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1

Are blue supergiants descendants of magnetic main sequence stars?  

NASA Astrophysics Data System (ADS)

Red and blue supergiants are, together with luminous blue variables and Wolf-Rayet stars, evolved phases of massive (OB) stars. The position of blue supergiants (BSG) near the main sequence band cannot be reproduced by standard stellar evolution calculations. However, the assumption of a reduced convective core mass during the main sequence (MS) due to strong internal magnetic fields, established in roughly 10% of all stars on the upper MS, can recover this BSG population. For our calculations of the (non-rotating) massive stars at solar metallicity we used the 1D stellar evolution code MESA and compare their evolutionary tracks with positions from stars obtained from the VLT Flames survey of massive stars.

Petermann, Ilka; Langer, Norbert

2013-06-01

2

Alfven waves in dusty winds of cool supergiant stars  

SciTech Connect

One of the most promising mechanisms that drive the winds of cool supergiant stars involves an outward-directed flux of Alfven waves. This mechanism can explain both the high mass-loss rate and the low terminal velocities of these winds. Many models were proposed using Alfven waves damping mechanisms such as surface resonant, non-linear, turbulent, or assuming a constant damping length. Since it is observed that late-type stars present great quantities of dust particles in their winds, we propose a damping mechanism for the waves that is caused due to their interaction with dust grains: the dust-cyclotron damping. We assume that particles are distributed over a range of sizes, implying a broad band of resonance frequencies. Our results show that this damping mechanism can accelerate the wind and reproduce observational data of cool supergiant stars, such as the mass-loss rate and the terminal velocity.

Vidotto, A.A.; Jatenco-Pereira, V. [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, USP, Rua do Matao 1226, 05508-900, Sao Paulo, SP (Brazil)

2005-09-28

3

Magnetic main sequence stars as progenitors of blue supergiants  

NASA Astrophysics Data System (ADS)

Blue supergiants (BSGs) to the right the main sequence band in the HR diagram can not be reproduced by standard stellar evolution calculations. We investigate whether a reduced convective core mass due to strong internal magnetic fields during the main sequence might be able to recover this population of stars. We perform calculations with a reduced mass of the hydrogen burning convective core of stars in the mass range 3-30 M ? in a parametric way, which indeed lead to BSGs. It is expected that these BSGs would still show large scale magnetic fields in the order of 10 G.

Petermann, I.; Castro, N.; Langer, N.

2015-01-01

4

P Cygni stars as a intermediate stage between red supergiants and Wolf-Rayet stars  

Microsoft Academic Search

From an accurate determination of the location of P Cygni in the HR diagram and from a comparison with evolutionary tracks the authors argue that P Cygni has been a red supergiant and is now on its way to become a WN star. The P Cygni type star AG Car already shows abundance anomalies which are typical for WN stars.

M. de Groot; A. Cassatella

1983-01-01

5

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

6

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

NASA Astrophysics Data System (ADS)

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

Tsuji, T.

2000-08-01

7

Outer atmospheres of giant and supergiant stars  

NASA Technical Reports Server (NTRS)

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

Brown, A.

1984-01-01

8

Detection of a red supergiant progenitor star of a type II-plateau supernova.  

PubMed

We present the discovery of a red supergiant star that exploded as supernova 2003gd in the nearby spiral galaxy M74. The Hubble Space Telescope (HST) and the Gemini Telescope imaged this galaxy 6 to 9 months before the supernova explosion, and subsequent HST images confirm the positional coincidence of the supernova with a single resolved star that is a red supergiant of 8(+4)(-2) solar masses. This confirms both stellar evolution models and supernova theories predicting that cool red supergiants are the immediate progenitor stars of type II-plateau supernovae. PMID:14739452

Smartt, Stephen J; Maund, Justyn R; Hendry, Margaret A; Tout, Christopher A; Gilmore, Gerard F; Mattila, Seppo; Benn, Chris R

2004-01-23

9

Delta-slow solution to explain B supergiant stars' winds  

NASA Astrophysics Data System (ADS)

A new radiation-driven wind solution called ?-slow was found by Curé et al. (2011) and it predicts a mass-loss rate and terminal velocity slower than the fast solution (m-CAK, Pauldrach et al. 1986). In this work, we present our first synthetic spectra based on the ?-slow solution for the wind of B supergiant (BSG) stars. We use the output of our hydrodynamical code HYDWIND as input in the radiative transport code FASTWIND (Puls et al. 2005). In order to obtain stellar and wind parameters, we try to reproduce the observed H?, H?, H?, H?, Hei 4471, Hei 6678 and Heii 4686 lines. The synthetic profiles obtained with the new hydrodynamical solutions are in good agreement with the observations and could give us clues about the parameters involved in the radiation force.

Haucke, M.; Araya, I.; Arcos, C.; Curé, M.; Cidale, L.; Kanaan, S.; Venero, R.; Kraus, M.

2015-01-01

10

Terminal velocities for a large sample of O stars, B supergiants, and Wolf-Rayet stars  

Microsoft Academic Search

It is argued that easily measured, reliable estimates of terminal velocities for early-type stars are provided by the central velocity asymptotically approached by narrow absorption features and by the violet limit of zero residual intensity in saturated P Cygni profiles. These estimators are used to determine terminal velocities, v(infinity), for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet

Raman K. Prinja; M. J. Barlow; Ian D. Howarth

1990-01-01

11

Do All Stars Form in Clusters?: Masses and Ages of Young Supergiants in Andromeda  

NASA Astrophysics Data System (ADS)

Currently it is not understood whether seemingly isolated stars formed in situ or were ejected from star clusters as runaway stars. Previous studies determined the origins of isolated stars by measuring their velocities, but past research was limited to OB stars in the Milky Way and Magellanic Clouds due to the difficulty of computing velocities of distant objects. This study proposed an innovative velocity test to statistically determine whether six seemingly isolated BA-type supergiants in Andromeda are runaways. We calculated the minimum relative transverse velocity needed for each supergiant to travel to its current location from the nearest open cluster. By comparing the minimum velocity with Andromeda’s known velocity dispersion, a statistical measure of the stars’ actual velocities, we determined whether the star had the necessary velocity to be a runaway. Minimum velocity was computed from the age of the star, which was calculated from its effective temperature and surface gravity. To compute effective temperature and surface gravity, we applied three new techniques based on Balmer absorption features. The results suggest that all six supergiants had the necessary velocities to be runaways. Although the proposed velocity test is a statistical assessment, it offers a valuable new tool for future investigation of isolated stars beyond the Milky Way and its satellites. This research was supported by the Science Internship Program (SIP) at UCSC, the National Science Foundation, NASA, and Palomar Observatory.

Choudhury, Zareen; Debs, C.; Kirby, E. N.; Guhathakurta, P.

2013-01-01

12

The red supergiants and Wolf-Rayet stars of NGC 604  

Microsoft Academic Search

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

John J. Eldridge; Mónica Relaño

2011-01-01

13

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

Microsoft Academic Search

The dependence of stellar molecular bands on the metallicity is studied using infrared L-band spectra of AGB stars (both carbon-rich and oxygen-rich) and M-type supergiants in the Large and Small Magellanic Clouds (LMC and SMC) and in the Sagittarius Dwarf Spheroidal Galaxy. The spectra cover SiO bands for oxygen-rich stars, and acetylene (C2H2), CH and HCN bands for carbon-rich AGB

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

2005-01-01

14

Pulsation and Mass Loss Across the HR Diagram: From OB stars to Cepheids to Red Supergiants  

E-print Network

Both pulsation and mass loss are commonly observed in stars and are important ingredients for understanding stellar evolution and structure, especially for massive stars. There is a growing body of evidence that pulsation can also drive and enhance mass loss in massive stars and that pulsation-driven mass loss is important for stellar evolution. In this review, I will discuss recent advances in understanding pulsation driven mass loss in massive main sequence stars, classical Cepheids and red supergiants and present some challenges remaining.

Neilson, Hilding R

2013-01-01

15

Near-infrared spectroscopy of candidate red supergiant stars in clusters  

NASA Astrophysics Data System (ADS)

Context. Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. Aims: We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. Methods: We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks< 7 mag) in GLIMPSE and 2MASS images. Results: A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10 M? to 15 M?. Two red supergiants are located at Galactic coordinates (l,b) = (16.°7, -0.°63) and at a distance of about ~3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b) = (49.°3, + 0.°72) and at a distance of ~7.0 kpc. Conclusions: Spectroscopic analysis of the brightest stars of detected overdensities and studies of interstellar extinction along their line of sights are fundamental to distinguish regions of low extinction from actual stellar clusters. The census of young star clusters containing red supergiants is incomplete; in the existing all-sky near-infrared surveys, they can be identified as overdensities of bright stars with infrared color-magnitude diagrams characterized by gaps. Based on observations collected at the European Southern Observatory (ESO Programme 60.A-9700(E), and 089.D-0876), and on observations collected at the UKIRT telescope (programme ID H243NS).MM is currently employed by the MPIfR. Part of this work was performed at RIT (2009), at ESA (2010), and at the MPIfR.Tables 3, 4, and 6 are available in electronic form at http://www.aanda.org

Messineo, Maria; Zhu, Qingfeng; Ivanov, Valentin D.; Figer, Donald F.; Davies, Ben; Menten, Karl M.; Kudritzki, Rolf P.; Chen, C.-H. Rosie

2014-11-01

16

Coronal Spectroscopy of the f0 Supergiant Canopus: Properties of Intermediate Mass Star Coronae after the he Flash  

Microsoft Academic Search

Canopus (F0 Ib), the nearest (96 pc) supergiant, is a He-burning, post-red supergiant star that recently redeveloped a 20 million K corona and powers this corona at log Lx = 29.8 erg\\/s despite having a very thin convection zone. The coronae of Canopus and similar stars are remarkably constant, suggesting that while, the magnetic loops are efficiently heated, there is

Alexander Brown

1999-01-01

17

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

18

Interacting supernovae from photoionization-confined shells around red supergiant stars  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

19

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

PubMed

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

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

2014-08-21

20

Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei  

E-print Network

We report a detection of water in emission in the spectrum of the M2 supergiant atar mu Cep (M2Ia) observed by the Short Wavelength Spectrometer (SWS) aboard Infrared Space Observatory (ISO) and now released as the ISO Archives. The emission first appears in the 6 micron region (nu2 fundamental) and then in the 40 micron region (pure rotation lines) despite the rather strong dust emission. The intensity ratios of the emission features are far from those of the optically thin gaseous emission. Instead, we could reproduce the major observed emission features by an optically thick water sphere of the inner radius about two stellar radii (1300Rsun), Tex = 1500K, and Ncol (H2O) = 3.0E+20/cm2. This model also accounts for the H2O absorption bands in the near infrared (1.4, 1.9, and 2.7 micron) as well. The detection of water in emission provides strong constraints on the nature of water in the early M supergiant stars, and especially its origin in the outer atmosphere is confirmed against other models such as the large convective cell model. We finally confirm that the early M supergiant star is surrounded by a huge optically thick sphere of the warm water vapor, which may be referred to as MOLsphere for simplicity. Thus, the outer atmosphere of M supergiant stars should have a complicated hierarchical and/or hybrid structure with at least three major constituents including the warm MOLsphere (T about 1.0E+3K) together with the previously known hot chromosphere (T about 1.0E+4K) and cool expanding gas-dust envelope (T about 1.0E+2K).

T. Tsuji

2000-08-03

21

The red supergiants & Wolf-Rayet stars of NGC 604  

Microsoft Academic Search

We study the post-main sequence stars in NGC 604, the most luminous HII\\u000aregion in M33. Previously, a number of Wolf-Rayet (WR) stars and one red\\u000asupergiant (RSG) have been discovered. Based on broadband photometry of the\\u000aregion, we present evidence that is consistent with the presence of this RSG\\u000aand with three more RSG candidates. Using SED fitting based

John J. Eldridge; Monica Relano

2010-01-01

22

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

23

Physical conditions near red giant and supergiant stars - An interpretation of SiO VLBI maps  

NASA Technical Reports Server (NTRS)

Understanding the dynamical structure of circumstellar envelopes around cool giant and supergiant stars depends critically on the knowledge of what happens in the 'near zone' of the envelope, within a few stellar radii of the star. One probe with adequate angular resolution to study the near zone is VLBI observation of the SiO masers. It is shown that VLBI maps of VX Sgr establish that the particle density in the SiO masers is very high (about 10 to the 12th/cu cm), indicating that the masers form in dense cloudlets and not in a spherically expanding wind. The implications of these results for the mechanism of mass loss are discussed.

Alcock, Charles; Ross, Randy R.

1986-01-01

24

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

25

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

26

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

NASA Astrophysics Data System (ADS)

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

Henrichs, H. F.; Sudnik, N.

2015-01-01

27

On the Origin of Hydrogen-deficient Supergiants and Their Relation to R Coronae Borealis Stars and Non-DA White Dwarfs  

Microsoft Academic Search

Scenarios for the formation and evolution of hydrogen-deficient supergiants are analyzed. Some of these supergiants may possibly be identified as R CrB stars. The main scenarios involve (1) a final, post-hydrogen burning, helium shell flash in the central star of a planetary nebula, (2) the merger of hydrogen-deficient components of evolved close binaries, and (3) the merger of a neutron

Icko Iben Jr.; Alexander V. Tutukov; Lev R. Yungelson

1996-01-01

28

The Temperatures of Red Supergiants: how cool are the coolest massive stars?  

NASA Astrophysics Data System (ADS)

We have re-appraised the temperatures of Red Supergiants (RSGs) in the Magellanic Clouds, by studying their spectral energy distributions (SEDs) from 400-2500 nm using VLT+XSHOOTER, in conjunction with MARCS model atmospheres. We determine temperatures using 3 methods: from model fits to the TiO bands in the optical; from model fits to the SED using the line-free continuum in the near-infrared; and from the integrated fluxes. We find that the temperatures from the TiO fits are systematically lower that those from the other methods by several hundred Kelvin. The TiO fits also dramatically over-predict the flux in the near-IR, and imply extinctions which are anomalously low compared to neighbouring stars. In contrast, the SED temperatures provide good fits to the fluxes at all wavelengths other than the TiO bands, are in agreement with the temperatures from the flux integration method, and imply extinctions consistent with nearby stars. We consider a number of ways to reconcile this discrepancy, concluding that 3-D effects are responsible, and that RSG temperatures are much warmer than previously thought.

Davies, B.; Kudritzki, R.-P.; Plez, B.; Bergemann, M.; Lançon, A.; Trager, S.; Gazak, Z.; Evans, C.; Chiavassa, A.

2013-05-01

29

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

SciTech Connect

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

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

2010-12-10

30

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

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 present an update of our investigation of differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

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

2015-01-01

31

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

32

Post-Red Supergiants  

E-print Network

The yellow hypergiants are found in a stage between the massive Red Supergiants and the Wolf-Rayet stars. This review addresses current issues concerning the evolution of massive stars, concentrating on the transitional post-Red Supergiant phase. Few yellow hypergiants are known and even fewer show direct evidence for having evolved off the Red Supergiant branch. Indeed, only two such rare objects with clear evidence for having gone through of a previous mass losing phase are known, IRC +10420 and HD 179821. We will review their properties and present recent results employing near-infrared interferometry, integral field spectroscopy and polarimetry. Finally, their real-time evolution is discussed.

Rene Oudmaijer; Ben Davies; Willem-Jan de Wit; Mitesh Patel

2008-01-15

33

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

34

Unveiling Type IIb Supernova Progenitors: SN 2011hs from a Supergiant Star  

NASA Astrophysics Data System (ADS)

Type IIb Supernovae are the final evolutionary stage of massive stars that were able to retain only a thin (lesssim 1 M_{odot}) H/He external envelope at the time of the explosion. The mechanism of mass-loss that made such final structure possible and the nature of such progenitor stars are still open issues. We present the results obtained from the study of a sample of Type IIb SNe, in particular, of SN 2011hs (Bufano et al., 2013, MNRAS submitted). SN 2011hs was a relatively faint (M_{B} = -15.6 mag) and red Type IIb SN, characterized by a narrow light curve shape. Its spectral evolution showed the metamorphosis typical of this class of SN, from spectra dominated by H I lines to spectra where He I features dominate, but with broad absorption line profiles indicating high expansion velocities. Modeling the light curve of SN 2011hs and its velocity evolution with hydrodynamical calculations, we estimated that the SN is consistent with the explosion of a 3-4 M_{odot} He-core star, from a main sequence mass of 12-15 M_{odot}, ejecting a ^{56}Ni mass equal to 0.04 M_{odot} and characterized by an explosion energy of E? 8.5× 10^{50} erg s^{-1}. Based on the light curve evolution, we assumed that the explosion occurred 6 days before the discovery (2,455,872 ± 4 JD), resulting in an adiabatic cooling phase lasting 8 days, similarly to SN 1993J. Since the duration and the decreasing rate of the cooling branch depends mainly on the progenitor size, we could infer from it a progenitor radius of ? 500-600 R_{odot}, like a supergiant star. Our modeling rules out models with He core mass >5 M_{odot}, i.e. main sequence masses above 20 M_{odot}. Such a lower limit for the progenitor mass could indicate the possibility of a binary origin, although the radio light curve does not show strong deviations, typically signature of the presence of a companion star.

Bufano, F.

2014-10-01

35

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

Microsoft Academic Search

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

M. de Groot; A. Cassatella

1984-01-01

36

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

SciTech Connect

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

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

2013-04-20

37

Study of molecular layers in the atmosphere of the supergiant star mu Cep by interferometry in the K band  

E-print Network

Infrared interferometry of supergiant and Mira stars has recently been reinterpreted as revealing the presence of deep molecular layers. Empirical models for a photosphere surrounded by a simple molecular layer or envelope have led to a consistent interpretation of previously inconsistent data. The stellar photospheres are found to be smaller than previously understood, and the molecular layer is much higher and denser than predicted by hydrostatic equilibrium. However, the analysis was based on spatial observations with medium-band optical filters, which mixed the visibilities of different spatial structures. This paper reports spatial interferometry with narrow spectral bands, isolating near-continuum and strong molecular features, obtained for the supergiant mu Cep. The measurements confirm strong variation of apparent diameter across the K-band. A layer model shows that a stellar photosphere of angular diameter 14.11+/-0.60 mas is surrounded by a molecular layer of diameter 18.56+/-0.26 mas, with an optical thickness varying from nearly zero at 2.15 microns to >1 at 2.39 microns. Although mu Cep and alpha Ori have a similar spectral type, interferometry shows that they differ in their radiative properties. Comparison with previous broad-band measurements shows the importance of narrow spectral bands. The molecular layer or envelope appears to be a common feature of cool supergiants.

G. Perrin; S. T. Ridgway; T. Verhoelst; P. A. Schuller; V. Coude du Foresto; W. A. Traub; R. Millan-Gabet; M. G. Lacasse

2005-02-21

38

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

39

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

40

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

41

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

42

The Vast Population of Wolf-Rayet and Red Supergiant Stars in M101. I. Motivation and First Results  

NASA Astrophysics Data System (ADS)

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

Shara, Michael M.; Bibby, Joanne L.; Zurek, David; Crowther, Paul A.; Moffat, Anthony F. J.; Drissen, Laurent

2013-12-01

43

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

44

Variability of Yellow Supergiants  

NASA Astrophysics Data System (ADS)

During the past three years 58 of 131 yellow supergiant stars selected from the Sky Catalogue 2000.0, Volume 1, Stars to magnitude 8.0 (1982), edited by Hershfeld and Sinnott, have been monitored at the SW Missouri State University Baker Observatory using a Photometrics PM512 liquid-nitrogen cooled CCD detector on a 0.4m Cassegrain reflector. These stars are being studied in order to determine what fraction of yellow supergiants are variable and whether low amplitude variations occur. The technique of CCD differential photometry was used, which required that a comparison star be within five arc minutes of a program star in order to be imaged simultaneously. Each program star was imaged on several nights for a total of at least 10 times with a signal-to-noise ratio of at least 100. Nightly bias and flat images were obtained in order to calibrate the program images. The aperture photometry package in IRAF was used for image analysis. Also, concurrent observations were made of several control pairs of main sequence A and G spectral class binaries not known to be variable. At the 3 sigma level of the standard deviation of the means of the differences in magnitude for the control pairs: six known variable stars have been recovered, three new suspected variables have been found, and 40 yellow supergiants have been found non-variable within the precision of the measurements. (Nine stars were later determined not to be supergiants.) These 40 non-variable yellow supergiants are distributed liberally across the Cepheid instability strip on the H-R diagram. The three suspected variables have V amplitudes of 0.02 to 0.06 magnitude. This work is supported by NSF grant AST-9315061.

Patterson, R. S.

1997-05-01

45

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

E-print Network

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

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

2006-02-14

46

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

47

QUANTITATIVE SPECTROSCOPY OF BLUE SUPERGIANT STARS IN THE DISK OF M81: METALLICITY, METALLICITY GRADIENT, AND DISTANCE  

SciTech Connect

The quantitative spectral analysis of low-resolution ({approx}5 A) Keck LRIS spectra of blue supergiants in the disk of the giant spiral galaxy M81 is used to determine stellar effective temperatures, gravities, metallicities, luminosities, interstellar reddening, and a new distance using the flux-weighted gravity-luminosity relationship. Substantial reddening and extinction are found with E(B - V) ranging between 0.13 and 0.38 mag and an average value of 0.26 mag. The distance modulus obtained after individual reddening corrections is 27.7 {+-} 0.1 mag. The result is discussed with regard to recently measured tip of the red giant branch and Cepheid distances. The metallicities (based on elements such as iron, titanium, magnesium) are supersolar ( Almost-Equal-To 0.2 dex) in the inner disk (R {approx}< 5 kpc) and slightly subsolar ( Almost-Equal-To - 0.05 dex) in the outer disk (R {approx}> 10 kpc) with a shallow metallicity gradient of 0.034 dex kpc{sup -1}. The comparison with published oxygen abundances of planetary nebulae and metallicities determined through fits of Hubble Space Telescope color-magnitude diagrams indicates a late metal enrichment and a flattening of the abundance gradient over the last 5 Gyr. This might be the result of gas infall from metal-rich satellite galaxies. Combining these M81 metallicities with published blue supergiant abundance studies in the Local Group and the Sculptor Group, a galaxy mass-metallicity relationship based solely on stellar spectroscopic studies is presented and compared with recent studies of Sloan Digital Sky Survey star-forming galaxies.

Kudritzki, Rolf-Peter; Urbaneja, Miguel A.; Gazak, Zachary; Bresolin, Fabio [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Przybilla, Norbert [Dr. Remeis-Sternwarte Bamberg and ECAP, D-96049 Bamberg (Germany); Gieren, Wolfgang; Pietrzynski, Grzegorz, E-mail: kud@ifa.hawaii.edu, E-mail: urbaneja@ifa.hawaii.edu, E-mail: zgazak@ifa.hawaii.edu, E-mail: bresolin@ifa.hawaii.edu, E-mail: przybilla@sternwarte.uni-erlangen.de, E-mail: wgieren@astro-udec.cl, E-mail: pietrzyn@astrouw.edu.pl [Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)

2012-03-01

48

RED SUPERGIANT STARS AS COSMIC ABUNDANCE PROBES: NLTE EFFECTS IN J-BAND IRON AND TITANIUM LINES  

SciTech Connect

Detailed non-LTE (NLTE) calculations for red supergiant (RSG) stars are presented to investigate the influence of NLTE on the formation of atomic iron and titanium lines in the J band. With their enormous brightness at J band RSG stars are ideal probes of cosmic abundances. Recent LTE studies have found that metallicities accurate to 0.15 dex can be determined from medium-resolution spectroscopy of individual RSGs in galaxies as distant as 10 Mpc. The NLTE results obtained in this investigation support these findings. NLTE abundance corrections for iron are smaller than 0.05 dex for effective temperatures between 3400 K and 4200 K and 0.1 dex at 4400 K. For titanium the NLTE abundance corrections vary smoothly between -0.4 dex and +0.2 dex as a function of effective temperature. For both elements, the corrections also depend on stellar gravity and metallicity. The physical reasons behind the NLTE corrections and the consequences for extragalactic J-band abundance studies are discussed.

Bergemann, Maria; Kudritzki, Rolf-Peter; Lind, Karin [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); Davies, Ben [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Gazak, Zach, E-mail: mbergema@mpa-garching.mpg.de, E-mail: klind@mpa-garching.mpg.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)

2012-06-01

49

The Identification of Extreme Asymptotic Giant Branch Stars and Red Supergiants in M33 With 24??m Variability  

NASA Astrophysics Data System (ADS)

We present the first detection of 24 ?m variability in 24 sources in the Local Group galaxy M33. These results are based on 4 epochs of Multiband Imaging Photometer for Spitzer observations, which are irregularly spaced over ˜ 750 days. We find that these sources are constrained exclusively to the Holmberg radius of the galaxy, which increases their chances of being members of M33. We have constructed spectral energy distributions (SEDs) ranging from the optical to the submillimeter to investigate the nature of these objects. We find that 23 of our objects are most likely heavily self-obscured, evolved stars, while the remaining source is the Giant H ii region, NGC 604. We believe that the observed variability is the intrinsic variability of the central star reprocessed through their circumstellar dust shells. Radiative transfer modeling was carried out to determine their likely chemical composition, luminosity, and dust production rate (DPR). As a sample, our modeling has determined an average luminosity of (3.8+/- 0.9)× {{10}4} L? and a total DPR of (2.3+/- 0.1)× {{10}-5} M? y{{r}-1}. Most of the sources, given the high DPRs and short wavelength obscuration, are likely extreme asymptotic giant branch (XAGB) stars. Five of the sources are found to have luminosities above the classical AGB limit (Mbol <-7.1 mag, L > 54,000 L?), which classifies them as probable red supergiants (RSGs). Almost all of the sources are classified as oxygen-rich. As also seen in the LMC, a significant fraction of the dust in M33 is produced by a handful of XAGB and RSG stars.

Montiel, Edward J.; Srinivasan, Sundar; Clayton, Geoffrey C.; Engelbracht, Charles W.; Johnson, Christopher B.

2015-02-01

50

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

51

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

52

IUE and Einstein survey of late-type giant and supergiant stars and the dividing line  

NASA Technical Reports Server (NTRS)

Results are presented on an IUE UV survey of 255 late-type G, K, and M stars, complementing the Maggio et al. (1990) Einstein X-ray survey of 380 late-type stars. The large data sample of X-ray and UV detections make it possible to examine the activity relationship between the X-ray and the UV emissions. The results confirm previous finding of a trend involving a steeply-dropping upper envelope of the transition region line fluxes, f(line)/f(V), as the dividing line is approached. This suggests that a sharp decrease in maximum activity accompanies the advancing spectral type, with the dividing line corresponding to this steep gradient region. The results confirm the rotation-activity connection for stars in this region of the H-R diagram.

Haisch, Bernhard M.; Bookbinder, Jay A.; Maggio, A.; Vaiana, G. S.; Bennett, Jeffrey O.

