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1

Spectral Classification of Cold IRAS Stars: Supergiants  

NASA Astrophysics Data System (ADS)

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

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

1994-12-01

2

Supergiant Stars as Extragalactic Probes of Cosmic Abundances and Distances  

NASA Astrophysics Data System (ADS)

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

Kudritzki, R.

2013-09-01

3

Yellow Hypergiants as Dynamically Unstable Post-Red-supergiant Stars  

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

4

IRC -10414: a bow-shock-producing red supergiant star  

NASA Astrophysics Data System (ADS)

Most runaway OB stars, like the majority of massive stars residing in their parent clusters, go through the red supergiant (RSG) phase during their lifetimes. Nonetheless, although many dozens of massive runaways were found to be associated with bow shocks, only two RSG bow-shock-producing stars, Betelgeuse and ? Cep, are known to date. In this paper, we report the discovery of an arc-like nebula around the late M-type star IRC -10414 using the SuperCOSMOS H-alpha Survey. Our spectroscopic follow-up of IRC -10414 with the Southern African Large Telescope (SALT) showed that it is a M7 supergiant, which supports previous claims on the RSG nature of this star based on observations of its maser emission. This was reinforced by our new radio- and (sub)millimetre-wavelength molecular line observations made with the Atacama Pathfinder Experiment 12-m telescope and the Effelsberg 100-m radio telescope, respectively. The SALT spectrum of the nebula indicates that its emission is the result of shock excitation. This finding along with the arc-like shape of the nebula and an estimate of the space velocity of IRC -10414 (?70 ± 20 km s-1) imply the bow shock interpretation for the nebula. Thus, IRC -10414 represents the third case of a bow-shock-producing RSG and the first one with a bow shock visible at optical wavelengths. We discuss the smooth appearance of the bow shocks around IRC -10414 and Betelgeuse and propose that one of the necessary conditions for stability of bow shocks generated by RSGs is the ionization of the stellar wind. Possible ionization sources of the wind of IRC -10414 are proposed and discussed.

Gvaramadze, V. V.; Menten, K. M.; Kniazev, A. Y.; Langer, N.; Mackey, J.; Kraus, A.; Meyer, D. M.-A.; Kami?ski, T.

2014-01-01

5

Elemental abundances of the supergiant stars ? Cygnus and ? Leonis  

NASA Astrophysics Data System (ADS)

This study aims to analyse the elemental abundances for the late B type supergiant star ? Cyg and the early A-type supergiant ? Leo using ATLAS9 (Kurucz, 1995; Sbordone et al., 2004), assuming local thermodynamic equilibrium (LTE). The spectra used in this study are obtained from Dominion Astrophysical Observatory and have high resolution and signal-to-noise ratios. The effective temperature and the surface gravity of ? Cyg are determined from the ionisation equilibria of Al I/II, Mg I/II, Fe I/II, Fe II/III, and by fitting to the wings of H? and H? profiles as Teff = 10388 K and log g = 1.80. The elemental abundances of ? Leo are determined using Teff = 9600 K and log g = 2.00, as reported by Przybilla et al. (2006). The ionisation equilibria of C I/II, N I/II, Mg I/II, Ca I/II, Cr I/II and Fe I/II/III are also satisfied in the atmosphere of ? Leo. The radial velocities of ? Cyg and ? Leo are -7.25 ± 7.57 km s-1 and 10.40 ± 13.37 km s-1, respectively. The derived projected rotational velocities vsini from synthetic spectra are 27 and 2 km s-1 for both stars, respectively. The macroturbulent velocities (?) are 24 ± 2 km s-1 and 14.5 ± 1.5 km s-1. Also, the microturbulent velocities (?) have been determined for both of stars as 3.5 km s-1. The CNO abundance results of ? Cyg and ? Leo show C deficiency, N overabundance and O in excess.

Tanr?verdi, Taner

2013-12-01

6

The Evolution of Massive Stars. I. Red Supergiants in the Magellanic Clouds  

Microsoft Academic Search

We investigate the red supergiant (RSG) content of the SMC and LMC using multiobject spectroscopy on a sample of red stars previously identified by BVR CCD photometry. We obtained high-accuracy (<1 km s-1) radial velocities for 118 red stars seen toward the SMC and 167 red stars seen toward the LMC, confirming most of these (89% and 95%, respectively) as

Philip Massey; K. A. G. Olsen

2003-01-01

7

On the Explosion Geometry of Red Supergiant Stars  

NASA Astrophysics Data System (ADS)

From progenitor studies, type II-Plateau supernovae (SNe II-P) have been decisively and uniquely determined to arise from isolated red supergiant stars, establishing the most homogeneous --- and well understood --- progenitor class of any type of core-collapse supernova. The precise nature of the mechanism responsible for the stellar explosion, however, remains the subject of considerable debate. A fundamental clue to the nature of the explosion mechanism is explosion geometry: In short, are supernovae round? Because young supernova atmospheres are electron-scattering dominated, their net linear polarization provides a direct probe of early-time supernova geometry, with higher degrees of polarization generally indicating greater departures from spherical symmetry. Here we present spectropolarimetry data for the most well-sampled SN II-P to date, SN 2008bk, and compare (and contrast) the results with those obtained for SN 2004dj, the only other SN II-P for which spectropolarimetry data were obtained with similar fine temporal sampling before, during, and after the fall off of the photometric plateau (Leonard et al. 2006). Both objects are polarized, indicating departures from spherical symmetry, although the timing of the onset -- as well as the persistence -- of the polarization differ between the two objects. Curiously, the detailed spectropolarimetric characteristics of the two objects at the epochs of recorded maximum polarization are extremely similar, feature by feature, suggesting a common cause --- or, at least, geometry. We interpret the data in light of non-Local-Thermodynamic Equilibrium, time-dependent radiative-transfer simulations specifically crafted for SN II-P ejecta. DCL acknowledges support from NSF grant AST-1009571, under which part of this research was carried out. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under observing programs 081.D-0128, 082.D-0151, and 085.D-0391 (PI: Dessart).

Leonard, Douglas C.; Dessart, L.; Hillier, D.; Pignata, G.

2012-01-01

8

The Coolest Stars in the Clouds: Unusual Red Supergiants in the Magellanic Clouds  

Microsoft Academic Search

Red supergiants (RSGs) are a He-burning phase in the evolution of moderately\\u000ahigh mass stars (10-25 solar masses). The evolution of these stars,\\u000aparticularly at low metallicities, is still poorly understood. The latest-type\\u000aRSGs in the Magellanic Clouds are cooler than the current evolutionary tracks\\u000aallow, occupying the region to the right of the Hayashi limit where stars are\\u000ano

Emily M. Levesque; Philip Massey; K. A. G. Olsen

2007-01-01

9

The Coolest Stars in the Clouds: Unusual Red Supergiants in the Magellanic Clouds  

Microsoft Academic Search

Red supergiants (RSGs) are a He-burning phase in the evolution of moderately high mass stars (10-25 solar masses). The evolution of these stars, particularly at low metallicities, is still poorly understood. The latest-type RSGs in the Magellanic Clouds are cooler than the current evolutionary tracks allow, occupying the region to the right of the Hayashi limit where stars are no

Emily M. Levesque; Philip Massey; K. A. G. Olsen; Bertrand Plez

2007-01-01

10

The Coolest Stars in the Clouds: Unusual Red Supergiants in the Magellanic Clouds  

Microsoft Academic Search

Red supergiants (RSGs) are a He-burning phase in the evolution of moderately high mass stars (10-25 solar masses). The evolution of these stars, particularly at low metallicities, is still poorly understood. The latest-type RSGs in the Magellanic Clouds are cooler than the current evolutionary tracks allow, occupying the region to the right of the Hayashi limit where stars are no

E. M. Levesque; P. Massey; K. A. G. Olsen; B. Plez

2009-01-01

11

The Red and Yellow Supergiants in M33: Kinematics and Massive Star Evolution  

NASA Astrophysics Data System (ADS)

Massive star evolution is hard to model, owing to the complications of mass-loss, uncertainties over mixing and convection, the effects of rotation, and so on. It is generally agreed that the most massive stars spend their He-burning lives as Wolf-Rayet stars. Stars of slightly smaller masses spend most of their He-burning phase as red supergiants, after briefly passing through a yellow supergiant phase. We are interested in identifying the numbers and physical properties of these stars throughout the star-forming galaxies of the Local Group in an effort to test stellar evolutionary models at varying metallicities. However, foreground contamination by Milky Way dwarfs is severe for both the yellow supergiants (YSGs) and red supergiants (RSGs). Using the photometry of the Local Group Galaxy Survey, we have used two-color information (B-V vs V-R) to separate likely foreground dwarfs from bona fide RSGs in M33, and obtained radial velocities with Hectospec on the 6.5-m MMT. The radial velocities refine the rotation curves of previous studies, and demonstrate that the rotation curve is quite flat. With the new velocity data we then separate the yellow supergiant population from the foreground using radial velocities as well. Since the number of Wolf-Rayet stars is now known to a few percent in M33 (Neugent et al. 2011, ApJ, in press, as well as poster at this meeting) it is now possible to compare the numbers of RSGs, YSGs, and WRs in this nearby spiral. This work is supported by the National Science Foundation through AST-1008020.

Massey, Philip; Drout, M.; Tokarz, S.; Caldwell, N.

2011-05-01

12

Red Supergiants, Luminous Blue Variables and Wolf-Rayet stars: the single massive star perspective  

NASA Astrophysics Data System (ADS)

We discuss, in the context of the single star scenario, the nature of the progenitors of Red Supergiants (RSG), of Luminous Blue Variables (LBV) and of Wolf-Rayet (WR) stars. These three different populations correspond to evolved phases of Main-Sequence (MS) OB stars. Axial rotation and mass loss have a great influence on massive star evolution in general and more specifically on the durations of these different phases. Moderate rotation and mass loss, during the MS phase, favor the evolution towards the RSG stage. Fast rotation and strong mass loss during the MS phase, in contrast, prevent the star from becoming a RSG and allow the star to pass directly from the OB star phase into the WR phase. Mass loss during the RSG stage may make the star evolve back in the blue part of the HR diagram. We argue that such an evolution may be more common than presently accounted for in stellar models. This might be the reason for the lack of type IIP SNe with RSG progenitors having initial masses between 18 and 30 M_?. The LBVs do appear as a possible transition phase between O and WR stars or between WNL and WNE stars. Fast rotation and/or strong mass loss during the Main-Sequence phase prevent the formation of LBV stars. The mechanisms driving the very strong ejections shown by LBV stars are still unknown. We present some arguments showing that axial rotation together with the proximity of the Eddington limit may play a role in driving the shell ejections. Rotation and mass loss favor the formation of Wolf-Rayet stars. The fact that WR stars and RSGs rarely occur in the same coeval populations indicates that the mass range of these two populations is different, WR stars originating from more massive stars than RSGs. Single star evolution models predict variations with the metallicity of the number ratios of Type Ibc to Type II supernovae, of Type Ib to Type II and of Type Ic to Type II, which are compatible with observations, provided that many stars leaving a black hole as a remnant produce an observable supernova event.

Meynet, Georges; Georgy, Cyril; Hirschi, Raphael; Maeder, André; Massey, Phil; Przybilla, Norbert; Nieva, M.-Fernanda

2011-01-01

13

Evidence for Tidal Heating in the Dynamics of LMC Carbon Stars and Red Supergiants  

NASA Astrophysics Data System (ADS)

We present an analysis of the kinematics of the HI gas, carbon stars, and red supergiants of the Large Magellanic Cloud. After correcting the line-of-sight velocities for the recent accurate measurement of the LMC's space motion, we find that each kinematic tracer clearly defines a flat rotation curve with similar shape but different amplitude for each tracer: 61 km s-1 for the carbon stars, 80 km s-1 for the HI gas, and 107 km s-1 for the red supergiants. We suggest that noncircular motions of the stars and gas in the LMC can at least in part explain the different rotation amplitudes. A significant fraction, 7-15%, of the total sample of carbon stars appears to be associated with previously identified tidal HI streamers. In addition, although the local velocity dispersion of the red supergiants is small, 8 km s-1, their velocity dispersion about the carbon star rotation solution is 17 km s-1, equal to the velocity dispersion of the carbon stars themselves. We thus appear to be witnessing the tidal heating of the LMC's stellar populations.

Olsen, Knut A.; Massey, P.

2006-12-01

14

The galatic and LMC extreme line supergiants compared: IUE observations of the Henize-Carlson and Zoo star samples of massive supergiants. [Large Magellanic cloud (LMC)  

NASA Technical Reports Server (NTRS)

The Henize-Carlson sample of galactic massive supergiants, and a comparison between the Galactic and LMC samples are discussed. Several of the stars, notably He3-395 and S 127/LMC, have very similar shell characteristics. There appears to be little difference, other than luminosity, between the LMC and Galactic samples. One star, He3-1482, was detected with the Very Large Array at 6 cm. The UV data is combined with IRAS and optical information.

Shore, S. N.; Sanduleak, N.; Brown, D. N.; Sonneborn, G.; Bopp, B. W.; Robinson, C. R.

1988-01-01

15

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

SciTech Connect

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.

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

16

Interferometric Studies of Dust Formation in the Red Supergiant Star S Persei  

Microsoft Academic Search

Few methods are as effective as interferometry for probing the dust formation regions around evolved stars at high spatial scales. Using multi-epoch VLBA monitoring observations of 43 GHz SiO (v=1J=1-0) maser emission Ostrowski-Fukuda et al.(2003 AAS meeting 201 poster 115) found that the red supergiant S Persei exhibits clumpy and variable SiO maser spots in a broken elongated (elliptical) ring

R. E. Stencel; C. A. Jurgenson; T. A. Ostrowski-Fukuda

2004-01-01

17

Triggered Star Formation and the Creation of the Supergiant H I Shell in IC 2574  

NASA Astrophysics Data System (ADS)

Based on deep imaging from the Advanced Camera for Surveys aboard the Hubble Space Telescope (HST), we present new evidence that stellar feedback created a ~1 kpc supergiant H I shell (SGS) and triggered star formation (SF) around its rim in the M81 Group dwarf irregular galaxy IC 2574. Using photometry of the resolved stars from the HST images, we measure the star formation history of a region including the SGS, focusing on the past 500 Myr, and employ the unique properties of blue helium-burning stars to create a movie of SF in the SGS. We find two significant episodes of SF inside the SGS from 200-300 Myr and ~25 Myr ago. Comparing the timing of the SF events to the dynamic age of the SGS and the energetics from the H I and SF, we find compelling evidence that stellar feedback is responsible for creating the SGS and triggering secondary SF around its rim.

Weisz, Daniel R.; Skillman, Evan D.; Cannon, John M.; Walter, Fabian; Brinks, Elias; Ott, Jürgen; Dolphin, Andrew E.

2009-01-01

18

Wolf-Rayet, Yellow and Red Supergiant in the single massive stars perspective  

NASA Astrophysics Data System (ADS)

Rotation and mass loss are the key ingredients determining the fate of single massive stars. In recent years, a large effort has been made to compute whole grids of stellar models at different metallicities, including or not the effects of rotation, with the Geneva evolution code. In this talk, I will focus on the evolved stages of massive star evolution (red and yellow supergiants, Wolf-Rayet stars), in the framework of these new grids of models. I will highlight the effects of rotation and mass loss on the post-main sequence evolution of massive stars at solar and lower metallicity. In particular, I will discuss their impact on the maximum mass for a star to end its life as a RSG (leading to a type IIP supernova), on the possibility for a star to finish as a YSG, and on the initial mass ranges leading to various WR star subtypes. I will then compare the results predicted by our code with observed populations of evolved massive stars, bringing constraints on our computations, as well as some indications on the binary star fraction needed to reproduce them.

Georgy, Cyril; Hirschi, R.; Ekstrom, S.; Meynet, G.

2013-06-01

19

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

SciTech Connect

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.

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

20

Ultraviolet and optical spectroscopy of a B supergiant star in M 31  

NASA Astrophysics Data System (ADS)

We present and discuss the UV spectrum of the supergiant star in NGC206-277 in M 31, obtained with the Faint Object Spectrograph (FOS) on Hubble Space Telescope (HST). An optical blue spectrum taken at Kitt Peak National Observatory (KPNO) is also shown. From the optical and UV line spectra we classify the star B1.5Ia. We fit the continuum far-UV flux distribution, deriving Teff = 20,000 K, and with this temperature we find log g = 2.5 by comparing the Hgamma line and He I lines with predictions from Non-Local Thermodynamic Equilibrium (NLTE) models. We analyze the stellar UV wind line profiles with the SEI method and derive a terminal velocity of upsiloninfinity approximately equal to 700 km/s. We fit the Halpha emission line obtained at the WHT with a newly developed (by H.J.G.L.M.L.) code similar to the SEI method for UV lines, and derive dm/dt = 1.3 +/- 0.5 10-6 solar mass/yr. We find that the P Cygni profiles of the M 31 star have slightly weaker and narrower absorptions, and no emission component. We correct our previously published mass-loss estimate for an O star (NGC206-231) in the same association. The correct value is dm/dt approximately equals 10-6 solar mass/yr, assuming solar abundances.

Bianchi, Luciana; Lamers, Henry J. G. L. M.; Hutchings, J. B.; Massey, Philip; Kudritzki, Rolf; Herrero, Artemio; Lennon, Danny J.

1994-12-01

21

The red supergiants and Wolf-Rayet stars of NGC 604  

NASA Astrophysics Data System (ADS)

We study the post-main-sequence stars in NGC 604, the most luminous H II region in M33. A number of Wolf-Rayet (WR) stars and one red supergiant (RSG) were discovered earlier. Based on the broad-band photometry of the region, we present evidence that is consistent with the presence of this RSG and with three more RSG candidates. Using spectral energy distribution (SED) fitting based on Hubble Space Telescope UVIJHK photometry, we estimate the ages of the WR stars and RSGs and find that the two populations are from distinct formation episodes with ages of 3.2 ± 1.0 and 12.4 ± 2.1 Myr, respectively. The RSGs have greater extinctions towards their line of sight than the WR stars which is consistent with the production of a large amount of dust by the RSGs. Using the WR and RSG populations and similar SED fits to the most massive O stars, we estimate that the total stellar mass is (3.8 ± 0.6) × 105 M?. We find a large discrepancy between the expected H? flux from such a massive cluster and the one observed. This suggests that 49+16-19 per cent of the ionizing photons produced by massive stars in NGC 604 are leaking from this H II region. We also suggest that the implications of an old RSG population mean that if NGC 604 were more distant and only observed in the infrared, it would be difficult to study the youngest burst of star formation due to the contamination of RSGs.

Eldridge, John J.; Relaño, Mónica

2011-02-01

22

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

NASA Astrophysics Data System (ADS)

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

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

23

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

SciTech Connect

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.

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

24

P-Cygni Stars as an Intermediate Stage Between Red Supergiants and Wolf-Rayet Stars  

NASA Astrophysics Data System (ADS)

P Cygni's evolutionary status is evaluated using its recently redetermined basic parameters (Lamers et al. 1983) to plot the star on the HRD. The theoretical evolutionary track of a 60 M_sun; star passes through P Cygni's error box twice. From a comparison of the time scales along the two parts of the track it is found to be twenty times more probable to find a star in the He-core burning plus H-shell burning phase evolving to higher Teff than in the thick H-shell burning phase evolving to the RSG region of the HRD.

Lamers, H. J. G. L. M.; de Groot, M.; Cassatella, A.

25

Visual, Near-IR, and TiO Spectrophotometry of Pulsating Giant and Supergiant M-Type Variable Stars  

NASA Astrophysics Data System (ADS)

Pulsating M-type giant and supergiant stars radiate mainly in the near to intermediate IR (1000-2000 nm). Since most prior long-term photometric observations have been done visually or with UBVRI filters, an on-going program was established to monitor selected stars using both wide-band visual (550 nm) and Wing (719 nm, 754 nm, and 1040 nm) intermediate band filters. Outer atmopsheric titanium-oxide (TiO) strenghts are calculated and compared with generated visual light curves to study correlations of stellar pulsa- tions with molecular formation. IR color temperatures are computed and are used in combination with measured bolome- tric magnitudes to estimate radii changes throughout pulsa- tional cycles. These results should provide information relevant for studies of internal structures, atmopsheres, and evolution of red giant and supergiant stars. Some stars currently being observed include Mira, Aldebaran, Alpha Her, Betelgeuse, V CVn, R Leo, and CE Tau. Additionally, a calibration of the Wing 3-color spectro- photometry sytem is in progress to correlate TiO strengths with known spectral types and near-IR color temperatures for the benefit of the community. Observations measuring spectral sub-type changes via cyclic pulsational variations in TiO-indices and near-IR color temperature changes will be more accurate once the calibration is completed. This work was in part supported by NSF grant AST-9315365, which we gratefully acknowledge.

Wasatonic, R. P.; Guinan, E. F.

1997-05-01

26

Chemical abundances and winds of massive stars in M31: a B-type supergiant and a WC star in OB 10  

NASA Astrophysics Data System (ADS)

We present high quality spectroscopic data for two massive stars in the OB 10 association of M31, OB 10-64 (B0 Ia) and OB 10-WR1 (WC6). Medium resolution spectra of both stars were obtained using the ISIS spectrograph on the William Herschel Telescope. This is supplemented with Hubble Space Telescope STIS UV spectroscopy and Keck I HIRES data for OB 10-64. A non-local thermodynamic equilibrium (LTE) model atmosphere and abundance analysis for OB 10-64 is presented, indicating that this star has similar photospheric CNO, Mg and Si abundances to solar neighbourhood massive stars. A wind analysis of this early B-type supergiant reveals a mass-loss rate of M?=1.6×10-6Msolaryr-1, and v?=1650kms-1. The corresponding wind momentum is in good agreement with the wind momentum-luminosity relationship found for Galactic early-B supergiants. Observations of OB 10-WR1 are analysed using a non-LTE, line-blanketed code, to reveal approximate stellar parameters of logL/Lsolar~5.7, T*~75kK, v?~3000kms-1, M?/(Msolaryr-1)~10-4.3 adopting a clumped wind with a filling factor of 10 per cent. Quantitative comparisons are made with the Galactic WC6 star HD 92809 (WR23) revealing that OB 10-WR1 is 0.4 dex more luminous, though it has a much lower C/He ratio (~0.1 versus 0.3 for HD 92809). Our study represents the first detailed, chemical model atmosphere analysis for either a B-type supergiant or a Wolf-Rayet (WR) star in Andromeda, and shows the potential of how such studies can provide new information on the chemical evolution of galaxies and the evolution of massive stars in the local Universe.

Smartt, S. J.; Crowther, P. A.; Dufton, P. L.; Lennon, D. J.; Kudritzki, R. P.; Herrero, A.; McCarthy, J. K.; Bresolin, F.

2001-07-01

27

Temperature, gravity, and bolometric correction scales for non-supergiant OB stars  

NASA Astrophysics Data System (ADS)

Context. Precise and accurate determinations of the atmospheric parameters effective temperature and surface gravity are mandatory to derive reliable chemical abundances in OB stars. Furthermore, fundamental parameters like distances, masses, radii, luminosities can also be derived from the temperature and gravity of the stars. Aims: Atmospheric parameters recently determined at high precision with several independent spectroscopic indicators in non-local thermodynamic equilibrium, with typical uncertainties of ~300 K for temperature and of ~0.05 dex for gravity, are employed to calibrate photometric relationships. This is in order to investigate whether a faster tool to estimate atmospheric parameters can be provided. Methods: Temperatures and gravities of 30 calibrators, i.e. well-studied OB main sequence to giant stars in the solar neighbourhood, are compared to reddening-independent quantities of the Johnson and Strömgren photometric systems, assuming normal reddening. In addition, we examine the spectral and luminosity classification of the star sample and compute bolometric corrections. Results: Calibrations of temperatures and gravities are proposed for various photometric indices and spectral types. Once the luminosity of the stars is well known, effective temperatures can be determined at a precision of ~400 K for luminosity classes III/IV and ~800 K for luminosity class V. Furthermore, surface gravities can reach internal uncertainties as low as ~0.08 dex when using our calibration to the Johnson Q-parameter. Similar precision is achieved for gravities derived from the ?-index and the precision is lower for both atmospheric parameters when using the Strömgren indices [c1] and [u - b] . In contrast, external uncertainties are larger for the Johnson than for the Strömgren calibrations. Our uncertainties are smaller than typical differences among other methods in the literature, reaching values up to ± 2000 K for temperature and ± 0.25 dex for gravity, and in extreme cases, + 6000 K and ± 0.4 dex, respectively. A parameter calibration for sub-spectral types is also proposed. Moreover, we present a new bolometric correction relation to temperature based on our empirical data, rather than on synthetic grids. Conclusions: The photometric calibrations presented here are useful tools to estimate effective temperatures and surface gravities of non-supergiant OB stars in a fast manner. This is also applicable to some single-line spectroscopic binaries, but caution has to be taken for undetected double-lined spectroscopic binaries and single objects with anomalous reddening-law, dubious photometric quantities and/or luminosity classes, for which the systematic uncertainties may increase significantly. We recommend to use these calibrations only as a first step of the parameter estimation, with subsequent refinements based on spectroscopy. A larger sample covering more uniformly the parameter space under consideration will allow refinements to the present calibrations. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max- Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), proposals H2001-2.2-011 and H2005-2.2-016.Based on observations collected at the European Southern Observatory, Chile, ESO 074.B-0455(A) and from the ESO Archive.Based on spectral data retrieved from the ELODIE archive at Observatoire de Haute-Provence (OHP).Appendices A and B are available in electronic form at http://www.aanda.org

Nieva, M.-F.

2013-02-01

28

A Five-year Spectroscopic and Photometric Campaign on the Prototypical ? Cygni Variable and A-type Supergiant Star Deneb  

NASA Astrophysics Data System (ADS)

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 Strömgren photometric measurements obtained during the same time frame. Our spectroscopic analysis included dynamical spectra of the H? profile, H? equivalent widths, and radial velocities measured from Si II ?? 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? 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.

Richardson, N. D.; Morrison, N. D.; Kryukova, E. E.; Adelman, S. J.

2011-01-01

29

Luminous and Variable Stars in M31 and M33. II. Luminous Blue Variables, Candidate LBVs, Fe II Emission Line Stars, and Other Supergiants  

NASA Astrophysics Data System (ADS)

An increasing number of non-terminal eruptions are being found in the numerous surveys for optical transients. Very little is known about these giant eruptions, their progenitors and their evolutionary state. A greatly improved census of the likely progenitor class, including the most luminous evolved stars, the luminous blue variables (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-supernova stages of very massive stars. We have begun a survey of the evolved and unstable luminous star populations in several nearby resolved galaxies. In this second paper on M31 and M33, we review the spectral characteristics, spectral energy distributions, circumstellar ejecta, and evidence for mass loss for 82 luminous and variable stars. We show that many of these stars have warm circumstellar dust including several of the Fe II emission line stars, but conclude that the confirmed LBVs in M31 and M33 do not. The confirmed LBVs have relatively low wind speeds even in their hot, quiescent or visual minimum state compared to the B-type supergiants and Of/WN stars which they spectroscopically resemble. The nature of the Fe II emission line stars and their relation to the LBV state remains uncertain, but some have properties in common with the warm hypergiants and the sgB[e] stars. Several individual stars are discussed in detail. We identify three possible candidate LBVs and three additional post-red supergiant candidates. We suggest that M33-013406.63 (UIT301,B416) is not an LBV/S Dor variable, but is a very luminous late O-type supergiant and one of the most luminous stars or pair of stars in M33. 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.

Humphreys, Roberta M.; Weis, Kerstin; Davidson, Kris; Bomans, D. J.; Burggraf, Birgitta

2014-07-01

30

Spectral variability of luminous early type stars . II. Supergiant alpha Camelopardalis  

NASA Astrophysics Data System (ADS)

Time-series of H? spectra with relatively high resolution in wavelength (R = lambda /delta lambda of 15 000 to 22 000) and time (Delta t = 1d) of the late-type O supergiant alpha Cam are analysed in terms of line-profile variability (lpv). The spectra cover an interval of one year, from February 1998 to February 1999. The analysis provides clear evidence of a continuous deep-seated wind activity traced by variations in the H? emission and He I lambda 6678.15 absorption lines. The observations indicate that the wind is not smooth but perturbed, starting from its base up to velocities of ~ 500 km s-1. The character of the medium-term (days) variations found in H? changes between epochs, and appears to require an explanation involving different kinds of wind perturbations. In particular, we found that in June and July 1998 as well as in February 1999 the lpv of H? was dominated by low-amplitude (<=+/-10%) variations in line flux which usually occupy the central part of the profile symmetrically with respect to the line center while in December 1998 and January 1999 the variations were organised in two wave-like modulations that run from ``red'' to ``blue" and back to ``red" within the profile (between +/-300 km s-1), being most of the time in antiphase. The timescale of variation, revealed via Fourier analysis, is respectively ~ 7 and ~ 10 days. Significant variations in emission equivalent width (up to 35%), closely linked to those in the line profile, are also noted. Short-term (3 to 4 days), low-amplitude (<=22%) variation in mass loss rate which recurs on a timescale of ~ 7 days giving rise to the formation of outward accelerating consecutive shells or/and blobs was suggested to explain the lpv of H? in June-July 1998 and in February 1999. Whereas the variability pattern observed in December-January 1999 seems to be qualitatively consistent with a model involving two rotationally-modulated wind perturbations, one of enhanced density and another of reduced density with respect to the mean, which are not symmetric about the center of the star. Strange-mode oscillations or radial fundamental pulsation are discussed as possible mechanisms generating the established wind variability.

Markova, N.

2002-04-01

31

HST Studies of the Chromospheres, Wind, and Mass-Loss Rates of Cool Giant and Supergiant Stars  

NASA Technical Reports Server (NTRS)

UV spectra of K-M giant and supergiant stars and of carbon stars have been acquired with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). These spectra have been used to measure chromospheric flow and turbulent velocities, study the acceleration of their stellar winds, acquire constraints on their outer atmospheric structure, and enable estimates of their mass-loss rates. Results from our observations of the giant stars Gamma Dra (K5 III hybrid), Alpha Tau (K5 III), Gamma Cru (M3.4 III), Mu Gem (M3 IIIab), and 30 Her (MG III), the supergiants Alpha Ori (M2 Iab) and Lambda Vel (K5 Ib), and the carbon stars TX Psc (NO; C6,2) and TW Hor (NO; C7,2) will be summarized and compared. The high resolution and wavelength accuracy of these data have allowed the direct measurement of the acceleration of the stellar winds in the chromospheres of several of these stars (from initial velocities of 3-9 km/s to upper velocities of 15-25 km/s) and of the chromospheric macroturbulence (-25-35 km/s). The high signal-to-noise and large dynamic range of these spectra have allowed the detection and identification of numerous new emission features, including weak C IV emission indicative of hot transition-region plasma in the non-coronal giant Alpha Tau, many new fluorescent lines of Fe II, and the first detection of fluorescent molecular hydrogen emission and of Ca II recombination lines in the UV spectrum of a giant star. The UV spectrum of two carbon stars have been studied with unprecedented resolution and reveal extraordinarily complicated Mg II lines nearly smothered by circumstellar absorptions. Finally, comparison of synthetic UV emission line profiles computed with the Lamers et al. (1987) Sobolev with Exact Integration (SEI) code with observations of chromospheric emission lines overlain with wind absorption features provides estimates of the mass-loss rates for four of these stars.

Carpenter, Kenneth G.

2000-01-01

32

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

NASA Astrophysics Data System (ADS)

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, Alfvén waves are, probably, the most interesting for their high efficiency in transfering energy and momentum to the wind. Typically, models of Alfvén 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 Alfvén wave flux is able to reproduce the low-velocity wind. We show that the magnetic flux tubes expand with a super-radial factor of 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 Msolar. 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-1. 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 r ~= 1.5r0 reaching 6000 K. Propagating outwards, the wind cools down mainly due to adiabatic expansion.

Falceta-Gonçalves, D.; Vidotto, A. A.; Jatenco-Pereira, V.

2006-05-01

33

Sharpest views of Betelgeuse reveal how supergiant stars lose mass-Unveiling the true face of a behemoth  

NASA Astrophysics Data System (ADS)

Using different state-of-the-art techniques on ESO's Very Large Telescope, two independent teams of astronomers have obtained the sharpest ever views of the supergiant star Betelgeuse. They show that the star has a vast plume of gas almost as large as our Solar System and a gigantic bubble boiling on its surface. These discoveries provide important clues to help explain how these mammoths shed material at such a tremendous rate. Betelgeuse - the second brightest star in the constellation of Orion (the Hunter) - is a red supergiant, one of the biggest stars known, and almost 1000 times larger than our Sun [1]. It is also one of the most luminous stars known, emitting more light than 100000 Suns. Such extreme properties foretell the demise of a short-lived stellar king. With an age of only a few million years, Betelgeuse is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be seen easily from Earth, even in broad daylight. Red supergiants still hold several unsolved mysteries. One of them is just how these behemoths shed such tremendous quantities of material - about the mass of the Sun - in only 10 000 years. Two teams of astronomers have used ESO's Very Large Telescope (VLT) and the most advanced technologies to take a closer look at the gigantic star. Their combined work suggests that an answer to the long-open mass-loss question may well be at hand. The first team used the adaptive optics instrument, NACO, combined with a so-called "lucky imaging" technique, to obtain the sharpest ever image of Betelgeuse, even with Earth's turbulent, image-distorting atmosphere in the way. With lucky imaging, only the very sharpest exposures are chosen and then combined to form an image much sharper than a single, longer exposure would be. The resulting NACO images almost reach the theoretical limit of sharpness attainable for an 8-metre telescope. The resolution is as fine as 37 milliarcseconds, which is roughly the size of a tennis ball on the International Space Station (ISS), as seen from the ground. "Thanks to these outstanding images, we have detected a large plume of gas extending into space from the surface of Betelgeuse," says Pierre Kervella from the Paris Observatory, who led the team. The plume extends to at least six times the diameter of the star, corresponding to the distance between the Sun and Neptune. "This is a clear indication that the whole outer shell of the star is not shedding matter evenly in all directions," adds Kervella. Two mechanisms could explain this asymmetry. One assumes that the mass loss occurs above the polar caps of the giant star, possibly because of its rotation. The other possibility is that such a plume is generated above large-scale gas motions inside the star, known as convection - similar to the circulation of water heated in a pot. To arrive at a solution, astronomers needed to probe the behemoth in still finer detail. To do this Keiichi Ohnaka from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and his colleagues used interferometry. With the AMBER instrument on ESO's Very Large Telescope Interferometer, which combines the light from three 1.8-metre Auxiliary Telescopes of the VLT, the astronomers obtained observations as sharp as those of a giant, virtual 48-metre telescope. With such superb resolution, the astronomers were able to detect indirectly details four times finer still than the amazing NACO images had already allowed (in other words, the size of a marble on the ISS, as seen from the ground). "Our AMBER observations are the sharpest observations of any kind ever made of Betelgeuse. Moreover, we detected how the gas is moving in different areas of Betelgeuse's surface ? the first time this has been done for a star other than the Sun", says Ohnaka. The AMBER observations revealed that the gas in Betelgeuse's atmosphere is moving vigorously up and down, and that these bubbles are as large as the supergiant star itself. Their unrivalled observations have led

2009-07-01

34

Imaging the spinning gas and dust in the disc around the supergiant A[e] star HD 62623  

NASA Astrophysics Data System (ADS)

Context. To progress in the understanding of evolution of massive stars one needs to constrain the mass-loss and determine the phenomenon responsible for the ejection of matter an its reorganization in the circumstellar environment Aims: In order to test various mass-ejection processes, we probed the geometry and kinematics of the dust and gas surrounding the A[e] supergiant HD 62623. Methods: We used the combined high spectral and spatial resolution offered by the VLTI/AMBER instrument. Thanks to a new multi-wavelength optical/IR interferometry imaging technique, we reconstructed the first velocity-resolved images with a milliarcsecond resolution in the infrared domain. Results: We managed to disentangle the dust and gas emission in the HD 62623 circumstellar disc. We measured the dusty disc inner rim, i.e. 6 mas, constrained the inclination angle and the position angle of the major-axis of the disc. We also measured the inner gaseous disc extension (2 mas) and probed its velocity field thanks to AMBER high spectral resolution. We find that the expansion velocity is negligible, and that Keplerian rotation is a favoured velocity field. Such a velocity field is unexpected if fast rotation of the central star alone is the main mechanism of matter ejection. Conclusions: As the star itself seems to rotate below its breakup-up velocity, rotation cannot explain the formation of the dense equatorial disc. Moreover, as the expansion velocity is negligible, radiatively driven wind is also not a suitable explanation to explain the disc formation. Consequently, the most probable hypothesis is that the accumulation of matter in the equatorial plane is due to the presence of the spectroscopic low mass companion. Based on CNRS Guaranteed Time Observations with ESO telescopes at the Paranal Observatory under program 084.D-0355, and on Director's Discretionary Time, 284.D-5059. Feasibility was assessed using open time, 083.C-0621.

Millour, F.; Meilland, A.; Chesneau, O.; Stee, Ph.; Kanaan, S.; Petrov, R.; Mourard, D.; Kraus, S.

2011-02-01

35

On the metallicity dependence of crystalline silicates in oxygen-rich asymptotic giant branch stars and red supergiants  

NASA Astrophysics Data System (ADS)

We investigate the occurrence of crystalline silicates in oxygen-rich evolved stars across a range of metallicities and mass-loss rates. It has been suggested that the crystalline silicate feature strength increases with increasing mass-loss rate, implying a correlation between lattice structure and wind density. To test this, we analyse Spitzer Infrared Spectrograph and Infrared Space Observatory Short Wavelength Spectrometer spectra of 217 oxygen-rich asymptotic giant branch and 98 red supergiants in the Milky Way, the Large and Small Magellanic Clouds, and Galactic globular clusters. These encompass a range of spectral morphologies from the spectrally rich which exhibit a wealth of crystalline and amorphous silicate features to 'naked' (dust-free) stars. We combine spectroscopic and photometric observations with the GRAMS grid of radiative transfer models to derive (dust) mass-loss rates and temperature. We then measure the strength of the crystalline silicate bands at 23, 28 and 33 ?m. We detect crystalline silicates in stars with dust mass-loss rates which span over 3 dex, down to rates of ˜10-9 M? yr-1. Detections of crystalline silicates are more prevalent in higher mass-loss rate objects, though the highest mass-loss rate objects do not show the 23-?m feature, possibly due to the low temperature of the forsterite grains or it may indicate that the 23-?m band is going into absorption due to high column density. Furthermore, we detect a change in the crystalline silicate mineralogy with metallicity, with enstatite seen increasingly at low metallicity.

Jones, O. C.; Kemper, F.; Sargent, B. A.; McDonald, I.; Gielen, C.; Woods, Paul M.; Sloan, G. C.; Boyer, M. L.; Zijlstra, A. A.; Clayton, G. C.; Kraemer, K. E.; Srinivasan, S.; Ruffle, P. M. E.

2012-12-01

36

RED SUPERGIANT STARS IN THE LARGE MAGELLANIC CLOUD. I. THE PERIOD-LUMINOSITY RELATION  

SciTech Connect

From previous samples of red supergiants (RSGs) by various groups, 191 objects are assembled to compose a large sample of RSG candidates in LMC. For 189 of them, the identity as an RSG is verified by their brightness and color indexes in several near- and mid-infrared bands related to the Two Micron All Sky Survey (2MASS) JHK{sub S} bands and the Spitzer/IRAC and Spitzer/MIPS bands. From the visual time-series photometric observations by the ASAS and MACHO projects which cover nearly 8-10 years, the period and amplitude of light variation are analyzed carefully using both the phase dispersion minimization and Period04 methods. According to the properties of light variation, these objects are classified into five categories: (1) 20 objects are saturated in photometry or located in crowded stellar field with poor photometric results, (2) 35 objects with too complex variation to have any certain period, (3) 23 objects with irregular variation, (4) 16 objects with semi-regular variation, and (5) 95 objects with long secondary period (LSP) among which 31 have distinguishable short period and 51 have a long period shorter than 3000 days that can be determined with reasonable accuracy. For the semi-regular variables and the LSP variables with distinguishable short periods, the period-luminosity (P-L) relation is analyzed in the visual, near-infrared, and mid-infrared bands. It is found that the P-L relation is tight in the infrared bands such as the 2MASS JHK{sub S} bands and the Spitzer/IRAC bands, in particular in the Spitzer/IRAC [3.6] and [4.5] bands; meanwhile, the P-L relation is relatively sparse in the V band which may be caused by inhomogeneous interstellar extinction. The results are compared with others' P-L relationships for RSGs and the P-L sequences of red giants in LMC.

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)

2011-01-20

37

A far-infrared survey of bow shocks and detached shells around AGB stars and red supergiants  

NASA Astrophysics Data System (ADS)

Aims: Our goal is to study the different morphologies associated to the interaction of the stellar winds of AGB stars and red supergiants with the interstellar medium (ISM) to follow the fate of the circumstellar matter injected into the interstellar medium. Methods: Far-infrared Herschel/PACS images at 70 and 160 ?m of a sample of 78 Galactic evolved stars are used to study the (dust) emission structures developing out of stellar wind-ISM interaction. In addition, two-fluid hydrodynamical simulations of the coupled gas and dust in wind-ISM interactions are used for comparison with the observations. Results: Four distinct classes of wind-ISM interaction (i.e. "fermata", "eyes", "irregular", and "rings") are identified, and basic parameters affecting the morphology are discussed. We detect bow shocks for ~40% of the sample and detached rings for ~20%. The total dust and gas mass inferred from the observed infrared emission is similar to the stellar mass loss over a period of a few thousand years, while in most cases it is less than the total ISM mass potentially swept-up by the wind-ISM interaction. De-projected stand-off distances (R0) - defined as the distance between the central star and the nearest point of the interaction region - of the detected bow shocks ("fermata" and "eyes") are derived from the PACS images and compared to previous results, model predictions, and the simulations. All observed bow shocks have stand-off distances smaller than 1 pc. Observed and theoretical stand-off distances are used together to independently derive the local ISM density. Conclusions: Both theoretical (analytical) models and hydrodynamical simulations give stand-off distances for adopted stellar properties that are in good agreement with the measured de-projected stand-off distance of wind-ISM bow shocks. The possible detection of a bow shock - for the distance-limited sample - appears to be governed by its physical size as set roughly by the stand-off distance. In particular the star's peculiar space velocity and the density of the ISM appear decisive in detecting emission from bow shocks or detached rings. In most cases the derived ISM densities concur with those typical of the warm neutral and ionised gas in the Galaxy, though some cases point towards the presence of cold diffuse clouds. Tentatively, the "eyes" class objects are associated to (visual) binaries, while the "rings" generally do not appear to occur for M-type stars, only for C or S-type objects that have experienced a thermal pulse. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Cox, N. L. J.; Kerschbaum, F.; van Marle, A.-J.; Decin, L.; Ladjal, D.; Mayer, A.; Groenewegen, M. A. T.; van Eck, S.; Royer, P.; Ottensamer, R.; Ueta, T.; Jorissen, A.; Mecina, M.; Meliani, Z.; Luntzer, A.; Blommaert, J. A. D. L.; Posch, Th.; Vandenbussche, B.; Waelkens, C.

