of model atmospheres was calculated using a modified version of the computer code ATLAS

  18. Hubble's View of Little Blue Dots

    Science.gov (United States)

    Kohler, Susanna

    2018-02-01

    The recent discovery of a new type of tiny, star-forming galaxy is the latest in a zoo of detections shedding light on our early universe. What can we learn from the unique little blue dots found in archival Hubble data?Peas, Berries, and DotsGreen pea galaxies identified by citizen scientists with Galaxy Zoo. [Richard Nowell Carolin Cardamone]As telescope capabilities improve and we develop increasingly deeper large-scale surveys of our universe, we continue to learn more about small, faraway galaxies. In recent years, increasing sensitivity first enabled the detection of green peas luminous, compact, low-mass (10 billion solar masses; compare this to the Milky Ways 1 trillion solar masses!) galaxies with high rates of star formation.Not long thereafter, we discovered galaxies that form stars similarly rapidly, but are even smaller only 330 million solar masses, spanning less than 3,000 light-years in size. These tiny powerhouses were termed blueberries for their distinctive color.Now, scientists Debra and Bruce Elmegreen (of Vassar College and IBM Research Division, respectively) report the discovery of galaxies that have even higher star formation rates and even lower masses: little blue dots.Exploring Tiny Star FactoriesThe Elmegreens discovered these unique galaxies by exploring archival Hubble data. The Hubble Frontier Fields data consist of deep images of six distant galaxy clusters and the parallel fields next to them. It was in the archival data for two Frontier Field Parallels, those for clusters Abell 2744 and MAS J0416.1-2403, that the authors noticed several galaxies that stand out as tiny, bright, blue objects that are nearly point sources.Top: a few examples of the little blue dots recently identified in two Hubble Frontier Field Parallels. Bottom: stacked images for three different groups of little blue dots. [Elmegreen Elmegreen 2017]The authors performed a search through the two Frontier Field Parallels, discovering a total of 55 little blue dots

  19. Pulsations of the R Coronae Borealis stars

    International Nuclear Information System (INIS)

    Cox, J.P.; King, D.S.; Cox, A.N.; Wheeler, J.C.; Hansen, C.J.; Hodson, S.W.

    1980-01-01

    The radial pulsations of very luminous, low-mass models (L/M approx. 10 4 , solar units), which are possible representatives of the R CrB stars, have been examined. These pulsations are extremely nonadiabatic. There are in some cases at least one extra (strange) mode which makes interpretation difficult. The blue instability edges are also peculiar, in that there is an abrupt excursion of the blue edge to the blue for L/M sufficiently large. The range of periods of the model encompasses observed periods of the Cepheid-like pulsations of actual R CrB stars

  20. The Blue Hook Populations of Massive Globular Clusters

    Science.gov (United States)

    Brown, Thomas

    2006-07-01

    Blue hook stars are a class of hot { 35,000 K} subluminous horizontal branch stars that have been recently discovered using HST ultraviolet images of the globular clusters omega Cen and NGC 2808. These stars occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. Using new theoretical evolutionary and atmospheric models, we have shown that the blue hook stars are very likely the progeny of stars that undergo extensive internal mixing during a late helium core flash on the white dwarf cooling curve. This "flash mixing" produces an enormous enhancement of the surface helium and carbon abundances, which suppresses the flux in the far ultraviolet. Although flash mixing is more likely to occur in stars that are born with high helium abundances, a high helium abundance, by itself, does not explain the presence of a blue hook population - flash mixing of the envelope is required. We propose ACS ultraviolet {SBC/F150LP and HRC/F250W} observations of the five additional globular clusters for which the presence of blue hook stars is suspected from longer wavelength observations. Like omega Cen and NGC 2808, these five targets are also among the most massive globular clusters, because less massive clusters show no evidence for blue hook stars. Because our targets span 1.5 dex in metallicity, we will be able to test our prediction that flash-mixing should be less drastic in metal-rich blue hook stars. In addition, our observations will test the hypothesis that blue hook stars only form in globular clusters massive enough to retain the helium-enriched ejecta from the first stellar generation. If this hypothesis is correct, then our observations will yield important constraints on the chemical evolution and early formation history in globular clusters, as well as the role of helium self-enrichment in producing blue horizontal branch morphologies and multiple main sequence turnoffs. Finally, our observations will provide new insight into the

  1. Star formation and the surface brightness of spiral galaxies

    International Nuclear Information System (INIS)

    Phillipps, S.; Disney, M.

    1985-01-01

    The (blue) surface brightness of spiral galaxies is significantly correlated with their Hα linewidth. This can be most plausibly interpreted as a correlation of surface brightness with star formation rate. There is also a significant difference in surface brightness between galaxies forming stars in a grand design spiral pattern and those with floc star formation regions. (author)

  2. Stars and Star Myths.

    Science.gov (United States)

    Eason, Oliver

    Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

  3. Blue-Green Algae

    Science.gov (United States)

    ... that taking a specific blue-green algae product (Super Blue-Green Algae, Cell Tech, Klamath Falls, OR) ... system. Premenstrual syndrome (PMS). Depression. Digestion. Heart disease. Memory. Wound healing. Other conditions. More evidence is needed ...

  4. Statistical properties of barium stars

    International Nuclear Information System (INIS)

    Hakkila, J.E.

    1986-01-01

    Barium stars are G- and K-giant stars with atmospheric excesses of s-process elements, and a broadband spectral depression in the blue portion of the spectrum. The strength of the λ4554 Ball line is used as a classification parameter known as the Barium Intensity. They have a mean absolute magnitude of 1.0 and a dispersion of 1.2 magnitudes (assuming a Gaussian distribution in absolute magnitude) as measured from secular and statistical parallaxes. These stars apparently belong to a young-disk population from analyses of both the solar reflex motion and their residual velocity distribution, which implies that they have an upper mass limit of around three solar masses. There is no apparent correlation of barium intensity with either luminosity or kinematic properties. The barium stars appear to be preferentially distributed in the direction of the local spiral arm, but show no preference to associate with or avoid the direction of the galactic center. They do not appear related to either the carbon or S-stars because of these tendencies and because of the stellar population to which each type of star belongs. The distribution in absolute magnitude combined with star count analyses implies that these stars are slightly less numerous than previously believed. Barium stars show infrared excesses that correlate with their barium intensities

  5. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star.......Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star....

  6. Blue Emission in Proteins

    OpenAIRE

    Sarkar, Sohini; Sengupta, Abhigyan; Hazra, Partha; Mandal, Pankaj

    2014-01-01

    Recent literatures reported blue-green emission from amyloid fibril as exclusive signature of fibril formation. This unusual visible luminescence is regularly used to monitor fibril growth. Blue-green emission has also been observed in crystalline protein and in solution. However, the origin of this emission is not known exactly. Our spectroscopic study of serum proteins reveals that the blue-green emission is a property of protein monomer. Evidences suggest that semiconductor-like band struc...

  7. Insight into star death

    International Nuclear Information System (INIS)

    Talcott, R.

    1988-01-01

    Nineteen neutrinos, formed in the center of a supernova, became a theorist's dream. They came straight from the heart of supernova 1987A and landed in two big underground tanks of water. Suddenly a new chapter in observational astronomy opened as these two neutrino telescopes gave astronomers their first look ever into the core of a supernova explosion. But the theorists' dream almost turned into a nightmare. Observations of the presupernova star showed conclusively that the star was a blue supergiant, but theorists have long believed only red supergiant stars could explode as supernovae. Do astronomers understand supernovae better now than when supernova 1987A exploded in the Large Magellanic Cloud (LMC) one year ago? Yes. The observations of neutrinos spectacularly confirmed a vital aspect of supernova theory. But the observed differences between 1987A and other supernovae have illuminated and advanced our perception of how supernovae form. By working together, observers and theorists are continuing to hone their ideas about how massive stars die and how the subsequent supernovae behave

  8. VizieR Online Data Catalog: Young star groups in NGC 300 (Rodriguez+, 2016)

    Science.gov (United States)

    Rodriguez, M. J.; Baume, G.; Feinstein, C.

    2016-08-01

    Fundamental characteristics of 1147 young star groups identified in 6 ACS/WFC fields of the galaxy NGC 300. For each group: field of the ACS/WFC, equatorial coordinates, radius, number of stars (the suffix bri indicates bright stars with F555W<25, the suffix dct indicate stars belonging to the decontaminated region, the suffixes blue and red refer to blue and red stars respectively), the magnitude of the brightest star in the group, PDMF slope with its error, and galactocentric distance. (1 data file).

  9. Pulsations in Subdwarf B Stars C. Simon Jeffery

    Indian Academy of Sciences (India)

    An examination of a false-colour ultraviolet photograph of the globular cluster. NGC2808 reveals a number of blue stars too bright to be white dwarfs, and too faint ..... Earth Telescope campaign to improve the overall frequency resolution.

  10. Unraveling the Mystery of the Blue Fog: Structure, Properties, and Applications of Amorphous Blue Phase III.

    Science.gov (United States)

    Gandhi, Sahil Sandesh; Chien, Liang-Chy

    2017-12-01

    The amorphous blue phase III of cholesteric liquid crystals, also known as the "blue fog," are among the rising stars in materials science that can potentially be used to develop next-generation displays with the ability to compete toe-to-toe with disruptive technologies like organic light-emitting diodes. The structure and properties of the practically unobservable blue phase III have eluded scientists for more than a century since it was discovered. This progress report reviews the developments in this field from both fundamental and applied research perspectives. The first part of this progress report gives an overview of the 130-years-long scientific tour-de-force that very recently resulted in the revelation of the mysterious structure of blue phase III. The second part reviews progress made in the past decade in developing electrooptical, optical, and photonic devices based on blue phase III. The strong and weak aspects of the development of these devices are underlined and criticized, respectively. The third- and-final part proposes ideas for further improvement in blue phase III technology to make it feasible for commercialization and widespread use. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Dermatoscopy of blue vitiligo.

    Science.gov (United States)

    Chandrashekar, L

    2009-07-01

    Blue vitiligo is a distinct variant of vitiligo characterized by a blue-grey appearance of the skin, which corresponds histologically with absence of epidermal melanocytes and presence of numerous dermal melanophages. A 23-year-old woman of Indian origin with Fitzpatrick skin type V presented with a 1-month history of normoaesthetic depigmented macules over the right forearm, dorsa of the hands and right areola. The macule over the right forearm had a bluish tinge. A clinical diagnosis of vitiligo vulgaris with blue vitiligo was made. Dermatoscopy of the interface between the blue macule and the hypopigmented macule revealed a linear depigmented macule in the centre with multiple blue dots and absence of epidermal melanin on the side of the blue macule, and reticular pigmentation with a few depigmented macules and scattered blue dots over the side of the hypopigmented macule. Blue vitiligo was described previously in a patient seropositive for human immunodeficiency virus, and believed to represent postinflammatory hyperpigmentation in areas bordering the vitiliginous patches as a result of psoralen ultraviolet A treatment. This case is unusual because of its rarity and the description of the associated dermatoscopical findings.

  12. Blue Ocean Thinking

    Science.gov (United States)

    Orem, Donna

    2016-01-01

    This article describes a concept called the "blue ocean thinking strategy," developed by W. Chan Kim and Renée Mauborgne, professors at INSEAD, an international graduate school of business in France. The "blue ocean" thinking strategy considers opportunities to create new markets for services, rather than focusing solely on…

  13. Radio stars

    International Nuclear Information System (INIS)

    Hjellming, R.M.

    1976-01-01

    Any discussion of the radio emission from stars should begin by emphasizing certain unique problems. First of all, one must clarify a semantic confusion introduced into radio astronomy in the late 1950's when most new radio sources were described as radio stars. All of these early 'radio stars' were eventually identified with other galactic and extra-galactic objects. The study of true radio stars, where the radio emission is produced in the atmosphere of a star, began only in the 1960's. Most of the work on the subject has, in fact, been carried out in only the last few years. Because the real information about radio stars is quite new, it is not surprising that major aspects of the subject are not at all understood. For this reason this paper is organized mainly around three questions: what is the available observational information; what physical processes seem to be involved; and what working hypotheses look potentially fruitful. (Auth.)

  14. Shooting stars

    International Nuclear Information System (INIS)

    Maurette, M.; Hammer, C.

    1985-01-01

    A shooting star passage -even a star shower- can be sometimes easily seen during moonless black night. They represent the partial volatilization in earth atmosphere of meteorites or micrometeorites reduced in cosmic dusts. Everywhere on earth, these star dusts are searched to be gathered. This research made one year ago on the Greenland ice-cap is this article object; orbit gathering projects are also presented [fr

  15. Sounds of a Star

    Science.gov (United States)

    2001-06-01

    Acoustic Oscillations in Solar-Twin "Alpha Cen A" Observed from La Silla by Swiss Team Summary Sound waves running through a star can help astronomers reveal its inner properties. This particular branch of modern astrophysics is known as "asteroseismology" . In the case of our Sun, the brightest star in the sky, such waves have been observed since some time, and have greatly improved our knowledge about what is going on inside. However, because they are much fainter, it has turned out to be very difficult to detect similar waves in other stars. Nevertheless, tiny oscillations in a solar-twin star have now been unambiguously detected by Swiss astronomers François Bouchy and Fabien Carrier from the Geneva Observatory, using the CORALIE spectrometer on the Swiss 1.2-m Leonard Euler telescope at the ESO La Silla Observatory. This telescope is mostly used for discovering exoplanets (see ESO PR 07/01 ). The star Alpha Centauri A is the nearest star visible to the naked eye, at a distance of a little more than 4 light-years. The new measurements show that it pulsates with a 7-minute cycle, very similar to what is observed in the Sun . Asteroseismology for Sun-like stars is likely to become an important probe of stellar theory in the near future. The state-of-the-art HARPS spectrograph , to be mounted on the ESO 3.6-m telescope at La Silla, will be able to search for oscillations in stars that are 100 times fainter than those for which such demanding observations are possible with CORALIE. PR Photo 23a/01 : Oscillations in a solar-like star (schematic picture). PR Photo 23b/01 : Acoustic spectrum of Alpha Centauri A , as observed with CORALIE. Asteroseismology: listening to the stars ESO PR Photo 23a/01 ESO PR Photo 23a/01 [Preview - JPEG: 357 x 400 pix - 96k] [Normal - JPEG: 713 x 800 pix - 256k] [HiRes - JPEG: 2673 x 3000 pix - 2.1Mb Caption : PR Photo 23a/01 is a graphical representation of resonating acoustic waves in the interior of a solar-like star. Red and blue

  16. Blue ocean strategy.

    Science.gov (United States)

    Kim, W Chan; Mauborgne, Renée

    2004-10-01

    Despite a long-term decline in the circus industry, Cirque du Soleil profitably increased revenue 22-fold over the last ten years by reinventing the circus. Rather than competing within the confines of the existing industry or trying to steal customers from rivals, Cirque developed uncontested market space that made the competition irrelevant. Cirque created what the authors call a blue ocean, a previously unknown market space. In blue oceans, demand is created rather than fought over. There is ample opportunity for growth that is both profitable and rapid. In red oceans--that is, in all the industries already existing--companies compete by grabbing for a greater share of limited demand. As the market space gets more crowded, prospects for profits and growth decline. Products turn into commodities, and increasing competition turns the water bloody. There are two ways to create blue oceans. One is to launch completely new industries, as eBay did with online auctions. But it's much more common for a blue ocean to be created from within a red ocean when a company expands the boundaries of an existing industry. In studying more than 150 blue ocean creations in over 30 industries, the authors observed that the traditional units of strategic analysis--company and industry--are of limited use in explaining how and why blue oceans are created. The most appropriate unit of analysis is the strategic move, the set of managerial actions and decisions involved in making a major market-creating business offering. Creating blue oceans builds brands. So powerful is blue ocean strategy, in fact, that a blue ocean strategic move can create brand equity that lasts for decades.

  17. Blue objects in the vicinity of M13. 1

    International Nuclear Information System (INIS)

    Oganesyan, Eh.Ya.

    1978-01-01

    Presented are photometric data in the UBV system for 225 objects in the region of 16 square degrees in size, adjacent to M13 cluster. ''Two-colour diagram'' and ''colour-luminosity'' diagram are built, and on their basis analysis of the data obtained is made. Half the objects investigated are subdwarfs. Among others there are white - blue dwarfs conventional stars of the main sequence stars, halo stars, stars of globular clusters and objects, which might be of extragalactic nature. On the basis of object distribution as to brightness and colour, and also according to their visible distribution several different groups can be singled out. Several variable stars are also found as a result of photometric investigation

  18. Star Polymers.

    Science.gov (United States)

    Ren, Jing M; McKenzie, Thomas G; Fu, Qiang; Wong, Edgar H H; Xu, Jiangtao; An, Zesheng; Shanmugam, Sivaprakash; Davis, Thomas P; Boyer, Cyrille; Qiao, Greg G

    2016-06-22

    Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

  19. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star.......Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star....

  20. Star Imager

    DEFF Research Database (Denmark)

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

    1997-01-01

    The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol.......The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol....

  1. Radio stars

    International Nuclear Information System (INIS)

    Hjellming, R.M.; Gibson, D.M.

    1985-01-01

    Studies of stellar radio emission became an important field of research in the 1970's and have now expanded to become a major area of radio astronomy with the advent of new instruments such as the Very Large Array in New Mexico and transcontinental telescope arrays. This volume contains papers from the workshop on stellar continuum radio astronomy held in Boulder, Colorado, and is the first book on the rapidly expanding field of radio emission from stars and stellar systems. Subjects covered include the observational and theoretical aspects of stellar winds from both hot and cool stars, radio flares from active double star systems and red dwarf stars, bipolar flows from star-forming regions, and the radio emission from X-ray binaries. (orig.)

  2. Polarimetry of symbiotic stars

    International Nuclear Information System (INIS)

    Piirola, V.

    1983-01-01

    Five symbiotic stars have been observed for linear polarization (UBVRI) in September 1981. Three systems, CH Cyg, CI Cyg and AG Peg show intrinsic polarization while in the case of Z And and AX Per the observed polarization seems to be mostly of interstellar origin. The position angle of polarization of CI Cyg and AG Peg rotates strongly vs. wavelength, as observed also for CH Cyg in 1977-80. The polarization of CH Cyg has decreased since May 1980, especially in the I, R and U bands, so that the maximum polarization is now in the blue (Psub(B) approx. 0.3%). Probably one is monitoring the formation, growth and disappearance of dust particles in the atmosphere of this star. Two related systems, PU Vul (Nova Vul 1979) and R Aql (Mira) have polarization behaviour rather similar to that of symbiotic stars which suggests that the M type giant present in these systems is responsible for most of the intrinsic polarization. (Auth.)

  3. Blue Ribbon Panel Report

    Science.gov (United States)

    An NCI Cancer Currents blog by the NCI acting director thanking the cancer community for contributing to the Cancer Moonshot Blue Ribbon Panel report, which was presented to the National Cancer Advisory Board on September 7.

  4. Northeast Atlantic blue whiting

    OpenAIRE

    Heino, Mikko

    2010-01-01

    Heino, M. 2010. Northeast Atlantic blue whiting. In Life cycle spatial patterns of small pelagic fish in the Northeast Atlantic, pp. 59-64. Ed by P. Petitgas. ICES Cooperative Research Report 306. ICES, Copenhagen.

  5. New York Blue

    Data.gov (United States)

    Federal Laboratory Consortium — New York Blue is used cooperatively by the Laboratory and Stony Brook University as part of the New York Center for Computation Sciences. Ranked as the 28th fastest...

  6. SALT Spectroscopy of Evolved Massive Stars

    Science.gov (United States)

    Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

    2017-06-01

    Long-slit spectroscopy with the Southern African Large Telescope (SALT) of central stars of mid-infrared nebulae detected with the Spitzer Space Telescope and Wide-Field Infrared Survey Explorer (WISE) led to the discovery of numerous candidate luminous blue variables (cLBVs) and other rare evolved massive stars. With the recent advent of the SALT fiber-fed high-resolution echelle spectrograph (HRS), a new perspective for the study of these interesting objects is appeared. Using the HRS we obtained spectra of a dozen newly identified massive stars. Some results on the recently identified cLBV Hen 3-729 are presented.

  7. Symbiotic stars

    International Nuclear Information System (INIS)

    Kafatos, M.; Michalitsianos, A.G.

    1984-01-01

    Among the several hundred million binary systems estimated to lie within 3000 light years of the solar system, a tiny fraction, no more than a few hundred, belong to a curious subclass whose radiation has a wavelength distribution so peculiar that it long defied explanation. Such systems radiate strongly in the visible region of the spectrum, but some of them do so even more strongly at both shorter and longer wavelengths: in the ultraviolet region and in the infrared and radio regions. This odd distribution of radiation is best explained by the pairing of a cool red giant star and an intensely hot small star that is virtually in contact with its larger companion. Such objects have become known as symbiotic stars. On photographic plate only the giant star can be discerned, but evidence for the existence of the hot companion has been supplied by satellite-born instruments capable of detecting ultraviolet radiation. The spectra of symbiotic stars indicate that the cool red giant is surrounded by a very hot ionized gas. Symbiotic stars also flared up in outbursts indicating the ejection of material in the form of a shell or a ring. Symbiotic stars may therefore represent a transitory phase in the evolution of certain types of binary systems in which there is substantial transfer of matter from the larger partner to the smaller

  8. Properties and origin of the old, metal rich, star cluster, NGC 6791

    OpenAIRE

    Carraro, Giovanni

    2013-01-01

    In this contribution I summarize the unique properties of the old, metal rich, star cluster NGC 6791, with particular emphasis on its population of extreme blue horizontal branch stars. I then conclude providing my personal view on the origin of this fascinating star cluster.

  9. Nonradial pulsations of hot evolved stars

    International Nuclear Information System (INIS)

    Starrfield, S.G.

    1987-01-01

    There are three classes of faint blue variable stars: the ZZ Ceti variables (DAV degenerate dwarfs), the DBV variables (DB degenerate dwarfs), and the GW Vir variables (DOV degenerate dwarfs). None of these classes of variable stars were known at the time of the last blue star meeting. Observational and theoretical studies of the ZZ Ceti variables, the DBV variables, and the GW Vir variables have shown them to be pulsating in nonradial g-modes. The cause of the pulsation has been determined for each class of variable star and, in all cases, also involves predictions of the stars envelope composition. The predictions are that the ZZ Ceti variables must have pure hydrogen surface layers, the DBV stars must have pure helium surface layers, and the GW Vir stars must have carbon and oxygen rich surface layers with less than 30% (by mass) of helium. Given these compositions, it is found that pulsation driving occurs as a result of the kappa and gamma effects operating in the partial ionization zones of either hydrogen or helium. In addition, a new driving mechanism, called convection blocking, also occurs in these variables. For the GW Vir variables, it is the kappa and gamma effects in the partial ionization regions of carbon and oxygen. 45 refs

  10. Star formation in active galaxies and quasars

    International Nuclear Information System (INIS)

    Heckman, T.M.

    1987-01-01

    I review the observational evidence for a causal or statistical link between star formation and active galactic nuclei. The chief difficulty is in quantitatively ascertaining the star formation rate in active galaxies: most of the readily observable manifestations of star formation superficially resemble those of an active nucleus. Careful multi-wavelength spatially-resolved observations demonstrate that many Seyfert galaxies are undergoing star formation. Our survey of CO emission from Seyferts (interpreted in conjunction IRAS data) suggests that type 2 Seyferts have unusually high rates of star formation, but type 1 Seyferts do not. Recent work also suggests that many powerful radio galaxies may be actively forming stars: radio galaxies with strong emission-lines often have blue colors and strong far-infrared emission. Determining the star formation rate in the host galaxies of quasars is especially difficult. Multi-color imaging and long-slit spectroscopy suggests that many of the host galaxies of radio-loud quasars are blue and a cold interstellar medium has been detected in some quasar hosts

  11. Unusual Metals in Galactic Center Stars

    Science.gov (United States)

    Hensley, Kerry

    2018-03-01

    Far from the galactic suburbs where the Sun resides, a cluster of stars in the nucleus of the Milky Way orbits a supermassive black hole. Can chemical abundance measurements help us understand the formation history of the galactic center nuclear star cluster?Studying Stellar PopulationsMetallicity distributions for stars in the inner two degrees of the Milky Way (blue) and the central parsec (orange). [Do et al. 2018]While many galaxies host nuclear star clusters, most are too distant for us to study in detail; only in the Milky Way can we resolve individual stars within one parsec of a supermassive black hole. The nucleus of our galaxy is an exotic and dangerous place, and its not yet clear how these stars came to be where they are were they siphoned off from other parts of the galaxy, or did they form in place, in an environment rocked by tidal forces?Studying the chemical abundances of stars provides a way to separate distinct stellar populations and discern when and where these stars formed. Previous studies using medium-resolution spectroscopy have revealed that many stars within the central parsec of our galaxy have very high metallicities possibly higher than any other region of the Milky Way. Can high-resolution spectroscopy tell us more about this unusual population of stars?Spectral Lines on DisplayTuan Do (University of California, Los Angeles, Galactic Center Group) and collaborators performed high-resolution spectroscopic observations of two late-type giant starslocated half a parsec from the Milky Ways supermassive black hole.Comparison of the observed spectra of the two galactic center stars (black) with synthetic spectra with low (blue) and high (orange) [Sc/Fe] values. Click to enlarge. [Do et al. 2018]In order to constrain the metallicities of these stars, Do and collaborators compared the observed spectra to a grid of synthetic spectra and used a spectral synthesis technique to determine the abundances of individual elements. They found that

  12. Star formation

    International Nuclear Information System (INIS)

    Woodward, P.R.

    1978-01-01

    Theoretical models of star formation are discussed beginning with the earliest stages and ending in the formation of rotating, self-gravitating disks or rings. First a model of the implosion of very diffuse gas clouds is presented which relies upon a shock at the edge of a galactic spiral arm to drive the implosion. Second, models are presented for the formation of a second generation of massive stars in such a cloud once a first generation has formed. These models rely on the ionizing radiation from massive stars or on the supernova shocks produced when these stars explode. Finally, calculations of the gravitational collapse of rotating clouds are discussed with special focus on the question of whether rotating disks or rings are the result of such a collapse. 65 references

  13. The blue supergiant MN18 and its bipolar circumstellar nebula

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Bestenlehner, J. M.; Bodensteiner, J.; Langer, N.; Greiner, J.; Grebel, E. K.; Berdnikov, L. N.; Beletsky, Y.

    2015-11-01

    We report the results of spectrophotometric observations of the massive star MN18 revealed via discovery of a bipolar nebula around it with the Spitzer Space Telescope. Using the optical spectrum obtained with the Southern African Large Telescope, we classify this star as B1 Ia. The evolved status of MN18 is supported by the detection of nitrogen overabundance in the nebula, which implies that it is composed of processed material ejected by the star. We analysed the spectrum of MN18 by using the code CMFGEN, obtaining a stellar effective temperature of ≈21 kK. The star is highly reddened, E(B - V) ≈ 2 mag. Adopting an absolute visual magnitude of MV = -6.8 ± 0.5 (typical of B1 supergiants), MN18 has a luminosity of log L/L⊙ ≈ 5.42 ± 0.30, a mass-loss rate of ≈(2.8-4.5) × 10- 7 M⊙ yr- 1, and resides at a distance of ≈5.6^{+1.5} _{-1.2} kpc. We discuss the origin of the nebula around MN18 and compare it with similar nebulae produced by other blue supergiants in the Galaxy (Sher 25, HD 168625, [SBW2007] 1) and the Large Magellanic Cloud (Sk-69°202). The nitrogen abundances in these nebulae imply that blue supergiants can produce them from the main-sequence stage up to the pre-supernova stage. We also present a K-band spectrum of the candidate luminous blue variable MN56 (encircled by a ring-like nebula) and report the discovery of an OB star at ≈17 arcsec from MN18. The possible membership of MN18 and the OB star of the star cluster Lynga 3 is discussed.

  14. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Frigaard, Peter

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star....

  15. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Andersen, Thomas Lykke

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star....

  16. STARS no star on Kauai

    International Nuclear Information System (INIS)

    Jones, M.

    1993-01-01

    The island of Kuai, home to the Pacific Missile Range Facility, is preparing for the first of a series of Star Wars rocket launches expected to begin early this year. The Strategic Defense Initiative plans 40 launches of the Stategic Target System (STARS) over a 10-year period. The focus of the tests appears to be weapons and sensors designed to combat multiple-warhead ICBMs, which will be banned under the START II Treaty that was signed in January. The focus of this article is to express the dubious value of testing the STARS at a time when their application will not be an anticipated problem

  17. Flare stars

    International Nuclear Information System (INIS)

    Nicastro, A.J.

    1981-01-01

    The least massive, but possibly most numerous, stars in a galaxy are the dwarf M stars. It has been observed that some of these dwarfs are characterized by a short increase in brightness. These stars are called flare stars. These flare stars release a lot of energy in a short amount of time. The process producing the eruption must be energetic. The increase in light intensity can be explained by a small area rising to a much higher temperature. Solar flares are looked at to help understand the phenomenon of stellar flares. Dwarfs that flare are observed to have strong magnetic fields. Those dwarf without the strong magnetic field do not seem to flare. It is believed that these regions of strong magnetic fields are associated with star spots. Theories on the energy that power the flares are given. Astrophysicists theorize that the driving force of a stellar flare is the detachment and collapse of a loop of magnetic flux. The mass loss due to stellar flares is discussed. It is believed that stellar flares are a significant contributor to the mass of interstellar medium in the Milky Way

  18. Natural Blue Food Colour

    DEFF Research Database (Denmark)

    Roda-Serrat, Maria Cinta

    In recent years, there has been a growing tendency to avoid the use of artificial colorants and additives in food products, especially after some studies linked their consumption with behavioural changes in children. However, the incorporation of colorants from natural origin remains a challenge...... for food technologists, as these are typically less vivid and less stable than their synthetic alternatives. Regarding blue colorants, phycocyanins from cyanobacteria are currently in the spotlight as promising new natural blue colorants. Phycocyanins are proteins which blue colour results from...... the presence of the chromophore phycocyanobilin (PCB), a covalently attached linear tetrapyrrole. The applications of phycocyanins as food colorants are however limited, as they show poor stability in certain conditions of pH, light and temperature. Cleavage of PCB from the protein followed by careful product...

  19. A Blue Lagoon Function

    DEFF Research Database (Denmark)

    Markvorsen, Steen

    2007-01-01

    We consider a specific function of two variables whose graph surface resembles a blue lagoon. The function has a saddle point $p$, but when the function is restricted to any given straight line through $p$ it has a {\\em{strict local minimum}} along that line at $p$.......We consider a specific function of two variables whose graph surface resembles a blue lagoon. The function has a saddle point $p$, but when the function is restricted to any given straight line through $p$ it has a {\\em{strict local minimum}} along that line at $p$....

  20. Symbiotic stars

    Science.gov (United States)

    Kafatos, M.; Michalitsianos, A. G.

    1984-01-01

    The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

  1. Stars Just Got Bigger - A 300 Solar Mass Star Uncovered

    Science.gov (United States)

    2010-07-01

    raises the challenge to theorists still further. "Either they were born so big or smaller stars merged together to produce them," explains Crowther. Stars between about 8 and 150 solar masses explode at the end of their short lives as supernovae, leaving behind exotic remnants, either neutron stars or black holes. Having now established the existence of stars weighing between 150 and 300 solar masses, the astronomers' findings raise the prospect of the existence of exceptionally bright, "pair instability supernovae" that completely blow themselves apart, failing to leave behind any remnant and dispersing up to ten solar masses of iron into their surroundings. A few candidates for such explosions have already been proposed in recent years. Not only is R136a1 the most massive star ever found, but it also has the highest luminosity too, close to 10 million times greater than the Sun. "Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon," concludes Crowther. Notes [1] The star A1 in NGC 3603 is a double star, with an orbital period of 3.77 days. The two stars in the system have, respectively, 120 and 92 times the mass of the Sun, which means that they have formed as stars weighing, respectively, 148 and 106 solar masses. [2] The team used the SINFONI, ISAAC and MAD instruments, all attached to ESO's Very Large Telescope at Paranal, Chile. [3] (note added on 26 July 2010) The "bigger" in the title does not imply that these stars are the biggest observed. Such stars, called red supergiants, can have radii up to about a thousand solar radii, while R136a1, which is blue, is about 35 times as large as the Sun. However, R136a1 is the star with the greatest mass known to date. More information This work is presented in an article published in the Monthly Notices of the Royal Astronomical Society ("The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit", by

  2. Heavy Metal Stars

    Science.gov (United States)

    2001-08-01

    that the CH-stars all belong to binary systems and that they therefore have a companion star [5]. That companion is now a white dwarf star and was therefore at some earlier moment an AGB star ! During its AGB-phase, the companion star expelled much of its material, eventually producing the "planetary nebula" phenomenon, referred to above. In this process, a lot of its material, enriched with heavy elements produced by the "s-process" during the AGB phase, was deposited in the atmosphere of the CH-star that is now observed. The former AGB-star, now a slowly cooling, dim white-dwarf star, still orbits the CH-star. For this reason, the atmospheric composition of a CH-star actually carries the signature of the nucleosynthesis that took place deep inside the companion AGB star at an earlier epoch. Spectroscopic observations of CH-stars thus provide the opportunity to probe the predicted s-process in low-metallicity stars. Three stars with Lead ESO PR Photo 26b/01 ESO PR Photo 26b/01 [Preview - JPEG: 400 x 371 pix - 95k] [Normal - JPEG: 800 x 741 pix - 240k] Caption : A high-resolution spectrum of the CH-star HD 196944, obtained with the CES instrument on the ESO 3.6-m telescope in September 2000. The observed spectrum (dots) shows many absorption lines from elements that are usually seen in stars. The red line shows a model in which elements (in particular those produced by the s-process) are present in normal quantities, compared to Iron. The blue line instead shows a model where s-processing has occured. It is obvious that the red line does not fit, only the blue line reproduces the observed absorption line at wavelength 405.781 nm caused by Lead (Pb) atoms in the atmosphere of this star. A subsequent, detailed analysis demonstrated that HD 196944 is a true "Lead star". Technical information about this photo is available below. A necessary condition for these observations to succeed is a very high spectral resolution in order to detect the spectral line of Lead (Pb), in

  3. Wolf-Rayet stars associated to giant regions of star formation

    International Nuclear Information System (INIS)

    D'Odorico, S.; Rosa, M.

    1982-01-01

    Data on Wolf-Rayet (WR) stars in extragalactic H II regions and emission line galaxies are presented and discussed. The sample is still limited and inhomogeneous but two important points appear to be already established: a) The WR stars are more numerous than the blue supergiants at least in same phase of the evolution of the stellar clusters which ionize the giant H II regions, b) When the WR stars are detected, two cases are apparently observed, one in which only WN, the other in which both WN and WC, are present. (Auth.)

  4. Dark stars

    DEFF Research Database (Denmark)

    Maselli, Andrea; Pnigouras, Pantelis; Nielsen, Niklas Grønlund

    2017-01-01

    to the formation of compact objects predominantly made of dark matter. Considering both fermionic and bosonic (scalar φ4) equations of state, we construct the equilibrium structure of rotating dark stars, focusing on their bulk properties and comparing them with baryonic neutron stars. We also show that these dark......Theoretical models of self-interacting dark matter represent a promising answer to a series of open problems within the so-called collisionless cold dark matter paradigm. In case of asymmetric dark matter, self-interactions might facilitate gravitational collapse and potentially lead...... objects admit the I-Love-Q universal relations, which link their moments of inertia, tidal deformabilities, and quadrupole moments. Finally, we prove that stars built with a dark matter equation of state are not compact enough to mimic black holes in general relativity, thus making them distinguishable...

  5. The "Blue Banana" Revisited

    NARCIS (Netherlands)

    Faludi, A.K.F.

    2015-01-01

    This essay is about the “Blue Banana”. Banana is the name given subsequently by others to a Dorsale européenne (European backbone) identified empirically by Roger Brunet. In a background study to the Communication of the European Commission ‘Europe 2000’, Klaus Kunzmann and Michael Wegener put

  6. Revealing evolved massive stars with Spitzer

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Fabrika, S.

    2010-06-01

    Massive evolved stars lose a large fraction of their mass via copious stellar wind or instant outbursts. During certain evolutionary phases, they can be identified by the presence of their circumstellar nebulae. In this paper, we present the results of a search for compact nebulae (reminiscent of circumstellar nebulae around evolved massive stars) using archival 24-μm data obtained with the Multiband Imaging Photometer for Spitzer. We have discovered 115 nebulae, most of which bear a striking resemblance to the circumstellar nebulae associated with luminous blue variables (LBVs) and late WN-type (WNL) Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). We interpret this similarity as an indication that the central stars of detected nebulae are either LBVs or related evolved massive stars. Our interpretation is supported by follow-up spectroscopy of two dozen of these central stars, most of which turn out to be either candidate LBVs (cLBVs), blue supergiants or WNL stars. We expect that the forthcoming spectroscopy of the remaining objects from our list, accompanied by the spectrophotometric monitoring of the already discovered cLBVs, will further increase the known population of Galactic LBVs. This, in turn, will have profound consequences for better understanding the LBV phenomenon and its role in the transition between hydrogen-burning O stars and helium-burning WR stars. We also report on the detection of an arc-like structure attached to the cLBV HD 326823 and an arc associated with the LBV R99 (HD 269445) in the LMC. Partially based on observations collected at the German-Spanish Astronomical Centre, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK); fabrika@sao.ru (SF)

  7. Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

    2011-11-01

    shells typical of luminous blue variable and late WN-type Wolf-Rayet stars.

  8. Blue objects in the field of M31

    Energy Technology Data Exchange (ETDEWEB)

    Romano, G [Padua Univ. (Italy). Istituto di Astronomia

    1976-10-01

    This paper gives the results of a photometric study of star-like blue objects Nos. 14, 15, 16, 17, and 18 discovered by Boerngen et al. (1970) in the field of M31 and of the QSO OA 33. Three of these objects - Nos. 14, 16 and 17 - exhibit variable light. No. 14 is a probable U Geminorum-star; No. 16 is a QSO and very likely also the No. 17. Finally, a candidate is suggested for the optical counterpart of OA 33.

  9. Wolf--Rayet stars of M33

    International Nuclear Information System (INIS)

    Corso, G.J. Jr.

    1975-01-01

    A comprehensive study of the 54 known Wolf--Rayet stars of M33 is undertaken with the intention of improving our knowledge of the Wolf--Rayet phenomenon, identifying significant features of their distribution in an Sc galaxy, and discerning possible trends in the variation of chemical composition of the interstellar medium from place to place within that galaxy. Thirty-seven of these stars were classified for the first time into carbon and nitrogen sequences on the basis of photographic photometry of image tube plates obtained with the Kitt Peak 84-inch telescope and an ITT magnetically focused image tube equipped with a set of narrow-band interference filters designed to isolate the broad emission features between 4640 A and 4686 A due to N III, C III-IV, and He II. The subclasses WC6-9, missing in the Large Magellanic Cloud, were found in M33, although there is a tendency for the known stars of both sequences to belong to the high-excitation subclasses. The distribution of these stars was compared with the distributions of luminous blue stars, dust, and H II regions. Star counts on the image tube plates indicated that one out of every 75 stars in M33 brighter than M/sub B/ = --4.5 is a Wolf--Rayet star

  10. White Dwarf Stars

    Science.gov (United States)

    1999-01-01

    Peering deep inside a cluster of several hundred thousand stars, NASA's Hubble Space Telescope has uncovered the oldest burned-out stars in our Milky Way Galaxy, giving astronomers a fresh reading on the age of the universe. Located in the globular cluster M4, these small, burned-out stars -- called white dwarfs -- are about 12 to 13 billion years old. By adding the one billion years it took the cluster to form after the Big Bang, astronomers found that the age of the white dwarfs agrees with previous estimates that the universe is 13 to 14 billion years old. The images, including some taken by Hubble's Wide Field and Planetary Camera 2, are available online at http://oposite.stsci.edu/pubinfo/pr/2002/10/ or http://www.jpl.nasa.gov/images/wfpc . The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif. In the top panel, a ground-based observatory snapped a panoramic view of the entire cluster, which contains several hundred thousand stars within a volume of 10 to 30 light-years across. The Kitt Peak National Observatory's .9-meter telescope took this picture in March 1995. The box at left indicates the region observed by the Hubble telescope. The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles indicate the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars. Globular clusters are among the oldest clusters of stars in the universe. The faintest and coolest white dwarfs within globular clusters can yield a globular cluster's age. Earlier Hubble observations showed that the first stars formed less than 1 billion years after the universe's birth in the big bang. So, finding the oldest stars puts astronomers within

  11. Hybrid stars

    Indian Academy of Sciences (India)

    Hybrid stars. AsHOK GOYAL. Department of Physics and Astrophysics, University of Delhi, Delhi 110 007, India. Abstract. Recently there have been important developments in the determination of neutron ... number and the electric charge. ... available to the system to rearrange concentration of charges for a given fraction of.

  12. Pulsating stars

    CERN Document Server

    Catelan, M?rcio

    2014-01-01

    The most recent and comprehensive book on pulsating stars which ties the observations to our present understanding of stellar pulsation and evolution theory.  Written by experienced researchers and authors in the field, this book includes the latest observational results and is valuable reading for astronomers, graduate students, nuclear physicists and high energy physicists.

  13. Variable stars

    International Nuclear Information System (INIS)

    Feast, M.W.; Wenzel, W.; Fernie, J.D.; Percy, J.R.; Smak, J.; Gascoigne, S.C.B.; Grindley, J.E.; Lovell, B.; Sawyer Hogg, H.B.; Baker, N.; Fitch, W.S.; Rosino, L.; Gursky, H.