1990-01-01

53

The Mass-loss Return from Evolved Stars to the Large Magellanic Cloud. IV. Construction and Validation of a Grid of Models for Oxygen-rich AGB Stars, Red Supergiants, and Extreme AGB Stars  

NASA Astrophysics Data System (ADS)

To measure the mass loss from dusty oxygen-rich (O-rich) evolved stars in the Large Magellanic Cloud (LMC), we have constructed a grid of models of spherically symmetric dust shells around stars with constant mass-loss rates using 2Dust. These models will constitute the O-rich model part of the "Grid of Red supergiant and Asymptotic giant branch star ModelS" (GRAMS). This model grid explores four parameters—stellar effective temperature from 2100 K to 4700 K luminosity from 103 to 106 L sun; dust shell inner radii of 3, 7, 11, and 15 R star; and 10.0 ?m optical depth from 10-4 to 26. From an initial grid of ~1200 2Dust models, we create a larger grid of ~69,000 models by scaling to cover the luminosity range required by the data. These models are available online to the public. The matching in color-magnitude diagrams and color-color diagrams to observed O-rich asymptotic giant branch (AGB) and red supergiant (RSG) candidate stars from the SAGE and SAGE-Spec LMC samples and a small sample of OH/IR stars is generally very good. The extreme AGB star candidates from SAGE are more consistent with carbon-rich (C-rich) than O-rich dust composition. Our model grid suggests lower limits to the mid-infrared colors of the dustiest AGB stars for which the chemistry could be O-rich. Finally, the fitting of GRAMS models to spectral energy distributions of sources fit by other studies provides additional verification of our grid and anticipates future, more expansive efforts.

Sargent, Benjamin A.; Srinivasan, S.; Meixner, M.

2011-02-01

54

The Aro 1 mm Survey of the Oxygen-Rich Envelope of Supergiant Star NML Cygnus  

NASA Astrophysics Data System (ADS)

Although a number of molecular line surveys of carbon-rich circumstellar envelopes (CSE) have been performed, only one oxygen-rich CSE, that of VY Canis Majoris (VY CMa), has been studied in depth. The Arizona Radio Observatory (ARO) 1 mm survey of VY CMa showed a very different and interesting chemistry dominated by sulfur- and silicon-bearing compounds as well as a number of more exotic species. A similar survey of the oxygen rich star NML Cygnus (NML Cyg) from 215 to 285 GHz is currently under way using the ARO Sub-millimeter Telescope. Initial observations show that this circumstellar envelope appears to be as chemically rich as that of VY CMa. Molecules including 12CO, 13CO, 12CN, 13CN, HCN, HCO+, CS, SO{_2}, SiO and 30SiO have been observed in NML Cyg. Line profiles of this source also suggest that there may be multiple outflows and that the circumstellar envelope is not spherically symmetric. Current results will be presented.

Edwards, Jessica L.; Ziurys, L. M.; Woolf, N. J.

2011-06-01

55

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

NASA Astrophysics Data System (ADS)

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

Harris, William

2010-09-01

56

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

57

NEAR-INFRARED COUNTERPARTS TO CHANDRA X-RAY SOURCES TOWARD THE GALACTIC CENTER. II. DISCOVERY OF WOLF-RAYET STARS AND O SUPERGIANTS  

SciTech Connect

We present new identifications of infrared counterparts to the population of hard X-ray sources near the Galactic center detected by the Chandra X-ray Observatory. We have spectroscopically confirmed 16 new massive stellar counterparts to the X-ray population, including nitrogen-type (WN) and carbon-type (WC) Wolf-Rayet stars, and O supergiants. These discoveries increase the total sample of massive stellar X-ray sources in the Galactic center region to 30 (possibly 31). For the majority of these sources, the X-ray photometry is consistent with thermal emission from plasma having temperatures in the range of kT = 1-8 keV or non-thermal emission having power-law indices in the range of -1 {approx}< GAMMA {approx}< 3, and X-ray luminosities in the range of L{sub X} {approx} 10{sup 32}-10{sup 34} erg s{sup -1} (0.5-8.0 keV). Several sources have exhibited X-ray variability of several factors between observations. These X-ray properties are not a ubiquitous feature of single massive stars but are typical of massive binaries, in which the high-energy emission is generated by the collision of supersonic winds, or by accretion onto a compact companion. However, without direct evidence for companions, the possibility of intrinsic hard X-ray generation from single stars cannot be completely ruled out. The spectral energy distributions of these sources exhibit significant infrared excess, attributable to free-free emission from ionized stellar winds, supplemented by hot dust emission in the case of the WC stars. With the exception of one object located near the outer regions of the Quintuplet cluster, most of the new stars appear isolated or in loose associations. Seven hydrogen-rich WN and O stars are concentrated near the Sagittarius B H II region, while other similar stars and more highly evolved hydrogen-poor WN and WC stars lie scattered within {approx}50 pc, in projection, of Sagitarrius A West. We discuss various mechanisms capable of generating the observed X-rays and the implications these stars have for massive star formation in the Galaxy's Central Molecular Zone.

Mauerhan, J. C.; Stolovy, S. R. [Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States); Muno, M. P. [Space Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125 (United States); Morris, M. R. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States); Cotera, A., E-mail: mauerhan@ipac.caltech.ed [SETI Institute, 515 N. Whisman Rd., Mountain View, CA (United States)

2010-02-10

58

Chandra HETG Spectroscopy of the F0 Ib Supergiant Canopus  

Microsoft Academic Search

The F0 supergiant Canopus (alpha Car) was observed by the Chandra X-ray Observatory on 2000 July 21 for 96 ksec using the High Energy Transmission Grating (HETG) and the ACIS-S detector. Canopus is the nearest supergiant star at a distance of only 96 pc and undergoing He-burning, post-M-supergiant evolution. It has a hot (107 K) corona with log Lx ~

A. Brown; T. R. Ayres; R. A. Osten; G. M. Harper

2000-01-01

59

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

60

Chemical composition of late-type supergiants. III. carbon, nitrogen, and oxygen abundances for 19 G and K Ib stars  

Microsoft Academic Search

Through an analysis of high-resolution, high signal-to-noise data, carbon, nitrogen, and oxygen abundances are investigated in 19 G and K Ib stars. The final analysis yields abundances for 16 of these objects; the other three have to be eliminated due to heavy blending of (C I) with a previously undetected line of FeH. The derived abundances show that, relative to

R. E. Luck

1978-01-01

61

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

62

Amplitude Variations in Pulsating Yellow Supergiants  

NASA Astrophysics Data System (ADS)

It was recently discovered that the amplitudes of pulsating red giants and supergiants vary significantly on time scales of 20-30 pulsation periods. Here, we analyze the amplitude variability in 29 pulsating yellow supergiants (5 RVa, 4 RVb, 9 SRd, 7 long-period Cepheid, and 4 yellow hypergiant stars), using visual observations from the AAVSO International Database, and Fourier and wavelet analysis using the AAVSO’s VSTAR package. We find that these stars vary in amplitude by factors of up to 10 or more (but more typically 3-5), on a mean time scale (L) of 33 ± 4 pulsation periods (P). Each of the five sub-types shows this same behavior, which is very similar to that of the pulsating red giants, for which the median L/P was 31. For the RVb stars, the lengths of the cycles of amplitude variability are the same as the long secondary periods, to within the uncertainty of each.

Percy, J. R.; Kim, R. Y. H.

2014-12-01

63

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

64

Supergiants: Stellar Winds and Mass-loss  

NASA Astrophysics Data System (ADS)

The knowledge of stellar wind properties and mass loss rates in massive stars is a milestone in the stellar evolution and disk formation process. Our current view of winds reveals they are often highly variable and inhomogeneous. We review here the wind structure of early-type stars, such as the new hydrodynamical solutions, the wind clumping and the weak-wind problem. We also discuss the peculiar circumstellar environment around some short-lived phases of evolved massive stars (i.e., LBV and B[e] supergiants). Accurate mass loss rate estimates are crucial keys to discuss the importance of different triggering mechanisms in driving a wind.

Cidale, L. S.

2014-10-01

65

Spectral Effects of Pulsations in Blue Supergiants  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

66

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

67

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

68

THE TEMPERATURES OF RED SUPERGIANTS  

SciTech Connect

We present a re-appraisal of the temperatures of red supergiants (RSGs) using their optical and near-infrared spectral energy distributions (SEDs). We have obtained data of a sample of RSGs in the Magellanic Clouds using VLT+XSHOOTER, and we fit MARCS model atmospheres to different regions of the spectra, deriving effective temperatures for each star from (1) the TiO bands, (2) line-free continuum regions of the SEDs, and (3) the integrated fluxes. We show that the temperatures derived from fits to the TiO bands are systematically lower than the other two methods by several hundred kelvin. The TiO fits also dramatically overpredict the flux in the near-IR, and imply extinctions which are anomalously low compared to neighboring stars. In contrast, the SED temperatures provide good fits to the fluxes at all wavelengths other than the TiO bands, are in agreement with the temperatures from the flux integration method, and imply extinctions consistent with nearby stars. After considering a number of ways to reconcile this discrepancy, we conclude that three-dimensional effects (i.e., granulation) are the most likely cause, as they affect the temperature structure in the upper layers where the TiO lines form. The continuum, however, which forms at much deeper layers, is apparently more robust to such effects. We therefore conclude that RSG temperatures are much warmer than previously thought. We discuss the implications of this result for stellar evolution and supernova progenitors, and provide relations to determine the bolometric luminosities of RSGs from single-band photometry.

Davies, Ben [Astrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)] [Astrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom); Kudritzki, Rolf-Peter; Gazak, Zach [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); 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); Trager, Scott [Kapteyn Institute, University of Groningen, P.O. Box 800, 9700-AV Groningen (Netherlands)] [Kapteyn Institute, University of Groningen, P.O. Box 800, 9700-AV Groningen (Netherlands); Lancon, Ariane [Observatoire Astronomique and CNRS UMR 7550, Universite de Strasbourg, F-67000 Strasbourg (France)] [Observatoire Astronomique and CNRS UMR 7550, Universite de Strasbourg, F-67000 Strasbourg (France); Bergemann, Maria [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); Evans, Chris [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)] [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Chiavassa, Andrea [CNRS Laboratoire Lagrange, Universite de Nice Sophia-Antipolis, Observatoire de la Cote d'Azur, BP 4229, F-06304 Nice Cedex 4 (France)] [CNRS Laboratoire Lagrange, Universite de Nice Sophia-Antipolis, Observatoire de la Cote d'Azur, BP 4229, F-06304 Nice Cedex 4 (France)

2013-04-10

69

The $^{13}$Carbon footprint of B[e] supergiants  

E-print Network

We report on the first detection of $^{13}$C enhancement in two B[e] supergiants in the Large Magellanic Cloud. Stellar evolution models predict the surface abundance in $^{13}$C to strongly increase during main-sequence and post-main sequence evolution of massive stars. However, direct identification of chemically processed material on the surface of B[e] supergiants is hampered by their dense, disk-forming winds, hiding the stars. Recent theoretical computations predict the detectability of enhanced $^{13}$C via the molecular emission in $^{13}$CO arising in the circumstellar disks of B[e] supergiants. To test this potential method and to unambiguously identify a post-main sequence B[e]SG by its $^{13}$CO emission, we have obtained high-quality $K$-band spectra of two known B[e] supergiants in the Large Magellanic Cloud, using the Very Large Telescope's Spectrograph for INtegral Field Observation in the Near-Infrared (VLT/SINFONI). Both stars clearly show the $^{13}$CO band emission, whose strength implies ...

Liermann, A; Schnurr, O; Fernandes, M Borges

2010-01-01

70

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

71

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

72

Chemical evolution of Magellanic Clouds. II - Equivalent widths and abundances for three young supergiants of the SMC  

Microsoft Academic Search

Spite et al. (1988) compared the chemical composition of the atmospheres of three F supergiants in the SMC to the chemical composition of the Galactic supergiant Canopus. In this paper, equivalent widths for the stars, AZ 140, AZ 197, and AZ 369, are presented along with the derived abundance, line by line. Various physical constants of the lines are presented.

M. Spite; S. Huille; F. Spite; P. Francois

1988-01-01

73

Scandium abundance in M supergiants  

SciTech Connect

The spectra of three type M supergiants (delta/sup 2/ Lyr, R Lyr, ..cap alpha.. Her) observed at 6-A/mm dispersion in the 6300--6400 A wavelength interval are compared with a synthetic spectrum based on the Minnaert formula. The ..gamma..-, ..gamma..'-system bands of TiO and the ..gamma..-system ZrO bands are taken into account. The atmospheres of these supergiants do not contain any significant scandium excess compared with the sun.

Orlov, M.Y.; Shavrina, A.V.

1981-01-01

74

Clumping in O-type Supergiants  

NASA Astrophysics Data System (ADS)

We have analyzed the spectra of seven Galactic O4 supergiants, with the NLTE wind code CMFGEN. For all stars, we have found that clumped wind models match well lines from different species spanning a wavelength range from FUV to optical, and remain consistent with H? data. We have achieved an excellent match of the P V ??1118, 1128 resonance doublet and N IV ?1718, as well as He II ?4686 suggesting that our physical description of clumping is adequate. We find very small volume filling factors and that clumping starts deep in the wind, near the sonic point. The most crucial consequence of our analysis is that the mass loss rates of O stars need to be revised downward significantly, by a factor of 3 and more compared to those obtained from smooth-wind models.

Bouret, J.-C.; Lanz, T.; Hillier, D. J.; Foellmi, C.

2008-04-01

75

B[e] supergiants: What is their evolutionary status?  

E-print Network

In this paper, we investigate the evolutionary status of B[e]~stars from the point of view of stellar evolution theory. We try to answer to the question of how massive hot supergiants --- i.e. evolved stars --- can be capable of producing a circumstellar disk. We find and discuss three possibilities: very massive evolved main sequence stars close to critical rotation due to their proximity to their Eddington-limit, blue supergiants which have just left the red supergiant branch, and single star merger remnants of a close binary system. While the latter process seems to be required to understand the properties of the spectroscopic binary R4 in the LMC, the other two scenarios may be capable of explaining the distribution of the B[e] stars in the HR~diagram. The three scenarios make different predictions about the duration of the B[e]~phase, the time integrated disk mass and the stellar properties during the B[e]~phase, which may ultimately allow to distinguish them observationally.

N. Langer; A. Heger

1997-11-25

76

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

77

CN status of a sample of galactic OB supergiants  

NASA Astrophysics Data System (ADS)

In our search for evidence for the CNO processed material in the atmospheres of galactic OB supergiants we measured the equivalent widths of photospheric lines in their high-resolution IUE spectra. A sample of 36 stars was investigated and the lines He II 1640, C III 1247, N IV 1718 and O IV 1339 were studied. All ions show a well-defined dependence on effective temperature. Comparison of stars with questionable CN status with normal stars gives evidence for a decrease in equivalent widths of C III and O IV lines accompanied by an increase in equivalent widths of N IV and He II lines, which leads to abundance differences.

Sarta Dekovic, M.; Kotnik-Karuza, D.

2005-11-01

78

First ultraviolet spectropolarimetry of hot supergiants  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

79

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

80

Evidence for processed material in the atmospheres of Large Magellanic Cloud B supergiants  

NASA Technical Reports Server (NTRS)

We present a high-dispersion study of the optical spectra of 11 LMC B-type supergiants. These stars had been shown previously to have a wide range in nitrogen absorption line strengths, despite having very similar temperatures and luminosities. The current study shows that the relatively rare nitrogen-weak stars also have weaker photospheric helium lines and stronger photospheric oxygen lines than the more spectroscopically typical supergiants. This pattern suggests that the vast majority of LMC B-type supergiants have had their surfaces contaminated by material from their original hydrogen-burning cores - with a resultant enhancement of surface nitrogen and helium and a depletion in oxygen - while the spectroscopically nitrogen-weak stars are more likely to have retained their main-sequence surface abundances.

Fitzpatrick, Edward L.; Bohannan, Bruce

1993-01-01

81

How thin B[e] supergiant disks can be?  

NASA Astrophysics Data System (ADS)

We investigate the shape of the envelope around B[e] supergiant stars using a model developed by Stee & Araujo (1994) for Be stars. We obtain mass loss rates {dot M} between 5.5*10(-7) and 6.2* 10(-6) M_?yr(-1) depending on mass flux variation from polar to equatorial regions. We find that winds from B[e] stars can be so dense that they become optically thick in the continuum, masking the photosphere of the central star. For mass loss rates larger than 10(-5) M_?yr(-1) it is not possible to see the stellar photosphere even for pole-on B[e] stars. Using a two-component wind model driven by optically thin lines in the equatorial regions and optically thick lines in the polar regions, we obtain a relation between the geometry of the envelope and the total mass loss. We also put limits on the inclination angle (i) beyond which the stellar photosphere is masked. Finally, this study seems to discard "wind-compressed disks" (WCD) models as a possible senario for B[e] supergiant envelopes.

Stee, Ph.

1998-08-01

82

Evolution and the period-luminosity relation for red supergiants in the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

Excitation of radial pulsations in red supergiants of Magellanic Clouds is investigated using the stellar evolution calculations and the self-consistent solution of the equations of radiation hydrodynamics and turbulent convection. The stars with initial masses 6 M ? ? M ZAMS ? 28 M ? and the initial chemical composition X = 0.7, 0.004 ? Z ? 0.008 are shown to be unstable against fundamental mode oscillations with periods from 17 to 1200 days as they become helium burning red supergiants. The period-luminosity relation slightly depends on the mass loss rate varying with a factor of three, whereas its dependence on the metal abundance is given by ?M bol = 0.89 ? log Z. In comparison with galactic red supergiants the low metal abundances in red supergiants of Magellanic Clouds are responsible for their higher effective temperatures and substantially narrower ranges of evolutionary radius change during helium burning. Therefore on the period-mass diagram the red supergiants of Magellanic Clouds are located within the strip with width of ? log M ? 0.09, so that the uncertainty of mass evaluation of the red supergiant with the known pulsation period is nearly 25%.

Fadeyev, Yu. A.

2013-05-01

83

Betelgeuse - Numerical Simulations of an Entire Supergiant  

NASA Astrophysics Data System (ADS)

The red supergiant Betelgeuse varies in visual brightness on time-scales of weeks, months, and years. In 1975 Martin Schwarzschild attributed these fluctuations to huge convection cells, each of them covering a significant fraction of the stellar surface, so that the individual brightness changes result in a non-vanishing variation of the total luminosity. Starting about 11 years ago, interferometric observations in the visible wavelength regime revealed the existence of large-scale inhomogeneities on the surface of Betelgeuse, typically described as 0 to 3 unresolved ``hot spots'' on a cooler circular stellar disk, varying with time in number, intensity, and position. Nevertheless, the observations still have a poor resolution, resulting in surface ``images'' with only a handful of pixels. And there has been some debate about the nature of the detected surface features: Are they of convective origin due to the action of granules or supergranules? And what is the role of shocks, stellar rotation, or magnetic fields? To improve the theoretical understanding of the surface phenomena of Betelgeuse, a new radiation hydrodynamics code (``COBOLD'') has been written with the aim to include the entire star in the computational box. It employs special inner (for the stellar core) and outer boundaries appropriate for this particular geometry. The simulated star shows indeed huge surface convection cells and high photospheric velocities. But the cells look different from solar granulation and produce features which might be interpreted as ``hot spots'' in low-resolution observations.

Freytag, Bernd

84

Massive Stars in Transition  

E-print Network

We discuss the various post-main sequence phases of massive stars, focusing on Wolf-Rayet stars, Luminous Blue Variables, plus connections with other early-type and late-type supergiants. End states for massive stars are also investigated, emphasising connections between Supernovae originating from core-collapse massive stars and Gamma Ray Bursts.

Paul A. Crowther

2003-05-08

85

Line Profile Variability and a Possible Magnetic Field in the Spectra of Supergiant ? Ori Aa  

NASA Astrophysics Data System (ADS)

Results of spectropolarimetric observations of the supergiant ? Ori are reported. The fast line profile variability (LPV) with a period of about 3 hours is found and a connection of LPV with a non-radial pulsation of the star is supposed. We did not find any evidence for a moderate stellar magnetic field as reported by Bouret et. al., 2008}.

Kholtygin, A. F.; Chountonov, G. A.; Dushin, V. V.

86

Problems in abundance determination from UV spectra of hot supergiants  

NASA Astrophysics Data System (ADS)

We present measurements of equivalent widths of the UV, presumably photospheric lines: C III 1247 Å, N III 1748 Å, N III 1752 Å, N IV 1718 Å and He II 1640 Å in high-resolution IUE spectra of 24 galactic OB supergiants. Equivalent widths measured from the observed spectra have been compared with their counterparts in the Tlusty NLTE synthetic spectra. We discuss possibilities of static plan-parallel model to reproduce observed UV spectra of hot massive stars and possible reasons why observations differ from the model so much.

Dekovi?, M. Sarta; Kotnik-Karuza, D.; Jurki?, T.; Prester, D. Dominis

2010-03-01

87

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

88

On the atmospheric structure and fundamental parameters of red supergiants  

NASA Astrophysics Data System (ADS)

We present near-infrared spectro-interferometric studies of red supergiant (RSG) stars using the VLTI/AMBER instrument, which are compared to previously obtained similar observations of AGB stars. Our observations indicate spatially extended atmospheric molecular layers of water vapor and CO, similar as previously observed for Mira stars. Data of VY~CMa indicate that the molecular layers are asymmetric, possibly clumpy. Thanks to the spectro-interferometric capabilities of the VLTI/AMBER instrument, we can isolate continuum bandpasses, estimate fundamental parameters of our sources, locate them in the HR diagram, and compare their positions to recent evolutionary tracks. For the example of VY CMa, this puts it close to evolutionary tracks of initial mass 25-32 M ?. Comparisons of our data to hydrostatic model atmospheres, 3d simulations of convection, and 1d dynamic model atmospheres based on self-excited pulsation models indicate that none of these models can presently explain the observed atmospheric extensions for RSGs. The mechanism that levitates the atmospheres of red supergiant is thus a currently unsolved problem.

Wittkowski, M.; Arroyo-Torres, B.; Marcaide, J. M.; Abellan, F. J.; Chiavassa, A.; Freytag, B.; Scholz, M.; Wood, P. R.; Hauschildt, P. H.

2015-01-01

89

Identification of Red Supergiants in the Magellanic Clouds.  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

90

A spectroscopic survey of B supergiants in the Large Magellanic Cloud  

NASA Technical Reports Server (NTRS)

The results of a low-dispersion digital optical spectral survey of about 100 B-type supergiants in the Large Magellanic Cloud are presented. The MK spectral classification framework for B supergiants has been transferred to the metal-weak LMC stars, and recommended classification standards have been designated. Variations among the metal line strengths are examined. The most extreme variations are found for the nitrogen lines, for which a range of a factor of 3 or more may be seen in the equivalent widths within some spectral subclasses. It is suggested that these variations indicate a range of nitrogen surface abundances among the B supergiants, resulting from contamination of some of the stellar surfaces by processed material from the original H-burning core.

Fitzpatrick, Edward L.

1991-01-01

91

Spectroscopy and Multi-Band Photometry of Yellow and Red Supergiants in M31 and M33  

NASA Astrophysics Data System (ADS)

Recent supernova and transient surveys have revealed an increasing number of non-terminal stellar eruptions. Though the progenitor class of these eruptions includes the most luminous stars, little is known of the pre-supernova mechanics of massive stars in their most evolved state, thus motivating a census of possible progenitors. From surveys of evolved and unstable luminous star populations in nearby galaxies, we select a sample of supergiant candidates in M31 and M33 for review of spectral characteristics and spectral energy distributions. Since the position of intermediate and late-type supergiants on the color-magnitude diagram can be heavily contaminated by foreground dwarfs, we employ spectral classification and multi-band photometry from optical and near-infrared surveys to confirm membership. In this study, we present spectral types and discussion of spectral energy distributions of intermediate-type red and yellow supergiants in M31 and M33.

Gordon, Michael; Humphreys, Roberta M.

2015-01-01

92

Two Circumstellar Bubbles around Blue Supergiants in the LMC  

NASA Astrophysics Data System (ADS)

During its evolution, a massive star loses mass via stellar winds. A fast stellar wind may sweep up the ambient medium into a shell, appearing as a ``ring nebula" around the central star. While ring nebulae around Wolf-Rayet stars have received considerable attention in recent years, ring nebulae around O and B stars are far less well-explored. This is because very few well-defined rings around OB stars are known; in our Galaxy only two cases are known, the Bubble Nebula and NGC6164-5. Last year we discovered two ring nebulae around blue supergiants, Sk-69 279 (O9f; V=12.8 mag) and Sk-69 271 (B2; V=12.0 mag), in the Large Magellanic Cloud (Weis et al. 1995, RevMexAASC 3, 237). Both nebulae have diameter ~ 19'', corresponding to ~ 5 pc. To investigate the origin of these nebulae, we obtained long-slit H? +[N II] echelle observations with the 4m telescope at the Cerro Tololo Inter-American Observatory. The nebula around Sk-69 279 shows line-split indicating an expansion velocity of 27km s(-1) , while the nebula around Sk-69 271 shows no line-split, suggesting an expansion velocity <15km s(-1) . Assuming that t = 0.5 r/v, the dynamic age of these nebulae are 1x10(5) yr and >2x10(5) yr, respectively. The most tale-telling information comes from the [N II]/H? ratio. Both nebulae show [N II]/H? ratios significantly higher than those of the background H II emission. This behavior is typical for ring nebulae around WR stars or luminous blue variables that contain stellar nucleosynthesis processed material. Therefore, we conclude that the ring nebulae around Sk-69 279 and Sk-69 271 must be ``circumstellar bubbles" containing processed stellar material. These two blue supergiants must have evolved past the red supergiant phase. The chemical composition of these two ring nebulae could place constraints on models of stellar evolution.

Weis, K.; Chu, Y.-H.; Bomans, D. J.

1996-05-01

93

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

94

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

E-print Network

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

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

2006-03-15

95

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

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 exhibits 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 effciently as a probe to study stellar winds.

Manousakis, Antonios; Walter, Roland; Blondin, John

2014-01-01

97

Stellar Activity and Mass Loss from A and F Supergiants  

NASA Technical Reports Server (NTRS)

This grant supported the observing and data analysis for FUSE Cycle 4 project DO47 to observe five late-A and F supergiants using a total observing allocation of 150 ksec. Stellar activity on A and F supergiants has been poorly studied in the past; primarily because the photospheric continuum dominates any chromospheric ( 10 4 K) or transition region (TR; 10 5 K) emission lines far into the ultraviolet. FUSE observations of A and F supergiants offer one of the best methods to study stellar activity on these stars, because many activity indicators longward of 1200 A are swamped by the photospheric continuum emission. We used FUSE FUV spectra to search for 0 VI and C I11 TR emission lines and obtained data for t Car (A8 Ib, for 60.5 ksec, on 2003 Apr 27), 8 Sco (F1 11, 22.7 ksec, 2003 Aug 2), ct Per (F5 Ib, 30.8 ksec, 2003 Oct l), a UMi (F7 Ib-11, 23.9 ksec, 2003 Oct 14), and y Cyg (F8 Ib, 25.8 ksec, 2003 Oct 18). These observations used the large LWRS aperture and collected data in time-tagged mode. The LWRS aperture is large enough that the target should remain within the aperture with the normal level of FUSE pointing jitter and target drift. We examined the stellar signal and found that the targets were well within the aperture throughout the observation. The data were split into night-time and day-time data so that the effects of airglow emission were recognizable, and combined day and night spectra were generated using CALFUSE 2.4.0 .