2012-01-01

38

The Contribution of Thermally-Pulsing Asymptotic Giant Branch and Red Supergiant Stars to the 1--24 Micron Flux of the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

Dust enshrouded Asymptotic Giant Branch (AGB) stars and their more massive counterparts, Red Supergiants (RSG), are among the brightest near- and mid-infrared (IR) sources in a galaxy. These stars constitute a tiny fraction of a galaxy's stellar mass, and yet can account for large fractions of the integrated near and mid-IR flux. Underestimating the AGB and RSG contributions to the IR luminosity can result in severely over-estimating a galaxy's stellar mass as well as inflation of the star formation rate estimated from the 8-micron rest-frame flux. Despite their importance, the AGB and RSG flux contribution has only been measured in a handful of galaxies at a handful of wavelengths. Recent Spitzer Space Telescope observations of the Small and Large Magellanic Clouds offer the first opportunity to quantify the IR contribution of the complete population of Thermally-pulsing (TP-)AGB stars and RSG stars to the total integrated IR light from 1 -24 microns. We find that the TP-AGB + RSG flux contribution peaks at 30% at 3--5 microns in the SMC and 25% in the LMC. Even at 8 microns these stars account for 20% of the SMC flux, with nearly half of that flux coming from a handful (3% of the AGB population) of extreme carbon stars. In the LMC, where PAH emission in the interstellar medium is stronger, the 8 micron TP-AGB + RSG flux contribution is much smaller, 4%.

Boyer, Martha L.; Melbourne, J.

2013-01-01

39

Dust Production Factories in the Early Universe: Formation of Carbon Grains in Red-supergiant Winds of Very Massive Population III Stars  

NASA Astrophysics Data System (ADS)

We investigate the formation of dust in a stellar wind during the red-supergiant (RSG) phase of a very massive Population III star with a zero-age main sequence mass of 500 M ?. We show that, in a carbon-rich wind with a constant velocity, carbon grains can form with a lognormal-like size distribution, and that all of the carbon available for dust formation finally condenses into dust for wide ranges of the mass-loss rate ((0.1-3) × 10-3 M ? yr-1) and wind velocity (1-100 km s-1). We also find that the acceleration of the wind, driven by newly formed dust, suppresses the grain growth but still allows more than half of the gas-phase carbon to finally be locked up in dust grains. These results indicate that, at most, 1.7 M ? of carbon grains can form during the RSG phase of 500 M ? Population III stars. Such a high dust yield could place very massive primordial stars as important sources of dust at the very early epoch of the universe if the initial mass function of Population III stars was top-heavy. We also briefly discuss a new formation scenario of carbon-rich ultra-metal-poor stars, considering feedback from very massive Population III stars.

Nozawa, Takaya; Yoon, Sung-Chul; Maeda, Keiichi; Kozasa, Takashi; Nomoto, Ken'ichi; Langer, Norbert

2014-06-01

40

GHRS Observations of Cool, Low-Gravity Stars. V. The Outer Atmosphere and Wind of the Nearby K Supergiant ? Velorum  

NASA Astrophysics Data System (ADS)

UV spectra of ? 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 Ib-II supergiant. VLA radio observations at ?=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 logNe~8.9+/-0.2 cm-3. The profiles of these lines indicate a chromospheric turbulence (v0~25-36 km s-1), 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 ~9-21 km s-1. 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 ?~0.9, a terminal velocity of 29-33 km s-1, and a mass-loss rate~3×10-9 Msolar yr-1. Modeling of the 3.6 cm radio flux observed in 1997 suggests a more slowly accelerating wind (higher ?) 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. Based on observations with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

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

1999-08-01

41

Nonradial pulsations of upsilon Orionis and supergiants  

SciTech Connect

The overshooting nonradial mode driving for a pulsating star very close to the main sequence (..nu.. Ori) and for the non radial pulsations of an A supergiant not too unlike ..cap alpha.. cyg is discussed. (GHT)

Cox, A.N.

1981-01-01

42

Betelgeuse and the Red Supergiants  

NASA Astrophysics Data System (ADS)

Betelgeuse is one of the most magnificent stars in the sky, and one of the nearest red supergiants. Astronomers gathered in Paris in the Autumn of 2012 to decide what we know about its structure, behaviour, and past and future evolution, and how to place this in the general context of the class of red supergiants. Here I reflect on the discussions and propose a synthesis of the presented evidence. I believe that, in those four days, we have achieved to solve a few riddles.

van Loon, J. Th.

2013-05-01

43

A grid of non-local thermodynamic equilibrium corrections for magnesium and calcium in late-type giant and supergiant stars: application to Gaia  

NASA Astrophysics Data System (ADS)

We investigate non-local thermodynamic equilibrium (NLTE) effects for magnesium and calcium in the atmospheres of late-type giant and supergiant stars. The aim of this paper is to provide a grid of NLTE/LTE equivalent width ratios W/W* of Mg and Ca lines for the following range of stellar parameters: Teff? [3500, 5250] K, log g? [0.5, 2.0] dex and [Fe/H] ? [- 4.0, 0.5] dex. We use realistic model atoms with the best physics available and taking into account the fine structure. The Mg and Ca lines of interest are in optical and near-IR ranges. A special interest concerns the lines in the Gaia spectrograph [Radial Velocity Spectrometer (RVS)] wavelength domain [8470, 8740] Å. The NLTE corrections are provided as a function of stellar parameters in an electronic table as well as in a polynomial form for the Gaia/RVS lines.

Merle, T.; Thévenin, F.; Pichon, B.; Bigot, L.

2011-12-01

44

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

NASA Astrophysics Data System (ADS)

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.

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

45

Chromospheres and Winds of Cool Supergiants  

NASA Astrophysics Data System (ADS)

Massive stars lose material via stellar winds on evolutionary timescales in the supergiant phases of their lives. In particular, stars between about 3 and 40 M_{?} spend a significant fraction of their post-main sequence lifetime as red supergiants of spectral classes G-M. The upper limit to red supergiant masses appears to be constrained by mass loss that increases rapidly with stellar mass. Although mass loss from red supergiants has been observed since the 1930s, we still don't understand the mechanism that drives it. Unfortunately, most observations of mass loss from supergiant stars include the entire, unresolved, circumstellar envelope, and provide no spatial information, especially about the inner part of the wind where mass loss starts. One way to achieve spatially resolved observations is to observe the select group of red supergiants with main-sequence companions (typically B stars) in eclipsing orbits. As the hot, and much smaller (in physical size, not mass) companion moves behind the supergiant during eclipse ingress, the line of sight sweeps through successively deeper layers of the supergiant's extended outer envelope. This circumstellar envelope superimposes an absorption upon the continuum of the hot companion, and this "chromospheric" eclipse spectrum can be used to infer the density, velocity and ionization state along the line of sight. By repeated observation of the spectrum of the binary through eclipse, the structure of the supergiant's outer atmosphere can be derived. All of this was realized decades ago. But, despite this potential, the early promise of the binary method to reveal atmospheric structure in red supergiants has never been fully achieved. There are many reasons for this: the additional data reduction complication caused by the need to separate composite spectra, the uncertain perturbing effect of the companion on the structure of the circumstellar envelope being probed, the difficulty of removing light scattered by the circumstellar envelope into the line of sight (which appears as emission), and sometimes, because of the sheer complexity of the chromospheric absorption line spectrum observed (e.g. VV Cephei). The situation has improved considerably with the advent of ultraviolet observations from space, which mostly obviate the need to disentangle composite spectra. The International Ultraviolet Explorer has provided a huge amount of spectroscopic data of limited resolution and signal-to-noise, while the Hubble Space Telescope GHRS and STIS spectrographs have obtained a limited number of observations of superb spectral resolution and signal-to-noise. The Far Ultraviolet Spectroscopic Explorer has also contributed results shortward of Lyman-alpha. In this talk, I will summarize the present state of the binary method, and present observations, results and prospects for several red supergiant binaries.

Bennett, P. D.

2009-09-01

46

Dusty Blue Supergiants: News from High-Angular Resolution Observations  

NASA Astrophysics Data System (ADS)

An overview is presented of the recent advances in understanding the B[e] phenomenon among blue supergiant stars in light of high-angular resolution observations and with an emphasis on the results obtained by means of long baseline optical stellar interferometry. The focus of the review is on the circumstellar material and evolutionary phase of B[e] supergiants, but recent results on dust production in regular blue supergiants are also highlighted.

de Wit, W. J.; Oudmaijer, R. D.; Vink, J. S.

47

Red supergiants and neutrino emission. II.  

NASA Technical Reports Server (NTRS)

Investigation of the variation with stellar mass of the ratio of the numbers of blue and red supergiants. Statistical data for supergiants in young open clusters and subgroups of associations are collected to supplement a more restricted list presented earlier. Improved methods are used to identify hydrogen-burning supergiants, as well as faint supergiant remnants of binary mass exchange, and to arrange the bright evolved supergiants in order of their masses. Neither of these two operations requires knowledge of stellar distances or luminosities. Relevant published work on stellar evolution, rotation, mass loss, and duplicity is used to predict upper and lower limits on the blue-to-red ratio. It is concluded that the observed paucity of very massive red supergiants (and of carbon stars) confirms and extends the trend previously observed, and thereby supports the idea of neutrino-induced acceleration of the carbon burning and later phases of evolution; the h and chi Persei association shows the same dependence of the blue-to-red-ratio on stellar mass as do other clusters and associations; and a moderate decrease of the blue-to-red ratio is observed with increasing galactocentric distance in the Galaxy (as in M33) and seems to be due to a relative scarcity of extremely young stars in distant galactic regions.

Stothers, R.

1972-01-01

48

LMC A-F supergiants (Stock+, 1976)  

NASA Astrophysics Data System (ADS)

A survey for A-F type supergiants in the Large Magellanic Cloud has been carried out using UV objective prism plates. 890 objects were detected and their spectral types, luminosity classes, magnitudes, and precise positions determined. The survey is practically complete to mpg=12.5 and extends for certain types of stars to mpg=14. It is found that the spatial distribution of the A-F supergiants is not correlated with the distribution of the gas and OB stars of the cloud. This is evidence in support of the tentative identification by Stock and Wroblewski of early-type galactic supergiants well off the plane. Several other implications of this result are also discussed. (2 data files).

Stock, J.; Osborn, W.; Ibanez, M.

2000-08-01

49

Enhancement of CO(3-2)/CO(1-0) Ratios and Star Formation Efficiencies in Supergiant H II Regions  

NASA Astrophysics Data System (ADS)

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, \\Sigma _H_2, and the star formation rate surface density, ?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 \\Sigma _SFR/\\Sigma _H_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 3-2/1-0, is also higher than the average over the disk. Such high SFEs and R 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 CO-N(H2) conversion factor, (2) the dense gas fraction traced by R 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 CO-N(H2) conversion factor.

Miura, Rie E.; Kohno, Kotaro; Tosaki, Tomoka; Espada, Daniel; Hirota, Akihiko; Komugi, Shinya; Okumura, Sachiko K.; Kuno, Nario; Muraoka, Kazuyuki; Onodera, Sachiko; Nakanishi, Kouichiro; Sawada, Tsuyoshi; Kaneko, Hiroyuki; Minamidani, Tetsuhiro; Fujii, Kosuke; Kawabe, Ryohei

2014-06-01

50

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

We present the most suitable data sets available in the International Ultraviolet Explorer (IUE) archive for the study of time-dependent stellar winds in early B supergiants. The UV line profile variability in 11 B0 to B3 stars is analyzed, compared and discussed, based on 16 separate data sets comprising over 600 homogeneously reduced high-resolution spectrograms. The targets include 'normal' stars with moderate rotation rates and examples of rapid rotators. A gallery of grey-scale images (dynamic spectra) is presented, which demonstrates the richness and range of wind variability and highlights different structures in the winds of these stars. This work emphasizes the suitability of B supergiants for wind studies, under-pinned by the fact that they exhibit unsaturated wind lines for a wide range of ionization. The wind activity of B supergiants is substantial and has highly varied characteristics. The variability evident in individual stars is classified and described in terms of discrete absorption components, spontaneous absorption, bowed structures, recurrence, and ionization variability and stratification. Similar structures can occur in stars of different fundamental parameters but also different structures may occur in the same star at a given epoch. We discuss the physical phenomena that may be associated with the spectral signatures, and highlight the challenges that these phenomena present to theoretical studies of time-dependent outflows in massive stars. In addition, SEI line-synthesis modelling of the UV wind lines is used to provide further information about the state of the winds in our program stars. Typically the range, implied by the line profile variability, in the product of mass-loss rate and ion fraction (M qi) is a factor of approximately 1.5, when integrated between 0.2 and 0.9 v infinity; it it can however be several times larger over localized velocity regions. At a given effective temperature the mean relative ion ratios can differ by a factor of 5. The general excess in predicted (forward-scattered) emission in the low velocity regime is discussed in turns of structured outflows. Mean ion fractions are estimated over the B0 to B1 spectral classes, and trends in the ionic ratios as a function of wind velocity are described. The low values obtained for the ion fractions of UV resonance lines may reflect the role of clumping in the wind.

Massa, Derck; West, D. (Technical Monitor)

2002-01-01

51

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

We present the most suitable data sets available in the International Ultraviolet Explorer (IUE) archive for the study of time-dependent stellar winds in early B supergiants. The UV line profile variability in 11 B0 to B3 stars is analyzed, compared and discussed, based on 16 separate data sets comprising over 600 homogeneously reduced high-resolution spectrograms. The targets include 'normal' stars with moderate rotation rates and examples of rapid rotators. A gallery of grey-scale images (dynamic spectra) is presented, which demonstrates the richness and range of wind variability and highlights different structures in the winds of these stars. This work emphasises the suitability of B supergiants for wind studies, under-pinned by the fact that they exhibit unsaturated wind lines for a wide range of ionization. The wind activity of B supergiants is substantial and has highly varied characteristics. The variability evident in individual stars is classified and described in terms of discrete absorption components, spontaneous absorption, bowed structures, recurrence, and ionization variability and stratification. Similar structures can occur in stars of different fundamental parameters, but also different structures may occur in the same star at a given epoch. We discuss the physical phenomena that may be associated with the spectral signatures, and highlight the challenges that these phenomena present to theoretical studies of time-dependent outflows in massive stars. In addition, SEI line-synthesis modelling of the UV wind lines is used to provide further information about the state of the winds in our program stars. Typically the range, implied by the line profile variability, in the product of mass-loss rate and ion fraction (M (dot) q(sub i)) is a factor of approximately 1.5, when integrated between 0.2 and 0.9 v infinity; it can however be several times larger over localized velocity regions. At a given effective temperature the mean relative ion ratios can differ by a factor of 5. The general excess in predicted (forward-scattered) emission in the low velocity regime is discussed in terms of structured outflows. Mean ion fractions are estimated over the B0 to B1 spectral classes, and trends in the ionic ratios as a function of wind velocity are described. The low values obtained for the ion fractions of UV resonance lines may reflect the role of clumping in the wind.

Massa, D.; Oliversen, R. (Technical Monitor)

2002-01-01

52

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)

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.

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

1999-01-01

53

Spectroscopy of F supergiants with infrared excess  

Microsoft Academic Search

Atmospheric parameters, abundances of 26 chemical elements and radial velocities, all based on CCD echelle spectra, are presented for two peculiar F supergiants with a large infrared excess: IRAS 07134+1005 and IRAS 18095+2704. A moderate underabundance of metallicity is revealed for both stars, [Fe\\/H]_=-1.0 and -0.78 dex, respectively. The significant overabundance of CNO elements is confirmed for IRAS 07134+0115: [C\\/Fe]=1.08

V. G. Klochkova

1995-01-01

54

Fossil dust shells around luminous supergiants  

NASA Technical Reports Server (NTRS)

The observed frequency with which infrared excesses appear in F, G, and K supergiants of luminosity class Ia supports the idea that these excesses arise in a 'fossil' circumstellar dust shell that was formed during a prior M-super-giant phase of evolution. The required leftward evolution of the star on the H-R diagram would then imply that the Ledoux, rather than the Schwarzschild, criterion for convective mixing is the correct criterion to use in stellar evolution calculations.

Stothers, R.

1975-01-01

55

Mass loss in red giants and supergiants  

NASA Technical Reports Server (NTRS)

The circumstellar envelopes surrounding late-type giants and supergiants were studied using high resolution, photoelectric scans of strong optical resonance lines. A method for extracting the circumstellar from the stellar components of the lines allowed a quantitative determination of the physical conditions in the envelopes and the rates of mass loss at various positions in the red giant region of the HR diagram. The observed strengthening of the circumstellar spectrum with increasing luminosity and later spectral type is probably caused by an increase in the mass of the envelopes. The mass loss rate for individual stars is proportional to the visual luminosity; high rates for the supergiants suggest that mass loss is important in their evolution. The bulk of the mass return to the interstellar medium in the red giant region comes from the normal giants, at a rate comparable to that of planetary nebulae.

Sanner, F.

1975-01-01

56

Red supergiants around the obscured open cluster Stephenson 2  

NASA Astrophysics Data System (ADS)

Context. Several clusters of red supergiants have been discovered in a small region of the Milky Way close to the base of the Scutum-Crux Arm and the tip of the Long Bar. Population synthesis models indicate that they must be very massive to harbour so many supergiants. Amongst these clusters, Stephenson 2, with a core grouping of 26 red supergiants, is a strong candidate to be the most massive young cluster in the Galaxy. Aims: Stephenson 2 is located close to a region where a strong over-density of red supergiants had been found. We explore the actual cluster size and its possible connection to this over-density. Methods: Taking advantage of Virtual Observatory tools, we have performed a cross-match between the DENIS, USNO-B1 and 2MASS catalogues to identify candidate obscured luminous red stars around Stephenson 2, and in a control nearby region. More than 600 infrared bright stars fulfill our colour criteria, with the vast majority having a counterpart in the I band and >400 being sufficiently bright in I to allow observation with a 4-m class telescope. We observed a subsample of ~250 stars, using the multi-object, wide-field, fibre spectrograph AF2 on the WHT telescope in La Palma, obtaining intermediate-resolution spectroscopy in the 7500-9000 Å range. We derived spectral types and luminosity classes for all these objects and measured their radial velocities. Results: Our targets turned out to be G and K supergiants, late (? M4) M giants, and M-type bright giants (luminosity class II) and supergiants. We found ~35 red supergiants with radial velocities similar to Stephenson 2 members, spread over the two areas surveyed. In addition, we found ~40 red supergiants with radial velocities incompatible in principle with a physical association. Conclusions: Our results show that Stephenson 2 is not an isolated cluster, but part of a huge structure likely containing hundreds of red supergiants, with radial velocities compatible with the terminal velocity at this Galactic longitude (and a distance ~6 kpc). In addition, we found evidence of several populations of massive stars at different distances along this line of sight. Based on observations collected at the William Herschel Telescope (La Palma, Spain).Tables 2 and 3 are available in electronic form at http://www.aanda.org

Negueruela, I.; Marco, A.; González-Fernández, C.; Jiménez-Esteban, F.; Clark, J. S.; Garcia, M.; Solano, E.

2012-11-01

57

B-type Supergiants in the SMC (Dufton+, 2005)  

NASA Astrophysics Data System (ADS)

Table 4 contains the adopted atomic data, equivalent widths and abundance estimates for all the metal lines observed in the SMC supergiants. It also contains data for the SMC near main sequence star AzV 304, which has been used in a differential analysis. (2 data files).

Dufton, P. L.; Ryans, R. S. I.; Trundle, C.; Lennon, D. J.; Hubeny, I.; Lanz, T.; Allende Prieto, C.

2005-01-01

58

THE DUSTY CIRCUMSTELLAR DISKS OF B[e] SUPERGIANTS IN THE MAGELLANIC CLOUDS  

SciTech Connect

To better ascertain the nature of the infrared excesses that are characteristic of B[e] supergiants, we obtained Spitzer IRS spectroscopy and IRAC/MIPS imaging for a sample of nine B[e] supergiant stars in the Magellanic Clouds. We find that all nine stars display mid- to far-IR spectral and spatial characteristics indicative of the presence of circumstellar dust disks. Several of the sample B[e] supergiants display crystalline silicate features in their IRS spectra, consistent with grain processing in long-lived (i.e., orbiting) disks. Although it is possible that these disks are primordial in origin, large shell structures (with size scales of tens of parsec) are associated with five of the nine B[e] supergiants, suggesting that mass loss has provided the circumstellar material now orbiting these stars. Hence-via analogy to the class of post-asymptotic giant branch stars with binary companions and dusty, circumbinary disks-we speculate that B[e] supergiant stars may be post-red supergiants in binary systems with orbiting, circumbinary disks that are derived from post-main-sequence mass loss.

Kastner, Joel H. [Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Buchanan, Catherine [School of Physics, University of Melbourne, Victoria, 3010 (Australia); Sahai, Raghvendra [NASA/JPL, 4800 Oak Grove Drive, Pasadena, CA 1109 (United States); Forrest, William J. [Department of Physics and Astronomy, University of Rochester, Bausch and Lomb Hall, P.O. Box 270171, Rochester, NY 14627-0171 (United States); Sargent, Benjamin A., E-mail: jhk@cis.rit.ed, E-mail: clb@unimelb.edu.a [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2010-05-15

59

Hot gas and cool dust around B[e] Supergiants  

NASA Astrophysics Data System (ADS)

We propose a joint Chandra/ACIS and Spitzer/IRS survey of plasma and thermal dust emission from CI Cam and five other galactic B[e] supergiant systems that are bright mid-IR sources. The results will test the hypothesis that many such stars harbor quiescent, "CI Cam-like" X-ray sources, and that these sources may be intimately related to the presence of binary companions as well as to the dusty disks recently detected in IRS spectoscopy of B[e] supergiants. ACIS spectrscopy will establish the presence and strength of any Fe fluorescence line emission in these systems. In parallel, the proposed joint Spitzer IRS observations will provide the means to ascertain the origin and evolution of dusty disks around B[e] supergiants.

Kastner, Joel

2006-09-01

60

Hot gas and cool dust around B[e] Supergiants  

NASA Astrophysics Data System (ADS)

We propose a joint Chandra/ACIS and Spitzer/IRS survey of plasma and thermal dust emission from CI Cam and five other galactic B[e] supergiant systems that are bright mid-IR sources. The results will test the hypothesis that many such stars harbor quiescent, "CI Cam-like" X-ray sources, and that these sources may be intimately related to the presence of binary companions as well as to the dusty disks recently detected in IRS spectoscopy of B[e] supergiants. ACIS spectrscopy will establish the presence and strength of any Fe fluorescence line emission in these systems. In parallel, the proposed joint Spitzer IRS observations will provide the means to ascertain the origin and evolution of dusty disks around B[e] supergiants.

Kastner, Joel; Buchanan, Catherine; Forrest, Bill; Sahai, Raghvendra; Sargent, Ben

2006-05-01

61

Red supergiants in the Small Magellanic Cloud: The effects of metallicity on narrow-band classification indices  

Microsoft Academic Search

Narrow-band classification photometry, on a six color system that measures near infrared bands of TiO and CN, has been obtained for a set of red supergiants in the Small Magellanic Cloud. To investigate the effects of metallicity on the band strength indices, comparisons are made to supergiants in the LMC and the Galaxy. Two new variable stars are reported.

Robert F. Wing; Kyle M. Walker; D. Jack MacConnell; Edgardo Costa

2004-01-01

62

Be Stars  

NASA Astrophysics Data System (ADS)

A Be star (pronounced `bee-ee' star) is a non-supergiant B-type star whose spectrum displays or has displayed one or more Balmer lines in emission and Be is the notation for the spectral classification of such a star (see also CLASSIFICATION OF STELLAR SPECTRA). `Classical' Be stars are believed to have acquired the circumstellar (CS) material that produces the Balmer emission through ejection of...

Peters, G.; Murdin, P.

2000-11-01

63

Water masers in red supergiants  

NASA Astrophysics Data System (ADS)

Results of long-term monitoring of circumstellar water maser sources in red supergiants are reviewed. The observations were carried out in 1980-2006 on the RT-22 radio telescope at Pushchino Radio Astronomy Observatory. We discuss the results for the semiregular variable M-supergiant VX Sgr and non-variable M-supergiant IRC-10414. In addition to our single-dish data, very-long-baseline interferometry results are invoked. VX Sgr and IRC-10414 display a characteristic water line profile, which suggests the presence of a rotating circumstellar disc and a bipolar outflow.

Pashchenko, M. I.; Rudnitskij, G. M.; Samodurov, V. A.; Tolmachev, A. M.

2006-10-01

64

Long term variability of B supergiant winds  

NASA Technical Reports Server (NTRS)

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.

Massa, Derck L.

1995-01-01

65

Chemical composition of late-type supergiants. IV. Homogeneous abundances and galactic metallicity trends  

SciTech Connect

In a recent series of papers by Luck and by Luck and Bond on the chemical composition of G and K lb supergiants, (Fe/H) ratios were determined from high-dispersion spectroscopic data for 54 stars. The main results were: (1) that supergiants in the solar neighborhood have about twice the iron content of the Sun (<(Fe/H)> = +0.3); and (2) that supergiants between 7.7 and 10.2 kpc from the galactic center show a steep radial metallicity gradient, d(Fe/H)/dR = -0.24 kpc/sup -1/.

Luck, R.E.

1982-05-01

66

Supergiants and the Galactic metallicity gradient. II. Spectroscopic abundances for 64 distant F- to M-type supergiants  

SciTech Connect

The metallicity gradient in the Galactic disk from in situ stars with visual magnitude ranging from 6 to 10 is analyzed. Atmospheric parameters and detailed chemical abundances for 64 Population I supergiants of spectral types F through M and luminosity classes Ia through II have been determined. The derived Fe/H ratios ranging from -0.5 to + 0.7 show a mean value of +0.13 with an estimated uncertainty of + or - 0.2. A subset of 25 supergiants fainter than 7th magnitude lying in the direction of the Galactic center shows a Fe/H mean of +0.18 + or - 0.04, while a similar sample of 15 faint supergiants lying in the direction of the Galactic anticenter shows a lower Fe/H mean of +0.07 + or - 0.06. For a sample of bright supergiants analyzed by Luck and Lambert (1985), the mean abundance pattern for all 64 stars showed the following: deficient C and O along with enhancement of N, indicating mixing of CNO-cycled material to the stellar surfaces; an apparent Sr enhancement attributed to departures from LTE; and an essentially solar pattern of other chemical elements. 50 refs.

Luck, R.E.; Bond, H.E. (Case Western Reserve Univ., Cleveland, OH (USA) Space Telescope Science Institute, Baltimore, MD (USA))

1989-11-01

67

Properties of Galactic B Supergiants  

NASA Astrophysics Data System (ADS)

Physical and wind properties of Galactic B supergiants are presented based upon non-LTE line blanketed model atmospheres, including Sher 25 toward the NGC 3603 cluster. We compare H? derived wind densities with recent results for SMC B supergiants and generally confirm theoretical expectations for stronger winds amongst Galactic supergiants. Mid B supergiant winds are substantially weaker than predictions from current radiatively driven wind theory, a problem which is exacerbated if winds are already clumped in the H? line forming region. We find that the so-called `bistability jump' at B1 (Teff ˜ 21kK) from Lamers et al. is rather a more gradual downward trend. CNO elemental abundances, including Sher 25, reveal partially processed material at their surfaces. In general, these are in good agreement with evolutionary predictions for blue supergiants evolving redward accounting for rotational mixing. A few cases, including HD 152236 (?1 Sco), exhibit strongly processed material which is more typical of Luminous Blue Variables. Our derived photospheric [N/O] ratio for Sher 25 agrees with that for its ring nebula, although a higher degree of CNO processing would be expected if the nebula originated during a red supergiant phase, as is suspected for the ring nebula ejected by the B supergiant progenitor of SN 1987A, Sk--69° 202. Sher 25 has an inferred age of ˜5 Myr in contrast with ˜2 Myr for HD 97950, the ionizing cluster of NGC 3603, so it may be a foreground object or close binary evolution may be responsible for its unusual location in the H-R diagram.

Crowther, P. A.; Lennon, D. J.; Walborn, N. R.; Smartt, S. J.

2008-06-01

68

CNO abundances in the quintuplet cluster M supergiant 5-7  

NASA Technical Reports Server (NTRS)

We present and analyze infrared spectra of the supergiant VR 5-7, in the Quintuplet cluster 30 pc from the Galactic center. Within the uncertainties, the [C/H],[N/H], and [O/H] abundances in this star are equal of Ori, a star which exhibits mixing of CNO processed elements, but distinct from the abundance patterns in IRS 7.

Ramirez, S. V.; Sellgren, K.; Blum, R.; Terndrup, D. M.

2002-01-01

69

Variability and mass loss in IA O-B-A supergiants  

NASA Technical Reports Server (NTRS)

Recently completed catalogs of MK spectral types and UBV photometry of 1227 OB stars in the southern Milky Way have been analyzed to investigate brightness and color variability among the Ia supergiants. It is found that brightness variability is common among the O9-B1 supergiants with typical amplitudes about 0.1 and time scales longer than a week and shorter than 1000 days. Among the A supergiants fluctuations in U-B color are found on similar time scales and with amplitude about 0.1. For many early Ia supergiants there is a poor correlation between Balmer jump and spectral type, as had been known previously. An attempt to correlate the Balmer jump deficiency with mass loss rate yielded uncertain results.

Schild, R. E.; Garrison, R. F.; Hiltner, W. A.

1983-01-01

70

The energy distributions of B supergiants in the Large Magellanic Cloud  

NASA Technical Reports Server (NTRS)

It is shown that line-blanketed, LTE, plane-parallel model atmosphere calculations provide excellent fits to the ultraviolet-through-visual energy distributions of B supergiants in the Large Magellanic Cloud. The models were computed using Kurucz's (1979) ATLAS atmosphere program, but with lower gravities than were contained in Kurucz's published model grid. The ultraviolet continua of low gravity stars are found to be sensitive to changes in temperature and gravity. Measurements of Teff and log g for ten LMC B supergiants from model atmosphere fits to the energy distributions yield estimates of their radii, luminosities, and masses. Model atmosphere fits suggest that the late B supergiants have significantly lower masses than the earlier B types of the same luminosity, contrary to stellar evolution theory which predicts that B supergiants are in a post-core hydrogen burning phase and should evolve very quickly and at essentially constant mass.

Fitzpatrick, Edward L.

1986-01-01

71

The luminosities of red supergiants from Wing's eight-color narrow-band infrared photometry  

NASA Astrophysics Data System (ADS)

Calibration relations have been obtained for the intrinsic color index 0 ( = 5040/Te, Te being the observed color temperature of a star) and absolute magnitudes M(104) (at = 1.04 , in Wing's narrow-band photometric system), MV and MK as functions of TiO and CN photometric indices for K5-M5 supergiant stars. The accuracy of the distance moduli obtained when using these calibrations is about 0m·2. The distance moduli have been calculated for red supergiants which are members of open clusters. The distance scale for red supergiants based upon the M(104) (TiO, CN) absolute magnitude calibration (the distance modulus of 11m·4 being assumed for the Per OB1 stellar association) agrees with the distance scale for young open clusters based upon uvby?-photometry and Crawford's (1978) ZAMS for B-type stars.

Dambis, A. K.

72

Amplitude Variations in Pulsating Red Supergiants  

NASA Astrophysics Data System (ADS)

We have used long-term AAVSO visual observations and Fourier and wavelet analysis to identify periods and to study long-term amplitude variations in forty-four red supergiants. Of these, twelve stars had data which were too sparse and/or had low amplitude and/or were without conspicuous peaks in the Fourier spectrum; six stars had only a long (2,500-4,000 days) period without significant amplitude variation. The other twenty-six stars had one or two periods, either "short" (hundreds of days) or "long" (thousands of days), whose amplitudes varied by up to a factor of 8, but more typically 2 to 4. The median timescale of the amplitude variation was 18 periods. We interpret the shorter periods as due to pulsation, and the longer periods as analogous to the "long secondary periods" found in pulsating red giants. We discuss possible explanations for the amplitude variations, including the effects of pulsation, rotation, convection cells, and stochastically-excited pulsations.

Percy, J. R.; Khatu, V. C.

2014-05-01

73

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

74

Red supergiants as tracers of Perseus Arm structure  

NASA Astrophysics Data System (ADS)

We have performed a systematic search for red supergiants in the Perseus Arm (from l = 95 degrees up to l = 150 degrees). For this purpose we made a selection of candidates through photometric criteria, using data from UCAC, USNO and 2MASS catalogs. 747 stars were observed in the spectral region around the infrared Ca triplet (8400-8900 Å) at R ~ 10000, using the Intermediate Dispersion Spectrograph (IDS) on the Isaac Newton Telescope (INT, Roque de los Muchachos Observatory). From these data we have obtained radial velocities, spectral type and luminosity class, finding 353 supergiants. Using them we have analysed the distribution in the radial velocity-galactic latitude diagram, tracing the young clusters and galactic structure in this region.

Dorda, Ricardo; Negueruela, Ignacio; Gonzalez-Fernandez, Carlos

2013-06-01

75

Infrared giants vs. supergiants. II. CO observations  

NASA Astrophysics Data System (ADS)

We report systematic observations of millimeter CO emission from a sample of 109 oxygen-rich evolved stars (AGB and supergiants), colour-selected from the IRAS Point Source Catalog (0.69 < S_{25microns }/S_{12microns } < 1.20). CO(1-0) has been searched with good sensitivity in 81 sources (74% of the sample). CO(1-0) is detected in 54 sources and a significant upper limit has been achieved in 27 sources. In our previous paper we reported on the statistical results of these observations. We showed that in almost 50% of the sources, the ratio of the IRAS 60;microns flux to CO intensity, {cal R} = S60/T_mb(1-0), is larger by a factor of 3 to more than 10 than what is expected according to the correlation found by \\cite[Nyman et al. (1992)]{nym92}. Supergiants only exhibit very high values (raise 0.6exhbox {> 200). In most cases, the observed spread in the values of this ratio can be explained by a large range of luminosities. This leads to a new criterion to identify AGB stars: an object with {cal R} < 150 must have a low mass progenitor. Here we study the correlations between {cal R} and various physical properties of the sources. Most sources with high values of {cal R} also have low galactic latitudes, small IRAS variability indices, and early spectral types (typically M1-M5). Conversely, there is no dependence on the IRAS colours, nor on the intensity of silicate 10;microns emission. However, a few AGB stars exhibit large {cal R}; other factors than luminosity are required to explain these values. Different hypotheses, such as the possible presence of a chromosphere, a low (12) C abundance or a variable mass-loss rate, are examined. Considering the global high OH detection rate ( ~ 67%), we studied the correlations with CO and OH emission. The detection of OH seems to be a useful discriminator of mechanisms that enhance {cal R}.

Josselin, E.; Loup, C.; Omont, A.; Barnbaum, C.; Nyman, L. Aa.; Sevre, F.

1998-04-01

76

Spectroscopy of F supergiants with infrared excess  

NASA Astrophysics Data System (ADS)

Atmospheric parameters, abundances of 26 chemical elements and radial velocities, all based on CCD echelle spectra, are presented for two peculiar F supergiants with a large infrared excess: IRAS 07134+1005 and IRAS 18095+2704. A moderate underabundance of metallicity is revealed for both stars, [Fe/H]_=-1.0 and -0.78 dex, respectively. The significant overabundance of CNO elements is confirmed for IRAS 07134+0115: [C/Fe]=1.08 dex, [N/Fe]=1.03 dex and [O/Fe]=0.6 dex. For IRAS 18095+2704 these overabundances are less marked: [X/Fe]~=0.5 dex,but they are real. Large excesses of lanthanides are derived for both stars. Significant unexplained non-LTE effects occur, revealed by differences for many metals in the abundances obtained from neutral and ionized atomic lines. All of the characteristics of the IRAS sources studied are consistent with the hypothesis that they are at a post-AGB evolutionary stage.

Klochkova, V. G.

1995-02-01

77

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

This quarterly report is comprised of a paper, "Rotational Modulation of B Supergiant Winds" presented at the ESO workshop "Cyclical Variability in Stellar Winds." Presented is a 30-day IUE time series of the BO Ia HD 91969, a member of the Carina open cluster NGC 3293, which showed, among other things, that wind lines that probe more deeply into the wind vary more regularly.

Massa, D.; Fullerton, A. W.; Prinja, R. K.

1998-01-01

78

Massive stars in the galaxies of the Local Group  

NASA Astrophysics Data System (ADS)

The star-forming galaxies of the Local Group act as our laboratories for testing massive star evolutionary models. In this review, I briefly summarize what we believe we know about massive star evolution, and the connection between OB stars, Luminous Blue Variables, yellow supergiants, red supergiants, and Wolf-Rayet stars. The difficulties and recent successes in identifying these various types of massive stars in the neighboring galaxies of the Local Group will be discussed.

Massey, Philip

2013-07-01

79

NGC 7419 as a template for red supergiant clusters  

NASA Astrophysics Data System (ADS)

Context. The open cluster NGC 7419 is known to contain five red supergiants and a very high number of Be stars. However, there are conflicting reports about its age and distance that prevent a useful comparison with other clusters. Aims: We intend to obtain more accurate parameters for NGC 7419, using techniques different from those of previous authors, so that it may be used as a calibrator for more obscured clusters. Methods: We obtained Strömgren photometry of the open cluster NGC 7419, as well as classification spectroscopy of ~20 stars in the area. We then applied standard analysis and classification techniques. Results: We find a distance of 4 ± 0.4 kpc and an age of 14 ± 2 Myr for NGC 7419. The main-sequence turn-off is found at spectral type B1, in excellent agreement. We identify 179 B-type members, implying that there are more than 1200 M? in B stars at present. Extrapolating this to lower masses indicates an initial cluster mass of between 7000 and 10 000 M?, depending on the shape of the initial mass function. We find a very high fraction (?40%) of Be stars around the turn-off, but very few Be stars at lower masses. We also report for the first time a strong variability in the emission characteristics of Be stars. We verified that the parameters of the red supergiant members can be used to obtain accurate cluster parameters. Conclusions: NGC 7419 is sufficiently massive to serve as a testbed for theoretical predictions and as a template to compare more obscured clusters. The distribution of stars above the main-sequence turn-off is difficult to accommodate with current evolutionary tracks. Though the presence of five red supergiants is marginally consistent with theoretical expectations, the high number of Be stars and very low number of luminous evolved B stars hint at some unknown physical factor that is not considered in current synthesis models. Partially based on observations collected at the Nordic Optical Telescope and the William Herschel Telescope (La Palma) and at the 1.93-m telescope at Observatoire de Haute Provence (CNRS), France.Tables 1 and 2 are available in electronic form at http://www.aanda.orgTables 3, 4 and 7 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/552/A92

Marco, A.; Negueruela, I.

2013-04-01

80

Masses and Mass Loss Rates of Red Supergiants in Binaries II  

NASA Astrophysics Data System (ADS)

We propose to observe all remaining cool, non-interacting supergiant binaries with hot companions from the Parsons & Ake (1998) catalog, satisfying certain feasibility requirements, that were not targets in FUSE program E937, as a Survey and Supplemental Program. The objective is to determine stellar masses of a diverse sample of massive, evolved, late-type stars and their B-type main sequence companions, accurate to 1--2 accurate stellar masses are known for any cool supergiants. An important secondary goal is to determine mass-loss rates of the stellar winds of these evolved stars by observation of wind absorption features superimposed on the hot companions FUV continua. These supergiant binary systems are important, fundamental stellar laboratories useful in verifying and constraining models of stellar structure and evolution. We will proceed by measuring the hot stars radial velocity, preferably at more than one epoch (we will propose continuing observations for FUSE Cycles 7--8). The orbits of the cool supergiant primaries of the target binaries are being accurately determined from the PIs decade-long radial velocity program on the DAO 1.2m McKellar coude telescope. Then the companions velocity amplitude, K_2, can be found from a single radial velocity observation, although multiple observations are preferable. Nevertheless, a single observation will suffice to determine the mass ratio of the stars to 2--4 separated in orbital phase, the accuracy will be 1--2 Some target stars eclipse, and for these accurate stellar masses can be directly obtained. Masses of the remaining stars will be obtained from optical interferometry; these binaries are on the NPOI target list. With the loss of HSTSTIS, bf FUSE is the only available UV spectrograph and therefore, the proposed program is essential to determining fundamental, accurate masses of cool supergiants.

Bennett, K.

81

First Stellar Abundance Measurements in the Galactic Center: The M Supergiant IRS 7.  

National Technical Information Service (NTIS)

The first measurement of the photospheric abundances in a star at the Galactic center are presented. A detailed abundance analysis of the Galactic center M2 supergiant IRS 7 was carried out using high-resolution near- infrared echelle spectra. The Fe abun...

J. S. Carr K. Sellgren S. C. Balachandran

2000-01-01

82

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

83

THE YELLOW AND RED SUPERGIANTS OF M33  

SciTech Connect

Yellow and red supergiants are evolved massive stars whose numbers and locations on the Hertzsprung-Russell (H-R) diagram can provide a stringent test for models of massive star evolution. Previous studies have found large discrepancies between the relative number of yellow supergiants (YSGs) observed as a function of mass and those predicted by evolutionary models, while a disagreement between the predicted and observed locations of red supergiants (RSGs) on the H-R diagram was only recently resolved. Here, we extend these studies by examining the YSG and RSG populations of M33. Unfortunately, identifying these stars is difficult as this portion of the color-magnitude diagram is heavily contaminated by foreground dwarfs. We identify the RSGs through a combination of radial velocities and a two-color surface gravity discriminant, and after re-characterizing the rotation curve of M33 with our newly selected RSGs, we identify the YSGs through a combination of radial velocities and the strength of the O I {lambda}7774 triplet. We examine {approx}1300 spectra in total and identify 121 YSGs (a sample that is unbiased in luminosity above log (L/L{sub Sun }) {approx} 4.8) and 189 RSGs. After placing these objects on the H-R diagram, we find that the latest generation of Geneva evolutionary tracks shows excellent agreement with the observed locations of our RSGs and YSGs, the observed relative number of YSGs with mass, and the observed RSG upper mass limit. These models therefore represent a drastic improvement over previous generations.

Drout, Maria R. [Center for Astrophysics, Harvard University, 60 Garden Street, M-S 10, Cambridge, MA 02138 (United States); Massey, Philip [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Meynet, Georges, E-mail: mdrout@cfa.harvard.edu, E-mail: phil.massey@lowell.edu, E-mail: georges.meynet@unige.ch [Geneva Observatory, Geneva University, CH-1290 Versoix (Switzerland)

2012-05-10

84

Ultraviolet analysis of the peculiar supergiant HD 112374 = HR 4912  

NASA Technical Reports Server (NTRS)

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.

Bohm-Vitense, E.; Proffitt, C.

1984-01-01

85

40 field red supergiants in the SMC (Meliani+, 1995)  

NASA Astrophysics Data System (ADS)

Low-resolution spectra (~5A) for 40 red supergiants in the Small Magellanic Cloud were compared with synthetic spectra, and their metallicities were derived. A mean metallicity of [Fe/He]=-0.71 is found for 38 stars cooler than Teff<4500K. Using the stellar parameters derived, the carbon abundances were determined by comparing synthetic spectra at the G-band region to the observed spectra. A mean {epsilon}(C)=7.85 is found, clearly higher than the low values suggested in the literature for the H II regions. (45 data files).

