Sample records for supergiant stars

  1. Spectral Classification of Cold IRAS Stars: Supergiants

    NASA Astrophysics Data System (ADS)

    Winfrey, S.; Barnbaum, C.; Morris, M.; Omont, A.

    1994-12-01

    We have observed 72 stars with low resolution optical spectra (85 A/mm with 2.3 A/pixel) covering 6000 to 8800 A in an attempt to identify the spectral type and luminosity class of a number of dusty IRAS sources. These stars were chosen from region IIIa of the van der Veen & Habing color-color diagram, where infrared late-type stars are found with generally strong 10?m silicate emission and often OH maser emission. We present here initial classficiation results. These include the probable identification of 19 new M0--4 supergiants and the re-classification of 3 stars formerly categorized as S stars: IRC+70012 (M8 III), NSV12260 (M8 III) and IRC+60374 (M4 I). \\begin{tabular}{|l|c|c|c|l|} IRAS name & old type & new type & other name 03572+5509 & M4 & M4 I & AG Cam 05361+4644 & M6 & M3 I & IRC+50149 17360-3140 & M6,K5 & M2 I & IRC-30309 17513-2313 & M5 & M4 I & V774 Sgr 18025-2113 & M2 & M3-4 I & IRC-20427 18135-1740 & M3 & M2 I & IRC-20455 18522+0021 & M5 & M4 I & IRC+00392 18539+0026 & M & M4 I & IRC+00396 19229+1708 & M4e & M3-4 I & 19307+1338 & & M0 I & 19325+2346 & K5,M0 & M2-3 I & 20004+2955 & K8 & K2-4 I & V1027 Cyg 20015+3019 & M4 & M4 I & V719 Cyg 22048+5914 & & M4 I & RAFGL 4286 22480+6002 & & M0 I & IRC+60370 22512+6100 & S & M4 I & IRC+60374 23000+5932 & M3 & M3 I & AS Cep 23252+6010 & & M4 I & 23278+6000 & M4 & M4 I & IRC+60409

  2. Yellow Hypergiants as Dynamically Unstable Post-Red Supergiant Stars

    NASA Astrophysics Data System (ADS)

    Stothers, Richard B.; Chin, Chao-wen

    2001-10-01

    According to recent theoretical studies, the majority of single stars more massive than 30 Msolar successfully evolve into red supergiants but then lose most of their hydrogen envelopes and metamorphose into hot blue remnants. While they are cool, they become dynamically unstable as a result of high radiation pressure and partial ionization of the gases in their outer layers. It is shown here that these unstable red supergiant models repeatedly shrink and reexpand on a thermal timescale when perturbed by heavy bursts of mass loss. Consequently, they fill up the domain of yellow hypergiants on the Hertzsprung-Russell diagram and display very fast rates of evolution there, as observed.

  3. Surface magnetism of cool giant and supergiant stars

    E-print Network

    Korhonen, Heidi

    2013-01-01

    The existence of starspots on late-type giant stars in close binary systems, that exhibit rapid rotation due to tidal locking, has been known for more than five decades. Photometric monitoring spanning decades has allowed studying the long-term magnetic activity in these stars revealing complicated activity cycles. The development of observing and analysis techniques that has occurred during the past two decades has also enabled us to study the detailed starspot and magnetic field configurations on these active giants. In the recent years magnetic fields have also been detected on slowly rotating giants and supergiant stars. In this paper I review what is known of the surface magnetism in the cool giant and supergiant stars.

  4. Yellow Hypergiants as Dynamically Unstable Post-Red-supergiant Stars

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.; Chin, Chao-wen; Hansen, James E. (Technical Monitor)

    2001-01-01

    According to recent theoretical studies, the majority of single stars more massive than 30 solar mass successfully evolve into red supergiants, but then lose most of their hydrogen envelopes and metamorphose into hot blue remnants. While they are cool, they become dynamically unstable as a result of high radiation pressure and partial ionization of the gases in their outer layers. It is shown here that these unstable red-supergiant models repeatedly shrink and re-expand on a thermal time scale when perturbed by heavy bursts of mass loss. Consequently, they fill up the domain of yellow hypergiants on the Hertzsprung-Russell diagram and display very fast rates of evolution there, as observed.

  5. Water on the Early M Supergiant Stars ? Orionis and ? Cephei

    NASA Astrophysics Data System (ADS)

    Tsuji, T.

    2000-08-01

    We reanalyze the spectra of ? Ori (M2 Iab) and ? Cep (M2 Ia) observed with the balloon-borne telescope Stratoscope II more than 35 years ago, and we confirm the presence of water in these early M supergiant stars. This identification was first proposed by the Stratoscope observers themselves (Woolf, Schwarzschild, and Rose in 1964; and Danielson, Woolf, and Gaustad in 1965), but this important discovery was overlooked for a long time without any follow-up observation. Consequently, this finding has so far had little influence on the theory of the atmosphere of red supergiant stars. A reason for this may be due to an early criticism by Wing and Spinrad, who suggested CN instead of H2O for the spectral features observed by Stratoscope II. This alternative proposition has more easily been accepted since CN has widely been observed from the Sun to red supergiants, while H2O has been observed only in very cool stars such as Mira variables. In fact, we confirm that the self-consistent photospheric model of the early M supergiants shows CN bands but no H2O band in the near-infrared. Nevertheless, we find that the contribution of CN is only minor and that H2O should be the dominant absorber for the 1.4 and 1.9 ?m features on the Stratoscope spectra of ? Ori and ? Cep, a conclusion opposite to that of Wing and Spinrad. The observed spectra can best be interpreted by the water gas with the column density of the order of 1020 cm-2 and temperature about 1500+/-500 K, but they cannot be originating in the photosphere. We suggest a possible presence of a gaseous component not as hot as the chromosphere but warmer than the cool expanding envelope. On the other hand, we notice that the mid-infrared pure-rotation lines of H2O recently discovered on Betelgeuse (? Ori) and Antares (? Sco) by Jennings and Sada may partly be originating in the photosphere, even though the larger part should again be nonphotospheric in origin. Thus, the presence of water possibly originating in the outer atmosphere of Betelgeuse is confirmed by the independent observation in the mid-infrared region. We now conclude that water should be an important new probe on the atmosphere of the early M supergiant stars, for which water has not been recognized as such until recently.

  6. Supergiant Stars as Extragalactic Probes of Cosmic Abundances and Distances

    NASA Astrophysics Data System (ADS)

    Kudritzki, R.

    2013-09-01

    The determination of chemical composition and distances of galaxies is crucial for constraining the theory of galaxy formation and evolution in a dark energy and cold dark matter dominated universe. However, the standard technique using HII regions to determine the metallicity of star forming galaxies, nearby and at high redshift, is subject to large systematic uncertainties that are poorly understood and the determination of accurate distances using Cepheids suffers from uncertainties caused by the metallicity dependence of the period luminosity relationship and extinction and crowding corrections. Multi-object spectroscopy of blue and red supergiant stars - the brightest stars in the universe at visual and NIR wavelengths - provides an attractive alternative. I will present results accumulated over recent years for galaxies in the Local Group and beyond out to a distance of 8 Mpc and will discuss the potential of future work with TMT and E-ELT. Combining the photon collecting power of these next generation telescopes with Adaptive Optics we will be able to study individual supergiant stars in galaxies as distant as the Coma cluster. With spectroscopy of the integrated light of young very massive Star Super Clusters and simple population synthesis techniques we can reach out ten times further

  7. Outer atmospheres of giant and supergiant stars

    NASA Technical Reports Server (NTRS)

    Brown, A.

    1984-01-01

    The properties of the chromospheres, transition regions and coronas of cool evolved stars are reviewed based primarily on recent ultraviolet and X-ray studies. Determinations of mass loss rates using new observational techniques in the ultraviolet and radio spectral regions are discussed and observations indicating general atmospheric motions are considered. The techniques available for the quantitative modeling of these atmospheres are outlined and recent results discussed. Finally, the current rudimentary understanding of the evolution of these outer atmospheres and its causes are considered.

  8. Evolved Massive Stars in the Local Group. I. Identification of Red Supergiants in NGC 6822, M31, and M33

    Microsoft Academic Search

    Philip Massey

    1998-01-01

    Knowledge of the red supergiant (RSG) population of nearby galaxies allows us to probe massive star evolution as a function of metallicity; however, contamination by foreground Galactic dwarfs dominates surveys for red stars in Local Group galaxies beyond the Magellanic Clouds. Model atmospheres predict that low-gravity supergiants will have B-V values that are redder by several tenths of a magnitude

  9. Sodium Excess in Yellow Supergiants: Implications for Rotational Mixing in Massive Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Denissenkov, Pavel A.

    2005-04-01

    Recent high-quality measurements of the sodium abundance in yellow supergiants are used to test the hypothesis of rotational mixing in massive main-sequence stars. It is shown that the Na excess in a large fraction of yellow supergiants with M>~7-10Msolar can only be understood as a result of mixing of Na between the convective core and the radiative envelope in their main-sequence progenitors. We demonstrate that the vertical turbulent diffusion from the Zahn model could be responsible for this extra mixing.

  10. RED SUPERGIANT STARS AS COSMIC ABUNDANCE PROBES. II. NLTE EFFECTS IN J-BAND SILICON LINES

    SciTech Connect

    Bergemann, Maria; Kudritzki, Rolf-Peter; Wuerl, Matthias [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str.1, D-85741 Garching (Germany)] [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str.1, D-85741 Garching (Germany); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Universite Montpellier 2, CNRS, F-34095 Montpellier (France)] [Laboratoire Univers et Particules de Montpellier, Universite Montpellier 2, CNRS, F-34095 Montpellier (France); Davies, Ben [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 OHA (United Kingdom)] [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 OHA (United Kingdom); Gazak, Zach, E-mail: mbergema@mpa-garching.mpg.de, E-mail: Matthias.Wuerl@physik.uni-muenchen.de, E-mail: kud@ifa.hawaii.edu, E-mail: zgazak@ifa.hawaii.edu, E-mail: bertrand.plez@univ-montp2.fr, E-mail: bdavies@ast.cam.ac.uk [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)] [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

    2013-02-20

    Medium-resolution J-band spectroscopy of individual red supergiant stars is a promising tool to investigate the chemical composition of the young stellar population in star-forming galaxies. As a continuation of recent work on iron and titanium, detailed non-LTE (NLTE) calculations are presented to investigate the influence of NLTE on the formation of silicon lines in the J-band spectra of red supergiants. Substantial effects are found resulting in significantly stronger absorption lines of neutral silicon in NLTE. As a consequence, silicon abundances determined in NLTE are significantly smaller than in local thermodynamic equilibrium (LTE) with the NLTE abundance corrections varying smoothly between -0.4 dex and -0.1 dex for effective temperatures between 3400 K and 4400 K. The effects are largest at low metallicity. The physical reasons behind the NLTE effects and the consequences for extragalactic J-band abundance studies are discussed.

  11. Interacting supernovae from photoionization-confined shells around red supergiant stars.

    PubMed

    Mackey, Jonathan; Mohamed, Shazrene; Gvaramadze, Vasilii V; Kotak, Rubina; Langer, Norbert; Meyer, Dominique M-A; Moriya, Takashi J; Neilson, Hilding R

    2014-08-21

    Betelgeuse, a nearby red supergiant, is a fast-moving star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have much more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas close to the star until it explodes. After the supernova explosion, massive shells dramatically affect the supernova light curve, providing a natural explanation for the many supernovae that have signatures of circumstellar interaction. PMID:25119040

  12. Radiative hydrodynamics simulations of red supergiant stars. IV. Gray versus non-gray opacities

    NASA Astrophysics Data System (ADS)

    Chiavassa, A.; Freytag, B.; Masseron, T.; Plez, B.

    2011-11-01

    Context. Red supergiants are massive evolved stars that contribute extensively to the chemical enrichment of our Galaxy. It has been shown that convection in those stars produces large granules that cause surface inhomogeneities and shock waves in the photosphere. The understanding of their dynamics is crucial for unveiling the unknown mass-loss mechanism, their chemical composition, and their stellar parameters. Aims: We present a new generation of red supergiant simulations with a more sophisticated opacity treatment performed with 3D radiative-hydrodynamics code CO5BOLD. Methods: In the code the coupled equations of compressible hydrodynamics and non-local radiation transport are solved in the presence of a spherical potential. The stellar core is replaced by a special spherical inner boundary condition, where the gravitational potential is smoothed and the energy production by fusion is mimicked by a simply producing heat corresponding to the stellar luminosity. All outer boundaries are transmitting for matter and light. The post-processing radiative transfer code OPTIM3D is used to extract spectroscopic and interferometric observables. Results: We show that if one relaxes the assumption of frequency-independent opacities, this leads to a steeper mean thermal gradient in the optical thin region that strongly affects the atomic strengths and the spectral energy distribution. Moreover, the weaker temperature fluctuations reduce the incertitude on the radius determination with interferometry. We show that 1D models of red supergiants must include a turbulent velocity that is calibrated on 3D simulations to obtain the effective surface gravity that mimics the effect of turbulent pressure on the stellar atmosphere. We provide an empirical calibration of the ad hoc micro- and macroturbulence parameters for 1D models using the 3D simulations: we find that there is no clear distinction between the different macroturbulent profiles needed in 1D models to fit 3D synthetic lines.

  13. Three-micron spectra of AGB stars and supergiants in nearby galaxies

    E-print Network

    M. Matsuura; A. A. Zijlstra; J. Th. van Loon; I. Yamamura; A. J. Markwick; P. A. Whitelock; P. M. Woods; J. R. Marshall; M. W. Feast; L. B. F. M. Waters

    2005-01-13

    The dependence of stellar molecular bands on the metallicity is studied using infrared L-band spectra of AGB stars (both carbon-rich and oxygen-rich) and M-type supergiants in the Large and Small Magellanic Clouds (LMC and SMC) and in the Sagittarius Dwarf Spheroidal Galaxy. The spectra cover SiO bands for oxygen-rich stars, and acetylene (C2H2), CH and HCN bands for carbon-rich AGB stars. The equivalent width of acetylene is found to be high even at low metallicity. The high C2H2 abundance can be explained with a high carbon-to-oxygen (C/O) ratio for lower metallicity carbon stars. In contrast, the HCN equivalent width is low: fewer than half of the extra-galactic carbon stars show the 3.5micron HCN band, and only a few LMC stars show high HCN equivalent width. HCN abundances are limited by both nitrogen and carbon elemental abundances. The amount of synthesized nitrogen depends on the initial mass, and stars with high luminosity (i.e. high initial mass) could have a high HCN abundance. CH bands are found in both the extra-galactic and Galactic carbon stars. None of the oxygen-rich LMC stars show SiO bands, except one possible detection in a low quality spectrum. The limits on the equivalent widths of the SiO bands are below the expectation of up to 30angstrom for LMC metallicity. Several possible explanations are discussed. The observations imply that LMC and SMC carbon stars could reach mass-loss rates as high as their Galactic counterparts, because there are more carbon atoms available and more carbonaceous dust can be formed. On the other hand, the lack of SiO suggests less dust and lower mass-loss rates in low-metallicity oxygen-rich stars. The effect on the ISM dust enrichment is discussed.

  14. LUMINOUS AND VARIABLE STARS IN M31 AND M33. I. THE WARM HYPERGIANTS AND POST-RED SUPERGIANT EVOLUTION

    SciTech Connect

    Humphreys, Roberta M.; Davidson, Kris; Grammer, Skyler; Kneeland, Nathan [Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota, Minneapolis, MN 55455 (United States); Martin, John C. [University of Illinois, Springfield, IL (United States); Weis, Kerstin; Burggraf, Birgitta, E-mail: roberta@umn.edu [Astronomical Institute, Ruhr-Universitaet Bochum (Germany)

    2013-08-10

    The progenitors of Type IIP supernovae (SNe) have an apparent upper limit to their initial masses of about 20 M{sub Sun }, suggesting that the most massive red supergiants evolve to warmer temperatures before their terminal explosion. But very few post-red supergiants are known. We have identified a small group of luminous stars in M31 and M33 that are candidates for post-red supergiant evolution. These stars have A-F-type supergiant absorption line spectra and strong hydrogen emission. Their spectra are also distinguished by the Ca II triplet and [Ca II] doublet in emission formed in a low-density circumstellar environment. They all have significant near- and mid-infrared excess radiation due to free-free emission and thermal emission from dust. We estimate the amount of mass they have shed and discuss their wind parameters and mass loss rates, which range from a few Multiplication-Sign 10{sup -6} to 10{sup -4} M{sub Sun} yr{sup -1}. On an H-R diagram, these stars will overlap the region of the luminous blue variables (LBVs) at maximum light; however, the warm hypergiants are not LBVs. Their non-spherical winds are not optically thick, and they have not exhibited any significant variability. We suggest, however, that the warm hypergiants may be the progenitors of the ''less luminous'' LBVs such as R71 and even SN1987A.

  15. Luminous and Variable Stars in M31 and M33. I. The Warm Hypergiants and Post-Red Supergiant Evolution

    NASA Astrophysics Data System (ADS)

    Humphreys, Roberta M.; Davidson, K.; Grammer, S.; Martin, J. C.; Weis, K.

    2013-06-01

    The progenitors of the Type IIP supernovae have an apparent upper mass limit of ~ 20 solar masses suggesting that the most massive red supergiants evolve to warmer temperatures before their terminal explosion. But very few post-red supergiants are known. We have identified a small group of luminous stars in M31 and M33 that are candidates for post-red supergiant evolution. These stars have A -- F-type supergiant absorption line spectra and strong hydrogen emission, hence the warm hypergiant name. Their spectra are also distinguished by the Ca II triplet and [Ca II] doublet in emission formed in a low density circumstellar environment. They all have significant near- and mid-infrared excess radiation due to free-free emission and thermal emission from dust. We discuss their wind parameters and mass loss rates which range from a few times 10^-6 to 10^-4 solar masses per year. On an HR Diagram, these stars will overlap the region of the LBVs at maximum light, however the warm hypergiants are not LBVs. Their winds are not optically thick and they have no significant variability. We suggest, howvwr, that the warm hypergiants may be the progenitors of the ``less luminous'' LBVs such as R71 and even SN1987A.

  16. Multiple, short-lived ``stellar prominences'' on O stars: the supergiant ? Cephei

    NASA Astrophysics Data System (ADS)

    Henrichs, H. F.; Sudnik, N.

    2015-01-01

    Many OB stars show unexplained cyclical variability in their winds and in many optical lines, which are formed at the base of the wind. For these stars no dipolar magnetic fields have been detected. We propose that these cyclical variations are caused by the presence of multiple, transient, short-lived, corotating magnetic loops, which we call ``stellar prominences''. We present a simplified model representing these prominences as corotating spherical blobs and fit the rapid variability in the Heii ?4686 line of the O supergiant ? Cep for time-resolved spectra obtained in 1989. Our conclusions are: (1) From model fits we find that the life time of the prominences varies, and is between 2-7 h. (2) The adopted inclination angle is 68° with a rotation period of ~ 4.1 d (but not well constrained). (3) The contribution of non-radial pulsations is negligible (4) Similar behavior is observed in at least 4 other O stars. We propose that prominences are a common phenomenon among O stars.

  17. GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC2

    NASA Astrophysics Data System (ADS)

    Origlia, L.; Oliva, E.; Maiolino, R.; Mucciarelli, A.; Baffa, C.; Biliotti, V.; Bruno, P.; Falcini, G.; Gavriousev, V.; Ghinassi, F.; Giani, E.; Gonzalez, M.; Leone, F.; Lodi, M.; Massi, F.; Montegriffo, P.; Mochi, I.; Pedani, M.; Rossetti, E.; Scuderi, S.; Sozzi, M.; Tozzi, A.

    2013-12-01

    Aims: The inner disk of the Galaxy has a number of young star clusters dominated by red supergiants that are heavily obscured by dust extinction and observable only at infrared wavelengths. These clusters are important tracers of the recent star formation and chemical enrichment history in the inner Galaxy. Methods: During the technical commissioning and as a first science verification of the GIANO spectrograph at the Telescopio Nazionale Galileo, we secured high-resolution (R ? 50 000) near-infrared spectra of three red supergiants in the young Scutum cluster RSGC2. Results: Taking advantage of the full YJHK spectral coverage of GIANO in a single exposure, we were able to identify several tens of atomic and molecular lines suitable for chemical abundance determinations. By means of spectral synthesis and line equivalent width measurements, we obtained abundances of Fe and other iron-peak elements such as V, Cr, Ni, of alpha (O, Mg, Si, Ca and Ti) and other light elements (C, N, Na, Al, K, Sc), and of some s-process elements (Y, Sr). We found iron abundances between half and one third solar and solar-scaled [X/Fe] abundance patterns of iron-peak, alpha and most of the light elements, consistent with a thin-disk chemistry. We found a depletion of [C/Fe] and enhancement of [N/Fe], consistent with CN burning, and low 12C/13C abundance ratios (between 9 and 11), requiring extra-mixing processes in the stellar interiors during the post-main-sequence evolution. Finally, we found a slight [Sr/Fe] enhancement and a slight [Y/Fe] depletion (by a factor of ?2), with respect to solar. Table 3 is available in electronic form at http://www.aanda.org

  18. THE PHYSICAL PROPERTIES OF THE RED SUPERGIANT WOH G64: THE LARGEST STAR KNOWN?

    SciTech Connect

    Levesque, Emily M. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822 (United States); Massey, Philip [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Plez, Bertrand [GRAAL, Universite Montpellier, CNRS, 34095 Montpellier (France); Olsen, Knut A. G. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85748 (United States)], E-mail: emsque@ifa.hawaii.edu, E-mail: phil.massey@lowell.edu, E-mail: bertrand.plez@graal.univ-montp2.fr, E-mail: kolsen@noao.edu

    2009-06-15

    WOH G64 is an unusual red supergiant (RSG) in the Large Magellanic Cloud (LMC), with a number of properties that set it apart from the rest of the LMC RSG population, including a thick circumstellar dust torus, an unusually late spectral type, maser activity, and nebular emission lines. Its reported physical properties are also extreme, including the largest radius for any star known and an effective temperature that is much cooler than other RSGs in the LMC, both of which are at variance with stellar evolutionary theory. We fit moderate-resolution optical spectrophotometry of WOH G64 with the MARCS stellar atmosphere models, determining an effective temperature of 3400 {+-} 25 K. We obtain a similar result from the star's broadband V - K colors. With this effective temperature, and taking into account the flux contribution from the asymmetric circumstellar dust envelope, we calculate log(L/L {sub sun}) = 5.45 {+-} 0.05 for WOH G64, quite similar to the luminosity reported by Ohnaka and collaborators based on their radiative transfer modeling of the star's dust torus. We determine a radius of R/R {sub sun} = 1540, bringing the size of WOH G64 and its position on the Hertzsprung-Russell diagram into agreement with the largest known Galactic RSGs, although it is still extreme for the LMC. In addition, we use the Ca II triplet absorption feature to determine a radial velocity of 294 {+-} 2 km s{sup -1} for the star; this is the same radial velocity as the rotating gas in the LMC's disk, which confirms its membership in the LMC and precludes it from being an unusual Galactic halo giant. Finally, we describe the star's unusual nebula emission spectrum; the gas is nitrogen-rich and shock-heated, and displays a radial velocity that is significantly more positive than the star itself by 50 km s{sup -1}.

  19. ISOLATED WOLF-RAYET STARS AND O SUPERGIANTS IN THE GALACTIC CENTER REGION IDENTIFIED VIA PASCHEN-{alpha} EXCESS

    SciTech Connect

    Mauerhan, J. C.; Stolovy, S. R. [Infrared Processing and Analysis Center, California Institute of Technology, Mail Code 220-6, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Cotera, A. [SETI Institute, 515 North Whisman Road, Mountain View, CA 94043 (United States); Dong, H.; Wang, Q. D. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Morris, M. R. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Lang, C., E-mail: mauerhan@ipac.caltech.edu [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52245 (United States)

    2010-12-10

    We report the discovery of 19 hot, evolved, massive stars near the Galactic center region (GCR). These objects were selected for spectroscopy owing to their detection as strong sources of Paschen-{alpha} (P{alpha}) emission-line excess, following a narrowband imaging survey of the central 0.{sup 0}65 x 0.{sup 0}25 (l, b) around Sgr A* with the Hubble Space Telescope. Discoveries include six carbon-type (WC) and five nitrogen-type (WN) Wolf-Rayet stars, six O supergiants, and two B supergiants. Two of the O supergiants have X-ray counterparts having properties consistent with solitary O stars and colliding-wind binaries. The infrared photometry of 17 stars is consistent with the Galactic center distance, but 2 of them are located in the foreground. Several WC stars exhibit a relatively large infrared excess, which is possibly thermal emission from hot dust. Most of the stars appear scattered throughout the GCR, with no relation to the three known massive young clusters; several others lie near the Arches and Quintuplet clusters and may have originated within one of these systems. The results of this work bring the total sample of Wolf-Rayet (WR) stars in the GCR to 88. All sources of strong P{alpha} excess have been identified in the area surveyed with HST, which implies that the sample of WN stars in this region is near completion, and is dominated by late (WNL) types. The current WC sample, although probably not complete, is almost exclusively dominated by late (WCL) types. The observed WR subtype distribution in the GCR is a reflection of the intrinsic rarity of early subtypes (WNE and WCE) in the inner Galaxy, an effect that is driven by metallicity.

  20. Spitzer-IRS Spectroscopic Studies of Oxygen-Rich Asymptotic Giant Branch Star and Red Supergiant Star Dust Properties

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin A.; Srinivasan, Sundar; Speck, Angela; Volk, Kevin; Kemper, Ciska; Reach, William T.; Lagadec, Eric; Bernard, Jean-Philippe; McDonald, Iain; Meixner, Margaret

    2015-01-01

    We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of Oxygen-rich (O-rich) asymptotic giant branch (AGB) and red supergiant (RSG) stars. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper) and other archival Spitzer-IRS programs. The broad 10 and 20 micron emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We present an update of our investigation of differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

  1. Luminous and Variable Stars in M31 and M33. I. The Warm Hypergiants and Post-red Supergiant Evolution

    NASA Astrophysics Data System (ADS)

    Humphreys, Roberta M.; Davidson, Kris; Grammer, Skyler; Kneeland, Nathan; Martin, John C.; Weis, Kerstin; Burggraf, Birgitta

    2013-08-01

    The progenitors of Type IIP supernovae (SNe) have an apparent upper limit to their initial masses of about 20 M ?, suggesting that the most massive red supergiants evolve to warmer temperatures before their terminal explosion. But very few post-red supergiants are known. We have identified a small group of luminous stars in M31 and M33 that are candidates for post-red supergiant evolution. These stars have A-F-type supergiant absorption line spectra and strong hydrogen emission. Their spectra are also distinguished by the Ca II triplet and [Ca II] doublet in emission formed in a low-density circumstellar environment. They all have significant near- and mid-infrared excess radiation due to free-free emission and thermal emission from dust. We estimate the amount of mass they have shed and discuss their wind parameters and mass loss rates, which range from a few × 10-6 to 10-4 M ? yr-1. On an H-R diagram, these stars will overlap the region of the luminous blue variables (LBVs) at maximum light; however, the warm hypergiants are not LBVs. Their non-spherical winds are not optically thick, and they have not exhibited any significant variability. We suggest, however, that the warm hypergiants may be the progenitors of the "less luminous" LBVs such as R71 and even SN1987A. Based on observations with the Multiple Mirror Telescope, a joint facility of the Smithsonian Institution and the University of Arizona and on observations obtained with the Large Binocular Telescope (LBT), an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona University system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

  2. THE PERIOD-LUMINOSITY RELATION OF RED SUPERGIANT STARS IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    Yang Ming; Jiang, B. W., E-mail: myang@mail.bnu.edu.cn, E-mail: bjiang@bnu.edu.cn [Department of Astronomy, Beijing Normal University, Beijing 100875 (China)

    2012-07-20

    The characteristics of light variation of red supergiant (RSG) stars in the Small Magellanic Cloud (SMC) are analyzed based on the nearly 8-10 year data collected by the ASAS and MACHO projects. The 126 identified RSGs are classified into five categories accordingly: 20 with poor photometry, 55 with no reliable period, 6 with semi-regular variation, 15 with a long secondary period (LSP) and distinguishable short period, and 30 with only an LSP. For the semi-regular variables and the LSP variables with distinguishable short period, the K{sub S} -band period-luminosity (P-L) relation is analyzed and compared with that of the Galaxy, the Large Magellanic Cloud, and M33. It is found that the RSGs in these galaxies obey a similar P-L relation except for those in the Galaxy. In addition, the P-L relations in the infrared bands, namely, the 2MASS JHK{sub S} , Spitzer/IRAC, and Spitzer/MIPS 24 {mu}m bands, are derived with high reliability. The best P-L relation occurs in the Spitzer/IRAC [3.6] and [4.5] bands. Based on the comparison with the theoretical calculation of the P-L relation, the mode of pulsation of RSGs in the SMC is suggested to be the first-overtone radial mode.

  3. X-ray Constraints on Magnetic Activity and Star Formation Associated with the Red Supergiant VY CMa

    NASA Astrophysics Data System (ADS)

    Montez, Rodolfo; Humphreys, R. M.; Kastner, J. H.; Turok, R. L.

    2014-01-01

    Magnetic field strengths inferred from maser observations of the optically thick circumstellar envelope enshrouding the red supergiant VY CMa indicate that its stellar surface fields may be capable of producing coronal X-ray emission. Evidence for episodic yet randomly directed mass ejections from VY CMa, coupled with the magnetism inferred from maser emission, further suggests that magnetic surface activity may play a fundamental role in mass loss from the red supergiant. Motivated by this evidence, we obtained X-ray observations of a field centered on VY CMa with the XMM-Newton X-ray Observatory in May of 2012. VY CMa is not detected in the ~20 ks XMM exposure. We have determined the upper limit on the X-ray flux of VY CMa as a function of assumed source plasma temperature and intervening absorption, and we use these results to constrain the level of surface magnetic activity on VY CMa at the epoch of the XMM observation. We also detected over a hundred X-ray emitting field sources within ~15' of VY CMa. Via cross-correlation of these sources with optical and infrared catalogs, we identify a few dozen X-ray sources that have stellar counterparts. Comparison with theoretical pre-main sequence (pre-MS) isochrones suggests most of these newly discovered X-ray-emitting stars in the immediate vicinity of VY CMa may be late-type, pre-MS stars at the approximate distance of the famous supergiant itself. We consider whether these stars may constitute a loose association that is coeval with VY CMa, and we discuss the potential relationship of this putative "VY CMa Association" to other nearby regions of recent star formation, including the young cluster NGC 2362.

  4. Einstein Observatory magnitude-limited X-ray survey of late-type giant and supergiant stars

    NASA Technical Reports Server (NTRS)

    Maggio, A.; Vaiana, G. S.; Haisch, B. M.; Stern, R. A.; Bookbinder, J.

    1990-01-01

    Results are presented of an extensive X-ray survey of 380 giant and supergiant stars of spectral types from F to M, carried out with the Einstein Observatory. It was found that the observed F giants or subgiants (slightly evolved stars with a mass M less than about 2 solar masses) are X-ray emitters at the same level of main-sequence stars of similar spectral type. The G giants show a range of emissions more than 3 orders of magnitude wide; some single G giants exist with X-ray luminosities comparable to RS CVn systems, while some nearby large G giants have upper limits on the X-ray emission below typical solar values. The K giants have an observed X-ray emission level significantly lower than F and F giants. None of the 29 M giants were detected, except for one spectroscopic binary.

  5. The Winds of B Supergiants

    NASA Technical Reports Server (NTRS)

    Fullerton, A. W.; Massa, D. L.; Prinja, R. K.; Owocki, S. P.; Cranmer, S. R.

    1998-01-01

    This report summarizes the progress of the work conducted under the program "The Winds of B Supergiants," conducted by Raytheon STX Corporation. The report consists of a journal article "Wind variability in B supergiants III. Corotating spiral structures in the stellar wind of HD 64760." The first step in the project was the analysis of the 1996 time series of 2 B supergiants and an O star. These data were analyzed and reported on at the ESO workshop, "Cyclical Variability in Stellar Winds."

  6. The flux-weighted gravity-luminosity relationship of blue supergiant stars as a constraint for stellar evolution

    E-print Network

    Meynet, Georges; Georgy, Cyril

    2015-01-01

    (abridged) The flux-weighted gravity-luminosity relationship (FGLR) of blue supergiant stars (BSG) links their absolute magnitude to the spectroscopically determined flux-weighted gravity log g = Teff^4. BSG are the brightest stars in the universe at visual light and the application of the FGLR has become a powerful tool to determine extragalactic distances. Observationally, the FGLR is a tight relationship with only small scatter. It is, therefore, ideal to be used as a constraint for stellar evolution models. The goal of this work is to investigate whether stellar evolution can reproduce the observed FGLR and to develop an improved foundation of the FGLR as an extragalactic distance indicator. We use different grids of stellar models for initial masses between 9 and 40 Msun, for metallicities between Z = 0.002 and 0.014, with and without rotation, computed with various mass loss rates during the red supergiant phase. For each of these models we discuss the details of post-main sequence evolution and constru...

  7. The vast population of Wolf-Rayet and red supergiant stars in M101. I. Motivation and first results

    SciTech Connect

    Shara, Michael M.; Bibby, Joanne L.; Zurek, David [Department of Astrophysics, American Museum of Natural History, Central Park West and 79th Street, New York, NY 10024-5192 (United States); Crowther, Paul A. [Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH (United Kingdom); Moffat, Anthony F. J. [Département de Physique, Université de Montréal, CP 6128 Succ. C-V, Montréal, QC H3C 3J7 (Canada); Drissen, Laurent [Département de Physique, Université Laval, Pavillon Vachon, Quebec City, QC G1K 7P4 (Canada)

    2013-12-01

    Assembling a catalog of at least 10,000 Wolf-Rayet (W-R) stars is an essential step in proving (or disproving) that these stars are the progenitors of Type Ib and Type Ic supernovae. To this end, we have used the Hubble Space Telescope (HST) to carry out a deep, He II optical narrowband imaging survey of the ScI spiral galaxy M101. Almost the entire galaxy was imaged with the unprecedented depth and resolution that only the HST affords. Differenced with archival broadband images, the narrowband images allow us to detect much of the W-R star population of M101. We describe the extent of the survey and our images, as well as our data reduction procedures. A detailed broadband-narrowband imaging study of a field east of the center of M101, containing the giant star-forming region NGC 5462, demonstrates our completeness limits, how we find W-R candidates, their properties and spatial distribution, and how we rule out most contaminants. We use the broadband images to locate luminous red supergiant (RSG) candidates. The spatial distributions of the W-R and RSG stars near NGC 5462 are strikingly different. W-R stars dominate the complex core, while RSGs dominate the complex halo. Future papers in this series will describe and catalog more than a thousand W-R and RSG candidates that are detectable in our images, as well as spectra of many of those candidates.

  8. Mass-loss rates and luminosity functions of dust-enshrouded AGB stars and red supergiants in the LMC

    E-print Network

    Jacco Th. van Loon; M. A. T. Groenewegen; A. de Koter; Norman R. Trams; L. B. F. M. Waters; Albert A. Zijlstra; Patricia A. Whitelock; Cecile Loup

    1999-09-24

    A radiative transfer code is used to model the spectral energy distributions of 57 mass-losing Asymptotic Giant Branch (AGB) stars and red supergiants (RSGs) in the Large Magellanic Cloud (LMC) for which ISO spectroscopic and photometric data are available. As a result we derive mass-loss rates and bolometric luminosities. A gap in the luminosity distribution around M_bol = -7.5 mag separates AGB stars from RSGs. The luminosity distributions of optically bright carbon stars, dust-enshrouded carbon stars and dust-enshrouded M-type stars have only little overlap, suggesting that the dust-enshrouded AGB stars are at the very tip of the AGB and will not evolve significantly in luminosity before mass loss ends their AGB evolution. Derived mass-loss rates span a range from Mdot about 10^-7 to 10^-3 M_sun/yr. More luminous and cooler stars are found to reach higher mass-loss rates. The highest mass-loss rates exceed the classical limit set by the momentum of the stellar radiation field, L/c, by a factor of a few due to multiple scattering of photons in the circumstellar dust envelope. Mass-loss rates are lower than the mass consumption rate by nuclear burning, Mdot_nuc, for most of the RSGs. Two RSGs have Mdot >> Mdot_nuc, however, suggesting that RSGs shed most of their stellar mantles in short phases of intense mass loss. Stars on the thermal pulsing AGB may also experience episodes of intensified mass loss, but their quiescent mass-loss rates are usually already higher than Mdot_nuc.

  9. On the magnetic structure and wind parameter profiles of Alfven wave driven winds in late-type supergiant stars

    E-print Network

    D. Falceta-Goncalves; A. A. Vidotto; V. Jatenco-Pereira

    2006-02-14

    Cool stars at giant and supergiant evolutionary phases present low velocity and high density winds, responsible for the observed high mass-loss rates. Although presenting high luminosities, radiation pressure on dust particles is not sufficient to explain the wind acceleration process. Among the possible solutions to this still unsolved problem, Alfven waves are, probably, the most interesting for their high efficiency in transfering energy and momentum to the wind. Typically, models of Alfven wave driven winds result in high velocity winds if they are not highly damped. In this work we determine self-consistently the magnetic field geometry and solve the momentum, energy and mass conservation equations, to demonstrate that even a low damped Alfven wave flux is able to reproduce the low velocity wind. We show that the magnetic fluxtubes expand with a super-radial factor S>30 near the stellar surface, larger than that used in previous semi-empirical models. The rapid expansion results in a strong spatial dilution of the wave flux. We obtained the wind parameter profiles for a typical supergiant star of 16 M_sun. The wind is accelerated in a narrow region, coincident with the region of high divergence of the magnetic field lines, up to 100 km/s. For the temperature, we obtained a slight decrease near the surface for low damped waves, because the wave heating mechanism is less effective than the radiative losses. The peak temperature occurs at 1.5 r_0 reaching 6000 K. Propagating outwards, the wind cools down mainly due to adiabatic expansion.

  10. Evidence for the pulsational origin of the Long Secondary Periods: The red supergiant star V424 Lac (HD 216946)

    NASA Astrophysics Data System (ADS)

    Messina, Sergio

    2007-10-01

    The results of a long-term UBV photometric monitoring of the red supergiant (RSG) star V424 Lac are presented. V424 Lac shows multiperiodic brightness variations which can be attributed to pulsational oscillations. A much longer period ( P = 1601 d), that allows us to classify this star as a long secondary period variable star (LSPV) has been also detected. The B - V and U - B color variations related to the long secondary period (LSP) are similar to those related to the shorter periods, supporting the pulsational nature of LSP. The long period brightness variation of V424 Lac is accompanied by a near-UV (NUV) excess, which was spectroscopically detected in a previous study [Massey, P., Plez, B., Levesque, E.M., et al., 2005. ApJ 634, 1286] and which is now found to be variable from photometry. On the basis of the results found for V424 Lac, the NUV excess recently found in a number of RSGs may be due not solely to circumstellar dust but may also have a contribution from a still undetected LSP variability.

  11. Herschel/HIFI View on Massive Evolved Stars: the HIFISTARS sample of Supergiant and Yellow Hypergiant envelopes

    NASA Astrophysics Data System (ADS)

    Teyssier, D.; Marston, A.; Alcolea, J.; Bujarrabal, V.; Hifistars Consortium

    2011-05-01

    We present the first results of one the HIFISTARS (Bujarrabal et al. 2010, see also Decin et al., this conference) sub-programmes dedicated to the study of the physico-chemical conditions and the mass-loss history in Red Supergiants and Yellow Hypergiants. Such sources are the most massive and luminous stars in the pathway of stellar evolution, and as such are fast-lived and characterised by very intense winds and mass-loss rates. These conditions and the large size of their envelope contribute to a particularly rich chemistry. At the end of their evolution, Super/Hyergiant stars are expected to die hard and form black holes or neutron stars after a supernova. The HIFISTARS' sample of evolved massive stars considers three Red Supergiants (NML Cyg, Betelgeuse, and VY CMa) and two Yellow Hypergiants (IRC+10420 and AFGL2343), in a handful of submm and FIR CO/13CO lines, as well as several water, HCN, SiO, SO, SO2, and other bonus lines collected over the whole HIFI frequency ranges. While most of the CO, the OH line at 1835 GHz, and both ortho- and para- ground-state water lines are detected in all targets, there is a clear difference for the less-abundant N-bearing, Si-bearing and S-bearing species. The various water lines covered by the survey are also relatively un-evenly represented from one source to another, with some of the transitions showing up as masers. The observed lines feature complex and distinct profiles, indicative of the strong and asymmetric wings at play for some of the transitions. Of the four sources observed so far (all but AFGL2343), VY CMa clearly stands out as an exceptional object, with most lines 2-10x stronger than any other Super/Hypergiants, and revealing in particular an extremely rich water chemistry observed nowhere in the other sources of the sample (Alcolea et al., in preparation, see also Menten et al., this conference).

  12. The circumstellar environment and evolutionary state of the supergiant B[e] star Wd1-9

    NASA Astrophysics Data System (ADS)

    Clark, J. S.; Ritchie, B. W.; Negueruela, I.

    2013-12-01

    Context. Historically, supergiant (sg)B[e] stars have been difficult to include in theoretical schemes for the evolution of massive OB stars. Aims: The location of Wd1-9 within the coeval starburst cluster Westerlund 1 means that it may be placed into a proper evolutionary context and we therefore aim to utilise a comprehensive multiwavelength dataset to determine its physical properties and consequently its relation to other sgB[e] stars and the global population of massive evolved stars within Wd1. Methods: Multi-epoch R- and I-band VLT/UVES and VLT/FORS2 spectra are used to constrain the properties of the circumstellar gas, while an ISO-SWS spectrum covering 2.45-45 ?m is used to investigate the distribution, geometry and composition of the dust via a semi-analytic irradiated disk model. Radio emission enables a long term mass-loss history to be determined, while X-ray observations reveal the physical nature of high energy processes within the system. Results: Wd1-9 exhibits the rich optical emission line spectrum that is characteristic of sgB[e] stars. Likewise its mid-IR spectrum resembles those of the LMC sgB[e] stars R66 and 126, revealing the presence of equatorially concentrated silicate dust, with a mass of ~10-4 M?. Extreme historical and ongoing mass loss (?10-4 M? yr-1) is inferred from the radio observations. The X-ray properties of Wd1-9 imply the presence of high temperature plasma within the system and are directly comparable to a number of confirmed short-period colliding wind binaries within Wd1. Conclusions: The most complete explanation for the observational properties of Wd1-9 is that it is a massive interacting binary currently undergoing, or recently exited from, rapid Roche-lobe overflow, supporting the hypothesis that binarity mediates the formation of (a subset of) sgB[e] stars. The mass loss rate of Wd1-9 is consistent with such an assertion, while viable progenitor and descendent systems are present within Wd1 and comparable sgB[e] binaries have been identified in the Galaxy. Moreover, the rarity of sgB[e] stars - only two examples are identified from a census of ~68 young massive Galactic clusters and associations containing ~600 post-Main Sequence stars - is explicable given the rapidity (~104 yr) expected for this phase of massive binary evolution. This work is based on observations collected at the European Southern Observatory, Paranal (programme IDs ESO 087.D-0355, 087.D-0440, 087.D-0673, and 073.D-0327) and uses the ISO-SWS database of Sloan et al. (2003).Table 1 and Appendix A are available in electronic form at http://www.aanda.org

  13. A FIVE-YEAR SPECTROSCOPIC AND PHOTOMETRIC CAMPAIGN ON THE PROTOTYPICAL {alpha} CYGNI VARIABLE AND A-TYPE SUPERGIANT STAR DENEB

    SciTech Connect

    Richardson, N. D. [Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Morrison, N. D.; Kryukova, E. E. [Ritter Astrophysical Research Center, Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft, Toledo, OH 43606 (United States); Adelman, S. J., E-mail: richardson@chara.gsu.edu, E-mail: nmorris@utnet.utoledo.edu, E-mail: eallga@physics.utoledo.edu, E-mail: adelmans@citadel.edu [Department of Physics, The Citadel, 171 Moultrie Street, Charleston, SC 29409 (United States)

    2011-01-15

    Deneb is often considered the prototypical A-type supergiant and is one of the visually most luminous stars in the Galaxy. A-type supergiants are potential extragalactic distance indicators, but the variability of these stars needs to be better characterized before this technique can be considered reliable. We analyzed 339 high-resolution echelle spectra of Deneb obtained over the five-year span of 1997 through 2001 as well as 370 Stroemgren photometric measurements obtained during the same time frame. Our spectroscopic analysis included dynamical spectra of the H{alpha} profile, H{alpha} equivalent widths, and radial velocities measured from Si II {lambda}{lambda} 6347, 6371. Time-series analysis reveals no obvious cyclic behavior that proceeds through multiple observing seasons, although we found a suspected 40 day period in two, non-consecutive observing seasons. Some correlations are found between photometric and radial velocity data sets and suggest radial pulsations at two epochs. No correlation is found between the variability of the H{alpha} profiles and that of the radial velocities or the photometry. Lucy found evidence that Deneb was a long-period single-lined spectroscopic binary star, but our data set shows no evidence for radial velocity variations caused by a binary companion.

  14. Supermassive Star Clusters in Supergiant Galaxies: Tracing the Enrichment of the Earliest Stellar Systems

    NASA Astrophysics Data System (ADS)

    Harris, William

    2010-09-01

    The cD-type Brightest Cluster Galaxies contain the richest globular cluster systems {GCSs} that exist. The wealth of results gathered from previous HST imaging programs in many smaller galaxies show that GCSs are powerful and unique tracers that link to origin and evolution of structure in two directions simultaneously: one direction is inward to the structure of the protoglobular clouds, star formation in the densest known conditions, and their chemical enrichment history. The other direction is outward to constraining early galaxy formation history, the nature of the pregalactic dwarfs, or the spatial and dynamic structure of the halo. But we have not yet tapped the vast mine of GCS data waiting for exploitation in the most luminous galaxies of all, the cDs. Surprisingly, we know little about these systems beyond the globular cluster populations in the nearby cDs M87 {Virgo} and NGC 1399 {Fornax}, and these two cases no longer provide adequate tests of the new phenomena now being uncovered, such as the correlation between GC mass and metallicity, the strikingly different formation efficiencies of metal-poor and metal-rich clusters, the galaxy-to-galaxy differences in GC mass distribution, and connections to Ultra-Compact Dwarfs and dE nuclei.We propose to image 7 cD-type systems within 200 Mpc that are representative of the very biggest galaxies known {Mv < -23}. These lie in far richer Abell-cluster environments than we could ever probe in Virgo, Fornax, or nearer systems. We will use ACS/WFC and WFC3 to image their GCSs down to the turnover point of the GC luminosity function, using the B and I filters for an optimal combination of exposure time, field size, and metallicity sensitivity. Our complete survey will produce luminosities, metallicities, and spatial distribution functions for more than 35,000 GCs, the largest GC database in existence and an order of magnitude larger than even the recent Virgo Cluster Survey. The legacy value of our survey will supply a rich resource for a wide array of other GC science and the formation histories of these unique systems.

  15. Spectral atlas of A-type supergiants

    E-print Network

    Klochkova, V G; Chentsov, E L

    2015-01-01

    Based on high-spectral-resolution observations (R=60000) performed with the 6-m BTA telescope in combination with the echelle spectrograph NES, we have studied the optical spectra of three A-type supergiants: a peculiar supergiant 3 Pup, a post-AGB star BD+48 1220, and a massive $\\alpha$ Cyg, which belong to essentially different stages of evolution. A spectral atlas for these stars is prepared in the wavelength interval of 3920 to 6720 \\AA.

  16. A study of several F and G supergiant-like stars with infrared excesses as candidates for proto-planetary nebulae

    NASA Technical Reports Server (NTRS)

    Hrivnak, Bruce J.; Kwok, Sun; Volk, Kevin M.

    1989-01-01

    Ground-based observations have been obtained for eight F and G supergiant-like stars showing large IR excesses. The combination of ground-based and IRAS data shows that these objects have dual-peak energy distributions, with comparable amounts of energy emitted in the visible and the IR. The IR-emitting cool dust shells are likely to represent the remnants of ejecta from an earlier phase of evolution. It is suggested that these eight objects are similar to IRAS 18095 + 2704 and are intermediate-mass stars in a post-AGB phase of evolution. Model fittings to the 0.4-100 micron energy distribution of these objects suggest that they left the AGB within the last 1000 yr.

  17. The chemical composition of B-supergiant atmospheres.

    NASA Astrophysics Data System (ADS)

    Lennon, D. J.

    The authors present new estimates of He/H and CNO abundance ratios in the atmospheres of a selection of B2 supergiants which imply that the C/N ratio in the most luminous Ia stars is close to its equilibrium value. There is also some evidence for more moderate CN abundance anomalies in the B2Ib and B2II supergiants. These results, together with other recent work, imply that the effects of the CNO bi-cycle on the composition of B-supergiant atmospheres are most severe for the more luminous and massive stars. Furthermore, studies of LMC B-supergiants indicate that a small fraction of these very luminous stars are nitrogen weak. This picture is qualitatively consistent with theoretical predictions whenever massive stars perform blue loops in the HR diagram, returning from a red supergiant phase to become core helium burning blue supergiants with atmospheres contaminated by nuclear processed material.

  18. The chemical composition of B-supergiant atmospheres

    NASA Astrophysics Data System (ADS)

    Lennon, D. J.

    1993-03-01

    We present new estimates of He/H and CNO abundance ratios in the atmospheres of a selection of B2 supergiants which imply that the C/N ratio in the most luminous Ia stars is close to its equilibrium value. The is also some evidence for more moderate CN abundance anomalies in the B2Ib and B2II supergiants. These results, together with other recent work, imply that the effects of the CNO bi-cycle on the composition of B-supergiant atmospheres are most severe for the more luminous and massive stars. Furthermore, studies of LMC B-supergiants indicate that a small fraction of these very luminous stars are nitrogen weak. This picture is qualitatively consistent with theoretical predictions whenever massive stars perform blue loops in the HR diagram, returning from a red supergiant phase to become core helium burning blue supergiants with atmospheres contaminated by nuclear processed material.

  19. Fundamental parameters of Galactic luminous OB stars VI. Temperatures, masses and WLR of Cyg OB2 supergiants

    Microsoft Academic Search

    A. Herrero; J. Puls; F. Najarro

    2002-01-01

    We have analyzed six OB supergiants and one giant covering spectral types from O3 to B1 in the Galactic OB association Cyg OB2 by means of an updated version of FASTWIND (Santolaya-Rey et al. \\\\cite{sph97}) that includes an approximate treatment of metal line blocking and blanketing. This large coverage in spectral type allows us to derive a new temperature scale

  20. Spitzer-IRS Spectroscopic Studies of the Properties of Dust from Oxygen-Rich Asymptotic Giant Branch and Red Supergiant Stars

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin A.; Speck, A.; Volk, K.; Kemper, C.; Reach, W. T.; Lagadec, E.; Bernard, J.; McDonald, I.; Meixner, M.; Srinivasan, S.

    2014-01-01

    We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of Oxygen-rich (O-rich) asymptotic giant branch (AGB) and red supergiant (RSG) stars. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper) and other archival Spitzer-IRS programs. The broad 10 and 20 micron emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We investigate differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

  1. Extragalactic Stellar Astronomy with Blue Supergiants

    E-print Network

    N. Przybilla; F. Bresolin; K. Butler; R. P. Kudritzki; M. A. Urbaneja; K. A. Venn

    2007-03-14

    The present generation of large telescopes facilitates spectroscopy of blue supergiants in galaxies out to distances beyond the Local Group. Recent developments in NLTE spectrum synthesis techniques allow for an accurate determination of stellar parameters and chemical abundances. Quantitative analyses of blue supergiants in different galactic environments can provide tight observational constraints on: I) the evolution of massive stars over a wide range of metallicities, II) the chemical evolution of different galaxy types, using stars as tracers of abundance gradients, III) the extragalactic distance scale. The current status of the field is summarised.

  2. Red supergiant identification and classification

    NASA Astrophysics Data System (ADS)

    Dorda, R.; Negueruela, I.; González-Fernández, C.; Marco, A.

    2015-05-01

    The interest for red supergiants has grown in the past few years, as these objects are being used for a number of different studies. In spite of this, their spectral identification and classification still present several problems and limitations that we expose in this work. To bring light to this topic, we have homogeneously observed and classified the largest sample of red supergiants to date. We are using this data to develop a system of identification and classification for these objects through the atomic and molecular features in the infrared Calcium Triplet spectral region. Also, our method will allow the identification and classification of the cool bright stars observed by Gaia without resorting to TiO bands, as none of their bandheads is inside the Gaia spectral range.

  3. Infrared Space Observatory Observations of Far-Infrared Rotational Emission Lines of Water Vapor Toward the Supergiant Star VY Canis Majoris

    NASA Technical Reports Server (NTRS)

    Neufeld, David A.; Feuchtgruber, Helmut; Harwit, Martin; Melnick, Gary J.

    1999-01-01

    We report the detection of numerous far-infrared emission lines of water vapor toward the supergiant star VY Canis Majoris. A 29.5-45 micron grating scan of VY CMa, obtained using the Short-Wavelength Spectrometer (SWS) of the Infrared Space Observatory at a spectral resolving power lambda/delat.lambda of approximately 2000, reveals at least 41 spectral features due to water vapor that together radiate a total luminosity of approximately 25 solar luminosity . In addition to pure rotational transitions within the ground vibrational state, these features include rotational transitions within the (010) excited vibrational state. The spectrum also shows the (sup 2)product(sub 1/2) (J = 5/2) left arrow (sup 2)product(sub 3/2) (J = 3/2) OH feature near 34.6 micron in absorption. Additional SWS observations of VY CMa were carried out in the instrument's Fabry-Perot mode for three water transitions: the 7(sub 25)-6(sub 16) line at 29.8367 micron, the 4(sub 41)-3(sub 12) line at 31.7721 micron, and the 4(sub 32)-3(sub 03) line at 40.6909 micron. The higher spectral resolving power lambda/delta.lambda of approximately 30,000 thereby obtained permits the line profiles to be resolved spectrally for the first time and reveals the "P Cygni" profiles that are characteristic of emission from an outflowing envelope.

  4. Enhancement of CO(3-2)/CO(1-0) ratios and star formation efficiencies in supergiant H II regions

    SciTech Connect

    Miura, Rie E.; Espada, Daniel; Komugi, Shinya; Nakanishi, Kouichiro; Sawada, Tsuyoshi; Fujii, Kosuke; Kawabe, Ryohei [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Kohno, Kotaro [Institute of Astronomy, School of Science, The University of Tokyo, Osawa, Mitaka, Tokyo 181-0015 (Japan); Tosaki, Tomoka [Joetsu University of Education, Yamayashiki-machi, Joetsu, Niigata 943-8512 (Japan); Hirota, Akihiko; Minamidani, Tetsuhiro [Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1805 (Japan); Okumura, Sachiko K. [Department of Mathematical and Physical Sciences, Faculty of Science, Japan Woman's University, Mejirodai 2-8-1, Bunkyo, Tokyo 112-8681 (Japan); Kuno, Nario [Department of Astronomical Science, The Graduate University for Advanced Studies (Sokendai), 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Muraoka, Kazuyuki; Onodera, Sachiko [Osaka Prefecture University, Gakuen 1-1, Sakai, Osaka 599-8531 (Japan); Kaneko, Hiroyuki, E-mail: rie.miura@nao.ac.jp [Department of Physics, Meisei University, Hino, Tokyo 191-8506 (Japan)

    2014-06-20

    We present evidence that super giant H II regions (GHRs) and other disk regions of the nearby spiral galaxy, M33, occupy distinct locations in the correlation between molecular gas, ?{sub H{sub 2}}, and the star formation rate surface density, ?{sub SFR}. This result is based on wide-field and high-sensitivity CO(3-2) observations at 100 pc resolution. Star formation efficiencies (SFEs), defined as ?{sub SFR}/?{sub H{sub 2}}, in GHRs are found to be ?1 dex higher than in other disk regions. The CO(3-2)/CO(1-0) integrated intensity ratio, R {sub 3-2/1-0}, is also higher than the average over the disk. Such high SFEs and R {sub 3-2/1-0} can reach the values found in starburst galaxies, which suggests that GHRs may be the elements building up a larger-scale starburst region. Three possible contributions to high SFEs in GHRs are investigated: (1) the I {sub CO}-N(H{sub 2}) conversion factor, (2) the dense gas fraction traced by R {sub 3-2/1-0}, and (3) the initial mass function (IMF). We conclude that these starburst-like properties in GHRs can be interpreted by a combination of both a top-heavy IMF and a high dense gas fraction, but not by changes in the I {sub CO}-N(H{sub 2}) conversion factor.

  5. CNO Abundances of BA-Type Supergiants

    E-print Network

    M. Firnstein; N. Przybilla

    2006-10-18

    Massive BA-type supergiants are among the visually brightest stars in galaxies with active star formation. As such they are versatile tools for studies of stellar and galactochemical evolution. Moreover, they can act as distance indicators for the calibration of the cosmological distance scale. In the present work abundance patterns of the light elements helium, carbon, nitrogen and oxygen are investigated in several Galactic BA-type supergiants in the mass range between 8 and 18 M_sun. Based on high-resolution and high-S/N Echelle spectra obtained with FOCES on the Calar Alto 2.2m telescope, model atmosphere analyses are performed using state-of-the-art non-LTE spectrum synthesis. Stellar parameters and chemical abundances are determined with high accuracy. This gives tight observational constraints on the evolutionary status of the stars. Objects evolving from the main sequence to the red supergiant stage and those on a blue loop can be distinguished by their mixing signature (pure rotational vs. first dredge-up). The most sensitive tracer of nuclear processed matter, the N/C ratio, indicates a higher mixing efficiency than predicted by current evolution models of rotating stars with mass-loss.

  6. GHRS Observations of Cool, Low-Gravity Stars. 5; The Outer Atmosphere and Wind of the Nearby K Supergiant Lambda Velorum

    NASA Technical Reports Server (NTRS)

    Carpenter, Kenneth G.; Robinson, Richard D.; Harper, Graham M.; Bennett, Philip D.; Brown, Alexander; Mullan, Dermott J.

    1999-01-01

    UV spectra of lambda Velorum taken with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope are used to probe the structure of the outer atmospheric layers and wind and to estimate the mass-loss rate from this K5 lb-II supergiant. VLA radio observations at lambda = 3.6 cm are used to obtain an independent check on the wind velocity and mass-loss rate inferred from the UV observations, Parameters of the chromospheric structure are estimated from measurements of UV line widths, positions, and fluxes and from the UV continuum flux distribution. The ratios of optically thin C II] emission lines indicate a mean chromospheric electron density of log N(sub e) approximately equal 8.9 +/- 0.2 /cc. The profiles of these lines indicate a chromospheric turbulence (v(sub 0) approximately equal 25-36 km/s), which greatly exceeds that seen in either the photosphere or wind. The centroids of optically thin emission lines of Fe II and of the emission wings of self-reversed Fe II lines indicate that they are formed in plasma approximately at rest with respect to the photosphere of the star. This suggests that the acceleration of the wind occurs above the chromospheric regions in which these emission line photons are created. The UV continuum detected by the GHRS clearly traces the mean flux-formation temperature as it increases with height in the chromosphere from a well-defined temperature minimum of 3200 K up to about 4600 K. Emission seen in lines of C III] and Si III] provides evidence of material at higher than chromospheric temperatures in the outer atmosphere of this noncoronal star. The photon-scattering wind produces self-reversals in the strong chromospheric emission lines, which allow us to probe the velocity field of the wind. The velocities to which these self-absorptions extend increase with intrinsic line strength, and thus height in the wind, and therefore directly map the wind acceleration. The width and shape of these self-absorptions reflect a wind turbulence of approximately equal 9-21 km/s. We further characterize the wind by comparing the observations with synthetic profiles generated with the Lamers et al. Sobolev with Exact Integration (SEI) radiative transfer code, assuming simple models of the outer atmospheric structure. These comparisons indicate that the wind in 1994 can be described by a model with a wind acceleration parameter beta approximately 0.9, a terminal velocity of 29-33 km/s, and a mass-loss rate approximately 3 x 10(exp -9) solar M/yr. Modeling of the 3.6 cm radio flux observed in 1997 suggests a more slowly accelerating wind (higher beta) and/or a higher mass-loss rate than inferred from the UV line profiles. These differences may be due to temporal variations in the wind or from limitations in one or both of the models. The discrepancy is currently under investigation.

  7. Spectral Effects of Pulsations in Blue Supergiants

    NASA Astrophysics Data System (ADS)

    Tomi?, S.; Kraus, M.; Oksala, M. E.

    2015-01-01

    We have been spectroscopically monitoring a number of blue supergiants, focusing on several strategic photospheric and wind lines. Our aim is to detect line profile variability, and to determine its origin. Here, we present preliminary results for ? Leo and ? Ori. We conduct an asteroseismic analysis of Hei ?6678. We find in each star multiple periods raging from hours to several days. In addition, we observe strong, night to night variability in H?.

  8. Spectral atlas of A-type supergiants

    NASA Astrophysics Data System (ADS)

    Klochkova, V. G.; Sendzikas, E. G.; Chentsov, E. L.

    2015-01-01

    Using the data from the observations carried out with a high spectral resolution of R = 60 000 at the 6-m BTA telescope in combination with the echelle spectrograph NES, we thoroughly studied the characteristics of the optical spectra of the A supergiants 3 Pup, BD+48°1220, and ? Cyg, which belong to essentially different stages of evolution. A spectral atlas for these stars was compiled in the wavelength interval of 3920 to 6720 Å.

  9. Maser Mapping of Dust-Driven Winds from Red Supergiants

    Microsoft Academic Search

    A. M. S. Richards; J. A. Yates

    1998-01-01

    High resolution MERLIN maps of water and OH masers in the circumstellar envelopes of red supergiant stars reveal complex velocity gradients. The water masers appear to emanate from dense clouds 15 to 20 AU in diameter which are being accelerated away from the star. OH masers are mostly seen in regions of more gently increasing velocity which are likely to

  10. Light variations of massive stars (alpha Cyg variables). XV. The LMC supergiants R99 (LBV), R103, R123 (LBV) and R128

    NASA Astrophysics Data System (ADS)

    van Genderen, A. M.; Sterken, C.; de Groot, M.; Reijns, R. A.

    1998-04-01

    VBLUW photometry (Walraven system) of the four variable LMC supergiants R99, R103, R123 and R128 is analysed, searched for periods and discussed. Based on former and present photometry we conclude that two of the three emission-line objects are undoubtedly active LBVs (R99 and R123), although not so spectacular. R123, like AG Car near minimum brightness, shows a low amplitude S Dor activity with superimposed alpha Cyg-type variations. Based on observations obtained at the European Southern Observatory at La Silla, Chile

  11. Yellow Supergiants in the Small Magellanic Cloud: Putting Current Evolutionary Theory to the Test

    NASA Astrophysics Data System (ADS)

    Neugent, Kathryn F.; Massey, Philip; Skiff, Brian; Drout, Maria R.; Meynet, Georges; Olsen, Knut A. G.

    2010-08-01

    The yellow supergiant content of nearby galaxies provides a critical test of massive star evolutionary theory. While these stars are the brightest in a galaxy, they are difficult to identify because a large number of foreground Milky Way stars have similar colors and magnitudes. We previously conducted a census of yellow supergiants within M31 and found that the evolutionary tracks predict a yellow supergiant duration an order of magnitude longer than we observed. Here we turn our attention to the Small Magellanic Cloud (SMC), where the metallicity is 10× lower than that of M31, which is important as metallicity strongly affects massive star evolution. The SMC's large radial velocity (~160 km s-1) allows us to separate members from foreground stars. Observations of ~500 candidates yielded 176 near-certain SMC supergiants, 16 possible SMC supergiants, along with 306 foreground stars, and provide good relative numbers of yellow supergiants down to 12 M sun. Of the 176 near-certain SMC supergiants, the kinematics predicted by the Besançon model of the Milky Way suggest a foreground contamination of <=4%. After placing the SMC supergiants on the Hertzsprung-Russell diagram (HRD) and comparing our results to the Geneva evolutionary tracks, we find results similar to those of the M31 study: while the locations of the stars on the HRD match the locations of evolutionary tracks well, the models overpredict the yellow supergiant lifetime by a factor of 10. Uncertainties about the mass-loss rates on the main sequence thus cannot be the primary problem with the models.

  12. The Swift view of Supergiant Fast X-ray Transients

    E-print Network

    Sidoli, L; Ducci, L; Paizis, A; Vercellone, S; Cusumano, G; La Parola, V; Mangano, V; Burrows, D N; Kennea, J A; Krimm, H A; Gehrels, N

    2010-01-01

    We report here on the recent results of a monitoring campaign we have been carrying out with Swift/XRT on a sample of four Supergiant Fast X-ray Transients. The main goal of this large programme (with a net Swift/XRT exposure of 540 ks, updated to 2009, August, 31) is to address several main open issues related to this new class of High Mass X-ray Binaries hosting OB supergiant stars as companions. Here we summarize the most important results obtained between October 2007 and August 2009.

  13. Wind emission of OB supergiants and the influence of clumping

    E-print Network

    Michaela Kraus; Jiri Kubat; Jiri Krticka

    2007-08-06

    The influence of the wind to the total continuum of OB supergiants is discussed. For wind velocity distributions with \\beta > 1.0, the wind can have strong influence to the total continuum emission, even at optical wavelengths. Comparing the continuum emission of clumped and unclumped winds, especially for stars with high \\beta values, delivers flux differences of up to 30% with maximum in the near-IR. Continuum observations at these wavelengths are therefore an ideal tool to discriminate between clumped and unclumped winds of OB supergiants.

  14. The pulsating yellow supergiant V810 Centauri

    E-print Network

    F. Kienzle; G. Burki; M. Burnet; G. Meynet

    1998-07-09

    The F8Ia supergiant V810 Centauri is part of a long-term high-precision photometric monitoring program on long period variables started twenty years ago. Time series analysis of this unique set of 500 data points, spanning almost fifteen years in the homogeneous Geneva photometric system, is presented. Cluster membership, physical parameters and evolutionary status of the star are reinvestigated. Radial velocity data do not support the cluster membership to Stock 14}. Ultraviolet and optical spectrophotometry is combined with optical and infrared photometry to evaluate the physical parameters of the yellow supergiant (Teff = 5970 K, M_bol = -8.5, R = 420 R_sun) and of its B0III companion. From theoretical stellar evolutionary tracks, an initial mass of 25 M_sun is estimated for V810 Cen, which is actually at the end of its first redward evolution. V810 Cen is a multi-periodic small amplitude variable star, whose amplitudes are variable with time. The period of the main mode, 156 d, is in agreement with the Period--Luminosity--Colour relation for supergiants. This mode is most probably the fundamental radial one. According to the theoretical pulsation periods for the radial modes, calculated from a linear non-adiabatic analysis, the period of the observed second mode, 107 d, is much too long to correspond to the first radial overtone . Thus, this second mode could be a non-radial p-mode. Other transient periods are observed, in particular at 187 d. The l ength of this period suggests a non-radial g-mode. Then, the complex variability of V810 Cen could be due to a mixing of unstable radial and non-radial p- and g-modes.

  15. Long term variability of B supergiant winds

    NASA Technical Reports Server (NTRS)

    Massa, Derck L.

    1995-01-01

    The object of this observing proposal was to sample wind variability in B supergiants on a daily basis over a period of several days in order to determine the time scale with which density variability occurs in their winds. Three stars were selected for this project: 69 Cyg (B0 Ib), HD 164402 (B0 Ib), and HD 47240 (B1 Ib). Three grey scale representations of the Si IV lambda lambda 1400 doublet in each star are attached. In these figures, time (in days) increases upward, and the wavelength (in terms of velocity relative to the rest wavelength of the violet component of the doublet) is the abscissa. The spectra are normalized by a minimum absorption (maximum flux) template, so that all changes appear as absorptions. As a result of these observations, we can now state with some certainty that typical B supergiants develop significant wind inhomogeneities with recurrence times of a few days, and that some of these events show signs of strong temporal coherence.

  16. Spectropolarimetric study of selected cool supergiants

    NASA Astrophysics Data System (ADS)

    Butkovskaya, V.; Plachinda, S.; Baklanova, D.

    2015-01-01

    Cool supergiants offer a good opportunity to study the interplay of magnetic fields and stellar evolution. We present the results of spectropolarimetric study of the cool supergiants and classical Cepheids ? Aql and ? Gem.

  17. Peculiar Type II supernovae from blue supergiants

    NASA Astrophysics Data System (ADS)

    Kleiser, Io K. W.; Poznanski, Dovi; Kasen, Daniel; Young, Timothy R.; Chornock, Ryan; Filippenko, Alexei V.; Challis, Peter; Ganeshalingam, Mohan; Kirshner, Robert P.; Li, Weidong; Matheson, Thomas; Nugent, Peter E.; Silverman, Jeffrey M.

    2011-07-01

    The vast majority of Type II supernovae (SNeII) are produced by red supergiants, but SN 1987A revealed that blue supergiants (BSGs) can produce members of this class as well, albeit with some peculiar properties. This best-studied event revolutionized our understanding of SNe and linking it to the bulk of Type II events is essential. We present here the optical photometry and spectroscopy gathered for SN 2000cb, which is clearly not a standard SNII and yet is not a SN 1987A analogue. The light curve of SN 2000cb is reminiscent of that of SN 1987A in shape, with a slow rise to a late optical peak, but on substantially different time-scales. Spectroscopically, SN 2000cb resembles a normal SNII, but with ejecta velocities that far exceed those measured for SN 1987A or normal SNeII, above 18 000 km s-1 for H? at early times. The red colours, high velocities, late photometric peak and our modelling of this object all point towards a scenario involving the high-energy explosion of a small-radius star, most likely a BSG, producing 0.1 M? of 56Ni. Adding a similar object to the sample, SN 2005ci, we derive a rate of ˜2 per cent of the core-collapse rate for this loosely defined class of BSG explosions.

  18. First ultraviolet spectropolarimetry of hot supergiants

    NASA Technical Reports Server (NTRS)

    Taylor, M.; Code, A. D.; Nordsieck, K. H.; Anderson, C. M.; Babler, B. L.; Bjorkman, K. S.; Clayton, G. C.; Magalhaes, A. M.; Meade, M. R.; Schulte-Ladbeck, R. E.

    1991-01-01

    UV spectropolarimetric observations of the early-type supergiant stars P Cygni and Kappa Cassiopeiae obtained with the Wisconsin UV Photo-Polarimeter Experiment (WUPPE) are presented. Contrary to model predictions, the intrinsic polarization of P Cyg remains constant in the Balmer continuum except for a broad dip between 2600 and 3000 A. This decrease in polarization is discussed in terms of possible Fe line blanketing effects. The intrinsic position angle is essentially constant in the UV except for a rotation across the feature between 2600 and 3000 A. The intrinsic polarization of Kappa Cas is small; most of the observed polarization is interstellar in nature. The Serkowski curve extrapolated into the UV is found to fall consistently below the observed polarization. A slight rotation in position angle from optical to UV wavelengths is noted. Very good agreement is found between the mean continuum polarization obtained by WUPPE and the broadband UV polarization measurement obtained by Gehrels (1968).