    1976-01-01

    A critical review of variable stars is presented. A fairly complete summary of major developments and discoveries during the period 1973-1975 is given. The broad developments and new trends are outlined. Essential problems for future research are identified. (B.R.H. )

  14. Star Products and Applications

    OpenAIRE

    Iida, Mari; Yoshioka, Akira

    2010-01-01

    Star products parametrized by complex matrices are defined. Especially commutative associative star products are treated, and star exponentials with respect to these star products are considered. Jacobi's theta functions are given as infinite sums of star exponentials. As application, several concrete identities are obtained by properties of the star exponentials.

  15. THE TRANSATLANTIC BLUE DIPLOMACY

    Directory of Open Access Journals (Sweden)

    Ioana GUTU

    2016-12-01

    Full Text Available The international diplomatic environment has reached to an unprecedented development, involving one of the newly specialized diplomatic types, namely the economic diplomacy. At the core of the fast movements in the diplomatic spheres across the Globe are the international agreements like the Transatlantic Trade and Investment Partnership (TTIP that determined diplomacy to dissolve into new subtypes, evolving from ground to the ocean and implementing new ways of achieving economic and climate sustainability. One of the newly created diplomatic spheres, is the blue ocean diplomacy that acts mainly in accordance with the rules and regulations that are being applied to the transatlantic economy. Even though TTIP encourages the increase of trade flows across the Atlantic, it will also ease the foreign investment procedures that, under the approach of keeping a sustainable environment, will represent one of the most important initiatives in implementing the blue economy concept within the framework of the transatlantic diplomacy.

  16. The Taxonomy of Blue Amorphous Galaxies. II. Structure and Evolution

    Science.gov (United States)

    Marlowe, Amanda T.; Meurer, Gerhardt R.; Heckman, Timothy M.

    1999-09-01

    Dwarf galaxies play an important role in our understanding of galaxy formation and evolution, and starbursts are believed to affect the structure and evolution of dwarf galaxies strongly. We have therefore embarked on a systematic study of 12 of the nearest dwarf galaxies thought to be undergoing bursts of star formation. These were selected primarily by their morphological type (blue ``amorphous'' galaxies). We show that these blue amorphous galaxies are not physically distinguishable from dwarfs selected as starbursting by other methods, such as blue compact dwarfs (BCDs) and H II galaxies. All these classes exhibit surface brightness profiles that are exponential in the outer regions (r>~1.5re) but often have a predominantly central blue excess, suggesting a young burst in an older, redder galaxy. Typically, the starbursting ``cores'' are young (~107-108 yr) events compared to the older (~109-1010 yr) underlying galaxy (the ``envelope''). The ratio of the core to envelope in blue light ranges from essentially zero to about 2. These starbursts are therefore modest events involving only a few percent of the stellar mass. The envelopes have surface brightnesses that are much higher than typical dwarf irregular (dI) galaxies, so it is unlikely that there is a straightforward evolutionary relation between typical dIs and dwarf starburst galaxies. Instead we suggest that amorphous galaxies may repeatedly cycle through starburst and quiescent phases, corresponding to the galaxies with strong and weak/absent cores, respectively. Once amorphous galaxies use up the available gas (either through star formation or galactic winds) so that star formation is shut off, the faded remnants would strongly resemble dwarf elliptical galaxies. However, in the current cosmological epoch, this is evidently a slow process that is the aftermath of a series of many weak, recurring bursts. Present-day dE's must have experienced more rapid and intense evolution than this in the distant past.

  17. HUBBLE CAPTURES THE HEART OF STAR BIRTH

    Science.gov (United States)

    2002-01-01

    NASA Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2) has captured a flurry of star birth near the heart of the barred spiral galaxy NGC 1808. On the left are two images, one superimposed over the other. The black-and-white picture is a ground-based view of the entire galaxy. The color inset image, taken with the Hubble telescope's Wide Field and Planetary Camera 2 (WFPC2), provides a close-up view of the galaxy's center, the hotbed of vigorous star formation. The ground-based image shows that the galaxy has an unusual, warped shape. Most spiral galaxies are flat disks, but this one has curls of dust and gas at its outer spiral arms (upper right-hand corner and lower left-hand corner). This peculiar shape is evidence that NGC 1808 may have had a close interaction with another nearby galaxy, NGC 1792, which is not in the picture Such an interaction could have hurled gas towards the nucleus of NGC 1808, triggering the exceptionally high rate of star birth seen in the WFPC2 inset image. The WFPC2 inset picture is a composite of images using colored filters that isolate red and infrared light as well as light from glowing hydrogen. The red and infrared light (seen as yellow) highlight older stars, while hydrogen (seen as blue) reveals areas of star birth. Colors were assigned to this false-color image to emphasize the vigorous star formation taking place around the galaxy's center. NGC 1808 is called a barred spiral galaxy because of the straight lines of star formation on both sides of the bright nucleus. This star formation may have been triggered by the rotation of the bar, or by matter which is streaming along the bar towards the central region (and feeding the star burst). Filaments of dust are being ejected from the core into a faint halo of stars surrounding the galaxy's disk (towards the upper left corner) by massive stars that have exploded as supernovae in the star burst region. The portion of the galaxy seen in this 'wide-field' image is

  18. The Stars behind the Curtain

    Science.gov (United States)

    2010-02-01

    ESO is releasing a magnificent VLT image of the giant stellar nursery surrounding NGC 3603, in which stars are continuously being born. Embedded in this scenic nebula is one of the most luminous and most compact clusters of young, massive stars in our Milky Way, which therefore serves as an excellent "local" analogue of very active star-forming regions in other galaxies. The cluster also hosts the most massive star to be "weighed" so far. NGC 3603 is a starburst region: a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust. Located 22 000 light-years away from the Sun, it is the closest region of this kind known in our galaxy, providing astronomers with a local test bed for studying intense star formation processes, very common in other galaxies, but hard to observe in detail because of their great distance from us. The nebula owes its shape to the intense light and winds coming from the young, massive stars which lift the curtains of gas and clouds revealing a multitude of glowing suns. The central cluster of stars inside NGC 3603 harbours thousands of stars of all sorts (eso9946): the majority have masses similar to or less than that of our Sun, but most spectacular are several of the very massive stars that are close to the end of their lives. Several blue supergiant stars crowd into a volume of less than a cubic light-year, along with three so-called Wolf-Rayet stars - extremely bright and massive stars that are ejecting vast amounts of material before finishing off in glorious explosions known as supernovae. Using another recent set of observations performed with the SINFONI instrument on ESO's Very Large Telescope (VLT), astronomers have confirmed that one of these stars is about 120 times more massive than our Sun, standing out as the most massive star known so far in the Milky Way [1]. The clouds of NGC 3603 provide us with a family picture of stars in different stages of their life, with gaseous structures that are

  19. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Frigaard, Peter; Brorsen, Michael

    Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004.......Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004....

  20. The Blue Marble

    Science.gov (United States)

    2002-01-01

    This spectacular Moderate Resolution Imaging Spectroradiometer (MODIS) 'blue marble' image is based on the most detailed collection of true-color imagery of the entire Earth to date. Using a collection of satellite-based observations, scientists and visualizers stitched together months of observations of the land surface, oceans, sea ice, and clouds into a seamless, true-color mosaic of every square kilometer (.386 square mile) of our planet. Most of the information contained in this image came from MODIS, illustrating MODIS' outstanding capacity to act as an integrated tool for observing a variety of terrestrial, oceanic, and atmospheric features of the Earth. The land and coastal ocean portions of this image is based on surface observations collected from June through September 2001 and combined, or composited, every eight days to compensate for clouds that might block the satellite's view on any single day. Global ocean color (or chlorophyll) data was used to simulate the ocean surface. MODIS doesn't measure 3-D features of the Earth, so the surface observations were draped over topographic data provided by the U.S. Geological Survey EROS Data Center. MODIS observations of polar sea ice were combined with observations of Antarctica made by the National Oceanic and Atmospheric Administration's AVHRR sensor-the Advanced Very High Resolution Radiometer. The cloud image is a composite of two days of MODIS imagery collected in visible light wavelengths and a third day of thermal infra-red imagery over the poles. A large collection of imagery based on the blue marble in a variety of sizes and formats, including animations and the full (1 km) resolution imagery, is available at the Blue Marble page. Image by Reto Stockli, Render by Robert Simmon. Based on data from the MODIS Science Team

  1. Massive stars with mass loss: Evolution, nucleosynthesis, and astrophysical implications

    International Nuclear Information System (INIS)

    Prantzos, N.

    1986-06-01

    Evolution and nucleosynthesis of mass loss WR stars is studied, particularly evolution of stars with initial mass between 50 and 100 solar masses, during combustion of H and He. A semi-empirical mass loss formalism, the Roxburgh criterion for convection, and nuclear data are used. Composition of the stellar surface and ejecta (and ejecta contribution to cosmic ray composition) are derived. The contribution of these stars to s elements in our solar system is shown. Their production of 26 Al is compared to the quantity in the galaxy. Gamma ray emission at 1.8 MeV from the decay of this radionuclide is estimated in galactic longitude. The stars evolve as 0 and 0f stars during H combustion and spend 20% of their He combustion period as WN stars and 80% as WC-W0. Evolution always occurs in the blue part of the HR diagram, and satisfies observational constraints on its upper part [fr

  2. New Insights into the Formation of the Blue Main Sequence in NGC 1850

    Science.gov (United States)

    Yang, Yujiao; Li, Chengyuan; Deng, Licai; de Grijs, Richard; Milone, Antonino P.

    2018-06-01

    Recent discoveries of bimodal main sequences (MSs) associated with young clusters (with ages ≲1 Gyr) in the Magellanic Clouds have drawn a lot of attention. One of the prevailing formation scenarios attributes these split MSs to a bimodal distribution in stellar rotation rates, with most stars belonging to a rapidly rotating population. In this scenario, only a small fraction of stars populating a secondary blue sequence are slowly or non-rotating stars. Here, we focus on the blue MS in the young cluster NGC 1850. We compare the cumulative number fraction of the observed blue-MS stars to that of the high-mass-ratio binary systems at different radii. The cumulative distributions of both populations exhibit a clear anti-correlation, characterized by a highly significant Pearson coefficient of ‑0.97. Our observations are consistent with the possibility that blue-MS stars are low-mass-ratio binaries, and therefore their dynamical disruption is still ongoing. High-mass-ratio binaries, on the other hand, are more centrally concentrated.

  3. THE GALACTIC POTENTIAL AND THE ASYMMETRIC DISTRIBUTION OF HYPERVELOCITY STARS

    International Nuclear Information System (INIS)

    Perets, Hagai B.; Alexander, Tal; Wu Xufen; Zhao Hongsheng; Famaey, Benoit; Gentile, Gianfranco

    2009-01-01

    In recent years several hypervelocity stars (HVSs) have been observed in the halo of our Galaxy. Such HVSs have possibly been ejected from the Galactic center and then propagated in the Galactic potential up to their current position. The recent survey for candidate HVSs show an asymmetry in the kinematics of candidate HVSs (position and velocity vectors), where more outgoing stars than ingoing stars (i.e., positive Galactocentric velocities versus negative ones) are observed. We show that such kinematic asymmetry, which is likely due to the finite lifetime of the stars and Galactic potential structure, could be used in a novel method to probe and constrain the Galactic potential, identify the stellar type of the stars in the survey and estimate the number of HVSs. Kinematics-independent identification of the stellar types of the stars in such surveys (e.g., spectroscopic identification) could further improve these results. We find that the observed asymmetry between ingoing and outgoing stars favors specific Galactic potential models. It also implies a lower limit of ∼54 ± 8 main-sequence HVSs in the survey sample (∼>648 ± 96 in the Galaxy), assuming that all of the MS stars in the survey originate from the GC. The other stars in the survey are likely to be hot blue horizontal branch stars born in the halo rather than stars ejected from the GC.

  4. Blue ocean leadership.

    Science.gov (United States)

    Kim, W Chan; Mauborgne, Renée

    2014-05-01

    Ten years ago, two INSEAD professors broke ground by introducing "blue ocean strategy," a new model for discovering uncontested markets that are ripe for growth. In this article, they apply their concepts and tools to what is perhaps the greatest challenge of leadership: closing the gulf between the potential and the realized talent and energy of employees. Research indicates that this gulf is vast: According to Gallup, 70% of workers are disengaged from their jobs. If companies could find a way to convert them into engaged employees, the results could be transformative. The trouble is, managers lack a clear understanding of what changes they could make to bring out the best in everyone. Here, Kim and Mauborgne offer a solution to that problem: a systematic approach to uncovering, at each level of the organization, which leadership acts and activities will inspire employees to give their all, and a process for getting managers throughout the company to start doing them. Blue ocean leadership works because the managers' "customers"-that is, the people managers oversee and report to-are involved in identifying what's effective and what isn't. Moreover, the approach doesn't require leaders to alter who they are, just to undertake a different set of tasks. And that kind of change is much easier to implement and track than changes to values and mind-sets.

  5. Massive Star Burps, Then Explodes

    Science.gov (United States)

    2007-04-01

    Berkeley -- In a galaxy far, far away, a massive star suffered a nasty double whammy. On Oct. 20, 2004, Japanese amateur astronomer Koichi Itagaki saw the star let loose an outburst so bright that it was initially mistaken for a supernova. The star survived, but for only two years. On Oct. 11, 2006, professional and amateur astronomers witnessed the star actually blowing itself to smithereens as Supernova 2006jc. Swift UVOT Image Swift UVOT Image (Credit: NASA / Swift / S.Immler) "We have never observed a stellar outburst and then later seen the star explode," says University of California, Berkeley, astronomer Ryan Foley. His group studied the event with ground-based telescopes, including the 10-meter (32.8-foot) W. M. Keck telescopes in Hawaii. Narrow helium spectral lines showed that the supernova's blast wave ran into a slow-moving shell of material, presumably the progenitor's outer layers ejected just two years earlier. If the spectral lines had been caused by the supernova's fast-moving blast wave, the lines would have been much broader. artistic rendering This artistic rendering depicts two years in the life of a massive blue supergiant star, which burped and spewed a shell of gas, then, two years later, exploded. When the supernova slammed into the shell of gas, X-rays were produced. (Credit: NASA/Sonoma State Univ./A.Simonnet) Another group, led by Stefan Immler of NASA's Goddard Space Flight Center, Greenbelt, Md., monitored SN 2006jc with NASA's Swift satellite and Chandra X-ray Observatory. By observing how the supernova brightened in X-rays, a result of the blast wave slamming into the outburst ejecta, they could measure the amount of gas blown off in the 2004 outburst: about 0.01 solar mass, the equivalent of about 10 Jupiters. "The beautiful aspect of our SN 2006jc observations is that although they were obtained in different parts of the electromagnetic spectrum, in the optical and in X-rays, they lead to the same conclusions," says Immler. "This

  6. Life of a star

    International Nuclear Information System (INIS)

    Henbest, Nigel.

    1988-01-01

    The paper concerns the theory of stellar evolution. A description is given of:- how a star is born, main sequence stars, red giants, white dwarfs, supernovae, neutron stars and black holes. A brief explanation is given of how the death of a star as a supernova can trigger off the birth of a new generation of stars. Classification of stars and the fate of our sun, are also described. (U.K.)

  7. Instant BlueStacks

    CERN Document Server

    Judge, Gary

    2013-01-01

    Get to grips with a new technology, understand what it is and what it can do for you, and then get to work with the most important features and tasks. A fast-paced, example-based approach guide for learning BlueStacks.This book is for anyone with a Mac or PC who wants to run Android apps on their computer. Whether you want to play games that are freely available for Android but not your computer, or you want to try apps before you install them on a physical device or use it as a development tool, this book will show you how. No previous experience is needed as this is written in plain English

  8. COLORFUL FIREWORKS FINALE CAPS A STAR'S LIFE

    Science.gov (United States)

    2002-01-01

    Glowing gaseous streamers of red, white, and blue -- as well as green and pink -- illuminate the heavens like Fourth of July fireworks. The colorful streamers that float across the sky in this photo taken by NASA's Hubble Space Telescope were created by one of the biggest firecrackers seen to go off in our galaxy in recorded history, the titanic supernova explosion of a massive star. The light from the exploding star reached Earth 320 years ago, nearly a century before our United States celebrated its birth with a bang. The dead star's shredded remains are called Cassiopeia A, or 'Cas A' for short. Cas A is the youngest known supernova remnant in our Milky Way Galaxy and resides 10,000 light-years away in the constellation Cassiopeia, so the star actually blew up 10,000 years before the light reached Earth in the late 1600s. This stunning Hubble image of Cas A is allowing astronomers to study the supernova's remains with great clarity, showing for the first time that the debris is arranged into thousands of small, cooling knots of gas. This material eventually will be recycled into building new generations of stars and planets. Our own Sun and planets are constructed from the debris of supernovae that exploded billions of years ago. This photo shows the upper rim of the supernova remnant's expanding shell. Near the top of the image are dozens of tiny clumps of matter. Each small clump, originally just a small fragment of the star, is tens of times larger than the diameter of our solar system. The colors highlight parts of the debris where chemical elements are glowing. The dark blue fragments, for example, are richest in oxygen; the red material is rich in sulfur. The star that created this colorful show was a big one, about 15 to 25 times more massive than our Sun. Massive stars like the one that created Cas A have short lives. They use up their supply of nuclear fuel in tens of millions of years, 1,000 times faster than our Sun. With their fuel exhausted, heavy

  9. SPITZER SAGE-SMC INFRARED PHOTOMETRY OF MASSIVE STARS IN THE SMALL MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Bonanos, A. Z.; Lennon, D. J.; Massa, D. L.

    2010-01-01

    We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE-SMC survey database, for which we present uniform photometry from 0.3to24 μm in the UBVIJHK s +IRAC+MIPS24 bands. We compare the color-magnitude diagrams and color-color diagrams to those of stars in the Large Magellanic Cloud (LMC), finding that the brightest infrared sources in the SMC are also the red supergiants, supergiant B[e] (sgB[e]) stars, luminous blue variables, and Wolf-Rayet stars, with the latter exhibiting less infrared excess, the red supergiants being less dusty and the sgB[e] stars being on average less luminous. Among the objects detected at 24 μm in the SMC are a few very luminous hypergiants, four B-type stars with peculiar, flat spectral energy distributions, and all three known luminous blue variables. We detect a distinct Be star sequence, displaced to the red, and suggest a novel method of confirming Be star candidates photometrically. We find a higher fraction of Oe and Be stars among O and early-B stars in our SMC catalog, respectively, when compared to the LMC catalog, and that the SMC Be stars occur at higher luminosities. We estimate mass-loss rates for the red supergiants, confirming the correlation with luminosity even at the metallicity of the SMC. Finally, we confirm the new class of stars displaying composite A and F type spectra, the sgB[e] nature of 2dFS1804 and find the F0 supergiant 2dFS3528 to be a candidate luminous blue variable with cold dust.

  10. Asteroseismology of Pulsating Stars Santosh Joshi∗ & Yogesh C ...

    Indian Academy of Sciences (India)

    It is then possible to 'invert' the observations to make a map of the ... surface lines, red and blue sections represent portions of the stellar surface that are moving in ...... Stars in clusters are believed to be formed from the same cloud of gas ...

  11. O stars and Wolf-Rayet stars

    International Nuclear Information System (INIS)

    Conti, P.S.; Underhill, A.B.; Jordan, S.; Thomas, R.

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented

  12. O stars and Wolf-Rayet stars

    Science.gov (United States)

    Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (Editor); Thomas, Richard (Editor)

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

  13. Project Blue: Optical Coronagraphic Imaging Search for Terrestrial-class Exoplanets in Alpha Centauri

    Science.gov (United States)

    Morse, Jon; Project Blue team

    2018-01-01

    Project Blue is a coronagraphic imaging space telescope mission designed to search for habitable worlds orbiting the nearest Sun-like stars in the Alpha Centauri system. With a 45-50 cm baseline primary mirror size, Project Blue will perform a reconnaissance of the habitable zones of Alpha Centauri A and B in blue light and one or two longer wavelength bands to determine the hue of any planets discovered. Light passing through the off-axis telescope feeds into a coronagraphic instrument that forms the heart of the mission. Various coronagraph designs are being considered, such as phase induced amplitude apodization (PIAA), vector vortex, etc. Differential orbital image processing techniques will be employed to analyze the data for faint planets embedded in the residual glare of the parent star. Project Blue will advance our knowledge about the presence or absence of terrestrial-class exoplanets in the habitable zones and measure the brightness of zodiacal dust around each star, which will aid future missions in planning their observational surveys of exoplanets. It also provides on-orbit demonstration of high-contrast coronagraphic imaging technologies and techniques that will be useful for planning and implementing future space missions by NASA and other space agencies. We present an overview of the science goals, mission concept and development schedule. As part of our cooperative agreement with NASA, the Project Blue team intends to make the data available in a publicly accessible archive.

  14. Egyptian "Star Clocks"

    Science.gov (United States)

    Symons, Sarah

    Diagonal, transit, and Ramesside star clocks are tables of astronomical information occasionally found in ancient Egyptian temples, tombs, and papyri. The tables represent the motions of selected stars (decans and hour stars) throughout the Egyptian civil year. Analysis of star clocks leads to greater understanding of ancient Egyptian constellations, ritual astronomical activities, observational practices, and pharaonic chronology.

  15. MAGNETIC FIELDS OF STARS

    OpenAIRE

    Bychkov, V. D.; Bychkova, L. V.; Madej, J.

    2008-01-01

    Now it is known about 1212 stars of the main sequence and giants (from them 610 stars - it is chemically peculiarity (CP) stars) for which direct measurements of magnetic fields were spent (Bychkov et al.,2008). Let's consider, what representations were generated about magnetic fields (MT) of stars on the basis of available observations data.

  16. An Unwelcome Place for New Stars (artist concept)

    Science.gov (United States)

    2006-01-01

    [figure removed for brevity, see original site] Poster Version Suppression of Star Formation from Supermassive Black Holes This artist's concept depicts a supermassive black hole at the center of a galaxy. NASA's Galaxy Evolution Explorer found evidence that black holes -- once they grow to a critical size -- stifle the formation of new stars in elliptical galaxies. Black holes are thought to do this by heating up and blasting away the gas that fuels star formation. The blue color here represents radiation pouring out from material very close to the black hole. The grayish structure surrounding the black hole, called a torus, is made up of gas and dust. Beyond the torus, only the old red-colored stars that make up the galaxy can be seen. There are no new stars in the galaxy.

  17. Peculiar early-type galaxies with central star formation

    International Nuclear Information System (INIS)

    Ge Chong; Gu Qiusheng

    2012-01-01

    Early-type galaxies (ETGs) are very important for understanding the formation and evolution of galaxies. Recent observations suggest that ETGs are not simply old stellar spheroids as we previously thought. Widespread recent star formation, cool gas and dust have been detected in a substantial fraction of ETGs. We make use of the radial profiles of g — r color and the concentration index from the Sloan Digital Sky Survey database to pick out 31 peculiar ETGs with central blue cores. By analyzing the photometric and spectroscopic data, we suggest that the blue cores are caused by star formation activities rather than the central weak active galactic nucleus. From the results of stellar population synthesis, we find that the stellar population of the blue cores is relatively young, spreading from several Myr to less than one Gyr. In 14 galaxies with H I observations, we find that the average gas fraction of these galaxies is about 0.55. The bluer galaxies show a higher gas fraction, and the total star formation rate (SFR) correlates very well with the H I gas mass. The star formation history of these ETGs is affected by the environment, e.g. in the denser environment the H I gas is less and the total SFR is lower. We also discuss the origin of the central star formation of these early-type galaxies.

  18. Compact stars

    Science.gov (United States)

    Estevez-Delgado, Gabino; Estevez-Delgado, Joaquin

    2018-05-01

    An analysis and construction is presented for a stellar model characterized by two parameters (w, n) associated with the compactness ratio and anisotropy, respectively. The reliability range for the parameter w ≤ 1.97981225149 corresponds with a compactness ratio u ≤ 0.2644959374, the density and pressures are positive, regular and monotonic decrescent functions, the radial and tangential speed of sound are lower than the light speed, moreover, than the plausible stability. The behavior of the speeds of sound are determinate for the anisotropy parameter n, admitting a subinterval where the speeds are monotonic crescent functions and other where we have monotonic decrescent functions for the same speeds, both cases describing a compact object that is also potentially stable. In the bigger value for the observational mass M = 2.05 M⊙ and radii R = 12.957 Km for the star PSR J0348+0432, the model indicates that the maximum central density ρc = 1.283820319 × 1018 Kg/m3 corresponds to the maximum value of the anisotropy parameter and the radial and tangential speed of the sound are monotonic decrescent functions.

  19. A complex approach to the blue-loop problem

    Science.gov (United States)

    Ostrowski, Jakub; Daszynska-Daszkiewicz, Jadwiga

    2015-08-01

    The problem of the blue loops during the core helium burning, outstanding for almost fifty years, is one of the most difficult and poorly understood problems in stellar astrophysics. Most of the work focused on the blue loops done so far has been performed with old stellar evolution codes and with limited computational resources. In the end the obtained conclusions were based on a small sample of models and could not have taken into account more advanced effects and interactions between them.The emergence of the blue loops depends on many details of the evolution calculations, in particular on chemical composition, opacity, mixing processes etc. The non-linear interactions between these factors contribute to the statement that in most cases it is hard to predict without a precise stellar modeling whether a loop will emerge or not. The high sensitivity of the blue loops to even small changes of the internal structure of a star yields one more issue: a sensitivity to numerical problems, which are common in calculations of stellar models on advanced stages of the evolution.To tackle this problem we used a modern stellar evolution code MESA. We calculated a large grid of evolutionary tracks (about 8000 models) with masses in the range of 3.0 - 25.0 solar masses from the zero age main sequence to the depletion of helium in the core. In order to make a comparative analysis, we varied metallicity, helium abundance and different mixing parameters resulting from convective overshooting, rotation etc.The better understanding of the properties of the blue loops is crucial for our knowledge of the population of blue supergiants or pulsating variables such as Cepheids, α-Cygni or Slowly Pulsating B-type supergiants. In case of more massive models it is also of great importance for studies of the progenitors of supernovae.

  20. Neutron Stars and NuSTAR

    Science.gov (United States)

    Bhalerao, Varun

    2012-05-01

    My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses

  1. MASSIVE INFANT STARS ROCK THEIR CRADLE

    Science.gov (United States)

    2002-01-01

    Extremely intense radiation from newly born, ultra-bright stars has blown a glowing spherical bubble in the nebula N83B, also known as NGC 1748. A new NASA Hubble Space Telescope image has helped to decipher the complex interplay of gas and radiation of a star-forming region in a nearby galaxy. The image graphically illustrates just how these massive stars sculpt their environment by generating powerful winds that alter the shape of the parent gaseous nebula. These processes are also seen in our Milky Way in regions like the Orion Nebula. The Hubble telescope is famous for its contribution to our knowledge about star formation in very distant galaxies. Although most of the stars in the Universe were born several billions of years ago, when the Universe was young, star formation still continues today. This new Hubble image shows a very compact star-forming region in a small part of one of our neighboring galaxies - the Large Magellanic Cloud. This galaxy lies only 165,000 light-years from our Milky Way and can easily be seen with the naked eye from the Southern Hemisphere. Young, massive, ultra-bright stars are seen here just as they are born and emerge from the shelter of their pre-natal molecular cloud. Catching these hefty stars at their birthplace is not as easy as it may seem. Their high mass means that the young stars evolve very rapidly and are hard to find at this critical stage. Furthermore, they spend a good fraction of their youth hidden from view, shrouded by large quantities of dust in a molecular cloud. The only chance is to observe them just as they start to emerge from their cocoon - and then only with very high-resolution telescopes. Astronomers from France, the U.S., and Germany have used Hubble to study the fascinating interplay between gas, dust, and radiation from the newly born stars in this nebula. Its peculiar and turbulent structure has been revealed for the first time. This high-resolution study has also uncovered several individual stars

  2. Innocent Bystanders and Smoking Guns: Dwarf Carbon Stars

    Science.gov (United States)

    Green, Paul J.

    2014-01-01

    As far as we know, most carbon throughout the Universe is created and dispersed by AGB stars. So it was at first surprising to find that the carbon stars most prevalent in the Galaxy are in fact dwarfs. We suspect that dC stars are most likely innocent bystanders in post-mass transfer binaries, and may be predominantly metal-poor. Among 1200 C stars found in the SDSS (Green 2013), we confirm 724 dCs, of which a dozen are DA/dC stars in composite spectrum binaries, quadrupling the total sample of these "smoking guns" for AGB binary mass transfer. The dCs likely span absolute magnitudes M_i from about 6.5 to 10.5. G-type dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C_2 bands. Eleven very red C stars with strong red CN bands appear to be N-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Le A. Two such stars within 30arcmin of each other may trace a previously unidentified dwarf galaxy or tidal stream at ~40 kpc. We describe follow-up projects to study the spatial, kinematic, and binary properties of these C-enriched dwarfs.

  3. China Mobile: Expanding "Blue Ocean"

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Driving force is crucial for realizing high-speed growth. The strong driving force from "Blue Ocean Strategy" is an important advantage for China Mobile to realize harmonious and leap-forward development.

  4. Giant CP stars

    International Nuclear Information System (INIS)

    Loden, L.O.; Sundman, A.

    1989-01-01

    This study is part of an investigation of the possibility of using chemically peculiar (CP) stars to map local galactic structure. Correct luminosities of these stars are therefore crucial. CP stars are generally regarded as main-sequence or near-main-sequence objects. However, some CP stars have been classified as giants. A selection of stars, classified in literature as CP giants, are compared to normal stars in the same effective temperature interval and to ordinary 'non giant' CP stars. There is no clear confirmation of a higher luminosity for 'CP giants', than for CP stars in general. In addition, CP characteristics seem to be individual properties not repeated in a component star or other cluster members. (author). 50 refs., 5 tabs., 3 figs

  5. Rates of star formation

    International Nuclear Information System (INIS)

    Larson, R.B.

    1977-01-01

    It is illustrated that a theoretical understanding of the formation and evolution of galaxies depends on an understanding of star formation, and especially of the factors influencing the rate of star formation. Some of the theoretical problems of star formation in galaxies, some approaches that have been considered in models of galaxy evolution, and some possible observational tests that may help to clarify which processes or models are most relevant are reviewed. The material is presented under the following headings: power-law models for star formation, star formation processes (conditions required, ways of achieving these conditions), observational indications and tests, and measures of star formation rates in galaxies. 49 references

  6. Energy production in stars

    International Nuclear Information System (INIS)

    Bethe, Hans.

    1977-01-01

    Energy in stars is released partly by gravitation, partly by nuclear reactions. For ordinary stars like our sun, nuclear reactions predominate. However, at the end of the life of a star very large amounts of energy are released by gravitational collapse; this can amount to as much as 10 times the total energy released nuclear reactions. The rotational energy of pulsars is a small remnant of the energy of gravitation. The end stage of small stars is generally a white dwarf, of heavy stars a neutron star of possibly a black hole

  7. [Acute blue urticaria following subcutaneous injection of patent blue dye].

    Science.gov (United States)

    Hamelin, A; Vial-Dupuy, A; Lebrun-Vignes, B; Francès, C; Soria, A; Barete, S

    2015-11-01

    Patent blue (PB) is a lymphatic vessel dye commonly used in France for sentinel lymph node detection in breast cancer, and less frequently in melanoma, and which may induce hypersensitivity reactions. We report a case of acute blue urticaria occurring within minutes of PB injection. Ten minutes after PB injection for sentinel lymph node detection during breast cancer surgery, a 49-year-old woman developed generalised acute blue urticaria and eyelid angioedema without bronchospasm or haemodynamic disturbance, but requiring discontinuation of surgery. Skin testing using PB and the anaesthetics given were run 6 weeks after the episode and confirmed PB allergy. PB was formally contra-indicated. Immediate hypersensitivity reactions to PB have been reported for between 0.24 and 2.2% of procedures. Such reactions are on occasion severe, chiefly involving anaphylactic shock. Two mechanisms are probably associated: non-specific histamine release and/or an IgE-mediated mechanism. Skin tests are helpful in confirming the diagnosis of PB allergy. Blue acute urticaria is one of the clinical manifestations of immediate hypersensitivity reactions to patent blue dye. Skin tests must be performed 6 weeks after the reaction in order to confirm the diagnosis and formally contra-indicate this substance. Copyright © 2015 Elsevier Masson SAS. All rights reserved.

  8. Massive runaway stars in the Large Magellanic Cloud

    Science.gov (United States)

    Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

    2010-09-01

    The origin of massive field stars in the Large Magellanic Cloud (LMC) has long been an enigma. The recent measurements of large offsets (˜ 100 km s-1) between the heliocentric radial velocities of some very massive (O2-type) field stars and the systemic LMC velocity provides a possible explanation of this enigma and suggests that the field stars are runaway stars ejected from their birthplaces at the very beginning of their parent cluster's dynamical evolution. A straightforward way to prove this explanation is to measure the proper motions of the field stars and to show that they are moving away from one of the nearby star clusters or OB associations. This approach is, however, complicated by the long distance to the LMC, which makes accurate proper motion measurements difficult. We used an alternative approach for solving the problem (first applied for Galactic field stars), based on the search for bow shocks produced by runaway stars. The geometry of detected bow shocks would allow us to infer the direction of stellar motion, thereby determining their possible parent clusters. In this paper we present the results of a search for bow shocks around six massive field stars that have been proposed as candidate runaway stars. Using archival Spitzer Space Telescope data, we found a bow shock associated with one of our programme stars, the O2 V((f*)) star BI 237, which is the first-ever detection of bow shocks in the LMC. Orientation of the bow shock suggests that BI 237 was ejected from the OB association LH 82 (located at ≃ 120 pc in projection from the star). A by-product of our search is the detection of bow shocks generated by four OB stars in the field of the LMC and an arc-like structure attached to the candidate luminous blue variable R81 (HD 269128). The geometry of two of these bow shocks is consistent with the possibility that their associated stars were ejected from the 30 Doradus star-forming complex. We discuss implications of our findings for the

  9. Regular Generalized Star Star closed sets in Bitopological Spaces

    OpenAIRE

    K. Kannan; D. Narasimhan; K. Chandrasekhara Rao; R. Ravikumar

    2011-01-01

    The aim of this paper is to introduce the concepts of τ1τ2-regular generalized star star closed sets , τ1τ2-regular generalized star star open sets and study their basic properties in bitopological spaces.

  10. Evolution of massive close binaries and formation of neutron stars and black holes

    International Nuclear Information System (INIS)

    Massevitch, A.G.; Tutukov, A.V.; Yungelson, L.R.

    1976-01-01

    Main results of computations of evolution for massive close binaries (10 M(Sun)+9.4 M(Sun), 16 M(Sun)+15 M(Sun), 32 M(Sun)+30 M(Sun), 64 M(Sun)+60 M(Sun)) up to oxygen exhaustion in the core are described. Mass exchange starting in core hydrogen, shell hydrogen and core helium burning stages was studied. Computations were performed assuming both the Ledoux and Schwarzschild stability criteria for semiconvection. The influence of UFI-neutrino emission on evolution of close binaries was investigated. The results obtained allow to outline the following evolutionary chain: two detached Main-Sequence stars - mass exchange - Wolf-Rayet star or blue supergiant plus main sequence star - explosion of the initially more massive star appearing as a supernova event - collapsed or neutron star plus Main-Sequence star, that may be observed as a 'runaway star' - mass exchange leading to X-rays emission - collapsed or neutron star plus WR-star or blue supergiant - second explosion of supernova that preferentially disrupts the system and gives birth to two single high spatial velocity pulsars. Numerical estimates concerning the number and properties of WR-stars, pulsars and X-ray sources are presented. The results are in favour of the existence of UFI-neutrino and of the Ledoux criterion for describing semiconvection. Properties of several well-known X-ray sources and the binary pulsar are discussed on base of evolutionary chain of close binaries. (Auth.)

  11. On the Evolution of Helium in Blue Compact Galaxies

    International Nuclear Information System (INIS)

    Fields, B.D.; Olive, K.A.

    1998-01-01

    We discuss the chemical evolution of dwarf irregular and blue compact galaxies in light of recent data, new stellar yields, and chemical evolution models. We examine the abundance data for evidence of H ii region self-enrichment effects, which would lead to correlations in the scatter of helium, nitrogen, and oxygen abundances around their mean trends. The observed helium abundance trends show no such correlations, although the nitrogen-oxygen trend does show strong evidence for real scatter beyond observational error. We construct simple models for the chemical evolution of these galaxies, using the most recent yields of 4 He, C, N, and O in intermediate- and high-mass stars. The effects of galactic outflows, which can arise both from bulk heating and evaporation of the interstellar medium and from the partial escape of enriched supernova ejecta are included. In agreement with other studies, we find that supernova-enriched outflows can roughly reproduce the observed He, C, N, and O trends; however, in models that fit N versus O, the slopes ΔY/ΔO and ΔY/ΔN consistently fall more than 2 σ below the fit to observations. We discuss the role of the models and their uncertainties in the extrapolation of primordial helium from the data. We also explore the model dependence arising from nucleosynthesis uncertainties associated with nitrogen yields in intermediate-mass stars, the fate of 8 endash 11 M circle-dot stars, and massive star winds. copyright copyright 1998. The American Astronomical Society

  12. Quark core stars, quark stars and strange stars

    International Nuclear Information System (INIS)

    Grassi, F.

    1988-01-01

    A recent one flavor quark matter equation of state is generalized to several flavors. It is shown that quarks undergo a first order phase transition. In addition, this equation of state depends on just one parameter in the two flavor case, two parameters in the three flavor case, and these parameters are constrained by phenomenology. This equation of state is then applied to the hadron-quark transition in neutron stars and the determination of quark star stability, the investigation of strange matter stability and possible strange star existence. 43 refs., 6 figs

  13. THE NATURE OF STARBURSTS. III. THE SPATIAL DISTRIBUTION OF STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    McQuinn, Kristen B. W.; Skillman, Evan D. [Minnesota Institute for Astrophysics, School of Physics and Astronomy, 116 Church Street, S.E., University of Minnesota, Minneapolis, MN 55455 (United States); Dalcanton, Julianne J.; Weisz, Daniel R.; Williams, Benjamin F. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Cannon, John M. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Holtzman, Jon, E-mail: kmcquinn@astro.umn.edu [Department of Astronomy, New Mexico State University, Box 30001-Department 4500, 1320 Frenger Street, Las Cruces, NM 88003 (United States)

    2012-11-01

    We map the spatial distribution of recent star formation over a few Multiplication-Sign 100 Myr timescales in 15 starburst dwarf galaxies using the location of young blue helium burning stars identified from optically resolved stellar populations in archival Hubble Space Telescope observations. By comparing the star formation histories from both the high surface brightness central regions and the diffuse outer regions, we measure the degree to which the star formation has been centrally concentrated during the galaxies' starbursts, using three different metrics for the spatial concentration. We find that the galaxies span a full range in spatial concentration, from highly centralized to broadly distributed star formation. Since most starbursts have historically been identified by relatively short timescale star formation tracers (e.g., H{alpha} emission), there could be a strong bias toward classifying only those galaxies with recent, centralized star formation as starbursts, while missing starbursts that are spatially distributed.

  14. Spectral Identification of New Galactic cLBV and WR Stars

    Science.gov (United States)

    Stringfellow, G. S.; Gvaramadze, V. V.; Beletsky, Y.; Kniazev, A. Y.

    2012-12-01

    We have undertaken a near-IR spectral survey of stars associated with compact nebulae recently revealed by the Spitzer and WISE imaging surveys. These circumstellar nebulae, produced by massive evolved stars, display a variety of symmetries and shapes and are often only evident at mid-IR wavelengths. Stars associated with ˜50 of these nebulae have been observed. We also obtained recent spectra of previously confirmed (known) luminous blue variables (LBVs) and candidate LBVs (cLBVs). The spectral similarity of the stars observed when compared directly to known LBVs and Wolf-Rayet (WR) stars indicate many are newly identified cLBVs, with a few being newly discovered WR stars, mostly of WN8-9h spectral type. These results suggest that a large population of previously unidentified cLBVs and related transitional stars reside in the Galaxy and confirm that circumstellar nebulae are inherent to most (c)LBVs.

  15. Multi-Epoch Hubble Space Telescope Observations of IZw18 : Characterization of Variable Stars at Ultra-Low Metallicities

    NARCIS (Netherlands)

    Fiorentino, G.; Ramos, R. Contreras; Clementini, G.; Marconi, M.; Musella, I.; Aloisi, A.; Annibali, F.; Saha, A.; Tosi, M.; van der Marel, R. P.

    2010-01-01

    Variable stars have been identified for the first time in the very metal-poor blue compact dwarf galaxy IZw18, using deep multi-band (F606W, F814W) time-series photometry obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope. We detected 34 candidate variable stars in the

  16. ENERGY STAR Certified Displays

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 7.0 ENERGY STAR Program Requirements for Displays that are effective as of July 1, 2016....

  17. ENERGY STAR Certified Boilers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Boilers that are effective as of October 1,...

  18. ENERGY STAR Certified Televisions

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 7.0 ENERGY STAR Program Requirements for Televisions that are effective as of October 30,...

  19. ENERGY STAR Certified Dehumidifiers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 4.0 ENERGY STAR Program Requirements for Dehumidifiers that are effective as of October...

  20. Observations of central stars

    International Nuclear Information System (INIS)

    Lutz, J.H.

    1978-01-01

    Difficulties occurring in the observation of central stars of planetary nebulae are reviewed with emphasis on spectral classifications and population types, and temperature determination. Binary and peculiar central stars are discussed. (U.M.G.)

  1. ENERGY STAR Certified Telephones

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Telephony (cordless telephones and VoIP...