Meliani, M. T.; Barbuy, B.; Richtler, T.

1996-01-01

86

Yellow and Red Supergiants in the Large Magellanic Cloud  

NASA Astrophysics Data System (ADS)

Due to their transitionary nature, yellow supergiants (YSGs) provide a critical challenge for evolutionary modeling. Previous studies within M31 and the Small Magellanic Cloud show that the Geneva evolutionary models do a poor job at predicting the lifetimes of these short-lived stars. Here, we extend this study to the Large Magellanic Cloud (LMC) while also investigating the galaxy's red supergiant (RSG) content. This task is complicated by contamination by Galactic foreground stars that color and magnitude criteria alone cannot weed out. Therefore, we use proper-motions and the LMC's large systemic radial velocity (~278 km s-1) to separate out these foreground dwarfs. After observing nearly 2000 stars, we identified 317 probable YSGs, 6 possible YSGs, and 505 probable RSGs. Foreground contamination of our YSG sample was ~80%, while that of the RSG sample was only 3%. By placing the YSGs on the Hertzsprung-Russell diagram and comparing them against the evolutionary tracks, we find that new Geneva evolutionary models do an exemplary job at predicting both the locations and the lifetimes of these transitory objects.

Neugent, Kathryn F.; Massey, Philip; Skiff, Brian; Meynet, Georges

2012-04-01

87

Discovery of a low mass B[e] supergiant in the SMC.  

NASA Astrophysics Data System (ADS)

Peculiar emission-line B supergiants are a group of early-type stars with the following typical characteristics: (a) strong Balmer emission lines frequently with P Cygni profiles, (b) permitted and forbidden lines of FeII, [FeII], [OI], etc. and (c) strong infrared excess possibly due to thermal radiation from circumstellar dust. They represent one of the two main groups of early-type emission line stars in the Magellanic Clouds (MCs). The other group consists of the classical P Cygni stars and their hotter counterparts, Of-like objects. The S Dor variables, also called Hubble-Sandage variables, are the most extreme variables of the P Cygni and Of-like objects (Stahl et al., 1985). The B[e] supergiants are located in the HR diagram in the same region as S Dor variables and represent evolved evolutionary stages of the most luminous and presumably the most massive O stars (Zickgraf et al., 1986).

Heydari-Malayeri, M.

1989-12-01

88

Supergiants and the galactic metallicity gradient. I. 27 late-type supergiants in the inner-arm regions  

SciTech Connect

From an analysis of high-dispersion Kitt Peak echelle data, atmospheric parameters and chemical abundances have been derived for 27 supergiants of spectral type F through M. Since the star studied lie within about 1 kpc of the Sun, their abundances will form the local reference point for extensions of this study to larger distances. The derived (Fe/H) ratios range from -0.6 to +0.1 dex, show a mean value of -0.15 dex, and have an internal uncertainty of +- 0.2 dex.

Luck, R.E.

1982-12-01

89

Quantitative spectroscopy of BA-type supergiants  

NASA Astrophysics Data System (ADS)

Luminous BA-type supergiants have enormous potential for modern astrophysics. They allow topics ranging from non-LTE physics and the evolution of massive stars to the chemical evolution of galaxies and cosmology to be addressed. A hybrid non-LTE technique for the quantitative spectroscopy of these stars is discussed. Thorough tests and first applications of the spectrum synthesis method are presented for the bright Galactic objects ? Leo (A0 Ib), HD 111613 (A2 Iabe), HD 92207 (A0 Iae) and ? Ori (B8 Iae), based on high-resolution and high-S/N Echelle spectra. Stellar parameters are derived from spectroscopic indicators, consistently from multiple non-LTE ionization equilibria and Stark-broadened hydrogen line profiles, and they are verified by spectrophotometry. The internal accuracy of the method allows the 1?-uncertainties to be reduced to ?1-2% in T_eff and to 0.05-0.10 dex in log g. Elemental abundances are determined for over 20 chemical species, with many of the astrophysically most interesting in non-LTE (H, He, C, N, O, Mg, S, Ti, Fe). The non-LTE computations reduce random errors and remove systematic trends in the analysis. Inappropriate LTE analyses tend to systematically underestimate iron group abundances and overestimate the light and ?-process element abundances by up to factors of two to three on the mean. This is because of the different responses of these species to radiative and collisional processes in the microscopic picture, which is explained by fundamental differences of their detailed atomic structure, and not taken into account in LTE. Contrary to common assumptions, significant non-LTE abundance corrections of ~0.3 dex can be found even for the weakest lines (W?? 10 mÅ). Non-LTE abundance uncertainties amount to typically 0.05-0.10 dex (random) and ~0.10 dex (systematic 1?-errors). Near-solar abundances are derived for the heavier elements in the sample stars, and patterns indicative of mixing with nuclear-processed matter for the light elements. These imply a blue-loop scenario for ? Leo because of first dredge-up abundance ratios, while the other three objects appear to have evolved directly from the main sequence. In the most ambitious computations several ten-thousand spectral lines are accounted for in the spectrum synthesis, permitting the accurate reproduction of the entire observed spectra from the visual to near-IR. This prerequisite for the quantitative interpretation of intermediate-resolution spectra opens up BA-type supergiants as versatile tools for extragalactic stellar astronomy beyond the Local Group. The technique presented here is also well suited to improve quantitative analyses of less extreme stars of similar spectral types.

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

2006-01-01

90

The spin-up of contracting red supergiants  

NASA Astrophysics Data System (ADS)

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 Msun 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.

Heger, A.; Langer, N.

1998-06-01

91

On the Balmer discontinuity of BIa supergiants  

NASA Astrophysics Data System (ADS)

Observed Balmer discontinuities of BIa supergiants, obtained in the Barbier-Chalonge-Divan system using 13-color photometry, are compared with those predicted using classical models of stellar atmospheres. The differences noted between observations and theory for beta = 1 are shown to be a function of the effective temperature. Radii of the supergiants are usually higher when the spectral type is later, suggesting that models of extended atmospheres may explain both the Balmer discontinuities of the supergiants and their far-UV flux distributions.

Zorec, Juan; Mercado-Ibanez, Roger

1987-11-01

92

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

NASA Technical Reports Server (NTRS)

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.

Ahmad, Imad A.; Stencel, Robert E.

1988-01-01

93

An analysis of STIS HST UV spectra of M 33 early B supergiants  

NASA Astrophysics Data System (ADS)

We present terminal velocities of M 33 B-supergiants, obtained from STIS HST spectra as part of our programme to investigate the Wind Momentum - Luminosity Relationship (WLR) in the Local Group. Terminal velocities are derived from their N V, C Iv, and Si Iv resonance lines in UV spectra. Comparing with IUE spectra of Galactic B-supergiants we found evidence of low metallicity in three of our objects. The terminal velocities are consistent with the corresponding values of Galactic stars, except for B-133. For this star we find a very large vinfty and a red Si Iv component deeper than the blue one, that might be an indication of binarity. The average ratio between terminal and turbulent wind velocities is 0.25, well above the value found for Galactic stars. Partly based on INES data from the IUE satellite.

Urbaneja, M. A.; Herrero, A.; Kudritzki, R. P.; Bresolin, F.; Corral, L. J.; Puls, J.

2002-05-01

94

Spectroscopy of be stars  

NASA Astrophysics Data System (ADS)

This chapter describes non supergiant B-type stars that show emission lines, called Be stars. The emission is caused by the presence of a circumstellar decretion disk. Many physical phenomena are thought to be involved in these stars, such as rapid rotation, pulsations and magnetic fields, and give rise to variations. Spectroscopy is used as a diagnostic tool to study Be stars, by professional astronomers as well as by amateurs.

Neiner, C.

2011-04-01

95

Chemical compositions of four high-latitude A-F supergiants  

SciTech Connect

The atmospheric parameters and chemical composition of HR 6144, HD 161796, 89 Her, and HR 7671, four representative members of the class of A- and F-type supergiants lying at high Galactic latitudes, are determined. The abundance results for HR 6144, HD 161796, and 89 Her are strongly atypical of Population I supergiants in that they are slightly metal-poor and have an overabundance of both C and N. Their locations in the H-R diagram and the difficulty of assigning them to Population I suggest that high-latitude supergiants are low-mass stars in a post-AGB evolutionary stage. However, they do not reveal the heavy s-process element enhancements seen in highly evolved B stars. HR 7671 differs from the other three stars in that it is very metal-poor, slightly deficient in C and O, has s-process abundances enhanced by a factor of four above solar, and has a surprising amount of Li. It may be a post-AGB star descended from a Li-rich S-type star. 81 refs.

Luck, R.E.; Bond, H.E.; Lambert, D.L. (Case Western Reserve Univ., Cleveland, OH (USA) Space Telescope Science Institute, Baltimore, MD (USA) Texas Univ., Austin (USA))

1990-07-01

96

Accretion in supergiant High Mass X-ray Binaries  

NASA Astrophysics Data System (ADS)

Supergiant High Mass X-ray Binary systems (sgHMXBs) consist of a massive, late type, star and a neutron star. The massive stars exhibit strong, radiatively driven, stellar winds. Wind accretion onto compact object triggers X-ray emission, which alters the stellar wind significantly. Hydrodynamic simulation has been used to study the neutron star - stellar wind interaction it two sgHMXBs: i) A heavily obscured sgHMXB (IGR J17252-3616) discovered by INTEGRAL. To account for observable quantities (i.e., absorbing column density) we have to assume a very slow wind terminal velocity of about 500 km/s and a rather massive neutron star. If confirmed in other obscured systems, this could provide a completely new stellar wind diagnostics. ii) A classical sgHMXB (Vela X-1) has been studied in depth to understand the origin of the off-states observed in this system. Among many models used to account for this observed behavior (clumpy wind, gating mechanism) we propose that self-organized criticality of the accretion stream is the likely reason for the observed behavior. In conclusion, the neutron star, in these two examples, acts very efficiently as a probe to study stellar winds.

Manousakis, A.; Blondin, J.; Walter, R.

2013-09-01

97

Lithium abundance in atmospheres of F- and G-type supergiants and bright giants  

NASA Astrophysics Data System (ADS)

Lithium in the atmosphere of a F or G supergiant reflects the initial Li abundance and the internal history of the star. During evolution of a star from the main sequence (MS) to the supergiant phase, lithium may be destroyed by, for example, rotationally induced mixing in the MS stars and strongly diluted by development of the supergiant's convective envelope. In order to probe the connection between atmospheric Li abundance and evolutionary predictions, we present a non-local thermodynamic equilibrium abundance analysis of the resonance doublet Li I at 6707.8 Å for 55 Galactic F and G supergiants and bright giants (we observed 43 of them, the remaining 12 are added from Luck and Wepfer's list). The derived lithium abundances log ?(Li) may be considered in three groups, namely: (i) 10 Li-rich giants with log ?(Li) = 2.0-3.2 (all 10 are F-type or A9 stars); (ii) 13 G- to K0-type stars with Li abundances in the narrow range log ?(Li) = 1.1-1.8; (iii) all other stars provide just upper limits to the Li abundance. The derived Li abundances are compared with theoretical predictions of 2-15 M? stars (both rotating and non-rotating). Our results are generally in good agreement with theory. In particular, the absence of detectable lithium for the majority of programme stars is explainable. The comparison suggests that the stars may be separated by mass M into two groups, namely M ? 6 M? and M > 6 M?. All Li-rich giants and supergiants with log ?(Li) ? 2.0 have masses M < 6 M?; this conclusion follows not only from our work but also from a scrutiny of published data. 11 of 13 stars with log ?(Li) = 1.1-1.8, specifically the stars with M < 6 M?, show good agreement with the post-first dredge-up surface abundance log ?(Li) ? 1.4 predicted for the non-rotating 2-6 M? stellar models. An absence of Li-rich stars in the range M > 6 M? agrees with the theoretical prediction that F and G supergiants and giants with M > 6 M? cannot show detectable lithium. We note that present theory appears unable to account for the derived Li abundances for some stars, namely for (i) a few relatively low-mass Li-rich giants (M < 6 M?), whose high Li abundances accompanied by rather high rotational velocities or substantial nitrogen excess contradict theoretical predictions; (ii) the relatively high-mass supergiants HR 461 and HR 8313 (M > 6 M?) with the detected abundances log ? = 1.3-1.5. It is possible that the lithium in such stars was synthesized recently.

Lyubimkov, Leonid S.; Lambert, David L.; Kaminsky, Bogdan M.; Pavlenko, Yakov V.; Poklad, Dmitry B.; Rachkovskaya, Tamara M.

2012-11-01

98

Quantitative studies of the optical and UV spectra of Galactic early B supergiants. I. Fundamental parameters  

NASA Astrophysics Data System (ADS)

Aims: 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_eff}, {log L*}, 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 {T_eff} 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 B0-B5 supergiants analysed show evidence of CNO processing. A mass discrepancy still exists between spectroscopic and evolutionary masses, with the largest discrepancy occurring at {log (L/L?}) 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. Appendix A is only available in electronic form at http://www.aanda.org

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

2008-04-01

99

Stellar winds in supergiant High Mass X-ray Binaries  

NASA Astrophysics Data System (ADS)

Supergiant High Mass X-ray Binary systems (sgHMXBs) consist of a massive, late type, star and a neutron star. The massive stars exhibit strong, radiatively driven, stellar winds. Wind accretion onto compact object triggers X-ray emission, which alters the stellar wind significantly. Hydrodynamic simulation has been used to study the neutron star - stellar wind interaction it two sgHMXBs: i) A heavily obscured sgHMXB (IGR J17252-3616) discovered by INTEGRAL. To account for observable quantities (i.e., absorbing column density) we have to assume a very slow wind terminal velocity of about 500 km/s and a rather massive neutron star. If confirmed in other obscured systems, this could provide a completely new stellar wind diagnostics. ii) A classical sgHMXB (Vela X-1) has been studied in depth to understand the origin of the off-states observed in this system. Among many models used to account for this observed behavior (clumpy wind, gating mechanism) we propose that self-organized criticality of the accretion stream is the likely reason for the observed behavior.

Manousakis, Antonios; Walter, Roland

2013-06-01

100

Evolutionary Status of the Peculiar B3IA Supergiant HD 157038  

NASA Astrophysics Data System (ADS)

HD157038 is a peculiar hot supergiant whose spectrum shows evidence of having been contaminated by the products of interior nuclear reactions. In particular, visible region observations (e.g. Walborn 1976, Lennon and Dufton 1985) indicate that nitrogen enrichment of the stellar atmosphere appears to have occurred. This proposal aims to extend our observations of this star into the UV to confirm our previous findings, to investigate the current mass loss rate from this star, and to obtain an estimate of the stellar mass. We propose to observe this star continuously for one NASA and one ESA shift.

Nichols-Bohlin, Joy

101

Division IV / Working Group on Massive Stars  

NASA Astrophysics Data System (ADS)

Our Working Group (WG) studies massive, luminous stars, both individually and in resolved and unresolved populations, with historical focus on early-type (OB) stars, A-supergiants, and Wolf-Rayet stars. Our group also studies lower mass stars (e.g., central stars of planetary nebulae and their winds) which display features similar or related to those present in massive stars, and thus may improve our understanding of the physical processes occurring in massive stars. In recent years, massive red supergiants that evolve from hot stars have been included into our activities as well. We emphasize the role of massive stars in other branches of astrophysics, particularly regarding the First Stars, long duration Gamma-Ray bursts, formation of massive stars and their feedback on star formation in general, pulsations of massive stars, and starburst galaxies.

Puls, Joachim; Leitherer, Claus; Owocki, Stan; Crowther, Paul; Hanson, Margaret; Herrero, Artemio; Langer, Norbert; Owocki, Stan; Rauw, Gregor; St-Louis, Nicole; Townsend, Richard

2012-04-01

102

A hot companion to Mu Sagittarii - An opportunity to sound the atmosphere of a B8 Ia supergiant  

NASA Technical Reports Server (NTRS)

It is argued that the bright supergiant star Mu Sagittarii is accompanied by a smaller and hotter star, of spectral type approximately B1.5 V. The single-line radial-velocity curve of the B8 star leads to a fairly large mass function, f(m) = 2.64 solar masses, implying that the companion should have at least 50 percent of the mass of the visible star. Older optical observations indicated the presence of a shallow eclipse at the time of the conjunction with the supergiant behind the companion. Since the Copernicus, IUE, and Voyager observations show that the companion is the hotter component, that eclipse must have been the secondary eclipse (if it was an eclipse at all). A deeper, primary eclipse has been predicted by Plavec in 1978. It was indeed observed as a marked decrease of the far-ultraviolet flux from the system both with the Copernicus and the IUE satellites. The presence of a hotter but smaller component in Mu Sagittarii offers a unique opportunity to study the outer atmospheric layers of a supergiant which is of a much earlier spectral type than the supergiants in the Zeta Aurigae systems.

Polidan, R. S.; Plavec, M. J.

1984-01-01

103

Elemental Abundances in Evolved Supergiants. II. The Young Clusters H and chi Persei  

Microsoft Academic Search

We report on the results of our analyses of high-quality spectra of M supergiants in the h and chi Persei double cluster. Our temperature estimates range from 3500 to 4000 K for a sample of 14 stars. There is a wide range in the lithium abundances, from [Li\\/Fe]=-1.7 to [Li\\/Fe]=-0.10. The 12C\\/13C ratio ranges from 10 to 16 and displays

Guillermo Gonzalez; George Wallerstein

2000-01-01

104

Just One New Measurement of the B[e] Supergiant Hen-S22  

NASA Astrophysics Data System (ADS)

This procedure-oriented paper presents a discussion of one new and various archival photometric measurements of the B[e] supergiant Henize-S 22, and outlines significant systematic differences between all involved systems of photometric measurement. The conclusion of this study is that the object is slowly brightening and reddening, a typical signature of an LBV S Doradus phase. The analysis reveals a strong aperture effect in the ASAS photometry of this very special star.

Sterken, C.

2011-09-01

105

The First Stellar Abundance Measurements in the Galactic Center: The M Supergiant IRS 7  

NASA Astrophysics Data System (ADS)

The first measurement of the photospheric abundances in a star at the Galactic center are presented. A detailed abundance analysis of the Galactic center M2 supergiant IRS 7 was carried out using high-resolution near-infrared echelle spectra. The Fe abundance for IRS 7 was found to be close to solar, [Fe/H]=-0.02+/-0.13, and nearly identical to the Fe abundance we obtained for the nearby M supergiants ? Ori and VV Cep. Analysis of the first and second overtone lines of CO was used to derive an effective temperature of 3600+/-230 K, a microturbulent velocity of 3.0+/-0.3 km s-1, and a carbon abundance log? (C)=7.78+/-0.13, or [C/H]=-0.77. In addition, we find a high depletion of 0.74+/-0.32 dex in O and an enhancement of 0.92+/-0.18 dex in N. These abundances are consistent with the dredge-up of CNO cycle products but require deep mixing in excess of that predicted by standard models for red supergiants. In light of our measured solar Fe abundance for IRS 7, we discuss other indicators of metallicity at the Galactic center, the interpretation of low-resolution near-infrared spectra of late-type giants and supergiants, including the need for caution in using such spectra as measures of metallicity, and the evolution of massive young stars at the Galactic center. We suggest the possibility that rapid stellar rotation is common for stars formed under conditions in the Galactic center, and that extra internal mixing induced by high rotation rates, rather than evolution at high metallicity, is the explanation for many of the unusual properties of the hot emission-line stars in the Galactic center.

Carr, John S.; Sellgren, K.; Balachandran, Suchitra C.

2000-02-01

106

Narrow-Band Photometry of Red Supergiants in the Small Magellanic Cloud  

Microsoft Academic Search

A set of 36 red supergiants belonging to the Small Magellanic Cloud have been observed on a six-color narrow-band photometric system that measures continuum points and bands of TiO and CN, all in the near-infrared. The TiO--based spectral types range from stars were observed twice at epochs separated by

R. F. Wing; K. M. Walker; E. Costa; M. L. Houdashelt; D. J. MacConnell

2003-01-01

107

Metallicities and carbon abundances of 40 field red supergiants in the Small Magellanic Cloud  

Microsoft Academic Search

Low-resolution spectra (~5A) for 40 red supergiants in the Small Magellanic Cloud were compared with synthetic spectra, and their metallicities were derived. A mean metallicity of [Fe\\/He]=-0.71 is found for 38 stars cooler than T_eff_<4500K. Using the stellar parameters derived, the carbon abundances were determined by comparing synthetic spectra at the G-band region to the observed spectra. A mean ?(C)=7.85

M. T. Meliani; B. Barbuy; T. Richtler

1995-01-01

108

Scattering of X-rays on the winds of supergiant X-ray binaries  

Microsoft Academic Search

Monte-Carlo simulations of Thomson scattering of X-rays in the stellar wind of OB stars in supergiant X-ray binaries show that at least part of the low-energy excess seen in the X-ray spectra during phases of high absorption can be explained by scattering of X-rays around a dense region in the wind obscuring the direct radiation. In the case of 4U

F. Haberl

1991-01-01

109

Maser Mapping of Dust-Driven Winds from Red Supergiants  

NASA Astrophysics Data System (ADS)

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 be less dense. Outside the dust formation zone, the stellar wind is driven by radiation pressure on grains. Chapman & Cohen (1986) found that in VX Sgr the wind continues to speed up out to a thousand or more AU from the star, and derived values for the dust absorption efficiency increasing with distance to account for this. Other authors pointed out grain growth at large distances is unlikely and suggested VX Sgr must have changed its mass loss rate in recent centuries. However this paper reports observations of continuing acceleration in all four supergiants which have now been studied. An increase in the absorption efficiency of dust is still the most likely generally applicable explanation. This paper proposes a new mechanism whereby the grain surface properties (but not the mass) change in the outflow on a timescale of many decades. Using the method of Chapman & Cohen (1986), it is found that at about 100 AU from the star, near the inner edge of the water maser shell, the dust absorption efficiency is kappaD ~ 0.2 m^2 kg^-1. kappaD increases with distance from the star, rising to >~ m^2 kg^-1 (similar to the conventional value for astronomical silicates) in thick circumstellar envelopes reaching high terminal velocities. The low values found nearer the star suggest that initially the dust grains are crystalline or have a composition high in metal oxides which renders them more transparent to the stellar IR radiation. Dust formation, and the influence of the stellar magnetic field on the grains, is also implicated in producing the small scale clumpiness and large scale axisymmetries which are seen in circumstellar envelopes.

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

1998-01-01

110

Galactovertical Oscillations of Blue Supergiants as a Test of the Theories of Stellar Evolution  

NASA Astrophysics Data System (ADS)

The absolute magnitudes, intrinsic colours, and distances are inferred for 619 Galactic blue supergiants using published UBV or uvby and H? photometry and absolute-magnitude and intrinsic-colour calibrations by Dambis (1990, 1991). The individual ages are determined for all stars based on different isochrone grids both classical and those including mass loss and overshooting. The vertical scale height of the subsample of blue supergiants located within 1.5 kpc of the Sun (a total of 226 stars) is found to decrease with the age from ~ 60 pc for the youngest stars down to ~ 20 pc for the oldest ones. The time scale of this decrease is known to be related to the period of galactovertical oscillations in the solar neighbourhood (M. Joeveer, Tartu Publ., 1974, vol. 47, p. 35). The latter can be independently inferred from the known mean density in the solar neighbourhood and Oort's constants and then compared with the values implied by the analysis of the evolution of the Galactovertical distribution of blue supergiants in terms of various isochrone grids in order to test the underlying theories of stellar evolution. Our results provide strong evidence in favor of classical theories of stellar evolution without overshooting and intense mass loss.

Dambis, A. K.

111

s-Process Elements in the M Supergiant ? Ori  

NASA Astrophysics Data System (ADS)

We present new results on a study of the weak s-process elemental abundances in the M supergiant a Ori (M2Iab). We have conducted the abundance analysis through comparison of synthetic with observed spectra in the two infrared spectral regions 0.7 - 1.1 ?m and 2.1 - 2.3 ?m, where the molecular and atomic line densities are less than in the optical region and where many of the relevant elements have strong lines. Our results show that there has been weak s-process production occurring during the life of the star and among the s-process elements is Sr the most overabundant with 1.4 dex higher abundance than the sun. The abundance of Fe in ? Ori is essentially solar. Other elements for which we have determined abundances are Rb, Y and Zr. We compare our results to nuclear evolutionary stellar model calculations and discuss their relevance.

Lundqvist, M.; Wahlgren, G. M.

2005-07-01

112

Crossing the Yellow Void: Spatially Resolved Spectroscopy of the Post-Red Supergiant IRC +10420 and Its Circumstellar Ejecta  

Microsoft Academic Search

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the H-R diagram. During their post-red supergiant evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semiforbidden region that de Jager and his collaborators have called the ``yellow void.'' We report

Roberta M. Humphreys; Kris Davidson; Nathan Smith

2002-01-01

113

A Transient Supergiant X-Ray Binary in IC 10: An Extragalactic SFXT?  

NASA Astrophysics Data System (ADS)

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 × 1037 erg s–1during 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 (NH = 6.3 × 1021 atom cm–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–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.

Laycock, Silas; Cappallo, Rigel; Oram, Kathleen; Balchunas, Andrew

2014-07-01

114

X-ray pulsations from the region of the supergiant fast X-ray transient IGR J17544-2619  

NASA Astrophysics Data System (ADS)

Phase-targeted RXTE observations have allowed us to detect a transient 71.49 ± 0.02 s signal that is most likely to be originating from the supergiant fast X-ray transient IGR J17544-2619. The phase-folded light curve shows a possible double-peaked structure with a pulsed flux of ~4.8 × 10-12 erg cm-2 s-1 (3-10 keV). Assuming the signal to indicate the spin period of the neutron star in the system, the provisional location of IGR J17544-2619 on the Corbet diagram places the system within the classical wind-fed supergiant XRB region. Such a result illustrates the growing trend of supergiant fast X-ray transients to span across both of the original classes of HMXB in Porb - Pspin space.

Drave, S. P.; Bird, A. J.; Townsend, L. J.; Hill, A. B.; McBride, V. A.; Sguera, V.; Bazzano, A.; Clark, D. J.

2012-03-01

115

Yellow and Red Supergiants in the Local Group  

NASA Astrophysics Data System (ADS)

Yellow and red supergiants are the "poor cousins" of massive star studies, often overlooked in favor of strong emission-lined Wolf-Rayets or the spectacular, enigmatic Luminous Blue Variables. Recent studies, however, are proving the truth of Kippenhahn & Weigert (1990)'s claim that these evolved stages act as a "sort of magnifying glass, revealing relentlessly the faults of calculations of earlier phases." Identifying complete samples of YSGs and RSGs among the galaxies of the Local Group is difficult, as foreground dwarfs are nearly indistinguishable from bona-fide extragalactic members. We have succeeded in this task only by using a combination of wide-area photometry surveys combined with spectroscopic followup. Since massive star evolution is greatly affected by mass-loss, and mass-loss rates depend upon metallicity, we have conducted such studies over a range of 10 in metallicity, including the SMC, LMC, M33, and M31. These studies not only allow us to test the stellar evolutionary models, but the identification of these stars provides interesting kinematic information on the youngest stellar populations in these galaxies. We will review here what we have learned over the past few years, and what new questions these studies are raising.

Massey, Philip; Neugent, Kathryn; Drout, Maria; Meynet, Georges

2013-06-01

116

Impact of non-LTE effects on the IR Ca II triplet and the Mg I 8736 Å equivalent widths in late-type giant and super-giant stars  

NASA Astrophysics Data System (ADS)

Calcium and magnesium are key ?-elements to study stellar populations in galaxies. Classical stellar abundances analyses rely on the local thermodynamic equilibrium (LTE) assumption which is not always appropriate, in particular for metal-poor and/or evolved stars. To better understand these stars and apprehend their impacts on the chemical enrichment of the Galaxy, it is necessary to use a Non-LTE (NLTE) description which is more realistic but also more complex to build up. For the calcium (Ca) and magnesium (Mg) lines in the RVS@Gaia, we computed theoretical NLTE corrections to apply to the measured equivalent widths of these lines using very complete model atoms of Mg and Ca. These corrections can be used by the automated abundance analysis methods based on equivalent widths for current and forthcoming large surveys.

Merle, T.; Thévenin, F.; Pichon, B.; Bigot, L.

2012-12-01

117

Analysis of Four A-F Supergiants in M31 from Keck HIRES Spectroscopy  

NASA Astrophysics Data System (ADS)

The first stellar abundances in M31 are presented, based on Keck I HIRES spectroscopy and model atmospheres analyses of three A-F supergiants, 41-2368, 41-3712, and A-207. We also present the preliminary analysis of a fourth star, 41-3654. We find that the stellar oxygen abundances are in good agreement with those determined from nebular studies, even though the stars do not show a clear radial gradient in oxygen. The uncertainties in the stellar abundances are smaller than the range in the nebular results, making these stars ideal objects for further studies of the distribution of oxygen in M31. We show that the stars can be used to study the abundance distributions of other elements as well, including iron-group and heavier elements. The A-F supergiants also provide direct information on the metallicity and reddening of nearby Cepheid stars. We have examined the metallicity and reddening assumptions used for Cepheids within 1' of our targets and noted the differences from values used in the literature. Based on observations obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Venn, K. A.; McCarthy, J. K.; Lennon, D. J.; Przybilla, N.; Kudritzki, R. P.; Lemke, M.

2000-10-01

118

Spectroscopic observations of AB-supergiants in M 31 and M 33  

NASA Astrophysics Data System (ADS)

We have observed a number of the most luminous A and B supergiants in the galaxies M 31 and M 33 at intermediate dispersion obtaining both blue and red spectrograms. We have determined spectral types and luminosity classifications from these data, in a few cases revising previous evaluations. From comparison with galactic analogues we estimate approximate metallicities for M 31 and M 33. In addition, for the first time we present Halpha_ profiles for these stars which we use to estimate mass loss rates. We conclude that M 31 is comparable in metallicity to our galaxy but M 33 is slightly deficient, more precise estimates requiring higher resolution data. The Halpha_ data are morphologically similar to those of galactic stars and clearly contradict claims that mass-loss rates for luminous stars in M 31 are up to a factor of ten less than their galactic counterparts. We note in particular that the M 31 star 40-1939 is confirmed here as a B1Ia^+^ hypergiant rather than an O6I supergiant (Hutchings et al. 1987) thus explaining the absence of typical wind features associated with an O6 classification. Also of particular interest are the luminous A-hypergiants in M 33, B324 especially appears to be more luminous than any comparable star in our galaxy or the Magellanic Clouds, has an Halpha_ equivalent width of 40A in emission and exhibits a number of FeII P-Cygni profiles.

Herrero, A.; Lennon, D. J.; Vilchez, J. M.; Kudritzki, R. P.; Humphreys, R. H.

1994-07-01

119

Really Cool Stars at the Galactic Center  

NASA Technical Reports Server (NTRS)

New and existing K-band spectra for 19 Galactic center late-type stars have been analyzed along with representative spectra of disk and bulge M giants and supergiants. Absorption strengths for strong atomic and molecular features have been measured. The Galactic center stars generally exhibit stronger absorption features centered near Na I (2.206 microns) and Ca I (2.264 microns) than representative disk M stars at the same CO absorption strength. Based on the absolute K-band magnitudes and CO and H2O absorption strengths for the Galactic center stars and known M supergiants and asymptotic giant branch (AGB) stars, we conclude that only IRS 7 must be a supergiant. Two other bright stars in our Galactic center sample are likely supergiants as well. The remaining bright, cool stars in the Galactic center that we have observed are most consistent with being intermediate mass/age AGB stars. We identify four of the Galactic center stars as long period variables based on their K-band spectral properties and associated photometric variability. Estimates of initial masses and ages for the GC stars suggest multiple epochs of star formation have occurred in the Galactic center over the last 7-100 Myr.

Blum, R. D.; Sellgren, K.; Depoy, D. L.

1996-01-01

120

Really Cool Stars at the Galactic Center  

NASA Technical Reports Server (NTRS)

New and existing K-band spectra for 19 Galactic center late-type stars have been analyzed along with representative spectra of disk and bulge M giants and supergiants. Absorption strengths for strong atomic and molecular features have been measured. The Galactic center stars generally exhibit stronger absorption features centered near Na I (2.206 microns) and Ca I (2.264 microns) than representative disk M stars at the same CO absorption strength. Based on the absolute K - band magnitudes and CO and H2O absorption strengths for the Galactic center stars and known M supergiants and asymptotic giant branch (AGB) stars, we conclude that only IRS 7 must be a supergiant. Two other bright stars in our Galactic center sample are likely supergiant as well. The remaining bright, cool stars in the Galactic center that we have observed are most consistent with being intermediate mass/age AGB stars. We identify four of the Galactic center stars as long period variables based on their K-band spectral properties and associated photometric variability. Estimates of initial masses and ages for the GC stars suggest multiple epochs of star formation have occurred in the Galactic center over the last 7-100 Myr. 0 1996 American Astronomical Society.

Blum, R. D.; Sellgren, K.; Depoy, D. L.

1996-01-01

121

Investigating supergiant fast X-ray transients with LOFT  

NASA Astrophysics Data System (ADS)

Supergiant Fast X-ray Transients (SFXT) are a class of High-Mass X-ray Binaries whose optical counterparts are O or B supergiant stars, and whose X-ray outbursts are about 4 orders of magnitude brighter than the quiescent state. LOFT, the Large Observatory For X-ray Timing, with its coded mask Wide Field Monitor (WFM) and its 10 m2 class collimated X-ray Large Area Detector (LAD), will be able to dramatically deepen the knowledge of this class of sources. It will provide simultaneous high S/N broad-band and time-resolved spectroscopy in several intensity states, and long term monitoring that will yield new determinations of orbital periods, as well as spin periods. We show the results of an extensive set of simulations performed using previous observational results on these sources obtained with Swift and XMM-Newton. The WFM will detect all SFXT flares within its field of view down to a 15-20 mCrab in 5 ks. Our simulations describe the outbursts at several intensities (F(2-10keV) = 5.9×10-9 to 5.5 × 10-10 erg cm-2 s-1), the intermediate and most common state (10-11 erg cm-2 s-1), and the low state (1.2 × 10-12 to 5 × 10-13 erg cm-2 s-1). We also considered large variations of NH and the presence of emission lines, as observed by Swift and XMM-Newton.

Romano, P.; Bozzo, E.; Esposito, P.; Ferrigno, C.; Mangano, V.

2012-12-01

122

AGB (asymptotic giant branch): Star evolution  

SciTech Connect

Asymptotic giant branch stars are red supergiant stars of low-to-intermediate mass. This class of stars is of particular interest because many of these stars can have nuclear processed material brought up repeatedly from the deep interior to the surface where it can be observed. A review of recent theoretical and observational work on stars undergoing the asymptotic giant branch phase is presented. 41 refs.

Becker, S.A.

1987-01-01

123

Stars  

NASA Astrophysics Data System (ADS)

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.

Capelato, Hugo Vicente

1999-01-01

124

The Discovery of a Massive Cluster of Red Supergiants with GLIMPSE  

NASA Astrophysics Data System (ADS)

We report the discovery of a previously unknown massive Galactic star cluster at ell = 29fdg22, b = -0fdg20. Identified visually in mid-IR images from the Spitzer GLIMPSE survey, the cluster contains at least eight late-type supergiants, based on follow-up near-IR spectroscopy, and an additional 3-6 candidate supergiant members having IR photometry consistent with a similar distance and reddening. The cluster lies at a local minimum in the 13CO column density and 8 ?m emission. We interpret this feature as a hole carved by the energetic winds of the evolving massive stars. The 13CO hole seen in molecular maps at V LSR ~ 95 km s-1 corresponds to near/far kinematic distances of 6.1/8.7 ± 1 kpc. We calculate a mean spectrophotometric distance of 7.0+3.7 -2.4 kpc, broadly consistent with the kinematic distances inferred. This location places it near the northern end of the Galactic bar. For the mean extinction of AV = 12.6 ± 0.5 mag (AK = 1.5 ± 0.1 mag), the color-magnitude diagram of probable cluster members is well fit by isochrones in the age range 18-24 Myr. The estimated cluster mass is ~20,000 M sun. With the most massive original cluster stars likely deceased, no strong radio emission is detected in this vicinity. As such, this red supergiant (RSG) cluster is representative of adolescent massive Galactic clusters that lie hidden behind many magnitudes of dust obscuration. This cluster joins two similar RSG clusters as residents of the volatile region where the end of our Galaxy's bar joins the base of the Scutum-Crux spiral arm, suggesting a recent episode of widespread massive star formation there.

Alexander, Michael J.; Kobulnicky, Henry A.; Clemens, Dan P.; Jameson, Katherine; Pinnick, April; Pavel, Michael

2009-06-01

125

Molecular and dust shells around cool supergiants  

NASA Astrophysics Data System (ADS)

The last decade has witnessed a remarkable expansion of our knowledge of the chemistry occuring in the huge envelopes surrounding supergiants. The development of highly sophisticated infrared - submillimeter telescopes was crucial for this progress due their potential to detect gas-phase and solid-state species. Instruments such as Herschel, ISO, IRAM, APEX, SMA, etc. were key for these discoveries. The opening of ALMA end 2011 heralded the start of a new era thanks to an increase in sensitivity and spatial resolution of ca. 2 orders-of-magnitude. Although some supergiants have now been studied in quite some detail, a comprehensive understanding of the main chemical routes and the impact of some dominant physical processes is still lacking. In this talk, I give an overview of the current knowledge on the molecular and dust content in shells around supergiants. I discuss the importance of some chemical formation routes and their relation with some dynamical process. I end the talk with some suggestion for future research.

Decin, Leen

2013-06-01

126

CCD Spectroscopy of New M-Type Supergiants in the Southern Milky way  

NASA Astrophysics Data System (ADS)

We are obtaining COD spectra of possible new M supergiants identified on low-dispersion, I-N objective-prism plates taken near the southern galactic plane. The spectra cover the range 6400-8800 Å with a resolution of 8 Å. The spectra of 180 stars have been observed at least once, and the spectra of about 40 late-type,. luminous MK standards have been obtained as well. The standards are used to calibrate equivalent widths of the Ca II triplet as a function of luminosity and temperature, and this is the principal criterion used to classify the COD spectra. Analysis of this material indicates that there are >60 new K/M super- giants, some very heavily reddened, and a few new S stars in the sample. This at least doubles the number of late supergiants known in the areas searched. We expect that some of these stars lie at distances of 5 to 6 kpc and that the survey will have a significant impact on studies of galactic structure and massive star evolution

MacConnell, D. J.; Wing, R. F.; Costa, E.

1987-05-01

127

Analysis of A-F Supergiants in M31 from Keck HIRES Spectroscopy  

NASA Astrophysics Data System (ADS)

The first stellar abundances in M31 are presented, based on Keck I HIRES spectroscopy and model atmospheres analyses of three A-F supergiants, 41-2368, 41-3712, and A-207. We find that the stellar oxygen abundances are in good agreement with those determined from nebular studies, even though the stars do NOT show a clear radial gradient in oxygen. The uncertainties in the stellar abundances are smaller than the range in the nebular results, making these stars ideal objects for further studies of the distribution of oxygen in M31. We show that the stars can be used to study the abundance distributions of other elements as well, including iron-group and heavier elements. The A-F supergiants also provide direct information on the metallicity and reddening of nearby Cepheid stars. We have examined the metallicity and reddening assumptions used for Cepheids within 1' of our targets and noted differences from values used in the literature. This work has recently been submitted to the Astrophysical Journal.

Venn, K. A.; McCarthy, J. K.; Lennon, D. J.; Przybilla, N.; Kudritzki, R. P.; Lemke, M.

2000-05-01

128

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

SciTech Connect

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.

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

129

Spectral atlas of O9.5-A1-Type supergiants  

NASA Astrophysics Data System (ADS)

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.

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

2007-09-01

130

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

National Technical Information Service (NTIS)

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...

J. Melbourne M. L. Boyer

2013-01-01

131

THE RED SUPERGIANT PROGENITOR OF SUPERNOVA 2012aw (PTF12bvh) IN MESSIER 95  

SciTech Connect

We report on the direct detection and characterization of the probable red supergiant (RSG) progenitor of the intermediate-luminosity Type II-Plateau (II-P) supernova (SN) 2012aw in the nearby (10.0 Mpc) spiral galaxy Messier 95 (M95; NGC 3351). We have identified the star in both Hubble Space Telescope images of the host galaxy, obtained 17-18 yr prior to the explosion, and near-infrared ground-based images, obtained 6-12 yr prior to the SN. The luminous supergiant showed evidence for substantial circumstellar dust, manifested as excess line-of-sight extinction. The effective total-to-selective ratio of extinction to the star was R'{sub V} Almost-Equal-To 4.35, which is significantly different from that of diffuse interstellar dust (i.e., R{sub V} = 3.1), and the total extinction to the star was therefore, on average, A{sub V} Almost-Equal-To 3.1 mag. We find that the observed spectral energy distribution for the progenitor star is consistent with an effective temperature of 3600 K (spectral type M3), and that the star therefore had a bolometric magnitude of -8.29. Through comparison with recent theoretical massive-star evolutionary tracks we can infer that the RSG progenitor had an initial mass 15 {approx}< M{sub ini}(M{sub Sun }) < 20. Interpolating by eye between the available tracks, we surmise that the star had initial mass {approx}17-18 M{sub Sun }. The circumstellar dust around the progenitor must have been destroyed in the explosion, as the visual extinction to the SN is found to be low (A{sub V} = 0.24 mag with R{sub V} = 3.1).

Van Dyk, Schuyler D. [Spitzer Science Center/Caltech, Mailcode 220-6, Pasadena, CA 91125 (United States); Cenko, S. Bradley; Filippenko, Alexei V., E-mail: vandyk@ipac.caltech.edu, E-mail: cenko@berkeley.edu, E-mail: afilippenko@berkeley.edu [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); and others

2012-09-10

132

Properties of galactic B[e] supergiants. III. MWC 300  

NASA Astrophysics Data System (ADS)

We present the results of optical and near-IR spectroscopic and mid-IR imaging observations of the emission-line star MWC 300. Its properties and evolutionary state are still under debate (a B[e] supergiant or a Herbig Be star). For the first time we detected radial velocity variations of the photospheric lines and found a correlation between them and those of the He I ?5876 Åline. Most of the pure emission lines had stable positions for nearly 20 years. New estimates of the object's luminosity (log L/L?=5.1±0.1), distance (D=1.8±0.2 kpc), and systemic velocity (+26±2 km s-1) were derived. We found that both the circumstellar extinction in the disk-like dusty envelope and the interstellar extinction play a significant role in the attenuation of the stellar brightness. Our 2D modeling of the observed spectral energy distribution in the wavelength range from 0.3 ?m to 1.3 mm suggests that the star is viewed through a gaseous-and-dusty flared disk with an opening angle of 30 °, an inclination angle of 10 °, an equatorial optical depth ?V=3.0, and a total mass of 0.08 M?. We argue that MWC 300 is most likely a binary system, because of the similarities of its observed parameters with those of recognized B[e] binaries. Partially based on observations collected at the Canada-France-Hawaii telescope (CFHT), operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique, and Univeristy of Hawaii.