  19. Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa

    E-print Network

    L. Decin; S. Hony; A. de Koter; K. Justtanont; A. G. G. M. Tielens; L. B. F. M. Waters

    2006-06-13

    Context: Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). The gas and dust ejected during this phase are a major source in the mass budget of the interstellar medium. Recent studies have pointed towards the importance of variations in the mass-loss history of such objects. Aims: By modelling the full line profile of low excitation CO lines emitted in the circumstellar envelope, we can study the mass-loss history of AGB stars. Methods: We have developed a non-LTE radiative transfer code, which calculates the velocity structure and gas kinetic temperature of the envelope in a self-consistent way. The resulting structure of the envelope provides the input for the molecular line radiative calculations which are evaluated in the comoving frame. The code allows for the implementation of modulations in the mass-loss rate. This code has been benchmarked against other radiative transfer codes and is shown to perform well and efficiently. Results: We illustrate the effects of varying mass-loss rates in case of a superwind phase. The model is applied to the well-studied case of VY CMa. We show that both the observed integrated line strengths as the spectral structure present in the observed line profiles, unambiguously demonstrate that this source underwent a phase of high mass loss (~ 3.2E-4 Msun/yr) some 1000 yr ago. This phase took place for some 100 yr, and was preceded by a low mass-loss phase (~ 1E-6 Msun/yr) taking some 800 yr. The current mass-loss rate is estimated to be in the order of 8E-5 Msun/yr. Conclusions: In this paper, we demonstrate that both the relative strength of the CO rotational line profiles and the (non)-occurrence of spectral structure in the profile offer strong diagnostics to pinpoint the mass-loss history.

  20. The blue supergiant Sher 25 and its intriguing hourglass nebula

    NASA Astrophysics Data System (ADS)

    Hendry, M. A.; Smartt, S. J.; Skillman, E. D.; Evans, C. J.; Trundle, C.; Lennon, D. J.; Crowther, P. A.; Hunter, I.

    2008-08-01

    The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN1987A. Here, we present long-slit spectroscopy of the circumstellar nebula around Sher25, and of the background nebula of the host cluster NGC3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + logO/H = 8.61 +/- 0.13dex) is similar to that in the background nebula (8.56 +/- 0.07), suggesting that the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 +/- 0.15, compared to the background value of 7.47 +/- 0.18. A new analysis of the stellar spectrum with the FASTWIND model atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models, they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50Msolar, which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances.

  1. The blue supergiant Sher 25 and its intriguing hourglass nebula

    E-print Network

    M. A. Hendry; S. J. Smartt; E. D. Skillman; C. J. Evans; C. Trundle; D. J. Lennon; P. A. Crowther; I. Hunter

    2008-03-29

    The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log[O/H] = 8.61 +/- 0.13 dex) is similar to that in the background nebula (8.56 +/- 0.07), suggesting the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 +/- 0.15, compared to the background value of 7.47 +/- 0.18. A new analysis of the stellar spectrum with the FASTWIND model atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher 25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50 M_sun, which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances.

  2. Quantitative Studies of the Optical and UV Spectra of Galactic Early B Supergiants

    NASA Technical Reports Server (NTRS)

    Searle, S. C.; Prinja, R. K.; Massa, D.; Ryans, R.

    2008-01-01

    We undertake an optical and ultraviolet spectroscopic analysis of a sample of 20 Galactic B0-B5 supergiants of luminosity classes Ia, Ib, Iab, and II. Fundamental stellar parameters are obtained from optical diagnostics and a critical comparison of the model predictions to observed UV spectral features is made. Methods. Fundamental parameters (e.g., T(sub eff), log L(sub *), mass-loss rates and CNO abundances) are derived for individual stars using CMFGEN, a nLTE, line-blanketed model atmosphere code. The impact of these newly derived parameters on the Galactic B supergiant Ten scale, mass discrepancy, and wind-momentum luminosity relation is examined. Results. The B supergiant temperature scale derived here shows a reduction of about 1000-3000 K compared to previous results using unblanketed codes. Mass-loss rate estimates are in good agreement with predicted theoretical values, and all of the 20 BO-B5 supergiants analysed show evidence of CNO processing. A mass discrepancy still exists between spectroscopic and evolutionary masses, with the largest discrepancy occuring at log (L/(solar)L approx. 5.4. The observed WLR values calculated for B0-B0.7 supergiants are higher than predicted values, whereas the reverse is true for B1-B5 supergiants. This means that the discrepancy between observed and theoretical values cannot be resolved by adopting clumped (i.e., lower) mass-loss rates as for O stars. The most surprising result is that, although CMFGEN succeeds in reproducing the optical stellar spectrum accurately, it fails to precisely reproduce key UV diagnostics, such as the N v and C IV P Cygni profiles. This problem arises because the models are not ionised enough and fail to reproduce the full extent of the observed absorption trough of the P Cygni profiles. Conclusions. Newly-derived fundamental parameters for early B supergiants are in good agreement with similar work in the field. The most significant discovery, however, is the failure of CMFGEN to predict the correct ionisation fraction for some ions. Such findings add further support to revising the current standard model of massive star winds, as our understanding of these winds is incomplete without a precise knowledge of the ionisation structure and distribution of clumping in the wind. Key words. techniques: spectroscopic - stars: mass-loss - stars: supergiants - stars: abundances - stars: atmospheres - stars: fundamental parameters

  3. Multiple flaring activity in the supergiant fast X-ray transient IGR J08408-4503 observed with Swift

    Microsoft Academic Search

    P. Romano; L. Sidoli; G. Cusumano; P. A. Evans; L. Ducci; H. A. Krimm; S. Vercellone; K. L. Page; A. P. Beardmore; D. N. Burrows; J. A. Kennea; N. Gehrels; V. La Parola; V. Mangano

    2009-01-01

    IGR J08408-4503 is a supergiant fast X-ray transient discovered in 2006 with a confirmed association with a O8.5Ib(f) supergiant star, HD 74194. We report on the analysis of two outbursts caught by Swift\\/Burst Alert Telescope (BAT) on 2006 October 4 and 2008 July 5, and followed up at softer energies with Swift\\/X-ray Telescope (XRT). The 2008 XRT light curve shows

  4. Ultraviolet analysis of the peculiar supergiant HD 112374 = HR 4912

    NASA Technical Reports Server (NTRS)

    Bohm-Vitense, E.; Proffitt, C.

    1984-01-01

    The ultraviolet energy distribution of the metal-poor supergiant HD 112374 is analyzed based on observations from the International Ultraviolet Explorer (IUE) satellite for the region between 1200 and 2000 A. A discontinuity was found in the UV spectra at 2600 A which confirmed the low-abundance of heavy elements found by Luck et al. (1983). Values for effective temperature and log g in HD112374 were consistent with the star being a very luminous Population II semi-regular variable. The full observational results are presented in a table.

  5. IUE observations of the Henize-Carlson sample of peculiar emission line supergiants: The galactic analogs of the Magellanic Zoo

    NASA Technical Reports Server (NTRS)

    Shore, Steven N.; Brown, Douglas N.; Sanduleak, N.

    1986-01-01

    Some 15 stars from the Carlson-Henize survey of southern peculiar emission line stars were studied. From both the optical and UV spectra, they appear to be galactic counterparts of the most extreme early-type emission line supergiants of the Magellanic Clouds.

  6. Identification of Red Supergiants in the Magellanic Clouds.

    NASA Astrophysics Data System (ADS)

    Barandi, Brian Allan; Massey, Philip; Levesque, Emily M.

    2015-01-01

    The number and characteristics of red supergiants (RSGs) in the low metallicity environment of the Large and Small Magellanic Clouds (LMC, SMC) provide tests of stellar evolutionary tracks for massive stars. One complication is identifying Magellanic members due to the contamination of foreground stars in the Milky Way. We used the colors and magnitudes from the 2MASS survey to identify RSG candidates in the LMC and SMC, and used the Anglo Australian Telescope coupled with the AAOmega spectrograph to take spectra of 325 LMC and 423 SMC RSG candidates. Using the Ca II triplet, we measured the radial velocity of each candidate by cross correlation and assigned membership. Methods along with physical properties of each star will be presented. We gratefully acknowledge support by the National Science Foundation through the REU program at Lowell Observatory and Northern Arizona University (AST-1004107) and through PM's grant AST-1008020.

  7. The Wind Momentum - Luminosity Relationship of Galactic A- and B- Supergiants

    E-print Network

    R. P. Kudritzki; J. Puls; D. J. Lennon; K. A. Venn; J. Reetz; E. Najarro; J. K. McCarthy; A. Herrero

    1999-10-25

    The Balmer lines of four A Ia - supergiants (spectral type A0 to A3) and fourteen B Ia and Ib - supergiants (spectral type B0 to B3) in the solar neighbourhood are analyzed by means of NLTE unified model atmospheres to determine the properties of their stellar winds, in particular their wind momenta. As in previous work for O-stars (Puls et al.) a tight relationship between stellar wind momentum and luminosity (`WLR'') is found. However, the WLR varies as function of spectral type. Wind momenta are strongest for O-supergiants, then decrease from early B (B0 and B1) to mid B (B1.5 to B3) spectral types and become stronger again for A-supergiants. The slope of the WLR appears to be steeper for A- and mid B-supergiants than for O-supergiants. The spectral type dependence is interpreted as an effect of ionization changing the effective number and the line strength distribution function of spectral lines absorbing photon momentum around the stellar flux maximum. This interpretation needs to be confirmed by theoretical calculations for radiation driven winds. A-supergiants in M31 observed with HIRES at the Keck telescope have wind momenta compatible with their galactic counterparts. The potential of the WLR as a new, independent extragalactic distance indicator is discussed. It is concluded that with ten to twenty objects, photometry with HST and medium resolution spectroscopy with 8m-telescopes from the ground distance moduli can be obtained with an accuracy of about 0.1m out to the Virgo and Fornax clusters of galaxies.

  8. Water vapor on supergiants. The 12 micron TEXES spectra of mu Cephei

    E-print Network

    N. Ryde; M. J. Richter; G. M. Harper; K. Eriksson; D. L. Lambert

    2006-03-15

    Several recent papers have argued for warm, semi-detached, molecular layers surrounding red giant and supergiant stars, a concept known as a MOLsphere. Spectroscopic and interferometric analyses have often corroborated this general picture. Here, we present high-resolution spectroscopic data of pure rotational lines of water vapor at 12 microns for the supergiant mu Cephei. This star has often been used to test the concept of molecular layers around supergiants. Given the prediction of an isothermal, optically thick water-vapor layer in Local Thermodynamic Equilibrium around the star (MOLsphere), we expected the 12 micron lines to be in emission or at least in absorption but filled in by emission from the molecular layer around the star. Our data, however, show the contrary; we find definite absorption. Thus, our data do not easily fit into the suggested isothermal MOLsphere scenario. The 12 micron lines, therefore, put new, strong constraints on the MOLsphere concept and on the nature of water seen in signatures across the spectra of early M supergiants. We also find that the absorption is even stronger than that calculated from a standard, spherically symmetric model photosphere without any surrounding layers. A cool model photosphere, representing cool outer layers is, however, able to reproduce the lines, but this model does not account for water vapor emission at 6 microns. Thus, a unified model for water vapor on mu Cephei appears to be lacking. It does seem necessary to model the underlying photospheres of these supergiants in their whole complexity. The strong water vapor lines clearly reveal inadequacies of classical model atmospheres.

  9. Winds and Shells Around Low-Mass Supergiants

    NASA Astrophysics Data System (ADS)

    Bond, Howard E.

    A class of F-type supergiants lying at high galactic latitudes (the 89 Herculis or UU Herculis stars) has been known for some years. More recent evidence suggests that these objects are not young Population I objects, but instead are much older low-mass stars evolving off the tip of the asymptotic giant branch toward the regime of central stars of planetary nebulae. It is possible that these stars are already surrounded by unionized planetary nebulae, if they have experienced an extreme mass-ejection episode (or "superwind") when they were at the tip of the asymptotic giant branch. We propose to obtain high-dispersion long-wavelength IUE spectra of several 89 Hertype stars, in order to study the profiles of the Mg II doublet at 2800. The observations should allow us to detect the presence of mass outflow from the stellar atmospheres, and to search for circumstellar material. Discovery of such material would provide support for the scenario for planetary-nebula formation outlined above. This program is a continuation of one begun during the eighth year of IUE observing. During the past year, we obtained one high-dispersion long-wavelength spectrum of HR 4912, a bright 89 Her-type object. A preliminary analysis does indicate evidence for circumstellar absorption. Moreover, the chromospheric Mg II emission shows an unusual inverse P Cygni profile. This observation shows that our program is likely to provide important new information not only about mass loss from, but also about chromospheric conditions in, the atmospheres of these rare, low-mass supergiants.

  10. A new survey of cool supergiants in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    González-Fernández, Carlos; Dorda, Ricardo; Negueruela, Ignacio; Marco, Amparo

    2015-06-01

    Aims: In this study we conduct a pilot program aimed at the red supergiant population of the Magellanic Clouds. We intend to extend the current known sample to the unexplored low end of the brightness distribution of these stars, building a more representative dataset with which to extrapolate their behaviour to other Galactic and extra-galactic environments. Methods: We select candidates using only near infrared photometry, and with medium resolution multi-object spectroscopy, we perform spectral classification and derive their line-of-sight velocities, confirming the nature of the candidates and their membership in the clouds. Results: Around two hundred new red supergiants have been detected, hinting at a yet to be observed large population. Using near- and mid-infrared photometry we study the brightness distribution of these stars, the onset of mass-loss, and the effect of dust in their atmospheres. Based on this sample, new a priori classification criteria are investigated, combining mid- and near-infrared photometry to improve the observational efficiency of similar programs to this. The catalogue of observed sources is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A3

  11. The spin-up of contracting red supergiants

    E-print Network

    Alexander Heger; Norbert Langer

    1998-03-02

    We report on a mechanism which may lead to a spin-up of the surface of a rotating single star leaving the Hayashi line, which is much stronger than the spin-up expected from the mere contraction of the star. By analyzing rigidly rotating, convective stellar envelopes, we qualitatively work out the mechanism through which these envelopes may be spun up or down by mass loss through their lower or upper boundary, respectively. We find that the first case describes the situation in retreating convective envelopes, which tend to retain most of the angular momentum while becoming less massive, thereby increasing the specific angular momentum in the convection zone and thus in the layers close to the stellar surface. We explore the spin-up mechanism quantitatively in a stellar evolution calculation of a rotating 12 M_sun star, which is found to be spun up to critical rotation after leaving the red supergiant branch. We discuss implications of this spin-up for the circumstellar matter around several types of stars, i.e., post-AGB stars, B[e] stars, pre-main sequence stars, and, in particular, the progenitor of Supernova 1987A.

  12. The stellar wind velocity function for red supergiants determined in eclipsing binaries

    NASA Technical Reports Server (NTRS)

    Ahmad, Imad A.; Stencel, Robert E.

    1988-01-01

    The potential for direct measurement of the acceleration of stellar winds from the supergiant component of Zeta Aurigae-type binary stars is discussed. The aberration angle of the interaction shock cone centered on the hot star provides a measure of the velocity of the cool star wind at the orbit of the secondary. This is confirmed by direct observations of stellar wind (P Cygni) line profile variations. This velocity is generally smaller than the final (terminal) velocity of the wind, deduced from the P Cygni line profiles. The contrast between these results and previously published supergiant wind models is discussed. The implication on the physics of energy source dissipation predicted in the theoretical models is considered.

  13. An observational evaluation of magnetic confinement in the winds of BA supergiants

    NASA Astrophysics Data System (ADS)

    Shultz, M.; Wade, G. A.; Petit, V.; Grunhut, J.; Neiner, C.; Hanes, D.; MiMeS Collaboration

    2014-02-01

    Magnetic wind confinement has been proposed as one explanation for the complex wind structures of supergiant stars of spectral types B and A. Observational investigation of this hypothesis was undertaken using high-resolution (?/?? ˜ 65 000) circular polarization (Stokes V) spectra of six late B- and early A-type supergiants (? Ori, B8Iae; 4 Lac, B9Iab; ? Leo, A0Ib; HR1040, A0Ib; ? Cyg, A2Iae; ? Cep, A2Iab), obtained with the instruments ESPaDOnS and Narval at the Canada-France-Hawaii Telescope and the Bernard Lyot Telescope. Least-squares deconvolution (LSD) analysis of the Stokes V spectra of all stars yields no evidence of a magnetic field, with best longitudinal field 1? error bars ranging from ˜0.5 to ˜4.5 G for most stars. Spectrum synthesis analysis of the LSD profiles using Bayesian inference yields an upper limit with 95.4 per cent credibility on the polar strength of the (undetected) surface dipole fields of individual stars ranging from 3 to 30 G. These results strongly suggest that magnetic wind confinement due to organized dipolar magnetic fields is not the origin of the wind variability of BA supergiant stars. Upper limits for magnetic spots may also be inconsistent with magnetic wind confinement in the limit of large spot size and filling factor, depending on the adopted wind parameters. Therefore, if magnetic spots are responsible for the wind variability of BA supergiant stars, they likely occupy a small fraction of the photosphere.

  14. X-ray Variability in the Hot Supergiant zgr Orionis.

    PubMed

    Berghöfer, T W; Schmitt, J H

    1994-09-16

    Hot massive stars represent only a small fraction of the stellar population of the galaxy, but their enormous luminosities make them visible over large distances. Therefore, they are ideal standard candles, used to determine distances of near galaxies. Their mass loss due to supersonic winds driven by radiation pressure contributes significantly to the interstellar medium and thus to the chemical evolution of galaxies. All hot stars are soft x-ray sources; in contrast to the sun with its highly variable x-ray flux, long time scale x-ray variability is not common among hot stars. An analysis is presented here of an unusual increase in x-ray flux observed with the roentgen observatory satellite during a period of 2 days for the hot supergiant zeta Orionis, the only episode of x-ray variability that has been found in a hot star. These observations provide the most direct evidence so far for the scenario of shock-heated gas in the winds of hot stars. PMID:17770897

  15. Spitzer Observations Of The Supergiant Shell Region In IC 2574

    E-print Network

    John M. Cannon; Fabian Walter; George J. Bendo; Daniela Calzetti; Daniel A. Dale; Bruce T. Draine; Charles W. Engelbracht; Karl D. Gordon; George Helou; Robert C. Kennicutt, Jr.; Eric J. Murphy; Michele D. Thornley; Lee Armus; David J. Hollenbach; Claus Leitherer; Michael W. Regan; Helene Roussel; Kartik Sheth

    2005-08-01

    We present spatially resolved Spitzer imaging of the supergiant shell region of the M81 group dwarf galaxy IC 2574 obtained as part of the Spitzer Infrared Nearby Galaxies Survey. This region harbors one of the best nearby examples of a kinematically distinct HI shell, with an associated remnant stellar cluster; the shell is initiating sequential star formation as it interacts with the surrounding interstellar medium. This region dominates the infrared luminosity of IC 2574 and is spatially resolved in all Spitzer imaging bands. We study the differences in dust temperature as a function of local environment and compare local star formation rates as inferred from H Alpha and total infrared luminosities. We find that the strong H Alpha sources are associated with regions of warm dust; however, the most luminous infrared and H Alpha sources are not necessarilyco-spatial. The coolest dust is found in the regions farthest from the rim of the shell; these regions show the best agreement between star formation rates derived from H Alpha and from total infrared luminosities (although discrepancies at the factor of 3-4 level still exist). There is considerable variation in the radio-far infrared correlation in different regions surrounding the shell. The low dust content of the region may influence the scatter seen in these relations; these data demonstrate that the expanding shell is dramatically affecting its surroundings by triggering star formation and altering the dust temperature.

  16. Winds and Shells Around Low-Mass Supergiants

    NASA Astrophysics Data System (ADS)

    Bond, Howard E.

    A class of metal-deficient F-type supergiants has recently been identified. They appear to be low-mass stars evolving rapidly off the asymptotic giant branch toward the regime of the central stars of planetary nebulae. All members of this class appear to be low-amplitude semiregular variables. We will obtain high-dispersion long-wavelength IUE spectra of three relatively bright members of this class, in order to study the profiles of the Mg II doublet at 2800. The observations should allow us to detect the presence of mass outflow from the stellar atmospheres, and to search for circumstellar material (an un-ionized "planetary nebula") that could be the remnant of a mass-ejection episode that occurred when the star was on the asymptotic giant branch. The observations will provide information not only on the transitory stage of evolution through which these stars are passing, but on the general question of the origin of planetary nebulae.

  17. Intrinsically variable stars

    NASA Technical Reports Server (NTRS)

    Bohm-Vitense, Erika; Querci, Monique

    1987-01-01

    The characteristics of intrinsically variable stars are examined, reviewing the results of observations obtained with the IUE satellite since its launch in 1978. Selected data on both medium-spectral-class pulsating stars (Delta Cep stars, W Vir stars, and related groups) and late-type variables (M, S, and C giants and supergiants) are presented in spectra, graphs, and tables and described in detail. Topics addressed include the calibration of the the period-luminosity relation, Cepheid distance determination, checking stellar evolution theory by the giant companions of Cepheids, Cepheid masses, the importance of the hydrogen convection zone in Cepheids, temperature and abundance estimates for Population II pulsating stars, mass loss in Population II Cepheids, SWP and LWP images of cold giants and supergiants, temporal variations in the UV lines of cold stars, C-rich cold stars, and cold stars with highly ionized emission lines.

  18. The main sequence of three red supergiant clusters

    NASA Astrophysics Data System (ADS)

    Froebrich, Dirk; Scholz, Alexander

    2013-12-01

    Massive clusters in our Galaxy are an ideal testbed to investigate the properties and evolution of high-mass stars. They provide statistically significant samples of massive stars of uniform ages. To accurately determine the intrinsic physical properties of these stars, we need to establish the distances, ages and reddening of the clusters. One avenue to achieve this is the identification and characterization of the main-sequence (MS) members of red supergiant (RSG) rich clusters. Here, we utilize publicly available data from the UKIDSS Galactic Plane Survey. We show that point spread function photometry in conjunction with standard photometric decontamination techniques allows us to identify the most likely MS members in the 10-20 Myr old clusters RSGC 1-3. We confirm the previous detection of the MS in RSGC 2 and provide the first MS detection in RSGC 1 and RSGC 3. There are in excess of 100 stars with more than 8 M? identified in each cluster. These MS members are concentrated towards the spectroscopically confirmed RSG stars. We utilize the J - K colours of the bright MS stars to determine the K-band extinction towards the clusters. The differential reddening is three times as large in the youngest cluster RSGC 1 as compared to the two older clusters RSGC 2 and RSGC 3. Spectroscopic follow-up of the cluster MS stars should lead to more precise distance and age estimates for these clusters as well as the determination of the stellar mass function in these high-mass environments.

  19. A transient supergiant X-ray binary in IC 10: An extragalactic SFXT?

    SciTech Connect

    Laycock, Silas; Cappallo, Rigel; Oram, Kathleen; Balchunas, Andrew [Department of Physics and Applied Physics, Olney Science Center, University of Massachusetts, Lowell, MA 01854 (United States)

    2014-07-01

    We report the discovery of a large amplitude (factor of ?100) X-ray transient (IC 10 X-2, CXOU J002020.99+591758.6) in the nearby dwarf starburst galaxy IC 10 during our Chandra monitoring project. Based on the X-ray timing and spectral properties, and an optical counterpart observed with Gemini, the system is a high-mass X-ray binary consisting of a luminous blue supergiant and a neutron star. The highest measured luminosity of the source was 1.8 × 10{sup 37} erg s{sup –1}during an outburst in 2003. Observations before, during, and after a second outburst in 2010 constrain the outburst duration to be less than 3 months (with no lower limit). The X-ray spectrum is a hard power law (? = 0.3) with fitted column density (N{sub H} = 6.3 × 10{sup 21} atom cm{sup –2}), consistent with the established absorption to sources in IC 10. The optical spectrum shows hydrogen Balmer lines strongly in emission at the correct blueshift (-340 km s{sup –1}) for IC 10. The N III triplet emission feature is seen, accompanied by He II [4686] weakly in emission. Together these features classify the star as a luminous blue supergiant of the OBN subclass, characterized by enhanced nitrogen abundance. Emission lines of He I are seen, at similar strength to H?. A complex of Fe II permitted and forbidden emission lines are seen, as in B[e] stars. The system closely resembles galactic supergiant fast X-ray transients, in terms of its hard spectrum, variability amplitude, and blue supergiant primary.

  20. Light variations of the population II F-type supergiant HD 46703

    NASA Astrophysics Data System (ADS)

    Bond, H. E.; Carney, B. W.; Grauer, A. D.

    1984-02-01

    Photometric monitoring has revealed brightness variations of 0m.1 on a time scale of weeks for HD 46703, a metal-deficient F-type field analog of the stars lying above the horizontal branch in globular clusters. The authors suggest that HD 46703 belongs to the "89 Her" class of luminous F-type variables. Since HD 46703 is unquestionably a halo object, it is almost certainly a low-mass star. The authors suggest that it, and probably the other 89 Her variables, are masquerading as supergiants during their final evolution off the asymptotic giant branch.

  1. Diffraction-limited Speckle-Masking Interferometry of the Red Supergiant VY CMa

    E-print Network

    M. Wittkowski; N. Langer; G. Weigelt

    1998-11-18

    We present the first diffraction-limited images of the mass-loss envelope of the red supergiant star VY CMa. The two-dimensional optical and NIR images were reconstructed from 3.6 m telescope speckle data using bispectrum speckle interferometry. At the wavelengths ~0.8 \\mum (RG 780 filter), 1.28 \\mum, and 2.17 \\mum the diffraction-limited resolutions of 46 mas, 73 mas, and 124 mas were achieved. All images clearly show that the circumstellar envelope of VY CMa is non-spherical. The RG 780, 1.28 \\mum, and 2.17 mum FWHM Gauss fit diameters are 67 mas * 83 mas, 80 mas * 116 mas and 138 mas * 205 mas, respectively, or 100 AU * 125 AU, 120 AU * 174 AU and 207 AU * 308 AU (for a distance of 1500 pc). We discuss several interpretations for the asymmetric morphology. Combining recent results about the angular momentum evolution of red supergiants and their pulsational properties, we suggest that VY CMa is an immediate progenitor of IRC +10420, a post red supergiant during its transformation into a Wolf-Rayet star.

  2. A cool supergiant with anomalous behavior of the 2800 Mg II doublet

    NASA Technical Reports Server (NTRS)

    Gurzadian, G. A.; Rustambekian, S. S.; Kondo, Y.; Perez, Mario R.; Terzian, Yervant

    1991-01-01

    The IUE ultraviolet spectrum for a supergiant of type G Ia, HD 135345, is obtained for the wavelength region 2000-3000 A. In the spectrum, the continuum as well as the feature of the Mg II doublet at 2800 A is found to be anomalous. The observed level of continuum increases toward short wavelengths to 2000 A, verifying that this supergiant is actually a binary system with a hot companion. The anomalies in the magnesium doublet are the complete absence of the chromospheric emission and the very small equivalent width of the doublet absorption: the equivalent width is 4 A, which is 7.5 times smaller than that for a typical G5 star. The main parameters of the binary system are obtained, namely, spectral classes, effective temperatures, ratio of radii, and visible magnitudes.

  3. Red Supergiants as Cosmic Abundance Probes: The Sculptor Galaxy NGC 300

    NASA Astrophysics Data System (ADS)

    Gazak, J. Zachary; Kudritzki, Rolf; Evans, Chris; Patrick, Lee; Davies, Ben; Bergemann, Maria; Plez, Bertrand; Bresolin, Fabio; Bender, Ralf; Wegner, Michael; Bonanos, Alceste Z.; Williams, Stephen J.

    2015-06-01

    We present a quantitative spectroscopic study of 27 red supergiants (RSGs) in the Sculptor Galaxy NGC 300. J-band spectra were obtained using KMOS on the Very Large Telescope and studied with state of the art synthetic spectra including NLTE corrections for the strongest diagnostic lines. We report a central metallicity of [Z] = ?0.03 ± 0.05 with a gradient of ?0.083 ± 0.014 [dex/kpc], in agreement with previous studies of blue supergiants and H ii-region auroral line measurements. This result marks the first application of the J-band spectroscopic method to a population of individual RSG stars beyond the Local Group of galaxies and reveals the great potential of this technique. Data collected under ESO Program ID 092.B-0088.

  4. Red Supergiants as Cosmic Abundance Probes: The Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Davies, Ben; Kudritzki, Rolf-Peter; Gazak, Zach; Plez, Bertrand; Bergemann, Maria; Evans, Chris; Patrick, Lee

    2015-06-01

    Red Supergiants (RSGs) are cool (?4000 K), highly luminous stars (L? {{10}5} L? ), and are among the brightest near-IR sources in star-forming galaxies. This makes them powerful probes of the properties of their host galaxies, such as kinematics and chemical abundances. We have developed a technique whereby metallicities of RSGs may be extracted from a narrow spectral window around 1 ?m from only moderate resolution data. The method is therefore extremely efficient, allowing stars at large distances to be studied, and so has tremendous potential for extragalactic abundance work. Here, we present an abundance study of the Large and Small Magellanic Clouds (LMC and SMC respectively) using samples of 9–10 RSGs in each. We find average abundances for the two galaxies of {{[Z]}LMC}=-0.37+/- 0.14 and {{[Z]}SMC}=-0.53+/- 0.16 (with respect to a solar metallicity of {{Z}? }=0.012). These values are consistent with other studies of young stars in these galaxies, and though our result for the SMC may appear high it is consistent with recent studies of hot stars which find 0.5–0.8 dex below solar. Our best-fit temperatures are on the whole consistent with those from fits to the optical-infrared spectral energy distributions, which is remarkable considering the narrow spectral range being studied. Combined with our recent study of RSGs in the Galactic cluster Per OB1, these results indicate that this technique performs well over a range of metallicities, paving the way for forthcoming studies of more distant galaxies beyond the Local Group.

  5. MSX SOURCES IN THE LMC: DUSTENSHROUDED AGB STARS AND POSTAGB STARS

    E-print Network

    Wood, Peter

    MSX SOURCES IN THE LMC: DUST­ENSHROUDED AGB STARS AND POST­AGB STARS P.R. Wood Research School bar has been searched for infrared sources using data from the MSX satellite. In the most sensitive that 125 of the MSX sources are red supergiants or foreground stars, 230 are dust­ enshrouded AGB stars

  6. Physics of Mass Loss in Massive Stars

    NASA Astrophysics Data System (ADS)

    Puls, Joachim; Sundqvist, Jon O.; Markova, Nevena

    2015-01-01

    We review potential mass-loss mechanisms in the various evolutionary stages of massive stars, from the well-known line-driven winds of O-stars and BA-supergiants to the less-understood winds of Red Supergiants. We discuss optically thick winds from Wolf-Rayet stars and Very Massive Stars, and the hypothesis of porosity-moderated, continuum-driven mass loss from stars formally exceeding the Eddington limit, which might explain the giant outbursts from Luminous Blue Variables. We finish this review with a glance on the impact of rapid rotation, magnetic fields and small-scale inhomogeneities in line-driven winds.

  7. Red Supergiants in the Andromeda Galaxy (M31)

    NASA Astrophysics Data System (ADS)

    Massey, Philip; Silva, D. R.; Levesque, E. M.; Plez, B.; Clayton, G. C.

    2009-01-01

    Red supergiants (RSGs) are the He-burning descendants of moderately massive (10-40 Mo) stars. Although they are not the most massive or bolometrically luminous, they are the physically largest stars in the universe, and their high luminosities and red colors result in their dominating the integrated NIR light of low redshift starbursts. Their high visual luminosities (Mv=-6 to -9) put them within reach for detailed studies within the Local Group and beyond. For years the location of these stars in the HRD has been at variance with stellar evolutionary theory, with the "observed" locations more luminous and cooler than theory allow. Our group has recently revised the effective temperature scale of RSGs in the Milky Way and Magellanic Clouds using the new generation of MARCS stellar atmospheres (Levesque et al. 2005, 2006), resulting in excellent agreement in the Milky Way and LMC, and moderately good agreement in the SMC. Here we extend this work to RSGs in the Andromeda Galaxy, M31. The metallicity of M31 is 2x solar, allowing us to now compare the physical properties of RSGS to that of evolution models at high metallicity. The sample was photometrically selected from the recent Local Group Galaxy Survey (Massey et al 2006, 2007), with membership confirmed by radial velocities obtained at WIYN. Optical spectrophotometry was obtained of a small subsample (17) of these objects using the mighty MMT 6.5-m. We also obtained contemporaneous V-K photometry using the Lowell Perkins 1.8-m telescope and the Mayall 4-m. The resulting distribution of stars in the HRD is shown, along with a comparison of their physical properties with lower metallicity RSGs. This work was supported by the NSF through AST-0604569.

  8. The early-type strong emission-line supergiants of the Magellanic Clouds - A spectroscopic zoology

    NASA Technical Reports Server (NTRS)

    Shore, S. N.; Sanduleak, N.

    1984-01-01

    The results of a spectroscopic survey of 21 early-type extreme emission line supergiants of the Large and Small Magellanic Clouds using IUE and optical spectra are presented. The combined observations are discussed and the literature on each star in the sample is summarized. The classification procedures and the methods by which effective temperatures, bolometric magnitudes, and reddenings were assigned are discussed. The derived reddening values are given along with some results concerning anomalous reddening among the sample stars. The derived mass, luminosity, and radius for each star are presented, and the ultraviolet emission lines are described. Mass-loss rates are derived and discussed, and the implications of these observations for the evolution of the most massive stars in the Local Group are addressed.

  9. The Yellow Supergiant Progenitor of the Type II Supernova 2011dh in M51

    NASA Astrophysics Data System (ADS)

    Maund, J. R.; Fraser, M.; Ergon, M.; Pastorello, A.; Smartt, S. J.; Sollerman, J.; Benetti, S.; Botticella, M.-T.; Bufano, F.; Danziger, I. J.; Kotak, R.; Magill, L.; Stephens, A. W.; Valenti, S.

    2011-10-01

    We present the detection of the putative progenitor of the Type IIb SN 2011dh in archival pre-explosion Hubble Space Telescope images. Using post-explosion Adaptive Optics imaging with Gemini NIRI+ALTAIR, the position of the supernova (SN) in the pre-explosion images was determined to within 23 mas. The progenitor candidate is consistent with an F8 supergiant star (logL/L sun = 4.92 ± 0.20 and T eff = 6000 ± 280 K). Through comparison with stellar evolution tracks, this corresponds to a single star at the end of core C-burning with an initial mass of M ZAMS = 13 ± 3 M sun. The possibility of the progenitor source being a cluster is rejected, on the basis of: (1) the source not being spatially extended, (2) the absence of excess H? emission, and (3) the poor fit to synthetic cluster spectral energy distributions (SEDs). It is unclear if a binary companion is contributing to the observed SED, although given the excellent correspondence of the observed photometry to a single star SED we suggest that the companion does not contribute significantly. Early photometric and spectroscopic observations show fast evolution similar to the transitional Type IIb SN 2008ax and suggest that a large amount of the progenitor's hydrogen envelope was removed before explosion. Late-time observations will reveal if the yellow supergiant or the putative companion star were responsible for this SN explosion.

  10. THE YELLOW SUPERGIANT PROGENITOR OF THE TYPE II SUPERNOVA 2011dh IN M51

    SciTech Connect

    Maund, J. R. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej, DK-2100 Copenhagen Oe (Denmark); Fraser, M.; Smartt, S. J.; Kotak, R.; Magill, L. [Astrophysics Research Center, School of Mathematics and Physics, Queens University Belfast, Belfast, BT7 1NN (United Kingdom); Ergon, M.; Sollerman, J. [Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, 106 91 Stockholm (Sweden); Pastorello, A. [Dipartimento di Astronomia, Universita di Padova, Vicolo dell'Osservatorio 3, 35122 Padova (Italy); Benetti, S.; Botticella, M.-T.; Valenti, S. [INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova (Italy); Bufano, F. [INAF-Osservatorio Astronomico di Catania, Via S.Sofia 78, 95123 Catania (Italy); Danziger, I. J. [INAF Osservatorio Astronomico di Trieste and Dipartimento di Fisica, Sezione di Astronomia, Universit di Trieste, via G.B. Tiepolo 11, 34131 Trieste (Italy); Stephens, A. W., E-mail: justyn@dark-cosmology.dk [Gemini Observatory, 670 North Aohoku Place, Hilo, HI 96720 (United States)

    2011-10-01

    We present the detection of the putative progenitor of the Type IIb SN 2011dh in archival pre-explosion Hubble Space Telescope images. Using post-explosion Adaptive Optics imaging with Gemini NIRI+ALTAIR, the position of the supernova (SN) in the pre-explosion images was determined to within 23 mas. The progenitor candidate is consistent with an F8 supergiant star (logL/L{sub sun} = 4.92 {+-} 0.20 and T {sub eff} = 6000 {+-} 280 K). Through comparison with stellar evolution tracks, this corresponds to a single star at the end of core C-burning with an initial mass of M{sub ZAMS} = 13 {+-} 3 M{sub sun}. The possibility of the progenitor source being a cluster is rejected, on the basis of: (1) the source not being spatially extended, (2) the absence of excess H{alpha} emission, and (3) the poor fit to synthetic cluster spectral energy distributions (SEDs). It is unclear if a binary companion is contributing to the observed SED, although given the excellent correspondence of the observed photometry to a single star SED we suggest that the companion does not contribute significantly. Early photometric and spectroscopic observations show fast evolution similar to the transitional Type IIb SN 2008ax and suggest that a large amount of the progenitor's hydrogen envelope was removed before explosion. Late-time observations will reveal if the yellow supergiant or the putative companion star were responsible for this SN explosion.

  11. SPECTROSCOPIC STUDY OF THE VARIABILITY OF THREE NORTHERN Of{sup +} SUPERGIANTS

    SciTech Connect

    De Becker, M. [Postdoctoral Researcher FRS/FNRS (Belgium). (Belgium); Rauw, G.; Linder, N., E-mail: debecker@astro.ulg.ac.b [Institut d'Astrophysique et de Geophysique, Universite de Liege, 17 Allee du 6 Aout, B5c, B-4000 Sart Tilman (Belgium)

    2009-10-20

    The transition from early Of stars to WN-type objects is poorly understood. O-type supergiants with emission lines (OIf{sup +}) are considered to be intermediate between these two classes. The scope of this paper is to investigate the spectral variability of three Of{sup +} supergiants. We constituted spectral time series of unprecedented quality for our targets (approx200 spectra in total), essentially in the blue domain, covering timescales from a few hours up to a few years. Temporal Variance Spectrum and Fourier analyses were performed in order to characterize their spectral variability. We report on a correlated significant line profile variability in the prominent He II lambda4686 and Hbeta lines most likely related to the strong stellar winds. The variability pattern is similar for the three stars investigated (HD 14947, HD 15570, and HD 16691), and the main differences are more quantitative than qualitative. However, the reported timescales are somewhat different, and the most striking variability pattern is reported for HD 16691. We did not find any clear evidence for binarity, and we focus mainly on an interpretation based on a single-star scenario. We show that the behavior of the three stars investigated in this study present strong similarities, pointing to a putative common scenario, even though a few differences should be noted. Our preferred interpretation scheme is that of Large-Scale Corotating Structures modulating the profile of the lines that are produced in the strong stellar wind.

  12. DOUBLE BOW SHOCKS AROUND YOUNG, RUNAWAY RED SUPERGIANTS: APPLICATION TO BETELGEUSE

    SciTech Connect

    Mackey, Jonathan; Mohamed, Shazrene; Neilson, Hilding R.; Langer, Norbert; Meyer, Dominique M.-A., E-mail: jmackey@astro.uni-bonn.de [Argelander-Institut fuer Astronomie, Auf dem Huegel 71, D-53121 Bonn (Germany)

    2012-05-20

    A significant fraction of massive stars are moving supersonically through the interstellar medium (ISM), either due to disruption of a binary system or ejection from their parent star cluster. The interaction of their wind with the ISM produces a bow shock. In late evolutionary stages these stars may undergo rapid transitions from red to blue and vice versa on the Hertzsprung-Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks. Recent three-dimensional simulations of the bow shock produced by the nearby runaway red supergiant (RSG) Betelgeuse, under the assumption of a constant wind, indicate that the bow shock is very young (<30, 000 years old), hence Betelgeuse may have only recently become an RSG. To test this possibility, we have calculated stellar evolution models for single stars which match the observed properties of Betelgeuse in the RSG phase. The resulting evolving stellar wind is incorporated into two-dimensional hydrodynamic simulations in which we model a runaway blue supergiant (BSG) as it undergoes the transition to an RSG near the end of its life. We find that the collapsing BSG wind bubble induces a bow shock-shaped inner shell around the RSG wind that resembles Betelgeuse's bow shock, and has a similar mass. Surrounding this is the larger-scale retreating bow shock generated by the now defunct BSG wind's interaction with the ISM. We suggest that this outer shell could explain the bar feature located (at least in projection) just in front of Betelgeuse's bow shock.

  13. Spectral atlas of O9.5-A1-Type supergiants

    NASA Astrophysics Data System (ADS)

    Chentsov, E. L.; Sarkisyan, A. N.

    2007-09-01

    High-resolution spectra of nine supergiants and three comparison stars taken with CCD echelle spectrographs in the coude’ foci of the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and 2-m telescope of Terskol Observatory (with R = 40000 and R = 45000, respectively) are reported in a tabular and graphic form. Two hundred ( ? Cam, O9.5 Ia) to 1000 (HD 12953, A1 Ia-0) stellar and interstellar lines and bands are identified in the 3600 7800 ÅÅ wavelength interval and most of them have their central intensities and heliocentric radial velocities measured. A spectral classification based on weak photospheric absorptions is tested. This is actual for the brightest supergiants and hypergiants, where the formation regions of strong lines, which are traditionally used for classification, also include the bases of stellar winds. Radial gradients of velocity are revealed in the atmospheres of supergiants. The cases of the refinement of the effective wavelengths, analysis of blends, and revealing of wind anomalies in line profiles are illustrated. The atlas is used extensively as a teaching tool.

  14. On the hydrogen neutral outflowing disks of B[e] supergiants

    E-print Network

    Kraus, M; D'Araújo, F X; Kraus, Michaela; Fernandes, Marcelo Borges; Araujo, Francisco X. de

    2006-01-01

    (abridged) B[e] supergiants are known to possess geometrically thick dusty disks. Disk-forming wind models have, however, been found to be insufficient in reproducing the observed dust emission. This problem arises due to the severe assumption that, as for classical Be stars, the near-infrared excess emission originates in the disk. Modeling of the free-free and free-bound emission therefore results in an upper limit for the disk mass loss rate, hampering dust condensation in the disk. We propose a revised scenario for the non-spherical winds of B[e] supergiants: a normal B-type line-driven polar wind and an outflowing disk-forming wind that is neutral in hydrogen at, or very close to the stellar surface. We concentrate on the pole-on seen LMC B[e] supergiant R126 and calculate the line luminosities of the optical [OI] emission lines with an outflowing disk scenario. In addition, we compute the free-free and free-bound emission from a line-driven polar wind and model the spectral energy distribution in the op...

  15. THE CURIOUS CASE OF THE ALPHA PERSEI CORONA: A DWARF IN SUPERGIANT'S CLOTHING?

    SciTech Connect

    Ayres, Thomas R., E-mail: Thomas.Ayres@Colorado.edu [Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389 (United States)

    2011-09-10

    Alpha Persei (HD 20902: F5 Iab) is a luminous, nonvariable supergiant located at the blue edge of the Cepheid instability strip. It is one of the brightest coronal X-ray sources in the young open cluster bearing its name, yet warm supergiants as a class generally avoid conspicuous high-energy activity. The Cosmic Origins Spectrograph on the Hubble Space Telescope has recently uncovered additional oddities. The 1290-1430 A far-ultraviolet (FUV) spectrum of {alpha} Per is dominated by photospheric continuum emission, with numerous superposed absorption features, mainly stellar. However, the normal proxies of coronal activity, such as the Si IV 1400 A doublet (T {approx} 8 x 10{sup 4} K), are very weak, as are the chromospheric C II 1335 A multiplet (T {approx} 3 x 10{sup 4} K) and O I 1305 A triplet. In fact, the Si IV features of {alpha} Per are not only narrower than those of later, G-type supergiants of similar L{sub X}/L{sub bol}, but are also fainter (in L{sub SiIV}/L{sub bol}) by two orders of magnitude. Further, a reanalysis of the ROSAT pointing on {alpha} Per finds the X-ray centroid offset from the stellar position by 9'', at a moderate level of significance. The FUV and X-ray discrepancies raise the possibility that the coronal source might be unrelated to the supergiant, perhaps an accidentally close dwarf cluster member; heretofore unrecognized in the optical, lost in the glare of the bright star.

  16. Postexplosion hydrodynamics of supernovae in red supergiants

    NASA Technical Reports Server (NTRS)

    Herant, Marc; Woosley, S. E.

    1994-01-01

    Shock propagation, mixing, and clumping are studied in the explosion of red supergiants as Type II supernovae using a two-dimensional smooth particle hydrodynamic (SPH) code. We show that extensive Rayleigh-Talor instabilities develop in the ejecta in the wake of the reverse shock wave. In all cases, the shell structure of the progenitor is obliterated to leave a clumpy, well-mixed supernova remnant. However, the occurrence of mass loss during the lifetime of the progenitor can significantly reduce the amount of mixing. These results are independent of the Type II supernova explosion mechanism.

  17. Star struck

    NASA Astrophysics Data System (ADS)

    Closer to home, astronomers using the Hubble Space Telescope recently took a close-up photograph of the red supergiant star Betelgeuse, providing astronomers with their first direct look at the surface of a star besides the Sun.Andrea Dupree of the Harvard-Smithsonian Center for Astrophysics and Ronald Gilliland of the Space Telescope Science Institute presented pictures of Betelgeuse revealing an extended atmosphere and a surface marked by a bright spot more than 10 Earths wide and as much as 2000 K warmer than the rest of the surface.

  18. WINDS IN CORONAE BOREALIS STARS Geoffrey Clayton,

    E-print Network

    Bianchi, Luciana

    WINDS IN CORONAE BOREALIS STARS Geoffrey Clayton, 1 Geballe, Luciana Bianchi Received February accepted 2003 ABSTRACT present spectroscopic observations the i #10830 line Coronae Borealis (RCB) stars R Coronae Borealis (RCB) stars small group of hydrogen­deficient, carbon­rich supergiants

  19. Searching for Complex, Weak or Tangled Magnetic Fields in the Blue Supergiant Rigel

    NASA Astrophysics Data System (ADS)

    Shultz, M.; Wade, G. A.; Neiner, C.; Manset, N.; Petit, V.; Grunhut, J.; Guinan, E.; Hanes, D.; Mimes Collaboration

    Seventy-eight high-resolution Stokes V, Q and U spectra of the B8 Iae supergiant Rigel were obtained with the ESPaDOnS instrument at the CFHT, and its clone NARVAL at the TBL in the context of the Magnetism in Massive Stars (MiMeS) Large Program, with the aim of scrutinizing this core-collapse supernova progenitor for direct evidence of weak and/or complex magnetic fields. In this paper we describe the reduction and analysis of the data, the constraints obtained on any magnetic field present in the stellar photosphere, and the variability of photospheric and wind lines.

  20. Interplay between pulsations and mass loss in the blue supergiant 55 Cygnus = HD 198478

    E-print Network

    Kraus, M; Cidale, L S; Venero, R O J; Nickeler, D H; Nemeth, P; Niemczura, E; Tomic, S; Aret, A; Kubat, J; Kubatova, B; Oksala, M E; Cure, M; Kaminski, K; Dimitrov, W; Fagas, M; Polinska, M

    2015-01-01

    Blue supergiant stars are known to display photometric and spectroscopic variability that is suggested to be linked to stellar pulsations. Pulsational activity in massive stars strongly depends on the star's evolutionary stage and is assumed to be connected with mass-loss episodes, the appearance of macroturbulent line broadening, and the formation of clumps in the wind. To investigate a possible interplay between pulsations and mass-loss, we carried out an observational campaign of the supergiant 55 Cyg over a period of five years to search for photospheric activity and cyclic mass-loss variability in the stellar wind. We modeled the H, He I, Si II and Si III lines using the nonlocal thermal equilibrium atmosphere code FASTWIND and derived the photospheric and wind parameters. In addition, we searched for variability in the intensity and radial velocity of photospheric lines and performed a moment analysis of the line profiles to derive frequencies and amplitudes of the variations. The Halpha line varies wit...

  1. The temperature of C II emission-line formation regions in cool stars

    NASA Technical Reports Server (NTRS)

    Brown, A.; Carpenter, K. G.

    1984-01-01

    An investigation has been conducted of the temperature of C II emission-line formation regions in the outer atmospheres of late-type giant and supergiant stars. A distinct dichotomy is seen in the C II lambda 2325/lambda 1335 ratio between coronal and noncoronal stars. It is found that C II emission from noncoronal giant and supergiant stars comes from regions with temperatures of 7000-9000 K, with the mean temperature being approximately 8500 K, whereas the C II emission from coronal stars likely comes from hotter regions. The C II ratio provides a powerful empirical tool for estimating the chromospheric temperatures of cool giants and supergiants.

  2. The Ultraviolet Spectral Morphology of a Sample of B Supergiants in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    McNeil, R. C.; Borchers, A. L.; Sonneborn, G.; Fahey, R. P.

    1995-05-01

    A study of the ultraviolet spectra of a sample of B supergiants in the Small Magellanic Cloud is being undertaken as a means of addressing some questions about the nature and evolution of massive stars. All spectra are new or archival low-dispersion SWP spectra (1200stars is being examined for consistency with their published spectral classifications. Analysis includes a tabulation of ultraviolet spectral features, evaluation of their variation with spectral type and luminosity class, and comparison with IUE spectral sequences of standard stars. The data analysis was performed at the IUE Data Analysis Center at Goddard Space Flight Center. Partial support of this work by NASA and Northern Kentucky University through the Joint Ventures (JOVE) program, and support of the Laboratory for Astronomy and Solar Physics at GSFC, is gratefully acknowledged.

  3. A-type Supergiant Abundances in the SMC: Probes of Evolution

    E-print Network

    Kim Venn

    1999-01-21

    New abundances of N, O, Na, Mg, Si, Ca, Sc, Ti, Cr, Fe, Sr, Zr, and Ba are presented for 10 A-type supergiants in the SMC, plus upper limits for C. In interpreting the CNO results for constraints on stellar evolution theories, careful attention has been paid to the comparison abundances, i.e., the present day abundances of SMC nebulae and B-dwarf stars. These new results are also compared to published results from F-K supergiant analyses, and found to be in good agreement when both sets of data are carefully examined as differential (SMC minus Galactic standard) abundances. With the exception of nitrogen, very small star-to-star abundance variations are found for all elements in this analysis. The N variations are not predicted by standard stellar evolution models. Instead, the results support the new predictions reported from rotating stellar models, where the range in nitrogen is the result of partial mixing of CN-cycled gas from the stellar interior due to main-sequence rotation at different rates (c.f., Langer & Heger 1998). The overall overabundance of nitrogen in the sampled stars also implies these stars have undergone the first dredge-up in addition to having been mixed while on the main-sequence. The alpha-elements (O, Mg, Si, Ca, Ti) have similar underabundances to Fe, which is not the same as seen in metal-poor stars in the solar neighborhood of the Galaxy. In addition, certain light s-process elements (Zr, Ba) are slightly more underabundant than Fe, which is predicted by the bursting chemical evolution model presented by Pagel & Tautvaisiene (1998) for the SMC.

  4. Time Series Analysis of the A0 Supergiant HR 1040

    NASA Astrophysics Data System (ADS)

    Corliss, David J.

    A time series analysis of spectroscopic and photometric observables of the A0Ia supergiant HR 1040 has been performed. The data, obtained from 1993 through 2007, include 152 spectroscopic observations from the Ritter Observatory and 269 Stromgren photometric observations from the Four College Automated Photoelectric Telescope (FCAPT). A number of spectroscopic and photometric features have been analyzed and compared, including Wlambda, radial velocities and Stromgren photometric indices. Typical of late B- and early A-type supergiants, HR 1040 has a highly variable stellar wind including High Velocity Absorption (HVA) events. The star was found to have an active phase with large variation in the physical characteristics of the wind and with the potential for HVAs. During the active phase, correlation between the H-alpha absorption equivalent width and blue-edge radial velocity was observed. If an HVA was present, the active phase was found to begin before the onset of the HVA and continue after the end of the event by as much as several weeks. This active phase alternated with a more common quiescent phase marked by little variability and equivalent width - radial velocity correlation and no HVAs. The active phase and HVAs were found to exhibit important connections to photospheric activity. Increases in H-alpha absorption and blue-edge radial velocity at the onset of HVAs was preceded by correlated increases in Si II Wlambda and second moment, with the atmospheric changes indicated by the H-alpha line lagging the photospheric changes seen in Si II by an interval of 13 to 23 days. The observed HVAs were found to be preceded by Si II radial velocity oscillations by an interval of 19 to 42 days. The equivalent width and second moment of the photospheric Si II lambdalambda6347, 6371 lines were found to be highly variable and strongly correlated throughout the two active phases when an HVA is observed but not during the quiescent phase or in the one active phase where no HVA was seen. The Si II Wlambda and second moment showed a short-lived increase during the first few weeks of an HVA and then quickly dropped back to quiescent phase levels. Time series cluster analysis of the two HVAs observed on HR 1040, in addition to three HVAs in alpha Orionis, identified four distinct stages in the development of these events. Possible factors contributing to HVA are discussed, including gas ejection and microturbulence at the photosphere, as well as co-rotation interaction regions (CIR) in the wind. HR 1040 exhibits a broad emission feature near Halpha commonly found in late B- and early A-type supergiants. The broad emission in HR 1040 was found to be variable and not correlated to photospheric or wind observables associated with the active phase. Some indication was found that this feature is limited to a wavelength range of 6532 A to 6597 A. While the wavelength range extends roughly the same amount to either side of H-alpha line center, an asymmetry in the flux of the broad emission is observed, with a local maximum in the flux varying between 6555 A to 6564 A. If this asymmetry is real and not an instrumental effect, it argues against a photospheric origin for this broad emission feature as it would require radial velocities up to -300 km/s, well in excess of the terminal wind speed.

  5. Bright flares in supergiant fast X-ray transients

    NASA Astrophysics Data System (ADS)

    Shakura, N.; Postnov, K.; Sidoli, L.; Paizis, A.

    2014-08-01

    At steady low-luminosity states, supergiant fast X-ray transients (SFXTs) can be at the stage of quasi-spherical settling accretion on to slowly rotating magnetized neutron stars from the OB-companion winds. At this stage, a hot quasi-static shell is formed above the magnetosphere, the plasma entry rate into magnetosphere is controlled by (inefficient) radiative plasma cooling, and the accretion rate on to the neutron star is suppressed by a factor of ˜30 relative to the Bondi-Hoyle-Littleton value. Changes in the local wind velocity and density due to, e.g. clumps, can only slightly increase the mass accretion rate (a factor of ˜10) bringing the system into the Compton-cooling-dominated regime and led to the production of moderately bright flares (Lx ? 1036 erg s-1). To interpret the brightest flares (Lx > 1036 erg s-1) displayed by the SFXTs within the quasi-spherical settling accretion regimes, we propose that a larger increase in the mass accretion rate can be produced by sporadic capture of magnetized stellar wind plasma. At sufficiently low accretion rates, magnetic reconnection can enhance the magnetospheric plasma entry rate, resulting in copious production of X-ray photons, strong Compton cooling and ultimately in unstable accretion of the entire shell. A bright flare develops on the free-fall time-scale in the shell, and the typical energy released in an SFXT bright flare corresponds to the mass of the shell. This view is consistent with the energy released in SFXT bright flares (˜1038-1040 erg), their typical dynamic range (˜100) and with the observed dependence of these characteristics on the average unflaring X-ray luminosity of SFXTs. Thus, the flaring behaviour of SFXTs, as opposed to steady HMXBs, may be primarily related to their low X-ray luminosity allowing sporadic magnetic reconnection to occur during magnetized plasma entry into the magnetosphere.

  6. Identification of red supergiants in nearby galaxies with mid-IR photometry

    NASA Astrophysics Data System (ADS)

    Britavskiy, N. E.; Bonanos, A. Z.; Mehner, A.; García-Álvarez, D.; Prieto, J. L.; Morrell, N. I.

    2014-02-01

    Context. The role of episodic mass loss in massive-star evolution is one of the most important open questions of current stellar evolution theory. Episodic mass loss produces dust and therefore causes evolved massive stars to be very luminous in the mid-infrared and dim at optical wavelengths. Aims: We aim to increase the number of investigated luminous mid-IR sources to shed light on the late stages of these objects. To achieve this we employed mid-IR selection criteria to identity dusty evolved massive stars in two nearby galaxies. Methods: The method is based on mid-IR colors, using 3.6 ?m and 4.5 ?m photometry from archival Spitzer Space Telescope images of nearby galaxies and J-band photometry from 2MASS. We applied our criteria to two nearby star-forming dwarf irregular galaxies, Sextans A and IC 1613, selecting eight targets, which we followed-up with spectroscopy. Results: Our spectral classification and analysis yielded the discovery of two M-type supergiants in IC 1613, three K-type supergiants and one candidate F-type giant in Sextans A, and two foreground M giants. We show that the proposed criteria provide an independent way for identifying dusty evolved massive stars that can be extended to all nearby galaxies with available Spitzer/IRAC images at 3.6 ?m and 4.5 ?m. Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio de El Roque de Los Muchachos of the Instituto de Astrofísica de Canarias, on the island of La Palma, and the 2.5 m du Pont telescope in operation at Las Campanas Observatory, Chile.Spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/562/A75

  7. Molecular Abundances in the Circumstellar Envelope of Oxygen-Rich Supergiant VY Canis Majoris

    NASA Astrophysics Data System (ADS)

    Edwards, Jessica L.; Ziurys, Lucy

    2014-06-01

    A complete set of molecular abundances have been established for the Oxygen-rich circumstellar envelope (CSE) surrounding the supergiant star VY Canis Majoris (VY CMa). These data were obtained from The Arizona Radio Observatory (ARO) 1-mm spectral line survey of this object using the ARO Sub-millimeter Telescope (SMT), as well as complimentary transitions taken with the ARO 12-meter. The non-LTE radiative transfer code ESCAPADE has been used to obtain the molecular abundances and distributions in VY CMa, including modeling of the various asymmetric outflow geometries in this source. For example, SO and SO2 were determined to arise from five distinct outflows, four of which are asymmetric with respect to the central star. Abundances of these two sulfur-bearing molecules range from 3 x 10-8 - 2.5 x 10-7 for the various outflows. Similar results will be presented for molecules like CS, SiS, HCN, and SiO, as well as more exotic species like NS, PO, AlO, and AlOH. The molecular abundances between the various outflows will be compared and implications for supergiant chemistry will be discussed.

  8. Physical Parameters and Wind Properties of Galactic Early B Supergiants

    E-print Network

    Paul Crowther; Daniel Lennon; Nolan Walborn

    2005-09-15

    We present optical studies of the physical and wind properties, plus CNO chemical abundances, of 25 O9.5-B3 Galactic supergiants. We employ non-LTE, line blanketed, extended model atmospheres, which provide a modest downward revision in the effective temperature scale of early B supergiants of up to 1-2kK relative to previous non-blanketed results. The so-called `bistability jump' at B1 (Teff ~ 21kK) from Lamers et al. is rather a more gradual trend (with large scatter) from v_inf/v_esc ~ 3.4 for B0--0.5 supergiants above 24kK to v_inf/v_esc ~ 2.5 for B0.7-1 supergiants with 20kK < Teff < 24kK, and v_inf/v_esc ~ 1.9 for B1.5-3 supergiants below 20kK. This, in part, explains the break in observed UV spectral characteristics between B0.5 and B0.7 subtypes as discussed by Walborn et al. We compare derived (homogeneous) wind densities with recent results for Magellanic Cloud B supergiants and generally confirm theoretical expectations for stronger winds amongst Galactic supergiants. However, winds are substantially weaker than predictions from current radiatively driven wind theory, especially at mid-B subtypes, a problem which is exacerbated if winds are already clumped in the H-alpha line forming region. In general, CNO elemental abundances reveal strongly processed material at the surface of Galactic B supergiants, with mean N/C and N/O abundances 10 and 5 times higher than the Solar value, respectively, with HD 2905 (BC0.7 Ia) indicating the lowest degree of processing in our sample, and HD 152236 (B1.5 Ia+) the highest.

  9. Discovery of H2O maser emission from the red supergiant IRAS04553-6825 in the Large Magellanic Cloud

    E-print Network

    Jacco Th. van Loon; Peter te Lintel Hekkert; Valentin Bujarrabal; Albert A. Zijlstra; Lars-Ake Nyman

    1998-06-15

    We report the detection of 22 GHz H2O maser emission from the red supergiant IRAS04553-6825 in the Large Magellanic Cloud. It is the first known source of circumstellar H2O maser emission outside the Milky Way. The measured flux density is comparable to that expected from scaling the galactic red supergiant NML Cyg. The peak velocity agrees with the SiO maser peak velocity. A near-infrared spectrum indicates that IRAS04553-6825 has a typical LMC metallicity. We argue that, possibly as a result of the low metallicity, the H2O emission probably occurs near or within the dust formation radius, rather than further out as appears to be the case in NML Cyg and galactic OH/IR stars.

  10. Supergiant radial and nonradial pulsations. Lecture 10

    Microsoft Academic Search

    Cox

    1983-01-01

    The stars that we consider here have luminosities above 10,000 solar luminosities and masses above 15 solar masses. We contact the 53 Per stars such as ..nu.. Ori, 10 Lac, and iota CMa at our lower luminosity limit, and at the most luminous limit, we have the famous stars eta Car, Cyg OB12, and P Cyg. Evolution tracks including a

  11. A study of B-type supergiants with the uvby,beta photometric system

    NASA Astrophysics Data System (ADS)

    Zhang, E.-H.

    1983-06-01

    The applicability of the uvby,beta photometric system to the classification and study of B-type supergiants (BTS) is investigated using published data on 157 BTS and observations of 17 BTS made with the 36-in. reflector at McDonald Observatory. The results are presented in tabular form and analyzed to produce preliminary calibrations of luminosity class vs. beta index and of absolute magnitude (Mv) vs. beta (or delta Mv vs. delta beta) for four associations of stars. The effectiveness of various color indices as temperature indicators is discussed. It is shown that there is good correspondence between MK and uvby,beta classifications of B-type main-sequence stars, giants, and BTS, confirming the usefulness of the uvby,beta system in further research on BTS.

  12. Clumped stellar winds in supergiant high-mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Oskinova, L. M.; Feldmeier, A.; Kretschmar, P.

    2013-02-01

    The clumping of massive star winds is an established paradigm, which is confirmed by multiple lines of evidence and is supported by stellar wind theory. We use the results from time-dependent hydrodynamical models of the instability in the line-driven wind of a massive supergiant star to derive the time-dependent accretion rate on to a compact object in the Bondi-Hoyle-Lyttleton approximation. The strong density and velocity fluctuations in the wind result in strong variability of the synthetic X-ray light curves. Photoionization of inhomogeneous winds is different from the photoinization of smooth winds. The degree of ionization is affected by the wind clumping. The wind clumping must also be taken into account when comparing the observed and model spectra of the photoionized stellar wind.

  13. OUTFLOW-INDUCED DYNAMICAL AND RADIATIVE INSTABILITY IN STELLAR ENVELOPES WITH AN APPLICATION TO LUMINOUS BLUE VARIABLES AND WOLF-RAYET STARS

    E-print Network

    TO LUMINOUS BLUE VARIABLES AND WOLF-RAYET STARS Richard B. Stothers Institute for Space Studies, NASA Goddard: evolution -- stars: mass loss -- stars: oscillations -- stars: variables: other -- stars: Wolf-Rayet 1 ABSTRACT Theoretical models of the remnants of massive stars in a very hot, post­red-supergiant phase

  14. Stars

    NASA Astrophysics Data System (ADS)

    Capelato, Hugo Vicente

    1999-01-01

    We will begin our study with a more or less superficial inspection of the "forest" of stars that we see in the skies. The first thing we notice is that, as sources of light, they are much weaker than the Sun. Second, their apparent colors vary; from a bluish-white in most of them to a reddish-yellow, which is rarer. There is also a third aspect, though it is not very obvious to the naked eye: most of the stars group themselves in small families of two, three or more members. A good example is the Alpha Centauri, the closest star to us, which, in fact, is a triple system of stars. Another is the group of 7 stars that make up the Pleiades, which will be discussed later on. In fact, almost half of the stars are double systems with only two members, called binary stars. Most of these double stars, though together, are separated by several astronomical units (one astronomical unit, AU, is the distance from Earth to the sun: see Chapter 1), and revolve around each other over periods of several years. And yet the revolutions of some binary stars, separated by much smaller distances, occur in only a few hours! These stars are so close to each other that they can share enveloping material. Often this exchange occurs in a somewhat violent manner. Local explosions may occur, expelling matter away from the system. In other binary systems, where one of the components is a very compact, dense star, companion material flows more calmly, making up a light disk around the compact star.

  15. Supergiant radial and nonradial pulsations. Lecture 10

    SciTech Connect

    Cox, A.N.

    1983-03-14

    The stars that we consider here have luminosities above 10,000 solar luminosities and masses above 15 solar masses. We contact the 53 Per stars such as ..nu.. Ori, 10 Lac, and iota CMa at our lower luminosity limit, and at the most luminous limit, we have the famous stars eta Car, Cyg OB12, and P Cyg. Evolution tracks including a reasonable mass loss rate are given for 15, 30, 60, and 120 solar masses. It appears that our pulsators have masses less than 60 solar masses, but how do the most luminous stars observed survive mass loss. Do they have masses above 100 solar masses as indicated, or are these stars somehow superluminous due to their erratic mass loss behavior. Popper (1980) studying the masses in binary systems has never found one with a value greater than 27 solar masses.

  16. INTEGRAL Long-Term Monitoring of the Supergiant Fast X-Ray Transient XTE J1739-302

    NASA Technical Reports Server (NTRS)

    Blay, P.; Martinez-Nunez, S.; Negueruela, I.; Pottschmidt, K.; Smith, D. M.; Torrejon, J. M.; Reig, P.; Kretschmar, P.; Kreykenbohm, I.

    2008-01-01

    Context. In the past few years, a new class of High Mass X-Ray Binaries (HMXRB) has been claimed to exist, the Supergiant Fast X-ray Transients (SFXT). These are X-ray binary systems with a compact companion orbiting a supergiant star which show very short and bright outbursts in a series of activity periods overimposed on longer quiescent periods. Only very recently the first attempts to model the behaviour of these sources have been published, some of them within the framework of accretion from clumpy stellar winds. Aims. Our goal is to analyze the properties of XTE J1739-302/IGR J17391-3021 within the context of the clumpy structure of the supergiant wind. Methods. We have used INTEGRAL and RXTE/PCA observations in order to obtain broad band (1 - 200 keV) spectra and light curves of XTE J1739-302 and investigate its X-ray spectrum and temporal variability. Results. We have found that XTE J1739-302 follows a much more complex behaviour than expected. Far from presenting a regular variability pattern, XTE J1739-302 shows periods of high, intermediate, and low flaring activity.

  17. X-Ray Observation of the Shocked Red Supergiant Wind of Cassiopeia A

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Joon; Park, Sangwook; Hughes, John P.; Slane, Patrick O.

    2014-07-01

    Cas A is a Galactic supernova remnant whose supernova explosion is observed to be of Type IIb from spectroscopy of its light echo. Having its SN type known, observational constraints on the mass-loss history of Cas A's progenitor can provide crucial information on the final fate of massive stars. In this paper, we study X-ray characteristics of the shocked ambient gas in Cas A using the 1 Ms observation carried out with the Chandra X-Ray Observatory and try to constrain the mass-loss history of the progenitor star. We identify thermal emission from the shocked ambient gas along the outer boundary of the remnant. Comparison of measured radial variations of spectroscopic parameters of the shocked ambient gas to the self-similar solutions of Chevalier show that Cas A is expanding into a circumstellar wind rather than into a uniform medium. We estimate a wind density n H ~ 0.9 ± 0.3 cm–3 at the current outer radius of the remnant (~3 pc), which we interpret as a dense slow wind from a red supergiant (RSG) star. Our results suggest that the progenitor star of Cas A had an initial mass around 16 M ?, and its mass before the explosion was about 5 M ?, with uncertainties of several tens of percent. Furthermore, the results suggest that, among the mass lost from the progenitor star (~11 M ?), a significant amount (more than 6 M ?) could have been via its RSG wind.

  18. The type IIb supernova 2013df and its cool supergiant progenitor

    SciTech Connect

    Van Dyk, Schuyler D. [Spitzer Science Center/Caltech, Mail Code 220-6, Pasadena, CA 91125 (United States); Zheng, WeiKang; Fox, Ori D.; Clubb, Kelsey I.; Filippenko, Alexei V.; Kelly, Patrick L. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Cenko, S. Bradley [Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771 (United States); Foley, Ryan J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Miller, Adam A. [Jet Propulsion Laboratory, MS 169-506, Pasadena, CA 91109 (United States); Smith, Nathan [Steward Observatory, University of Arizona, Tucson, AZ 85720 (United States); Lee, William H. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264, Cd. Universitaria, México DF 04510 (Mexico); Ben-Ami, Sagi; Gal-Yam, Avishay, E-mail: vandyk@ipac.caltech.edu [Benoziyo Center for Astrophysics, The Weizmann Institute of Science, Rehovot 76100 (Israel)

    2014-02-01

    We have obtained early-time photometry and spectroscopy of supernova (SN) 2013df in NGC 4414. The SN is clearly of Type IIb, with notable similarities to SN 1993J. From its luminosity at secondary maximum light, it appears that less {sup 56}Ni (? 0.06 M {sub ?}) was synthesized in the SN 2013df explosion than was the case for the SNe IIb 1993J, 2008ax, and 2011dh. Based on a comparison of the light curves, the SN 2013df progenitor must have been more extended in radius prior to explosion than the progenitor of SN 1993J. The total extinction for SN 2013df is estimated to be A{sub V} = 0.30 mag. The metallicity at the SN location is likely to be solar. We have conducted Hubble Space Telescope (HST) Target of Opportunity observations of the SN with the Wide Field Camera 3, and from a precise comparison of these new observations to archival HST observations of the host galaxy obtained 14 yr prior to explosion, we have identified the progenitor of SN 2013df to be a yellow supergiant, somewhat hotter than a red supergiant progenitor for a normal Type II-Plateau SN. From its observed spectral energy distribution, assuming that the light is dominated by one star, the progenitor had effective temperature T {sub eff} = 4250 ± 100 K and a bolometric luminosity L {sub bol} = 10{sup 4.94±0.06} L {sub ?}. This leads to an effective radius R {sub eff} = 545 ± 65 R {sub ?}. The star likely had an initial mass in the range of 13-17 M {sub ?}; however, if it was a member of an interacting binary system, detailed modeling of the system is required to estimate this mass more accurately. The progenitor star of SN 2013df appears to have been relatively similar to the progenitor of SN 1993J.