  2. Wolf-Rayet stars

    Energy Technology Data Exchange (ETDEWEB)

    Sahade, J

    1981-12-01

    Aspects of the problems of the Wolf-Rayet stars related to their chemical composition, their evolutionary status, and their apparent dichotomy in two spectral sequences are discussed. Dogmas concerning WR stars are critically discussed, including the belief that WR stars lack hydrogen, that they are helium stars evolved from massive close binaries, and the existence of a second WR stage in which the star is a short-period single-lined binary. The relationship of WR stars with planetary nebulae is addressed, as is the membership of these stars in clusters and associations. The division of WR stars into WN and WC sequences is considered, questioning the reasonability of accounting for WR line formation in terms of abundance differences.

  3. Star formation: Cosmic feast

    Science.gov (United States)

    Scaringi, Simone

    2017-03-01

    Low-mass stars form through a process known as disk accretion, eating up material that orbits in a disk around them. It turns out that the same mechanism also describes the formation of more massive stars.

  4. Autonomous Star Tracker Algorithms

    DEFF Research Database (Denmark)

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

    1998-01-01

    Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances.......Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances....

  5. Bimodal star formation - constraints from galaxy colors at high redshift

    International Nuclear Information System (INIS)

    Wyse, R.F.G.; Silk, J.

    1987-01-01

    The possibility that at early epochs the light from elliptical galaxies is dominated by stars with an initial mass function (IMF) which is deficient in low-mass stars, relative to the solar neighborhood is investigated. V-R colors for the optical counterparts of 3CR radio sources offer the most severe constraints on the models. Reasonable fits are obtained to both the blue, high-redshift colors and the redder, low-redshift colors with a model galaxy which forms with initially equal star formation rates in each of two IMF modes: one lacking low-mass stars, and one with stars of all masses. The net effect is that the time-integrated IMF has twice as many high-mass stars as the solar neighborhood IMF, relative to low mass stars. A conventional solar neighborhood IMF does not simultaneously account for both the range in colors at high redshift and the redness of nearby ellipticals, with any single star formation epoch. Models with a standard IMF require half the stellar population to be formed in a burst at low redshift z of about 1. 38 references

  6. A Survey for hot Central Stars of Planetary Nebulae I. Methods and First Results

    OpenAIRE

    Kanarek, Graham C.; Shara, Michael M.; Faherty, Jacqueline K.; Zurek, David; Moffat, Anthony F. J.

    2015-01-01

    We present the results of initial spectrographic followup with the Very Large Telescope (UT3, Melipal) for $K_s \\ge 14$ Galactic plane CIV emission-line candidates in the near-infrared (NIR). These 7 faint stars all display prominent HeI and CIV emission lines characteristic of a carbon-rich Wolf-Rayet star. They have NIR colours which are much too blue to be those of distant, classical WR stars. The magnitudes and colours are compatible with those expected for central stars of planetary nebu...

  7. Theoretical pulsation of metallic-line stars

    International Nuclear Information System (INIS)

    Cox, A.N.; King, D.S.; Hodson, S.W.

    1979-01-01

    The linear-theory radial-pulsation stability of low-helium delta Scuti variable models (1.0--2.5 Msun) has been investigated to see if metallicism and pulsation can occur simultaneously. Metallicism, which occurs in slowly rotating stars after the gravitational settling of He and the loss of the He II convection zone and its deep mixing for Y< or approx. =0.1, can then be established rapidly compared with the evolution time scale. Pulsation can still occur with driving due to the residual helium and the enhanced hydrogen. With the reduced helium giving no connection zone, the pulsation instability strip, whose blue and edges are estimated in this paoer, is about half as wide as with a normal helium abundance. Zero helium in the surface driving regions, however, produces blue edges so red that probably no instability strip exists at all. The red edge, predicted theoretically on the basis of the importance of convection in the outer zone, agrees well with the observational one. Cool, low-helium and metallic-line stars are then predicted to pulsate in a 200--500 K wide strip that is widest between the main-sequence luminosity of 5 Lsun and 15 Lsun. This strip reasonably includes the observed pulsating delta Del and mild Am stars, but there may be conflicts. Since blue edges for varying ionization-zone helium content occur across the entire instability strip, bluer first and higher overtone pulsations are also predicted everywhere from less than 7000 K to over 8000 K, the redder ones probably showing metallicism

  8. Covering tree with stars

    DEFF Research Database (Denmark)

    Baumbach, Jan; Guo, Jian-Ying; Ibragimov, Rashid

    2013-01-01

    We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting ...

  9. America's Star Libraries

    Science.gov (United States)

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

  10. Crystalline liquids: the blue phases

    Science.gov (United States)

    Wright, David C.; Mermin, N. David

    1989-04-01

    The blue phases of cholesteric liquid crystals are liquids that exhibit orientational order characterized by crystallographic space-group symmetries. We present here a pedagogical introduction to the current understanding of the equilibrium structure of these phases accompanied by a general overview of major experimental results. Using the Ginzburg-Landau free energy appropriate to the system, we first discuss in detail the character and stability of the usual helical phase of cholesterics, showing that for certain parameter ranges the helical phase is unstable to the appearance of one or more blue phases. The two principal models for the blue phases are two limiting cases of the Ginzburg-Landau theory. We explore each limit and conclude with some general considerations of defects in both models and an exact minimization of the free energy in a curved three-dimensional space.

  11. The University of Montana's Blue Mountain Observatory

    Science.gov (United States)

    Friend, D. B.

    2004-12-01

    The University of Montana's Department of Physics and Astronomy runs the state of Montana's only professional astronomical observatory. The Observatory, located on nearby Blue Mountain, houses a 16 inch Boller and Chivens Cassegrain reflector (purchased in 1970), in an Ash dome. The Observatory sits just below the summit ridge, at an elevation of approximately 6300 feet. Our instrumentation includes an Op-Tec SSP-5A photoelectric photometer and an SBIG ST-9E CCD camera. We have the only undergraduate astronomy major in the state (technically a physics major with an astronomy option), so our Observatory is an important component of our students' education. Students have recently carried out observing projects on the photometry of variable stars and color photometry of open clusters and OB associations. In my poster I will show some of the data collected by students in their observing projects. The Observatory is also used for public open houses during the summer months, and these have become very popular: at times we have had 300 visitors in a single night.

  12. HDE 323771: a new Herbig Ae star

    International Nuclear Information System (INIS)

    Persi, P.; Polcaro, V.F.; Viotti, R.

    1991-01-01

    From an analysis of the blue and red spectrum, and a study of the energy distribution from the optical up to the far infrared, we identify HDE 323771 as a new PMS Herbig Ae star. The P Cygni line profiles observed in the Balmer and Fe II lines indicate the presence of a stellar wind with a velocity of about 250-350 km s -1 . An upper limit of mass loss rate is derived from the observed upper limit for the Br γ luminosity. The near-IR images and the IR energy distribution indicate the presence of an extended circumstellar dust envelope with a temperature of about 1500 K. (author)

  13. Pulsation of high luminosity helium stars

    International Nuclear Information System (INIS)

    King, D.S.; Wheeler, J.C.; Cox, J.P.; Cox, A.N.; Hodson, S.W.

    1979-01-01

    Preliminary calculations are made on a systematic restudy of the linear and nonlinear pulsations of helium stars allowing for more recent and higher estimates of the effective temperature and for the high carbon abundance. Linear and nonlinear models are used. Results show qualitative agreement with earlier ones, models with sufficiently large L/M have a very hot blue edge for their instability strip, very large L/M values lead to dynamically unstable models which would appear to eject mass and therefore may not be realistic models for the pulsating RCrB stars, for the sequence studied a reasonable mass could be greater than or equal to 1.5 Msub solar. 12 references

  14. Spectrophotometry of emission-line stars in the magellanic clouds

    Science.gov (United States)

    Bohannan, Bruce

    1990-01-01

    The strong emission lines in the most luminous stars in the Magellanic Clouds indicate that these stars have such strong stellar winds that their photospheres are so masked that optical absorption lines do not provide an accurate measure of photospheric conditions. In the research funded by this grant, temperatures and gravities of emission-line stars both in the Large (LMC) and Small Magellanic Clouds (SMC) have been measured by fitting of continuum ultraviolet-optical fluxes observed with IUE with theoretical model atmospheres. Preliminary results from this work formed a major part of an invited review 'The Distribution of Types of Luminous Blue Variables'. Interpretation of the IUE observations obtained in this grant and archive data were also included in a talk at the First Boulder-Munich Hot Stars Workshop. Final results of these studies are now being completed for publication in refereed journals.

  15. A deep near-infrared spectroscopic survey of the Scutum-Crux arm for Wolf-Rayet stars

    Science.gov (United States)

    Rosslowe, C. K.; Crowther, Paul A.

    2018-01-01

    We present a New Technology Telescope/Son-of-Isaac spectroscopic survey of infrared selected Wolf-Rayet (WR) candidates in the Scutum-Crux spiral arm (298° ≤ l ≤ 340°, |b| ≤ 0.5°. We obtained near-IR spectra of 127 candidates, revealing 17 WR stars - a ∼13 per cent success rate - of which 16 are newly identified here. The majority of the new WR stars are classified as narrow-lined WN5-7 stars, with two broad-lined WN4-6 stars and three WC6-8 stars. The new stars, with distances estimated from previous absolute magnitude calibrations, have no obvious association with the Scutum-Crux arm. Refined near-infrared (YHJK) classification criteria based on over a hundred Galactic and Magellanic Cloud WR stars, providing diagnostics for hydrogen in WN stars, plus the identification of WO stars and intermediate WN/C stars. Finally, we find that only a quarter of WR stars in the survey region are associated with star clusters and/or H II regions, with similar statistics found for luminous blue variables (LBVs) in the Milky Way. The relative isolation of evolved massive stars is discussed, together with the significance of the co-location of LBVs and WR stars in young star clusters.

  16. White Dwarf Stars

    OpenAIRE

    Kepler, S. O.; Romero, Alejandra Daniela; Pelisoli, Ingrid; Ourique, Gustavo

    2017-01-01

    White dwarf stars are the final stage of most stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white dwarf stars from 5000 to 39000. This number includes only white dwarf stars with log g >= 6.5 stars, i.e., excluding the Extremely Low Mass white dw...

  17. Rotating Stars in Relativity

    Directory of Open Access Journals (Sweden)

    Stergioulas Nikolaos

    2003-01-01

    Full Text Available Rotating relativistic stars have been studied extensively in recent years, both theoretically and observationally, because of the information they might yield about the equation of state of matter at extremely high densities and because they are considered to be promising sources of gravitational waves. The latest theoretical understanding of rotating stars in relativity is reviewed in this updated article. The sections on the equilibrium properties and on the nonaxisymmetric instabilities in f-modes and r-modes have been updated and several new sections have been added on analytic solutions for the exterior spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating stars in numerical relativity.

  18. Nuclear physics of stars

    CERN Document Server

    Iliadis, Christian

    2015-01-01

    Most elements are synthesized, or ""cooked"", by thermonuclear reactions in stars. The newly formed elements are released into the interstellar medium during a star's lifetime, and are subsequently incorporated into a new generation of stars, into the planets that form around the stars, and into the life forms that originate on the planets. Moreover, the energy we depend on for life originates from nuclear reactions that occur at the center of the Sun. Synthesis of the elements and nuclear energy production in stars are the topics of nuclear astrophysics, which is the subject of this book

  19. Evolution of variable stars

    International Nuclear Information System (INIS)

    Becker, S.A.

    1986-08-01

    Throughout the domain of the H R diagram lie groupings of stars whose luminosity varies with time. These variable stars can be classified based on their observed properties into distinct types such as β Cephei stars, δ Cephei stars, and Miras, as well as many other categories. The underlying mechanism for the variability is generally felt to be due to four different causes: geometric effects, rotation, eruptive processes, and pulsation. In this review the focus will be on pulsation variables and how the theory of stellar evolution can be used to explain how the various regions of variability on the H R diagram are populated. To this end a generalized discussion of the evolutionary behavior of a massive star, an intermediate mass star, and a low mass star will be presented. 19 refs., 1 fig., 1 tab

  20. Star bursts and giant HII regions

    International Nuclear Information System (INIS)

    Pagel, B.E.J.

    1990-01-01

    Massive star formation bursts occur in a variety of galactic environments and can temporarily dominate the light output of a galaxy even when a relatively small proportion of its mass is involved. Inferences about their ages, the IMF and its dependence on chemical composition are still somewhat wobbly owing to an excess of unknowns, but certain things can be deduced from emission spectra of associated H II regions when due regard is paid to the effects of chemical composition and ionization parameter: In particular, largest ionization parameters and effective temperatures of exciting stars, at any given oxygen abundance, are anti-correlated with the abundance, and the second effect suggests an increasing proportion of more massive stars at lower abundances, although this is not yet satisfactorily quantified. A new blue compact galaxies could be very young, but it is equally possible that there is an older population of low surface brightness. Some giant H II regions may be self-polluted with nitrogen and helium due to winds from massive stars in the associated burst. (orig.)

  1. Blue Ocean vs. Five Forces

    NARCIS (Netherlands)

    A.E. Burke (Andrew); A.J. van Stel (André); A.R. Thurik (Roy)

    2010-01-01

    textabstractThe article reports on the authors' research in the Netherlands which focused on a profit model in Dutch retail stores and a so-called blue-ocean approach which requires a new market that attracts consumers and increases profits. Topics include the competitive strategy approach to

  2. Cooling compact stars and phase transitions in dense QCD

    Energy Technology Data Exchange (ETDEWEB)

    Sedrakian, Armen [J.W. Goethe University, Institute for Theoretical Physics, Frankfurt am Main (Germany)

    2016-03-15

    We report new simulations of cooling of compact stars containing quark cores and updated fits to the Cas A fast cooling data. Our model is built on the assumption that the transient behaviour of the star in Cas A is due to a phase transition within the dense QCD matter in the core of the star. Specifically, the fast cooling is attributed to an enhancement in the neutrino emission triggered by a transition from a fully gapped, two-flavor, red-green color-superconducting quark condensate to a superconducting crystalline or an alternative gapless, color-superconducting phase. The blue-colored condensate is modeled as a Bardeen-Cooper-Schrieffer (BCS)-type color superconductor with spin-one pairing order parameter. We study the sensitivity of the fits to the phase transition temperature, the pairing gap of blue quarks and the timescale characterizing the phase transition (the latter modelled in terms of a width parameter). Relative variations in these parameter around their best-fit values larger than 10{sup -3} spoil the fit to the data. We confirm the previous finding that the cooling curves show significant variations as a function of compact star mass, which allows one to account for dispersion in the data on the surface temperatures of thermally emitting neutron stars. (orig.)

  3. Star-Branched Polymers (Star Polymers)

    KAUST Repository

    Hirao, Akira; Hayashi, Mayumi; Ito, Shotaro; Goseki, Raita; Higashihara, Tomoya; Hadjichristidis, Nikolaos

    2015-01-01

    The synthesis of well-defined regular and asymmetric mixed arm (hereinafter miktoarm) star-branched polymers by the living anionic polymerization is reviewed in this chapter. In particular, much attention is being devoted to the synthetic

  4. Star-Branched Polymers (Star Polymers)

    KAUST Repository

    Hirao, Akira

    2015-09-01

    The synthesis of well-defined regular and asymmetric mixed arm (hereinafter miktoarm) star-branched polymers by the living anionic polymerization is reviewed in this chapter. In particular, much attention is being devoted to the synthetic development of miktoarm star polymers since 2000. At the present time, the almost all types of multiarmed and multicomponent miktoarm star polymers have become feasible by using recently developed iterative strategy. For example, the following well-defined stars have been successfully synthesized: 3-arm ABC, 4-arm ABCD, 5-arm ABCDE, 6-arm ABCDEF, 7-arm ABCDEFG, 6-arm ABC, 9-arm ABC, 12-arm ABC, 13-arm ABCD, 9-arm AB, 17-arm AB, 33-arm AB, 7-arm ABC, 15-arm ABCD, and 31-arm ABCDE miktoarm star polymers, most of which are quite new and difficult to synthesize by the end of the 1990s. Several new specialty functional star polymers composed of vinyl polymer segments and rigid rodlike poly(acetylene) arms, helical polypeptide, or helical poly(hexyl isocyanate) arms are introduced.

  5. The Mystery of the Lonely Neutron Star

    Science.gov (United States)

    2000-09-01

    .5 hrs; red); and B (10; 138 sec; ~0.4 hrs; blue). The seeing was good to excellent during the exposures (0.66 arcsec on average). The trails of some moving objects, most likely asteroids in the solar system, are seen in the field with intermittent blue, green and red colours. The large field ( PR Photo 23a/00 ) measures 6.6 x 6.7 arcmin 2 , with 0.2 arcsec/pixel. For clarity, a smaller area around the neutron star and the cone ("bowshock") nebula has been enlarged in PR Photo 23b/00 . The object is at the centre of the circle and the neutron star is indicated with an arrow; the field measures 80 x 80 arcsec 2. North is to the lower right and East is upper right. The motion of the neutron star as seen on the sky (see the text) is towards East, exactly in the direction indicated by the nebula. In order to test these ideas, additional observing time was granted on the VLT to obtain very "deep", direct images that would attempt to map the hydrogen glow. They were carried out by ESO staff astronomers at Paranal in "service mode". Exposures lasting more than five hours in total were taken through a narrow optical filter that isolates the H-alpha hydrogen emission. In addition, shorter exposures were taken through B(lue) and R(ed) filters. The exposures have been combined into the false-colour PR Photos 23a-b/00 . Legions of stars are seen in the photos. This is partly because of the extraordinary light sensitivity of the VLT, and partly because a star-forming region is located in this direction. Stars like our Sun appear whitish, relatively cool stars emit little blue light and appear more reddish, while hot stars appear blue. The photos clearly show a lot of diffuse light, especially in the lower left area. This is most likely starlight reflected off interstellar dust grains. The cone-shaped nebula near RX J1856.5-3754 A small area, just a little above and to the right of the centre of PR Photo 23a/00 , has been enlarged in PR Photo 23b/00 . It shows a small, cone

  6. Classification of O Stars in the Yellow-Green: The Exciting Star VES 735

    Science.gov (United States)

    Kerton, C. R.; Ballantyne, D. R.; Martin, P. G.

    1999-05-01

    Acquiring data for spectral classification of heavily reddened stars using traditional criteria in the blue-violet region of the spectrum can be prohibitively time consuming using small to medium sized telescopes. One such star is the Vatican Observatory emission-line star VES 735, which we have found excites the H II region KR 140. In order to classify VES 735, we have constructed an atlas of stellar spectra of O stars in the yellow-green (4800-5420 Å). We calibrate spectral type versus the line ratio He I lambda4922:He II lambda5411, showing that this ratio should be useful for the classification of heavily reddened O stars associated with H II regions. Application to VES 735 shows that the spectral type is O8.5. The absolute magnitude suggests luminosity class V. Comparison of the rate of emission of ionizing photons and the bolometric luminosity of VES 735, inferred from radio and infrared measurements of the KR 140 region, to recent stellar models gives consistent evidence for a main-sequence star of mass 25 M_solar and age less than a few million years with a covering factor 0.4-0.5 by the nebular material. Spectra taken in the red (6500-6700 Å) show that the stellar Hα emission is double-peaked about the systemic velocity and slightly variable. Hβ is in absorption, so that the emission-line classification is ``(e)''. However, unlike the case of the more well-known O(e) star zeta Oph, the emission from VES 735 appears to be long-lived rather than episodic.

  7. INNOCENT BYSTANDERS: CARBON STARS FROM THE SLOAN DIGITAL SKY SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Green, Paul [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

    2013-03-01

    Among stars showing carbon molecular bands (C stars), the main-sequence dwarfs, likely in post-mass transfer binaries, are numerically dominant in the Galaxy. Via spectroscopic selection from the Sloan Digital Sky Survey, we retrieve 1220 high galactic latitude C stars, {approx}5 times more than previously known, including a wider variety than past techniques such as color or grism selection have netted, and additionally yielding 167 DQ white dwarfs. Of the C stars with proper motion measurements, we identify 69% clearly as dwarfs (dCs), while {approx}7% are giants. The dCs likely span absolute magnitudes M{sub i} from {approx}6.5 to 10.5. 'G-type' dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C{sub 2} bands. We report Balmer emission in 22 dCs, none of which are G-types. We find 8 new DA/dC stars in composite spectrum binaries, quadrupling the total sample of these 'smoking guns' for AGB binary mass transfer. Eleven very red C stars with strong red CN bands appear to be 'N'-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Leo A. Two such stars within 30' of each other may trace a previously unidentified dwarf galaxy or tidal stream at {approx}40 kpc. We explore the multiwavelength properties of the sample and report the first X-ray detection of a dC star, which shows strong Balmer emission. Our own spectroscopic survey additionally provides the dC surface density from a complete sample of dwarfs limited by magnitude, color, and proper motion.

  8. INNOCENT BYSTANDERS: CARBON STARS FROM THE SLOAN DIGITAL SKY SURVEY

    International Nuclear Information System (INIS)

    Green, Paul

    2013-01-01

    Among stars showing carbon molecular bands (C stars), the main-sequence dwarfs, likely in post-mass transfer binaries, are numerically dominant in the Galaxy. Via spectroscopic selection from the Sloan Digital Sky Survey, we retrieve 1220 high galactic latitude C stars, ∼5 times more than previously known, including a wider variety than past techniques such as color or grism selection have netted, and additionally yielding 167 DQ white dwarfs. Of the C stars with proper motion measurements, we identify 69% clearly as dwarfs (dCs), while ∼7% are giants. The dCs likely span absolute magnitudes M i from ∼6.5 to 10.5. 'G-type' dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C 2 bands. We report Balmer emission in 22 dCs, none of which are G-types. We find 8 new DA/dC stars in composite spectrum binaries, quadrupling the total sample of these 'smoking guns' for AGB binary mass transfer. Eleven very red C stars with strong red CN bands appear to be 'N'-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Leo A. Two such stars within 30' of each other may trace a previously unidentified dwarf galaxy or tidal stream at ∼40 kpc. We explore the multiwavelength properties of the sample and report the first X-ray detection of a dC star, which shows strong Balmer emission. Our own spectroscopic survey additionally provides the dC surface density from a complete sample of dwarfs limited by magnitude, color, and proper motion.

  9. Innocent Bystanders: Carbon Stars from the Sloan Digital Sky Survey

    Science.gov (United States)

    Green, Paul

    2013-03-01

    Among stars showing carbon molecular bands (C stars), the main-sequence dwarfs, likely in post-mass transfer binaries, are numerically dominant in the Galaxy. Via spectroscopic selection from the Sloan Digital Sky Survey, we retrieve 1220 high galactic latitude C stars, ~5 times more than previously known, including a wider variety than past techniques such as color or grism selection have netted, and additionally yielding 167 DQ white dwarfs. Of the C stars with proper motion measurements, we identify 69% clearly as dwarfs (dCs), while ~7% are giants. The dCs likely span absolute magnitudes Mi from ~6.5 to 10.5. "G-type" dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C2 bands. We report Balmer emission in 22 dCs, none of which are G-types. We find 8 new DA/dC stars in composite spectrum binaries, quadrupling the total sample of these "smoking guns" for AGB binary mass transfer. Eleven very red C stars with strong red CN bands appear to be "N"-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Leo A. Two such stars within 30' of each other may trace a previously unidentified dwarf galaxy or tidal stream at ~40 kpc. We explore the multiwavelength properties of the sample and report the first X-ray detection of a dC star, which shows strong Balmer emission. Our own spectroscopic survey additionally provides the dC surface density from a complete sample of dwarfs limited by magnitude, color, and proper motion.

  10. MN48: a new Galactic bona fide luminous blue variable revealed by Spitzer and SALT

    Science.gov (United States)

    Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

    2016-07-01

    In this paper, we report the results of spectroscopic and photometric observations of the candidate evolved massive star MN48 disclosed via detection of a mid-infrared circular shell around it with the Spitzer Space Telescope. Follow-up optical spectroscopy of MN48 with the Southern African Large Telescope (SALT) carried out in 2011-2015 revealed significant changes in the spectrum of this star, which are typical of luminous blue variables (LBVs). The LBV status of MN48 was further supported by photometric monitoring which shows that in 2009-2011 this star has brightened by ≈0.9 and 1 mag in the V and Ic bands, respectively, then faded by ≈1.1 and 1.6 mag during the next four years, and apparently started to brighten again recently. The detected changes in the spectrum and brightness of MN48 make this star the 18th known Galactic bona fide LBV and increase the percentage of LBVs associated with circumstellar nebulae to more than 70 per cent. We discuss the possible birth place of MN48 and suggest that this star might have been ejected either from a putative star cluster embedded in the H II region IRAS 16455-4531 or the young massive star cluster Westerlund 1.

  11. Massive stars in galaxies

    International Nuclear Information System (INIS)

    Humphreys, R.M.

    1987-01-01

    The relationship between the morphologic type of a galaxy and the evolution of its massive stars is explored, reviewing observational results for nearby galaxies. The data are presented in diagrams, and it is found that the massive-star populations of most Sc spiral galaxies and irregular galaxies are similar, while those of Sb spirals such as M 31 and M 81 may be affected by morphology (via differences in the initial mass function or star-formation rate). Consideration is also given to the stability-related upper luminosity limit in the H-R diagram of hypergiant stars (attributed to radiation pressure in hot stars and turbulence in cool stars) and the goals of future observation campaigns. 88 references

  12. MASSIVE STARS IN THE Cl 1813-178 CLUSTER: AN EPISODE OF MASSIVE STAR FORMATION IN THE W33 COMPLEX

    International Nuclear Information System (INIS)

    Messineo, Maria; Davies, Ben; Figer, Donald F.; Trombley, Christine; Kudritzki, R. P.; Valenti, Elena; Najarro, F.; Michael Rich, R.

    2011-01-01

    Young massive (M > 10 4 M sun ) stellar clusters are a good laboratory to study the evolution of massive stars. Only a dozen of such clusters are known in the Galaxy. Here, we report about a new young massive stellar cluster in the Milky Way. Near-infrared medium-resolution spectroscopy with UIST on the UKIRT telescope and NIRSPEC on the Keck telescope, and X-ray observations with the Chandra and XMM satellites, of the Cl 1813-178 cluster confirm a large number of massive stars. We detected 1 red supergiant, 2 Wolf-Rayet stars, 1 candidate luminous blue variable, 2 OIf, and 19 OB stars. Among the latter, twelve are likely supergiants, four giants, and the faintest three dwarf stars. We detected post-main-sequence stars with masses between 25 and 100 M sun . A population with age of 4-4.5 Myr and a mass of ∼10, 000 M sun can reproduce such a mixture of massive evolved stars. This massive stellar cluster is the first detection of a cluster in the W33 complex. Six supernova remnants and several other candidate clusters are found in the direction of the same complex.

  13. 75 FR 65525 - Anthem Blue Cross Blue Shield, Claim Management Services, Inc. Operations, a Division of...

    Science.gov (United States)

    2010-10-25

    ... DEPARTMENT OF LABOR Employment and Training Administration [TA-W-74,327] Anthem Blue Cross Blue Shield, Claim Management Services, Inc. Operations, a Division of Wellpoint, Inc., Green Bay, WI; Notice... former workers of Anthem Blue Cross Blue Shield, Claim Management Services, Inc. Operations, a Division...

  14. MN112: a new Galactic candidate luminous blue variable

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Fabrika, S.; Sholukhova, O.; Berdnikov, L. N.; Cherepashchuk, A. M.; Zharova, A. V.

    2010-06-01

    We report the discovery of a new Galactic candidate luminous blue variable (cLBV) via detection of an infrared circular nebula and follow-up spectroscopy of its central star. The nebula, MN112, is one of many dozens of circular nebulae detected at 24μm in the Spitzer Space Telescope archival data, whose morphology is similar to that of nebulae associated with known (c)LBVs and related evolved massive stars. Specifically, the core-halo morphology of MN112 bears a striking resemblance to the circumstellar nebula associated with the Galactic cLBV GAL079.29+00.46, which suggests that both nebulae might have a similar origin and that the central star of MN112 is an LBV. The spectroscopy of the central star showed that its spectrum is almost identical to that of the bona fide LBV PCygni, which also supports the LBV classification of the object. To further constrain the nature of MN112, we searched for signatures of possible high-amplitude (>~1mag) photometric variability of the central star using archival and newly obtained photometric data covering a 45-yr period. We found that the B magnitude of the star was constant within error margins, while in the I band the star brightened by ~=0.4mag during the last 17 yr. Although the non-detection of large photometric variability leads us to use the prefix `candidate' in the classification of MN112, we remind the readers that the long-term photometric stability is not unusual for genuine LBVs and that the brightness of PCygni remained relatively stable during the last three centuries. Partially based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK); fabrika@sao.ru (SF); olga@sao.ru (OS); berdnik@sai.msu.ru (LNB); cher@sai.msu.ru (AMC); alla@sai.msu.ru (AVZ)

  15. Evolution of massive stars

    International Nuclear Information System (INIS)

    Loore, C. de

    1984-01-01

    The evolution of stars with masses larger than 15 sun masses is reviewed. These stars have large convective cores and lose a substantial fraction of their matter by stellar wind. The treatment of convection and the parameterisation of the stellar wind mass loss are analysed within the context of existing disagreements between theory and observation. The evolution of massive close binaries and the origin of Wolf-Rayet Stars and X-ray binaries is also sketched. (author)

  16. THE DUSTIEST POST-MAIN SEQUENCE STARS IN THE MAGELLANIC CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Olivia C.; Meixner, Margaret; Roman-Duval, Julia [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Sargent, Benjamin A. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Boyer, Martha L. [Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Sewiło, Marta [The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Hony, Sacha [Institut für Theoretische Astrophysik, Zentrum für Astronomie, Universitt Heidelberg, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)

    2015-10-01

    Using observations from the Herschel Inventory of The Agents of Galaxy Evolution (HERITAGE) survey of the Magellanic Clouds (MC), we have found 35 evolved stars and stellar end products that are bright in the far-infrared. These 28 (LMC) and 7 (SMC) sources were selected from the 529 evolved star candidates in the HERITAGE far-infrared point source catalogs. Our source identification method is based on spectral confirmation, spectral energy distribution characteristics, careful examination of the multiwavelength images and includes constraints on the luminosity, resulting in a thoroughly vetted list of evolved stars. These sources span a wide range in luminosity and hence initial mass. We found 13 low- to intermediate-mass evolved stars, including asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae, and a symbiotic star. We also identify 10 high mass stars, including 4 of the 15 known B[e] stars in the MC, 3 extreme red supergiants that are highly enshrouded by dust, a Luminous Blue Variable, a Wolf–Rayet star, and two supernova remnants. Further, we report the detection of 9 probable evolved objects which were previously undescribed in the literature. These sources are likely to be among the dustiest evolved objects in the MC. The Herschel emission may either be due to dust produced by the evolved star or it may arise from swept-up interstellar medium material.

  17. The Physics of the Blues

    Science.gov (United States)

    Gibson, J. Murray

    2009-03-01

    In looking at the commonalities between music and science, one sees that the musician's palette is based on the principles of physics. The pitch of a musical note is determined by the frequency of the sound wave. The scales that musicians use to create and play music can be viewed as a set of rules. What makes music interesting is how musicians develop those rules and create ambiguity with them. I will discuss the evolution of western musical scales in this context. As a particular example, ``Blue'' notes are very harmonic notes that are missing from the equal temperament scale. The techniques of piano blues and jazz represent the melding of African and Western music into something totally new and exciting. Live keyboard demonstrations will be used. Beyond any redeeming entertainment value the talk will emphasize the serious connections between science and art in music. Nevertheless tips will be accepted.

  18. Evolutionary status of stars with M> or approx. =50 M/sub sun/

    International Nuclear Information System (INIS)

    Tutukov, A.V.; Yungel'son, L.R.

    1980-01-01

    The observed masses and space velocities of main-sequence stars with M> or approx. =50 M/sub sun/ and of some of the brightest Wolf--Rayet stars (type WN 7/WN 8) are attributed to mass exchange and supernova explosions in close binary systems. Similar arguments suggest that blue supergiants intensively shedding mass may have an envelope in common with a compact, relativistic object

  19. Fast pulsars, strange stars

    International Nuclear Information System (INIS)

    Glendenning, N.K.

    1990-02-01

    The initial motivation for this work was the reported discovery in January 1989 of a 1/2 millisecond pulsar in the remnant of the spectacular supernova, 1987A. The status of this discovery has come into grave doubt as of data taken by the same group in February, 1990. At this time we must consider that the millisecond signal does not belong to the pulsar. The existence of a neutron star in remnant of the supernova is suspected because of recent observations on the light curve of the remnant, and of course by the neutrino burst that announced the supernova. However its frequency is unknown. I can make a strong case that a pulsar rotation period of about 1 ms divides those that can be understood quite comfortably as neutron stars, and those that cannot. What we will soon learn is whether there is an invisible boundary below which pulsar periods do not fall, in which case, all are presumable neutron stars, or whether there exist sub- millisecond pulsars, which almost certainly cannot be neutron stars. Their most plausible structure is that of a self-bound star, a strange-quark-matter star. The existence of such stars would imply that the ground state of the strong interaction is not, as we usually assume, hadronic matter, but rather strange quark matter. Let us look respectively at stars that are bound only by gravity, and hypothetical stars that are self-bound, for which gravity is so to speak, icing on the cake

  20. Covering tree with stars

    DEFF Research Database (Denmark)

    Baumbach, Jan; Guo, Jiong; Ibragimov, Rashid

    2015-01-01

    We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting...... tree is isomorphic to T? We prove that in the general setting, CST is NP-complete, which implies that the tree edit distance considered here is also NP-hard, even when both input trees having diameters bounded by 10. We also show that, when the number of distinct stars is bounded by a constant k, CTS...

  1. Introduction to neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Lattimer, James M. [Dept. of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States)

    2015-02-24

    Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

  2. Strangeon and Strangeon Star

    Science.gov (United States)

    Xiaoyu, Lai; Renxin, Xu

    2017-06-01

    The nature of pulsar-like compact stars is essentially a central question of the fundamental strong interaction (explained in quantum chromo-dynamics) at low energy scale, the solution of which still remains a challenge though tremendous efforts have been tried. This kind of compact objects could actually be strange quark stars if strange quark matter in bulk may constitute the true ground state of the strong-interaction matter rather than 56Fe (the so-called Witten’s conjecture). From astrophysical points of view, however, it is proposed that strange cluster matter could be absolutely stable and thus those compact stars could be strange cluster stars in fact. This proposal could be regarded as a general Witten’s conjecture: strange matter in bulk could be absolutely stable, in which quarks are either free (for strange quark matter) or localized (for strange cluster matter). Strange cluster with three-light-flavor symmetry is renamed strangeon, being coined by combining “strange nucleon” for the sake of simplicity. A strangeon star can then be thought as a 3-flavored gigantic nucleus, and strangeons are its constituent as an analogy of nucleons which are the constituent of a normal (micro) nucleus. The observational consequences of strangeon stars show that different manifestations of pulsarlike compact stars could be understood in the regime of strangeon stars, and we are expecting more evidence for strangeon star by advanced facilities (e.g., FAST, SKA, and eXTP).

  3. Interacting binary stars

    CERN Document Server

    Sahade, Jorge; Ter Haar, D

    1978-01-01

    Interacting Binary Stars deals with the development, ideas, and problems in the study of interacting binary stars. The book consolidates the information that is scattered over many publications and papers and gives an account of important discoveries with relevant historical background. Chapters are devoted to the presentation and discussion of the different facets of the field, such as historical account of the development in the field of study of binary stars; the Roche equipotential surfaces; methods and techniques in space astronomy; and enumeration of binary star systems that are studied

  4. Polarization of Be stars

    International Nuclear Information System (INIS)

    Johns, M.W.

    1975-01-01

    Linear polarization of starlight may be produced by electron scattering in the extended atmospheres of early type stars. Techniques are investigated for the measurement and interpretation of this polarization. Polarimetric observations were made of twelve visual double star systems in which at least one member was a B type star as a means of separating the intrinsic stellar polarization from the polarization produced in the interstellar medium. Four of the double stars contained a Be star. Evidence for intrinsic polarization was found in five systems including two of the Be systems, one double star with a short period eclipsing binary, and two systems containing only normal early type stars for which emission lines have not been previously reported. The interpretation of these observations in terms of individual stellar polarizations and their wavelength dependence is discussed. The theoretical basis for the intrinsic polarization of early type stars is explored with a model for the disk-like extended atmospheres of Be stars. Details of a polarimeter for the measurement of the linear polarization of astronomical point sources are also presented with narrow band (Δ lambda = 100A) measurements of the polarization of γ Cas from lambda 4000 to lambda 5800

  5. ENERGY STAR Unit Reports

    Data.gov (United States)

    Department of Housing and Urban Development — These quarterly Federal Fiscal Year performance reports track the ENERGY STAR qualified HOME units that Participating Jurisdictions record in HUD's Integrated...

  6. Blue breath holding is benign.

    OpenAIRE

    Stephenson, J B

    1991-01-01

    In their recent publication in this journal, Southall et al described typical cyanotic breath holding spells, both in otherwise healthy children and in those with brainstem lesions and other malformations. Their suggestions regarding possible autonomic disturbances may require further study, but they have adduced no scientific evidence to contradict the accepted view that in the intact child blue breath holding spells are benign. Those families in which an infant suffers an 'apparently life t...

  7. THE MASSIVE STAR POPULATION IN M101. I. THE IDENTIFICATION AND SPATIAL DISTRIBUTION OF THE VISUALLY LUMINOUS STARS

    International Nuclear Information System (INIS)

    Grammer, Skyler; Humphreys, Roberta M.

    2013-01-01

    An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. But very little is known about the origin of these giant eruptions and their progenitors, many of which are presumably very massive, evolved stars. Motivated by the small number of progenitors positively associated with these giant eruptions, we have begun a survey of the evolved massive star populations in nearby galaxies. The nearby, nearly face-on, giant spiral M101 is an excellent laboratory for studying a large population of very massive stars. In this paper, we present BVI photometry obtained from archival HST/ACS Wide Field Camera images of M101. We have produced a catalog of luminous stars with photometric errors <10% for V < 24.5 and 50% completeness down to V ∼ 26.5 even in regions of high stellar crowding. Using color and luminosity criteria, we have identified candidate luminous OB-type stars and blue supergiants, yellow supergiants, and red supergiants for future observation. We examine their spatial distributions across the face of M101 and find that the ratio of blue to red supergiants decreases by two orders of magnitude over the radial extent of M101 corresponding to 0.5 dex in metallicity. We discuss the resolved stellar content in the giant star-forming complexes NGC 5458, 5453, 5461, 5451, 5462, and 5449 and discuss their color-magnitude diagrams in conjunction with the spatial distribution of the stars to determine their spatio-temporal formation histories

  8. A 'variable' stellar object in a variable blue nebula V-V 1-7

    International Nuclear Information System (INIS)

    Rao, N.K.; Gilra, D.P.

    1981-01-01

    V-V 1-7 is supposed to be one of the few planetary nebulae with Ao central stars and was included in the planetary-nebula catalogue as PK 235 + 1 0 1. The nebula was seen on the blue Palomar Observatory Sky Survey (POSS) print but not on the red print; as a result it was thought that it might be a reflection nebula. However, the symmetry of the nebula around the central star (HD 62001), and also the ultraviolet photometric variability of this central star led others to suggest that the nebula might be a nova shell. Subsequently it was found that the nebula V-V 1-7 has disappeared. It is not seen on any direct plate known to us except the POSS blue plate. In this paper the disappearance is reported (along with the nebula) of a stellar object, which appears within the 'nebular shell' of V-V 1-7 on the POSS blue plate, but not on the red plate. (author)

  9. FORMATION OF ULTRA-COMPACT BLUE DWARF GALAXIES AND THEIR EVOLUTION INTO NUCLEATED DWARFS

    International Nuclear Information System (INIS)

    Bekki, Kenji

    2015-01-01

    We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf–dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf–dwarf mergers. We find that the remnants of dwarf–dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z ∼ [0.2–1]Z ⊙ ). We also find that the remnants of these mergers can have rather high mass densities (10 4 M ⊙ pc −3 ) within the central 10 pc and small half-light radii (40−100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R < 100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after the young stars fade. We discuss these results in the context of the origins of metal-rich ultra-compact dwarfs and SGNs

  10. FORMATION OF ULTRA-COMPACT BLUE DWARF GALAXIES AND THEIR EVOLUTION INTO NUCLEATED DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Bekki, Kenji [ICRAR, M468, The University of Western Australia 35 Stirling Highway, Crawley Western Australia, 6009 (Australia)

    2015-10-10

    We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf–dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf–dwarf mergers. We find that the remnants of dwarf–dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z ∼ [0.2–1]Z{sub ⊙}). We also find that the remnants of these mergers can have rather high mass densities (10{sup 4} M{sub ⊙} pc{sup −3}) within the central 10 pc and small half-light radii (40−100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R < 100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after the young stars fade. We discuss these results in the context of the origins of metal-rich ultra-compact dwarfs and SGNs.

  11. Stars and Flowers, Flowers and Stars

    Science.gov (United States)

    Minti, Hari

    2012-12-01

    The author, a graduated from the Bucharest University (1964), actually living and working in Israel, concerns his book to variable stars and flowers, two domains of his interest. The analogies includes double stars, eclipsing double stars, eclipses, Big Bang. The book contains 34 chapters, each of which concerns various relations between astronomy and other sciences and pseudosciences such as Psychology, Religion, Geology, Computers and Astrology (to which the author is not an adherent). A special part of the book is dedicated to archeoastronomy and ethnoastronomy, as well as to history of astronomy. Between the main points of interest of these parts: ancient sanctuaries in Sarmizegetusa (Dacia), Stone Henge(UK) and other. The last chapter of the book is dedicated to flowers. The book is richly illustrated. It is designed for a wide circle of readers.