Brown, Alexander

2005-01-01

98

The significance of stellar magnetic field measurements obtained with the photographic technique - The spurious magnetic field of the supergiant Canopus  

Microsoft Academic Search

The author proposes a number of straightforward statistical tests aimed at establishing the significance of stellar magnetic field measurements obtained with Babcock's photographic technique. The power of these methods is illustrated with three Ap stars for which the presence of a magnetic field can be established at an exceedingly high significance level. Application to the supergiant Canopus on the contrary

M. J. Stift

1987-01-01

99

Spitzer Observations of the Supergiant Shell Region in IC 2574  

NASA Astrophysics Data System (ADS)

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

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

2005-09-01

100

Spitzer Observations Of The Supergiant Shell Region In IC 2574  

E-print Network

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

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

2005-08-01

101

Betelgeuse - Numerical Simulations of an Entire Supergiant  

Microsoft Academic Search

The red supergiant Betelgeuse varies in visual brightness on time-scales of weeks, months, and years. In 1975 Martin Schwarzschild attributed these fluctuations to huge convection cells, each of them covering a significant fraction of the stellar surface, so that the individual brightness changes result in a non-vanishing variation of the total luminosity. Starting about 11 years ago, interferometric observations in

Bernd Freytag

2001-01-01

102

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

103

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

104

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

NASA Technical Reports Server (NTRS)

Photometric monitoring has revealed brightness variations of 0.1 m on a time scale of weeks for HD 46703, a metal-deficient F-type field analog of the stars lying above the horizontal branch in globular clusters. It is suggested that HD 46703 belongs to the '89 Her' class of luminous F-type variables. Since HD 46703 is unquestionably a halo object, it is almost certainly a low-mass star. It is suggested that it, and probably the other 89 Her variables, are masquerading as supergiants during their final evolution off the asymptotic giant branch.

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

1984-01-01

105

Investigating the transitional nature of extreme O-type supergiants in X-rays  

NASA Astrophysics Data System (ADS)

We propose to investigate the X-ray properties of HD14947, an O5 supergiant believed to be a transition object between O and Wolf-Rayet stars. Stars belonging to this scarce category display several properties strongly pointing to their transitional status, including broad and strong emission lines in the visible and infrared, and the existence is some cases of surrounding nebulae similar to those existing close to WR stars. We request observation time with XMM-Newton to check whether the X-ray emission of HD14947 deviates significantly from the expected behaviour of regular O-type stars, as recently revealed by our team on the basis of an XMM-Newton observation of a similar object, attempting to establish an additional transition criterion in X-rays for evolved O-type stars.

De Becker, Michael

2011-10-01

106

Stellar winds from Massive Stars  

E-print Network

We review the various techniques through which wind properties of massive stars - O stars, AB supergiants, Luminous Blue Variables (LBVs), Wolf-Rayet (WR) stars and cool supergiants - are derived. The wind momentum-luminosity relation (e.g. Kudritzki et al. 1999) provides a method of predicting mass-loss rates of O stars and blue supergiants which is superior to previous parameterizations. Assuming the theoretical sqrt(Z) metallicity dependence, Magellanic Cloud O star mass-loss rates are typically matched to within a factor of two for various calibrations. Stellar winds from LBVs are typically denser and slower than equivalent B supergiants, with exceptional mass-loss rates during giant eruptions Mdot=10^-3 .. 10^-1 Mo/yr (Drissen et al. 2001). Recent mass-loss rates for Galactic WR stars indicate a downward revision of 2-4 relative to previous calibrations due to clumping (e.g. Schmutz 1997), although evidence for a metallicity dependence remains inconclusive (Crowther 2000). Mass-loss properties of luminous (> 10^5 Lo) yellow and red supergiants from alternative techniques remain highly contradictory. Recent Galactic and LMC results for RSG reveal a large scatter such that typical mass-loss rates lie in the range 10^-6 .. 10^-4 Mo/yr, with a few cases exhibiting 10^-3 Mo/yr.

Paul A. Crowther

2000-10-27

107

X-Ray Photoionized Bubble in the Wind of Vela X-1 Pulsar Supergiant Companion  

NASA Astrophysics Data System (ADS)

Vela X-1 is the archetype of high-mass X-ray binaries (HMXBs), composed of a neutron star and a massive B supergiant. The supergiant is a source of a strong radiatively driven stellar wind. The neutron star sweeps up this wind and creates a huge amount of X-rays as a result of energy release during the process of wind accretion. Here, we provide detailed NLTE models of the Vela X-1 envelope. We study how the X-rays photoionize the wind and destroy the ions responsible for the wind acceleration. The resulting decrease of the radiative force explains the observed reduction of the wind terminal velocity in a direction to the neutron star. The X-rays create a distinct photoionized region around the neutron star filled with a stagnating flow. The existence of such photoionized bubbles is a general property of HMXBs. We unveil a new principle governing these complex objects, according to which there is an upper limit to the X-ray luminosity the compact star can have without suspending the wind due to inefficient line driving.

Krti?ka, Ji?í; Kubát, Ji?í; Skalický, Jan

2012-10-01

108

SLOW RADIATION-DRIVEN WIND SOLUTIONS OF A-TYPE SUPERGIANTS  

SciTech Connect

The theory of radiation-driven winds succeeded in describing terminal velocities and mass-loss rates of massive stars. However, for A-type supergiants the standard m-CAK solution predicts values of mass loss and terminal velocity higher than the observed values. Based on the existence of a slow wind solution in fast rotating massive stars, we explore numerically the parameter space of radiation-driven flows to search for new wind solutions in slowly rotating stars that could explain the origin of these discrepancies. We solve the one-dimensional hydrodynamical equation of rotating radiation-driven winds at different stellar latitudes and explore the influence of ionization changes throughout the wind in the velocity profile. We have found that for particular sets of stellar and line-force parameters, a new slow solution exists over the entire star when the rotational speed is slow or even zero. In the case of slow rotating A-type supergiant stars, the presence of this novel slow solution at all latitudes leads to mass losses and wind terminal velocities which are in agreement with the observed values. The theoretical wind-momentum-luminosity relationship derived with these slow solutions shows very good agreement with the empirical relationship. In addition, the ratio between the terminal and escape velocities, which provides a simple way to predict stellar wind energy and momentum input into the interstellar medium, is also properly traced.

Cure, M. [Departamento de Fisica y Astronomia, Facultad de Ciencias, Universidad de Valparaiso Av. Gran Bretana 1111, Casilla 5030, Valparaiso (Chile); Cidale, L.; Granada, A., E-mail: michel.cure@uv.cl [Departamento de EspectroscopIa, Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata (UNLP), and Instituto de Astrofisica La Plata, CCT La Plata, CONICET-UNLP Paseo del Bosque S/N, 1900 La Plata (Argentina)

2011-08-10

109

X-RAY PHOTOIONIZED BUBBLE IN THE WIND OF VELA X-1 PULSAR SUPERGIANT COMPANION  

SciTech Connect

Vela X-1 is the archetype of high-mass X-ray binaries (HMXBs), composed of a neutron star and a massive B supergiant. The supergiant is a source of a strong radiatively driven stellar wind. The neutron star sweeps up this wind and creates a huge amount of X-rays as a result of energy release during the process of wind accretion. Here, we provide detailed NLTE models of the Vela X-1 envelope. We study how the X-rays photoionize the wind and destroy the ions responsible for the wind acceleration. The resulting decrease of the radiative force explains the observed reduction of the wind terminal velocity in a direction to the neutron star. The X-rays create a distinct photoionized region around the neutron star filled with a stagnating flow. The existence of such photoionized bubbles is a general property of HMXBs. We unveil a new principle governing these complex objects, according to which there is an upper limit to the X-ray luminosity the compact star can have without suspending the wind due to inefficient line driving.

Krticka, Jiri; Skalicky, Jan [Ustav teoreticke fyziky a astrofyziky, Masarykova univerzita, Kotlarska 2, CZ-611 37 Brno (Czech Republic); Kubat, Jiri [Astromomicky ustav Akademie ved Ceske republiky, Fricova 298, CZ-251 65 Ondrejov (Czech Republic)

2012-10-01

110

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

111

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

112

Physics of Mass Loss in Massive Stars  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

113

Infrared stars in binary systems  

NASA Technical Reports Server (NTRS)

The peculiar F-type supergiant HD 101584, which has a large and unusual infrared excess, is discussed along with the possibility that the infrared radiation could be accounted for by a cool companion. The peculiar F supergiants 89 Her, v Sgr, and R CrB are also considered as possible binary systems containing an infrared star. It is pointed out that all four of these stars have infrared excesses with characteristics similar to the infrared radiation from several cool objects which are known single stars.

Humphreys, R. M.; Ney, E. P.

1974-01-01

114

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

NASA Technical Reports Server (NTRS)

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

Shore, S. N.; Sanduleak, N.

1984-01-01

115

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

116

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

SciTech Connect

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

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

2011-09-10

117

WINDS IN CORONAE BOREALIS STARS Geoffrey Clayton,  

E-print Network

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

Bianchi, Luciana

118

Extinction and Scattering Properties of Dust Around Red Supergiants  

NASA Astrophysics Data System (ADS)

We have been amassing a unique dataset which can be used to investigate the amount and nature of dust produced by red supergiants (RSGs) in very different environments. To this end, optical spectra are being obtained for RSGs in various galaxies in the Local Group. Moderate-resolution, high S/N, spectrophotometry, covering 3500-9000A, has been obtained for a sample of RSGs in the Milky Way and the Magellanic Clouds. Using the the MARCS stellar atmosphere models to fit the SEDs, we are deriving extinction curves from 3500A to the K-band for the Local Group RSGs. In particular, for the LMC and SMC stars, the problem is more tractable than for the Milky Way RSGs, given the small and relatively uniform foreground extinction of the Clouds. We will construct extinction curves using the classic "pair method". The feasibility of using the model SEDs as "unreddened" standards will be examined, as well as the more conventional pairing of stars that are closely matched in spectral type but have different reddenings. These extinction curves are actually attenuation curves since the RSG circumstellar dust shells are not resolved and light can be scattered back into the beam. In particular, we plan to examine the apparent NUV excess seen in the Galactic RSG extinction curves. The NUV excess is possibly due to scattering of the star's light by circumstellar dust and/or a larger average size than that typical of grains found in the diffuse interstellar medium. This project is being supported by NSF grant AST-0707691 and a LaSPACE Undergraduate Research Assistantship (NASA grant NNG05GH22H).

Bright, Stacey; Clayton, G.; Massey, P.; Gordon, K.; Levesque, E.; Plez, B.

2007-12-01

119

Chemical evolution of the Magellanic Clouds. VI. Chemical composition of nine F supergiants from different regions of the large Magellanic Cloud  

Microsoft Academic Search

In an effort to increase the available information on the chemical content of the Magellanic Clouds, we investigated nine F supergiants from the field of the LMC by high-resolution spectroscopy, in order to obtain the elemental abundance ratios for C, O, alpha-elements, Fe peak and heavy elements. The stars are widely distributed over the LMC. An LTE analysis has given

V. Hill; S. Andrievsky; M. Spite

1995-01-01

120

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

121

The progenitor of supernova 1993J - A stripped supergiant in a binary system?  

NASA Technical Reports Server (NTRS)

Supernova 1993J in the spiral galaxy M81 is the brightest supernova since SN1987A and, like the latter, appears to be another 'peculiar' type II supernova. The available photometry of the supernova region before the explosion requires the presence of at least two supergiants (one of early spectral type and the other of late type), but the actual progenitor has yet to be identified. We show that the explosion of a late-type supergiant can explain the initial sharp peak in the supernova light curve, provided that the star had lost almost all of its hydrogen-rich envelope before the explosion. In our model, the secondary brightening of the supernova, about 10 days later, is then a consequence of the radioactive decay of Ni-56 (and subsequently Co-56) produced in the explosion. The progenitor could have lost its hydrogen-rich envelope either in a strong stellar wind or, as seems more likely, through mass transfer to a companion star. In the latter case, the companion should reappear after the supernova photosphere has receded, the system having become a binary composed of a neutron star with a massive stellar companion.

Podsiaklowski, PH.; Hsu, J. J. L.; Joss, P. C.; Ross, R. R.

1993-01-01

122

The atmospheric structure and fundamental parameters of Red Supergiants  

NASA Astrophysics Data System (ADS)

We present studies of the atmospheric structure and fundamental properties of the red supergiants (RSGs) VY CMa, AH Sco, UY Sct, and KW Sgr based on near-infrared K-band interferometry obtained with the VLTI/AMBER instrument with a spectral resolution of 1500. In our visibility data, we observe the presence of molecular layers of water and CO in extended atmospheres. For a uniform disk modeling, we observe size increases in the water band centered at 1.9 ?m and in the CO band at 2.3-2.5 ?m, with respect to the near-continuum bandpass (2.20-2.25 ?m). With our spectral resolution, we obtain diameters in the near-continuum, that are free from contamination by molecular layers. Using PHOENIX atmosphere models, we estimate Rosseland-mean photospheric angular diameters of VY CMa, AH Sco, UY Sct, and KW Sgr of 11.13 ± 0.3mas, 5.81 ± 0.15mas, 5.48 ± 0.10mas, and 3.91 ± 0.25mas, respectively. We estimate radii and effective temperatures, and place the stars in the HR diagram. The PHOENIX atmosphere models predict the spectra and the continuum visibility values, but do not predict the molecular layers visibility well: The model atmosphere is too compact when compared with the observations. This may be caused by pulsation and/or convection, which are not included in the models.

Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H.

2013-05-01

123

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

124

RAPIDLY ACCRETING SUPERGIANT PROTOSTARS: EMBRYOS OF SUPERMASSIVE BLACK HOLES?  

SciTech Connect

Direct collapse of supermassive stars (SMSs) is a possible pathway for generating supermassive black holes in the early universe. It is expected that an SMS could form via very rapid mass accretion with M-dot{sub *} {approx} 0.1-1 M{sub Sun} yr{sup -1} during the gravitational collapse of an atomic-cooling primordial gas cloud. In this paper, we study how stars would evolve under such extreme rapid mass accretion, focusing on the early evolution until the stellar mass reaches 10{sup 3} M{sub Sun }. To this end, we numerically calculate the detailed interior structure of accreting stars with primordial element abundances. Our results show that for accretion rates higher than 10{sup -2} M{sub Sun} yr{sup -1}, stellar evolution is qualitatively different from that expected at lower rates. While accreting at these high rates, the star always has a radius exceeding 100 R{sub Sun }, which increases monotonically with the stellar mass. The mass-radius relation for stellar masses exceeding {approx}100 M{sub Sun} follows the same track with R{sub *}{proportional_to}M {sup 1/2}{sub *} in all cases with accretion rates {approx}> 10{sup -2} M{sub Sun} yr{sup -1}; at a stellar mass of 10{sup 3} M{sub Sun }, the radius is {approx_equal} 7000 R{sub Sun} ({approx_equal} 30 AU). With higher accretion rates, the onset of hydrogen burning is shifted toward higher stellar masses. In particular, for accretion rates exceeding M-dot{sub *}{approx}>0.1 M{sub Sun} yr{sup -1}, there is no significant hydrogen burning even after 10{sup 3} M{sub Sun} have accreted onto the protostar. Such 'supergiant' protostars have effective temperatures as low as T{sub eff} {approx_equal} 5000 K throughout their evolution and because they hardly emit ionizing photons, they do not create an H II region or significantly heat their immediate surroundings. Thus, radiative feedback is unable to hinder the growth of rapidly accreting stars to masses in excess of 10{sup 3} M{sub Sun} as long as material is accreted at rates M-dot{sub *}{approx}>10{sup -2} M{sub Sun} yr{sup -1}.

Hosokawa, Takashi; Yorke, Harold W. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Omukai, Kazuyuki, E-mail: Takashi.Hosokawa@jpl.nasa.gov, E-mail: hosokwtk@gmail.com, E-mail: omukai@tap.scphys.kyoto-u.ac.jp [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)

2012-09-01

125

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

126

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

E-print Network

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

Kim Venn

1999-01-21

127

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.

128

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

129

Supergiant halos as an integral record of natural pionic radioactivity  

E-print Network

In this paper an unified interpretation of the supergiant halos (SGH), discovered by Grady, Walker and Laemmlein, is discussed. So, it is proved that SGH`s can be considered as integral records of the nuclear pionic radioactivity.

D. B. Ion; Reveica Ion-Mihai; M. L. Ion; Adriana I. Sandru

2004-01-09

130

X-RAY EMISSION FROM THE SUPERGIANT SHELL IN IC 2574  

SciTech Connect

The M81 group member dwarf galaxy IC 2574 hosts a supergiant shell of current and recent star formation activity surrounding a 1000 Multiplication-Sign 500 pc hole in the ambient H I gas distribution. Chandra X-ray Observatory imaging observations reveal a luminous, L{sub X} {approx} 6.5 Multiplication-Sign 10{sup 38} erg s{sup -1} in the 0.3-8.0 keV band, point-like source within the hole but offset from its center and fainter diffuse emission extending throughout and beyond the hole. The star formation history at the location of the point source indicates a burst of star formation beginning {approx}25 Myr ago and currently weakening and there is a young nearby star cluster, at least 5 Myr old, bracketing the likely age of the X-ray source at between 5 and {approx}25 Myr. The source is thus likely a bright high-mass X-ray binary-either a neutron star or black hole accreting from an early B star undergoing thermal-timescale mass transfer through Roche lobe overflow. The properties of the residual diffuse X-ray emission are consistent with those expected from hot gas associated with the recent star formation activity in the region.

Yukita, Mihoko [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL (United States); Swartz, Douglas A. [Universities Space Research Association, NASA Marshall Space Flight Center, ZP12 Huntsville, AL 35812 (United States)

2012-05-01

131

Departure from centrosymmetry of red giants and supergiants measured with VLTI/AMBER  

NASA Astrophysics Data System (ADS)

We study a sample of 16 bright and well-resolved late-type stars (10 O-rich giants, 2 red supergiants, and 4 C-rich giants) using the ESO VLTI/AMBER facility at medium resolution (R=1500}) in the K band to detect and measure the deviation from centrosymmetry of their resolved surface brightness distribution. As indicator for departure from centrosymmetry, we use the centrosymmetry parameter (CSP). We observe that CSP increases along the asymptotic giant branch, reaching values as large as 30°. These large CSP values are likely attributable to a few large photospheric convective cells. Carbon stars like W Ori and R Scl, being close to the AGB tip, have the second largest CSP values (17.6° and 22.3°, respectively), being only surpassed by the M5.5Ib/II supergiant T Cet (with CSP of 30.4°.). For K and early M giants, CSP values are smaller, never exceeding 10°, with a clear tendency to increase with the atmospheric pressure scaleheight. This supports the hypothesis that the observed deviations from centrosymmetry are somehow related to convective cells, whose size depends upon the atmospheric pressure scaleheight.

Cruzalèbes, P.; Jorissen, A.; Chiavassa, A.; Paladini, C.; Rabbia, Y.; Spang, A.

2015-02-01

132

MESS (Mass-loss of Evolved StarS), a Herschel Key Program  

Microsoft Academic Search

MESS (Mass-loss of Evolved StarS) is a Guaranteed Time Key Program that uses\\u000athe PACS and SPIRE instruments on board the Herschel Space Observatory to\\u000aobserve a representative sample of evolved stars, that include asymptotic giant\\u000abranch (AGB) and post-AGB stars, planetary nebulae and red supergiants, as well\\u000aas luminous blue variables, Wolf-Rayet stars and supernova remnants. In total,\\u000aof

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

2010-01-01

133

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

Microsoft Academic Search

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

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

2011-01-01

134

Supergiant X-Ray Binaries Observed by Suzaku  

NASA Technical Reports Server (NTRS)

Suzaku observations are presented for the high-mass X-ray binaries IGR 116207-5129 and IGR 117391-3021. For IGR 116207-5129, we provide the first X-ray broadband (0.5-60 keV) spectrum from which we confirm a large intrinsic column density (N(sub H) = 1.6 x 10(exp 23)/sq cm), and we constrain the cutoff energy for the first time (E(sub cut) = 19 keV). A prolonged (> 30 ks) attenuation of the X-ray flux was observed which we tentatively attribute to an eclipse of the probable neutron star by its massive companion, in a binary system with an orbital period between 4 and 9 days, and inclination angles> 50 degrees. For IGRJ17391-3021, we witnessed a transition from quiescence to a low-activity phase punctuated by weak flares whose peak luminosities in the 0.5-10keV band are only a factor of 5 times that of the pre-flare emission. These micro flares are accompanied by an increase in NH which suggests the accretion of obscuring clumps of wind. We now recognize that these low-activity epochs constitute the most common emission phase for this system, and perhaps in other supergiant fast X-ray transients (SFXTs) as well. We close with an overview of our upcoming program in which Suzaku will provide the first ever observation of an SFXT (IGRJ16479-4514) during a binary orbit enabling us to probe the accretion wind at every phase.

Bodaghee, A.; Tomsick, J. A.; Rodriquez, J.; Chaty, S.; Pottschmidt, K.; Walter, R.; Romano, P.

2011-01-01

135

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

136

Ionization structure in the winds of B[e] supergiants II. Influence of rotation on the formation of equatorial hydrogen neutral zones  

E-print Network

Context: B[e] supergiants are known to have non-spherical winds, and the existence of disks that are neutral in hydrogen close to their stellar surface has been postulated. A suitable mechanism to produce non-spherical winds seems to be rapid rotation, and at least for three B[e] supergiants in the Magellanic Clouds rotation velocities at a substantial fraction of their critical velocity have been found. Aims: We want to find suitable recombination distances in the equatorial plane of rapidly rotating stars that explain the observed huge amounts of neutral material in the vicinity of B[e] supergiants. Methods: We perform ionization structure calculations in the equatorial plane around rapidly rotating luminous supergiants. The restriction to the equatorial plane allows us to treat the ionization balance equations 1-dimensionally, while the stellar radiation field is calculated 2-dimensionally, taking into account the latitudinal variation of the stellar surface parameters. The stellar parameters used correspond to those known for B[e] supergiants. The assumptions made in the computations all have in common that the total number of available ionizing photons at any location within the equatorial plane is overestimated, resulting in upper limits for the recombination distances. Results: We find that despite the drop in equatorial surface density of rapidly rotating stars (neglecting effects like bi-stability and/or wind compression), hydrogen and helium recombine at or close to the stellar surface, for mass loss rates Mdot > 5d-5 M_sun/yr and rotation speeds in excess of v(rot,eq)/v(crit)=0.8.

Michaela Kraus

2006-05-05

137

Fast ray-tracing algorithm for circumstellar structures (FRACS). II. Disc parameters of the B[e] supergiant CPD-57°,2874 from VLTI/MIDI data  

NASA Astrophysics Data System (ADS)

Context. B[e] supergiants are luminous, massive post-main sequence stars exhibiting non-spherical winds, forbidden lines, and hot dust in a disc-like structure. The physical properties of their rich and complex circumstellar environment (CSE) are not well understood, partly because these CSE cannot be easily resolved at the large distances found for B[e] supergiants (typically ?1 kpc). Aims: From mid-IR spectro-interferometric observations obtained with VLTI/MIDI we seek to resolve and study the CSE of the Galactic B[e] supergiant CPD-57° 2874. Methods: For a physical interpretation of the observables (visibilities and spectrum) we use our ray-tracing radiative transfer code (FRACS), which is optimised for thermal spectro-interferometric observations. Results: Thanks to the short computing time required by FRACS (<10 s per monochromatic model), best-fit parameters and uncertainties for several physical quantities of CPD-57° 2874 were obtained, such as inner dust radius, relative flux contribution of the central source and of the dusty CSE, dust temperature profile, and disc inclination. Conclusions: The analysis of VLTI/MIDI data with FRACS allowed one of the first direct determinations of physical parameters of the dusty CSE of a B[e] supergiant based on interferometric data and using a full model-fitting approach. In a larger context, the study of B[e] supergiants is important for a deeper understanding of the complex structure and evolution of hot, massive stars. Based on VLTI/MIDI observations collected at the European Southern Observatory (ESO), Paranal, Chile under ESO Programmes 074.D-0101 and 078.D-0213. Also based on observations at the ESO 2.2-m telescope, La Silla, Chile, under agreement with the Observatório Nacional-MCT (Brazil).Figure 5 is only available in electronic form at http://www.aanda.org

Domiciano de Souza, A.; Bendjoya, P.; Niccolini, G.; Chesneau, O.; Borges Fernandes, M.; Carciofi, A. C.; Spang, A.; Stee, P.; Driebe, T.

2011-01-01

138

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

139

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

NASA Technical Reports Server (NTRS)

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

Brown, Alexander

1998-01-01

140

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

141

Abundances of the heavy elements in the Magellanic Clouds. I. Metal abundances of F-type supergiants  

SciTech Connect

Metal abundances of eight F-type supergiants in each of the Magellanic Clouds were determined using the results of high-resolution spectroscopy analysis of these stars, together with new Stromgren uvby and Cousins (1980) BVRI photometry. It was found that the mean Fe abundance (Fe/H) for the SMC is -0.65 + or - 0.2 dex, and the mean Fe abundance for the LMC is -0.30 + or - 0.2 dex. The abundances of stars in both the SMC and LMC appear relatively uniform, and the abundances of the elements relative to Fe are very similar in both Magellanic Clouds and in Canopus (the carbon-to-iron abundances are the same for all three). It was also found that Nd and Sm are overabundant in both clouds, supporting the trends found by Spite et al. (1988) for the three SMC stars they studied. 140 refs.

Russell, S.C.; Bessell, M.S. (Mount Stromlo and Siding Spring Observatories, Canberra (Australia))

1989-08-01

142

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

143

Search for weak magnetic fields of stars  

Microsoft Academic Search

The magnetic fields of some normal stars of the main sequence, supergiants and Hg-Mn stars have been measured from metallic and hydrogen lines on the 6-m telescope with the Fabry-Perot magnetometer and spectropolarimeter. These results and the data of other authors are statistically analysed. A conclusion is drawn that the studied types of stars hardly contain a magnetic field exceeding

Yu. V. Glagolevskij; I. I. Romanyuk; I. D. Najdenov; V. G. Shtol

1989-01-01

144

Geology of supergiant Cano Limon field and Llanos basin, Colombia  

Microsoft Academic Search

After 40 years of sporadic exploration that yielded negative or marginal results, the Llanos basin of eastern Colombia was thrust to the forefront of world attention by the discovery of the supergiant Cano Limon field in July 1983. This discovery culminated an intensive 3-year exploration effort by Occidental involving 4000 km of dynamite seismic, 20 stratigraphic tests from 1300 to

C. N. McCollough; E. P. Padfield

1986-01-01

145

Pulsations of red supergiant pair-instability supernova progenitors leading to extreme mass loss  

NASA Astrophysics Data System (ADS)

Recent stellar evolution models show consistently that very massive metal-free stars evolve into red supergiants shortly before they explode. We argue that the envelopes of these stars, which will form pair-instability supernovae, become pulsationally unstable and that this will lead to extreme mass-loss rates despite the tiny metal content of the envelopes. We investigate the pulsational properties of such models and derive pulsationally induced mass-loss rates, which take the damping effects of the mass loss on the pulsations selfconsistently into account. We find that the pulsations may induce mass-loss rates of ~10-4 - 10-2M? yr-1 shortly before the explosions, which may create a dense circumstellar medium. Our results show that very massive stars with dense circumstellar media may stem from a wider initial mass range than pulsational-pair instability supernovae. The extreme mass loss will cease when so much of the hydrogen-rich envelope is lost that the star becomes more compact and stops pulsating. The helium core of these stars therefore remains unaffected, and their fate as pair-instability supernovae remains unaltered. The existence of dense circumstellar media around metal-free pair-instability supernovae can make them brighter and bluer, and they may be easier to detect at high redshifts than previously expected. We argue that the mass-loss enhancement in pair-instability supernova progenitors can naturally explain some observational properties of superluminous supernovae: the energetic explosions of stars within hydrogen-rich dense circumstellar media with little 56Ni production and the lack of a hydrogen-rich envelope in pair-instability supernova candidates with large 56Ni production.