  19. The Type IIb Supernova 2013df and its Cool Supergiant Progenitor

    NASA Technical Reports Server (NTRS)

    VanDyk, Schuyler D.; Zeng, Weikang; Fox, Ori D.; Cenko, S. Bradley; Clubb, Kelsey I.; Filippenko, Alexei; Foley, Ryan J.; Miller, Adam A.; Smith, Nathan; Kelly, Patrick L.; Lee, William H.; Ben-Ami, Sagi; Gal-Yam, Avishay

    2014-01-01

    We have obtained early-time photometry and spectroscopy of supernova (SN) 2013df in NGC 4414. The SN is clearly of Type II b, with notable similarities to SN 1993J. From its luminosity at secondary maximum light, it appears that less Ni-56 (is approximately less than 0.06M) was synthesized in the SN 2013df explosion than was the case for the SNe II b 1993J, 2008ax, and 2011dh. Based on a comparison of the light curves, the SN 2013df progenitor must have been more extended in radius prior to explosion than the progenitor of SN 1993J. The total extinction for SN 2013dfis estimated to be A(sub V) = 0.30 mag. The metallicity at the SN location is likely to be solar. We have conducted Hubble Space Telescope(HST) Target of Opportunity observations of the SN with the Wide Field Camera 3, and from a precise comparison of these new observations to archival HST observations of the host galaxy obtained 14 yr prior to explosion, we have identified the progenitor of SN 2013df to be a yellow supergiant, somewhat hotter than a red supergiant progenitor for a normal Type II-Plateau SN. From its observed spectral energy distribution, assuming that the light is dominated by one star, the progenitor had effective temperature T(sub eff) = 4250+/-100 K and a bolometric luminosity L(sub bol) =10(exp 4.94+/-0.06) Solar Luminosity. This leads to an effective radius Reff = 545+/-65 Solar Radius. The star likely had an initial mass in the range of 13-17Solar Mass; however, if it was a member of an interacting binary system, detailed modeling of the system is required to estimate this mass more accurately. The progenitor star of SN 2013df appears to have been relatively similar to the progenitor of SN 1993J.

  20. Transient outburst mechanisms in Supergiant Fast X-ray Transients

    E-print Network

    L. Sidoli

    2009-02-17

    The recent discovery of a new class of recurrent and fast X-ray transient sources, the Supergiant Fast X-ray Transients, poses interesting questions on the possible mechanisms responsible for their transient X-ray emission. The association with blue supergiants, the spectral properties similar to those of accreting pulsars and the detection, in a few cases, of X-ray pulsations, confirm that these transients are High Mass X-ray Binaries. I review the different mechanisms proposed to explain their transient outbursts and the link to persistent wind accretors. I discuss the different models in light of the new observational results coming from an on-going monitoring campaign of four Supergiant Fast X-ray Transients with Swift.

  1. R Coronae Borealis stars in the Galactic bulge discovered by EROS2

    Microsoft Academic Search

    P. Tisserand; J. B. Marquette; P. R. Wood; É. Lesquoy; J. P. Beaulieu; A. Milsztajn; C. Hamadache; C. Afonso; J. N. Albert; J. Andersen; R. Ansari; É. Aubourg; P. Bareyre; X. Charlot; C. Coutures; R. Ferlet; P. Fouqué; J. F. Glicenstein; B. Goldman; A. Gould; M. Gros; J. Haissinski; J. de Kat; L. Le Guillou; C. Loup; C. Magneville; É. Maurice; A. Maury; M. Moniez; N. Palanque-Delabrouille; O. Perdereau; Y. Rahal; J. Rich; M. Spiro; A. Vidal-Madjar; S. Zylberajch

    2008-01-01

    Context: Rare types of variable stars may provide unique insight into short-lived stages of stellar evolution. The systematic monitoring of millions of stars and advanced light curve analysis techniques of microlensing surveys make them ideal for discovering such rare variable stars. One example is the R Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. Aims: We have

  2. MASSIVE STARS IN THE LOCAL GROUP: Implications for Stellar Evolution and Star Formation

    Microsoft Academic Search

    Philip Massey

    2003-01-01

    The galaxies of the Local Group serve as important laboratories for understanding the physics of massive stars. Here I discuss what is involved in identifying various kinds of massive stars in nearby galaxies: the hydrogen-burning O-type stars and their evolved He-burning evolutionary descendants, the luminous blue variables, red supergiants, and Wolf-Rayet stars. Primarily I review what our knowledge of the

  3. MOST Detects g- and p-Modes in the B Supergiant HD 163899 (B2 Ib/II)

    NASA Astrophysics Data System (ADS)

    Saio, H.; Kuschnig, R.; Gautschy, A.; Cameron, C.; Walker, G. A. H.; Matthews, J. M.; Guenther, D. B.; Moffat, A. F. J.; Rucinski, S. M.; Sasselov, D.; Weiss, W. W.

    2006-10-01

    The Microvariability and Oscillations of Stars (MOST) satellite observed the B supergiant HD 163899 (B2 Ib/II) for 37 days as a guide star and detected 48 frequencies <~2.8 cycles day-1 with amplitudes of a few millimagnitudes (mmag) and less. The frequency range embraces g- and p-mode pulsations. It was generally thought that no g-modes are excited in less luminous B supergiants because strong radiative damping is expected in the core. Our theoretical models, however, show that such g-modes are excited in massive post-main-sequence stars, in accordance with these observations. The nonradial pulsations excited in models between 20 Msolar at logTeff~4.41 and 15 Msolar at logTeff~4.36 are roughly consistent with the observed frequency range. Excitation by the Fe bump in opacity is possible because g-modes can be partially reflected at a convective zone associated with the hydrogen-burning shell, which significantly reduces radiative damping in the core. The MOST light curve of HD 163899 shows that such a reflection of g-modes actually occurs and reveals the existence of a previously unrecognized type of variable, slowly pulsating B supergiants (SPBsg) distinct from ? Cyg variables. Such g-modes have great potential for asteroseismology. Based on data from the MOST satellite, a Canadian Space Agency mission, operated jointly by Dynacon, Inc., the University of Toronto Institute of Aerospace Studies, and the University of British Columbia, with the assistance of the University of Vienna.

  4. Stars

    NSDL National Science Digital Library

    Roberta Johnson

    2000-07-01

    This section of the Windows to the Universe web site provides information and images about stars including star statistics, and a star gallery. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging web site that spans the Earth and Space sciences and includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.

  5. Red Supergiants in the Local Group

    NASA Astrophysics Data System (ADS)

    Levesque, E. M.

    2013-05-01

    Galaxies in the Local Group span a factor of 15 in metallicity, ranging from the super-solar M 31 to the Wolf-Lundmark-Melotte (WLM) galaxy, which is the lowest-metallicity (0.1 Z?) Local Group galaxy currently forming stars. Studies of massive star populations across this broad range of environments have revealed important metal-licity-dependent evolutionary trends, allowing us to test the accuracy of stellar evolutionary tracks at these metallicities for the first time. The RSG population is particularly valuable as a key mass-losing phase of moderately massive stars and a source of core-collapse supernova progenitors. By reviewing recent work on the RSG populations in the Local Group, we are able to quantify limits on these stars' effective temperatures and masses and probe the relationship between RSG mass loss behaviors and host environments. Extragalactic surveys of RSGs have also revealed several unusual RSGs that display signs of unusual spectral variability and dust production, traits that may potentially also correlate with the stars' host environments. I will present some of the latest work that has advanced our understanding of RSGs in the Local Group, and consider the many new questions posed by our ever-evolving picture of these stars.

  6. The role of structured OB supergiant winds in producing the X-ray flaring emission from High Mass X-ray Binaries

    E-print Network

    Ducci, L; Paizis, A; Mereghetti, S; Romano, P

    2010-01-01

    Supergiant Fast X-ray Transients (SFXTs) are a new class of High Mass X-ray Binaries, discovered by the INTEGRAL satellite, which display flares lasting from minutes to hours, with peak luminosity of 1E36-1E37 erg/s. Outside the bright outbursts, they show a frequent long-term flaring activity reaching an X-ray luminosity level of 1E33-1E34 erg/s, as recently observed with the Swift satellite. Since a few persistent High Mass X-ray Binaries (HMXBs) with supergiant donors show flares with properties similar to those observed in SFXTs, it has been suggested that the flaring activity in both classes could be produced by the same mechanism, probably the accretion of clumps composing the supergiant wind. We have developed a new clumpy wind model for OB supergiants with both a spherical and a non spherical symmetry for the outflow. We have investigated the effects of the accretion of a clumpy wind onto a neutron star in both classes of persistent and transient HMXBs.

  7. Coronal Temperature and Emission Measure Distributions for he Active G Supergiant Beta Dra and other ASCA Projects

    NASA Technical Reports Server (NTRS)

    Brown, Alexander

    1998-01-01

    This NASA grant supported my ASCA observing and data analysis programs during AOs 1-4. This research involved four Guest Observer projects. Analysis of data from all four programs has been completed. This grant included the following ASCA GO programs: AO1 - "Coronal Temperature and Emission Measure Distributions for the Active G Supergiant Beta Dra" AO2 - "Contemporaneous ASCA, EUVE, IUE, and VLA/AT Observations of Atmospheric Structure of the RS CVn Binary HR1099". AO3 - "Coronal Temperature and Emission Measure Distributions for the hybrid-chromosphere star alpha TrA". AO4-"Activity on the edge of convection: The atmosphere of Canopus (alpha Car, FO Ib-II)".

  8. Integral-Field Spectroscopy of the Post-Red Supergiant IRC +10420: Evidence for an Axisymmetric Wind

    NASA Astrophysics Data System (ADS)

    Davies, Ben; Oudmaijer, René D.; Sahu, Kailash C.

    2007-12-01

    We present NAOMI/OASIS adaptive-optics-assisted integral-field spectroscopy of the transitional massive hypergiant IRC +10420, an extreme mass-losing star apparently in the process of evolving from a red supergiant toward the Wolf-Rayet phase. To investigate the present-day mass-loss geometry of the star, we study the appearance of the line emission from the inner wind as viewed when reflected off the surrounding nebula. We find that, contrary to previous work, there is strong evidence for wind axisymmetry, based on the equivalent width and velocity variations of H? and Fe II ?6516. We attribute this behavior to the appearance of the complex line profiles when viewed from different angles. We also speculate that the Ti II emission originates in the outer nebula in a region analogous to the strontium filament of ? Carinae, based on the morphology of the line emission. Finally, we suggest that the present-day axisymmetric wind of IRC +10420, combined with its continued blueward evolution, is evidence that the star is evolving toward the B[e] supergiant phase.

  9. Narrow polarized components in the OH 1612-MHz maser emission from supergiant OH-IR sources

    NASA Technical Reports Server (NTRS)

    Cohen, R. J.; Downs, G.; Emerson, R.; Grimm, M.; Gulkis, S.; Stevens, G.

    1987-01-01

    High-resolution (300 Hz) OH 1612-MHz spectra of the supergiant OH-IR sources VY CMa, VX Sgr, IRC 10420, and NML Cyg are presented. Linewidths as small as 550 Hz (0.1 km/s) are found for narrow components in the spectra. The present results are consistent with current models for maser line-narrowing and for the physical properties in the OH maser regions. A significant degree of circular polarization is noted in many of the narrow components. The circular polarization suggests the presence of magnetic fields of about 1 mG in the circumstellar envelopes which would be strong enough to influence the outflow from the stars, and which may explain asymmetries found in the circumstellar envelopes.

  10. Submillimeter vibrationally excited water emission from the peculiar red supergiant VY CMa

    E-print Network

    K. M. Menten; S. D. Philipp; R. Guesten; J. Alcolea; E. T. Polehampton; S. Bruenken

    2006-06-02

    Vibrationally excited emission from the SiO and H2O molecules probes the innermost circumstellar envelopes of oxygen-rich red giant and supergiant stars. VY CMa is the most prolific known stellar emission source in these molecules. Observations were made to search for rotational lines in the lowest vibrationally excited state of H2O. The APEX telescope was used for observations of H2O lines at frequencies around 300 GHz. Two vibrationally excited H2O lines were detected, a third one could not be found. In one of the lines we find evidence for weak maser action, similar to known (sub)millimeter H2O lines. We find that the other line's intensity is consistent with thermal excitation by the circumstellar infrared radiation field. Several SiO lines were detected together with the H2O lines.

  11. The high-latitude F supergiant IRAS 18095 + 2704 - A proto-planetary nebula

    NASA Technical Reports Server (NTRS)

    Hrivnak, Bruce J.; Kwok, Sun; Volk, Kevin M.

    1988-01-01

    The paper reports the discovery of a new high-latitude F supergiant, IRAS 18095 + 2704, which shows a large excess in the far-infrared. Ground-based observations have identified it as a V = 10.4 mag F3 Ib star which displays light and velocity variability. Comparison with the post-asymptotic giant branch (AGB) evolution model of Volk and Kwok suggests that it is an excellent candidate for a protoplanetary nebula. Model fitting of the spectrum of 18095 + 2704 from 0.35 to 100 microns suggests that it evolved from the AGB approximately 265 yr ago and had a mass-loss rate of 0.00003 solar mass/yr at the end of the AGB.

  12. Tracing the mass-loss history of B[e] supergiants

    NASA Astrophysics Data System (ADS)

    Kraus, Michaela; Cidale, Lydia S.; Arias, Maria L.; Torres, Andrea F.; Aret, Anna; Fernandes, Marcelo Borges; Muratore, Florencia; Cure, Michel; Oksala, Mary E.

    2013-06-01

    The post-main sequence evolution of massive stars encompasses several phases with strong, often eruptive mass-loss events, including the puzzling B[e] supergiants (B[e]SG). Stars in this group are surrounded by disks which are cool and dense, and give rise to a complex chemistry, producing molecules and dust. The original idea was that these disks have been formed via a steady, but slow, high density equatorially confined wind. However, recent observations revealed that the circumstellar material is located in detached disks or rings, sometimes even multiple rings, favouring a scenario in which mass loss happens episodically rather than smoothly. Furthermore, time-resolved observations of these disk or ring structures implied a high variability in density and kinematics. Some Galactic B[e]SGs were recently found to be in binaries, and in a few cases, the disks are circumbinary instead of circumstellar. We have initiated an observing campaign using high-resolution optical and near-infrared spectroscopy aimed at studying the structure and kinematics of the circumstellar material of B[e]SGs. While in the optical spectral range several forbidden emission lines can be used as ideal tracers for the ionized and neutral atomic disk regions close to the star, near-infrared spectra host band emission from molecules such as CO, which are excellent indicators for the disk conditions at larger distances. Here we present first results and discuss possible mass-loss history scenarios for some of these enigmatic stars.

  13. UV Observations of the Powering Source of the Supergiant Shell in IC2574

    E-print Network

    Stewart, S G; Stewart, Susan G.; Walter, Fabian

    2000-01-01

    A multi-band analysis of the region containing the supergiant HI shell in the nearby dwarf irregular galaxy IC2574 presents evidence of a causal relationship between a central star cluster, the surrounding expanding HI shell, and secondary star formation sites on the rim of the HI shell. Comparisons of the far-UV (FUV, 1521 A), optical broad-band, H-alpha, X-ray, and HI morphologies suggest that the region is in an auspicious moment of star formation triggered by the central stellar cluster. The derived properties of the HI shell, the central stellar cluster, and the star forming regions on the rim support this scenario: The kinematic age of the HI shell is <14 Myr and in agreement with the age of the central stellar cluster derived from the FUV observations (sim 11 Myr). An estimate for the mechanical energy input from SN and stellar winds of the central stellar cluster made from FUV photometry and the derived cluster age is 4.1 x 10^52 erg, roughly a few times higher than the kinetic energy of the HI she...

  14. Quantitative spectroscopic J-band study of red supergiants in Perseus OB-1

    SciTech Connect

    Gazak, J. Zachary; Kudritzki, Rolf [Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Davies, Ben [Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Bergemann, Maria [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS, F-34095 Montpellier (France)

    2014-06-10

    We demonstrate how the metallicities of red supergiant (RSG) stars can be measured from quantitative spectroscopy down to resolutions of ?3000 in the J-band. We have obtained high resolution spectra on a sample of the RSG population of h and ? Persei, a double cluster in the solar neighborhood. We show that careful application of the MARCS model atmospheres returns measurements of Z consistent with solar metallicity. Using two grids of synthetic spectra–one in pure LTE and one with non-LTE (NLTE) calculations for the most important diagnostic lines–we measure Z = +0.04 ± 0.10 (LTE) and Z = –0.04 ± 0.08 (NLTE) for the sample of eleven RSGs in the cluster. We degrade the spectral resolution of our observations and find that those values remain consistent down to resolutions of less than ?/?? of 3000. Using measurements of effective temperatures we compare our results with stellar evolution theory and find good agreement. We construct a synthetic cluster spectrum and find that analyzing this composite spectrum with single-star RSG models returns an accurate metallicity. We conclude that the RSGs make ideal targets in the near infrared for measuring the metallicities of star forming galaxies out to 7-10 Mpc and up to 10 times farther by observing the integrated light of unresolved super star clusters.

  15. The velocity gradient in the pseudo-photosphere of the peculiar supergiant HD101584

    E-print Network

    Eric J. Bakker

    1995-10-23

    In this paper preliminary results are presented based on a study of the low and high resolution ultraviolet spectrum of the peculiar supergiant (post-AGB star) HD101584. By a comparison of the low resolution spectrum (1200-3200ang) with standard stars, the star is classified as an A7I, indicating an effective temperature of 8150 K, where literature quotes spectral type F0I. The Doppler shift of the FeII absorption lines in the high resolution spectrum (2500-3000ang) show a relation with the line optical depth. This suggests an expanding accelerating wind, c.q. pseudo-photosphere. The relation is extended by a factor 10^5 in optical depth by using available data from optical HeI and NI lines. The relation suggests that the radial heliocentric velocity of the star is at least 54.5km/s. From the Halpha line a velocity of 96km/s is measured for the terminal velocity of the wind.

  16. Spectroscopic Study of HD 179821 (IRAS 19114+0002): Proto-Planetary Nebula or Supergiant?

    NASA Technical Reports Server (NTRS)

    Reddy, B. E.; Hrivnak, Bruce J.

    1999-01-01

    A detailed chemical composition analysis of the bright post-AGB candidate HD 179821 (IRAS 19114 + 0002) is presented. The LTE analysis, based on high-resolution (R approximately equal 50,000) and high-quality (S/N approximately equal 300) spectra, yields atmospheric parameters T(sub eff) = 6750 K, log g = 0.5, and xi(sub t) = 5.25 km/s. The elemental abundance results of HD 179821 are found to be [Fe/H] = -0.1, [C/Fe] = +0.2, [N/Fe] = +1.3, [O/Fe] = +0.2, [alpha-process/Fe] = +0.5, and [s-process/Fe] = +0.4. These values clearly differ from the elemental abundances of Population I F supergiants. The C, N, and O abundances and the total CNO abundance value relative to Fe, [C+N+O/Fe] = +0.5, indicate that the photosphere of HD 179821 is contaminated with both the H- and He-burning products of the AGB phase. The evidence for He burning through the 3.alpha process and deep AGB mixing also comes from the observed overabundances of s-process elements. Remarkably, the abundance of the element Na is found to be very large, [Na/Fe] = +0.9. The ratio O/C = 2.6 indicates that the atmosphere is oxygen rich. The results of this abundance study support the argument that HD 179821 is a proto-planetary nebula,. probably with an intermediate-mass progenitor. However, the strength of the O I triplet lines at 7774 A and the distance derived from the interstellar Na I D1 and D2 components imply that the star is a luminous object (M(sub bol) approximately -8.9 +/- 1) and thus a massive supergiant. Thus, while this study contributes important new observational results for this star, an unambiguous determination of its evolutionary status has yet to be achieved.

  17. Exploring jet-launching conditions for supergiant fast X-ray transients

    NASA Astrophysics Data System (ADS)

    García, Federico; Aguilera, Deborah N.; Romero, Gustavo E.

    2014-05-01

    Context. In the magneto-centrifugal mechanism for jet formation, accreting neutron stars are assumed to produce relativistic jets only if their surface magnetic field is weak enough (B ~ 108 G). However, the most common manifestation of neutron stars are pulsars, whose magnetic field distribution peaks at B ~ 1012 G. If the neutron star magnetic field has at least this strength at birth, it must decay considerably before jets can be launched in binary systems. Aims: We study the magnetic field evolution of a neutron star that accretes matter from the wind of a high-mass stellar companion so that we can constrain the accretion rate and the impurities in the crust, which are necessary conditions for jet formation. Methods: We solved the induction equation for the diffusion and convection of the neutron star magnetic field confined to the crust, assuming spherical accretion in a simpliflied one-dimensional treatment. We incorporated state-of-the-art microphysics, including consistent thermal evolution profiles, and assumed two different neutron star cooling scenarios based on the superfluidity conditions at the core. Results: We find that in this scenario, magnetic field decay at long timescales is governed mainly by the accretion rate, while the impurity content and thermal evolution of the neutron star play a secondary role. For accretion rates ? ? 10-10 M? yr-1, surface magnetic fields can decay up to four orders of magnitude in ~107 yr, which is the timescale imposed by the evolution of the high-mass stellar companion in these systems. Based on these results, we discuss the possibility of transient jet-launching in strong wind-accreting high-mass binary systems like supergiant fast X-ray transients.

  18. The structure of blue supergiant winds and the accretion in supergiant High Mass X-ray Binaries

    E-print Network

    Ducci, L; Mereghetti, S; Paizis, A; Romano, P

    2009-01-01

    We have developed a stellar wind model for OB supergiants to investigate the effects of accretion from a clumpy wind on the luminosity and variability properties of High Mass X-ray Binaries. Assuming that the clumps are confined by ram pressure of the ambient gas and exploring different distributions for their mass and radii, we computed the expected X-ray light curves in the framework of the Bondi-Hoyle accretion theory, modified to take into account the presence of clumps. The resulting variability properties are found to depend not only on the assumed orbital parameters but also on the wind characteristics. We have then applied this model to reproduce the X-ray light curves of three representative High Mass X-ray Binaries: two persistent supergiant systems (VelaX-1 and 4U1700-377) and the Supergiant Fast X-ray Transient IGRJ11215-5952. The model can reproduce well the observed light curves, but requiring in all cases an overall mass loss from the supergiant about a factor 3-10 smaller than the values infer...

  19. Discovery of SiO band emission from Galactic B[e] supergiants

    E-print Network

    Kraus, Michaela; Cidale, Lydia; Arias, Maria Laura; Torres, Andrea; Fernandes, Marcelo Borges

    2015-01-01

    B[e] supergiants (B[e]SGs) are evolved massive stars in a short-lived transition phase. During this phase, these objects eject large amounts of material, which accumulates in a circumstellar disk-like structure. The expelled material is typically dense and cool, providing the cradle for molecule and dust condensation and for a rich, ongoing chemistry. Very little is known about the chemical composition of these disks, beyond the emission from dust and CO revolving around the star on Keplerian orbits. As massive stars preserve an oxygen-rich surface composition throughout their life, other oxygen-based molecules can be expected to form. As SiO is the second most stable oxygen compound, we initiated an observing campaign to search for first-overtone SiO emission bands. We obtained high-resolution near-infrared L-band spectra for a sample of Galactic B[e]SGs with reported CO band emission. We clearly detect emission from the SiO first-overtone bands in CPD-52 9243 and indications for faint emission in HD 62623, ...

  20. Investigating the semi-regular light variations of the bright M5 supergiant: ? Herculis

    NASA Astrophysics Data System (ADS)

    Moravveji, E.; Guinan, E. F.; Wasatonic, R.; Sobouti, Y.; Nasiri, S.

    2010-07-01

    Analysis of over 15 years of V-band and Wing three filter near-IR photometry of the bright M5Ib-II supergiant has been carried out. Wavelet analysis of these data reveals that the star pulsates with several complicated oscillation modes. Different time scales of variability are identified, and with the aid of discrete Fourier analysis, depending on the filter, up to seven significant pulsation modes are identified and their frequencies and amplitudes extracted. The Long Secondary Period (LSP) with a mean period of ˜1343 d has been identified, as well as other periods of the order of ˜125 d. The longer period appears to be attributed to the radial pulsational mode, while the various peaks near ˜125 d appear to arise from stochastically excited p-modes. After removing the light contribution of the 5th magnitude binary companion and calibrating the intermediate-band photometry to the Wing photometric system, TiO (719 nm) and near-IR (B-C) Wing color indices were formed. These indices have been calibrated with T eff, while the Wing-C bandpass (1025 nm) serves as a proxy for bolometric magnitude and was transformed to approximate m bol. Finally, the derivation of the variations in the star’s temperature, luminosity and radius is straightforward.

  1. Evidence for extended chromospheres surrounding red giant stars

    NASA Technical Reports Server (NTRS)

    Stencel, R. E.

    1982-01-01

    Observational evidence and theoretical arguments are summarized which indicate that regions of partially ionized hydrogen extending several stellar radii are an important feature of red giant and supergiant stars. The implications of the existence of extended chromospheres are examined in terms of the nature of the other atmospheres of, and mass loss from cool stars.

  2. Multiple flaring activity in the supergiant fast X-ray transient IGR J08408-4503 observed with Swift

    E-print Network

    P. Romano; L. Sidoli; G. Cusumano; P. A. Evans; L. Ducci; H. A. Krimm; S. Vercellone; K. L. Page; A. P. Beardmore; D. N. Burrows; J. A. Kennea; N. Gehrels; V. La Parola; V. Mangano

    2008-10-07

    IGR J08408-4503 is a supergiant fast X-ray transient discovered in 2006 with a confirmed association with a O8.5Ib(f) supergiant star, HD 74194. We report on the analysis of two outbursts caught by Swift/BAT on 2006 October 4 and 2008 July 5, and followed up at softer energies with Swift/XRT. The 2008 XRT light curve shows a multiple-peaked structure with an initial bright flare that reached a flux of ~1E-9 erg/cm2/s (2-10 keV), followed by two equally bright flares within 75 ks. The spectral characteristics of the flares differ dramatically, with most of the difference, as derived via time-resolved spectroscopy, being due to absorbing column variations. We observe a gradual decrease of the NH, derived with a fit using absorbed power law model, as time passes. We interpret these NH variations as due to an ionization effect produced by the first flare, resulting in a significant decrease in the measured column density towards the source. The durations of the flares, as well as the times of the outbursts suggest that the orbital period is ~35 days, if the flaring activity is interpreted within the framework of the Sidoli et al 2007 model with the outbursts triggered by the neutron star passage inside an equatorial wind inclined with respect to the orbital plane.

  3. On the hydrogen neutral outflowing disks of B[e] supergiants

    E-print Network

    Michaela Kraus; Marcelo Borges Fernandes; Francisco X. de Araujo

    2006-11-24

    (abridged) B[e] supergiants are known to possess geometrically thick dusty disks. Disk-forming wind models have, however, been found to be insufficient in reproducing the observed dust emission. This problem arises due to the severe assumption that, as for classical Be stars, the near-infrared excess emission originates in the disk. Modeling of the free-free and free-bound emission therefore results in an upper limit for the disk mass loss rate, hampering dust condensation in the disk. We propose a revised scenario for the non-spherical winds of B[e] supergiants: a normal B-type line-driven polar wind and an outflowing disk-forming wind that is neutral in hydrogen at, or very close to the stellar surface. We concentrate on the pole-on seen LMC B[e] supergiant R126 and calculate the line luminosities of the optical [OI] emission lines with an outflowing disk scenario. In addition, we compute the free-free and free-bound emission from a line-driven polar wind and model the spectral energy distribution in the optical and near-infrared. Good fits to the [OI] line luminosities are achieved for an outflowing disk that is neutral in hydrogen right from the stellar surface. Neutral thereby means that hydrogen is ionized by less than 0.1%. Consequently, the free-free and free-bound emission cannot (dominantly) arise from the disk and cannot limit the disk mass loss rate. The hydrogen neutral outflowing disk scenario therefore provides an ideal environment for efficient dust formation. The spectral energy distribution in the optical and near-infrared range can be well fitted with the stellar continuum plus free-free and free-bound emission from the polar line-driven wind. Our modeling further delivers minimum values for \\dot{M}(disk) > 2.5d-5 M_sun/yr and for the density contrast between equatorial and polar wind of ~10.

  4. High spectral resolution spectroscopy of the SiO fundamental lines in red giants and red supergiants with VLT/VISIR

    NASA Astrophysics Data System (ADS)

    Ohnaka, K.

    2014-01-01

    Context. The mass-loss mechanism in red giants and red supergiants is not yet understood well. The SiO fundamental lines near 8 ?m are potentially useful for probing the outer atmosphere, which is essential for clarifying the mass-loss mechanism. However, these lines have been little explored until now. Aims: We present high spectral resolution spectroscopic observations of the SiO fundamental lines near 8.1 ?m in 16 bright red giants and red supergiants. Our sample consists of seven normal (i.e., non-Mira) K-M giants (from K1.5 to M6.5), three Mira stars, three optically bright red supergiants, two dusty red supergiants, and the enigmatic object GCIRS3 near the Galactic center. Methods: Our program stars were observed between 8.088 ?m and 8.112 ?m with a spectral resolution of 30 000 using VLT/VISIR. Results: We detected SiO fundamental lines in all of our program stars except for GCIRS3. The SiO lines in normal K and M giants as well as optically bright (i.e., not dusty) red supergiants do not show P-Cyg profiles or blueshifts, which means the absence of systematic outflows in the SiO line forming region. We detected P-Cyg profiles in the SiO lines in the dusty red supergiants VY CMa and VX Sgr, with the latter object being a new detection. These SiO lines originate in the outflowing gas with the thermal dust continuum emission seen as the background. The outflow velocities of the SiO line forming region in VY CMa and VX Sgr are estimated to be 27 km s-1 and 17 km s-1, respectively. We derived basic stellar parameters (effective temperature, surface gravity, luminosity, and mass) for the normal K-M giants and optically bright red supergiants in our sample and compared the observed VISIR spectra with synthetic spectra predicted from MARCS photospheric models. Most of the SiO lines observed in the program stars warmer than ~3400 K are reasonably reproduced by the MARCS models, which allowed us to estimate the silicon abundance as well as the 28Si/29Si and 28Si/30Si ratios. However, we detected possible absorption excess in some SiO lines. Moreover, the SiO lines in the cooler red giants and red supergiant cannot be explained by the MARCS models at all, even if the dust emission is taken into account. This disagreement may be a signature of the dense, extended molecular outer atmosphere. Based on VISIR observations made with the Very Large Telescope of the European Southern Observatory. Program ID: 087.D-0522(A).Reduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/561/A47

  5. Self-Correlation Analysis of R Coronae Borealis Stars: A Pilot Project

    Microsoft Academic Search

    John R. Percy; Kaushala Bandara; J. Donald Fernie; P. L. Cottrell; Ljiljana Skuljan

    2004-01-01

    R. Coronae Borealis (RCB) stars are peculiar yellow supergiant stars which suddenly and unpredictably decrease in brightness by up to several magnitudes, then slowly return to normal. Most (perhaps all) RCB stars also pulsate, and the pulsations may be related to the ejection of the dust clouds which produce the fadings. As a pilot project, we have applied self-correlation analysis

  6. Quantitative Spectroscopy of BA-type Supergiants

    E-print Network

    N. Przybilla; K. Butler; S. R. Becker; R. P. Kudritzki

    2005-09-22

    Luminous BA-SGs allow topics ranging from NLTE physics and the evolution of massive stars to the chemical evolution of galaxies and cosmology to be addressed. A hybrid NLTE technique for the quantitative spectroscopy of BA-SGs is discussed. Thorough tests and first applications of the spectrum synthesis method are presented for four bright Galactic objects. Stellar parameters are derived from spectroscopic indicators. The internal accuracy of the method allows the 1sigma-uncertainties to be reduced to BA-SGs as versatile tools for extragalactic stellar astronomy beyond the Local Group. (abridged)

  7. X-ray observation of the shocked red supergiant wind of Cassiopeia A

    SciTech Connect

    Lee, Jae-Joon [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Park, Sangwook [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States); Hughes, John P. [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019 (United States); Slane, Patrick O., E-mail: leejjoon@kasi.re.kr [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2014-07-01

    Cas A is a Galactic supernova remnant whose supernova explosion is observed to be of Type IIb from spectroscopy of its light echo. Having its SN type known, observational constraints on the mass-loss history of Cas A's progenitor can provide crucial information on the final fate of massive stars. In this paper, we study X-ray characteristics of the shocked ambient gas in Cas A using the 1 Ms observation carried out with the Chandra X-Ray Observatory and try to constrain the mass-loss history of the progenitor star. We identify thermal emission from the shocked ambient gas along the outer boundary of the remnant. Comparison of measured radial variations of spectroscopic parameters of the shocked ambient gas to the self-similar solutions of Chevalier show that Cas A is expanding into a circumstellar wind rather than into a uniform medium. We estimate a wind density n {sub H} ? 0.9 ± 0.3 cm{sup –3} at the current outer radius of the remnant (?3 pc), which we interpret as a dense slow wind from a red supergiant (RSG) star. Our results suggest that the progenitor star of Cas A had an initial mass around 16 M {sub ?}, and its mass before the explosion was about 5 M {sub ?}, with uncertainties of several tens of percent. Furthermore, the results suggest that, among the mass lost from the progenitor star (?11 M {sub ?}), a significant amount (more than 6 M {sub ?}) could have been via its RSG wind.

  8. The Massive Star Population in M101

    NASA Astrophysics Data System (ADS)

    Grammer, Skyler H.

    An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. Very little is known about the origin of these giant eruptions and their progenitors which are presumably very-massive, evolved stars such as luminous blue variables, hypergiants, and supergiants. Motivated by the small number of progenitors positively associated with these giant eruptions, we have begun a survey of the luminous and evolved massive star populations in several nearby galaxies. We aim to identify the likely progenitors of the giant eruptions, study the spatial variations in the stellar populations, and examine the relationship between massive star populations and their environment. The work presented here is focused on stellar populations in the relatively nearby, giant, spiral galaxy M101 from sixteen archival BVI HST/ACS images. We create a catalog of stars in the direction to M101 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 magnitude 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. From our catalog, we derive the star formation history (SFH) for the stellar populations in five 2' wide annuli by fitting the color-magnitude diagrams. Binning the SFH into time frames corresponding to populations traced by Halpha, far ultraviolet (FUV), and near ultraviolet (NUV) emission, we show that the fraction of stellar populations young enough to contribute in Halpha is 15% " 35% in the inner regions, compared to less than 5% in the outer regions. This provides a sufficient explanation for the lack of Halpha emission at large radii. We also model the blue to red supergiant ratio in our five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into the modeled ratios, we are able to reproduce the observed values at large radii (low metallicity), but at small radii (high metallicity) the modeled and observed ratios are discrepant. Though photometry has proven to be a powerful tool to identify candidate evolved massive stars and their effects on their host galaxy, spectroscopy is necessary to study the physical properties of individual stars. We observed moderate-resolution optical spectra for 56 of the brightest stars in the direction to M101 using the Multiple Mirror Telescope. We also created light curves for each target using multi-epoch U BV R images from the Large Binocular Telescope. We separate the spectroscopially confirmed members of M101 into four groups: hot supergiants, intermediate supergiants, emission-line stars, and LBVs. Several stars in each group are discussed in detail. Of the spectroscopically confirmed members, we find that eight meet our criterion for variability. We present light curves for the known LBV candidates, V2, V4, and V9, and introduce a new candidate: 9492 &barbelow;14 &barbelow;11998. Additionally, we identify 20 new variables in M101. Lacking spectra, we separated the variables, by their photometric properties, into three groups: hot, intermediate, and cool. We find two hot stars with V-band variability of +/-1 magnitude; we flag these stars as LBV candidates. Of the intermediate and cool variables, we identify several stars with low- to moderate-amplitude variability (0.1--0.5 magnitudes).

  9. The blue supergiant Sher 25 and its intriguing hourglass nebula

    Microsoft Academic Search

    M. A. Hendry; S. J. Smartt; E. D. Skillman; C. J. Evans; C. Trundle; D. J. Lennon; P. A. Crowther; I. Hunter

    2008-01-01

    The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN1987A. Here, we present long-slit spectroscopy of the circumstellar nebula around Sher25, and of the background nebula of the host cluster NGC3603. We perform a

  10. The blue supergiant Sher 25 and its intriguing hourglass nebula

    Microsoft Academic Search

    M. A. Hendry; S. J. Smartt; E. D. Skillman; C. J. Evans; C. Trundle; D. J. Lennon; P. A. Crowther; I. Hunter

    2008-01-01

    The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped\\u000acircumstellar nebula. Its structure and dynamics have been studied previously\\u000athrough high-resolution imaging and spectroscopy, and it appears dynamically\\u000asimilar to the ring structure around SN 1987A. Here we present long-slit\\u000aspectroscopy of the circumstellar nebula around Sher 25, and of the background\\u000anebula of the host cluster NGC

  11. Stellar winds and the evolution of luminous stars

    NASA Technical Reports Server (NTRS)

    Stothers, R.; Chin, C.-W.

    1978-01-01

    The effect of a stellar wind on the evolution of stars in the mass range 7-60 solar masses has been investigated for stellar models in which Carson's opacities have been employed. Several cases of mass loss have been considered. It is found that the assumption of heavy mass loss from both blue and red supergiants can account well for the relevant observations of OBN stars, WN stars, and very luminous supergiants of all spectral types. But no amount of mass loss can account adequately for the properties of the B supergiants of lowest luminosity. A critical comparison is made between the present results and some earlier results based on the adoption of Cox-Stewart opacities.

  12. Convective overshooting in the evolution of very massive stars

    NASA Technical Reports Server (NTRS)

    Stothers, R.; Chin, C.-W.

    1981-01-01

    Possible convective overshooting in stars of 30-120 solar masses are considered, including a merger between the convective core and the intermediate zone, and penetration by the outer convection zone into the hydrogen-shell region when the star is a supergiant. Convective mixing between the core and inner envelopes is found to lead to a brief renewal of hydrogen burning in the core, and a moderate widening of the main sequence bond in the H-R diagram. Deep penetration by the outer convection zone is found to force the star out of the red supergiant configuration and into a configuration near the main sequence. This would account for the apparent spread of the uppermost part of the main sequence and the concentration of luminous supergiants towards earlier spectral types. In addition, heavy mass loss need not be assumed to achieve the points of agreement, and are tentatively considered unimportant from an evolutionary point of view.

  13. UV emission from he M1 supergiant TV Gem

    NASA Technical Reports Server (NTRS)

    Michalitsianos, A. G.; Kafatos, M.

    1982-01-01

    Low and high dispersion ultraviolet spectra were obtained of the M1 supergiant TV Gem with IUE. Previous IUE observations of this late type supergiant revealed unexpected UV continuum emission, perhaps arising from an early B companion. Low resolution spectra obtained approximately one year apart suggest that the strong Si III in combination perhaps with O I at wavelengths approximately 1300 A varies considerably with time. Large variation in the column density is required to explain these changes. Sporadic mass expulsion with mass loss rates dM/dt approximately 0.00001 solar mass yr minus 1st power from the M supergiant could lead to a dense circumstellar wind near the hot early companion, and thus could account for these observed variations in equivalent width. The high resolution spectrum in the 2000 to 3200 A wavelength range is characterized by narrow absorption lines primarily due to Fe II, Mn II and Mg II (h and k), which are skewed in profile with an extended red wing. This profile structure is tentatively attributed to interstellar absorption and an intervening differentially moving cloud in the direction of Gem OB1, of which TV Gem is a known association member.

  14. The VLT-FLAMES Tarantula Survey. XIX. B-type supergiants: Atmospheric parameters and nitrogen abundances to investigate the role of binarity and the width of the main sequence

    NASA Astrophysics Data System (ADS)

    McEvoy, C. M.; Dufton, P. L.; Evans, C. J.; Kalari, V. M.; Markova, N.; Simón-Díaz, S.; Vink, J. S.; Walborn, N. R.; Crowther, P. A.; de Koter, A.; de Mink, S. E.; Dunstall, P. R.; Hénault-Brunet, V.; Herrero, A.; Langer, N.; Lennon, D. J.; Maíz Apellániz, J.; Najarro, F.; Puls, J.; Sana, H.; Schneider, F. R. N.; Taylor, W. D.

    2015-03-01

    Context. Model atmosphere analyses have been previously undertaken for both Galactic and extragalactic B-type supergiants. By contrast, little attention has been given to a comparison of the properties of single supergiants and those that are members of multiple systems. Aims: Atmospheric parameters and nitrogen abundances have been estimated for all the B-type supergiants identified in the VLT-FLAMES Tarantula survey. These include both single targets and binary candidates. The results have been analysed to investigate the role of binarity in the evolutionary history of supergiants. Methods: tlusty non-local thermodynamic equilibrium (LTE) model atmosphere calculations have been used to determine atmospheric parameters and nitrogen abundances for 34 single and 18 binary supergiants. Effective temperatures were deduced using the silicon balance technique, complemented by the helium ionisation in the hotter spectra. Surface gravities were estimated using Balmer line profiles and microturbulent velocities deduced using the silicon spectrum. Nitrogen abundances or upper limits were estimated from the N ii spectrum. The effects of a flux contribution from an unseen secondary were considered for the binary sample. Results: We present the first systematic study of the incidence of binarity for a sample of B-type supergiants across the theoretical terminal age main sequence (TAMS). To account for the distribution of effective temperatures of the B-type supergiants it may be necessary to extend the TAMS to lower temperatures. This is also consistent with the derived distribution of mass discrepancies, projected rotational velocities and nitrogen abundances, provided that stars cooler than this temperature are post-red supergiant objects. For all the supergiants in the Tarantula and in a previous FLAMES survey, the majority have small projected rotational velocities. The distribution peaks at about 50 km s-1 with 65% in the range 30 km s-1 ? vesini ? 60 km s-1. About ten per cent have larger vesini (?100 km s-1), but surprisingly these show little or no nitrogen enhancement. All the cooler supergiants have low projected rotational velocities of ?70 km s-1and high nitrogen abundance estimates, implying that either bi-stability braking or evolution on a blue loop may be important. Additionally, there is a lack of cooler binaries, possibly reflecting the small sample sizes. Single-star evolutionary models, which include rotation, can account for all of the nitrogen enhancement in both the single and binary samples. The detailed distribution of nitrogen abundances in the single and binary samples may be different, possibly reflecting differences in their evolutionary history. Conclusions: The first comparative study of single and binary B-type supergiants has revealed that the main sequence may be significantly wider than previously assumed, extending to Teff = 20 000 K. Some marginal differences in single and binary atmospheric parameters and abundances have been identified, possibly implying non-standard evolution for some of the sample. This sample as a whole has implications for several aspects of our understanding of the evolutionary status of blue supergiants. Tables 1, 4, 7 are available in electronic form at http://www.aanda.org

  15. The structure of blue supergiant winds and the accretion in supergiant high-mass X-ray binaries

    Microsoft Academic Search

    L. Ducci; L. Sidoli; S. Mereghetti; A. Paizis; P. Romano

    2009-01-01

    We have developed a stellar wind model for OB supergiants to investigate the effects of accretion from a clumpy wind on the luminosity and variability properties of high-mass X-ray binaries. Assuming that the clumps are confined by ram pressure of the ambient gas and exploring different distributions for their mass and radii, we computed the expected X-ray light curves in

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

    SciTech Connect

    Bonanos, A. Z. [Institute of Astronomy and Astrophysics, National Observatory of Athens, I. Metaxa and Vas. Pavlou St., P. Penteli, 15236 Athens (Greece); Lennon, D. J.; Massa, D. L., E-mail: bonanos@astro.noa.g, E-mail: lennon@stsci.ed, E-mail: massa@stsci.ed [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2010-08-15

    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 {mu}m in the UBVIJHK{sub 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 {mu}m 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.

  17. Spitzer SAGE-SMC Infrared Photometry of Massive Stars in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Bonanos, A. Z.; Lennon, D. J.; Köhlinger, F.; van Loon, J. Th.; Massa, D. L.; Sewilo, M.; Evans, C. J.; Panagia, N.; Babler, B. L.; Block, M.; Bracker, S.; Engelbracht, C. W.; Gordon, K. D.; Hora, J. L.; Indebetouw, R.; Meade, M. R.; Meixner, M.; Misselt, K. A.; Robitaille, T. P.; Shiao, B.; Whitney, B. A.

    2010-08-01

    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 ?m in the UBVIJHKs +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 ?m 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 & 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.

  18. GCIRS 7, a pulsating M1 supergiant at the Galactic centre . Physical properties and age

    NASA Astrophysics Data System (ADS)

    Paumard, T.; Pfuhl, O.; Martins, F.; Kervella, P.; Ott, T.; Pott, J.-U.; Le Bouquin, J. B.; Breitfelder, J.; Gillessen, S.; Perrin, G.; Burtscher, L.; Haubois, X.; Brandner, W.

    2014-08-01

    Context. The stellar population in the central parsec of the Galaxy is dominated in mass and number by an old (several Gyr) population, but young (6 ± 2 Myr), massive stars dominate the luminosity function. The most luminous of these stars is an M1 supergiant, GCIRS 7. Aims: We have studied GCIRS 7 in order to constrain the age of the recent star formation event in the Galactic centre and to characterise it as a visibility and phase reference for observations of the Galactic centre with the interferometric instrument GRAVITY, which will equip the Very Large Telescope Interferometer (VLTI) in the near future. Methods: We present the first H-band interferometric observations of GCIRS 7, obtained using the PIONIER visitor instrument on the VLTI using the four 8.2-m unit telescopes. In addition, we present unpublished K-band VLTI/AMBER data and build JHKL light curves based on archival data spanning almost 40 years, and measured the star's effective temperature using SINFONI integral field spectroscopy. Results: GCIRS 7 is marginally resolved in the H band with a uniform-disk diameter ?UD(2013) = 1.076 ± 0.093 mas (RUD(2013) = 960 ± 92 R? at 8.33 ± 0.35 kpc). We detect a significant circumstellar contribution in the K band. The star and its environment are variable in brightness and in size. The photospheric H-band variations are modelled well with two periods: P0 ? 470 ± 10 days (amplitude ?0.64 mag) and long secondary period PLSP ? 2700 - 2850 days (amplitude ?1.1 mag). As measured from 12CO equivalent width, ?Teff? = 3600 ± 195 K. Conclusions: The size, periods, luminosity (?Mbol? = -8.44 ± 0.22), and effective temperature are consistent with an M1 supergiant with an initial mass of 22.5 ± 2.5 M? and an age of 6.5-10 Myr (depending on rotation). This age is in remarkable agreement with most estimates for the recent star formation event in the central parsec. Caution should be taken when using this star as a phase reference or visibility calibrator because it is variable in size, is surrounded by a variable circumstellar environment, and large convection cells may form on its photosphere. This work relies on interferometric, spectroscopic, and imaging data obtained at the VLT and VLTI in Cerro Paranal Chile between 2003 and 2013. The observations were carried out under the programme IDs 075.B-0547, 076.B-0259, 077.B-0503, 179.B-0261, 381.D-0529, 183.B-0100, 087.B-0117, 087.B-0280, 088.B-0308, 288.B-5040, and 091.D-0682.This work was supported by the French ANR POLCA project (Processing of pOLychromatic interferometriC data for Astrophysics, ANR-10-BLAN-0511).

  19. Multiple flaring activity in the supergiant fast X-ray transient IGR J08408-4503 observed with Swift

    E-print Network

    Romano, P; Cusumano, G; Evans, P A; Ducci, L; Krimm, H A; Vercellone, S; Page, K L; Beardmore, A P; Burrows, D N; Kennea, J A; Gehrels, N; La Parola, V; Mangano, V

    2008-01-01

    IGR J08408-4503 is a supergiant fast X-ray transient discovered in 2006 with a confirmed association with a O8.5Ib(f) supergiant star, HD 74194. We report on the analysis of two outbursts caught by Swift/BAT on 2006 October 4 and 2008 July 5, and followed up at softer energies with Swift/XRT. The 2008 XRT light curve shows a multiple-peaked structure with an initial bright flare that reached a flux of ~1E-9 erg/cm2/s (2-10 keV), followed by two equally bright flares within 75 ks. The spectral characteristics of the flares differ dramatically, with most of the difference, as derived via time-resolved spectroscopy, being due to absorbing column variations. We observe a gradual decrease of the NH, derived with a fit using absorbed power law model, as time passes. We interpret these NH variations as due to an ionization effect produced by the first flare, resulting in a significant decrease in the measured column density towards the source. The durations of the flares, as well as the times of the outbursts sugges...

  20. The mass-loss return from evolved stars to the Large Magellanic Cloud. V. The GRAMS carbon-star model grid

    Microsoft Academic Search

    S. Srinivasan; B. A. Sargent; M. Meixner

    2011-01-01

    Context. Outflows from asymptotic giant branch (AGB) and red supergiant (RSG) stars inject dust into the interstellar medium. The total rate of dust return provides an important constraint to galactic chemical evolution models. However, this requires detailed radiative transfer (RT) modeling of individual stars, which becomes impractical for large data sets. An alternative approach is to select the best-fit spectral

  1. Herschel/HIFI observations of red supergiants and yellow hypergiants. I. Molecular inventory

    NASA Astrophysics Data System (ADS)

    Teyssier, D.; Quintana-Lacaci, G.; Marston, A. P.; Bujarrabal, V.; Alcolea, J.; Cernicharo, J.; Decin, L.; Dominik, C.; Justtanont, K.; de Koter, A.; Melnick, G.; Menten, K. M.; Neufeld, D. A.; Olofsson, H.; Planesas, P.; Schmidt, M.; Soria-Ruiz, R.; Schöier, F. L.; Szczerba, R.; Waters, L. B. F. M.

    2012-09-01

    Context. Red supergiant stars (RSGs) and yellow hypergiant stars (YHGs) are believed to be the high-mass counterparts of stars in the asymptotic giant branch (AGB) and early post-AGB phases. As such, they are scarcer and the properties and evolution of their envelopes are still poorly understood. Aims: We study the mass-loss in the post main-sequence evolution of massive stars, through the properties of their envelopes in the intermediate and warm gas layers. These are the regions where the acceleration of the gas takes place and the most recent mass-loss episodes can be seen. Methods: We used the HIFI instrument on-board the Herschel Space Observatory to observe sub-millimetre and far-infrared (FIR) transitions of CO, water, and their isotopologues in a sample of two RSGs (NML Cyg and Betelgeuse) and two YHGs (IRC+10420 and AFGL 2343) stars. We present an inventory of the detected lines and analyse the information revealed by their spectral profiles. A comparison of the line intensity and shape in various transitions is used to qualitatively derive a picture of the envelope physical structure. On the basis of the results presented in an earlier study, we model the CO and 13CO emission in IRC+10420 and compare it to a set of lines ranging from the millimetre to the FIR. Results: Red supergiants have stronger high-excitation lines than the YHGs, indicating that they harbour dense and hot inner shells contributing to these transitions. Consequently, these high-J lines in RSGs originate from acceleration layers that have not yet reached the circumstellar terminal velocity and have narrower profiles than their flat-topped lower-J counterparts. The YHGs tend to lack this inner component, in line with the picture of detached, hollow envelopes derived from studies at longer wavelengths. NH3 is only detected in two sources (NML Cyg and IRC+10420), which are also observed to be the strongest water-line emitters of the studied sample. In contrast, OH is detected in all sources and does not seem to correlate with the water line intensities. We show that the IRC+10420 model derived solely from millimetre low-J CO transitions is capable of reproducing the high-J transitions when the temperature in the inner shell is simply lowered by about 30%. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix A is available in electronic form at http://www.aanda.orgFITS files of the spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/545/A99

  2. ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY CMa

    E-print Network

    O'Gorman, E; Richards, A M S; Baudry, A; De Beck, E; Decin, L; Harper, G M; Humphreys, E M; Kervella, P; Khouri, T; Muller, S

    2014-01-01

    The processes leading to dust formation and the subsequent role it plays in driving mass-loss in cool evolved stars is an area of intense study. Here, we present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These data enable us to study the dust in its inner circumstellar environment at a spatial resolution of 129 mas at 321 GHz and 59 mas at 658 GHz, allowing us to trace dust on spatial scales down to 11 R$_{\\star}$ (71 AU). Two prominent dust components are detected and resolved. The brightest dust component, C, is located 334 mas (61 R$_{\\star}$) south-east of the star and has a dust mass of at least $2.5\\times 10^{-4} $M$_{\\odot}$. It has an emissivity spectral index of $\\beta =-0.1$ at its peak, implying that it is either optically thick at these frequencies with a cool core of $T_{d}\\lesssim 100$ K, and/or contains very large dust grains. Interestingly, not a single molecule in the ALMA data has emission close to th...

  3. A study on the nature of the peculiar supergiant HD101584

    E-print Network

    Eric J. Bakker; Henny J. G. L. M. Lamers; L. B. F. M. Waters; Christoffel Waelkens; Norman R. Trams; Hans van Winckel

    1995-10-23

    We present a study of low- and high-resolution ultraviolet, high-resolution optical CAT/CES spectra and ultraviolet, optical and infrared photometry of the peculiar supergiant HD101584. From the photometry we learn that the ultraviolet and optical energy distribution cannot be fitted in a consistent way and we need a model in which the UV and optical energy distribution are formed by different gas. The Geneva photometry is best fitted to a B9II Kurucz model, Teff=12000+-1000K and log g=3.0 +-1.0, with an extinction of E(B-V)=0.49+-0.05. The observed spectral features in the spectrum of HD101584 are classified in eight different categories based on the velocity, shape of profile and the identification. The high-excitation HeI(chi=20.87eV), NII(chi=18.40eV), CII (chi=14.39eV) and NI (chi=10.29eV) optical absorption lines are formed in the photosphere of a late B-star (e.g. B8-9I-II). These absorption lines show radial velocity variations which are attributed to binary motion, with the secondary being a

  4. Swift observations of two supergiant fast X-ray transient prototypes in outburst

    E-print Network

    Farinelli, R; Mangano, V; Ceccobello, C; Ducci, L; Vercellone, S; Esposito, P; Kennea, J A; Burrows, D N

    2012-01-01

    We report on the results from observations of the most recent outbursts of XTE J1739-302 and IGR J17544-2619, which are considered to be the prototypes of the supergiant fast X-ray transient (SFXT) class. They triggered the Swift/BAT on 2011 February 22 and March 24, respectively, and each time a prompt Swift slew allowed us to obtain the rich broad-band data we present. The XRT light curves show the descending portion of very bright flares that reached luminosities of ~2x10^{36} and ~5x10^{36} erg/s, respectively. The broad-band spectra, when fit with the usual phenomenological models adopted for accreting neutron stars, yield values of both high energy cut-off and e-folding energy consistent with those obtained from previously reported outbursts from these sources. In the context of more physical models, the spectra of both sources can be well fitted either with a two-blackbody model, or with a single unsaturated Comptonization model. In the latter case, the model can be either a classical static Comptoniza...

  5. Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars

    NASA Technical Reports Server (NTRS)

    Underhill, A. B.; Divan, L.; Prevot-Burnichon, M.-L.; Doazan, V.

    1979-01-01

    This paper discusses effective temperatures, angular diameters, distances, and linear diameters that have been determined for 160 O and B stars on the basis of published UV spectrophotometry, visible and near-IR intermediate-band photometry, and model-atmosphere fluxes. The results are compared with previous measurements and calculations for main-sequence and giant O and B stars. It is found that: (1) the flux effective temperatures of O and B supergiants are systematically lower than those of main-sequence and giant stars of the same subtype; (2) the effective temperatures and radii of Beta Cep stars are the same as those of nonvariable stars of the same spectral type; (3) Be stars that do not have two Balmer jumps have effective temperatures very similar to those of normal B stars of the same subtype; (4) O and B stars increase in size from the main sequence to supergiants; and (5) late B supergiants are approximately twice as large as O9 supergiants.

  6. Theoretical velocity structure of long-period variable star photospheres

    Microsoft Academic Search

    S. J. Hill; L. A. Willson

    1979-01-01

    Numerical models for shock waves propagating through atmospheres of cool supergiant stars for a grid of masses and surface gravities have been calculated calculated, assuming spherical symmetry, isothermality, and a periodic piston boundary condition. The results of these models can be restated using parameters derived in Willson and Hill; the reparametrization allows the generalization of these results to arbitrary stellar

  7. Evolved Star Sizes, Temperatures as Directly Measured with Interferometry

    Microsoft Academic Search

    Gerard van Belle; Robert R. Thompson

    1998-01-01

    Recent advances in throughput, reliability and accuracy of results have greatly increased the scientific output of astronomical interferometers. Near-infrared results from the Palomar Testbed Interferometer (PTI) and the IR-Optical Telescope Array (IOTA) have been collected and are now presented as an unprecedented large database of stellar angular sizes for giants, supergiants, Mira variables and carbon stars. In conjunction with measurements

  8. Spatially resolved dusty torus toward the red supergiant WOH G64 in the Large Magellanic Cloud

    E-print Network

    Keiichi Ohnaka; Thomas Driebe; Karl-Heinz Hofmann; Gerd Weigelt; Markus Wittkowski

    2008-03-26

    We present N-band spectro-interferometric observations of the red supergiant WOH G64 in the Large Magellanic Cloud (LMC) using MIDI at the Very Large Telescope Interferometer (VLTI). The location of WOH G64 on the H-R diagram based on the previously estimated luminosities is in serious disagreement with the current stellar evolution theory. The dust envelope around WOH G64 has been spatially resolved with a baseline of ~60 m--the first MIDI observations to resolve an individual stellar source in an extragalactic system. The observed N-band visibilities show a slight decrease from 8 to 10 micron and a gradual increase longward of 10 micron, reflecting the 10 micron silicate feature in self-absorption. The visibilities measured at four position angles differing by ~60 degrees but at approximately the same baseline length (~60 m) do not show a noticeable difference, suggesting that the object appears nearly centrosymmetric. The observed N-band visibilities and spectral energy distribution can be reproduced by an optically and geometrically thick silicate torus model viewed close to pole-on. The luminosity of the central star is derived to be 2.8 x 10^5 Lsun, which is by a factor of 2 lower than the previous estimates based on spherical models. The lower luminosity newly derived from our MIDI observations and two-dimensional modeling brings the location of WOH G64 on the H-R diagram in much better agreement with theoretical evolutionary tracks for a 25 Msun star. We also identify the H2O absorption features at 2.7 and 6 micron in the spectra obtained with the Infrared Space Observatory and the Spitzer Space Telescope. The 2.7 micron feature originates in the photosphere and/or the extended molecular layers, while the 6 micron feature is likely to be of circumstellar origin.

  9. Supergiant fast X-ray transients: the Swift monitoring program

    E-print Network

    Romano, P; Cusumano, G; La Parola, V; Kennea, J A; Vercellone, S; Ducci, L; Krimm, H A; Esposito, P; Mangano, V; Paizis, A; Burrows, D N; Gehrels, N

    2010-01-01

    For the first time, Swift is giving us the opportunity to study supergiant fast X-ray transients (SFXTs) throughout all phases of their life: outbursts, intermediate level, and quiescence. We present our intense monitoring of four SFXTs, observed 2-3 times per week since October 2007. We find that, unexpectedly, SFXTs spend most of their time in an intermediate level of accretion ($L_{X}\\sim 10^{33-34} $ erg s$^{-1}$), characterized by rich flaring activity. We present an overview of our investigation on SFXTs with Swift, the key results of our Project. We highlight the unique contribution Swift is giving to this field, both in terms of outburst observations and through a systematic monitoring.

  10. The VLT-FLAMES Tarantula Survey. V. The peculiar B[e]-like supergiant, VFTS698, in 30 Doradus

    NASA Astrophysics Data System (ADS)

    Dunstall, P. R.; Fraser, M.; Clark, J. S.; Crowther, P. A.; Dufton, P. L.; Evans, C. J.; Lennon, D. J.; Soszy?ski, I.; Taylor, W. D.; Vink, J. S.

    2012-06-01

    Aims: We present an analysis of a peculiar supergiant B-type star (VFTS698/Melnick 2/Parker 1797) in the 30 Doradus region of the Large Magellanic Cloud which exhibits characteristics similar to the broad class of B[e] stars. Methods: We analyse optical spectra from the VLT-FLAMES survey, together with archival optical and infrared photometry and X-ray imaging to characterise the system. Results: We find radial velocity variations of around 400 km s-1 in the high excitation Si iv, N iii and He ii spectra, and photometric variability of ~0.6 mag with a period of 12.7 d. In addition, we detect long-term photometric variations of ~0.25 mag, which may be due to a longer-term variability with a period of ~400 d. Conclusions: We conclude that VFTS698 is likely an interacting binary comprising an early B-type star secondary orbiting a veiled, more massive companion. Spectral evidence suggests a mid-to-late B-type primary, but this may originate from an optically-thick accretion disc directly surrounding the primary. Based on observations at the European Southern Observatory Very Large Telescope in programme 182.D-0222.Table 8 is available in electronic form at http://www.aanda.org

  11. Discovery of the First B[e] Supergiants in M 31

    NASA Astrophysics Data System (ADS)

    Kraus, M.; Cidale, L. S.; Arias, M. L.; Oksala, M. E.; Borges Fernandes, M.

    2014-01-01

    B[e] supergiants (B[e]SGs) are transitional objects in the post-main sequence evolution of massive stars. The small number of B[e]SGs known so far in the Galaxy and the Magellanic Clouds indicates that this evolutionary phase is short. Nevertheless, the strong aspherical mass loss occurring during this phase, which leads to the formation of rings or disk-like structures, and the similarity to possible progenitors of SN1987 A emphasize the importance of B[e]SGs for the dynamics of the interstellar medium as well as stellar and galactic chemical evolution. The number of objects and their mass-loss behavior at different metallicities are essential ingredients for accurate predictions from stellar and galactic evolution calculations. However, B[e]SGs are not easily identified, as they share many characteristics with luminous blue variables (LBVs) in their quiescent (hot) phase. We present medium-resolution near-infrared K-band spectra for four stars in M 31, which have been assigned a hot LBV (candidate) status. Applying diagnostics that were recently developed to distinguish B[e]SGs from hot LBVs, we classify two of the objects as bonafide LBVs; one of them currently in outburst. In addition, we firmly classify the two stars 2MASS J00441709+4119273 and 2MASS J00452257+4150346 as the first B[e]SGs in M 31 based on strong CO band emission detected in their spectra, and infrared colors typical for this class of stars. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), under program ID GN-2013B-Q-10.

  12. Identification of the Red Supergiant Progenitor of Supernova 2005cs: Do the Progenitors of Type II-P Supernovae Have Low Mass?

    E-print Network

    Weidong Li; Schuyler D. Van Dyk; Alexei V. Filippenko; Jean-Charles Cuillandre; Saurabh Jha; Joshua S. Bloom; Adam G. Riess; Mario Livio

    2005-07-18

    The stars that end their lives as supernovae (SNe) have been directly observed in only a handful of cases, due mainly to the extreme difficulty in identifying them in images obtained prior to the SN explosions. Here we report the identification of the progenitor for the recent Type II-plateau (core-collapse) SN 2005cs in pre-explosion archival images of the Whirlpool Galaxy (M51) obtained with the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS). From high-quality ground-based images of the SN from the Canada-France-Hawaii Telescope, we precisely determine the position of the SN and are able to isolate the SN progenitor to within 0".04 in the HST/ACS optical images. We further pinpoint the SN location to within 0".005 from HST/ACS ultraviolet images of the SN, confirming our progenitor identification. From photometry of the SN progenitor obtained with the pre-SN ACS images, and also limits to its brightness in pre-SN HST/NICMOS images, we infer that the progenitor is a red supergiant star of spectral type K0--M3, with initial mass 7--9 Msun. We also discuss the implications of the SN 2005cs progenitor identification and its mass estimate. There is an emerging trend that the most common Type II-plateau SNe originate from low-mass supergiants 8--15 Msun.

  13. MMT HYPERVELOCITY STAR SURVEY. II. FIVE NEW UNBOUND STARS

    SciTech Connect

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J., 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)

    2012-05-20

    We present the discovery of five new unbound hypervelocity stars (HVSs) in the outer Milky Way halo. Using a conservative estimate of Galactic escape velocity, our targeted spectroscopic survey has now identified 16 unbound HVSs as well as a comparable number of HVSs ejected on bound trajectories. A Galactic center origin for the HVSs is supported by their unbound velocities, the observed number of unbound stars, their stellar nature, their ejection time distribution, and their Galactic latitude and longitude distribution. Other proposed origins for the unbound HVSs, such as runaway ejections from the disk or dwarf galaxy tidal debris, cannot be reconciled with the observations. An intriguing result is the spatial anisotropy of HVSs on the sky, which possibly reflects an anisotropic potential in the central 10-100 pc region of the Galaxy. Further progress requires measurement of the spatial distribution of HVSs over the southern sky. Our survey also identifies seven B supergiants associated with known star-forming galaxies; the absence of B supergiants elsewhere in the survey implies there are no new star-forming galaxies in our survey footprint to a depth of 1-2 Mpc.

  14. Outer atmospheres of late-type stars

    NASA Technical Reports Server (NTRS)

    Linsky, J. L.

    1981-01-01

    Recent observational results concerning chromospheres and coronae in late-type stars are described. In particular, it is indicated where in the cool half of the HR diagram chromospheres, transition regions, coronae, and large mass loss occur and what the important parameters determining the energy balance of these layers are. The chromospheric modelling process is summarized and models of the late-type supergiants Beta Dra, Epsilon Gem, and Alpha Ori recently computed by Basri and Linsky (1980) are detailed.

  15. Imaging the outward motions of clumpy dust clouds around the red supergiant Antares with VLT/VISIR

    NASA Astrophysics Data System (ADS)

    Ohnaka, K.

    2014-08-01

    Aims: We present a 0."5-resolution 17.7 ?m image of the red supergiant Antares. Our aim is to study the structure of the circumstellar envelope in detail. Methods: Antares was observed at 17.7 ?m with the VLT mid-infrared instrument VISIR. Taking advantage of the BURST mode, in which a large number of short exposure frames are taken, we obtained a diffraction-limited image with a spatial resolution of 0."5. Results: The VISIR image shows six clumpy dust clouds located at 0."8-1."8 (43-96 R? = 136-306 AU) away from the star. We also detected compact emission within a radius of 0."5 around the star. Comparison of our VISIR image taken in 2010 and the 20.8 ?m image taken in 1998 with the Keck Telescope reveals the outward motions of four dust clumps. The proper motions of these dust clumps (with respect to the central star) amount to 0."2-0."6 in 12 years. This translates into expansion velocities (projected onto the plane of the sky) of 13-40 km s-1 with an uncertainty of ± 7 km s-1. The inner compact emission seen in the 2010 VISIR image is presumably newly formed dust, because it is not detected in the image taken in 1998. If we assume that the dust is ejected in 1998, the expansion velocity is estimated to be 34 km s-1, in agreement with the velocity of the outward motions of the clumpy dust clouds. The mass of the dust clouds is estimated to be (3-6) × 10-9 M?. These values are lower by a factor of 3-7 than the amount of dust ejected in one year estimated from the (gas+dust) mass-loss rate of 2 × 10-6 M? yr-1, suggesting that the continuous mass loss is superimposed on the clumpy dust cloud ejection. Conclusions: The clumpy dust envelope detected in the 17.7 ?m diffraction-limited image is similar to the clumpy or asymmetric circumstellar environment of other red supergiants. The velocities of the dust clumps cannot be explained by a simple accelerating outflow, implying the possible random nature of the dust cloud ejection mechanism. Based on VISIR observations made with the Very Large Telescope of the European Southern Observatory. Program ID: 385.D-0120(A), 286.D-5007(A).

  16. Clumped stellar winds in supergiant high-mass X-ray binaries: X-ray variability and photoionization

    NASA Astrophysics Data System (ADS)

    Oskinova, L. M.; Feldmeier, A.; Kretschmar, P.

    2012-04-01

    The clumping of massive star winds is an established paradigm, which is confirmed by multiple lines of evidence and is supported by stellar wind theory. The purpose of this paper is to bridge the gap between detailed models of inhomogeneous stellar winds in single stars and the phenomenological description of donor winds in supergiant high-mass X-ray binaries (HMXBs). We use the results from time-dependent hydrodynamical models of the instability in the line-driven wind of a massive supergiant star to derive the time-dependent accretion rate on to a compact object in the Bondi-Hoyle-Lyttleton approximation. The strong density and velocity fluctuations in the wind result in strong variability of the synthetic X-ray light curves. The model predicts a large-scale X-ray variability, up to eight orders of magnitude, on relatively short time-scales. The apparent lack of evidence for such strong variability in the observed HMXBs indicates that the details of the accretion process act to reduce the variability resulting from the stellar wind velocity and density jumps. We study the absorption of X-rays in the clumped stellar wind by means of a two-dimensional stochastic wind model. The monochromatic absorption in the cool stellar wind, depending on the orbital phase, is computed for realistic stellar wind opacity. We find that the absorption of X-rays changes strongly at different orbital phases. The degree of the variability resulting from the absorption in the wind depends on the shape of the wind clumps, and this is stronger for oblate clumps. We address the photoionization in the clumped wind, and we show that the degree of ionization is affected by the wind clumping. We derive a correction factor for the photoionization parameter, and we show that the photoionization parameter is reduced by a factor ? compared to the smooth wind models with the same mass-loss rate, where ? is the wind inhomogeneity parameter. We conclude that wind clumping must also be taken into account when comparing the observed and model spectra of the photoionized stellar wind.

  17. High-latitude supergiant V5112 Sgr: Enrichment of the envelope with heavy s-process metals

    NASA Astrophysics Data System (ADS)

    Klochkova, V. G.

    2013-11-01

    High-resolution ( R = 60 000) echelle spectroscopy of the post-AGB supergiant V5112 Sgr performed in 1996-2012 with the 6-m BTA telescope has revealed peculiarities of the star's optical spectrum and has allowed the variability of the velocity field in the stellar atmosphere and envelope to be studied in detail. An asymmetry and splitting of strong absorption lines with a low lower-level excitation potential have been detected for the first time. The effect is maximal in Ba II lines whose profile is split into three components. The profile shape and positions of the split lines change with time. The short-wavelength components of the split absorption lines are shown to be formed in a structured circumstellar envelope, suggesting an efficient dredge-up of the heavy metals produced during the preceding evolution of this star into the envelope. The envelope expansion velocities have been estimated to be V exp ? 20 and 30 km s-1. The mean radial velocity from diffuse bands in the spectrum of V5112 Sgr coincides with that from the short-wavelength shell component of the Na I D lines, which leads to the conclusion about their formation in the circumstellar envelope. Analysis of the set of radial velocities V r based on symmetric absorption lines has confirmed the presence of pulsations in the stellar atmosphere with an amplitude ? V r ? 8 km s-1.

  18. Swift/X-ray telescope monitoring of the supergiant fast X-ray transient IGR J17354-3255

    NASA Astrophysics Data System (ADS)

    Ducci, L.; Romano, P.; Esposito, P.; Bozzo, E.; Krimm, H.; Vercellone, S.; Mangano, V.; Kennea, J.

    2014-07-01

    We report on the first monitoring of the supergiant fast X-ray transient IGR J17354-3255 with the soft X-ray instrument Swift/XRT. The Swift observations span 1.2 orbital periods (P=8.4474 d) for a total exposure of about 24 ks. The study of the flux variability of the sources in the XRT field of view allowed us to unambiguously identify the soft X-ray counterpart of IGR J17354-3255. The 0.3-10 keV XRT light curve shows a moderate orbital modulation and a dip. We compared the observed X-ray light curve with those calculated with a model based on the Bondi-Hoyle accretion theory, for different wind parameters, eccentricities and spectral type of the donor star. We found that the X-ray orbital modulation produced by a neutron star in an eccentric orbit cannot explain the presence of the dip. We showed that an eclipse or the onset of a gated mechanism are the most likely explanations for the dip.

  19. B Stars with and without emission lines, parts 1 and 2

    NASA Technical Reports Server (NTRS)

    Underhill, A. (editor); Doazan, V. (editor)

    1982-01-01

    The spectra for B stars for which emission lines occur not on the main sequence, but only among the supergiants, and those B stars for which the presence of emission in H ahlpa is considered to be a significant factor in delineating atmospheric structure are examined. The development of models that are compatible with all known facts about a star and with the laws of physics is also discussed.