  12. BRITE-Constellation: Nanosatellites for precision photometry of bright stars

    Science.gov (United States)

    Weiss, W. W.; Moffat, A. F. J.; Schwarzenberg-Czerny, A.; Koudelka, O. F.; Grant, C. C.; Zee, R. E.; Kuschnig, R.; Mochnacki, St.; Rucinski, S. M.; Matthews, J. M.; Orleański, P.; Pamyatnykh, A. A.; Pigulski, A.; Alves, J.; Guedel, M.; Handler, G.; Wade, G. A.; Scholtz, A. L.; Scholtz

    2014-02-01

    BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, brightness and temperature variations of stars brighter than V ~ 4, with precision and time coverage not possible from the ground. The current mission design consists of three pairs of 7 kg nanosats (hence ``Constellation'') from Austria, Canada and Poland carrying optical telescopes (3 cm aperture) and CCDs. One instrument in each pair is equipped with a blue filter; the other, a red filter. The first two nanosats (funded by Austria) are UniBRITE, designed and built by UTIAS-SFL (University of Toronto Institute for Aerospace Studies-Space Flight Laboratory) and its twin, BRITE-Austria, built by the Technical University Graz (TUG) with support of UTIAS-SFL. They were launched on 25 February 2013 by the Indian Space Agency, under contract to the Canadian Space Agency. Each BRITE instrument has a wide field of view (~ 24 degrees), so up to 15 bright stars can be observed simultaneously in 32 × 32 sub-rasters. Photometry (with reduced precision but thorough time sampling) of additional fainter targets will be possible through on-board data processing. A critical technical element of the BRITE mission is the three-axis attitude control system to stabilize a nanosat with very low inertia. The pointing stability is better than 1.5 arcminutes rms, a significant advance by UTIAS-SFL over any previous nanosatellite. BRITE-Constellation will primarily measure p- and g-mode pulsations to probe the interiors and ages of stars through asteroseismology. The BRITE sample of many of the brightest stars in the night sky is dominated by the most intrinsically luminous stars: massive stars seen at all evolutionary stages, and evolved medium-mass stars at the very end of their nuclear burning phases (cool giants and AGB stars). The Hertzsprung-Russell diagram for stars brighter than mag V=4 from which the BRITE-Constellation sample

  13. Science Through ARts (STAR)

    Science.gov (United States)

    Kolecki, Joseph; Petersen, Ruth; Williams, Lawrence

    2002-01-01

    Science Through ARts (STAR) is an educational initiative designed to teach students through a multidisciplinary approach to learning. This presentation describes the STAR pilot project, which will use Mars exploration as the topic to be integrated. Schools from the United Kingdom, Japan, the United States, and possibly eastern Europe are expected to participate in the pilot project.

  14. European Stars and Stripes

    National Research Council Canada - National Science Library

    Hendricks, Nancy

    1994-01-01

    The European Stars and Stripes (ES&S) organization publishes a daily newspaper, The Stars and Stripes, for DoD personnel stationed in Germany, Italy, the United Kingdom, and other DoD activities in the U.S. European Command...

  15. Nebraska STARS: Achieving Results

    Science.gov (United States)

    Roschewski, Pat; Isernhagen, Jody; Dappen, Leon

    2006-01-01

    In 2000, the state of Nebraska passed legislation requiring the assessment of student performance on content standards, but its requirements were very different from those of any other state. Nebraska created what has come to be known as STARS (School-based Teacher-led Assessment and Reporting System). Under STARS, each of Nebraska's nearly 500…

  16. Convective overshooting in stars

    NARCIS (Netherlands)

    Andrássy, R.

    2015-01-01

    Numerous observations provide evidence that the standard picture, in which convective mixing is limited to the unstable layers of a star, is incomplete. The mixing layers in real stars are significantly more extended than what the standard models predict. Some of the observations require changing

  17. By Draconis Stars

    Science.gov (United States)

    Bopp, Bernard W.

    An optical spectroscopic survey of dK-M stars has resulted in the discovery of several new H-alpha emission objects. Available optical data suggest these stars have a level of chromospheric activity midway between active BY Dra stars and quiet dM's. These "marginal" BY Dra stars are single objects that have rotation velocities slightly higher than that of quiet field stars but below that of active flare/BY Dra objects. The marginal BY Dra stars provide us with a class of objects rotating very near a "trigger velocity" (believed to be 5 km/s) which appears to divide active flare/BY Dra stars from quiet dM's. UV data on Mg II emission fluxes and strength of transition region features such as C IV will serve to fix activity levels in the marginal objects and determine chromosphere and transition-region heating rates. Simultaneous optical magnetic field measures will be used to explore the connection between fieldstrength/filling-factor and atmospheric heating. Comparison of these data with published information on active and quiet dM stars will yield information on the character of the stellar dynamo as it makes a transition from "low" to "high" activity.

  18. Observing Double Stars

    Science.gov (United States)

    Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca

    2012-05-01

    Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.

  19. Brilliant Star in a Colourful Neighbourhood

    Science.gov (United States)

    2010-07-01

    A spectacular new image from ESO's Wide Field Imager at the La Silla Observatory in Chile shows the brilliant and unusual star WR 22 and its colourful surroundings. WR 22 is a very hot and bright star that is shedding its atmosphere into space at a rate many millions of times faster than the Sun. It lies in the outer part of the dramatic Carina Nebula from which it formed. Very massive stars live fast and die young. Some of these stellar beacons have such intense radiation passing through their thick atmospheres late in their lives that they shed material into space many millions of times more quickly than relatively sedate stars such as the Sun. These rare, very hot and massive objects are known as Wolf-Rayet stars [1], after the two French astronomers who first identified them in the mid-nineteenth century, and one of the most massive ones yet measured is known as WR 22. It appears at the centre of this picture, which was created from images taken through red, green and blue filters with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile. WR 22 is a member of a double star system and has been measured to have a mass at least 70 times that of the Sun. WR 22 lies in the southern constellation of Carina, the keel of Jason's ship Argo in Greek mythology. Although the star lies over 5000 light-years from the Earth it is so bright that it can just be faintly seen with the unaided eye under good conditions. WR 22 is one of many exceptionally brilliant stars associated with the beautiful Carina Nebula (also known as NGC 3372) and the outer part of this huge region of star formation in the southern Milky Way forms the colourful backdrop to this image. The subtle colours of the rich background tapestry are a result of the interactions between the intense ultraviolet radiation coming from hot massive stars, including WR 22, and the vast gas clouds, mostly hydrogen, from which they formed. The central part of this enormous complex

  20. Neutron Stars and Pulsars

    CERN Document Server

    Becker, Werner

    2009-01-01

    Neutron stars are the most compact astronomical objects in the universe which are accessible by direct observation. Studying neutron stars means studying physics in regimes unattainable in any terrestrial laboratory. Understanding their observed complex phenomena requires a wide range of scientific disciplines, including the nuclear and condensed matter physics of very dense matter in neutron star interiors, plasma physics and quantum electrodynamics of magnetospheres, and the relativistic magneto-hydrodynamics of electron-positron pulsar winds interacting with some ambient medium. Not to mention the test bed neutron stars provide for general relativity theories, and their importance as potential sources of gravitational waves. It is this variety of disciplines which, among others, makes neutron star research so fascinating, not only for those who have been working in the field for many years but also for students and young scientists. The aim of this book is to serve as a reference work which not only review...

  1. Spectrophotometry of carbon stars

    Energy Technology Data Exchange (ETDEWEB)

    Oganesyan, R.K.; Karapetyan, M.S.; Nersisyan, S.E.

    1986-01-01

    The results are given of the spectrophotometric investigation of 56 carbon stars in the spectral range from 4000 to 6800 A with resolution 3 A. The observed energy distributions of these stars are determined relative to the flux at the wavelength /sub 0/ = 5556; they are presented in the form of graphs. The energy distributions have been obtained for the first time for 35 stars. Variation in the line Ba II 4554 A has been found in the spectra of St Cam, UU Aur, and RV Mon. Large changes have taken place in the spectra of RT UMa and SS Vir. It is noted that the spectra of carbon stars have a depression, this being situated in different spectral regions for individual groups of stars.

  2. Rotating stars in relativity.

    Science.gov (United States)

    Paschalidis, Vasileios; Stergioulas, Nikolaos

    2017-01-01

    Rotating relativistic stars have been studied extensively in recent years, both theoretically and observationally, because of the information they might yield about the equation of state of matter at extremely high densities and because they are considered to be promising sources of gravitational waves. The latest theoretical understanding of rotating stars in relativity is reviewed in this updated article. The sections on equilibrium properties and on nonaxisymmetric oscillations and instabilities in f -modes and r -modes have been updated. Several new sections have been added on equilibria in modified theories of gravity, approximate universal relationships, the one-arm spiral instability, on analytic solutions for the exterior spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating stars in numerical relativity including both hydrodynamic and magnetohydrodynamic studies of these objects.

  3. On the evolution of stars

    International Nuclear Information System (INIS)

    Kippenhahn, R.

    1989-01-01

    A popular survey is given of the present knowledge on evolution and ageing of stars. Main sequence stars, white dwarf stars, and red giant stars are classified in the Hertzsprung-Russell (HR)-diagram by measurable quantities: surface temperature and luminosity. From the HR-diagram it can be concluded to star mass and age. Star-forming processes in interstellar clouds as well as stellar burning processes are illustrated. The changes occurring in a star due to the depletion of the nuclear energy reserve are described. In this frame the phenomena of planetary nebulae, supernovae, pulsars, neutron stars as well as of black holes are explained

  4. Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

    Energy Technology Data Exchange (ETDEWEB)

    Theodorakis, P E [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Avgeropoulos, A [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Freire, J J [Departamento de Ciencias y Tecnicas FisicoquImicas, Universidad Nacional de Educacion a Distancia, Facultad de Ciencias, Senda del Rey 9, 28040 Madrid (Spain); Kosmas, M [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece); Vlahos, C [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece)

    2007-11-21

    The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.

  5. Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

    Science.gov (United States)

    Theodorakis, P. E.; Avgeropoulos, A.; Freire, J. J.; Kosmas, M.; Vlahos, C.

    2007-11-01

    The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.

  6. Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

    International Nuclear Information System (INIS)

    Theodorakis, P E; Avgeropoulos, A; Freire, J J; Kosmas, M; Vlahos, C

    2007-01-01

    The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results

  7. Evaluation of Code Blue Implementation Outcomes

    Directory of Open Access Journals (Sweden)

    Bengü Özütürk

    2015-09-01

    Full Text Available Aim: In this study, we aimed to emphasize the importance of Code Blue implementation and to determine deficiencies in this regard. Methods: After obtaining the ethics committee approval, 225 patient’s code blue call data between 2012 and 2014 January were retrospectively analyzed. Age and gender of the patients, date and time of the call and the clinics giving Code Blue, the time needed for the Code Blue team to arrive, the rates of false Code Blue calls, reasons for Code Blue calls and patient outcomes were investigated. Results: A total of 225 patients (149 male, 76 female were evaluated in the study. The mean age of the patients was 54.1 years. 142 (67.2% Code Blue calls occurred after hours and by emergency unit. The mean time for the Code Blue team to arrive was 1.10 minutes. Spontaneous circulation was provided in 137 patients (60.8%; 88 (39.1% died. The most commonly identified possible causes were of cardiac origin. Conclusion: This study showed that Code Blue implementation with a professional team within an efficient and targeted time increase the survival rate. Therefore, we conclude that the application of Code Blue carried out by a trained team is an essential standard in hospitals. (The Medical Bulletin of Haseki 2015; 53:204-8

  8. Star Cluster Structure from Hierarchical Star Formation

    Science.gov (United States)

    Grudic, Michael; Hopkins, Philip; Murray, Norman; Lamberts, Astrid; Guszejnov, David; Schmitz, Denise; Boylan-Kolchin, Michael

    2018-01-01

    Young massive star clusters (YMCs) spanning 104-108 M⊙ in mass generally have similar radial surface density profiles, with an outer power-law index typically between -2 and -3. This similarity suggests that they are shaped by scale-free physics at formation. Recent multi-physics MHD simulations of YMC formation have also produced populations of YMCs with this type of surface density profile, allowing us to narrow down the physics necessary to form a YMC with properties as observed. We show that the shallow density profiles of YMCs are a natural result of phase-space mixing that occurs as they assemble from the clumpy, hierarchically-clustered configuration imprinted by the star formation process. We develop physical intuition for this process via analytic arguments and collisionless N-body experiments, elucidating the connection between star formation physics and star cluster structure. This has implications for the early-time structure and evolution of proto-globular clusters, and prospects for simulating their formation in the FIRE cosmological zoom-in simulations.

  9. Liquid biofuels from blue biomass

    DEFF Research Database (Denmark)

    Kádár, Zsófia; Jensen, Annette Eva; Bangsø Nielsen, Henrik

    2011-01-01

    Marine (blue) biomasses, such as macroalgaes, represent a huge unexploited amount of biomass. With their various chemical compositions, macroalgaes can be a potential substrate for food, feed, biomaterials, pharmaceuticals, health care products and also for bioenergy. Algae use seawater as a growth...... medium, light as energy source and they capture CO2 for the synthesis of new organic material, thus can grow on non-agricultural land, without increasing food prices, or using fresh water. Due to all these advantages in addition to very high biomass yield with high carbohydrate content, macroalgaes can...

  10. Markkinointisuunnitelma Case: Ringetteseura Blue Rings

    OpenAIRE

    Seppälä, Minna

    2012-01-01

    Tämän opinnäytetyön tarkoituksena on markkinointisuunnitelman laatiminen ringetteseura Blue Ringsin edustusjoukkueelle. Lähtökohtana on pidetty suunnitelman toteutuskelpoisuutta käytännössä sekä suunnitelman reaalisuutta. Opinnäytetyö on toteutettu projektityönä, jossa on käytetty benchmarkkauksen lisäksi sekä kvalitatiivisia että empiirisiä tutkimusmenetelmiä. Opinnäytetyö koostuu kahdesta osiosta; teoreettinen viitekehys sekä empiirinen osio. Teoriana opinnäytetyössä on käytetty markkinoinn...

  11. WS1: one more new Galactic bona fide luminous blue variable★

    Science.gov (United States)

    Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

    2015-04-01

    In this Letter, we report the results of spectroscopic and photometric monitoring of the candidate luminous blue variable (LBV) WS1, which was discovered in 2011 through the detection of a mid-infrared circular shell and follow-up optical spectroscopy of its central star. Our monitoring showed that WS1 brightened in the B, V and I bands by more than 1 mag during the last three years, while its spectrum revealed dramatic changes during the same time period, indicating that the star became much cooler. The light curve of WS1 demonstrates that the brightness of this star has reached maximum in 2013 December and then starts to decline. These findings unambiguously proved the LBV nature of WS1 and added one more member to the class of Galactic bona fide LBVs, bringing their number to sixteen (an updated census of these objects is provided).

  12. Central Stars of Mid-Infrared Nebulae Discovered with Spitzer and WISE

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.

    2017-02-01

    Searches for compact mid-IR nebulae with the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE), accompanied by spectroscopic observations of central stars of these nebulae led to the discovery of many dozens of massive stars at different evolutionary stages, of which the most numerous are candidate luminous blue variables (LBVs). In this paper, we give a census of candidate and confirmed Galactic LBVs revealed with Spitzer and WISE, and present some new results of spectroscopic observations of central stars of mid-IR nebulae.

  13. Ultraviolet spectra of field horizontal-branch A-type stars. II

    International Nuclear Information System (INIS)

    Philip, A.G.D.; Hayes, D.S.; Adelman, S.J.

    1990-01-01

    The spectra of six additional A-type stars have been obtained at low resolution between 1200 and 1900 A with the IUE. The energy distributions of four of the stars match that of the field horizontal branch (FHB) distribution in Huenemoerder et al. (1984) while those of the other two do not. Three of the FHB stars fall above a line in the C(19 - V)0 vs. (b-y)0 diagram; however, HD 60825 is anomalously blue for its C(19 - V) color. 7 refs

  14. Making star teams out of star players.

    Science.gov (United States)

    Mankins, Michael; Bird, Alan; Root, James

    2013-01-01

    Top talent is an invaluable asset: In highly specialized or creative work, for instance, "A" players are likely to be six times as productive as "B" players. So when your company has a crucial strategic project, why not multiply all that firepower and have a team of your best performers tackle it? Yet many companies hesitate to do this, believing that all-star teams don't work: Big egos will get in the way. The stars won't be able to work with one another. They'll drive the team Leader crazy. Mankins, Bird, and Root of Bain & Company believe it's time to set aside that thinking. They have seen all-star teams do extraordinary work. But there is a right way and a wrong way to organize them. Before you can even begin to assemble such a team, you need to have the right talent management practices, so you hire and develop the best people and know what they're capable of. You have to give the team appropriate incentives and leaders and support staffers who are stars in their own right. And projects that are ill-defined or small scale are not for all-star teams. Use them only for critical missions, and make sure their objectives are clear. Even with the right setup, things can still go wrong. The wise executive will take steps to manage egos, prune non-team-players, and prevent average coworkers from feeling completely undervalued. She will also invest a lot of time in choosing the right team Leader and will ask members for lots of feedback to monitor how that leader is doing.

  15. Stability of boson stars

    International Nuclear Information System (INIS)

    Gleiser, M.

    1988-01-01

    Boson stars are gravitationally bound, spherically symmetric equilibrium configurations of cold, free, or interacting complex scalar fields phi. As these equilibrium configurations naturally present local anisotropy, it is sensible to expect departures from the well-known stability criteria for fluid stars. With this in mind, I investigate the dynamical instability of boson stars against charge-conserving, small radial perturbations. Following the method developed by Chandrasekhar, a variational base for determining the eigenfrequencies of the perturbations is found. This approach allows one to find numerically an upper bound for the central density where dynamical instability occurs. As applications of the formalism, I study the stability of equilibrium configurations obtained both for the free and for the self-interacting [with V(phi) = (λ/4)chemical bondphichemical bond 4 ] massive scalar field phi. Instabilities are found to occur not for the critical central density as in fluid stars but for central densities considerably higher. The departure from the results for fluid stars is sensitive to the coupling λ; the higher the value of λ, the more the stability properties of boson stars approach those of a fluid star. These results are linked to the fractional anisotropy at the radius of the configuration

  16. From clouds to stars

    International Nuclear Information System (INIS)

    Elmegreen, B.G.

    1982-01-01

    At the present time, the theory of star formation must be limited to what we know about the lowest density gas, or about the pre-main sequence stars themselves. We would like to understand two basic processes: 1) how star-forming clouds are created from the ambient interstellar gas in the first place, and 2) how small parts of these clouds condense to form individual stars. We are interested also in knowing what pre-main sequence stars are like, and how they can interact with their environment. These topics are reviewed in what follows. In this series of lectures, what we know about the formation of stars is tentatively described. The lectures begin with a description of the interstellar medium, and then they proceed along the same direction that a young star would follow during its creation, namely from clouds through the collapse phase and onto the proto-stellar phase. The evolution of viscous disks and two models for the formation of the solar system are described in the last lectures. The longest lectures, and the topics that are covered in most detail, are not necessarily the ones for which we have the most information. Physically intuitive explanations for the various processes are emphasized, rather then mathematical explanations. In some cases, the mathematical aspects are developed as well, but only when the equations can be used to give important numerical values for comparison with the observations

  17. Electronic properties of blue phosphorene/graphene and blue phosphorene/graphene-like gallium nitride heterostructures.

    Science.gov (United States)

    Sun, Minglei; Chou, Jyh-Pin; Yu, Jin; Tang, Wencheng

    2017-07-05

    Blue phosphorene (BlueP) is a graphene-like phosphorus nanosheet which was synthesized very recently for the first time [Nano Lett., 2016, 16, 4903-4908]. The combination of electronic properties of two different two-dimensional materials in an ultrathin van der Waals (vdW) vertical heterostructure has been proved to be an effective approach to the design of novel electronic and optoelectronic devices. Therefore, we used density functional theory to investigate the structural and electronic properties of two BlueP-based heterostructures - BlueP/graphene (BlueP/G) and BlueP/graphene-like gallium nitride (BlueP/g-GaN). Our results showed that the semiconducting nature of BlueP and the Dirac cone of G are well preserved in the BlueP/G vdW heterostructure. Moreover, by applying a perpendicular electric field, it is possible to tune the position of the Dirac cone of G with respect to the band edge of BlueP, resulting in the ability to control the Schottky barrier height. For the BlueP/g-GaN vdW heterostructure, BlueP forms an interface with g-GaN with a type-II band alignment, which is a promising feature for unipolar electronic device applications. Furthermore, we discovered that both G and g-GaN can be used as an active layer for BlueP to facilitate charge injection and enhance the device performance.

  18. Nuclear physics of stars

    CERN Document Server

    Iliadis, Christian

    2007-01-01

    Thermonuclear reactions in stars is a major topic in the field of nuclear astrophysics, and deals with the topics of how precisely stars generate their energy through nuclear reactions, and how these nuclear reactions create the elements the stars, planets and - ultimately - we humans consist of. The present book treats these topics in detail. It also presents the nuclear reaction and structure theory, thermonuclear reaction rate formalism and stellar nucleosynthesis. The topics are discussed in a coherent way, enabling the reader to grasp their interconnections intuitively. The book serves bo

  19. Entropy Production of Stars

    Directory of Open Access Journals (Sweden)

    Leonid M. Martyushev

    2015-06-01

    Full Text Available The entropy production (inside the volume bounded by a photosphere of main-sequence stars, subgiants, giants, and supergiants is calculated based on B–V photometry data. A non-linear inverse relationship of thermodynamic fluxes and forces as well as an almost constant specific (per volume entropy production of main-sequence stars (for 95% of stars, this quantity lies within 0.5 to 2.2 of the corresponding solar magnitude is found. The obtained results are discussed from the perspective of known extreme principles related to entropy production.

  20. Geothermal Technologies Program Blue Ribbon Panel Recommendations

    Energy Technology Data Exchange (ETDEWEB)

    none,

    2011-06-17

    The Geothermal Technologies Program assembled a geothermal Blue Ribbon Panel on March 22-23, 2011 in Albuquerque, New Mexico for a guided discussion on the future of geothermal energy in the United States and the role of the DOE Program. The Geothermal Blue Ribbon Panel Report captures the discussions and recommendations of the experts. An addendum is available here: http://www.eere.energy.gov/geothermal/pdfs/gtp_blue_ribbon_panel_report_addendum10-2011.pdf

  1. Hot HB Stars in Globular Clusters: Physical Parameters and Consequences for Theory. 5; Radiative Levitation Versus Helium Mixing

    Science.gov (United States)

    Moehler, S.; Sweigart, A. V.; Landsman, W. B.; Heber, U.

    2000-01-01

    Atmospheric parameters (T(sub eff), log g), masses and helium abundances are derived for 42 hot horizontal branch (HB) stars in the globular cluster NGC6752. For 19 stars we derive magnesium and iron abundances as well and find that iron is enriched by a factor of 50 on average with respect to the cluster abundance whereas the magnesium abundances are consistent with the cluster abundance. Radiation pressure may levitate heavy elements like iron to the surface of the star in a diffusive process. Taking into account the enrichment of heavy elements in our spectroscopic analyses we find that high iron abundances can explain part, but not all, of the problem of anomalously low gravities along the blue HB. The blue HB stars cooler than about 15,100 K and the sdB stars (T(sub eff) greater than or = 20,000 K) agree well with canonical theory when analysed with metal-rich ([M/H] = +0.5) model atmospheres, but the stars in between these two groups remain offset towards lower gravities and masses. Deep Mixing in the red giant progenitor phase is discussed as another mechanism that may influence the position of the blue HB stars in the (T(sub eff), log g)-plane but not their masses.

  2. Why Blue-Collar Blacks Help Less

    OpenAIRE

    Smith, Sandra Susan; Young, Kara Alexis

    2013-01-01

    Why are blue-collar blacks less likely to help jobseekers than jobholders from other ethnoracial groups or even than more affluent blacks? Drawing from in-depth, semi-structured interviews with 97 black and Latino workers at one large, public sector employer, we find that blue-collar black workers both helped less proactively and rejected more requests for assistance than did blue-collar Latino and white-collar black workers. We attribute blue-collar blacks’ more passive engagement to their...

  3. Carbon Stars T. Lloyd Evans

    Indian Academy of Sciences (India)

    that the features used in estimating luminosities of ordinary giant stars are just those whose abundance ... This difference between the spectral energy distributions (SEDs) of CH stars and the. J stars, which belong to .... that the first group was binaries, as for the CH stars of the solar vicinity, while those of the second group ...

  4. A survey of northern Bok globules for H-alpha emission stars

    International Nuclear Information System (INIS)

    Ogura, Katsuo; Hasegawa, Tatsuhiko.

    1983-01-01

    Northern globules in the catalog of Bok and Cordwell (1973) have been surveyed for Hα-emission stars of T Tau type by using the Kiso Schmidt telescope with an objective prism. The results for 15 globules are presented here. A total of 60 emission-line stars, of which 80 % are new, and 17 suspected ones have been discovered. Some of them are known T Tau stars; one star shows Ca 2 H and K lines in emission on objective-prism plates in the blue-violet and presumably is a new T Tau star. The celestial coordinates and rough estimates of magnitude and color are given for all of the objects. (author)

  5. AgSTAR

    Science.gov (United States)

    AgSTAR promotes biogas recovery projects, which generate renewable energy and other beneficial products from the anaerobic digestion of livestock manure and organic wastes while decreasing greenhouse gas emissions from the agriculture sector.

  6. Orbiting radiation stars

    International Nuclear Information System (INIS)

    Foster, Dean P; Langford, John; Perez-Giz, Gabe

    2016-01-01

    We study a spherically symmetric solution to the Einstein equations in which the source, which we call an orbiting radiation star (OR-star), is a compact object consisting of freely falling null particles. The solution avoids quantum scale regimes and hence neither relies upon nor ignores the interaction of quantum mechanics and gravitation. The OR-star spacetime exhibits a deep gravitational well yet remains singularity free. In fact, it is geometrically flat in the vicinity of the origin, with the flat region being of any desirable scale. The solution is observationally distinct from a black hole because a photon from infinity aimed at an OR-star escapes to infinity with a time delay. (paper)

  7. Cataclysmic Variable Stars

    Science.gov (United States)

    Hellier, Coel

    2001-01-01

    Cataclysmic variable stars are the most variable stars in the night sky, fluctuating in brightness continually on timescales from seconds to hours to weeks to years. The changes can be recorded using amateur telescopes, yet are also the subject of intensive study by professional astronomers. That study has led to an understanding of cataclysmic variables as binary stars, orbiting so closely that material transfers from one star to the other. The resulting process of accretion is one of the most important in astrophysics. This book presents the first account of cataclysmic variables at an introductory level. Assuming no previous knowledge of the field, it explains the basic principles underlying the variability, while providing an extensive compilation of cataclysmic variable light curves. Aimed at amateur astronomers, undergraduates, and researchers, the main text is accessible to those with no mathematical background, while supplementary boxes present technical details and equations.

  8. SX Phoenicis stars

    International Nuclear Information System (INIS)

    Nemec, J.; Mateo, M.

    1990-01-01

    The purpose of this paper is to review the basic observational information concerning SX Phe stars, including recent findings such as the discovery of about 40 low-luminosity variable stars in the Carina dwarf galaxy and identification of at least one SX Phe star in the metal-rich globular cluster M71. Direct evidence supporting the hypothesis that at least some BSs are binary systems comes from the discovery of two contact binaries and a semidetached binary among the 50 BSs in the globular cluster NGC 5466. Since these systems will coalesce on a time scale 500 Myr, it stands to reason that many (if not most) BSs are coalesced binaries. The merger hypothesis also explains the relatively-large masses (1.0-1.2 solar masses) that have been derived for SX Phe stars and halo BSs, and may also account for the nonvariable BSs in the 'SX Phe instability strip'. 132 refs

  9. The Fictional Black Blues Figure: Blues Music and the Art of Narrative Self-Invention

    OpenAIRE

    Mack, Kimberly

    2015-01-01

    The Fictional Black Blues Figure: Blues Music and the Art of Narrative Self-Invention, Kimberly MackMy dissertation examines representations of black American blues musicians in contemporary American fiction, drama, and popular music, and it argues that blues music can be examined as a narrative art rooted in the tradition of fictionalized autobiographical self-fashioning. I contend that the contemporary, multi-racial, literary and musical characters in my project who participate in so-called...

  10. HUBBLE'S PANORAMIC PORTRAIT OF A VAST STAR-FORMING REGION

    Science.gov (United States)

    2002-01-01

    NASA's Hubble Space Telescope has snapped a panoramic portrait of a vast, sculpted landscape of gas and dust where thousands of stars are being born. This fertile star-forming region, called the 30 Doradus Nebula, has a sparkling stellar centerpiece: the most spectacular cluster of massive stars in our cosmic neighborhood of about 25 galaxies. The mosaic picture shows that ultraviolet radiation and high-speed material unleashed by the stars in the cluster, called R136 [the large blue blob left of center], are weaving a tapestry of creation and destruction, triggering the collapse of looming gas and dust clouds and forming pillar-like structures that are incubators for nascent stars. The photo offers an unprecedented, detailed view of the entire inner region of 30 Doradus, measuring 200 light-years wide by 150 light-years high. The nebula resides in the Large Magellanic Cloud (a satellite galaxy of the Milky Way), 170,000 light-years from Earth. Nebulas like 30 Doradus are the 'signposts' of recent star birth. High-energy ultraviolet radiation from the young, hot, massive stars in R136 causes the surrounding gaseous material to glow. Previous Hubble telescope observations showed that R136 contains several dozen of the most massive stars known, each about 100 times the mass of the Sun and about 10 times as hot. These stellar behemoths all formed at the same time about 2 million years ago. The stars in R136 are producing intense 'stellar winds' (streams of material traveling at several million miles an hour), which are wreaking havoc on the gas and dust in the surrounding neighborhood. The winds are pushing the gas away from the cluster and compressing the inner regions of the surrounding gas and dust clouds [the pinkish material]. The intense pressure is triggering the collapse of parts of the clouds, producing a new generation of star formation around the central cluster. The new stellar nursery is about 30 to 50 light-years from R136. Most of the stars in the

  11. Discovery of two new Galactic candidate luminous blue variables with Wide-field Infrared Survey Explorer

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Miroshnichenko, A. S.; Berdnikov, L. N.; Langer, N.; Stringfellow, G. S.; Todt, H.; Hamann, W.-R.; Grebel, E. K.; Buckley, D.; Crause, L.; Crawford, S.; Gulbis, A.; Hettlage, C.; Hooper, E.; Husser, T.-O.; Kotze, P.; Loaring, N.; Nordsieck, K. H.; O'Donoghue, D.; Pickering, T.; Potter, S.; Romero Colmenero, E.; Vaisanen, P.; Williams, T.; Wolf, M.; Reichart, D. E.; Ivarsen, K. M.; Haislip, J. B.; Nysewander, M. C.; LaCluyze, A. P.

    2012-04-01

    We report the discovery of two new Galactic candidate luminous blue variable (LBV) stars via detection of circular shells (typical of confirmed and candidate LBVs) and follow-up spectroscopy of their central stars. The shells were detected at 22 μm in the archival data of the Mid-Infrared All Sky Survey carried out with the Wide-field Infrared Survey Explorer (WISE). Follow-up optical spectroscopy of the central stars of the shells conducted with the renewed Southern African Large Telescope (SALT) showed that their spectra are very similar to those of the well-known LBVs P Cygni and AG Car, and the recently discovered candidate LBV MN112, which implies the LBV classification for these stars as well. The LBV classification of both stars is supported by detection of their significant photometric variability: one of them brightened in the R and I bands by 0.68 ± 0.10 and 0.61 ± 0.04 mag, respectively, during the last 13-18 years, while the second one (known as Hen 3-1383) varies its B, V, R, I and Ks brightnesses by ≃0.5-0.9 mag on time-scales from 10 d to decades. We also found significant changes in the spectrum of Hen 3-1383 on a time-scale of ≃3 months, which provides additional support for the LBV classification of this star. Further spectrophotometric monitoring of both stars is required to firmly prove their LBV status. We discuss a connection between the location of massive stars in the field and their fast rotation, and suggest that the LBV activity of the newly discovered candidate LBVs might be directly related to their possible runaway status. a USNO B-1 (Monet et al. 2003); bDENIS; c2MASS; dSALT; ePROMPT.

  12. Active Luminous Blue Variables in the Large Magellanic Cloud

    Energy Technology Data Exchange (ETDEWEB)

    Walborn, Nolan R. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Gamen, Roberto C.; Lajús, Eduardo Fernández [Instituto de Astrofísica de La Plata, CONICET–UNLP and Facultad de Ciencias Astronómicas y Geofísicas, UNLP, Paseo del Bosque s/n, La Plata (Argentina); Morrell, Nidia I. [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile); Barbá, Rodolfo H. [Departamento de Física y Astronomía, Universidad de La Serena, Cisternas 1200 Norte, La Serena (Chile); Angeloni, Rodolfo, E-mail: walborn@stsci.edu, E-mail: rgamen@fcaglp.unlp.edu.ar, E-mail: eflajus@fcaglp.unlp.edu.ar, E-mail: nmorrell@lco.cl, E-mail: rbarba@dfuls.cl, E-mail: rangelon@gemini.edu [Gemini Observatory, Colina El Pino, Casilla 603, La Serena (Chile)

    2017-07-01

    We present extensive spectroscopic and photometric monitoring of two famous and currently highly active luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC), together with more limited coverage of three further, lesser known members of the class. R127 was discovered as an Ofpe/WN9 star in the 1970s but entered a classical LBV outburst in or about 1980 that is still in progress, thus enlightening us about the minimum state of such objects. R71 is currently the most luminous star in the LMC and continues to provide surprises, such as the appearance of [Ca ii] emission lines, as its spectral type becomes unprecedentedly late. Most recently, R71 has developed inverse P Cyg profiles in many metal lines. The other objects are as follows: HDE 269582, now a “second R127” that has been followed from Ofpe/WN9 to A type in its current outburst; HDE 269216, which changed from late B in 2014 to AF in 2016, its first observed outburst; and R143 in the 30 Doradus outskirts. The light curves and spectroscopic transformations are correlated in remarkable detail and their extreme reproducibility is emphasized, both for a given object and among all of them. It is now believed that some LBVs proceed directly to core collapse. One of these unstable LMC objects may thus oblige in the near future, teaching us even more about the final stages of massive stellar evolution.

  13. Active Luminous Blue Variables in the Large Magellanic Cloud

    Science.gov (United States)

    Walborn, Nolan R.; Gamen, Roberto C.; Morrell, Nidia I.; Barbá, Rodolfo H.; Fernández Lajús, Eduardo; Angeloni, Rodolfo

    2017-07-01

    We present extensive spectroscopic and photometric monitoring of two famous and currently highly active luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC), together with more limited coverage of three further, lesser known members of the class. R127 was discovered as an Ofpe/WN9 star in the 1970s but entered a classical LBV outburst in or about 1980 that is still in progress, thus enlightening us about the minimum state of such objects. R71 is currently the most luminous star in the LMC and continues to provide surprises, such as the appearance of [Ca II] emission lines, as its spectral type becomes unprecedentedly late. Most recently, R71 has developed inverse P Cyg profiles in many metal lines. The other objects are as follows: HDE 269582, now a “second R127” that has been followed from Ofpe/WN9 to A type in its current outburst; HDE 269216, which changed from late B in 2014 to AF in 2016, its first observed outburst; and R143 in the 30 Doradus outskirts. The light curves and spectroscopic transformations are correlated in remarkable detail and their extreme reproducibility is emphasized, both for a given object and among all of them. It is now believed that some LBVs proceed directly to core collapse. One of these unstable LMC objects may thus oblige in the near future, teaching us even more about the final stages of massive stellar evolution.

  14. Active Luminous Blue Variables in the Large Magellanic Cloud

    International Nuclear Information System (INIS)

    Walborn, Nolan R.; Gamen, Roberto C.; Lajús, Eduardo Fernández; Morrell, Nidia I.; Barbá, Rodolfo H.; Angeloni, Rodolfo

    2017-01-01

    We present extensive spectroscopic and photometric monitoring of two famous and currently highly active luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC), together with more limited coverage of three further, lesser known members of the class. R127 was discovered as an Ofpe/WN9 star in the 1970s but entered a classical LBV outburst in or about 1980 that is still in progress, thus enlightening us about the minimum state of such objects. R71 is currently the most luminous star in the LMC and continues to provide surprises, such as the appearance of [Ca ii] emission lines, as its spectral type becomes unprecedentedly late. Most recently, R71 has developed inverse P Cyg profiles in many metal lines. The other objects are as follows: HDE 269582, now a “second R127” that has been followed from Ofpe/WN9 to A type in its current outburst; HDE 269216, which changed from late B in 2014 to AF in 2016, its first observed outburst; and R143 in the 30 Doradus outskirts. The light curves and spectroscopic transformations are correlated in remarkable detail and their extreme reproducibility is emphasized, both for a given object and among all of them. It is now believed that some LBVs proceed directly to core collapse. One of these unstable LMC objects may thus oblige in the near future, teaching us even more about the final stages of massive stellar evolution.

  15. Young Stars with SALT

    Energy Technology Data Exchange (ETDEWEB)

    Riedel, Adric R. [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Alam, Munazza K.; Rice, Emily L.; Cruz, Kelle L. [Department of Astrophysics, The American Museum of Natural History, New York, NY 10024 (United States); Henry, Todd J., E-mail: arr@caltech.edu [RECONS Institute, Chambersburg, PA (United States)

    2017-05-10

    We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77 systems. All of these dwarfs are low-proper-motion southern hemisphere objects and were identified in a nearby star survey with a demonstrated sensitivity to young stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph on the South African Large Telescope, we have determined radial velocities, H-alpha, lithium 6708 Å, and potassium 7699 Å equivalent widths linked to age and activity, and spectral types for all of our targets. Combined with astrometric information from literature sources, we identify 44 young stars. Eighteen are previously known members of moving groups within 100 pc of the Sun. Twelve are new members, including one member of the TW Hydra moving group, one member of the 32 Orionis moving group, 9 members of Tucana-Horologium, one member of Argus, and two new members of AB Doradus. We also find 14 young star systems that are not members of any known groups. The remaining 33 star systems do not appear to be young. This appears to be evidence of a new population of nearby young stars not related to the known nearby young moving groups.

  16. STAR facility tritium accountancy

    International Nuclear Information System (INIS)

    Pawelko, R. J.; Sharpe, J. P.; Denny, B. J.

    2008-01-01

    The Safety and Tritium Applied Research (STAR) facility has been established to provide a laboratory infrastructure for the fusion community to study tritium science associated with the development of safe fusion energy and other technologies. STAR is a radiological facility with an administrative total tritium inventory limit of 1.5 g (14,429 Ci) [1]. Research studies with moderate tritium quantities and various radionuclides are performed in STAR. Successful operation of the STAR facility requires the ability to receive, inventory, store, dispense tritium to experiments, and to dispose of tritiated waste while accurately monitoring the tritium inventory in the facility. This paper describes tritium accountancy in the STAR facility. A primary accountancy instrument is the tritium Storage and Assay System (SAS): a system designed to receive, assay, store, and dispense tritium to experiments. Presented are the methods used to calibrate and operate the SAS. Accountancy processes utilizing the Tritium Cleanup System (TCS), and the Stack Tritium Monitoring System (STMS) are also discussed. Also presented are the equations used to quantify the amount of tritium being received into the facility, transferred to experiments, and removed from the facility. Finally, the STAR tritium accountability database is discussed. (authors)

  17. Asteroseismology of white dwarf stars

    OpenAIRE

    Córsico, A. H.

    2014-01-01

    Most of low- and intermediate-mass stars that populate the Universe will end their lives as white dwarf stars. These ancient stellar remnants have encrypted inside a precious record of the evolutionary history of the progenitor stars, providing a wealth of information about the evolution of stars, star formation, and the age of a variety of stellar populations, such as our Galaxy and open and globular clusters. While some information like surface chemical composition, temperature and gravity ...

  18. THE VERY MASSIVE STAR CONTENT OF THE NUCLEAR STAR CLUSTERS IN NGC 5253

    Energy Technology Data Exchange (ETDEWEB)

    Smith, L. J. [Space Telescope Science Institute and European Space Agency, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Crowther, P. A. [Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom); Calzetti, D. [Department of Astronomy, University of Massachusetts—Amherst, Amherst, MA 01003 (United States); Sidoli, F., E-mail: lsmith@stsci.edu [London Centre for Nanotechnology, University College London, London WC1E 6BT (United Kingdom)

    2016-05-20

    The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters, separated by a projected distance of 5 pc. One cluster (#5) coincides with the peak of the H α emission and the other (#11) with a massive ultracompact H ii region. A recent analysis of these clusters shows that they have a photometric age of 1 ± 1 Myr, in apparent contradiction with the age of 3–5 Myr inferred from the presence of Wolf-Rayet features in the cluster #5 spectrum. We examine Hubble Space Telescope ultraviolet and Very Large Telescope optical spectroscopy of #5 and show that the stellar features arise from very massive stars (VMSs), with masses greater than 100 M {sub ⊙}, at an age of 1–2 Myr. We further show that the very high ionizing flux from the nuclear clusters can only be explained if VMSs are present. We investigate the origin of the observed nitrogen enrichment in the circumcluster ionized gas and find that the excess N can be produced by massive rotating stars within the first 1 Myr. We find similarities between the NGC 5253 cluster spectrum and those of metal-poor, high-redshift galaxies. We discuss the presence of VMSs in young, star-forming galaxies at high redshift; these should be detected in rest-frame UV spectra to be obtained with the James Webb Space Telescope . We emphasize that population synthesis models with upper mass cutoffs greater than 100 M {sub ⊙} are crucial for future studies of young massive star clusters at all redshifts.