Miroshnichenko, A. S.; Levato, H.; Bjorkman, K. S.; Grosso, M.; Manset, N.; Men'shchikov, A. B.; Rudy, R. J.; Lynch, D. K.; Mazuk, S.; Venturini, C. C.; Puetter, R. C.; Perry, R. B.

2004-04-01

133

On the H? behaviour of blue supergiants: rise and fall over the bi-stability jump  

NASA Astrophysics Data System (ADS)

Context. The evolutionary state of blue supergiants is still unknown. Stellar wind mass loss is one of the dominant processes determining the evolution of massive stars, and it may provide clues to the evolutionary properties of blue supergiants. As the H? line is the most oft-used mass-loss tracer in the OB-star regime, we investigate H? line formation as a function of Teff. Aims: We provide a detailed analysis of the H? line for OB supergiant models over an Teff range between 30 000 and 12 500 K, with the aim of understanding the mass-loss properties of blue supergiants. Methods: We model the H? line using the non-LTE code cmfgen, in the context of the bi-stability jump at Teff ~ 22 500 K. Results: We find a maximum in the H? equivalent width at 22 500 K exactly at the location of the bi-stability jump. The H? line-profile behaviour is characterised by two branches of effective temperature: (i) a hot branch between 30 000 and 22 500 K, where H? emission becomes stronger with decreasing Teff; and (ii) a cool branch between 22 500 and 12 500 K, where the H? line becomes weaker. Our models show that this non-monotonic H? behaviour is related to the optical depth of Ly?, finding that at the "cool" branch the population of the 2nd level of hydrogen is enhanced in comparison to the 3rd level. This is expected to increase line absorption, leading to weaker H? flux when Teff drops from 22 500 K downwards. We also show that for late B supergiants (at Teff below ~15 000 K), the differences in the H? line between homogeneous and clumpy winds becomes insignificant. Moreover, we show that, at the bi-stability jump, H? changes its character completely, from an optically thin to an optically thick line, implying that macro-clumping should play an important role at temperatures below the bi-stability jump. This would not only have consequences for the character of observed H? line profiles, but also for the reported discrepancies between theoretical and empirical mass-loss rates.

Petrov, Blagovest; Vink, Jorick S.; Gräfener, Götz

2014-05-01

134

X-ray scanning a supergiant wind-accretor: eclipse egress in Vela X-1  

NASA Astrophysics Data System (ADS)

We propose to use one XMM-Newton orbit observing the eclipse egress and early post-eclipse phase of the Vela~X-1/HD~77581 binary system. We plan to use EPIC-pn CCD spectra and pulse profiles together with RGS results for emission lines in order to study in unprecedented detail the emerging neutron star's emission and measure the scale height of the supergiant's extended atmosphere with high accuracy. Small time scale variations in the observed column density will track clumps in the lower stellar wind.

Kretschmar, Peter

2005-10-01

135

A critical test of empirical mass loss formulas applied to individual giants and supergiants  

NASA Astrophysics Data System (ADS)

To test our new, improved Reimers-type mass-loss relation, given by Schröder & Cuntz in 2005 (ApJ, 630, L73), we take a look at the best studied galactic giants and supergiants - particularly those with spatially resolved circumstellar shells and winds, obtained directly or by means of a companion acting as a probing light source. Together with well-known physical parameters, the selected stars provide the most powerful and critical observational venues for assessing the validity of parameterized mass-loss relations for cool winds not driven by molecules or dust. In this study, star by star, we compare our previously published relation with the original Reimers relation (1975, Mem. Roy. Soc. Liège 6. Ser. 8, 369), the Lamers relation (1981, ApJ, 245, 593), and the two relations by de Jager and his group (1988, A&AS, 72, 259; 1990, A&A, 231, 134). The input data, especially the stellar masses, have been constrained using detailed stellar evolution models. We find that only the relationship by Schröder & Cuntz agrees, within the error bars, with the observed mass-loss rates for all giants and supergiants.

Schröder, K.-P.; Cuntz, M.

2007-04-01

136

The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought  

NASA Astrophysics Data System (ADS)

We use moderate-resolution optical spectrophotometry and the new MARCS stellar atmosphere models to determine the effective temperatures of 74 Galactic red supergiants (RSGs). The stars are mostly members of OB associations or clusters with known distances, allowing a critical comparison with modern stellar evolutionary tracks. We find we can achieve excellent matches between the observations and the reddened model fluxes and molecular transitions, although the atomic lines Ca I ?4226 and Ca II H and K are found to be unrealistically strong in the models. Our new effective temperature scale is significantly warmer than those in the literature, with the differences amounting to 400 K for the latest type M supergiants (i.e., M5 I). We show that the newly derived temperatures and bolometric corrections give much better agreement with stellar evolutionary tracks. This agreement provides a completely independent verification of our new temperature scale. The combination of effective temperature and bolometric luminosities allows us to calculate stellar radii; the coolest and most luminous stars (KW Sgr, Case 75, KY Cyg, HD 206936=? Cep) have radii of roughly 1500 Rsolar (7 AU), in excellent accordance with the largest stellar radii predicted from current evolutionary theory, although smaller than that found by others for the binary VV Cep and for the peculiar star VY CMa. We find that similar results are obtained for the effective temperatures and bolometric luminosities using only the dereddened V-K colors, providing a powerful demonstration of the self-consistency of the MARCS models.

Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges

2005-08-01

137

HD16691: an extreme O-type supergiant with magnetically confined wind?  

NASA Astrophysics Data System (ADS)

We propose to investigate the X-ray properties of HD16691, an O4 supergiant believed to be a transition object between O and Wolf-Rayet stars. Recent spectroscopic investigations by our team in the visible domain revealed a stellar wind affected by a large scale corotating structure, perhaps related to the interplay between the stellar magnetic field and the plasma outflow. This object constitutes therefore a valuable target for investigating the role of the potential magnetic confinement of the stellar wind. In addition, most of the O-type stars observed so far in X-rays belong to spectral types later than O5. An XMM-Newton study of HD16691 will therefore contribute to complete the picture of the X-ray properties of early-type stars.

De Becker, Michael

2010-10-01

138

Spectrophotometry of A and F stars  

Microsoft Academic Search

This book is devoted primarily to the determination of observational parameters associated with the physical properties of stellar atmospheres. Results of spectrophotometric observations are used to study the absolute energy distribution between 3200 and 7500 A in the spectra of 150 A and F stars. This sample includes 90 normal stars of luminosity classes III, IV, and V; 16 supergiants

A. V. Kharitonov; V. M. Tereshchenko; E. A. Glushkova; V. T. Rebristyi; L. D. Frishberg

1974-01-01

139

Red supergiants in M33 galaxy  

NASA Astrophysics Data System (ADS)

In the present work the spatial distribution of the red supergiants in M33 galaxy is discussed. The observational data exhibit stellar groups of high stellar density. The smallest 60 groups with stellar density corresponding to signal-to-noise ratio S/N > 5 have a mean size of 8.1" (?30 pc). They are real stellar associations in M33. The size of the largest stellar groups found in M33 is of about 200" (~0.8 kpc) and is typical for a stellar complex.

Vassilev, O.; Vassileva, L.; Ivanov, G.; Vassilev, D.

2002-07-01

140

Direct imaging with a hypertelescope of red supergiant stellar surfaces  

NASA Astrophysics Data System (ADS)

High angular resolution images obtained with a hypertelescope can strongly constrain the radiative-hydrodynamics simulations of red supergiant (RSG) stars, in terms of intensity contrast, granulation size and temporal variations of the convective motions that are visible on their surface. The characterization of the convective pattern in RSGs is crucial to solve the mass-loss mechanism which contributes heavily to the chemical enrichment of the Galaxy. We show here how the astrophysical objectives and the array configuration are highly dependent to design a hypertelescope. For a given field of view and a given resolution, there is a trade-off between the array geometry and the number of required telescopes to optimize either the (u,v) coverage (to recover the intensity distribution) or the dynamic range (to recover the intensity contrast). To obtain direct snapshot images of Betelgeuse with a hypertelescope, a regular and uniform layout of telescopes is the best array configuration to recover the intensity contrast and the distribution of both large and small granulation cells, but it requires a huge number of telescopes (several hundreds or thousands). An annular configuration allows a reasonable number of telescopes (lower than one hundred) to recover the spatial structures but it provides a low-contrast image. Concerning the design of a pupil densifier to combine all the beams, the photometric fluctuations are not critical (Delta photometry < 50%) contrary to the residual piston requirements (OPD < ?/8) which requires the development of an efficient cophasing system to fully exploit the imaging capability of a hypertelecope.

Patru, F.; Chiavassa, A.; Mourard, D.; Tarmoul, N.

2010-07-01

141

SUPERNOVA 2008bk AND ITS RED SUPERGIANT PROGENITOR  

SciTech Connect

We have obtained limited photometric and spectroscopic data for supernova (SN) 2008bk in NGC 7793, primarily at {approx}> 150 days after explosion. We find that it is a Type II-Plateau (II-P) SN that most closely resembles the low-luminosity SN 1999br in NGC 4900. Given the overall similarity between the observed light curves and colors of SNe 2008bk and 1999br, we infer that the total visual extinction to SN 2008bk (A{sub V} = 0.065 mag) must be almost entirely due to the Galactic foreground, similar to what has been assumed for SN 1999br. We confirm the identification of the putative red supergiant (RSG) progenitor star of the SN in high-quality g'r'i' images we had obtained in 2007 at the Gemini-South 8 m telescope. Little ambiguity exists in this progenitor identification, qualifying it as the best example to date, next to the identification of the star Sk -69 Degree-Sign 202 as the progenitor of SN 1987A. From a combination of photometry of the Gemini images with that of archival, pre-SN, Very Large Telescope JHK{sub s} images, we derive an accurate observed spectral energy distribution (SED) for the progenitor. We find from nebular strong-intensity emission-line indices for several H II regions near the SN that the metallicity in the environment is likely subsolar (Z Almost-Equal-To 0.6 Z{sub Sun }). The observed SED of the star agrees quite well with synthetic SEDs obtained from model RSG atmospheres with effective temperature T{sub eff} = 3600 {+-} 50 K. We find, therefore, that the star had a bolometric luminosity with respect to the Sun of log (L{sub bol}/L{sub Sun} ) = 4.57 {+-} 0.06 and radius R{sub *} = 496 {+-} 34 R{sub Sun} at {approx}6 months prior to explosion. Comparing the progenitor's properties with theoretical massive-star evolutionary models, we conclude that the RSG progenitor had an initial mass in the range of 8-8.5 M{sub Sun }. This mass is consistent with, albeit at the low end of, the inferred range of initial masses for SN II-P progenitors. It is also consistent with the estimated upper limit on the initial mass of the progenitor of SN 1999br, and it agrees with the low initial masses found for the RSG progenitors of other low-luminosity SNe II-P.

Van Dyk, Schuyler D.; Elias-Rosa, Nancy [Spitzer Science Center/Caltech, Mailcode 220-6, Pasadena, CA 91125 (United States); Davidge, Tim J., E-mail: vandyk@ipac.caltech.edu, E-mail: tim.davidge@nrc.ca [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, B.C., V9E 2E7 (Canada); and others

2012-01-15

142

Winds from Cool Stars  

NASA Astrophysics Data System (ADS)

The structure of the outer atmospheres of luminous cool stars reveals the evolution of magnetic activity as dynamo heating decreases and atmospheres expand while the stars evolve across the color-magnitude diagram. The relationship between winds and high temperature material can also be investigated. A comprehensive picture of the dynamics of the outer atmospheres is constructed based principally upon recent spectroscopic evidence from FUSE HST and optical and infrared spectra. In contrast to the solar example winds from cool giant and supergiant stars can exhibit supersonic acceleration in their chromospheres carry away more material and possess temperatures ranging from 10000K to 80000K. Coronal material near 107 K appears confined and does not participate in atmospheric expansion. Empirical relations between atmospheric structure and mass loss will be discussed. For metal deficient stars the discovery of signatures of pulsation may play an important role in driving mass loss. The detection of warm winds in cool giants and supergiants provides the crucial link between the hot fast solar wind with low mass loss and cool slow supergiant winds with substantially larger rates of mass loss.

Dupree, A. K.

2004-01-01

143

VV Cephei Type Stars  

NASA Astrophysics Data System (ADS)

Three new VV Cephei-type stars were discovered by Barbier (1971). We propose to observe these systems to detect and characterize the continuum of the companion and to investigate emission lines from the cool M star and/or by circumstellar material. One star (BD+63 0003) has been monitored extensively by one of the investigators (EFG) and observations would be scheduled about 6 to 9 months apart to coincide with maximum and minimum light in order to detect any dependence of emission activity or interaction with the hot component on the pulsations of the M supergiant component.

Shaw, J. Scott

1984-07-01

144

Bright flares in supergiant fast X-ray transients  

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

145

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

146

Time Series Analysis of the A0 Supergiant HR 1040  

NASA Astrophysics Data System (ADS)

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.

Corliss, David J.

147

Swift's Christmas Burst From Blue Supergiant Star Explosion  

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...

148

Nature of the peculiar supergiant HD 101584 (Bakker+, 1996)  

NASA Astrophysics Data System (ADS)

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 HD 101584. 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 logg=3.0+/-1.0, with an extinction of E(B-V)=0.49+/-0.05. The observed spectral features in the spectrum of HD 101584 are classified in eight different categories based on the velocity, shape of profile and the identification. The high-excitation HeI (?=20.87eV), NII (?=18.40eV), CII (?=14.39eV) and NI (?=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 white dwarf or a low-mass main sequence object. The low-excitation P-Cygni lines in the optical and UV are formed in the wind. The number density of absorption lines in the UV is so large that the wind spectrum acts as an iron curtain in front of the B-star. The terminal velocity of the wind of v{infinity}=100+/-30km/s is consistent with the star being a low-mass post-AGB star and the low effective gravity is attributed to the presence of a nearby, unseen, secondary. We estimate a mass-loss rate of M?=~10-8M?/yr. Narrow absorption and emission lines are observed which are formed in a circumsystem disk with a typical radius of 102R*. (2 data files).

Bakker, E. J.; Lamers, H. J. G. L. M.; Waters, L. B. F. M.; Waelkens, C.; Trams, N. R.; van Winckel, H.

1995-07-01

149

The Fundamental Parameters and Chromospheric Structure of the M Supergiant VV Cephei  

NASA Astrophysics Data System (ADS)

The long-period binary VV Cephei (M2 Iab + B0-2, V=4.9, P=20.34 yr) is the brightest M supergiant eclipsing binary in the sky. The M star primary is a close spectral match to that of Betelgeuse. In the ultraviolet (UV), the early B-type hot companion dominates the spectrum, and as the system emerges from eclipse, the line of sight to the B star probes deep into the outer atmosphere (the "chromosphere") of the M supergiant. The UV spectrum of VV Cep has been observed from total eclipse (in 1997-98) through quadrature (2002) and periastron (2005) at a total of 22 epochs, 20 of these using STIS high-resolution ( 100,000) ultraviolet spectroscopy from the Hubble Space Telescope, and two with the Far Ultraviolet Spectroscopic Explorer satellite. I will present a brief overview of spectrum formation in the system, and focus on the subset of the STIS observations (those immediately following the egress from totality) that probed the chromosphere of VV Cephei. From these observations, I have constructed a spatially-resolved empirical model chromosphere that includes the temperature, density, velocity, and ionization structure of the outer atmosphere of VV Cep above the classical photosphere. I will present these results, and also constraints on the fundamental stellar and orbital parameters provided by these UV observations.

Bennett, Philip D.

2013-07-01

150

Properties of Galactic early-type O-supergiants. A combined FUV-UV and optical analysis  

NASA Astrophysics Data System (ADS)

Aims: We aim to constrain the properties and evolutionary status of early and mid-spectral type supergiants (from O4 to O7.5). These posses the highest mass-loss rates among the O stars, and exhibit conspicuous wind profiles. Methods: Using the non-LTE wind code cmfgen we simultaneously analyzed the FUV-UV and optical spectral range to determine the photospheric properties and wind parameters. We derived effective temperatures, luminosities, surface gravities, surface abundances, mass-loss rates, wind terminal velocities, and clumping filling factors. Results: The supergiants define a very clear evolutionary sequence, in terms of ages and masses, from younger and more massive stars to older stars with lower initial masses. O4 supergiants cluster around the 3 Myr isochrone and are more massive than 60 M?, while the O5 to O7.5 stars have masses in the range 50-40 M? and are 4 ± 0.3 Myr old. The surface chemical composition is typical of evolved O supergiants (nitrogen-rich, carbon- and oxygen-poor). While the observed ranges of carbon and nitrogen mass-fractions are compatible with those expected from evolutionary models for the measured stellar masses, the N/C ratios as a function of age are inconsistent with the theoretical predictions for the four earliest (O4 spectral type) stars of the sample. We question the efficiency of rotational mixing as a function of age for these stars and suggest that another mechanism may be needed to explain the observed abundance patterns. Mass-loss rates derived with clumped-models range within a factor of three of the theoretical mass-loss rates. The corresponding volume-filling factors associated with small-scale clumping are 0.05 ± 0.02. Clumping is found to start close to the photosphere for all but three stars, two of which are fast rotators. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer (FUSE) and by the NASA-ESA-SERC International Ultraviolet Explorer (IUE), and retrieved from the Multimission Archive at the Space Telescope Science Institute (MAST). Based on observations collected with the ELODIE spectrograph on the 1.93-m telescope (Observatoire de Haute-Provence, France). Based on observations collected with the FEROS instrument on the ESO 2.2 m telescope, program 074.D-0300 and 075.D-0061.Appendix A is available in electronic form at http://www.aanda.org

Bouret, J.-C.; Hillier, D. J.; Lanz, T.; Fullerton, A. W.

2012-08-01

151

The behavior of the Mg II doublet features near 2800 A observed in F, A, and B supergiants  

NASA Technical Reports Server (NTRS)

The Mg II doublet features near 2800 A were recently observed in F-, A-, and B-type supergiants with a balloon-borne ultraviolet stellar spectrometer. The stars observed are Alpha UMi (F8 Ib), Alpha Per (F5 Ib), Eta Leo (A0 Ib), and Rho Leo (B1 Ib). The Mg II doublet features in Alpha UMi and Alpha Per show emission superposed on photospheric absorption. In the spectrum of Eta Leo, the Mg II lines are in absorption and show shortward-shifted components attributable to mass loss. In the spectrum of Rho Leo, the Mg II lines are primarily a composite of the photospheric and interstellar absorption features. The general behavior of the Mg II lines for supergiants of spectral types M through B are also discussed.

Kondo, Y.; Morgan, T. H.; Modisette, J. L.

1976-01-01

152

Model-atmosphere analysis of high-dispersion spectra of four red giants and supergiants  

NASA Astrophysics Data System (ADS)

A model atmosphere analysis of three cool giants (? Cet, ? Tau, ? TrA) and one supergiant (? Peg) is presented. One of the principal reasons for the analysis being the search for possible non-LTE effects, the measured lines are split into high excitation lines and low excitation lines in order to test the sensitivity of the ionization balance method against deviations from LTE. Even though for iron no pronounced split can be found to occur, other elements, e.g. Mn and Ni, hint at the existence of deviations from LTE in cool giant stars. Deviations from the solar abundance pattern are found for the elements of medium atomic number. Two of the stars (? TrA and ? Peg) display over-abundances in barium.

Kovacs, N.

1983-04-01

153

Energy Distributions of B Supergiants in the Large Magellanic Cloud.  

National Technical Information Service (NTIS)

It is shown that line-blanketed, LTE, plane-parallel model atmosphere calculations provide excellent fits to the ultraviolet-through-visual energy distributions of B supergiants in the Large Magellanic Cloud. The models were computed using Kurucz's (1979)...

E. L. Fitzpatrick

1986-01-01

154

Distribution and luminosity function of OB stars in M 31  

NASA Astrophysics Data System (ADS)

The catalog of bright stars in the field of M 31 (Berkhuijsen et al., 1988) was used to investigate the distribution and luminosity function of upper main-sequence stars and supergiants in M 31. More than 700 blue stars brighter than V = 20 mag were detected, of which about 300 are probable O stars. The eastern spiral arms contain about 30 percent more O stars than the western arms. The slope of the luminosity function depends on the color criterion used to select the stars in the sample. The conclusion of Freedman (1985) that the slope of the luminosity function of upper main-sequence stars does not significantly vary between galaxies is confirmed. The luminosity function for supergiants, however, is considerably flatter than that for O stars, possibly because the corresponding main-sequence stars are missing from this sample.

Berkhuijsen, E. M.; Humphreys, R. M.

1989-04-01

155

Physical parameters and wind properties of galactic early B supergiants  

NASA Astrophysics Data System (ADS)

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 1-2 kK relative to previous non-blanketed results. The so-called "bistability jump" at B1 (Teff ˜ 21 kK) from Lamers et al. is rather a more gradual trend (with large scatter) from v?/vesc˜3.4 for B0-0.5 supergiants above 24 kK to v?/vesc˜ 2.5 for B0.7-1 supergiants with 20 kK ? Teff ? 24 kK, and v?/vesc˜ 1.9 for B1.5-3 supergiants below 20 kK. 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? 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.

Crowther, P. A.; Lennon, D. J.; Walborn, N. R.

2006-01-01

156

Mass Loss from Highly Evolved Stars  

NASA Astrophysics Data System (ADS)

This is a summarizing discussion about detailed studies of stellar winds from hot, subluminous stars of different classes: two sdO's (Hamann et al., 1981), three extreme helium stars (Hamann et al., 1982), and one CPN (Hamann et al., 1983). For comparison, the author has also included the Of-supergiant ? Pup and the B-main sequence star ? Sco, because their winds have been investigated in detail by the same methods as applied in this paper (Hamann, 1980, 1981).

Hamann, W. R.

157

Massive star abundances in the Galaxy and the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

The use of photospheric abundances in OB-type main-sequence stars and A and B-type supergiants as probes of rotation and evolutionary status is reviewed. The abundances of CNO and boron can be compared quantitatively with stellar evolutionary calculations. In particular the abundance ratios of N/O and N/C can be derived in blue supergiants to determine if they are consistent with the stars having gone through a red supergiant phase and dredge-up of core material to the surface. The results from several different studies are reviewed and compared. For blue supergiant stars in the mass-range 5 - 80 Msun the situation appears consistent -- there is no evidence for stars of any mass having undergone blue-loops in the HR diagram. The stellar samples show significant signs of having N enriched atmospheres, and the quantitative values are consistent with stellar evolutionary calculations which invoke turbulent diffusive mixing while massive stars are on the main-sequence. Results on the interesting blue supergiant Sher 25 are presented, and linked to sk; the B3Ia progenitor of SN 1987A. A spectacular ejection nebula surrounds Sher 25, much like that which was ejected by sk during its final stages of evolution. Both of these were thought to have been formed during a mass-loss event when the stars were in the red supergiant phase. The CNO abundances derived in Sher 25 suggest the nebula was ejected during the blue supergiant phase, and that rotation can explain the N-enrichment found in the stellar photosphere.

Smartt, Stephen J.

158

Swift Optimized Strategy for Supergiant Fast X-ray Transients Study  

NASA Astrophysics Data System (ADS)

Supergiant Fast X-ray Transients (SFXTs) are HMXBs with OB supergiant companions and are known for hour-long X-ray outbursts characterized by 3-5 orders of magnitude luminosity increases. Our Swift Supergiant Fast X-ray Transients Project, active since 2007, has taken advantage of Swift's flexible scheduling for a systematic investigation on both the SFXT bright flares which triggered the Burst Alert Monitor (BAT) with fast X-Ray Telescope (XRT) follow-up (1-2 min repointing time), and the emission outside the bright outbursts with XRT regular monitoring of several SFXTs and candidates with 2-3 observations per week (1-2 ks) for at least one year per source. This has allowed us to study for the first time broadband spectra of SFXT outbursts, to prove that timescales of source activity during outburts are of the order of weeks, to determine long-term properties of SFXTs, and to obtain an assessment of the fraction of the time these sources spend in each luminosity phase (outbursts, intermediate level, and quiescence) and their duty cycle of inactivity by means of very sensitive and non-serendipitous observations. We summarize the results achieved to date with our observing strategy and focus on the time resolved broadband spectral analysis of the 2011 and 2013 Swift detected outbursts of IGR J08408-4503, carried out with different spectral models, including the COMPMAG model specifically dedicated to the physical framework of accretion at the polar cap of a neutron star with a high magnetic field (>= 1E12 G), expected to be typical of these accreting systems.

Mangano, Vanessa; Romano, P.; Kennea, J. A.; Vercellone, S.; Burrows, D. N.; Ducci, L.; Esposito, P.; Krimm, H. A.; Barthelmy, S. D.; Gehrels, N.; Swift

2014-01-01

159

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

160

Circumstellar Material Around Evolved Massive Stars  

NASA Astrophysics Data System (ADS)

I review multiwavelength observations of material seen around different types of evolved massive stars (i.e. red supergiants, yellow hypergiants, luminous blue variables, B[e] supergiants, and Wolf-Rayet stars), concentrating on diagnostics of mass, composition, and kinetic energy in both local and distant examples. Circumstellar material has significant implications for the evolutionary state of the star, the role of episodic mass loss in stellar evolution, and the roles of binarity and rotation in shaping the ejecta. This mass loss determines the type of supernova that results via the stripping of the star's outer layers, but the circumstellar gas can also profoundly influence the immediate pre-supernova environment. Dense circumstellar material can actually change the type of supernova that is seen when it is illuminated by the supernova or heated by the blast wave. As such, unresolved circumstellar material illuminated by distant supernovae can provide a way to study mass loss in massive stars in distant environments.

Smith, Nathan

2011-01-01

161

Spectroscopic and Temporal Properties of Supergiant Fast X-ray Transients with Swift  

NASA Astrophysics Data System (ADS)

We present a review of the Swift Supergiant Fast X-ray Transients (SFXT) project. Swift has recently opened a brand new way of investigating this class of High-Mass X-ray Binaries whose optical counterparts are O or B supergiant stars, and whose X-ray outbursts are about 4 orders of magnitude brighter than the quiescent state. Thanks to its scheduling flexibility, Swift has allowed us to regularly monitor a small sample of SFXTs with 2-3 observations per week (1-2 ks) with the X-Ray Telescope (XRT) over their entire visibility period (9 months/year) for over 2 years. This intense monitoring has allowed us to study them throughout all phases of their lives (outbursts, intermediate level, and quiescence) and to determine the long-term properties and their duty cycles, through very sensitive and non-serendipitous observations. We also monitored one source along its whole orbital period. Furthermore, thanks to its autonomous and rapid repointing, Swift has allowed us for the first time to catch and study, from optical to hard X-ray, the bright outbursts, and to follow them in the X-ray for days, thus determining the actual duration of the outburst episodes and the shape of their X-ray spectra through simultaneous broadband spectroscopy. We acknowledge financial contribution from the agreement ASI-INAF I/009/10/0.

Romano, Patrizia; Kennea, J. A.; Vercellone, S.; Burrows, D. N.; Cusumano, G.; Esposito, P.; Farinelli, R.; Krimm, H. A.; La Parola, V.; Mangano, V.; Pagani, C.; Gehrels, N.

2011-09-01

162

Evidence for extended chromospheres surrounding red giant stars  

NASA Technical Reports Server (NTRS)

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.

Stencel, R. E.

1982-01-01

163

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

NASA Technical Reports Server (NTRS)

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.

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

2008-01-01

164

Silicate and hydrocarbon emission from Galactic M supergiants  

NASA Astrophysics Data System (ADS)

Following our discovery of unidentified infrared (UIR) band emission in a number of M supergiants in h and chi Per, we have obtained 10-?m spectra of a sample of 60 galactic M supergiants. Only three new sources, V1749 Cyg, UW Aql and IRC+40 427, appear to show the UIR bands; the others show the expected silicate emission or a featureless continuum. The occurrence of UIR-band emission in M supergiants is therefore much higher in the h and chi Per cluster than in the Galaxy as a whole. Possible explanations for the origin and distribution of UIR bands in oxygen-rich supergiants are discussed. We use our spectra to derive mass-loss rates ranging from 10^-8 to 10^-4 M_solar yr^-1 for the new sample, based on the power emitted in the silicate feature. The relationship between mass-loss rate and luminosity for M supergiants is discussed, and correlations are explored between their mid-infrared emission properties.

Sylvester, R. J.; Skinner, C. J.; Barlow, M. J.

1998-12-01

165

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

Microsoft Academic Search

Aims: We provide a quantitative analysis of time-variable phenomena in the photospheric, near-star, and outflow regions of the late-B supergiant (SG) HD 199 478. This study aims to provide new perspectives on the nature of outflows in late-B SGs and on the influence of large-scale structures rooted at the stellar surface. Methods: The analysis is based primarily on optical spectroscopic

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

2008-01-01

166

Quantitative Spectroscopic J-band study of Red Supergiants in Perseus OB-1  

NASA Astrophysics Data System (ADS)

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. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Gazak, J. Zachary; Davies, Ben; Kudritzki, Rolf; Bergemann, Maria; Plez, Bertrand

2014-06-01

167

Red Supergiants in the Local Group  

NASA Astrophysics Data System (ADS)

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.

Levesque, E. M.

2013-05-01

168

The B Supergiant problem and mass loss through H?  

NASA Astrophysics Data System (ADS)

The evolutionary status of B supergiants represents an awkward but important riddle in today's stellar astrophysics. We do not even know the most basic facts of whether B supergiants are burning hydrogen or helium. Until this is resolved, we will not be able to unravel the final evolution of objects such as the progenitor of SN 1987A. What is clear is that we need to understand B supergiant mass loss in order to understand its evolutionary state. Here we present our results from a comprehensive H? analysis with the CMFGEN code over the bistability (BS) region. We have already confirmed the existence of the BS jump at 22,000 Kelvin in H?, and we will discuss the rise and fall of the H? emission over the BS jump in detail.

Petrov, Blagovest; Vink, J. S.; Graefener, G.

2013-06-01

169

The Infrared Properties of Massive Stars in the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

We present highlights of our study of the infrared properties of massive stars in the Large and Small Magellanic Clouds (from Bonanos et al. 2009, 2010), which are based on the Spitzer SAGE surveys of these galaxies. We have compiled catalogs of spectroscopically confirmed massive stars in each galaxy, as well as photometric catalogs for a subset of these stars that have infrared counterparts in the SAGE database, with uniform photometry from 0.3 to 24 ?m in the UBVIJHKs+IRAC+MIPS24 bands. These catalogs enable a comparative study of infrared excesses of OB stars, classical Be stars, yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables and supergiant B[e] stars, as a function of metallicity, and provide the first roadmaps for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.

Bonanos, A. Z.; Lennon, D. J.; Massa, D. L.; Sewilo, M.; Koehlinger, F.; Panagia, N.; van Loon, J. Th.; Evans, C. J.; Smith, L. J.; Meixner, M.; Gordon, K.; SAGE Teams

2011-01-01

170

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

171

A semiempirical model for the red supergiant's wind in Zeta Aurigae systems  

NASA Technical Reports Server (NTRS)

A semiempirical model for the wind in four Zeta Aur binary systems is developed, basing the analyses on the velocity function, nonthermal velocities, and upper limits to Ne/N(H) inferred from observations of the winds from the cool supergiants. The model assumes that the energy fluxes needed to drive the wind are supplied by Alfven waves, since the acoustic wave flux estimated from line broadening is too low. The damping scale length of the waves, is found to change from very small values near the star to larger values of the order of the local radius further out in the wind. The temperature structure and hydrogen ionization are derived for these models. Limits to the stellar magnetic field are found, as well as a necessary constraint for the existence of cool massive winds, suggesting that the dividing line in the H-R diagram is where this constraint is violated.

Kuin, N. P. M.; Ahmad, I. A.

1989-01-01

172

Calibration of the normal color indices (b-y)0 and absolute stellar magnitudes M(V) for A4-F3-class supergiants on the basis of uvby-beta-photometry data  

NASA Astrophysics Data System (ADS)

Calibration relations obtained for the color index (b-y)0 = F (/m1/, r) and absolute magnitudes M(V) = M(V) (beta) for high-luminosity stars are presented. The regions where the calibrations are valid include stars of spectral types ranging from A4 to F3 and luminosity classes from I to II. The calibration relations are used to estimate the distance moduli of 10 supergiants in the LMC.

Dambis, A. K.

1991-08-01

173

Cool luminous stars  

NASA Technical Reports Server (NTRS)

The consequences of magnetic fields for the atmospheres of cool stars are addressed based on IUE and Einstein Observatory observations. Gross atmospheric structure data for cool luminous stars are discussed, and the relevance of the observations for the energy balance and nonradiative heating rates is considered. Data from X-ray fluxes, low dispersion UV spectra, and high dispersion spectra in the region of the Mg II resonance lines are presented. New results on cool star atmospheres provided by high dispersion UV spectra are considered, including those pertaining to spectral line identification, identification of emission components in close binary systems, densities and atmospheric extension, emission line widths, properties of stellar winds as derived from IUE data, and systematic flows of transition region plasma. An explanation for the observed spectra of cool giants and supergiants is proposed in terms of active, quiet, and hybrid stars.

Linsky, J. L.

1982-01-01

174

Red Supergiants as Cosmic Abundance Probes  

NASA Astrophysics Data System (ADS)

The chemical abundances of galaxies provide key constraints to models of their formation and evolution. Unfortunately, the standard method of determining abundances, from the strong emission lines of Hii-regions, is well-known to be subject to large systematic errors, particularly at high metallicities. To address this problem we are currently working on a project to measure a galaxy's chemical abundances from spectral analysis of individual RSGs. By focussing on a spectral window in the J-band which contains few molecular lines, we are able to derive accurate chemical abundances from relatively low resolution data. In fact, we show that this technique can operate at distances of 3-4 Mpc using the VLT, and a factor of 10 further if we target massive RSG-dominated star clusters. Furthermore, in the ELT-era, we show that we can perform abundance analysis on individual stars out to 70 Mpc, and redshifts of 0.1 for star clusters.

Davies, B.; Kudritzki, R.-P.; Plez, B.; Bergemann, M.; Gazak, Z.; Evans, C.

2013-05-01

175

Late-Type Red Supergiants: Too Cool for the Clouds?  

Microsoft Academic Search

It has long been known that the median spectral types of red supergiants change from M2 I in the Milky Way to M1 I in the Large Magellanic Cloud (LMC) and to K5-7 I in the Small Magellanic Cloud (SMC) (Elias et al 1985, Massey & Olsen 2002). This is now understood in terms of the shifting of the evolutionary

Emily M. Levesque; P. Massey; K. A. Olsen; B. Plez

2006-01-01

176

Dust Around Red Supergiants in the Magellanic Clouds  

Microsoft Academic Search

We have gathered together a unique dataset for red supergiants (RSGs) in the Magellanic Clouds, which can be used to investigate the amount and nature of dust produced by RSGs in different environments. For a sample of 40 RSGs in each of the LMC and the SMC, we have obtained visible spectrophotometry (4000-9000 A), 2MASS photometry (JHK), and photometry in

Stacey N. Bright; J. Chatelain; W. Freeman; G. Clayton; K. Gordon; J. Nordhaus; P. Massey; E. Levesque; B. Plez; K. Olsen; D. Silva

2009-01-01

177

A new interpretation of luminous blue stars  

NASA Technical Reports Server (NTRS)

A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's (1976) radiative opacities are adopted in stellar models. Unlike earlier opacities, these exhibit a large 'bump' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot diffuse stellar envelopes. Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. The stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures for O stars and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than about 20 solar masses. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars.

Stothers, R.

1976-01-01

178

Revised Stellar Temperatures for Magellanic Cloud O Supergiants from Far Ultraviolet Spectroscopic Explorer and Very Large Telescope UV-Visual Echelle Spectrograph Spectroscopy  

NASA Astrophysics Data System (ADS)

We have undertaken quantitative analysis of four LMC and SMC O4-9.7 extreme supergiants using far-ultraviolet FUSE, ultraviolet IUE/Hubble Space Telescope, and optical Very Large Telescope UV-Visual Echelle Spectrograph spectroscopy. Extended, non-LTE model atmospheres that allow for the consistent treatment of line blanketing, developed by Hillier & Miller, are used to analyze wind and photospherics spectral features simultaneously. Using H? to constrain mass-loss rates, He I-He II photospheric lines reveal stellar temperatures that are systematically (5-7.5 kK) and substantially (15%-20%) lower than previously derived from unblanketed, plane-parallel, non-LTE photospheric studies. We have confidence in these revisions since derived temperatures generally yield consistent fits across the entire 912-7000 Å observed spectral range. In particular, we are able to resolve the UV-optical temperature discrepancy identified for AzV 232 (O7 Iaf+) in the SMC by Fullerton and coworkers. The temperature and abundance sensitivity of far-ultraviolet, UV, and optical lines are discussed. ``Of'' classification criteria are directly linked to (strong) nitrogen enrichment (via N III ?4097) and (weak) carbon depletion (via C III ??4647-4651), providing evidence for mixing of unprocessed and CNO-processed material at their stellar surfaces. Oxygen abundances are more difficult to constrain, except via O II lines in the O9.7 supergiant, for which it is also found to be somewhat depleted. Unfortunately, He/H is very difficult to determine in individual O supergiants because of uncertainties in microturbulence and the atmospheric scale height. The effect of wind clumping is also investigated, for which P V ??1118-1128 potentially provides a useful diagnostic in O star winds, unless phosphorus can be independently demonstrated to be underabundant relative to other heavy elements. Revised stellar properties affect existing calibrations of (1) Lyman continuum photons-a factor of 2 lower for the O4 supergiant-and (2) kinetic energy released into the ISM by O supergiants. Our results also have importance for the calibration of the wind momentum-luminosity relationship for OB stars, particularly since the stars studied here are among the visually brightest OB stars in external galaxies. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by Johns Hopkins University under NASA contract NAS 5-32985. Also based in part on observations collected at the European Southern Observatory Very Large Telescopes in programs 65.H-0705 and 67.D-0238, plus archival data obtained with the NASA-ESA Hubble Space Telescope and NASA-ESA-PPARC International Ultraviolet Explorer.

Crowther, P. A.; Hillier, D. J.; Evans, C. J.; Fullerton, A. W.; De Marco, O.; Willis, A. J.

2002-11-01

179

Massive Stars: Life and Death  

NASA Astrophysics Data System (ADS)

One of the most powerful tests of stellar evolution theory for massive stars is to observationally establish the causal mapping between different populations of massive stars (e.g., red-supergiants, wolf-rayet stars) and their explosions (e.g., supernovae). This connection has been firmly proven only for a handful of objects, most notably in the case of supernova 1987A in the LMC with its blue-supergiant progenitor star Sk -69 202. However, the progenitors of most supernova types have not been identified directly. I will present two supernova-like transients discovered this year in the nearby galaxies NGC 6946 and NGC 300 for which we have identified the progenitors as dust-enshrouded massive stars in Spitzer images. This new class of luminous transients has progenitors that are extremely rare compared to known massive stellar populations in M33 identified in the mid-infrared. I will discuss the implications of these findings in the context of "low-mass" massive stars (i.e., close to 8 Msun) and connect it to electron-capture supernovae.

Prieto, Jose

2009-01-01

180

Synchrotron radiation from the winds of O supergiants - Tb = 10 to the 7. 6th K at 60 stellar radii  

SciTech Connect

Results are presented on VLBI measurements of the nonthermal radio components around two O supergiant stars: Cyg OB2 No. 9 and HD 167971. The measurements were used to characterize the brightness temperature of the emission and to measure the size of compact 5-10 mJy components in these stars, reported by Bieging et al. (1989). The sizes found for the 5-10 mJy components are consistent with the free-free wind radii, indicating that the compact companions are not the sources of nonthermal radiation. Results suggest that there is a small fractional population (10 to the -4th to 10 to the -7th) of ultrarelativistic electrons (Teff of about 10 to the 11th K) coexisting with the stellar wind, which emit optically thin synchrotron radiation. This is in agreement with the synchrotron model of White (1985). 21 refs.

Phillips, R.B.; Titus, M.A. (Haystack Observatory, Westford, MA (USA))

1990-08-01

181

Quantitative Spectroscopy of Blue Supergiants in Metal-poor Dwarf Galaxy NGC 3109  

NASA Astrophysics Data System (ADS)

We present a quantitative analysis of the low-resolution (~4.5 Å) spectra of 12 late-B and early-A blue supergiants (BSGs) in the metal-poor dwarf galaxy NGC 3109. A modified method of analysis is presented which does not require use of the Balmer jump as an independent T eff indicator, as used in previous studies. We determine stellar effective temperatures, gravities, metallicities, reddening, and luminosities, and combine our sample with the early-B-type BSGs analyzed by Evans et al. to derive the distance to NGC 3109 using the flux-weighted gravity-luminosity relation (FGLR). Using primarily Fe-group elements, we find an average metallicity of [\\bar{Z}] = –0.67 ± 0.13, and no evidence of a metallicity gradient in the galaxy. Our metallicities are higher than those found by Evans et al. based on the oxygen abundances of early-B supergiants ([\\bar{Z}] = –0.93 ± 0.07), suggesting a low ?/Fe ratio for the galaxy. We adjust the position of NGC 3109 on the BSG-determined galaxy mass-metallicity relation accordingly and compare it to metallicity studies of H II regions in star-forming galaxies. We derive an FGLR distance modulus of 25.55 ± 0.09 (1.27 Mpc) that compares well with Cepheid and tip of the red giant branch distances. The FGLR itself is consistent with those found in other galaxies, demonstrating the reliability of this method as a measure of extragalactic distances.

Hosek, Matthew W., Jr.; Kudritzki, Rolf-Peter; Bresolin, Fabio; Urbaneja, Miguel A.; Evans, Christopher J.; Pietrzy?ski, Grzegorz; Gieren, Wolfgang; Przybilla, Norbert; Carraro, Giovanni

2014-04-01

182

X-Ray Emission from an Expanding Supergiant Shell in IC 2574  

NASA Astrophysics Data System (ADS)

We present a multiwavelength study of a supergiant shell within the violent interstellar medium of the nearby dwarf galaxy IC 2574, which is a member of the M81 group of galaxies. Neutral hydrogen (H I) observations obtained with the Very Large Array (VLA) reveal a prominent expanding supergiant H I shell in the northeast quadrant of IC 2574 which is thought to be produced by the combined effects of stellar winds and supernova explosions. It measures roughly 1000×500 pc in size and is expanding at ~25 km s-1. The H I data suggest an age of ~1.4×106 yr; the energy input must have been of order (2.6+/-1)×1053 ergs. Massive star-forming regions, as traced by H? emission, are situated predominantly on the rim of this H I shell. This supports the view that the accumulated H I on the rim has reached densities that are high enough for secondary star formation to commence. VLA radio continuum observations at ?=6 cm show that these star-forming regions are the main sources of radio continuum emission in this galaxy. This emission is mainly thermal in origin. Soft X-ray emission from within the H I hole is detected by a pointed ROSAT PSPC observation. The emission is resolved, coinciding in size and orientation with the H I shell. These spatial properties suggest that the emission is generated by an X-ray-emitting plasma located within the H I shell, although a contribution from X-ray binaries cannot be completely ruled out. The X-ray luminosity within the 0.11-2.4 keV energy range is LX=(1.6+/-0.5)×1038 ergs s-1. The X-ray data are compatible with emission coming from a Raymond-Smith plasma at a temperature of about log(T[K])=6.8 and a density of ne~0.03 cm-3. The energy content of the coronal gas corresponds to (4+/-2)×1053 ergs, or broadly in agreement with the energy input derived on the basis of the H I observations.