  20. Populations of massive stars in galaxies, implications for the stellar evolution theory

    E-print Network

    Georges Meynet; Patrick Eggenberger; Andre Maeder

    2007-02-20

    After a brief review of the observational evidences indicating how the populations of Be stars, red/blue supergiants, Wolf-Rayet stars vary as a function of metallicity, we discuss the implications of these observed trend for our understanding of the massive star evolution. We show how the inclusion of the effects of rotation in stellar models improves significantly the correspondence between theory and observation.

  1. PACS and SPIRE Spectroscopy of the Red Supergiant VY CMa

    E-print Network

    Royer, P; Wesson, R; Barlow, M J; Polehampton, E T; Matsuura, M; Agundez, M; Blommaert, J A D L; Cernicharo, J; Cohen, M; Daniel, F; Degroote, P; De Meester, W; Exter, K; Feuchtgruber, H; Gear, W K; Gomez, H L; Groenewegen, M A T; Hargrave, P C; Huygen, R; Imhof, P; Ivison, R J; Jean, C; Kerschbaum, F; Leeks, S J; Lim, T; Lombaert, R; Olofsson, G; Posch, T; Regibo, S; Savini, G; Sibthorpe, B; Swinyard, B M; Vandenbussche, B; Waelkens, C; Witherick, D K; Yates, J A

    2010-01-01

    With a luminosity > 10^5 Lsun and a mass-loss rate of about 2.10-4 Msun/yr, the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VYCMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55 to 672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as 1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope.

  2. The molecular envelope around the red supergiant VY CMa

    E-print Network

    S. Muller; Dinh-V-Trung; J. Lim; N. Hirano; C. Muthu; S. Kwok

    2006-11-17

    We present millimeter interferometric observations of the molecular envelope around the red supergiant VY CMa with the SubMillimeter Array (SMA). The high angular resolution (< 2'') allows us to derive the structure of the envelope as observed in the 1.3 mm continuum, 12CO(2-1), 13CO(2-1) and SO(6,5-5,4) lines emission. The circumstellar envelope is resolved into three components: a dense, compact and dusty central component, embedded in a more diffuse and extended envelope plus a high velocity component. We construct a simple model, consisting of a spherically symmetric slowly expanding envelope and bipolar outflows with a wide opening angle (~ 120 deg.) viewed close to the line of sight (i = 15 deg.). Our model can explain the main features of the SMA data and previous single-dish CO multi-line observations. An episode of enhanced mass loss along the bipolar direction is inferred from our modelling. The SMA data provide a better understanding of the complicated morphology seen in the optical/IR high resolution observations.

  3. The blue supergiant Sher 25 and its intriguing hourglass nebula

    E-print Network

    Hendry, M A; Skillman, E D; Evans, C J; Trundle, C; Lennon, D J; Crowther, P A; Hunter, I

    2008-01-01

    The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log[O/H] = 8.61 +/- 0.13 dex) is similar to that in the background nebula (8.56 +/- 0.07), suggesting the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 +/- 0.15, compared to the background value of 7.47 +/- 0.18. A new analysis of the stellar spectrum with the FASTWIND model atmosphere code suggests that the ph...

  4. ON THE PERIODIC VARIABILITY OF THE LONGITUDINAL MAGNETIC FIELDS OF STARS

    SciTech Connect

    Bychkov, V. D.; Bychkova, L. V. [Special Astrophysical Observatory of the Russian Academy of Sciences (SAO), Nizhnij Arkhyz 369167 (Russian Federation); Madej, J., E-mail: vbych@sao.ru, E-mail: lbych@sao.ru, E-mail: jm@astrouw.edu.pl [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland)

    2013-10-01

    There exist 218 stars with measured phase curves of their longitudinal (effective) magnetic field B{sub e} . In that group, 172 objects are classified as magnetic chemically peculiar stars. The remaining objects are stars of various spectral types, from the most massive hot Of?p supergiants to low-mass red dwarfs and stars with planets. In this paper, we discuss the behavior of the longitudinal magnetic field B{sub e} and present estimated parameters of the apparent magnetic variability for stars of each spectral type. This paper also aims to briefly review the properties of the observed magnetic behavior among various types of stars.

  5. A Far-Ultraviolet Spectroscopic Survey of Luminous Cool Stars

    E-print Network

    A. K. Dupree; A. Lobel; P. R. Young; T. B. Ake; J. Linsky; S. Redfield

    2004-12-20

    FUSE ultraviolet spectra of 8 giant and supergiant stars reveal that high temperature (3 X 10^5 K) atmospheres are common in luminous cool stars and extend across the color-magnitude diagram from Alpha Car (F0 II) to the cool giant Alpha Tau (K5 III). Emission present in these spectra includes chromospheric H-Lyman Beta, Fe II, C I, and transition region lines of C III, O VI, Si III, Si IV. Emission lines of Fe XVIII and Fe XIX signaling temperatures of ~10^7 K and coronal material are found in the most active stars, Beta Cet and 31 Com. A short-term flux variation, perhaps a flare, was detected in Beta Cet during our observation. Stellar surface fluxes of the emission of C III and O VI are correlated and decrease rapidly towards the cooler stars, reminiscent of the decay of magnetically-heated atmospheres. Profiles of the C III (977A) lines suggest that mass outflow is underway at T~80,000 K, and the winds are warm. Indications of outflow at higher temperatures (3 X 10^5K) are revealed by O VI asymmetries and the line widths themselves. High temperature species are absent in the M-supergiant Alpha Ori. Narrow fluorescent lines of Fe II appear in the spectra of many giants and supergiants, apparently pumped by H Lyman Alpha, and formed in extended atmospheres. Instrumental characteristics that affect cool star spectra are discussed.

  6. Discovery of a New Dusty B[e] Star in the Small Magellanic Cloud

    E-print Network

    John P. Wisniewski; Karen S. Bjorkman; Jon E. Bjorkman; Mark Clampin

    2007-08-07

    We present new optical spectroscopic and archival Spitzer IRAC photometric observations of a B-type star in the SMC cluster NGC 346, NGC 346:KWBBe 200. We detect numerous Fe II, [O I], and [Fe II] lines, as well as strong P-Cygni profile H I emission lines in its optical spectrum. The star's near-IR color and optical to IR SED clearly indicate the presence of an infrared excess, consistent with the presence of gas and warm, T ~800 K, circumstellar dust. Based on a crude estimate of the star's luminosity and the observed spectroscopic line profile morphologies, we find that the star is likely to be a B-type supergiant. We suggest that NGC 346:KWBBe 200 is a newly discovered B[e] supergiant star, and represents the fifth such object to be identified in the SMC.

  7. Two Cases of Super-Giant Coronary Aneurysms after Kawasaki Disease

    PubMed Central

    Lee, Joowon; Kwon, Bo Sang; Bae, Eun Jung; Noh, Chung Il

    2014-01-01

    Acute giant coronary aneurysm after Kawasaki disease (KD) is a catastrophic complication that can be fatal and very difficult to manage. However, no fixed consensus has been reached for the management of super-giant coronary aneurysms in the acute setting. Here, we report the successful management of young children with super-giant coronary aneurysms after KD. Based on our experience, hemodynamic stabilization to prevent further coronary dilation or rupture and strict anticoagulation to avoid thrombus formation are mandatory in the management of this condition. PMID:24497892

  8. The Contribution of Thermally-Pulsing Asymptotic Giant Branch and Red Supergiant Starts to the Luminosities of the Magellanic Clouds at 1-24 micrometers

    NASA Technical Reports Server (NTRS)

    Melbourne, J.; Boyer, Martha L.

    2013-01-01

    We present the near-through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red supergiant (RSG) stars to the luminosities of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Combined, the peak contribution from these cool evolved stars occurs at approx 3 - 4 micron, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at approx 3 - 4 micron and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 micron, where they provide 11% of the SMC flux, and 7% for the LMC. Both TP-AGB and RSG stars are short lived, and thus potentially impose a large stochastic scatter on the near-IR derived mass-to-light (M/L) ratios of galaxies at rest-frame 1 - 4 micron. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g., at 0.8 - 1 micron). At longer wavelengths (much > 8 micron), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong polycyclic aromatic hydrocarbon (PAH) emission at 8 micron, TP-AGB and RSG contribute less than 4% of the 8 micron flux. However, 19% of the SMC 8 micron flux is from evolved stars, nearly half of which is produced by the rarest, dustiest, carbon-rich TP-AGB stars. Thus, star formation rates of galaxies, based on an 8 micron flux (e.g., observed-frame 24 micron at z = 2), may be biased modestly high, especially for galaxies with little PAH emission.

  9. Evidence of the evolved nature of the B[e] star MWC 137

    SciTech Connect

    Muratore, M. F.; Arias, M. L.; Cidale, L. [Departamento de Espectroscopía Estelar, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, and Instituto de Astrofísica de La Plata, CCT La Plata, CONICET-UNLP, Paseo del Bosque S/N, B1900FWA, La Plata (Argentina); Kraus, M.; Oksala, M. E. [Astronomický ústav, Akademie v?d ?eské Republiky, Fri?ova 298, 251 65 Ond?ejov (Czech Republic); Fernandes, M. Borges [Observatório Nacional, Rua General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro (Brazil); Liermann, A., E-mail: fmuratore@carina.fcaglp.unlp.edu.ar [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany)

    2015-01-01

    The evolutionary phase of B[e] stars is difficult to establish due to the uncertainties in their fundamental parameters. For instance, possible classifications for the Galactic B[e] star MWC 137 include pre-main-sequence and post-main-sequence phases, with a large range in luminosity. Our goal is to clarify the evolutionary stage of this peculiar object, and to study the CO molecular component of its circumstellar medium. To this purpose, we modeled the CO molecular bands using high-resolution K-band spectra. We find that MWC 137 is surrounded by a detached cool (T=1900±100 K) and dense (N=(3±1)×10{sup 21} cm{sup ?2}) ring of CO gas orbiting the star with a rotational velocity, projected to the line of sight, of 84 ± 2 km s{sup ?1}. We also find that the molecular gas is enriched in the isotope {sup 13}C, excluding the classification of the star as a Herbig Be. The observed isotopic abundance ratio ({sup 12}C/{sup 13}C = 25 ± 2) derived from our modeling is compatible with a proto-planetary nebula, main-sequence, or supergiant evolutionary phase. However, based on some observable characteristics of MWC 137, we propose that the supergiant scenario seems to be the most plausible. Hence, we suggest that MWC 137 could be in an extremely short-lived phase, evolving from a B[e] supergiant to a blue supergiant with a bipolar ring nebula.

  10. Massive stars and the energy balance of the interstellar medium. II. The 35 solar mass star and a solution to the \\

    Microsoft Academic Search

    Tim Freyer; Gerhard Hensler; Harold W. Yorke

    2005-01-01

    We continue our numerical analysis of the morphological and energetic\\u000ainfluence of massive stars on their ambient interstellar medium for a 35 solar\\u000amass star that evolves from the main sequence through red supergiant and\\u000aWolf-Rayet phases, until it ultimately explodes as a supernova. We find that\\u000astructure formation in the circumstellar gas during the early main-sequence\\u000aevolution occurs as

  11. Swift/XRT orbital monitoring of the candidate supergiant fast X-ray transient IGR J17354-3255

    E-print Network

    Ducci, L; Esposito, P; Bozzo, E; Krimm, H A; Vercellone, S; Mangano, V; Kennea, J A

    2013-01-01

    We report on the Swift/X-ray Telescope (XRT) monitoring of the field of view around the candidate supergiant fast X-ray transient (SFXT) IGR J17354-3255, which is positionally associated with the AGILE/GRID gamma-ray transient AGL J1734-3310. Our observations, which cover 11 days for a total on-source exposure of about 24 ks, span 1.2 orbital periods (P_orb=8.4474 d) and are the first sensitive monitoring of this source in the soft X-rays. These new data allow us to exploit the timing variability properties of the sources in the field to unambiguously identify the soft X-ray counterpart of IGR J17354-3255. The soft X-ray light curve shows a moderate orbital modulation and a dip. We investigated the nature of the dip by comparing the X-ray light curve with the prediction of the Bondi-Hoyle-Lyttleton accretion theory, assuming both spherical and nonspherical symmetry of the outflow from the donor star. We found that the dip cannot be explained with the X-ray orbital modulation. We propose that an eclipse or the...

  12. The Orbit and Position of the X-ray Pulsar XTE J1855-026: An Eclipsing Supergiant System

    NASA Technical Reports Server (NTRS)

    Corbet, Robin H. D.; Mukai, Koji; White, Nicholas E. (Technical Monitor)

    2002-01-01

    A pulse timing orbit has been obtained for the X-ray binary XTEJ1855-026 using observations made with the Proportional Counter Array on board the Rossi X-ray Timing Explorer. The mass function obtained of approximately 16 solar mass together with the detection of an extended near-total eclipse confirm that the primary star is supergiant as predicted. The orbital eccentricity is found to be very low with a best fit value of 0.04 +/- 0.02. The orbital period is also refined to be 6.0724 +/- 0.0009 days using an improved and extended light curve obtained with RXTE's All Sky Monitor. Observations with the ASCA satellite provide an improved source location of R.A.= 18 hr 55 min 31.3 sec, decl.= -02 deg 36 min 24.0 sec (2000) with an estimated systematic uncertainty of less than 12 min. A serendipitous new source, AX J1855.4-0232, was also discovered during the ASCA observations.

  13. A STAR IN THE M31 GIANT STREAM: THE HIGHEST NEGATIVE STELLAR VELOCITY KNOWN

    SciTech Connect

    Caldwell, Nelson; Kenyon, Scott J. [Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Morrison, Heather; Harding, Paul [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106-7215 (United States); Schiavon, Ricardo [Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720 (United States); Rose, James A. [Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599 (United States)], E-mail: caldwell@cfa.harvard.edu, E-mail: kenyon@cfa.harvard.edu, E-mail: heather@vegemite.case.edu, E-mail: paul.harding@case.edu, E-mail: rschiavo@gemini.edu, E-mail: jim@physics.unc.edu

    2010-02-15

    We report on a single star, B030D, observed as part of a large survey of objects in M31, which has the unusual radial velocity of -780 km s{sup -1}. Based on details of its spectrum, we find that the star is an F supergiant, with a circumstellar shell. The evolutionary status of the star could be one of a post-main-sequence close binary, a symbiotic nova, or less likely, a post-asymptotic giant branch star, which additional observations could help sort out. Membership of the star in the Andromeda Giant Stream can explain its highly negative velocity.

  14. Pionic Supergiant Radiohalos as Integral Record of Pion Emission During Nuclear Fission

    E-print Network

    D. B. Ion; Reveica Ion-Mihai; M. L. Ion

    2011-08-18

    In this paper we presented a short review of radioactive halos as from the perspective of their interpretation as integral record in time of different kind of known or unknown radioactivities. A special attention is paid for the unified interpretation of the supergiant halos (SGH), discovered by Grady, Walker and Laemlein, as integral record of pion emission during fission.

  15. Life Cycle of Stars

    NASA Technical Reports Server (NTRS)

    1999-01-01

    In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA's Hubble Space Telescope captures various stages of the life cycle of stars in one single view. To the upper left of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material. Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster. The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2.

  16. Evolutionary helium and CNO anomalies in the atmospheres and winds of massive hot stars

    NASA Technical Reports Server (NTRS)

    Walborn, Nolan R.

    1987-01-01

    The ubiquitous evidence for processed materials in the atmospheres, winds, and circumstellar ejecta of massive stars is reviewed. A broad array of normal and peculiar evolutionary stages is considered, up to and including Type II supernova progenitors. The quantitative analysis of these spectra is difficult, and until recently for the most part only qualitative or approximate results have been available. However, several important current programs promise reliable abundance calculations. A significant emerging result is that the morphologically normal majority of both hot and cold supergiants may already display an admixture of CNO-cycle products in their atmospheres. It may become possible in this way to identify blue supergiants returning from the red supergiant region, as appears to have been the case for the SN 1987A progenitor.

  17. Fundamental parameters of Wolf-Rayet stars. III. The evolutionary status of WNL stars.

    NASA Astrophysics Data System (ADS)

    Crowther, P. A.; Smith, L. J.; Hillier, D. J.; Schmutz, W.

    1995-01-01

    New high S/N optical observations of 9 Galactic WNL (WN7-8) stars are presented. The spectra have been analysed using tailored non-LTE model atmospheres by Crowther et al. (1994c). Here we use the derived stellar parameters and abundances for a thorough investigation of the evolutionary status and mass-loss properties of WNL stars. We have identified two distinct groups of WNL stars from their observed properties. The WNL+abs and WN7 stars have high luminosities (log L/Lsun_~5.9) and form a continuity in morphology and physical parameters from the Of stars. They appear to be intimately related to these stars, confirming the suspicion of Walborn (1973) and are descended from extremely massive progenitors (M_initial_>60Msun_) through the sequence O->Of->WNL+abs->WN7(->WNE)->WC->SN. In contrast, the evolutionary sequence for WN8 stars is identified as O->LBV or RSG->WN8->WNE->WC->SN. These stars, with lower luminosities (log L/Lsun_~5.5), are descended from less massive stars, and have either red supergiant (RSG, 25Msun_stars have in common with LBVs, e.g. spatial distribution, association with ejecta nebulae, low binary frequency, large photometric variability. We also find that those stars with the highest terminal velocities (WN7+abs stars) have the lowest variability while the WN8 stars and LBVs (low wind velocities) are the most variable. The smooth progression of mass loss properties from O supergiants to WNL stars found by Lamers & Leitherer (1993) is confirmed with the WNL+abs stars lying intermediately between the WN8 stars and O stars. The spectroscopic differences between Ofpe and WNL+abs stars appear to be attributable principally to a difference in wind density. This naturally explains the often ambiguous Of-WN spectral classification of some Of and WNL stars (Conti & Bohannan 1989). Finally, interstellar reddenings are determined using two independent methods based on the model atmosphere continuum distributions and the observed ubv colours. We find that the UV reddening towards WR25 (WN7+abs) is highly anomalous (R=4.6), confiming the findings of Tapia et al. (1988) for stars in Tr 16 in the Carina nebula.

  18. Swift's Christmas Burst From Blue Supergiant Star Explosion - Duration: 104 seconds.

    NASA Video Gallery

    GRB 101225A, better known as the "Christmas burst," was an unusually long-lasting gamma-ray burst. Because its distance was not measured, astronomers came up with two radically different interpreta...

  19. HUBBLE SNAPSHOT CAPTURES LIFE CYCLE OF STARS

    NASA Technical Reports Server (NTRS)

    2002-01-01

    In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA's Hubble Space Telescope captures various stages of the life cycle of stars in one single view. To the upper right of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material. Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster. The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right and lower left of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). The 'proplyds' in NGC 3603 are 5 to 10 times larger in size and correspondingly also more massive. This single view nicely illustrates the entire stellar life cycle of stars, starting with the Bok globules and giant gaseous pillars, followed by circumstellar disks, and progressing to evolved massive stars in the young starburst cluster. The blue supergiant with its ring and bipolar outflow marks the end of the life cycle. The color difference between the supergiant's bipolar outflow and the diffuse interstellar medium in the giant nebula dramatically visualizes the enrichment in heavy elements due to synthesis of heavier elements within stars. This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2. This picture is being presented at the 194th Meeting of the American Astronomical Society in Chicago. Credit: Wolfgang Brandner (JPL/IPAC), Eva K. Grebel (Univ. Washington), You-Hua Chu (Univ. Illinois Urbana-Champaign), and NASA

  20. Observations of Circumstellar Material Around Evolved Stars With the ISI

    NASA Technical Reports Server (NTRS)

    Danchi, W. C.; Hale, D. S.; Monnier, J. D.; Tuthill, P. G.; Weiner, J.; Townes, C. H.; Fisher, Richard R. (Technical Monitor)

    2001-01-01

    The U.C. Berkeley Infrared Spatial Interferometer (ISI) is a stellar interferometer operating in the 9-12 micron region and has been in operation from 1988 until the present. It utilizes heterodyne detection using CO2 laser local oscillators and currently includes two 1.65 m movable telescopes mounted in semi-trailers and baselines up to about 65 m in length. A third telescope is being integrated with the other two and within the next year will operate as an imaging interferometer providing data with three simultaneous baselines and a closure phase, and baselines up to about 75 m. During the past twelve years the ISI has been used extensively for studies of circumstellar material around evolved stars. Multi-epoch observations of a sample of prototypical sources have elucidated the location and time scales for dust formation around these stars. These time scales can be as short as approx.10 years for Mira stars and as long as approx. 100 years for supergiants. For stars like Mira itself there is evidence for departure from spherical symmetry and episodes of dust formation and destruction. For some stars motion of dust has been observed -- IK Tau is one example, and NML Cyg is another. The molecules Silane and Ammonia were observed for the extreme carbon star IRC +10216 and the supergiant VY CMa pinpointing their location relative to the inner radius of the dust shell. Somewhat surprisingly, these molecules were found to form many stellar radii away from the inner radius of the dust shell, implying that they form by interactions with the surfaces of dust grains. Last year observations with the longest baselines lead to new precision diameters of $o$ Ceti and $\\alpha$ Orionis, and are continuing on a somewhat larger set of Mira variable and supergiant stars.

  1. SPITZER SAGE INFRARED PHOTOMETRY OF MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Bonanos, A. Z.; Massa, D. L.; Sewilo, M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)], E-mail: bonanos@stsci.edu, E-mail: massa@stsci.edu, E-mail: sewilo@stsci.edu (and others)

    2009-10-15

    We present a catalog of 1750 massive stars in the Large Magellanic Cloud (LMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 1268 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3 to 24 {mu}m in the UBVIJHK{sub s} +IRAC+MIPS24 bands. The resulting infrared color-magnitude diagrams illustrate that the supergiant B[e], red supergiant, and luminous blue variable (LBV) stars are among the brightest infrared point sources in the LMC, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to free-free emission among {approx}900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant B[e] stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of B[e] supergiants (log L/L {sub sun} {>=} 4) and the rare, dusty progenitors of the new class of optical transients (e.g., SN 2008S and NGC 300 OT), plus the fact that dust is present in both types of objects, suggests a common origin for them. We find the infrared colors for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict. The results of this study provide the first comprehensive roadmap for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.

  2. Clustered star formation and the origin of stellar masses.

    PubMed

    Pudritz, Ralph E

    2002-01-01

    Star clusters are ubiquitous in galaxies of all types and at all stages of their evolution. We also observe them to be forming in a wide variety of environments, ranging from nearby giant molecular clouds to the supergiant molecular clouds found in starburst and merging galaxies. The typical star in our galaxy and probably in others formed as a member of a star cluster, so star formation is an intrinsically clustered and not an isolated phenomenon. The greatest challenge regarding clustered star formation is to understand why stars have a mass spectrum that appears to be universal. This review examines the observations and models that have been proposed to explain these fundamental issues in stellar formation. PMID:11778037

  3. The central galaxy in abell 2029: an old supergiant.

    PubMed

    Uson, J M; Boughn, S P; Kuhn, J R

    1990-10-26

    A mosaic of images shows the extended structure of the cD galaxy that resides at the center of the rich cluster of galaxies Abell 2029. After correcting for the scattered light of nearby stars and galaxies, the faint halo of this giant can be traced out to a distance of more than 1 megaparsec, making it one of the largest and most luminous galaxies known. The smoothness of this halo suggests that it was formed early in the history of the cluster. PMID:17751483

  4. New insights on accretion in supergiant fast X-ray transients from XMM-Newton and INTEGRAL observations of IGR J17544-2619

    NASA Astrophysics Data System (ADS)

    Drave, S. P.; Bird, A. J.; Sidoli, L.; Sguera, V.; Bazzano, A.; Hill, A. B.; Goossens, M. E.

    2014-04-01

    XMM-Newton observations of the supergiant fast X-ray transient IGR J17544-2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provide a refined estimate of the orbital period at 4.9272 ± 0.0004 d. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM-Newton observations (each lasting ˜15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR J17544-2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 1033 erg s-1 (0.5-10 keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR J17544-2619 dropped to ˜4 × 1032 erg s-1 (0.5-10 keV), comparable with the lowest luminosities ever detected from this source, despite the observations being taken near to periastron. We consider the possible orbital geometry of IGR J17544-2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR J17544-2619 and the supergiant fast X-ray transients (SFXTs) population. We conclude that accretion under the `quasi-spherical accretion' model provides a good description of the behaviour of IGR J17544-2619 and suggests an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the neutron star under the quasi-spherical formulation. Hence, we hope to aid in explaining the varied outburst behaviours observed across the SFXT population with a consistent underlying physical model.

  5. The galactic space frequency of close binary systems. [early stars in spiral arms

    NASA Technical Reports Server (NTRS)

    Stothers, R.

    1973-01-01

    An investigation of the galactic space frequency of close binary systems and other stars with high angular momentum is made on the basis of several criteria for the binary nature of a star. Within an accessible range of 3 kpc around the sun, which includes parts of three spiral arms, there occurs no significant variation (to within a factor of about 2) in the space frequencies of B-type radial-velocity variables, M-type supergiants with blue companions, and Be stars. Implications of this result for the problems of the origin of close binary systems, the distribution of angular momentum in the Galaxy, and the relative numbers of blue and red supergiants are discussed.

  6. Monitoring supergiant fast X-ray transients with Swift: results from the first year

    Microsoft Academic Search

    P. Romano; L. Sidoli; G. Cusumano; V. La Parola; S. Vercellone; C. Pagani; L. Ducci; V. Mangano; J. Cummings; H. A. Krimm; C. Guidorzi; J. A. Kennea; E. A. Hoversten; D. N. Burrows; N. Gehrels

    2009-01-01

    The advent of Swift has allowed, for the first time, the possibility to give supergiant fast X-ray transients (SFXTs), the new class of high-mass X-ray binaries discovered by the International Gamma-Ray Astrophysics Laboratory, non-serendipitous attention throughout most phases of their life. In this paper, we present our results based on the first year of intense Swift monitoring of four SFXTs,

  7. HR 4511: A probable Cepheid with a supergiant-like hot companion

    Microsoft Academic Search

    S. B. Parsons

    1981-01-01

    HR 4511, a slightly variable late F-type supergiant, has been suspected of duplicity for some time, and is now found from observations with the IUE satellite to have an early B-type companion with a strong stellar wind. P. Cygni profiles are observed as Si IV lambdalambda1394, 1403 and C IV lambda1549, with terminal velocities of 1250--1400 km s⁻¹. These resonance

  8. Ultraviolet studies of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330 and the Galactic cluster NGC 6530

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, E.; Hodge, P.

    1984-01-01

    High-resolution and low-resolution IUE spectra of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330, and the young Galactic cluster NGC 6530 are investigated. Temperatures and luminosities are determined. In the LMC and SMC clusters, the most luminous stars are evolved stars on the horizontal supergiant branch, while in NGC 6530 the stars are all still on the main sequence. Extinction laws were determined. They confirm the known differences between LMC and Galactic extinctions. No mass loss was detected for the evolved B stars in the LMC and SMC clusters, while the high-luminosity stars in NGC 6530 show P Cygni profiles.

  9. SUPERGIANT SHELLS AND MOLECULAR CLOUD FORMATION IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Dawson, J. R.; Dickey, John M. [School of Mathematics and Physics, University of Tasmania, Sandy Bay Campus, Churchill Avenue, Sandy Bay, TAS 7005 (Australia)] [School of Mathematics and Physics, University of Tasmania, Sandy Bay Campus, Churchill Avenue, Sandy Bay, TAS 7005 (Australia); McClure-Griffiths, N. M. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Marsfield NSW 2122 (Australia)] [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Marsfield NSW 2122 (Australia); Wong, T. [Astronomy Department, University of Illinois, Urbana, IL 61801 (United States)] [Astronomy Department, University of Illinois, Urbana, IL 61801 (United States); Hughes, A. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany)] [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany); Fukui, Y. [Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya (Japan)] [Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya (Japan); Kawamura, A., E-mail: joanne.dawson@utas.edu.au [National Astronomical Observatory of Japan, Tokyo 181-8588 (Japan)

    2013-01-20

    We investigate the influence of large-scale stellar feedback on the formation of molecular clouds in the Large Magellanic Cloud (LMC). Examining the relationship between H I and {sup 12}CO(J = 1-0) in supergiant shells (SGSs), we find that the molecular fraction in the total volume occupied by SGSs is not enhanced with respect to the rest of the LMC disk. However, the majority of objects ({approx}70% by mass) are more molecular than their local surroundings, implying that the presence of a supergiant shell does on average have a positive effect on the molecular gas fraction. Averaged over the full SGS sample, our results suggest that {approx}12%-25% of the molecular mass in supergiant shell systems was formed as a direct result of the stellar feedback that created the shells. This corresponds to {approx}4%-11% of the total molecular mass of the galaxy. These figures are an approximate lower limit to the total contribution of stellar feedback to molecular cloud formation in the LMC, and constitute one of the first quantitative measurements of feedback-triggered molecular cloud formation in a galactic system.

  10. 10830 A He I observations of 455 stars

    NASA Technical Reports Server (NTRS)

    Zirin, H.

    1982-01-01

    A comparison with K line, X-ray and other data, of 10830 A equivalent widths (EW) measurements in 890 image tube spectra of 455 stars shows that for the case of G stars, the EW correlates well with K line intensity. Good correlation is also found between 10830 A EW and soft X-ray fluxes, confirming the excitation of the line by coronal soft X-rays, which can serve as a measure of coronal emission. It is also found that, in contradiction to published models, 10830 A is weak or absent in O, B and A stars, and is absent in F and M supergiants. Moderate to high 10830 A EW is frequent in F and M dwarfs, G and K supergiants, and class K3 III. The 58 stars whose 10830 A EW was found to be of 300 A or more should be relatively intense X-ray emitters. Almost all RS CVn stars show strong 10830 A absorption, and T Tauri stars show both absorption and emission.

  11. Properties of Hot, Massive Stars: The Impact of FUSE

    E-print Network

    Paul A. Crowther

    2004-10-01

    The impact of FUSE upon the fundamental parameters of OB stars and Wolf-Rayet stars is reviewed. The stellar wind signatures available in the far-UV provide us with important additional diagnostics of effective temperature. Together with improved non-LTE stellar atmosphere models allowing for line blanketing and stellar winds, this has led to a downward revision in the spectral type-temperature calibration for O stars versus Vacca et al. (1996) In addition, the Lyman continuum ionizing fluxes from O dwarfs are compared with previous calibrations of Panagia (1973) and Vacca et al. We also discuss mass-loss rates in OB stars, such that agreement between recent theoretical predictions (Vink et al. 2000, 2001) and observations of O supergiants is possible, solely if winds are clumped in the far-UV and H-alpha line forming regions, as favoured by line profile comparisons for PV 1118-28 (early to mid O) or SIV 1062-1073 (late O to early B) in FUSE datasets. In contrast, B supergiant wind strengths are predicted to be much higher than observations indicates, especially if their winds are also clumped. Finally, significant upward revisions in wind velocities of very late WN stars are indicated by NII 1085 resonance line observations, plus elemental abundances in OB and WR stars are briefly discussed.

  12. DISTANCE AND PROPER MOTION MEASUREMENT OF THE RED SUPERGIANT, PZ CAS, IN VERY LONG BASELINE INTERFEROMETRY H{sub 2}O MASER ASTROMETRY

    SciTech Connect

    Kusuno, K.; Asaki, Y. [Department of Space and Astronautical Science, School of Physical Sciences, Graduate University for Advanced Studies (SOKENDAI), 3-1-1 Yoshinodai, Chuou-Ku, Sagamihara, Kanagawa 252-5210 (Japan); Imai, H. [Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065 (Japan); Oyama, T., E-mail: kusuno@vsop.isas.jaxa.jp, E-mail: asaki@vsop.isas.jaxa.jp, E-mail: hiroimai@sci.kagoshima-u.ac.jp, E-mail: t.oyama@nao.ac.jp [Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2013-09-10

    We present the very long baseline interferometry H{sub 2}O maser monitoring observations of the red supergiant, PZ Cas, at 12 epochs from 2006 April to 2008 May. We fitted maser motions to a simple model composed of a common annual parallax and linear motions of the individual masers. The maser motions with the parallax subtracted were well modeled by a combination of a common stellar proper motion and a radial expansion motion of the circumstellar envelope. We obtained an annual parallax of 0.356 {+-} 0.026 mas and a stellar proper motion of {mu}{sub {alpha}}{sup *} cos {delta} = -3.7 {+-} 0.2 and {mu}{sup *}{sub {delta}}=-2.0{+-}0.3 mas yr{sup -1} eastward and northward, respectively. The annual parallax corresponds to a trigonometric parallax of 2.81{sup +0.22}{sub -0.19} kpc. By rescaling the luminosity of PZ Cas in any previous studies using our trigonometric parallax, we estimated the location of PZ Cas on a Hertzsprung-Russell diagram and found that it approaches a theoretically evolutionary track around an initial mass of {approx}25 M{sub Sun }. The sky position and the distance to PZ Cas are consistent with the OB association, Cas OB5, which is located in a molecular gas super shell. The proper motion of PZ Cas is close to that of the OB stars and other red supergiants in Cas OB5 measured by the Hipparcos satellite. We derived the peculiar motion of PZ Cas of U{sub s} = 22.8 {+-} 1.5, V{sub s} = 7.1 {+-} 4.4, and W{sub s} = -5.7 {+-} 4.4 km s{sup -1}. This peculiar motion has rather a large U{sub s} component, unlike those of near high-mass star-forming regions with negatively large V{sub s} motions. The uniform proper motions of the Cas OB5 member stars suggest random motions of giant molecular clouds moving into local potential minima in a time-dependent spiral arm, rather than a velocity field caused by the spiral arm density wave.

  13. Distance and Proper Motion Measurement of the Red Supergiant, PZ Cas, in Very Long Baseline Interferometry H2O Maser Astrometry

    NASA Astrophysics Data System (ADS)

    Kusuno, K.; Asaki, Y.; Imai, H.; Oyama, T.

    2013-09-01

    We present the very long baseline interferometry H2O maser monitoring observations of the red supergiant, PZ Cas, at 12 epochs from 2006 April to 2008 May. We fitted maser motions to a simple model composed of a common annual parallax and linear motions of the individual masers. The maser motions with the parallax subtracted were well modeled by a combination of a common stellar proper motion and a radial expansion motion of the circumstellar envelope. We obtained an annual parallax of 0.356 ± 0.026 mas and a stellar proper motion of \\mu ^{*}_{\\alpha } \\cos {\\delta }=-3.7 +/- 0.2 and \\mu ^{*}_{\\delta }=-2.0 +/- 0.3 mas yr-1 eastward and northward, respectively. The annual parallax corresponds to a trigonometric parallax of 2.81 ^{+0.22}_{-0.19} kpc. By rescaling the luminosity of PZ Cas in any previous studies using our trigonometric parallax, we estimated the location of PZ Cas on a Hertzsprung-Russell diagram and found that it approaches a theoretically evolutionary track around an initial mass of ~25 M ?. The sky position and the distance to PZ Cas are consistent with the OB association, Cas OB5, which is located in a molecular gas super shell. The proper motion of PZ Cas is close to that of the OB stars and other red supergiants in Cas OB5 measured by the Hipparcos satellite. We derived the peculiar motion of PZ Cas of U s = 22.8 ± 1.5, V s = 7.1 ± 4.4, and W s = -5.7 ± 4.4 km s-1. This peculiar motion has rather a large U s component, unlike those of near high-mass star-forming regions with negatively large V s motions. The uniform proper motions of the Cas OB5 member stars suggest random motions of giant molecular clouds moving into local potential minima in a time-dependent spiral arm, rather than a velocity field caused by the spiral arm density wave.

  14. Blue supergiant model for ultra-long gamma-ray burst with superluminous-supernova-like bump

    SciTech Connect

    Nakauchi, Daisuke; Nakamura, Takashi [Department of Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan); Kashiyama, Kazumi [Department of Astronomy and Astrophysics, Department of Physics, Center for Particle and Gravitational Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Suwa, Yudai [Yukawa Institute for Theoretical Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan)

    2013-11-20

    Long gamma-ray bursts (LGRBs) have a typical duration of ?30 s, and some of them are associated with hypernovae, such as Type Ic SN 1998bw. Wolf-Rayet stars are the most plausible LGRB progenitors, since the free fall time of the envelope is consistent with the duration, and the natural outcome of the progenitor is a Type Ic SN. While a new population of ultra-long GRBs (ULGRBs), GRB 111209A, GRB 101225A, and GRB 121027A, has a duration of ?10{sup 4} s, two of them are accompanied by superluminous-supernova-like (SLSN-like) bumps, which are ? 10 times brighter than typical hypernovae. Wolf-Rayet progenitors cannot explain ULGRBs because of durations that are too long and SN-like bumps that are too bright. A blue supergiant (BSG) progenitor model, however, can explain the duration of ULGRBs. Moreover, SLSN-like bumps can be attributed to the so-called cocoon fireball photospheric emissions (CFPEs). Since a large cocoon is inevitably produced during the relativistic jet piercing though the BSG envelope, this component can be smoking gun evidence of the BSG model for ULGRBs. In this paper, we examine u-, g-, r-, i-, and J-band light curves of three ULGRBs and demonstrate that they can be fitted quite well by our BSG model with the appropriate choices of the jet opening angle and the number density of the ambient gas. In addition, we predict that for 121027A, SLSN-like bump could have been observed for ?20-80 days after the burst. We also propose that some SLSNe might be CFPEs of off-axis ULGRBs without visible prompt emissions.

  15. Periodic mass-loss episodes due to an oscillation mode with variable amplitude in the hot supergiant HD 50064

    NASA Astrophysics Data System (ADS)

    Aerts, C.; Lefever, K.; Baglin, A.; Degroote, P.; Oreiro, R.; Vu?kovi?, M.; Smolders, K.; Acke, B.; Verhoelst, T.; Desmet, M.; Godart, M.; Noels, A.; Dupret, M.-A.; Auvergne, M.; Baudin, F.; Catala, C.; Michel, E.; Samadi, R.

    2010-04-01

    Aims: We aim to interpret the photometric and spectroscopic variability of the luminous blue variable supergiant HD 50064 (V = 8.21). Methods: CoRoT space photometry and follow-up high-resolution spectroscopy with a time base of 137 d and 169 d, respectively, was gathered, analysed, and interpreted using standard time series analysis and light curve modelling methods, as well as spectral line diagnostics. Results: The space photometry reveals one period of 37 d, which undergoes a sudden amplitude change with a factor 1.6. The pulsation period is confirmed in the spectroscopy, which additionally reveals metal line radial velocity values differing by 30 km s-1 depending on the spectral line and on the epoch. We estimate Teff 13 500 K, log g 1.5 from the equivalent width of Si lines. The Balmer lines reveal that the star undergoes episodes of changing mass loss on a time scale similar to the changes in the photometric and spectroscopic variability, with an average value of log dot{M} ? -5 (in M_? yr-1). We tentatively interpret the 37 d period as the result of a strange mode oscillation. Based on high-resolution spectroscopy assembled with the CORALIE spectrograph attached to the 1.2 m Euler telescope at La Silla, Chile and on CoRoT space-based photometry. The CoRoT space mission was developed and is operated by the French space agency CNES, with the participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.Postdoctoral Fellow of the Fund for Scientific Research of Flanders (FWO), Belgium.

  16. Properties of the CO and H2O MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observations

    NASA Astrophysics Data System (ADS)

    Montargès, M.; Kervella, P.; Perrin, G.; Ohnaka, K.; Chiavassa, A.; Ridgway, S. T.; Lacour, S.

    2014-12-01

    Context. Betelgeuse is the closest red supergiant (RSG); therefore, it is well suited for studying the complex processes in its atmosphere that lead to the chemical enrichment of the interstellar medium. Aims: We intend to investigate the shape and composition of the close molecular layer (also known as the MOLsphere) that surrounds the star. This analysis is part of a wider program that aims at understanding the dynamics of the circumstellar envelope of Betelgeuse. Methods: On January and February 2011, Betelgeuse was observed using the Astronomical Multi-BEam combineR (AMBER) instrument of the Very Large Telescope Interferometer (VLTI) in the H and K bands. Using the medium spectral resolution of the instrument (R ~ 1500), we were able to investigate the carbon monoxide band heads and the water-vapor bands. We used two different approaches to analyse our data: a model fit in both the continuum and absorption lines and then a fit with a radiative hydrodynamics (RHD) simulation. Results: Using the continuum data, we derive a uniform disk diameter of 41.01 ± 0.41 mas, a power law type limb-darkened disk diameter of 42.28 ± 0.43 mas and a limb-darkening exponent of 0.155 ± 0.009. Within the absorption lines, using a single layer model, we obtain parameters of the MOLsphere. Using a RHD simulation, we unveil the convection pattern in the visibilities. Conclusions: We derived a new value of the angular diameter of Betelgeuse in the K band continuum. Our observations in the absorption lines are well reproduced by a molecular layer at 1.2 stellar radii containing both CO and H2O. The visibilities at higher spatial frequencies are matching a convection pattern in a RHD simulation. Based on AMBER observations made with ESO Telescopes at the Paranal Observatory under programmes ID 086.D-0351 and 286.D-5036(A).Table 1 is available in electronic form at http://www.aanda.org

  17. An atlas of ground UV spectra of selected stars

    NASA Astrophysics Data System (ADS)

    Klochkova, Valentina G.; Chentsov, Eugene L.; Kipper, Tonu; Panchuk, Vladimir E.; Tavolganskaya, Nonna S.; Yushkin, Maxim V.

    2011-09-01

    We present a spectral atlas of 4 B and A stars containing spectra in a poorly studied spectral range of 305-452 nm. The atlas is based on high resolution (R=60 000) spectra obtained with the 6 meter telescope (SAO, Russia) combined with the NES-spectrograph. The procedure of spectral lines identification and compilation of the atlas is discussed in detail. Using the spectral data we thoroughly investigated the velocity field in expanding atmospheres and envelopes of hot evolved stars ? Ori, ? Cyg and supergiant KS Per with the extreme hydrogen deficiency. The complete atlas and list of the identified spectral lines will be available via the astronomical database SIMBAD.

  18. Long-lasting X-ray emission from type IIb supernova 2011dh and mass-loss history of the yellow supergiant progenitor

    SciTech Connect

    Maeda, Keiichi [Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Katsuda, Satoru [RIKEN (The Institute of Physical and Chemical Research) Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Bamba, Aya [Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258 (Japan); Terada, Yukikatsu [Graduate School of Science and Engineering, Saitama University, Shimo-Okubo 255, Sakura, Saitama 338-8570 (Japan); Fukazawa, Yasushi, E-mail: keiichi.maeda@kusastro.kyoto-u.ac.jp [Department of Physical Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)

    2014-04-20

    Type IIb supernova (SN) 2011dh, with conclusive detection of an unprecedented yellow supergiant (YSG) progenitor, provides an excellent opportunity to deepen our understanding on the massive star evolution in the final centuries toward the SN explosion. In this paper, we report on detection and analyses of thermal X-ray emission from SN IIb 2011dh at ?500 days after the explosion on Chandra archival data, providing a solidly derived mass-loss rate of a YSG progenitor for the first time. We find that the circumstellar media should be dense, more than that expected from a Wolf-Rayet (W-R) star by one order of magnitude. The emission is powered by a reverse shock penetrating into an outer envelope, fully consistent with the YSG progenitor but not with a W-R progenitor. The density distribution at the outermost ejecta is much steeper than that expected from a compact W-R star, and this finding must be taken into account in modeling the early UV/optical emission from SNe IIb. The derived mass-loss rate is ?3 × 10{sup –6} M {sub ?} yr{sup –1} for the mass-loss velocity of ?20 km s{sup –1} in the final ?1300 yr before the explosion. The derived mass-loss properties are largely consistent with the standard wind mass-loss expected for a giant star. This is not sufficient to be a main driver to expel nearly all the hydrogen envelope. Therefore, the binary interaction, with a huge mass transfer having taken place at ? 1300 yr before the explosion, is a likely scenario to produce the YSG progenitor.

  19. What are the R Coronae Borealis Stars?

    E-print Network

    Clayton, Geoffrey C

    2012-01-01

    The R Coronae Borealis (RCB) stars are rare hydrogen-deficient, carbon-rich, supergiants, best known for their spectacular declines in brightness at irregular intervals. Efforts to discover more RCB stars have more than doubled the number known in the last few years and they appear to be members of an old, bulge population. Two evolutionary scenarios have been suggested for producing an RCB star, a double degenerate merger of two white dwarfs, or a final helium shell flash in a planetary nebula central star. The evidence pointing toward one or the other is somewhat contradictory, but the discovery that RCB stars have large amounts of 18O has tilted the scales towards the merger scenario. If the RCB stars are the product of white dwarf mergers, this would be a very exciting result since RCB stars would then be low-mass analogs of type Ia supernovae. The predicted number of RCB stars in the Galaxy is consistent with the predicted number of He/CO WD mergers. But, so far, only about 65 of the predicted 5000 RCB s...

  20. The structure, energy balance, and winds of cool stars

    NASA Technical Reports Server (NTRS)

    Linsky, J. L.

    1982-01-01

    The phenomena associated with magnetic fields in the Sun are summarized and it is shown that similar phenomena occur in cool stars. High dispersion spectra are providing unique information concerning densities, atmospheric extension, and emission line widths. A recent unanticipated discovery is that the transition lines are redshifted (an antiwind) in beta Dra (G2 Ib) and perhaps other stars. This is interpreted as indicating downflows in closed magnetic flux tubes as are seen in the solar flux tubes above sunspots. The G and K giants and supergiants are classified as active stars, quiet stars, or hybrid stars depending on whether their atmospheres are dominated by closed magnetic flux tubes, open field geometries, or a predominately open geometry with a few closed flux tubes embedded.

  1. Star Caught Smoking

    NASA Astrophysics Data System (ADS)

    2007-08-01

    VLTI Snapshots Dusty Puff Around Variable Star Using ESO's Very Large Telescope Interferometer, astronomers from France and Brazil have detected a huge cloud of dust around a star. This observation is further evidence for the theory that such stellar puffs are the cause of the repeated extreme dimming of the star. ESO PR Photo 34a/07 ESO PR Photo 34a/07 Dust Cloud in a R CrB Star (Artist's Impression) R Coronae Borealis stars are supergiants exhibiting erratic variability. Named after the first star that showed such behaviour [1], they are more than 50 times larger than our Sun. R Coronae Borealis stars can see their apparent brightness unpredictably decline to a thousandth of their nominal value within a few weeks, with the return to normal light levels being much slower. It has been accepted for decades that such fading could be due to obscuration of the stellar surface by newly formed dusty clouds. This 'Dust Puff Theory' suggests that mass is lost from the R Coronae Borealis (or R CrB for short) star and then moves away until the temperature is low enough for carbon dust to form. If the newly formed dust cloud is located along our line-of-sight, it eclipses the star. As the dust is blown away by the star's strong light, the 'curtain' vanishes and the star reappears. RY Sagittarii is the brightest member in the southern hemisphere of this family of weird stars. Located about 6,000 light-years away towards the constellation of Sagittarius (The Archer), its peculiar nature was discovered in 1895 by famous Dutch astronomer Jacobus Cornelius Kapteyn. In 2004, near-infrared adaptive optics observations made with NACO on ESO's Very Large Telescope allowed astronomers Patrick de Laverny and Djamel Mékarnia to clearly detect the presence of clouds around RY Sagittarii. This was the first direct confirmation of the standard scenario explaining the light variations of R CrB stars by the presence of heterogeneities in their envelope surrounding the star. ESO PR Photo 32e/07 ESO PR Photo 34b/07 Clouds around RY Sagittarii (NACO/VLT) However, the precise place where such dust clouds would form was still unclear. The brightest cloud detected was several hundred stellar radii from the centre, but it had certainly formed much closer. But how much closer? To probe the vicinity of the star, the astronomers then turned to ESO's Very Large Telescope Interferometer. Combining two different pairs of the 8.2-m Unit Telescopes and using the mid-infrared MIDI instrument that allows detecting cold structures, the astronomers explored the inner 110 astronomical units [2] around the star. Given the remoteness of RY Sagittarii, this corresponds to looking at details on a one-euro coin that is about 75 km away! The astronomers found that a huge envelope, about 120 times as big as RY Sagittarii itself, surrounds the supergiant star. But more importantly, the astronomers also found evidence for a dusty cloud lying only about 30 astronomical units away from the star, or 100 times the radius of the star. "This is the closest dusty cloud ever detected around a R CrB-type variable since our first direct detection in 2004," says Patrick de Laverny, leader of the team. "However, it is still detected too far away from the star to distinguish between the different scenarios proposed within the Dust Puff Theory for the possible locations in which the dusty clouds form." If the cloud moves at the speed of 300 km/s, as one can conservatively assume, it was probably ejected more than 6 months before its discovery from deeper inside the envelope. The astronomers are now planning to monitor RY Sagittarii more carefully to shed more light on the evolution of the dusty clouds surrounding it. "Two hundred years after the discovery of the variable nature of R CrB, many aspects of the R CrB phenomenon remain mysterious," concludes de Laverny.

  2. Grids of evolutionary models of massive stars with mass loss and overshooting - Properties of Wolf-Rayet stars sensitive to overshooting

    NASA Astrophysics Data System (ADS)

    Maeder, A.; Meynet, G.

    1987-08-01

    An attempt is made to establish a reference grid of massive star models, following the evolution of stars whose initial mass is 120, 85, 69, 40, 25, 20, and 15 solar masses from the zero-age sequence to the end of the C-burning phase. The overshooting parameter chosen, together with the extent and mass loss rates adopted, generates an MS narrowing for O-stars and a large MS widening for early B-type stars. When compared to other sets of models, the present results allow the identification of several novel observable properties that are sensitive to overshooting for a given mass loss: (1) the mapping of surface C/N and O/N ratios for stars in the upper HR diagram, (2) the mass limits for red supergiants and W-R stars, and (3) the slope of the mass-luminosity relation for W-R stars.

  3. Wind Variability of B Supergiants. No. 1; The Rapid Rotator HD 64760 (B0.5 Ib)

    NASA Technical Reports Server (NTRS)

    Massa, Derck; Prinja, Raman K.; Fullerton, Alexander W.

    1995-01-01

    We present the results of a 6 day time series of observations of the rapidly rotating B0.5 Ib star HD 64760. We point out several reasons why such intermediate luminosity B supergiants are ideal targets for wind variability studies and then present our results that show the following: continuous wind activity throughout the 6 day run with the wind never in steady state for more than a few hr; wind variability very near nu = 0 km sec(exp -1) in the resonance lines from the lower ionization stages (Al III and C II); a distinct correlation between variability in the Si III ; lambda(lambda)1300 triplets, the strong C III (lambda)1247 singlet, and the onset of extremely strong wind activity, suggesting a connection between photospheric and wind activity; long temporal coherence in the behavior of the strong absorption events; evidence for large-scale spatial coherence, implied by a whole scale, simultaneous weakening in the wind absorption over a wide range in velocities; and ionization variability in the wind accompanying the largest changes in the absorption strengths of the wind lines. In addition, modeling of the wind lines provides the following information about the state the wind in HD 64760. The number of structures on the portion of a constant velocity surface occulting the stellar disk at a particular time must be quite small, while the number on the entire constant velocity surface throughout the wind must be large. The escape probability at low velocity is overestimated by a normal beta approx. 1 velocity law, perhaps due to the presence of low-velocity shocks deep in the wind or a shallow velocity gradient at low velocity. Estimates of the ionization structure in the wind indicate that the ionization ratios are not those expected from thermal equilibrium wind models or from an extrapolation of previous O star results. The large observed q(N V)/q(Si IV) ratio is almost certainly due to distributed X-rays, but the level of ionization predicted by distributed X-ray wind models is inconsistent with the predicted mass-loss rate. Thus, it is impossible to reconcile the observed ionization ratios and the predicted mass-loss rate within the framework of the available models.

  4. Oxygen isotopic ratios in cool R Coronae Borealis stars

    E-print Network

    Garcia-Hernandez, D Anibal; Rao, N Kameswara; Hinkle, Ken H; Eriksson, Kjell

    2010-01-01

    We investigate the relationship between R Coronae Borealis (RCB) stars and hydrogen-deficient carbon (HdC) stars by measuring precise 16O/18O ratios for five cool RCB stars. The 16O/18O ratios are derived by spectrum synthesis from high-resolution (R=50,000) K-band spectra. Lower limits to the 16O/17O and 14N/15}N ratios as well as Na and S abundances (when possible) are also given. RCB stars in our sample generally display less 18O than HdC stars - the derived 16O/18O ratios range from 3 to 20. The only exception is the RCB star WX CrA, which seems to be a HdC-like star with 16O/18O=0.3. Our result of a higher 16O/18O ratio for the RCB stars must be accounted for by a theory of the formation and evolution of HdC and RCB stars. We speculate that a late dredge-up of products of He-burning, principally 12C and 16O, may convert a 18O-rich HdC star into a 18O-poor RCB star as the H-deficient star begins its final evolution from a cool supergiant to the top of the white dwarf cooling track.

  5. Are 2-micron absorptions and 11-micron emissions of M stars related. [solor and spectral band correlations with boundary temperature

    NASA Technical Reports Server (NTRS)

    Fay, T. D., Jr.

    1974-01-01

    Three properties of M stars are compared: (1) /3.5/ - /11/ colors, (2) two measures of 2.3-micron band absorption, and (3) two measures of 1.9-micron band absorption. We find that the 2.3-micron bands of 21 M giants and supergiants correlate with /3.5/ - /11/ colors at better than 99 per cent confidence. A comparable relation exists between the mean 1.9-micron bands and /3.5/ - /11/ colors of 23 M giants and Miras. The sum of the 1.9-micron + 2.3-micron band intensities correlates with /3.5/ - /11/ color at better than the 99.8 per cent level for 31 M stars. These relations are consistent with both CO and H2O cooling of M star boundaries. Binaries and Ia supergiants appear to depart from these relations.

  6. Supergiant, fast, but not so transient 4U 1907+09

    E-print Network

    Doroshenko, V; Ducci, L; Klochkov, D

    2012-01-01

    We have investigated the dipping activity observed in the high-mass X-ray binary 4U 1907+09 and shown that the source continues to pulsate in the "off" state, noting that the transition between the "on" and "off" states may be either dip-like or flare-like. This behavior may be explained in the framework of the "gated accretion" scenario proposed to explain the flares in supergiant fast X-ray transients (SFXTs). We conclude that 4U 1907+09 might prove to be a missing link between the SFXTs and ordinary accreting pulsars.

  7. The nature of FS CMa stars as revealed by host young clusters

    NASA Astrophysics Data System (ADS)

    de la Fuente, D.; Najarro, F.; Trombley, C.; Davies, B.; Figer, D. F.

    2015-05-01

    The nature and evolutionary state of the diverse objects displaying the B[e] phenomenon are reasonably known, except for a rare subtype named FS CMa stars. These are surrounded by compact disks of warm dust whose origin is unclear. Although the luminosity of these objects corresponds to main-sequence stars, mass loss rates derived from emission lines are 2 orders of magnitude larger than predicted by wind theory. Hitherto, FS CMa stars have been only found in isolation, which hinders the study of their nature. In this contribution, we present the discovery of FS CMa stars in two young Galactic clusters, which host Wolf-Rayet stars and OB supergiants. Membership to these coeval populations allows us to constrain the luminosity, circumstellar extinction and age of FS CMa stars in an unprecedented way. Due to their relatively low brightness when compared with coeval evolved massive stars, a high number of these objects may remain unnoticed in young clusters.

  8. The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large Magellanic Cloud

    Microsoft Academic Search

    C. Alcock; R. A. Allsman; D. R. Alves; T. S. Axelrod; A. Basu; A. C. Becker; D. P. Bennett; K. H. Cook; A. J. Drake; K. C. Freeman; M. Geha; K. Griest; L. King; M. J. Lehner; S. L. Marshall; D. Minniti; C. A. Nelson; P. Popowski; M. R. Pratt; P. J. Quinn; C. W. Stubbs; W. Sutherland; A. B. Tomaney; T. Vandehei; D. L. Welch

    2000-01-01

    We present a 9 million star color-magnitude diagram (9M CMD) of the Large Magellanic Cloud (LMC) bar. The 9M CMD reveals a complex superposition of different-age and -metallicity stellar populations, with important stellar evolutionary phases occurring over 3 orders of magnitude in number density. First, we count the nonvariable red and blue supergiants and the associated Cepheid variables and measure

  9. The Fundamental Parameters of Massive Stars Luciana Bianchi , James Herald and Miriam Garcia +

    E-print Network

    Bianchi, Luciana

    samples. Figure 1 shows the lines in the FUSE range for the supergiants in our final sample, from spectral the sensitivity of the H Balmer lines (progressively increasing from Hg to Ha) and HeIIl4686 to mass­loss rate massive stars in the Milky Way with non­LTE, line­blanketed models with sphericity and expanding winds. We

  10. Evidence of the Evolved Nature of the B[e] Star MWC 137

    NASA Astrophysics Data System (ADS)

    Muratore, M. F.; Kraus, M.; Oksala, M. E.; Arias, M. L.; Cidale, L.; Borges Fernandes, M.; Liermann, A.

    2015-01-01

    The evolutionary phase of B[e] stars is difficult to establish due to the uncertainties in their fundamental parameters. For instance, possible classifications for the Galactic B[e] star MWC 137 include pre-main-sequence and post-main-sequence phases, with a large range in luminosity. Our goal is to clarify the evolutionary stage of this peculiar object, and to study the CO molecular component of its circumstellar medium. To this purpose, we modeled the CO molecular bands using high-resolution K-band spectra. We find that MWC 137 is surrounded by a detached cool (T=1900+/- 100 K) and dense (N=(3+/- 1)× {{10}21} {{cm}-2}) ring of CO gas orbiting the star with a rotational velocity, projected to the line of sight, of 84 ± 2 km s-1. We also find that the molecular gas is enriched in the isotope 13C, excluding the classification of the star as a Herbig Be. The observed isotopic abundance ratio (12C/13C = 25 ± 2) derived from our modeling is compatible with a proto-planetary nebula, main-sequence, or supergiant evolutionary phase. However, based on some observable characteristics of MWC 137, we propose that the supergiant scenario seems to be the most plausible. Hence, we suggest that MWC 137 could be in an extremely short-lived phase, evolving from a B[e] supergiant to a blue supergiant with a bipolar ring nebula. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), under program IDs GN-2011B-Q-24 and GN-2013B-Q-11.

  11. Optical and infrared observations of 27 oxygen-rich stars. Modelling of the circumstellar dust shells

    Microsoft Academic Search

    P. Le Sidaner; T. Le Bertre

    1996-01-01

    We present mid-infrared (10-20mum) photometry obtained on 27 variable oxygen-rich late-type stars, at different epochs during the period 1984-1990. The sample includes representative objects of miras with optical counterparts, as well as type II OH\\/IR sources; there are also at least 2 supergiants. These measurements are merged with near-infrared ones, already reported and obtained quasi-simultaneously, to derive 72 (1-20mum) broad

  12. Near-unstable stars: the yellow-white hypergiants.

    NASA Astrophysics Data System (ADS)

    de Jager, C.

    The yellow-white hypergiants are stars of extreme luminosities. Atmospheric abundances and mass determinations suggest that the stars are evolved objects, moving blueward in their evolution. Three well-studied objects are described (Rho Cas, HR 8752, and HD 33579). Methods of spectroscopic diagnosis allows for a determination of the various accelerations acting on the photospheric gas. In the Hertzsprung-Russell diagram the yellow hypergiants are situated at the low-temperature side of a region of atmospheric instability: the Yellow Evolutionary Void. This suggests a relation: since these stars are evolving in the HR diagram from the red supergiant region towards the blue, it is natural that the atmospheres become unstable, with a consequent increased rate of mass loss, when the star is nearing the Void.

  13. Supergiant Fast X-ray Transients: interpretation of archival INTEGRAL data

    E-print Network

    Ducci, L; Paizis, A; Mereghetti, S

    2008-01-01

    INTEGRAL monitoring of the Galactic Plane in the last 5 years revealed a new subclass of High Mass X-ray Binaries (HMXBs), the Supergiant Fast X-ray Transients (SFXTs). They display flares lasting from minutes to hours, with peak luminosity of 1E36-1E37 erg/s and a frequent long term flaring activity reaching an X-ray luminosity of 1E33-1E34 erg/s, as recently detected by the Swift satellite. The quiescent level is around 1E32 erg/s. We performed a systematic re-analysis of archival INTEGRAL data of four SFXTs: IGRJ16479-4514, XTEJ1739-302, IGRJ17544-2619, IGRJ18410-0535. This led to the discovery of previously unnoticed outbursts from IGRJ16479-4514 and IGRJ17544-2619. We discuss these results in the framework of the different structure of the supergiant wind proposed to explain the outburst from this new class of sources.

  14. Supergiant Fast X-ray Transients: interpretation of archival INTEGRAL data

    E-print Network

    L. Ducci; L. Sidoli; A. Paizis; S. Mereghetti

    2008-10-30

    INTEGRAL monitoring of the Galactic Plane in the last 5 years revealed a new subclass of High Mass X-ray Binaries (HMXBs), the Supergiant Fast X-ray Transients (SFXTs). They display flares lasting from minutes to hours, with peak luminosity of 1E36-1E37 erg/s and a frequent long term flaring activity reaching an X-ray luminosity of 1E33-1E34 erg/s, as recently detected by the Swift satellite. The quiescent level is around 1E32 erg/s. We performed a systematic re-analysis of archival INTEGRAL data of four SFXTs: IGRJ16479-4514, XTEJ1739-302, IGRJ17544-2619, IGRJ18410-0535. This led to the discovery of previously unnoticed outbursts from IGRJ16479-4514 and IGRJ17544-2619. We discuss these results in the framework of the different structure of the supergiant wind proposed to explain the outburst from this new class of sources.

  15. The 100-month Swift Catalogue of Supergiant Fast X-ray Transients

    NASA Astrophysics Data System (ADS)

    Romano, Patrizia; Krimm, Hans A.; Palmer, David; Ducci, Lorenzo; Esposito, Paolo; Vercellone, Stefano; Evans, Phil; Guidorzi, Cristiano; Mangano, Vanessa; Kennea, Jamie A; Barthelmy, Scott Douglas; Burrows, David N.; Gehrels, Neil

    2014-08-01

    The 100-month Swift Catalogue of Supergiant Fast X-ray Transients, collects over a thousand Swift/BAT flares from 11 Supergiant Fast X-ray Transients (SFXTs), and is complete down to fluxes of about 6x1E-10 erg/cm2/s (daily timescale) and about 1.5x1E-9 erg/cm2/s (orbital timescale, averaging about 800 s) in the 15-150 keV energy band. These hard X-ray flares typically last a few hundred seconds, reach fluxes in excess of 100 mCrab (15-50 keV), and last much less than a day. Their clustering in orbital phase-space,however, demonstrates that the outbursts are a much longer phenomenon, lasting up to a few days, as previously observed in deeper Swift soft X-ray observations. This large dataset is used to probe the properties of the high and intermediate emission states in SFXTs, and to infer the properties of these binary systems, as well as to estimate the number of flares per year each source is likely to produce as a function of the detection threshold and limiting flux. We also present preliminary results from our analysis of spectral evolution-dependent flux light curves and broad-band spectroscopy of the outbursts.

  16. RED SUPERGIANTS AS POTENTIAL TYPE IIn SUPERNOVA PROGENITORS: SPATIALLY RESOLVED 4.6 {mu}m CO EMISSION AROUND VY CMa AND BETELGEUSE

    SciTech Connect

    Smith, Nathan [Astronomy Department, University of California, 601 Campbell Hall, Berkeley, CA 94720 (United States); Hinkle, Kenneth H. [National Optical Astronomy Observatory, 950 North Cherry Ave., Tucson, AZ 85719 (United States); Ryde, Nils [Lund Observatory, Box 43, SE-221 00, Lund (Sweden)], E-mail: nathans@astro.berkeley.edu, E-mail: hinkle@noao.edu, E-mail: ryde@astro.lu.se

    2009-03-15

    We present high-resolution 4.6 {mu}m CO spectra of the circumstellar environments of two red supergiants (RSGs) that are potential supernova (SN) progenitors: Betelgeuse and VY Canis Majoris (VY CMa). Around Betelgeuse, {sup 12}CO emission within {+-}3'' ({+-}12 km s{sup -1}) follows a mildly clumpy but otherwise spherical shell, smaller than its {approx}55'' shell in K I {lambda}7699. In stark contrast, 4.6 {mu}m CO emission around VY CMa is coincident with bright K I in its clumpy asymmetric reflection nebula, within {+-}5'' ({+-}40 km s{sup -1}) of the star. Our CO data reveal redshifted features not seen in K I spectra of VY CMa, indicating a more isotropic distribution of gas punctuated by randomly distributed asymmetric clumps. The relative CO and K I distribution in Betelgeuse arises from ionization effects within a steady wind, whereas in VY CMa, K I is emitted from skins of CO cloudlets resulting from episodic mass ejections 500-1000 yr ago. In both cases, CO and K I trace potential pre-SN circumstellar matter: we conclude that an extreme RSG like VY CMa might produce a Type IIn event like SN 1988Z if it were to explode in its current state, but Betelgeuse will not. VY CMa demonstrates that luminous blue variables are not necessarily the only progenitors of SNe IIn, but it underscores the requirement that SNe IIn suffer enhanced episodic mass loss shortly before exploding.

  17. The superflares of soft Gamma-ray repeatres: giant quakes in solid quark stars?

    E-print Network

    R. X. Xu; D. J. Tao; Y. Yang

    2006-08-28

    Three times of supergiant flares from soft $\\gamma$-ray repeatres are observed, with typical released energy of $\\sim 10^{44-47}$ erg. A conventional model (i.e., the magnetar model) for such events is catastrophic magnetism-powered instability through magnetohydrodynamic process, in which a significant part of short-hard $\\gamma$-ray bursts could also be the results of magnetars. Based on various observational features (e.g., precession, glitch, thermal photon emission) and the underlying theory of strong interaction (quantum chromodynamics, QCD), it could not be ruled out yet that pulsar-like stars might be actually solid quark stars. Strain energy develops during a solid star's life, and starquakes could occur when stellar stresses reach a critical value, with huge energy released. An alternative model for supergiant flares of soft $\\gamma$-ray repeatres is presented, in which energy release during a star quake of solid quark stars is calculated. Numerical results for spherically asymmetric solid stars show that the released gravitational energy during a giant quake could be as high as $10^{48}$ erg if the tangential pressure is slightly higher than the radial one. Difficulties in magnetar models may be overcome if AXPs/SGRs are accreting solid quark stars with mass $\\sim (1-2)M_\\odot$.

  18. How Many R Coronae Borealis Stars Are There Really? (Abstract)

    NASA Astrophysics Data System (ADS)

    Clayton, G. C.

    2014-12-01

    (Abstract only) The R Coronae Borealis (RCB) stars are rare hydrogen-deficient, carbon-rich supergiants. Two evolutionary scenarios have been suggested, a double degenerate merger of two white dwrfs (WDs), or a final helium shell flash in a planetary nebula central star. Only about 100 of the predicted 3,000 RCB stars in the Galaxy have been discovered. But the pace of discovery of new RCB stars in the Milky Way has been accelerating. We recently discovered over twenty new RCB stars by examining ASAS-e light curves. Using the recent release of the WISE All-Sky Catalog, a series of IR color-color cuts have produced a sample of candidates that may yield over 200 new RCB stars. We are trying to obtain spectra of these stars to confirm their identifications. The evidence pointing toward a WD merger or a final-flash origin for RCB stars is contradictory. Increasing the sample of known RCB stars, so that we can better study their spatial distribution in the Galaxy, can give us clues to their origins. Their number and distribution may be consistent with WD mergers. If so, this would be an exciting result since RCB stars may be low-mass analogs of Type Ia supernovae.

  19. Effects of stellar evolution and ionizing radiation on the environments of massive stars

    NASA Astrophysics Data System (ADS)

    Mackey, J.; Langer, N.; Mohamed, S.; Gvaramadze, V. V.; Neilson, H. R.; Meyer, D. M.-A.

    2014-09-01

    We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3-D simulations show that H ii regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

  20. Evolution of surface CNO abundances in massive stars

    NASA Astrophysics Data System (ADS)

    Maeder, André; Przybilla, Norbert; Nieva, María-Fernanda; Georgy, Cyril; Meynet, Georges; Ekström, Sylvia; Eggenberger, Patrick

    2014-05-01

    Aims: The nitrogen-to-carbon (N/C) and nitrogen-to-oxygen (N/O) ratios are the most sensitive quantities to mixing in stellar interiors of intermediate and massive stars. We further investigate the theoretical properties of these ratios as well as put in context recent observational results obtained by the VLT-FLAMES Survey of massive stars in the Galaxy and the Magellanic Clouds. Methods: We consider analytical relations and numerical models of stellar evolution as well as our own stellar atmosphere models, and we critically re-investigate observed spectra. Results: On the theoretical side, the N/C vs. N/O plot shows little dependence on the initial stellar masses, rotation velocities, and nature of the mixing processes up to relative enrichment of N/O by a factor of about four, thus this plot constitutes an ideal quality test for observational results. The comparison between the FLAMES Survey and theoretical values shows overall agreement, despite the observational scatter of the published results. The existence of some mixing of CNO products is clearly confirmed, however the accuracy of the data is not sufficient for allowing a test of the significant differences between different models of rotating stars and the Geneva models. We discuss reasons (for the most part due to observational bias) why part of the observational data points should not be considered for this comparison. When these observational data points are not considered, the scatter is reduced. Finally, the N/C vs. N/O plot potentially offers a powerful way for discriminating blue supergiants before the red supergiant stage from those after it. Also, red supergiants of similar low velocities may exhibit different N enrichments, depending on their initial rotation during the main-sequence phase. Appendices A and B are available in electronic form at http://www.aanda.org

  1. Investigation of ultraviolet fluxes of normal and peculiar stars

    NASA Technical Reports Server (NTRS)

    Deutschman, W. A.; Schild, R. E.

    1974-01-01

    Data from Project Celescope, a program that photographed the ultraviolet sky, in order to study several problems in current astrophysics are analyzed. Two star clusters, the Pleiades and the Hyades, reveal differences between the two that we are unable to explain simply from their differences in chemical abundance, rotation, or reddening. Data for Orion show large scatter, which appears to be in the sense that the Orion stars are too faint for their ground-based photometry. Similarly, many supergiants in the association Sco OB1 are too faint in the ultraviolet, but the ultraviolet brightness appears to be only poorly correlated with spectral type. Ultraviolet Celescope data for several groups of peculiar stars have also been analyzed. The strong He I stars are too faint in the ultraviolet, possibly owing to enhancement of O II continuous opacity due to oxygen overabundance. The Be stars appear to have ultraviolet colors normal for their MK spectral types. The P Cygni stars are considerably fainter than main-sequence stars of comparable spectral type, probably owing, at least in part, to line blocking by resonance lines of multiply ionized light metals. The Wolf-Rayet stars have ultraviolet color temperatures of O stars.

  2. The Swift Supergiant Fast X-ray Transients Project: a review, new results, and future perspectives

    E-print Network

    Romano, P; Ducci, L; Esposito, P; Vercellone, S; Bocchino, F; Burrows, D N; Kennea, J A; Krimm, H A; Gehrels, N; Farinelli, R; Ceccobello, C

    2013-01-01

    We present a review of the Supergiant Fast X-ray Transients (SFXT) Project, a systematic investigation of the properties of SFXTs with a strategy that combines Swift monitoring programs with outburst follow-up observations. This strategy has quickly tripled the available sets of broad-band data of SFXT outbursts, and gathered a wealth of out-of-outburst data, which have led us to a broad-band spectral characterization, an assessment of the fraction of the time these sources spend in each phase, and their duty cycle of inactivity. We present some new observational results obtained through our outburst follow-ups, as fitting examples of the exceptional capabilities of Swift in catching bright flares and monitor them panchromatically.