Moriya, Takashi J.; Langer, Norbert

2015-01-01

146

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

147

An HST COS "SNAPshot" Spectrum of the K Supergiant ? Vel (K4Ib-II)  

NASA Astrophysics Data System (ADS)

We present a far-ultraviolet spectrum of the K4 Ib-II supergiant ? Vel obtained with the Hubble Space Telescope's Cosmic Origins Spectrograph (COS) as a part of the SNAPshot program "SNAPing coronal iron" (GO 11687). The observation covers a wavelength region (1326-1467 Å) not previously recorded for ? Vel at a spectral resolving power of R ~ 20,000 and displays strong emission and absorption features, superposed on a bright chromospheric continuum. Fluorescent excitation is responsible for much of the observed emission, mainly powered by strong H I Ly? and the O I (UV 2) triplet emission near ?1304. The molecular CO and H2 fluorescences are weaker than in the early-K giant ? Boo while the Fe II and Cr II lines, also pumped by H I Ly?, are stronger in ? Vel. This pattern of relative line strengths between the two stars is explained by the lower iron-group element abundance in ? Boo, which weakens that star's Fe II and Cr II emission without reducing the molecular fluorescences. The ? Vel spectrum shows fluorescent Fe II, Cr II, and H2 emission similar to that observed in the M supergiant ? Ori, but more numerous well-defined narrow emissions from CO. The additional CO emissions are visible in the spectrum of ? Vel since that star does not have the cool, opaque circumstellar shells that surround ? Ori and produce broad circumstellar CO (A-X) band absorptions that hide those emissions in the cooler star. The presence of Si IV emission in ? Vel indicates a ~8 × 104 K plasma that is mixed into the cooler chromosphere. Evidence of the stellar wind is seen in the C II ??1334,1335 lines and in the blueshifted Fe II and Ni II wind absorption lines. Line modeling using Sobolev with Exact Integration for the C II lines indicates a larger terminal velocity (~45 versus ~30 km s-1) and turbulence (~27 versus <21 km s-1) with a more quickly accelerating wind (? = 0.35 versus 0.7) at the time of this COS observation in 2010 than derived from Goddard High Resolution Spectrograph data obtained in 1994. The Fe II and Ni II absorptions are blueshifted by 7.6 km s-1 relative to the chromospheric emission, suggesting formation in lower levels of the accelerating wind and their widths indicate a higher turbulence in the ? Vel wind compared to ? Ori. 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, Incorporated, under NASA contract NAS5-26555.

Carpenter, Kenneth G.; Ayres, Thomas R.; Harper, Graham M.; Kober, Gladys; Nielsen, Krister E.; Wahlgren, Glenn M.

2014-10-01

148

The Massive Star Population in M101  

NASA Astrophysics Data System (ADS)

An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. Very little is known about the origin of these giant eruptions and their progenitors which are presumably very-massive, evolved stars such as luminous blue variables, hypergiants, and supergiants. Motivated by the small number of progenitors positively associated with these giant eruptions, we have begun a survey of the luminous and evolved massive star populations in several nearby galaxies. We aim to identify the likely progenitors of the giant eruptions, study the spatial variations in the stellar populations, and examine the relationship between massive star populations and their environment. The work presented here is focused on stellar populations in the relatively nearby, giant, spiral galaxy M101 from sixteen archival BVI HST/ACS images. We create a catalog of stars in the direction to M101 with photometric errors < 10% for V < 24.5 and 50% completeness down to V ˜ 26.5 even in regions of high stellar crowding. Using color and magnitude criteria we have identified candidate luminous OB type stars and blue supergiants, yellow supergiants, and red supergiants for future observation. We examine their spatial distributions across the face of M101 and find that the ratio of blue to red supergiants decreases by two orders of magnitude over the radial extent. From our catalog, we derive the star formation history (SFH) for the stellar populations in five 2' wide annuli by fitting the color-magnitude diagrams. Binning the SFH into time frames corresponding to populations traced by Halpha, far ultraviolet (FUV), and near ultraviolet (NUV) emission, we show that the fraction of stellar populations young enough to contribute in Halpha is 15% " 35% in the inner regions, compared to less than 5% in the outer regions. This provides a sufficient explanation for the lack of Halpha emission at large radii. We also model the blue to red supergiant ratio in our five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into the modeled ratios, we are able to reproduce the observed values at large radii (low metallicity), but at small radii (high metallicity) the modeled and observed ratios are discrepant. Though photometry has proven to be a powerful tool to identify candidate evolved massive stars and their effects on their host galaxy, spectroscopy is necessary to study the physical properties of individual stars. We observed moderate-resolution optical spectra for 56 of the brightest stars in the direction to M101 using the Multiple Mirror Telescope. We also created light curves for each target using multi-epoch U BV R images from the Large Binocular Telescope. We separate the spectroscopially confirmed members of M101 into four groups: hot supergiants, intermediate supergiants, emission-line stars, and LBVs. Several stars in each group are discussed in detail. Of the spectroscopically confirmed members, we find that eight meet our criterion for variability. We present light curves for the known LBV candidates, V2, V4, and V9, and introduce a new candidate: 9492 &barbelow;14 &barbelow;11998. Additionally, we identify 20 new variables in M101. Lacking spectra, we separated the variables, by their photometric properties, into three groups: hot, intermediate, and cool. We find two hot stars with V-band variability of +/-1 magnitude; we flag these stars as LBV candidates. Of the intermediate and cool variables, we identify several stars with low- to moderate-amplitude variability (0.1--0.5 magnitudes).

Grammer, Skyler H.

149

H? Variability in the A0 Ia-Type Supergiant HR 1040  

NASA Astrophysics Data System (ADS)

HR 1040 (= HD 21389) is a well-known example of a luminous star with mass loss, photometric and radial-velocity variability, and a variable H? profile. Caplinger (1991, M. S. thesis, U. Toledo) found that the H? profile shows, at various times, different morphologies: P Cygni, inverse P Cygni, and Type III P Cygni (emission on both sides of the absorption). This result indicates that this star's wind is not steady and/or not spherically symmetric. We studied 43 CCD echelle spectra obtained between 1993 Sep. and 1994 Dec. with the 1-m telescope of Ritter Observatory. The spectral resolution of this material is 0.23 Angstroms at lambda 5800, and the continuum SNR is usually comfortably above 100 in an exposure time of 20 min or less. The spectral coverage consists of 9 disjoint 70- Angstroms regions in the yellow and red; features of interest in these spectra are H? , He I lambda 5876, and Si II lambda lambda 6347, 6371. In addition to confirming the morphological variability found by Caplinger, our data show two episodes of dramatic increases in the width and the equivalent width of the absorption component of H? , with the equivalent width attaining values as large as 2 Angstroms, as compared to a baseline value around 0.5 Angstroms. During these episodes, the absorption feature often showed two or more sub-components. In addition, the equivalent width of Si II lambda 6347 increased by amounts up to 50%. Presumably, these events can be interpreted as episodes of enhanced mass loss. Collection and analysis of spectra of this star are continuing at Ritter Observatory. If this star is typical of A-type supergiants in the variability of its H? profile, our results can be used to assess the accuracy of distance estimates to external galaxies based on mass loss as a luminosity indicator in these stars (Kudritzki et al. 1992, A&A 257, 655).

Morrison, N. D.; Gordon, K. D.

1995-12-01

150

Luminosities for two yellow supergiants - Nonvariables and the instability strip  

NASA Technical Reports Server (NTRS)

The luminosities for two yellow supergiants HD 183864 and Psi And = HD 223047 are determined from the IUE spectra of their hot companions. The absolute magnitudes of HD 183864 and HD 223047 are -2.3 and -2.1 mag, respectively, and their companions have spectral types of A0.0 V and B8.8 V. The companion of Psi And is compatible with the orbital motion tentatively detected by speckle interferometric observations. The supergiant luminosities are combined with the Cepheid luminosities determined in the same way, and also the variables and nonvariables from Schmidt's studies of open clusters. As found by Schmidt, the variable and nonvariable supergiants have almost no overlap in the HR diagram. The combined sample defines the locus of the helium burning blue loops of evolutionary tracks. Because no nonvariables are found to the blue of fainter Cepheids, the observed blue edge of the Cepheid region may be partly determined by the blue loops rather than by the region of pulsational instability.

Evans, Nancy R.

1993-01-01

151

A comparison of lyman alpha and HeI lambda 10830 line structure and variations in early-type star atmospheres  

NASA Technical Reports Server (NTRS)

Fabry-Perot interferometric profiles for fifty of the early-type stars including supergiants, eclipsing binaries, Bp and Ap stars, Be and shell stars, and variable stars have been obtained. Results for beta Persei (Algol) just before primary and secondary eclipses show strong emission profiles lasting about 0.1 phase. An absorption line was seen during secondary eclipse. Bright supergiant stars (O9-A2) show time-variable, complicated absorption/emission profiles similar to those obtained for the Be/shell stars.

Meisel, D. D.

1977-01-01

152

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

153

Blue-to-red ratios and Wolf-Rayet stars in M33  

Microsoft Academic Search

The relative numbers of blue and red supergiants in M33 are compared, based on a photographic study undertaken at the Canada-France-Hawaii 3.6 m telescope. In addition, the ratio of Wolf-Rayet to red supergiant stars is investigated. Both of these ratios show very little variation with radius, contrary to the results of several previous studies. The differences arise primarily due to

W. L. Freedman

1985-01-01

154

Insight into star death  

SciTech Connect

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

Talcott, R.

1988-02-01

155

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

SciTech Connect

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

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

2010-08-15

156

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

157

On the nature of the bi-stability jump in the winds of early-type supergiants  

NASA Astrophysics Data System (ADS)

We study the origin of the bi-stability jump in the terminal velocity of the winds of supergiants near spectral type B1. Observations show that here the ratio {v_infty/v_esc} drops steeply from about 2.6 at types earlier than B1 to a value of {v_infty/v_esc}=1.3 at types later than B2. To this purpose, we have calculated wind models and mass-loss rates for early-type supergiants in a T_eff grid covering the range between T_eff = 12 500 and 40 000 K. These models show the existence of a jump in mass loss around T_eff = 25 000 K for normal supergiants, with dot {M} increasing by about a factor five from T_eff =~ 27 500 to 22 500 K for constant luminosity. The wind efficiency number eta =M? {v_infty} / (L_*/c) also increases drastically by a factor of 2 - 3 near that temperature. We argue that the jump in mass loss is accompanied by a decrease of the ratio {v_infty/v_esc}, which is the observed bi-stability jump in terminal velocity. Using self-consistent models for two values of T_eff, we have derived {v_infty/v_esc} = 2.4 for T_eff = 30 000 K and {v_infty/v_esc} = 1.2 for T_eff = 17 500 K. This is within 10 percent of the observed values around the jump. Up to now, a theoretical explanation of the observed bi-stability jump was not yet provided by radiation driven wind theory. To understand the origin of the bi-stability jump, we have investigated the line acceleration for models around the jump in detail. These models demonstrate that M? increases around the bi-stability jump due to an increase in the line acceleration of Fe iii below the sonic point. This shows that the mass-loss rate of B-type supergiants is very sensitive to the abundance and the ionization balance of iron. Furthermore, we show that the elements C, N and O are important line drivers in the supersonic part of the wind. The subsonic part of the wind is dominated by the line acceleration due to Fe. Therefore, CNO-processing is expected not to have a large impact on dot {M},but it might have impact on the terminal velocities. Finally, we discuss the possible role of the bi-stability jump on the mass loss during typical variations of Luminous Blue Variable stars.

Vink, J. S.; de Koter, A.; Lamers, H. J. G. L. M.

1999-10-01

158

Pulsations in B-type supergiants with masses M<20 M_{?} before and after core helium ignition  

NASA Astrophysics Data System (ADS)

Evolutionary tracks and pulsational analysis of models with masses of 13-18 M? are presented. We address two important questions. The first one deals with one of the most unresolved problems in astrophysics, i.e. the existence of a blue loop after core helium ignition; the so-called to loop or not to loop problem. We show that inward overshooting from the outer convective zone in the red giant phase is prerequisite for the development of the blue loop. Our second question concerns pulsational instability of models in the core helium burning phase. We present for the first time that models on the blue loop can have unstable modes driven by the ? mechanism operating in the Z-bump. Contrary to post-main-sequence models in the shell hydrogen burning phases, pulsational instability of the blue loop models depends mainly on effective temperature and metallicity is of secondary importance. Finally, we try to interpret the oscillation spectrum of the blue supergiant HD 163899, the only member of the slowly pulsating B-type supergiant class and to get some clue on the evolutionary status of the star.

Ostrowski, J.; Daszy?ska-Daszkiewicz, J.

2015-03-01

159

X-shooter Science Verification Proposal Shooting the massive post-Red Supergiants, IRC +10420 and HD 179821  

E-print Network

hypergiants found in the evolutionary phase between the Red Supergiants and the Wolf-Rayet or Luminous BlueX-shooter Science Verification Proposal Shooting the massive post-Red Supergiants, IRC +10420. With this proposal we plan to observe the massive post-red supergiants IRC +10420 and HD 179821, objects that have

Liske, Jochen

160

Spectropolarimetry of hot, luminous stars  

NASA Technical Reports Server (NTRS)

I review polarimetric observations of presumably single, hot luminous stars. The stellar types discussed are OB stars. B(e) supergiants, Luminous Blue Variables (LBV), Wolf-Rayet (W-R) stars, and type II supernovae (SN). It is shown that variable, intrinsic polarization is a common phenomenon in that part of the Hertzsprung-Russell (HR) diagram which these stars occupy. However, much observational work remains to be done before we can answer the most basic, statistical questions about the polarimetric properties of different groups of hot, luminous stars. Insight into the diagnostic power of polarization observations has been gained, but cannot be exploited without detailed models. Thus, while polarimetric observations do tell us that the mass-loss processes of all types of massive stars are time-dependent and anisotropic, the significance that this might have for the accuracy of their stellar parameters and evolutionary paths remains elusive.

Schulte-Ladbeck, Regina E.

1994-01-01

161

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

E-print Network

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. Displaying short and bright flares and an unusually very-low quiescent level implying intensity dynamical range as large as 1e3-4, the source was classified as a Supergiant Fast X-ray Transient. 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. We analysed archival INTEGRAL data on SAX J1818.6-1703. We built short- and long-term light curves and performed timing analysis in order to study the temporal behaviour of SAX J1818.6-1703 on different time scales. 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 average fundamental parameters of supergiant stars). During the accretion phase, the source behaved like classical SGXBs. 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.

J. A. Zurita Heras; S. Chaty

2008-11-18

162

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

2012-10-01

163

SN 2004A: Another Type II-P Supernova with a Red Supergiant Progenitor  

E-print Network

We present a monitoring study of SN 2004A and probable discovery of a progenitor star in pre-explosion HST images. The photometric and spectroscopic monitoring of SN 2004A show that it was a normal Type II-P which was discovered in NGC 6207 about two weeks after explosion. We compare SN 2004A to the similar Type II-P SN 1999em and estimate an explosion epoch of 2004 January 6. We also calculate three new distances to NGC 6207 of 21.0 +/-4.3, 21.4 +/-3.5 and 25.1 +/-1.7Mpc. The former was calculated using the Standard Candle Method (SCM) for SNe II-P, and the latter two from the Brightest Supergiants Method (BSM). We combine these three distances with existing kinematic distances, to derive a mean value of 20.3 +/-3.4Mpc. Using this distance we estimate that the ejected nickel mass in the explosion is 0.046(+0.031,-0.017) Msolar. The progenitor of SN 2004A is identified in pre-explosion WFPC2 F814W images with a magnitude of mF814W = 24.3 +/-0.3, but is below the detection limit of the F606W images. We show th...

Hendry, M A; Cenko, S B; Crockett, R M; Fox, D W; Gal-Yam, A; Kudritzki, R P; Maund, J R; Moon, D S; Smartt, S J

2006-01-01

164

THE ULTRA-LONG GAMMA-RAY BURST 111209A: THE COLLAPSE OF A BLUE SUPERGIANT?  

SciTech Connect

We present optical, X-ray and gamma-ray observations of GRB 111209A, observed at a redshift of z = 0.677. We show that this event was active in its prompt phase for about 25000 s, making it the longest burst ever observed. This rare event could have been detected up to z {approx} 1.4 in gamma-rays. Compared to other long gamma-ray bursts (GRBs), GRB 111209A is a clear outlier in the energy-fluence and duration plane. The high-energy prompt emission shows no sign of a strong blackbody component, the signature of a tidal disruption event, or a supernova shock breakout. Given the extreme longevity of this event, and lack of any significant observed supernova signature, we propose that GRB 111209A resulted from the core-collapse of a low-metallicity blue supergiant star. This scenario is favored because of the necessity to supply enough mass to the central engine over a duration of thousands of seconds. Hence, we suggest that GRB 111209A could have more in common with population III stellar explosions, rather than those associated with normal long GRBs.

Gendre, B.; Cutini, S.; D'Elia, V. [ASI Science Data Center, via Galileo Galilei, I-00044 Frascati (Italy)] [ASI Science Data Center, via Galileo Galilei, I-00044 Frascati (Italy); Stratta, G. [Osservatorio Astronomico di Roma, OAR-INAF, via Frascati 33, I-00040, Monte Porzio Catone (Italy)] [Osservatorio Astronomico di Roma, OAR-INAF, via Frascati 33, I-00040, Monte Porzio Catone (Italy); Atteia, J. L.; Klotz, A. [Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France)] [Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France); Basa, S. [Aix Marseille Universite, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France)] [Aix Marseille Universite, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France); Boeer, M. [CNRS, ARTEMIS, UMR 7250, Boulevard de l'Observatoire, BP 4229, F-06304 Nice Cedex 4 (France)] [CNRS, ARTEMIS, UMR 7250, Boulevard de l'Observatoire, BP 4229, F-06304 Nice Cedex 4 (France); Coward, D. M.; Howell, E. J [University of Western Australia, School of Physics, University of Western Australia, Crawley WA 6009 (Australia)] [University of Western Australia, School of Physics, University of Western Australia, Crawley WA 6009 (Australia); Piro, L., E-mail: bruce.gendre@gmail.com [Istituto di Astrofisica e Planetologia Spaziali di Roma, INAF, via fosso del cavaliere 100, I-00133 Roma (Italy)

2013-03-20

165

More nitrogen rich B-type stars in the SMC cluster, NGC 330  

Microsoft Academic Search

High resolution spectra of seven early B-type giant\\/supergiant stars in the SMC cluster NGC 330 are analysed to obtain their chemical compositions relative to SMC field and Galactic B-type stars. It is found that all seven stars are nitrogen rich with an abundance approximately 1.3 dex higher than an SMC main-sequence field B-type star, AV304. They also display evidence for

D. J. Lennon; P. L. Dufton; C. Crowley

2003-01-01

166

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

167

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

E-print Network

TO LUMINOUS BLUE VARIABLES AND WOLF-RAYET STARS Richard B. Stothers Institute for Space Studies, NASA Goddard ABSTRACT Theoretical models of the remnants of massive stars in a very hot, post­red-supergiant phase radiatively unstable Wolf-Rayet stars. Fur- thermore, when accurate main-sequence mass-loss rates are used

168

ES Aquilae Is an R Coronae Borealis Star  

Microsoft Academic Search

ES Aql, initially classified as a semiregular variable, is now believed to be a member of the R Coronae Borealis (RCB) class of stars, a small group of carbon-rich supergiants that undergo dramatic declines in brightness at irregular intervals. We present photometry of ES Aql going back as far as 1893 using plates from the Harvard College Observatory as well

Geoffrey C. Clayton; D. Hammond; J. Lawless; D. Kilkenny; T. Lloyd Evans; J. Mattei; A. U. Landolt

2002-01-01

169

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

170

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

171

CHEMICAL ABUNDANCE PATTERNS IN THE INNER GALAXY: THE SCUTUM RED SUPERGIANT CLUSTERS  

SciTech Connect

The location of the Scutum Red Supergiant (RSG) clusters at the end of the Galactic Bar makes them an excellent probe of the Galaxy's secular evolution, while the clusters themselves are ideal testbeds in which to study the predictions of stellar evolutionary theory. To this end, we present a study of the RSG's surface abundances using a combination of high-resolution Keck/NIRSPEC H-band spectroscopy and spectral synthesis analysis. We provide abundance measurements for elements C, O, Si, Mg, Ti, and Fe. We find that the surface abundances of the stars studied are consistent with CNO burning and deep, rotationally enhanced mixing. The average {alpha}/Fe ratios of the clusters are solar, consistent with a thin-disk population. However, we find significantly subsolar Fe/H ratios for each cluster, a result which strongly contradicts a simple extrapolation of the Galactic metallicity gradient to lower Galactocentric distances. We suggest that a simple one-dimensional parameterization of the Galaxy's abundance patterns is insufficient at low Galactocentric distances, as large azimuthal variations may be present. Indeed, we show that the abundances of O, Si, and Mg are consistent with independent measurements of objects in similar locations in the Galaxy. In combining our results with other data in the literature, we present evidence for large-scale ({approx} kpc) azimuthal variations in abundances at Galactocentric distances of 3-5 kpc. While we cannot rule out that this observed behavior is due to systematic offsets between different measurement techniques, we do find evidence for similar behavior in a study of the barred spiral galaxy NGC 4736 which uses homogeneous methodology. We suggest that these azimuthal abundance variations could result from the intense but patchy star formation driven by the potential of the central bar.

Davies, Ben [School of Physics and Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT (United Kingdom); Origlia, Livia [INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna (Italy); Kudritzki, Rolf-Peter [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI, 96822 (United States); Figer, Don F. [Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester NY, 14623 (United States); Rich, R. Michael [Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States); Najarro, Francisco [Centro de AstrobiologIa (CSIC-INTA), Ctra. Torrejon-Ajalvir km 4, 28850 Torrejon de Ardoz (Spain); Negueruela, Ignacio [Departamento. de Fisica, IngenierIa de Sistemas y TeorIa de la Senal, Universidad de Alicante, Apdo. 99, E03080 Alicante (Spain); Clark, J. Simon [Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)

2009-05-10

172

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

173

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

E-print Network

We present an analysis of a peculiar supergiant B-type star (VFTS698/Melnick 2/Parker 1797) in the 30 Doradus region of the Large Magellanic Cloud which exhibits characteristics similar to the broad class of B[e] stars. We analyse optical spectra from the VLT-FLAMES survey, together with archival optical and infrared photometry and X-ray imaging to characterise the system. We find radial velocity variations of around 400 km/s in the high excitation Si IV, N III and He II spectra, and photometric variability of ~0.6 mag with a period of 12.7 days. In addition, we detect long-term photometric variations of ~0.25 mag, which may be due to a longer-term variability with a period of ~400 days. We conclude that VFTS698 is likely an interacting binary comprising an early B-type star secondary orbiting a veiled, more massive companion. Spectral evidence suggests a mid-to-late B-type primary, but this may originate from an optically-thick accretion disc directly surrounding the primary.

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

2012-01-01

174

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

175

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

176

The Outer Atmosphere of Canopus: Detection of a Fast Stellar Wind from an F Supergiant  

Microsoft Academic Search

We have investigated the outer atmospheric structure of the F0 Ib supergiant Canopus using HST, Chandra and FUSE and have discovered a number of unexpected properties, including the presence of an unusually fast stellar wind from this post-M supergiant. Our observations consist of 96 ksec of Chandra HETGS spectroscopy obtained on 2000 July 21, a set of HST-STIS (E140M, E230M,

A. Brown; G. M. Harper; T. R. Ayres; J. M. Brown

2003-01-01

177

Supergiant fast X-ray transients as an under-luminous class of supergiant X-ray binaries  

NASA Astrophysics Data System (ADS)

The usage of cumulative luminosity distributions, constructed thanks to the long-term observations available through wide field hard X-ray imagers, has been recently exploited to study the averaged high energy emission (>17 keV) from supergiant fast X-ray transients (SFXTs) and classical Supergiant High Mass X-ray Binaries (SgXBs). Here, we take advantage of the long term monitorings now available with Swift/XRT to construct for the first time the cumulative luminosity distributions of a number of SFXTs and the classical SgXB IGR J18027-2016 in the soft X-ray domain with a high sensitivity focusing X-ray telescope (0.3-10 keV). By complementing previous results obtained in the hard X-rays, we found that classical SgXBs are characterized by cumulative distributions with a single knee around ? 1036-1037 erg s-1, while SFXTs are found to be systematically sub-luminous and their distributions are shifted at significantly lower luminosities (a factor of ? 10-100). As the luminosity states in which these sources spend most of their time are typically below the sensitivity limit of large field of view hard X-ray imagers, we conclude that soft X-ray monitorings carried out with high sensitivity telescopes are particularly crucial to reconstruct the complete profile of the SFXT cumulative luminosity distributions. The difference between the cumulative luminosity distributions of classical SgXBs and SFXTs is interpreted in terms of accretion from a structured wind in the former sources and the presence of magnetic/centrifugal gates or a quasi-spherical settling accretion regime in the latter.

Bozzo, E.; Romano, P.; Ducci, L.; Bernardini, F.; Falanga, M.

2015-02-01

178

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

179

Effects of Metallicity on the Rotation Rates of Massive Stars  

Microsoft Academic Search

Recent theoretical predictions for low metallicity massive stars predict that\\u000athese stars should have drastically reduced equatorial winds (mass loss) while\\u000aon the main sequence, and as such should retain most of their angular momentum.\\u000aObservations of both the Be\\/(B+Be) ratio and the blue-to-red supergiant ratio\\u000aappear to have a metallicity dependence that may be caused by high rotational\\u000avelocities.

Laura R. Penny; Amanda J. Sprague; George Seago; Douglas R. Gies

2004-01-01

180

Effects of Metallicity on the Rotational Velocities of Massive Stars  

Microsoft Academic Search

Recent theoretical predictions for low metallicity massive stars predict that these stars should have drastically reduced equatorial winds (mass loss) while on the main sequence, and as such should retain most of their angular momen- tum. Observations of both the Be\\/(B+Be) ratio and the blue-to-red supergiant ratio appear to have a metallicity dependence that may be caused by high rota-

Laura R. Penny; Amanda J. Sprague; George Seago; Douglas R. Gies

2004-01-01

181

Effects of Metallicity on the Rotational Velocities of Massive Stars  

Microsoft Academic Search

Recent theoretical predictions for low-metallicity massive stars predict that these stars should have drastically reduced equatorial winds (mass loss) while on the main sequence, and so should retain most of their angular momentum. Observations of both the Be\\/(B+Be) ratio and the blue-to-red supergiant ratio appear to have a metallicity dependence that may be caused by high rotational velocities. We have

Laura R. Penny; Amanda J. Sprague; George Seago; Douglas R. Gies

2004-01-01

182

Outer atmospheres of late-type stars  

NASA Technical Reports Server (NTRS)

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

Linsky, J. L.