  19. Reduction of blue tungsten oxide

    International Nuclear Information System (INIS)

    Wilken, T.; Wert, C.; Woodhouse, J.; Morcom, W.

    1975-01-01

    A significant portion of commercial tungsten is produced by hydrogen reduction of oxides. Although several modes of reduction are possible, hydrogen reduction is used where high purity tungsten is required and where the addition of other elements or compounds is desired for modification of the metal, as is done for filaments in the lamp industry. Although several investigations of the reduction of oxides have been reported (1 to 5), few principles have been developed which can aid in assessment of current commercial practice. The reduction process was examined under conditions approximating commercial practice. The specific objectives were to determine the effects of dopants, of water vapor in the reducing atmosphere, and of reduction temperature upon: (1) the rate of the reaction by which blue tungsten oxide is reduced to tungsten metal, (2) the intermediate oxides associated with reduction, and (3) the morphology of the resulting tungsten powder

  20. Profile of He I lambda5876 in the P-Cygni-type of star HD 152408

    International Nuclear Information System (INIS)

    Walborn, N.R.

    1975-01-01

    The blue-shifted absorption component of the P-Cygni profile at He I lambda 5876 in HD 152408 (O8: Iafpe) has been found to be extremely broad, extending -1000 km sec -1 from the emission maximum. This unusual profile is probably due to overpopulation of the lower level of lambda 5876, which permits it to form throughout a greater extent of the expanding atmosphere than most other lines. This observation confirms Hutchings' identification of very large velocities in the blue-violet spectrum of HD 152408, and in particular his interpretation of a similar feature at He I lambda 3889, which is metastable. The lambda 5876 profile in HD 152408 is compared to those in the similar but less extreme P-Cygni star HD 151804 (O8 Iaf), and in the Wolf-Rayet star HD 151932 (WN7-A). The similarity between the absorption components in HD 152408 and the WN star is striking

  1. A robust star identification algorithm with star shortlisting

    Science.gov (United States)

    Mehta, Deval Samirbhai; Chen, Shoushun; Low, Kay Soon

    2018-05-01

    A star tracker provides the most accurate attitude solution in terms of arc seconds compared to the other existing attitude sensors. When no prior attitude information is available, it operates in "Lost-In-Space (LIS)" mode. Star pattern recognition, also known as star identification algorithm, forms the most crucial part of a star tracker in the LIS mode. Recognition reliability and speed are the two most important parameters of a star pattern recognition technique. In this paper, a novel star identification algorithm with star ID shortlisting is proposed. Firstly, the star IDs are shortlisted based on worst-case patch mismatch, and later stars are identified in the image by an initial match confirmed with a running sequential angular match technique. The proposed idea is tested on 16,200 simulated star images having magnitude uncertainty, noise stars, positional deviation, and varying size of the field of view. The proposed idea is also benchmarked with the state-of-the-art star pattern recognition techniques. Finally, the real-time performance of the proposed technique is tested on the 3104 real star images captured by a star tracker SST-20S currently mounted on a satellite. The proposed technique can achieve an identification accuracy of 98% and takes only 8.2 ms for identification on real images. Simulation and real-time results depict that the proposed technique is highly robust and achieves a high speed of identification suitable for actual space applications.

  2. The multiplicity of massive stars: A high angular resolution survey with the HST fine guidance sensor

    International Nuclear Information System (INIS)

    Aldoretta, E. J.; Gies, D. R.; Henry, T. J.; Jao, W.-C.; Norris, R. P.

    2015-01-01

    We present the results of an all-sky survey made with the Fine Guidance Sensor on the Hubble Space Telescope to search for angularly resolved binary systems among massive stars. The sample of 224 stars is comprised mainly of Galactic O- and B-type stars and luminous blue variables, plus a few luminous stars in the Large Magellanic Cloud. The FGS TRANS mode observations are sensitive to the detection of companions with an angular separation between 0.″01 and 1.″0 and brighter than △m=5. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets (43 of these are new detections). These numbers yield a companion detection frequency of 29% for the FGS survey. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample, and we present estimates of the frequency of multiple systems and the companion frequency for subsets of stars residing in clusters and associations, field stars, and runaway stars. These results confirm the high multiplicity fraction, especially among massive stars in clusters and associations. We show that the period distribution is approximately flat in increments of logP. We identify a number of systems of potential interest for long-term orbital determinations, and we note the importance of some of these companions for the interpretation of the radial velocities and light curves of close binaries that have third companions.

  3. Ultracompact Blue Dwarfs: Galaxy Formation in the Local Universe?

    Science.gov (United States)

    Corbin, Michael

    2004-07-01

    Recent observations suggest that very low-mass galaxies in the local universe are still in the process of formation. To investigate this issue we propose to obtain deep ACS HRC images in the U, V and I bands of a sample of 11 "ultracompact" blue dwarf galaxies {UCBDs} identified in the Sloan Digital Sky Survey. These objects are nearby {z small angular and physical sizes {d POX 186, reveal this tiny object to have a highly disturbed morphlogy indicative of a recent {within 10^8 yr} collision between two small { 100 pc} clumps of stars that could represent the long-sought building blocks predicted by the Press-Schechter model of hierarchical galaxy formation. This collision has also triggered the formation of a "super" star cluster {SSC} at the object's core that may be the progenitor of a globular cluster. POX 186 thus appears to be a very small dwarf galaxy in the process of formation. This exciting discovery strongly motivates HST imaging of a full sample of UCBDs in order to determine if they have morphologies similar to POX 186. HST images are essential for resolving the structure of these objects, including establishing the presence of SSCs. HST also offers the only way to determine their morphologies in the near UV. The spectra of the objects available from the SDSS will also allow us to measure their star formation rates, dust content and metallicities. In addition to potentially providing the first direct evidence of Press-Schechter building blocks, these data could yield insight into the relationship between galaxy and globular cluster formation, and will serve as a test of the recent "downsizing" model of galaxy formation in which the least massive objects are the last to form.

  4. Quirks of dye nomenclature. 1. Evans blue.

    Science.gov (United States)

    Cooksey, C J

    2014-02-01

    The history, origin, identity, chemistry and use of Evans blue dye are described along with the first application to staining by Herbert McLean Evans in 1914. In the 1930s, the dye was marketed under the name, Evans blue dye, which was profoundly more acceptable than the ponderous chemical name.

  5. Blue jay attacks and consumes cedar waxwing

    Science.gov (United States)

    Daniel Saenz; Joshua B. Pierce

    2009-01-01

    Blue Jays (Cyanocitta cristata) are known to be common predators on bird nests (Wilcove 1985, Picman and Schriml 1994). In addition to predation on eggs and nestlings, Blue Jays occasionally prey on fledgling and adult birds (Johnson and Johnson 1976, Dubowy 1985). A majority of reports involve predation on House Sparrows (Passer domesticus) and other small birds (...

  6. The secret of the blue fog

    Science.gov (United States)

    Henrich, Oliver; Marenduzzo, Davide

    2017-04-01

    Why certain liquids turn blue when cooled was a mystery that stumped scientists for more than a century. As Oliver Henrich and Davide Marenduzzo explain, solving the secret of the “blue fog” proved to be an intellectual tour de force - and one that could lead to new types of display devices

  7. Wolf-Rayet Stars

    Science.gov (United States)

    Hamann, Wolf-Rainer; Sander, Andreas; Todt, Helge

    Nearly 150 years ago, the French astronomers Charles Wolf and Georges Rayet described stars with very conspicuous spectra that are dominated by bright and broad emission lines. Meanwhile termed Wolf-Rayet Stars after their discoverers, those objects turned out to represent important stages in the life of massive stars. As the first conference in a long time that was specifically dedicated to Wolf-Rayet stars, an international workshop was held in Potsdam, Germany, from 1.-5. June 2015. About 100 participants, comprising most of the leading experts in the field as well as as many young scientists, gathered for one week of extensive scientific exchange and discussions. Considerable progress has been reported throughout, e.g. on finding such stars, modeling and analyzing their spectra, understanding their evolutionary context, and studying their circumstellar nebulae. While some major questions regarding Wolf-Rayet stars still remain open 150 years after their discovery, it is clear today that these objects are not just interesting stars as such, but also keystones in the evolution of galaxies. These proceedings summarize the talks and posters presented at the Potsdam Wolf-Rayet workshop. Moreover, they also include the questions, comments, and discussions emerging after each talk, thereby giving a rare overview not only about the research, but also about the current debates and unknowns in the field. The Scientific Organizing Committee (SOC) included Alceste Bonanos (Athens), Paul Crowther (Sheffield), John Eldridge (Auckland), Wolf-Rainer Hamann (Potsdam, Chair), John Hillier (Pittsburgh), Claus Leitherer (Baltimore), Philip Massey (Flagstaff), George Meynet (Geneva), Tony Moffat (Montreal), Nicole St-Louis (Montreal), and Dany Vanbeveren (Brussels).

  8. Models of symbiotic stars

    Science.gov (United States)

    Friedjung, Michael

    1993-01-01

    One of the most important features of symbiotic stars is the coexistence of a cool spectral component that is apparently very similar to the spectrum of a cool giant, with at least one hot continuum, and emission lines from very different stages of ionization. The cool component dominates the infrared spectrum of S-type symbiotics; it tends to be veiled in this wavelength range by what appears to be excess emission in D-type symbiotics, this excess usually being attributed to circumstellar dust. The hot continuum (or continua) dominates the ultraviolet. X-rays have sometimes also been observed. Another important feature of symbiotic stars that needs to be explained is the variability. Different forms occur, some variability being periodic. This type of variability can, in a few cases, strongly suggest the presence of eclipses of a binary system. One of the most characteristic forms of variability is that characterizing the active phases. This basic form of variation is traditionally associated in the optical with the veiling of the cool spectrum and the disappearance of high-ionization emission lines, the latter progressively appearing (in classical cases, reappearing) later. Such spectral changes recall those of novae, but spectroscopic signatures of the high-ejection velocities observed for novae are not usually detected in symbiotic stars. However, the light curves of the 'symbiotic nova' subclass recall those of novae. We may also mention in this connection that radio observations (or, in a few cases, optical observations) of nebulae indicate ejection from symbiotic stars, with deviations from spherical symmetry. We shall give a historical overview of the proposed models for symbiotic stars and make a critical analysis in the light of the observations of symbiotic stars. We describe the empirical approach to models and use the observational data to diagnose the physical conditions in the symbiotics stars. Finally, we compare the results of this empirical

  9. Infrared spectrum of an extremely cool white-dwarf star

    Science.gov (United States)

    Hodgkin; Oppenheimer; Hambly; Jameson; Smartt; Steele

    2000-01-06

    White dwarfs are the remnant cores of stars that initially had masses of less than 8 solar masses. They cool gradually over billions of years, and have been suggested to make up much of the 'dark matter' in the halo of the Milky Way. But extremely cool white dwarfs have proved difficult to detect, owing to both their faintness and their anticipated similarity in colour to other classes of dwarf stars. Recent improved models indicate that white dwarfs are much more blue than previously supposed, suggesting that the earlier searches may have been looking for the wrong kinds of objects. Here we report an infrared spectrum of an extremely cool white dwarf that is consistent with the new models. We determine the star's temperature to be 3,500 +/- 200 K, making it the coolest known white dwarf. The kinematics of this star indicate that it is in the halo of the Milky Way, and the density of such objects implied by the serendipitous discovery of this star is consistent with white dwarfs dominating the dark matter in the halo.

  10. First Hours of the GW170817 Kilonova: Why So Blue?

    Science.gov (United States)

    Kohler, Susanna

    2018-04-01

    Now that the hubbub of GW170817 the first coincident detection of gravitational waves and an electromagnetic signature has died down, scientists are left with the task of taking the spectrum-spanning observations and piecing them together into a coherent picture. Researcher Iair Arcavi examines one particular question: what caused the blue color in the early hours of the neutron-star merger?Observations of the GW170817 kilonova by Hubble over a week-long span. [ESA/Hubble]Early ColorWhen the two neutron stars of GW170817 merged in August of last year, they produced not only gravitational waves, but a host of electromagnetic signatures. Chief among these was a flare of emission thought to be powered by the radioactive decay of heavy elements formed in the merger a kilonova.The emission during a kilonova can come from a number of different sources from the heavy-element-rich tidal tails of the disrupting neutron stars, or from fast, light polar jets, or from a wind or a disk outflow and each of these components could reveal different information about the original neutron stars and the merger.Its therefore important that we understand the sources of the emission that we observed in the GW170817 kilonova. In particular, wed like to know where the early blue emission came from that was spotted in the first hours of the kilonova.The combined ultravioletopticalinfrared light curve of the GW170817 kilonova. The rise in the emission occurs on roughly a day-long timescale. [Arcavi 2018]Comparing ModelsTo explore this question, Iair Arcavi (Einstein Fellow at University of California, Santa Barbara and Las Cumbres Observatory) compiled infrared through ultraviolet observations of the GW170817 kilonova from nearly 20 different telescopes. To try to distinguish between possible sources, Arcavi then compared the resulting combined light curves to a variety of models.Arcavi found that the light curves for the GW170817 kilonova indicate an initial 24-hour rise of emission. This

  11. Ultracompact Blue Dwarf Galaxies: Hubble Space Telescope Imaging and Stellar Population Analysis

    Science.gov (United States)

    Corbin, Michael R.; Vacca, William D.; Cid Fernandes, Roberto; Hibbard, John E.; Somerville, Rachel S.; Windhorst, Rogier A.

    2006-11-01

    We present deep Hubble Space Telescope (HST) Advanced Camera for Surveys/High Resolution Channel U-, narrow-V-, and I-band images of nine ``ultracompact'' blue dwarf galaxies (UCBDs) selected from the Sloan Digital Sky Survey (SDSS). We define UCBDs as local (zPOX 186, but the structure of several of them suggests that their current star formation has been triggered by the collisions/mergers of smaller clumps of stars. In one case, HS 0822+3542, the images resolve what may be two small (~100 pc) components that have recently collided, supporting this interpretation. In six of the objects much of the star formation is concentrated in young massive clusters, contributing to their compactness in ground-based images. The evidence that the galaxies consist mainly of ~10 Gyr old stars establishes that they are not protogalaxies, forming their first generation of stars. Their low metallicities are more likely to be the result of the escape of supernova ejecta, rather than youth.

  12. On the Nature and History of Blue Amorphous Galaxies

    Science.gov (United States)

    Marlowe, Amanda True

    1998-07-01

    Dwarf galaxies play an important role in our understanding of galaxy formation and evolution. We have embarked on a systematic study of 12 blue amorphous galaxies (BAGs) whose properties suggest that they are dwarf galaxies in a starburst or post-burst state. It seems likely that BAGs are related to other 'starburst' dwarfs such as blue compact dwarfs (BCDs) and HII galaxies. The BAGs in our sample, however, are considerably closer than BCDs and HII galaxies in other samples, and therefore easier to study. These galaxies may offer important insights into dwarf galaxy evolution. In an effort to clarify the role of BAGs in evolutionary scenarios for dwarf galaxies, we present and analyze Hα and UBVI data for our sample. BAGs, like BCDs and HII galaxies, have surface brightness profiles that are exponential in the outer regions but have a predominantly blue central blue excess, suggesting a young burst in an older, redder galaxy. Seven of the galaxies have the bubble or filamentary Hα morphology and double peaked emission lines that are the signature of superbubbles or superwind activity. These galaxies are typically the ones with the strongest central excesses. The starbursting regions are young events compared to the older underlying galaxy, which follow an exponential surface brightness law. Not all of the galaxies develop superwinds: the appearance of superwinds is most sensitive to the concentration and rate of star formation in the starbursting core. The underlying exponential galaxies are very similar to those found in BCDs and HII galaxies, though the 'burst' colors are slightly redder than those found in HII galaxies. BAGs are structurally similar to BCDs and HII galaxies. How BAGs fit into the dwarf galaxy evolutionary debate is less clear. While some compact dIs have properties similar to those of the underlying exponential galaxy in our sample, issues such as mass loss from superwinds, the impact of the starbursting core on the underlying galaxy, and

  13. Circulation of Stars

    Science.gov (United States)

    Boitani, P.

    2016-01-01

    Since the dawn of man, contemplation of the stars has been a primary impulse in human beings, who proliferated their knowledge of the stars all over the world. Aristotle sees this as the product of primeval and perennial “wonder” which gives rise to what we call science, philosophy, and poetry. Astronomy, astrology, and star art (painting, architecture, literature, and music) go hand in hand through millennia in all cultures of the planet (and all use catasterisms to explain certain phenomena). Some of these developments are independent of each other, i.e., they take place in one culture independently of others. Some, on the other hand, are the product of the “circulation of stars.” There are two ways of looking at this. One seeks out forms, the other concentrates on the passing of specific lore from one area to another through time. The former relies on archetypes (for instance, with catasterism), the latter constitutes a historical process. In this paper I present some of the surprising ways in which the circulation of stars has occurred—from East to West, from East to the Far East, and from West to East, at times simultaneously.

  14. Tapered photonic crystal fibers for blue-enhanced supercontinuum generation

    DEFF Research Database (Denmark)

    Møller, Uffe; Sørensen, Simon Toft; Larsen, Casper

    2012-01-01

    Tapering of photonic crystal fibers is an effective way of shifting the blue edge of a supercontinuum spectrum down in the deep-blue. We discuss the optimum taper profile for enhancing the power in the blue edge....

  15. Four new Delta Scuti stars

    Science.gov (United States)

    Schutt, R. L.

    1991-01-01

    Four new Delta Scuti stars are reported. Power, modified into amplitude, spectra, and light curves are used to determine periodicities. A complete frequency analysis is not performed due to the lack of a sufficient time base in the data. These new variables help verify the many predictions that Delta Scuti stars probably exist in prolific numbers as small amplitude variables. Two of these stars, HR 4344 and HD 107513, are possibly Am stars. If so, they are among the minority of variable stars which are also Am stars.

  16. Red Misfits in the Sloan Digital Sky Survey: properties of star-forming red galaxies

    Science.gov (United States)

    Evans, Fraser A.; Parker, Laura C.; Roberts, Ian D.

    2018-06-01

    We study Red Misfits, a population of red, star-forming galaxies in the local Universe. We classify galaxies based on inclination-corrected optical colours and specific star formation rates derived from the Sloan Digital Sky Survey Data Release 7. Although the majority of blue galaxies are star-forming and most red galaxies exhibit little to no ongoing star formation, a small but significant population of galaxies (˜11 per cent at all stellar masses) are classified as red in colour yet actively star-forming. We explore a number of properties of these galaxies and demonstrate that Red Misfits are not simply dusty or highly inclined blue cloud galaxies or quiescent red galaxies with poorly constrained star formation. The proportion of Red Misfits is nearly independent of environment, and this population exhibits both intermediate morphologies and an enhanced likelihood of hosting an active galactic nucleus. We conclude that Red Misfits are a transition population, gradually quenching on their way to the red sequence and this quenching is dominated by internal processes rather than environmentally driven processes. We discuss the connection between Red Misfits and other transition galaxy populations, namely S0s, red spirals, and green valley galaxies.

  17. What Happens in the Atmospheres of Hot Horizontal Branch Stars Near 20, 000K?

    Science.gov (United States)

    Brown, Thomas

    2016-10-01

    In the color-magnitude diagrams (CMDs) of many globular clusters, the horizontal branch (HB) exhibits a long blue tail extending to high effective temperatures. In such clusters, two discontinuities appear within the HB locus. The first discontinuity occurs at 12,000K, and was discovered by Grundahl et al. (1998). It is associated with the radiative levitation of metals and the gravitational settling of helium in the atmospheres of HB stars hotter than 12,000K. The hot subdwarf stars of the Galactic field population exhibit the same phenomenon. The second discontinuity occurs at 20,000K, and was discovered by Momany et al. (2002). Its origin is unknown, but it appears at the same effective temperature in all globular clusters hosting HB stars near 20,000K, regardless of cluster properties (age, chemical composition, mass, etc.). We propose STIS long-slit spectroscopy of 6 HB stars that straddle this feature in the HB distribution of omega Cen, the nearest globular cluster where the feature is well populated. With this approach, we can efficiently obtain high-quality UV and blue spectra that span the full wavelength range of the photometric bands where this CMD feature is most prominent - a range this is only accessible by HST. The resulting spectra will unambiguously reveal the nature of this phenomenon - one that is universal in the atmospheres of hot evolved stars - and will yield new insight into the role of diffusion and radiative levitation in these stars.

  18. Neutron star/red giant encounters in globular clusters

    International Nuclear Information System (INIS)

    Bailyn, C.D.

    1988-01-01

    The author presents a simple expression for the amount by which xsub(crit) is diminished as a star evolves xsub(crit) Rsub(crit)/R*, where Rsub(crit) is the maximum distance of closest approach between two stars for which the tidal energy is sufficient to bind the system, and R* is the radius of the star on which tides are being raised. Also it is concluded that tidal capture of giants by neutron stars resulting in binary systems is unlikely in globular clusters. However, collisions between neutron stars and red giants, or an alternative process involving tidal capture of a main-sequence star into an initially detached binary system, may result either in rapidly rotating neutron stars or in white dwarf/neutron star binaries. (author)

  19. Can greening of aquaculture sequester blue carbon?

    Science.gov (United States)

    Ahmed, Nesar; Bunting, Stuart W; Glaser, Marion; Flaherty, Mark S; Diana, James S

    2017-05-01

    Globally, blue carbon (i.e., carbon in coastal and marine ecosystems) emissions have been seriously augmented due to the devastating effects of anthropogenic pressures on coastal ecosystems including mangrove swamps, salt marshes, and seagrass meadows. The greening of aquaculture, however, including an ecosystem approach to Integrated Aquaculture-Agriculture (IAA) and Integrated Multi-Trophic Aquaculture (IMTA) could play a significant role in reversing this trend, enhancing coastal ecosystems, and sequestering blue carbon. Ponds within IAA farming systems sequester more carbon per unit area than conventional fish ponds, natural lakes, and inland seas. The translocation of shrimp culture from mangrove swamps to offshore IMTA could reduce mangrove loss, reverse blue carbon emissions, and in turn increase storage of blue carbon through restoration of mangroves. Moreover, offshore IMTA may create a barrier to trawl fishing which in turn could help restore seagrasses and further enhance blue carbon sequestration. Seaweed and shellfish culture within IMTA could also help to sequester more blue carbon. The greening of aquaculture could face several challenges that need to be addressed in order to realize substantial benefits from enhanced blue carbon sequestration and eventually contribute to global climate change mitigation.

  20. Atomic diffusion in stars

    CERN Document Server

    Michaud, Georges; Richer, Jacques

    2015-01-01

    This book gives an overview of atomic diffusion, a fundamental physical process, as applied to all types of stars, from the main sequence to neutron stars. The superficial abundances of stars as well as their evolution can be significantly affected. The authors show where atomic diffusion plays an essential role and how it can be implemented in modelling.  In Part I, the authors describe the tools that are required to include atomic diffusion in models of stellar interiors and atmospheres. An important role is played by the gradient of partial radiative pressure, or radiative acceleration, which is usually neglected in stellar evolution. In Part II, the authors systematically review the contribution of atomic diffusion to each evolutionary step. The dominant effects of atomic diffusion are accompanied by more subtle effects on a large number of structural properties throughout evolution. One of the goals of this book is to provide the means for the astrophysicist or graduate student to evaluate the importanc...

  1. Dynamical Boson Stars

    Directory of Open Access Journals (Sweden)

    Steven L. Liebling

    2012-05-01

    Full Text Available The idea of stable, localized bundles of energy has strong appeal as a model for particles. In the 1950s, John Wheeler envisioned such bundles as smooth configurations of electromagnetic energy that he called geons, but none were found. Instead, particle-like solutions were found in the late 1960s with the addition of a scalar field, and these were given the name boson stars. Since then, boson stars find use in a wide variety of models as sources of dark matter, as black hole mimickers, in simple models of binary systems, and as a tool in finding black holes in higher dimensions with only a single Killing vector. We discuss important varieties of boson stars, their dynamic properties, and some of their uses, concentrating on recent efforts.

  2. GRACE star camera noise

    Science.gov (United States)

    Harvey, Nate

    2016-08-01

    Extending results from previous work by Bandikova et al. (2012) and Inacio et al. (2015), this paper analyzes Gravity Recovery and Climate Experiment (GRACE) star camera attitude measurement noise by processing inter-camera quaternions from 2003 to 2015. We describe a correction to star camera data, which will eliminate a several-arcsec twice-per-rev error with daily modulation, currently visible in the auto-covariance function of the inter-camera quaternion, from future GRACE Level-1B product releases. We also present evidence supporting the argument that thermal conditions/settings affect long-term inter-camera attitude biases by at least tens-of-arcsecs, and that several-to-tens-of-arcsecs per-rev star camera errors depend largely on field-of-view.

  3. Molecules in stars

    International Nuclear Information System (INIS)

    Tsuji, T.

    1986-01-01

    Recently, research related to molecules in stars has rapidly expanded because of progress in related fields. For this reason, it is almost impossible to cover all the topics related to molecules in stars. Thus, here the authors focus their attention on molecules in the atmospheres of cool stars and do not cover in any detail topics related to circumstellar molecules originating from expanding envelopes located far from the stellar surface. However, the authors do discuss molecules in quasi-static circumstellar envelopes (a recently discovered new component of circumstellar envelopes) located near the stellar surface, since molecular lines originating from such envelopes show little velocity shift relative to photospheric lines, and hence they directly affect the interpretation and analysis of stellar spectra

  4. CARBON NEUTRON STAR ATMOSPHERES

    International Nuclear Information System (INIS)

    Suleimanov, V. F.; Klochkov, D.; Werner, K.; Pavlov, G. G.

    2014-01-01

    The accuracy of measuring the basic parameters of neutron stars is limited in particular by uncertainties in the chemical composition of their atmospheres. For example, the atmospheres of thermally emitting neutron stars in supernova remnants might have exotic chemical compositions, and for one of them, the neutron star in Cas A, a pure carbon atmosphere has recently been suggested by Ho and Heinke. To test this composition for other similar sources, a publicly available detailed grid of the carbon model atmosphere spectra is needed. We have computed this grid using the standard local thermodynamic equilibrium approximation and assuming that the magnetic field does not exceed 10 8  G. The opacities and pressure ionization effects are calculated using the Opacity Project approach. We describe the properties of our models and investigate the impact of the adopted assumptions and approximations on the emergent spectra

  5. Instability and star evolution

    International Nuclear Information System (INIS)

    Mirzoyan, L.V.

    1981-01-01

    The observational data are discussed which testify that the phenomena of dynamical instability of stars and stellar systems are definite manifestations of their evolution. The study of these phenomena has shown that the instability is a regular phase of stellar evolution. It has resulted in the recognition of the most important regularities of the process of star formation concerning its nature. This became possible due to the discovery in 1947 of stellar associations in our Galaxy. The results of the study of the dynamical instability of stellar associations contradict the predictions of classical hypothesis of stellar condensation. These data supplied a basis for a new hypothesis on the formation of stars and nebulae by the decay of superdense protostars [ru

  6. The twinkling of stars

    International Nuclear Information System (INIS)

    Jakeman, E.; Parry, G.; Pike, E.R.; Pusey, P.N.

    1978-01-01

    This article collects together some of the main ideas and experimental results on the twinkling of stars. Statistical methods are used to characterise the features of the scintillation and to investigate the ways in which these depend on the zenith angle of the star, the bandwidth of the light and various other parameters. Some new results are included which demonstrate the advantages of using photon counting methods in experiments on stellar scintillation. Since the twinkling of stars is a consequence of the turbulence in the Earth's magnetic atmosphere then measurements can be used to deduce some features of the structure of the turbulence. Some of the experiments designed to do this are discussed and the results reported. (author)

  7. Hot HB Stars in Globular Clusters: Physical Parameters and Consequences for Theory. VI; The Second Parameter Pair M 3 and M 13

    Science.gov (United States)

    Moehler, S.; Landsman, W. B.; Sweigart, A. V.; Grundahl, F.

    2003-01-01

    We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M 13 and M 3, which form a famous "second parameter" pair. F rom the spectra and Stromgren photometry we derived - for the first time in M 13 - atmospheric parameters (effective temperature and surface gravity). For stars with Stromgren temperatures between 10,000 and 12,000 K we found excellent agreement between the atmospheric parameters derived from Stromgren photometry and those derived from Balmer line profile fits. However, for cooler stars there is a disagreement in the parameters derived by the two methods, for which we have no satisfactory explanation. Stars hotter than 12,000 K show evidence for helium depletion and iron enrichment, both in M 3 and M 13. Accounting for the iron enrichment substantially improves the agreement with canonical evolutionary models, although the derived gravities and masses are still somewhat too low. This remaining discrepancy may be an indication that scaled-solar metal-rich model atmospheres do not adequately represent the highly non-solar abundance ratios found in blue HB stars affected by diffusion. We discuss the effects of an enhancement in the envelope helium abundance on the atmospheric parameters of the blue HB stars, as might be caused by deep mixing on the red giant branch or primordial pollution from an earlier generation of intermediate mass asymptotic giant branch stars. Key words. Stars: atmospheres - Stars: evolution - Stars: horizontal branch - Globular clusters: individual: M 3 - Globular clusters: individual: M 13

  8. Results of a search for γ Dor and δ SCT stars with the Kepler spacecraft

    Energy Technology Data Exchange (ETDEWEB)

    Bradley, P. A.; Miles, L. F. [XCP-6, MS F-699 Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Guzik, J. A. [XTD-NTA, MS T-086 Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Uytterhoeven, K. [Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain and Departamento de Astrofisica, Universidad de La Laguna, E-38200 La Laguna, Tenerife (Spain); Jackiewicz, J. [New Mexico State University, Las Cruces, NM 88003 (United States); Kinemuchi, K., E-mail: pbradley@lanl.gov [Apache Point Observatory, Sunspot, NM 88349 (United States)

    2015-02-01

    The light curves of 2768 stars with effective temperatures and surface gravities placing them near the gamma Doradus (γ Dor)/delta Scuti (δ Sct) instability region were observed as part of the Kepler Guest Observer program from Cycles 1 through 5. The light curves were analyzed in a uniform manner to search for γ Dor, δ Sct, and hybrid star pulsations. The γ Dor, δ Sct, and hybrid star pulsations extend asteroseismology to stars slightly more massive (1.4–2.5 M{sub ⊙}) than our Sun. We find 207 γ Dor, 84 δ Sct, and 32 hybrid candidate stars. Many of these stars are cooler than the red edge of the γ Dor instability strip as determined from ground-based observations made before Kepler. A few of our γ Dor candidate stars lie on the hot side of the ground-based γ Dor instability strip. The hybrid candidate stars cover the entire region between 6200 K and the blue edge of the ground-based δ Sct instability strip. None of our candidate stars are hotter than the hot edge of the ground-based δ Sct instability strip. Our discoveries, coupled with the work of others, show that Kepler has discovered over 2000 γ Dor, δ Sct, and hybrid star candidates in the 116 square degree Kepler field of view. We found relatively few variable stars fainter than magnitude 15, which may be because they are far enough away to lie between spiral arms in our Galaxy, where there would be fewer stars.

  9. Results of a search for γ Dor and δ SCT stars with the Kepler spacecraft

    International Nuclear Information System (INIS)

    Bradley, P. A.; Miles, L. F.; Guzik, J. A.; Uytterhoeven, K.; Jackiewicz, J.; Kinemuchi, K.

    2015-01-01

    The light curves of 2768 stars with effective temperatures and surface gravities placing them near the gamma Doradus (γ Dor)/delta Scuti (δ Sct) instability region were observed as part of the Kepler Guest Observer program from Cycles 1 through 5. The light curves were analyzed in a uniform manner to search for γ Dor, δ Sct, and hybrid star pulsations. The γ Dor, δ Sct, and hybrid star pulsations extend asteroseismology to stars slightly more massive (1.4–2.5 M ⊙ ) than our Sun. We find 207 γ Dor, 84 δ Sct, and 32 hybrid candidate stars. Many of these stars are cooler than the red edge of the γ Dor instability strip as determined from ground-based observations made before Kepler. A few of our γ Dor candidate stars lie on the hot side of the ground-based γ Dor instability strip. The hybrid candidate stars cover the entire region between 6200 K and the blue edge of the ground-based δ Sct instability strip. None of our candidate stars are hotter than the hot edge of the ground-based δ Sct instability strip. Our discoveries, coupled with the work of others, show that Kepler has discovered over 2000 γ Dor, δ Sct, and hybrid star candidates in the 116 square degree Kepler field of view. We found relatively few variable stars fainter than magnitude 15, which may be because they are far enough away to lie between spiral arms in our Galaxy, where there would be fewer stars.

  10. Infiltrating giant cellular blue naevus.

    Science.gov (United States)

    Bittencourt, A L; Monteiro, D A; De Pretto, O J

    2007-01-01

    Cellular blue naevi (CBN) measure 1-2 cm in diameter and affect the dermis, occasionally extending into the subcutaneous fat. The case of a 14-year-old boy with a giant CBN (GCBN) involving the right half of the face, the jugal mucosa and the lower eyelid with a tumour that had infiltrated the bone and the maxillary and ethmoidal sinuses is reported. Biopsies were taken from the skin, jugal mucosa and maxillary sinus. The following markers were used in the immunohistochemical evaluation: CD34, CD56, HMB-45, anti-S100, A-103, Melan A and MIB-1. The biopsy specimens showed a biphasic pattern affecting the lower dermis, subcutaneous fat, skeletal muscle, bone, jugal mucosa and maxillary sinus, but there was no histological evidence of malignancy. The tumour cells were CD34-, CD56-, HMB45+, anti-S100+ and A-103+. Melan A was focally expressed. No positive MIB-1 cells were identified. The present case shows that GCBN may infiltrate deeply, with no evidence of malignancy.

  11. Weighing the Smallest Stars

    Science.gov (United States)

    2005-01-01

    VLT Finds Young, Very Low Mass Objects Are Twice As Heavy As Predicted Summary Thanks to the powerful new high-contrast camera installed at the Very Large Telescope, photos have been obtained of a low-mass companion very close to a star. This has allowed astronomers to measure directly the mass of a young, very low mass object for the first time. The object, more than 100 times fainter than its host star, is still 93 times as massive as Jupiter. And it appears to be almost twice as heavy as theory predicts it to be. This discovery therefore suggests that, due to errors in the models, astronomers may have overestimated the number of young "brown dwarfs" and "free floating" extrasolar planets. PR Photo 03/05: Near-infrared image of AB Doradus A and its companion (NACO SDI/VLT) A winning combination A star can be characterised by many parameters. But one is of uttermost importance: its mass. It is the mass of a star that will decide its fate. It is thus no surprise that astronomers are keen to obtain a precise measure of this parameter. This is however not an easy task, especially for the least massive ones, those at the border between stars and brown dwarf objects. Brown dwarfs, or "failed stars", are objects which are up to 75 times more massive than Jupiter, too small for major nuclear fusion processes to have ignited in its interior. To determine the mass of a star, astronomers generally look at the motion of stars in a binary system. And then apply the same method that allows determining the mass of the Earth, knowing the distance of the Moon and the time it takes for its satellite to complete one full orbit (the so-called "Kepler's Third Law"). In the same way, they have also measured the mass of the Sun by knowing the Earth-Sun distance and the time - one year - it takes our planet to make a tour around the Sun. The problem with low-mass objects is that they are very faint and will often be hidden in the glare of the brighter star they orbit, also when viewed

  12. General Relativity and Compact Stars

    International Nuclear Information System (INIS)

    Glendenning, Norman K.

    2005-01-01

    Compact stars--broadly grouped as neutron stars and white dwarfs--are the ashes of luminous stars. One or the other is the fate that awaits the cores of most stars after a lifetime of tens to thousands of millions of years. Whichever of these objects is formed at the end of the life of a particular luminous star, the compact object will live in many respects unchanged from the state in which it was formed. Neutron stars themselves can take several forms--hyperon, hybrid, or strange quark star. Likewise white dwarfs take different forms though only in the dominant nuclear species. A black hole is probably the fate of the most massive stars, an inaccessible region of spacetime into which the entire star, ashes and all, falls at the end of the luminous phase. Neutron stars are the smallest, densest stars known. Like all stars, neutron stars rotate--some as many as a few hundred times a second. A star rotating at such a rate will experience an enormous centrifugal force that must be balanced by gravity or else it will be ripped apart. The balance of the two forces informs us of the lower limit on the stellar density. Neutron stars are 10 14 times denser than Earth. Some neutron stars are in binary orbit with a companion. Application of orbital mechanics allows an assessment of masses in some cases. The mass of a neutron star is typically 1.5 solar masses. They can therefore infer their radii: about ten kilometers. Into such a small object, the entire mass of our sun and more, is compressed

  13. NICMOS PEERS INTO HEART OF DYING STAR

    Science.gov (United States)

    2002-01-01

    The Egg Nebula, also known as CRL 2688, is shown on the left as it appears in visible light with the Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2) and on the right as it appears in infrared light with Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS). Since infrared light is invisible to humans, the NICMOS image has been assigned colors to distinguish different wavelengths: blue corresponds to starlight reflected by dust particles, and red corresponds to heat radiation emitted by hot molecular hydrogen. Objects like the Egg Nebula are helping astronomers understand how stars like our Sun expel carbon and nitrogen -- elements crucial for life -- into space. Studies on the Egg Nebula show that these dying stars eject matter at high speeds along a preferred axis and may even have multiple jet-like outflows. The signature of the collision between this fast-moving material and the slower outflowing shells is the glow of hydrogen molecules captured in the NICMOS image. The distance between the tip of each jet is approximately 200 times the diameter of our solar system (out to Pluto's orbit). Credits: Rodger Thompson, Marcia Rieke, Glenn Schneider, Dean Hines (University of Arizona); Raghvendra Sahai (Jet Propulsion Laboratory); NICMOS Instrument Definition Team; and NASA Image files in GIF and JPEG format and captions may be accessed on the Internet via anonymous ftp from ftp.stsci.edu in /pubinfo.

  14. Atmospheres of central stars

    International Nuclear Information System (INIS)

    Hummer, D.G.

    1978-01-01

    The author presents a brief summary of atmospheric models that are of possible relevance to the central stars of planetary nebulae, and then discusses the extent to which these models accord with the observations of both nebulae and central stars. Particular attention is given to the significance of the very high Zanstra temperature implied by the nebulae He II lambda 4686 A line, and to the discrepancy between the Zanstra He II temperature and the considerably lower temperatures suggested by the appearance of the visual spectrum for some of these objects. (Auth.)

  15. The Drifting Star

    Science.gov (United States)

    2008-04-01

    By studying in great detail the 'ringing' of a planet-harbouring star, a team of astronomers using ESO's 3.6-m telescope have shown that it must have drifted away from the metal-rich Hyades cluster. This discovery has implications for theories of star and planet formation, and for the dynamics of our Milky Way. ESO PR Photo 09a/08 ESO PR Photo 09a/08 Iota Horologii The yellow-orange star Iota Horologii, located 56 light-years away towards the southern Horologium ("The Clock") constellation, belongs to the so-called "Hyades stream", a large number of stars that move in the same direction. Previously, astronomers using an ESO telescope had shown that the star harbours a planet, more than 2 times as large as Jupiter and orbiting in 320 days (ESO 12/99). But until now, all studies were unable to pinpoint the exact characteristics of the star, and hence to understand its origin. A team of astronomers, led by Sylvie Vauclair from the University of Toulouse, France, therefore decided to use the technique of 'asteroseismology' to unlock the star's secrets. "In the same way as geologists monitor how seismic waves generated by earthquakes propagate through the Earth and learn about the inner structure of our planet, it is possible to study sound waves running through a star, which forms a sort of large, spherical bell," says Vauclair. The 'ringing' from this giant musical instrument provides astronomers with plenty of information about the physical conditions in the star's interior. And to 'listen to the music', the astronomers used one of the best instruments available. The observations were conducted in November 2006 during 8 consecutive nights with the state-of-the-art HARPS spectrograph mounted on the ESO 3.6-m telescope at La Silla. Up to 25 'notes' could be identified in the unique dataset, most of them corresponding to waves having a period of about 6.5 minutes. These observations allowed the astronomers to obtain a very precise portrait of Iota Horologii: its

  16. The star of Bethlehem

    International Nuclear Information System (INIS)

    Hughes, D.W.

    1976-01-01

    It is stated that the cause and form of the star are still uncertain. The astrologically significant triple conjunction of Saturn and Jupiter in the constellation of Pisces appears to be the most likely explanation, although the two comets of March 5 BC and April 4 BC cannot be dismissed, nor can the possibility that the 'star' was simply legendary. The conjunction occurred in 7 BC and there are indications that Jesus Christ was probably born in the Autumn of that year, around October 7 BC. (U.K.)

  17. The formation of stars

    CERN Document Server

    Stahler, Steven W

    2008-01-01

    This book is a comprehensive treatment of star formation, one of the most active fields of modern astronomy. The reader is guided through the subject in a logically compelling manner. Starting from a general description of stars and interstellar clouds, the authors delineate the earliest phases of stellar evolution. They discuss formation activity not only in the Milky Way, but also in other galaxies, both now and in the remote past. Theory and observation are thoroughly integrated, with the aid of numerous figures and images. In summary, this volume is an invaluable resource, both as a text f

  18. Chaplygin dark star

    International Nuclear Information System (INIS)

    Bertolami, O.; Paramos, J.