  3. Properties of Supergiant Fast X-Ray Transients as Observed by Swift

    NASA Technical Reports Server (NTRS)

    Romano, P.; Vercellone, S.; Krimm, H. A.; Esposito, P.; Cusumano, C.; LaParola, V.; Mangano, V.; Kennea, J. A.; Burrows, D. N.; Pagani, C.; Gehrels, N.

    2011-01-01

    We present the most recent results from our investigation on Supergiant Fast X-ray Transients, a class of High-Mass X-ray Binaries, with a possible counterpart in the gamma-ray energy band. Since 2007 Swift has contributed to this new field by detecting outbursts from these fast transients with the BAT and by following them for days with the XRT. Thus, we demonstrated that while the brightest phase of the outburst only lasts a few hours, further activity is observed at lower fluxes for a remarkably longer time, up to weeks. Furthermore, we have performed several campaigns of intense monitoring with the XRT, assessing the fraction of the time these sources spend in each phase, and their duty cycle of inactivity.

  4. OBSERVATIONAL EVIDENCE FOR A CORRELATION BETWEEN MACROTURBULENT BROADENING AND LINE-PROFILE VARIATIONS IN OB SUPERGIANTS

    SciTech Connect

    Simon-Diaz, S.; Herrero, A.; Castro, N. [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife (Spain); Uytterhoeven, K. [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, CEA, IRFU, SAp, centre de Saclay, F-91191, Gif-sur-Yvette (France); Aerts, C. [Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Puls, J., E-mail: ssimon@iac.e [Universitaetssternwarte Muenchen, Scheinerstr. 1, D-81679 Muenchen (Germany)

    2010-09-10

    The spectra of O and B supergiants (Sgs) are known to be affected by a significant form of extra line broadening (usually referred to as macroturbulence) in addition to that produced by stellar rotation. Recent analyses of high-resolution spectra have shown that the interpretation of this line broadening as a consequence of large-scale turbulent motions would imply highly supersonic velocity fields in photospheric regions, making this scenario quite improbable. Stellar oscillations have been proposed as a likely alternative explanation. As part of a long-term observational project, we are investigating the macroturbulent broadening in O and B Sgs and its possible connection with spectroscopic variability phenomena and stellar oscillations. In this Letter, we present the first encouraging results of our project, namely, firm observational evidence for a strong correlation between the extra broadening and photospheric line-profile variations in a sample of 13 Sgs with spectral types ranging from O9.5 to B8.

  5. The ARAUCARIA project: Grid-based quantitative spectroscopic study of massive blue stars in NGC 55

    NASA Astrophysics Data System (ADS)

    Castro, N.; Urbaneja, M. A.; Herrero, A.; Garcia, M.; Simón-Díaz, S.; Bresolin, F.; Pietrzy?ski, G.; Kudritzki, R.-P.; Gieren, W.

    2012-06-01

    Context. The quantitative study of the physical properties and chemical abundances of large samples of massive blue stars at different metallicities is a powerful tool to understand the nature and evolution of these objects. Their analysis beyond the Milky Way is challenging, nonetheless it is doable and the best way to investigate their behavior in different environments. Fulfilling this task in an objective way requires the implementation of automatic analysis techniques that can perform the analyses systematically, minimizing at the same time any possible bias. Aims: As part of the ARAUCARIA project we carry out the first quantitative spectroscopic analysis of a sample of 12 B-type supergiants in the galaxy NGC 55 at 1.94 Mpc away. By applying the methodology developed in this work, we derive their stellar parameters, chemical abundances and provide a characterization of the present-day metallicity of their host galaxy. Methods: Based on the characteristics of the stellar atmosphere/line formation code fastwind, we designed and created a grid of models for the analysis of massive blue supergiant stars. Along with this new grid, we implemented a spectral analysis algorithm. Both tools were specially developed to perform fully consistent quantitative spectroscopic analyses of low spectral resolution of B-type supergiants in a fast and objective way. Results: We present the main characteristics of our fastwind model grid and perform a number of tests to investigate the reliability of our methodology. The automatic tool is applied afterward to a sample of 12 B-type supergiant stars in NGC 55, deriving the stellar parameters, Si , C , N , O and Mg abundances. The results indicate that our stars are part of a young population evolving towards a red supergiant phase. For half of the sample we find a remarkable agreement between spectroscopic and evolutionary masses, whilst for the rest larger discrepancies are present, but still within the uncertainties. The derived chemical composition hints to an average metallicity similar to the one of the Large Magellanic Cloud, with no indication of a spatial trend across the galaxy. Conclusions: The consistency between the observed spectra and our stellar models supports the reliability of our methodology. This objective and fast approach allows us to deal with large samples in an accurate and more statistical way. These are two key issues to achieve an unbiased characterization of the stars and their host galaxies. Based on observations obtained at the ESO VLT Large Programme 171.D-0004.

  6. The VLT-FLAMES survey of massive stars: constraints on stellar evolution from the chemical compositions of rapidly rotating Galactic and Magellanic Cloud B-type stars

    NASA Astrophysics Data System (ADS)

    Hunter, I.; Brott, I.; Langer, N.; Lennon, D. J.; Dufton, P. L.; Howarth, I. D.; Ryans, R. S. I.; Trundle, C.; Evans, C. J.; de Koter, A.; Smartt, S. J.

    2009-03-01

    Aims: We have previously analysed the spectra of 135 early B-type stars in the Large Magellanic Cloud (LMC) and found several groups of stars that have chemical compositions that conflict with the theory of rotational mixing. Here we extend this study to Galactic and Small Magellanic Cloud (SMC) metallicities. Methods: We provide chemical compositions for ~50 Galactic and ~100 SMC early B-type stars and compare these to the LMC results. These samples cover a range of projected rotational velocities up to ~300 km s-1 and hence are well suited to testing rotational mixing models. The surface nitrogen abundances are utilised as a probe of the mixing process since nitrogen is synthesized in the core of the stars and mixed to the surface. Results: In the SMC, we find a population of slowly rotating nitrogen-rich stars amongst the early B type core-hydrogen burning stars, which is comparable to that found previously in the LMC. The identification of non-enriched rapid rotators in the SMC is not possible due to the relatively high upper limits on the nitrogen abundance for the fast rotators. In the Galactic sample we find no significant enrichment amongst the core hydrogen-burning stars, which appears to be in contrast with the expectation from both rotating single-star and close binary evolution models. However, only a small number of the rapidly rotating stars have evolved enough to produce a significant nitrogen enrichment, and these may be analogous to the non-enriched rapid rotators previously found in the LMC sample. Finally, in each metallicity regime, a population of highly enriched supergiants is observed, which cannot be the immediate descendants of core-hydrogen burning stars. Their abundances are, however, compatible with them having gone through a previous red supergiant phase. Together, these observations paint a complex picture of the nitrogen enrichment in massive main sequence and supergiant stellar atmospheres, where age and binarity cause crucial effects. Whether rotational mixing is required to understand our results remains an open question at this time, but could be answered by identifying the true binary fraction in those groups of stars that do not agree with single-star evolutionary models. Based on observations at the European Southern Observatory in programmes 171.0237 and 073.0234. Figure 1 and Tables 1 and 2 are only available in electronic form at http://www.aanda.org

  7. X-ray Diagnostics of Mass-loss Rates and Wind Structure in O-stars

    NASA Astrophysics Data System (ADS)

    Cohen, David; Sundqvist, Jon; Leutenegger, Maurice

    2013-06-01

    X-ray emission provides information about the shock heating of massive star winds. But in recent years it has become clear that X-ray absorption can also provide important constraints on the bulk wind properties. Because the X-ray spectral absorption signature is dependent on the column density of the wind, it can be used as a reliable, clumping-independent mass-loss rate diagnostic for the dense, partially optically thick winds of O supergiants. When combined with density-squared diagnostics like H-?, it also provides information about the wind clumping factor. I will report mass-loss rate and clumping measurements of the canonical O supergiant, zeta Pup, and the extreme O2 supergiant, HD 93129A. For both stars, mass-loss rates three to four times lower than unclumped H-? rates are preferred. These mass-loss rates are consistent with the observed H-? if clumping factors of order f_{cl} = 10 are assumed. The detailed X-ray line shapes also favor smaller, optically thin clumps and no significant porosity effects. Further, to reconcile the X-ray and the H-? emission line profiles, clumping must start very close to the photosphere, at r ? 1.1 R_*, while the X-ray emission turns on only at larger radii, at r ? 1.5 R_*.

  8. Influence of a stellar wind on the evolution of a star of 30 solar masses

    NASA Technical Reports Server (NTRS)

    Stothers, R.; Chin, C.

    1980-01-01

    A coarse grid of theoretical evolutionary tracks was calculated for a 30 solar mass star to determine the role of mass loss in the evolution of the star during core He burning. The Cox-Stewart opacities were applied, and the rate of mass loss, criterion for convection, and initial chemical composition were taken into consideration. Using the Schwarzschild criterion, the star undergoes little mass loss during core He burning and remains a blue supergiant separated from main sequence stars on the H-R diagram. The stellar remnant consists of the original He core and may appear bluer than equally luminous main sequence stars; a variety of possible evolutionary tracks can be obtained for an initial solar mass of 30 with proper choices of free parameters.

  9. Supergiant Fast X-ray Transients: A new class of high mass X-ray binaries unveiled by INTEGRAL

    E-print Network

    Ignacio Negueruela; David M. Smith; Pablo Reig; Sylvain Chaty; Jose Miguel Torrejon

    2005-11-02

    INTEGRAL monitoring of the Galactic Plane is revealing a growing number of recurrent X-ray transients, characterised by short outbursts with very fast rise times (~ tens of minutes) and typical durations of a few hours. Here we show that several of these transients are associated with OB supergiants and hence define a new class of massive X-ray binaries which we call Supergiant Fast X-ray Transients (SFXTs). Many other transient X-ray sources display similar X-ray characteristics, suggesting that they belong to the same class. Since they are difficult to detect and their number is growing fast and steadily, they could represent a major class of X-ray binaries.

  10. The Araucaria Project: the Local Group Galaxy WLM--Distance and metallicity from quantitative spectroscopy of blue Supergiants

    E-print Network

    M. A. Urbaneja; R. -P. Kudritzki; F. Bresolin; N. Przybilla; W. Gieren; G. Pietrzynski

    2008-05-22

    The quantitative analysis of low resolution spectra of A and B supergiants is used to determine a distance modulus of 24.99 +/- 0.10 mag (995 +/- 46 Kpc) to the Local Group galaxy WLM. The analysis yields stellar effective temperatures and gravities, which provide a distance through the Flux weighted Gravity--Luminosity Relationship (FGLR). Our distance is 0.07 mag larger than the most recent results based on Cepheids and the tip of the RGB. This difference is within the 1-sigma overlap of the typical uncertainties quoted in these photometric investigations. In addition, non-LTE spectral synthesis of the rich metal line spectra (mostly iron, chromium and titanium) of the A supergiants is carried out, which allows the determination of stellar metallicities. An average metallicity of -0.87 +/- 0.06 dex with respect to solar metallicity is found.

  11. Searching for hidden Wolf-Rayet stars in the Galactic Plane - 15 new Wolf-Rayet stars

    E-print Network

    L. J. Hadfield; S. D. Van Dyk; P. W. Morris; J. D. Smith; A. P. Marston; D. E. Peterson

    2006-12-20

    We report the discovery of fifteen previously unknown Wolf-Rayet (WR) stars found as part of an infrared broad-band study of candidate WR stars in the Galaxy. We have derived an empirically-based selection algorithm which has selected ~5000 WR candidate stars located within the Galactic Plane drawn from the GLIMPSE (mid-infrared) and 2MASS (near-infrared) catalogues. Spectroscopic follow-up of 184 of these reveals eleven WN and four WC-type WR stars. Early WC subtypes are absent from our sample and none show evidence for circumstellar dust emission. Of the candidates which are not WR stars, ~120 displayed hydrogen emission line features in their spectra. Spectral features suggest that the majority of these are in fact B supergiants/hypergiants, ~40 of these are identified Be/B[e] candidates. Here, we present the optical spectra for six of the newly-detected WR stars, and the near-infrared spectra for the remaining nine of our sample. With a WR yield rate of ~7% and a massive star detection rate of ~65%, initial results suggest that this method is one of the most successful means for locating evolved, massive stars in the Galaxy.

  12. FURTHER RESULTS FROM THE GALACTIC O-STAR SPECTROSCOPIC SURVEY: RAPIDLY ROTATING LATE ON GIANTS

    SciTech Connect

    Walborn, Nolan R. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); MaIz Apellaniz, Jesus; Sota, Alfredo; Alfaro, Emilio J. [Instituto de Astrofisica de Andalucia-CSIC, Glorieta de la Astronomia s/n, 18008 Granada (Spain); Morrell, Nidia I. [Las Campanas Observatory, Observatories of the Carnegie Institution of Washington, Casilla 601, La Serena (Chile); Barba, Rodolfo H.; Arias, Julia I. [Departamento de Fisica, Universidad de La Serena, Cisternas 1200 Norte, La Serena (Chile); Gamen, Roberto C., E-mail: walborn@stsci.edu, E-mail: jmaiz@iaa.es, E-mail: sota@iaa.es, E-mail: emilio@iaa.es, E-mail: nmorrell@lco.cl, E-mail: rbarba@dfuls.cl, E-mail: julia@dfuls.cl, E-mail: rgamen@fcaglp.unlp.edu.ar [Instituto de Astrofisica de La Plata-CONICET and Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, 1900 La Plata (Argentina)

    2011-11-15

    With new data from the Galactic O-Star Spectroscopic Survey, we confirm and expand the ONn category of late-O, nitrogen-enriched (N), rapidly rotating (n) giants. In particular, we have discovered two 'clones' (HD 102415 and HD 117490) of one of the most rapidly rotating O stars previously known (HD 191423, 'Howarth's Star'). We compare the locations of these objects in the theoretical H-R diagram to those of slowly rotating ON dwarfs and supergiants. All ON giants known to date are rapid rotators, whereas no ON dwarf or supergiant is, but all ON stars are small fractions of their respective spectral-type/luminosity-class/rotational subcategories. The ONn giants, displaying both substantial processed material and high rotation at an intermediate evolutionary stage, may provide significant information about the development of these properties. They may have preserved high initial rotational velocities or may have been spun up by terminal-age main-sequence core contraction; alternatively, and perhaps more likely, they may be products of binary mass transfer. At least some of them are also runaway stars.

  13. The massive binary companion star to the progenitor of supernova 1993J.

    PubMed

    Maund, Justyn R; Smartt, Stephen J; Kudritzki, Rolf P; Podsiadlowski, Philipp; Gilmore, Gerard F

    2004-01-01

    The massive star that underwent a collapse of its core to produce supernova (SN)1993J was subsequently identified as a non-variable red supergiant star in images of the galaxy M81 taken before explosion. It showed an excess in ultraviolet and B-band colours, suggesting either the presence of a hot, massive companion star or that it was embedded in an unresolved young stellar association. The spectra of SN1993J underwent a remarkable transformation from the signature of a hydrogen-rich type II supernova to one of a helium-rich (hydrogen-deficient) type Ib. The spectral and photometric peculiarities were best explained by models in which the 13-20 solar mass supergiant had lost almost its entire hydrogen envelope to a close binary companion, producing a 'type IIb' supernova, but the hypothetical massive companion stars for this class of supernovae have so far eluded discovery. Here we report photometric and spectroscopic observations of SN1993J ten years after the explosion. At the position of the fading supernova we detect the unambiguous signature of a massive star: the binary companion to the progenitor. PMID:14712269

  14. Further Results from the Galactic O-Star Spectroscopic Survey: Rapidly Rotating Late ON Giants

    NASA Astrophysics Data System (ADS)

    Walborn, Nolan R.; Maíz Apellániz, Jesús; Sota, Alfredo; Alfaro, Emilio J.; Morrell, Nidia I.; Barbá, Rodolfo H.; Arias, Julia I.; Gamen, Roberto C.

    2011-11-01

    With new data from the Galactic O-Star Spectroscopic Survey, we confirm and expand the ONn category of late-O, nitrogen-enriched (N), rapidly rotating (n) giants. In particular, we have discovered two "clones" (HD 102415 and HD 117490) of one of the most rapidly rotating O stars previously known (HD 191423, "Howarth's Star"). We compare the locations of these objects in the theoretical H-R diagram to those of slowly rotating ON dwarfs and supergiants. All ON giants known to date are rapid rotators, whereas no ON dwarf or supergiant is, but all ON stars are small fractions of their respective spectral-type/luminosity-class/rotational subcategories. The ONn giants, displaying both substantial processed material and high rotation at an intermediate evolutionary stage, may provide significant information about the development of these properties. They may have preserved high initial rotational velocities or may have been spun up by terminal-age main-sequence core contraction; alternatively, and perhaps more likely, they may be products of binary mass transfer. At least some of them are also runaway stars.

  15. Physical Theories of Winds From Cool Stars

    NASA Technical Reports Server (NTRS)

    Tielens, A. G. G. M.; Cuzzi, Jeffrey N. (Technical Monitor)

    1994-01-01

    Cool stars in the late stages of their evolution generally lose mass at a prodigious rate. This includes low mass stars on the red giant branch, on the asymptotic giant branch, and those transiting from the asymptotic giant branch to the planetary nebula phase, as well as massive supergiants. All of these objects are surrounded by dense circumstellar gas and often dust envelopes. This mass loss is an important source of gas and dust for the interstellar medium. For some of these objects, the mass loss rate exceeds the nuclear burning rate and, hence, mass loss determines the subsequent evolution of the star. A variety processes have been invoked to explain the mass loss of these objects. A consensus has developed over the last decade: photospheric processes create an extended atmosphere which extends to several stellar radii. At this height above the photosphere, dust grains can form and radiation pressure drives the dust out. The gas is dragged along by friction. While the detailed processes involved, in particular those lifting the atmosphere, may differ from object to object, this paradigm seems applicable to all of these objects. The process of mass loss breaks up into three parts: 1) The formation of the extended atmosphere; 2) the nucleation and condensation of dust; and 3) The radiation pressure driven wind. Each of these processes will be discussed with an emphasis on those processes that play a role in the mass loss from asymptotic giant branch stars for which the most detailed theories have been developed.

  16. The massive star population in M101. II. Spatial variations in the recent star formation history

    SciTech Connect

    Grammer, Skyler; Humphreys, Roberta M., E-mail: grammer@astro.umn.edu, E-mail: roberta@umn.edu [Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota, Minneapolis, MN 55455 (United States)

    2014-09-01

    We investigate star formation history (SFH) as a function of radius in M101 using archival Hubble Space Telescope Advanced Camera for Surveys photometry. We derive the SFH from the resolved stellar populations in five 2' wide annuli. Binning the SFH into time frames corresponding to stellar populations traced by H?, far-ultraviolet, and near-ultraviolet emission, we find that the fraction of stellar populations young enough to contribute in H? is 15%-35% in the inner regions, compared to less than 5% in the outer regions. This provides a sufficient explanation for the lack of H? emission at large radii. We also model the blue to red supergiant ratio in our five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into modeled ratios, we find that we are able to reproduce the observed values at large radii (low metallicity), but at small radii (high metallicity) the modeled and observed ratios are discrepant.

  17. Wind structure of late B supergiants I. Multi-line analyses of near-surface and wind structure in HD 199 478 (B8 Iae)

    E-print Network

    N. Markova; R. Prinja; H. Markov; I. Kolka; N. Morrison; J. Percy; S. Adelman

    2008-06-05

    We provide a quantitative analysis of time-variable phenomena in the photospheric, near-star, and outflow regions of the late-B supergiant (SG) HD 199478. The analysis is based primarily on optical spectroscopic datasets secured between 1999 and 2000 from the Bulgarian NAO, Tartu, and Ritter Observatories. The temporal behaviour of HD 199478 is characterised by three key empirical properties: (i) systematic central velocity shifts in the photospheric absorption lines, including C II and He I, over a characteristic time-scale of abou 20 days; (ii) extremely strong, variable H alpha emission with no clear modulation signal, and (iii) the occurrence in 2000 of a (rare) high-velocity absorption (HVA) event in H alpha, which evolved over about 60 days, showing the clear signature of mass infall and outflows. In these properties HD 199478 resembles few other late-B SGs with peculiar emission and HVAs in H alpha (HD 91619, HD 34085, HD 96919). Non-LTE line synthesis modelling is conducted using FASTWIND for these late-B SGs to constrain and compare their fundamental parameters within the context of extreme behaviour in the H alpha lines. Our analysis indicate that at the cooler temperature edge of B SGs, there are objects whose wind properties, as traced by H alpha, are inconsistent with the predictions of the smooth, spherically symmetric wind approximation. This discordance is still not fully understood and may highlight the role of a non-spherical, disk-like, geometry, which may result from magnetically-driven equatorial compression of the gas. Ordered dipole magnetic fields may also lead to confined plasma held above the stellar surface, which ultimately gives rise to transient HVA events.

  18. OXYGEN ISOTOPIC RATIOS IN COOL R CORONAE BOREALIS STARS

    SciTech Connect

    Garcia-Hernandez, D. A. [Instituto de Astrofisica de Canarias (IAC), C/Via Lactea s/n, 38200 La Laguna, Tenerife (Spain); Lambert, David L. [W. J. McDonald Observatory, University of Texas at Austin. 1 University Station, C1400. Austin, TX 78712-0259 (United States); Rao, N. Kameswara [Indian Institute of Astrophysics, Bangalore 560 034 (India); Hinkle, Ken H. [National Optical Astronomy Observatory (NOAO), Tucson, AZ 85726 (United States); Eriksson, Kjell, E-mail: agarcia@iac.e, E-mail: dll@astro.as.utexas.ed, E-mail: nkrao@iiap.res.i, E-mail: hinkle@noao.ed, E-mail: Kjell.Eriksson@astro.uu.s [Department of Physics and Astronomy, Uppsala University, Box 515, 75120 Uppsala (Sweden)

    2010-05-01

    We investigate the relationship between R Coronae Borealis (RCB) stars and hydrogen-deficient carbon (HdC) stars by measuring precise {sup 16}O/{sup 18}O ratios for five cool RCB stars. The {sup 16}O/{sup 18}O ratios are derived by spectrum synthesis from high-resolution (R {approx} 50, 000) K-band spectra. Lower limits to the {sup 16}O/{sup 17}O and {sup 14}N/{sup 15}N ratios as well as Na and S abundances (when possible) are also given. RCB stars in our sample generally display less {sup 18}O than HdC stars-the derived {sup 16}O/{sup 18}O ratios range from 3 to 20. The only exception is the RCB star WX CrA, which seems to be an HdC-like star with {sup 16}O/{sup 18}O = 0.3. Our result of a higher {sup 16}O/{sup 18}O ratio for the RCB stars must be accounted for by a theory of the formation and evolution of HdC and RCB stars. We speculate that a late dredge-up of products of He burning, principally {sup 12}C and {sup 16}O, may convert an {sup 18}O-rich HdC star into an {sup 18}O-poor RCB star as the H-deficient star begins its final evolution from a cool supergiant to the top of the white dwarf cooling track.

  19. Investigation of atmosphere nonstationarity in the supergiant 55Cyg. I. Temporal line profile variability

    NASA Astrophysics Data System (ADS)

    Rzaev, A. Kh.

    2012-07-01

    The CCD spectra taken with echelle spectrographs of the 2-m telescope of the Shemakha Astrophysical Observatory of the National Academy of Sciences of Azerbaijan and the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences are used to study the line profile variations in the spectrum of the hot supergiant 55Cyg. The variability of the radial velocity and profiles of the lines of heavy elements is shown to be due to radial pulsation type motions. The corresponding variations for He I lines are due to nonradial pulsations. In the case of the H ? and H ? lines the pattern and behavior of variations differ for different observing periods. The variability of these lines is mostly due to the photometric and positional variability of the absorption and emission components of their profiles. The profiles of these lines show additional emission components, which move from the blue toward the red line wing. Such a behavior is indicative of the clumpy structure of the stellar envelope.

  20. Supergiant Fast X-ray Transients with Swift: spectroscopic and temporal properties

    E-print Network

    Romano, P; Ducci, L; Esposito, P; Farinelli, R; Ceccobello, C; Vercellone, S; Burrows, D N; Kennea, J A; Krimm, H A; Gehrels, N

    2012-01-01

    Supergiant fast X-ray transients (SFXTs) are a class of high-mass X-ray binaries with possible counterparts in the high energy gamma rays. The Swift SFXT Project has conducted a systematic investigation of the properties of SFTXs on timescales ranging from minutes to years and in several intensity states (from bright flares, to intermediate intensity states, and down to almost quiescence). We also performed broad-band spectroscopy of outbursts, and intensity-selected spectroscopy outside of outbursts. We demonstrated that while the brightest phase of the outburst only lasts a few hours, further activity is observed at lower fluxes for a remarkably longer time, up to weeks. Furthermore, we assessed the fraction of the time these sources spend in each phase, and their duty cycle of inactivity. We present the most recent results from our investigation. The spectroscopic and, most importantly, timing properties of SFXTs we have uncovered with Swift will serve as a guide in search for the high energy emission from...

  1. Monitoring Supergiant Fast X-ray Transients with Swift. Results from the first year

    E-print Network

    Romano, P; Cusumano, G; La Parola, V; Vercellone, S; Pagani, C; Ducci, L; Mangano, V; Cummings, J; Krimm, H A; Guidorzi, C; Kennea, J A; Hoversten, E A; Burrows, D N; Gehrels, N

    2009-01-01

    Swift has allowed the possibility to give Supergiant Fast X-ray Transients (SFXTs), the new class of High Mass X-ray Binaries discovered by INTEGRAL, non serendipitous attention throughout all phases of their life. We present our results based on the first year of intense Swift monitoring of four SFXTs, IGR J16479-4514, XTE J1739-302, IGR J17544-2619 and AX J1841.0-0536. We obtain the first assessment of how long each source spends in each state using a systematic monitoring with a sensitive instrument. The duty-cycle of inactivity is 17, 28, 39, 55% (5% uncertainty), for IGR J16479-4514, AX J1841.0-0536, XTE J1739-302, and IGR J17544-2619, respectively, so that true quiescence is a rare state. This demonstrates that these transients accrete matter throughout their life at different rates. AX J1841.0-0536 is the only source which has not undergone a bright outburst during our campaign. Although individual sources behave somewhat differently, common X-ray characteristics of this class are emerging such as outb...

  2. New results with Swift on Supergiant Fast X-ray Transients

    E-print Network

    Sidoli, L; Ducci, L; Paizis, A; Vercellone, S; Cusumano, G; La Parola, V; Mangano, V; Kennea, J A; Burrows, D N; Krimm, H A; Gehrels, N; Sguera, V; Bazzano, A

    2010-01-01

    We report here on the most recent results obtained on a new class of High Mass X-ray Binaries, the Supergiant Fast X-ray Transients. Since October 2007, we have been performing a monitoring campaign with Swift of four SFXTs (IGRJ17544-2916, XTEJ1739-302, IGRJ16479-4514 and the X-ray pulsar AXJ1841.0-0536) for about 1-2 ks, 2-3 times per week, allowing us to derive the previously unknown long term properties of this new class of sources (their duty cycles, spectral properties in outbursts and out-of-outbursts, temporal behaviour). We also report here on additional Swift observations of two SFXTs which are not part of the monitoring: IGRJ18483-0311 (observed with Swift/XRT during a whole orbital cycle) and SAXJ1818.6-1703 (observed for the first time simultaneously in the energy range 0.3-100 keV during a bright flare).

  3. STOCHASTIC ACCRETION AND THE VARIABILITY OF SUPERGIANT FAST X-RAY TRANSIENTS

    SciTech Connect

    Pizzolato, Fabio; Sidoli, Lara, E-mail: fabio@iasf-milano.inaf.it, E-mail: sidoli@iasf-milano.inaf.it [INAF-IASF Milano, Via Bassini No. 15, I-20133 Milano (Italy)] [INAF-IASF Milano, Via Bassini No. 15, I-20133 Milano (Italy)

    2013-01-10

    In this paper, we consider the variability of the luminosity of a compact object (CO) powered by the accretion of an extremely inhomogeneous (clumpy) stream of matter. The accretion of a single clump results in an X-ray flare; we adopt a simple model for the response of the CO to its arrival, and derive a stochastic differential equation (SDE) for the accretion-powered luminosity L(t). We set the SDE in the equivalent form of an equation for the flare luminosity distribution (FLD) and discuss its solution in the stationary case. We apply our formalism to the analysis of the FLDs of supergiant fast X-ray transients (SFXTs), a peculiar sub-class of high-mass X-ray binary (HMXB) systems. We compare our theoretical FLDs to the distributions observed in the SFXTs IGR J16479-4514, IGR J17544-2619, and XTE J1739-302. Despite its simplicity, our model agrees well with the observed distributions and allows us to predict some properties of the stellar wind. Finally, we discuss how our model may explain the difference between the broad FLDs of SFXTs and the much narrower FLDs of persistent HMXBs.

  4. Type IIP supernova 2008in: the explosion of a normal red supergiant

    NASA Astrophysics Data System (ADS)

    Utrobin, V. P.; Chugai, N. N.

    2013-07-01

    Context. The explosion energy and the ejecta mass of a type IIP supernova make up the basis for the theory of explosion mechanism. So far, these parameters have only been determined for seven events. Aims: Type IIP supernova 2008in is another well-observed event for which a detailed hydrodynamic modeling can be used to derive the supernova parameters. Methods: Hydrodynamic modeling was employed to describe the bolometric light curve and the expansion velocities at the photosphere level. A time-dependent model for hydrogen ionization and excitation was applied to model the H? and H? line profiles. Results: We found an ejecta mass of 13.6 ± 1.9 M?, an explosion energy of (5.05 ± 3.4) × 1050 erg, a presupernova radius of 570 ± 100 R?, and a radioactive 56Ni mass of 0.015 ± 0.005 M?. The estimated progenitor mass is 15.5 ± 2.2 M?. We uncovered a problem of the H? and H? description at the early phase, which cannot be resolved within a spherically symmetric model. Conclusions: The presupernova of SN 2008in was a normal red supergiant with the minimum mass of the progenitor among eight type IIP supernovae explored by means of the hydrodynamic modeling. The problem of the absence of type IIP supernovae with the progenitor masses <15 M? in this sample remains open.

  5. Strange stars

    NASA Technical Reports Server (NTRS)

    Alcock, Charles; Farhi, Edward; Olinto, Angela

    1986-01-01

    Strange matter, a form of quark matter that is postulated to be absolute stable, may be the true ground stage of the hadrons. If this hypothesis is correct, neutron stars may convert to 'strange stars'. The mass-radius relation for strange stars is very different from that of neutron stars; there is no minimum mass, and for mass of 1 solar mass or less, mass is proportional to the cube of the radius. For masses between 1 solar mass and 2 solar masses, the radii of strange stars are about 10 km, as for neutron stars. Strange stars may have an exposed quark surface, which is capable of radiating at rates greatly exceeding the Eddington limit, but has a low emissivity for X-ray photons. The stars may have a thin crust with the same composition as the preneutron drip outer layer of a conventional neutron star crust. Strange stars cool efficiently via neutrino emission.

  6. Eta Carinae and Nebulae Around Massive Stars: Similarities to Planetary Nebulae?

    E-print Network

    Nathan Smith

    2008-02-13

    I discuss some observational properties of aspherical nebulae around massive stars, and conclusions inferred for how they may have formed. Whether or not these ideas are applicable to the shaping of planetary nebulae is uncertain, but the observed similarities between some PNe and bipolar nebulae around massive stars is compelling. In the well-observed case of Eta Carinae, several lines of observational evidence point to a scenario where the shape of its bipolar nebula resulted from an intrinsically bipolar explosive ejection event rather than an interacting winds scenario occurring after ejection from teh star. A similar conclusion has been inferred for some planetary nebulae. I also briefly mention bipolar nebulae around some other massive stars, such as the progenitor of SN 1987A and related blue supergiants.

  7. Massive Stars in the W33 Giant Molecular Complex

    NASA Astrophysics Data System (ADS)

    Messineo, Maria; Clark, J. Simon; Figer, Donald F.; Kudritzki, Rolf-Peter; Najarro, Francisco; Rich, R. Michael; Menten, Karl M.; Ivanov, Valentin D.; Valenti, Elena; Trombley, Christine; Chen, C.-H. Rosie; Davies, Ben

    2015-06-01

    Rich in H ii regions, giant molecular clouds are natural laboratories to study massive stars and sequential star formation. The Galactic star-forming complex W33 is located at l=? 12\\buildrel{\\circ}\\over{.} 8 and at a distance of 2.4 kpc and has a size of ? 10 pc and a total mass of ? (0.8?8.0) × {{10}5} M ? . The integrated radio and IR luminosity of W33—when combined with the direct detection of methanol masers, the protostellar object W33A, and the protocluster embedded within the radio source W33 main—mark the region as a site of vigorous ongoing star formation. In order to assess the long-term star formation history, we performed an infrared spectroscopic search for massive stars, detecting for the first time 14 early-type stars, including one WN6 star and four O4–7 stars. The distribution of spectral types suggests that this population formed during the past ?2–4 Myr, while the absence of red supergiants precludes extensive star formation at ages 6–30 Myr. This activity appears distributed throughout the region and does not appear to have yielded the dense stellar clusters that characterize other star-forming complexes such as Carina and G305. Instead, we anticipate that W33 will eventually evolve into a loose stellar aggregate, with Cyg OB2 serving as a useful, albeit richer and more massive, comparator. Given recent distance estimates, and despite a remarkably similar stellar population, the rich cluster Cl 1813–178 located on the northwest edge of W33 does not appear to be physically associated with W33.

  8. The peculiar, luminous early-type emission line stars of the Magellanic clouds: A preliminary taxonomy

    NASA Technical Reports Server (NTRS)

    Shore, S. N.; Sanduleak, N.

    1982-01-01

    A sample of some 20 early type emission supergiants in the Magellanic clouds was observed with both the SWP and LWR low resolution mode of IUE. All stars have strong H-emission, some showing P-Cygni structure as well with HeI, HeII, FeII and other ions also showing strong emission. It is found that the stars fall into three distinct groups on the basis of the HeII/HeI and HeI/HI strengths: (1) HeII strong, HeI, HI; (2) HeII absent, HeI, HI strong; (3) HeI absent, HI, FeII, FeII, strong in addition to low excitation ions. The two most extreme emission line stars found in the Clouds S 134/LMC and S 18/SMC are discussed. Results for the 2200A feature in these supergiants, and evidence for shells around the most luminous stars in the clouds are also described.

  9. Variable Stars Pulsating Stars: periodic

    E-print Network

    Basu, Shantanu

    Variable Stars · Pulsating Stars: periodic expansion and contraction, e.g., Cepheids, RR Lyrae increases . Why? #12;Pulsating Stars Cepheid variables: giant stars, very luminous Type II Cepheids: lower Z's · Catacylsmic and Eruptive Variables: sudden large changes, e.g., novae and supernovae · Others: changes

  10. Massive stars and the energy balance of the interstellar medium. II. The 35 solar mass star and a solution to the "missing wind problem"

    E-print Network

    Tim Freyer; Gerhard Hensler; Harold W. Yorke

    2005-12-05

    We continue our numerical analysis of the morphological and energetic influence of massive stars on their ambient interstellar medium for a 35 solar mass star that evolves from the main sequence through red supergiant and Wolf-Rayet phases, until it ultimately explodes as a supernova. We find that structure formation in the circumstellar gas during the early main-sequence evolution occurs as in the 60 solar mass case but is much less pronounced because of the lower mechanical wind luminosity of the star. Since on the other hand the shell-like structure of the HII region is largely preserved, effects that rely on this symmetry become more important. At the end of the stellar lifetime 1% of the energy released as Lyman continuum radiation and stellar wind has been transferred to the circumstellar gas. From this fraction 10% is kinetic energy of bulk motion, 36% is thermal energy, and the remaining 54% is ionization energy of hydrogen. The sweeping up of the slow red supergiant wind by the fast Wolf-Rayet wind produces remarkable morphological structures and emission signatures, which are compared with existing observations of the Wolf-Rayet bubble S308. Our model reproduces the correct order of magnitude of observed X-ray luminosity, the temperature of the emitting plasma as well as the limb brightening of the intensity profile. This is remarkable, because current analytical and numerical models of Wolf-Rayet bubbles fail to consistently explain these features. A key result is that almost the entire X-ray emission in this stage comes from the shell of red supergiant wind swept up by the shocked Wolf-Rayet wind rather than from the shocked Wolf-Rayet wind itself as hitherto assumed and modeled. This offers a possible solution to what is called the ``missing wind problem'' of Wolf-Rayet bubbles.

  11. The Stars behind the Curtain

    NASA Astrophysics Data System (ADS)

    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 still growing into stars, newborn stars, adult stars and stars nearing the end of their life. All these stars have roughly the same age, a million years, a blink of an eye compared to our five billion year-old Sun and Solar System. The fact that some of the stars have just started their lives while others are already dying is due to their extraordinary range of masses: high-mass stars, being very bright and hot, burn through their existence much faster than their less massive, fainter and cooler counterparts. The newly released image, obtained with the FORS instrument attached to the VLT at Cerro Paranal, Chile, portrays a wide field around the stellar cluster and reveals the rich texture of the surrounding clouds of gas and dust. Notes [1] The star, NGC 3603-A1, is an eclipsing system of two stars orbiting around each other in 3.77 days. The most massive star has an estimated mass of 116 solar masses, while its companion has a mass of 89 solar masses. More information ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large op

  12. A catalog of rotational and radial velocities for evolved stars. V. Southern stars

    NASA Astrophysics Data System (ADS)

    De Medeiros, J. R.; Alves, S.; Udry, S.; Andersen, J.; Nordström, B.; Mayor, M.

    2014-01-01

    Rotational and radial velocities have been measured for 1589 evolved stars of spectral types F, G, and K and luminosity classes IV, III, II, and Ib, based on observations carried out with the CORAVEL spectrometers. The precision in radial velocity is better than 0.30 km s-1 per observation, whereas rotational velocity uncertainties are typically 1.0 km s-1 for subgiants and giants and 2.0 km s-1 for class II giants and Ib supergiants. Based on observations collected at the Haute-Provence Observatory, Saint-Michel, France, and at the European Southern Observatory, La Silla, Chile.Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/561/A126

  13. Coronal Structures in Cool Stars: XMM-NEWTON Hybrid Stars and Coronal Evolution

    NASA Technical Reports Server (NTRS)

    Dupree, Andrea K.; Mushotzky, Richard (Technical Monitor)

    2003-01-01

    This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Beta Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, alpha TrA (K2 II-III). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars. We are attempting to determine if this model of coronal evolution is correct by using XMM-NEWTON RGS spectra for the 2 targets we were allocated through the Guest Observer program.

  14. Post-AGB Stars as Standard Extragalactic Candles

    E-print Network

    Howard E. Bond

    1997-02-01

    Stars evolving off the asymptotic giant branch and passing through spectral types F and A are excellent candidates for a new extragalactic candle. These post-AGB (PAGB) stars are the brightest members of Population II systems. They should have a narrow luminosity function, bounded from above by the shorter transition times of more massive and more luminous remnants, and from below by the core mass corresponding to the lowest-mass stars that are leaving the main sequence. Moreover, PAGB A-F supergiants are easily recognized because of their enormous Balmer jumps, and should lie both in ellipticals and the halos of spirals. I describe a photometric system that combines Gunn u with the standard BVI bandpasses, and report a successful search for PAGB stars in the halo of M31 using this uBVI system. The zero-point calibration will come from PAGB A and F stars in Galactic globular clusters. Four are presently known, and have a mean Mv = -3.4 with a scatter of only 0.2 mag. With this Mv we exactly reproduce the accepted M31 distance from its halo PAGB stars. Future plans include a uBVI survey of Milky Way globular clusters and Local Group galaxies in order to strengthen the zero-point calibration. Ultimately we can reach the Virgo Cluster through a distance ladder with only three rungs: subdwarf parallaxes, Milky Way globular clusters, and then directly to Virgo (with HST).

  15. Obscured Asymptotic Giant Branch stars in the Magellanic Clouds III. New IRAS counterparts

    E-print Network

    Jacco Th. van Loon; Albert A. Zijlstra; Patricia A. Whitelock; L. B. F. M. Waters; Cecile Loup; Norman R. Trams

    1997-04-21

    We have searched for near-infrared stellar counterparts of IRAS point sources in the Large Magellanic Cloud (LMC), in J and K-bands. This resulted in the detection of 21 counterparts, of which 19 are new discoveries. Using colour-magnitude and colour-colour diagrams, we identify 13 Asymptotic Giant Branch (AGB) stars with thick circumstellar dust envelopes, 7 possible early post-AGB stars or stars recovering from a thermal pulse, and 1 red supergiant or foreground star. For 10 of the IRAS targets we do not succeed in detecting and/or identifying a near-infrared counterpart. We serendipitously detect 14 other red sources, of which 2 are known Long Period Variables, and a few galaxies. The near-infrared and optical colours of the galaxies may indicate considerable interstellar extinction through the LMC, as much as A_V about 2-4 mag. The relative number of AGB carbon stars over oxygen stars is shown to decrease as the luminosity increases. Yet amongst the faintest mass-losing AGB stars oxygen-rich stars still exist, which puts constraints on current convection theories that predict the occurrence of third dredge-up and Hot Bottom Burning. We investigate the nature of some LMC stars that have infrared properties very similar to suspected Galactic post-AGB stars.

  16. Pulsating Stars

    NASA Astrophysics Data System (ADS)

    Catelan, M.; Smith, H. A.

    2015-03-01

    This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

  17. NUCLEOSYNTHESIS AND EVOLUTION OF MASSIVE METAL-FREE STARS

    SciTech Connect

    Heger, Alexander [School of Physics and Astronomy, University of Minnesota, Twin Cities, 116 Church Street SE, Minneapolis, MN 55455-0149 (United States); Woosley, S. E., E-mail: alex@physics.umn.ed, E-mail: woosley@ucolick.or [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2010-11-20

    The evolution and explosion of metal-free stars with masses 10-100 M{sub 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] {approx}< -3. The amount of ionizing radiation from this generation of stars is {approx}2.16 MeV per baryon (4.15 B per M{sub sun}; where 1 B = 1 Bethe = 10{sup 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{sub sun}, with the value depending on explosion energy, black holes are copiously formed by fallback, with a maximum hole mass of {approx}40 M{sub 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 contrast, explosion energies somewhat less than 1.2 B seem to be preferred in most cases.

  18. Long-term spectroscopic monitoring of BA-type supergiants. III. Variability of photospheric lines.

    NASA Astrophysics Data System (ADS)

    Kaufer, A.; Stahl, O.; Wolf, B.; Fullerton, A. W.; Gaeng, T.; Gummersbach, C. A.; Jankovics, I.; Kovacs, J.; Mandel, H.; Peitz, J.; Rivinius, T.; Szeifert, T.

    1997-04-01

    We obtained time series of spectra with high S/N and high resolution in wavelength and time of early-type A and late-type B supergiants (cf. Kaufer et al. 1996A&A...305..887K, Paper I, and Kaufer et al. 1996A&A...314..599K, Paper II for the analysis of the variability of the stellar envelopes). In this work we inspect the time variations of the numerous photospheric line profiles in the optical spectrum. We find complex cyclical variations of the radial velocities with a typical velocity dispersion of ?=~3km/s. The corresponding equivalent-width variations are less than 1% of their mean if we assume a common modulation mechanism for both radial velocities and equivalent width. We do not find any depth dependence of the velocity fields in the metallic lines. For ?Cyg the Balmer lines show an increase of the radial velocity from H27 to H8 by 3km/s, which is identified with the onset of the radially accelerating velocity field of the stellar wind. The Cleaned periodograms of the radial-velocity curves show the simultaneous excitation of multiple pulsation modes with periods longer and shorter than the estimated radial fundamental periods of the objects, which might indicate the excitation of non-radial and radial overtones, respectively. The analysis of the line-profile variations (LPV) of the photospheric line spectrum reveals prograde travelling features in the dynamical spectra. The travelling times of these features are in contradiction to the possible rotation periods of these extended, slowly rotating objects. Therefore, we suggest that these features should be identified with non-radial pulsation modes, possibly g-modes, of low order (l=|m|<~5).

  19. Long-term spectroscopic monitoring of BA-type supergiants. I. Halpha_ line-profile variability.

    NASA Astrophysics Data System (ADS)

    Kaufer, A.; Stahl, O.; Wolf, B.; Gaeng, T.; Gummersbach, C. A.; Kovacs, J.; Mandel, H.; Szeifert, T.

    1996-01-01

    We have obtained time series of spectra in the wavelength range 4000-6800 A over several months with high S/N and high resolution in wavelength (?/{DELTA}?=~20000) and time ({DELTA}t=~1d) of the late-type B and early-type A supergiants HD91619 (B7Ia), ?Ori (B8Ia), HD96919 (B9Ia), HD92207 (A0Ia), HD100262 (A2Ia) and ?Cyg (A2Ia). Halpha_ is found to show broad emission extended to about +/-1200km/s for all objects except ?Cyg. Due to the lack of strong line-emission in Halpha_ the electron-scattered photons are expected to originate in deep atmospheric layers. In all of the objects the Halpha_-line profiles are found to be highly variable on different time scales reaching from days to months. Patterns of variation in Halpha_ are found to be quite symmetric about the systemic velocity and are mainly due to variable blue and red-shifted emission superimposed on almost constant photospheric and/or wind profiles. These V/R variations are interpreted in terms of axial symmetry of the envelopes of these objects. Time-series analyses of the variations reveal Halpha_ time scales up to a factor of 6 longer than expected radial fundamental pulsation periods but consistent with rotational periods. Therefore, rotational modulation as a possible source of variability is concluded. Corotating weak magnetic surface structures are suggested as the source for a rotationally modulated lower wind region. Suddenly appearing deep and highly blue-shifted absorptions in Halpha_ are ascribed to instabilities of the ionization structure of the wind. Outwards propagating discrete absorption components have been observed only once in HD92207.

  20. Definition and empirical structure of the range of stellar chromospheres-coronae across the H-R diagram: Cool stars

    NASA Technical Reports Server (NTRS)

    Linsky, J. L.

    1986-01-01

    Major advances in our understanding of non-radiative heating and other activity in stars cooler than T sub eff = 10,000K has occured in the last few years. This observational evidence is reviewed and the trends that are now becoming apparent are discussed. The evidence for non-radiatively heated outer atmospheric layers (chromospheres, transition regions, and coronae) in dwarf stars cooler than spectral type A7, in F and G giants, pre-main sequence stars, and close bindary systems is unambiguous, as is the evidence for chromospheres in the K and M giants and supergiants. The existence of non-radiative heating in the outer layers of the A stars remains undetermined despite repeated searches at all wavelengths. Two important trends in the data are the decrease in plasma emission measure with age on the main sequence and decreasing rotational velocity. Variability and atmospheric inhomogeneity are commonly seen, and there is considerable evidence that magnetic fields define the geometry and control the energy balance in the outer atmospheric layers. In addition, the microwave observations imply that non-thermal electrons are confined in coronal magnetic flux tubes in at least the cool dwarfs and RS CVn systems. The chromospheres in the K and M giants and supergiants are geometrically extended, as are the coronae in the RS CVn systems and probably also in other stars.

  1. Massive Stars

    NASA Astrophysics Data System (ADS)

    Livio, Mario; Villaver, Eva

    2009-11-01

    Participants; Preface Mario Livio and Eva Villaver; 1. High-mass star formation by gravitational collapse of massive cores M. R. Krumholz; 2. Observations of massive star formation N. A. Patel; 3. Massive star formation in the Galactic center D. F. Figer; 4. An X-ray tour of massive star-forming regions with Chandra L. K. Townsley; 5. Massive stars: feedback effects in the local universe M. S. Oey and C. J. Clarke; 6. The initial mass function in clusters B. G. Elmegreen; 7. Massive stars and star clusters in the Antennae galaxies B. C. Whitmore; 8. On the binarity of Eta Carinae T. R. Gull; 9. Parameters and winds of hot massive stars R. P. Kudritzki and M. A. Urbaneja; 10. Unraveling the Galaxy to find the first stars J. Tumlinson; 11. Optically observable zero-age main-sequence O stars N. R. Walborn; 12. Metallicity-dependent Wolf-Raynet winds P. A. Crowther; 13. Eruptive mass loss in very massive stars and Population III stars N. Smith; 14. From progenitor to afterlife R. A. Chevalier; 15. Pair-production supernovae: theory and observation E. Scannapieco; 16. Cosmic infrared background and Population III: an overview A. Kashlinsky.

  2. Scanner observations of cool stars from 3400 to 11,000 A.

    NASA Technical Reports Server (NTRS)

    Fay, T.; Honeycutt, R. K.

    1972-01-01

    Evaluation of photoelectric scans of the M supergiant alpha Ori and the carbon stars 19 Psc, W Ori, and DS Peg made at 20-A resolution from 3400 to 6000 A and at 40-A resolution from 6000 to 11,000 A. The data are corrected for atmospheric extinction and for the instrumental response to obtain plots of log flux per unit frequency interval versus wavelength. The dominant spectral features are due to C2, CN, and TiO; the variation of these features with spectral class is pointed out.

  3. An updated wing TiO sensitive index for classification of M-type stars

    NASA Astrophysics Data System (ADS)

    Azizi, F.; Mirtorabi, M. T.

    2015-06-01

    By careful searching of synthetic and observed spectra in a sample of cool giant and supergiant stars, we have updated the continuum band-passes of near-infrared Wing three filter system. This photometric system measures the strength of titanium oxide (TiO) absorption in Near-Infrared (NIR) at 719 nm. We show that new reference continuum band-passes are essentially free from molecular absorptions and the updated TiO-index defines the temperature variation in a sample of cool giants with less scatter. A TiO-index vs. effective temperature calibration is derived based on new continuum band-passes.

  4. VizieR Online Data Catalog: RV and vsini of southern stars (de Medeiros+, 2014)

    NASA Astrophysics Data System (ADS)

    de Medeiros, J. R.; Alves, S.; Udry, S.; Andersen, J.; Nordstrom, B.; Mayor, M.

    2013-11-01

    Rotational and radial velocities have been measured for 1589 evolved stars of spectral types F, G, and K and luminosity classes IV, III, II, and Ib, based on observations carried out with the CORAVEL spectrometers. The precision in radial velocity is better than 0.30km/s per observation, whereas rotational velocity uncertainties are typically 1.0km/s for subgiants and giants and 2.0km/s for class II giants and Ib supergiants. (1 data file).

  5. HV2112, a Thorne-?ytkow object or a super asymptotic giant branch star

    NASA Astrophysics Data System (ADS)

    Tout, Christopher A.; ?ytkow, Anna N.; Church, Ross P.; Lau, Herbert H. B.; Doherty, Carolyn L.; Izzard, Robert G.

    2014-11-01

    The very bright red star HV2112 in the Small Magellanic Cloud could be a massive Thorne-?ytkow object (T?O), a supergiant-like star with a degenerate neutron core. With a luminosity of over 105 L?, it could also be a super asymptotic giant branch (SAGB) star, a star with an oxygen/neon core supported by electron degeneracy and undergoing thermal pulses with third dredge up. Both T?Os and SAGB stars are expected to be rare. Abundances of heavy elements in HV2112's atmosphere, as observed to date, do not allow us to distinguish between the two possibilities based on the latest models. Molybdenum and rubidium can be enhanced by both the irp-process in a T?O or by the s-process in SAGB stars. Lithium can be generated by hot bottom burning at the base of the convective envelope in either. HV2112's enhanced calcium could thus be the key determinant. Neither SAGB stars nor T?Os are known to be able to synthesize their own calcium but it may be possible to produce it in the final stages of the process that forms a T?O, when the degenerate electron core of a giant star is tidally disrupted by a neutron star. Hence, it is more likely, on a fine balance, that HV2112 is indeed a genuine T?O.

  6. R Coronae Borealis stars in the Galactic Bulge discovered by EROS-2

    E-print Network

    Tisserand, P; Wood, P R; Lesquoy, E; Beaulieu, J P; Milsztajn, A; Hamadache, C; Afonso, C; Albert, J N; Andersen, J; Ansari, R; Aubourg, E; Bareyre, P; Charlot, X; Coutures, C; Ferlet, R; Fouqué, P; Glicenstein, J F; Goldman, B; Gould, A; Gros, M; Haïssinski, J; De Kat, J; Guillou, L Le; Loup, C; Magneville, C; Maurice, E; Maury, A; Moniez, M; Palanque-Delabrouille, Nathalie; Perdereau, O; Rahal, Y; Rich, J; Spiro, M; Vidal-Madjar, A; Zylberajch, S

    2008-01-01

    Rare types of variable star may give unique insight into short-lived stages of stellar evolution. The systematic monitoring of millions of stars and advanced light curve analysis techniques of microlensing surveys make them ideal for discovering also such rare variable stars. One example is the R Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. We have conducted a systematic search of the EROS-2 database for the Galactic catalogue Bulge and spiral arms to find Galactic RCB stars. The light curves of $\\sim$100 million stars, monitored for 6.7 years (from July 1996 to February 2003), have been analysed to search for the main signature of RCB stars, large and rapid drops in luminosity. Follow-up spectroscopy has been used to confirm the photometric candidates. We have discovered 14 new RCB stars, all in the direction of the Galactic Bulge, bringing the total number of confirmed Galactic RCB stars to about 51. After reddening correction, the colours and absolute magnitudes of at least ...

  7. Properties of the molecular gas around the most massive evolved stars

    NASA Astrophysics Data System (ADS)

    Quintana-Lacaci, G., Cernicharo, J., Bujarrabal, V., Castro-Carrizo, A., Sanchez-Contreras, C., Agundez, M., Alcolea J.

    2014-04-01

    The kinematical and chemical properties of gas ejected by the most massive evolved stars are far from being understood. The observation of molecular rovibrational transitions has been shown to be an extremely powerful tool to study theses characteristics of the gas. In order to study these properties we have obtained a large amount of molecular data. In particular, we have obtained interferometric CO maps of the red supergiant stars (RSGs) Mu Cep and S Per, of the yellow hypergiant stars (YHGs) AFGL2343 and IRC+10420 and of two C-rich stars showing gas with high expansion velocities, AFGL2233 and IRC+10401. In addition we have performed a line surveys of the RSG VY CMa, the YHG IRC+10420 and C-rich stars AFGL2233 and IRC+10401 with the IRAM 30m telescope and the HIFI instrument. These observations revealed the rich chemistry present in these objects. In particular we have confirmed the enrichment in nitrogen predicted for the massive stars by the hot bottom burning (HBB) process. Also, we have found evidences that support that the C-rich stars AFGL2233 and IRC+10401 are massive stars that have deactivated the HBB process. Finally, we will propose an evolutionary scenario for the late massive stars, based in the kinematical study of the CO interferometric maps obtained for the RSGs and the YHGs.

  8. Giant outburst from the supergiant fast X-ray transient IGR J17544-2619: accretion from a transient disc?

    E-print Network

    Romano, P; Mangano, V; Esposito, P; Israel, G; Tiengo, A; Campana, S; Ducci, L; Ferrigno, C; Kennea, J A

    2015-01-01

    Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries associated with OB supergiant companions and characterised by an X-ray flaring behaviour whose dynamical range reaches 5 orders of magnitude on timescales of a few hundred to thousands of seconds. Current investigations concentrate on finding possible mechanisms to inhibit accretion in SFXTs and explain their unusually low average X-ray luminosity. We present the Swift observations of an exceptionally bright outburst displayed by the SFXT IGR J17544-2619 on 2014 October 10 when the source achieved a peak luminosity of $3\\times10^{38}$ erg s$^{-1}$. This extends the total source dynamic range to $\\gtrsim$10$^6$, the largest (by a factor of 10) recorded so far from an SFXT. Tentative evidence for pulsations at a period of 11.6 s is also reported. We show that these observations challenge, for the first time, the maximum theoretical luminosity achievable by an SFXT and propose that this giant outburst was due to the formation of a transient ac...

  9. Swift/XRT monitoring of the candidate Supergiant Fast X-ray Transient IGR J16418-4532

    E-print Network

    Romano, P; Ducci, L; Esposito, P; Evans, P A; Vercellone, S; Kennea, J A; Burrows, D N; Gehrels, N

    2011-01-01

    We report on the Swift monitoring of the candidate supergiant fast X-ray transient (SFXT) IGR J16418-4532, for which both orbital and spin periods are known (~3.7d and ~1250s, respectively). Our observations, for a total of ~43ks, span over three orbital periods and represent the most intense and complete sampling of the light curve of this source with a sensitive X-ray instrument. With this unique set of observations we can address the nature of this transient. By applying the clumpy wind model for blue supergiants to the observed X-ray light curve, and assuming a circular orbit, the X-ray emission from this source can be explained in terms of the accretion from a spherically symmetric clumpy wind, composed of clumps with different masses, ranging from ~5E16 g to 1E21g. Our data suggest, based on the X-ray behaviour, that this is an intermediate SFXT.

  10. Herschel SPIRE and PACS observations of the red supergiant VY CMa: analysis of the molecular line spectra

    E-print Network

    Matsuura, Mikako; Barlow, M J; Swinyard, B M; Royer, P; Cernicharo, J; Decin, L; Wesson, R; Polehampton, E T; Blommaert, J A D L; Groenewegen, M A T; Van de Steene, G C; van Hoof, P A M

    2013-01-01

    We present an analysis of the far-infrared and submillimetre molecular emission line spectrum of the luminous M-supergiant VY CMa, observed with the SPIRE and PACS spectrometers aboard the Herschel Space Observatory. Over 260 emission lines were detected in the 190-650-micron SPIRE FTS spectra, with one-third of the observed lines being attributable to H2O. Other detected species include CO, 13CO, H2^18O, SiO, HCN, SO, SO2, CS, H2S, and NH3. Our model fits to the observed 12CO and 13CO line intensities yield a 12C/13C ratio of 5.6+-1.8, consistent with measurements of this ratio for other M supergiants, but significantly lower than previously estimated for VY CMa from observations of lower-J lines. The spectral line energy distribution for twenty SiO rotational lines shows two temperature components: a hot component at 1000 K, which we attribute to the stellar atmosphere and inner wind, plus a cooler ~200 K component, which we attribute to an origin in the outer circumstellar envelope. We fit the line fluxes ...

  11. Probing Dust Formation Around Evolved Stars with Near-Infrared Interferometry

    NASA Astrophysics Data System (ADS)

    Sargent, B.; Srinivasan, S.; Riebel, D.; Meixner, M.

    2014-09-01

    Near-infrared interferometry holds great promise for advancing our understanding of the formation of dust around evolved stars. For example, the Magdalena Ridge Observatory Interferometer (MROI), which will be an optical/near-infrared interferometer with down to submilliarcsecond resolution, includes studying stellar mass loss as being of interest to its Key Science Mission. With facilities like MROI, many questions relating to the formation of dust around evolved stars may be probed. How close to an evolved star such as an asymptotic giant branch (AGB) or red supergiant (RSG) star does a dust grain form? Over what temperature ranges will such dust form? How does dust formation temperature and distance from star change as a function of the dust composition (carbonaceous versus oxygen-rich)? What are the ranges of evolved star dust shell geometries, and does dust shell geometry for AGB and RSG stars correlate with dust composition, similar to the correlation seen for planetary nebula outflows? At what point does the AGB star become a post-AGB star, when dust formation ends and the dust shell detaches? Currently we are conducting studies of evolved star mass loss in the Large Magellanic Cloud using photometry from the Surveying the Agents of a Galaxy's Evolution (SAGE; PI: M. Meixner) Spitzer Space Telescope Legacy program. We model this mass loss using the radiative transfer program 2Dust to create our Grid of Red supergiant and Asymptotic giant branch ModelS (GRAMS). For simplicity, we assume spherical symmetry, but 2Dust does have the capability to model axisymmetric, non-spherically-symmetric dust shell geometries. 2Dust can also generate images of models at specified wavelengths. We discuss possible connections of our GRAMS modeling using 2Dust of SAGE data of evolved stars in the LMC and also other data on evolved stars in the Milky Way's Galactic Bulge to near-infrared interferometric studies of such stars. By understanding the origins of dust around evolved stars, we may learn more about the later parts of the life of stardust; e.g., its residence in the interstellar medium, its time spent in molecular clouds, and its inclusion into solid bodies in future planetary systems.

  12. Does the HMXB IGR J18214-1318 contain a black hole or neutron star?

    NASA Astrophysics Data System (ADS)

    Fornasini, Francesca; Tomsick, John; Bachetti, Matteo; Fuerst, Felix; Natalucci, Lorenzo; Pottschmidt, Katja; Smith, David M.; Wilms, Joern

    2015-01-01

    Measuring the fraction of high-mass X-ray binaries (HMXBs) that harbors a black hole (BH) rather than a neutron star (NS) can improve our understanding of the role of stellar winds and mass transfer in the evolution of massive stars and help constrain estimates of the numbers of NS/BH and BH/BH binaries in the Galaxy, potential sources of gravitational waves that could be detected by Advanced-LIGO. Some population synthesis studies have shown that BHs are likely to be rare among the Be HMXB population (Belczynki & Ziolkowski, 2009, ApJ, 707, 870) and the one BH Be HMXB that has been discovered has very low X-ray luminosity (Casares et al., 2014, Nature, 505, 378), indicating that BH Be HMXBs may exist but remain undetected by current surveys. However, since luminous supergiant BH HMXBs are known to exist (i.e. Cyg X-1), it is possible that some of the supergiant HMXBs discovered by INTEGRAL may host BHs. Therefore, we are trying to identify the nature of the compact objects in the IGR HMXBs by using NuSTAR and XMM-Newton to search for NS signatures in these systems: pulsations, cyclotron absorption lines, and exponential cutoffs with e-folding energies below ~20 keV. The absence of such features would make an HMXB an excellent black hole candidate. We present the spectral and timing properties of our first target, IGR J18214-1318.

  13. Hadron star models. [neutron stars

    NASA Technical Reports Server (NTRS)

    Cohen, J. M.; Boerner, G.

    1974-01-01

    The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as about 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.

  14. ON THE ORIGIN OF THE SUPERGIANT H I SHELL AND PUTATIVE COMPANION IN NGC 6822

    SciTech Connect

    Cannon, John M.; O'Leary, Erin M. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Weisz, Daniel R. [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85706 (United States); Bigiel, Frank [Institut fuer Theoretische Astrophysik, Universitaet Heidelberg, Albert-Ueberle-Str. 2, 69120 Heidelberg (Germany); Cole, Andrew A.; Walter, Fabian [School of Mathematics and Physics, University of Tasmania, Private Bag 37, Hobart 7001, Tasmania (Australia); De Blok, W.J.G., E-mail: jcannon@macalester.edu, E-mail: eoleary@macalester.edu, E-mail: dweisz@astro.washington.edu, E-mail: skillman@astro.umn.edu, E-mail: adolphin@raytheon.com, E-mail: bigiel@uni-heidelberg.de, E-mail: andrew.cole@utas.edu.au, E-mail: edeblok@ast.uct.ac.za, E-mail: walter@mpia.de [Department of Astronomy, University of Cape Town, Rondebosch 7700 (South Africa)

    2012-03-10

    We present new Hubble Space Telescope Advanced Camera for Surveys imaging of six positions spanning 5.8 kpc of the H I major axis of the Local Group dIrr NGC 6822, including both the putative companion galaxy and the large H I hole. The resulting deep color-magnitude diagrams show that NGC 6822 has formed >50% of its stars in the last {approx}5 Gyr. The star formation histories of all six positions are similar over the most recent 500 Myr, including low-level star formation throughout this interval and a weak increase in star formation rate during the most recent 50 Myr. Stellar feedback can create the giant H I hole, assuming that the lifetime of the structure is longer than 500 Myr; such long-lived structures have now been observed in multiple systems and may be the norm in galaxies with solid-body rotation. The old stellar populations (red giants and red clump stars) of the putative companion are consistent with those of the extended halo of NGC 6822; this argues against the interpretation of this structure as a bona fide interacting companion galaxy and against its being linked to the formation of the H I hole via an interaction. Since there is no evidence in the stellar population of a companion galaxy, the most likely explanation of the extended H I structure in NGC 6822 is a warped disk inclined to the line of sight.

  15. Periodogram and Wavelet Analysis of the Semi-Regular Variable Supergiant Y Cvn

    NASA Astrophysics Data System (ADS)

    Kudashkina, L. S.; Andronov, I. L.

    2010-12-01

    Time series analysis of the bright cold carbon SR-type star Y CVn was studied. The star belongs at a rare subclass "J" and has a separate asymmetric envelope. It is assumed that no "s" pro cess takes place in this star. Due to this, Y CVn may belong not to the AGB, but to the RGB stage, or to a stage of helium burning in a nucleus after a helium flash. The data from the published international databases of AFOEV (France) and VSOLJ (Japan) were studied using the periodogram and wavelet analysis and the "running sine" approximation. The cycle of variations is 267d (varying from 247d to 343d which are superimposed on 1000d -10000d waves.

  16. Gone without a bang: An archival HST survey for disappearing massive stars

    E-print Network

    Reynolds, Thomas; Gilmore, Gerard

    2015-01-01

    It has been argued that a substantial fraction of massive stars may end their lives without an optically bright supernova (SN), but rather collapse to form a black hole. Such an event would not be detected by current SN surveys, which are focused on finding bright transients. Kochanek et al. (2008) proposed a novel survey for such events, using repeated observations of nearby galaxies to search for the disappearance of a massive star. We present such a survey, using the first systematic analysis of archival Hubble Space Telescope images of nearby galaxies with the aim of identifying evolved massive stars which have disappeared, without an accompanying optically bright supernova. We consider a sample of 15 galaxies, with at least three epochs of Hubble Space Telescope imaging taken between 1994 and 2013. Within this data, we find one candidate which is consistent with a 25-30 solar mass yellow supergiant which has undergone an optically dark core-collapse.

  17. Radial velocities of late-type stars in the galactic center

    NASA Technical Reports Server (NTRS)

    Sellgren, K.; Hall, D. N. B.; Kleinmann, S. G.; Scoville, N. Z.

    1987-01-01

    The 2.0-2.4 micron spectra, with 120 km/s resolution, obtained for six late-type stars within 2 pc of the center of the Galaxy were used to derive spectral types and reddenings for these stars. The supergiant density in the Galactic center is lower than in previous determinations. The radial velocities of the Galactic center stars are measured to an uncertainty of 10 km/s using a cross-correlation technique. No correspondence is found between the stellar velocities and the Ne II velocities or other gas velocities observed along the same line of sight. No systematic rotation or ordered motion is seen in the stellar velocity distribution. The total mass distribution derived from the stellar velocity dispersion is compared to the stellar mass distribution derived from the 2 micron light and the total mass distribution derived from gas velocities.

  18. WFPC2 Observations of Massive and Compact Young Star Clusters in M31

    E-print Network

    Benjamin F. Williams; Paul W. Hodge

    2000-10-09

    We present color magnitude diagrams of four blue massive and compact star clusters in M31: G38, G44, G94, and G293. The diagrams of the four clusters reveal a well-populated upper main sequence and various numbers of supergiants. The U-B and B-V colors of the upper main sequence stars are used to determine reddening estimates of the different lines of sight in the M31 disk. Reddening values range from E(B-V) = 0.20 +/- 0.10 to 0.31 +/- 0.11. We statistically remove field stars on the basis of completeness, magnitude and color. Isochrone fits to the field-subtracted, reddening-corrected diagrams yield age estimates ranging from 63 +/- 15 Myr to 160 +/- 60 Myr. Implications for the recent evolution of the disk near NGC 206 are discussed.

  19. Stellar evolution in real time: The exciting star of the Stingray nebula

    NASA Astrophysics Data System (ADS)

    Reindl, N.; Rauch, T.; Parthasarathy, M.; Kruk, J. W.

    2014-04-01

    SAO 244567 (Hen 3-1357) was classified as a B-type supergiant in the 1970s. Within twenty years only, nebula emission lines became visible in the ultraviolet and optical wavelength range. Imaging in 1994 showed that SAO 244567 had become the central star of the bi-polar Stingray nebula. Prominent P-Cygni profiles that were exhibited in the first ultraviolet spectra from 1988 became weaker with time, but can still be seen in the FUSE spectrum in 2006. Recent observations show that the rapid evolution of this enigmatic star is still going on. For the first time, we performed a comprehensive spectral analysis by means of state-of-the NLTE models for static and expanding atmospheres based on all available spectra from 1988 until 2006. We determined the temporal evolution of its effective temperature, surface gravity, mass-loss rate, and photospheric abundances. We discuss possible single- and binary-star evolutionary scenarios.

  20. Quantitative studies of the Far-UV, UV and optical spectra of late O and early B-type supergiants in the Magellanic Clouds

    E-print Network

    C. J. Evans; P. A. Crowther; A. W. Fullerton; D. J. Hillier

    2004-04-12

    We present quantitative studies of 8 late O and early B-type supergiants in the Magellanic Clouds using far-ultraviolet FUSE, ultraviolet IUE/HST and optical VLT-UVES spectroscopy. Temperatures, mass-loss rates and CNO abundances are obtained using the non-LTE, spherical, line-blanketed model atmosphere code of Hillier & Miller (1998). We support recent results for lower temperatures of OB-type supergiants as a result of stellar winds and blanketing, which amounts to ~2000 K at B0 Ia. In general, H$\\alpha$ derived mass-loss rates are consistent with UV and far-UV spectroscopy, although from consideration of the SIV $\\lambda\\lambda$1063-1073 doublet, clumped winds are preferred over homogenous models. AV 235 (B0 Iaw) is a notable exception, which has an unusually strong H$\\alpha$ profile that is inconsistent with the other Balmer lines and UV wind diagnostics. We also derive CNO abundances for our sample, revealing substantial nitrogen enrichment, with carbon and oxygen depletion. Our results are supported by comparison with the Galactic supergiant HD 2905 (BC0.7 Ia) for which near-solar CNO abundances are obtained. This bolsters previous suggestions that ``normal'' OB-type supergiants exhibit atmospheric compositions indicative of partical CNO processing.

  1. R Coronae Borealis stars in the Galactic Bulge discovered by EROS-2

    E-print Network

    P. Tisserand; J. B. Marquette; P. R. Wood; E. Lesquoy; J. P. Beaulieu; A. Milsztajn; C. Hamadache; C. Afonso; J. N. Albert; J. Andersen; R. Ansari; E. Aubourg; P. Bareyre; X. Charlot; C. Coutures; R. Ferlet; P. Fouqué; J. F. Glicenstein; B. Goldman; A. Gould; M. Gros; J. Haissinski; J. de Kat; L. Le Guillou; C. Loup; C. Magneville; E. Maurice; A. Maury; M. Moniez; N. Palanque-Delabrouille; O. Perdereau; Y. Rahal; J. Rich; M. Spiro; A. Vidal-Madjar; S. Zylberajch

    2008-01-11

    Rare types of variable star may give unique insight into short-lived stages of stellar evolution. The systematic monitoring of millions of stars and advanced light curve analysis techniques of microlensing surveys make them ideal for discovering also such rare variable stars. One example is the R Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. We have conducted a systematic search of the EROS-2 database for the Galactic catalogue Bulge and spiral arms to find Galactic RCB stars. The light curves of $\\sim$100 million stars, monitored for 6.7 years (from July 1996 to February 2003), have been analysed to search for the main signature of RCB stars, large and rapid drops in luminosity. Follow-up spectroscopy has been used to confirm the photometric candidates. We have discovered 14 new RCB stars, all in the direction of the Galactic Bulge, bringing the total number of confirmed Galactic RCB stars to about 51. After reddening correction, the colours and absolute magnitudes of at least 9 of the stars are similar to those of Magellanic RCB stars. This suggests that these stars are in fact located in the Galactic Bulge, making them the first RCB stars discovered in the Bulge. The localisation of the 5 remaining RCBs is more uncertain: 4 are either located behind the Bulge at an estimated maximum distance of 14 kpc or have an unusual thick circumstellar shell; the other is a DY Per RCB which may be located in the Bulge, even if it is fainter than the known Magellanic DY Per. From the small scale height found using the 9 new Bulge RCBs, $61stars follow a disk-like distribution inside the Bulge.