Walter, Fabian; Kerp, Jürgen; Duric, Neb; Brinks, Elias; Klein, Uli

1998-08-01

183

The Unevolved Massive Star Content of the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

The Magellanic Clouds offer a unique astrophysical laboratory where we can actually obtain an unbiased estimate of the number of unevolved massive stars above a certain mass. Comparing this number with the {known} number of evolved massive stars, such as Wolf-Rayets, yellow supergiants, and red supergiants, provides a hiterto unavailable test of massive star evolutionary theory. We are engaged in a long-term {5 year} effort to characterize the massive star content of select OB associations of the SMC and LMC using spectroscopy with the Magellan 6.5-m telescopes. Here we are asking for a short { 1 sec} SNAPshot of each of 23 OB associations in the F225W filter. These HST data will provide a crucial complement to our ground based data, allowing us to concentrate on the early and mid O-type stars with our spectroscopy, and to recognize close doubles that would otherwise be unrecognized from the ground.;

Massey, Philip

2011-07-01

184

Red supergiants in M31: extinction, metallicities and gas-to-dust ratio  

NASA Astrophysics Data System (ADS)

We derived individual extinction values for selected red supergiant (RSGs) candidates in M31 with broadband photometry. Taking into account their position on the colour-magnitude diagram and using a probability method, the metallicity of each star was estimated. In the range 2-15 kpc the ratio [O/H] is nearly constant. The derived individual extinctions and pencil beams values from three different gas maps (Westerbork HI, VLA HI and IRAM CO (1?0)-line survey) were used to obtain gas-to-dust ratio in M31. For the 9 most luminous stars both the ratios N(HI)/2 EB-V and N(HI+H2)/2EB-V are not very different from those in the Milky Way. Significant fractions outside the expected range of Galactic atomic gas-to-dust ratio are obtained for ~1/3 of the sample using Westerbork and for ~1/2 of the sample using VLA maps. The ratios are overestimated for objects located high above the midplane of M31 and underestimated - due to resolution effects, - for several RSGs coinciding with small HI clouds.

Nedialkov, Petko; Veltchev, Todor

2002-07-01

185

Spectroscopic study of the O-type runaway supergiant HD 195592  

NASA Astrophysics Data System (ADS)

The scope of this paper is to perform a detailed spectroscopic study of the northern O-type supergiant HD 195592. We use a large sample of high quality spectra in order to investigate its multiplicity, and to probe the line profile variability. Our analysis reveals a clear spectroscopic binary signature in the profile of the He I? 6678 line, pointing to a probable O + B system. We report on low amplitude radial velocity variations in every strong absorption line in the blue spectrum of HD 195592. These variations are ruled by two time-scales, respectively, of 5.063 and about 20 days. The former is firmly established, whilst the latter is poorly constrained. We report also on a very significant line profile variability of the H ? line, with time scales strongly related to those of the radial velocities. Our results provide significant evidence that HD 195592 is a binary system, with a period that might be the variability time-scale of about 5 days. The second time scale may be the signature of an additional star moving along a wider orbit provided its mass is low enough, even though direct evidence for the presence of a third star is still lacking. Alternatively, the second time-scale may be the signature of a variability intrinsic to the stellar wind of the primary, potentially related to the stellar rotation.

De Becker, M.; Linder, N.; Rauw, G.

2010-01-01

186

Spectral Types of Red Supergiants in NGC 6822 and the Wolf-Lundmark-Melotte Galaxy  

NASA Astrophysics Data System (ADS)

We present moderate-resolution spectroscopic observations of red supergiants (RSGs) in the low-metallicity Local Group galaxies NGC 6822 (Z = 0.4 Z ?) and Wolf-Lundmark-Melotte (WLM; Z = 0.1 Z ?). By combining these observations with reduction techniques for multislit data reduction and flux calibration, we are able to analyze spectroscopic data of 16 RSGs in NGC 6822 and spectrophotometric data of 11 RSGs in WLM. Using these observations, we determine spectral types for these massive stars, comparing them to Milky Way and Magellanic Cloud RSGs and thus extending observational evidence of the abundance-dependent shift of RSG spectral types to lower metallicities. In addition, we have uncovered two RSGs with unusually late spectral types (J000158.14-152332.2 in WLM, with a spectral type of M3 I, and J194453.46-144552.6 in NGC 6822, with a spectral type of M4.5 I) and a third RSG (J194449.96-144333.5 in NGC 6822) whose spectral type has varied from an M2.5 in 1997 to a K5 in 2008. All three of these stars could potentially be members of a recently discovered class of extreme RSG variables. This paper is based on data gathered with the 6.5 m Magellan telescopes located at Las Campanas, Chile.

Levesque, Emily M.; Massey, Philip

2012-07-01

187

Constraining massive star evolution from massive clusters  

NASA Astrophysics Data System (ADS)

The exact evolution of massive stars is not accurately known at present. The general trend is that stars with masses above 40 - 60 Mo go from O-type stars to H-rich WN stars, and Luminous Blue Variables (?), before turning into H-poor WN stars and finally WC stars. At lower masses, the H-rich WN and LBV phases are replaced by a blue and a red supergiant phases, respectively. However, what are the details of such evolutionary sequences? The study of massive clusters is a golden opportunity to establish this. Indeed, the turn-off mass of massive clusters can be directly translated into the mass, and hence the nature, of the progenitors of their evolved objects contents. So far, only the Arches, Quintuplet, NGC3603, NGC2244 and central clusters have been studied this way. But 6 newly discovered heavily-obscured clusters in the large survey â"VISTA Variables in the Via Lactea" (VVV) have been found to have Wolf-Rayet stars as well as blue and/or red supergiants, together with many main sequence OB stars. This poster presents our efforts to model the massive star components of these clusters using CMFGEN, bringing new blocks to the pavement of massive stellar evolution and more than doubling the number of clusters in which such evolutionary sequence are established.

Chene, Andre-Nicolas; Herve, Anthony; Martins, Fabrice; Bouret, Jean-Claude; Borissova, Jordanka; Ramirez, Sebastian; Kurtev, Radostin; Kumar, Nanda; Amigo, Pia; Fierro, Celia

2013-06-01

188

The Evolution of High-Mass Stars  

NASA Astrophysics Data System (ADS)

The evolution of stars more massive than 8 M? is discussed in this chapter. On the main sequence, these stars have spectral types of B2 or earlier, but depending on their mass can evolve into red supergiants, blue supergiants, Cepheids, Wolf-Rayet stars, Of stars, or luminous blue variables before ending their evolution as core collapse supernovae and neutron stars or black holes. The chapter begins with a general discussion of the energy production in the interior of a massive star as it evolves. The main fusion reactions that generate the star's energy are listed. Some observed properties of the O and early B main-sequence stars and their evolved products are discussed including the best determinations of their masses. The computation of contemporary evolutionary tracks that include stellar rotation and magnetic fields is detailed. The equations of stellar structure including those for energy conservation, momentum transfer, mass conservation, and energy transport are listed. The discussion includes the meridional circulation in the interior of a rotating massive star and its effect on the transport of nuclear-processed material to the surface and the impact of rotation, mass loss, and metallicity on the evolutionary tracks. Recent evolutionary tracks from the Geneva group are presented. Finally the newest evolutionary tracks and the surface abundances predicted by the calculations are compared with recent observations.

Peters, Geraldine J.; Hirschi, Raphael

189

Infrared properties of active OB stars in the Magellanic Clouds from the Spitzer SAGE survey  

NASA Astrophysics Data System (ADS)

We present a study of the infrared properties of 4922 spectroscopically confirmed massive stars in the Large and Small Magellanic Clouds, focusing on the active OB star population. Besides OB stars, our sample includes yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the red, and find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We also find photometric variability among the active OB population and evidence for transitions of Be stars to B stars and vice versa. We furthermore confirm the presence of dust around all the supergiant B[e] stars in our sample, 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.

Bonanos, Alceste Z.; Lennon, Danny J.; Massa, Derck L.; Sewilo, Marta; Köhlinger, Fabian; Panagia, Nino; van Loon, Jacco Th.; Evans, Chris J.; Meixner, Margaret; Gordon, Karl D.; Gordon

2011-07-01

190

Fundamental parameters of intermediate and high mass stars  

NASA Astrophysics Data System (ADS)

Knowledge of the fundamental stellar properties: mass, radius, effective temperature and wind mass-loss rate are essential for constraining models of the late stages of evolution. The only accurate, fundamental method is to determine these parameters from binary stars but this has been done for few binaries --- and no red supergiants --- to the accuracy needed to significantly constrain models. We seek to determine the masses of red supergiant (RSG) stars in massive binaries accurate to 1%. In detached RSG binaries, the component stars evolve independently and the (lower mass) companions are still on the main sequence as B or A stars. To determine accurate orbits of the supergiant primaries, radial velocity observations of ˜50 detached RSG binaries have been carried out at the DAO 1.2m McKellar Telescope over the past decade. The early-type spectra of the companions are nearly featureless in the optical, and furthermore, these spectra must be separated from those of the brighter RSG primary. Therefore, it is advantageous to use the companion's spectrum in the ultraviolet (UV) to determine radial velocity shifts. Eclipsing binaries are especially useful because stellar masses can be found from analyses of the eclipse light curve and spectroscopy alone. We present preliminary analyses of fundamental parameters of three red supergiant eclipsing binary systems for which HST/GHRS and STIS high-resolution UV spectroscopy is available: ? Aur, HR 2554, and VV Cep.

Bennett, P. D.; Brown, A.; Fawcett, S. M.; Yang, S.; Bauer, W. H.

2004-12-01

191

Short time-scale spectral variability in the A0 supergiant HD 92207 and the importance of line profile variations for the interpretation of FORS 2 spectropolarimetric observations  

NASA Astrophysics Data System (ADS)

Our recent search for the presence of a magnetic field in the bright early A-type supergiant HD 92207 using FOcal reducer low dispersion spectrograph (FORS) 2 in spectropolarimetric mode indicated the presence of a longitudinal magnetic field of the order of a few hundred gauss. Assuming the ideal case of a non-variable star, this discovery has recently been questioned in one work trying to demonstrate the importance of non-photon noise in FORS 2 observations. The assumption of non-variability of HD 92207 can, however, not be held since substantial profile variations of diverse lines on a time-scale of minutes or maybe even a fraction of a minute are detected in FORS 2 spectra. The presence of short-term spectral variability in blue supergiants, which are considered as Type II supernova progenitors, has not been a subject of systematic studies before and is critical for the current theoretical understanding of their physics. Given the detected short-term variability, the question of the presence of a magnetic field cannot be answered without proper modelling of the impact of such a variability on the measurements of the magnetic field. Since the short-term periodicity does not fit into the currently known domain of non-radially pulsating supergiants, its confirmation is of great importance for models of stellar evolution.

Hubrig, S.; Schöller, M.; Kholtygin, A. F.

2014-05-01

192

Determination of the Masses of the Hyades Binary VA351 and the Circumstellar Structure of the Supergiant VV Cep {HD 208816}  

NASA Astrophysics Data System (ADS)

A search with Hubble Space Telescope Fine Guidance Sensor 3 in TRANS mode of 36 probable Hyades cluster members in the magnitude range V=10--15 has yielded nine certain binary detections. Subsequent observations have shown that among these, VA351 has a period of approximately 5 years. We propose to carry out astrometry of this faint Hyades binary with FGS in a combination of POS and TRANS modes. Such new observations, combined with FGS astrometry already in hand, and with orbital radial velocity measures, will yield masses and absolute magnitudes of this low- luminosity Hyades members independent of the kinematic mean cluster distance and with an accuracy of 5 percent or better. VV Cep is a eclipsing spectroscopic binary consisting of a very massive supergiant and a hot main sequence companion. At the time requested in this proposal, the hot companion will be eclipsed by the supergiant, thus affording the opportunity to study at high angular resolution the supergiant star and its extended envelope.

Franz, Otto

1996-07-01

193

Really Cool Stars and the Star Formation History at the Galactic Center  

NASA Astrophysics Data System (ADS)

We present ?/??=550-1200 near-infrared H and K spectra for a magnitude-limited sample of 79 asymptotic giant branch and cool supergiant stars in the central ~5 pc (diameter) of the Galaxy. We use a set of similar spectra obtained for solar neighborhood stars with known Teff and Mbol that is in the same range as the Galactic center (GC) sample to derive Teff and Mbol for the GC sample. We then construct the H-R diagram for the GC sample. Using an automated maximum likelihood routine, we derive a coarse star formation history of the GC. We find that (1) roughly 75% of the stars formed in the central few parsecs are older than 5 Gyr; (2) the star formation rate (SFR) is variable over time, with a roughly 4 times higher SFR in the last 100 Myr compared to the average SFR; (3) our model can match dynamical limits on the total mass of stars formed only by limiting the initial mass function to masses above 0.7 Msolar (this could be a signature of mass segregation or of the bias toward massive star formation from the unique star formation conditions in the GC); (4) blue supergiants account for 12% of the total sample observed, and the ratio of red to blue supergiants is roughly 1.5; and (5) models with isochrones with [Fe/H]=0.0 over all ages fit the stars in our H-R diagram better than models with lower [Fe/H] in the oldest age bins, consistent with the finding of Ramírez et al. that stars with ages between 10 Myr and 1 Gyr have solar [Fe/H].

Blum, R. D.; Ramírez, Solange V.; Sellgren, K.; Olsen, K.

2003-11-01

194

MMT HYPERVELOCITY STAR SURVEY. II. FIVE NEW UNBOUND STARS  

SciTech Connect

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.

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

195

MMT Hypervelocity Star Survey. II. Five New Unbound Stars  

NASA Astrophysics Data System (ADS)

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.

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

2012-05-01

196

Water in stars: expected and unexpected  

NASA Astrophysics Data System (ADS)

We have confirmed the presence of water in the early M giant ? Cet (M1.5III) and supergiant KK Per (M2Iab) by the highest resolution grating mode of SWS, but this result is quite unexpected from present model atmospheres. In late M giant and supergiant stars, water observed originates partly in the photosphere as expected by the model atmospheres, but ISO SWS has revealed that the 2.7 mic\\ absorption bands appear to be somewhat stronger than predicted while 6.5 mic\\ bands weaker, indicating the contamination by an emission component. In the mid-infrared region extending to 45 mic, pure rotation lines of hho\\ appear as distinct emission on the high resolution SWS spectra of 30g Her (M7III) and S Per (M4-7Ia), along with the dust emission at 10, 13, 20 mic\\ and a new unidentified feature at 30 mic. Thus, together with the dust, water contributes to the thermal balance of the outer atmosphere already in the mid-infrared. The excitation temperature of hho\\ gas is estimated to be 500 - 1000 K. In view of this result for late M (super)giants, unexpected water observed in early M (super)giants should also be of non-photospheric in origin. Thus, ISO has finally established the presence of a new component of the outer atmosphere - a warm molecular envelope - in red giant and supergiant stars from early to late types. Such a rather warm molecular envelope will be a site of various activities such as chemical reactions, dust formation, mass-outflow etc.

Tsuji, T.; Aoki, W.; Ohnaka, K.

1999-03-01

197

The nature of B supergiants: clues from a steep drop in rotation rates at 22 000 K. The possibility of Bi-stability braking  

NASA Astrophysics Data System (ADS)

The location of B supergiants in the Hertzsprung-Russell diagram (HRD) represents a long-standing problem in massive star evolution. Here we propose their nature may be revealed utilising their rotational properties, and we highlight a steep drop in massive star rotation rates at an effective temperature of 22 000 K. We discuss two potential explanations for it. On the one hand, the feature might be due to the end of the main sequence, which could potentially constrain the core overshooting parameter. On the other hand, the feature might be the result of enhanced mass loss at the predicted location of the bi-stability jump. We term this effect "bi-stability braking" and discuss its potential consequences for the evolution of massive stars.

Vink, Jorick S.; Brott, I.; Gräfener, G.; Langer, N.; de Koter, A.; Lennon, D. J.

2010-03-01

198

A Far-Ultraviolet Spectroscopic Survey of Luminous Cool Stars  

Microsoft Academic Search

The Far Ultraviolet Spectroscopic Explorer (FUSE) ultraviolet spectra of eight giant and supergiant stars reveal that high-temperature (3×105 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 Lybeta, Fe II, C I, and transition

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

2005-01-01

199

A Far-Ultraviolet Spectroscopic Survey of Luminous Cool Stars  

Microsoft Academic Search

FUSE ultraviolet spectra of 8 giant and supergiant stars reveal that high\\u000atemperature (3 X 10^5 K) atmospheres are common in luminous cool stars and\\u000aextend across the color-magnitude diagram from Alpha Car (F0 II) to the cool\\u000agiant Alpha Tau (K5 III). Emission present in these spectra includes\\u000achromospheric H-Lyman Beta, Fe II, C I, and transition region lines

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

2004-01-01

200

Properties of galactic B[e] supergiants. I. CI Camelopardalis  

NASA Astrophysics Data System (ADS)

We present a study of the high-resolution (R=60 000) optical spectrum of the B[e] supergiant CI Cam obtained 4 years after its all-wavelength outburst. The profiles of most of the emission lines show a triple-peaked structure, an effect previously not observed. The Na I D-lines clearly have 2 interstellar absorption components, suggesting that the system is most probably located within the Perseus arm at a distance of le 3 kpc. Uncertainties of the distance toward the object, its luminosity, and physical parameters of the circumstellar disk are discussed. Simple observational tests are suggested to clarify these issues.

Miroshnichenko, A. S.; Klochkova, V. G.; Bjorkman, K. S.; Panchuk, V. E.

2002-08-01

201

An atlas of spectra of B6-A2 hypergiants and supergiants from 4800 to 6700 Å  

NASA Astrophysics Data System (ADS)

We present an atlas of spectra of 5 emission-line stars: the low-luminosity luminous blue variables (LBVs) HD 168625 and HD 160529, the white hypergiants (and LBV candidates) HD 168607 and AS 314, and the supergiant HD 183143. The spectra were obtained with 2 echelle spectrometers at the 6-m telescope of the Russian Academy of Sciences in the spectral range 4800 to 6700 Å, with a resolution of 0.4 Å. We have identified 380 spectral lines and diffuse interstellar bands within the spectra. Specific spectral features of the objects are described. The complete atlas and Table 2 are only available in electronic form at the CDS via anonymous ftp to\\ cdsarc.u-strasbg.fr (130.79.128.5) or via\\ http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/1035

Chentsov, E. L.; Ermakov, S. V.; Klochkova, V. G.; Panchuk, V. E.; Bjorkman, K. S.; Miroshnichenko, A. S.

2003-01-01

202

Winds in late-type stars - Mechanisms of mass outflow  

NASA Technical Reports Server (NTRS)

The four basic mechanisms that have been proposed for explaining the acceleration of winds in late-type stars are thermal pressure gradients, radiation pressure on circumstellar dust grains, momentum addition by Alfven waves, and momentum addition by periodic shock waves. Recent work in applying these mechanisms to stars is reviewed, with consideration given to whether these mechanisms can work, even in principle, and whether they are consistent with recent ultraviolet and X-ray data from the IUE and Einstein spacecraft. It is noted that thermally driven winds are likely important for late-type dwarfs, where the mass loss rates are small, and perhaps also in G giants and supergiants, but they cannot operate alone in the K and M giants and supergiants. It is thought that radiatively driven winds are probably unimportant for all cool stars, even the M supergiants with dusty circumstellar envelopes. In principle, Alfven waves can accelerate winds to high speeds so long as the field lines are initially open or forced open by some mechanism, but detailed calculations are needed. It is noted that, for the Miras and semiregular variable supergiants, periodic shock waves provide a simple way of producing rapid mass loss.

Linsky, J. L.

1981-01-01

203

The K stars - Orange giants and dwarfs  

NASA Astrophysics Data System (ADS)

The three brightest stars in the northern half of the sky include the orange Arcturus, a K1 giant. It is pointed out that the K giants are intrinsically smaller and less luminous than their cooler M counterparts, while the main-sequence K dwarf stars are brighter and larger than similar M objects. According to the spectral features of K stars, their atmospheres are significantly warmer than those of class M. Aspects of classification are discussed, taking into account the effects of the higher temperatures found, the determination of the luminosities of K stars, and the necessity to consider all useful criteria for an accurate classification. Attention is also given to K lines and chromospheres, supergiant K stars, subgiant stars, K dwarfs, and subdwarfs.

Kaler, J. B.

1986-08-01

204

The Reddening of Red Supergiants: When Smoke Gets in Your Eyes  

NASA Astrophysics Data System (ADS)

Deriving the physical properties of red supergiants (RSGs) depends on accurate corrections for reddening by dust. We use our recent modeling of the optical spectra of RSGs to address this topic. First, we find that previous broadband studies have underestimated the correction for extinction in the visible, and hence the luminosities (if derived from V); the shift in the effective wavelengths of the standard B and V bandpasses necessitates using an effective value of the ratio R'V=4.2 to correct broadband photometry of RSGs if RV=3.1 for early-type stars viewed through the same dust, where we have assumed the standard reddening law of Cardelli and coauthors. Use of the Fitzpatrick reddening law would lead to R'V=3.8, as well as slightly lower values of extinction derived from spectrophotometry, but results in slightly poorer fits. Second, we find that a significant fraction of RSGs in Galactic OB associations and clusters show up to several magnitudes of excess visual extinction compared to OB stars in the same regions; we argue that this is likely due to circumstellar dust around the RSGs. We also show that the RSG dust production rate (as indicated by the 12 ?m excess) is well correlated with bolometric luminosity, contrary to what has been found by earlier studies. The stars with the highest amount of extra visual extinction also show significant near-UV (NUV) excesses compared to the stellar models reddened by the standard reddening law. This NUV excess is likely due to scattering of the star's light by the dust and/or a larger average grain size than that typical of grains found in the diffuse interstellar medium. Similar excesses have been attributed to circumstellar dust around R Coronae Borealis stars. Finally, we estimate that the RSGs contribute dust grains at the rate of 3×10-8Msolar yr-1 kpc-2 in the solar neighborhood, comparable to what we estimate for late-type WCs, 1×10-7Msolar yr-1 kpc-2. In the solar neighborhood this represents only a few percent of the dust production (which is dominated by low-mass AGBs), but we note that in low-metallicity starbursts, dust production by RSGs would likely dominate over other sources.

Massey, Philip; Plez, Bertrand; Levesque, Emily M.; Olsen, K. A. G.; Clayton, Geoffrey C.; Josselin, Eric

2005-12-01

205

A FEROS spectroscopic study of the extreme O supergiant He 3-759  

NASA Astrophysics Data System (ADS)

We present a study of the extreme O-type supergiant He 3-759 using new high-resolution FEROS data, revealing that it is a near spectroscopic twin of HD 151804 (O8 Iaf). We investigate the extinction towards He 3-759 using a variety of methods, revealing AV ˜ 4.7^m. If we assume He 3-759 has an identical absolute K-band magnitude to HD 151804 we find that it lies in the Sagittarius-Carina spiral arm at a distance of 6.5 kpc. We derive the physical and wind properties for He 3-759, revealing Tast = 30.5 kK, log L/L? = 5.9 and dot{M} = 10-5.17 M? yr-1 for a clumped wind whose terminal velocity is estimated at 1000 km s-1. The atmosphere of He 3-759 is enriched in helium (X_He = 49%) and nitrogen (XN = 0.3%). A reanalysis of HD 151804 and HD 152408 (WN9ha) reveals similar parameters except that the WN9ha star possesses a stronger wind and reduced surface hydrogen content. HD 151804 and HD 152408 lie within the Sco OB1 association, with initial masses of 60 M? and ages 2.7 Myr, consistent with NGC 6231 cluster members using standard Geneva isochrones. Improved agreement with observed surface abundances are obtained for similar initial masses with more recent Geneva group predictions from which higher ages of 3.75 Myr are obtained. No young, massive star cluster is known to be associated with He 3-759. Based on observations made with ESO telescopes at the La Silla observatory under program ID 082-D.0136.

Crowther, P. A.; Evans, C. J.

2009-09-01

206

ON THE PERIODIC VARIABILITY OF THE LONGITUDINAL MAGNETIC FIELDS OF STARS  

SciTech Connect

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.

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

207

Rotating massive stars: From first stars to gamma ray bursts  

NASA Astrophysics Data System (ADS)

This article first reviews the basic physics of rotating stars and their evolution. The changes of the mechanical and thermal equilibrium of rotating stars are examined. An important, predicted and observed, effect is that rotating stars are hotter at the poles and cooler at the equator. The mass loss by stellar winds, which are influenced by the anisotropic temperature distribution, is discussed. These anisotropies in the interior are also driving circulation currents, which transports the chemical elements and the angular momentum in stars. Internal differential rotation, if present, creates instabilities and mixing, in particular, the shear mixing, the horizontal turbulence and their interactions. A major check of the model predictions concerns the changes of the surface abundances, which are modified by mass loss in the very massive stars and by rotational mixing in O-type and B-type stars. The observations are shown to confirm the existence of rotational mixing, with much larger effects at lower metallicities. The predictions of stellar models concerning the evolution of the surface velocities, the evolutionary tracks in the Hertzsprung-Russell diagram and lifetimes, the populations of blue, red supergiants and Wolf-Rayet stars, and the progenitors of type Ibc supernovae are discussed. In many aspects, rotating models are shown to provide a much better fit than nonrotating ones. Using the same physical ingredients as those which fit the best observations of stars at near solar metallicities, the consequences of rotating models for the status of Be stars, the progenitors of gamma ray bursts, the evolution of Pop III stars and of very metal-poor stars, the early chemical evolution of galaxies, the origin of the C-enhanced metal poor stars and of the chemical anomalies in globular clusters are explored. Rotation together with mass loss are two key physical ingredients shaping the evolution of massive stars during the whole cosmic history.

Maeder, André; Meynet, Georges

2012-01-01

208

Wind Variability of B Supergiants. No. 2; The Two-component Stellar Wind of gamma Arae  

NASA Technical Reports Server (NTRS)

The stellar wind of the rapidly rotating early-B supergiant, gamma Ara, is studied using time series, high-resolution IUE spectroscopy secured over approx. 6 days in 1993 March. Results are presented based on an analysis of several line species, including N(N), C(IV), Si(IV), Si(III), C(II), and Al(III). The wind of this star is grossly structured, with evidence for latitude-dependent mass loss which reflects the role of rapid rotation. Independent, co-existing time variable features are identified at low-velocity (redward of approx. -750 km/s) and at higher-speeds extending to approx. -1500 km/s. The interface between these structures is 'defined' by the appearance of a discrete absorption component which is extremely sharp (in velocity space). The central velocity of this 'Super DAC' changes only gradually, over several days, between approx. -400 and -750 km/s in most of the ions. However, its location is shifted redward by almost 400 km/s in Al(III) and C(II), indicating that the physical structure giving rise to this feature has a substantial velocity and ionization jump. Constraints on the relative ionization properties of the wind structures are discussed, together with results based on SEI line-profile-fitting methods. The overall wind activity in gamma Ara exhibits a clear ion dependence, such that low-speed features are promoted in low-ionization species, including Al(III), C(II), and Si(III). We also highlight that - in contrast to most OB stars - there are substantial differences in the epoch-to-epoch time-averaged wind profiles of gamma Ara. We interpret the results in terms of a two-component wind model for gamma Ara, with an equatorially compressed low ionization region, and a high speed, higher-ionization polar outflow. This picture is discussed in the context of the predicted bi-stability mechanism for line-driven winds in rapidly rotating early-B type stars, and the formation of compressed wind regions in rapidly rotating hot stars. The apparent absence of a substantial shift in the wind ionization mixture of gamma Ara, and the normal nature of its photospheric spectrum, suggests wind-compression as the likely dominant cause for the observed equatorial density enhancements.

Prinja, R. K.; Massa, D.; Fullerton, A. W.; Howarth, I. D.; Pontefract, M.

1996-01-01

209

A study on the nature of the peculiar supergiant HD 101584.  

NASA Astrophysics Data System (ADS)

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 HD 101584. 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, T_eff_=12000+/-1000K and logg=3.0+/-1.0, with an extinction of E(B-V)=0.49+/-0.05. The observed spectral features in the spectrum of HD 101584 are classified in eight different categories based on the velocity, shape of profile and the identification. The high-excitation HeI (?=20.87eV), NII (?=18.40eV), CII (?=14.39eV) and NI (?=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 white dwarf or a low-mass main sequence object. The low-excitation P-Cygni lines in the optical and UV are formed in the wind. The number density of absorption lines in the UV is so large that the wind spectrum acts as an iron curtain in front of the B-star. The terminal velocity of the wind of vinfinity_=100+/-30km/s is consistent with the star being a low-mass post-AGB star and the low effective gravity is attributed to the presence of a nearby, unseen, secondary. We estimate a mass-loss rate of M?=~10^-8^Msun_/yr. Narrow absorption and emission lines are observed which are formed in a circumsystem disk with a typical radius of 10^2^R_*_.

Bakker, E. J.; Lamers, H. J. G. L. M.; Waters, L. B. F. M.; Waelkens, C.; Trams, N. R.; Van Winckel, H.

1996-03-01

210

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

NASA Astrophysics Data System (ADS)

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 massive star population in nearby galaxies has taught us about stellar evolution and star formation. I show that the current generation of stellar evolutionary models do well at matching some of the observed features and provide a look at the sort of new observational data that will provide a benchmark against which new models can be evaluated.

Massey, Philip

211

SWS spectral classification of ordinary stars  

NASA Astrophysics Data System (ADS)

We present an overview of the spectroscopic characteristics of ordinary stars observed with SWS in the low-resolution mode (R~250-400), covering the full instrumental wavelength range 2.38-45.2 ?m. Our sample contains stars that fill a grid with spectral types between B and M, and luminosity classes dwarf to supergiant. We have identified the spectral features (H lines and molecular bands) that are of interest for classification purposes, and analyzed the dependence of the relative intensity of these features on spectral type and luminosity class.

Heras, A. M.; Shipman, R. F.; Price, S. D.; Cohen, M.; de Graauw, Th.; Walker, H. J.; Jourdain de Muizon, M.; Kessler, M. F.; Prusti, T.

1999-03-01

212

The FIP Effect in RV Tauri Stars  

NASA Astrophysics Data System (ADS)

RV Tauri stars are evolved low-mass supergiants of spectral type F5 to K3 and are thought to be in the post-AGB (Asymptotic Giant Branch) phase evolving to planetary nebulae. They show deep and shallow minima with periods ranging from 40 to 150 days. While reviewing the abundances of CE Vir and EQ Cas (RV Tauri stars of semi-regular variable type D), we found that they show a clear trend with first ionization potential (FIP; Rao and Reddy 2005, MNRAS, 357, 235). This is an interesting twist to element depletion in stellar atmospheres. Our further search in a sample of 60 RV Tauri stars resulted in finding one more star with a clear FIP effect (Reddy and Rao, in preparation). At 3 out of 60, the phenomenon may not be uncommon among RV Tauri stars.

Reddy, B. E.

213

Discovery of a New Dusty B[E] Star in the Small Magellanic Cloud  

NASA Technical Reports Server (NTRS)

We present new optical spectroscopic and 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], [Fe II], 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.

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

2007-01-01

214

Crossing the Yellow Void: Spatially Resolved Spectroscopy of the Post-Red Supergiant IRC +10420 and Its Circumstellar Ejecta  

NASA Astrophysics Data System (ADS)

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the H-R diagram. During their post-red supergiant evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semiforbidden 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 H? 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. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Humphreys, Roberta M.; Davidson, Kris; Smith, Nathan

2002-08-01

215

Magnetic Fields and Convection in the Cool Supergiant Betelgeuse  

NASA Astrophysics Data System (ADS)

We present the outcome of a highly-sensitive search for magnetic fields on the cool supergiant Betelgeuse. A time-series of six circularly polarized spectra was obtained using the NARVAL spectropolarimeter at Télescope Bernard Lyot (Pic du Midi Observatory (F)), between March and April 2010. Zeeman signatures were repeatedly detected in cross-correlation profiles, corresponding to a longitudinal component of about 1 G. The time-series unveils a smooth increase of the longitudinal field from 0.5 to 1.5 G, correlated with radial velocity fluctuations. We observe a strong asymmetry of Stokes V signatures, also varying in correlation with the radial velocity. The Stokes V line profiles are red-shifted by about 9 km s-1 with respect to the Stokes I profiles, suggesting that the observed magnetic elements may be concentrated in the sinking components of the convective flows.

Petit, P.; Aurière, M.; Konstantinova-Antova, R.; Morgenthaler, A.; Perrin, G.; Roudier, T.; Donati, J.-F.

216

Nonthermal X-ray emission from winds of OB supergiants  

SciTech Connect

The mechanisms responsible for the hard X-ray emission of OB supergiants (OBSGs) are investigated theoretically, modifying the periodic-shock model of Lucy (1982). The physical processes discussed include (1) the particle acceleration (PA) mechanism and its effect on the structure of individual shocks, (2) the energy cutoff and spectral index of the relativistic electrons and ions, and (3) the efficiency of PA by shocks and its implications for the number densities of relativistic particles. The model is used to predict the spectrum and intensity of the dominant nonthermal X-ray emission source from OBSGs, and the results are shown to be in good agreement with Einstein Observatory Solid-State Spectrometer observations of three OBSGs in Orion (Cassinelli and Swank, 1983). It is inferred that the surface magnetic fields of OBSGs are no greater than a few G, and that the PA rates are significantly lower than generally predicted for collisionless astrophysical shocks. 66 refs.

Chen, W.; White, R.L. (Johns Hopkins Univ., MD (USA) Space Telescope Science Institute, Baltimore, MD (USA))

1991-01-01

217

Supergiant Complexes of Solar Activity and Convection Zone  

NASA Astrophysics Data System (ADS)

The global distribution of solar surface activity (active regions) is apparently connected with processes in the convection zone. The large-scale magnetic structures above the tachocline could in a pronounced way be observable in the surface magnetic field. To get the information regarding large-scale magnetic formations in the convection zone, a set of solar synoptic charts (Mount Wilson 1998 - 2004, Fe i, 525.02 nm) have been analyzed. It is shown that the longitudinal dimensions and dynamics of supergiant complexes of solar surface activity carry valuable information about the processes in the convection zone of the Sun. A clear effect of large-scale (global) turbulence is found. This is a `fingerprint' of deep convection, because there are no such large-scale turbulent eddies in the solar photosphere. The preferred scales of longitudinal variations in surface solar activity are revealed. These are: ˜ 24° (gigantic convection cells), 90°, 180° and 360°.

Arkhypov, O. V.; Antonov, O. V.; Khodachenko, M. L.

2011-05-01

218

Life Cycle of Stars  

NASA Technical Reports Server (NTRS)

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.

1999-01-01

219

UV wind variability in B supergiants and its implications for wind structures  

Microsoft Academic Search

We discuss why B supergiant winds are particularly well suited for wind studies, and present or refer to dynamic spectra which\\u000a suggest the presence of disks, bifurcated winds, shock formation, rotationally modulated winds and the spontaneous generation\\u000a of wind enhancements. They underscore the strength and richness of wind variability in B supergiants and the challenges these\\u000a phenomena present to theoretical

Derck Massa; Raman K. Prinja

1999-01-01

220

Evolution of close binary stars - Observational aspects  

NASA Technical Reports Server (NTRS)

Detached close binary systems define the main sequence band satisfactorily, but very little is known about the masses of giants and supergiants. High-dispersion IUE observations promise an improvement, since blue companions are now frequently found to late-type supergiants. The interesting cases of Mu Sagittarii and in particular of Epsilon Aurigae are discussed in more detail. The barium star abundance anomaly appears now to be due to mass transfer in interacting systems. The symbiotic stars are another type of binary systems containing late-type giants; several possible models for the hotter star and for the type of interaction are discussed. The W Serpentis stars appear to be Algols in the rapid phase of mass transfer, but a possible link relating them to the symbiotics is also indicated. Evidence of hot circumstellar plasmas has now been found in several ordinary Algols; there may exist a smooth transition between very quiescent Algols and the W Serpentis stars. Bet2 Lyrae is discussed in the light of new spectrophotometric results.

Plavec, M. J.

1982-01-01

221

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

NASA Astrophysics Data System (ADS)

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.

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

1995-01-01

222

A catalog of blue and red supergiants in M33  

NASA Technical Reports Server (NTRS)

We present a catalog of blue and red stars in M33 based on photographic photometry of over 65,000 objects extracted from plates taken with the 3.6 m Canada-France-Hawaii Telescope (CFHT) and the 2.0 m Rozhen (Bulgarian) Telescope. The completeness limit of the various surveys are estimated here to be V = 19.5 mag for those stars situated in crowded associations, and V = 20.0 mag for stars in the interarm fields. We list magnitudes and positions for 2112 blue stars, defined by (U - V) less than 0.0 mag, (U - B) less than 0.0 mag, and V less than 19.5 mag, and 389 red stars defined by (B - V) greater than 1.8 mag and V less than 19.5 mag. Of these, 1156 are candidate O stars on the basis of (U - V) less than -0.9 mag.

Ivanov, Georgi R.; Freedman, Wendy L.; Madore, Barry F.

1993-01-01

223

A New Distance to M33 Using Blue Supergiants and the FGLR Method  

NASA Astrophysics Data System (ADS)

The quantitative spectral analysis of medium resolution optical spectra of A and B supergiants obtained with DEIMOS and ESI at the Keck Telescopes is used to determine a distance modulus of 24.93 ± 0.11 mag (968 ± 50 kpc) for the Triangulum Galaxy M33. The analysis yields stellar effective temperatures, gravities, interstellar reddening, and extinction, the combination of which provides a distance estimate via the flux-weighted gravity-luminosity relationship (FGLR). This result is based on an FGLR calibration that is continually being polished. An average reddening of langE(B - V)rang ~ 0.08 mag is found, with a large variation ranging from 0.01 to 0.16 mag, however, demonstrating the importance of accurate individual reddening measurements for stellar distance indicators in galaxies with evident signatures of interstellar absorption. The large-distance modulus found is in good agreement with recent work on eclipsing binaries, planetary nebulae, long-period variables, RR Lyrae stars, and also with Hubble Space Telescope (HST) observations of Cepheids, if reasonable reddening assumptions are made for the Cepheids. Since distances based on the tip of the red giant branch (TRGB) method found in the literature give conflicting results, we have used HST Advanced Camera for Surveys V- and I-band images of outer regions of M33 to determine a TRGB distance of 24.84 ± 0.10 mag, in basic agreement with the FGLR result. We have also determined stellar metallicities and discussed the metallicity gradient in the disk of M33. We find metallicity of Z sun at the center and 0.3 Z sun in the outskirts at a distance of one isophotal radius. The average logarithmic metallicity gradient is -0.07 ± 0.01 dex kpc-1. However, there is a large scatter around this average value, very similar to what has been found for the H II regions in M33.

U, Vivian; Urbaneja, Miguel A.; Kudritzki, Rolf-Peter; Jacobs, Bradley A.; Bresolin, Fabio; Przybilla, Norbert

2009-10-01

224

Winds of Low-metallicity OB-type Stars: HST-COS Spectroscopy in IC 1613  

NASA Astrophysics Data System (ADS)

We present the first quantitative ultraviolet spectroscopic analysis of resolved OB stars in IC 1613. Because of its alleged very low metallicity (lsim1/10 Z ?, from H II regions), studies in this Local Group dwarf galaxy could become a significant step forward from the Small Magellanic Cloud (SMC) toward the extremely metal-poor massive stars of the early universe. We present HST-COS data covering the ~1150-1800 Å wavelength range with resolution R ~ 2500. We find that the targets do exhibit wind features, and these are similar in strength to SMC stars. Wind terminal velocities were derived from the observed P Cygni profiles with the Sobolev plus Exact Integration method. The v ?-Z relationship has been revisited. The terminal velocity of IC 1613 O stars is clearly lower than Milky Way counterparts, but there is no clear difference between IC 1613 and SMC or LMC analog stars. We find no clear segregation with host galaxy in the terminal velocities of B-supergiants, nor in the v ?/v esc ratio of the whole OB star sample in any of the studied galaxies. Finally, we present the first evidence that the Fe-abundance of IC 1613 OB stars is similar to the SMC, which is in agreement with previous results on red supergiants. With the confirmed ~1/10 solar oxygen abundances of B-supergiants, our results indicate that IC 1613's ?/Fe ratio is sub-solar.

Garcia, Miriam; Herrero, Artemio; Najarro, Francisco; Lennon, Daniel J.; Alejandro Urbaneja, Miguel

2014-06-01

225

HD 105262, A Newly-Discovered HR 4049 Star with a Large Proper Motion  

NASA Astrophysics Data System (ADS)

HD 105262 has a spectrum like that of HR 4049 in having Balmer liens as in a Ib supergiant but very weak lines due to He I, Ca II, Si II, Ti II, fe I, Fe II, and Mg II. It has a published proper motion of 0.057" +/- 0.011" yr^-1. If the star had the luminosity of a Ib supergiant, its space motion would be several times the escape velocity from the Galaxy. HD 105262 does not have the spectral appearance of a horizontal-branch or post AGB star. The most likely explanation for the spectrum is the model proposed for HR 4049 by Lamers et al. (1986), Waelkens et al. (1987), and Lambert et al. (1988), namely a low-mass proto-planetary nebula star in which the narrow Balmer lines are formed in an extended atmosphere. (SECTION: Stars)

Abt, Helmut A.

1996-10-01

226

Theoretical Radial Pulsation Properties of Massive Yellow Supergiants  

Microsoft Academic Search

We have studied the theoretical linear nonadiabatic radial pulsation periods and amplitude growth rates of two stellar models with initial masses of 30 and 40 solar masses. The intrinsic variability and dynamical properties of massive stars are very important to the understanding of the evolutionary behavior of these stars, especially those at, or near, the Humphreys-Davidson (H-D) Line, an empirically

M. S. Soukup; A. N. Cox

1996-01-01

227

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)

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.

Melbourne, J.; Boyer, Martha L.

2013-01-01

228

Discovery of an eccentric 30 day period in the supergiant X-ray binary SAX J1818.6-1703 with INTEGRAL  

NASA Astrophysics Data System (ADS)

Context: SAX J1818.6-1703 is a flaring transient X-ray source serendipitously discovered by BeppoSAX in 1998 during an observation of the Galactic centre. The source was identified as a high-mass X-ray binary with an OB supergiant companion (SGXB). Displaying short and bright flares and an unusually very low quiescent level implying an intensity dynamical range as large as 103-4, the source was classified as a supergiant fast X-ray transient (SFXT). Aims: The mechanism triggering the different temporal behaviour observed between the classical SGXBs and the recently discovered class of SFXTs is still debated. The discovery of long orbits (>15 d) should help to discriminate between emission models and bring constraints. Methods: We analysed archival INTEGRAL data on SAX J1818.6-1703. We built short- and long-term light curves and performed a timing analysis in order to study the temporal behaviour of SAX J1818.6-1703 on different time scales. Results: INTEGRAL revealed an unusually long orbital period of 30.0 ± 0.2 d and an elapsed accretion phase of ~6 d in the transient SGXB SAX J1818.6-1703. This implies an elliptical orbit and constraints the possible supergiant spectral type between B0.5-1I with eccentricities e ~ 0.3-0.4 (for the average fundamental parameters of supergiant stars). During the accretion phase, the source behaved like a classical SGXB. The huge variations of the observed X-ray flux can be explained through accretion of macro-clumps formed within the stellar wind. Our analysis strengthens the model which predicts that SFXTs behave as SGXBs but with different orbital parameters, thus different temporal behaviour. Discovery first reported at the 7th INTEGRAL workshop (Zurita Heras et al., in press). Based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA.