1981-01-01

183

Evolution of helium stars  

NASA Technical Reports Server (NTRS)

The evolution of helium stars in the mass range from 4 to 15 solar masses has been followed from the initial helium main sequence to the end of carbon burning in the core, with the use of Carson's (1976) radiative opacities. As compared with earlier work based on smaller opacities, the main-sequence band in the H-R diagram is now both wider and cooler than before. If neutrino losses are neglected in the stellar models, the phase of carbon burning in the core occurs in the red-supergiant region; otherwise, it occurs, as it does in the earlier models with or without neutrino emission, close to the helium main sequence. Observational data for Wolf-Rayet stars and R Coronae Borealis variables are found to lend some support to the present models.

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

1977-01-01

184

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

185

IGR J16328-4726: A NEW CANDIDATE SUPERGIANT FAST X-RAY TRANSIENT  

SciTech Connect

The unidentified source IGR J16328-4726 was covered with INTEGRAL observations for a long period ({approx}9.8 Ms) and was undetectable for most of the time while showing a very recurrent micro-activity with a duration from tens of minutes to several hours. We report the discovery of two strong outbursts started at 53420.65 MJD and 54859.99 MJD, respectively, the first with a duration of {approx}1 hr and the second with a lower limit on the duration of {approx}3.5 hr. Furthermore, the sources have been detected in nine other short pointings with significance between 4{sigma} and 5{sigma} as well as in one of the revolutions (during the exposure {approx}130 ks) at a significance level of {approx}7{sigma}. The stronger outburst spectrum is well described by a power-law model with a photon index of {approx}2.0 and a flux of {approx}3.3 x10{sup -10} erg cm{sup -2} s{sup -1} in the 20-50 keV energy band. The weaker outburst and revolution spectra show the same spectral shape and different fluxes. The combined timing and spectral properties observed during the outburst, the recurrent nature of this transient source, the Galactic plane location, a dynamic range >170 in the 0.3-10 keV band and >165 in the 20-50 keV, and the presence of an IR star in the error circle of a Swift X-ray Telescope pointing are suggesting this source as a member of the class of the supergiant fast X-ray transients.

Fiocchi, M.; Bazzano, A.; Natalucci, L.; Ubertini, P. [Instituto di Astrofisica Spaziale e Fisica Cosmica di Roma (INAF), Via Fosso del Cavaliere 100, Roma, I-00133 (Italy); Sguera, V.; Bassani, L. [Instituto di Astrofisica Spaziale e Fisica Cosmica di Bologna (INAF), Via Gobetti 101, Bologna, I-40129 (Italy); Bird, A. J. [School of Physics and Astronomy, University of Southampton, Highfield, SO17 1BJ (United Kingdom)

2010-12-10

186

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

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

187

The Massive Star Population in M101. I. The Identification and Spatial Distribution of the Visually Luminous Stars  

NASA Astrophysics Data System (ADS)

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

Grammer, Skyler; Humphreys, Roberta M.

2013-11-01

188

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

SciTech Connect

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

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

2013-11-01

189

PACS and SPIRE spectroscopy of the red supergiant VY CMa  

NASA Astrophysics Data System (ADS)

With a luminosity >105 L? and a mass-loss rate of ~2 × 10-4 M? yr-1, the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VY CMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55-672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as ~1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

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

2010-07-01

190

MMT Hypervelocity Star Survey. II. Five New Unbound Stars  

E-print Network

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-fo...

Brown, Warren R; Kenyon, Scott J

2012-01-01

191

Elemental abundance analyses with DAO spectrograms: XXXI. The early F supergiants ? Her (F2 II) and 41 Cyg (F5 Ib-II)  

NASA Astrophysics Data System (ADS)

This series of high quality elemental abundance analyses of mostly Main Sequence normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (? 200) spectrograms obtained with CCD detectors at the long camera of the 1.22-m Dominion Astrophysical Observatory telescope's coudé spectrograph. Here we expand the range of stars examined to include two relatively quiescent F supergiants. ? Her (F2 II) and 41 Cyg (F5 Ib-II) are analyzed as consistently as possible with previous studies. These LTE fine analyses use the ATLAS9 and the WIDTH9 programs of R. L. Kurucz. High signal-to-noise spectrograms and high quality atomic data were employed. The derived values of these photometrically constant stars are somewhat different with the abundances of ? Her being somewhat metal-poor and those of 41 Cyg being crudely solar-like. Our analyses indicate that the basic results of Luck & Wepfer (1995) who also studied ? Her and 41 Cyg are not likely to be significantly changed by new studies of all their stars. Table 3 of this article is available at the CDS via http://cdsarc.u-strasbg.fr/ftp/cats/J/other/AN/329.4

Adelman, S. J.; Cay, I. H.; Tektunali, H. G.; Gulliver, A. F.; Teker, A.

2008-01-01

192

Does the Period of a Pulsating Star Depend on its Amplitude?  

NASA Astrophysics Data System (ADS)

Several classes of pulsating stars are now known to undergo slow changes in amplitude; these include pulsating red giants and supergiants, and yellow supergiants. We have used visual observations from the AAVSO International Database and wavelet analysis of 39 red giants, 7 red supergiants, and 3 yellow supergiants to test the hypothesis that an increase in amplitude would result in an increase in period because of non-linear effects in the pulsation. For most of the stars, the results are complex and/or indeterminate, due to the limitations of the data, the small amplitude or amplitude variation, and/or other processes such as random cycle-to-cycle period fluctuations. For the carbon giants, however, of those which have substantial amplitude variation, and reasonably simple behavior, over 90 % show a positive correlation between amplitude and period. For the non-carbon giants, and the red and yellow supergiants, the numbers showing positive and negative correlation between amplitude and period are comparable.

Percy, J. R.; Yook, J. Y.

2014-12-01

193

A survey of ultraviolet circumstellar absorption lines in the spectra of early Be and shell stars  

NASA Technical Reports Server (NTRS)

Copernicus UV data are used to examine the rich shell absorption spectra between 1120 and 1140 A in 17 Be and shell stars. Previous observations of the program stars are reviewed, the general appearance of the shell spectra between 1120 and 1140 A is described, and the shell spectra are compared with the spectra of four bright B-type supergiants in the same wavelength region. The line strengths are analyzed to determine quantitative shell strengths and shell column densities; the shell line velocities are discussed in the context of different models. It is shown that UV shell lines can exist in stars with no visible-wavelength shell features, that Fe III shell lines dominate the spectra between 1120 and 1140 A in Be and shell stars with circumstellar absorption features, and that the spectra of Be and shell stars in this region strongly resemble those of supergiants of similar effective temperature.

Snow, T. P., Jr.; Mathieu, R. D.; Peters, G. J.

1979-01-01

194

Expected number of supergiant fast X-ray transients in the Milky Way  

NASA Astrophysics Data System (ADS)

In the past fifteen years a new generation of X-ray satellites led to the discovery of a subclass of high-mass X-ray binaries (HMXBs) with supergiant companions and a peculiar transient behaviour: supergiant fast X-ray transients (SFXTs). We calculate the expected number of Galactic SFXTs for the first time, using two different statistical approaches and two sets of data based on Swift and INTEGRAL surveys, with the aim to determine how common the SFXT phenomenon really is. We find that the expected number of SFXTs in the Galaxy is 37+53-22, which shows that SFXTs constitute a large portion of X-ray binaries with supergiant companions in the Galaxy. We compare our estimate with the expected number of Galactic HMXBs predicted from observations and evolutionary models and discuss the implications for the nature of SFXTs.

Ducci, L.; Doroshenko, V.; Romano, P.; Santangelo, A.; Sasaki, M.

2014-08-01

195

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

196

Stars in the Tarantula Nebula  

NASA Technical Reports Server (NTRS)

In the most active starburst region in the local universe lies a cluster of brilliant, massive stars, known to astronomers as Hodge 301. Hodge 301, seen in the lower right hand corner of this image, lives inside the Tarantula Nebula in our galactic neighbor, the Large Magellanic Cloud. This star cluster is not the brightest, or youngest, or most populous star cluster in the Tarantula Nebula, that honor goes to the spectacular R136. In fact, Hodge 301 is almost 10 times older than the young cluster R136. But age has its advantages; many of the stars in Hodge 301 are so old that they have exploded as supernovae. These exploded stars are blasting material out into the surrounding region at speeds of almost 200 miles per second. This high speed ejecta are plowing into the surrounding Tarantula Nebula, shocking and compressing the gas into a multitude of sheets and filaments, seen in the upper left portion of the picture. Hodge 301 contains three red supergiants - stars that are close to the end of their evolution and are about to go supernova, exploding and sending more shocks into the Tarantula. Also present near the center of the image are small, dense gas globules and dust columns where new stars are being formed today, as part of the overall ongoing star formation throughout the Tarantula region.

1999-01-01

197

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.

198

ALMA observations of anisotropic dust mass loss in the inner circumstellar environment of the red supergiant VY Canis Majoris  

NASA Astrophysics Data System (ADS)

The processes leading to dust formation and the subsequent role it plays in driving mass loss in cool evolved stars is an area of intense study. Here we present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These data enable us to study the dust in its inner circumstellar environment at a spatial resolution of 129 mas at 321 GHz and 59 mas at 658 GHz, thus allowing us to trace dust on spatial scales down to 11 R? (71 AU). Two prominent dust components are detected and resolved. The brightest dust component, C, is located 334 mas (61 R?) southeast of the star and has a dust mass of at least 2.5 × 10-4 M?. It has a dust emissivity spectral index of ? = -0.1 at its peak, implying that it is optically thick at these frequencies with a cool core of Td ? 100 K. Interestingly, not a single molecule in the ALMA data has emission close to the peak of this massive dust clump. The other main dust component, VY, is located at the position of the star and contains a total dust mass of 4.0 × 10-5 M?. It also contains a weaker dust feature extending over 60 R? to the north with the total component having a typical dust emissivity spectral index of ? = 0.7. We find that at least 17% of the dust mass around VY CMa is located in clumps ejected within a more quiescent roughly spherical stellar wind, with a quiescent dust mass loss rate of 5 × 10-6 M?yr-1. The anisotropic morphology of the dust indicates a continuous, directed mass loss over a few decades, suggesting that this mass loss cannot be driven by large convection cells alone. Appendices are available in electronic form at http://www.aanda.org

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

2015-01-01

199

The young Large Magellanic Cloud cluster NGC 2214 with a single supergiant branch  

NASA Astrophysics Data System (ADS)

The young LMC cluster NGC 2214 has been suspected to be in the stage of merging two clusters, because it shows a significantly elliptical core structure embedded in an almost spherical halo and two central sub-components. Recently Sagar et al. (1991) have claimed that NGC 2214 has two distinct supergiant branches with ages of about 60 Myr and about 170 Myr, respectively. Based on deep UBVI CCD photometry, we suggest that NGC 2214 shows only one supergiant branch of age about 60 Myr. This result implies either that NGC 2214 is a single cluster or, if it is a binary cluster, it may consist of two components of similar age.

Lee, Myung G.

1992-11-01

200

The Star Clusters in the Starburst Irregular Galaxy NGC 1569  

E-print Network

We examine star clusters in the irregular, starburst galaxy NGC 1569 from HST images. In addition to the two known super star clusters, we identify 45 other clusters that are compact but resolved. Integrated UVI colors of the clusters span a large range, and suggest that ages range from 3 Myrs to 1 Gyr. However, most of the clusters were formed at the tail end of the recent starburst. Numerous clusters in addition to the know super star clusters are similar in luminosity to a small globular cluster. We examined the radial surface brightness of four of the clusters. Their half-light radii and core radii are in the range observed in present-day globular clusters. Therefore, conditions that produced the recent starburst have also been those necessary for producing compact, bright star clusters. We examine resolved stars in the outer parts of the two super star clusters. Cluster A is dominated by bright blue stars with a small population of red supergiants. Sub-components A1 and A2 have similar colors and a two-dimensional color map does not offer evidence that one component is dominated by red supergiants and the other not. The contradiction of the presence of red super- giants with Wolf-Rayet stars may instead not be a contradiction at all since there coexistence in a coeval population is not inconsistent with the evolution of massive stars. Cluster B is dominated by red supergiants, and this is confirmed by the presence of the stellar CO absorption feature in an integrated spectrum. The various age indicators are consistent with a picture in which cluster B is of order 10--20 Myrs old, and cluster A is >4-5 Myrs old.

D. A. Hunter; R. W. O'Connell; J. S. Gallagher; T. A. Smecker-Hane

2000-09-18

201

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

202

Are the R Coronae Borealis Stars Produced by White Dwarf Mergers?  

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 in a PN central star. The evidence pointing toward a WD merger or a FF origin for RCB stars is contradictory. The population of RCB stars in the Galaxy may be consistent with the number of He/CO WD mergers. If so, this would be an exciting result since RCB stars may be low-mass analogs of Type Ia SNe.

Clayton, G. C.

2013-01-01

203

Classification of Population II Stars in the Vilnius Photometric System. II. Results  

NASA Astrophysics Data System (ADS)

The results of photometric classification of 848 true and suspected Population II stars, some of which were found to belong to Population I, are presented. The stars were classified using a new calibration described in Paper I (Bartkevicius & Lazauskaite 1996). We combine these results with our results from Paper I and discuss in greater detail the following groups of stars: UU Herculis-type stars and other high-galactic-latitude supergiants, field red horizontal-branch stars, metal-deficient visual binaries, metal-deficient subgiants, stars from the Catalogue of Metal-deficient F--M Stars Classified Photometrically (MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs (Bartkevicius 1994a). It is confirmed that high galactic latitude supergiants from the Bartaya (1979) catalog are giants or even dwarfs. Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as field RHB stars, appear to be ordinary giants according to our classification. Some of the visual binaries studied can be considered as physical pairs. Quite a large fraction of stars from the MDPH catalog are found to have solar metallicity. A number of new possible UU Herculis-type stars, RHB stars and metal-deficient subgiants are identified.

Bartkevicius, A.; Lazauskaite, R.

1997-12-01

204

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

205

The atmospheric structure and fundamental parameters of the red supergiants AH Sco, UY Sct, and KW Sgr  

NASA Astrophysics Data System (ADS)

We present the atmospheric structure and the fundamental parameters of the Red Supergiants (RSGs) AH Sco, UY Sct, and KW Sgr. We have carried out spectro-interferometric observations in the near-infrared bands (between 1.9 ?m and 2.5 ?m) with the VLTI/AMBER instrument in medium resolution. In the visibility data, we detect the presence of molecular layers of water and CO in extended atmospheres. For a uniform disk modelling, we observe size increases in the water band centered at 1.9 ?m and in the CO band at 2.3--2.5 ?m, with respect to the near-continuun bandpass (2.20-2.25 ?m). Our near-infrared spectra of AH Sco, UY Sct, and KW Sgr are well reproduced by the PHOENIX model. However the synthetic visibility amplitudes of the model do not predict the large extensions of the molecular bands. The continuum (2.15-2.25 ?m) appears free from contamination by molecular layers. Thus, the continuum fitting to the PHOENIX can be used to estimate the diameter. We estimate the Rosseland-mean photospheric angular diameter of AH Sco, UY Sct, and KW Sgr to be 6.12±0.7 mas, 5.67± 0.55 mas, and 4.07±0.65 mas, respectively (preliminary values). We estimate radii and effective temperatures, and place the stars in the HR diagram.

Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H.

2013-05-01

206

Stability boundaries for massive stars in the sHR diagram  

NASA Astrophysics Data System (ADS)

Stability boundaries of radial pulsations in massive stars are compared with positions of variable and non-variable blue-supergiants in the spectroscopic HR (sHR) diagram (Langer & Kudritzki 2014), whose vertical axis is 4 log T eff - log g(= log L/M). Observational data indicate that variables tend to have higher L/M than non-variables in agreement with the theoretical prediction. However, many variable blue-supergiants are found to have values of L/M below the theoretical stability boundary; i.e., surface gravities seem to be too high by around 0.2-0.3 dex.

Saio, Hideyuki; Georgy, Cyril; Meynet, Georges

2015-01-01

207

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

208

Swift's Christmas Burst From Blue Supergiant Star Explosion - Duration: 1:44.  

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...

209

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

210

The past and future evolution of a star like Betelgeuse  

NASA Astrophysics Data System (ADS)

We discuss the physics and the evolution of a typical massive star passing through an evolutionary stage similar to that of Betelgeuse. After a brief introduction recalling various observed parameters of Betelgeuse, we discuss the Pre-Main-Sequence phase (PMS), the Main-Sequence (MS) phase, the physics governing the duration of the first crossing of the HR diagram, the red supergiant stage (RSG), the post-red supergiant phases and the final fate of solar metallicity stars with masses between 9 and 25 M?. We examine the impact of different initial rotation and of various prescriptions for the mass loss rates during the red supergiant phase. We show that, whatever the initial rotation rate (chosen between 0 and 0.7 × ?crit, ?crit being the surface equatorial velocity producing a centrifugal acceleration balancing exactly the gravity) and the mass loss rates during the RSG stage (varied between a standard value and 25 times that value), a 15 M? star always ends its lifetime as a RSG and explodes as a type II-P or II-L supernova.

Meynet, G.; Haemmerlé, L.; Ekström, S.; Georgy, C.; Groh, J.; Maeder, A.

2013-05-01

211

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

212

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

SciTech Connect

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

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

2009-10-15

213

Spitzer SAGE Infrared Photometry of Massive Stars in the Large Magellanic Cloud  

NASA Astrophysics Data System (ADS)

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

Bonanos, A. Z.; Massa, D. L.; Sewilo, M.; Lennon, D. J.; Panagia, N.; Smith, L. J.; Meixner, M.; Babler, B. L.; Bracker, S.; Meade, M. R.; Gordon, K. D.; Hora, J. L.; Indebetouw, R.; Whitney, B. A.

2009-10-01

214

From the atmosphere to the circumstellar environment in cool evolved stars  

E-print Network

We discuss and illustrate contributions that optical interferometry has made on our current understanding of cool evolved stars. We include red giant branch (RGB) stars, asymptotic giant branch (AGB) stars, and red supergiants (RSGs). Studies using optical interferometry from visual to mid-infrared wavelengths have greatly increased our knowledge of their atmospheres, extended molecular shells, dust formation, and winds. These processes and the morphology of the circumstellar environment are important for the further evolution of these stars toward planetary nebulae (PNe) and core-collapse supernovae (SNe), and for the return of material to the interstellar medium.

Wittkowski, Markus

2015-01-01

215

Winds of low-metallicity OB-type stars: HST-COS spectroscopy in IC1613  

E-print Network

We present the first quantitative UV spectroscopic analysis of resolved OB stars in IC1613. Because of its alleged very low metallicity (terminal velocities were derived from the observed PCygni profiles with the SEI method. The vinf-Z relationship has been revisited. The terminal velocity of IC1613 O-stars is clearly lower than Milky Way counterparts, but there is no clear difference between IC1613 and SMC or LMC analogue stars. We find no clear segregation with host galaxy in the terminal velocities of B-supergiants, nor in the vinf/vesc ratio of the whole OB star sample in any of the studied galaxies. Finally, we prese...

Garcia, Miriam; Najarro, Francisco; Lennon, Daniel J; Urbaneja, Miguel A

2014-01-01

216

More nitrogen rich B-type stars in the SMC cluster, NGC 330  

Microsoft Academic Search

High resolution spectra of seven early B-type giant\\/supergiant stars in the\\u000aSMC cluster NGC330 are analysed to obtain their chemical compositions relative\\u000ato SMC field and Galactic B-type stars. It is found that all seven stars are\\u000anitrogen rich with an abundance approximately 1.3 dex higher than an SMC\\u000amain-sequence field B-type star, AV304. They also display evidence for\\u000adeficiencies

D. J. Lennon; P. L. Dufton; C. Crowley

2002-01-01

217

What Are the R Coronae Borealis Stars?  

NASA Astrophysics Data System (ADS)

The R Coronae Borealis (RCB) stars are rare hydrogen-deficient, carbon-rich, supergiants, best known for their spectacular declines in brightness at irregular intervals. Efforts to discover more RCB stars have more than doubled the number known in the last few years and they appear to be members of an old, bulge population. Two evolutionary scenarios have been suggested for producing an RCB star, a double degenerate merger of two white dwarfs, or a final helium shell flash in a planetary nebula central star. The evidence pointing toward one or the other is somewhat contradictory, but the discovery that RCB stars have large amounts of 18O has tilted the scales towards the merger scenario. If the RCB stars are the product of white dwarf mergers, this would be a very exciting result since RCB stars would then be low-mass analogs of type Ia supernovae. The predicted number of RCB stars in the Galaxy is consistent with the predicted number of He/CO WD mergers. But, so far, only about sixty-five of the predicted 5,000 RCB stars in the Galaxy have been discovered. The mystery has yet to be solved.

Clayton, G. C.

2012-06-01

218

A VLT/UVES spectroscopy study of O2 stars in the LMC  

NASA Astrophysics Data System (ADS)

We have analysed VLT/UVES spectra of six O2 stars within the Large Magellanic Cloud using the non-LTE atmospheric code CMFGEN. A range of physical properties was determined by employing a temperature calibration based upon N IV - N V diagnostics. Wind properties were also obtained from the H? line, while CNO surface abundances were supplied through various diagnostics. Our results reveal effective temperatures in excess of T_{eff} ˜50 kK in all cases. We also addressed their evolutionary status and favour a mass dependent division. For lower masses ?100 M?Mar, an O2 star follows the classical sequence, evolving from dwarf on to giant, through to supergiant. At higher masses, the dwarf phase may be circumvented and instead O2 stars begin their lives as giants or supergiants, evolving to the H-rich WN stage within ˜1.5 Myr.

Doran, Emile I.; Crowther, Paul A.

2011-01-01

219

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

220

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

221

Properties of Hot, Massive Stars: The Impact of FUSE  

E-print Network

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

Paul A. Crowther

2004-10-01

222

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

223

Spectral and temporal properties of the supergiant fast X-ray transient IGR J18483-0311 observed by INTEGRAL  

NASA Astrophysics Data System (ADS)

Context. IGR J18483-0311 is a supergiant fast X-ray transient whose compact object is located in a wide (18.5 d) and eccentric (e ~ 0.4) orbit, which shows sporadic outbursts that reach X-ray luminosities of ~1036 erg s-1. Aims: We investigated the timing properties of IGR J18483-0311 and studied the spectra during bright outbursts by fitting physical models based on thermal and bulk Comptonization processes for accreting compact objects. Methods: We analysed archival INTEGRAL data collected in the period 2003-2010, focusing on the observations with IGR J18483-0311 in outburst. We searched for pulsations in the INTEGRAL light curves of each outburst. We took advantage of the broadband observing capability of INTEGRAL for the spectral analysis. Results: We observed 15 outbursts, seven of which we report here for the first time. This data analysis almost doubles the statistics of flares of this binary system detected by INTEGRAL. A refined timing analysis did not reveal a significant periodicity in the INTEGRAL observation where a ~21 s pulsation was previously detected. Neither did we find evidence for pulsations in the X-ray light curve of an archival XMM-Newton observation of IGR J18483-0311. In the light of these results the nature of the compact object in IGR J18483-0311 is unclear. The broadband X-ray spectrum of IGR J18483-0311 in outburst is well fitted by a thermal and bulk Comptonization model of blackbody seed photons by the infalling material in the accretion column of a neutron star. We also obtained a new measurement of the orbital period using the Swift/BAT light curve.

Ducci, L.; Doroshenko, V.; Sasaki, M.; Santangelo, A.; Esposito, P.; Romano, P.; Vercellone, S.

2013-11-01

224

Terminal velocities of luminous, early-type SMC stars  

E-print Network

Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are used to determine terminal velocities for 11 O and B-type giants and supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV resonance lines. Using archival data from observations with the Goddard High-Resolution Spectrograph and the International Ultraviolet Explorer telescope, terminal velocities are obtained for a further five B-type supergiants. We discuss the metallicity dependence of stellar terminal velocities, finding no evidence for a significant scaling between Galactic and SMC metallicities for Teff < 30,000 K, consistent with the predictions of radiation driven wind theory for supergiant stars. A comparison of the $v_\\infty / v_{esc}$ ratio between the SMC and Galactic samples, while consistent with the above statement, emphasizes that the uncertainties in the distances to galactic O-stars are a serious obstacle to a detailed comparison with theory. For the SMC sample there is considerable scatter in this ratio at a given effective temperature, perhaps indicative of uncertainties in stellar masses.

C. J. Evans; D. J. Lennon; C. Trundle; S. R. Heap; D. J. Lindler

2004-01-20

225

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

226

What are the R Coronae Borealis Stars?  

E-print Network

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

Clayton, Geoffrey C

2012-01-01

227

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

228

Star Caught Smoking  

NASA Astrophysics Data System (ADS)

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

2007-08-01

229

Copernicus observations of the N v resonance doublet in 53 early-type stars  

NASA Technical Reports Server (NTRS)

UV spectra in the wavelength interval 1170-1270 A are presented for 53 early-type stars ranging in spectral type from O6.5 V to B2.5 IV. The sample includes four Wolf-Rayet stars, seven known Oe-Be stars, and six galactic halo OB stars. A qualitative analysis of the stellar N v doublet reveals that: (1) N v is present in all stars hotter and more luminous than type B0 for the main sequence, B1 for giants, and B2 for supergiants; (2) shell components of N v and an unidentified absorption feature at 1230 A are present in about half of the stars; (3) the column density of N v is well correlated with bolometric luminosity over the spectral range O6 to B2; and (4) the ratio of emission to absorption equivalent width is a factor of 2 smaller in the main sequence stars than in supergiants, which suggests that the wind structure changes as a star evolves. For several stars, this ratio is too small to be explained by traditional wind models.

Abbott, D. C.; Bohlin, R. C.; Savage, B. D.