  2. R Coronae Borealis stars in the Galactic bulge discovered by EROS-2

    NASA Astrophysics Data System (ADS)

    Tisserand, P.; Marquette, J. B.; Wood, P. R.; Lesquoy, É.; Beaulieu, J. P.; Milsztajn, A.; Hamadache, C.; Afonso, C.; Albert, J. N.; Andersen, J.; Ansari, R.; Aubourg, É.; Bareyre, P.; Charlot, X.; Coutures, C.; Ferlet, R.; Fouqué, P.; Glicenstein, J. F.; Goldman, B.; Gould, A.; Gros, M.; Haissinski, J.; de Kat, J.; Le Guillou, L.; Loup, C.; Magneville, C.; Maurice, É.; Maury, A.; Moniez, M.; Palanque-Delabrouille, N.; Perdereau, O.; Rahal, Y.; Rich, J.; Spiro, M.; Vidal-Madjar, A.; Zylberajch, S.

    2008-04-01

    Context: Rare types of variable stars may provide unique insight into short-lived stages of stellar evolution. The systematic monitoring of millions of stars and advanced light curve analysis techniques of microlensing surveys make them ideal for discovering such rare variable stars. One example is the R Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. Aims: We have conducted a systematic search of the EROS-2 database for the Galactic catalogue Bulge and spiral arms to find Galactic RCB stars. Methods: The light curves of ~100 million stars, monitored for 6.7 years (from July 1996 to February 2003), have been analysed to search for the main signature of RCB stars, large and rapid drops in luminosity. Follow-up spectroscopy has been used to confirm the photometric candidates. Results: We have discovered 14 new RCB stars, all in the direction of the Galactic Bulge, bringing the total number of confirmed Galactic RCB stars to about 51. Conclusions: After reddening correction, the colours and absolute magnitudes of at least 9 of the stars are similar to those of Magellanic RCB stars. This suggests that these stars are in fact located in the Galactic Bulge, making them the first RCB stars discovered in the Bulge. The localisation of the 5 remaining RCBs is more uncertain: 4 are either located behind the Bulge at an estimated maximum distance of 14 kpc or have an unusual thick circumstellar shell; the other is a DY Per RCB which may be located in the Bulge, even if it is fainter than the known Magellanic DY Per. From the small scale height found using the 9 new Bulge RCBs, 61stars follow a disk-like distribution inside the Bulge. Based on observations made with the CNRS/INSU MARLY telescope at the European Southern Observatory, La Silla, Chile.

  3. Sea Stars

    NSDL National Science Digital Library

    2012-07-28

    At first glance, starfish, more properly called sea stars, aren’t doing much of anything. In this video, Jonathan’s investigations reveal a slow-motion predator that hunts and attacks its prey. Traveling the world, Jonathan investigates sea stars from the tropics to the Antarctic and uses time-lapse photography to reveal an amazing complexity to the world of the sea star. Please see the accompanying study guide for educational objectives and discussion points.

  4. VARIABILITY OF LUMINOUS STARS IN THE LARGE MAGELLANIC CLOUD USING 10 YEARS OF ASAS DATA

    SciTech Connect

    Szczygiel, D. M.; Stanek, K. Z. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Bonanos, A. Z. [Institute of Astronomy and Astrophysics, National Observatory of Athens, I. Metaxa and Vas. Pavlou St., P. Penteli, 15236 Athens (Greece); Pojmanski, G.; Pilecki, B. [Warsaw University Astronomical Observatory, Al. Ujazdowskie 4, 00-478 Warsaw (Poland); Prieto, J. L., E-mail: szczygiel@astronomy.ohio-state.ed, E-mail: kstanek@astronomy.ohio-state.ed, E-mail: bonanos@astro.noa.g, E-mail: gp@astrouw.edu.p, E-mail: pilecki@astrouw.edu.p, E-mail: jose@obs.carnegiescience.ed [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

    2010-07-15

    Motivated by the detection of a recent outburst of the massive luminous blue variable LMC-R71, which reached an absolute magnitude M{sub V} = -9.3 mag, we undertook a systematic study of the optical variability of 1268 massive stars in the Large Magellanic Cloud, using a recent catalog by Bonanos et al. as the input. The ASAS All Star Catalog provided well-sampled light curves of these bright stars spanning 10 years. Combining the two catalogs resulted in 599 matches, on which we performed a variability search. We identified 117 variable stars, 38 of which were not known before, despite their brightness and large amplitude of variation. We found 13 periodic stars that we classify as eclipsing binary (EB) stars, 8 of which are newly discovered bright massive EBs composed of OB-type stars. The remaining 104 variables are either semi- or non-periodic, the majority (85) being red supergiants (RSGs). Most (26) of the newly discovered variables in this category are also RSGs with only three B and four O stars.

  5. FUSE Observations of the Wolf-Rayet Star WR136 and its Circumstellar Environment

    NASA Astrophysics Data System (ADS)

    Moore, B. D.; Dufour, R. J.; Aufdenberg, J. P.; Sankrit, R.

    2003-05-01

    The Wolf-Rayet star WR 136, classified as a WN6, is the central star powering the ring nebula NGC 6888. The material in the nebula was shed by the central star during its preceeding post-main sequence phase, presumably a red supergiant (RSG). Evolutionary models of massive stars suggest an initial mass for the progenitor star of ˜ 30 M? ; models for the WR star suggest a mass of 10 M? . Of the 20 M? shed, however, only one-quarter can be accounted for in the nebular shell. It has been suggested previously that this material is present as a rarified shell outside the visible nebula, with all of the material ionized by the considerable UV flux from the central star. Here we present FUSE observations of WR 136 (HD 192163). In addition to the expected stellar and wind features of the WR star (e.g., P Cygni profiles) there are narrow absorption lines from intervening material. We identify and separate the various components, focussing on those lines we associate with the proposed rarified circumstellar matter. Particular attention is paid to the C iii ? 977 line; in conjunction with a grid of photoionization models, we can infer a range of C/H for the rarified material, and by extension the ring nebula. This research was supported in part by NASA grant NAG5-12266 to Rice University.

  6. Testing the wind-shock paradigm for B-type star X-ray production with theta Carinae (B0.2V)

    NASA Astrophysics Data System (ADS)

    Petit, Veronique

    2013-09-01

    We propose a 125 ks observation of the B0.2V star theta Car, leveraging the unrivaled spectral resolution and sensitivity of the HETG to characterize the kinematics and energetics of the embedded wind shocks. This key star is at the transition between the efficient radiative cooling regime of O supergiants and the low-density, adiabatic regime of the early-B dwarfs. We will use the width the emission lines and the Mg XI f/i ratio to study its shock structure, and test whether an extension of the classical line-driving instabilities operating in O-star to a lower density regime can reproduce the observed X-ray properties of early B-stars. These observations will be essential to improve our classification of the many available broad-band X-ray spectra of B-stars from large cluster studies.

  7. Grids of evolutionary models of massive stars with mass loss and overshooting. Properties of Wolf-Rayet stars sensitive to overshooting

    NASA Astrophysics Data System (ADS)

    Maeder, A.; Meynet, G.

    In order to establish a reference grid of massive star models, the evolution of stars of initial mass 120, 85, 60, 40, 25, 20, and 15 solar masses is followed from the 0 age sequence to the end of the C-burning phase. An overshooting parameter which reproduces at best the observed main sequence (MS) width as found by Mermilliod and Maeder (1986) for young clusters and associations is chosen. The overshooting, with the extent and the mass loss rates adopted, produces an MS narrowing for O-stars and a large MS widening for early B-type stars. When compared to other sets of models, the results allow the identification of observable properties sensitive to overshooting for a given mass loss. These are the mapping of surface C/N and O/N ratios for stars in the upper HR diagram, the mass limits for red supergiants and WR stars, and the slope of the mass-luminosity relation for WR stars.

  8. Scintillating Stars

    NSDL National Science Digital Library

    Bob Riddle

    2003-02-01

    Often, a bright planet that is visible over the horizon will be mistaken for a star. Some believe they can tell the difference between a star and a planet because stars twinkle, or scintillate , and planets do not. In actuality however, both will twinkle because any light that passes through our atmosphere, whether it be reflected from a planet or generated by a star, will be interfered with by the atmospheric elements. This month's column sheds light on this "scintillating" subject and engages students in a research activity that revolves around the question: Is Pluto a planet?

  9. Neutron Stars

    NASA Technical Reports Server (NTRS)

    Cottam, J.

    2007-01-01

    Neutron stars were discovered almost 40 years ago, and yet many of their most fundamental properties remain mysteries. There have been many attempts to measure the mass and radius of a neutron star and thereby constrain the equation of state of the dense nuclear matter at their cores. These have been complicated by unknown parameters such as the source distance and burning fractions. A clean, straightforward way to access the neutron star parameters is with high-resolution spectroscopy. I will present the results of searches for gravitationally red-shifted absorption lines from the neutron star atmosphere using XMM-Newton and Chandra.

  10. The B Supergiant Components of the Double-lined Binary HD 1383

    NASA Astrophysics Data System (ADS)

    Boyajian, T. S.; Gies, D. R.; Helsel, M. E.; Kaye, A. B.; McSwain, M. V.; Riddle, R. L.; Wingert, D. W.

    2006-08-01

    We present new results from a study of high-quality red spectra of the massive binary star system HD 1383 (B0.5 Ib + B0.5 Ib). We determined radial velocities and revised orbital elements (P=20.28184+/-0.0002 days) and made Doppler tomographic reconstructions of the component spectra. A comparison of these with model spectra from non-LTE, line-blanketed atmospheres indicates that the two stars have almost identical masses (M2/M1=1.020+/-0.014), temperatures (Teff=28,000+/-1000 K), gravities (logg=3.25+/-0.25), and projected rotational velocities (Vsini<~30 km s-1). We investigate a number of constraints on the radii and masses of the stars based on the absence of eclipses, surface gravity, stellar wind terminal velocity, and probable location in the Perseus spiral arm of the Galaxy, and these indicate a range in probable radius and mass of R/Rsolar=14-20 and M/Msolar=16-35, respectively. These values are consistent with model evolutionary masses for single stars of this temperature and gravity. Both stars are much smaller than their respective Roche radii, so the system is probably in a precontact stage of evolution. A fit of the system's spectral energy distribution yields a reddening of E(B-V)=0.55+/-0.05 and a ratio of total-to-selective extinction of R=2.97+/-0.15. We find no evidence of H? emission from colliding stellar winds, which is probably the consequence of the low gas densities in the colliding winds zone.

  11. Modeling populations of rotationally mixed massive stars

    NASA Astrophysics Data System (ADS)

    Brott, I.

    2011-02-01

    Massive stars can be considered as cosmic engines. With their high luminosities, strong stellar winds and violent deaths they drive the evolution of galaxies through-out the history of the universe. Despite the importance of massive stars, their evolution is still poorly understood. Two major issues have plagued evolutionary models of massive stars until today: mixing and mass loss On the main sequence, the effects of mass loss remain limited in the considered mass and metallicity range, this thesis concentrates on the role of mixing in massive stars. This thesis approaches this problem just on the cross road between observations and simulations. The main question: Do evolutionary models of single stars, accounting for the effects of rotation, reproduce the observed properties of real stars. In particular we are interested if the evolutionary models can reproduce the surface abundance changes during the main-sequence phase. To constrain our models we build a population synthesis model for the sample of the VLT-FLAMES Survey of Massive stars, for which star-formation history and rotational velocity distribution are well constrained. We consider the four main regions of the Hunter diagram. Nitrogen un-enriched slow rotators and nitrogen enriched fast rotators that are predicted by theory. Nitrogen enriched slow rotators and nitrogen unenriched fast rotators that are not predicted by our model. We conclude that currently these comparisons are not sufficient to verify the theory of rotational mixing. Physical processes in addition to rotational mixing appear necessary to explain the stars in the later two regions. The chapters of this Thesis have been published in the following Journals: Ch. 2: ``Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones'', I. Brott, S. E. de Mink, M. Cantiello, N. Langer, A. de Koter, C. J. Evans, I. Hunter, C. Trundle, J.S. Vink submitted to Astronomy & Astrop hysics Ch. 3: ``The VLT-FLAMES Survey of Massive Stars: Rotation and Nitrogen Enrichment as the Key to Understanding Massive Star Evolution'', I.Hunter, I.Brott, D.J. Lennon, N. Langer, C. Trundle, A. de Koter, C.J. Evans and R.S.I. Ryans The Astrophysical Journal, 2008, 676, L29-L32 Ch. 4: ``The VLT-FLAMES Survey of Massive Stars: Constraints on Stellar Evolution from the Chemical Compositions of Rapidly Rotating Galactic and Magellanic Cloud B-type Stars '', I. Hunter, I. Brott, N. Langer, D.J. Lennon, P.L. Dufton, I.D. Howarth R.S.I. Ryan, C. Trundle, C. Evans, A. de Koter and S.J. Smartt Published in Astronomy & Astropysics, 2009, 496, 841- 853 Ch. 5: ``Rotating Massive Main-Sequence Stars II: Simulating a Population of LMC early B-type Stars as a Test of Rotational Mixing '', I. Brott, C. J. Evans, I. Hunter, A. de Koter, N. Langer, P. L. Dufton, M. Cantiello, C. Trundle, D. J. Lennon, S.E. de Mink, S.-C. Yoon, P. Anders submitted to Astronomy & Astrophysics Ch 6: ``The Nature of B Supergiants: Clues From a Steep Drop in Rotation Rates at 22 000 K - The possibility of Bi-stability braking'', Jorick S. Vink, I. Brott, G. Graefener, N. Langer, A. de Koter, D.J. Lennon Astronomy & Astrophysics, 2010, 512, L7

  12. STAR FORMATION HISTORY OF A YOUNG SUPER-STAR CLUSTER IN NGC 4038/39: DIRECT DETECTION OF LOW-MASS PRE-MAIN SEQUENCE STARS

    SciTech Connect

    Greissl, Julia; Meyer, Michael R. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Christopher, Micol H.; Scoville, Nick Z., E-mail: jgreissl@as.arizona.ed [California Institute of Technology, Pasadena, CA 91125 (United States)

    2010-02-20

    We present an analysis of the near-infrared spectrum of a young massive star cluster in the overlap region of the interacting galaxies NGC 4038/39 using population synthesis models. Our goal is to model the cluster population as well as provide rough constraints on its initial mass function (IMF). The cluster shows signs of youth, such as thermal radio emission and strong hydrogen emission lines in the near-infrared. Late-type absorption lines are also present which are indicative of late-type stars in the cluster. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence (PMS) stars or red supergiants alone. Thus, we interpret the spectrum as a superposition of two star clusters of different ages, which is feasible since the 1'' spectrum encompasses a physical region of {approx}90 pc and radii of super-star clusters (SSCs) are generally measured to be a few parsecs. One cluster is young (<= 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr-18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. Both are required to accurately reproduce the near-infrared spectrum of the object. Thus, we have directly detected PMS objects in an unresolved SSC for the first time using a combination of population synthesis models and PMS tracks. This analysis serves as a testbed of our technique to constrain the low-mass IMF in young SSCs as well as an exploration of the star formation history of young UC H II regions.

  13. Near-IR spectroscopic ages of massive star clusters in M82

    E-print Network

    A. Lançon; J. S. Gallagher III; M. Mouhcine; L. J. Smith; D. Ladjal; R. de Grijs

    2008-12-29

    Like other starburst galaxies, M82 hosts compact, massive young star clusters that are interesting both in their own right and as benchmarks for population synthesis models. Can spectral synthesis models at resolutions around 1000 adequately reproduce the near-IR spectral features and the energy distribution of these clusters between 0.8 and 2.4 microns? How do the derived cluster properties compare with previous results from optical studies? We analyse the spectra of 5 massive clusters in M82, using data acquired with the spectrograph SpeX on the InfraRed Telescope Facility (NASA/IRTF) and a new population synthesis tool with a highly improved near-IR extension, based on a recent collection of empirical and theoretical spectra of red supergiant stars. We obtain excellent fits across the near-IR with models at quasi-solar metallicity and a solar neighbourhood extinction law. Spectroscopy breaks a strong degeneracy between age and extinction in the near-IR colours in the red supergiant-dominated phase of evolution. The estimated near-IR ages cluster between 9 and 30 Myr, i.e. the ages at which the molecular bands due to luminous red supergiants are strongest in the current models. They do not always agree with optical spectroscopic ages. Adding optical data sometimes leads to the rejection of the solar neighbourhood extinction law. This is not surprising considering small-scale structure around the clusters, but it has no significant effect on the near-IR based spectroscopic ages. [abridged

  14. Massive stars in the giant molecular cloud G23.3-0.3 and W41

    NASA Astrophysics Data System (ADS)

    Messineo, Maria; Menten, Karl M.; Figer, Donald F.; Davies, Ben; Clark, J. Simon; Ivanov, Valentin D.; Kudritzki, Rolf-Peter; Rich, R. Michael; MacKenty, John W.; Trombley, Christine

    2014-09-01

    Context. Young massive stars and stellar clusters continuously form in the Galactic disk, generating new Hii regions within their natal giant molecular clouds and subsequently enriching the interstellar medium via their winds and supernovae. Aims: Massive stars are among the brightest infrared stars in such regions; their identification permits the characterisation of the star formation history of the associated cloud as well as constraining the location of stellar aggregates and hence their occurrence as a function of global environment. Methods: We present a stellar spectroscopic survey in the direction of the giant molecular cloud G23.3-0.3. This complex is located at a distance of ~4-5 kpc, and consists of several Hii regions and supernova remnants. Results: We discovered 11 OfK+ stars, one candidate luminous blue variable, several OB stars, and candidate red supergiants. Stars with K-band extinction from ~1.3-1.9 mag appear to be associated with the GMC G23.3-0.3; O and B-types satisfying this criterion have spectrophotometric distances consistent with that of the giant molecular cloud. Combining near-IR spectroscopic and photometric data allowed us to characterize the multiple sites of star formation within it. The O-type stars have masses from ~25-45 M?, and ages of 5-8 Myr. Two new red supergiants were detected with interstellar extinction typical of the cloud; along with the two RSGs within the cluster GLIMPSE9, they trace an older burst with an age of 20-30 Myr. Massive stars were also detected in the core of three supernova remnants - W41, G22.7-0.2, and G22.7583-0.4917. Conclusions: A large population of massive stars appears associated with the GMC G23.3-0.3, with the properties inferred for them indicative of an extended history of stars formation. Based on observations collected at the European Southern Observatory (ESO Programmes 084.D-0769, 085.D-019, 087.D-09609).MM is currently employed by the MPIfR. This works was partially carried out at RIT (2009), at ESA (2010), and at the MPIfR.Table 4 and Appendix C are available in electronic form at http://www.aanda.org

  15. On the reality of a boundary in the H-R diagram between late-type stars with and without high temperature outer atmospheres

    NASA Technical Reports Server (NTRS)

    Simon, T.; Linsky, J. L.; Stencel, R. E.

    1982-01-01

    The Linsky-Haisch hypothesis (1979) that a boundary exists in the H-R diagram separating yellow giants from red giants and supergiants is tested. IUE 1150-2000 A low-resolution spectra of 10 stars chosen to constitute a reverse bias sample are presented and discussed. Despite the bias, weak C IV emission indicative of high-temperature plasma was observed in four of the six stars chosen to be probable red stars, while no C IV emission was detected in the four stars chosen to be yellows. In a second test using the entire sample of 39 stars, nearly all of the yellow giants and supergiants were found to have an emission feature at 1549 A, which is attributed to C IV. The large magnitude dispersion could be attributed to temporal or spatial variability, differing magnetic field strengths and geometries, or age-related effects during post-main-sequence evolution. It is concluded that the Linsky-Haisch transition region boundary is a real phenomenon.

  16. PTF11iqb: cool supergiant mass-loss that bridges the gap between Type IIn and normal supernovae

    NASA Astrophysics Data System (ADS)

    Smith, Nathan; Mauerhan, Jon C.; Cenko, S. Bradley; Kasliwal, Mansi M.; Silverman, Jeffrey M.; Filippenko, Alexei V.; Gal-Yam, Avishay; Clubb, Kelsey I.; Graham, Melissa L.; Leonard, Douglas C.; Horst, J. Chuck; Williams, G. Grant; Andrews, Jennifer E.; Kulkarni, Shrinivas R.; Nugent, Peter; Sullivan, Mark; Maguire, Kate; Xu, Dong; Ben-Ami, Sagi

    2015-05-01

    The supernova (SN) PTF11iqb was initially classified as a Type IIn event caught very early after explosion. It showed narrow Wolf-Rayet (WR) spectral features on day 2 (as in SN 1998S and SN 2013cu), but the narrow emission weakened quickly and the spectrum morphed to resemble Types II-L and II-P. At late times, H? exhibited a complex, multipeaked profile reminiscent of SN 1998S. In terms of spectroscopic evolution, we find that PTF11iqb was a near twin of SN 1998S, although with somewhat weaker interaction with circumstellar material (CSM) at early times, and stronger interaction at late times. We interpret the spectral changes as caused by early interaction with asymmetric CSM that is quickly (by day 20) enveloped by the expanding SN ejecta photosphere, but then revealed again after the end of the plateau when the photosphere recedes. The light curve can be matched with a simple model for CSM interaction (with a mass-loss rate of roughly 10-4 M? yr-1) added to the light curve of a normal SN II-P. The underlying plateau requires a progenitor with an extended hydrogen envelope like a red supergiant at the moment of explosion, consistent with the slow wind speed (<80 km s-1) inferred from narrow H? emission. The cool supergiant progenitor is significant because PTF11iqb showed WR features in its early spectrum - meaning that the presence of such WR features does not necessarily indicate a WR-like progenitor. Overall, PTF11iqb bridges SNe IIn with weaker pre-SN mass-loss seen in SNe II-L and II-P, implying a continuum between these types.

  17. SN 2009ip and SN 2010mc: core-collapse Type IIn supernovae arising from blue supergiants

    NASA Astrophysics Data System (ADS)

    Smith, Nathan; Mauerhan, Jon C.; Prieto, Jose L.

    2014-02-01

    The recent supernova (SN) known as SN 2009ip had dramatic precursor eruptions followed by an even brighter explosion in 2012. Its pre-2012 observations make it the best documented SN progenitor in history, but have fuelled debate about the nature of its 2012 explosion - whether it was a true SN or some type of violent non-terminal event. Both could power shock interaction with circumstellar material (CSM), but only a core-collapse SN provides a self-consistent explanation. The persistent broad emission lines in the spectrum require a relatively large ejecta mass, and a corresponding kinetic energy of at least 1051 erg, while the faint 2012a event is consistent with published models of core-collapse SNe from compact (˜60 R?) blue supergiants. The light curves of SN 2009ip and another Type IIn, SN 2010mc, were nearly identical; we demonstrate that their spectra match as well, and that both are standard SNe IIn. Our observations contradict the recent claim that the late-time spectrum of SN 2009ip is returning to its progenitor's luminous blue variable-like state, and we show the that late-time spectra of SN 2009ip closely resemble the spectra of SN 1987A. Moreover, SN 2009ip's changing H? equivalent width after explosion matches behaviour typically seen in core-collapse SNe IIn. Several key facts about SN 2009ip and SN 2010mc argue strongly in favour of a core-collapse interpretation, and make a non-terminal 1050 erg event implausible. The most straightforward and self-consistent interpretation is that SN 2009ip was an initially faint core-collapse explosion of a blue supergiant that produced about half as much 56Ni as SN 1987A, with most of the peak luminosity from CSM interaction.

  18. DISTANCE AND PROPER MOTION MEASUREMENT OF THE RED SUPERGIANT, S PERSEI, WITH VLBI H{sub 2}O MASER ASTROMETRY

    SciTech Connect

    Asaki, Y. [Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Chuou, Sagamihara, Kanagawa 252-5210 (Japan); Deguchi, S. [Nobeyama Radio Observatory, Nobeyama, Minamimaki, Minamisaku 384-1305 (Japan); Imai, H. [Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065 (Japan); Hachisuka, K. [Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (China); Miyoshi, M. [Division of Radio Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Honma, M., E-mail: asaki@vsop.isas.jaxa.j, E-mail: deguchi@nro.nao.ac.j, E-mail: hiroimai@sci.kagoshima-u.ac.j, E-mail: khachi@shao.ac.c, E-mail: makoto.miyoshi@nao.ac.j, E-mail: mareki.honma@nao.ac.j [Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2010-09-20

    We have conducted Very Long Baseline Array phase-referencing monitoring of H{sub 2}O masers around the red supergiant, S Persei, for six years. We have fitted maser motions to a simple expanding-shell model with a common annual parallax and stellar proper motion, and obtained the annual parallax as 0.413 {+-} 0.017 mas and the stellar proper motion as (-0.49 {+-} 0.23 mas yr{sup -1}, -1.19 {+-} 0.20 mas yr{sup -1}) in right ascension and declination, respectively. The obtained annual parallax corresponds to the trigonometric distance of 2.42{sup +0.11}{sub -0.09} kpc. Assuming a Galactocentric distance of the Sun of 8.5 kpc, the circular rotational velocity of the local standard of rest at a distance of the Sun of 220 km s{sup -1}, and a flat Galactic rotation curve, S Persei is suggested to have a non-circular motion deviating from the Galactic circular rotation for 15 km s{sup -1}, which is mainly dominated by the anti-rotation direction component of 12.9 {+-} 2.9 km s{sup -1}. This red supergiant is thought to belong to the OB association, Per OB1, so that this non-circular motion is representative of a motion of the OB association in the Milky Way. This non-circular motion is somewhat larger than that explained by the standard density-wave theory for a spiral galaxy and is attributed to either a cluster shuffling of the OB association, or to non-linear interactions between non-stationary spiral arms and multi-phase interstellar media. The latter comes from a new view of a spiral arm formation in the Milky Way suggested by recent large N-body/smoothed particle hydrodynamics numerical simulations.

  19. Radio stars.

    PubMed

    Hjellming, R M; Wade, C M

    1971-09-17

    Up to the present time six classes of radio stars have been established. The signals are almost always very faint and drastically variable. Hence their discovery has owed as much to serendipity as to the highly sophisticated equipment and techniques that have been used. When the variations are regular, as with the pulsars, this characteristic can be exploited very successfully in the search for new objects as well as in the detailed study of those that are already known. The detection of the most erratically variable radio stars, the flare stars and the x-ray stars, is primarily a matter of luck and patience. In the case of the novas, one at least knows where and oughly when to look for radio emission. A very sensitive interferometer is clearly the best instrument to use in the initial detection of a radio star. The fact that weak background sources are frequently present makes it essential to prove that the position of a radio source agrees with that of a star to within a few arc seconds. The potential of radio astronomy for the study of radio stars will not be realized until more powerful instruments than those that are available today can be utilized. So far, we have been able to see only the most luminous of the radio stars. PMID:17836594

  20. Clues to the Evolution of the R Coronae Borealis Stars from their Unique 16O/18O ratios

    NASA Astrophysics Data System (ADS)

    Clayton, Geoffrey C.; Montiel, Edward J.; Geballe, Thomas R.; Welch, Douglas L.; Tisserand, Patrick

    2014-06-01

    We report new spectroscopic observations of the CO bands near 2.3 micron in order to measure the 16O/18O isotopic ratio in the R Coronae Borealis (RCB) stars using IRTF/SpeX. These observations of ten additional stars confirm the remarkable discovery made a few years ago that the hydrogen-deficient carbon (HdC) and RCB stars have 16O/18O ratios that are close to and in some cases less than unity, values that are orders of magnitude smaller than measured in other stars (the Solar value is 500). The RCB stars are a small group of carbon-rich supergiants. Only about 100 RCB stars are known in the Galaxy. Their defining characteristics are hydrogen deficiency and unusual variability - RCB stars undergo massive declines of up to 8 mag due to the formation of carbon dust at irregular intervals. The six known HdC stars are very similar to the RCB stars spectroscopically, but do not show declines or IR excesses. Two scenarios have been proposed for the origin of an RCB star: the double degenerate and the final helium-shell flash models. The former involves the merger of a CO- and a He-white dwarf. In the latter, a star evolving into a planetary nebula central star expands to supergiant size by a final, helium-shell flash. Greatly enhanced 18O is evident in every HdC and RCB we have measured that is cool enough to have detectable CO bands. This discovery is important evidence to help distinguish between the proposed evolutionary pathways of HdC and RCB stars. No overproduction of 18O is expected in a final flash, so we are investigating the merger scenario. We are working to reproduce the observed 16O/18O ratios by performing hydrodynamical simulations of the merger of CO- and He-WDs to investigate the formation of RCB stars. We are also using the MESA stellar evolution and NuGrid nucleosynthesis codes to construct post-merger 1D spherical models and follow their evolution into the region of the HR diagram where RCB stars are located.

  1. The Brief Lives of Massive Stars as Witnessed by Interferometry

    NASA Astrophysics Data System (ADS)

    Hummel, C.

    2014-09-01

    Massive stars present the newest and perhaps most challenging opportunity for long baseline interferometry to excel. Large distances require high angular resolution both to study the means of accreting enough mass in a short time and to split new-born multiples into their components for the determination of their fundamental parameters. Dust obscuration of young stellar objects requires interferometry in the mid-infrared, while post-main-sequence stellar phases require high-precision measurements to challenge stellar evolution models. I will summarize my recent work on modeling mid-IR observations of a massive YSO in NGC 3603, and on the derivation of masses and luminosities of a massive hot supergiant star in another star-forming region in Orion. Challenges presented themselves when constraining the geometry of a hypothetical accretion disk as well as obtaining spectroscopy matching the interferometric precision when working with only a few photospheric lines. As a rapidly evolving application of interferometry, massive stars have a bright future.

  2. The peculiar early-type emission line supergiant S 18/SMC - An optical and ultraviolet study

    NASA Technical Reports Server (NTRS)

    Shore, S. N.; Sanduleak, N.; Allen, D. A.

    1987-01-01

    Spectroscopic observations of S 18/SMC, obtained in the visible at CTIO, the AAT, and ESO and in the UV with the IUE SWP and LWR instruments during 1978-1983, are reported. The data are presented in tables and spectra and characterized in detail. The variability of the object in He II, C IV, N IV, N V, and Si IV and the lack of detectable photometric variation between 120 and 1000 nm are discussed in terms of a stellar-envelope model with mass-loss rate greater than or equal to 0.00001 solar mass/yr and N abundance 3-5 times the solar value, corresponding to a transitional phase between extreme mass loss (near the Humphrey-Davidson limit) and the presupernova stage. The FUV flux is tentatively attributed to an extremely hot He-star or neutron-star companion.

  3. Star Journey

    NSDL National Science Digital Library

    Carolyn Anderson

    This National Geographic web-site contains information about the Hubble Space Telescope (HST) along with a star chart and facts about objects in the night sky. The HST section contains details about the building and structure of the HST, how it captures light, positioning the HST to targets, instruments used to record and measure infrared through UV wavelengths, how the HST is powered and communicates with the Earth. Star Attractions discusses properties of constellations, the Milky Way galaxy, other galaxies, star clusters and nebulae. This information is then put together on the National Geographic Star Chart. This chart contains maps of the heavens for the northern and southern hemispheres. The chart contains constellation names, location of stars and other objects, and links to HST images of various galaxies and objects on the chart with names and detailed descriptions. There is an image index to find HST images from the site, details about chart symbol meanings, and links for more information.

  4. Star dust.

    PubMed

    Ney, E P

    1977-02-11

    Infrared astronomy has shown that certain classes of stars are abundant producers of refractory grains, which condense in their atmospheres and are blown into interstellar space by the radiation pressure of these stars. Metallic silicates of the kind that produce terrestrial planets are injected by the oxygen-rich stars and carbon and its refractories by carbon stars. Much of the interstellar dust may be produced by this mechanism. A number of "infrared stars" are completely surrounded by their own dust, and a few of these exhibit a unique morphology that suggests the formation of a planetary system or a stage in the evolution of a planetary nebula. Certain novae also condense grains, which are blown out in their shells. In our own solar system, comets are found to contain the same silicates that are present elsewhere in the galaxy, suggesting that these constituents were present in the primeval solar nebula. PMID:17732279

  5. Mass-loss predictions for O and B stars as a function of metallicity

    E-print Network

    Jorick S. Vink; Alex de Koter; Henny J. G. L. M. Lamers

    2001-01-29

    We have calculated a grid of massive star wind models and mass-loss rates for a wide range of metal abundances between 1/100 and 10 Z/Zsun. The calculation of this grid completes the Vink et al. (2000) mass-loss recipe with an additional parameter Z. We have found that the exponent of the power law dependence of mass loss vs. metallicity is constant in the range between 1/30 and 3 Z/Zsun. The mass-loss rate scales as Mdot \\propto Z^0.85 Vinf^p with p = -1.23 for stars with Teff \\ga 25000 K, and p = -1.60 for the B supergiants with Teff \\la 25000 K. Taking also into account the metallicity dependence of Vinf, using the power law dependence Vinf \\propto Z^0.13 from Leitherer et al. (1992), the overall result of mass loss as a function of metallicity can be represented by Mdot \\propto Z^0.69 for stars with Teff \\ga 25000 K, and Mdot \\propto Z^0.64 for B supergiants with Teff \\la 25000 K. Our mass-loss predictions are successful in explaining the observed mass-loss rates for Galactic and Small Magellanic Cloud O-type stars, as well as in predicting the observed Galactic bi-stability jump. Hence, we believe that our predictions are reliable and suggest that our mass-loss recipe be used in future evolutionary calculations of massive stars at different metal abundance. A computer routine to calculate mass loss is publicly available.

  6. HUBBLE SPACE TELESCOPE CAPTURES FIRST DIRECT IMAGE OF A STAR

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This is the first direct image of a star other than the Sun, made with NASA's Hubble Space Telescope. Called Alpha Orionis, or Betelgeuse, it is a red supergiant star marking the shoulder of the winter constellation Orion the Hunter (diagram at right). The Hubble image reveals a huge ultraviolet atmosphere with a mysterious hot spot on the stellar behemoth's surface. The enormous bright spot, more than ten times the diameter of Earth, is at least 2,000 Kelvin degrees hotter than the surface of the star. The image suggests that a totally new physical phenomenon may be affecting the atmospheres of some stars. Follow-up observations will be needed to help astronomers understand whether the spot is linked to oscillations previously detected in the giant star, or whether it moves systematically across the star's surface under the grip of powerful magnetic fields. The observations were made by Andrea Dupree of the Harvard- Smithsonian Center for Astrophysics in Cambridge, MA, and Ronald Gilliland of the Space Telescope Science Institute in Baltimore, MD, who announced their discovery today at the 187th meeting of the American Astronomical Society in San Antonio, Texas. The image was taken in ultraviolet light with the Faint Object Camera on March 3, 1995. Hubble can resolve the star even though the apparent size is 20,000 times smaller than the width of the full Moon -- roughly equivalent to being able to resolve a car's headlights at a distance of 6,000 miles. Betelgeuse is so huge that, if it replaced the Sun at the center of our Solar System, its outer atmosphere would extend past the orbit of Jupiter (scale at lower left). Credit: Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA and ESA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo.

  7. Theory of winds in late-type evolved and pre-main-sequence stars

    NASA Technical Reports Server (NTRS)

    Macgregor, K. B.

    1983-01-01

    Recent observational results confirm that many of the physical processes which are known to occur in the Sun also occur among late-type stars in general. One such process is the continuous loss of mass from a star in the form of a wind. There now exists an abundance of either direct or circumstantial evidence which suggests that most (if not all) stars in the cool portion of the HR diagram possess winds. An attempt is made to assess the current state of theoretical understanding of mass loss from two distinctly different classes of late-type stars: the post-main-sequence giant/supergiant stars and the pre-main-sequence T Tauri stars. Toward this end, the observationally inferred properties of the wind associated with each of the two stellar classes under consideration are summarized and compared against the predictions of existing theoretical models. Although considerable progress has been made in attempting to identify the mechanisms responsible for mass loss from cool stars, many fundamental problems remain to be solved.

  8. BLUE LUMINOUS STARS IN NEARBY GALAXIES-UIT 005: A POSSIBLE LINK TO THE LUMINOUS BLUE VARIABLE STAGE

    SciTech Connect

    Urbaneja, M. A. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Herrero, A. [Instituto de Astrofisica de Canarias, VIa Lactea S/N, E-38200 La Laguna, Canary Islands (Spain); Lennon, D. J. [ESA, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Corral, L. J. [Instituto de AstronomIa y MetereologIa, Universidad de Guadalajara, Avda. Vallarta 2602, Guadalajara, Jalisco, C.P. 44130 (Mexico); Meynet, G. [Geneva Observatory, Ch. des Mailettes 51, 1290 Sauverny (Switzerland)

    2011-07-01

    A detailed study of the blue supergiant UIT 005 (B2-2.5Ia{sup +}) in M 33 is presented. The results of our quantitative spectral analysis indicate that the star is a very luminous (log L/L{sub sun} {approx} 5.9 dex) and massive (M {approx} 50 M{sub sun}) object, showing a very high nitrogen-to-oxygen ratio in its surface (N/O{approx}8, by mass). Based on the derived Mg and Si abundances, we argue that this high N/O ratio cannot be the result of an initial low O content due to its location on the disk of M 33, a galaxy known to present a steep metallicity gradient. In combination with the He abundance, the most plausible interpretation is that UIT 005 is in an advanced stage of evolution, showing in its surface N enrichment and O depletion resulting from mixing with CNO processed material from the stellar interior. A comparison with the predictions of current stellar evolutionary models indicates that there are significant discrepancies, in particular with regard to the degree of chemical processing, with the models predicting a much lower degree of O depletion than observed. At the same time, the mass-loss rate derived in our analysis is an order of magnitude lower than the values considered in the evolutionary calculations. Based on a study of the surrounding stellar population and the nearby cluster, NGC 588, using Hubble Space Telescope/WFPC2 photometry, we suggest that UIT 005 could be in fact a runaway star from this cluster. Regardless of its origin, the derived parameters place the star in a region of the Hertzsprung-Russell diagram where luminous blue variables (LBVs) are usually found, but we find no evidence supporting photometric or spectroscopic variability, except for small H{alpha} changes, otherwise observed in Galactic B-type supergiants. Whether UIT 005 is an LBV in a dormant state or a regular blue supergiant could not be discerned in this study. Subsequent monitoring would help us to improve our knowledge of the more massive stars, bridging the gap between regular and more exotic blue supergiants.

  9. New Magellanic Cloud R Coronae Borealis and DY Per type stars from the EROS-2 database: the connection between RCBs, DYPers and ordinary carbon stars

    E-print Network

    Tisserand, P; Marquette, J B; Afonso, C; Albert, J N; Andersen, J; Ansari, R; Aubourg, E; Bareyre, P; Beaulieu, J P; Charlot, X; Coutures, C; Ferlet, R; Fouqué, P; Glicenstein, J F; Goldman, B; Gould, A; Gros, M; De Kat, J; Lesquoy, E; Loup, C; Magneville, C; Maurice, E; Maury, A; Milsztajn, A; Moniez, M; Palanque-Delabrouille, Nathalie; Perdereau, O; Rich, J; Schwemling, P; Spiro, M; Vidal-Madjar, A

    2009-01-01

    R Coronae Borealis stars (RCB) are a rare type of evolved carbon-rich supergiant stars that are increasingly thought to result from the merger of two white dwarfs, called the Double degenerate scenario. This scenario is also studied as a source, at higher mass, of type Ia Supernovae (SnIa) explosions. Therefore a better understanding of RCBs composition would help to constrain simulations of such events. We searched for and studied RCB stars in the EROS Magellanic Clouds database. We also extended our research to DY Per type stars (DYPers) that are expected to be cooler RCBs (T~3500 K) and much more numerous than their hotter counterparts. The light curves of ~70 millions stars have been analysed to search for the main signature of RCBs and DYPers: a large drop in luminosity. Follow-up optical spectroscopy was used to confirm each photometric candidate found. We have discovered and confirmed 6 new Magellanic Cloud RCB stars and 7 new DYPers, but also listed new candidates: 3 RCBs and 14 DYPers. We estimated a...

  10. Sublimating comets as the source of nucleation seeds for grain condensation in the gas outflow from AGB stars

    NASA Technical Reports Server (NTRS)

    Whitmire, D. P.; Matese, John J.; Reynolds, R. T.

    1989-01-01

    A growing amount of observational and theoretical evidence suggests that most main sequence stars are surrounded by disks of cometary material. The dust production by comets in such disks is investigated when the central stars evolve up the red giant and asymptotic giant branch (AGB). Once released, the dust is ablated and accelerated by the gas outflow and the fragments become the seeds necessary for condensation of the gas. The origin of the requisite seeds has presented a well known problem for classical nucleation theory. This model is consistent with the dust production observed in M giants and supergiants (which have increasing luminosities) and the fact that earlier supergiants and most WR stars (whose luminosities are unchanging) do not have significant dust clouds even though they have significant stellar winds. Another consequence of the model is that the spatial distribution of the dust does not, in general, coincide with that of the gas outflow, in contrast to the conventional condensation model. A further prediction is that the condensation radius is greater that that predicted by conventional theory which is in agreement with IR interferometry measurements of alpha-Ori.

  11. SN 2011hs: a fast and faint Type IIb supernova from a supergiant progenitor

    NASA Astrophysics Data System (ADS)

    Bufano, F.; Pignata, G.; Bersten, M.; Mazzali, P. A.; Ryder, S. D.; Margutti, R.; Milisavljevic, D.; Morelli, L.; Benetti, S.; Cappellaro, E.; Gonzalez-Gaitan, S.; Romero-Cañizales, C.; Stritzinger, M.; Walker, E. S.; Anderson, J. P.; Contreras, C.; de Jaeger, T.; Förster, F.; Gutierrez, C.; Hamuy, M.; Hsiao, E.; Morrell, N.; Olivares E., F.; Paillas, E.; Parker, S.; Pian, E.; Pickering, T. E.; Sanders, N.; Stockdale, C.; Turatto, M.; Valenti, S.; Fesen, R. A.; Maza, J.; Nomoto, K.; Phillips, M. M.; Soderberg, A.

    2014-04-01

    Observations spanning a large wavelength range, from X-ray to radio, of the Type IIb supernova (SN) 2011hs are presented, covering its evolution during the first year after explosion. The optical light curve presents a narrower shape and a fainter luminosity at peak than previously observed for Type IIb SNe. High expansion velocities are measured from the broad absorption H I and He I lines. From the comparison of the bolometric light curve and the time evolution of the photospheric velocities with hydrodynamical models, we found that SN 2011hs is consistent with the explosion of a 3-4 M? He-core progenitor star, corresponding to a main-sequence mass of 12-15 M?, that ejected a mass of 56Ni of about 0.04 M?, with an energy of E = 8.5 × 1050 ERG. Such a low-mass progenitor scenario is in full agreement with the modelling of the nebular spectrum taken at ˜215 d from maximum. From the modelling of the adiabatic cooling phase, we infer a progenitor radius of ?500-600 R?, clearly pointing to an extended progenitor star. The radio light curve of SN 2011hs yields a peak luminosity similar to that of SN 1993J, but with a higher mass-loss rate and a wind density possibly more similar to that of SN 2001ig. Although no significant deviations from a smooth decline have been found in the radio light curves, we cannot rule out the presence of a binary companion star.

  12. X-Rays from Hybrid Stars

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas R.

    2005-01-01

    The late-type giants and supergiants of the ``hybrid chromosphere'' class display signatures of cool (T<~2×104 K) winds together with hot emission lines from species like C IV (T~105 K). A survey of such stars by Reimers et al. using ROSAT reported numerous X-ray detections (T~106 K), strengthening the (then heretical) idea that hot coronae and cool winds can coexist in luminous giants. However, several of the candidate sources were offset from the predicted stellar coordinates, calling into question the identifications. In an effort to secure better knowledge of the X-ray luminosities of the hybrids, the ROSAT fields from the Reimers et al. survey were reexamined, exploiting the USNO-A2.0 astrometric catalog to register the pointings to a few arcseconds accuracy. On the basis of positional mismatches, at least two of the previously reported detections of key hybrid stars-? Dra (K5 III) and ? Aqr (G0 Ib)-must be rejected. The new X-ray upper limits for these stars, combined with the remaining candidate detections (and nondetections) from the original survey, place the hybrids into the same ``X-ray deficient'' category as the ``noncoronal'' red giants like Arcturus (? Boo: K1.5 III) and Aldebaran (? Tau: K5 III). A few of the hybrid X-ray sources are exceptional, however. The archetype ? TrA (K2 II-III), in particular, is securely detected in terms of positional coincidence, but its anomalous, contradictory coronal properties suggest that an unseen companion-a young hyperactive G dwarf-might dominate the X-ray emission.

  13. Stars equilibrium

    NSDL National Science Digital Library

    University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)

    2003-01-01

    What causes the fusion reaction in a star's core? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to processes inside a star. Students read about the equilibrium process in a star, in which outward gas pressure equals inward gravitational pressure. Then, an interactive lab activity offers students the opportunity to predict temperature, pressure, and gravity changes that occur during equilibrium. The chemical reactions of the fusion process are presented, and more specific detailed reactions are available in a pop-up box. Student practice quizzes about the equilibrium process and pressure and gravity interactions inside the star are included, as are answers. Copyright 2005 Eisenhower National Clearinghouse

  14. Neutron stars

    NASA Astrophysics Data System (ADS)

    Lattimer, James M.

    2014-05-01

    Neutron stars are laboratories for dense matter and gravitational physics. Observations of neutron stars from sources such as radio pulsars, low-mass X-ray binaries, X-ray bursts and thermally-emitting neutron stars are setting bounds to neutron star masses, radii, rotation rates, temperatures and ages. Mass measurements constrain the equation of state at the highest densities and set firm bounds to the highest possible density of cold matter. Radii constrain the equation of state in the vicinity of the nuclear saturation density and yield information about the density dependence of the nuclear symmetry energy. Laboratory measurements and theoretical studies of pure neutron matter are in remarkable agreement with observational bounds.

  15. Tycho's Star

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    A supernova remnant in Cassiopeia, 7.7° north of ? Cas, which suddenly appeared as a brilliant naked-eye star in November 1572 and reached a maximum apparent magnitude of -3.5. Until its disappearance 16 months later, it was extensively studied by the Danish astronomer Tycho Brahe (1546-1601), who described its early appearance as follows: `Initially, the new star was brighter than any other fixe...

  16. Tycho's Star

    Microsoft Academic Search

    P. Murdin

    2000-01-01

    A supernova remnant in Cassiopeia, 7.7° north of alpha Cas, which suddenly appeared as a brilliant naked-eye star in November 1572 and reached a maximum apparent magnitude of -3.5. Until its disappearance 16 months later, it was extensively studied by the Danish astronomer Tycho Brahe (1546-1601), who described its early appearance as follows: `Initially, the new star was brighter than

  17. Massive Star Burps, Then Explodes

    NASA Astrophysics Data System (ADS)

    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 event was a complete surprise," added Alex Filippenko, leader of the UC Berkeley/Keck supernova group and a member of NASA'S Swift team. "It opens up a fascinating new window on how some kinds of stars die." All the observations suggest that the supernova's blast wave took only a few weeks to reach the shell of material ejected two years earlier, which did not have time to drift very far from the star. As the wave smashed into the ejecta, it heated the gas to millions of degrees, hot enough to emit copious X-rays. The Swift satellite saw the supernova continue to brighten in X-rays for 100 days, something that has never been seen before in a supernova. All supernovae previously observed in X-rays have started off bright and then quickly faded to invisibility. "You don't need a lot of mass in the ejecta to produce a lot of X-rays," notes Immler. Swift's ability to monitor the supernova's X-ray rise and decline over six months was crucial to his team's mass determination. But he adds that Chandra's sharp resolution enabled his group to resolve the supernova from a bright X-ray source that appears in the field of view of Swift's X-ray Telescope. "We could not have made this measurement without Chandra," says Immler, who will submit his team's paper next week to the Astrophysical Journal. "The synergy between Swift's fast response and its ability to observe a supernova every day for a long period, and Chandra's high spatial resolution, is leading to a lot of interesting results." Foley and his colleagues, whose paper appears in the March 10 Astrophysical Journal Letters, propose that the star recently transitioned from a Luminous Blue Variable (LBV) star to a Wolf-Rayet star. An LBV is a massive star in a brief but unstable phase of stellar evolution. Similar to the 2004 eruption, LBVs are prone to blow off large amounts of mass in outbursts so extreme that they are frequently mistaken for supernovae, events dubbed "supernova impostors." Wolf-Rayet stars are hot, highly evolved stars tha

  18. A modern search for Wolf-Rayet stars in the Magellanic Clouds: First results

    SciTech Connect

    Massey, Philip; Neugent, Kathryn F. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Morrell, Nidia [Las Campanas Observatory, Carnegie Observatories, Casilla 601 La Serena (Chile); Hillier, D. John, E-mail: phil.massey@lowell.edu, E-mail: kneugent@lowell.edu, E-mail: nmorrell@lco.cl, E-mail: hillier@pitt.edu [Department of Physics and Astronomy and Pittsburgh Particle Physics, Astrophysics, and Cosmology Center (PITT PACC), University of Pittsburgh, Pittsburgh, PA 15260 (United States)

    2014-06-10

    Over the years, directed surveys and incidental spectroscopy have identified 12 Wolf-Rayet (WR) stars in the Small Magellanic Cloud (SMC) and 139 in the Large Magellanic Cloud (LMC), numbers which are often described as 'essentially complete'. Yet, new WRs are discovered in the LMC almost yearly. We have therefore initiated a new survey of both Magellanic Clouds using the same interference-filter imaging technique previously applied to M31 and M33. We report on our first observing season, in which we have successfully surveyed ?15% of our intended area of the SMC and LMC. Spectroscopy has confirmed nine newly found WRs in the LMC (a 6% increase), including one of WO-type, only the third known in that galaxy and the second to be discovered recently. The other eight are WN3 stars that include an absorption component. In two, the absorption is likely from an O-type companion, but the other six are quite unusual. Five would be classified naively as 'WN3+O3 V', but such a pairing is unlikely given the rarity of O3 stars, the short duration of this phase (which is incommensurate with the evolution of a companion to a WN star), and because these stars are considerably fainter than O3 V stars. The sixth star may also fall into this category. CMFGEN modeling suggests these stars are hot, bolometrically luminous, and N-rich like other WN3 stars, but lack the strong winds that characterize WNs. Finally, we discuss two rare Of?p stars and four Of supergiants we found, and propose that the B[e] star HD 38489 may have a WN companion.

  19. HD 46703 - A high-luminosity population II F-type star

    NASA Astrophysics Data System (ADS)

    Luck, R. E.; Bond, H. E.

    1984-04-01

    It is pointed out that A- and F-type stars lying several magnitudes above the horizontal branch occur occasionally in globular clusters. The chemical compositions and other properties of these highly evolved stars are of considerable interest. The present investigation is concerned with HD 46703, which is believed to be another field analog of the Population II A- and F-type supergiants. A description of photometry and low-resolution spectroscopy is presented, and aspects of high-resolution spectroscopy are discussed, taking into account radial velocities and equivalent widths, lines of carbon and oxygen, and H-alpha emission, Chemical abundances and their determination are considered, giving attention to the method of analysis, the iron group and light metals, the s-process elements, carbon and oxygen abundances, and the relationship to halo planetary nebulae. The evolutionary status of HD 46703 is also studied.

  20. Convection and convective overshooting in stars more massive than 10 $M_\\odot$

    E-print Network

    Jie, Jin; Lv, Guoliang

    2015-01-01

    In this paper, four sets of evolutionary models are computed with different values of the mixing length parameter $\\alpha_{\\rm p}$ and the overshooting parameter $\\delta_{\\rm ov}$. The properties of the convective cores and the convective envelopes are studied in the massive stars. We get three conclusions: First, the larger $\\alpha_{\\rm p}$ leads to enhancing the convective mixing, removing the chemical gradient, and increasing the convective heat transfer efficiency. Second, core potential $\\phi_{\\rm c} = M_{\\rm c} / R_{\\rm c}$ describes sufficiently the evolution of a star, whether it is a red or blue supergiant at central helium ignition. Third, the discontinuity of hydrogen profile above the hydrogen burning shell seriously affect the occurrence of blue loops in the Hertzsprung--Russell diagram.

  1. Swift/XRT monitoring of the Supergiant Fast X-ray Transient IGR J18483-0311 for an entire orbital period

    E-print Network

    Romano, P; Ducci, L; Cusumano, G; La Parola, V; Pagani, C; Page, K L; Kennea, J A; Burrows, D N; Gehrels, N; Sguera, V; Bazzano, A

    2009-01-01

    IGR J18483-0311 is an X-ray pulsar with transient X-ray activity, belonging to the new class of High Mass X-ray Binaries called Supergiant Fast X-ray Transients. This system is one of the two members of this class, together with IGR J11215-5952, where both the orbital (18.52d) and spin period (21s) are known. We report on the first complete monitoring of the X-ray activity along an entire orbital period of a Supergiant Fast X-ray Transient. These Swift observations, lasting 28d, cover more than one entire orbital phase consecutively. They are a unique data-set, which allows us to constrain the different mechanisms proposed to explain the nature of this new class of X-ray transients. We applied the new clumpy wind model for blue supergiants developed by Ducci et al. (2009), to the observed X-ray light curve. Assuming an eccentricity of e=0.4, the X-ray emission from this source can be explained in terms of the accretion from a spherically symmetric clumpy wind, composed of clumps with different masses, ranging...

  2. Swift/XRT monitoring of the supergiant fast X-ray transient IGR J18483-0311 for an entire orbital period

    NASA Astrophysics Data System (ADS)

    Romano, P.; Sidoli, L.; Ducci, L.; Cusumano, G.; La Parola, V.; Pagani, C.; Page, K. L.; Kennea, J. A.; Burrows, D. N.; Gehrels, N.; Sguera, V.; Bazzano, A.

    2010-01-01

    IGR J18483-0311 is an X-ray pulsar with transient X-ray activity, belonging to the new class of high-mass X-ray binaries called supergiant fast X-ray transients. This system is one of the two members of this class, together with IGR J11215-5952, where both the orbital (18.52 d) and spin period (21 s) are known. We report on the first complete monitoring of the X-ray activity along an entire orbital period of a supergiant fast X-ray transient. These Swift observations, lasting 28 d, cover more than one entire orbital phase consecutively. They are a unique data set, which allows us to constrain the different mechanisms proposed to explain the nature of this new class of X-ray transients. We applied the new clumpy wind model for blue supergiants developed by Ducci et al. to the observed X-ray light curve. Assuming an eccentricity of e = 0.4, the X-ray emission from this source can be explained in terms of the accretion from a spherically symmetric clumpy wind, composed of clumps with different masses, ranging from 1018 g to 5 × 1021 g.

  3. A search for SiO, OH, CO and HCN radio emission from silicate-carbon stars

    NASA Technical Reports Server (NTRS)

    Little-Marenin, I. R.; Sahai, R.; Wannier, P. G.; Benson, P. J.; Gaylard, M.; Omont, A.

    1994-01-01

    We report upper limits for radio emission of SiO at 86 and 43 GHz, of OH at 1612 and 1665/1667 MHz, of CO at 115 GHz and HCN at 88.6 GHz in the silicate-carbon stars. These upper limits of SiO imply that oxygen-rich material has not been detected within 2R(sub star) of a central star even though the detected emission from silicate dust grains, H2O and OH maser establishes the presence of oxygen-rich material from about tens to thousands of AU of a central star. The upper limit of the SiO abundance is consistent with that found in oxygen-rich envelopes. Upper limits of the mass loss rate (based on the CO data) are estimated to be between 10(exp -6) to 10(exp -7) solar mass/yr assuming a distance of 1.5 kpc for these stars. The absence of HCN microwave emission implies that no carbon-rich material can be detected at large distances (thousands of AU) from a central star. The lack of detections of SiO, CO, and HCN emission is most likely due to the large distances of these stars. A number of C stars were detected in CO and HCN, but only the M supergiant VX Sgr was detected in CO.

  4. VizieR Online Data Catalog: VLT-FLAMES Tarantula Survey. 30 Dor luminous stars (Doran+, 2013)

    NASA Astrophysics Data System (ADS)

    Doran, E. I.; Crowther, P. A.; de Koter, A.; Evans, C. J.; McEvoy, C.; Walborn, N. R.; Bastian, N.; Bestenlehner, J. M.; Grafener, G.; Herrero, A.; Kohler, K.; Maiz Apellaniz, J.; Najarro, F.; Puls, J.; Sana, H.; Schneider, F. R. N.; Taylor, W. D.; van Loon, J. T.; Vink, J. S.

    2013-08-01

    A census was compiled of all the hot luminous stars within the central 10 arcminutes of 30 Doradus. Candidate hot luminous stars were selected from a series of photometric catalogues, using a set of criteria explained in the paper. All stars meeting this photometric criteria are listed in Tabled1.dat. In addition, Table D1 includes all known Wolf-Rayet and Of/WN stars in the region, which may not have been selected due to photometric effects. Spectral Types were then matched to as many of the candidate stars in Tabled1.dat as possible. Stellar parameters were determined for all stars with the following spectral types: W-R, Of/WN, O-type, B-supergiant, B-giant B1I or earlier, B-dwarf, B0.5V or earlier. These parameters are listed in Tabled2.dat. Parameters of all O-type and B-type stars were derived through various calibrations. Parameters of W-R and Of/WN stars were based on previous work or various template models explained in the paper. (2 data files).

  5. Herschel SPIRE and PACS observations of the red supergiant VY CMa: analysis of the molecular line spectra

    NASA Astrophysics Data System (ADS)

    Matsuura, Mikako; Yates, J. A.; Barlow, M. J.; Swinyard, B. M.; Royer, P.; Cernicharo, J.; Decin, L.; Wesson, R.; Polehampton, E. T.; Blommaert, J. A. D. L.; Groenewegen, M. A. T.; Van de Steene, G. C.; van Hoof, P. A. M.

    2014-01-01

    We present an analysis of the far-infrared and submillimetre molecular emission-line spectrum of the luminous M-supergiant VY CMa, observed with the Spectral and Photometric Imaging Receiver (SPIRE) and Photodetector Array Camera and Spectrometer for Herschel spectrometers aboard the Herschel Space Observatory. Over 260 emission lines were detected in the 190-650 ?m SPIRE Fourier Transform Spectrometer spectra, with one-third of the observed lines being attributable to H2O. Other detected species include CO, 13CO, H_2^{18}O, SiO, HCN, SO, SO2, CS, H2S and NH3. Our model fits to the observed 12CO and 13CO line intensities yield a 12C/13C ratio of 5.6 ± 1.8, consistent with measurements of this ratio for other M-supergiants, but significantly lower than previously estimated for VY CMa from observations of lower-J lines. The spectral line energy distribution for 20 SiO rotational lines shows two temperature components: a hot component at ˜1000 K, which we attribute to the stellar atmosphere and inner wind, plus a cooler ˜200 K component, which we attribute to an origin in the outer circumstellar envelope. We fit the line fluxes of 12CO, 13CO, H2O and SiO, using the SMMOL non-local thermodynamic equilibrium (LTE) line transfer code, with a mass-loss rate of 1.85 × 10-4 M? yr-1 between 9R* and 350R*. We also fit the observed line fluxes of 12CO, 13CO, H2O and SiO with SMMOL non-LTE line radiative transfer code, along with a mass-loss rate of 1.85 × 10-4 M? yr-1. To fit the high rotational lines of CO and H2O, the model required a rather flat temperature distribution inside the dust condensation radius, attributed to the high H2O opacity. Beyond the dust condensation radius the gas temperature is fitted best by an r-0.5 radial dependence, consistent with the coolant lines becoming optically thin. Our H2O emission-line fits are consistent with an ortho:para ratio of 3 in the outflow.

  6. The uBVI Photometric System. II. Standard Stars

    E-print Network

    Michael H. Siegel; Howard E. Bond

    2005-03-03

    Paper I of this series described the design of a CCD-based photometric system that is optimized for ground-based measurements of the size of the Balmer discontinuity in stellar spectra. This "uBVI" system combines the Thuan-Gunn u filter with the standard Johnson-Kron-Cousins BVI filters, and it can be used to discover luminous yellow supergiants in extragalactic systems and post-asymptotic-giant-branch stars in globular clusters and galactic halos. In the present paper we use uBVI observations obtained on 54 nights with 0.9-m telescopes at Kitt Peak and Cerro Tololo to construct a catalog of standardized u magnitudes for standard stars taken from the 1992 catalog of Landolt. We describe the selection of our 14 Landolt fields, and give details of the photometric reductions, including red-leak and extinction corrections, transformation of all of the observations onto a common magnitude system, and establishment of the photometric zero point. We present a catalog of u magnitudes of 103 stars suitable for use as standards. We show that data obtained with other telescopes can be transformed to our standard system with better than 1% accuracy.

  7. The structure and energy balance of cool star atmospheres

    NASA Technical Reports Server (NTRS)

    Linsky, J. L.

    1982-01-01

    The atmospheric structure and energy balance phenomena associated with magnetic fields in the Sun are reviewed and it is shown that similar phenomena occur in cool stars. The evidence for the weakening or disappearance of transition regions and coronae is discussed together with the appearance of extended cool chromospheres with large mass loss, near V-R = 0.80 in the H-R diagram. Like the solar atmosphere, these atmospheres are not homogeneous and there is considerable evidence for plage regions with bright TR emission lines that overlie dark (presumably magnetic) star spots. The IUE observations are providing important information on the energy balance in these atmospheres that should guide theoretical calculations of the nonradiative heating rate. Recent high dispersion spectra are providing unique information concerning which components of close binary systems are the dominant contributors to the observed emission. A recent unanticipated discovery is that the transition lines are redshifted (an antiwind) in DRa (G2 Ib) and perhaps other stars. Finally, the G and K giants and supergiants are classified into three groups depending on whether their atmospheres are dominated by closed magnetic flux tubes, open field geometries, or a predominately open geometry with a few closed flux tubes embedded.

  8. Lyman alpha initiated winds in late-type stars

    NASA Technical Reports Server (NTRS)

    Haisch, B. M.; Van Der Hucht, K. A.; Linsky, J. L.

    1979-01-01

    One of the first major results of the IUE survey of late-type stars was the discovery of a sharp division in the HR diagram between stars with solar type spectra (chromosphere and transition region lines) and those with non-solar type spectra (only chromosphere lines). This result is especially interesting in view of observational evidence for mass loss from G and K giants and super-giants discussed recently by both Reimers and Stencel. In the present paper models of both hot coronae and cool wind flows are calculated using stellar model chromospheres as starting points for stellar wind calculations in order to investigate the possibility of having a 'supersonic transition locus' in the HR diagram dividing hot coronae from cool winds. It is concluded from these models that the Lyman-alpha flux may play an important role in determining the location of a stellar wind critical point. The interaction of Lyman-alpha radiation pressure with Alfven waves in producing strong, low temperature stellar winds in the star Arcturus is investigated.

  9. Tracking down R Coronae Borealis stars from their mid-infrared WISE colours

    E-print Network

    Tisserand, Patrick

    2011-01-01

    R Coronae Borealis stars (RCBs) are hydrogen-deficient and carbon-rich supergiant stars. They are very rare, as only $\\sim50$ are actually known in our Galaxy. Interestingly, RCBs are strongly suspected to be the evolved merger product of two white dwarfs and could therefore be an important tool to understand Supernovae type Ia in the double degenerate scenario. Constraints on the spatial distribution and the formation rate of such stars are needed to picture their origin and test it in the context of actual population synthesis results. To do so, it is crucial to increase significantly the number of known RCBs. With an absolute magnitude $\\mathrm{M_V\\sim-5}$ and a bright/hot circumstellar shell made of amorphous carbon grains, RCBs are really distinctive stars. Mono-epoch mid-infrared data can help us to discriminate RCBs among other dust-producing stars. The aim is to produce from the WISE and 2MASS infrared catalogues a new catalogue of reasonable size, enriched with RCB stars. Colour-Colour cuts used on a...

  10. A massive hypergiant star as the progenitor of the supernova SN 2005gl.

    PubMed

    Gal-Yam, A; Leonard, D C

    2009-04-16

    Our understanding of the evolution of massive stars before their final explosions as supernovae is incomplete, from both an observational and a theoretical standpoint. A key missing piece in the supernova puzzle is the difficulty of identifying and studying progenitor stars. In only a single case-that of supernova SN 1987A in the Large Magellanic Cloud-has a star been detected at the supernova location before the explosion, and been subsequently shown to have vanished after the supernova event. The progenitor of SN 1987A was a blue supergiant, which required a rethink of stellar evolution models. The progenitor of supernova SN 2005gl was proposed to be an extremely luminous object, but the association was not robustly established (it was not even clear that the putative progenitor was a single luminous star). Here we report that the previously proposed object was indeed the progenitor star of SN 2005gl. This very massive star was likely a luminous blue variable that standard stellar evolution predicts should not have exploded in that state. PMID:19305392

  11. A massive hypergiant star as the progenitor of the supernova SN 2005gl

    NASA Astrophysics Data System (ADS)

    Gal-Yam, A.; Leonard, D. C.

    2009-04-01

    Our understanding of the evolution of massive stars before their final explosions as supernovae is incomplete, from both an observational and a theoretical standpoint. A key missing piece in the supernova puzzle is the difficulty of identifying and studying progenitor stars. In only a single case-that of supernova SN 1987A in the Large Magellanic Cloud-has a star been detected at the supernova location before the explosion, and been subsequently shown to have vanished after the supernova event. The progenitor of SN 1987A was a blue supergiant, which required a rethink of stellar evolution models. The progenitor of supernova SN 2005gl was proposed to be an extremely luminous object, but the association was not robustly established (it was not even clear that the putative progenitor was a single luminous star). Here we report that the previously proposed object was indeed the progenitor star of SN 2005gl. This very massive star was likely a luminous blue variable that standard stellar evolution predicts should not have exploded in that state.

  12. What is the True Population of R Coronae Borealis Stars in the Galaxy?

    NASA Astrophysics Data System (ADS)

    Clayton, Geoffrey C.; Tisserand, P.; Welch, D. L.; Zhang, W.

    2013-01-01

    The R Coronae Borealis (RCB) stars are rare hydrogen-deficient, carbon-rich supergiants. Two evolutionary scenarios have been suggested, a double degenerate merger of two white dwarfs (WDs), or a final helium shell flash in a PN central star. The evidence pointing toward a WD merger or a FF origin for RCB stars is contradictory. The distribution on the sky and radial velocities of the RCB stars tend toward those of the bulge population but a much larger sample of stars is needed to determine the true population. We need to discover RCB much more efficiently. In order to do this we are pursuing three lines of attack: 1. Light Curves: Using the traditional technique of identifying RCB stars from their characteristic large and irregular light variations, we have we have investigated the stars in the ASAS-3 south survey. We have discovered 21 new RCB stars. The different analysis applied allowed us to extend our detection efficiency to fainter magnitudes that would not have been easily accessible to classical analysis based on light-curve variability. 2. Color-Color Diagrams: All RCB stars have IR excesses. Using the recent release of the WISE All-Sky Catalog, a series of IR color-color cuts have produced a sample of candidates 1600) that may yield over 200 new RCB star identifications. A pilot project to get spectra of the 200 brighter candidates has yielded an unexpectedly high new discovery rate 20%) based on photometric colors alone. 3. Spectral Classification: We are attempting to develop a quantitative spectral classification system for the RCB stars so that they can perhaps be identified without an accompanying light curve. The cooler RCB stars look like carbon stars with strong C2 bands, but they can be differentiated from carbon stars by their extreme hydrogen deficiency and very low 13C/12C ratio. Also, the red CN bands are much weaker in RCB stars than in carbon stars. The number of RCB stars in the Galaxy may be consistent with the predicted number of He/CO WD mergers. Solving the mystery of how the RCB stars evolve would be a watershed event in the study of stellar evolution that will lead to a better understanding of other important types of stellar merger events such as Type Ia SNe.

  13. An ISO/SWS study of the dust composition around S stars. A novel view of S-star dust

    NASA Astrophysics Data System (ADS)

    Hony, S.; Heras, A. M.; Molster, F. J.; Smolders, K.

    2009-07-01

    Aims: We investigate the composition of the solid-state materials in the winds around S-type AGB stars. The S stars produce dust in their wind that bears a resemblance to the dust produced in some O-rich AGB stars. However, the reported resemblance is mostly based on IRAS/LRS spectra with limited spectral resolution, sensitivity, and wavelength coverage. Methods: We investigate the dust composition around S stars using ISO/SWS data that surpass the previous studies in terms of spectral resolution and wavelength coverage. We selected the dust producing S stars in the ISO/SWS archive with enough signal to perform a detailed dust analysis, and then compare the dust spectra from the 9 sources with the O-rich AGB spectra and a subset of M super-giants. We constructed average dust emission spectra of the different categories. Results: We report the discovery of several previously unreported dust emission features in the S star spectra. The long wavelength spectra of W Aql and ?1 Gru exhibit the “30” ?m feature attributed to MgS. Two sources exhibit a series of emission bands between 20 and 40 ?m that we tentatively ascribe to Diopside. We show that the 10-20 ?m spectra of the S stars are significantly different from the O-rich AGB stars. The O-rich stars exhibit a structured emission feature that is believed to arise from amorphous silicate and aluminium-oxide. The S stars lack the substructure found in the O-rich stars. Instead they show a smooth peak with a varying peak-position from source to source. We suggest that this feature is caused by a family of related materials, whose exact composition determines the peak position. The observed trend mimics the laboratory trend of non-stoichiometric silicates. In this scenario the degree of non-stoichiometry is related to the Mg to SiO4 ratio, in other words, to the amount of free O available during the dust grain growth. based on observations obtained with ISO, an ESA project with instruments funded by ESA Member states (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

  14. Obscured AGB stars in the Magellanic Clouds II. Near-infrared and mid-infrared counterparts

    E-print Network

    Albert A. Zijlstra; Cecile Loup; L. B. F. M. Waters; P. A. Whitelock; Jacco Th. van Loon; F. Guglielmo

    1995-10-13

    We have carried out an infrared search for obscured AGB stars in the Magellanic Clouds. The survey uncovered a number of obscured AGB stars as well as some supergiants with infrared excess. We present photometry of the sources and discuss the colour diagrams and bolometric luminosities. Most of the AGB stars are luminous, often close to the classical limit of $M_{\\rm bol}=-7.1$. To determine whether the stars are oxygen-rich or carbon-rich, we have acquired narrow-band mid-infrared photometry with the ESO TIMMI camera for several sources. All but one are found to show the silicate feature and therefore to have oxygen-rich dust: the colours of the remaining source are consistent with either an oxygen-rich or a carbon-rich nature. A method to distinguish carbon and oxygen stars based on H$-$K versus K$-$[12] colours is presented. We discuss several methods of calculating the mass-loss rate: for the AGB stars the mass-loss rates vary between approximately 5 times 10**-4 and 5 times 10**-6 solar masses per year, depending on assumed dust-to-gas mass ratio. We present a new way to calculate mass-loss rates from the OH-maser emission. We find no evidence for a correlation of the mass-loss rates with luminosity in these obscured stars. Neither do the mass-loss rates for the LMC and SMC stars differ in any clear systematic way from each other. Expansion velocities appear to be slightly lower in the LMC than in the Galaxy. Period determinations are discussed for two sources: the periods are comparable to those of the longer-period galactic OH/IR stars. All of the luminous stars for which periods are available, have significantly higher luminosities than predicted from the period--luminosity relations.