Zurita Heras, J. A.; Chaty, S.

2009-01-01

229

Massive star evolution: luminous blue variables as unexpected supernova progenitors  

NASA Astrophysics Data System (ADS)

Stars more massive than about 8 M? end their lives as a supernova (SN), an event of fundamental importance Universe-wide. Theoretically, these stars have been expected to be either at the red supergiant, blue supergiant, or Wolf-Rayet stage before the explosion. We performed coupled stellar evolution and atmospheric modeling of stars with initial masses between 20 M? and 120 M?. We found that the 20 M? and 25 M? rotating models, before exploding as SN, have spectra that do not resemble any of the aforementioned classes of massive stars. Rather, they have remarkable similarities with rare, unstable massive stars known as luminous blue variables (LBV). While observations show that some SNe seem to have had LBVs as progenitors, no theoretical model had yet predicted that a star could explode at this stage. Our models provide theoretical support for relatively low-luminosity LBVs exploding as SN in the framework of single stellar evolution. This is a significant shift in paradigm, meaning that a fraction of LBVs could be the end stage of massive star evolution, rather than a transitory evolutionary phase. We suggest that type IIb SN could have LBV as progenitors, and a prime example could be SN 2008ax.

Groh, J. H.; Meynet, G.; Ekström, S.

2013-02-01

230

Massive Stars in the Cl 1813-178 Cluster: An Episode Of Massive Star Formation in the W33 Complex  

NASA Astrophysics Data System (ADS)

Young massive (M > 104 M sun) stellar clusters are a good laboratory to study the evolution of massive stars. Only a dozen of such clusters are known in the Galaxy. Here, we report about a new young massive stellar cluster in the Milky Way. Near-infrared medium-resolution spectroscopy with UIST on the UKIRT telescope and NIRSPEC on the Keck telescope, and X-ray observations with the Chandra and XMM satellites, of the Cl 1813-178 cluster confirm a large number of massive stars. We detected 1 red supergiant, 2 Wolf-Rayet stars, 1 candidate luminous blue variable, 2 OIf, and 19 OB stars. Among the latter, twelve are likely supergiants, four giants, and the faintest three dwarf stars. We detected post-main-sequence stars with masses between 25 and 100 M sun. A population with age of 4-4.5 Myr and a mass of ~10, 000 M sun can reproduce such a mixture of massive evolved stars. This massive stellar cluster is the first detection of a cluster in the W33 complex. Six supernova remnants and several other candidate clusters are found in the direction of the same complex. Based on observations collected at the European Southern Observatory (ESO Programme 081.D-0371(A)).

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

2011-05-01

231

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

NASA Technical Reports Server (NTRS)

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.

Walborn, Nolan R.

1987-01-01

232

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

NASA Astrophysics Data System (ADS)

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

Stringfellow, Guy; Gvaramadze, Vasilii

2010-02-01

233

Spectra of 8 supergiants in nearby galaxies (Britavskiy+, 2014)  

NASA Astrophysics Data System (ADS)

The spectra of all program stars are presented. The log of observations and other information about these spectra are available into the article. The names of the files with spectra are the same as in the article. (3 data files).

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

2013-11-01

234

The Importance of Long Time Domain Observations for Understanding Pulsation in Cepheids and M Supergiants  

NASA Astrophysics Data System (ADS)

Continuous monitoring of both Cepheids and type C semiregular variables is essential for understanding their pulsation. Cepheids, for example, can undergo regular, periodic, and irregular changes in pulsation period and amplitude that are attributed to stellar evolution, orbital motion about companions, and stochastic processes, respectively. All such information helps to characterize Cepheids in terms of physical attributes. Similar information is also very useful for pulsating M supergiants, which are still poorly understood in terms of their pulsation. Specific examples are provided by BC Cyg and ? Cep, the former a M3 supergiant displaying regular pulsation, the latter a M1 supergiant apparently pulsating in fundamental and overtone modes. Both appear to provide long-period extensions of the Cepheid period-mass and period-age relations.

Turner, David G.

2014-06-01

235

Scanner observations of selected cool stars  

NASA Technical Reports Server (NTRS)

Photoelectric spectral scans at 30-A resolution of 9 dwarfs, 10 giants and 6 supergiants with spectral types GO to M5 were presented. All stars were observed every 4 A from wavelength 3300 to wavelength 7000. Absorption features at this resolution coincide with: strong atomic lines of Fe 1,11, Ca 1,11, Mg 1, and Na 1; vibrational bands of the electronic transitions of TiO, MgH, CaH, SiH, AlH, Cn, Ch, C2, OH, and NH. The dependence of the wavelength 3740 Fe 1 blend and the wavelength 3440 depression on temperature is discussed.

Fay, T. D., Jr.; Stein, W. L.; Warren, W. H., Jr.

1974-01-01

236

Scanner observations of selected cool stars  

NASA Technical Reports Server (NTRS)

Photoelectric spectral scans at 30 A resolution of nine dwarfs, ten giants, and six supergiants with spectral types G0 to M5 are presented. (All stars were observed every 4 A from 3300 to 7000 A.) Absorption features observed at this resolution coincide with: strong atomic lines of Fe I, Fe II, Ca I, Ca II, Mg I, and Na I; vibrational bands of the electronic transitions of TiO, MgH, CaH, SiH, AlH, CN, CH, C2, OH, and NH. The dependences of the 3740-A Fe I blend and the 3440-A depression on temperature are discussed.

Fay, T. D., Jr.; Stein, W. L.; Warren, W. H., Jr.

1974-01-01

237

MOST Ultra-High Precision Photometry of the Luminous Blue Supergiant Rigel - Probing the Interior of a Future Type II Supernova  

NASA Astrophysics Data System (ADS)

Rigel (B8 Ia; B-V = -0.03; V 0.08- 0.24 mag; 240 +/- 35 pc) is the 7th brightest star in the sky and is the nearest luminous supergiant. From evolutionary tracks, Rigel has an inferred mass of 17 +/- 3 solar masses and an age of 5-10 Myr. Interestingly, Rigel has similar physical properties to the 12th-mag blue supergiant progenitor of SN 1987A: Sanduleak -69° 202a. Rigel (along with its co-asterism Betelgeuse) is likely to be the nearest progenitor of a Type II supernova. Such a nearby explosion would have an apparent magnitude of -10.5 mag (equivalent to the light from the nearly full moon).   We report on initial results of intensive photometry and spectroscopy of Rigel carried out during 2009/10. These observations are part of an international campaign in support of nearly a month of continuous ultra-high precision photometry of Rigel with the Canadian Microsatellite MOST. These observations indicate brightness and radial velocity variations on nearly all time scales - from hours to weeks. These data are being analyzed for periods using various period-search routines. Evidence for a multitude of cyclic/periodic oscillations (with variable amplitudes) appears present in the datasets in addition to stochastic variations. These data will be used to carry out an asteroseismic study of this evolved high mass star. The preliminary results from this program are presented. We acknowledge support for this research from NASA/MOST Grant NNX09AH28G and NSF/RUI Grants AST05-07542 and AST05-07536. We also wish to thank to thank Jaymie Matthews, Rainer Kuschnig and the MOST team for acquiring and reducing the MOST observations.

Guinan, Edward F.; Wasatonic, R.; Engle, S.; Aerts, C.; Morajjevi, E.; Eaton, J.; Fekel, F.; Coughlin, J.; Stewart, H.

2010-05-01

238

Observation of winds in cool stars  

NASA Technical Reports Server (NTRS)

Sufficient observational material - ultraviolet spectroscopic measures, quantitative optical spectroscopy, and X-ray photometry exists to enable discernment of the presence and character of mass loss in cool stars and to establish meaningful constraints on theoretical models. 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 more extensive observations demonstrate the importance of magnetic surface activity and its particular geometrical configuration. Successive observations of an active binary system and a supergiant star reveal that magnetic activity and perhaps mass loss occur on restricted regions of a stellar surface and that long lived structures are present in a wind.

Dupree, A. K.

1983-01-01

239

X1908+075: A Late O-Type Supergiant with a Neutron Star Companion  

NASA Astrophysics Data System (ADS)

X1908 + 075 is a highly-absorbed Galactic X-ray source likely made up of a pulsar accreting wind material from a massive companion. We have used near-IR photometric data complemented by follow-up spectroscopy to identify the likely counterpart to this X-ray source and to assign a spectral type O7.5 9.5 If to the primary. Further details can be found in Morel and Grosdidier (2005).

Morel, Thierry; Grosdidier, Yves

2006-08-01

240

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

NASA Astrophysics Data System (ADS)

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 ~24 ks, span 1.2 orbital periods (Porb = 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 onset of a gated mechanism is the most likely explanation for the observed light curve.

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

2013-08-01

241

On the disappearance of O I in some high-luminosity cool stars  

NASA Technical Reports Server (NTRS)

Far UV spectra and flux measurements of cool giant and supergiant stars, focusing on the O I (UV 2) and S I/Si II fluxes and their dependence on stellar parameters are presented. The de-reddened O I surface fluxes vary by factors of several hundred over the 11 stars in the sample and, at a given luminosity, decrease with decreasing effective temperature. No flux at all is detected in the three M supergiants observed to date. In contrast, the S I/Si II blend near 1810 angstrom is clearly detected in all the stars. Its strength generally increases with luminosity, but has little effective temperature dependence. Possible explanations for the behavior of O I include changes in the intensities of Lyman alpha and beta which excite the lines of S I and O I, respectively, as well as scattering and/or absorption of the O I flux in a dense, circumstellar gas shell.

Carpenter, K. G.; Norman, D.; Robinson, R.; Fernandez-Villacanas, J. L.; Jordan, C.; Judge, P.

1990-01-01

242

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

NASA Technical Reports Server (NTRS)

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.

Stothers, R.

1973-01-01

243

Spectroscopic observations of AB supergiants in M 33.  

NASA Astrophysics Data System (ADS)

We have observed 10 luminous blue stars in M 33 at intermediate dispersion and have determined spectral types and luminosity classes from the blue and red spectrograms by comparing with galactic and SMC stars. Halpha_ profiles have proved to be very useful in disentangling luminosity and metallicity effects, and constitute a valuable diagnostic when comparing spectral classifications in galaxies with different metallicities. We derive qualitative estimates of the stellar metallicities which range from solar to SMC-like and are broadly consistent with abundance gradient results obtained for M 33 from Hii region studies. Comparison of the new data for B 324 with previous work shows that there is evidence for significant spectral variability strongly suggesting an LBV nature for this star.

Monteverde, M. I.; Herrero, A.; Lennon, D. J.; Kudritzki, R. P.

1996-08-01

244

What does C II lambda 2325 A emission tell us about chromospheres of red supergiants? - A critical test using Zeta Aurigae-type K supergiants  

NASA Technical Reports Server (NTRS)

The limitations of the Carpenter et al. (1985) C II intercombination multiplet method of determining the density and geometric extent of red giant chromospheres are presently tested through observation of the C II 2325 A emission of two K-type supergiants whose empirical model chromospheres have been derived by high-resolution IUE observations at eclipse phases. While the observed C II emission fluxes are well reproduced, much of this emission originates in the high-density lower chromosphere.

Schroeder, K.-P.; Reimers, D.; Carpenter, K. G.; Brown, A.

1988-01-01

245

What is the True Population of the R Coronae Borealis Stars  

NASA Astrophysics Data System (ADS)

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 (FF) in a PN central star. The evidence pointing toward a WD merger or a FF origin for RCB stars is contradictory. Therefore, determining the population of RCB stars is very important. Predictions of the number of RCB stars in the Galaxy range as high as 5,000 but very few RCB stars are known. The discovery rate for RCB stars has been accelerated by the use of WISE IR colors and the ASAS-3 lightcurves. The number of Milky Way RCB stars identified has doubled in just a few years to about 100 and may double again soon.

Clayton, G.

2014-04-01

246

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

NASA Astrophysics Data System (ADS)

Aims: 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). While the very high luminosity (˜ 5 × 105 L?) previously estimated for WOH G64 suggests that it is a very massive star with an initial mass of ~40 M?, its low effective temperature (~3200 K) is in serious disagreement with the current stellar evolution theory. Methods: WOH G64 was observed with VLTI/MIDI using the UT2-UT3 and UT3-UT4 baseline configurations. Results: 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 ?m and a gradual increase longward of ~10 ?m, reflecting the 10 ?m silicate feature in self-absorption. This translates into a steep increase of the uniform-disk diameter from 8 to 10 ?m (from 18 to 26 mas) and a roughly constant diameter above 10 ?m. The visibilities measured at four position angles differing by ~60° 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 × 105 L?, which is by a factor of 2 lower than the previous estimates based on spherical models. We also identify the H2O absorption features at 2.7 and 6 ?m in the spectra obtained with the Infrared Space Observatory and the Spitzer Space Telescope. The 2.7 ?m feature originates in the photosphere and/or the extended molecular layers, while the 6 ?m feature is likely to be of circumstellar origin. Conclusions: 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 M? star. However, the effective temperature is still somewhat too cool for the theory. The low effective temperature of WOH G64 places it very close to or even beyond the Hayashi limit, which implies that this object may be experiencing unstable, violent mass loss. Based on observations made with the Very Large Telescope Interferometer of the European Southern Observatory. Program ID: 076.D-0253, 080.D-0222. This work is based [in part] on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

Ohnaka, K.; Driebe, T.; Hofmann, K.-H.; Weigelt, G.; Wittkowski, M.

2008-06-01

247

The structure, energy balance, and winds of cool stars  

NASA Technical Reports Server (NTRS)

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.

Linsky, J. L.

1982-01-01

248

Oxygen Isotopic Ratios in Cool R Coronae Borealis Stars  

NASA Astrophysics Data System (ADS)

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/15N 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 an 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 an 18O-rich HdC star into an 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.

García-Hernández, D. A.; Lambert, David L.; Kameswara Rao, N.; Hinkle, Ken H.; Eriksson, Kjell

2010-05-01

249

Lithium in late-type giants. II. 31 M giants and supergiants  

SciTech Connect

High resolution, high signal-to-noise spectra have provided Li abundances for 31 M giants and supergiants. The spectrum around the Li I 6707 A doublet is depressed by unresolved TiO lines. A spectrum synthesis technique was developed to account for the TiO line blanketing and to extract the Li abundance.

Luck, R.E.; Lambert, D.L.

1982-05-01

250

Dynamical Mass of the O-Type Supergiant in Zeta Orionis A.  

National Technical Information Service (NTIS)

Aims. A close companion of Orionis A was found in 2000 with the Navy Precision Optical Interferometer (NPOI), and shown to be a physical companion. Because the primary is a supergiant of type O, for which dynamical mass measurements are very rare, the com...

C. A. Hummel G. Belle M. Nieva O. Stahl T. Rivinius

2013-01-01

251

Carbon and nitrogen abundances in the BN supergiant HD 93840, and their implications for normal Galactic supergiants  

NASA Technical Reports Server (NTRS)

It is demonstrated how carbon and nitrogen abundances of luminous B stars can be determined by a combined analysis of their UV photospheric and wind lines. It is shown that HD 93840 has nearly the same temperature and surface gravity as the normal B1 Ib star Zeta Per. These two stars are compared on the basis of their UV photospheric silicon spectra and the differences in their photospheric CNO and metallic lines are discussed. A quantitative comparison between the wind profiles of the two stars is made. A simple model for the compositions of both atmospheres is used to derive the fraction of material in each atmosphere which has undergone CNO processing. It is argued that the enriched material must have resided in a nuclear burning core for only a very short time. Best estimates of 0.09 + or - 0.07 and 0.90 + or - 0.1 are made for the carbon abundances relative to cosmic ones for HD 93840 and Zeta Per, respectively.

Massa, D.; Wynne, D.; Altner, B.; Lamers, H. J. G. L. M.

1991-01-01

252

Hot Stars in the Galactic Halo  

NASA Astrophysics Data System (ADS)

Participants; Preface; Foreword; Acknowledgements; Part I. Introductory Papers: 1. What is the galaxy's halo population?; 2. Theoretical properties of horizontal-branch stars; 3. A review of A-type horizontal-branch stars; Part II. Surveys: 4. A progress report on the Edinburgh-Cape object survey; 5. A 300 square degree survey of young stars at high galactic latitudes; 6. The isolation of a new sample of B stars in the halo; 7. A northern catalog of FHB/A stars; 8. Recent progress on a continuing survey of galactic globular clusters for blue stragglers; 9. UV observations with FAUST and the galactic model; 10. Hot stars at the South Galactic Pole; Part III. Clusters: 11. Population II horizontal branches: a photometric study of globular clusters; 12. The period-shift effect in Oosterhoff type II globular clusters; 13. UV photometry of hot stars in omega centauri; 14. Spectroscopic and UBV observations of blue stars at the NGP; 15. Population I horizontal branches: probing the halo-to-disk transition; Part IV. Stars: 16. Very hot subdwarf O stars; 17. Quantitative spectroscopy of the very hot subluminous O-stars: K646, PG1159-035, and KPD0005+5106; 18. Analyzing the helium-rich hot sdO stars in the Palomar Green Survey; 19. Late type companions of hot sd O stars; 20. Hot stars in globular clusters; 21. Faint blue stars from the Hamburg Schmidt Survey; 22. Stellar winds and the evolution of sdB's to sdO's; 23. Halo stars in the Vilnius photometric system; 24. Horizontal branch stars in the geneva photometric system; 25. Zeeman observations of FHB stars and hot subdwarf stars; 26. What does a FHB star's spectrum look like?; 27. A technique for distinguishing FHB stars from A-type stars; 28. eEemental abundances of halo A and interloper stars; 29. The mass of blue horizontal branch stars in the globular cluster NGC6397; 30. IUE observations of blue HB stars in the globular clusters M3 and NGC6752; 31. Metallicities and kinematics of the local RR lyraes: lukewarm stars in the halo; 32. Baade-Wesselink analyses of field vs. cluster RR lyrae variables; 33. The rotation of population II A stars; 34. Horizontal branch stars and possibly related objects; 35. A new group of post-AGB objects - the hot carbon-poor stars; 36. MK classifications of hot stars in the halo 37. Photometry of XX Virginis and V716 Ophiuchi and the period luminosity relations of type II cepheids; 38. Rotation and oxygen line strengths in blue horizontal branch stars; Part V. Miscellaneous: 39. UBV CCd photometry of the halo of M31; 40. Can stars still form in the galactic halo?; 41. The ultraviolet imaging telescope on the Astro -1 and Astro -2 missions; 42. Are analogues of hot subdwarf stars responsible for the UVX phenomenon in galaxy nucleli; 43. A survey for field BHB stars outside the solar circle; 44. Post-AGB A and F supergiants as standard candles; 45. The extended horizontal-branch: a challenge for stellar evolution theory; 46. Astronomical patterns in fractals: the work of A. G. Davis Philip on the Mandelbrot Set; Part VI. Summary: 47. Final remarks; Author index; Subject index.

Adelman, Saul J.; Upgren, Arthur R.; Adelman, Carol J.

2011-03-01

253

Six Years of Short-Spaced Monitoring of the v=1 and v=2 J=1-0 (28)SiO Maser Emission in Evolved Stars.  

National Technical Information Service (NTIS)

We present the results from a monitoring of the v=1 and v=2 J=1-0 (28)SiO maser emission in 21 objects, covering all types of known SiO maser emitters: 13 Mira variables, 2 long period semiregulars (SRGs), 3 variable supergiants (SGs), 2 OH/IR stars, and ...

J. Alcolea J. R. Pardo V. Bujarrabal R. Bachiller A. Barcia F. Colomer J. D. Gallego J. Gomez-Gonzalez A. delPino P. Planesas

1999-01-01

254

Spatially-resolved high-spectral resolution observations of the red supergiant Betelgeuse  

NASA Astrophysics Data System (ADS)

Red supergiants (RSGs) experience slow, intensive mass loss up to 10-4 M? yr-1. Despite its importance not only in stellar evolution but also in the chemical enrichment of the interstellar matter, the mass loss mechanism in RSGs is not well understood. A better understanding of the outer atmosphere of RSGs is a key to unraveling the mass-loss mechanism in these stars. High spatial resolution observations in IR molecular lines are very effective for probing the physical properties of the inhomogeneous outer atmosphere. We observed the prototypical RSG Betelgeuse (M1-2Ia-Ibe) in the CO first overtone lines with the spectro-interferometric instrument AMBER at the ESO's Very Large Telescope Interferometer (VLTI) using baselines of 16, 32, and 48 m. Details of the observations and the modeling are described in Ohnaka et al. (2009). The high-spectral (R = 4800-12000) and high-spatial resolution (9 mas) provided with AMBER allowed us to study inhomogeneities seen in the individual CO first overtone lines. Our AMBER observations represent the highest spatial resolution achieved for Betelgeuse, corresponding to five resolution elements over its stellar disk. The AMBER visibilities and closure phases in the K-band continuum can be reasonably fitted by a uniform disk with a diameter of 43.19 ± 0.03 mas or a limb-darkening disk with 43.56 ± 0.06 mas and a limb-darkening parameter of (1.2 ± 0.07) × 10-1. On the other hand, our AMBER data in the CO lines reveal salient inhomogeneous structures. The visibilities and phases (closure phases, as well as differential phases representing asymmetry in lines with respect to the continuum) measured within the CO lines show that the blue and red wings originate in spatially distinct regions over the stellar disk, indicating an inhomogeneous velocity field that makes the star appear different in the blue and red wings. Our AMBER data in the CO lines can be roughly explained by a simple model, in which a patch of CO gas is moving outward or inward with velocities of 10-15 km s-1, while the CO gas in the remaining region in the atmosphere is moving in the opposite direction at the same velocities. These velocities compare favorably with the macroturbulent velocities of 10-20 km s-1 derived by spectroscopic analyses. Also, the AMBER data are consistent with the presence of warm molecular layers (so-called MOLsphere) extending to ~1.4-1.5 R* with a CO column density of ~ 1 × 1020 cm-2. However, the present data are insufficient to constrain the surface pattern uniquely or to reconstruct an image. Our AMBER observations of Betelgeuse are the first spatially resolved study of the macroturbulence in a stellar atmosphere (photosphere and possibly MOLsphere as well) other than the Sun. The spatially resolved CO gas motion is likely to be related to convective motion in the upper atmosphere or intermittent mass ejections in clumps or arcs.

Ohnaka, K.

2010-11-01

255

The discovery of nonthermal radio emission from magnetic Bp-Ap stars  

NASA Technical Reports Server (NTRS)

In a VLA survey of chemically peculiar B- and A-type stars with strong magnetic fields, five of the 34 stars observed have been identified as 6 cm continuum sources. Three of the detections are helium-strong early Bp stars (Sigma Ori E, HR 1890, and Delta Ori C), and two are helium weak, silicon-strong stars with spectral types near A0p (IQ Aur = HD 34452, Babcock's star = HD 215441). The 6 cm luminosities L6 (ergs/s Hz) range from log L6 = 16.2 to 17.9, somewhat less than the OB supergiants and W-R stars. Three-frequency observations indicate that the helium-strong Bp stars are variable nonthermal sources.

Drake, Stephen A.; Abbott, David C.; Bastian, T. S.; Bieging, J. H.; Churchwell, E.

1987-01-01

256

Gamma-Ray Bursts of First Stars  

NASA Astrophysics Data System (ADS)

We show that a relativistic gamma-ray burst (GRB) jet can potentially pierce the envelope of very massive first generation star (Population III; Pop III) by using the stellar density profile to estimate both the jet luminosity (via accretion) and its penetrability. The jet breakout is possible even if the Pop III star has a supergiant hydrogen envelope without mass loss, thanks to the long-lived powerful accretion of the envelope itself. While the Pop III GRB is estimated to be energetic E?,iso~1055 erg, the supergiant envelope hides the initial bright phase into the cocoon component, leading to a GRB with a long duration ~1000(1+z) sec and an ordinary isotropic luminosity ~1052 erg s-1 (~10-9 erg cm-2 s-1 at redshift z~20). The neutrino-annihilation is not effective for Pop III GRBs because of a low central temperature, while the magnetic mechanism is viable. We also derive analytic estimates of the breakout conditions, which are applicable to various progenitor models. The GRB luminosity and duration are found to be very sensitive to the core and envelope mass, providing possible probes of the first luminous objects at the end of the high redshift dark ages.

Suwa, Yudai; Ioka, Kunihito

2011-08-01

257

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)

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.

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

2014-04-01

258

Hydrocarbon emission features in the IR spectra of warm supergiants  

NASA Technical Reports Server (NTRS)

Observations in the 3-13 micron range are presented for two objects possessing the unidentified 21-micron feature, IRAS 22272 and IRAS 07134, which were obtained in the course of search for circumstellar aromatic hydrocarbon (PAH) emission bands. The 3.3 and 6.2 micron bands are attributed to circumstellar PAH molecules, and the 6-9 micron plateau and the 12- and 6.9-micron lines are attributed to larger, aromatic hydrocarbon clusters. These are the coolest stars known to exhibit the IR emission bands. The 21-micron feature is conjectured to also originate in a carbonaceous carrier.

Buss, R. H., Jr.; Cohen, M.; Tielens, A. G. G. M.; Werner, M. W.; Bregman, J. D.

1990-01-01

259

Models of transition regions in hybrid stars  

NASA Astrophysics Data System (ADS)

Models for the transition regions of six hybrid stars, four bright giants and two supergiants, are calculated. The models include mass loss and prescribe Alfven waves as the source of mechanical energy. The momentum and energy deposition rates required at each level of the atmosphere are evaluated. The final models for all six stars have mass loss rates lying below the current VLA upper limits by factors of two to ten, and have densities which agree with those derived by density-sensitive line ratios. The density vs. temperature structure in Alpha TrA agree well with that derived by Hartmann et al. (1985). Wave amplitudes and magnetic field strengths are derived as functions of height, and the amplitudes are found to agree well with the observed line widths in Alpha TrA.

Brosius, J. W.; Mullan, D. J.

1986-02-01

260

Models of transition regions in hybrid stars  

NASA Technical Reports Server (NTRS)

Models for the transition regions of six hybrid stars, four bright giants and two supergiants, are calculated. The models include mass loss and prescribe Alfven waves as the source of mechanical energy. The momentum and energy deposition rates required at each level of the atmosphere are evaluated. The final models for all six stars have mass loss rates lying below the current VLA upper limits by factors of two to ten, and have densities which agree with those derived by density-sensitive line ratios. The density vs. temperature structure in Alpha TrA agree well with that derived by Hartmann et al. (1985). Wave amplitudes and magnetic field strengths are derived as functions of height, and the amplitudes are found to agree well with the observed line widths in Alpha TrA.

Brosius, J. W.; Mullan, D. J.

1986-01-01

261

Evolution and appearance of Be stars in SMC clusters  

NASA Astrophysics Data System (ADS)

Star clusters are privileged laboratories for studying the evolution of massive stars (OB stars). One particularly interesting question concerns the phases during which the classical Be stars occur, which—unlike HAe/Be stars—are not pre-main-sequence objects, nor supergiants. Rather, they are extremely rapidly rotating B-type stars with a circumstellar decretion disk formed by episodic ejections of matter from the central star. To study the impact of mass, metallicity, and age on the Be phase, we observed Small Magellanic Cloud (SMC) open clusters with two different techniques: (i) with the ESO-WFI in slitless mode, which allowed us to find the brighter Be and other emission-line stars in 84 SMC open clusters, and (ii) with the VLT-FLAMES multifiber spectrograph to determine accurately the evolutionary phases of Be stars in the Be-star-rich SMC open cluster NGC 330. Based on a comparison to the Milky Way, a model of Be stellar evolution, appearance as a function of metallicity and mass, and spectral type is developed, involving the fractional critical rotation rate as a key parameter.

Martayan, C.; Baade, D.; Frémat, Y.; Zorec, J.

2010-01-01

262

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

SciTech Connect

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.

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

263

Low-amplitude rotational modulation rather than pulsations in the CoRoT B-type supergiant HD 46769  

NASA Astrophysics Data System (ADS)

Aims: We aim to detect and interpret photometric and spectroscopic variability of the bright CoRoT B-type supergiant target HD 46769 (V = 5.79). We also attempt to detect a magnetic field in the target. Methods: We analyse a 23-day oversampled CoRoT light curve after detrending and spectroscopic follow-up data using standard Fourier analysis and phase dispersion minimization methods. We determine the fundamental parameters of the star, as well as its abundances from the most prominent spectral lines. We perform a Monte Carlo analysis of spectropolarimetric data to obtain an upper limit of the polar magnetic field, assuming a dipole field. Results: In the CoRoT data, we detect a dominant period of 4.84 d with an amplitude of 87 ppm and some of its (sub-)multiples. Given the shape of the phase-folded light curve and the absence of binary motion, we interpret the dominant variability in terms of rotational modulation, with a rotation period of 9.69 d. Subtraction of the rotational modulation signal does not reveal any sign of pulsations. Our results are consistent with the absence of variability in the Hipparcos light curve. The spectroscopy leads to a projected rotational velocity of 72 ± 2 km s-1 and does not reveal periodic variability or the need to invoke macroturbulent line broadening. No signature of a magnetic field is detected in our data. A field stronger than ~500 G at the poles can be excluded, unless the possible non-detected field were more complex than dipolar. Conclusions: The absence of pulsations and macroturbulence of this evolved B-type supergiant is placed into the context of instability computations and of observed variability of evolved B-type stars. Based on CoRoT space-based photometric data; the CoRoT space mission was developed and operated by the French space agency CNES, with the participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain. Based on observations collected at La Silla Observatory, ESO (Chile) with the HARPS spectrograph at the 3.6 m telescope, under programme LP185.D-0056. Based on observations obtained with the HERMES spectrograph attached to the 1.2 m Mercator telescope, which is supported by the Fund for Scientific Research of Flanders (FWO), Belgium, the Research Council of KU Leuven, Belgium, the Fonds National de la Recherche Scientific (FNRS), Belgium, the Royal Observatory of Belgium, the Observatoire de Genève, Switzerland, and the Thüringer Landessternwarte Tautenburg, Germany. Based on observations obtained with the Narval spectropolarimeter at the Observatoire du Pic du Midi (France), which is operated by the Institut National des Sciences de l'Univers (INSU).

Aerts, C.; Simón-Díaz, S.; Catala, C.; Neiner, C.; Briquet, M.; Castro, N.; Schmid, V. S.; Scardia, M.; Rainer, M.; Poretti, E.; Pápics, P. I.; Degroote, P.; Bloemen, S.; Østensen, R. H.; Auvergne, M.; Baglin, A.; Baudin, F.; Michel, E.; Samadi, R.

2013-09-01

264

Modeling of the spectrum of Cygnus OB2 No. 7 supergiant  

NASA Astrophysics Data System (ADS)

We report the results of modeling of the spectrum of the O3 If* Cyg OB2 No. 7 supergiant in a broad wavelength range. We determine the physical properties and chemical composition of its atmosphere not assuming the presence of local thermodynamic equilibrium. The atmosphere reveals an excess of nitrogen X(N)/ X(N)? = 3.2 and the carbon and oxygen deficiency X(C)/ X(C)? = 0.08, X(O)/ X(O)? = 0.09. The lines in the stellar spectrum are divided into three groups which fail to be describedwithin a single model. Themodels describing each of these groups differ by themass-loss rate and the law of wind velocity variation. Thus, the numerical modeling suggests that the wind of the supergiant is heterogeneous. In addition, this paper describes the features of the CMFGEN code used and investigates the sensitivity of its results to the variations of different parameters.

Maryeva, O. V.; Klochkova, V. G.; Chentsov, E. L.

2013-01-01

265

MESS (Mass-loss of Evolved StarS), a Herschel key program  

NASA Astrophysics Data System (ADS)

MESS (Mass-loss of Evolved StarS) is a guaranteed time key program that uses the PACS and SPIRE instruments on board the Herschel space observatory to observe a representative sample of evolved stars, that include asymptotic giant branch (AGB) and post-AGB stars, planetary nebulae and red supergiants, as well as luminous blue variables, Wolf-Rayet stars and supernova remnants. In total, of order 150 objects are observed in imaging and about 50 objects in spectroscopy. This paper describes the target selection and target list, and the observing strategy. Key science projects are described, and illustrated using results obtained during Herschel's science demonstration phase. Aperture photometry is given for the 70 AGB and post-AGB stars observed up to October 17, 2010, which constitutes the largest single uniform database of far-IR and sub-mm fluxes for late-type stars. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices and Tables 1 and 2 are only available in electronic form at http://www.aanda.org

Groenewegen, M. A. T.; Waelkens, C.; Barlow, M. J.; Kerschbaum, F.; Garcia-Lario, P.; Cernicharo, J.; Blommaert, J. A. D. L.; Bouwman, J.; Cohen, M.; Cox, N.; Decin, L.; Exter, K.; Gear, W. K.; Gomez, H. L.; Hargrave, P. C.; Henning, Th.; Hutsemékers, D.; Ivison, R. J.; Jorissen, A.; Krause, O.; Ladjal, D.; Leeks, S. J.; Lim, T. L.; Matsuura, M.; Nazé, Y.; Olofsson, G.; Ottensamer, R.; Polehampton, E.; Posch, T.; Rauw, G.; Royer, P.; Sibthorpe, B.; Swinyard, B. M.; Ueta, T.; Vamvatira-Nakou, C.; Vandenbussche, B.; van de Steene, G. C.; van Eck, S.; van Hoof, P. A. M.; van Winckel, H.; Verdugo, E.; Wesson, R.

2011-02-01

266

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

NASA Astrophysics Data System (ADS)

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.

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

267

The Orbit and Properties of the BD+60 73 + IGRJ00370+612 Supergiant X-Ray Binary  

NASA Astrophysics Data System (ADS)

Spectrograms of the blue and H alpha regions of BD+60 73 obtained with the Cassegrain spectrograph on the David Dunlap Observatory 1.88 m telescope have been measured for radial velocities. These measures confirm that BD+60 73 is a single-line spectroscopic binary with the same period, 15.665 d, as the x-ray flux variations of IGRJ00370+612. The x-ray maxima occur at or just after the time of periastron passage, even though the eccentricity e=0.37 does not seem large enough to produce a large increase in the mass flux at the position of the compact object at the time of periastron passage. The mass function combined with a plausible range of possible masses for a neutron star companion yields primary masses within the range expected for the spectral type of BD+60 73. The compact companion cannot be a black hole unless the supergiant has an exceptionally high mass for its B1Ib spectral type or the inclination of the orbit is very low. The H alpha line shows weak, variable emission, but we have insufficient data to test whether these variations are correlated with orbital phase. We note, as have other authors, that BD+60_73 is projected on the sky within the bounds of Cas OB5. It also lies close to the "adolescent" supernova remnant CTB1. However, the binary system has a radial velocity of approximately -40 km/s with respect to Cas OB5.

Bolton, C. T.; Grunhut, J. H.

2007-08-01

268

Blue Supergiant Model for Ultra-long Gamma-Ray Burst with Superluminous-supernova-like Bump  

NASA Astrophysics Data System (ADS)

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 ~104 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.

Nakauchi, Daisuke; Kashiyama, Kazumi; Suwa, Yudai; Nakamura, Takashi

2013-11-01

269

Star Formation  

NASA Astrophysics Data System (ADS)

Stars are one of the most important constituents of the Universe, and understanding their formation is crucial to many areas of astrophysics. Stars form from dense molecular gas, and they tend not to form in isolation. Stars often form in binary and multiple systems, and these systems tend to form in clusters with 102-105 members. Stars also form with a wide range of masses, from substellar brown dwarfs with masses < 0. 1 M ? to massive stars > 100 M ?, and wherever stars form the distribution of their masses seems always to be the same. This chapter will review our current understanding of star formation from cold gas to young star clusters.

Goodwin, Simon

270

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

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

271

Evolution of surface CNO abundances in massive stars  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

272

Concerning the Wolf-Rayet and other luminous early-type stars  

NASA Technical Reports Server (NTRS)

Effective temperatures, radii, and luminosities were determined from S2/68, ANS, UBV, and uvby photometry for four B0/B1 supergiants, four O4 stars, and four WN7/WN8 stars as well as for four test stars having spectral types between B1.5 V and 09 V and five stars with known angular diameters and effective temperatures. The effective temperatures of B1 Ia+ stars are found to be near 17,000 K, those of O4 stars near 45,000, and those of WN7/WN8 stars near 26,000 K. The question of modeling the atmospheres of hot luminous stars is examined, and it is noted that the photosphere can be modeled adequately using a classical plane-parallel layer model atmosphere. In addition, it is found that the Wolf-Rayet stars of types WN7/WN8 fall in the H-R diagram near the B0 Ia stars, while the others fall near B0.5 III stars. The evolutionary relationship between the Wolf-Rayet and O stars is considered; it is suggested that a Wolf-Rayet spectrum is a short-lived phase in the life of a massive star.

Underhill, A. B.

1981-01-01

273

Surface imaging of long-period variable stars  

NASA Astrophysics Data System (ADS)

The photospheric surfaces of five long-period variables (o Cet, R Leo, W Hya, chi Cyg and R Cas) have been imaged in the optical/near-IR with the 4.2-m William Herschel Telescope. All exhibit departures from circular symmetry. Our data are consistent with the presence of bright compact features, individually contributing between 5 and 20 per cent of the total stellar flux, on most of the stars. The characteristics and behaviour of the features are similar to those reported on the surfaces of late-type supergiants. However, the data presented here are inadequate to identify a common physical origin.

Tuthill, P. G.; Haniff, C. A.; Baldwin, J. E.

1999-06-01

274

How Strong is Mass Loss from B[e] Stars?  

NASA Astrophysics Data System (ADS)

The B[e] phenomenon is defined as a combination of the presence of forbidden line emission and near-infrared excess in the spectra of B-type stars. It is observed in objects with extended gas-and-dust circumstellar envelopes at a wide range of evolutionary stages: from the pre-main-sequence to the post-AGB. The extremely strong Balmer emission lines in many, especially non-supergiant, B[e] stars may imply high mass loss rates, whose estimates are available for only a few such objects and do not agree with wind models and observational relationships published by Henny Lamers and collaborators. Here I review the existing mass loss rate determinations for B[e] stars and discuss ways to interpret the disagreement.

Miroshnichenko, A.

2008-06-01

275

Strange stars  

Microsoft Academic Search

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

Charles Alcock; Edward Farhi; Angela Olinto

1986-01-01

276

Strange stars  

NASA Technical Reports Server (NTRS)

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.

Alcock, Charles; Farhi, Edward; Olinto, Angela

1986-01-01

277

Stars and Star Myths.  

ERIC Educational Resources Information Center

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

Eason, Oliver

278

Dust clouds around red giant stars - Evidence of sublimating comet disks?  

NASA Astrophysics Data System (ADS)

The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated.

Matese, J. J.; Whitmire, D. P.; Reynolds, R. T.

1989-09-01

279

Dust clouds around red giant stars - evidence of sublimating comet disks  

SciTech Connect

The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated. 41 refs.

Matese, J.J.; Whitmire, D.P.; Reynolds, R.T. (Southwestern Louisiana Univ., Lafayette (USA); NASA, Ames Research Center, Moffett Field, CA (USA))

1989-09-01

280

Dust clouds around red giant stars - Evidence of sublimating comet disks?  

NASA Technical Reports Server (NTRS)

The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated.

Matese, John J.; Whitmire, Daniel P.; Reynolds, Ray T.

1989-01-01

281

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

282

Interferometric Constraints on Surface Brightness Asymmetries in Long-Period Variable Stars: A Threat to Accurate Gaia Parallaxes  

NASA Astrophysics Data System (ADS)

A monitoring of surface brightness asymmetries in evolved giants and supergiants is necessary to estimate the threat that they represent to accurate Gaia parallaxes. Closure-phase measurements obtained with AMBER/VISA in a 3-telescope configuration are fitted by a simple model to constrain the photocenter displacement. The results for the C-type star TX Psc show a large deviation of the photocenter displacement that could bias the Gaia parallax.

Sacuto, S.; Jorissen, A.; Cruzalèbes, P.; Pasquato, E.; Chiavassa, A.; Spang, A.; Rabbia, Y.; Chesneau, O.

2011-09-01

283

The local complex of O and B stars. I - Distribution of stars and interstellar dust  

NASA Technical Reports Server (NTRS)

The O-B5 stars, supergiants, young clusters, and associations within 1 kpc of the sun populate two flat systems inclined to each other by 19 to 22 deg. The historical background, statistical significance, composition, spatial arrangement of the contents, and interstellar extinction in the two belts are discussed. A more or less random distribution in space and in age characterizes the O-B5 stars of the 'galactic belt', which is aligned nearly along the Milky Way. The 'Gould belt' is inclined to the Milky Way (north in Sco-Oph and south in Orion), and exhibits a projected distribution of O-B5 stars in its mean plane that resembles a 'dragonfly', with five major features defining it. A crude 'diameter' of the system is 750 to 1000 pc, and the sun's position is eccentric, lying toward Ophiuchus. The nuclear age of the system, while not unique, may be characterized as 30 m.y. from the spectral type of the broad main-sequence turnup near B2-5. Most of the O-B2 stars and youngest stellar groups near the sun belong to the Gould belt, but both belts have approximately equal space densities of B3-B5 stars and similar average values of interstellar extinction.-

Stothers, R.; Frogel, J. A.

1974-01-01

284

The evolutionary stage of five southern Galactic unclassified B[e] stars  

NASA Astrophysics Data System (ADS)

The spectra of stars with the B[e] phenomenon are dominated by features that are related to physical conditions of circumstellar material around these objects and are not intrinsic to the stars. Because of this, they form a very heterogeneous group. This group contains objects with different evolutionary stages. Lamers et al. (1998) have suggested a new designation with five sub-groups, which indicate the evolutionary stage. They are: supergiants, pre-main sequence or Herbig Ae/Be, compact planetary nebulae, symbiotic and unclassified. The unclassified group has many objects that need a better study to resolve their evolutionary status. Forbidden lines can be a useful tool to solve this problem. They can give informations about chemical composition, ionization and density of the circunstellar medium and probably the evolutionary phase of these objects. We analize spectra of some galactic objects, obtained with the FEROS and B&c} spectrographs at the 1.52m telescope in ESO (La Silla-Chile), with a special focus on the forbidden lines. We have studied the spectra of five B[e] stars of uncertain evolutionary stage. We find that one of them is a pre-WN star, the other four are supergiant B[e] stars.

Borges Fernandes, Marcelo; de Araújo, Francisco X.; Lamers, H.

285

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

NASA Astrophysics Data System (ADS)

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.