    2005-01-01

    We study the general properties of a spherically symmetric body described through the generalized Chaplygin equation of state. We conclude that such an object, dubbed generalized Chaplygin dark star, should exist within the context of the generalized Chaplygin gas (GCG) model of unification of dark energy and dark matter, and derive expressions for its size and expansion velocity. A criteria for the survival of the perturbations in the GCG background that give origin to the dark star are developed, and its main features are analyzed

  19. Corneal edema and permanent blue discoloration of a silicone intraocular lens by methylene blue.

    Science.gov (United States)

    Stevens, Scott; Werner, Liliana; Mamalis, Nick

    2007-01-01

    To report a silicone intraocular lens (IOL) stained blue by inadvertent intraoperative use of methylene blue instead of trypan blue and the results of experimental staining of various lens materials with different concentrations of the same dye. A "blue dye" was used to enhance visualization during capsulorhexis in a patient undergoing phacoemulsification with implantation of a three-piece silicone lens. Postoperatively, the patient presented with corneal edema and a discolored IOL. Various IOL materials were experimentally stained using methylene blue. Sixteen lenses (4 silicone, 4 hydrophobic acrylic, 4 hydrophilic acrylic, and 4 polymethylmethacrylate) were immersed in 0.5 mL of methylene blue at concentrations of 1%, 0.1%, 0.01%, and 0.001%. These lenses were grossly and microscopically evaluated for discoloration 6 and 24 hours after immersion. The corneal edema resolved within 1 month after the initial surgical procedure. After explantation, gross and microscopic analyses of the explanted silicone lens revealed that its surface and internal substance had been permanently stained blue. In the experimental study, all of the lenses except the polymethylmethacrylate lenses were permanently stained by methylene blue. The hydrophilic acrylic lenses showed the most intense blue staining in all dye concentrations. This is the first clinicopathological report of IOL discoloration due to intraocular use of methylene blue. This and other tissue dyes may be commonly found among surgical supplies in the operating room and due diligence is necessary to avoid mistaking these dyes for those commonly used during ocular surgery.

  20. ENERGY STAR Certified Commercial Dishwashers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 2.0 ENERGY STAR Program Requirements for Commercial Dishwashers that are effective as of...

  1. ENERGY STAR Certified Commercial Ovens

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 2.2 ENERGY STAR Program Requirements for Commercial Ovens that are effective as of...

  2. Star Formation in Irregular Galaxies.

    Science.gov (United States)

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  3. ENERGY STAR Certified Commercial Boilers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 1.0 ENERGY STAR Program Requirements for Commercial Boilers that are effective as of...

  4. ENERGY STAR Certified Commercial Griddles

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 1.2 ENERGY STAR Program Requirements for Commercial Griddles that are effective as of May...

  5. ENERGY STAR Certified Smart Thermostats

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 1.0 ENERGY STAR Program Requirements for Connected Thermostats that are effective as of...

  6. ENERGY STAR Certified Residential Dishwashers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 6.0 ENERGY STAR Program Requirements for Residential Dishwashers that are effective as of...

  7. ENERGY STAR Certified Roof Products

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Roof Products that are effective as of July 1,...

  8. ENERGY STAR Certified Pool Pumps

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 1.1 ENERGY STAR Program Requirements for Pool Pumps that are effective as of February 15,...

  9. Understand B-type stars

    Science.gov (United States)

    1982-01-01

    When observations of B stars made from space are added to observations made from the ground and the total body of observational information is confronted with theoretical expectations about B stars, it is clear that nonthermal phenomena occur in the atmospheres of B stars. The nature of these phenomena and what they imply about the physical state of a B star and how a B star evolves are examined using knowledge of the spectrum of a B star as a key to obtaining an understanding of what a B star is like. Three approaches to modeling stellar structure (atmospheres) are considered, the characteristic properties of a mantle, and B stars and evolution are discussed.

  10. ENERGY STAR Certified Imaging Equipment

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 2.0 ENERGY STAR Program Requirements for Imaging Equipment that are effective as of...

  11. ENERGY STAR Certified Vending Machines

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.1 ENERGY STAR Program Requirements for Refrigerated Beverage Vending Machines that are...

  12. ENERGY STAR Certified Water Coolers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 2.0 ENERGY STAR Program Requirements for Water Coolers that are effective as of February...

  13. ENERGY STAR Certified Audio Video

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Audio Video Equipment that are effective as of...

  14. ENERGY STAR Certified Ceiling Fans

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.1 ENERGY STAR Program Requirements for Ceiling Fans that are effective as of April 1,...

  15. ENERGY STAR Certified Ventilating Fans

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 4.0 ENERGY STAR Program Requirements for Ventilating Fans that are effective as of...

  16. ENERGY STAR Certified Commercial Fryers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Commercial Fryers that are effective as of...

  17. Lithium in the barium stars

    International Nuclear Information System (INIS)

    Pinsonneault, M.H.; Sneden, C.

    1984-01-01

    New high-resolution spectra of the lithium resonance doublet have provided lithium abundances or upper limits for 26 classical and mild barium stars. The lithium lines always are present in the classical barium stars. Lithium abundances in these stars obey a trend with stellar masses consistent with that previously derived for ordinary K giants. This supports the notion that classical barium stars are post-core-He-flash or core-He-burning stars. Lithium contents in the mild barium stars, however, often are much smaller than those of the classical barium stars sometimes only upper limits may be determined. The cause for this difference is not easily understood, but may be related to more extensive mass loss by the mild barium stars. 45 references

  18. Which of Kepler's Stars Flare?

    Science.gov (United States)

    Kohler, Susanna

    2017-12-01

    The habitability of distant exoplanets is dependent upon many factors one of which is the activity of their host stars. To learn about which stars are most likely to flare, a recent study examines tens of thousands of stellar flares observed by Kepler.Need for a Broader SampleArtists rendering of a flaring dwarf star. [NASAs Goddard Space Flight Center/S. Wiessinger]Most of our understanding of what causes a star to flare is based on observations of the only star near enough to examine in detail the Sun. But in learning from a sample size of one, a challenge arises: we must determine which conclusions are unique to the Sun (or Sun-like stars), and which apply to other stellar types as well.Based on observations and modeling, astronomers think that stellar flares result from the reconnection of magnetic field lines in a stars outer atmosphere, the corona. The magnetic activity is thought to be driven by a dynamo caused by motions in the stars convective zone.HR diagram of the Kepler stars, with flaring main-sequence (yellow), giant (red) and A-star (green) stars in the authors sample indicated. [Van Doorsselaere et al. 2017]To test whether these ideas are true generally, we need to understand what types of stars exhibit flares, and what stellar properties correlate with flaring activity. A team of scientists led by Tom Van Doorsselaere (KU Leuven, Belgium) has now used an enormous sample of flares observed by Kepler to explore these statistics.Intriguing TrendsVan Doorsselaere and collaborators used a new automated flare detection and characterization algorithm to search through the raw light curves from Quarter 15 of the Kepler mission, building a sample of 16,850 flares on 6,662 stars. They then used these to study the dependence of the flare occurrence rate, duration, energy, and amplitude on the stellar spectral type and rotation period.This large statistical study led the authors to several interesting conclusions, including:Flare star incidence rate as a a

  19. ENERGY STAR Certified Residential Freezers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 5.0 ENERGY STAR Program Requirements for Residential Refrigerators and Freezers that are...

  20. ENERGY STAR Certified Residential Refrigerators

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 5.0 ENERGY STAR Program Requirements for Residential Refrigerators and Freezers that are...

  1. Distances of Dwarf Carbon Stars

    Science.gov (United States)

    Harris, Hugh C.; Dahn, Conard C.; Subasavage, John P.; Munn, Jeffrey A.; Canzian, Blaise J.; Levine, Stephen E.; Monet, Alice B.; Pier, Jeffrey R.; Stone, Ronald C.; Tilleman, Trudy M.; Hartkopf, William I.

    2018-06-01

    Parallaxes are presented for a sample of 20 nearby dwarf carbon stars. The inferred luminosities cover almost two orders of magnitude. Their absolute magnitudes and tangential velocities confirm prior expectations that some originate in the Galactic disk, although more than half of this sample are halo stars. Three stars are found to be astrometric binaries, and orbital elements are determined; their semimajor axes are 1–3 au, consistent with the size of an AGB mass-transfer donor star.

  2. RADIAL STABILITY IN STRATIFIED STARS

    International Nuclear Information System (INIS)

    Pereira, Jonas P.; Rueda, Jorge A.

    2015-01-01

    We formulate within a generalized distributional approach the treatment of the stability against radial perturbations for both neutral and charged stratified stars in Newtonian and Einstein's gravity. We obtain from this approach the boundary conditions connecting any two phases within a star and underline its relevance for realistic models of compact stars with phase transitions, owing to the modification of the star's set of eigenmodes with respect to the continuous case

  3. Spectral Confirmation of New Galactic LBV and WN Stars Associated With Mid-IR Nebulae

    Science.gov (United States)

    Stringfellow, Guy; Gvaramadze, Vasilii V.

    2014-08-01

    Luminous Blue Variable (LBV) stars represent an extremely rare class and short-lived phase in the lives of very luminous massive stars with high mass loss rates. Extragalactic LBVs are responsible for producing false supernovae (SN), the SN Impostors, and have been directly linked with the progenitors of actual SN, indicating the LBV phase can be a final endpoint for massive star evolution. Yet only a few confirmed LBVs have been identified in the Galaxy. Their stellar evolution is poorly constrained by observations, and the physical reason for their unstable nature, both in terms of moderate spectral and photometric variability of a few magnitudes and the giant eruptions a la η Car that rival SN explosions, remains a mystery. Newly discovered mid-IR shells act as signposts, pointing to the central massive stars (LBV and Wolf-Rayet [WR] stars) that produced them. We have undertaken a spectroscopic survey of possible progenitor stars within these shells and are discovering that many are LBVs and WN-type WR transitional stars. We propose to extend this IR spectral survey to the south to search for new progenitor stars associated with dozens of newly identified shells. This survey should result in a substantial increase of new WRs and candidate LBVs for continued future study. Spectral analysis will yield new insights into the winds and physical properties of these rare and important objects, and lead to a better understanding of the physics driving giant eruptions.

  4. The stellar content of NGC 346 - A plethora of O stars in the SMC

    International Nuclear Information System (INIS)

    Massey, P.; Parker, J.W.; Garmany, C.D.

    1989-01-01

    The stellar content of NGC 346, the largest and brightest H II region in the SMC, was investigated using the results of CCD UBV photometry and spectroscopy. Spectra of 42 blue stars were classified, showing that 33 are of the O type, of which 11 are of type O6.5 or earlier, which is as many early-type O stars known in the rest of the SMC. The results identify 25-30 NGC 346 stars more massive than 25 solar masses, and six stars more massive than 40 solar masses, indicating that the upper-mass cutoff to the IMF is not lower in the SMC than in the Galaxy or the LMC. The presence of evolved 15 solar-mass stars in the NGC 346 indicates that some massive stars formed 15 million yr ago. The results of spatial distribution suggest that star formation began at the southwest side of the association and has spread to where the central cluster lies now, providing an example of sequential star formation in the SMC. 69 refs

  5. Optical-NIR dust extinction towards Galactic O stars

    Science.gov (United States)

    Maíz Apellániz, J.; Barbá, R. H.

    2018-05-01

    Context. O stars are excellent tracers of the intervening ISM because of their high luminosity, blue intrinsic SED, and relatively featureless spectra. We are currently conducting the Galactic O-Star Spectroscopic Survey (GOSSS), which is generating a large sample of O stars with accurate spectral types within several kpc of the Sun. Aims: We aim to obtain a global picture of the properties of dust extinction in the solar neighborhood based on optical-NIR photometry of O stars with accurate spectral types. Methods: We have processed a carefully selected photometric set with the CHORIZOS code to measure the amount [E(4405 - 5495)] and type [R5495] of extinction towards 562 O-type stellar systems. We have tested three different families of extinction laws and analyzed our results with the help of additional archival data. Results: The Maíz Apellániz et al. (2014, A&A, 564, A63) family of extinction laws provides a better description of Galactic dust that either the Cardelli et al. (1989, ApJ, 345, 245) or Fitzpatrick (1999, PASP, 111, 63) families, so it should be preferentially used when analysing samples similar to the one in this paper. In many cases O stars and late-type stars experience similar amounts of extinction at similar distances but some O stars are located close to the molecular clouds left over from their births and have larger extinctions than the average for nearby late-type populations. In qualitative terms, O stars experience a more diverse extinction than late-type stars, as some are affected by the small-grain-size, low-R5495 effect of molecular clouds and others by the large-grain-size, high-R5495 effect of H II regions. Late-type stars experience a narrower range of grain sizes or R5495, as their extinction is predominantly caused by the average, diffuse ISM. We propose that the reason for the existence of large-grain-size, high-R5495 regions in the ISM in the form of H II regions and hot-gas bubbles is the selective destruction of small dust

  6. Substantial Research Secures the Blue Future for our Blue Plant

    Directory of Open Access Journals (Sweden)

    Moustafa Abdel Maksoud

    2016-06-01

    Full Text Available Earth, the blue planet, is our home, and seas and oceans cover more than 70% of its surface. As the earth’s population rapidly increases and available resources decrease, seas and oceans can play a key role in assuring the long-term survival of humankind. Renewable maritime energy has huge potential to provide a considerable part of the earth’s population with decarbonised electricity generation systems. Renewable maritime energy is very flexible and can be harvested above the water’s free surface by using offshore wind turbines, on the water’s surface by using wave energy converters or below the water’s surface by using current or tidal turbines. The supposed conflict between environmental protection measures and economic interests is neither viable nor reasonable. Renewable maritime energy can be the motor for considerable substantial economic growth for many maritime regions and therefore for society at large. The fastest growing sector of renewable maritime energy is offshore wind. The annual report of the European Wind Energy Association from the year 2015 confirms the growing relevance of the offshore wind industry. In 2015, the total installed and grid-connected capacity of wind power was 12,800 MW in the EU and 6,013.4 MW in Germany. 38% of the 2015 annual installation in Germany was offshore, accounting for a capacity of 2,282.4 MW. However, there are a limited number of available installation sites in shallow water, meaning that there is an urgent need to develop new offshore structures for water depths greater than 50m. The persistent trend towards deeper waters has encouraged the offshore wind industry to look for floating wind turbine structures and larger turbines. Floating wind turbine technologies are at an early stage of development and many technical and economic challenges will still need to be faced. Nonetheless, intensive research activities and the employment of advanced technologies are the key factors in

  7. High-luminosity blue and blue-green gallium nitride light-emitting diodes.

    Science.gov (United States)

    Morkoç, H; Mohammad, S N

    1995-01-06

    Compact and efficient sources of blue light for full color display applications and lighting eluded and tantalized researchers for many years. Semiconductor light sources are attractive owing to their reliability and amenability to mass manufacture. However, large band gaps are required to achieve blue color. A class of compound semiconductors formed by metal nitrides, GaN and its allied compounds AIGaN and InGaN, exhibits properties well suited for not only blue and blue-green emitters, but also for ultraviolet emitters and detectors. What thwarted engineers and scientists from fabricating useful devices from these materials in the past was the poor quality of material and lack of p-type doping. Both of these obstacles have recently been overcome to the point where highluminosity blue and blue-green light-emitting diodes are now available in the marketplace.

  8. The Biology of blue-green algae

    National Research Council Canada - National Science Library

    Carr, Nicholas G; Whitton, B. A

    1973-01-01

    .... Their important environmental roles, their part in nitrogen fixation and the biochemistry of phototrophic metabolism are some of the attractions of blue-geen algae to an increasing number of biologists...

  9. BLUES function method in computational physics

    Science.gov (United States)

    Indekeu, Joseph O.; Müller-Nedebock, Kristian K.

    2018-04-01

    We introduce a computational method in physics that goes ‘beyond linear use of equation superposition’ (BLUES). A BLUES function is defined as a solution of a nonlinear differential equation (DE) with a delta source that is at the same time a Green’s function for a related linear DE. For an arbitrary source, the BLUES function can be used to construct an exact solution to the nonlinear DE with a different, but related source. Alternatively, the BLUES function can be used to construct an approximate piecewise analytical solution to the nonlinear DE with an arbitrary source. For this alternative use the related linear DE need not be known. The method is illustrated in a few examples using analytical calculations and numerical computations. Areas for further applications are suggested.

  10. Nanotubes based on monolayer blue phosphorus

    KAUST Repository

    Montes Muñ oz, Enrique; Schwingenschlö gl, Udo

    2016-01-01

    We demonstrate structural stability of monolayer zigzag and armchair blue phosphorus nanotubes by means of molecular dynamics simulations. The vibrational spectrum and electronic band structure are determined and analyzed as functions of the tube

  11. New stars for old

    International Nuclear Information System (INIS)

    Henbest, N.

    1980-01-01

    Observations of novas made through the ages, the identity of the close double stars which make up these cataclysmic variables and the physics of nova explosions, are discussed. A picture is outlined which explains novas, dwarf novas and recurrent novas and provides a basis for interpreting the latest so called x-ray novas. (U.K.)

  12. Hadrons in compact stars

    Indian Academy of Sciences (India)

    At normal nuclear matter density, neutron star matter mainly consists of neutrons, protons and electrons. The particle population is so arranged as to attain a min- imum energy configuration maintaining electrical charge neutrality and chemical equilibrium. At higher baryon density, hyperon formation becomes energetically.

  13. Millet's Shooting Stars

    Science.gov (United States)

    Beech, M.

    1988-12-01

    In this essay two paintings by the French artist Jean-Francois Millet are described. These paintings, Les Etoiles Filantes and Nuit Etoilée are particularly interesting since they demonstrate the rare artistic employment of the shooting-star image and metaphor.

  14. Asteroseismology of Scuti Stars

    Indian Academy of Sciences (India)

    Abstract. We briefly outline the state-of-the-art seismology of Scuti stars from a theoretical point of view: why is it so difficult a task? The recent theoretical advances in the field that these difficulties have influenced are also discussed.

  15. The STAR trigger

    International Nuclear Information System (INIS)

    Bieser, F.S.; Crawford, H.J.; Engelage, J.; Eppley, G.; Greiner, L.C.; Judd, E.G.; Klein, S.R.; Meissner, F.; Minor, R.; Milosevich, Z.; Mutchler, G.; Nelson, J.M.; Schambach, J.; VanderMolen, A.S.; Ward, H.; Yepes, P.

    2003-01-01

    We describe the trigger system that we designed and implemented for the STAR detector at RHIC. This is a 10 MHz pipelined system based on fast detector output that controls the event selection for the much slower tracking detectors. Results from the first run are presented and new detectors for the 2001 run are discussed

  16. Sleeping under the stars

    Science.gov (United States)

    Zirkel, Jack

    Sherlock Holmes and Dr. Watson went on a camping trip. As they lay down for the night, Holmes said, “Watson, look up at the sky and tell me what you see.”Watson:“! see millions and millions of stars.”

  17. StarLogo TNG

    Science.gov (United States)

    Klopfer, Eric; Scheintaub, Hal; Huang, Wendy; Wendel, Daniel

    Computational approaches to science are radically altering the nature of scientific investigatiogn. Yet these computer programs and simulations are sparsely used in science education, and when they are used, they are typically “canned” simulations which are black boxes to students. StarLogo The Next Generation (TNG) was developed to make programming of simulations more accessible for students and teachers. StarLogo TNG builds on the StarLogo tradition of agent-based modeling for students and teachers, with the added features of a graphical programming environment and a three-dimensional (3D) world. The graphical programming environment reduces the learning curve of programming, especially syntax. The 3D graphics make for a more immersive and engaging experience for students, including making it easy to design and program their own video games. Another change to StarLogo TNG is a fundamental restructuring of the virtual machine to make it more transparent. As a result of these changes, classroom use of TNG is expanding to new areas. This chapter is concluded with a description of field tests conducted in middle and high school science classes.

  18. THE STAR OFFLINE FRAMEWORK

    International Nuclear Information System (INIS)

    FINE, V.; FISYAK, Y.; PEREVOZTCHIKOV, V.; WENAUS, T.

    2000-01-01

    The Solenoidal Tracker At RHIC (STAR) is a-large acceptance collider detector, commissioned at Brookhaven National Laboratory in 1999. STAR has developed a software framework supporting simulation, reconstruction and analysis in offline production, interactive physics analysis and online monitoring environments that is well matched both to STAR's present status of transition between Fortran and C++ based software and to STAR's evolution to a fully OO software base. This paper presents the results of two years effort developing a modular C++ framework based on the ROOT package that encompasses both wrapped Fortran components (legacy simulation and reconstruction code) served by IDL-defined data structures, and fully OO components (all physics analysis code) served by a recently developed object model for event data. The framework supports chained components, which can themselves be composite subchains, with components (''makers'') managing ''data sets'' they have created and are responsible for. An St-DataSet class from which data sets and makers inherit allows the construction of hierarchical organizations of components and data, and centralizes almost all system tasks such as data set navigation, I/O, database access, and inter-component communication. This paper will present an overview of this system, now deployed and well exercised in production environments with real and simulated data, and in an active physics analysis development program

  19. Triggered star formation

    Czech Academy of Sciences Publication Activity Database

    Palouš, Jan; Ehlerová, Soňa

    2002-01-01

    Roč. 12, - (2002), s. 35-36 ISSN 1405-2059 R&D Projects: GA AV ČR IAA3003705; GA AV ČR KSK1048102 Institutional research plan: CEZ:AV0Z1003909 Keywords : interstellar medium * star formation * HI shells Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  20. Highlights from STAR

    International Nuclear Information System (INIS)

    Schweda, Kai

    2004-01-01

    Selected results from the STAR collaboration are presented. We focus on recent results on jet-like correlations, nuclear modification factors of identified hadrons, elliptic flow of multi-strange baryons Ξ and Ω, and resonance yields. First measurements of open charm production at RHIC are presented

  1. Supernovae from massive AGB stars

    NARCIS (Netherlands)

    Poelarends, A.J.T.; Izzard, R.G.; Herwig, F.; Langer, N.; Heger, A.

    2006-01-01

    We present new computations of the final fate of massive AGB-stars. These stars form ONeMg cores after a phase of carbon burning and are called Super AGB stars (SAGB). Detailed stellar evolutionary models until the thermally pulsing AGB were computed using three di erent stellar evolution codes. The

  2. Do All O Stars Form in Star Clusters?

    Science.gov (United States)

    Weidner, C.; Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

    The question whether or not massive stars can form in isolation or only in star clusters is of great importance for the theory of (massive) star formation as well as for the stellar initial mass function of whole galaxies (IGIMF-theory). While a seemingly easy question it is rather difficult to answer. Several physical processes (e.g. star-loss due to stellar dynamics or gas expulsion) and observational limitations (e.g. dust obscuration of young clusters, resolution) pose severe challenges to answer this question. In this contribution we will present the current arguments in favour and against the idea that all O stars form in clusters.

  3. Halo Star Lithium Depletion

    International Nuclear Information System (INIS)

    Pinsonneault, M. H.; Walker, T. P.; Steigman, G.; Narayanan, Vijay K.

    1999-01-01

    The depletion of lithium during the pre-main-sequence and main-sequence phases of stellar evolution plays a crucial role in the comparison of the predictions of big bang nucleosynthesis with the abundances observed in halo stars. Previous work has indicated a wide range of possible depletion factors, ranging from minimal in standard (nonrotating) stellar models to as much as an order of magnitude in models that include rotational mixing. Recent progress in the study of the angular momentum evolution of low-mass stars permits the construction of theoretical models capable of reproducing the angular momentum evolution of low-mass open cluster stars. The distribution of initial angular momenta can be inferred from stellar rotation data in young open clusters. In this paper we report on the application of these models to the study of lithium depletion in main-sequence halo stars. A range of initial angular momenta produces a range of lithium depletion factors on the main sequence. Using the distribution of initial conditions inferred from young open clusters leads to a well-defined halo lithium plateau with modest scatter and a small population of outliers. The mass-dependent angular momentum loss law inferred from open cluster studies produces a nearly flat plateau, unlike previous models that exhibited a downward curvature for hotter temperatures in the 7Li-Teff plane. The overall depletion factor for the plateau stars is sensitive primarily to the solar initial angular momentum used in the calibration for the mixing diffusion coefficients. Uncertainties remain in the treatment of the internal angular momentum transport in the models, and the potential impact of these uncertainties on our results is discussed. The 6Li/7Li depletion ratio is also examined. We find that the dispersion in the plateau and the 6Li/7Li depletion ratio scale with the absolute 7Li depletion in the plateau, and we use observational data to set bounds on the 7Li depletion in main-sequence halo

  4. Kinematic and spatial distributions of barium stars - are the barium stars and Am stars related?

    International Nuclear Information System (INIS)

    Hakkila, J.

    1989-01-01

    The possibility of an evolutionary link between Am stars and barium stars is considered, and an examination of previous data suggests that barium star precursors are main-sequence stars of intermediate mass, are most likely A and/or F dwarfs, and are intermediate-mass binaries with close to intermediate orbital separations. The possible role of mass transfer in the later development of Am systems is explored. Mass transfer and loss from systems with a range of masses and orbital separations may explain such statistical peculiarities of barium stars as the large dispersion in absolute magnitude, the large range of elemental abundances from star to star, and the small number of stars with large peculiar velocities. 93 refs

  5. Galactic Astronomy in the Ultraviolet

    Science.gov (United States)

    Rastorguev, A. S.; Sachkov, M. E.; Zabolotskikh, M. V.

    2017-12-01

    We propose a number of prospective observational programs for the ultraviolet space observatory WSO-UV, which seem to be of great importance to modern galactic astronomy. The programs include the search for binary Cepheids; the search and detailed photometric study and the analysis of radial distribution of UV-bright stars in globular clusters ("blue stragglers", blue horizontal-branch stars, RR Lyrae variables, white dwarfs, and stars with UV excesses); the investigation of stellar content and kinematics of young open clusters and associations; the study of spectral energy distribution in hot stars, including calculation of the extinction curves in the UV, optical and NIR; and accurate definition of the relations between the UV-colors and effective temperature. The high angular resolution of the observatory allows accurate astrometric measurements of stellar proper motions and their kinematic analysis.

  6. The Hot Horizontal-Branch Stars in NGC288 - Effects of Diffusion and Stratification on Their Atmospheric Parameters*

    Science.gov (United States)

    Moehler, S.; Dreizler, S.; LeBlanc, F.; Khalack, V.; Michaud, G.; Richer, J.; Sweigart, Allen V.; Grundahl, F.

    2014-01-01

    Context. NGC288 is a globular cluster with a well developed blue horizontal branch covering the so-called u-jump which indicates the onset of diffusion. It is therefore well suited to study the effects of diffusion in blue horizontal branch (HB) stars. Aims. We compare observed abundances to predictions from stellar evolution models calculated with diffusion and from stratified atmospheric models. We verify the effect of using stratified model spectra to derive atmospheric parameters. In addition we investigate the nature of the overluminous blue HB stars around the u-jump. Methods. We define a new photometric index sz from uvby measurements that is gravity sensitive between 8 000K and 12 000 K. Using medium-resolution spectra and Stroemgren photometry we determine atmospheric parameters (Teff, logg) and abundances for the blue HB stars. We use both homogeneous and stratified model spectra for our spectroscopic analyses. Results. The atmospheric parameters and masses of the hot HB stars in NGC288 show a behaviour seen also in other clusters for temperatures between 9 000K and 14 000 K. Outside this temperature range, however, they follow rather the results found for such stars in (omega)Cen. The abundances derived from our observations are for most elements (except He and P) within the abundance range expected from evolutionary models that include the effects of atomic diffusion and assume a surface mixed mass of 10(exp -7) M. The abundances predicted by stratified model atmospheres are generally significantly more extreme than observed, except for Mg. The use of stratified model spectra to determine effective temperatures, surface gravities and masses moves the hotter stars to a closer agreement with canonical evolutionary predictions. Conclusions. Our results show definite promise towards solving the long-standing issue of surface gravity and mass discrepancies for hot HB stars, but there is still much work needed to arrive at a self-consistent solution.

  7. Blue space geographies: Enabling health in place.

    Science.gov (United States)

    Foley, Ronan; Kistemann, Thomas

    2015-09-01

    Drawing from research on therapeutic landscapes and relationships between environment, health and wellbeing, we propose the idea of 'healthy blue space' as an important new development Complementing research on healthy green space, blue space is defined as; 'health-enabling places and spaces, where water is at the centre of a range of environments with identifiable potential for the promotion of human wellbeing'. Using theoretical ideas from emotional and relational geographies and critical understandings of salutogenesis, the value of blue space to health and wellbeing is recognised and evaluated. Six individual papers from five different countries consider how health can be enabled in mixed blue space settings. Four sub-themes; embodiment, inter-subjectivity, activity and meaning, document multiple experiences within a range of healthy blue spaces. Finally, we suggest a considerable research agenda - theoretical, methodological and applied - for future work within different forms of blue space. All are suggested as having public health policy relevance in social and public space. Copyright © 2015 Elsevier Ltd. All rights reserved.

  8. Multi-messenger Observations of a Binary Neutron Star Merger

    DEFF Research Database (Denmark)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.

    2017-01-01

    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A...... Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution....../optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A...

  9. DISCOVERY OF A WOLF-RAYET STAR THROUGH DETECTION OF ITS PHOTOMETRIC VARIABILITY

    Energy Technology Data Exchange (ETDEWEB)

    Littlefield, Colin [Law School, University of Notre Dame, Notre Dame, IN 46556 (United States); Garnavich, Peter; McClelland, Colin; Rettig, Terrence [Physics Department, University of Notre Dame, Notre Dame, IN 46556 (United States); Marion, G. H. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Vinko, Jozsef [Department of Optics, University of Szeged (Hungary); Wheeler, J. Craig [Astronomy Department, University of Texas, Austin, TX 78712 (United States)

    2012-06-15

    We report the serendipitous discovery of a heavily reddened Wolf-Rayet star that we name WR 142b. While photometrically monitoring a cataclysmic variable, we detected weak variability in a nearby field star. Low-resolution spectroscopy revealed a strong emission line at 7100 A, suggesting an unusual object and prompting further study. A spectrum taken with the Hobby-Eberly Telescope confirms strong He II emission and an N IV 7112 A line consistent with a nitrogen-rich Wolf-Rayet star of spectral class WN6. Analysis of the He II line strengths reveals no detectable hydrogen in WR 142b. A blue-sensitive spectrum obtained with the Large Binocular Telescope shows no evidence for a hot companion star. The continuum shape and emission line ratios imply a reddening of E(B - V) = 2.2-2.6 mag. We estimate that the distance to WR 142b is 1.4 {+-} 0.3 kpc.

  10. PG 0832 + 676 - An apparently normal B1 V star 18 kiloparsecs above the galactic plane

    International Nuclear Information System (INIS)

    Brown, P.J.F.; Dufton, P.L.; Keenan, F.P.; Boksenberg, A.; King, D.L.

    1989-01-01

    Stellar equivalent widths and line profiles, measured from optical spectra obtained with the 5 m Hale telescope and the 2.5 m Isaac Newton telescope, are used in conjunction with model atmosphere calculations to determine the atmospheric parameters and chemical composition of the faint, blue, high-galactic latitude star PG 0832 + 676. The effective temperature (Teff = 25,000 K), surface gravity (log g = 3.9), and abundances of He, C, N, O, Mg, Al, and Si are similar to those of Population I OB-type stars, from which it is concluded that PG 0832 + 676 is a normal star at a distance from the galactic plane of about 18 kpc. The star's kinematics and evolutionary age suggest that it formed in the halo, possibly from galactic fountain material. 51 refs

  11. Star formation at high redshift and the importance of dust obscuration

    DEFF Research Database (Denmark)

    Michalowski, Michal

    One of the aspects of the understanding of the Universe evolution is its star formation history. In order to gain a complete picture of the Universe evolution it is important to know when the stars we see today were formed. One of the method to study this problem is to use far-infrared and radio...... emission of galaxies. In this way it is possible to investigate the sites of star formation that are totally obscured by dust and therefore invisible at the optical wavelengths. It is because the energy absorbed by dust in the optical is re-emitted in the infrared, whereas radio emission is unaffected...... and/or radio, namely their enhanced submillimeter / radio emission combined with optical faintness and blue colors. I find that these four galaxies are young, highly star-forming, low-mass and dusty....

  12. Extreme isolation of WN3/O3 stars and implications for their evolutionary origin as the elusive stripped binaries

    Science.gov (United States)

    Smith, Nathan; Götberg, Ylva; de Mink, Selma E.

    2018-03-01

    Recent surveys of the Magellanic Clouds have revealed a subtype of Wolf-Rayet (WR) star with peculiar properties. WN3/O3 spectra exhibit both WR-like emission and O3 V-like absorption - but at lower luminosity than O3 V or WN stars. We examine the projected spatial distribution of WN3/O3 stars in the Large Magellanic Cloud as compared to O-type stars. Surprisingly, WN3/O3 stars are among the most isolated of all classes of massive stars; they have a distribution similar to red supergiants dominated by initial masses of 10-15 M⊙, and are far more dispersed than classical WR stars or luminous blue variables. Their lack of association with clusters of O-type stars suggests strongly that WN3/O3 stars are not the descendants of single massive stars (30 M⊙ or above). Instead, they are likely products of interacting binaries at lower initial mass (10-18 M⊙). Comparison with binary models suggests a probable origin with primaries in this mass range that were stripped of their H envelopes through non-conservative mass transfer by a low-mass secondary. We show that model spectra and positions on the Hertzsprung-Russell diagram for binary-stripped stars are consistent with WN3/O3 stars. Monitoring radial velocities with high-resolution spectra can test for low-mass companions or runaway velocities. With lower initial mass and environments that avoid very massive stars, the WN3/O3 stars fit expectations for progenitors of Type Ib and possibly Type Ibn supernovae.

  13. Star identification methods, techniques and algorithms

    CERN Document Server

    Zhang, Guangjun

    2017-01-01

    This book summarizes the research advances in star identification that the author’s team has made over the past 10 years, systematically introducing the principles of star identification, general methods, key techniques and practicable algorithms. It also offers examples of hardware implementation and performance evaluation for the star identification algorithms. Star identification is the key step for celestial navigation and greatly improves the performance of star sensors, and as such the book include the fundamentals of star sensors and celestial navigation, the processing of the star catalog and star images, star identification using modified triangle algorithms, star identification using star patterns and using neural networks, rapid star tracking using star matching between adjacent frames, as well as implementation hardware and using performance tests for star identification. It is not only valuable as a reference book for star sensor designers and researchers working in pattern recognition and othe...

  14. POX 186: the ultracompact blue compact dwarf galaxy reveals its nature

    Science.gov (United States)

    Doublier, V.; Kunth, D.; Courbin, F.; Magain, P.

    2000-01-01

    High resolution, ground based R and I band observations of the ultra compact dwarf galaxy POX 186 are presented. The data, obtained with the ESO New Technology Telescope (NTT), are analyzed using a new deconvolution algorithm which allows one to resolve the innermost regions of this stellar-like object into three Super-Star Clusters (SSC). Upper limits to both masses (M ~ 105 Msun) and physical sizes (<=60pc) of the SSCs are set. In addition, and maybe most importantly, extended light emission underlying the compact star-forming region is clearly detected in both bands. The R-I color rules out nebular Hα contamination and is consistent with an old stellar population. This casts doubt on the hypothesis that Blue Compact Dwarf Galaxies (BCDG) are young galaxies. based on observations carried out at NTT in La Silla, operated by the European Southern Observatory, during Director's Discretionary Time.

  15. Discovery of a new Galactic bona fide luminous blue variable with Spitzer★

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Berdnikov, L. N.; Langer, N.; Grebel, E. K.; Bestenlehner, J. M.

    2014-11-01

    We report the discovery of a circular mid-infrared shell around the emission-line star Wray 16-137 using archival data of the Spitzer Space Telescope. Follow-up optical spectroscopy of Wray 16-137 with the Southern African Large Telescope revealed a rich emission spectrum typical of the classical luminous blue variables (LBVs) like P Cygni. Subsequent spectroscopic and photometric observations showed drastic changes in the spectrum and brightness during the last three years, meaning that Wray 16-137 currently undergoes an S Dor-like outburst. Namely, we found that the star has brightened by ≈1 mag in the V and Ic bands, while its spectrum became dominated by Fe II lines. Taken together, our observations unambiguously show that Wray 16-137 is a new member of the family of Galactic bona fide LBVs.

  16. Supernovae from massive stars with extended tenuous envelopes

    Science.gov (United States)

    Dessart, Luc; Yoon, Sung-Chul; Livne, Eli; Waldman, Roni

    2018-04-01

    Massive stars with a core-halo structure are interesting objects for stellar physics and hydrodynamics. Using simulations for stellar evolution, radiation hydrodynamics, and radiative transfer, we study the explosion of stars with an extended and tenuous envelope (i.e. stars in which 95% of the mass is contained within 10% or less of the surface radius). We consider both H-rich supergiant and He-giant progenitors resulting from close-binary evolution and dying with a final mass of 2.8-5 M⊙. An extended envelope causes the supernova (SN) shock to brake and a reverse shock to form, sweeping core material into a dense shell. The shock-deposited energy, which suffers little degradation from expansion, is trapped in ejecta layers of moderate optical depth, thereby enhancing the SN luminosity at early times. With the delayed 56Ni heating, we find that the resulting optical and near-IR light curves all exhibit a double-peak morphology. We show how an extended progenitor can explain the blue and featureless optical spectra of some Type IIb and Ib SNe. The dense shell formed by the reverse shock leads to line profiles with a smaller and near-constant width. This ejecta property can explain the statistically narrower profiles of Type IIb compared to Type Ib SNe, as well as the peculiar Hα profile seen in SN 1993J. At early times, our He-giant star explosion model shows a high luminosity, a blue colour, and featureless spectra reminiscent of the Type Ib SN 2008D, suggesting a low-mass progenitor.

  17. Smashing a Jet into a Cloud to Form Stars

    Science.gov (United States)

    Kohler, Susanna

    2017-12-01

    What happens when the highly energetic jet from the center of an active galaxy rams into surrounding clouds of gas and dust? A new study explores whether this might be a way to form stars.The authors simulations at an intermediate (top) and final (bottom) stage show the compression in the gas cloud as a jet (red) enters from the left. Undisturbed cloud material is shown in blue, whereas green corresponds to cold, compressed gas actively forming stars. [Fragile et al. 2017]Impacts of FeedbackCorrelation between properties of supermassive black holes and their host galaxies suggest that there is some means of communication between them. For this reason, we suspect that feedback from an active galactic nucleus (AGN) in the form of jets, for instance controls the size of the galaxy by influencing star formation. But how does this process work?AGN feedback can be either negative or positive. In negative feedback, the gas necessary for forming stars is heated or dispersed by the jet, curbing or halting star formation. In positive feedback, jets propagate through the surrounding gas with energies high enough to create compression in the gas, but not so high that they heat it. The increased density can cause the gas to collapse, thereby triggering star formation.In a recent study, a team of scientists led by Chris Fragile (College of Charleston) modeled what happens when an enormous AGN jet slams into a dwarf-galaxy-sized, inactive cloud of gas. In particular, the team explored the possibility of star-forming positive feedback with the goal of reproducing recent observations of something called Minkowskis Object, a stellar nursery located at the endpoint of a radio jet emitted from the active galaxy NGC 541.The star formation rate in the simulated cloud increases dramatically as a result of the jets impact, reaching the rate currently observed for Minkowskis Objects within 20 million years. [Fragile et al. 2017]Triggering Stellar BirthFragile and collaborators used a

  18. What Determines Star Formation Rates?

    Science.gov (United States)

    Evans, Neal John

    2017-06-01

    The relations between star formation and gas have received renewed attention. We combine studies on scales ranging from local (within 0.5 kpc) to distant galaxies to assess what factors contribute to star formation. These include studies of star forming regions in the Milky Way, the LMC, nearby galaxies with spatially resolved star formation, and integrated galaxy studies. We test whether total molecular gas or dense gas provides the best predictor of star formation rate. The star formation ``efficiency," defined as star formation rate divided by mass, spreads over a large range when the mass refers to molecular gas; the standard deviation of the log of the efficiency decreases by a factor of three when the mass of relatively dense molecular gas is used rather than the mass of all the molecular gas. We suggest ways to further develop the concept of "dense gas" to incorporate other factors, such as turbulence.

  19. Spectrophotometry of Symbiotic Stars (Abstract)

    Science.gov (United States)

    Boyd, D.

    2017-12-01

    (Abstract only) Symbiotic stars are fascinating objects - complex binary systems comprising a cool red giant star and a small hot object, often a white dwarf, both embedded in a nebula formed by a wind from the giant star. UV radiation from the hot star ionizes the nebula, producing a range of emission lines. These objects have composite spectra with contributions from both stars plus the nebula and these spectra can change on many timescales. Being moderately bright, they lend themselves well to amateur spectroscopy. This paper describes the symbiotic star phenomenon, shows how spectrophotometry can be used to extract astrophysically useful information about the nature of these systems, and gives results for three symbiotic stars based on the author's observations.

  20. Mass loss from S stars

    International Nuclear Information System (INIS)

    Jura, M.

    1988-01-01

    The mass-loss process in S stars is studied using 65 S stars from the listing of Wing and Yorka (1977). The role of pulsations in the mass-loss process is examined. It is detected that stars with larger mass-loss rates have a greater amplitude of pulsations. The dust-to-gas ratio for the S stars is estimated as 0.002 and the average mass-loss rate is about 6 x 10 to the -8th solar masses/yr. Some of the properties of the S stars, such as scale height, surface density, and lifetime, are measured. It is determined that scale height is 200 pc; the total duration of the S star phase is greater than or equal to 30,000 yr; and the stars inject 3 x 10 to the -6th solar masses/sq kpc yr into the interstellar medium. 46 references

  1. Dynamical and photometric models of star formation in tidal tails

    International Nuclear Information System (INIS)

    Wallin, J.F.