  15. Massive Star Evolution as a Function of Metallicity: Closing the Loop in the Local Group

    NASA Astrophysics Data System (ADS)

    Massey, Philip; Levesque, Emily; Maeder, Andre; Meynet, Georges; Olsen, Knut; Silva, David R.

    2009-08-01

    The NOAO Local Group Galaxy Survey (LGGS) obtained photometry of half a million stars in M31 and M33 (Massey et al. 2006, 2007a). We are applying here for the spectroscopic followup needed to construct physical (T_eff, log L/L_?) H-R diagrams for the unevolved (core H-burning) massive stars in these two galaxies. These will be compared to the number of evolved massive stars in these system (Wolf-Rayets, red supergiants, and luminous blue variables), providing critical tests of stellar evolutionary models as a function of metallicity. This study will be complete for massive stars brighter than M_V<-5.5 (V<19.5), corresponding to masses > 50M_? for zero-age main-sequence stars, and >25M_? for older (5 Myr) stars. This sample consists of 600 stars in M31 and 1700 stars in M33, and our project will lead to a 100-fold increase in the number of main-sequence stars classified in our spiral neighbors. M31 has a (young-age) metallicity that is roughly 2× solar, with only a slight gradient, while M33 has a galactocentric gradient in metallicity from 0.6 to 0.3 solar. This will allow us to test the latest generation of Geneva stellar evolution models at a variety of metallicities, which is important given that rotation plays a dominant role at low metallicity, while radiatively driven stellar winds dominate at high metallicities. The data gathered here will help to refine the stellar evolutionary models, not only improving our knowledge of massive star evolution, but also the interpretation of the integrated spectra of distant galaxies. This proposal was awarded time by the 2008B TAC, but never scheduled.

  16. Energy Star 

    E-print Network

    Reihl, K.; Tullos, A.

    2012-01-01

    to design, track, and report energy use of projects ESL-KT-12-10-08 CATEE 2012: Clean Air Through Energy Efficiency Conference, Galveston, TX, October 9-11, 2012 Source: 2006 Lunch & Learn Workshop. ?Energy Star ? New Building Design.? Karen P. Butler.... US Environmental Protection Agency. ESL-KT-12-10-08 CATEE 2012: Clean Air Through Energy Efficiency Conference, Galveston, TX, October 9-11, 2012 Source: 2006 Lunch & Learn Workshop. ?Energy Star ? New Building Design.? Karen P. Butler. US...

  17. INTEGRAL sources: from obscured high mass X-ray binaries to supergiant fast X-ray transients

    E-print Network

    Chaty, S

    2008-01-01

    A new type of high-energy binary system has been revealed by the INTEGRAL satellite. These sources are being unveiled by means of multi-wavelength optical, near- and mid-infrared observations. Among these sources, two distinct classes are appearing: the first one is constituted of intrinsically obscured high-energy sources, of which IGR J16318-4848 seems to be the most extreme example. The second one is populated by the so-called supergiant fast X-ray transients, with IGR J17544-2619 being the archetype. We first give here a general introduction on INTEGRAL sources, before reporting on multi-wavelength optical to mid-infrared observations of a sample constituted of 21 INTEGRAL sources. We show that in the case of the obscured sources our observations suggest the presence of absorbing material (dust and/or cold gas) enshrouding the whole binary system. We finally discuss the nature of these two different types of sources, in the context of high energy binary systems, and give a scenario of unification of all t...

  18. Spectral and temporal properties of the supergiant fast X-ray transient IGR J18483-0311 observed by INTEGRAL

    E-print Network

    Ducci, L; Sasaki, M; Santangelo, A; Esposito, P; Romano, P; Vercellone, S

    2013-01-01

    IGR J18483-0311 is a supergiant fast X-ray transient whose compact object is located in a wide (18.5 d) and eccentric (e~0.4) orbit, which shows sporadic outbursts that reach X-ray luminosities of ~1e36 erg/s. We investigated the timing properties of IGR J18483-0311 and studied the spectra during bright outbursts by fitting physical models based on thermal and bulk Comptonization processes for accreting compact objects. We analysed archival INTEGRAL data collected in the period 2003-2010, focusing on the observations with IGR J18483-0311 in outburst. We searched for pulsations in the INTEGRAL light curves of each outburst. We took advantage of the broadband observing capability of INTEGRAL for the spectral analysis. We observed 15 outbursts, seven of which we report here for the first time. This data analysis almost doubles the statistics of flares of this binary system detected by INTEGRAL. A refined timing analysis did not reveal a significant periodicity in the INTEGRAL observation where a ~21s pulsation w...

  19. MASER OBSERVATIONS OF WESTERLUND 1 AND COMPREHENSIVE CONSIDERATIONS ON MASER PROPERTIES OF RED SUPERGIANTS ASSOCIATED WITH MASSIVE CLUSTERS

    SciTech Connect

    Fok, Thomas K. T.; Nakashima, Jun-ichi; Yung, Bosco H. K.; Hsia, Chih-Hao [Department of Physics, University of Hong Kong, Pokfulam Road (Hong Kong); Deguchi, Shuji, E-mail: junichi@hku.hk [Nobeyama Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Minamisaku, Nagano 384-1305 (Japan)

    2012-11-20

    We report the results of Australia Telescope Compact Array observations of the Westerlund 1 (Wd1) region in the SiO v = 1, J = 1-0, and H{sub 2}O 6{sub 16}-5{sub 23} maser lines, and we also report the analysis of maser properties of red supergiants (RSGs) associated with six massive clusters including Wd1. The primary purpose of this research is to explore possibilities of using maser emission for investigating the nature of massive clusters and associated RSGs. The SiO v = 1, J = 1-0, and H{sub 2}O 6{sub 16}-5{sub 23} maser lines are detected toward two of four known RSGs in Wd1. The large velocity ranges of maser emission are consistent with the RSG status. RSGs with maser emission tend to exhibit redder log (F {sub 21}/F {sub 12}) and [K-12.13] colors compared to RSGs with no maser emission. The mass-loss rates derived from dust radiative transfer modeling suggest that RSGs with maser emission tend to exhibit larger mass-loss rates compared to RSGs with no maser emission. In an extended sample of 57 RSGs in six massive clusters, detections in the SiO line tend to homogeneously distribute in absolute luminosity L, whereas those in the H{sub 2}O line tend to distribute in a region with large L values.

  20. Fundamental properties and atmospheric structure of the red supergiant VY CMa based on VLTI/AMBER spectro-interferometry

    E-print Network

    Wittkowski, M; Torres, B Arroyo; Marcaide, J M

    2012-01-01

    We investigate the atmospheric structure and fundamental properties of the red supergiant VY CMa. We obtained near-infrared spectro-interferometric observations of VY CMa with spectral resolutions of 35 and 1500 using the AMBER instrument at the VLTI. The visibility data indicate the presence of molecular layers of water vapor and CO in the extended atmosphere with an asymmetric morphology. The uniform disk diameter in the water band around 2.0 mu is increased by \\sim20% compared to the near-continuum bandpass at 2.20-2.25 mu and in the CO band at 2.3-2.5 mu it is increased by up to \\sim50%. The closure phases indicate relatively small deviations from point symmetry close to the photospheric layer, and stronger deviations in the extended H2O and CO layers. Making use of the high spatial and spectral resolution, a near-continuum bandpass can be isolated from contamination by molecular and dusty layers, and the Rosseland-mean photospheric angular diameter is estimated to 11.3 +/- 0.3 mas based on a PHOENIX atmo...

  1. CHARA/MIRC observations of two M supergiants in Perseus OB1: Temperature, bayesian modeling, and compressed sensing imaging

    SciTech Connect

    Baron, F.; Monnier, J. D.; Anderson, M.; Aarnio, A. [Department of Astronomy, University of Michigan, 918 Dennison Building, Ann Arbor, MI 48109-1090 (United States); Kiss, L. L. [Sydney Institute for Astrophysics, School of Physics, University of Sydney, NSW 2006 (Australia); Neilson, H. R. [Department of Physics and Astronomy, East Tennessee State University, Box 70652, Johnson City, TN 37614 (United States); Zhao, M. [Department of Astronomy and Astrophysics, Penn State University, University Park, PA 16802 (United States); Pedretti, E.; Thureau, N. [Department of Physics and Astronomy, University of St. Andrews (United Kingdom); Ten Brummelaar, T. A.; Sturmann, J.; Sturmann, L.; Turner, N. [The CHARA Array, Georgia State University, P.O. Box 3965, Atlanta, GA 30302-3965 (United States); Ridgway, S. T. [National Optical Astronomy Observatory, Tucson, AZ 85726-6732 (United States); McAlister, H. A., E-mail: baron@phy-astr.gsu.edu [CHARA and Department of Physics and Astronomy, Georgia State University, P. O. Box 4106, Atlanta, GA 30302-4106 (United States)

    2014-04-10

    Two red supergiants (RSGs) of the Per OB1 association, RS Per and T Per, have been observed in the H band using the Michigan Infra-Red Combiner (MIRC) instrument at the CHARA array. The data show clear evidence of a departure from circular symmetry. We present here new techniques specially developed to analyze such cases, based on state-of-the-art statistical frameworks. The stellar surfaces are first modeled as limb-darkened disks based on SATLAS models that fit both MIRC interferometric data and publicly available spectrophotometric data. Bayesian model selection is then used to determine the most probable number of spots. The effective surface temperatures are also determined and give further support to the recently derived hotter temperature scales of RSGs. The stellar surfaces are reconstructed by our model-independent imaging code SQUEEZE, making use of its novel regularizer based on Compressed Sensing theory. We find excellent agreement between the model-selection results and the reconstructions. Our results provide evidence for the presence of near-infrared spots representing about 3%-5% of the stellar flux.

  2. New Herbig Ae/Be stars confirmed via high-resolution optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Carmona, A.; van den Ancker, M. E.; Audard, M.; Henning, Th.; Setiawan, J.; Rodmann, J.

    2010-07-01

    We present FEROS high-resolution (R ~ 45 000) optical spectroscopy of 34 Herbig Ae/Be star candidates with previously unknown or poorly constrained spectral types. Within the sample, 16 sources are positionally coincident with nearby (d < 250 pc) star-forming regions (SFRs). All the candidates have reported infrared excess. We determine the spectral type and luminosity class of the sources, derive their radial and projected rotational velocities, and constrain their distances employing spectroscopic parallaxes and photometry from the literature. We confirm 13 sources as Herbig Ae/Be stars and find one classical T Tauri star. Three sources are emission line early-type giants (B, A, and F stars with luminosity class III) and may be Herbig Ae/Be stars. One source is a main-sequence A-type star. Fourteen sources are post-main-sequence giant and supergiant stars (7 with H? emission and 7 without). Two sources are extreme emission-line stars and no accurate spectral classification was possible because of strong veiling. Most of the sources appear to be background stars at distances over 700 pc. We show that high-resolution optical spectroscopy is a crucial tool for distinguishing young stars (in particular Herbig Be stars) from post-main sequence stars in samples taken from emission-line star catalogs based on low-resolution spectroscopy. Within the sample, three young stars (CD-38 4380, Hen 3-1145, and HD 145718) and one early-type luminosity class III giant with emission lines (Hen 3-416) are at distances closer than 300 pc and are positionally coincident with a nearby SFR. These 4 sources are likely to be nearby young stars and are interesting for follow-up observations at high-angular resolution. Furthermore, seven confirmed Herbig Ae/Be stars at d>700 pc (Hen 2-80, Hen 3-1121 N&S, HD 313571, MWC 953, WRAY 15-1435, and Th 17-35) are inside or close (< 5') to regions with extended 8 ?m continuum emission and in their 20' vicinity have astronomical sources characteristic of SFRs (e.g., HII regions, molecular clouds, dark nebulae, masers, young stellar-objects). These 7 sources are likely to be members of SFRs. Based on observations collected at the ESO-MPG 2.2 m telescope at la Silla Observatory, Chile (program IDs: 072.A-9006, 073.A-9008, 079.A-9014, 081.A-9003).Appendix is only available in electronic form at http://www.aanda.org

  3. Kinematic structure of the supergiant shell LMC 9 - I. The nebular complex DEM L208

    NASA Astrophysics Data System (ADS)

    Oddone, M. A.; Ambrocio-Cruz, P.; Le Coarer, E.; Goldes, G. V.

    2014-08-01

    This work describes an extensive and eminently observational study, carried out with an H? filter, of the kinematics of the ionized gas in the large emission region (220 pc) DEM L208 which is located in the south-east part of the Large Magellanic Cloud (LMC). The intention was to establish the region's general kinematic and morphological characteristics, and to analyse its possible association with a larger structure, aiming above all to contribute to the elaboration of a detailed global kinematics image of the LMC. The nebula's edges are well defined, with fairly regular Gaussian profiles, and can be represented by a systemic radial velocity of approximately 250 km s-1 for the brightest area of DEM L208. The radial velocity fields obtained present a main component with a well-defined profile, as well as other weaker components of larger speed, which may be indicative of expansion motion or of another layer of gas. In some regions we find evidence that the disturbance of the medium is due to stellar winds from the interior of the nebula; in others the profiles observed are found to be consistent with very intense stellar winds from Wolf-Rayet stars.

  4. The ultra-long Gamma-Ray Burst 111209A: the collapse of a blue supergiant?

    E-print Network

    Gendre, B; Atteia, J L; Basa, S; Boër, M; Coward, D M; Cutini, S; D'Elia, V; Howell, E; Klotz, A; Piro, L

    2012-01-01

    We present optical, X-ray and gamma-ray observations of GRB 111209A, at a redshift of z = 0.677. We show that this event was active in its prompt phase for about 25000 seconds, making it the longest burst ever observed. This rare event could have been detected up to z ~ 1.4. Compared to other long GRBs, GRB 111209A is a clear outlier in the energy-fluence and duration plane. The high-energy prompt emission shows no sign of a strong black body component, as expected if the event was caused by a tidal disruption event or a supernova shock breakout. Given the extreme longevity of this event, and a lack of a supernova signature, we propose that GRB 111209A is a relatively rare stellar collapse of a low metallicity blue super giant star. Only this progenitor can supply mass to the central engine over a duration of thousands of seconds. Hence, GRB 111209A could have more in common with population III stellar explosions, rather than normal long gamma ray bursts.

  5. The Spectral Energy Distribution and Mass-loss Rate of the A-Type Supergiant Deneb

    E-print Network

    J. P. Aufdenberg; P. H. Hauschildt; E. Baron; T. E. Nordgren; I. D. Howarth; A. W. Burnley; K. D. Gordon; J. A. Stansberry

    2002-01-14

    A stellar wind module has been developed for the PHOENIX stellar atmosphere code for the purpose of computing non-LTE, line-blanketed, expanding atmospheric structures and detailed synthetic spectra of hot luminous stars with winds. We apply the code to observations of Deneb, for which we report the first positive detections of mm and cm emission (obtained using the SCUBA and the VLA), as well a strong upper limit on the 850 micron flux (using the HHT). The slope of the radio spectrum shows that the stellar wind is partially ionized. We report a uniform-disk angular diameter measurement, 2.40 +/- 0.06 mas, from the Navy Prototype Optical Interferometer (NPOI). The measured bolometric flux and corrected NPOI angular diameter yield an effective temperature of 8600 +/- 500 K. Least-squares comparisons of synthetic spectral energy distributions from 1220 A to 3.6 cm with the observations provide estimates for the effective temperature and the mass-loss rate of 8400 +/- 100 K and 8 +/- 3 E-7 M_sun/yr, respectively. This range of mass-loss rates is consistent with that derived from high dispersion UV spectra when non-LTE metal-line blanketing is considered. We are unable achieve a reasonable fit to a typical Halpha P-Cygni profile with any model parameters over a reasonable range. This is troubling because the \\ha profile is the observational basis for Wind Momentum-Luminosity Relationship.

  6. The Spectral Energy Distribution and Mass-loss Rate of the A-Type Supergiant Deneb

    E-print Network

    Aufdenberg, J P; Baron, E; Nordgren, T E; Howarth, I D; Burnley, A W; Gordon, K D; Stansberry, J A

    2002-01-01

    A stellar wind module has been developed for the PHOENIX stellar atmosphere code for the purpose of computing non-LTE, line-blanketed, expanding atmospheric structures and detailed synthetic spectra of hot luminous stars with winds. We apply the code to observations of Deneb, for which we report the first positive detections of mm and cm emission (obtained using the SCUBA and the VLA), as well a strong upper limit on the 850 micron flux (using the HHT). The slope of the radio spectrum shows that the stellar wind is partially ionized. We report a uniform-disk angular diameter measurement, 2.40 +/- 0.06 mas, from the Navy Prototype Optical Interferometer (NPOI). The measured bolometric flux and corrected NPOI angular diameter yield an effective temperature of 8600 +/- 500 K. Least-squares comparisons of synthetic spectral energy distributions from 1220 A to 3.6 cm with the observations provide estimates for the effective temperature and the mass-loss rate of 8400 +/- 100 K and 8 +/- 3 E-7 M_sun/yr, respectively...

  7. STAR Highlights

    E-print Network

    Hiroshi Masui; for the STAR Collaboration

    2011-06-29

    We report selected results from STAR collaboration at RHIC, focusing on jet-hadron and jet-like correlations, quarkonium suppression and collectivity, di-electron spectrum in both p+p and Au+Au, and higher moments of net-protons as well as azimuthal anisotropy from RHIC Beam Energy Scan program.

  8. Star Power

    ScienceCinema

    None

    2014-11-18

    The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

  9. Star Power

    NSDL National Science Digital Library

    Twin Cities Public Television

    2010-01-01

    In this activity, learners create a star show and discover how they can prevent light pollution. Using simple materials, learners first design constellation boxes. Next, learners use their constellation boxes and desk lamps to explore how city lights impact the visibility of constellations. Finally, learners design shields to reduce light pollution and increase the visibility of constellations.

  10. Brittle Star

    USGS Multimedia Gallery

    A tiny brittle star (the central disc is smaller than a dime) clings to the branches of a soft coral in a sample bucket brought into the shipboard laboratory from a submersible dive. This creature makes its home on the deep, dark ocean floor. ...

  11. Star Power

    SciTech Connect

    None

    2014-10-17

    The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

  12. The MiMeS survey of magnetism in massive stars: CNO surface abundances of Galactic O stars

    NASA Astrophysics Data System (ADS)

    Martins, F.; Hervé, A.; Bouret, J.-C.; Marcolino, W.; Wade, G. A.; Neiner, C.; Alecian, E.; Grunhut, J.; Petit, V.

    2015-03-01

    Context. The evolution of massive stars is still partly unconstrained. Mass, metallicity, mass loss, and rotation are the main drivers of stellar evolution. Binarity and the magnetic field may also significantly affect the fate of massive stars. Aims: Our goal is to investigate the evolution of single O stars in the Galaxy. Methods: For that, we used a sample of 74 objects comprising all luminosity classes and spectral types from O4 to O9.7. We relied on optical spectroscopy obtained in the context of the MiMeS survey of massive stars. We performed spectral modelling with the code CMFGEN. We determined the surface properties of the sample stars, with special emphasis on abundances of carbon, nitrogen, and oxygen. Results: Most of our sample stars have initial masses in the range of 20 to 50 M?. We show that nitrogen is more enriched and carbon and oxygen are more depleted in supergiants than in dwarfs, with giants showing intermediate degrees of mixing. CNO abundances are observed in the range of values predicted by nucleosynthesis through the CNO cycle. More massive stars, within a given luminosity class, appear to be more chemically enriched than lower mass stars. We compare our results with predictions of three types of evolutionary models and show that for two sets of models, 80% of our sample can be explained by stellar evolution including rotation. The effect of magnetism on surface abundances is unconstrained. Conclusions: Our study indicates that in the 20-50 M? mass range, the surface chemical abundances of most single O stars in the Galaxy are fairly well accounted for by stellar evolution of rotating stars. Based on observations obtained at 1) the Telescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées, Université de Toulouse (Paul Sabatier), Centre National de la Recherche Scientifique of France; 2) at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii; 3) at the ESO/La Silla Observatory under program ID 187.D-0917.

  13. Circumstellar medium around rotating massive stars at solar metallicity

    NASA Astrophysics Data System (ADS)

    Georgy, Cyril; Walder, Rolf; Folini, Doris; Bykov, Andrei; Marcowith, Alexandre; Favre, Jean M.

    2013-11-01

    Aims: Observations show nebulae around some massive stars but not around others. If observed, their chemical composition is far from homogeneous. Our goal is to put these observational features into the context of the evolution of massive stars and their circumstellar medium (CSM) and, more generally, to quantify the role of massive stars for the chemical and dynamical evolution of the ISM. Methods: Using the A-MAZE code, we perform 2d-axisymmetric hydrodynamical simulations of the evolution of the CSM, shaped by stellar winds, for a whole grid of massive stellar models from 15 to 120 M? and following the stellar evolution from the zero-age main-sequence to the time of supernova explosion. In addition to the usual quantities, we also follow five chemical species: H, He, C, N, and O. Results: We show how various quantities evolve as a function of time: size of the bubble, position of the wind termination shock, chemical composition of the bubble, etc. The chemical composition of the bubble changes considerably compared to the initial composition, particularly during the red-supergiant (RSG) and Wolf-Rayet (WR) phases. In some extreme cases, the inner region of the bubble can be completely depleted in hydrogen and nitrogen, and is mainly composed of carbon, helium, and oxygen. We argue why the bubble typically expands at a lower rate than predicted by self-similarity theory. In particular, the size of the bubble is very sensitive to the density of the ISM, decreasing by a factor of ~2.5 for each additional dex in ISM density. The bubble size also decreases with the metallicity of the central star, because low-metallicity stars have weaker winds. Our models qualitatively fit the observations of WR ejecta nebulae.

  14. Formation of primordial supermassive stars by rapid mass accretion

    SciTech Connect

    Hosokawa, Takashi; Yoshida, Naoki [Department of Physics and Research Center for the Early Universe, The University of Tokyo, Tokyo 113-0033 (Japan); Yorke, Harold W. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Inayoshi, Kohei; Omukai, Kazuyuki, E-mail: takashi.hosokawa@phys.s.u-tokyo.ac.jp, E-mail: hosokwtk@gmail.com [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)

    2013-12-01

    Supermassive stars (SMSs) forming via very rapid mass accretion ( M-dot {sub ?}?0.1 M{sub ?} yr{sup ?1}) could be precursors of supermassive black holes observed beyond a redshift of about six. Extending our previous work, here we study the evolution of primordial stars growing under such rapid mass accretion until the stellar mass reaches 10{sup 4–5} M {sub ?}. Our stellar evolution calculations show that a star becomes supermassive while passing through the 'supergiant protostar' stage, whereby the star has a very bloated envelope and a contracting inner core. The stellar radius increases monotonically with the stellar mass until ? 100 AU for M {sub *} ? 10{sup 4} M {sub ?}, after which the star begins to slowly contract. Because of the large radius, the effective temperature is always less than 10{sup 4} K during rapid accretion. The accreting material is thus almost completely transparent to the stellar radiation. Only for M {sub *} ? 10{sup 5} M {sub ?} can stellar UV feedback operate and disturb the mass accretion flow. We also examine the pulsation stability of accreting SMSs, showing that the pulsation-driven mass loss does not prevent stellar mass growth. Observational signatures of bloated SMSs should be detectable with future observational facilities such as the James Webb Space Telescope. Our results predict that an inner core of the accreting SMS should suffer from the general relativistic instability soon after the stellar mass exceeds 10{sup 5} M {sub ?}. An extremely massive black hole should form after the collapse of the inner core.

  15. An atlas of 2.4 to 4.1 microns ISO/SWS spectra of early-type stars

    E-print Network

    A. Lenorzer; B. Vandenbussche; P. Morris; A. de Koter; T. R. Geballe; L. B. F. M. Waters; S. Hony; L. Kaper

    2002-01-11

    We present an atlas of spectra of O- and B-type stars, obtained with the Short Wavelength Spectrometer (SWS) during the Post-Helium program of the Infrared Space Observatory (ISO). This program is aimed at extending the Morgan & Keenan classification scheme into the near-infrared. Later type stars will be discussed in a seperate publication. The observations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1 microns, supplemented with 10 spectra acquired during the nominal mission with a similar observational setting. For B-type stars, this sample provides ample spectral converage in terms of subtype and luminosity class. For O-type stars,the ISO sample is coarse and therefore is complemented with 8 UKIRT L'-band observations. In terms of the presence of diagnostic lines, the L'-band is likely the most promising of the near-infrared atmospheric windows for the study of the physical properties of B stars. Specifically, this wavelength interval contains the Brackett alpha, Pfund gamma, and other Pfund lines which are probes of spectral type, luminosity class and mass loss. Here, we present simple empirical methods based on the lines present in the 2.4 to 4.1 microns interval that allow the determination of: the spectral type of B dwarfs and giants to within two subtypes; the luminosity class of B stars to within two classes; the mass-loss rate of O stars and B supergiants to within 0.25 dex.

  16. Stellar evolution with rotation. VII. . Low metallicity models and the blue to red supergiant ratio in the SMC

    Microsoft Academic Search

    A. Maeder; G. Meynet

    2001-01-01

    We calculate a grid of models with and without the effects of axial rotation for massive stars in the range of 9 to 60 Msun and metallicity Z = 0.004 appropriate for the SMC. Remarkably, the ratios Omega \\/Omega crit of the angular velocity to the break-up angular velocity grow strongly during the evolution of high mass stars, contrary to

  17. Non-LTE analysis of the Ofpe/WN9 star HDE 269227 (R84)

    NASA Technical Reports Server (NTRS)

    Schmutz, Werner; Leitherer, Claus; Hubeny, Ivan; Vogel, Manfred; Hamann, Wolf-Rainer

    1991-01-01

    The paper presents the results of a spectral analysis of the Ofpe/WN9 star HD 269227 (R84), which assumes a spherically expanding atmosphere to find solutions for equations of radiative transfer. The spectra of hydrogen and helium were predicted with a non-LTE model. Six stellar parameters were determined for R84. The shape of the velocity law is empirically found, since it can be probed from the terminal velocity of the wind. The six stellar parameters are further employed in a hydrodynamic model where stellar wind is assumed to be directed by radiation pressure, duplicating the mass-loss rate and the terminal wind velocity. The velocity laws found by computation and analysis are found to agree, supporting the theory of radiation-driven stellar wind. R84 is surmised to be a post-red supergiant which lost half of its initial mass, possibly during the red-supergiant phase. This mass loss is also suggested by its spectroscopic similarity to S Doradus.

  18. Spectroscopy: Star Light, Star Bright

    NSDL National Science Digital Library

    This is a student reading about the different types of spectra: continuous, absorption, and emission. Learners will read about the differences between each and see graphical representations of each. This activity is from the Stanford Solar Center's All About the Sun: Sun and Stars activity guide for Grades 5-8 and can also accompany the Stanford Solar Center's Build Your Own Spectroscope activity.

  19. Mass loss and rotational CO emission from Asymptotic Giant Branch stars

    E-print Network

    F. Kemper; R. Stark; K. Justtanont; A. de Koter; A. G. G. M. Tielens; L. B. F. M. Waters; J. Cami; C. Dijkstra

    2003-05-12

    We present submillimeter observations of rotational transitions of carbon monoxide from J = 2 -> 1 up to 7 -> 6 for a sample of Asymptotic Giant Branch stars and red supergiants. It is the first time that the high transitions J = 6 -> 5 and 7 -> 6 are included in such a study. With line radiative transfer calculations, we aim to determine the mass-loss history of these stars by fitting the CO line intensities. We find that the observed line intensities of the high transitions, including the J = 4 -> 3 transition, are significantly lower than the predicted values. We conclude that the physical structure of the outflow of Asymptotic Giant Branch stars is more complex than previously thought. In order to understand the observed line intensities and profiles, a physical structure with a variable mass-loss rate and/or a gradient in stochastic gas velocity is required. A case study of the AGB star WX Psc is performed. We find that the CO line strengths may be explained by variations in mass-loss on time scales similar to those observed in the separated arc-like structures observed around post-AGB stars. In addition, a gradient in the stochastic velocity may play a role. Until this has been sorted out fully, any mass loss determinations based upon single CO lines will remain suspect.

  20. VLTI observations of the dust geometry around R Coronae Borealis stars

    E-print Network

    Bright, S N; Clayton, G C; De Marco, O; Leão, I C; Nordhaus, J; Gallagher, J S

    2011-01-01

    We are investigating the formation and evolution of dust around the hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim to determine the connection between the probable merger past of these stars and their current dust-production activities. We carried out high-angular resolution interferometric observations of three RCB stars, namely RY Sgr, V CrA, and V854 Cen with the mid-IR interferometer, MIDI on the VLTI, using two telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the dusty environment at very small spatial scales (~ 50 mas or 400 stellar radii). The observations of the RCB star dust environments were interpreted using both geometrical models and one-dimensional radiative transfer codes. From our analysis we find that asymmetric circumstellar material is apparent in RY Sgr, may also exist in V CrA, and is possible for V854 Cen. Overall, we find that our observations are consistent with dust forming in clumps ejected randomly around the RCB star so tha...

  1. Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams

    E-print Network

    R. D. Blum; J. R. Mould; K. A. Olsen; J. A. Frogel; M. Werner; M. Meixner; F. Markwick-Kemper; R. Indebetouw; B. Whitney; M. Meade; B. Babler; E. B. Churchwell; K. Gordon; C. Engelbracht; B. -Q. For; K. Misselt; U. Vijh; C. Leitherer; K. Volk; S. Points; W. Reach; J. L. Hora; J. -P. Bernard; F. Boulanger; S. Bracker; M. Cohen; Y. Fukui; J. Gallagher; V. Gorjian; J. Harris; D. Kelly; A. Kawamura; W. B. Latter; S. Madden; A. Mizuno; N. Mizuno; A. Nota; M. S. Oey; T. Onishi; R. Paladini; N. Panagia; P. Perez-Gonzalez; H. Shibai; S. Sato; L. Smith; L. Staveley-Smith; A. G. G. M. Tielens; T. Ueta; S. Van Dyk; D. Zaritsky

    2006-08-08

    Color-magnitude diagrams (CMDs) are presented for the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the Large Magellanic Cloud (LMC). IRAC and MIPS 24 um epoch one data are presented. These data represent the deepest, widest mid-infrared CMDs of their kind ever produced in the LMC. Combined with the 2MASS survey, the diagrams are used to delineate the evolved stellar populations in the Large Magellanic Cloud as well as Galactic foreground and extragalactic background populations. Some 32000 evolved stars brighter than the tip of the red giant branch are identified. Of these, approximately 17500 are classified as oxygen-rich, 7000 carbon-rich, and another 1200 as ``extreme'' asymptotic giant branch (AGB) stars. Brighter members of the latter group have been called ``obscured'' AGB stars in the literature owing to their dusty circumstellar envelopes. A large number (1200) of luminous oxygen--rich AGB stars/M supergiants are also identified. Finally, there is strong evidence from the 24 um MIPS channel that previously unexplored, lower luminosity oxygen-rich AGB stars contribute significantly to the mass loss budget of the LMC (1200 such sources are identified).

  2. VizieR Online Data Catalog: Lick indicies for FGK stars (Franchini+, 2014)

    NASA Astrophysics Data System (ADS)

    Franchini, M.; Morossi, C.; Marcantonio, P. D.; Malagnini, M. L.; Chavez, M.

    2015-02-01

    The stars observed by FEROS and studied by the AMBRE project (Worley et al., 2012A&A...542A..48W) constitute an ideal working data set for our purposes since they include a large number of non-supergiant FGK stars with individual estimates of Teff, log g, [M/H], and ?-to-iron ratio ([alpha/Fe]). We searched the European Southern Observatory (ESO) Science Archive Facility and retrieved, through the FEROS/HARPS pipeline processed data Query Form, all the public available spectra of FGK stars with AMBRE atmospheric parameter values in the following ranges: 38003.5, and global metallicity [M/H]>-3.0. A list of 1085 stars, corresponding to 2511 available spectra, was obtained. Since AMBRE provides individual estimates of stellar parameters derived from each spectrum, we computed for 202 stars with more than one observed spectrum average atmospheric parameter values. In any case, the dispersion of values for the same object resulted to be less than the external errors associated with AMBRE results. (1 data file).

  3. Low-metallicity massive single stars with rotation. Evolutionary models applicable to I Zwicky 18

    E-print Network

    Szécsi, D; Yoon, S -C; Sanyal, D; de Mink, S; Evans, C J; Dermine, T

    2015-01-01

    Massive rotating single stars with an initial metal composition appropriate for the dwarf galaxy I Zw 18 ([Fe/H]=$-$1.7) are modelled during hydrogen burning for initial masses of 9-300 M$_{\\odot}$ and rotational velocities of 0-900 km s$^{-1}$. Internal mixing processes in these models were calibrated based on an observed sample of OB-type stars in the Magellanic Clouds. Even moderately fast rotators, which may be abundant at this metallicity, are found to undergo efficient mixing induced by rotation resulting in quasi chemically-homogeneous evolution. These homogeneously-evolving models reach effective temperatures of up to 90 kK during core hydrogen burning. This, together with their moderate mass-loss rates, make them Transparent Wind Ultraviolet INtense stars (TWUIN star), and their expected numbers might explain the observed HeII ionizing photon flux in I Zw 18 and other low-metallicity HeII galaxies. Our slowly rotating stars above $\\sim$80 M$_{\\odot}$ evolve into late B- to M-type supergiants during c...

  4. Fundamental parameters of Wolf-Rayet stars. I. Ofpe/WN9 stars.

    NASA Astrophysics Data System (ADS)

    Crowther, P. A.; Hillier, D. J.; Smith, L. J.

    1995-01-01

    A detailed study has been carried out for 4 LMC Ofpe/WN9 (`slash') stars, and the sole Galactic WN9 star WR108 (HDE 313846), using new high S/N spectroscopy and archive UV and near-IR spectroscopy. Our observations reveal that photospheric Of features such as HeII?4542 are absent from the optical spectra of our sampled stars. All observed optical lines are formed in the stellar wind, and so we prefer WN9 or WN10 classifications based on the relative strengths of NII?3995 and NIII?4634-41, with BE 381 and Sk-66 40 prototype WN9 and WN10 stars, respectively. HDE 269927c and R84 are given WN9 classifications, with WR108 newly assigned WN9+abs due to the spectral appearance of the upper Balmer series. The distance to WR108 is determined from an analysis of its interstellar spectrum. Previously WR108 has been considered to be a possible member of Sgr OB1 (1.6 kpc, Lundstroem & Stenholm 1984[LS84]) which results in a uniquely low stellar luminosity for this type of object. Using the standard Galactic rotation curve of Fich et al. (1989) we derive 5+/-1 kpc, resulting in a luminosity very similar to R84. Tailored analyses using the WR standard model, including metals, result in the following stellar parameters for all stars: T_*_=29.5+/-1.0kK, L/Lsun_=10^5.65+/-0.2^, ?(M)=3.5+/-1x10^-5^Msun_/yr and vinfinity_=400+/-100km/s (vinfinity_=1170km/s for WR108). The stellar parameters determined for R84 compare well with those determined previously by Schmutz et al. (1991)[SCH+91] indicating that the effect of CNO elements is negligible for WN stars. The metallicity of the LMC stars is around Z~0.008 while Z~0.035 results for the Galactic WN9 star. Abundances for the LMC stars (H/He=2.5+/-1, N/He~0.003, C/N~0.1) are in reasonable agreement with the results of evolutionary models at low metallicity (Schaerer et al. 1993a) although observed luminosities are significantly lower than predictions for stars entering the WR phase. The luminosity and chemistry of R84 are identical to that of the Luminous Blue Variable (LBV) R71 indicating that it is probably associated with an LBV phase rather than a post-red supergiant as suggested by Schmutz et al. (1991). The status of the remaining LMC stars is less clear, although their common spectral characteristics suggest that they are also related to LBVs, with Sk-66 40 the least evolved of the present sample. For WR108, its spectral appearance, derived parameters and abundances (H/He=1.5, C/N~0.10) suggest an intimate relationship with extreme Galactic Ofpe stars, with the wind density being the principal difference, and evolution probably proceeding directly from Of to Wolf-Rayet.

  5. New Magellanic Cloud R Coronae Borealis and DY Persei type stars from the EROS-2 database: the connection between RCBs, DYPers, and ordinary carbon stars

    NASA Astrophysics Data System (ADS)

    Tisserand, P.; Wood, P. R.; Marquette, J. B.; Afonso, C.; Albert, J. N.; Andersen, J.; Ansari, R.; Aubourg, É.; Bareyre, P.; Beaulieu, J. P.; Charlot, X.; Coutures, C.; Ferlet, R.; Fouqué, P.; Glicenstein, J. F.; Goldman, B.; Gould, A.; Gros, M.; de Kat, J.; Lesquoy, É.; Loup, C.; Magneville, C.; Maurice, É.; Maury, A.; Milsztajn, A.; Moniez, M.; Palanque-Delabrouille, N.; Perdereau, O.; Rich, J.; Schwemling, P.; Spiro, M.; Vidal-Madjar, A.

    2009-07-01

    Context: R Coronae Borealis stars (RCB) are a rare type of evolved carbon-rich supergiant stars that are increasingly thought to result from the merger of two white dwarfs, called the Double degenerate scenario. This scenario is also studied as a source, at higher mass, of type Ia Supernovae (SnIa) explosions. Therefore a better understanding of RCBs composition would help to constrain simulations of such events. Aims: We searched for and studied RCB stars in the EROS Magellanic Clouds database. We also extended our research to DY Per type stars (DYPers) that are expected to be cooler RCBs (T ˜ 3500 K) and much more numerous than their hotter counterparts. With the aim of studying possible evolutionary connections between RCBs and DYPers, and also ordinary carbon stars, we compared their publically available broad band photometry in the optical, near, and mid-infrared. Methods: The light curves of ~70 millions stars, monitored for 6.7 years (from July 1996 to February 2003), have been analysed to search for the main signature of RCBs and DYPers: a large (up to 9 mag) drop in luminosity. Carbon stars with fading episodes were also found by inspecting numerous light curves of objects that presented an infrared excess in the 2MASS and Spitzer- SAGE and S^3MC databases. Follow-up optical spectroscopy was used to confirm each photometric candidate found. Results: We have discovered and confirmed 6 new Magellanic Cloud RCB stars and 7 new DYPers, but also listed new candidates: 3 RCBs and 14 DYPers. Optical and infrared colour magnitude diagrams that give new insights into these two sets of stars are discussed. We estimated a range of Magellanic RCB shell temperatures between 360 and 600 K. Conclusions: We confirm the wide range of absolute luminosity known for RCB stars, MV ˜ -5.2 to -2.6. Our study further shows that mid-infrared surveys are ideal to search for RCB stars, since they have thinner and cooler circumstellar shells than classical post-AGB stars. In addition, by increasing the number of known DYPers by ~400%, we have been able to shed light on the similarities in the spectral energy distribution between DYPers and ordinary carbon stars. We also observed that DYPer circumstellar shells are fainter and hotter than those of RCBs. This suggests that DYPers may simply be ordinary carbon stars with ejection events, but more abundance analysis is necessary to give a status on a possible evolutionnary connexion between RCBs and DYPers. Based on observations made with the CNRS/INSU MARLY telescope at the European Southern Observatory, La Silla, Chile. Figures 7-13 are only available in electronic form at http://www.aanda.org

  6. Boron Abundances in A and B-type Stars

    NASA Technical Reports Server (NTRS)

    Lambert, David L.

    1997-01-01

    Boron abundances in A- and B-type stars may be a successful way to track evolutionary effects in these hot stars. The light elements - Li, Be, and B - are tracers of exposure to temperatures more moderate than those in which the H-burning CN-cycle operates. Thus, any exposure of surface stellar layers to deeper layers will affect these light element abundances. Li and Be are used in this role in investigations of evolutionary processes in cool stars, but are not observable in hotter stars. An investigation of boron, however, is possible through the B II 1362 A resonance line. We have gathered high resolution spectra from the IUE database of A- and B-type stars near 10 solar mass for which nitrogen abundances have been determined. The B II 1362 A line is blended throughout; the temperature range of this program, requiring spectrum syntheses to recover the boron abundances. For no star could we synthesize the 1362 A region using the meteoritic/solar boron abundance of log e (B) = 2.88; a lower boron abundance was necessary which may reflect evolutionary effects (e.g., mass loss or mixing near the main-sequence), the natal composition of the star forming regions, or a systematic error in the analyses (e.g., non-LTE effects). Regardless of the initial boron abundance, and despite the possibility of non-LTE effects, it seems clear that boron is severely depleted in some stars. It may be that the nitrogen and boron abundances are anticorrelated, as would be expected from mixing between the H-burning and outer stellar layers. If, as we suspect, a residue of boron is present in the A-type supergiants, we may exclude a scenario in which mixing occurs continuously between the surface and the deep layers operating the CN-cycle. Further exploitation of the B II 1362 A line as an indicator of the evolutionary status of A- and B-type stars will require a larger stellar sample to be observed with higher signal-to-noise as attainable with the Hubble Space Telescope.

  7. Observational constraints for the circumstellar disk of the B[e] star CPD-52 9243

    NASA Astrophysics Data System (ADS)

    Cidale, L. S.; Borges Fernandes, M.; Andruchow, I.; Arias, M. L.; Kraus, M.; Chesneau, O.; Kanaan, S.; Curé, M.; de Wit, W. J.; Muratore, M. F.

    2012-12-01

    Context. The formation and evolution of gas and dust environments around B[e] supergiants are still open issues. Aims: We intend to study the geometry, kinematics and physical structure of the circumstellar environment (CE) of the B[e] supergiant CPD-52 9243 to provide further insights into the underlying mechanism causing the B[e] phenomenon. Methods: The influence of the different physical mechanisms acting on the CE (radiation pressure, rotation, bi-stability or tidal forces) is somehow reflected in the shape and kinematic properties of the gas and dust regions (flaring, Keplerian, accretion or outflowing disks). To investigate these processes we mainly used quasi-simultaneous observations taken with high spatial resolution optical long-baseline interferometry (VLTI/MIDI), near-IR spectroscopy of CO bandhead features (Gemini/Phoenix and VLT/CRIRES) and optical spectra (CASLEO/REOSC). Results: High angular resolution interferometric measurements obtained with VLTI/MIDI provide strong support for the presence of a dusty disk(ring)-like structure around CPD-52 9243, with an upper limit for its inner edge of ~8 mas (~27.5 AU, considering a distance of 3.44 kpc to the star). The disk has an inclination angle with respect to the line of sight of 46 ± 7°. The study of CO first overtone bandhead evidences a disk structure in Keplerian rotation. The optical spectrum indicates a rapid outflow in the polar direction. Conclusions: The IR emission (CO and warm dust) indicates Keplerian rotation in a circumstellar disk while the optical line transitions of various species are consistent with a polar wind. Both structures appear simultaneously and provide further evidence for the proposed paradigms of the mass-loss in supergiant B[e] stars. The presence of a detached cold CO ring around CPD-52 9243 could be due to a truncation of the inner disk caused by a companion, located possibly interior to the disk rim, clearing the center of the system. More spectroscopic and interferometric data are necessary to determine a possible binary nature of the star. Based on observations taken with: 1) Telescopes at Paranal ESO Observatory under the program 085.D-0454 and 385.D-0513A; 2) Gemini South/Phoenix instrument, science program GS-2010A-Q-41; 3) J. Sahade Telescope at Complejo Astronómico El Leoncito (CASLEO), operated under an agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, the Secretaría de Ciencia y Tecnología de la Nación and the National Universities of La Plata, Córdoba and San Juan.

  8. THE NUCLEOSYNTHETIC IMPRINT OF 15-40 M{sub sun} PRIMORDIAL SUPERNOVAE ON METAL-POOR STARS

    SciTech Connect

    Joggerst, C. C.; Woosley, S. E. [Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95060 (United States); Almgren, A.; Bell, J. [Computational Research Division, Lawrence Berkeley National Lab, Berkeley, CA 94720 (United States); Heger, Alexander [School of Physics and Astronomy, University of Minnesota, Twin Cities, Minneapolis, MN 55455 (United States); Whalen, Daniel, E-mail: cchurch@ucolick.or [Theoretical Astrophysics (T-2), Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2010-01-20

    The inclusion of rotationally induced mixing in stellar evolution can alter the structure and composition of pre-supernova stars. We survey the effects of progenitor rotation on nucleosynthetic yields in Population III and II supernovae (SNe) using the new adaptive mesh refinement code CASTRO. We examine piston-driven spherical explosions in 15, 25, and 40 M{sub sun} stars at Z = 0 and 10{sup -4} Z{sub sun} with three explosion energies and two rotation rates. Rotation in the Z = 0 models resulted in primary nitrogen production and a stronger hydrogen burning shell which led all models to die as red supergiants (in contrast to the blue supergiant progenitors made without rotation). On the other hand, the Z = 10{sup -4} Z{sub sun} models that included rotation ended their lives as compact blue stars. Because of their extended structure, the hydrodynamics favors more mixing and less fallback in the metal-free stars than the Z = 10{sup -4} models. As expected, higher energy explosions produce more enrichment and less fallback than do lower energy explosions, and at constant explosion energy, less massive stars produce more enrichment and leave behind smaller remnants than do more massive stars. We compare our nucleosynthetic yields to the chemical abundances in the three most iron-poor stars yet found and reproduce the abundance pattern of one, HE 0557-4840, with a zero metallicity, 15 M{sub sun}, 2.4 x 10{sup 51} erg SN. A Salpeter IMF-averaged integration of our yields for Z = 0 models with explosion energies of 2.4 x 10{sup 51} erg or less is in good agreement with the abundances observed in larger samples of extremely metal-poor (EMP) stars, provided 15 M{sub sun} stars are included. Since the abundance patterns of EMP stars likely arise from a representative sample of progenitors, our yields suggest that 15-40 M{sub sun} core-collapse SNe with moderate explosion energies contributed the bulk of the metals to the early universe.

  9. Energy Star

    E-print Network

    Reihl, K.; Tullos, A.

    2012-01-01

    ENERGY STAR ENERGY TARGETS ESL-KT-12-10-08 CATEE 2012: Clean Air Through Energy Efficiency Conference, Galveston, TX, October 9-11, 2012 POP QUIZ!!!! What is EUI?? Energy Use Intensity Do you know the EUI and any of the buildings you designed... submit anytime before earn utility bills ? Project Types ? Commercial buildings (office, schools, hotels, banks, courthouses, warehouses, big box retail, etc.) ? Target Finder ? Achieve an EPA rating of 75 or greater ? Submit two documents 1...

  10. Christmas star.

    NASA Astrophysics Data System (ADS)

    Bia?a, J.

    There are continuous attempts to identify the legendary Christmas Star with a real astronomical event accompanying the birth of Jesus from Nazareth. Unfortunately, the date of birth is difficult to establish on the basis of historical records with better accuracy than a few years. During that period a number of peculiar astronomical events were observed and it seem to be impossible to identify the right one unambiguously.

  11. IGR J17544-2619 in Depth With Suzaku: Direct Evidence for Clumpy Winds in a Supergiant Fast X-ray Transient

    NASA Astrophysics Data System (ADS)

    Rampy, Rachel A.; Smith, David M.; Negueruela, Ignacio

    2009-12-01

    We present direct evidence for dense clumps of matter in the companion wind in a Supergiant Fast X-ray Transient (SFXT) binary. This is seen as a brief period of enhanced absorption during one of the bright, fast flares that distinguish these systems. The object under study was IGR J17544-2619, and a total of 236 ks of data were accumulated with the Japanese satellite Suzaku. The activity in this period spans a dynamic range of almost 104 in luminosity and gives a detailed look at SFXT behavior.

  12. IGR J17544-2619 IN DEPTH WITH SUZAKU: DIRECT EVIDENCE FOR CLUMPY WINDS IN A SUPERGIANT FAST X-RAY TRANSIENT

    SciTech Connect

    Rampy, Rachel A.; Smith, David M. [Physics Department and Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA (United States); Negueruela, Ignacio, E-mail: rrampy@ucsc.ed [Departamento de Fisica, IngenierIa de Sistemas y TeorIa de la Senal, Universidad de Alicante, Apartado 99 E03080, Alicante (Spain)

    2009-12-10

    We present direct evidence for dense clumps of matter in the companion wind in a Supergiant Fast X-ray Transient (SFXT) binary. This is seen as a brief period of enhanced absorption during one of the bright, fast flares that distinguish these systems. The object under study was IGR J17544-2619, and a total of 236 ks of data were accumulated with the Japanese satellite Suzaku. The activity in this period spans a dynamic range of almost 10{sup 4} in luminosity and gives a detailed look at SFXT behavior.

  13. Mass loss from cool stars, facts, fads, and fallacies

    NASA Astrophysics Data System (ADS)

    Dupree, A. K.

    The accumulation of observational material (ultraviolet spectroscopic measures, quantitative optical spectroscopy, and X-ray photometry) and its use in discerning the presence and character of mass loss across the cool half of the H-R diagram and establishing constraints on theoretical models are discussed. Analogies with closed and open solar magnetic structures are found. Two determinants of atmospheric wind structure, temperature and gravity, may suffice in a most superficial way to define the wind and atmospheric structure in a star, however it is apparent that there is still a missing parameter which may stem from magnetic activity and its particular configuration. Theories that appear successful in reproducing observed line profiles, wind temperatures, and terminal velocities incorporate Alfven wave heating and momentum deposition. Successive observations of an active binary (lambda and G8III-IV) and a supergiant star, alpha Aqr (G2 Ib) revealed that magnetic activity and perhaps mass loss occur on restricted regions of a stellar surface and that long-term structures are present in the wind. These phenomena are present in the solar atmosphere and wind and may be considered a general characteristic of stellar winds.

  14. Mass loss from cool stars, facts, fads, and fallacies

    NASA Technical Reports Server (NTRS)

    Dupree, A. K.

    1982-01-01

    The accumulation of observational material (ultraviolet spectroscopic measures, quantitative optical spectroscopy, and X-ray photometry) and its use in discerning the presence and character of mass loss across the cool half of the H-R diagram and establishing constraints on theoretical models are discussed. Analogies with closed and open solar magnetic structures are found. Two determinants of atmospheric wind structure, temperature and gravity, may suffice in a most superficial way to define the wind and atmospheric structure in a star, however it is apparent that there is still a missing parameter which may stem from magnetic activity and its particular configuration. Theories that appear successful in reproducing observed line profiles, wind temperatures, and terminal velocities incorporate Alfven wave heating and momentum deposition. Successive observations of an active binary (lambda and G8III-IV) and a supergiant star, alpha Aqr (G2 Ib) revealed that magnetic activity and perhaps mass loss occur on restricted regions of a stellar surface and that long-term structures are present in the wind. These phenomena are present in the solar atmosphere and wind and may be considered a general characteristic of stellar winds.

  15. The Abundance of Boron in Evolved A- and B-Type Stars

    E-print Network

    Kim A. Venn; David L. Lambert; Michael Lemke

    1995-08-01

    Boron abundances in A- and B-type stars may be a successful way to track evolutionary effects in these hot stars. The light elements -- Li, Be, and B -- are tracers of exposure to temperatures more moderate than those in which the H-burning CN-cycle operates. Thus, any exposure of surface stellar layers to deeper layers will affect these light element abundances. Li and Be are used in this role in investigations of evolutionary processes in cool stars, but are not observable in hotter stars. An investigation of boron, however, is possible through the B II 1362=C5 resonance line. We have gathered high resolution spectra from the IUE database of A- and B-type stars near 10~M$_\\odot$ for which nitrogen abundances have been determined (by Gies & Lambert, 1992, and Venn 1995). The B II 1362=C5 line is blended throughout the temperature range of this program, requiring spectrum syntheses to recover the boron abundances. For no star could we synthesize the 1362=C5 region using the meteoritic/solar boron abundance of log(B) =3D 2.88 (Anders & Grevesse 1989); a lower boron abundance was necessary which may reflect evolutionary effects (e.g., mass loss or mixing near the main-sequence), the natal composition of the star forming regions, or a systematic error in the analyses (e.g., non-LTE effects). Regardless of the initial boron abundance, and despite the possibility of non-LTE effects, it seems clear that boron is severely depleted in some stars. It may be that the nitrogen and boron abundances are anticorrelated, as would be expected from mixing between the H-burning and outer stellar layers. If, as we suspect, a residue of boron is present in the A-type supergiants, we may exclude a scenario in which mixing occurs continuously between the surface and the deep

  16. New R Coronae Borealis stars discovered in OGLE-III Galactic Bulge fields from their mid- and near- infrared properties

    E-print Network

    Tisserand, P; Wood, P R; Udalski, A; Szyma?ski, M K; Kubiak, M; Pietrzy?ski, G; Soszy?ski, I; Szewczyk, O; Ulaczyk, K; Poleski, R

    2010-01-01

    An R Coronae Borealis (RCB) star is a rare type of supergiant star that is increasingly thought to be the evolved merger product of two white dwarfs. Recently, many of them have been found distributed in a thin disk structure embedded inside the Galactic Bulge. This unexpected high density can give us more insight into the nature and age of RCB stars. We applied and tested successfully a new technique to find RCB stars based on the particular infrared emission. We demonstrated that RCB stars can now be found without the need of a light curve analysis, and therefore outside optically monitored fields. The selection of RCB candidates was based on their near-infrared excess and on particular mid-infrared emission of RCB shells, using photometric data from the 2MASS and Spitzer/GLIMPSE surveys. The OGLE light curves of all RCB candidates were then inspected visually and the ones presenting large and fast declines were followed-up spectroscopically . We discovered two new R Coronae Borealis stars, but also propose...

  17. Binary stars.

    PubMed

    Paczynacuteski, B

    1984-07-20

    Most stars in the solar neighborhood are either double or multiple systems. They provide a unique opportunity to measure stellar masses and radii and to study many interesting and important phenomena. The best candidates for black holes are compact massive components of two x-ray binaries: Cygnus X-1 and LMC X-3. The binary radio pulsar PSR 1913 + 16 provides the best available evidence for gravitational radiation. Accretion disks and jets observed in close binaries offer a very good testing ground for models of active galactic nuclei and quasars. PMID:17749544

  18. Double core evolution. 7: The infall of a neutron star through the envelope of its massive star companion

    NASA Technical Reports Server (NTRS)

    Terman, James L.; Taam, Ronald E.; Hernquist, Lars

    1995-01-01

    Binary systems with properties similar to those of high-mass X-ray binaries are evolved through the common envelope phase. Three-dimensional simulations show that the timescale of the infall phase of the neutron star depends upon the evolutionary state of its massive companion. We find that tidal torques more effectively accelerate common envelope evolution for companions in their late core helium-burning stage and that the infall phase is rapid (approximately several initial orbital periods). For less evolved companions the decay of the orbit is longer; however, once the neutron star is deeply embedded within the companion's envelope the timescale for orbital decay decreases rapidly. As the neutron star encounters the high-density region surrounding the helium core of its massive companion, the rate of energy loss from the orbit increases dramatically leading to either partial or nearly total envelope ejection. The outcome of the common envelope phase depends upon the structure of the evolved companion. In particular, it is found that the entire common envelope can be ejected by the interaction of the neutron star with a red supergiant companion in binaries with orbital periods similar to those of long-period Be X-ray binaries. For orbital periods greater than or approximately equal to 0.8-2 yr (for companions of mass 12-24 solar mass) it is likely that a binary will survive the common envelope phase. For these systems, the structure of the progenitor star is characterized by a steep density gradient above the helium core, and the common envelope phase ends with a spin up of the envelope to within 50%-60% of corotation and with a slow mass outflow. The efficiency of mass ejection is found to be approximately 30%-40%. For less evolved companions, there is insufficient energy in the orbit to unbind the common envelope and only a fraction of it is ejected. Since the timescale for orbital decay is always shorter than the mass-loss timescale from the common envelope, the two cores will likely merge to form a Thorne-Zytkow object. Implications for the origin of Cyg X-3, an X-ray source consisting of a Wolf-Rayet star and a compact companion, and for the fate of the remnant binary consisting of a helium star and a neutron star are briefly discussed.

  19. Bispectrum speckle interferometry observations and radiative transfer modelling of the red supergiant NML Cyg Multiple dust-shell structures evidencing previous superwind phases

    E-print Network

    Blöcker, T; Hofmann, Karl Heinrich; Weigelt, G

    2001-01-01

    (abridged) NML Cyg is a highly evolved OH/IR supergiant and supposed to be among the most luminous supergiants in the galaxy. We present the first diffraction limited 2.13micron observations of NML Cyg with 73mas resolution. The speckle interferograms were obtained with the SAO 6m telescope, image reconstruction is based on the bispectrum speckle interferometry method. Radiative transfer calculations have been carried out to model the spectral energy distribution, our 2.13micron visibility function, and mid-infrared visibility functions. The observed dust shell properties do not appear to be in accordance with single-shell models but seem to require multiple components. Considering previous periods of enhanced mass-loss, various density enhancements in the dust shell were taken into account. An extensive grid of models was calculated for different locations and strenghts of such superwind regions in the dust shell. To match the observations from the optical to the sub-mm domain requires at least two superwind...

  20. Spectral synthesis in the ultraviolet. II - Stellar populations and star formation in blue compact galaxies

    NASA Technical Reports Server (NTRS)

    Fanelli, Michael N.; O'Connell, Robert W.; Thuan, Trinh X.

    1988-01-01

    An initial attempt to apply optimizing spectral synthesis techniques to the far-UV spectra of blue compact galaxies (BCGs) is presented. The far-UV absorption-line spectra of the galaxies are clearly composite, with the signatures of the main-sequence types between O3 and mid-A. Most of the low-ionization absorption lines have a stellar origin. The Si IV and C IV features in several objects have P Cygni profiles. In Haro I the strength of Si IV indicates a significant blue supergiant population. The metal-poor blue compact dwarf Mrk 209 displays weak absorption lines, evidence that the stellar component has the same low metallicity as observed in the ionized gas. Good fits to the data are obtained the technique of optimizing population synthesis. The solutions yield stellar luminosity functions which display large discontinuities, indicative of discrete star formation episodes or bursts. The amount of UV extinction is low.

  1. Mining the Advanced Spectral Library (ASTRAL): Fluorescence in Evolved M-Stars

    NASA Astrophysics Data System (ADS)

    Carpenter, Kenneth G.; Nielsen, K. E.; Kober, G. V.; Cheng, K.; Ayres, T. R.; Wahlgren, G. M.; Harper, G.

    2013-01-01

    The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres) is an HST Cycle 18 Treasury Program designed to collect a definitive set of representative, high-resolution ( 46,000 in the FUV up to ~1700 Å, 30,000 for 1700-2150 Å, and 114,000 >2150 Å) and high signal/noise (S/N>100) UV spectra of eight F-M evolved cool stars. These extremely high-quality STIS UV echelle spectra are available from the HST archive and through the University of Colorado (http://casa.colorado.edu ayres/ASTRAL/) and will enable investigations of a broad range of problems -- stellar, interstellar, and beyond -- for many years. In this paper, we use the very rich emission-line spectra of the two evolved M stars in the sample, the M3.4 giant Gamma Crucis (GaCrux) and the M2Iab supergiant Alpha Orionis (Betelgeuse), to study the fluorescence processes operating in their outer atmospheres. We summarize the pumping transitions and fluorescent line products known on the basis of previous work (e.g. Carpenter 1988 and references therein) and newly identified in our current, on-going analysis and provide some comments on their implications for the structure of the outer atmospheres of these stars.

  2. Non-linear Oscillations of Massive Stars Near the Eddington Limit

    NASA Astrophysics Data System (ADS)

    Sanyal, Debashis; Langer, Norbert

    2013-06-01

    The physics of massive star evolution, even on the main sequence is marred by uncertainties and hence, poorly understood. The focus of our work lies on the evolution of very massive stars on the main sequence when they approach the Eddington limit. Massive stars evolving near the Eddington limit are characterized by pronounced core-halo structures (Ishii et al. 1999) with extended low density envelopes accounting for even ~ 70% of the stellar radius, and density inversions (Petrovic et al. 2006, Graefener et al. 2011). These are ideal conditions or radial oscillations called ``strange modes'' (Glatzel 2004) which have very small growth times (~ dynamical timescale). We present non-linear calculations of these pulsations using a state-of-the-art one-dimensional hydrodynamic stellar evolution code (BEC) and latest input physics. The brightness perturbations caused as a result may relate to the microvariations observed in LBVs like AG Car (Lamers et al. 2004) or in supergiants like Deneb. Moreover, the feature of inflated envelopes coupled with the dynamic pulsations can play a major role in the modelling of mass transfer in very massive binary systems. We investigate how mass loss (through RLOF or wind) from such inflated stars may affect the envelope structure.

  3. H? Variability in the A-Type Hypergiant Star 6 Cassiopeiae

    NASA Astrophysics Data System (ADS)

    Fischer, W. J.; Morrison, N. D.

    1999-05-01

    The star 6 Cas (A3 Ia(+) ) is typical of the optically brightest stars in external galaxies, which have been proposed as extragalactic distance indicators through the wind momentum-luminosity relation (e.g., McCarthy et al. 1997, ApJ, 482, 757). In this method, usually a single high-resolution, long-exposure spectrum is modeled to derive the stellar parameters, including the wind momentum. Therefore, variability in the profile is a potentially significant source of error. The aims of the present study are to estimate the magnitude of this error by quantifying the H? profile variability in this nearby example of the class and to gain better insight into the nature and cause of the wind variability. Our observational material consists of 28 high-resolution (R =~ 26,000) spectra of 6 Cas obtained between 1993 and 1998 and including H? and several photospheric lines. Our preliminary results include the finding that the photospheric radial velocities and the positions and strengths of the absorption and the emission components H? are variable, but no single, dominant periodicity appears in a PDM analysis. The absorption radial velocity is correlated with the emission equivalent width, more negative velocities being associated with stronger emission. The absorption component shows variable structure, which may be caused by blended, moving subcomponents; they sometimes emerge to appear as discrete absorption components (DACs). The temporal variance spectrum of H? is similar in amplitude and shape to that of HD 92207 (Kaufer et al. 1996, A&A, 305, 887). If this similarity denotes a typical variability pattern in extremely luminous A-type supergiants, then it may provide a constraint on the variability-induced error in the distance estimates to extragalactic supergiants.

  4. THE MASS-LOSS RETURN FROM EVOLVED STARS TO THE LARGE MAGELLANIC CLOUD. VI. LUMINOSITIES AND MASS-LOSS RATES ON POPULATION SCALES

    SciTech Connect

    Riebel, D.; Meixner, M. [Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Srinivasan, S. [UPMC-CNRS UMR7095, Institut d'Astrophysique de Paris, F-75014 Paris (France); Sargent, B., E-mail: driebel@pha.jhu.edu [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

    2012-07-01

    We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to {approx}30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 Multiplication-Sign 10{sup -5} M{sub Sun} yr{sup -1}, equivalent to a total mass injection rate (including the gas) into the ISM of {approx}6 Multiplication-Sign 10{sup -3} M{sub Sun} yr{sup -1}. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K{sub s} band as a function of J - K{sub s} color, BC{sub K{sub s}}= -0.40(J-K{sub s}){sup 2} + 1.83(J-K{sub s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (M-dot{sub d}) from C-rich AGB stars, such as log M-dot{sub d} = (-18.90/((K{sub s}-[8.0])+3.37) - 5.93. We find that a larger fraction of AGB stars exhibiting the 'long-secondary period' phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.

  5. Star Search

    NSDL National Science Digital Library

    2012-04-02

    In this online activity, learners can test their skills at finding constellations in the northern hemisphere's night sky. Learners can choose during which season to look, and then look for four constellations in that season. The simulation shows a simple representation of the night sky with key stars highlighted. Use this as a practice before going outside or just to give learners an idea of the difficulties involved in identifying constellations. When learners set up a free account at Kinetic City, they can answer bonus questions at the end of the activity as a quick assessment. As a larger assessment, learners can complete the Smart Attack game after they've completed several activities.

  6. Triggered Star Formation in the LMC4/Constellation III Region of the Large Magellanic Cloud

    E-print Network

    Yuri Efremov; Bruce Elmegreen

    1998-05-07

    The origin of a regular, 600 pc-long arc of young stars and clusters in the Constellation III region of the Large Magellanic Cloud is considered. The circular form of this arc suggests that the prestellar gas was uniformly swept up by a central source of pressure. In the center of the arc are six $\\sim30$ My old A-type supergiant stars and a Cepheid variable of similar age, which may be related to the source of this pressure. We calculate the expansion of a bubble around a cluster of this age, and show that it could have triggered the formation of the arc at the right time and place. Surrounding the central old stars and extending well outside the young arc is the LMC4 superbubble and giant HI shell. We show how this superbubble and shell could have formed by the continued expansion of the 15 My old cavity, following star formation in the arc and the associated new pressures. The age sequence proposed here was not evident in the recent observations by Olsen et al. and Braun et al. because the first generation stars in the center of the LMC superbubble are relatively faint and scarce compared to the more substantial population of stars less than 15 My old that formed throughout the region in a second generation. These considerations lead to an examination of the origin of the LMC4/Constellation III region and other large rings in the LMC and other galaxies. Their size and circularity could be the result of low galactic shear and a thick disk, with several generations of star formation in their interiors now too faint to see.

  7. O stars and Wolf-Rayet stars

    NASA Technical Reports Server (NTRS)

    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.

  8. Counting Your Lucky Stars

    NSDL National Science Digital Library

    Shannon Ricles

    2013-01-30

    In this activity, learners sample a star field to estimate the number of stars in the universe. This activity simulates how astronomers use sampling instead of census (counting) to more easily collect data in space. Learners predict, count, approximate, and average the number of stars in a Star Field Sheet.

  9. RR Lyrae Stars

    NASA Astrophysics Data System (ADS)

    Smith, Horace A.

    2004-09-01

    Preface; 1. Introduction; 2. The absolute magnitude of the RR Lyrae stars; 3. RR Lyrae stars in globular clusters; 4. RR Lyrae stars of the galactic field; 5. Period changes, the Blanzhko effect, and the double mode pulsation; 6. RR Lyrae stars beyond the Milky Way; Glossary of symbols; Short list of journal abbreviations; References; Index.

  10. Crossing the `Yellow Void' -- Spatially Resolved Spectroscopy of the Post- Red Supergiant IRC+10420 and Its Circumstellar Ejecta

    E-print Network

    Roberta M. Humphreys; Kris Davidson; Nathan Smith

    2002-05-15

    IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the HR diagram. During their post--RSG evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semi--forbidden region, that de Jager and his collaborators have called the `yellow void'. We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double--peaked Halpha emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and mass loss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently the observed variations in apparent spectral type and inferred temperature are changes in the wind and do not necessarily mean that the underlying stellar radius and interior structure are evolving on such a short timescale. To explain the evidence for simultaneous outflow and infall of material near the star, we propose a `rain' model in which blobs of gas condense in regions of lowered opacity outside the dense wind. With the apparent warming of its wind, the recent appearance of strong emission, and a decline in the mass loss rate, IRC +10420 may be about to shed its opaque wind, cross the `yellow void', and emerge as a hotter star.

  11. Young, massive star clusters in the antennae

    NASA Astrophysics Data System (ADS)

    Christopher, Micol Huw

    2008-12-01

    While massive star clusters have been detected in almost every galaxy with appreciable star formation, they are most prevalent in interacting and merging galaxies. As many as 95% of these clusters will ultimately be disrupted, often in the first 10 Myr, but those clusters that do survive may be the progenitors of globular clusters. Many questions exist regarding these massive clusters and the processes that lead to their formation and disruption, including the uniformity of these processes within a galaxy and between galaxies with different degrees of cluster formation (e.g., quiescent spirals, starbursts, and merging systems). To address these questions, we present a detailed spectroscopic survey of young, massive star clusters in the Antennae, one of the best examples of cluster formation in a merging galaxy. Using near-infrared imaging, we selected a sample of 117 clusters to observe with a combination of near-infrared and optical spectroscopy at the W.M. Keck Observatory. These clusters were chosen to sample the major star-forming regions within the Antennae. This is the largest spectroscopic survey of young massive star clusters in any merging galaxy. Comparing the equivalent widths of hydrogen recombination lines and CO absorption bandheads to the population synthesis models of Starburst99, we measure the age of each cluster. More than half of the clusters show the simultaneous presence of hydrogen recombination lines and CO bandheads, which is not predicted by an instantaneous burst model of cluster formation. We determine that cluster formation is better modeled by a 5 Myr duration constant rate burst of star formation, which we apply to our cluster measurements. We find the vast majority of clusters have ages between 7 and 12 Myr, with a few younger clusters. Comparing cluster ages with predictions of the temporal evolution of cluster luminosity, we find the lack of older (>12 Myr) clusters (and to a lesser extent younger (<7 Myr) clusters) is not a selection effect but a true deficit. Variation in cluster ages exists with location in the Antennae, with the youngest clusters found in the overlap region where the disks of the two galaxies coincide. We interpret these age variations as an indication that cluster disruption rates differ by location within the Antennae. Cluster masses are measured by comparing the extinction-corrected K-band luminosity with model luminosity predictions. We find most cluster masses are between 10^5 and 10^6 Msun with a median cluster mass around 3.5 x 10^5 Msun. Substantial variation exists in masses between different regions, with the overlap region having the most massive clusters on average. These mass differences can be interpreted as size-of-sample effects and our results are consistent with a uniform cluster initial mass function throughout the Antennae. Improved spatial resolution CO (1-0) observations of the Antennae show that younger clusters coincide with areas of enhanced molecular gas concentration and, not surprisingly, also have on average higher extinctions. From two metallicity tracers, we find cluster metallicities consistent with solar values. Based on CO bandhead and SiI equivalent widths in the near-infrared spectra, we uncover strong evidence of a substantial population of M2--M4 supergiants in many of the older clusters.

  12. The donor star of the X-ray pulsar X1908+075

    NASA Astrophysics Data System (ADS)

    Martínez-Núñez, S.; Sander, A.; Gímenez-García, A.; Gónzalez-Galán, A.; Torrejón, J. M.; Gónzalez-Fernández, C.; Hamann, W.-R.

    2015-06-01

    High-mass X-ray binaries consist of a massive donor star and a compact object. While several of those systems have been well studied in X-rays, little is known for most of the donor stars as they are often heavily obscured in the optical and ultraviolet regime. There is an opportunity to observe them at infrared wavelengths, however. The goal of this study is to obtain the stellar and wind parameters of the donor star in the X1908+075 high-mass X-ray binary system with a stellar atmosphere model to check whether previous studies from X-ray observations and spectral morphology lead to a sufficient description of the donor star. We obtained H- and K-band spectra of X1908+075 and analysed them with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. For the first time, we calculated a stellar atmosphere model for the donor star, whose main parameters are: Mspec = 15 ± 6 M?, T? = 23-3+6 kK, log geff = 3.0 ± 0.2 and log L/L? = 4.81 ± 0.25. The obtained parameters point towards an early B-type (B0-B3) star, probably in a supergiant phase. Moreover we determined a more accurate distance to the system of 4.85 ± 0.50 kpc than the previously reported value. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.Appendix A is available in electronic form at http://www.aanda.org

  13. New OB star candidates in the Carina Arm around Westerlund 2 from VPHAS+

    NASA Astrophysics Data System (ADS)

    Mohr-Smith, M.; Drew, J. E.; Barentsen, G.; Wright, N. J.; Napiwotzki, R.; Corradi, R. L. M.; Eislöffel, J.; Groot, P.; Kalari, V.; Parker, Q. A.; Raddi, R.; Sale, S. E.; Unruh, Y. C.; Vink, J. S.; Wesson, R.