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

286

Rotating `star-in-a-box' experiments  

NASA Astrophysics Data System (ADS)

Using the radiation hydrodynamics code CO5BOLD in its `star-in-a-box' setup, we have performed exploratory simulations of global convection in a rotating reference frame. The goal is to study the interaction of convection and rotation by direct numerical simulation. For these first experiments, we chose an idealized configuration (a scaled-down, fast rotating Sun) whose properties resemble those of red supergiants in some respect. We describe the setup and time evolution of these models, and discuss the particular problems we have encountered. Finally, we derive the resulting differential rotation pattern and meridional flow field by temporal and azimuthal averaging of the simulation data. We find anti-solar differential rotation for all cases studied so far. Movies are available via http://www.aip.de/AN/movies

Steffen, M.; Freytag, B.

2007-12-01

287

3-D simulations of shells around massive stars  

NASA Astrophysics Data System (ADS)

As massive stars evolve, their winds change. This causes a series of hydrodynamical interactions in the surrounding medium. Whenever a fast wind follows a slow wind phase, the fast wind sweeps up the slow wind in a shell, which can be observed as a circumstellar nebula. One of the most striking examples of such an interaction is when a massive star changes from a red supergiant into a Wolf-Rayet star. Nebulae resulting from such a transition have been observed around many Wolf-Rayet stars and show detailed, complicated structures owing to local instabilities in the swept-up shells. Shells also form in the case of massive binary stars, where the winds of two stars collide with one another. Along the collision front gas piles up, forming a shell that rotates along with the orbital motion of the binary stars. In this case the shell follows the surface along which the ram pressure of the two colliding winds is in balance. Using the MPI-AMRVAC hydrodynamics code we have made multi-dimensional simulations of these interactions in order to model the formation and evolution of these circumstellar nebulae and explore whether full 3D simulations are necessary to obtain accurate models of such nebulae.

van Marle, Allard Jan; Keppens, Rony; Meliani, Zakaria

2011-01-01

288

Wind variability in the Large Magellanic Cloud B(e) supergiant HD 34664  

NASA Technical Reports Server (NTRS)

We present optical linear spectropolarimetry of the B(e) supergiant HD 34664. The polarization and position angle display significant spectral features which correspond to the H-alpha and H-beta emission lines. We use the line polarizations to separate the interstellar foreground polarization from the intrinsic polarization of HD 34664. The intrinsic polarization is consistent with electron scattering in a circumstellar disk seen at high inclination and provides further and independent evidence for the two-component wind model of the B(e) supergiants. We compare the polarization and spectrum of HD 34664 to observations published in the literature. In our data the continuum polarization is by a factor of two larger and the H-alpha line-to-continuum ratio is by a factor of at least four increased over previous observations. Since both the polarization and the line intensity are measures of the electron density in the stellar wind, we suggest that the observed variations can be attributed to a rise in the stellar mass-loss rate.

Schulte-Ladbeck, R. E.; Clayton, G. C.

1993-01-01

289

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

NASA Astrophysics Data System (ADS)

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.

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

290

<3D> NLTE line formation in the atmospheres of red supergiants  

NASA Astrophysics Data System (ADS)

Red supergiants with their enormous brightness at J-band are ideal probes of cosmic chemical composition. It is therefore crucial to have realistic models of radiative transfer in their atmospheres, which will permit determination of abundances accurate to 0.15 dex, the precision attainable with future telescope facilities in galaxies as distant as tens of Mpc. Here, we study the effects of non-local thermodynamic equilibrium (NLTE) on the formation of iron, titanium, and silicon lines, which dominate J-band spectra of red supergiants. It is shown that the NLTE radiative transfer models enable accurate derivation of metallicity and effective temperature in the J-band. We also discuss consequences for RSG spectrum synthesis in different spectral windows, including the heavily TiO-blanketed optical region, and atmospheric structure. We then touch upon challenges of NLTE integration with new generation of 3D hydrodynamical RSG models and present the first calculations of NLTE spectra with the mean 3D model of Betelgeuse.

Bergemann, M.; Kudritzki, R. P.; Davies, B.; Plez, B.; Gazak, Z.; Chiavassa, A.

2013-05-01

291

The Stars behind the Curtain  

NASA Astrophysics Data System (ADS)

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

2010-02-01

292

STAR Publications  

Cancer.gov

STAR Publications The following citations are of reports that have been published in the scientific literature concerning the Study of Tamoxifen and Raloxifene (STAR). The citations are listed in reverse chronological order.

293

STAR System.  

ERIC Educational Resources Information Center

The STAR System is a developmental guidance approach to be used with elementary school children in the 5th or 6th grades. Two basic purposes underlie STAR: to increase learning potential and to enhance personal growth and development. STAR refers to 4 basic skills: sensory, thinking, adapting, and revising. Major components of the 4 skills are:…

Doverspike, James E.

294

Chemical compositions of 26 distant late-type supergiants and the metallicity gradient in the galactic disk  

SciTech Connect

From an analysis of high-dispersion Mount Wilson spectroscopic data, we have obtained atmospheric parameters and chemical abundances for 26 distant supergiants of spectral types G through M. Iron-to-hydrogen ratios wth respect to the Sun, (Fe/H), can be determined from this material with an uncertaintly of +- 0.2 dex.

Luck, R.E.; Bond, H.E.

1980-10-01

295

Statistical properties of rotational and extra broadening velocities for massive OB stars of solar metallicity  

NASA Astrophysics Data System (ADS)

Using own ESO-MTI/FEROS observations for 31 Galactic O-type stars, we performed a detailed quantitative analysis of these stars in terms of fundamental parameters, and rotational and extra line-broadening velocities. In practice, effective temperatures and surface gravities were determined by means of the recently updated version of the FASTWIND atmosphere code, while rotational and extra line-broadening velocities were evaluated applying a newly developed Fourier-transform + goodness-of-fit technique, assuming a radial-tangential distribution of velocities for the extra broadening. By means of the resulting data and incorporation of similar data for O-stars and B-supergiants from the literature, we investigate the properties of projected rotational and extra line-broadening velocities as a function of stellar parameters and stellar evolution, trying to put constraints on model predictions for the evolution of rotational rates of hot massive stars.

Markova, Nevena; Puls, Joachim; Simon Diaz, S.; Herrero, A.; Markov, H.

2013-06-01

296

The size, structure, and variability of late-type stars measured with mid-infrared interferometry  

NASA Astrophysics Data System (ADS)

The size and variability of the photospheres of several late-type stars has been probed using 11 mum heterodyne interferometry. High resolution observations performed during the years 1999--2001 yielded diameter measurements accurate to about 1% for a variety of stars of the supergiant and mira variable types. Using narrow bandwidths (?0.2 cm-1) to avoid spectral lines, visibilities were measured for the stars alpha Her, chi Cyg, alpha Ori, o Cet, and R Leo. On the latter three stars, observations were made at several different wavelengths, in some cases overlapping an observed spectral feature. In all cases, the 11 mum sizes are larger than previously measured visible and near-infrared diameters. The discrepancies will be addressed. In addition, a variation of the diameter of o Cet (Mira) with phase has been observed.

Weiner, Jonathon Michael

2002-12-01

297

Theoretical studies of chromospheres and winds in cool stars  

NASA Technical Reports Server (NTRS)

Calculated radiative losses from H, H-, Ca II, and Mg II show that cooling for the chromosphere of the supergiant epsilon Gem do not differ greatly from the solar law, although there are differences at approximately 6000K due to ionization effects. With a rough standard law for computation of stellar winds using the Hartmann-MacGregor theory and standard stellar evolutionary calculations, the wind velocities and temperatures in the HR diagram were systematically explored. Results show that cool winds with tempratures 1,000,00K are not possible for log g or = 2. Predicted wind velocities are approximately 1.5 to 2 x larger than observed, particularly for the most luminous cool stars. The ionization balance for the wind of alpha ORI and the hydrogen profile lines for T Tauri stars were computed using the PANDORA computer program.

Dupree, A. K.

1981-01-01

298

L'-Band Interferometric Observations of Evolved Stars  

NASA Astrophysics Data System (ADS)

Ten bright Miras, six semiregular variable giants, and two semiregular variable supergiants have been observed with the Infrared-Optical Telescope Array interferometer in the L' band (from 3.4 to 4.1 ?m). Observations were carried out in 2000 March and November with the FLUOR/TISIS instrument, using optimized single-mode waveguides for optical recombination and a dedicated chopping system for accurate subtraction of slow thermal background drifts. Four of the sources (the Mira stars R Leo and R Cnc, ? Ori, and RS Cnc) were observed in both runs. We report on visibility measurements and derive L' broadband uniform disk (UD) diameter best fits for all 18 stars in our sample. We also detect strong departures from UD models in some peculiar cases.

Chagnon, G.; Mennesson, B.; Perrin, G.; Coudé du Foresto, V.; Salomé, P.; Bordé, P.; Lacasse, M.; Traub, W.

2002-11-01

299

Evolution of massive stars in very young clusters and associations  

NASA Technical Reports Server (NTRS)

Statistics concerning the stellar content of young galactic clusters and associations which show well defined main sequence turnups have been analyzed in order to derive information about stellar evolution in high-mass galaxies. The analytical approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram together with the stars' apparent magnitudes. The new approach does not depend on absolute luminosities and requires only the most basic elements of stellar evolution theory. The following conclusions are offered on the basis of the statistical analysis: (1) O-tupe main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most O-type blue stragglers are newly formed massive stars burning core hydrogen; (3) supergiants lying redward of the main-sequence turnup are burning core helium; and most Wolf-Rayet stars are burning core helium and originally had masses greater than 30-40 solar mass. The statistics of the natural spectroscopic stars in young galactic clusters and associations are given in a table.

Stothers, R. B.

1985-01-01

300

Sharp Vision Reveals Intimacy of Stars  

NASA Astrophysics Data System (ADS)

Sharp Vision Reveals Intimacy of Stars AMBER instrument on VLTI Probes Environment of Stars Using the newly installed AMBER instrument on ESO's Very Large Telescope Interferometer, which combines the light from two or three 8.2-m Unit Telescopes thereby amounting to observe with a telescope of 40 to 90 metres in diameter, two international teams of astronomers observed with unprecedented detail the environment of two stars. One is a young, still-forming star and the new results provide useful information on the conditions leading to the creation of planets. The other is on the contrary a star entering the latest stages of its life. The astronomers found, in both cases, evidence for a surrounding disc. ESO PR Photo 36a/05 ESO PR Photo 36a/05 The Young Stellar Object MWC 297 (Artist's View) [Preview - JPEG: 400 x 502 pix - 50k] [Normal - JPEG: 800 x 1004 pix - 330k] A first group of astronomers [1], led by Fabien Malbet from the Laboratoire d'Astrophysique de Grenoble, France, studied the young 10-solar mass stellar object MWC 297, which is still in the very early stage of its life [2]. "This scientific breakthrough opens the doors to an especially detailed scrutiny of the very close environment of young stars and will bring us invaluable knowledge on how planets form", says Malbet. It is amazing to see the amount of details the astronomers could achieve while observing an object located more than 800 light-years away and hidden by a large amount of gas and dust. They found the object to be surrounded by a proto-planetary disc extending to about the size of our Solar System, but truncated in his inner part until about half the distance between the Earth and the Sun. Moreover, the scientists found the object to be surrounded by an outflowing wind, the velocity of which increased by a factor 9, from about 70 km/s near the disc to 600 km/s in the polar regions [3]. "The reason why the inner part of the disc should be truncated is not clear", adds Malbet. "This raises new questions on the physics of the environment of intermediate mass young stars." The astronomers now plan to perform observations with AMBER [4] with three telescopes to measure departure from symmetry of the material around MWC 297. ESO PR Photo 36b/05 ESO PR Photo 36b/05 The B[e] Supergiant CPD -57o2874 (Artist's View) [Preview - JPEG: 400 x 502 pix - 50k] [Normal - JPEG: 800 x 1004 pix - 330k] Another international team of astronomers [5] has just done this kind of observations to study the surroundings of a star entering the last stages of its life. In a world premiere, they combined with AMBER the light of three 8.2-m Unit Telescopes of the VLT, gaining unsurpassed knowledge on a B[e] supergiant, a star that is more luminous than our Sun by more than a factor 10,000. This supergiant star is located ten times further away than MCW 297 at more than 8,000 light-years. The astronomers made the observations to investigate the crucial questions concerning the origin, geometry, and physical structure of the envelope surrounding the star. These unique observations have allowed the scientists to see structures on scale as small as 1.8 thousandths of an arcsecond - that is the same as distinguishing between the headlights of a car from about 230,000 km away, or slightly less than 2/3 of the distance from the Earth to the Moon! Armando Domiciano de Souza, from the MPI für Radioastronomie in Bonn (Germany) and his colleagues made also use of the MIDI instrument on the VLTI [6], using two Unit Telescopes. Using their full dataset, they found the circumstellar envelope around the supergiant to be non-spherical, most probably because the star is also surrounded by an equatorial disc made of hot dust and a strong polar wind. "These observations are really opening the doors for a new era of understanding of these complex and intriguing objects", says Domiciano de Souza. "Such results could be achieved only due to the spectral resolution as well as spatial resolution that AMBER offers. There isn't any similar instrument in the w

2005-11-01

301

Rb-Rich Asymptotic Giant Branch Stars in the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

We present high-resolution (R ~ 60,000) optical spectra of a carefully selected sample of heavily obscured and presumably massive O-rich asymptotic giant branch (AGB) stars in the Magellanic Clouds. We report the discovery of strong Rb I lines at 7800 Å in four Rb-rich LMC stars at luminosities equal to or greater than the standard adopted luminosity limit for AGB stars (M bol ~ -7.1), confirming that "hot bottom burning" may produce a flux excess in the more massive AGB stars. In the SMC sample, just one of the five stars with M bol < -7.1 was detected in Rb; the other stars may be massive red supergiants. The Rb-rich LMC AGB stars might have stellar masses of at least ~6-7 M sun. Our abundance analyses show that these Rb-rich stars are extremely enriched in Rb by up to 103-105 times solar but seem to have only mild Zr enhancements. The high Rb/Zr ratios, if real, represent a severe problem for the s-process, even if the 22Ne source is operational as expected for massive AGB stars; it is not possible to synthesize copious amounts of Rb without also overproducing Zr. The solution to the problem may lie with an incomplete present understanding of the atmospheres of luminous AGB stars.

García-Hernández, D. A.; Manchado, A.; Lambert, D. L.; Plez, B.; García-Lario, P.; D'Antona, F.; Lugaro, M.; Karakas, A. I.; van Raai, M. A.

2009-11-01

302

Rb-RICH ASYMPTOTIC GIANT BRANCH STARS IN THE MAGELLANIC CLOUDS  

SciTech Connect

We present high-resolution (R approx 60,000) optical spectra of a carefully selected sample of heavily obscured and presumably massive O-rich asymptotic giant branch (AGB) stars in the Magellanic Clouds. We report the discovery of strong Rb I lines at 7800 A in four Rb-rich LMC stars at luminosities equal to or greater than the standard adopted luminosity limit for AGB stars (M{sub bol} approx -7.1), confirming that 'hot bottom burning' may produce a flux excess in the more massive AGB stars. In the SMC sample, just one of the five stars with M{sub bol} < -7.1 was detected in Rb; the other stars may be massive red supergiants. The Rb-rich LMC AGB stars might have stellar masses of at least approx6-7 M{sub sun}. Our abundance analyses show that these Rb-rich stars are extremely enriched in Rb by up to 10{sup 3}-10{sup 5} times solar but seem to have only mild Zr enhancements. The high Rb/Zr ratios, if real, represent a severe problem for the s-process, even if the {sup 22}Ne source is operational as expected for massive AGB stars; it is not possible to synthesize copious amounts of Rb without also overproducing Zr. The solution to the problem may lie with an incomplete present understanding of the atmospheres of luminous AGB stars.

GarcIa-Hernandez, D. A.; Manchado, A. [Instituto de Astrofisica de Canarias, C/Via Lactea s/n, 38200 La Laguna (Spain); Lambert, D. L. [W. J. McDonald Observatory, University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States); Plez, B. [GRAAL, Universite Montpellier 2, CNRS, Montpellier (France); GarcIa-Lario, P. [Herschel Science Centre, European Space Astronomy Centre, Research and Scientific Support Department of ESA, Villafranca del Castillo, P.O. Box 50727, E-28080 Madrid (Spain); D'Antona, F. [INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Roma (Italy); Lugaro, M. [Centre for Stellar and Planetary Astrophysics, Monash University, Clayton 3800, Victoria (Australia); Karakas, A. I. [Research School of Astronomy and Astrophysics, Mt. Stromlo Observatory, Weston Creek ACT 2611 (Australia); Van Raai, M. A., E-mail: agarcia@iac.e, E-mail: amt@iac.e, E-mail: dll@astro.as.utexas.ed, E-mail: bertrand.plez@graal.univ-montp2.f, E-mail: Pedro.Garcia-Lario@sciops.esa.in, E-mail: dantona@mporzio.astro.i, E-mail: Maria.Lugaro@sci.monash.edu.a, E-mail: akarakas@mso.anu.edu.a, E-mail: M.A.vanRaai@students.uu.n [Sterrenkundig Instituut, University of Utrecht, Postbus 80000, 3508 TA Utrecht (Netherlands)

2009-11-01

303

Limits on core-driven ILOT outbursts of asymptotic giant branch stars  

NASA Astrophysics Data System (ADS)

We find that single-star mechanisms for Intermediate-Luminosity Optical Transients (ILOTs; red transients; red novae), which are powered by energy release in the core of asymptotic giant branch (AGB) stars are likely to eject the entire envelope, and hence cannot explain ILOTs in AGB and similar stars. There are single-star and binary models for the powering of ILOTs, which are eruptive stars with peak luminosities between those of novae and supernovae. In single-star models, the ejection of gas at velocities of ˜500-1000 km s-1 and a possible bright ionizing flash require a shock to propagate from the core outwards. Using a self-similar solution to follow the propagation of the shock through the envelope of two evolved stellar models, a 6 M? AGB star and an 11 M? yellow supergiant (YSG) star, we find that the shock that is required to explain the observed mass-loss also ejects most of the envelope. We also show that for the event to have a strong ionizing flash the required energy expels most of the envelope. The removal of most of the envelope is in contradiction with observations. We conclude that single-star models for ILOTs of evolved giant stars encounter severe difficulties.

Mcley, Liron; Soker, Noam

2014-05-01

304

NUCLEOSYNTHESIS AND EVOLUTION OF MASSIVE METAL-FREE STARS  

SciTech Connect

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.

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

305

Nucleosynthesis and Evolution of Massive Metal-free Stars  

NASA Astrophysics Data System (ADS)

The evolution and explosion of metal-free stars with masses 10-100 M sun are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. Such stars would have been the first to form after the big bang and may have left a distinctive imprint on the composition of the early universe. When the supernova yields are integrated over a Salpeter initial mass function (IMF), the resulting elemental abundance pattern is qualitatively solar, but with marked deficiencies of odd-Z elements with 7 <= Z <= 13. Neglecting the contribution of the neutrino wind from the neutron stars that they form, no appreciable abundances are made for elements heavier than germanium. The computed pattern compares favorably with what has been observed in metal-deficient stars with [Z] <~ -3. The amount of ionizing radiation from this generation of stars is ~2.16 MeV per baryon (4.15 B per M sun; where 1 B = 1 Bethe = 1051 erg) for a Salpeter IMF, and may have played a role in reionizing the universe. Neglecting rotation, most of the stars end their lives as blue supergiants and form supernovae with distinctive light curves resembling SN 1987A, but some produce primary nitrogen due to dredge-up and become red supergiants. These make brighter supernovae like typical Type IIp's. For the lower mass supernovae considered, the distribution of remnant masses clusters around typical modern neutron star masses, but above 20-30 M sun, with the value depending on explosion energy, black holes are copiously formed by fallback, with a maximum hole mass of ~40 M sun. A novel automated fitting algorithm is developed for determining optimal combinations of explosion energy, mixing, and IMF in the large model database to agree with specified data sets. The model is applied to the low-metallicity sample of Cayrel et al. and the two ultra-iron-poor stars HE0107-5240 and HE1327-2326. Best agreement with these very low metallicity stars is achieved with very little mixing, and none of the metal-deficient data sets considered show the need for a high-energy explosion component. In contrast, explosion energies somewhat less than 1.2 B seem to be preferred in most cases.

Heger, Alexander; Woosley, S. E.

2010-11-01

306

IUE observations of HR 6902 - Effect of luminosity on supergiant chromospheres  

NASA Technical Reports Server (NTRS)

IUE observations of the most recently discovered Zeta Aurigae system, HR 6902, are reported to reveal profound differences in the spectrum of the chromosphere of the cool primary from those of all other Zeta Aurigae systems. Unlike its sister systems, HR 6902 shows evidence of neither strong wind nor an extended chromosphere for the cool primary. Instead, the spectrum is like that of a single blue dwarf. The most likely reason for this contrast to all other Zeta Aur systems observed with IUE is the lower luminosity of the HR 6902 primary: a type-II 'bright giant' as opposed to the type I (or Ib-II in the case of 22 Vul) 'supergiants' in the other Zeta Aur systems.

Ahmad, Imad A.

1990-01-01

307

Carbon and nitrogen abundances in the supergiants HD 93840 and zeta Per  

NASA Technical Reports Server (NTRS)

The BN supergiant HD 93840 is shown to have the same temperature and surface gravity as the normal Bi Ib zeta Per. Differential abundance analysis of their C 4 and N 5 wind line profiles are found. The results are independent of the usual model atmosphere analyses and, therefore, a valuable check on them. Ratios for the C and N surface abundances in HD 93840 compared to Per of 1:10 and 4.6:1 are found respectively. By introducing a simple model for the compositions of both atmospheres the fraction of material in each atmosphere which has undergone CNO processing, more than 90 percent for HD 93840 and less than about 15 percent for zeta Per, is derived.

Massa, Derck; Altner, Bruce; Wynne, David; Lamers, H. J. G. L. M.

1990-01-01

308

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

NASA Astrophysics Data System (ADS)

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.

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

2013-11-01

309

Superorbital Periods in Supergiant High-Mass X-ray Binaries  

NASA Astrophysics Data System (ADS)

Using data from the Swift Burst Alert Telescope (BAT) we discovered superorbital periods in four high-mass X-ray binaries accreting from the winds of supergiant primaries: 4U 1909+07 (= X 1908+075), IGR J16418-4532, IGR J16479-4514 and IGR J16493-4348. Together with a previously known superorbital period in 2S 0114+650, the systems show a surprising monotonic relationship between superorbital and orbital periods. We report on a continuing investigation of the superorbital modulation and searches for new superorbital periods including candidate superorbital modulation in IGR J16393-4643 (= AX J16390.4-4642) and 1E 1145.1-6141.

Corbet, Robin; Krimm, Hans A.

2014-08-01

310

Stationary Star  

NSDL National Science Digital Library

This is an activity about star movement due to the Earth's rotation. Learners will utilize the Sky Tonight online program to find the star that appears stationary in our night sky. They will then draw conclusions about the Earthâs rotation based on the position changes of certain stars. This activity requires the use of a computer with Internet access. This activity is Sky Tonight Activity 2 in a larger resource, Space Update.

311

Neutron Stars  

NASA Technical Reports Server (NTRS)

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.

Cottam, J.

2007-01-01

312

Properties of the molecular gas around the most massive evolved stars  

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

313

Star Images, Star Performances (College Course File).  

ERIC Educational Resources Information Center

Describes a course that focuses attention on the position of the actor, especially the star actor, in cinematic and television signification. Divides the course into three sections: "The Star System,""Stars as Images," and "Star Performance." (RS)

Butler, Jeremy G.

1990-01-01

314

Observations of recently recognized candidate Herbig Ae/Be stars  

NASA Astrophysics Data System (ADS)

The results of multicolor photometric and low-resolution spectroscopic observations of 9 Herbig Ae/Be candidate stars are reported. This sample includes two newly recognized objects, MQ Cas and BD+11degr829 , which were found by means of cross-correlation of the IRAS Point Source Catalogue and the catalogue of the galactic early-type emission-line stars (Wackerling \\cite{wack}). Near-IR excesses were detected in two stars (AS 116 and BD+11degr829 ) for the first time. Algol-type variability, which is not common in Herbig Ae/Be stars, was detected in MQ Cas and V1012 Ori. Spectral types are determined for MQ Cas, GSC 1811-0767, HDE 244604, BD+11degr829 , V1012 Ori, AS116, AS117, and HDE 290380 from low-resolution spectroscopy. Analysis of our and previously published data suggests that 8 of the 9 objects are pre-main-sequence stars, while the last one, Hen 938, is more likely a B[e] supergiant. Based on observations collected at the Astrophysical National Laboratory (LNA -- Brazil), the South--African Astronomical Observatory, the Dark Sky Observatory (USA), and the Tien--Shan Observatory (Kazakhstan)

Miroshnichenko, A. S.; Gray, R. O.; Vieira, S. L. A.; Kuratov, K. S.; Bergner, Yu. K.

1999-07-01

315

Evolution of chemical abundances in massive stars. I - OB stars, Hubble-Sandage variables and Wolf-Rayet stars - Changes at stellar surfaces and galactic enrichment by stellar winds. II - Abundance anomalies in Wolf-Rayet stars in relation with cosmic rays and 22/Ne in meteorites  

NASA Astrophysics Data System (ADS)

Evolutionary models with mass loss and a detailed study of changes in the abundances of 1H, 3He, 4He, 12C, 13C, 14N, 15N, 16O, 17O, 18O, 20Ne, 22Ne, 25Mg, and 26Mg are made for initial stellar masses of 120, 85, and 60 Msun. The evolution has been followed through stages corresponding to OB stars, blue super- giants, Hubble-Sandage variables and various Wolf-Rayet stages (WNL, WNE, WC, WO). The evolutionary status of the Hubble-Sandage variables is examined. In the case of ? Car, the C/N and 0/N ratios observed by Davidson et al. (1982) agree remarkably well with the theoretical abundance ratios for a massive post-main sequence supergiant having experienced strong mass loss. The origin of the variability of the Hubble-Sandage variables is discussed in relation with the instability limit (de Jager's limit) for deep turbulent external convective zones in supergiants. This limit may also be responsible for the fact that the brightest red supergiants are 2 mag fainter in Mbol than the brightest OB stars. A theoretical mass-luminosity relation is found for the blue, non-degenerate stellar cores left after the loss of the envelopes by stellar winds and which are likely to correspond to WR stars. Due to the removal of the outer layers by mass loss, matter produced by the CNO tri-cycle is revealed at stellar surfaces in OB stars, supergiants and WN stars. 3He, 15N, 18O disappear. The C/N ratio suddenly changes from about 4.1 to 0.03 (in mass), and 0/N from 9.1 to less than 0.1. 13C keeps a factor of 3.3 lower than 12C. The abundance of 17O strongly rises and becomes nearly equal to that of 16O. A very large discontinuity (whose physical origin is explained) marks the appearance of the various products of He-burning at the surface, what is likely to correspond to the beginning of the WC stage. We note then a very steep disappearance of 13C and 14N, a very temporary peak of 18O, and above all a vertiginous rise by more than 2 orders of magnitude of 12C, 16O, and 22Ne. The abundances of 25Mg and 26Mg also rise strongly, particularly in the most massive WC stars, where s-elements are therefore to be expected. Comparisons are made between the theoretical C/He, N/He, and C/N ratios and those observed by Smith and Willis (1982) and by Nugis (1982) for WNL, WNE, and WC stars. The general agreement strongly supports the advanced evolutionary stage of WR stars as left-over cores resulting from the peeling of massive stars by stellar winds. If confirmed, the presence of 14N in WC stars may bring some indication on mixing. Observations of other interesting elements are desirable. The contributions of the winds of WR star to the galactic enrichment in various elements and isotopes is estimated. The main part of the 22Ne in the Galaxy probably results from the winds of WC stars, which also strongly contribute to the galactic enrichment in 4He and 12C and moderately to those in 26Mg, 25Mg, and 16O. WN stars are likely to be major contributors to the 17O-enrichment with a modest yield in 14N.

Maeder, A.

1983-04-01

316

The Wind of the B[e] Supergiant Henize S22 Viewed through a Reflection Nebula in DEM L106  

Microsoft Academic Search

Narrowband HST WFPC2 images reveal a bow-shock-like halo around the H II region N30B toward the B[e] supergiant Hen S22 located within the larger DEM L106 nebula in the Large Magellanic Cloud. High-dispersion spectra of N30B show a narrow Halpha emission component from the ionized gas; the velocity variations indicate a gas flow of -5 to -10 km s-1 in

You-Hua Chu; C.-H. Rosie Chen; Charles Danforth; Bryan C. Dunne; Robert A. Gruendl; Yaël Nazé; M. S. Oey

2003-01-01

317

Distance and proper motion measurement of the Red Supergiant, S Persei, with VLBI H2O Maser astrometry  

Microsoft Academic Search

We have conducted Very Long Baseline Array phase-referencing monitoring of H2O 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

Y. Asaki; S. Deguchi; H. Imai; K. Hachisuka; M. Miyoshi; M. Honma

2010-01-01

318

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

NASA Astrophysics Data System (ADS)

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.

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

319

LUMINOUS SUPERNOVA-LIKE UV/OPTICAL/INFRARED TRANSIENTS ASSOCIATED WITH ULTRA-LONG GAMMA-RAY BURSTS FROM METAL-POOR BLUE SUPERGIANTS  

SciTech Connect

Metal-poor massive stars typically end their lives as blue supergiants (BSGs). Gamma-ray bursts (GRBs) from such progenitors could have an ultra-long duration of relativistic jets. For example, Population III (Pop III) GRBs at z {approx} 10-20 might be observable as X-ray-rich events with a typical duration of T{sub 90} {approx} 10{sup 4}(1 + z) s. The recent GRB111209A at z = 0.677 has an ultra-long duration of T{sub 90} {approx} 2.5 Multiplication-Sign 10{sup 4} s and it has been suggested that its progenitor might have been a metal-poor BSG in the local universe. Here, we suggest that luminous UV/optical/infrared emission is associated with this new class of GRBs from metal-poor BSGs. Before the jet head breaks out of the progenitor envelope, the energy injected by the jet is stored in a hot plasma cocoon, which finally emerges and expands as a baryon-loaded fireball. We show that the photospheric emissions from the cocoon fireball could be intrinsically very bright (L{sub peak} {approx} 10{sup 42}-10{sup 44} erg s{sup -1}) in UV/optical bands ({epsilon}{sub peak} {approx} 10 eV) with a typical duration of {approx}100 days in the rest frame. Such cocoon emissions from Pop III GRBs might be detectable in infrared bands at {approx}years after Pop III GRBs at up to z {approx} 15 by upcoming facilities such as the James Webb Space Telescope. We also suggest that GRB111209A might have been rebrightening in UV/optical bands up to an AB magnitude of {approx}< 26. The cocoon emission from local metal-poor BSGs might have been observed previously as luminous supernovae without GRBs since they can be seen from the off-axis direction of the jet.

Kashiyama, Kazumi; Yajima, Hidenobu [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Nakauchi, Daisuke; Nakamura, Takashi [Department of Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan); Suwa, Yudai, E-mail: kzk15@psu.edu [Yukawa Institute for Theoretical Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan)

2013-06-10

320

Modeling populations of rotationally mixed massive stars  

NASA Astrophysics Data System (ADS)

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

Brott, I.

2011-02-01

321

HST/GHRS Spectroscopy of the Hybrid Star Alpha Aquarii  

NASA Astrophysics Data System (ADS)

GHRS observations were made in July 1993 of the luminous hybrid supergiant Alpha Aqr (HD 209750, G2 Ib). This cool supergiant gives evidence for both high temperature emission from N V and C IV (T= 2 times 10(5) K) and a massive wind. In addition, the He I lambda 10830 transition indicates supersonic wind velocities in the chromosphere. To identify the emitting regions, and determine the profile of wind acceleration, we obtained moderate resolution (G160 M) observations and wavelength calibration exposures at four grating positions centered on He II (lambda 1640), C II (lambda 1335), C IV (lambda 1550), and N V (lambda 1240). All four species were detected. The IUE obtained simultaneous ultraviolet spectra including profiles of Mg II (lambda 2800). The C IV and N V lines appear blue-shifted (~ 30 km\\ s(-1) ), and broad, with FWHM ranging from 125 to 180 km\\ s(-1) , similar to those found previously in alpha TrA, another hybrid star, and interpreted as arising from wind expansion. Hydrostatic and dynamic atmospheric models are calculated with and spherical geometry in order to interpret the observed line profiles.

Dupree, A. K.; Sasselov, D. D.; Keener, S. R.

1993-12-01

322

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

323

Radial velocities of late-type stars in the galactic center  

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

324

Magnetic fields around late-type stars using H_2O maser observations  

NASA Astrophysics Data System (ADS)

We present the analysis of the circular polarization, due to Zeeman splitting, of the H_2O masers around a sample of late-type stars to determine the magnetic fields in their circumstellar envelopes (CSEs). The magnetic field strengths in the H_2O maser regions around the Mira variable stars U Ori and U Her are shown to be several Gauss while those of the supergiants S Per, NML Cyg and VY CMa are several hundred mG. We also show that large scale magnetic fields permeate the CSE of an evolved star; the polarization of the H_2O masers around VX Sgr reveals a dipole field structure. We shortly discuss the coupling of the magnetic field with the stellar outflow, as such fields could possibly be the cause of distinctly aspherical mass-loss and the resulting aspherical planetary nebulae.

Vlemmings, W. H. T.; van Langevelde, H. J.; Diamond, P. J.

325

A WISE Look at Evolved Massive Stars and Their Environments  

NASA Astrophysics Data System (ADS)

Massive stars play a key role in the chemical and mechanical evolution of the ISM in galaxies. These luminous stars with their strong winds and mass outflows are the dominating influence on their environment in terms of energetics and chemical modification of the ISM. Despite their importance, our knowledge about their formation and evolution is surprisingly limited. In particular, the post main sequence evolution of massive stars, where they shed most of their mass, is poorly understand. Observationally, this stage can be explored through the study of Wolf-Rayet stars (WRs), luminous blue variables (LBVs) and red supergiants (RSGs). Recently, a large population of obscured evolved massive stars has been revealed by observations with the Spitzer Space Telescope through their prominent circumstellar shells at 24 micron, highlighting that the mid-IR is especially suited to the study of these objects. WISE will for the first time enable an unbiased, comprehensive, and homogeneous look at the known population of evolved massive stars at these wavelengths. We will present WISE photometry and images for evolved massive stars and their environments. As part of this effort, we have already discovered a previously unknown shell around WR 8 at 22 micron. We will provide an overview of the mid-IR morphology of such nebulae for all known WRs and LBVs and a comparison to their optical properties. We will also explore the photometric characteristics of evolved massive stars in the WISE bands. 2MASS and Spitzer data have been used to identify the missing population of highly obscured WRs in the Galaxy. We will define equivalent color criteria for the WISE bands to support similar search efforts with the WISE archive.

Wachter, Stefanie; Cohen, M.; Leisawitz, D.

2011-01-01

326

Abundance analysis of post-AGB stars  

NASA Astrophysics Data System (ADS)

Using BD+46 442 as an example, we describe our analysis of the spectra of post-AGB stars (SpTs F-K, luminosity types I-II, [Fe/H]=-2.0...+0.5), obtained with the échelle spectrograph HERMES on the 1.2 m Mercator telescope. We obtain atmospheric parameters and atomic abundances using hydrogen line profiles and equivalent widths (EW) of weak metal lines. Our oscillator strengths and solar abundances for the majority of elements have been consistently adjusted to match the observed solar spectrum. The EW analysis is performed using F. Castelli's modified ATLAS9 photospheric models and C. Sneden's radiative transfer code MOOG. The resulting abundances are compared to those obtained by using the original R. Kurucz's ATLAS9 models and the WIDTH9 code. The outlined procedure can be employed for the spectroscopic analysis of the high-resolution spectra of warm (super-)giant stars in ground-based follow-up programs of Gaia.

Gorlova, Nadya

2011-12-01

327

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

SciTech Connect

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.

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

328

VLT-FLAMES Tarantula Survey. 30 Dor luminous stars (Doran+, 2013)  

NASA Astrophysics Data System (ADS)

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).

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

329

A search for far-infrared (IRAS) emission from early-type stars at high Galactic latitudes  

NASA Astrophysics Data System (ADS)

Recently Lamers et al. (1986) have found that HR 4049 (B supergiant at z = 1300 pc) is surrounded by a dust cloud which produces a large IR excess, from which it is inferred that the star may be a much less luminous low mass object close to the Galactic plane. Here, the results of a search for strong FIR (IRAS) emission from a sample of early-type high-Galactic-latitude stars, estimated to be at z-distances of up to 9000 pc from optical spectral analyses, are reported. No IR emission was detected for any of the stars investigated, which would not be expected if they were nearby objects with dust clouds. It is therefore concluded that they are normal stars at the large distances previously estimated.

Keenan, F. P.; Conlon, E. S.; Brown, P. J. F.

1987-05-01

330

Evidence for chromospheres and coronae in stars - Recent observations, some unanswered theoretical questions, and a speculative scenario  

NASA Technical Reports Server (NTRS)

The paper discusses recent UV and X-ray evidence for the existence of solar-type chromospheres, transition regions and coronae in stars other than the sun. The stellar spectral types associated with emission lines indicative of chromospheres and transition regions and X-ray fluxes indicative of coronae are examined, and the possibility of chromospheres and transition regions existing in stars hotter or cooler than the late-type stars is considered. The stellar parameters determining the properties of stellar chromospheres, transition regions and coronae are discussed, including varying magnetic fields, stellar rotation and convection zone parameters. A speculative scenario for the source of chromospheres, transition regions and coronae in O, B and A stars, late-type dwarfs, and G-M giants and supergiants is then presented which is based on the predominant role of magnetic fields in the nonradiative heating of outer atmospheres.

Linsky, J. L.

1981-01-01

331

Neutron stars  

NASA Astrophysics Data System (ADS)

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.

Lattimer, James M.

2014-05-01

332

FEROS Finds a Strange Star  

NASA Astrophysics Data System (ADS)

New Spectrograph Explores the Skies from La Silla While a major effort is now spent on the Very Large Telescope and its advanced instruments at Paranal, ESO is also continuing to operate and upgrade the extensive research facilities at La Silla, its other observatory site. ESO PR Photo 03a/99 ESO PR Photo 03a/99 [Preview - JPEG: 800 x 1212 pix - 606k] [High-Res - JPEG: 1981 x 3000 pix - 3.6M] Caption to PR Photo 03a/99 : This photo shows the ESO 1.52-m telescope, installed since almost 30 years in its dome at the La Silla observatory in the southern Atacama desert. The new FEROS spectrograph is placed in an adjacent, thermally and humidity controlled room in the telescope building (where a classical coudé spectrograph was formerly located). The light is guided from the telescope to the spectrograph by 14-m long optical fibres. Within this programme, a new and powerful spectrograph, known as the Fibre-fed Extended Range Optical Spectrograph (FEROS) , has recently been built by a consortium of European institutes. It was commissioned in late 1998 at the ESO 1.52-m telescope by a small team of astronomers and engineers and has already produced the first, interesting scientific results. FEROS is able to record spectra of comparatively faint stars. For instance, it may be used to measure the chemical composition of stars similar to our Sun at distances of up to about 2,500 light-years, or to study motions in the atmospheres of supergiant stars in the Magellanic Clouds. These satellite galaxies to the Milky Way are more than 150,000 light-years away and can only be observed with telescopes located in the southern hemisphere. First FEROS observations uncover an unusual star ESO PR Photo 03b/99 ESO PR Photo 03b/99 [Preview - JPEG: 800 x 958 pix - 390k] [High-Res - JPEG: 3000 x 3594 pix - 1.7M] Caption to PR Photo 03b/99 : This diagramme shows the spectrum of the Lithium rich giant star S50 in the open stellar cluster Be21 , compared to that of a normal giant star ( S156 ) in the same cluster. The comparatively strong absorption line at the centre, at wavelength 6708 Å (671 nm), is caused by Lithium atoms (Li I) in the upper layers of the star's atmosphere. Lines from Iron (Fe I) and Calcium (Ca I) atoms are also present in this spectral region. While they are of about equal strength in the two stars, the Lithium line is not seen in the comparison spectrum of S156 . Stellar evolution theories do not predict the presence of Lithium in a giant star like S50 . Technical information: FEROS obtained two spectra (each of 90 min exposure) of S50 , both showing this strong Lithium line and thus proving that it cannot have been caused by an instrumental effect. These spectra also illustrate the great amount of information that may be obtained in each exposure with FEROS - the shown spectral interval is just 1/280 of the total range recorded. The (visual) magnitude of S50 is 15.6, i.e., about 7,000 times fainter than what can be seen with the unaided eye. During the first tests of FEROS at the 1.52-m telescope, spectra were obtained of many different stars. Some of these observational data could be used for scientific purposes and, in one case, led to the discovery of unusual properties of a giant star in a stellar cluster. Its spectrum shows an unexplained large amount of the cosmologically important, light element Lithium, cf. PR Photo 03b/99 . The star is thus an obvious object for further, even more detailed studies with ESO's Very Large Telescope (VLT). This giant star, designated as S50 , is a member of the open-type stellar cluster Be21 (less dense than globular clusters). This cluster is of special interest, since its stars contain few elements heavier than hydrogen and helium. It is located in the direction opposite to the Galactic Center and the distance has been measured as approximately 16,000 light-years. All of its stars were formed at the same time, about 2,000 - 2,500 million years ago; this corresponds to half of the age of the Solar System. The study of stars in this cluster provides important information about the chem

1999-02-01

333

Eclipse Mapping of the Chromopsheric and Transition Region Structure of the Hybrid Chromosphere Star HR2554 (G6 Ii)  

NASA Astrophysics Data System (ADS)

We propose to observe an eclipse of the Zeta Aurigae-type binary HR2554 using the GHRS. Every 195 days the A1 dwarf secondary passes behind the outer atmosphere of the G6 II primary and can be used as light source to observe absorption lines from plasma in the G star atmopshere. The G star has a hybrid-chromosphere structure with hot transition region plasma and a cool stellar wind. THESE OBSERVATIONS WOULD BE THE FIRST ECLIPSE OBSRRVATIONS OF THIS TYPE OF ATMOSPHERE WITH GHRS AND COMPARED WITH OUR RESULTS FOR THE K4 SUPERGIANT Zeta Aur, which shows only the typical red supergiant wind. We shall model the observed line profiles and determine the temperature structure, density stratification, wind acceleration/turbulence/ionization as a function of distance above the G star photosphere. The hot and cool plasma are intermixed in this outer atmosphere and we will quantify this "thermal bifurcation". Both the static and outflowing components of the atmopshere will be modelled. The mass loss rate and the wind velocity and density laws as a function of radius will be determined. The vast majority of the needed modelling code will have been developed already for our Zeta Aur analysis. This project represents an opportunity to significantly advance knowledge about the spatial structuring of cool star outer atmospheres and the physical process operating within them.