1982-01-01

230

Oxygen isotopic ratios in cool R Coronae Borealis stars  

E-print Network

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

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

2010-01-01

231

Neutral and ionised gas around the post-red supergiant IRC +10 420 at AU size scales  

NASA Astrophysics Data System (ADS)

Context. IRC +10 420 is one of the few known massive stars in rapid transition from the red supergiant phase to the Wolf-Rayet or luminous blue variable phase. Aims: The star has an ionised wind and using the Br? line we assess the mass-loss on spatial scales of ~1 AU. Methods: We present new VLT Interferometer AMBER data which are combined with all other AMBER data present in the literature. The final dataset covers a position angle range of ~180° and baselines up to 110 m. The spectrally dispersed visibilities, differential phases and line flux are conjointly analysed and modelled. We also present the first AMBER/FINITO observations which cover a larger wavelength range and allow us to observe the Na i doublet at 2.2 ?m. The data are complemented by X-Shooter data, which provide a higher spectral resolution view. Results: The Br? emission line and the Na i doublet are both spatially resolved. After correcting the AMBER data for the fact that the lines are not spectrally resolved, we find that Br? traces a ring with a diameter of 4.18 mas, in agreement with higher spectral resolution data. We consider a geometric model in which the Br? emission emerges from the top and bottom rings of an hour-glass shaped structure, viewed almost pole-on. It provides satisfactory fits to most visibilities and differential phases. The fact that we detect line emission from a neutral metal like Na i within the ionised region, a very unusual occurrence, suggests the presence of a dense pseudo-photosphere. Conclusions: The ionised wind can be reproduced with a polar wind, which could well have the shape of an hour-glass. Closer in, the resolved Na i emission is found to occur on scales barely larger than the continuum. This fact and that many yellow hypergiants exhibit this comparatively rare emission hints at the presence of a "Yellow" or even "White Wall" in the Hertzsprung-Russell diagram, preventing them from visibly evolving to the blue. Based on observations at ESO, and in particular with VLTI, proposals 079.D-0123(A), and 383.C-0166(A) and X-Shooter, proposal SV-9434.FITS files are 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/551/A69

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

2013-03-01

232

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

233

Carbon abundance and the N/C ratio in atmospheres of A-, F- and G-type supergiants and bright giants  

NASA Astrophysics Data System (ADS)

Based on our prior accurate determination of fundamental parameters for 36 Galactic A-, F- and G-type supergiants and bright giants (luminosity classes I and II), we undertook a non-LTE analysis of the carbon abundance in their atmospheres. It is shown that the non-LTE corrections to the C abundances derived from C I lines are negative and increase with the effective temperature Teff; the corrections are especially significant for the infrared C I lines with wavelengths 9060-9660 Å. The carbon underabundance as a general property of the stars in question is confirmed; a majority of the stars studied has the carbon deficiency [C/Fe] between -0.1 and -0.5 dex, with a minimum at -0.7 dex. When comparing the derived C deficiency with the N excess found by us for the same stars earlier, we obtain a pronounced N versus C anticorrelation, which could be expected from predictions of the theory. We found that the ratio [N/C] spans mostly the range from 0.3 to 1.7 dex. Both these enhanced [N/C] values and the C and N anomalies themselves are an obvious evidence of the presence on a star's surface of mixed material from stellar interiors; so, a majority of programme stars passed through the deep mixing during the main sequence (MS) and/or the first dredge-up (FD) phase. Comparison with theoretical predictions including rotationally induced mixing shows that the stars are either post-MS objects with the initial rotational velocities V0 = 200-300 km s-1 or post-FD objects with V0 = 0-300 km s-1. The observed N versus C anticorrelation reflects a dependence of the C and N anomalies on the V0 value: on average the higher V0 the greater the anomalies. It is shown that an absence of detectable lithium in the atmospheres of the stars, which is accompanied with the observed N excess and C deficiency, is quite explainable.

Lyubimkov, Leonid S.; Lambert, David L.; Korotin, Sergey A.; Rachkovskaya, Tamara M.; Poklad, Dmitry B.

2015-02-01

234

Massive Stars in the Quintuplet Cluster  

E-print Network

We present near-infrared photometry and K-band spectra of newly-identified massive stars in the Quintuplet Cluster, one of the three massive clusters projected within 50 pc of the Galactic Center. We find that the cluster contains a variety of massive stars, including more unambiguously identified Wolf-Rayet stars than any cluster in the Galaxy, and over a dozen stars in earlier stages of evolution, i.e., LBV, Ofpe/WN9, and OB supergiants. One newly identified star is the second ``Luminous Blue Variable'' in the cluster, after the ``Pistol Star.'' Given the evolutionary stages of the identified stars, the cluster appears to be about 4 \\pm 1 Myr old, assuming coeval formation. The total mass in observed stars is $\\sim 10^3 \\Msun$, and the implied mass is $\\sim 10^4 \\Msun$, assuming a lower mass cutoff of 1 \\Msun and a Salpeter initial mass function. The implied mass density in stars is at least a few thousand $\\Msun pc^{-3}$. The newly-identified stars increase the estimated ionizing flux from this cluster by about an order of magnitude with respect to earlier estimates, to 10^{50.9} photons/s, or roughly what is required to ionize the nearby ``Sickle'' HII region (G0.18 - 0.04). The total luminosity from the massive cluster stars is $\\approx 10^{7.5}$ \\Lsun, enough to account for the heating of the nearby molecular cloud, M0.20 - 0.033. We propose a picture which integrates most of the major features in this part of the sky, excepting the non-thermal filaments. We compare the cluster to other young massive clusters and globular clusters, finding that it is unique in stellar content and age, except, perhaps, for the young cluster in the central parsec of the Galaxy. In addition, we find that the cluster is comparable to small ``super star clusters.''

Donald F. Figer; Ian S. McLean; Mark Morris

1999-03-18

235

Changes of surface chemistry for standard massive star evolution - Cartography in the HR diagram  

NASA Astrophysics Data System (ADS)

The time evolution of surface abundances in stars of initial mass 15, 20, 25, 40, and 60 solar mass is investigated by means of numerical simulations, using mass-loss/convective-dredge-up models analogous to those constructed by Maeder (1983) for stars with initial mass 60-120 solar mass. Particular attention is given to the distribution of peculiar CNO abundances in the upper part of the HR diagram. The results are presented in extensive tables and graphs and characterized in detail, with reference to available observational data. Findings reported include He/H lifetime ratio = 0.2, CN abundance equilibrium only above 80 solar masses, no ON equilibrium, normal abundances in blue supergiants (except Hubble-Sandage variables and postred supergiants), and greater than normal CN and ON processing in Alpha Sco and Alpha Ori.

Maeder, A.

1987-02-01

236

Extensions of the Wilson-Bappu effect among very luminous stars  

NASA Technical Reports Server (NTRS)

It has been stated that the technique used by Wilson and Bappu (1957) in their study of the observational correlation of M sub V and the logarithm of the full width at half maximum of the Ca II K-line central emission for G, K, and M stars has a plus or minus 0.5 mag accuracy. A tabulation by Wilson (1976) suggests, however, that the error may be only plus or minus 0.3 mag. This accuracy makes the approach valuable for late-type supergiants since other methods suffer from comparable errors. A description is in this connection presented of a new class of emission lines in late-type giant and supergiant spectra that exhibit M sub V correlated widths, yet are detectable among the brightest stars.

Stencel, R. E.

1978-01-01

237

Supergiant Fast X-Ray Transients: Swift Results and Theoretical Progress  

NASA Astrophysics Data System (ADS)

We present an overview of our Supergiant Fast X-ray Transients (SFXT) project, by highlighting the unique observational contribution Swift is giving to this exciting new field. Since 2007 Swift has been detecting outbursts from these fast transients with the BAT and following them intensively for days with the XRT so that we now have a firm estimate of the time SFXTs spend in each intensity phase. We summarize some preliminary results on our XSPEC model that numerically solves the bulk-motion radiative transfer equation with a strong magnetic field, in the Fokker-Planck approximation.

Farinelli, Ruben; Romano, Patrizia; Vercellone, Stefano; Ceccobello, C.; Titarchuk, L.

238

LMC O Supergiant Mass Loss Rates Determined from P V, S V and IR Excesses  

NASA Astrophysics Data System (ADS)

We use HST/STIS and FUSE spectra and Spitzer/IRAC photometry to obtain independent mass loss rates for 7 LMC O supergiants. The mass loss rates are derived from the P Cygni profiles of the P V 1118, 1128 resonance doublet, the S V 1502 and N IV 1718 excited state lines, and the IR excesses of a combination of ground based and Spitzer photometry. The different mass loss rates are compared to each other and to theoretical expectations. We discuss the causes for the differences between the various determinations.

Massa, Derck; Prinja, R.; Fullerton, A.; Lennon, D.

2012-05-01

239

The intrinsic values and color excesses of (B-V) for 115 F-K supergiants  

NASA Technical Reports Server (NTRS)

Color excesses in B-V are determined indirectly from a study of Stromgren's b-y color for a sample of F0 - K5 supergiants. The resulting E(B-V)'s are estimated to have an expected precision of + or - 0.05. With the calculated color excesses and the observed values of B-V given in various catalogs, the run of B-V with spectral type is obtained. This B-V/(spectral type) relationship is compared with those found previously by other investigators.

Kelsall, T.

1972-01-01

240

The stellar content of the super star clusters in NGC 1569  

E-print Network

We discuss HST FOS ultraviolet spectroscopy and NICMOS near-infrared photometry of four young super star clusters in the central region of the irregular starburst galaxy NGC 1569. The new observations coupled with previous HST WFPC2 photometry and ground-based optical spectroscopy allow us to isolate and age-date the hot and cool stellar components of these massive clusters. We analyze the two components A1 and A2 of the brightest super star cluster NGC 1569-A. This cluster received previous attention due to the simultaneous presence of Wolf-Rayet stars and red supergiants. The FOS spectra provide the first evidence for O-stars in NGC 1569-A, indicating a young (5 Myr) stellar component in A1 and/or A2. Comparison with other high-mass star-forming regions suggests that the O- and Wolf-Rayet stars are spatially coincident. If so, cluster A2 could be the host of the very young O- and Wolf-Rayet population, and the somewhat older red supergiants could be predominantly located in A1. The mass-to-light ratio of NGC 1569-A1 is analyzed in five optical and infrared photometric bands and compared to evolutionary synthesis models. No indications for an anomalous initial mass function are found, consistent with a scenario where this cluster is the progenitor of present-day globular clusters. The clusters A1 and A2 are compared to clusters B and #30. The latter two clusters are older and fully dominated by red supergiants. All four super star clusters provide a significant fraction (20 - 25%) of the total optical and near-infrared light in the central region of the galaxy. The photometric properties of the super star cluster population in NGC 1569 resemble those of the populous clusters in the Magellanic Clouds.

L. Origlia; C. Leitherer; A. Aloisi; L. Greggio; M. Tosi

2001-05-11

241

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

242

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.

1994-08-01

243

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

244

Soft X-ray characterisation of the long-term properties of supergiant fast X-ray transients  

NASA Astrophysics Data System (ADS)

Context. Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs) that are characterised by a hard X-ray (? 15 keV) flaring behaviour. These flares reach peak luminosities of 1036-1037 erg s-1 and last a few hours in the hard X-rays. Aims: We investigate the long-term properties of SFXTs by examining the soft (0.3-10 keV) X-ray emission of the three least active SFXTs in the hard X-ray and by comparing them with the remainder of the SFXT sample. Methods: We performed the first high-sensitivity soft X-ray long-term monitoring with Swift/XRT of three relatively unexplored SFXTs, IGR J08408-4503, IGR J16328-4726, and IGR J16465-4507, whose hard X-ray duty cycles are the lowest measured among the SFXT sample. We assessed how long each source spends in each flux state and compared their properties with those of the prototypical SFXTs. Results: The behaviour of IGR J08408-4503 and IGR J16328-4726 resembles that of other SFXTs, and it is characterised by a relatively high inactivity duty cycle (IDC) and pronounced dynamic range (DR) in the X-ray luminosity. We found DR ~ 7400, IDC ~ 67% for IGR J08408-4503, and DR ~ 750, IDC ~ 61% for IGR J16328-4726 (in all cases the IDC is given with respect to the limiting flux sensitivity of XRT, that is 1-3 × 10-12 erg cm-2 s-1). In common with all the most extreme SFXT prototypes (IGR J17544-2619, XTE J1739-302, and IGR J16479-4514), IGR J08408-4503 shows two distinct flare populations. The first one is associated with the brightest outbursts (X-ray luminosity LX ? 1035 - 36 erg s-1), while the second comprises dimmer events with typical luminosities of LX ? 1035 erg s-1. This double-peaked distribution of the flares as a function of the X-ray luminosity seems to be a ubiquitous feature of the extreme SFXTs. The lower DR of IGR J16328-4726 suggests that this is an intermediate SFXT. IGR J16465-4507 is characterised by a low IDC ~ 5% and a relatively narrow DR ~ 40, reminiscent of classical supergiant HMXBs. The duty cycles measured with XRT are found to be comparable with those reported previously by BAT and INTEGRAL, when the higher limiting sensitivities of these instruments are taken into account and sufficiently long observational campaigns are available. By making use of these new results and those we reported previously, we prove that no clear correlation exists between the duty cycles of the SFXTs and their orbital periods. Conclusions: The unique sensitivity and scheduling flexibility of Swift/XRT allowed us to carry out an efficient long-term monitoring of the SFXTs, following their activity across more than 4 orders of magnitude in X-ray luminosity. While it is not possible to exclude that particular distributions of the clump and wind parameters may produce double-peaked differential distributions in the X-ray luminosities of the SFXTs, the lack of a clear correlation between the duty cycles and orbital periods of these sources make it difficult to interpret their peculiar variability by only using arguments related to the properties of supergiant star winds. Our findings favour the idea that a correct interpretation of the SFXT phenomenology requires a mechanism to strongly reduce the mass accretion rate onto the compact object during most of its orbit around the companion, as proposed in a number of theoretical works. Tables 1-4 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/568/A55

Romano, P.; Ducci, L.; Mangano, V.; Esposito, P.; Bozzo, E.; Vercellone, S.

2014-08-01

245

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

246

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

NASA Astrophysics Data System (ADS)

We present the 100-month Swift Catalogue of Supergiant Fast X-ray Transients, a collection of over a thousand Swift/BAT flares from 11 Supergiant Fast X-ray Transients (SFXT), complete down to 15-150 keV fluxes of about ˜6×10^{-10} erg cm^{-2} s^{-1} (daily timescale) and about ˜ 1.5×10^{-9} erg cm^{-2} s^{-1} (orbital timescale, averaging about 800 s). This population is characterized by short (a few hundred seconds) and relatively bright (in excess of 100 mCrab, 15-50 keV) events, lasting much less than a day in the hard X-rays. The outbursts are a much longer phenomenon however, as testified by the clustering of flares in orbital phase-space. They last up to a few days, as previously discovered from Swift deeper soft X-ray observations. We use this large dataset to probe the properties of the high and intermediate emission states in SFXTs, and to infer the properties of these binary systems. We also present preliminary results from our analysis of spectral evolution dependent flux light curves and broad-band spectroscopy of the outbursts. Finally, we provide a recipe to estimate the number of flares per year each source is likely to produce as a function of the detection threshold and limiting flux.

Romano, P.; Ducci, L.; Krimm, H.; Palmer, D.; Esposito, P.; Vercellone, S.; Evans, P.; Guidorzi, C.; Mangano, V.; Kennea, J.

2014-07-01

247

Terminal velocities of luminous, early-type SMC stars  

E-print Network

Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are used to determine terminal velocities for 11 O and B-type giants and supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV resonance lines. Using archival data from observations with the Goddard High-Resolution Spectrograph and the InternationalUltravioletExplorer telescope, terminal velocities are obtained for a further five B-type supergiants. We discuss the metallicity dependence of stellar terminal velocities for supergiants, finding no evidence for a significant scaling between Galactic and SMC metallicities for Teff < 30,000K, consistent with the predictions of radiation driven wind theory. A comparison of the v?/vesc ratio between the SMC and Galactic samples, while consistent with the above statement, emphasizes that the uncertainties in the distances to galactic OB-type stars are a serious obstacle to a detailed comparison with theory. For the SMC sample there is considerable scatter in v?/vesc at a given effective temperature, perhaps indicative of uncertainties in stellar masses.

C. J. Evans; D. J. Lennon; C. Trundle; S. R. Heap; D. J. Lindler

2004-01-01

248

Neutron-capture nucleosynthesis in HdC stars: the case of HE 1015-2050  

NASA Astrophysics Data System (ADS)

Hydrogen-deficient carbon (HdC) stars and R Coronae Borealis (RCB) type stars form a rare class of carbon-rich supergiants. A fraction of these stars in our Galaxy are known to exhibit strong features of light neutron-capture elements such as Sr, Y and Zr usually attributed to the weak component of the s-process. These stars are believed to be in a very short-lived evolutionary phase; hence, their ejecta could have significantly contributed to chemical enrichment in the Galaxy. From medium-resolution spectral analyses of faint high latitude carbon (FHLC) stars of Hamburg/ESO survey Goswami et al. (2010) have added a new member HE 1015-2050, to this rare class. This object is found to exhibit anomalously strong features of Sr in its spectrum. Possible scenarios that might have led to the formation of this object are discussed in the light of existing scenarios of HdC star formation.

Goswami, Aruna; Karinkuzhi, Drisya

249

Resolved photometry of extragalactic young massive star clusters  

NASA Astrophysics Data System (ADS)

Aims: We present colour-magnitude diagrams (CMDs) of young massive star clusters in several galaxies located well beyond the Local Group. The richness of these clusters allows us to obtain large samples of post-main sequence stars and test how well the observed CMDs are reproduced by canonical stellar isochrones. Methods: We use imaging of seven clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC 7793 obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope and carry out PSF-fitting photometry of individual stars in the clusters. The clusters have ages in the range ~(5-50) × 106 years and masses of ~105 M?-106 M?. Although crowding prevents us from obtaining photometry in the inner regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. Results: In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergiants from the main sequence complicates this comparison. In several cases we observe a large spread (1-2 mag) in the luminosities of the supergiant stars that cannot be accounted for by observational errors. We find that this spread can be reproduced by including an age spread of ~(10-30) × 106 years in the models. However, age spreads cannot fully account for the observed morphology of the CMDs and other processes, such as the evolution of interacting binary stars, may also play a role. Conclusions: Colour-magnitude diagrams can be successfully obtained for massive star clusters out to distances of at least 4-5 Mpc. Comparing such CMDs with models based on canonical isochrones we find several areas of disagreement. One interesting possibility is that an age spread of up to ~30 Myr may be present in some clusters. The data presented here may provide useful constraints on models for single and/or binary stellar evolution. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555Tables 4-10 are only available in electronic form 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/532/A147

Larsen, S. S.; de Mink, S. E.; Eldridge, J. J.; Langer, N.; Bastian, N.; Seth, A.; Smith, L. J.; Brodie, J.; Efremov, Yu. N.

2011-08-01

250

Investigation of ultraviolet fluxes of normal and peculiar stars  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

251

Hypervelocity Stars. I. The Spectroscopic Survey  

E-print Network

We discuss our targeted search for hypervelocity stars (HVSs), stars traveling with velocities so extreme that dynamical ejection from a massive black hole is their only suggested origin. Our survey, now half complete, has successfully identified a total of four probable HVSs plus a number of other unusual objects. Here we report the most recently discovered two HVSs: SDSS J110557.45+093439.5 and possibly SDSS J113312.12+010824, traveling with Galactic rest-frame velocities at least +508+-12 and +418+-10 km/s, respectively. The other late B-type objects in our survey are consistent with a population of post main-sequence stars or blue stragglers in the Galactic halo, with mean metallicity [Fe/H]=-1.3 and velocity dispersion 108+-5 km/s. Interestingly, the velocity distribution shows a tail of objects with large positive velocities that may be a mix of low-velocity HVSs and high-velocity runaway stars. Our survey also includes a number of DA white dwarfs with unusually red colors, possibly extremely low mass objects. Two of our objects are B supergiants in the Leo A dwarf, providing the first spectroscopic evidence for star formation in this dwarf galaxy within the last ~30 Myr.

Warren R. Brown; Margaret J. Geller; Scott J. Kenyon; Michael J. Kurtz

2006-04-13

252

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

253

Chemical compositions of Four B-type Supergiants in the SMC Wing  

E-print Network

High-resolution UCLES/AAT spectra of four B-type supergiants in the SMC South East Wing have been analysed using non-LTE model atmosphere techniques to determine their atmospheric parameters and chemical compositions. The principle aim of this analysis was to determine whether the very low metal abundances ($-$1.1 dex compared with Galactic value) previously found in the Magellanic Inter Cloud region (ICR) were also present in SMC Wing. The chemical compositions of the four targets are similar to those found in other SMC objects and appear to be incompatible with those deduced previously for the ICR. Given the close proximity of the Wing to the ICR, this is difficult to understand and some possible explanations are briefly discussed.

J. -K. Lee; W. R. J. Rolleston; P. L. Dufton; R. S. I. Ryan

2004-10-12

254

The Swift Supergiant Fast X-Ray Transients Project:. [A Review, New Results and Future Perspectives  

NASA Technical Reports Server (NTRS)

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.

2013-01-01

255

Spitzer Observations of Dust Around R Coronae Borealis Stars  

NASA Astrophysics Data System (ADS)

The RCB stars are rare hydrogen-deficient carbon-rich supergiants, all apparently single stars which are consistent with being post-AGB stars. Their rarity may stem from the fact that they are in an extremely rapid phase of their evolution or in an evolutionary phase that most stars do not undergo. Several evolutionary scenarios have been suggested to account for the RCB stars including, a merger of two white dwarfs, or a final helium shell flash in a Planetary Nebula (PN) central star. Therefore, in the RCB stars, the presence or absence of circumstellar material and the nature of this material provides a fossil record of previous evolutionary stages. We have mapped the shells around four RCB stars, R CrB, UW Cen, SU Tau, and V CrA, with MIPS at 24, 70 and 160 microns. We will model the dust shells using dust grains appropriate to the RCB stars to reproduce the observed morphology. While most RCB stars are relatively cool (<7000; K), a few are significantly hotter ( 20,000 K). Two of these stars, V348 Sgr and HV 2671 show similarities to the [WC] central stars of PNe such as CPD -56 8032. We have obtained IRS spectra of V348 Sgr and HV 2671. We will compare their IR spectra with those of the [WC] stars and the cooler RCB stars. CPD -56 8032 shows emission features of PAHs as well as crystalline silicates, indicating a dual dust chemistry. These systems may all be binaries in which the O-rich silicates are trapped in a disk as a result of a past mass transfer event, with the C-rich particles being widely distributed in the nebula as a result of recent ejections of C-rich material. This work was supported by Spitzer Space Telescope contracts 1287678 and 1287524 issued by Caltech/JPL.

Clayton, Geoffrey C.; De Marco, O.; Gordon, K.; Nordhaus, J.; Bond, H.; Sugerman, B.; Barlow, M.; Lawson, W.; Pollacco, D.

2007-12-01

256

The ultraviolet spectra of three N-type carbon stars  

NASA Technical Reports Server (NTRS)

The paper reports the successful detection of the ultraviolet spectra of three N-type carbon stars: BL Ori, TX Psc, and T Ind. Exposures of approximately 2-3 hours with the LWR camera of the IUE Satellite at low dispersion were necessary to record the ultraviolet flux. The shortward extension of the photospheric continuum is well exposed down to about 2800 A, with strong molecular and atomic absorption features. The spectrum appears not to be seriously affected by the unknown opacity source which blankets N stars (especially redder ones) in the violet. Emission lines of Mg II (h and k) and C II (2325 A) are conspicuous, indicating the presence of chromospheres in the stars. The ratios of integrated fluxes in the Mg II lines and C II lines to bolometric flux are respectively much smaller and slightly smaller than values observed in oxygen-rich M giants and supergiants.

Johnson, H. R.; Obrien, G. T.

1983-01-01

257

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

258

Infrared circumstellar shells - Origins, and clues to the evolution of massive stars  

NASA Technical Reports Server (NTRS)

The infrared fluxes, spatial and spectral characteristics for a sample of 111 supergiant stars of spectral types F0 through M5 are tabulated, and correlations examined with respect to the nature of their circumstellar envelopes. One-fourth of these objects were spatialy resolved by IRAS at 60 microns and possess extended circumstellar shell material, with implied expansion ages of about 10 to the 5th yr. Inferences about the production of dust, mass loss, and the relation of these characteristics of the evolution of massive stars, are discussed.

Stencel, Robert E.; Pesce, Joseph E.; Bauer, Wendy Hagen

1989-01-01

259

Submitted to Ap.J Terminal velocities of luminous, early-type SMC stars  

E-print Network

Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are used to determine terminal velocities for 11 O and B-type giants and supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV resonance lines. Using archival data from observations with the Goddard High-Resolution Spectrograph and the InternationalUltravioletExplorer telescope, terminal velocities are obtained for a further five B-type supergiants. We discuss the metallicity dependence of stellar terminal velocities, finding no evidence for a significant scaling between Galactic and SMC metallicities for Teff < 30,000K, consistent with the predictions of radiation driven wind theory for supergiant stars. A comparison of the ratio v?/vesc between the SMC and Galactic samples, while consistent with the above statement, emphasizes that the uncertainties in the distances to galactic O-stars are a serious obstacle to a detailed comparison with theory. Furthermore, for the SMC sample, there is considerable scatter in this ratio at a given effective temperature, perhaps indicative of uncertainties in stellar masses.

C. J. Evans; D. J. Lennon; C. Trundle; S. R. Heap; D. J. Lindler

2004-01-01

260

Keck/NIRSPEC Spectroscopy of Stars Near Sgr A*  

NASA Astrophysics Data System (ADS)

We present moderate (R approx 2,700) and high resolution (R approx 22,000) 2.0-2.4 um spectroscopy of the central 0.1 square arcseconds of the Galaxy obtained with NIRSPEC on the Keck II telescope. The composite spectra do not have any features attributable to the brightest stars in the central cluster, i.e. after background subtraction, WCO < 2 Angstroms. This stringent limit, and previously reported photometry, lead us to conclude that the majority, if not all, of the stars are hotter than typical red giants, and are likely OB main sequence stars. In addition, we preview several other Galactic Center programs initiated with NIRSPEC which address the following topics: 1) the accelerations of stars around the central black hole, 2) the velocities of ionized gas in the central parsec, 3) the extent of the main sequence population and star formation history in the central parsec, 4) the mass magnitude relation and IMF in the Arches cluster, 5) the nature of the MIR sources in the central parsec and Quintuplet clusters, 6) the physical parameters of stellar atmosphere/winds of super luminous stars (Pistol Star), and 7) the metallicity in the GC as inferred from observations of red supergiants, red giants, and hot stars. We present a survey of these data, including a high resolution slit scan movie of the central parsec, and show how they can be used to vastly improve the current state of the art in the related science topics.

Figer, D. F.; Becklin, E. E.; Morris, M.; McLean, I. S.; Graham, J. R.; Gilbert, A. M.; Larkin, J. E.; Levenson, N. A.; Teplitz, H. I.

1999-12-01

261

MULTIPLE GENERATIONS OF STARS IN THE TARANTULA NEBULA  

NASA Technical Reports Server (NTRS)

In the most active starburst region in the local universe lies a cluster of brilliant, massive stars, known to astronomers as Hodge 301. Hodge 301, seen in the lower right hand corner of this image, lives inside the Tarantula Nebula in our galactic neighbor, the Large Magellanic Cloud. This star cluster is not the brightest, or youngest, or most populous star cluster in the Tarantula Nebula -- that honor goes to the spectacular R136. In fact, Hodge 301 is almost 10 times older than the young cluster R136. But age has its advantages; many of the stars in Hodge 301 are so old that they have exploded as supernovae. These exploded stars are blasting material out into the surrounding region at speeds of almost 200 miles per second. This high speed ejecta are plowing into the surrounding Tarantula Nebula, shocking and compressing the gas into a multitude of sheets and filaments, seen in the upper left portion of the picture. Note for your calendar; Hodge 301 contains three red supergiants - stars that are close to the end of their evolution and are about to go supernova, exploding and sending more shocks into the Tarantula. Also present near the center of the image are small, dense gas globules and dust columns where new stars are being formed today, as part of the overall ongoing star formation throughout the Tarantula region. Credit: Hubble Heritage Team (AURA/STScI/NASA)

2002-01-01

262

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

263

A Clue to the Extent of Convective Mixing Inside Massive Stars: The Surface Hydrogen Abundances of Luminous Blue Variables and Hydrogen-Poor Wolf-Rayet Stars  

NASA Technical Reports Server (NTRS)

Interior layers of stars that have been exposed by surface mass loss reveal aspects of their chemical and convective histories that are otherwise inaccessible to observation. It must be significant that the surface hydrogen abundances of luminous blue variables (LBVs) show a remarkable uniformity, specifically X(sub surf) = 0.3 - 0.4, while those of hydrogen-poor Wolf-Rayet (WN) stars fall, almost without exception, below these values, ranging down to X(sub surf) = 0. According to our stellar model calculations, most LBVs are post-red-supergiant objects in a late blue phase of dynamical instability, and most hydrogen-poor WN stars are their immediate descendants. If this is so, stellar models constructed with the Schwarzschild (temperature-gradient) criterion for convection account well for the observed hydrogen abundances, whereas models built with the Ledoux (density-gradient) criterion fail. At the brightest luminosities, the observed hydrogen abundances of LBVs are too large to be explained by any of our highly evolved stellar models, but these LBVs may occupy transient blue loops that exist during an earlier phase of dynamical instability when the star first becomes a yellow supergiant. Independent evidence concerning the criterion for convection, which is based mostly on traditional color distributions of less massive supergiants on the Hertzsprung-Russell diagram, tends to favor the Ledoux criterion. It is quite possible that the true criterion for convection changes over from something like the Ledoux criterion to something like the Schwarzschild criterion as the stellar mass increases.