    1990-01-01

    An investigation into the causes of star formation in tidal tails has been conducted using a restricted three-body dynamical model in conjunction with a broadband photometric evolutionary code. Test particles are initially placed in circular orbits around a softened point mass and then perturbed by a companion passing in a parabotic orbit. During the passage, the density evolution of the galaxy is examined both in regions within the disk and in selected comoving regions in the tidal features. Even without the inclusion of self-gravity and hydrodynamics, regions of compression form inside the disk, along the tidal tail, and in the tidal bridge causing local density increases of up to 500 percent. By assuming that the density changes relate to the star-formation rate via a Schmidt (1959) law, limits on the density changes needed to make detectable changes in the colors are calculated. A spiral galaxy population is synthesized and the effects of modest changes in the star-formation rate are explored using a broadband photometric evolutionary code. Density changes similar to those found in the dynamical models will cause detectable changes in the colors of a stellar population. From these models, it is determined that the blue colors and knotty features observed in the tidal features of some galaxies result from increased rates of star formation induced by tidally produced density increases. Limitations of this model are discussed along with photometric evolutionary models based on the density evolution in the tails. 52 refs

  2. On the 3He anomaly in hot subdwarf B stars

    Science.gov (United States)

    Schneider, David; Irrgang, Andreas; Heber, Ulrich; Nieva, Maria F.; Przybilla, Norbert

    2017-12-01

    Decades ago, 3He isotope enrichment in helium-weak B-type main-sequence, in blue horizontal branch and in hot subdwarf B (sdB) stars, i.e., helium-core burning stars of the extreme horizontal branch, were discovered. Diffusion processes in the atmosphere of these stars lead to the observed abundance anomalies. Quantitative spectral analyses of high-resolution spectra to derive photospheric isotopic helium abundance ratios for known 3He sdBs have not been performed yet. We present preliminary results of high-resolution and high S/N spectra to determine the 3He and 4He abundances of nine known 3He sdBs. We used a hybrid local/non-local thermodynamic equilibrium (LTE/NLTE) approach for B-type stars investigating multiple He i lines, including λ4922 Å and λ6678 Å, which show the strongest isotopic shifts in the optical spectral range.We also report the discovery of four new 3He sdBs from the ESO Supernova Progenitor survey. Most of the 3He sdBs cluster in a narrow temperature strip between ˜ 26000 K and ˜ 30000 K and have almost no atmospheric 4He at all. Interestingly, three 3He sdBs show evidence for vertical helium stratification.

  3. On the 3He anomaly in hot subdwarf B stars

    Directory of Open Access Journals (Sweden)

    Schneider David

    2017-12-01

    Full Text Available Decades ago, 3He isotope enrichment in helium-weak B-type main-sequence, in blue horizontal branch and in hot subdwarf B (sdB stars, i.e., helium-core burning stars of the extreme horizontal branch, were discovered. Diffusion processes in the atmosphere of these stars lead to the observed abundance anomalies. Quantitative spectral analyses of high-resolution spectra to derive photospheric isotopic helium abundance ratios for known 3He sdBs have not been performed yet. We present preliminary results of high-resolution and high S/N spectra to determine the 3He and 4He abundances of nine known 3He sdBs. We used a hybrid local/non-local thermodynamic equilibrium (LTE/NLTE approach for B-type stars investigating multiple He i lines, including λ4922 Å and λ6678 Å, which show the strongest isotopic shifts in the optical spectral range.We also report the discovery of four new 3He sdBs from the ESO Supernova Progenitor survey. Most of the 3He sdBs cluster in a narrow temperature strip between ∼ 26000 K and ∼ 30000 K and have almost no atmospheric 4He at all. Interestingly, three 3He sdBs show evidence for vertical helium stratification.

  4. Integrated photometry of globular star clusters in the Vilnius system

    International Nuclear Information System (INIS)

    Zdanavichyus, K.V.

    1983-01-01

    Integrated colour indices in the Vilnius photometric system and newly determined colour excesses Esub(B-V) for 39 globular clusters are presented. It is shown that the coincidence of integrated spectral types are not a sufficient criterion for the identity of intrinsic colour indices of globular clusters. Relation of integrated colour indices with the slope of the giant branch S and with the horizontal branch morphological type D is investigated. Integrated colour indices of clusters with a blue horizontal branch show no correlation with either D or S. The increase of colour indices of the clusters of types D >= 4 correlates with the distribution of stars along the horizontal branch. Integrated photometry of globular star clusters in the Vilnius multicoloured photometric system permits to determine their colour excesses from some Q diagrams and normal colour index. Integral normal colour indexes and Q parameters for I globular star clusters of the Mironov group display small changes as compared to clusters of group 2. Colour indexes among star clusters having only red horizontal branches (D=7) change most considerably

  5. Little Blue Dots in the Hubble Space Telescope Frontier Fields: Precursors to Globular Clusters?

    Science.gov (United States)

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.

    2017-12-01

    Galaxies with stellar masses {10}-7.4 yr‑1 were examined on images of the Hubble Space Telescope Frontier Field Parallels for Abell 2744 and MACS J0416.1-02403. They appear as unresolved “Little Blue Dots” (LBDs). They are less massive and have higher specific star formation rates (sSFRs) than “blueberries” studied by Yang et al. and higher sSFRs than “Blue Nuggets” studied by Tacchella et al. We divided the LBDs into three redshift bins and, for each, stacked the B435, V606, and I814 images convolved to the same stellar point-spread function (PSF). Their radii were determined from PSF deconvolution to be ∼80 to ∼180 pc. The high sSFRs suggest that their entire stellar mass has formed in only 1% of the local age of the universe. The sSFRs at similar epochs in local dwarf galaxies are lower by a factor of ∼100. Assuming that the star formation rate is {ε }{ff}{M}{gas}/{t}{ff} for efficiency {ε }{ff}, gas mass M gas, and free-fall time, t ff, the gas mass and gas-to-star mass ratio are determined. This ratio exceeds 1 for reasonable efficiencies, and is likely to be ∼5 even with a high {ε }{ff} of 0.1. We consider whether these regions are forming today’s globular clusters. With their observed stellar masses, the maximum likely cluster mass is ∼ {10}5 {M}ȯ , but if star formation continues at the current rate for ∼ 10{t}{ff}∼ 50 {Myr} before feedback and gas exhaustion stop it, then the maximum cluster mass could become ∼ {10}6 {M}ȯ .

  6. Optical spectroscopy of the blue supergiant Sk-69° 279 and its circumstellar shell with SALT

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Maryeva, O. V.; Berdnikov, L. N.

    2018-02-01

    We report the results of optical spectroscopy of the blue supergiant Sk-69° 279 and its circular shell in the Large Magellanic Cloud (LMC) with the Southern African Large Telescope (SALT). We classify Sk-69° 279 as an O9.2 Iaf star and analyse its spectrum by using the stellar atmosphere code CMFGEN, obtaining a stellar temperature of ≈30 kK, a luminosity of log (L*/ L⊙) = 5.54, a mass-loss rate of log (\\dot{M}/ M_{⊙} yr^{-1}) = -5.26, and a wind velocity of 800km s-1. We found also that Sk-69° 279 possesses an extended atmosphere with an effective temperature of ≈24 kK and that its surface helium and nitrogen abundances are enhanced, respectively, by factors of ≈2 and 20-30. This suggests that either Sk-69° 279 was initially a (single) fast-rotating ( ≳ 400 km s- 1) star, which only recently evolved off the main sequence, or that it is a product of close binary evolution. The long-slit spectroscopy of the shell around Sk-69° 279 revealed that its nitrogen abundance is enhanced by the same factor as the stellar atmosphere, which implies that the shell is composed mostly of the CNO processed material lost by the star. Our findings support previous propositions that some massive stars can produce compact circumstellar shells and, presumably, appear as luminous blue variables while they are still on the main sequence or have only recently left it.

  7. Exciting Message from a Dying Monster Star

    Science.gov (United States)

    1996-03-01

    this is radiation from a SiO maser in the atmosphere of the star. If it would not have been a maser, it would have been far too weak to have been detected. Although we know several hundred masers of this type in the Milky Way, this is the first discovery of a SiO maser in another galaxy than our own . Since then, the observations have been continued in collaboration with Australian astronomers, using radio telescopes at Parkes and Mopra on that continent. A most unusual star When Swedish astronomer Bengt Westerlund and his colleagues first observed this LMC maser star in 1981 with optical telescopes, they thought that it was a rather normal, cool and not particularly bright star. However, a few years later, the Dutch-British-USA InfraRed Astronomical Satellite (IRAS) revealed its true nature. The IRAS measurements showed that the star radiates most of its light in the form of infrared radiation [4], making it one of the most powerful stars in the LMC; in fact, it emits about half a million times more energy than the Sun. On this occasion, it was given the designation IRAS 04553-6825 , the number indicating its position in the sky. IRAS 04553-6825 is unusual in other ways. It is some fifty times as heavy as our Sun, and it is the biggest known star in the LMC: if it were to take the place of our Sun, it would fill the solar system out to the planet Neptune, thirty times the distance from the Earth to the Sun. It is rather cool when compared to other stars - although it still has a temperature of about 2,000 C - and it therefore has a very red colour [5]. This Press Release is accompanied by ESO Press Photo 15/96 which demonstrates that while the star is hardly visible in blue light, it shines brightly in red and infrared light. Stars like IRAS 04553-6825 are known as red supergiants. It has been unofficially dubbed `The Monster', and having reached the end of a short and hectic life, it is now dying. The nuclear reactions deep inside are undergoing important changes at

  8. On the evolutionary status and pulsations of the recently discovered blue large-amplitude pulsators (BLAPs)

    Science.gov (United States)

    Romero, Alejandra D.; Córsico, A. H.; Althaus, L. G.; Pelisoli, I.; Kepler, S. O.

    2018-06-01

    The blue large-amplitude pulsators (BLAPs) constitute a new class of pulsating stars. They are hot stars with effective temperatures of ˜30 000 K and surface gravities of log g ˜ 4.9, that pulsate with periods in the range 20-40 min. Until now, their origin and evolutionary state, as well as the nature of their pulsations, were not been unveiled. In this paper, we propose that the BLAPs are the hot counterpart of the already known pulsating pre-extremely low mass (pre-ELM) white dwarf (WD) stars, that are He-core low-mass stars resulting from interacting binary evolution. Using fully evolutionary sequences, we show that the BLAPs are well represented by pre-ELM WD models with high effective temperature and stellar masses ˜0.34 M⊙. From the analysis of their pulsational properties, we find that the observed variabilities can be explained by high-order non-radial g-mode pulsations or, in the case of the shortest periods, also by low-order radial modes, including the fundamental radial mode. The theoretical modes with periods in the observed range are unstable due to the κ mechanism associated with the Z-bump in the opacity at log T ˜ 5.25.

  9. Neutron Star Science with the NuSTAR

    Energy Technology Data Exchange (ETDEWEB)

    Vogel, J. K. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-10-16

    The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, helped scientists obtain for the first time a sensitive high-­energy X-­ray map of the sky with extraordinary resolution. This pioneering telescope has aided in the understanding of how stars explode and neutron stars are born. LLNL is a founding member of the NuSTAR project, with key personnel on its optics and science team. We used NuSTAR to observe and analyze the observations of different neutron star classes identified in the last decade that are still poorly understood. These studies not only help to comprehend newly discovered astrophysical phenomena and emission processes for members of the neutron star family, but also expand the utility of such observations for addressing broader questions in astrophysics and other physics disciplines. For example, neutron stars provide an excellent laboratory to study exotic and extreme phenomena, such as the equation of state of the densest matter known, the behavior of matter in extreme magnetic fields, and the effects of general relativity. At the same time, knowing their accurate populations has profound implications for understanding the life cycle of massive stars, star collapse, and overall galactic evolution.

  10. Massive open star clusters using the VVV survey. II. Discovery of six clusters with Wolf-Rayet stars

    Science.gov (United States)

    Chené, A.-N.; Borissova, J.; Bonatto, C.; Majaess, D. J.; Baume, G.; Clarke, J. R. A.; Kurtev, R.; Schnurr, O.; Bouret, J.-C.; Catelan, M.; Emerson, J. P.; Feinstein, C.; Geisler, D.; de Grijs, R.; Hervé, A.; Ivanov, V. D.; Kumar, M. S. N.; Lucas, P.; Mahy, L.; Martins, F.; Mauro, F.; Minniti, D.; Moni Bidin, C.

    2013-01-01

    Context. The ESO Public Survey "VISTA Variables in the Vía Láctea" (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims: This is the second in a series of papers about young, massive open clusters observed using the VVV survey. We present the first study of six recently discovered clusters. These clusters contain at least one newly discovered Wolf-Rayet (WR) star. Methods: Following the methodology presented in the first paper of the series, wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results: We find that the six studied stellar groups are real young (2-7 Myr) and massive (between 0.8 and 2.2 × 103 M⊙) clusters. They are highly obscured (AV ~ 5-24 mag) and compact (1-2 pc). In addition to WR stars, two of the six clusters also contain at least one red supergiant star, and one of these two clusters also contains a blue supergiant. We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission lines which could be classified WR or OIf. Preliminary analysis provides initial masses of ~30-50 M⊙ for the WR stars. Finally, we discuss the spiral structure of the Galaxy using the six new clusters as tracers, together with the previously studied VVV clusters. Based on observations with ISAAC, VLT, ESO (programme 087.D-0341A), New Technology Telescope at ESO's La Silla Observatory (programme 087.D-0490A) and with the Clay telescope at the Las Campanas Observatory (programme CN2011A-086). Also based on data from the VVV survey (programme 172.B-2002).

  11. Alchemy of stars

    Energy Technology Data Exchange (ETDEWEB)

    Parashar, D [A.R.S.D. Coll., New Delhi (India); Bhatia, V B [Delhi Univ. (India). Dept. of Physics and Astrophysics

    1976-05-01

    Developments in studies on stellar evolution during this century are reviewed. Recent considerations indicate that almost all elements between helium and zinc (a range which comprises more than 99 percent by mass of elements heavier than helium) can be synthesised in nuclear processes occurring during the late violent stages of an exploding star or supernova and a vigorous study in the new field of explosive nucleosynthesis is in progress. The process of nucleosynthesis has been classified into 8 sets of nuclear reactions, namely, (1) hydrogen burning, (2) helium burning, (3) ..cap alpha..-process, (4) e-process, (5) s-process, (6) r-process, (7) p-process and (8) x-process. The abundance of helium and heavier elements are explained and the formation of various elements during supernova explosions is discussed. The questions regarding the appropriate astrophysical conditions for the formation of massive stars (3 to 8 times solar mass) is still unanswered.

  12. Very low mass stars

    International Nuclear Information System (INIS)

    Liebert, J.; Probst, R.G.

    1987-01-01

    This paper discusses several theoretical and observational topics involved in discovering and analyzing very low mass stellar objects below about 0.3 M circle, as well as their likely extension into the substellar range. The authors hereafter refer to these two classes of objects as VLM stars and brown dwarfs, respectively; collectively, they are called VLM objects. The authors outline recent theoretical work on low-mass stellar interiors and atmospheres, the determination of the hydrogen-burning mass limit, important dynamical evidence bearing on the expected numbers of such objects, and the expectations for such objects from star-formation theory. They focus on the properties of substellar objects near the stellar mass limit. Observational techniques used to discover and analyze VLM objects are summarized

  13. Pulsating stars harbouring planets

    Directory of Open Access Journals (Sweden)

    Moya A.

    2013-04-01

    Full Text Available Why bother with asteroseismology while studying exoplanets? There are several answers to this question. Asteroseismology and exoplanetary sciences have much in common and the synergy between the two opens up new aspects in both fields. These fields and stellar activity, when taken together, allow maximum extraction of information from exoplanet space missions. Asteroseismology of the host star has already proved its value in a number of exoplanet systems by its unprecedented precision in determining stellar parameters. In addition, asteroseismology allows the possibility of discovering new exoplanets through time delay studies. The study of the interaction between exoplanets and their host stars opens new windows on various physical processes. In this review I will summarize past and current research in exoplanet asteroseismology and explore some guidelines for the future.

  14. Shells around stars

    International Nuclear Information System (INIS)

    Olnon, F.M.

    1977-01-01

    This thesis deals with optically visible stars surrounded by gas and dust and hot enough to ionize the hydrogen atoms in their envelopes. The ionized gas emits radio continuum radiation by the thermal Bremsstrahlung mechanism. Cool giant stars that show radio line emission from molecules in their circumstellar envelopes are discussed. Under favourable conditions the so-called maser effect gives rise to very intense emission lines. Up till now seven different maser transitions have been found in the envelopes of cool giants. Four of these lines from OH, H 2 O and SiO are studied here. Each of them originates in a different layer so that these lines can be used to probe the envelope. The profile of a maser line gives information about the velocity structure of the region where it is formed

  15. Structure of neutron stars

    International Nuclear Information System (INIS)

    Cheong, C.K.

    1974-01-01

    Structure of neutron stars consisting of a cold and catalyzed superdense matter were investigated by integrating the equations for hydrostatic equilibrium based on the General Relativity theory. The equations of state were obtained with the help of semiempirical nuclear mass formulae. A large phase transition was found between the nuclear and subnuclear density regions. The density phase transition points were calculated as 6.2 x 10 11 and 3.8 x 10 13 g/cm 3 . Due to such a large phase transition, the equation of state practically consists of two parts: The nuclear and subnuclear phases wich are in contact under the thermodynamical equilibrium at the corresponding pressure. Some macroscopic properties of neutron stars are discussed. (Author) [pt

  16. What stars become supernovae

    International Nuclear Information System (INIS)

    Tinsley, B.M.

    1975-01-01

    A variety of empirical lines of evidence is assembled on the masses and stellar population types of stars that trigger supernova (SN) explosions. The main theoretical motivations are to determine whether type I supernovae (SN I) can have massive precursors, and whether there is an interval of stellar mass, between the masses of precursors of pulsars and white dwarfs, that is disrupted by carbon detonation. Statistical and other uncertainties in the empirical arguments are given particular attention, and are found to be more important than generally realized. Relatively secure conclusions include the following. Statistics of stellar birthrates, SN, pulsars, and SN remnants in the Galaxy show that SN II (or all SN) could arise from stars with masses greater than M/sub s/ where M/sub s/ approximately 49 to 12 M solar mass; the precursor mass range cannot be more closely defined from present data; nor can it be said whether all SN leave pulsars and/or extended radio remnants. Several methods of estimating the masses of stars that become white dwarfs are consistent with a lower limit, M/sub s/ greater than or equal to 5 M solar mass, so carbon detonation may indeed be avoided, although this conclusion is not secure. Studies of the properties of galaxies in which SN occur, and their distributions within galaxies, support the usual views that SN I have low-mass precursors (less than or equal to 5 M solar mass and typically less than or equal to 1 M solar mass) and SN II have massive precursors (greater than or equal to 5 M solar mass); the restriction of known SN II to Sc and Sb galaxies, to date, is shown to be consistent, statistically, with massive stars in other galaxies also dying as SN II. Possible implications of the peculiarities of some SN-producing galaxies are discussed. Suggestions are made for observational and theoretical studies that would help answer important remaining questions on the nature of SN precursors

  17. Detector limitations, STAR

    Energy Technology Data Exchange (ETDEWEB)

    Underwood, D. G.

    1998-07-13

    Every detector has limitations in terms of solid angle, particular technologies chosen, cracks due to mechanical structure, etc. If all of the presently planned parts of STAR [Solenoidal Tracker At RHIC] were in place, these factors would not seriously limit our ability to exploit the spin physics possible in RHIC. What is of greater concern at the moment is the construction schedule for components such as the Electromagnetic Calorimeters, and the limited funding for various levels of triggers.

  18. Oscillations in neutron stars

    International Nuclear Information System (INIS)

    Hoeye, Gudrun Kristine

    1999-01-01

    We have studied radial and nonradial oscillations in neutron stars, both in a general relativistic and non-relativistic frame, for several different equilibrium models. Different equations of state were combined, and our results show that it is possible to distinguish between the models based on their oscillation periods. We have particularly focused on the p-, f-, and g-modes. We find oscillation periods of II approx. 0.1 ms for the p-modes, II approx. 0.1 - 0.8 ms for the f-modes and II approx. 10 - 400 ms for the g-modes. For high-order (l → 4) f-modes we were also able to derive a formula that determines II l+1 from II l and II l-1 to an accuracy of 0.1%. Further, for the radial f-mode we find that the oscillation period goes to infinity as the maximum mass of the star is approached. Both p-, f-, and g-modes are sensitive to changes in the central baryon number density n c , while the g-modes are also sensitive to variations in the surface temperature. The g-modes are concentrated in the surface layer, while p- and f-modes can be found in all parts of the star. The effects of general relativity were studied, and we find that these are important at high central baryon number densities, especially for the p- and f-modes. General relativistic effects can therefore not be neglected when studying oscillations in neutron stars. We have further developed an improved Cowling approximation in the non-relativistic frame, which eliminates about half of the gap in the oscillation periods that results from use of the ordinary Cowling approximation. We suggest to develop an improved Cowling approximation also in the general relativistic frame. (Author)

  19. Oscillations in neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Hoeye, Gudrun Kristine

    1999-07-01

    We have studied radial and nonradial oscillations in neutron stars, both in a general relativistic and non-relativistic frame, for several different equilibrium models. Different equations of state were combined, and our results show that it is possible to distinguish between the models based on their oscillation periods. We have particularly focused on the p-, f-, and g-modes. We find oscillation periods of II approx. 0.1 ms for the p-modes, II approx. 0.1 - 0.8 ms for the f-modes and II approx. 10 - 400 ms for the g-modes. For high-order (l (>{sub )} 4) f-modes we were also able to derive a formula that determines II{sub l+1} from II{sub l} and II{sub l-1} to an accuracy of 0.1%. Further, for the radial f-mode we find that the oscillation period goes to infinity as the maximum mass of the star is approached. Both p-, f-, and g-modes are sensitive to changes in the central baryon number density n{sub c}, while the g-modes are also sensitive to variations in the surface temperature. The g-modes are concentrated in the surface layer, while p- and f-modes can be found in all parts of the star. The effects of general relativity were studied, and we find that these are important at high central baryon number densities, especially for the p- and f-modes. General relativistic effects can therefore not be neglected when studying oscillations in neutron stars. We have further developed an improved Cowling approximation in the non-relativistic frame, which eliminates about half of the gap in the oscillation periods that results from use of the ordinary Cowling approximation. We suggest to develop an improved Cowling approximation also in the general relativistic frame. (Author)

  20. "Blue-Collar Blues" uurib töösuhteid uutes oludes / Janar Ala

    Index Scriptorium Estoniae

    Ala, Janar, 1979-

    2009-01-01

    Tööproblemaatikat käsitlev näitus "Blue-Collar Blues" Tallinna Kunstihoones ja Tallinna Kunstihoone galeriis 31. jaanuarini 2010, kuraator Anders Härm. Lähemalt belgia-mehhiko kunstniku Francis Alys'e videost, austria kunstniku Oliver Ressleri ning venetsueela-saksa politoloogi Dario Azzelini videost "Viis tehast. Tööliste kontroll Venezuelas"

  1. Star clouds of Magellan

    International Nuclear Information System (INIS)

    Tucker, W.

    1981-01-01

    The Magellanic Clouds are two irregular galaxies belonging to the local group which the Milky Way belongs to. By studying the Clouds, astronomers hope to gain insight into the origin and composition of the Milky Way. The overall structure and dynamics of the Clouds are clearest when studied in radio region of the spectrum. One benefit of directly observing stellar luminosities in the Clouds has been the discovery of the period-luminosity relation. Also, the Clouds are a splendid laboratory for studying stellar evolution. It is believed that both Clouds may be in the very early stage in the development of a regular, symmetric galaxy. This raises a paradox because some of the stars in the star clusters of the Clouds are as old as the oldest stars in our galaxy. An explanation for this is given. The low velocity of the Clouds with respect to the center of the Milky Way shows they must be bound to it by gravity. Theories are given on how the Magellanic Clouds became associated with the galaxy. According to current ideas the Clouds orbits will decay and they will spiral into the Galaxy

  2. Stars of strange matter

    International Nuclear Information System (INIS)

    Bethe, H.A.; Brown, G.E.; Cooperstein, J.

    1987-01-01

    We investigate suggestions that quark matter with strangeness per baryon of order unity may be stable. We model this matter at nuclear matter densities as a gas of close packed Λ-particles. From the known mass of the Λ-particle we obtain an estimate of the energy and chemical potential of strange matter at nuclear densities. These are sufficiently high to preclude any phase transition from neutron matter to strange matter in the region near nucleon matter density. Including effects from gluon exchange phenomenologically, we investigate higher densities, consistently making approximations which underestimate the density of transition. In this way we find a transition density ρ tr > or approx.7ρ 0 , where ρ 0 is nuclear matter density. This is not far from the maximum density in the center of the most massive neutron stars that can be constructed. Since we have underestimated ρ tr and still find it to be ∝7ρ 0 , we do not believe that the transition from neutron to quark matter is likely in neutron stars. Moreover, measured masses of observed neutron stars are ≅1.4 M sun , where M sun is the solar mass. For such masses, the central (maximum) density is ρ c 0 . Transition to quark matter is certainly excluded for these densities. (orig.)

  3. Stable dark energy stars

    International Nuclear Information System (INIS)

    Lobo, Francisco S N

    2006-01-01

    The gravastar picture is an alternative model to the concept of a black hole, where there is an effective phase transition at or near where the event horizon is expected to form, and the interior is replaced by a de Sitter condensate. In this work a generalization of the gravastar picture is explored by considering matching of an interior solution governed by the dark energy equation of state, ω ≡ p/ρ < -1/3, to an exterior Schwarzschild vacuum solution at a junction interface. The motivation for implementing this generalization arises from the fact that recent observations have confirmed an accelerated cosmic expansion, for which dark energy is a possible candidate. Several relativistic dark energy stellar configurations are analysed by imposing specific choices for the mass function. The first case considered is that of a constant energy density, and the second choice that of a monotonic decreasing energy density in the star's interior. The dynamical stability of the transition layer of these dark energy stars to linearized spherically symmetric radial perturbations about static equilibrium solutions is also explored. It is found that large stability regions exist that are sufficiently close to where the event horizon is expected to form, so that it would be difficult to distinguish the exterior geometry of the dark energy stars, analysed in this work, from an astrophysical black hole

  4. Spheroidal Populated Star Systems

    Science.gov (United States)

    Angeletti, Lucio; Giannone, Pietro

    2008-10-01

    Globular clusters and low-ellipticity early-type galaxies can be treated as systems populated by a large number of stars and whose structures can be schematized as spherically symmetric. Their studies profit from the synthesis of stellar populations. The computation of synthetic models makes use of various contributions from star evolution and stellar dynamics. In the first sections of the paper we present a short review of our results on the occurrence of galactic winds in star systems ranging from globular clusters to elliptical galaxies, and the dynamical evolution of a typical massive globular cluster. In the subsequent sections we describe our approach to the problem of the stellar populations in elliptical galaxies. The projected radial behaviours of spectro-photometric indices for a sample of eleven galaxies are compared with preliminary model results. The best agreement between observation and theory shows that our galaxies share a certain degree of heterogeneity. The gas energy dissipation varies from moderate to large, the metal yield ranges from solar to significantly oversolar, the dispersion of velocities is isotropic in most of the cases and anisotropic in the remaining instances.

  5. What are the stars?

    CERN Document Server

    Srinivasan, Ganesan

    2014-01-01

    The outstanding question in astronomy at the turn of the twentieth century was: What are the stars and why are they as they are? In this volume, the story of how the answer to this fundamental question was unravelled is narrated in an informal style, with emphasis on the underlying physics. Although the foundations of astrophysics were laid down by 1870, and the edifice was sufficiently built up by 1920, the definitive proof of many of the prescient conjectures made in the 1920s and 1930s came to be established less than ten years ago. This book discusses these recent developments in the context of discussing the nature of the stars, their stability and the source of the energy they radiate.  Reading this book will get young students excited about the presently unfolding revolution in astronomy and the challenges that await them in the world of physics, engineering and technology. General readers will also find the book appealing for its highly accessible narrative of the physics of stars.  “... The reade...

  6. The Structure of the Blue Whirl

    Science.gov (United States)

    Hariharan, Sriram Bharath; Hu, Yu; Xiao, Huahua; Gollner, Michael; Oran, Elaine

    2017-11-01

    Recent experiments have led to the discovery of the blue whirl, a small, stable regime of the fire whirl that burns typically sooty liquid hydrocarbons without producing soot. The physical structure consists of three regions - the blue cone, the vortex rim and the purple haze. The physical nature of the flame was further investigated through digital imaging techniques, which suggest that the transition (from the fire whirl to the blue whirl) and shape of the flame may be influenced by vortex breakdown. The flame was found to develop over a variety of surfaces, which indicates that the formation of the blue whirl is strongly influenced by the flow structure over the incoming boundary layer. The thermal structure was investigated using micro-thermocouples, thin-filament pyrometry and OH* spectroscopy. These revealed a peak temperature around 2000 K, and that most of the combustion occurs in the relatively small, visibly bright vortex rim. The results of these investigations provide a platform to develop a theory on the structure of the blue whirl, a deeper understanding of which may affirm potential for applications in the energy industry. This work was supported by an NSF EAGER award and Minta Martin Endowment Funds in the Department of Aerospace Engineering at the University of Maryland.

  7. Dyes adsorption blue vegetable and blue watercolor by natural zeolites modified with surfactants

    International Nuclear Information System (INIS)

    Jardon S, C. C.; Olguin G, M. T.; Diaz N, M. C.

    2009-01-01

    In this work was carried out the dyes removal blue vegetable and blue watercolor of aqueous solutions, to 20 C, at different times and using a zeolite mineral of Parral (Chihuahua, Mexico) modified with hexadecyl trimethyl ammonium bromide or dodecyl trimethyl ammonium bromide. The zeolite was characterized before and after of its adaptation with NaCl and later with HDTMABr and DTMABr. For the materials characterization were used the scanning electron microscopy of high vacuum; elementary microanalysis by X-ray spectroscopy of dispersed energy and X-ray diffraction techniques. It was found that the surfactant type absorbed in the zeolite material influences on the adsorption process of the blue dye. Likewise, the chemical structure between the vegetable blue dye and the blue watercolor, determines the efficiency of the color removal of the water, by the zeolites modified with the surfactants. (Author)

  8. Improved autonomous star identification algorithm

    International Nuclear Information System (INIS)

    Luo Li-Yan; Xu Lu-Ping; Zhang Hua; Sun Jing-Rong

    2015-01-01

    The log–polar transform (LPT) is introduced into the star identification because of its rotation invariance. An improved autonomous star identification algorithm is proposed in this paper to avoid the circular shift of the feature vector and to reduce the time consumed in the star identification algorithm using LPT. In the proposed algorithm, the star pattern of the same navigation star remains unchanged when the stellar image is rotated, which makes it able to reduce the star identification time. The logarithmic values of the plane distances between the navigation and its neighbor stars are adopted to structure the feature vector of the navigation star, which enhances the robustness of star identification. In addition, some efforts are made to make it able to find the identification result with fewer comparisons, instead of searching the whole feature database. The simulation results demonstrate that the proposed algorithm can effectively accelerate the star identification. Moreover, the recognition rate and robustness by the proposed algorithm are better than those by the LPT algorithm and the modified grid algorithm. (paper)

  9. THE BHB STARS IN THE SURVEY FIELDS OF RODGERS ET AL. (1993): NEW OBSERVATIONS AND COMPARISONS WITH OTHER RECENT SURVEYS

    International Nuclear Information System (INIS)

    Kinman, T. D.; Brown, Warren R.

    2011-01-01

    We study blue horizontal branch (BHB) and RR Lyrae stars in the Rodgers et al. fields and compare their velocity and density distributions with other surveys in the same part of the sky. Photometric data are given for 176 early-type stars in the northern field. We identify fourteen BHB stars and four possible BHB stars, and determine the selection efficiency of the Century survey, the HK survey, and the SDSS survey for BHB stars. We give light curves and γ radial velocities for three type ab RR Lyrae stars in the northern field; comparison with the nearby LONEOS survey shows that there is likely to be an equal number of lower-amplitude type ab RR Lyrae stars that we do not find. There are therefore at least twice as many BHB stars as type ab RR Lyrae stars in the northern field-similar to the ratio in the solar neighborhood. The velocity distribution of the southern field shows no evidence for an anomalous thick disk that was found by Gilmore et al.; the halo velocity peaks at a slightly prograde rotational velocity but there is also a significant retrograde halo component in this field. The velocity distribution in the northern field shows no evidence of Galactic rotation for |Z| ≥ 4 kpc and a slight prograde motion for |Z| < 4 kpc. The space densities of BHB stars in the northern field agree with an extrapolation of the power-law distribution recently derived by de Propris et al. For |Z| < 4 kpc, however, we observe an excess of BHB stars compared with this power law. We conclude that these BHB stars mostly belong to a spatially flattened, non-rotating inner halo component of the Milky Way in confirmation of the Kinman et al. analysis of Century survey BHB stars.

  10. Origin of colour stability in blue/orange/blue stacked phosphorescent white organic light-emitting diodes

    International Nuclear Information System (INIS)

    Kim, Sung Hyun; Jang, Jyongsik; Yook, Kyoung Soo; Lee, Jun Yeob

    2009-01-01

    The origin of colour stability in phosphorescent white organic light-emitting diodes (PHWOLEDs) with a blue/orange/blue stacked emitting structure was studied by monitoring the change in a recombination zone. A balanced recombination zone shift between the blue and the orange light-emitting layers was found to be responsible for the colour stability in the blue/orange/blue stacked PHWOLEDs.

  11. First stars X. The nature of three unevolved carbon-enhanced metal-poor stars

    DEFF Research Database (Denmark)

    Sivarani, T.; Beers, T.C.; Bonifacio, P.

    2006-01-01

    Stars: abundances, stars: population II, Galaxy: abundances, stars: AGB and post-AGB Udgivelsesdato: Nov.......Stars: abundances, stars: population II, Galaxy: abundances, stars: AGB and post-AGB Udgivelsesdato: Nov....

  12. Echoes from a Dying Star

    Science.gov (United States)

    Kohler, Susanna

    2017-06-01

    When a passing star is torn apart by a supermassive black hole, it emits a flare of X-ray, ultraviolet, and optical light. What can we learn from the infrared echo of a violent disruption like this one?Stellar DestructionOptical (black triangles) and infrared (blue circles and red squares) observations of F010042237. Day 0 marks the day the optical emission peaked. The infrared emission rises steadily through the end of the data. [Dou et al. 2017]Tidal disruption events occur when a star passes within the tidal radius of a supermassive black hole. After tidal forces pull the star apart, much of the stellar matter falls onto the black hole, radiating briefly in X-ray, ultraviolet and optical as it accretes. This signature rise and gradual fall of emission has allowed us to detect dozens of tidal disruption events thus far.One of the recently discovered candidate events is a little puzzling. Not only does the candidate in ultraluminous infrared galaxy F010042237 have an unusual host most disruptions occur in galaxies that are no longer star-forming, in contrast to this one but its optical light curve also shows an unusually long decay time.Now mid-infrared observations of this event have beenpresented by a team of scientists led by Liming Dou (Guangzhou University and Department of Education, Guangdong Province, China), revealing why this disruption is behaving unusually.Schematic of a convex dusty ring (red bows) that absorbs UV photons and re-emits in the infrared. It simultaneously scatters UV and optical photons into our line of sight. The dashed lines illustrate the delays at lags of 60 days, 1, 2, 3, 4, and 5 years. [Adapted from Dou et al. 2017]A Dusty Solution?The optical flare from F010042237s nucleus peaked in 2010, so Dou and collaborators obtained archival mid-infrared data from the WISE and NEOWISE missions from 2010 to 2016. The data show that the galaxy is quiescent in mid-infrared in 2010 but in data from three years later, the infrared emission has

  13. StarDOM: From STAR format to XML

    International Nuclear Information System (INIS)

    Linge, Jens P.; Nilges, Michael; Ehrlich, Lutz

    1999-01-01

    StarDOM is a software package for the representation of STAR files as document object models and the conversion of STAR files into XML. This allows interactive navigation by using the Document Object Model representation of the data as well as easy access by XML query languages. As an example application, the entire BioMagResBank has been transformed into XML format. Using an XML query language, statistical queries on the collected NMR data sets can be constructed with very little effort. The BioMagResBank/XML data and the software can be obtained at http://www.nmr.embl-heidelberg.de/nmr/StarDOM/

  14. DISCOVERY OF TWO RARE RIGIDLY ROTATING MAGNETOSPHERE STARS IN THE APOGEE SURVEY

    International Nuclear Information System (INIS)

    Eikenberry, Stephen S.; Garner, Alan; Chojnowski, S. Drew; Majewski, Steven R.; Whelan, David G.; Borish, H. Jacob; Hearty, Fred; Li, Zhi-Yun; Nidever, David L.; Skrutskie, Michael; Wisniewski, John; Shetrone, Matthew; Bizyaev, Dmitry; Ebelke, Garrett; Davenport, James R. A.; Feuillet, Diane; Holtzman, Jon; Frinchaboy, Peter M.; Mészáros, Sz.; Schneider, Donald P.

    2014-01-01

    The Apache Point Observatory Galactic Evolution Experiment (APOGEE)—one of the Sloan Digital Sky Survey III programs—is using near-infrared (NIR) spectra of ∼100,000 red giant branch star candidates to study the structure of the Milky Way. In the course of the survey, APOGEE also acquires spectra of hot field stars to serve as telluric calibrators for the primary science targets. We report the serendipitous discovery of two rare, fast-rotating B-stars of the σ Ori E type among those blue field stars observed during the first year of APOGEE operations. Both of the discovered stars display the spectroscopic signatures of rigidly rotating magnetospheres (RRM) common to this class of highly magnetized (B ∼ 10 kGauss) stars, increasing the number of known RRM stars by ∼10%. One (HD 345439) is a main-sequence B-star with unusually strong He absorption (similar to σ Ori E), while the other (HD 23478) fits a ''He-normal'' B3IV classification. We combine the APOGEE discovery spectra with other optical and NIR spectra of these two stars, and of σ Ori E itself, to show how NIR spectroscopy can be a uniquely powerful tool for discovering more of these rare objects, which may show little/no RRM signatures in their optical spectra. We discuss the potential for further discovery of σ Ori E type stars, as well as the implications of our discoveries for the population of these objects and insights into their origin and evolution

  15. DISCOVERY OF TWO RARE RIGIDLY ROTATING MAGNETOSPHERE STARS IN THE APOGEE SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Eikenberry, Stephen S.; Garner, Alan [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611 (United States); Chojnowski, S. Drew; Majewski, Steven R.; Whelan, David G.; Borish, H. Jacob; Hearty, Fred; Li, Zhi-Yun; Nidever, David L.; Skrutskie, Michael [Department of Astronomy, University of Virginia, 530 McCormick Rd, Charlottesville, VA 22904 (United States); Wisniewski, John [Department of Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK 73019 (United States); Shetrone, Matthew [University of Texas, McDonald Observatory, 3640 Dark Sky Drive, Fort Davis, TX (United States); Bizyaev, Dmitry; Ebelke, Garrett [Apache Point Observatory, 2001 Apache Point Rd, Sunspot, NM 88349 (United States); Davenport, James R. A. [Department of Astronomy, University of Washington, Box 351580, U.W., Seattle, WA 98195-1580 (United States); Feuillet, Diane; Holtzman, Jon [Department of Astronomy, New Mexico State University, 1780 E University Ave, Las Cruces, NM 88003 (United States); Frinchaboy, Peter M. [Department of Physics and Astronomy, Texas Christian University, Box 298840, Fort Worth, TX 76129 (United States); Mészáros, Sz. [Instituto de Astrofísica de Canarias (IAC), E-38200 La Laguna, Tenerife (Spain); Schneider, Donald P. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); and others

    2014-04-01

    The Apache Point Observatory Galactic Evolution Experiment (APOGEE)—one of the Sloan Digital Sky Survey III programs—is using near-infrared (NIR) spectra of ∼100,000 red giant branch star candidates to study the structure of the Milky Way. In the course of the survey, APOGEE also acquires spectra of hot field stars to serve as telluric calibrators for the primary science targets. We report the serendipitous discovery of two rare, fast-rotating B-stars of the σ Ori E type among those blue field stars observed during the first year of APOGEE operations. Both of the discovered stars display the spectroscopic signatures of rigidly rotating magnetospheres (RRM) common to this class of highly magnetized (B ∼ 10 kGauss) stars, increasing the number of known RRM stars by ∼10%. One (HD 345439) is a main-sequence B-star with unusually strong He absorption (similar to σ Ori E), while the other (HD 23478) fits a ''He-normal'' B3IV classification. We combine the APOGEE discovery spectra with other optical and NIR spectra of these two stars, and of σ Ori E itself, to show how NIR spectroscopy can be a uniquely powerful tool for discovering more of these rare objects, which may show little/no RRM signatures in their optical spectra. We discuss the potential for further discovery of σ Ori E type stars, as well as the implications of our discoveries for the population of these objects and insights into their origin and evolution.

  16. Intraoral blue (Jadassohn-Tieche) nevus.

    Science.gov (United States)

    Hasse, C D; Zoutendam, G L; Gombas, O F

    1978-05-01

    Blue nevus of the oral mucosa is a distinctly uncommon clincial entity. Careful review of the literature yielded thirty-one previously reported cases. The present article reports the occurrence of a blue nevus of the hard palate in a 58-year-old man. It is of interest since it is the smallest (1 by 1 mm.) intraoral blue nevus to be reported. A clinicopathologic study of the previous thirty-one cases and of our case suggests that this lesion has no age or sex predilection. The most common site of occurrence was the hard palate. There appears to be no tendency toward recurrence. A brief review of the historical background, clinical features, theories of possible origin, and differential diagnosis is presented. Excisional biopsy of localized areas of oral pibmentation, together with histopathologic study, is indicated to rule out melanoma.