Brown, Alexander

1994-07-01

334

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

335

O, B and Be stars equivalent widths (Lenorzer+, 2002)  

NASA Astrophysics Data System (ADS)

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 (1973ARA&A..11...29M) classification scheme into the near-infrared. Later type stars will be discussed in a separate publication. The observations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1{mu}m, supplemented with 10 spectra acquired during the nominal mission with a similar observational setting. For B-type stars, this sample provides ample spectral coverage 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 Br{alpha}, Pf{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{mu}m interval that allow the determination of i) the spectral type of B dwarfs and giants to within two subtypes; ii) the luminosity class of B stars to within two classes; iii) the mass-loss rate of O stars and B supergiants to within 0.25dex. (4 data files).

Lenorzer, A.; Vandenbussche, B.; Morris, P.; de Koter, A.; Geballe, T.; Waters, L. B. F. M.; Hony, S.; Kaper, L.

2002-01-01

336

Asteroseismology of massive stars with the MOST satellite  

NASA Astrophysics Data System (ADS)

Since 2003 the MOST (Microvariability and Oscillations of STars) microsatellite has obtained typically a month of non-stop, minute-of-time resolution, high-precision, single-broadband optical photometry for each of a significant number of Galactic OB and WR stars. Numerous p- and g-modes were clearly detected in several OB stars, including discovery of g-modes for the first time in a blue supergiant (Saio et al. 2006). True rotation periods were found for some SPBe pulsators (Cameron et al. 2008). Many O stars are remarkably quiet. Five presumably single WR stars have been observed so far, each interesting in its own way. In particular, the cool WR stars WR123 (WN8) and WR103 (WC9d) both show mostly short-lived, multimode oscillations with most of the Fourier power occurring on a day or longer timescale (Moffat et al. 2008a). WR123 also revealed a fairly stable 10-hour periodicity (Lefèvre et al. 2005). All of these oscillations probably arise in the stellar cores. WR111 (WC5) shows no (coherent) oscillations above the detection limit of 0.05 mmag in the 10-minute period range predicted for strange-mode pulsations at a level of 2 mmag (Moffat et al. 2008b). WR110 (WN5-6 and a stronger-than-average X-ray source) and WR124 (WN8h, i.e. in contrast with the previously observed, hydrogen-free WR123 of otherwise similar subtype), both strongly variable with MOST, are currently being analyzed. The next target just observed (late-June to early Aug 2009) is the 30-day eclipsing binary CV Ser = WR113 (WC8d + O8-9IV). Besides stellar oscillations, we will also search for orbital-phase dependent, stochastic variability in CV Ser as wind clumps in the WR component's dense wind pass in front of the O-star.

Moffat, Anthony F. J.

2010-11-01

337

Symbiotic stars  

NASA Technical Reports Server (NTRS)

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

Kafatos, M.; Michalitsianos, A. G.

1984-01-01

338

Infrared spectra of evolved stars with unusual dust shells  

NASA Astrophysics Data System (ADS)

New mid-infrared spectra are presented of a number of oxygen-rich evolved stars which have IRAS LRS (Low Resolution Spectrometer) spectra that were classified as showing SiC emission. Two of the sources, IRC-20445 and IRC-20461, show the unidentified infrared (UIR) bands superposed on silicate emission features. Both objects have been classified as M supergiants. Several other sources show three-component spectra, with peaks at 10, 11 and 13?m. The 13-?m source FI Lyr shows a narrow emission feature at 19?m. Emission by oxide grains may be responsible for the 11-, 13- and 19-?m features. One object, IRC-20455, shows a self-absorbed silicate feature. There is no clear evidence for SiC emission in any of the spectra: the LRS spectra were erroneously classified as showing SiC emission because of the relatively strong 11-?m emission.

Sylvester, R. J.

1999-10-01

339

Massive Star Burps, Then Explodes  

NASA Astrophysics Data System (ADS)

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

2007-04-01

340

HUBBLE WATCHES STAR TEAR APART ITS NEIGHBORHOOD  

NASA Technical Reports Server (NTRS)

NASA's Hubble Space Telescope has snapped a view of a stellar demolition zone in our Milky Way Galaxy: a massive star, nearing the end of its life, tearing apart the shell of surrounding material it blew off 250,000 years ago with its strong stellar wind. The shell of material, dubbed the Crescent Nebula (NGC 6888), surrounds the 'hefty,' aging star WR 136, an extremely rare and short-lived class of super-hot star called a Wolf-Rayet. Hubble's multicolored picture reveals with unprecedented clarity that the shell of matter is a network of filaments and dense knots, all enshrouded in a thin 'skin' of gas [seen in blue]. The whole structure looks like oatmeal trapped inside a balloon. The skin is glowing because it is being blasted by ultraviolet light from WR 136. Hubble's view covers a small region at the northeast tip of the structure, which is roughly three light-years across. A picture taken by a ground-based telescope [lower right] shows almost the entire nebula. The whole structure is about 16 light-years wide and 25 light-years long. The bright dot near the center of NGC 6888 is WR 136. The white outline in the upper left-hand corner represents Hubble's view. Hubble's sharp vision is allowing scientists to probe the intricate details of this complex system, which is crucial to understanding the life cycle of stars and their impact on the evolution of our galaxy. The results of this study appear in the June issue of the Astronomical Journal. WR 136 created this web of luminous material during the late stages of its life. As a bloated, red super-giant, WR 136 gently puffed away some of its bulk, which settled around it. When the star passed from a super-giant to a Wolf-Rayet, it developed a fierce stellar wind - a stream of charged particles released from its surface - and began expelling mass at a furious rate. The star began ejecting material at a speed of 3.8 million mph (6.1 million kilometers per hour), losing matter equal to that of our Sun's every 10,000 years. Then the stellar wind collided with the material around the star and swept it up into a thin shell. That shell broke apart into the network of bright clumps seen in the image. The present-day strong wind of the Wolf-Rayet star has only now caught up with the outer edge of the shell, and is stripping away matter as it flows past [the tongue-shaped material in the upper right of the Hubble image]. The stellar wind continues moving outside the shell, slamming into more material and creating a shock wave. This powerful force produces an extremely hot, glowing skin [seen in blue], which envelops the bright nebula. A shock wave is analogous to the sonic boom produced by a jet plane that exceeds the speed of sound; in a cosmic setting, this boom is seen rather than heard. The outer material is too thin to see in the image until the shock wave hits it. The cosmic collision and subsequent shock wave implies that a large amount of matter resides outside the visible shell. The discovery of this material may explain the discrepancy between the mass of the entire shell (four solar masses) and the amount of matter the star lost when it was a red super-giant (15 solar masses). The nebula's short-term fate is less spectacular. As the stellar wind muscles past the clumps of material, the pressure around them drops. A decrease in pressure means that the clumps expand, leading to a steady decline in brightness and fading perhaps to invisibility. Later, the shell may be compressed and begin glowing again, this time as the powerful blast wave of the Wolf-Rayet star completely destroys itself in a powerful supernova explosion. The nebula resides in the constellation Cygnus, 4,700 light-years from Earth. If the nebula were visible to the naked eye, it would appear in the sky as an ellipse one-quarter the size of the full moon. The observations were taken in June 1995 with the Wide Field and Planetary Camera 2. Scientists selected the colors in this composite image to correspond with the ionization (the process of stripping electrons from atoms) state of the gases, with blue r

2002-01-01

341

The Luminous Blue Variable phase---do low metallicity stars go through it?  

NASA Astrophysics Data System (ADS)

The most massive stars, above roughly 50 M_?, pass an unstable phase, the Luminous Blue Variable (LBVs) phase. In this transitional phase between the main-sequence and Wolf-Rayet state, the stars loose large amounts of mass (>10^{-5}M_? yr^{-1}). As a consequence the evolution of these stars towards cooler temperatures is stalled and reversed. The most massive stars seem not to enter the red supergiant phase. The coolest location of these stars in the Hertzsprung-Russell Diagram marks the vertical part of the empirical Humphreys-Davidson limit (HDL). The question is whether stars with lower metallicities go through the LBV phase, and if so is there a limit in metallicity above or below which stars do not enter an LBV phase. Observations of local galaxies with a slightly lower metallicity show that LBVs are present but given the still small number of LBVs known, a more extended study is needed to fully answer this question. So far the SMC and NGC 2366 are galaxies with the lowest and M31 and M101 are the ones with the highest metallicities in which LBVs are found.

Weis, K.

2006-12-01

342

Calibration of Post-AGB Supergiants as Standard Extragalactic Candles for HST  

NASA Technical Reports Server (NTRS)

This report summarizes activities carried out with support from the NASA Ultraviolet, Visible, and Gravitational Astrophysics Research and Analysis Program. The aim of the program is to calibrate the absolute magnitudes of post-asymptotic-giant-branch (post-AGB or PAGB) stars, which we believe will be an excellent new "standard candle" for measuring extragalactic distances. The reason for this belief is that in old populations, the stars that are evolving through the PAGB region of the HR (Hertzsprung-Russell) diagram arise from only a single main-sequence turnoff mass. In addition, the theoretical PAGB evolutionary tracks show that they evolve through this region at constant luminosity; hence the PAGB stars should have an extremely narrow luminosity function. Moreover, as the PAGB stars evolve through spectral types F and A (en route from the AGB to hot stellar remnants and white dwarfs), they have the highest luminosities attained by old stars (both bolometrically and in the visual band). Finally, the PAGB stars of these spectral types are very easily identified, due to their large Balmer jumps, which are due to their very low surface gravities.

Bond, Howard E.

1998-01-01

343

Chameleon stars  

SciTech Connect

We consider a gravitating spherically symmetric configuration consisting of a scalar field nonminimally coupled to ordinary matter in the form of a perfect fluid. For this system we find static, regular, asymptotically flat solutions for both relativistic and nonrelativistic cases. It is shown that the presence of the nonminimal interaction leads to substantial changes both in the radial matter distribution of the star and in the star's total mass. A simple stability test indicates that, for the choice of parameters used in the paper, the solutions are unstable.

Dzhunushaliev, Vladimir [Institute for Basic Research, Eurasian National University, Astana, 010008 (Kazakhstan); Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, 265 a, Chui Street, Bishkek, 720071 (Kyrgyzstan); Folomeev, Vladimir [Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, 265 a, Chui Street, Bishkek, 720071 (Kyrgyzstan); Singleton, Douglas [Institute for Basic Research, Eurasian National University, Astana, 010008 (Kazakhstan); Physics Department, CSU Fresno, Fresno, California 93740-8031 (United States)

2011-10-15

344

Cumulative luminosity distributions of supergiant fast X-ray transients in hard X-rays  

NASA Astrophysics Data System (ADS)

We have analysed in a systematic way about nine years of INTEGRAL data (17-100 keV) focusing on supergiant fast X-ray transients (SFXTs) and three classical high-mass X-ray binaries (HMXBs). Our approach has been twofold: image-based analysis, sampled over a ˜ks time frame to investigate the long-term properties of the sources and light-curve-based analysis, sampled over a 100 s time frame to seize the fast variability of each source during its ˜ ks activity. We find that while the prototypical SFXTs (IGR J17544-2619, XTE J1739-302 and SAX J1818.6-1703) are among the sources with the lowest ˜ ks-based duty cycle (<1 per cent activity over nine years of data), when studied at the 100 s level, they are the ones with the highest detection percentage, meaning that, when active, they tend to have many bright short-term flares with respect to the other SFXTs. To investigate in a coherent and self-consistent way all the available results within a physical scenario, we have extracted cumulative luminosity distributions for all the sources of the sample. The characterization of such distributions in hard X-rays, presented for the first time in this work for the SFXTs, shows that a power-law model is a plausible representation for SFXTs, while it can only reproduce the very high luminosity tail of the classical HMXBs, and even then, with a significantly steeper power-law slope with respect to SFXTs. The physical implications of these results within the frame of accretion in wind-fed systems are discussed.

Paizis, A.; Sidoli, L.

2014-04-01

345

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

NASA Astrophysics Data System (ADS)

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.

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

1996-01-01

346

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

NASA Astrophysics Data System (ADS)

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).

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

347

X-Rays from Hybrid Stars  

NASA Astrophysics Data System (ADS)

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.

Ayres, Thomas R.

2005-01-01

348

The Wind of the B[e] Supergiant Hen S22 Viewed through a Reflection Nebula in DEM L 106  

Microsoft Academic Search

Narrow-band HST WFPC2 images reveal a bow-shock-like halo around the HII\\u000aregion N30B toward the B[e] supergiant Hen S22 located within the larger DEM L\\u000a106 nebula in the Large Magellanic Cloud. High-dispersion spectra of N30B show\\u000aa narrow H-alpha emission component from the ionized gas; the velocity\\u000avariations indicate a gas flow of -5 to -10 km\\/s in the

Y.-H. Chu; C.-H. R. Chen; C. Danforth; B. C. Dunne; R. A. Gruendl; Y. Naze; M. S. Oey

2002-01-01

349

The period - K-band luminosity relation for pulsating variable red supergiants in the Galaxy and in M 33  

NASA Astrophysics Data System (ADS)

The paper reports the detection of a double-mode period - IR-luminosity relation for pulsating red supergiants (SRC-type variables) in the Galaxy. Distance moduli of LMC and of M 33 are estimated on the basis of the adopted distance modulus of 11.4 for the Per OB1 stellar association. The ratio of the first overtone pulsation period to that of the main tone is found to be the same both in the Galaxy and in M 33 (0.70 +/- 0.04).

Dambis, A. K.

1993-05-01

350

ALE OF TWO CLUSTERS YIELDS SECRETS OF STAR BIRTH IN THE EARLY UNIVERSE  

NASA Technical Reports Server (NTRS)

This NASA Hubble Space Telescope (HST) image shows rich detail, previously only seen in neighboring star birth regions, in a pair of star clusters 166,000 light-years away in the Large Magellanic Cloud (LMC), in the southern constellation Doradus. The field of view is 130 light-years across and was taken with the Wide Field Planetary Camera 2. HST's unique capabilities -- ultraviolet sensitivity, ability to see faint stars, and high resolution -- have been utilized fully to identify three separate populations in this concentration of nearly 10,000 stars down to the 25th magnitude (more that twice as many as can be seen over the entire sky with the naked eye on a clear night on Earth). The field of view is only 130 light-years across. Previous observations with ground-based telescopes resolve less than 1,000 stars in the same region. About 60 percent of the stars belong to the dominant yellow cluster called NGC 1850, which is estimated to be 50 million years old. A scattering of white stars in the image are massive stars that are only about 4 million years old and represent about 20 percent of the stars in the image. (The remainder are field stars in the LMC.) Besides being much younger, the white stars are much more loosely distributed than the yellow cluster. The significant difference between the two cluster ages suggests these are two separate star groups that lie along the same line of sight. The younger, more open cluster probably lies 200 light-years beyond the older cluster. If it were in the foreground, then dust contained in the white cluster would obscure stars in the older yellow cluster. To observe two well-defined star populations separated by such a small gap of space is unusual. This juxtaposition suggests that supernova explosions in the older cluster might have triggered the birth of the younger cluster. This color composite image is assembled from exposures taken in ultraviolet, visible, and near-infrared light. Yellow stars correspond to Main Sequence stars (like our Sun) with average surface temperatures of 6000 Kelvin; red stars are cool giants and supergiants (3500 K); white stars are hot young stars (25,000 K or more) that are bright in ultraviolet. Credit: R. Gilmozzi, Space Telescope Science Institute/European Space Agency; Shawn Ewald, JPL; and NASA

2002-01-01

351

Spectral Analysis of YSOs and Other Emission-Line Stars in the North America and Pelican Nebulae Region  

NASA Astrophysics Data System (ADS)

Far red spectra for 34 stars with V magnitudes between 15 and 18 in the direction of the North America and Pelican nebulae (NAP) star-forming region are obtained. Some of these stars were known earlier as emission-line objects, others were suspected as pre-main-sequence stars from photometry in the J, H, Ks and Vilnius systems. We confirm the presence of the H? line emission in the spectra of 19 stars, some of them exhibit also emission in the O I and Ca II lines. In some of the stars the H? absorption line is filled with emission. To estimate their evolutionary status, the spectral energy distributions, based on Vilnius, 2MASS, MSX and Spitzer photometry, are applied. Only eight emission-line stars are found to be located at a distance of the NAP complex. Others are either chromospherically active stars in front of the complex or distant luminous stars with H? absorption and emission components. For five stars with faint emission the data are not sufficient to estimate their distance. One star is found to be a heavily reddened K-supergiant located in the Outer arm. The stars, for which we failed to confirm the emission in H? , are mostly red dwarfs located in front of the NAP complex, two of them could be binaries with L-type components. Taking into account the stars suspected to be YSOs by their 2MASS colors we conclude that the NAP complex can possess a considerable population of young stars hidden behind the dust cloud.

Corbally, C. J.; Straižys, V.; Laugalys, V.

352

A Modern Search for Wolf-Rayet Stars in the Magellanic Clouds: First Results  

NASA Astrophysics Data System (ADS)

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. This paper includes data gathered with the 1 m Swope and 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Massey, Philip; Neugent, Kathryn F.; Morrell, Nidia; Hillier, D. John

2014-06-01

353

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. ...

2010-04-15

354

Can Gamma-ray Burst Jets Break Out the First Stars?  

NASA Astrophysics Data System (ADS)

We show that a relativistic gamma-ray burst (GRB) jet can potentially pierce the envelope of a very massive first generation star (Population III, hereafter Pop III) by using the stellar density profile to estimate both the jet luminosity (via accretion) and its penetrability. The jet breakout is possible even if the Pop III star has a supergiant hydrogen envelope without mass loss, thanks to the long-lived powerful accretion of the envelope itself. While the Pop III GRB is estimated to be energetic (E ?,iso ~ 1055 erg), the supergiant envelope hides the initial bright phase in the cocoon component, leading to a GRB with a long duration ~1000(1 + z) s and an ordinary isotropic luminosity ~1052 erg s-1 (~10-9 erg cm-2 s-1 at redshift z ~ 20). The neutrino annihilation is not effective for Pop III GRBs because of a low central temperature, while the magnetic mechanism is viable. We also derive analytic estimates of the breakout conditions, which are applicable to various progenitor models. The GRB luminosity and duration are found to be very sensitive to the core and envelope mass, providing possible probes of the first luminous objects at the end of the high-redshift dark ages.

Suwa, Yudai; Ioka, Kunihito

2011-01-01

355

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

SciTech Connect

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.

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

356

Recycling of neutron stars in common envelopes and hypernova explosions  

NASA Astrophysics Data System (ADS)

In this paper, we propose a new plausible mechanism of supernova explosions specific to close binary systems. The starting point is the common envelope phase in the evolution of a binary consisting of a red supergiant and a neutron star. As the neutron star spirals towards the centre of its companion it spins up via disc accretion. Depending on the specific angular momentum of the gas captured by the neutron star via the Bondi-Hoyle mechanism, it may reach millisecond periods either when it is still inside the common envelope or after it has merged with the companion core. The high accretion rate may result in the strong differential rotation of the neutron star and generation of the magnetar-strength magnetic field. The magnetar wind can blow away the common envelope if its magnetic field is as strong as 1015 G and can destroy the entire companion if it is as strong as 1016 G. The total explosion energy can be comparable to the rotational energy of a millisecond pulsar and reach 1052 erg. However, only a small amount of 56Ni is expected to be produced this way. The result is an unusual Type II supernova with very high luminosity during the plateau phase, followed by a sharp drop in brightness and a steep light-curve tail. The remnant is either a solitary magnetar or a close binary involving a Wolf-Rayet star and a magnetar. When this Wolf-Rayet star explodes, it will be a third supernova explosion in the same binary.

Barkov, Maxim V.; Komissarov, Serguei S.

2011-07-01

357

The Drop in X-ray Flux at Spectral Type B1: Evidence for a B-Star Dividing Line?  

NASA Astrophysics Data System (ADS)

All B star luminosity classes show a substantial drop in their X-ray emission between spectral type B1 and B2 suggesting an H-R diagram B-star dividing line somewhat analogous to the one for K giants. This emission appears to be related to the bi-stability jump at spectral type B1. But our analyses of B supergiant and giant XMM data revealed several interesting and unexpected results that do not support theoretical predictions. There seems to be a fundamental, unknown, underlying process at work in this spectral region. We now wish to extent our study by requesting XMM EPIC observations of 4 B main sequence stars and 2 additional B giants to help us explain the abrupt X-ray changes that are occurring in this intriguing region of the H-R diagram.

Waldron, Wayne

2009-10-01

358

The Drop in X-ray Flux at Spectral Type B1: Evidence for a B-Star Dividing Line?  

NASA Astrophysics Data System (ADS)

All B star luminosity classes show a substantial drop in their X-ray emission between spectral type B1 and B2 suggesting an H-R diagram B-star dividing line somewhat analogous to the one for K giants. This emission appears to be related to the bi-stability jump at spectral type B1. But our analyses of B supergiant and giant XMM data revealed several interesting and unexpected results that do not support theoretical predictions. There seems to be a fundamental, unknown, underlying process at work in this spectral region. We now wish to extent our study by requesting XMM EPIC observations of 4 B main sequence stars and 1 additional B giant to help us explain the abrupt X-ray changes that are occurring in this intriguing region of the H-R diagram.

Waldron, Wayne

2010-10-01

359

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.

360

Swift/XRT Monitoring of the Candidate Supergiant Fast X-ray Transient IGR J16418-4532  

NASA Technical Reports Server (NTRS)

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 (approx. 3.7d and approx. 1250 s, respectively). Our observations, for a total of approx. 43 ks, 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 5 X 10(exp 16) g to 10(exp 21) g. Our data suggest, based on the X-ray behaviour, that this is an intermediate SFXT

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

2011-01-01

361

Converting neutron stars into strange stars  

NASA Technical Reports Server (NTRS)

If strange matter is formed in the interior of a neutron star, it will convert the entire neutron star into a strange star. The proposed mechanisms are reviewed for strange matter seeding and the possible strange matter contamination of neutron star progenitors. The conversion process that follows seeding and the recent calculations of the conversion timescale are discussed.

Olinto, A. V.

1991-01-01

362

Mg II h and k profiles in high-liminosity, late-type stars  

NASA Technical Reports Server (NTRS)

Using high-resolution spectroscopic data taken with the Goddard High Resolution Spectrographic (GHRS) aboard the Hubble Space Telescope (HST) and with the International Ultraviolet Expolorer (IUE) satellite, we compare the profiles of the Mg II h and k lines seen in stars with spectral types ranging from early K through mid-M and luminosities from giants to supergiants. For all of these stars the lines are broad emission features with a central absorption. When plotted on a velocity scale the absorption features of the h and k lines agree very well in both shape and position, as do the blue wings of the emission component. The red wings of the emission, however, show a pronounced difference, with the k line wing consistently shifted to the red of the h line wing. At present the reason for this discrepancy is unknown, but we suggest several possibilities, including radiative transfer effects and high-speed stellar winds.

Robinson, R. D.; Carpenter, K. G.

1995-01-01

363

Cosmic Ray Electrons and Positrons from Supernova Explosions of Massive Stars  

NASA Astrophysics Data System (ADS)

We attribute the recently discovered cosmic ray electron and cosmic ray positron excess components and their cutoffs to the acceleration in the supernova shock in the polar cap of exploding Wolf-Rayet and red supergiant stars. Considering a spherical surface at some radius around such a star, the magnetic field is radial in the polar cap as opposed to most of 4? (the full solid angle), where the magnetic field is nearly tangential. This difference yields a flatter spectrum, and also an enhanced positron injection for the cosmic rays accelerated in the polar cap. This reasoning naturally explains the observations. Precise spectral measurements will be the test, as this predicts a simple E-2 spectrum for the new components in the source, steepened to E-3 in observations with an E-4 cutoff.

Biermann, P. L.; Becker, J. K.; Meli, A.; Rhode, W.; Seo, E. S.; Stanev, T.

2009-08-01

364

The stellar wind of an O8.5 I(f) star in M 31  

NASA Technical Reports Server (NTRS)

We rediscuss the UV spectrum of OB 78#231, an O8.5 I(f) star in the Andromeda galaxy M 31, which has been obtained with the Faint Object Spectrograph on the Hubble Space Telescope by Hutchings et al. (1992). The spectrum has been re-extracted with better knowledge of background, calibration, and scattered light. The empirical analysis of the stellar wind lines results in a terminal velocity and mass loss rate similar to those typically found in comparable galactic objects. Furthermore, a comparison with an FOS spectrum of an O7 supergiant in the Small Magellanic Cloud and IUE spectra of galactic objects implies a metallicity close to galactic counterparts. These results are confirmed quantitatively by spectrum synthesis calculations using a theoretical description of O-star winds.

Haser, S. M.; Lennon, D. J.; Kudritzki, R.-P.; Puls, J.; Pauldrach, A. W. A.; Bianchi, L.; Hutchings, J. B.

1995-01-01

365

Classification of KP2001 stars using spectra obtained with a slit spectrograph. II  

NASA Astrophysics Data System (ADS)

A two-dimensional classification of thirteen stars from the KP2001 catalog is described. CCD spectra of these stars were obtained at the 2.6-m telescope of the Byurakan Observatory with the SCORPIO and Byu FOSC2 spectral cameras. The classification employs methods based on the depression bands of the TiO and CaH molecules, as well as absorption lines of FeI, the NaI D lines, a BaII ion, the H? line, and others. The luminosity classes were determined using the CaH band with a minimum depression depth observed at ? 6975Å. The results of the classification are given in Table 1. The subclasses of the stars range from M5 to M10 and the luminosity classes, from supergiants (I) to giants (III). Since the KP2001 stars are close to the plane of our galaxy, interstellar absorption was taken into account and they fall in the LPV region on a (J-H), (H-K) diagram. The stars KP2001-6, 7, 70, and 230 are variable, as confirmed by the behavior of their light curves taken from the NSVS data base. Of these, KP2001-6, 7, and 70 are semiregular (SR) variables and KP2001-230 is a Mira variable. The variability of this last star was revealed in 2003 on photographic plates from a year apart (the difference in the photographic magnitudes was 1m.2).

Petrosyan, G. V.

2013-09-01

366

International Ultraviolet Explorer observations of stars in 30 Doradus - Extinction and stellar continua  

NASA Technical Reports Server (NTRS)

A study of ultraviolet interstellar extinction in and near the core of the 30 Doradus nebula is presented. The pair method is used to determine the shape of the ultraviolet extinction curve, and reddened stars from within 80 pc of the core and unreddened stars from a variety of locations in the Large Magellanic Cloud (LMC) are considered. All stars near the core appear to be reddened by E(B-V) = 0.09-0.16 with an extinction law similar to previous LMC extinction laws. Some stars, including R136a, R145, and R147, are additionally reddened by E(B-V) = 0.18 with a 'nebular-type' extinction law. A model consisting of a layer of 'LMC foreground dust' which affects all of the stars and a deeper layer of 'nebular dust' which affects some of the stars is used for an explanation of the extinction properties. The extinction curves are then applied to the ultraviolet energy distribution of R136a for a determination of its intrinsic continuum shape. Evidence showing that the brightest LMC OB supergiants have intrinsic (B-V) colors and UV-to-visual continuum slopes which are redder than expected is presented.

Fitzpatrick, E. L.; Savage, B. D.

1984-01-01

367

Abundance patterns in stars in the bulge and Galactic center  

NASA Astrophysics Data System (ADS)

We discuss oxygen and iron abundance patterns in K and M red-giant members of the Galactic bulge and in the young and massive M-type stars inhabiting the very center of the Milky Way. The abundance results from the different bulge studies in the literature, both in the optical and the infrared, indicate that the [O/Fe]-[Fe/H] relation in the bulge does not follow the disk relation, with [O/Fe] values falling above those of the disk. Based on these elevated values of [O/Fe] extending to large Fe abundances, it is suggested that the bulge underwent a rapid chemical enrichment with perhaps a top-heavy initial mass function. The Galactic Center stars reveal a nearly uniform and slightly elevated (relative to solar) iron abundance for a studied sample which is composed of 10 red giants and supergiants. Perhaps of more significance is the fact that the young Galactic Center M-type stars show abundance patterns that are reminiscent of those observed for the bulge population and contain enhanced abundance ratios of ?-elements relative to either the Sun or Milky Way disk at near-solar metallicities.

Cunha, Katia; Smith, V. V.; Sellgren, K.; Blum, R. D.; Ramírez, S. V.; Terndrup, D. M.

2008-07-01

368

{Delta}a photometry of CP stars (Paunzen+, 2005)  

NASA Astrophysics Data System (ADS)

We have summarized all {Delta}a measurements for galactic field stars (1474 objects) from the literature published over more than two decades. These measurements were, for the first time, compiled and homogeneously analyzed. The {Delta}a intermediate band photometric system samples the depth of the 5200{AA} flux depression by comparing the flux at the center with the adjacent regions with bandwidths of 110{AA} to 230{AA}. Because it was slightly modified over the last three decades, we checked for systematic trends for the different measurements but found no correlations whatsoever. The {Delta}a photometric system is most suitable to detecting magnetic chemically peculiar (CP) stars with high efficiency, but is also capable of detecting a small percentage of non-magnetic CP objects. Furthermore, the groups of (metal-weak) lambda Bootis, as well as classical Be/shell stars, can be successfully investigated. In addition, we also analyzed the behaviour of supergiants (luminosity class I and II). On the basis of apparent normal type objects, the correlation of the 3sigma significance limit and the percentage of positive detection for all groups was derived. (1 data file).

Paunzen, E.; Stuetz, C.; Maitzen, H. M.

2006-07-01

369

The brief lives of massive stars as witnessed by interferometry}  

NASA Astrophysics Data System (ADS)

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 require interferometry in the infrared, while post-mainsequence stellar phases require high-precision measurements to challenge stellar evolution models. I will summarize our work on a massive YSO in NGC 3603 including modeling mid-IR interferometric observations, as well as recent sub-mm imaging and spectroscopy with APEX. We find some evidence for a disk in the MIR, resolve multiple cores in the sub-mm with emission line spectra untypical for hot cores. I also report on the derivation of masses and luminosities of a massive O-type supergiant (? Orionis) in another star forming region in Orion. The small radial velocity semi-amplitudes coupled with few usable (i.e. wind-free) lines have made this work very challenging and forced us to base the mass determination on a photometric distance estimate. As a rapidly evolving application of interferometry, massive stars have a bright future.

Hummel, Christian

2013-06-01

370

A newly discovered young massive star cluster at the far end of the Galactic Bar  

NASA Astrophysics Data System (ADS)

We present a near-infrared study of the candidate star cluster Mercer 81, located at the centre of the G338.4+0.1 H II region and close to the TeV gamma-ray source HESS 1640-465. Using Hubble Space Telescope/NICMOS imaging and VLT/ISAAC spectroscopy, we have detected a compact and highly reddened cluster of stars, although the bright stars in the centre of the field are in fact foreground objects. The cluster contains nine stars with strong P? emission, one of which we identify as a Wolf-Rayet (WR) star, as well as an A-type supergiant. The line-of-sight extinction is very large, AV˜ 45, illustrating the challenges of locating young star clusters in the Galactic plane. From a quantitative analysis of the WR star, we argue for a cluster age of 3.7? Myr, and, assuming that all emission-line stars are WR stars, a cluster mass of ?104 M?. A kinematic analysis of the cluster's surrounding H II region shows that the cluster is located in the Galactic disc at a distance of 11 ± 2 kpc. This places the cluster close to where the far end of the Bar intersects the Norma spiral arm. This cluster, as well as the nearby cluster [DBS2003]179, represents the first detections of active star cluster formation at this side of the Bar, in contrast to the near side which is well known to have recently undergone a ˜106 M? starburst episode.

Davies, Ben; de La Fuente, Diego; Najarro, Francisco; Hinton, Jim A.; Trombley, Christine; Figer, Donald F.; Puga, Elena

2012-01-01

371

The birth and death of stars  

NASA Astrophysics Data System (ADS)

We present analytical models for two violent phases of stellar evolution whose effects upon the interstellar medium are most profound: supernova explosions and protostellar outflows. Using models for outflows, we analyze the efficiency and dynamics of a forming stellar cluster. The distribution of ejecta that expand away from a core- collapse supernova can be predicted once one knows the velocity of the blastwave shock that crossed the stellar envelope. We identify a new model for this shock's velocity that is simple and accurate, with which we construct detailed models relating stellar structures to their ejecta distributions. The shock model also permits us to calculate the observable features of shock emergence, including the energy and duration of the soft- X-ray burst, the upper limit of ejecta velocities, and the mass (if any) of relativistic ejecta. The latter may help to understand weak gamma-ray bursts from supernovae. We also use the structural similarity of red and blue supergiants to approximate their ejecta with simpler, less flexible models. We show that hydromagnetic winds from accreting protostars will assume a common force distribution at large distances, whether or not the wind emanates from a narrow region of disk radii. In any power-law density distribution, such a wind sweeps ambient gas into thin shells whose features match those commonly observed in bipolar molecular outflows, regardless how the driving wind's intensity varies over time. This implies that prompt entrainment, not turbulence, is responsible for these features. This model predicts the rate of mass ejection from a star-forming region, and thus the efficiency with which a star cluster can form. Using the energy injection and mass ejection implied by this model, we address the dynamical evolution of a dense clump inside a molecular cloud as it creates a cluster of low-mass stars. We use the virial equation of motion and assume that star formation is limited by ambipolar diffusion. For lower pressures than within starburst nuclei, an equilibrium state is possible if turbulence does not decay extremely rapidly. However, clumps tend to oscillate about their equilibria, and this can cause star formation to proceed in bursts.

Matzner, Christopher David

372

Wolf-Rayet and OB Star Self-Enrichment of Globular Clusters?  

NASA Astrophysics Data System (ADS)

Nitrogen abundance inhomogeneities are present among main-sequence stars in globular clusters of the Milky Way. Since N-rich cluster dwarfs are unlikely to have nucleosynthesized nitrogen within their own interiors, they presumably obtained their excess N from elsewhere. If the abundance inhomogeneities are due to the self-enrichment of a globular cluster, then the earliest source of nitrogen could have been massive cluster OB stars and Wolf-Rayet stars of type N. Several obstacles to WN stars' being a viable enrichment mode for globular clusters are discussed: (1) a W-R phase may have been inhibited for metal-poor OB stars, due to the low mass-loss rates expected of their radiatively driven winds, and (2) unless globular clusters had top-heavy stellar mass functions, their WN stars would have been too few in number to explain the amount of CNO-processed material in their nitrogen-rich, low-mass stars. In contrast, it is pointed out that OB stars in their main-sequence and supergiant phases of evolution might also eject CNO-processed material even if they do not evolve through a WN phase, while W-R stars have been discovered in some metal-poor dwarf galaxies and starburst galaxies. In addition, low metallicities could favor the production of WN stars over WC stars, and this could explain why the abundance inhomogeneities in Milky Way globular clusters generally involve excesses of CNO-processed material. One scenario is discussed in which globular clusters form at the interface between massive, colliding gas clouds. If such clouds have masses comparable to dwarf galaxies, with relative velocities characteristic of the Galactic halo, then the collision process could drive gas into an accreting protocluster at a rate that is sufficient to complete cluster formation within several million years. This timescale could allow nitrogen-rich wind ejecta from WN or OB stars to be incorporated into later cluster star formation. The ram pressure associated with a colliding-cloud environment might not only confine the stellar wind ejecta, but also funnel it into sites of active star formation within the protocluster. In this picture, globular clusters form as open systems with gas continuing to flow into them from a greater cloud-merger environment while star formation is occurring. In such a circumstance, not only may cluster WN and OB stars have promoted enrichment, but wind ejecta from massive stars that are external to the protocluster may also have been acquired.

Smith, Graeme H.

2006-09-01

373

Runaway stars as progenitors of supernovae and gamma-ray bursts  

NASA Astrophysics Data System (ADS)

When a core-collapse supernova occurs in a binary system, the surviving star as well as the compact remnant emerging from the supernova may reach a substantial space velocity. With binary population synthesis modelling at solar and one-fifth of solar metallicity, we predict the velocities of such runaway stars or binaries. We compile predictions for runaway OB stars, red supergiants and Wolf-Rayet stars, either isolated or with a compact companion. For those stars or binaries which undergo a second stellar explosion we compute their further evolution and the distance travelled until a Type II or Type Ibc supernova or a long or short gamma-ray burst (GRB) occurs. We find our predicted population of OB runaway stars broadly matches the observed population of stars but, to match the fastest observed Wolf-Rayet runaway stars, we require that black holes receive an asymmetric kick upon formation. We find that at solar metallicity Type Ic supernova progenitors travel shorter distances than the progenitors of other supernova types because they are typically more massive and thus have shorter lifetimes. Those of Type IIP supernovae can fly farthest about 48 pc on average at solar metallicity, with about 8 per cent of them reaching 100 pc. In considering the consequences of assuming that the progenitors of long GRBs are spun-up secondary stars that experience quasi-homogeneous evolution, we find that such evolution has a dramatic effect on the population of runaway Wolf-Rayet stars and that some 30 per cent of GRBs could occur a hundred parsec or more from their initial positions. We also consider mergers of double compact object binaries consisting of neutron stars and/or black holes. We find the most common type of visible mergers are neutron star-black hole mergers that are roughly 10 times more common than neutron star-neutron star mergers. All compact mergers have a wide range of merger times from years to Gyr and are predicted to occur 300 times less often than supernovae in the Milky Way. We also find that there may be a population of low-velocity neutron stars that are ejected from a binary rather than by their own natal kick. These neutron stars need to be included when the distribution of neutron star kicks is deduced from observations.

Eldridge, John J.; Langer, Norbert; Tout, Christopher A.

2011-07-01

374

Fundamental parameters of Wolf-Rayet stars. I. Ofpe/WN9 stars.  

NASA Astrophysics Data System (ADS)

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.

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

1995-01-01

375

A search for SiO, OH, CO and HCN radio emission from silicate-carbon stars  

NASA Astrophysics Data System (ADS)

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 2Rstar 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 10-6 to 10-7 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.

Little-Marenin, I. R.; Sahai, R.; Wannier, P. G.; Benson, P. J.; Gaylard, M.; Omont, A.

1994-01-01

376

O-star parameters from line profiles of wind-blanketed model atmospheres  

SciTech Connect

The basic stellar parameters (i.e. effective temperature, gravity, helium content, bolometric correction, etc...) of several O-stars are determined by matching high signal-to-noise observed line profiles of optical hydrogen and helium line transitions with theoretical line profiles from a core-halo model of the stellar atmosphere. The core-halo atmosphere includes the effect of radiation backscattered from a stellar wind by incorporating the stellar wind model of Abbott and Lucy as a reflective upper boundary condition in the Mihalas atmosphere model. Three of the four supergiants analyzed showed an enhanced surface abundance of helium. Using a large sample of equivalent width data from Conti a simple argument is made that surface enhancement of helium may be a common property of the most luminous supergiants. The stellar atmosphere theory is sufficient to determine the stellar parameters only if careful attention is paid to the detection and exclusion of lines which are not accurately modeled by the physical processes included. It was found that some strong lines which form entirely below the sonic point are not well modeled due to effects of atmospheric extension. For spectral class 09.5, one of these lines is the classification line He I {lambda}4471{angstrom}. For supergiant, the gravity determined could be systematically low by up to 0.05 dex as the radiation pressure due to lines is neglected. Within the error ranges, the stellar parameters determined, including helium abundance, agree with those from the stellar evolution calculations of Maeder and Maynet.

Voels, S.A.

1989-01-01

377

DB Pulsating Stars  

NASA Astrophysics Data System (ADS)

Pulsating WHITE DWARF stars with nearly pure helium atmospheres exist in a narrow temperature range near 25 000 K. At this writing, there are eight of these stars known. Collectively, they go by two names: the V777 Her stars, named after the VARIABLE STAR designation of the first known star in the class, and the more informative name, the DBV stars. The name DBV follows the standard convention fo...

Winget, D.; Murdin, P.

2000-11-01

378

Constraints on the low-mass IMF in young super-star clusters in starburst galaxies  

NASA Astrophysics Data System (ADS)

As evidence for variations in the initial mass function (IMF) in nearby star forming regions remains elusive we are forced to expand our search to more extreme regions of star formation. Starburst galaxies, which contain massive young clusters have in the past been reported to have IMFs different than that characterizing the field star IMF. In this thesis we use high signal-to-noise near-infrared spectra to place constraints on the shape of the IMF in extreme regions of extragalactic star formation and also try to understand the star formation history in these regions. Through high signal-to-noise near-infrared spectra it is possible to directly detect low-mass PMS stars in unresolved young super-star clusters, using absorption features that trace cool stars. Combining Starburst99 and available PMS tracks it is then possible to constrain the IMF in young super-star clusters using a combination of absorption lines each tracing different ranges of stellar masses and comparing observed spectra to models. Our technique can provide a direct test of the universality of the IMF compared to the Milky Way. We have obtained high signal-to-noise H- and K-band spectra of two young super-star clusters in the starburst galaxies NGC 4039/39 and NGC 253 in order to constrain the low-mass IMF and star formation history in the clusters. The cluster in NGC 4038/39 shows signs of youth such as thermal radio emission and strong hydrogen emission lines as well as late-type absorption lines indicative of cool stars. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence stars or red supergiants alone. We interpret the spectrum as a superposition of two star clusters of different ages over the physical region of 90 pc our spectrum represents. 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. While the superposition of clusters does not allow us to place stringent constraints on the IMF there is no evidence of a low-mass cutoff in the cluster and the IMF is consistent with a Chabrier and Kroupa IMF typical of the field. The cluster in NGC 253 shows the same signs of youth as the cluster in NGC 4038/39 and sits in front of a background population of older stars. The background population has an age of ? 12 Myr and thus contains red supergiants. After carefully subtracting this background we model the spectrum of the young cluster. We find that its IMF is consistent with a Chabrier and Kroupa IMF with a best-fit power-law slope of 1.0 in linear units. Slopes of 0.0 - 1.5 are also formally consistent with the cluster spectrum. We conclude that there is no strong evidence for an unusual IMF or a lack of low-mass stars (? 1 M? ) in either of these galaxies.

Greissl, Julia Jennifer

2010-12-01

379

The supergiant amphipod Alicella gigantea (Crustacea: Alicellidae) from hadal depths in the Kermadec Trench, SW Pacific Ocean  

NASA Astrophysics Data System (ADS)

Here we provide the first record of the 'supergiant' amphipod Alicella gigantea Chevreux, 1899 (Alicellidae) from the Southern Hemisphere, and extend the known bathymetric range by over 1000 m to 7000 m. An estimated nine individuals were observed across 1500 photographs taken in situ by baited camera at 6979 m in the Kermadec Trench, SW Pacific Ocean. Nine specimens, ranging in length from 102 to 290 mm were recovered by baited trap at depths of 6265 m and 7000 m. Mitochondrial and nuclear DNA sequences obtained indicate a cosmopolitan distribution for the species. Data and observations from the study are used to discuss the reason for gigantism in this species, and its apparently disjunct geographical distribution.

Jamieson, A. J.; Lacey, N. C.; Lörz, A.-N.; Rowden, A. A.; Piertney, S. B.

2013-08-01

380

A Near-infrared Study of the Obscured, Young, Massive Star Cluster, Mercer 23  

NASA Astrophysics Data System (ADS)

We determine the physical parameters and investigate the high-mass stellar content of the infrared star cluster Mercer 23, situated near the Galactic plane (l=53.772, b=+0.164). Our analysis is based on new Baade/PANIC JHK imaging of Mercer 23 and ISAAC/VLT moderate resolution (R 4000) spectroscopy of the brightest cluster members in the H- and K