Stothers, Richard B.; Chin, Chao-wen

1999-01-01

264

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

Microsoft Academic Search

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

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

2010-01-01

265

Spectroscopic Classification of 42 LMC OB Stars: Selection of Probes for the Hot Gaseous Halo of the LMC  

E-print Network

Interstellar C IV absorption line studies of the hot gaseous halo of the Large Magellanic Cloud (LMC) have been hindered by non-ideal selections of early-type probe stars in regions where C+3 can be produced locally via photoionization, fast stellar winds, or supernovae. To observe stars outside such regions, precise spectral classifications of OB stars in the field are needed. Therefore, we have obtained medium-dispersion spectra of 42 early-type stars in the LMC that are distributed outside superbubbles or supergiant shells. The spectral classification of these stars is presented in this paper. Nineteen of these program stars have spectral types between B1 and O7, and are thus suitable probes for interstellar C IV absorption line studies of the hot gaseous halo of the LMC.

Elizabeth G. Jaxon; Martin A. Guerrero; J. Chris Howk; Nolan R. Walborn; You-Hua Chu; Bart P. Wakker

2001-05-31

266

Massive stars in their death-throes  

E-print Network

The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently there are 8 detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants as theory has long predicted. However no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae which, given the expected progenitors, is an unlikely result. Also observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict current stellar evolution theory. This suggests that we may need to update our understanding.

J. J. Eldridge

2008-09-07

267

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

268

Extrinsic and intrinsic S stars in the Henize sample  

NASA Astrophysics Data System (ADS)

Previous studies have identified two distinct families among S stars: intrinsic S stars exhibiting Tc lines in their spectrum, and extrinsic S stars lacking Tc lines. Extrinsic S stars were found to be binaries, and probably owe their chemical peculiarities to mass transfer in the binary system. On the contrary, intrinsic S stars are thermally-pulsating AGB stars where the third dredge-up brought heavy elements to the surface. The Henize sample of 205 S stars south of declination -25^circ is especially well suited for inferring the relative frequency of extrinsic/intrinsic S stars, since it is not biased towards low galactic latitudes where intrinsic S stars tend to concentrate. Each star has been measured 3 or 4 times over a period of 5 years with the spectrovelocimeter CORAVEL. The search for binaries is complicated by the fact that Mira-type pulsations are frequent among intrinsic S stars. Fortunately, radial-velocity variations due to atmospheric motions are generally associated with very broad and asymmetric CORAVEL cross-correlation profiles [see also poster P2-14!]. Therefore extrinsic and intrinsic S stars can be distinguished thanks to (1) radial velocity variations, (2) the shape of the CORAVEL cross-correlation profiles, (3) the presence or absence of the radioactive element Tc, as derived from high-resolution spectroscopy, (4) photometric variability, as derived from a survey in the Geneva photometric system. These criteria correlate in a nice way and allow to derive the frequency of intrinsic-genuine AGB-S stars. The galactic distributions of the two families of S stars are clearly distinct, intrinsic S stars being much more concentrated along the galactic plane that extrinsic S stars. High-resolution spectroscopy led to the discovery of two symbiotic stars among the Henize sample (symbiotic stars are interacting binary systems in which a hot compact object accretes matter ejected by a cool (super)giant). The physical parameters responsible for the symbiotic nature of these two stars remain to be identified (short period, high luminosity, high mass loss rate?), in order to understand why only these two stars among the 40-fold binary stars in the Henize sample appear as symbiotics.

Van Eck, Sophie; Jorissen, Alain; Mayor, Michel; Udry, Stephane; Burnet, Michel

269

The Massive Star Population in M101. II. Spatial Variations in the Recent Star Formation History  

E-print Network

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

Grammer, Skyler

2014-01-01

270

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

271

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

NASA Astrophysics Data System (ADS)

We present a composite 9 million star color-magnitude diagram (9M CMD) of the LMC bar using calibrated MACHO project photometry. The large number of stars reveal numerous low-level features, many of which can be attributed to short-lived stages of stellar evolution. The star formation and chemical enrichment history of the LMC is investigated, with additional discussion of the ~ 10(5) LMC variable stars in the MACHO database. Example features are intermediate mass supergiant sequences, multiple sequences of AGB stars, a bump on the RGB, and possible evidence for extended HB evolution. The 9M CMD is interpreted with theoretical isochrones, CMDs of LMC clusters, an HST CMD, and artificial CMDs. The latter include the effects of differential reddening and blending. The intermediate mass supergiants, including Cepheids, suggest a variable recent star formation history. The RGB and multiple AGB sequences are consistent with two superposed populations; an ancient population with [Fe/H] ~ -1.6 dex, and a few Gyr-old population with [Fe/H] ~ -0.7 dex. The location of the bump on the RGB constrains the age and metallicity of the younger population; no other RGB bump is observed. The possibility of an intervening stellar population in the Galactic halo is probed with the 9M CMD and archival data. Galactic star count model predictions agree well with foreground stars observed in the 9M CMD. We predict the planetary nebulae and carbon stars associated with an hypothetical intervening population. Lastly, we discuss the 9M CMD and MACHO microlensing detection efficiencies. Alves dedicates this paper to Alex Rodgers, who greatly influenced this work and will be fondly remembered.

Alves, D.; Alcock, C.; Cook, K.; Marshall, S.; Minniti, D.; Allsman, R.; Axelrod, T.; Freeman, K.; Peterson, B.; Rodgers, A.; Becker, A.; Stubbs, C.; Tomaney, A.; Griest, K.; Vandehei, T.; Bennett, D.; Lehner, M.; Nelson, C.; Pratt, M.; Quinn, P.; Sutherland, W.; Welch, D.

1997-12-01

272

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

SciTech Connect

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

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

2013-01-10

273

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

NASA Astrophysics Data System (ADS)

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

Rzaev, A. Kh.

2012-07-01

274

Tidal Interaction in High Mass X-ray Binaries and Symbiotic Stars  

NASA Astrophysics Data System (ADS)

This paper summarizes our recent results on tidal interaction in high mass X-ray binaries and symbiotic stars. We demonstrate that the giant in symbiotic stars with orbital periods ? 1200 d are co-rotating (synchronized). The symbiotics MWC 560 and CD-43^014304 probably have high orbital eccentricity. The giants in symbiotic binaries rotate faster than the field giants, likely their rotation is accelerated by the tidal force of the white dwarf. The giant/supergiant High mass X-ray binaries with orbital periods ? 40 d are synchronized. However the Be/X-ray binaries are not synchronized. In the Be/X-ray binaries the circumstellar disks are denser and smaller than those in isolated Be stars, probably truncated by the orbiting neutron star.

Zamanov, Radoslav K.

275

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

E-print Network

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

Nathan Smith

2008-02-13

276

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

277

Photospheres of hot stars. IV - Spectral type O4  

NASA Technical Reports Server (NTRS)

The basic stellar parameters of a supergiant (Zeta Pup) and two main-sequence stars, 9 Sgr and HD 46223, at spectral class O4 are determined using line profile analysis. The stellar parameters are determined by comparing high signal-to-noise hydrogen and helium line profiles with those from stellar atmosphere models which include the effect of radiation scattered back onto the photosphere from an overlying stellar wind, an effect referred to as wind blanketing. At spectral class O4, the inclusion of wind-blanketing in the model atmosphere reduces the effective temperature by an average of 10 percent. This shift in effective temperature is also reflected by shifts in several other stellar parameters relative to previous O4 spectral-type calibrations. It is also shown through the analysis of the two O4 V stars that scatter in spectral type calibrations is introduced by assuming that the observed line profile reflects the photospheric stellar parameters.

Bohannan, Bruce; Abbott, David C.; Voels, Stephen A.; Hummer, David G.

1990-01-01

278

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

279

KMOS First Sight - Probing the Star Clusters of the Antennae  

NASA Astrophysics Data System (ADS)

We present a spectroscopic survey of Young Massive Clusters in the Antennae galaxies using the new KMOS Multi-object Integral Field Spectrometer at the ESO VLT. Our results are based on intermediate spectral resolution (~ 3400-3800) near-infrared data taken in the H, K and YJ bands. We present stellar population and enviroment parameters derived from emission and absorption line measurements in an initial sample of 49 star clusters. Based on stellar population synthesis models, most of the clusters in our survey have ages ranging between 3-10 Myrs and masses between 10^5-10^7 M_sun. We find that the youngest and most massive clusters are located in the southern part of the overlap region, an area which is also abundant with supergiant molecular complexes. The association between the two suggests that the molecular complexes are highly active sites of star formation.

Miah, J. A.; Sharples, R.

2014-09-01

280

Distance and absolute magnitudes of the brightest stars in the dwarf galaxy Sextans A  

NASA Technical Reports Server (NTRS)

In an attempt to improve present bright star calibration, data were gathered for the brightest red and blue stars and the Cepheids in the Im V dwarf galaxy, Sextans A. On the basis of a magnitude sequence measured to V and B values of about 22 and 23, respectively, the mean magnitudes of the three brightest blue stars are V=17.98 and B=17.88. The three brightest red supergiants have V=18.09 and B=20.14. The periods and magnitudes measured for five Cepheids yield an apparent blue distance modulus of 25.67 + or - 0.2, via the P-L relation, and the mean absolute magnitudes of V=-7.56 and B=-5.53 for the red supergiants provide additional calibration of the brightest red stars as distance indicators. If Sextans A were placed at the distance of the Virgo cluster, it would appear to have a surface brightness of 23.5 mag/sq arcec. This, together with the large angular diameter, would make such a galaxy easily discoverable in the Virgo cluster by means of ground-based surveys.

Sandage, A.; Carlson, G.

1982-01-01

281

Combining observational techniques to constrain convection in evolved massive star models  

NASA Astrophysics Data System (ADS)

Recent stellar evolution computations indicate that massive stars in the range ~ 20-30 M ? are located in the blue supergiant (BSG) region of the Hertzsprung-Russell diagram at two different stages of their life: immediately after the main sequence (MS, group 1) and during a blueward evolution after the red supergiant phase (group 2). From the observation of the pulsationnal properties of a subgroup of variable BSGs (? Cyg variables), one can deduce that these stars belongs to group 2. It is however difficult to simultaneously fit the observed surface abundances and gravity for these stars, and this allows to constrain the physical processes of chemical species transport in massive stars. We will show here that the surface abundances are extremely sensitive to the physics of convection, particularly the location of the intermediate convective shell that appears at the ignition of the hydrogen shell burning after the MS. Our results show that the use of the Ledoux criterion to determine the convective regions in the stellar models leads to a better fit of the surface abundances for ? Cyg variables than the Schwarzschild one.

Georgy, C.; Saio, H.; Meynet, G.

2015-01-01

282

The circumstellar environment of the B[e] star GG Car: an interferometric modeling  

NASA Astrophysics Data System (ADS)

The research of stars with the B[e] phenomenon is still in its infancy, with several unanswered questions. Physically realistic models that treat the formation and evolution of their complex circumstellar environments are rare. The code HDUST (developed by A. C. Carciofi and J. Bjorkman) is one of the few existing codes that provides a self-consistent treatment of the radiative transfer in a gaseous and dusty circumstellar environment seen around B[e] supergiant stars. In this work we used the HDUST code to study the circumstellar medium of the binary system GG Car, where the primary component is probably an evolved B[e] supergiant. This system also presents a disk (probably circumbinary), which is responsible for the molecular and dusty signatures seen in GG Car spectra. We obtained VLTI/MIDI data on GG~Car at eight baselines, which allowed to spatially resolve the gaseous and dusty circumstellar environment. From the interferometric visibilities and SED modeling with HDUST, we confirm the presence of a compact ring, where the hot dust lies. We also show that large grains can reproduce the lack of structure in the SED and visibilities across the silicate band. We conclude the dust condensation site is much closer to the star than previously thought. This result provides stringent constraints on future theories of grain formation and growth around hot stars.

de Souza, A. Domiciano; Fernandes, M. Borges; Carciofi, A. C.; Chesneau, O.

2015-01-01

283

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

NASA Technical Reports Server (NTRS)

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

Shore, S. N.; Sanduleak, N.

1982-01-01

284

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

E-print Network

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

Tim Freyer; Gerhard Hensler; Harold W. Yorke

2005-12-05

285

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

286

A multiwavelength study of the Carlson-Henize sample of early-type Galactic extreme emission-line stars  

NASA Technical Reports Server (NTRS)

A UV, optical, and radio study of nine early spectral type extreme emission-line Galactic stars from the Carlson and Henize (1979) sample is presented. He 3-407 and He 3-1482 appear to be analogs of the massive evolved B(e) and luminous blue variable stars of the Magellanic Clouds. The sample appears to be confined to a narrow range in spectral type from about B0 to B6. Most of the observed stars do not show strong N emission, with the striking exception of He 3-1482, and these Galactic stars may not have mixed significant quantities of nitrogen into their envelopes, unlike many of the LMC supergiants, Most of the Galactic stars are considerably fainter than those in the Magellanic Clouds, although their spectral properties are quite similar.

Shore, Steven N.; Brown, Douglas N.; Bopp, B. W.; Robinson, C. R.; Sanduleak, N.

1990-01-01

287

Post-AGB Stars as Standard Extragalactic Candles  

E-print Network

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

Howard E. Bond

1997-02-01

288

High spectral resolution imaging of the dynamical atmosphere of the red supergiant Antares in the CO first overtone lines with VLTI/AMBER  

NASA Astrophysics Data System (ADS)

Aims: We present aperture-synthesis imaging of the red supergiant Antares (? Sco) in the CO first overtone lines. Our goal is to probe the structure and dynamics of the outer atmosphere. Methods: Antares was observed between 2.28 ?m and 2.31 ?m with VLTI/AMBER with spectral resolutions of up to 12 000 and angular resolutions as high as 7.2 mas at two epochs with a time interval of one year. Results: The reconstructed images in individual CO lines reveal that the star appears differently in the blue wing, line center, and red wing. In 2009, the images in the line center and red wing show an asymmetrically extended component, while the image in the blue wing shows little trace of it. In 2010, however, the extended component appears in the line center and blue wing, and the image in the red wing shows only a weak signature of the extended component. Our modeling of these AMBER data suggests that there is an outer atmosphere (MOLsphere) extending to 1.2-1.4 R? with CO column densities of (0.5-1) × 1020 cm-2 and a temperature of ~2000 K. The CO line images observed in 2009 can be explained by a model in which a large patch or clump of CO gas is infalling at only 0-5 km s-1, while the CO gas in the remaining region is moving outward much faster at 20-30 km s-1. The images observed in 2010 suggest that a large clump of CO gas is moving outward at 0-5 km s-1, while the CO gas in the remaining region is infalling much faster at 20-30 km s-1. In contrast to the images in the CO lines, the AMBER data in the continuum show only a slight deviation from limb-darkened disks and only marginal time variations. We derive a limb-darkened disk diameter of 37.38 ± 0.06 mas and a power-law-type limb-darkening parameter of (8.7 ± 1.6) × 10-2 (2009) and 37.31 ± 0.09 mas and (1.5 ± 0.2) × 10-1 (2010). We also obtain an effective temperature of 3660 ± 120 K (the error includes the effects of the temporal flux variation that is assumed to be the same as Betelgeuse) and a luminosity of log L?/L? = 4.88 ± 0.23. Comparison with theoretical evolutionary tracks suggests a mass of 15 ± 5 M? with an age of 11-15 Myr, which is consistent with the recently estimated age for the Upper Scorpius OB association. Conclusions: The properties of the outer atmosphere of Antares are similar to those of another well-studied red supergiant, Betelgeuse. The density of the extended outer atmosphere of Antares and Betelgeuse is higher than predicted by the current 3D convection simulations by at least six orders of magnitude, implying that convection alone cannot explain the formation of the extended outer atmosphere. Based on AMBER observations made with the Very Large Telescope Interferometer of the European Southern Observatory. Program ID: 083.D-0333(A/B) (AMBER guaranteed time observation), 085.D-0085(A/B).Appendices are available in electronic form at http://www.aanda.orgMovies of data cube 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/555/A24

Ohnaka, K.; Hofmann, K.-H.; Schertl, D.; Weigelt, G.; Baffa, C.; Chelli, A.; Petrov, R.; Robbe-Dubois, S.

2013-07-01

289

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

NASA Technical Reports Server (NTRS)

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

Linsky, J. L.

1986-01-01

290

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

291

A K-band spectral mini-survey of Galactic B[e] stars  

NASA Astrophysics Data System (ADS)

We present a mini-survey of Galactic B[e] stars mainly undertaken with the Large Binocular Telescope (LBT). B[e] stars show morphological features with hydrogen emission lines and an infrared excess, attributed to warm circumstellar dust. In general, these features are assumed to arise from dense, non-spherical, disc-forming circumstellar material in which molecules and dust can condensate. Due to the lack of reliable luminosities, the class of Galactic B[e] stars contains stars at very different stellar evolutionary phases like Herbig AeBe, supergiants or planetary nebulae. We took near-infrared long-slit K-band spectra for a sample of Galactic B[e] stars with the LBT-LUCI 1. Prominent spectral features, such as the Brackett ? line and CO band heads are identified in the spectra. The analysis shows that the stars can be characterized as evolved objects. Among others we find one luminous blue variable candidate (MWC 314), one supergiant B[e]candidate with 13CO (MWC 137), and in two cases (MWC 623 and AS 381) indications for the existence of a late-type binary companion, complementary to previous studies. For MWC 84, IR spectra were taken at different epochs with LBT-LUCI 1 and the GNIRS spectrograph at the Gemini North telescope. The new data show the disappearance of the circumstellar CO emission around this star, previously detectable over decades. Also no signs of a recent prominent eruption leading to the formation of new CO disc emission are found during 2010 and 2013.

Liermann, A.; Schnurr, O.; Kraus, M.; Kreplin, A.; Arias, M. L.; Cidale, L. S.

2014-09-01

292

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

E-print Network

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

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

2008-01-01

293

Probing Dust Formation Around Evolved Stars with Near-Infrared Interferometry  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

294

What are the Hot R Coronae Borealis Stars?  

E-print Network

We investigate the evolutionary status of four stars: V348 Sgr, DY Cen and MV Sgr in the Galaxy and HV 2671 in the LMC. These stars have in common random deep declines in visual brightness which are characteristic for R Coronae Borealis (RCB) stars. RCB stars are typically cool, hydrogen deficient supergiants. The four stars studied in this paper are hotter (T$_{\\rm eff}$ = 15-20 kK) than the majority of RCB stars (T$_{\\rm eff}$ = 5000-7000 K). Although these are commonly grouped together as the \\emph{hot RCB stars} they do not necessarily share a common evolutionary history. We present new observational data and an extensive collection of archival and previously-published data which is reassessed to ensure internal consistency. We find temporal variations of various properties on different time scales which will eventually help us to uncover the evolutionary history of these objects. DY Cen and MV Sgr have typical RCB helium abundances which excludes any currently known post-AGB evolutionary models. Moreover, their carbon and nitrogen abundances present us with further problems for their interpretation. V348 Sgr and HV 2671 are in general agreement with a born-again post-AGB evolution and their abundances are similar to Wolf-Rayet central stars of PN. The three Galactic stars in the sample have circumstellar nebulae which produce forbidden line radiation (for HV 2671 we have no information). V348 Sgr and DY Cen have low density, low expansion velocity nebulae (resolved in the case of V348 Sgr), while MV Sgr has a higher density, higher expansion velocity nebula.

Orsola De Marco; Geoffrey C. Clayton; F. Herwig; D. L. Pollacco; J. S. Clark; David Kilkenny

2002-03-08

295

Stellar winds and mass loss from extreme helium stars  

NASA Astrophysics Data System (ADS)

Extreme helium stars are very rare low-mass supergiants in a late stage of evolution. They are probably contracting to become white dwarfs following a violent phase of evolution which caused them to become hydrogen-deficient giants, possibly R CrB stars. Using the latest generation of models for spherically expanding stellar atmospheres, we set out to measure mass-loss rates for a representative fraction of these stars. We have used high-resolution ultraviolet and optical spectra, and ultraviolet, optical and near-infrared photometry from a variety of archives. Overall atmospheric parameters have mostly been taken from previous analyses and checked for consistency. Mass-loss rates were measured by fitting the P Cygni and asymmetric profiles of C, N and Si ultraviolet resonance lines and lie in the range of 10-10-10-7 Msolar yr-1. These rates follow a Castor-type () relation marking a lower limit for the mass loss from hot stars of all kinds. The mass-loss rates of the stars studied also show a strong correlation with their proximity to the Eddington limit. There is no firm evidence for variability in the stellar wind, although photospheric pulsations have been reported in many cases.

Jeffery, C. S.; Hamann, W.-R.

2010-06-01

296

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

297

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

298

Swift-X-Ray Telescope 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. 3.7 d 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 approx. 5 × 10(exp 16) 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.

2012-01-01

299

Comparative Precise Parameters for OB Stars in Three Galaxies  

NASA Astrophysics Data System (ADS)

The chemical abundances, wind terminal velocities, and mass-loss rates of OB stars in the Small and Large Magellanic Clouds will be determined homogeneously from high-resolution spectroscopic data in the Mikulski Archive; and they will be further compared with analogous determinations in the Solar Neighborhood. As is well known, the three systems offer a metallicity sequence with values in solar units generally given as 0.2, 0.5, and 1, respectively, which should have corresponding effects on the metallic-line-driven winds. However, the quantitative basis for that general result can and should be improved for various reasons. For instance, it is based on heterogeneous analyses, some dated, of data with varying quality. Moreover, there is not a single metallicity but different relative values for different elements, seldom available for individual stars, with CNO significantly affected by internal evolutionary processes. We propose advances with state-of-the-art analyses of the best data, primarily from STIS and COS in the UV, but also incorporating FUSE observations of the same stars, and IUE high-resolution of a few. We shall also analyze correlative groundbased optical data. J-CB and collaborators have already published recent results for Galactic supergiants and SMC dwarfs, while work on the SMC giants/supergiants is in progress. We shall build upon that work with further Galactic and SMC data, and especially with the still relatively small but significant LMC UV sample, with detailed spectral-type matching insofar as possible. We shall also produce an atlas of all spectra analyzed, to be placed in the Archive as a high-level product to guide future work.

Walborn, Nolan

2014-10-01

300

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

E-print Network

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

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

2008-01-11

301

The VLT-FLAMES Tarantula Survey XIX. B-type Supergiants - Atmospheric Parameters and Nitrogen Abundances to Investigate the Role of Binarity and the Width of the Main Sequence  

E-print Network

TLUSTY non-LTE model atmosphere calculations have been used to determine atmospheric parameters and nitrogen (N) abundances for 34 single and 18 binary B-type supergiants (BSGs). The effects of flux contribution from an unseen secondary were considered for the binary sample. We present the first systematic study of the incidence of binarity for a sample of BSGs across the theoretical terminal age main sequence (TAMS). To account for the distribution of effective temperatures of the BSGs it may be necessary to extend the TAMS to lower temperatures. This is consistent with the derived distribution of mass discrepancies, projected rotational velocities (vsini) and N abundances, provided that stars cooler than this temperature are post RSG objects. For the BSGs in the Tarantula and previous FLAMES surveys, most have small vsini. About 10% have larger vsini (>100 km/s) but surprisingly these show little or no N enhancement. All the cooler BSGs have low vsini of <70km/s and high N abundance estimates, implying t...

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

2014-01-01

302

Medium resolution spectroscopy of the supergiant O31f Cyg OB2 No. 7  

NASA Astrophysics Data System (ADS)

We examine the feasibility of using medium resolution spectra for determining the parameters of the atmospheres of hot stars by means of numerical simulations. We chose the star Cyg OB2 No. 7 as a test object and obtained its spectrum (?/?? = 2500) with the Russian-Turkish RTT150 telescope. The CMFGEN code was used to construct a model of the atmosphere of Cyg OB2 No. 7. For the first time we have detected the NIV ??7103.-2-7129.2 lines in the spectrum of this star and used them to determine the physical parameters of the wind. The rate of mass loss measured using the H? line exceeds the loss rate measured using lines from the wind. This indicates that the wind is nonuniform, apparently owing to rotation.

Maryeva, O. V.; Zhuchkov, R. Ya.

2012-09-01

303

Absorption line profiles in a companion spectrum of a mass losing cool supergiant  

NASA Technical Reports Server (NTRS)

Cool star winds can best be observed in resonance absorption lines seen in the spectrum of a hot companion, due to the wind passing in front of the blue star. We calculated absorption line profiles that would be seen in the ultraviolet part of the blue companion spectrum. Line profiles are derived for different radial dependences of the cool star wind and for different orbital phases of the binary. Bowen and Wilson find theoretically that stellar pulsations drive mass loss. We therefore apply our calculations to the Cepheid binary S Muscae which has a B5V companion. We find an upper limit for the Cepheid mass loss of M less than or equal to 7 x 10(exp -10) solar mass per year provided that the stellar wind of the companion does not influence the Cepheid wind at large distances.

Rodrigues, Liliya L.; Boehm-Vitense, Erika

1990-01-01

304

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.

305

Sea Stars  

NSDL National Science Digital Library

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

2012-07-28

306

Scintillating Stars  

NSDL National Science Digital Library

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

Riddle, Bob

2003-02-01

307

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

308

Lucky Star  

NSDL National Science Digital Library

Watch this video from Cyberchase and then play the Lucky Star game! The Lucky Star game show the will ask you math-related questions and give you four possible answers to choose from. Your goal is to answer the questions correctly and score as many points as you can. You can score points during two different rounds: the pick-a-star round and the lightning round. During the pick-a-star round you have as much time as you want to answer the questions. During the lightning round you have to think fast in order to earn the points. Good luck!

2008-01-01

309

The geometry and dynamics of mass-loss at milli-arcsecond scales of massive stars in transition  

NASA Astrophysics Data System (ADS)

The dynamics, geometry and abundances of circumstellar material provide the crucial information necessary to reconstruct the post-main sequence evolution and final fate of high-mass stars. In this context, we will present recent discoveries made by means of infra-red high spectral and spatial resolution observations using VLTI/AMBER, VLTI/PIONIER and VLT/CRIRES. The observations shed new light on the ongoing mass-loss of high-mass stars transiting the HR-diagram. In particular, we discuss new results on the milli-arcsecond (mas) scale mass-loss geometry of the yellow hypergiant IRC+10420. They indicate an hour-glass wind geometry and a high mass-loss rate that results in a pseudo-photosphere (Oudmaijer & de Wit 2013). Whether the wind is shaped because of a secondary component or because of slow/fast wind interactions is discussed. In the case of supergiant B[e] stars, binarity may have an important effect on the dynamics and geometry of the mass loss on masscales (Wheelwright et al. 2012a, 2012b, 2013). Our studies of the circumstellar environment of sgB[e] stars have discovered several circumbinary discs that exhibit Keplerian rotation, contrary to expectations based on the dual outflow model. We raise the question of whether binarity is responsible for the Galactic sgB[e] phenomenon or whether the blue supergiant component's mass loss is intrinsically peculiar in sgB[e]s.

de Wit, W. J.; Wheelwright, H.; Oudmaijer, R. D.; Mehner, A.