    2015-07-01

    O and early B stars are at the apex of galactic ecology, but in the Milky Way, only a minority of them may yet have been identified. We present the results of a pilot study to select and parametrize OB star candidates in the Southern Galactic plane, down to a limiting magnitude of g = 20. A 2 deg2 field capturing the Carina Arm around the young massive star cluster, Westerlund 2, is examined. The confirmed OB stars in this cluster are used to validate our identification method, based on selection from the (u - g, g - r) diagram for the region. Our Markov Chain Monte Carlo fitting method combines VPHAS+ u, g, r, i with published J, H, K photometry in order to derive posterior probability distributions of the stellar parameters log (Teff) and distance modulus, together with the reddening parameters A0 and RV. The stellar parameters are sufficient to confirm OB status while the reddening parameters are determined to a precision of ?(A0) ˜ 0.09 and ?(RV) ˜ 0.08. There are 489 objects that fit well as new OB candidates, earlier than ˜B2. This total includes 74 probable massive O stars, 5 likely blue supergiants and 32 reddened subdwarfs. This increases the number of previously known and candidate OB stars in the region by nearly a factor of 10. Most of the new objects are likely to be at distances between 3 and 6 kpc. We have confirmed the results of previous studies that, at these longer distances, these sight lines require non-standard reddening laws with 3.5 < RV < 4.

  14. Maximum mass-loss rates of line-driven winds of massive stars

    NASA Astrophysics Data System (ADS)

    Aerts, C.; Lamers, H. J. G. L. M.

    2003-05-01

    We develop a theoretical treatment that allows us to determine the maximum mass-loss rate of a hot rotating star with a wind that is accelerated by radiation pressure due to spectral lines, taking into account finite disk correction as well as the effect of photon tiring but neglecting multiple scattering. The maximum mass-loss rate of a star is obtained by subsequent numerical integrations of the momentum equation from an assumed position of the sonic point onwards for increasing values of the mass loss, until the wind can no longer escape. For stars rotating below 80% of the critical velocity the decrease in the velocity far out in the wind due to the maximisation of the mass loss is negligible. Stars rotating at >80% of the critical speed have a kinked velocity law connected with the highest possible mass-loss rate. In such cases the wind velocity increases up to typically a few stellar radii, and decreases subsequently almost ballistically outwards. In these cases the terminal wind velocity is much smaller than the maximum wind velocity. For O-type main-sequence stars, the maximum mass-loss rates derived from our formalism are somewhat smaller than those derived for self-regulated line-driven winds including multiple scattering. For B-type supergiants, however, the maximum mass-loss rate is higher by about a factor 1.5-2. Including rotation, but without gravity darkening, results in a maximum mass-loss rate that is twice as high as for a non-rotating star.

  15. Bispectrum speckle interferometry observations and radiative transfer modelling of the red supergiant NML Cyg: Multiple dust-shell structures evidencing previous superwind phases

    E-print Network

    T. Bloecker; Y. Balega; K. -H. Hofmann; G. Weigelt

    2001-02-06

    (abridged) NML Cyg is a highly evolved OH/IR supergiant and supposed to be among the most luminous supergiants in the galaxy. We present the first diffraction limited 2.13micron observations of NML Cyg with 73mas resolution. The speckle interferograms were obtained with the SAO 6m telescope, image reconstruction is based on the bispectrum speckle interferometry method. Radiative transfer calculations have been carried out to model the spectral energy distribution, our 2.13micron visibility function, and mid-infrared visibility functions. The observed dust shell properties do not appear to be in accordance with single-shell models but seem to require multiple components. Considering previous periods of enhanced mass-loss, various density enhancements in the dust shell were taken into account. An extensive grid of models was calculated for different locations and strenghts of such superwind regions in the dust shell. To match the observations from the optical to the sub-mm domain requires at least two superwind regions embedded in the shell. The best model includes a dust shell with a temperature of 1000K at its inner radius of 6.2Rstar, a close embedded superwind shell extending from 15.5Rstar to 21.7Rstar with amplitude 10 (factor of density enhancement), and a far-out density enhancement at 186Rstar with amplitude 5. The angular diameter of the inner dust-shell rim amounts to 105mas. Within the various parts of the dust shell, 1/r^2 density distributions could be maintained differing only in their amplitude A. The present-day mass-loss rate was determined to be 1.2 10^-4 Msol/yr. The inner embedded superwind shell corresponds to a phase of enhanced mass-loss which began ~59yr ago and lasted for ~18yr, and the outer superwind region to a high mass-loss period which terminated 529yr ago.

  16. VizieR Online Data Catalog: Far-UV spectral atlas of O-type stars (Smith, 2012)

    NASA Astrophysics Data System (ADS)

    Smith, M. A.

    2012-10-01

    In this paper, we present a spectral atlas covering the wavelength interval 930-1188Å for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188Å. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas (Cat. J/ApJS/186/175), to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. (4 data files).

  17. Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction

    E-print Network

    Steven R. Cranmer

    2007-01-19

    It is notoriously difficult to measure the winds of solar-type stars. Traditional spectroscopic and radio continuum techniques are sensitive to mass loss rates at least two to three orders of magnitude stronger than the Sun's relatively feeble wind. Much has been done with these methods to probe the more massive outflows of younger (T Tauri) and older (giant, AGB, supergiant) cool stars, but the main sequence remains terra incognita. This presentation reviews the limits on traditional diagnostics and outlines more recent ideas such as Lyman alpha astrospheres and charge-exchange X-ray emission. In addition, there are hybrid constraints on mass loss rates that combine existing observables and theoretical models. The Sackmann/Boothroyd conjecture of a more massive young Sun (and thus a much stronger ZAMS wind) is one such idea that needs to be tested further. Another set of ideas involves a strong proposed coupling between coronal heating and stellar mass loss rates, where the former is easier to measure in stars down to solar-like values. The combined modeling of stellar coronae and stellar winds is developing rapidly, and it seems to be approaching a level of development where the only remaining ``free parameters'' involve the sub-photospheric convection. This talk will also summarize these theoretical efforts to predict the properties of solar-type main-sequence winds.

  18. R Coronae Borealis Stars in M31 from the Palomar Transient Factory

    E-print Network

    Tang, Sumin; Bildsten, Lars; Nugent, Peter; Bellm, Eric; Kulkarni, Shrinivas R; Laher, Russ; Levitan, David; Masci, Frank; Ofek, Eran O; Prince, Thomas A; Sesar, Branimir; Surace, Jason

    2013-01-01

    We report the discovery of R Coronae Borealis (RCB) stars in the Andromeda galaxy (M31) using the Palomar Transient Factory (PTF). RCB stars are rare hydrogen-deficient, carbon-rich supergiant variables, most likely the merger products of two white dwarfs. These new RCBs, including two confirmed ones and two candidates, are the first to be found beyond the Milky Way and the Magellanic Clouds. All of M31 RCBs showed >1.5 mag irregular declines over timescales of weeks to months. Due to the limiting magnitude of our data (R~21-22 mag), these RCB stars have R~19.5 to 20.5 mag at maximum light, corresponding to M_R= -4 to -5, making them some of the most luminous RCBs known. Spectra of two objects show that they are warm RCBs, similar to the Milky Way RCBs RY Sgr and V854 Cen. We consider these results, derived from a pilot study of M31 variables, as an important proof-of-concept for the study of rare bright variables in nearby galaxies with the PTF or other synoptic surveys.

  19. JVN observations of H2O masers around the evolved star IRAS 22480+6002

    E-print Network

    H. Imai; T. Fujii; T. Omodaka; S. Deguchi

    2007-10-10

    We report on the H2O maser distributions around IRAS 22480+6002 (=IRC+60370) observed with the Japanese VLBI Network (JVN) at three epochs spanning 2 months. This object was identified as a K-type supergiant in 1970s, which was unusual as a stellar maser source. The spectrum of H2O masers consists of 5 peaks separated roughly equally by a few km/s each. The H2O masers were spatially resolved into more than 15 features, which spread about 50 mas along the east--west direction. However, no correlation was found between the proper motion vectors and their spatial distributions; the velocity field of the envelope seems random. A statistical parallax method applied to the observed proper-motion data set gives a distance of 1.0+-0.4 kpc for this object, that is considerably smaller than previously thought. The distance indicates that this is an evolved star with L~5800 Lsun. This star shows radio, infrared, and optical characteristics quite similar to those of the population II post-AGB stars such as RV Tau variables.

  20. The ongoing pursuit of R Coronae Borealis stars: ASAS-3 survey strikes again

    E-print Network

    Tisserand, P; Welch, D L; Pilecki, B; Wyrzykowski, L; Kilkenny, D

    2012-01-01

    R Coronae Borealis stars (RCBs) are rare, hydrogen-deficient, carbon-rich supergiant variable stars that are likely the evolved merger products of pairs of CO and He white dwarfs. Only 55 RCB stars are known in our galaxy and their distribution on the sky is weighted heavily by microlensing survey field positions. A less-biased wide-area survey would provide the ability to test competing evolutionary scenarios, understand the population or populations that produce RCBs and constraint their formation rate. The ASAS-3 survey monitored the sky south of declination +28 deg since 2000 to a limiting magnitude of V=14. We searched ASAS-3 for RCB variables using a number of different methods to ensure that the probability of RCB detection was as high as possible and to reduce selection biases based on luminosity, temperature, dust production activity and shell brightness. Candidates whose light curves were visually inspected were pre-selected based on their infrared excesses due to warm dust in their circumstellar sh...

  1. A new method for measuring metallicities of young super star clusters

    SciTech Connect

    Gazak, J. Zachary; Kudritzki, Rolf; Bresolin, Fabio [Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Dr, Honolulu, HI 96822 (United States); Davies, Ben; Bastian, Nate [Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Bergemann, Maria [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS, F-34095 Montpellier (France); Evans, Chris [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Patrick, Lee [Institute for Astronomy, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Schinnerer, Eva [MPI for Astronomy, Konigstuhl 17, D-69117 Heidelberg (Germany)

    2014-06-01

    We demonstrate how the metallicities of young super star clusters (SSC) can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of SSCs older than ?6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z] = +0.28 ± 0.14 dex using a moderate resolution (R ? 3500) J-band spectrum and in NGC 6496 we report [Z] = -0.32 ± 0.20 dex from a low resolution spectrum of R ? 1800. Recently commissioned low resolution multiplexed spectrographs on the Very Large Telescope (KMOS) and Keck (MOSFIRE) will allow accurate measurements of SSC metallicities across the disks of star-forming galaxies up to distances of 70 Mpc with single night observation campaigns using the method presented in this paper.

  2. The C-12/C-13 ratio in stellar atmospheres. VI - Five luminous cool stars

    NASA Technical Reports Server (NTRS)

    Hinkle, K. H.; Lambert, D. L.; Snell, R. L.

    1976-01-01

    A simple curve-of-growth technique is described for extracting the C-12/C-13 ratio for M stars from high-resolution spectra of CO infrared vibration-rotation lines. The technique is applied to the CO lines at 1.6 and 2.3 microns in spectra of two M supergiants (Alpha Ori and Alpha Sco), two M giants (Alpha Her and Beta Peg), and a Mira-type variable (Chi Cyg). As a check on the CO analysis, the C-12/C-13 ratio is derived from the red CN system at 8000 A for Alpha Sco, Alpha Ori, and Beta Peg. The CO analysis is also applied to the K giant Alpha Boo as a check. The CN and CO results are found to be in general agreement, and the C-12/C-13 ratio in all the examined stars is shown to be considerably lower than the solar-system value. It is suggested that these stars were formed from clouds with a C-12/C-13 ratio of 40 to 89 and that their atmospheres now exhibit an enhancement of C-13 abundance due to internal production and mixing to the surface.

  3. R Coronae Borealis Stars in M31 from the Palomar Transient Factory

    NASA Astrophysics Data System (ADS)

    Tang, Sumin; Cao, Yi; Bildsten, Lars; Nugent, Peter; Bellm, Eric; Kulkarni, Shrinivas R.; Laher, Russ; Levitan, David; Masci, Frank; Ofek, Eran O.; Prince, Thomas A.; Sesar, Branimir; Surace, Jason

    2013-04-01

    We report the discovery of R Coronae Borealis (RCB) stars in the Andromeda galaxy (M31) using the Palomar Transient Factory (PTF). RCB stars are rare hydrogen-deficient, carbon-rich supergiant variables, most likely the merger products of two white dwarfs. These new RCBs, including two confirmed ones and two candidates, are the first to be found beyond the Milky Way and the Magellanic Clouds. All of M31 RCBs showed >1.5 mag irregular declines over timescales of weeks to months. Due to the limiting magnitude of our data (R ? 21-22 mag), these RCB stars have R ? 19.5-20.5 mag at maximum light, corresponding to MR = -4 to -5, making them some of the most luminous RCBs known. Spectra of two objects show that they are warm RCBs, similar to the Milky Way RCBs RY Sgr and V854 Cen. We consider these results, derived from a pilot study of M31 variables, as an important proof-of-concept for the study of rare bright variables in nearby galaxies with the PTF or other synoptic surveys.

  4. Surveying the Agents of Galaxy Evolution in the Tidally-Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC) II. Cool Evolved Stars

    E-print Network

    Boyer, Martha L; van Loon, Jacco Th; McDonald, Iain; Meixner, Margaret; Zaritsky, Dennis; Gordon, Karl D; Kemper, F; Babler, Brian; Block, Miwa; Bracker, Steve; Engelbracht, Charles W; Hora, Joe; Indebetouw, Remy; Meade, Marilyn; Misselt, Karl; Robitaille, Thomas; Sewilo, Marta; Shiao, Bernie; Whitney, Barbara

    2011-01-01

    We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled: "Surveying the Agents of Galaxy Evolution in the Tidally-stripped, Low Metallicity SMC", or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at infrared (IR) wavelengths (3.6 - 160 microns). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute ~20% of the global SMC flux (extended + point-source) at 3.6 microns, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies. The equivalent SAGE survey of t...

  5. Extragalactic Stellar Astronomy with the Brightest Stars in the Universe

    E-print Network

    R. -P. Kudritzki; M. A. Urbaneja; F. Bresolin; N. Przybilla

    2008-03-26

    A supergiants are objects in transition from the blue to the red (and vice versa) in the uppermost HRD. They are the intrinsically brightest "normal" stars at visual light with absolute visual magnitudes up to -9. They are ideal to study young stellar populations in galaxies beyond the Local Group to determine chemical composition and evolution, interstellar extinction, reddening laws and distances. We discuss most recent results on the quantitative spectral analysis of such objects in galaxies beyond the Local Group based on medium and low resolution spectra obtained with the ESO VLT and Keck. We describe the analysis method including the determination of metallicity and metallicity gradients. A new method to measure accurate extragalactic distances based on the stellar gravities and effective temperatures is presented, the flux weighted gravity - luminosity relationship (FGLR). The FGLR is a purely spectroscopic method, which overcomes the untertainties introduced by interstellar extinction and variations of metallicity, which plague all photometric stellar distance determination methods. We discuss the perspectives of future work using the giant ground-based telescopes of the next generation such as the TMT, the GMT and the E-ELT.

  6. IntrAst2 (Petrovay) Variable stars VARIABLE STARS

    E-print Network

    Petrovay, Kristóf

    ) A variable star is what is listed in GCVS or VSX GCVS: General Catalogue of Variable Stars; http (version 4.2, 47 811 stars). AAVSO VSX: International Variable Star Index http://www.aavso.org/vsx (AAVSO

  7. The Massive Star Population in M101. III. Spectra and Photometry of the Luminous and Variable Stars

    NASA Astrophysics Data System (ADS)

    Grammer, Skyler H.; Humphreys, Roberta M.; Gerke, Jill

    2015-05-01

    We discuss moderate-resolution spectra, multicolor photometry, and light curves of 31 of the most luminous stars and variables in the giant spiral M101. The majority are intermediate A- to F-type supergiants. We present new photometry and light curves for three known “irregular blue variables,” V2, V4, and V9, and identify a new candidate. Their spectra and variability confirm that they are luminous blue variable (LBV) candidates and V9 may be in an LBV-like maximum light state or eruption. Based on observations with the Multiple Mirror Telescope, a joint facility of the Smithsonian Institution and the University of Arizona and on observations obtained with the Large Binocular Telescope (LBT), an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

  8. CARBON CHEMISTRY IN THE ENVELOPE OF VY CANIS MAJORIS: IMPLICATIONS FOR OXYGEN-RICH EVOLVED STARS

    SciTech Connect

    Ziurys, L. M.; Tenenbaum, E. D.; Pulliam, R. L.; Woolf, N. J. [Department of Astronomy and Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Milam, S. N. [SETI Institute, NASA Ames Research Center, M/S 245-6, Moffet Field, CA 94035 (United States)], E-mail: lziurys@as.arizona.edu, E-mail: emilyt@as.arizona.edu, E-mail: rpulliam@email.arizona.edu, E-mail: nwoolf@as.arizona.edu, E-mail: Stefanie.N.Milam@nasa.gov

    2009-04-20

    Observations of the carbon-bearing molecules CO, HCN, CS, HNC, CN, and HCO{sup +} have been conducted toward the circumstellar envelope of the oxygen-rich red supergiant star, VY Canis Majoris (VY CMa), using the Arizona Radio Observatory (ARO). CO and HCN were also observed toward the O-rich shells of NML Cyg, TX Cam, IK Tau, and W Hya. Rotational transitions of these species at 1 mm, 0.8 mm, and 0.4 mm were measured with the ARO Submillimeter Telescope, including the J = 6 {yields} 5 line of CO at 691 GHz toward TX Cam and W Hya. The ARO 12 m was used for 2 mm and 3 mm observations. Four transitions were observed for HCO{sup +} in VY CMa, the first definitive identification of this ion in a circumstellar envelope. Molecular line profiles from VY CMa are complex, indicating three separate outflows: a roughly spherical flow and separate red- and blueshifted winds, as suggested by earlier observations. Spectra from the other sources appear to trace a single outflow component. The line data were modeled with a radiative transfer code to establish molecular abundances relative to H{sub 2} and source distributions. Abundances for CO derived for these objects vary over an order of magnitude, f {approx} 0.4-5 x 10{sup -4}, with the lower values corresponding to the supergiants. For HCN, a similar range in abundance is found (f {approx} 0.9-9 x 10{sup -6}), with no obvious dependence on the mass-loss rate. In VY CMa, HCO{sup +} is present in all three outflows with f {approx} 0.4-1.6 x 10{sup -8} and a spatial extent similar to that of CO. HNC is found only in the red- and blueshifted components with [HCN]/[HNC] {approx} 150-190, while [CN]/[HCN] {approx} 0.01 in the spherical flow. All three velocity components are traced in CS, which has a confined spatial distribution and f {approx} 2-6 x 10{sup -7}. These observations suggest that carbon-bearing molecules in O-rich shells are produced by a combination of photospheric shocks and photochemistry. Shocks may play a more prominent role in the supergiants because of their macroturbulent velocities.

  9. Star Formation in Galaxies

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

  10. Lone Star Trail 

    E-print Network

    Unknown

    2011-09-05

    The Energy Star performance rating system for buildings has achieved widespread adoption in the building sector as a standard benchmark for energy performance. In 2011, the U.S. EPA released an updated technical methodology for its Energy Star...

  11. Theory of star formation

    E-print Network

    McKee, Christopher F.; Ostriker, Eve C.

    2007-01-01

    the star is at rest in a medium of ?nite temperature. Today,by the star. The outer-disk temperature is not much largerstars, are more subject to fragmentation (Kratter & Matzner, 2006). At temperatures

  12. QCD in Neutron Stars and Strange Stars

    SciTech Connect

    Weber, Fridolin [Department of Physics, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1233 (United States); Negreiros, Rodrigo [FIAS, Goethe University, Ruth Moufang Str 1, 60438 Frankfurt (Germany)

    2011-05-24

    This paper provides an overview of the possible role of Quantum Chromo Dynamics (QCD) for neutron stars and strange stars. The fundamental degrees of freedom of QCD are quarks, which may exist as unconfined (color superconducting) particles in the cores of neutron stars. There is also the theoretical possibility that a significantly large number of up, down, and strange quarks may settle down in a new state of matter known as strange quark matter, which, by hypothesis, could be more stable than even the most stable atomic nucleus, {sup 56}Fe. In the latter case new classes of self-bound, color superconducting objects, ranging from strange quark nuggets to strange quark stars, should exist. The properties of such objects will be reviewed along with the possible existence of deconfined quarks in neutron stars. Implications for observational astrophysics are pointed out.

  13. Star formation Simon Goodwin

    E-print Network

    Crowther, Paul

    Star formation Simon Goodwin Dept Physics & Astronomy, University of Sheffield, Hounsfield Road, Sheffield, S3 7RH, UK. s.goodwin@sheffield.ac.uk 1 Abstract Stars are one of the most important consituents of the Universe, and understanding their formation is crucial to many areas of astrophysics. Stars form from dense

  14. White Dwarf Stars

    Microsoft Academic Search

    Steven Kawaler; Michael Dahlstrom

    2000-01-01

    A white dwarf is a very dense star: The earth-sized remains of a Sun-like star that has burned all of its nuclear fuel. Although it's unable to carry out the workaday activities of a living star, a white dwarf is still an interesting object to astronomers. For one thing, white dwarfs experience \\

  15. The MONS Star Trackers

    E-print Network

    Timothy R. Bedding; Hans Kjeldsen

    2000-03-17

    The MONS satellite will have two Star Trackers to sense the spacecraft attitude, and we plan to use them as scientific instruments to perform high-precision photometry of thousands of stars. We briefly describe the current plans for the Star Trackers and their expected capabilities.

  16. Supernova Star Maps

    NSDL National Science Digital Library

    2012-12-26

    This fun astronomy activity allows learners to experience finding stars in the night sky that will eventually go supernova. This activity is perfect for a star party outdoors. The PDF contains step-by-step instructions, photos, presentation tips, ready-to-print star maps, and links to background information.

  17. Life Cycles of Stars

    NSDL National Science Digital Library

    This Powerpoint presentation inroduces younger students to the life cycles of stars. Topics include stellar nurseries, types of stars, supernovae, the fates of stars of either high or low mass, and the creation of heavier elements by continued fusion of successively heavier elements.

  18. Spots on Am stars

    E-print Network

    Balona, L A; Abedigamba, O P; Ripepi, V; Smalley, B

    2015-01-01

    We investigate the light variations of 15 Am stars using four years of high-precision photometry from the Kepler spacecraft and an additional 14 Am stars from the K2 Campaign 0 field. We find that most of the Am stars in the Kepler field have light curves characteristic of rotational modulation due to star spots. Of the 29 Am stars observed, 12 are {\\delta} Scuti variables and one is a {\\gamma} Doradus star. One star is an eclipsing binary and another was found to be a binary from time-delay measurements. Two Am stars show evidence for flares which are unlikely to be due to a cool companion. The fact that 10 out of 29 Am stars are rotational variables and that some may even flare strongly suggests that Am stars possess significant magnetic fields. This is contrary to the current understanding that the enhanced metallicity in these stars is due to diffusion in the absence of a magnetic field. The fact that so many stars are {\\delta} Scuti variables is also at odds with the prediction of diffusion theory. We su...

  19. Main Sequence Stars

    NSDL National Science Digital Library

    This website from the Australian Telescope Outreach and Education group provides a thorough introduction to the life and death of stars. The website uses text, diagrams, and images to help explain how stars evolve. Highlights include a discussion of stellar fusion reactions and also a straightforward calculation of the lifetime of a star.

  20. Star Formation Ralf Klessen

    E-print Network

    Klessen,Ralf

    need to explain dynamic star formation theory gravity vs. turbulence (and all the rest) examples, green radio: blue Star formation in interacting galaxies: (from the Chandra Webpage) #12;(HST. The Trapezium cluster is only visible in the IR and contains about 2000 newly born stars. Orion molecular cloud

  1. A Spitzer/IRAC characterization of Galactic AGB and RSG stars

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Marengo, Massimo; Hora, Joseph L.; Fazio, Giovanni G.

    2015-03-01

    We present new Spitzer/InfraRed Array Camera (IRAC) observations of 55 dusty long-period variables (48 asymptotic giant branch, AGB, and 6 red supergiant stars) in the Galaxy that have different chemistry, variability type, and mass-loss rate. O-rich AGB stars (including intrinsic S-type) tend to have redder [3.6]-[8.0] colours than carbon stars for a given [3.6]-[4.5] colour due to silicate features increasing the flux in the 8.0-?m IRAC band. For colours including the 5.8 ?m band, carbon stars separate into two distinct sequences, likely due to a variable photospheric C3 feature that is only visible in relatively unobscured, low mass-loss rate sources. Semiregular variables tend to have smaller infrared (IR) excess in [3.6]-[8.0] colour than Miras, consistent with the hypothesis that semiregular variables lose mass discontinuously. Miras have redder colours for longer periods while semiregular variables do not. Galactic AGB stars follow the period-luminosity sequences found for the Magellanic Clouds. Mira variables fall along the fundamental pulsation sequence, while semiregular variables are mostly on overtone sequences. We also derive a relationship between mass-loss rate and [3.6]-[8.0] colour. The fits are similar in shape to those found by other authors for AGBs in the Large Magellanic Cloud, but discrepant in overall normalization, likely due to different assumptions in the models used to derive mass-loss rates. We find that IR colours are not unique discriminators of chemical type, suggesting caution when using colour selection techniques to infer the chemical composition of AGB dust returned to the interstellar medium.

  2. Asteroseismology of B stars

    NASA Astrophysics Data System (ADS)

    Thoul, A.

    2009-03-01

    Numerous B stars on the main sequence are found to be variable. These stars have a relatively simple structure, and yet they present some very interesting challenges. It is important to understand these stars before we can expect to be able to understand stars which have a more complicated internal structure. Asteroseismology of B stars has made considerable progress in the last few years, thanks to the observations obtained from large multisite campaigns, and it is now possible to determine global parameters for these stars such as their masses, ages, metallicities, with very high accuracy. Many variable B stars are also observed with the CoRoT space mission, and statistical studies may become possible in the near future. Detailed studies of the oscillation spectra of ? Cephei stars have already allowed to put some limits on the overshooting parameter, and this overshooting parameter is found to vary from one star to the next. Some ? Cephei stars are found to present differential rotation in their envelopes, while others are compatible with solid body rotation. Some B stars present nitrogen enhancement, even though they are very slow rotators. The instability strips of B stars differ depending on the composition and the opacity tables adopted. Microscopic diffusion and radiative accelerations could produce an accumulation of iron-group elements in some layers of these stars. Hybrid pulsators, showing both ? Cephei and SPB pulsations have been observed. Some of the best observed stars have pulsation spectra which still cannot be reproduced by modelling. Here I review the present status of the observations and of the modelling of ? Cephei stars, emphasizing both the successes reached and the questions and problems which remain open today.

  3. Stars and Constellations

    NSDL National Science Digital Library

    Kaler, James, B.

    This site from Jim Kaler, a Professor of Astronomy at the University of Illinois, is geared toward amateur and budding astronomers. Kaler offers detailed but non-technical descriptions of selected stars and a link to a photo of their respective constellations. Another section of the site, The Natures of Stars, consists of basic overviews of key concepts. The star descriptions are interesting to beginner and avid starwatchers alike, but the photos would benefit perhaps from superimposed arrows or other finding aids. The Stars site grows by one celestial body each week: the Star of the Week from Kaler's other site, Skylights.

  4. Ponderable soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

    The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.

  5. Ponderable soliton stars

    NASA Astrophysics Data System (ADS)

    Chiu, Hong-Yee

    1990-12-01

    The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.

  6. The initial mass function and star-formation history in the 30 Doradus super- association

    NASA Astrophysics Data System (ADS)

    Selman, Fernando J.

    2004-12-01

    We present a study of the star-formation history (SFH), and the initial mass function (IMF) in the 30 Doradus super-association. The study is divided in six natural stages: (1) profile fitting photometry; (2) characterization of the instrument; (3) calibration using stars with spectroscopy; (4) visualization of the stellar properties using the color-magnitude stereogram; (5) Bayesian analysis to obtain physical quantities; and (6) the construction of the SFH and IMF. The reduction and characterization of systematic errors are the most important steps of any IMF study: we note the following sources of systematic errors: (a) the upper magnitude cut-off, used to filter out saturated and non- linear stars, results in a false steepening of the high-mass end of the IMF, particularly affecting older systems; (b) Be stars and blue B-type supergiants mimic luminosity class V stars of higher effective temperatures, thus flattening the IMF; (c) the magnitude limit effect introduced by variable reddening, that flattens the low mass end of the derived IMF. For IMF determination we have identified the mass window 10[Special characters omitted.] <= M <= 40[Special characters omitted.] , that is free of effects (a) and (c) in our photometry. We have found that the SFH of the region is characterized by a 7-15 My old burst, across the whole area studied , followed by a period of reduced, nearly constant, star-formation activity. This activity has been punctuated by clustered, burst-like, star-formation episodes of varying intensity in several places. For NGC2070, the OB association LH104, and the field, the derived IMFs are consistent with a power law with Salpeter slope only if they have different SFH : a young and almost instantaneous burst for NGC2070, and nearly constant star formation, after the 7-15 My burst for the field and LH104. Other studies reveal star-formation episodes across the LMC, starting 15-30 My ago. We propose that the origin of such an apparently synchronized, large-scale, activity, is the recent entry of the LMC into a thick disk of ionized gas, analogous to that proposed by Moore and Davis (1994) to explain the origin of the Magellanic Stream.

  7. The ongoing pursuit of R Coronae Borealis stars: the ASAS-3 survey strikes again

    NASA Astrophysics Data System (ADS)

    Tisserand, P.; Clayton, G. C.; Welch, D. L.; Pilecki, B.; Wyrzykowski, L.; Kilkenny, D.

    2013-03-01

    Context. R Coronae Borealis stars (RCBs) are rare, hydrogen-deficient, carbon-rich supergiant variable stars that are likely the evolved merger products of pairs of CO and He white dwarfs. Only 55 RCB stars have been found in our galaxy and their distribution on the sky is weighted heavily by microlensing survey field positions. A less biased wide-area survey would enable us to test competing evolutionary scenarios, understand the population or populations that produce RCBs, and constrain their formation rate. Aims: The ASAS-3 survey monitored the sky south of declination +28 deg between 2000 and 2010 to a limiting magnitude of V = 14. We searched ASAS-3 for RCB variables using several different methods to ensure that the probability of RCB detection was as high as possible and to reduce selection biases based on luminosity, temperature, dust production activity and shell brightness. Methods: Candidates whose light curves were visually inspected were pre-selected based on their infrared (IR) excesses due to warm dust in their circumstellar shells using the WISE and/or 2MASS catalogues. Criteria on light curve variability were also applied when necessary to minimise the number of objects. Initially, we searched for RCB stars among the ASAS-3 ACVS1.1 variable star catalogue, then among the entire ASAS-3 south source catalogue, and finally directly interrogated the light curve database for objects that were not catalogued in either of those. We then acquired spectra of 104 stars to determine their real nature using the SSO/WiFeS spectrograph. Results: We report 21 newly discovered RCB stars and 2 new DY Per stars. Two previously suspected RCB candidates were also spectroscopically confirmed. Our methods allowed us to extend our detection efficiency to fainter magnitudes that would not have been easily accessible to discovery techniques based on light curve variability. The overall detection efficiency is about 90% for RCBs with maximum light brighter than V ~ 13. Conclusions: With these new discoveries, 76 RCBs are now known in our Galaxy and 22 in the Magellanic Clouds. This growing sample is of great value to constrain the peculiar and disparate atmosphere composition of RCBs. Most importantly, we show that the spatial distribution and apparent magnitudes of Galactic RCB stars is consistent with RCBs being part of the Galactic bulge population.

  8. The Wolf-Rayet stars in the Large Magellanic Cloud. A comprehensive analysis of the WN class

    NASA Astrophysics Data System (ADS)

    Hainich, R.; Rühling, U.; Todt, H.; Oskinova, L. M.; Liermann, A.; Gräfener, G.; Foellmi, C.; Schnurr, O.; Hamann, W.-R.

    2014-05-01

    Context. Massive stars, although being important building blocks of galaxies, are still not fully understood. This especially holds true for Wolf-Rayet (WR) stars with their strong mass loss, whose spectral analysis requires adequate model atmospheres. Aims: Following our comprehensive studies of the WR stars in the Milky Way, we now present spectroscopic analyses of almost all known WN stars in the LMC. Methods: For the quantitative analysis of the wind-dominated emission-line spectra, we employ the Potsdam Wolf-Rayet (PoWR) model atmosphere code. By fitting synthetic spectra to the observed spectral energy distribution and the available spectra (ultraviolet and optical), we obtain the physical properties of 107 stars. Results: We present the fundamental stellar and wind parameters for an almost complete sample of WN stars in the LMC. Among those stars that are putatively single, two different groups can be clearly distinguished. While 12% of our sample are more luminous than 106L? and contain a significant amount of hydrogen, 88% of the WN stars, with little or no hydrogen, populate the luminosity range between log (L/L?) = 5.3 ... 5.8. Conclusions: While the few extremely luminous stars (log (L/L?) > 6), if indeed single stars, descended directly from the main sequence at very high initial masses, the bulk of WN stars have gone through the red-supergiant phase. According to their luminosities in the range of log (L/L?) = 5.3 ... 5.8, these stars originate from initial masses between 20 and 40 M?. This mass range is similar to the one found in the Galaxy, i.e. the expected metallicity dependence of the evolution is not seen. Current stellar evolution tracks, even when accounting for rotationally induced mixing, still partly fail to reproduce the observed ranges of luminosities and initial masses. Moreover, stellar radii are generally larger and effective temperatures correspondingly lower than predicted from stellar evolution models, probably due to subphotospheric inflation. Partly based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA), and the Canadian Astronomy Data Centre (CADC/NRC/CSA).Appendices A-C are available in electronic form at http://www.aanda.org

  9. Massive stars and miniature robots: today's research and tomorrow's technologies

    NASA Astrophysics Data System (ADS)

    Taylor, William David

    2013-03-01

    This thesis documents the reduction of the VLT-FLAMES Tarantula Survey (VFTS) data set, whilst also describing the analysis for one of the serendipitous discoveries: the massive binary R139. This high-mass binary will provide an excellent future calibration point for stellar models, in part as it seems to defy certain expectations about its evolution. Out with the VFTS, a search for binary companions around a trio of B-type supergiants is presented. These stars are surrounded by nebulae that closely resemble the triple-ring structure associated with the poorly-understood SN1987A. Do these stars share a similar evolutionary fate? While strong evidence is found for periodic pulsations in one of the stars, there appears to be no indication of a short-period binary companion suggested in the literature. Gathering observations from a wide range of environments builds a fuller picture of massive stars, but the samples remain somewhat limited. The coming generation of extremely large telescopes will open new regions for studies like the VFTS. Fully utilising these remarkable telescopes will require many new technologies, and this thesis presents one such development project. For adaptive-optics corrected, multi-object instruments it will be necessary to position small pick-off mirrors in the telescope¿s focal plane to select the sub-fields on the sky. This could be most efficiently achieved if the mirrors were self-propelled, which has led to a miniature robot project called MAPS - the Micro Autonomous Positioning System. A number of robots have been built with a footprint of only 30 x 30mm. These wirelessly-controlled robots draw their power from the floor on which they operate and have shown the potential to be positioned to an accuracy of tens of microns. This thesis details much of the early design work and testing of the robots, and also the development of the camera imaging system used to determine the position of the robots. The MAPS project is ongoing and a number of the potential future tests, and avenues for new research, are discussed. This is a thesis that brings together an area of active astronomical research with cutting-edge technological development, highlighting how tomorrow's telescopes will be an essential tool to answer some of today's most puzzling research questions

  10. Modeling the wind and photosphere of massive stars with the radiative transfer code CMFGEN

    NASA Astrophysics Data System (ADS)

    Groh, Jose H.

    2011-12-01

    Massive stars are extremely luminous and characterized by mass loss through radiation-driven stellar winds. The radiation emitted at the stellar surface may interact with the wind, making the analysis of the emerging spectrum a very challenging task. In addition to the luminosity, effective temperature, and surface gravity, several other stellar parameters impact the spectral morphology of these objects, remarkably the mass-loss rate and the wind terminal velocity. That is generally the case for OB supergiants, Luminous Blue Variables, and WR stars. CMFGEN [1] comprises the state-of-the-art in non-LTE radiative transfer and has been successfully applied to the above classes of objects over the last decade. The code assumes spherical symmetry, stationary outflow, and both photospheric and wind lines can be treated in non-LTE. Full line blanketing due to hundreds of thousands of spectral lines is included, as well as wind clumping. Here I discuss the assumptions behind CMFGEN and present examples of models and spectroscopic analyses.

  11. A comprehensive exploration of late-type stars in the far-ultraviolet

    NASA Astrophysics Data System (ADS)

    Bennett, Jeffrey Owen

    An examination of far ultraviolet emissions as a function of stellar type was undertaken using a database of spectra from the International Ultraviolet Explorer (IUE) and the Solar Mesosphere Explorer (SME). The existence of the dividing line between coronal and noncoronal giants is confirmed, as is the observation that O I lambda 1304 emission is enhanced relative to other chromospheric diagnostics among giants and supergiants. Far-ultraviolet emissions are found to be separated into a chromospheric group and related transition-zone group. With respect to solar variability during the declining phase of cycle 21, good correlations are found among solar far-ultraviolet emissions and between these emissions and sunspot numbers, as a function of time. The functional relations for temporal changes on the Sun are generally the same as those for stars as a function of mean activity, with the exception of relations involving C II lambda 1335 which show significant differences in the solar and stellar cases. Finally, an examination of far-ultraviolet variability of several stars which have been frequently observed for the last ten years is presented.

  12. Rotating massive stars @ very low Z: high C and N production

    E-print Network

    Raphael Hirschi

    2006-01-23

    Two series of models and their yields are presented in this paper. The first series consists of 20 Mo models with varying initial metallicity (solar down to $Z=10^{-8}$) and rotation (Vini=0-600 km/s). The second one consists of models with an initial metallicity of $Z=10^{-8}$, masses between 20 and 85 Mo and average rotation velocities at these metallicities (Vini=600-800 km/s). The most interesting models are the models with $Z=10^{-8}$ ([Fe/H]=~-6.6). In the course of helium burning, carbon and oxygen are mixed into the hydrogen burning shell. This boosts the importance of the shell and causes a reduction of the size of the CO core. Later in the evolution, the hydrogen shell deepens and produces large amount of primary nitrogen. For the most massive models (M>~60 Mo), significant mass loss occurs during the red supergiant stage. This mass loss is due to the surface enrichment in CNO elements via rotational and convective mixing. The yields of the fast rotating 20 Mo models can best reproduce (within our study) the observed abundances at the surface of extremely metal poor (EMP) stars. The wind of the massive models can reproduce the CNO abundances of the carbon--rich UMPs, in particular for the most metal poor star known to date, HE1327-2326.

  13. Star formation on the leading edge of a ring-like density wave in Arp 143

    NASA Technical Reports Server (NTRS)

    Appleton, P. N.

    1990-01-01

    NGC 2445 is a member of the pair of interacting galaxies Arp 143 (=VV117) and has been classified as an irregular ring galaxy by deVaucouleurs et al. (1976). Although not obviously a classical ring galaxy from its optical appearance, it nevertheless shows many of the symptoms of a collisional off-center ring galaxy in the early stages of development. Optically the galaxy shows a rough ring of super-giant HII regions distributed asymmetrically with respect to the nucleus with most of the emission concentrated on the western side of the galaxy. Researchers mapped the HI emission in this system (with F. Ghigo and J. van Gorkom; NRAO) and the observations show that the disk of NGC 2445 is characterized by a large-scale banana-shaped HI wave with its peak to the west of the nucleus. Nearing-IR imaging (with E. I. Robson and A. J. Adamson; Lancs. Polytechnic, U.K.) demonstrates that, like the HI, the underlying population of old stars is very asymmetrically distributed with the bulk of the stars concentrated to the western side of the galaxy.

  14. Non-LTE Line-Blanketed Model Atmospheres of B-type Stars

    NASA Astrophysics Data System (ADS)

    Lanz, T.; Hubeny, I.

    2005-12-01

    We present an extension of our OSTAR2002 grid of NLTE model atmospheres to B-type stars. We have calculated over 1,300 metal line-blanketed, NLTE, plane-parallel, hydrostatic model atmospheres for the basic parameters appropriate to B stars. The grid covers 16 effective temperatures from 15,000 to 30,000 K, with 1000 K steps, 13 surface gravities, log g? 4.75 down to the Eddington limit, and 5 compositions (2, 1, 0.5, 0.2, and 0.1 times solar). We have adopted a microturbulent velocity of 2 km/s for all models. In the lower surface gravity range (log g? 3.0), we supplemented the main grid with additional model atmospheres accounting for higher microtutbulent velocity (10 km/s) and for alterated surface composition (He and N-rich, C-deficient), as observed in B supergiants. The models incorporate basically all known atomic levels of 46 ions of H, He, C, N, O, Ne, Mg, Al, Si, S, and Fe, which are grouped into 1127 superlevels. Models and spectra will be available at our Web site, http://nova.astro.umd.edu.

  15. A Grid of NLTE Line-blanketed Model Atmospheres of Early B-Type Stars

    NASA Astrophysics Data System (ADS)

    Lanz, Thierry; Hubeny, Ivan

    2007-03-01

    We have constructed a comprehensive grid of 1540 metal line-blanketed, NLTE, plane-parallel, hydrostatic model atmospheres for the basic parameters appropriate to early B-type stars. The BSTAR2006 grid considers 16 values of effective temperatures, 15,000 K<=Teff<=30,000 K with 1000 K steps, 13 surface gravities, 1.75<=logg<=4.75 with 0.25 dex steps, six chemical compositions, and a microturbulent velocity of 2 km s-1. The lower limit of logg for a given effective temperature is set by an approximate location of the Eddington limit. The selected chemical compositions range from twice to one-tenth of the solar metallicity and metal-free. Additional model atmospheres for B supergiants (logg<=3.0) have been calculated with a higher microturbulent velocity (10 km s-1) and a surface composition that is enriched in helium and nitrogen and depleted in carbon. This new grid complements our earlier OSTAR2002 grid of O-type stars (our Paper I). The paper contains a description of the BSTAR2006 grid and some illustrative examples and comparisons. NLTE ionization fractions, bolometric corrections, radiative accelerations, and effective gravities are obtained over the parameter range covered by the grid. By extrapolating radiative accelerations, we have determined an improved estimate of the Eddington limit in absence of rotation between 55,000 and 15,000 K. The complete BSTAR2006 grid is available at the TLUSTY Web site.

  16. Supergiant Fast X-ray Transients in outburst: new Swift observations of XTEJ1739-302, IGRJ17544-2619, and IGRJ08408-4503

    E-print Network

    Sidoli, L; Ducci, L; Paizis, A; Cusumano, G; Mangano, V; Krimm, H A; Vercellone, S; Burrows, D N; Kennea, J A; Gehrels, N

    2009-01-01

    We report on new X-ray outbursts observed with Swift from three Supergiant Fast X-ray Transients (SFXTs): XTEJ1739-302, IGRJ17544-2619 and IGRJ08408-4503. The former two outbursts were caught during the monitoring campaign we have been performing with the Swift satellite since October 2007: XTEJ1739-302 underwent a new outburst on 2008, August 13, IGRJ17544-2619 on 2008, September 4, while IGRJ08408-4503 on 2008, September 21. While XTEJ1739-302 and IGRJ08408-4503 bright emission triggered the Swift/Burst Alert Telescope, IGRJ17544-2619 did not, thus we could perform a spectral investigation only of the spectrum below 10 keV. The broad band spectra from XTEJ1739-302 and IGRJ08408-4503 were compatible with the X-ray spectral shape displayed during the previous flares. A variable absorbing column density during the flare was observed in XTEJ1739-302 for the first time. The broad band spectrum of IGRJ08408-4503 requires the presence of two distinct photon populations, a cold one (0.3 keV) most likely from a ther...

  17. INTEGRAL results on Supergiant Fast X-ray Transients and accretion mechanism interpretation: ionization effect and formation of transient accretion disks

    E-print Network

    Ducci, L; Paizis, A

    2010-01-01

    We performed a systematic analysis of all INTEGRAL observations from 2003 to 2009 of 14 Supergiant Fast X-ray Transients (SFXTs), implying a net exposure time of about 30Ms. For each source we obtained lightcurves and spectra (3-100keV), discovering several new outbursts. We discuss the X-ray behaviour of SFXTs emerging from our analysis in the framework of the clumpy wind accretion mechanism we proposed (Ducci et al. 2009). We discuss the effect of X-ray photoionization on accretion in close binary systems like IGRJ16479-4514 and IGRJ17544-2619. We show that, because of X-ray photoionization, there is a high probability of formation of an accretion disk from capture of angular momentum in IGRJ16479-4514, and we suggest that the formation of transient accretion disks could be responsible of part of the flaring activity in SFXTs with narrow orbits. We also propose an alternative way to explain the origin of flares with peculiar shapes observed in our analysis applying the model of Lamb et al. (1977), which is ...

  18. Distance and Proper Motion Measurement of the Red Supergiant, PZ Cas, in Very Long Baseline Interferometry H2O Maser Astrometry

    E-print Network

    Kusuno, Kozue; Imai, Hiroshi; Oyama, Tomoaki

    2013-01-01

    We present the very long baseline interferometry H2O maser monitoring observations of the red supergiant, PZ Cas, at 12 epochs from 2006 April to 2008 May. We fitted maser motions to a simple model composed of a common annual parallax and linear motions of the individual masers. The maser motions with the parallax subtracted were well modeled by a combination of a common stellar proper motion and a radial expansion motion of the circumstellar envelope. We obtained an annual parallax of 0.356+/-0.026 mas and a stellar proper motion of {\\mu}*{\\alpha}cos{\\delta}=-3.7+/-0.2 and {\\mu}*{\\delta}=-2.0+/-0.3 mas/yr eastward and northward, respectively. The annual parallax corresponds to a trigonometric parallax of 2.81+0.22-0.19 kpc. By rescaling the luminosity of PZ Cas in any previous studies using our trigonometric parallax, we estimated the location of PZ Cas on a Hertzsprung-Russell diagram and found that it approaches a theoretically evolutionary track around an initial mass of ~25M(sun). The sky position and th...

  19. Cooling of dense stars

    NASA Technical Reports Server (NTRS)

    Tsuruta, S.

    1972-01-01

    Cooling rates were calculated for neutron stars of about one solar mass and 10 km radius, with magnetic fields from zero to about 10 to the 14th power gauss, for extreme cases of maximum and zero superfluidity. The results show that most pulsars are so cold that thermal ionization of surface atoms would be negligible. Nucleon superfluidity and crystallization of heavy nuclei were treated quantitatively, and more realistic hadron star models were chosen. Cooling rates were calculated for a stable hyperon star near the maximum mass limit, a medium weight neutron star, and a light neutron star with neutron-rich heavy nuclei near the minimum mass limit. Results show that cooling rates are a sensitive function of density. The Crab and Vela pulsars are considered, as well as cooling of a massive white dwarf star.

  20. Sizing up the stars

    NASA Astrophysics Data System (ADS)

    Boyajian, Tabetha S.

    For the main part of this dissertation, I have executed a survey of nearby, main sequence A, F, and G-type stars with the CHARA Array, successfully measuring the angular diameters of forty-four stars to better than 4% accuracy. The results of these observations also yield empirical determinations of stellar linear radii and effective temperatures for the stars observed. In addition, these CHARA-determined temperatures, radii, and luminosities are fit to Yonsei-Yale isochrones to constrain the masses and ages of the stars. These quantities are compared to the results found in Allende Prieto & Lambert (1999), Holmberg et al. (2007), and Takeda (2007), who indirectly determine these same properties by fitting models to observed photometry. I find that for most cases, the models underestimate the radius of the star by ~ 12%, while in turn they overestimate the effective temperature by ~ 1.5-4%, when compared to my directly measured values, with no apparent correlation to the star's metallicity or color index. These overestimated temperatures and underestimated radii in these works appear to cause an additional offset in the star's surface gravity measurements, which consequently yield higher masses and younger ages, in particular for stars with masses greater than ~ 1.3 [Special characters omitted.] . Alternatively, these quantities I measure are also compared to direct measurements from a large sample of eclipsing binary stars in Andersen (1991), and excellent agreement is seen within both data sets. Finally, a multi-parameter solution is found to fit color-temperature-metallicity values of the stars in this sample to provide a new calibration of the effective temperature scale for these types of stars. Published work in the field of stellar interferometry and optical spectroscopy of early-type stars are presented in Appendix D and E, respectively. INDEX WORDS: Interferometry, Infrared, Stellar Astronomy, Fundamental Properties, Effective Temperatures, Stellar Radii

  1. Examining the Infrared Variable Star Population Discovered in the Small Magellanic Cloud Using the SAGE-SMC Survey

    NASA Astrophysics Data System (ADS)

    Polsdofer, Elizabeth; Seale, J.; Sewi?o, M.; Vijh, U. P.; Meixner, M.; Marengo, M.; Terrazas, M.

    2015-02-01

    We present our study on the infrared variability of point sources in the Small Magellanic Cloud (SMC). We use the data from the Spitzer Space Telescope Legacy Program “Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud” (SAGE-SMC) and the “Spitzer Survey of the Small Magellanic Cloud” (S3MC) survey, over three different epochs, separated by several months to 3 years. Variability in the thermal infrared is identified using a combination of Spitzer’s InfraRed Array Camera 3.6, 4.5, 5.8, and 8.0 ?m bands, and the Multiband Imaging Photometer for Spitzer 24 ?m band. An error-weighted flux difference between each pair of three epochs (“variability index”) is used to assess the variability of each source. A visual source inspection is used to validate the photometry and image quality. Out of ˜2 million sources in the SAGE-SMC catalog, 814 meet our variability criteria. We matched the list of variable star candidates to the catalogs of SMC sources classified with other methods, available in the literature. Carbon-rich Asymptotic Giant Branch (AGB) stars make up the majority (61%) of our variable sources, with about a third of all of our sources being classified as extreme AGB stars. We find a small, but significant population of oxygen-rich (O-rich) AGB (8.6%), Red Supergiant (2.8%), and Red Giant Branch (<1%) stars. Other matches to the literature include Cepheid variable stars (8.6%), early type stars (2.8%), Young-stellar objects (5.8%), and background galaxies (1.2%). We found a candidate OH maser star, SSTISAGE1C J005212.88-730852.8, which is a variable O-rich AGB star, and would be the first OH/IR star in the SMC, if confirmed. We measured the infrared variability of a rare RV Tau variable (a post-AGB star) that has recently left the AGB phase. 59 variable stars from our list remain unclassified.

  2. Massive soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

    The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

  3. Introduction to neutron stars

    NASA Astrophysics Data System (ADS)

    Lattimer, James M.

    2015-02-01

    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.

  4. Delta Scuti stars: Theory

    SciTech Connect

    Guzik, J.A.

    1998-03-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one`s understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying {delta} Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for {delta} Scuti stars, using FG Vir, {delta} Scuti, and CD-24{degree} 7599 as examples.

  5. Massive soliton stars

    NASA Astrophysics Data System (ADS)

    Chiu, Hong-Yee

    1990-05-01

    The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

  6. Very low metallicity massive star models: Pre-SN evolution and primary nitrogen production

    E-print Network

    Raphael Hirschi

    2006-08-08

    Two series of models were computed. The first series consists of 20 solar mass models with varying initial metallicity (Z=0.02 down to Z=10^{-8}) and rotation (V_{ini}=0-600 km/s). The second one consists of models with an initial metallicity of Z=10^{-8}, masses between 9 and 85 solar masses and fast initial rotation velocities (V_{ini}=600-800 km/s). The most interesting models are the models with Z=10^{-8} ([Fe/H]~-6.6). In the course of helium burning, carbon and oxygen are mixed into the hydrogen burning shell. This boosts the importance of the shell and causes a reduction of the CO core mass. Later in the evolution, the hydrogen shell deepens and produces large amount of primary nitrogen. For the most massive models (M>~60 solar masses), significant mass loss occurs during the red supergiant stage. This mass loss is due to the surface enrichment in CNO elements via rotational and convective mixing. The 85 solar mass model ends up as a WO type Wolf-Rayet star. Therefore the models predict SNe of type Ic and possibly long and soft GRBs at very low metallicities. The rotating 20 solar mass models can best reproduce the observed CNO abundances at the surface of extremely metal poor (EMP) stars and the metallicity trends when their angular momentum content is the same as at solar metallicity (and therefore have an increasing surface velocity with decreasing metallicity). The wind of the massive star models can also reproduce the CNO abundances of the most metal-poor carbon-rich star known to date, HE1327-2326.

  7. Combinations of 148 navigation stars and the star tracker

    NASA Technical Reports Server (NTRS)

    Duncan, R.

    1980-01-01

    The angular separation of all star combinations for 148 nav star on the onboard software for space transportation system-3 flight and following missions is presented as well as the separation of each pair that satisfies the viewing constraints of using both star trackers simultaneously. Tables show (1) shuttle star catalog 1980 star position in M 1950 coordinates; (2) two star combination of 148 nav stars; and (3) summary of two star-combinations of the star tracker 5 deg filter. These 148 stars present 10,875 combinations. For the star tracker filters of plus or minus 5 deg, there are 875 combinations. Formalhaut (nav star 26) has the best number of combinations, which is 33.

  8. Scope on the Skies: Star Light, Star Bright

    NSDL National Science Digital Library

    Bob Riddle

    2009-03-01

    In astronomy, the brightness of a star is described in terms of a star’s magnitude. Stellar magnitude is expressed two different ways, using the terms apparent magnitude and absolute magnitude. For both magnitudes, the numbering scale is the same, with negative numbers being brighter stars and positive numbers being dimmer stars. This month’s column sheds light on the stars and how astronomers measure distances to these celestial objects.

  9. Neutron star models

    NASA Technical Reports Server (NTRS)

    Canuto, V.; Bowers, R. L.

    1981-01-01

    The current state of neutron star structure calculations is reviewed. Uncertainties in the equation of state for matter at and above nuclear density remain. The role of the delta resonance, pion condensates, and quark matter is reviewed. It is found that recent models yield stable neutron star masses which are consistent with observational estimates.

  10. Party with the Stars.

    ERIC Educational Resources Information Center

    Blaine, Lloyd

    1997-01-01

    Describes a Star Party which involves comparing the different colors of the stars, demonstrating how astronomers measure the sky with degrees, determining the cardinal direction, discussing numerous stories that ancient civilizations gave to constellations, exercising science process skills, and using science instruments. (JRH)

  11. Science Through ARts (STAR)

    NASA Technical Reports Server (NTRS)

    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.

  12. Lithium in Evolved Stars

    Microsoft Academic Search

    Daniel D. Hiltgen; Christopher Sneden

    1994-01-01

    I. Lithium in F-G Giants at the Rotational Break As a star crosses the Hertzprung Gap, its surface rotational velocity declines abruptly between between spectral types G0 and G3 III. This rotational break must in large part be due to the growth of of the convective envelope and, thus, the star must exhibit a decline of the surface Li abundance.

  13. White dwarf stars

    Microsoft Academic Search

    J. Liebert

    1980-01-01

    Observations and properties of white-dwarf stars are reviewed. Observational constraints are discussed in terms of methods of discovery, selection effects, white dwarfs in binaries and clusters, stellar colors, spectral types, and kinematic properties. The following stellar and atmospheric parameters are examined: astrometric masses and radii; temperatures, radii, and gravities of DA stars; abundances in white dwarfs with helium atmospheres; and

  14. StarLogo TNG

    Microsoft Academic Search

    Eric Klopfer; Hal Scheintaub; Wendy Huang; Daniel Wendel

    2009-01-01

    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

  15. Science through ARts (STAR)

    ERIC Educational Resources Information Center

    Densmore, Marycay; Kolecki, Joseph C.; Miller, Allan; Petersen, Ruth; Terrell, Mike

    2005-01-01

    Science Through ARts (STAR) is a free, international, cross-curricular program thematically aligned with "The Vision for Space Exploration," a framework of goals and objectives published by NASA in February 2004. Through the STAR program, students in grades 5 through 12 are encouraged to apply their knowledge in creative ways as they approach a…

  16. The Violent Neutron Star

    NASA Astrophysics Data System (ADS)

    Watts, A. L.

    2012-12-01

    Neutron stars enable us to study both the highest densities and the highest magnetic fields in the known Universe. In this article I review what can be learned about such fundamental physics using magnetar bursts. Both the instability mechanisms that trigger the bursts, and the subsequent dynamical and radiative response of the star, can be used to explore stellar and magnetospheric structure and composition.

  17. Colors of Stars

    NSDL National Science Digital Library

    David Joiner

    The Colors of Stars Lesson studies how we study temperature of objects through the radiation they emit. This lesson has the student compare three stars in Orion (one red, one whitish-blue, one deep blue) and try to determine which is hottest and which is coolest.

  18. Dissolving star cluster candidates

    Microsoft Academic Search

    E. Bica; B. X. Santiago; C. M. Dutra; H. Dottori; M. R. de Oliveira; D. Pavani

    2001-01-01

    We present a list of 34 neglected entries from star cluster catalogues located at relatively high galactic latitudes (|b| > 15deg) which appear to be candidate late stages of star cluster dynamical evolution. Although underpopulated with respect to usual open clusters, they still present a high number density contrast as compared to the galactic field. This was verified by means

  19. Carbon star effective temperatures

    Microsoft Academic Search

    S. T. Ridgway; G. H. Jacoby; R. R. Joyce; D. C. Wells

    1981-01-01

    Possible methods for measuring the effective temperatures of individual carbon stars are discussed. Since calibrations of broad or narrow-band photometric colors is impractical at present, empirical corrections to narrow band color temperatures is the only valid procedure. The effective temperature of the star TW Oph is estimated, based on preliminary reduction of the occultation and associated photometry

  20. Extreme helium stars: non-LTE matters Helium and hydrogen spectra of the unique objects V652 Her and HD144941

    E-print Network

    N. Przybilla; K. Butler; U. Heber; C. S. Jeffery

    2005-10-03

    Quantitative analyses of low-mass hydrogen-deficient (super-)giant stars - so-called extreme helium stars - to date face two major difficulties. First, theory fails to reproduce the observed helium lines in their entirety, wings and line cores. Second, a general mismatch exists for effective temperatures derived from ionization equilibria and from spectral energy distributions. Here, we demonstrate how the issue can be resolved using state-of-the-art non-LTE line-formation for these chemically peculiar objects. Two unique high-gravity B-type objects are discussed in detail, the pulsating variable V652 Her and the metal-poor star HD144941. In the first case atmospheric parameters from published LTE analyses are largely recovered, in the other a systematic offset is found. Hydrogen abundances are systematically smaller than previously reported, by up to a factor ~2. Extreme helium stars turn out to be important testbeds for non-LTE model atoms for helium. Improved non-LTE computations show that analyses assuming LTE or based on older non-LTE model atoms can predict equivalent widths, for the HeI 10830A transition in particular, in error by up to a factor ~3.

  1. Linear Relation for Wind-blown Bubble Sizes of Main-sequence OB Stars in a Molecular Environment and Implication for Supernova Progenitors

    NASA Astrophysics Data System (ADS)

    Chen, Yang; Zhou, Ping; Chu, You-Hua

    2013-05-01

    We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R b ? 1.22 M/M ? - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M ? will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring the properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.

  2. Star spot location estimation using Kalman filter for star tracker.

    PubMed

    Liu, Hai-bo; Yang, Jian-kun; Wang, Jiong-qi; Tan, Ji-chun; Li, Xiu-jian

    2011-04-20

    Star pattern recognition and attitude determination accuracy is highly dependent on star spot location accuracy for the star tracker. A star spot location estimation approach with the Kalman filter for a star tracker has been proposed, which consists of three steps. In the proposed approach, the approximate locations of the star spots in successive frames are predicted first; then the measurement star spot locations are achieved by defining a series of small windows around each predictive star spot location. Finally, the star spot locations are updated by the designed Kalman filter. To confirm the proposed star spot location estimation approach, the simulations based on the orbit data of the CHAMP satellite and the real guide star catalog are performed. The simulation results indicate that the proposed approach can filter out noises from the measurements remarkably if the sampling frequency is sufficient. PMID:21509065

  3. Lives and Deaths of Stars

    NSDL National Science Digital Library

    Strobel, Nick

    Stars live for a very long time compared to human lifetimes. Your great, great grandparents saw the same stars as you will see tonight (if it's clear). Our lifetimes are measured in years. Star lifetimes are measured in millions of years. Even though star timescales are enormous, it is possible to know how stars are born, live, and die. This chapter covers the stages a star will go through in its life and how it was figured out. The last part of the chapter will cover the remains of stars, white dwarfs, neutron stars, and the Hollywood favorite: black holes.

  4. Star Formation Thresholds

    NASA Astrophysics Data System (ADS)

    Schaye, Joop

    2008-05-01

    To make predictions for the existence of “dark galaxies”, it is necessary to understand what determines whether a gas cloud will form stars. Star formation thresholds are generally explained in terms of the Toomre criterion for gravitational instability. I contrast this theory with the thermo-gravitational instability hypothesis of Schaye (2004), in which star formation is triggered by the formation of a cold gas phase and which predicts a nearly constant surface density threshold. I argue that although the Toomre analysis is useful for the global stability of disc galaxies, it relies on assumptions that break down in the outer regions, where star formation thresholds are observed. The thermo-gravitational instability hypothesis can account for a number of observed phenomena, some of which were thought to be unrelated to star formation thresholds.

  5. Revised Anatomy of Stars

    E-print Network

    Dubin, M; Dubin, Maurice; Soberman, Robert K.

    1997-01-01

    Stars accrete near invisible hydrogen dominated agglomerates. This population, the `dark matter,' effects the nature of stars. Measurements show plasma streams impacting Earth, planets, Sun and stars. This mass-energy source contradicts nebula collapse model for stars. The visual derived model, to which later discoveries (e.g., fusion) were appended, is confounded and contradicted by new observations. Discovery of a quantity of beryllium 7 (53 day half-life) in the Earth's upper atmosphere, fusion produced, hence from the solar outer zone, proves core fusion wrong. Magnetically pinched plasmas from aggregates impact stars at hundreds of km/s, create impulsive conditions for nuclear explosions below the surface. Disks with planets aid cluster capture. Planets modulate the influx varying fusion, hence luminosity (e.g., solar cycle). This population, with no assumptions or ad hoc physics, explains mysterious phenomena, e.g., luminosity/wind variation, sunspots, high temperature corona, CMEs, etc. Standard explan...

  6. Activity Cycles in Stars

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.

    2009-01-01

    Starspots and stellar activity can be detected in other stars using high precision photometric and spectrometric measurements. These observations have provided some surprises (starspots at the poles - sunspots are rarely seen poleward of 40 degrees) but more importantly they reveal behaviors that constrain our models of solar-stellar magnetic dynamos. The observations reveal variations in cycle characteristics that depend upon the stellar structure, convection zone dynamics, and rotation rate. In general, the more rapidly rotating stars are more active. However, for stars like the Sun, some are found to be inactive while nearly identical stars are found to be very active indicating that periods like the Sun's Maunder Minimum (an inactive period from 1645 to 1715) are characteristic of Sun-like stars.

  7. The Brightest Carbon Stars

    E-print Network

    Cheryl Frost; Robert Cannon; John Lattanzio; Peter Wood; Manuel Forestini

    1997-10-06

    It is currently accepted that Hot-Bottom-Burning (HBB) in intermediate-mass asymptotic giant branch (AGB) stars prevents the formation of C~stars. Nevertheless, we present in this paper the results of some detailed evolutionary calculations which show that even with HBB we obtain C~stars at the highest luminosities reached on the AGB. This is due to mass-loss reducing the envelope mass so that HBB ceases but dredge-up continues. The high mass-loss rate produces an optically thick wind before the star reaches C/O>1. This is consistent with the recent results of van Loon et al. (1997a,b) who find obscured C~stars in the Magellanic Clouds at luminosities up to M_{bol} = -6.8.

  8. Ages of young stars

    E-print Network

    Soderblom, David R; Jeffries, Rob D; Mamajek, Eric E; Naylor, Tim

    2013-01-01

    Determining the sequence of events in the formation of stars and planetary systems and their time-scales is essential for understanding those processes, yet establishing ages is fundamentally difficult because we lack direct indicators. In this review we discuss the age challenge for young stars, specifically those less than ~100 Myr old. Most age determination methods that we discuss are primarily applicable to groups of stars but can be used to estimate the age of individual objects. A reliable age scale is established above 20 Myr from measurement of the Lithium Depletion Boundary (LDB) in young clusters, and consistency is shown between these ages and those from the upper main sequence and the main sequence turn-off -- if modest core convection and rotation is included in the models of higher-mass stars. Other available methods for age estimation include the kinematics of young groups, placing stars in Hertzsprung-Russell diagrams, pulsations and seismology, surface gravity measurement, rotation and activ...

  9. Extreme Horizontal Branch Stars

    E-print Network

    Ulrich Heber

    2008-04-03

    A review is presented on the properties, origin and evolutionary links of hot subluminous stars which are generally believed to be extreme Horizontal Branch stars or closely related objects. Amongst the field stars a large fraction of sdBs are found to reside in close binaries. The companions are predominantly white dwarfs, or low mass main sequence stars. Systems with sufficiently massive WD companions may qualify as SN Ia progenitors. Recently evidence has been found that the masses of some unseen companions might exceed the Chandrasekhar mass, hence they must be neutron stars or black holes. Even a planet has recently been detected orbiting the pulsating sdB star V391 Peg. Quite to the opposite, in globular clusters, only very few sdB binaries are found indicating that the dominant sdB formation processes is different in a dense environment. Binary population synthesis models identify three formation channels, (i) stable Roche lobe overflow, (ii) one or two common envelope ejection phases and (iii) the merger of two helium white dwarfs. The latter channel may explain the properties of the He-enriched sdO stars because their binary fraction is lower than that of the sdBs by a factor of ten or more. Pulsating subluminous B (sdB) stars play an important role for asteroseismology as this technique has already led to mass determinations for a handful of stars. A unique hyper-velocity sdO star moving so fast that it is unbound to the Galaxy has probably been ejected by the super-massive black hole in the Galactic centre. (abridged)

  10. A POPULATION OF ACCRETED SMALL MAGELLANIC CLOUD STARS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Olsen, Knut A. G.; Blum, Robert D. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Zaritsky, Dennis [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Boyer, Martha L.; Gordon, Karl D., E-mail: kolsen@noao.edu, E-mail: rblum@noao.edu, E-mail: dzaritsky@as.arizona.edu, E-mail: mboyer@stsci.edu, E-mail: kgordon@stsci.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2011-08-10

    We present an analysis of the stellar kinematics of the Large Magellanic Cloud (LMC) based on {approx}5900 new and existing velocities of massive red supergiants, oxygen-rich and carbon-rich asymptotic giant branch (AGB) stars, and other giants. After correcting the line-of-sight velocities for the LMC's space motion and accounting for asymmetric drift in the AGB population, we derive a rotation curve that is consistent with all of the tracers used, as well as that of published H I data. The amplitude of the rotation curve is v{sub 0} = 87 {+-} 5 km s{sup -1} beyond a radius R{sub 0} = 2.4 {+-} 0.1 kpc and has a position angle of the kinematic line of nodes of {theta} = 142 deg. {+-} 5 deg. By examining the outliers from our fits, we identify a population of 376 stars, or {approx}>5% of our sample, that have line-of-sight velocities that apparently oppose the sense of rotation of the LMC disk. We find that these kinematically distinct stars are either counter-rotating in a plane closely aligned with the LMC disk, or rotating in the same sense as the LMC disk, but in a plane that is inclined by 54 deg. {+-} 2 deg. to the LMC. Their kinematics clearly link them to two known H I arms, which have previously been interpreted as being pulled out from the LMC. We measure metallicities from the Ca triplet lines of {approx}1000 LMC field stars and 30 stars in the kinematically distinct population. For the LMC field, we find a median [Fe/H] = -0.56 {+-} 0.02 with dispersion of 0.5 dex, while for the kinematically distinct stars the median [Fe/H] is -1.25 {+-} 0.13 with a dispersion of 0.7 dex. The metallicity differences provide strong evidence that the kinematically distinct population originated in the Small Magellanic Cloud. This interpretation has the consequence that the H I arms kinematically associated with the stars are likely falling into the LMC, instead of being pulled out.

  11. Catch a Star!

    NASA Astrophysics Data System (ADS)

    2006-11-01

    ESO and the European Association for Astronomy Education are launching today the 2007 edition of 'Catch a Star!', their international astronomy competition for school students. Now in its fifth year, the competition offers students the chance to win a once-in-a-lifetime trip to ESO's flagship observatory in Chile, as well as many other prizes. Students are invited to 'become astronomers' and embark on a journey to explore the Universe. ESO PR Photo 42/06 The competition includes separate categories - 'Catch a Star Researchers' and 'Catch a Star Adventurers' - to ensure that every student, whatever their level, has the chance to enter and win exciting prizes. For the artistically minded, 'Catch a Star!' also includes an artwork competition, 'Catch a Star Artists'. "'Catch a Star!' offers a unique opportunity for students to learn more about astronomy and about the methods scientists use to discover new things about the Universe", said Douglas Pierce-Price, Education Officer at ESO. In teams, students choose an astronomical topic to study and produce an in-depth report. An important part of the project for 'Catch a Star Researchers' is to think about how ESO's telescopes or a telescope of the future can contribute to their investigations of the subject. As well as the top prize - a trip to one of ESO's observatory sites in Chile - visits to observatories in Germany, Austria and Spain, and many other prizes are also available to be won. 'Catch a Star Researchers' winners will be chosen by an international jury, and 'Catch a Star Adventurers' will be awarded further prizes by lottery. Entries for 'Catch a Star Artists' will be displayed on the web and winners chosen with the help of a public online vote. The first editions of 'Catch a Star!' have attracted several hundred entries from more than 25 countries worldwide. Previous winning entries have included "Star clusters and the structure of the Milky Way" (Budapest, Hungary), "Vega" (Acqui Terme, Italy) and "Venus transit" (Lleida, Spain). Some previous winning entries are visible on the Catch a Star! Web site. Detailed entry information can be found on ESO's website, at http://www.eso.org/catchastar/ The deadline for submitting an entry for the 2007 competition is Friday 2 March 2007, 17:00 Central European Time.

  12. INTEGRAL discovery of unusually long broad-band X-ray activity from the Supergiant Fast X-ray Transient IGR J18483-0311

    NASA Astrophysics Data System (ADS)

    Sguera, V.; Sidoli, L.; Bird, A. J.; Bazzano, A.

    2015-05-01

    We report on a broad-band X-ray study (0.5-250 keV) of the Supergiant Fast X-ray Transient IGR J18483-0311 using archival INTEGRAL data and a new targeted XMM-Newton observation. Our INTEGRAL investigation discovered for the first time an unusually long X-ray activity (3-60 keV) which continuously lasted for at least ˜11 d, i.e. a significant fraction (˜60 per cent) of the entire orbital period, and spanned orbital phases corresponding to both periastron and apastron passages. This prolongated X-ray activity is at odds with the mu