  17. Determination of the upper mass limit for stars producing white-dwarf remnants

    International Nuclear Information System (INIS)

    Romanishin, W.; Angel, J.R.P.

    1980-01-01

    We have searched ultraviolet and red plates of four open clusters (NGC 2168, 2287, 2422, and 6633) for faint blue objects which might be white dwarf members of the clusters. The most massive stars in these clusters range from 3 to 6 M/sub sun/. We find a definite concentration of faint blue objects in the clusters. This fact, plus initial photoelectric photometry, provides strong support for the identification of many of these objects as cluster white dwarfs. By modeling the expected number of possible white dwarfs in each cluster, we are able to put some limits on m/sub w/, the upper stellar mass limit for formation of white dwarfs. Our data require that some stars of at least 5 M/sub sun/ have evolved into white dwarfs and give a most probable value of 7 M/sub sun/ for m/sub w/

  18. A RE-EVALUATION OF THE EVOLVED STARS IN THE GLOBULAR CLUSTER M13

    International Nuclear Information System (INIS)

    Sandquist, Eric L.; Gordon, Mark; Levine, Daniel; Bolte, Michael

    2010-01-01

    We have analyzed photometry from space- and ground-based cameras to identify all bright red giant branch (RGB), horizontal branch (HB), and asymptotic giant branch (AGB) stars within 10' of the center of the globular cluster M13. We identify a modest (7%) population of HB stars redder than the primary peak (including RR Lyrae variables at the blue end of the instability strip) that is somewhat more concentrated to the cluster core than the rest of the evolved stars. We find support for the idea that they are noticeably evolved and in the late stages of depleting helium in their cores. This resolves a disagreement between distance moduli derived from the tip of the RGB and from stars in or near the RR Lyrae instability strip. We identified disagreements between HB model sets on whether stars with T eff ∼ eff ∼ eff ∼ 22, 000 K) as previously suggested. These stars are brighter than other stars of similar color (either redder or bluer), and may be examples of 'early hot flashers' that ignite core helium fusion shortly after leaving the RGB. We used ultraviolet photometry to identify hot post-HB stars, and based on their numbers (relative to canonical AGB stars) we estimate the position on the HB where the morphology of the post-HB tracks change to I ∼ 17.3, between the two peaks in the HB distribution. Concerning the possibility of helium enrichment in M13, we revisited the helium-sensitive R ratio, applying a new method for correcting star counts for larger lifetimes of hot HB stars. We find that M13's R ratio is in agreement with theoretical values for primordial helium abundance Y P = 0.245 and inconsistent with a helium enhancement ΔY = 0.04. The brightness of the HB (both in comparison to the end of the canonical HB and to the tip of the RGB) also appears to rule out the idea that the envelopes of the reddest HB stars have been significantly enriched in helium. The absolute colors of the turnoffs of M3 and M13 potentially may be used to look for

  19. Confirmation of the Luminous Blue Variable Status of MWC 930

    Directory of Open Access Journals (Sweden)

    A. S. Miroshnichenko

    2014-01-01

    Full Text Available We present spectroscopic and photometric observations of the emission-line star MWC 930 (V446 Sct during its long-term optical brightening in 2006–2013. Based on our earlier data we suggested that the object has features found in Luminous Blue Variables (LBV, such as a high luminosity (~3 105 L⊙, a low wind terminal velocity (~140 km s−1, and a tendency to show strong brightness variations (~1 mag over 20 years. For the last ~7 years it has been exhibiting a continuous optical and near-IR brightening along with a change of the emission-line spectrum appearance and cooling of the star’s photosphere. We present the object’s V-band light curve, analyze the spectral variations, and compare the observed properties with those of other recognized Galactic LBVs, such as AG Car and HR Car. Overall we conclude the MWC 930 is a bona fide Galactic LBV that is currently in the middle of an S Dor cycle.

  20. Early Blue Excess from the Type Ia Supernova 2017cbv and Implications for Its Progenitor

    International Nuclear Information System (INIS)

    Hosseinzadeh, Griffin; Howell, D. Andrew; McCully, Curtis; Arcavi, Iair; Sand, David J.; Tartaglia, Leonardo; Valenti, Stefano; Bostroem, K. Azalee; Brown, Peter; Kasen, Daniel; Hsiao, Eric Y.; Davis, Scott; Shahbandeh, Melissa; Stritzinger, Maximilian D.

    2017-01-01

    We present very early, high-cadence photometric observations of the nearby Type Ia SN 2017cbv. The light curve is unique in that it has a blue bump during the first five days of observations in the U , B , and g bands, which is clearly resolved given our photometric cadence of 5.7 hr during that time span. We model the light curve as the combination of early shocking of the supernova ejecta against a nondegenerate companion star plus a standard SN Ia component. Our best-fit model suggests the presence of a subgiant star 56 R _☉ from the exploding white dwarf, although this number is highly model-dependent. While this model matches the optical light curve well, it overpredicts the observed flux in the ultraviolet bands. This may indicate that the shock is not a blackbody, perhaps because of line blanketing in the UV. Alternatively, it could point to another physical explanation for the optical blue bump, such as interaction with circumstellar material or an unusual nickel distribution. Early optical spectra of SN 2017cbv show strong carbon (C ii λ 6580) absorption up through day −13 with respect to maximum light, suggesting that the progenitor system contains a significant amount of unburned material. These early results on SN 2017cbv illustrate the power of early discovery and intense follow-up of nearby supernovae to resolve standing questions about the progenitor systems and explosion mechanisms of SNe Ia.

  1. Early Blue Excess from the Type Ia Supernova 2017cbv and Implications for Its Progenitor

    Energy Technology Data Exchange (ETDEWEB)

    Hosseinzadeh, Griffin; Howell, D. Andrew; McCully, Curtis; Arcavi, Iair [Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117-5575 (United States); Sand, David J.; Tartaglia, Leonardo [Department of Astronomy/Steward Observatory, 933 North Cherry Avenue, Room N204, Tucson, AZ 85721-0065 (United States); Valenti, Stefano; Bostroem, K. Azalee [Department of Physics, University of California, 1 Shields Avenue, Davis, CA 95616-5270 (United States); Brown, Peter [Mitchell Institute for Fundamental Physics and Astronomy, Texas A and M University, College Station, TX 77843-4242 (United States); Kasen, Daniel [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720-8169 (United States); Hsiao, Eric Y.; Davis, Scott; Shahbandeh, Melissa [Department of Physics, Florida State University, 77 Chieftain Way, Tallahassee, FL 32306-4350 (United States); Stritzinger, Maximilian D., E-mail: griffin@lco.global [Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark)

    2017-08-20

    We present very early, high-cadence photometric observations of the nearby Type Ia SN 2017cbv. The light curve is unique in that it has a blue bump during the first five days of observations in the U , B , and g bands, which is clearly resolved given our photometric cadence of 5.7 hr during that time span. We model the light curve as the combination of early shocking of the supernova ejecta against a nondegenerate companion star plus a standard SN Ia component. Our best-fit model suggests the presence of a subgiant star 56 R {sub ☉} from the exploding white dwarf, although this number is highly model-dependent. While this model matches the optical light curve well, it overpredicts the observed flux in the ultraviolet bands. This may indicate that the shock is not a blackbody, perhaps because of line blanketing in the UV. Alternatively, it could point to another physical explanation for the optical blue bump, such as interaction with circumstellar material or an unusual nickel distribution. Early optical spectra of SN 2017cbv show strong carbon (C ii λ 6580) absorption up through day −13 with respect to maximum light, suggesting that the progenitor system contains a significant amount of unburned material. These early results on SN 2017cbv illustrate the power of early discovery and intense follow-up of nearby supernovae to resolve standing questions about the progenitor systems and explosion mechanisms of SNe Ia.

  2. The unusual ISM in Blue and Dusty Gas Rich Galaxies (BADGRS).

    Science.gov (United States)

    Dunne, L.; Zhang, Z.; De Vis, P.; Clark, C. J. R.; Oteo, I.; Maddox, S. J.; Cigan, P.; de Zotti, G.; Gomez, H. L.; Ivison, R. J.; Rowlands, K.; Smith, M. W. L.; van der Werf, P.; Vlahakis, C.; Millard, J. S.

    2018-06-01

    The Herschel-ATLAS unbiased survey of cold dust in the local Universe is dominated by a surprising population of very blue (FUV - K 0.5). Dubbed `Blue and Dusty Gas Rich Sources' (BADGRS) they have cold diffuse dust temperatures, and the highest dust-to-stellar mass ratios of any galaxies in the local Universe. Here, we explore the molecular ISM in a representative sample of BADGRS, using very deep {CO(J_{up}=1,2,3)} observations across the central and outer disk regions. We find very low CO brightnesses (Tp = 5 - 30 mK), despite the bright far-infrared emission and metallicities in the range 0.5 UV attenuation for their UV colour suggestive of an SMC-type dust attenuation curve, different star formation histories or different dust/star geometry. They lie in a similar part of the IRX-β space as z ˜ 5 galaxies and may be useful as local analogues for high gas fraction galaxies in the early Universe.

  3. Large Magellanic Cloud helium-rich peculiar blue supergiants and SN 1987A

    International Nuclear Information System (INIS)

    Tuchman, Y.; Wheeler, J.C.

    1990-01-01

    The theoretical distribution of massive stars in the H-R diagram is compared to the revised data of Fitzpatrick and Garmany for the LMC. Preferred models of about 20 M solar masses undergo a thermal contraction at T(eff) about 35,000 K at the end of core hydrogen burning but reestablish thermal equilibrium to the red of the main sequence at T(eff) about 20,000 K after ignition of a hydrogen-burning shell. They then evolve on a nuclear time scale to T(eff) about 6000 K where they lose thermal equilibrium and jump to the Hayashi track. The theoretical and observed distributions agree with two significant exceptions: the blue thermal contraction gap is overpopulated compared to the theory, and there is a ledge crossing the center of the H-R diagram. The hypothesis that some of the observed stars in the blue gap are secondaries that have accreted helium-rich matter from deep within the hydrogen envelope of a red supergiant primary is explored. Some preliminary observational justification is given. 27 refs

  4. Star-shaped ladder-type ter(p-phenylene)s for efficient multiphoton absorption.

    Science.gov (United States)

    Guo, Lei; Li, King Fai; Wong, Man Shing; Cheah, Kok Wai

    2013-05-04

    Star-shaped ladder-type ter(p-phenylene)s exhibit remarkably efficient multiphoton absorption properties with 2PA cross-section up to 2579 GM at 700 nm and 3PA cross-section up to 3.35 × 10(-76) cm(6) s(2) in the femtosecond regime for a blue-emissive molecule despite having such a short π-conjugated framework.

  5. Observation of Bowen fluorescence and other phenomena in five symbiotic stars

    International Nuclear Information System (INIS)

    Wallerstein, G.; Garnavich, P.M.; Schachter, J.; Oke, J.B.

    1991-01-01

    Wavelength measurements and line identifications in the 3200-3600 A regions are presented for the symbiotic stars AG Dra, HM Sge, V1016 Cyg, V1329 Cyg, Z And, and R Aqr. The O III lines excited via Bowen's mechanism are analyzed in detail, and a shell model yielding reasonable shell thicknesses and electron densities is described. The Ne/Fe ratio is derived for five of the systems, and spectra in the blue region are briefly described. 42 refs

  6. Ultracompact X-ray binary stars

    NARCIS (Netherlands)

    Haaften, L.M. van

    2013-01-01

    Ultracompact X-ray binary stars usually consist of a neutron star and a white dwarf, two stars bound together by their strong gravity and orbiting each other very rapidly, completing one orbit in less than one hour. Neutron stars are extremely compact remnants of the collapsed cores of massive stars

  7. Numerical study of rotating relativistic stars

    International Nuclear Information System (INIS)

    Wilson, J.R.

    1975-01-01

    The equations of structure for rotating stars in general relativity are presented and put in a form suitable for computer calculations. The results of equilibrium calculations for supermassive stars, neutron stars, and magnetically supported stars are reported, as are calculations of collapsing, rotating, and magnetized stars in the slowly changing gravitational field approximation. (auth)

  8. The spectrum of dermatoscopic patterns in blue nevi.

    Science.gov (United States)

    Di Cesare, Antonella; Sera, Francesco; Gulia, Andrea; Coletti, Gino; Micantonio, Tamara; Fargnoli, Maria Concetta; Peris, Ketty

    2012-08-01

    Blue nevi are congenital or acquired, dermal dendritic melanocytic proliferations that can simulate melanocytic and nonmelanocytic lesions including melanoma, cutaneous metastasis of melanoma, Spitz/Reed nevi, and basal cell carcinoma. We sought to investigate global and local dermatoscopic patterns of blue nevi compared with melanomas and basal cell carcinomas. We retrospectively analyzed global and local features in 95 dermatoscopic images of blue nevi and in 190 melanomas and basal cell carcinomas that were selected as control lesions on the basis of similar pigmentation. Lesion pigmentation was classified as monochromatic, dichromatic, or multichromatic. A global pattern characterized by homogeneous pigmentation was observed in all of 95 (100%) blue nevi. Eighty of 95 (84.2%) blue nevi presented a homogeneous pattern consisting of one color (blue, black, or brown) or two colors (blue-brown, blue-gray, or blue-black). Fifteen of 95 (15.8%) blue nevi had a multichromatic (blue, gray, black, brown, and/or red) pigmentation. In all, 47 of 95 (49.5%) blue nevi were characterized by pigmentation in the absence of pigment network or any other local dermatoscopic features. And 48 of 95 (50.5%) blue nevi showed local dermatoscopic patterns including whitish scarlike depigmentation, dots/globules, vascular pattern, streaks, and networklike pattern. The study was retrospective and involved only Caucasian people of Italian origin. The characteristic feature of blue nevi is a homogeneous pigmentation that is blue, blue-gray, blue-brown, or blue-black. We showed that a wide spectrum of local dermatoscopic features (whitish scarlike depigmentation, dots/globules, peripheral streaks or vessels) may also be present. In such cases, clinical and dermatoscopic distinction from melanoma or nonmelanocytic lesions may be difficult or impossible, and surgical excision is necessary. Copyright © 2011 American Academy of Dermatology, Inc. Published by Mosby, Inc. All rights reserved.

  9. Investigation of Υ Dor - δ Sct hybrid stars based on high precission space photometry and complementary ground based spectroscopy

    International Nuclear Information System (INIS)

    Hareter, M.

    2013-01-01

    in the gamma Dor regime, but not for stars hotter than the blue border of the gamma Dor instability strip, as the hybrids are. Thus, my finding is an evidence for another driving mechanism, which excites the observed g modes of hybrid stars and gamma Dor candidates beyond the hot border of the gamma Dor instability strip. A comparison to the pulsation periods of delta Sct stars show a discrepancy for p modes as well. For delta Sct stars a temperature - period relation was found but none for hybrids. This finding suggests that the hybrid stars form a different class of pulsating stars and are not merely a mixture of delta Sct and gamma Dor type pulsation. On the other hand the hybrid stars occupy the same area in the Hertzsprung-Russell diagram as delta Sct do and therefore a different stellar structure seems unreasonable. The investigation of constant period spacings of the g modes of the gamma Dor stars yields generally too low values of what is expected from theory. I find spacings that would require l > 3 modes to explain my findings. Such modes, however, suffer from cancellation effects and are hardly detectable even by such a high precision photometer as CoRoT is. As a caveat I mention that based on my data no mode identification can be done which leaves the possi- bility that modes of different l mimic a constant period spacing. To explore a possible connection between the hybrid pulsation and chemical abundance patterns, a detailed abundance analysis was done for two stars. This analysis resulted in one hybrid and Am star, while the other hybrid does not show this kind of chemical peculiarity. Thus, there is no connection be- tween the hybrid phenomenon and hybrid pulsation. (author) [de

  10. The Spacelab IPS Star Simulator

    Science.gov (United States)

    Wessling, Francis C., III

    The cost of doing business in space is very high. If errors occur while in orbit the costs grow and desired scientific data may be corrupted or even lost. The Spacelab Instrument Pointing System (IPS) Star Simulator is a unique test bed that allows star trackers to interface with simulated stars in a laboratory before going into orbit. This hardware-in-the loop testing of equipment on earth increases the probability of success while in space. The IPS Star Simulator provides three fields of view 2.55 x 2.55 degrees each for input into star trackers. The fields of view are produced on three separate monitors. Each monitor has 4096 x 4096 addressable points and can display 50 stars (pixels) maximum at a given time. The pixel refresh rate is 1000 Hz. The spectral output is approximately 550 nm. The available relative visual magnitude range is 2 to 8 visual magnitudes. The star size is less than 100 arc seconds. The minimum star movement is less than 5 arc seconds and the relative position accuracy is approximately 40 arc seconds. The purpose of this paper is to describe the LPS Star Simulator design and to provide an operational scenario so others may gain from the approach and possible use of the system.

  11. The birth of star clusters

    CERN Document Server

    2018-01-01

    All stars are born in groups. The origin of these groups has long been a key question in astronomy, one that interests researchers in star formation, the interstellar medium, and cosmology. This volume summarizes current progress in the field, and includes contributions from both theorists and observers. Star clusters appear with a wide range of properties, and are born in a variety of physical conditions. Yet the key question remains: How do diffuse clouds of gas condense into the collections of luminous objects we call stars? This book will benefit graduate students, newcomers to the field, and also experienced scientists seeking a convenient reference.

  12. Dynamical Friction in Multi-component Evolving Globular Clusters

    Science.gov (United States)

    Alessandrini, Emiliano; Lanzoni, Barbara; Miocchi, Paolo; Ciotti, Luca; Ferraro, Francesco R.

    2014-11-01

    We use the Chandrasekhar formalism and direct N-body simulations to study the effect of dynamical friction on a test object only slightly more massive than the field stars, orbiting a spherically symmetric background of particles with a mass spectrum. The main goal is to verify whether the dynamical friction time (t DF) develops a non-monotonic radial dependence that could explain the bimodality of the blue straggler radial distributions observed in globular clusters. In these systems, in fact, relaxation effects lead to a mass and velocity radial segregation of the different mass components, so that mass-spectrum effects on t DF are expected to be dependent on radius. We find that in spite of the presence of different masses, t DF is always a monotonic function of radius, at all evolutionary times and independently of the initial concentration of the simulated cluster. This is because the radial dependence of t DF is largely dominated by the total mass density profile of the background stars (which is monotonically decreasing with radius). Hence, a progressive temporal erosion of the blue straggler star (BSS) population at larger and larger distances from the cluster center remains the simplest and the most likely explanation of the shape of the observed BSS radial distributions, as suggested in previous works. We also confirm the theoretical expectation that approximating a multi-mass globular cluster as made of (averaged) equal-mass stars can lead to significant overestimations of t DF within the half-mass radius.

  13. NUCLEOSYNTHESIS AND EVOLUTION OF MASSIVE METAL-FREE STARS

    International Nuclear Information System (INIS)

    Heger, Alexander; Woosley, S. E.

    2010-01-01

    The evolution and explosion of metal-free stars with masses 10-100 M sun are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. Such stars would have been the first to form after the big bang and may have left a distinctive imprint on the composition of the early universe. When the supernova yields are integrated over a Salpeter initial mass function (IMF), the resulting elemental abundance pattern is qualitatively solar, but with marked deficiencies of odd-Z elements with 7 ≤ Z ≤ 13. Neglecting the contribution of the neutrino wind from the neutron stars that they form, no appreciable abundances are made for elements heavier than germanium. The computed pattern compares favorably with what has been observed in metal-deficient stars with [Z] ∼ sun ; where 1 B = 1 Bethe = 10 51 erg) for a Salpeter IMF, and may have played a role in reionizing the universe. Neglecting rotation, most of the stars end their lives as blue supergiants and form supernovae with distinctive light curves resembling SN 1987A, but some produce primary nitrogen due to dredge-up and become red supergiants. These make brighter supernovae like typical Type IIp's. For the lower mass supernovae considered, the distribution of remnant masses clusters around typical modern neutron star masses, but above 20-30 M sun , with the value depending on explosion energy, black holes are copiously formed by fallback, with a maximum hole mass of ∼40 M sun . A novel automated fitting algorithm is developed for determining optimal combinations of explosion energy, mixing, and IMF in the large model database to agree with specified data sets. The model is applied to the low-metallicity sample of Cayrel et al. and the two ultra-iron-poor stars HE0107-5240 and HE1327-2326. Best agreement with these very low metallicity stars is achieved with very little mixing, and none of the metal-deficient data sets considered show the need for a high-energy explosion component. In

  14. The Double Star mission

    Directory of Open Access Journals (Sweden)

    Liu

    2005-11-01

    Full Text Available The Double Star Programme (DSP was first proposed by China in March, 1997 at the Fragrant Hill Workshop on Space Science, Beijing, organized by the Chinese Academy of Science. It is the first mission in collaboration between China and ESA. The mission is made of two spacecraft to investigate the magnetospheric global processes and their response to the interplanetary disturbances in conjunction with the Cluster mission. The first spacecraft, TC-1 (Tan Ce means "Explorer", was launched on 29 December 2003, and the second one, TC-2, on 25 July 2004 on board two Chinese Long March 2C rockets. TC-1 was injected in an equatorial orbit of 570x79000 km altitude with a 28° inclination and TC-2 in a polar orbit of 560x38000 km altitude. The orbits have been designed to complement the Cluster mission by maximizing the time when both Cluster and Double Star are in the same scientific regions. The two missions allow simultaneous observations of the Earth magnetosphere from six points in space. To facilitate the comparison of data, half of the Double Star payload is made of spare or duplicates of the Cluster instruments; the other half is made of Chinese instruments. The science operations are coordinated by the Chinese DSP Scientific Operations Centre (DSOC in Beijing and the European Payload Operations Service (EPOS at RAL, UK. The spacecraft and ground segment operations are performed by the DSP Operations and Management Centre (DOMC and DSOC in China, using three ground station, in Beijing, Shanghai and Villafranca.

  15. Symbiotic star AG Dra

    International Nuclear Information System (INIS)

    Ipatov, A.P.; Yudin, B.F.; Moskovskij Gosudarstvennyj Univ.

    1986-01-01

    The results obtained from photometric (in the UBVRJHKLM system) and spectrophotometric (in the range 0.33-0.75 μm) observations of symbiotic star AG Dra are presented. The cool component of this star is a red giant with approximately constant brightness (ΔJ ≤ 0 m .3) classified as K4-K5. This red giant fills it's Roche loble and probably is on the assymptotic giant branch of the HR diagramm. The presence of IR excess in 5 μm associated with radiation of the gaseous envelope with the mass of M≅ 10 -6 M sun have been detected. Observations of AG Dra indicate that growing of the bolometric flux of a hot component is accompanied with decreasing effective temperature. The hot component of the system is probably an accerting red dwarf with the mass M≅ 0.4 M sun and disk accretion of matter of cool star with the rate M >or ∼ 10 -4 M sun year in equatorial region. Increase of accretion rate during the outburst of AG Dra leads to the increase of stellar wind from the red dwarf surface and the decrease of it's effective temperature. The hot component of AG Dra may also be considered as a white Dwarf with luminosity L 3 L sun and R eff >or approx. 0.2 R sun . In this case gravitational energy of accreting matter M > or ∼ 10 -6 M sun / year would be the source of the hot component outbursts. The luminosity between outbursts is determined by energy generation from the burning hydrogen layer source

  16. Inner Milky Way Raging with Star Formation

    Science.gov (United States)

    2008-01-01

    More than 444,580 frames from NASA's Spitzer Space Telescope were stitched together to create this portrait of the raging star-formation occurring in the inner Milky Way. As inhabitants of a flat galactic disk, Earth and its solar system have an edge-on view of their host galaxy, like looking a glass dish from its edge. From our perspective, most of the galaxy is condensed into a blurry narrow band of light that stretches completely around the sky, also known as the galactic plane. In this mosaic the galactic plane is broken up into five components: the far-left side of the plane (top image); the area just left of the galactic center (second to top); galactic center (middle); the area to the right of galactic center (second to bottom); and the far-right side of the plane (bottom). Together, these panels represent more than 50 percent of our entire Milky Way galaxy. The red haze that permeates the picture comes from organic molecules called polycyclic aromatic hydrocarbons, which are illuminated by light from massive baby stars. On Earth, these molecules are found in automobile exhaust, or charred barbeque grills anywhere carbon molecules are burned incompletely. The patches of black are dense, obscuring dust clouds impenetrable by even Spitzer's super-sensitive infrared eyes. Bright arcs of white throughout the image are massive stellar incubators. The bluish-white haze that hovers heavily in the middle panel is starlight from the older stellar population towards the center of the galaxy. This picture was taken with Spitzer's infrared array camera, as part of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) project. This is a four-color composite where blue is 3.6-micron light, green is 4.5 microns, orange is 5.8 microns and red is 8.0 microns.

  17. Stars of heaven

    CERN Document Server

    Pickover, Clifford A

    2004-01-01

    Do a little armchair space travel, rub elbows with alien life forms, and stretch your mind to the furthest corners of our uncharted universe. With this astonishing guidebook, you don't have to be an astronomer to explore the mysteries of stars and their profound meaning for human existence. Clifford A. Pickover tackles a range of topics from stellar evolution to the fundamental reasons why the universe permits life to flourish. He alternates sections that explain the mysteries of the cosmos with sections that dramatize mind-expanding concepts through a fictional dialog between futuristic human

  18. Elemental diffusion in stars

    International Nuclear Information System (INIS)

    Michaud, Georges; Montmerle, Thierry

    1977-01-01

    This paper is dealing with the origin of the elements in the universe. The scheme of nucleosynthesis is kept to explain the stellar generation of helium, carbon, etc... from the initial hydrogen; but a nonlinear theory is then elaborated to account for the anomalous abundances which were observed. The chemical elements would diffuse throughout the outer layers of a star under the action of the opposite forces of gravitation and radiation. This theory, with completing the nucleosynthesis, would contribute to give a consistent scheme of the elemental origin and abundances [fr

  19. Hadronic Resonances from STAR

    Directory of Open Access Journals (Sweden)

    Wada Masayuki

    2012-11-01

    Full Text Available The results of resonance particle productions (ρ0, ω, K*, ϕ, Σ*, and Λ* measured by the STAR collaboration at RHIC from various colliding systems and energies are presented. Measured mass, width, 〈pT〉, and yield of those resonances are reviewed. No significant mass shifts or width broadening beyond the experiment uncertainties are observed. New measurements of ϕ and ω from leptonic decay channels are presented. The yields from leptonic decay channels are compared with the measurements from hadronic decay channels and the two results are consistent with each other.

  20. O3 stars

    International Nuclear Information System (INIS)

    Walborn, N.R.

    1982-01-01

    A brief review of the 10 known objects in this earliest spectral class is presented. Two new members are included: HD 64568 in NGC 2467 (Puppis OB2), which provides the first example of an O3 V((f*)) spectrum; and Sk -67 0 22 in the Large Magellanic Cloud, which is intermediate between types O3 If* and WN6-A. In addition, the spectrum of HDE 269810 in the LMC is reclassified as the first of type O3 III (f*). The absolute visual magnitudes of these stars are rediscussed

  1. Star-forming galaxy models: Blending star formation into TREESPH

    Science.gov (United States)

    Mihos, J. Christopher; Hernquist, Lars

    1994-01-01

    We have incorporated star-formation algorithms into a hybrid N-body/smoothed particle hydrodynamics code (TREESPH) in order to describe the star forming properties of disk galaxies over timescales of a few billion years. The models employ a Schmidt law of index n approximately 1.5 to calculate star-formation rates, and explicitly include the energy and metallicity feedback into the Interstellar Medium (ISM). Modeling the newly formed stellar population is achieved through the use of hybrid SPH/young star particles which gradually convert from gaseous to collisionless particles, avoiding the computational difficulties involved in creating new particles. The models are shown to reproduce well the star-forming properties of disk galaxies, such as the morphology, rate of star formation, and evolution of the global star-formation rate and disk gas content. As an example of the technique, we model an encounter between a disk galaxy and a small companion which gives rise to a ring galaxy reminiscent of the Cartwheel (AM 0035-35). The primary galaxy in this encounter experiences two phases of star forming activity: an initial period during the expansion of the ring, and a delayed phase as shocked material in the ring falls back into the central regions.

  2. I-Love relations for incompressible stars and realistic stars

    Science.gov (United States)

    Chan, T. K.; Chan, AtMa P. O.; Leung, P. T.

    2015-02-01

    In spite of the diversity in the equations of state of nuclear matter, the recently discovered I-Love-Q relations [Yagi and Yunes, Science 341, 365 (2013), 10.1126/science.1236462], which relate the moment of inertia, tidal Love number (deformability), and the spin-induced quadrupole moment of compact stars, hold for various kinds of realistic neutron stars and quark stars. While the physical origin of such universality is still a current issue, the observation that the I-Love-Q relations of incompressible stars can well approximate those of realistic compact stars hints at a new direction to approach the problem. In this paper, by establishing recursive post-Minkowskian expansion for the moment of inertia and the tidal deformability of incompressible stars, we analytically derive the I-Love relation for incompressible stars and show that the so-obtained formula can be used to accurately predict the behavior of realistic compact stars from the Newtonian limit to the maximum mass limit.

  3. TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

    Energy Technology Data Exchange (ETDEWEB)

    Liu Tie; Wu Yuefang; Zhang Huawei [Department of Astronomy, Peking University, 100871 Beijing (China); Qin Shengli, E-mail: liutiepku@gmail.com [I. Physikalisches Institut, Universitaet zu Koeln, Zuelpicher Str. 77, 50937 Koeln (Germany)

    2012-05-20

    The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10{sup 3} cm{sup -3} and kinematic temperature {approx}20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

  4. TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

    International Nuclear Information System (INIS)

    Liu Tie; Wu Yuefang; Zhang Huawei; Qin Shengli

    2012-01-01

    The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10 3 cm –3 and kinematic temperature ∼20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

  5. Coomassie Brilliant Blue G is a more potent antagonist of P2 purinergic responses than Reactive Blue 2 (Cibacron Blue 3GA) in rat parotid acinar cells

    International Nuclear Information System (INIS)

    Soltoff, S.P.; McMillian, M.K.; Talamo, B.R.

    1989-01-01

    The ability of Brilliant Blue G (Coomassie Brilliant Blue G) and Reactive Blue 2 (Cibacron Blue 3GA) to block the effects of extracellular ATP on rat parotid acinar cells was examined by evaluating their effects on ATP-stimulated 45Ca 2+ entry and the elevation of [Ca 2+ ]i (Fura 2 fluorescence). ATP (300 microM) increased the rate of Ca 2+ entry to more than 25-times the basal rate and elevated [Ca 2+ ]i to levels more than three times the basal value. Brilliant Blue G and Reactive Blue 2 greatly reduced the entry of 45 Ca 2+ into parotid cells, but the potency of Brilliant Blue G (IC50 approximately 0.4 microM) was about 100-times that of Reactive Blue 2. Fura 2 studies demonstrated that inhibitory concentrations of these compounds did not block the cholinergic response of these cells, thus demonstrating the selectivity of the dye compounds for purinergic receptors. Unlike Reactive Blue 2, effective concentrations of Brilliant Blue G did not substantially quench Fura 2 fluorescence. The greater potency of Brilliant Blue G suggests that it may be very useful in identifying P2-type purinergic receptors, especially in studies which utilize fluorescent probes

  6. Prussian Blue Analogues of Reduced Dimensionality

    NARCIS (Netherlands)

    Gengler, Regis Y. N.; Toma, Luminita M.; Pardo, Emilio; Lloret, Francesc; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Gournis, Dimitrios; Rudolf, Petra

    2012-01-01

    Mixed-valence polycyanides (Prussian Blue analogues) possess a rich palette of properties spanning from room-temperature ferromagnetism to zero thermal expansion, which can be tuned by chemical modifications or the application of external stimuli (temperature, pressure, light irradiation). While

  7. Blue whales respond to anthropogenic noise.

    Directory of Open Access Journals (Sweden)

    Mariana L Melcón

    Full Text Available Anthropogenic noise may significantly impact exposed marine mammals. This work studied the vocalization response of endangered blue whales to anthropogenic noise sources in the mid-frequency range using passive acoustic monitoring in the Southern California Bight. Blue whales were less likely to produce calls when mid-frequency active sonar was present. This reduction was more pronounced when the sonar source was closer to the animal, at higher sound levels. The animals were equally likely to stop calling at any time of day, showing no diel pattern in their sensitivity to sonar. Conversely, the likelihood of whales emitting calls increased when ship sounds were nearby. Whales did not show a differential response to ship noise as a function of the time of the day either. These results demonstrate that anthropogenic noise, even at frequencies well above the blue whales' sound production range, has a strong probability of eliciting changes in vocal behavior. The long-term implications of disruption in call production to blue whale foraging and other behaviors are currently not well understood.

  8. African Retentions in Blues and Jazz.

    Science.gov (United States)

    Meadows, Eddie S.

    1979-01-01

    The perseverance of African musical characteristics among American Blacks is an historic reality. African retentions have been recorded in Black music of the antebellum period. Various African scales and rhythms permeate Black American music today as evidenced in the retentions found in blues and jazz. (RLV)

  9. Nanotubes based on monolayer blue phosphorus

    KAUST Repository

    Montes Muñoz, Enrique

    2016-07-08

    We demonstrate structural stability of monolayer zigzag and armchair blue phosphorus nanotubes by means of molecular dynamics simulations. The vibrational spectrum and electronic band structure are determined and analyzed as functions of the tube diameter and axial strain. The nanotubes are found to be semiconductors with a sensitive indirect band gap that allows flexible tuning.

  10. Statistical thermodynamics of supercapacitors and blue engines

    NARCIS (Netherlands)

    van Roij, R.H.H.G.

    2013-01-01

    We study the thermodynamics of electrode-electrolyte systems, for instance supercapacitors filled with an ionic liquid or blue-energy devices filled with river- or sea water. By a suitable mapping of thermodynamic variables, we identify a strong analogy with classical heat engines. We introduce

  11. Improper, Blue-Shifting Hydrogen Bond

    Czech Academy of Sciences Publication Activity Database

    Hobza, Pavel; Havlas, Zdeněk

    2002-01-01

    Roč. 108, - (2002), s. 325-334 ISSN 1432-881X R&D Projects: GA MŠk LN00A032 Institutional research plan: CEZ:AV0Z4055905; CEZ:AV0Z4040901 Keywords : improper, blue-shifting hydrogen bond * properties * nature Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.421, year: 2002

  12. Blue laser phase change recording system

    International Nuclear Information System (INIS)

    Hofmann, Holger; Dambach, S.Soeren; Richter, Hartmut

    2002-01-01

    The migration paths from DVD phase change recording with red laser to the next generation optical disk formats with blue laser and high NA optics are discussed with respect to optical aberration margins and disc capacities. A test system for the evaluation of phase change disks with more than 20 GB capacity is presented and first results of the recording performance are shown

  13. Biodecolorization and biodegradation of Reactive Blue by ...

    African Journals Online (AJOL)

    SERVER

    2007-06-18

    Jun 18, 2007 ... Aspergillus sp. effectively decolorized Reactive Blue and other structurally different synthetic dyes. Agitation was found to be an important ... Few chemically different dyes such as Reactive Black (75%), Reactive Yellow (70%),. Reactive Red (33%) and ..... Degradation of azo dyes by the lignin degrading ...

  14. T's and Blues. Specialized Information Service.

    Science.gov (United States)

    Do It Now Foundation, Phoenix, AZ.

    This compilation of journal articles provides basic information on abuse of Talwin, a mild prescription painkiller (T's), and Pyribenzamine, a nonprescription antihistimine (Blues). These two drugs, taken in combination, produce an effect similar to that produced by heroin. Stories from "Drug Survival News,""Emergency…

  15. [The dangers of blue light: True story!].

    Science.gov (United States)

    Renard, G; Leid, J

    2016-05-01

    The dangers of the blue light are the object of numerous publications, for both the scientific community and the general public. The new prolific development of light sources emitting potentially toxic blue light (415-455nm) ranges from LED (Light Emitting Diodes) lamps for interior lighting to television screens, computers, digital tablets and smartphones using OLED (Organic Light Emitting Diode) or AMOLED (Active-Matrix Organic Light Emitting Diode) technology. First we will review some technical terms and the main characteristics of light perceived by the human eye. Then we will discuss scientific proof of the toxicity of blue light to the eye, which may cause cataract or macular degeneration. Analysis of the light spectra of several light sources, from natural light to LED lamps, will allow us to specify even better the dangers related to each light source. LED lamps, whether used as components for interior lighting or screens, are of concern if they are used for extended viewing times and at short distance. While we can protect ourselves from natural blue light by wearing colored glasses which filter out, on both front and back surfaces, the toxic wavelengths, it is more difficult to protect oneself from LED lamps in internal lighting, the use of which should be restricted to "white warmth" lamps (2700K). As far as OLED or AMOLED screens are concerned, the only effective protection consists of using them occasionally and only for a short period of time. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

  16. Blue LED irradiation to hydration of skin

    Science.gov (United States)

    Menezes, Priscila F. C.; Requena, Michelle B.; Lizarelli, Rosane F., Z.; Bagnato, Vanderlei S.

    2015-06-01

    Blue LED system irradiation shows many important properties on skin as: bacterial decontamination, degradation of endogenous skin chromophores and biostimulation. In this clinical study we prove that the blue light improves the skin hydration. In the literature none authors reports this biological property on skin. Then this study aims to discuss the role of blue light in the skin hydration. Twenty patients were selected to this study with age between 25-35 years old and phototype I, II and III. A defined area from forearm was pre determined (A = 4.0 cm2). The study was randomized in two treatment groups using one blue light device (power of 5.3mW and irradiance of 10.8mW/cm2). The first treatment group was irradiated with 3J/cm2 (277seconds) and the second with 6J/cm2 (555 seconds). The skin hydration evaluations were done using a corneometer. The measurements were collected in 7, 14, 21 and 30 days, during the treatment. Statistical test of ANOVA, Tukey and T-Student were applied considering 5% of significance. In conclusion, both doses were able to improve the skin hydration; however, 6J/cm2 has kept this hydration for 30 days.

  17. Biodecolorization and biodegradation of Reactive Blue by ...

    African Journals Online (AJOL)

    Aspergillus sp. effectively decolorized Reactive Blue and other structurally different synthetic dyes. Agitation was found to be an important parameter, while glucose (99%), sucrose (97%) and mannitol (98%) were the best carbon sources for the decolorization. Decolorization was effective in an acidic environment (pH 3).

  18. Statistical investigation of flare stars. III. Flare stars in the general galactic star field

    International Nuclear Information System (INIS)

    Mirzoyan, L.V.; Ambaryan, V.V.; Garibdzhanyan, A.T.; Mirzoyan, A.L.

    1989-01-01

    Some questions relating to the existence of a large number of flare stars in the general star field of the Galaxy are discussed. It is shown that only a small proportion of them can be found by photographic observations, and the fraction of field flare stars among such stars found in the regions of star clusters and associations does not exceed 10%. The ratio of the numbers of flare stars of the foreground and the background for a particular system depends on its distance, reaching zero at a distance of about 500 pc. The spatial density of flare stars in the Pleiades is at least two orders of magnitude greater than in the general galactic field. A lower limit for the number of flare stars in the Galaxy is estimated at 4.2 ·10 9 , and the number of nonflare red dwarfs at 2.1·10 10 . There are grounds for believing that they were all formed in star clusters and associations

  19. The Stars of Heaven

    Science.gov (United States)

    Pickover, Clifford A.

    2004-05-01

    Do a little armchair space travel, rub elbows with alien life forms, and stretch your mind to the furthest corners of our uncharted universe. With this astonishing guidebook, you don't have to be an astronomer to explore the mysteries of stars and their profound meaning for human existence. Clifford A. Pickover tackles a range of topics from stellar evolution to the fundamental reasons why the universe permits life to flourish. He alternates sections that explain the mysteries of the cosmos with sections that dramatize mind-expanding concepts through a fictional dialog between futuristic humans and their alien peers (who embark on a journey beyond the reader's wildest imagination). This highly accessible and entertaining approach turns an intimidating subject into a scientific game open to all dreamers. Told in Pickover's inimitable blend of fascinating state-of-the-art science and whimsical science fiction, and packed with numerous diagrams and illustrations, The Stars of Heaven unfolds a world of paradox and mystery, one that will intrigue anyone who has ever pondered the night sky with wonder.

  20. Stars and Planets

    Science.gov (United States)

    Neta, Miguel

    2014-05-01

    'Estrelas e Planetas' (Stars and Planets) project was developed during the academic year 2009/2010 and was tested on three 3rd grade classes of one school in Quarteira, Portugal. The aim was to encourage the learning of science and the natural and physical phenomena through the construction and manipulation of materials that promote these themes - in this case astronomy. Throughout the project the students built a small book containing three themes of astronomy: differences between stars and planets, the solar system and the phases of the Moon. To each topic was devoted two sessions of about an hour each: the first to teach the theoretical aspects of the theme and the second session to assembly two pages of the book. All materials used (for theoretical sessions and for the construction of the book) and videos of the finished book are available for free use in www.miguelneta.pt/estrelaseplanetas. So far there is only a Portuguese version but soon will be published in English as well. This project won the Excellency Prize 2011 of Casa das Ciências, a portuguese site for teachers supported by the Calouste Gulbenkian Fundation (www.casadasciencias.org).