2013-06-01

310

Stellar and wind properties of massive stars in the central parsec of the Galaxy  

NASA Astrophysics Data System (ADS)

Context: How star formation proceeds in the Galactic Center is a debated question. Addressing this question will help us understand the origin of the cluster of massive stars near the supermassive black hole, and more generally, starburst phenomena in galactic nuclei. In that context, it is crucial to know the properties of young massive stars in the central parsec of the Galaxy. Aims: The main goal of this study is to derive the stellar and wind properties of the massive stars orbiting the supermassive black hole SgrAstar in two counter-rotating disks. Methods: We use non-LTE atmosphere models including winds and line-blanketing to reproduce H and K band spectra of these stars obtained with SINFONI on the ESO/VLT. Results: The GC massive stars appear to be relatively similar to other Galactic stars. The currently known population of massive stars emit a total 6.0 × 1050 s-1 (resp. 2.3 × 1049 s-1) H (resp. He I) ionising photons. This is sufficient to produce the observed nebular emission and implies that, in contrast to previous claims, no peculiar stellar evolution is required in the Galactic Center. We find that most of the Ofpe/WN9 stars are less chemically evolved than initially thought. The properties of several WN8 stars are given, as well as two WN/C stars confirmed quantitatively to be stars in transition between the WN and WC phase. We propose the sequence (Ofpe/WN9 rightleftharpoons LBV) ? WN8 ? WN/C for most of the observed GC stars. Quantitative comparison with stellar evolutionary tracks including rotation favour high mass loss rates in the Wolf-Rayet phase in these models. In the OB phase, these tracks nicely reproduce the average properties of bright supergiants in the Galactic Center.

Martins, F.; Genzel, R.; Hillier, D. J.; Eisenhauer, F.; Paumard, T.; Gillessen, S.; Ott, T.; Trippe, S.

2007-06-01

311

Star Life  

NSDL National Science Digital Library

Visitors to this site can follow the life cycle of a star, beginning with its formation from matter exploded outward by the Big Bang, followed by its expansion into a red giant as nuclear "fuel" is consumed, and ending with its "death" in a supernova, after which it becomes a neutron star or black hole.

312

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

313

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 requires interferometry in the mid-infrared, while post-main-sequence stellar phases require high-precision measurements to challenge stellar evolution models. I will summarize my recent work on modeling mid-IR observations of a massive YSO in NGC 3603, and on the derivation of masses and luminosities of a massive hot supergiant star in another star-forming region in Orion. Challenges presented themselves when constraining the geometry of a hypothetical accretion disk as well as obtaining spectroscopy matching the interferometric precision when working with only a few photospheric lines. As a rapidly evolving application of interferometry, massive stars have a bright future.

Hummel, C.

2014-09-01

314

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

315

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

SciTech Connect

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

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

2010-09-20

316

Exploding star  

NASA Astrophysics Data System (ADS)

Three astronomers report that the star Eta Carinae, 100 times more massive than the sun, is nearing its life expectancy and will explode sometime in the next 10,000 years. Until now, astronomers have been unable to discern whether the star was in the process of being born, was a middle-aged star with an unusual outflow of material, or an aged star about to explode.The huge star is coming to the end of what is considered a normal lifetime—about 2 million years—for a star of its size, according to Kris Davidson at the University of Minnesota, Nolan R. Walborn (presently at the Goddard Space Flight Center) of Cerro Tololo Inter-American Observatory, and Theodore R. Gull at Goddard. When Eta Carinae explodes, the astronomers report, it could emit more light than all the hundreds of billions of other stars in the galaxy for weeks. The expected explosion, or supernova, could produce a bright point of light that would be visible in broad daylight, they add.

317

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

318

HUBBLE SPACE TELESCOPE CAPTURES FIRST DIRECT IMAGE OF A STAR  

NASA Technical Reports Server (NTRS)

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

2002-01-01

319

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

NASA Technical Reports Server (NTRS)

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

Macgregor, K. B.

1983-01-01

320

The death of massive stars - I. Observational constraints on the progenitors of type II-P supernovae  

E-print Network

We present the results of a 10.5 yr, volume limited (28 Mpc) search for supernova (SN) progenitor stars. We compile all SNe discovered within this volume (132, of which 27% are type Ia) and determine the relative rates of each sub-type from literature studies : II-P (59%), Ib/c (29%), IIb (5%), IIn (4%) and II-L (3%). Twenty II-P SNe have high quality optical or near-IR pre-explosion images that allow a meaningful search for the progenitor stars. In five cases they are clearly red supergiants, one case is unconstrained, two fall on compact coeval star clusters and the other twelve have no progenitor detected. We review and update all the available data for the host galaxies (distance, metallicity and extinction) and determine masses and upper mass estimates using the STARS stellar evolutionary code and a single consistent homogeneous method. A maximum likelihood calculation suggests that the minimum stellar mass for a type II-P to form is m(min)=8.5 +1/-1.5 Msol and the maximum mass for II-P progenitors is m(max)=16.5 +/- 1.5 Msol, assuming a Salpeter initial mass function (in the range Gamma = -1.35 +0.3/-0.7). The minimum mass is consistent with current estimates for white dwarf progenitor masses, but the maximum mass does not appear consistent with massive star populations. Red supergiants in the Local Group have masses up to 25Msol and the minimum mass to produce a Wolf-Rayet star in single star evolution (between solar and LMC metallicity) is similarly 25-30 Msol. We term this discrepancy the "red supergiant problem" and speculate that these stars could have core masses high enough to form black holes and SNe which are too faint to have been detected. Low luminosity SNe with low 56Ni production seem to arise from explosions of low mass progenitors near the mass threshold for core-collapse. (abridged).

S. J. Smartt; J. J. Eldridge; R. M. Crockett; J. R. Maund

2008-09-02

321

New Magellanic Cloud R Coronae Borealis and DY Per type stars from the EROS-2 database: the connection between RCBs, DYPers and ordinary carbon stars  

E-print Network

R Coronae Borealis stars (RCB) are a rare type of evolved carbon-rich supergiant stars that are increasingly thought to result from the merger of two white dwarfs, called the Double degenerate scenario. This scenario is also studied as a source, at higher mass, of type Ia Supernovae (SnIa) explosions. Therefore a better understanding of RCBs composition would help to constrain simulations of such events. We searched for and studied RCB stars in the EROS Magellanic Clouds database. We also extended our research to DY Per type stars (DYPers) that are expected to be cooler RCBs (T~3500 K) and much more numerous than their hotter counterparts. The light curves of ~70 millions stars have been analysed to search for the main signature of RCBs and DYPers: a large drop in luminosity. Follow-up optical spectroscopy was used to confirm each photometric candidate found. We have discovered and confirmed 6 new Magellanic Cloud RCB stars and 7 new DYPers, but also listed new candidates: 3 RCBs and 14 DYPers. We estimated a...

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

2009-01-01

322

A tale of two telescopes: Taking a closer look at the multiplicity properties of massive stars in Cygnus  

NASA Astrophysics Data System (ADS)

Massive stars profoundly influence the evolution of the Universe, from Galactic dynamics and structure to star formation. They are often found with bound companions. However, our knowledge of O-type multiple systems with periods in the range from years to thousands of years is incomplete due their great distances. We present results from a high angular resolution survey to find angularly resolved companions using the Fine Guidance Sensor (FGS) on the Hubble Space Telescope and using ground-based adaptive optics at Gemini North. We observed 75 O- and early B-type stars in Cyg OB2 and determined that 42% of the sample have at least one companion that meets a statistical criterion for gravitationally bound status. As a case study, we present an examination of high resolution, ultraviolet spectroscopy from Hubble Space Telescope of the photospheric spectrum of the O-supergiant in the massive X-ray binary HDE 226868 = Cyg X-1. We analyzed the ultraviolet and ground-based optical spectra to determine the effective temperature and gravity of the O9.7 Iab supergiant. Using non-LTE, line blanketed, plane parallel models from the TLUSTY grid, we obtain Teff = 8.0±2.5 kK and log g ? 3.00±0.25, both lower than found in previous studies. The optical spectrum is best fit with models that have enriched He and N abundances. We fit the model spectral energy distribution for this temperature and gravity to the UV, optical, and IR fluxes to determine the angular size of and extinction towards the binary. By assuming that the supergiant rotates synchronously with the orbit, we can use the radius - distance relation to find mass estimates for both components as a function of the distance and the ratio of stellar to Roche radius. Our results indicate masses of 23 +8/-6 solarmasses for the supergiant and 11 +5/-3 solarmasses for the black hole. These results agree with subsequent mass estimates by Orosz et al. (2011) based on the trigonometric parallax distance measurements of Reid et al. (2011). The results of this survey provide fundamental information on the impact of environment on massive binaries and also the role multiplicity has on massive star formation and evolution.

Caballero Nieves, Saida M.

323

Classifying stars  

NSDL National Science Digital Library

You will be able to describe the H-R diagram and explain how astronomers use it. The most important characteristics for classifying stars are: a) Color b) Temperature c) Size d) Composition e) Brightness The classification scheme that we currently use is the H-R diagram which is in the Earth Science Reference Tables (ESRT). The H-R diagram groups stars by surface temperature compared to their luminosity. 1)Today you will be reading a short tutorial ...

B, Mr.

2007-11-10

324

Tycho's Star  

NASA Astrophysics Data System (ADS)

A supernova remnant in Cassiopeia, 7.7° north of ? Cas, which suddenly appeared as a brilliant naked-eye star in November 1572 and reached a maximum apparent magnitude of -3.5. Until its disappearance 16 months later, it was extensively studied by the Danish astronomer Tycho Brahe (1546-1601), who described its early appearance as follows: `Initially, the new star was brighter than any other fixe...

Murdin, P.

2000-11-01

325

The Mass Loss Return From Evolved Stars to the LMC: Empirical Relations For Excess Emission at 8 and 24 ?m  

NASA Astrophysics Data System (ADS)

We will present empirical relations for excess emission from evolved stars in the Large Magellanic Cloud (LMC) using data from the Spitzer Space Telescope SAGE (Surveying the Agents of a Galaxy's Evolution) survey. Combined with the 2MASS survey and the optical Magellanic Cloud Photometric Survey (MCPS) catalog, these data enable multiband analysis of evolved stars, and can help probe the life cycle of dust in the LMC. Outflows from evolved asymptotic giant branch (AGB) stars and supergiants are the main producers of dust in a galaxy, and the aim of this work is to investigate the mass loss return by AGBs and supergiants to the interstellar medium of the LMC. The spectral energy distributions (SEDs) are compared with plane-parallel (for Carbon-rich AGBs) and spherical (for Oxygen-rich AGBs) atmosphere models to obtain the excess flux in the 8 and 24 micron bands, which is plotted against the total integrated flux. We will show that this excess emission increases with total integrated flux, and the 24 micron flux for heavily obscured AGBs is entirely due to excess emission from dust. The SAGE Project is supported by NASA/Spitzer grant 1275598 and NASA NAG5-12595.

Srinivasan, Sundar; Meixner, M.; Vijh, U.; Leitherer, C.; Volk, K.; Markwick-Kemper, F.; Blum, R. D.; Mould, J. R.; Olsen, K. A.; Points, S.; Whitney, B. A.; Meade, M.; Babler, B.; Indebetouw, R.; Hora, J. L.; Gordon, K.; Engelbracht, C.; For, B.; Block, M.; Misselt, K.

2006-12-01

326

STARS no star on Kauai  

SciTech Connect

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

Jones, M.

1993-04-01

327

SN 2004A: Another Type IIP Supernova with a Red Supergiant Progenitor  

Microsoft Academic Search

We present a monitoring study of SN 2004A and probable discovery of a\\u000aprogenitor star in pre-explosion HST images. The photometric and spectroscopic\\u000amonitoring of SN 2004A show that it was a normal Type II-P which was discovered\\u000ain NGC 6207 about two weeks after explosion. We compare SN 2004A to the similar\\u000aType II-P SN 1999em and estimate an

M. A. Hendry; S. J. Smartt; R. M. Crockett; J. R. Maund; A. Gal-Yam; D.-S. Moon; S. B. Cenko; D. W. Fox; R. P. Kudritzki; C. R. Benn; R. Østensen

2006-01-01

328

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

329

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

330

VizieR Online Data Catalog: 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

331

The R Coronae Borealis stars - atmospheres and abundances  

NASA Astrophysics Data System (ADS)

An abundance analysis of the H-deficient and He- and C-rich R Coronae Borealis (R CrB) stars has been undertaken to examine the ancestry of the stars. The investigation is based on high-resolution spectra and line-blanketed H-deficient model atmospheres. The models successfully reproduce the flux distributions and all spectral features, both molecular bands and high-excitation transitions, with one important exception, the C i lines. Since photoionization of C i dominates the continuous opacity, the line strengths of C i are essentially independent of the adopted carbon abundance and stellar parameters. All predicted C i lines are, however, much too strong compared with observations, with a discrepancy in abundance corresponding to 0.6 dex with little star-to-star scatter. Various solutions of this ``carbon problem'' have been investigated. A possible solution is that classical model atmospheres are far from adequate descriptions of supergiants such as the R CrB stars. We can also not exclude completely, however, the possibility that the gf-values for the C i lines are in error. This is supported by the fact that the C ii, [C i] and C_2 lines are reproduced by the models with no apparent complications. In spite of the carbon problem, various tests suggest that abundance ratios are little affected by the uncertainties. Judging by chemical composition, the R CrB stars can be divided into a homogeneous majority group and a diverse minority, which is characterized by extreme abundance ratios, in particular as regards Si/Fe and S/Fe. All stars show evidence of H- and He-burning in different episodes as well as mild s-process enhancements. Four of the majority members are Li-rich, while overabundances of Na, Al, Si and S are attributes of all stars. An anti-correlation found between the H and Fe abundances of H-deficient stars remains unexplained. These enigmatic stars are believed to be born-again giants, formed either through a final He-shell flash in a post-AGB star or through a merger of two white dwarfs. Owing to a lack of theoretical predictions of the resulting chemical compositions, identification of the majority and minority groups with the two scenarios is unfortunately only preliminary. Furthermore, Sakurai's object and V854 Cen exhibit aspects of both majority and minority groups, which may suggest that the division into two groups is too simplistic.

Asplund, M.; Gustafsson, B.; Lambert, D. L.; Rao, N. K.

2000-01-01

332

Chemical abundances of massive stars in Local Group galaxies  

NASA Astrophysics Data System (ADS)

The relative abundances of elements in galaxies can provide valuable information on the stellar and chemical evolution of a galaxy. While nebulae can provide abundances for a variety of light elements, stars are the only way to directly determine the abundances of iron-group and s-process and r-process elements in a galaxy. The new 8m and 10m class telescopes and high-efficiency spectrographs now make high-quality spectral observations of bright supergiants possible in dwarf galaxies in the Local Group. We have been concentrating on elemental abundances in the metal-poor dwarf irregular galaxies, NGC 6822, WLM, Sextants A, and GR 8. Comparing abundance ratios to those predicted from their star formation histories, determined from color-magnitude diagrams, and comparing those ratios between these galaxies can give us new insights into the evolution of these dwarf irregular galaxies. Iron-group abundances also allow us to examine the metallicities of the stars in these galaxies directly, which affects their inferred mass loss rates and predicted stellar evolution properties.

Venn, Kim A.; Kaufer, Andreas; Tolstoy, Eline; Kudritzki, Rolf-Peter; Przybilla, Norbert; Smartt, Stephen J.; Lennon, Daniel J.

333

The uBVI Photometric System. II. Standard Stars  

NASA Astrophysics Data System (ADS)

Paper I of this series described the design of a CCD-based photometric system that is optimized for ground-based measurements of the size of the Balmer discontinuity in stellar spectra. This ``uBVI'' system combines the Thuan-Gunn u filter with the standard Johnson-Kron-Cousins BVI filters and can be used to discover luminous yellow supergiants in extragalactic systems and post-asymptotic giant branch stars in globular clusters and galactic halos. In the present paper we use uBVI observations obtained on 54 nights with 0.9 m telescopes at Kitt Peak and Cerro Tololo to construct a catalog of standardized u magnitudes for standard stars taken from the 1992 catalog of Landolt. We describe the selection of our 14 Landolt fields and give details of the photometric reductions, including red leak and extinction corrections, transformation of all the observations onto a common magnitude system, and the establishment of the photometric zero point. We present a catalog of u magnitudes of 103 stars suitable for use as standards. We show that data obtained with other telescopes can be transformed to our standard system with better than 1% accuracy.

Siegel, Michael H.; Bond, Howard E.

2005-06-01

334

Lyman alpha initiated winds in late-type stars  

NASA Technical Reports Server (NTRS)

One of the first major results of the IUE survey of late-type stars was the discovery of a sharp division in the HR diagram between stars with solar type spectra (chromosphere and transition region lines) and those with non-solar type spectra (only chromosphere lines). This result is especially interesting in view of observational evidence for mass loss from G and K giants and super-giants discussed recently by both Reimers and Stencel. In the present paper models of both hot coronae and cool wind flows are calculated using stellar model chromospheres as starting points for stellar wind calculations in order to investigate the possibility of having a 'supersonic transition locus' in the HR diagram dividing hot coronae from cool winds. It is concluded from these models that the Lyman-alpha flux may play an important role in determining the location of a stellar wind critical point. The interaction of Lyman-alpha radiation pressure with Alfven waves in producing strong, low temperature stellar winds in the star Arcturus is investigated.

Haisch, B. M.; Van Der Hucht, K. A.; Linsky, J. L.

1979-01-01

335

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

336

A massive hypergiant star as the progenitor of the supernova SN 2005gl.  

PubMed

Our understanding of the evolution of massive stars before their final explosions as supernovae is incomplete, from both an observational and a theoretical standpoint. A key missing piece in the supernova puzzle is the difficulty of identifying and studying progenitor stars. In only a single case-that of supernova SN 1987A in the Large Magellanic Cloud-has a star been detected at the supernova location before the explosion, and been subsequently shown to have vanished after the supernova event. The progenitor of SN 1987A was a blue supergiant, which required a rethink of stellar evolution models. The progenitor of supernova SN 2005gl was proposed to be an extremely luminous object, but the association was not robustly established (it was not even clear that the putative progenitor was a single luminous star). Here we report that the previously proposed object was indeed the progenitor star of SN 2005gl. This very massive star was likely a luminous blue variable that standard stellar evolution predicts should not have exploded in that state. PMID:19305392

Gal-Yam, A; Leonard, D C

2009-04-16

337

Tracking down R Coronae Borealis stars from their mid-infrared WISE colours  

E-print Network

R Coronae Borealis stars (RCBs) are hydrogen-deficient and carbon-rich supergiant stars. They are very rare, as only $\\sim50$ are actually known in our Galaxy. Interestingly, RCBs are strongly suspected to be the evolved merger product of two white dwarfs and could therefore be an important tool to understand Supernovae type Ia in the double degenerate scenario. Constraints on the spatial distribution and the formation rate of such stars are needed to picture their origin and test it in the context of actual population synthesis results. To do so, it is crucial to increase significantly the number of known RCBs. With an absolute magnitude $\\mathrm{M_V\\sim-5}$ and a bright/hot circumstellar shell made of amorphous carbon grains, RCBs are really distinctive stars. Mono-epoch mid-infrared data can help us to discriminate RCBs among other dust-producing stars. The aim is to produce from the WISE and 2MASS infrared catalogues a new catalogue of reasonable size, enriched with RCB stars. Colour-Colour cuts used on a...

Tisserand, Patrick

2011-01-01

338

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

339

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

340

What is the True Population of R Coronae Borealis Stars in the Galaxy?  

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 in a PN central star. The evidence pointing toward a WD merger or a FF origin for RCB stars is contradictory. The distribution on the sky and radial velocities of the RCB stars tend toward those of the bulge population but a much larger sample of stars is needed to determine the true population. We need to discover RCB much more efficiently. In order to do this we are pursuing three lines of attack: 1. Light Curves: Using the traditional technique of identifying RCB stars from their characteristic large and irregular light variations, we have we have investigated the stars in the ASAS-3 south survey. We have discovered 21 new RCB stars. The different analysis applied allowed us to extend our detection efficiency to fainter magnitudes that would not have been easily accessible to classical analysis based on light-curve variability. 2. Color-Color Diagrams: All RCB stars have IR excesses. Using the recent release of the WISE All-Sky Catalog, a series of IR color-color cuts have produced a sample of candidates 1600) that may yield over 200 new RCB star identifications. A pilot project to get spectra of the 200 brighter candidates has yielded an unexpectedly high new discovery rate 20%) based on photometric colors alone. 3. Spectral Classification: We are attempting to develop a quantitative spectral classification system for the RCB stars so that they can perhaps be identified without an accompanying light curve. The cooler RCB stars look like carbon stars with strong C2 bands, but they can be differentiated from carbon stars by their extreme hydrogen deficiency and very low 13C/12C ratio. Also, the red CN bands are much weaker in RCB stars than in carbon stars. The number of RCB stars in the Galaxy may be consistent with the predicted number of He/CO WD mergers. Solving the mystery of how the RCB stars evolve would be a watershed event in the study of stellar evolution that will lead to a better understanding of other important types of stellar merger events such as Type Ia SNe.

Clayton, Geoffrey C.; Tisserand, P.; Welch, D. L.; Zhang, W.

2013-01-01

341

The Nature of Variability in M Supergiants: The Forgotten Type C Semiregulars  

NASA Astrophysics Data System (ADS)

The characteristics of SRC variables are summarized from a comprehensive survey of the Galactic population based on new and archival spectroscopic (Moncrieff, Ph.D. Thesis, Saint Mary's University, 2011) and spectrophotometric (White and Wing, Astrophys. J. 222:209-219, 1978) observations, and brightness estimates from Harvard plates and AAVSO visual archives, with attention on Berkeley 87 member BC Cyg. New spectroscopic observations of BC Cyg phased using a 692d.8 period, found by a new analysis tied to times of light maximum, are consistent with radial pulsation, similar to that in Cepheids. Results for other SRCs are more ambiguous, with starspot activity or supergranulation cycles constituting a complication for small-amplitude stars displaying longer term trends.

Turner, D. G.; Moncrieff, K. E.; Short, C. I.; Wing, R. F.

342

Energy Star  

E-print Network

ENERGY STAR ENERGY TARGETS ESL-KT-12-10-08 CATEE 2012: Clean Air Through Energy Efficiency Conference, Galveston, TX, October 9-11, 2012 POP QUIZ!!!! What is EUI?? Energy Use Intensity Do you know the EUI and any of the buildings you designed... Efficiency Conference, Galveston, TX, October 9-11, 2012 The CFLs in an ENERGY STAR qualified light fixture only need to be changed once every 8 years on average, compared with an annual ladder-climb for incandescent light bulbs. 6 CONSIDERING TIME...

Reihl, K.; Tullos, A.

2012-01-01

343

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

344

Star Power  

ScienceCinema

The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

None

2014-11-18

345

Star Power  

NSDL National Science Digital Library

In this activity, learners create a star show and discover how they can prevent light pollution. Using simple materials, learners first design constellation boxes. Next, learners use their constellation boxes and desk lamps to explore how city lights impact the visibility of constellations. Finally, learners design shields to reduce light pollution and increase the visibility of constellations.

Twin Cities Public Television

2010-01-01

346

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. ...

347

Star Power  

SciTech Connect

The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

None

2014-10-17

348

STAR Highlights  

E-print Network

We report selected results from STAR collaboration at RHIC, focusing on jet-hadron and jet-like correlations, quarkonium suppression and collectivity, di-electron spectrum in both p+p and Au+Au, and higher moments of net-protons as well as azimuthal anisotropy from RHIC Beam Energy Scan program.

Hiroshi Masui; for the STAR Collaboration

2011-06-29

349

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

350

New Herbig Ae/Be stars confirmed via high-resolution optical spectroscopy  

NASA Astrophysics Data System (ADS)

We present FEROS high-resolution (R ~ 45 000) optical spectroscopy of 34 Herbig Ae/Be star candidates with previously unknown or poorly constrained spectral types. Within the sample, 16 sources are positionally coincident with nearby (d < 250 pc) star-forming regions (SFRs). All the candidates have reported infrared excess. We determine the spectral type and luminosity class of the sources, derive their radial and projected rotational velocities, and constrain their distances employing spectroscopic parallaxes and photometry from the literature. We confirm 13 sources as Herbig Ae/Be stars and find one classical T Tauri star. Three sources are emission line early-type giants (B, A, and F stars with luminosity class III) and may be Herbig Ae/Be stars. One source is a main-sequence A-type star. Fourteen sources are post-main-sequence giant and supergiant stars (7 with H? emission and 7 without). Two sources are extreme emission-line stars and no accurate spectral classification was possible because of strong veiling. Most of the sources appear to be background stars at distances over 700 pc. We show that high-resolution optical spectroscopy is a crucial tool for distinguishing young stars (in particular Herbig Be stars) from post-main sequence stars in samples taken from emission-line star catalogs based on low-resolution spectroscopy. Within the sample, three young stars (CD-38 4380, Hen 3-1145, and HD 145718) and one early-type luminosity class III giant with emission lines (Hen 3-416) are at distances closer than 300 pc and are positionally coincident with a nearby SFR. These 4 sources are likely to be nearby young stars and are interesting for follow-up observations at high-angular resolution. Furthermore, seven confirmed Herbig Ae/Be stars at d>700 pc (Hen 2-80, Hen 3-1121 N&S, HD 313571, MWC 953, WRAY 15-1435, and Th 17-35) are inside or close (< 5') to regions with extended 8 ?m continuum emission and in their 20' vicinity have astronomical sources characteristic of SFRs (e.g., HII regions, molecular clouds, dark nebulae, masers, young stellar-objects). These 7 sources are likely to be members of SFRs. Based on observations collected at the ESO-MPG 2.2 m telescope at la Silla Observatory, Chile (program IDs: 072.A-9006, 073.A-9008, 079.A-9014, 081.A-9003).Appendix is only available in electronic form at http://www.aanda.org

Carmona, A.; van den Ancker, M. E.; Audard, M.; Henning, Th.; Setiawan, J.; Rodmann, J.

2010-07-01

351

The death of massive stars - I. Observational constraints on the progenitors of Type II-P supernovae  

NASA Astrophysics Data System (ADS)

We present the results of a 10.5-yr, volume-limited (28-Mpc) search for supernova (SN) progenitor stars. In doing so we compile all SNe discovered within this volume (132, of which 27 per cent are Type Ia) and determine the relative rates of each subtype from literature studies. The core-collapse SNe break down into 59 per cent II-P and 29 per cent Ib/c, with the remainder being IIb (5 per cent), IIn (4 per cent) and II-L (3 per cent). There have been 20 II-P SNe with high-quality optical or near-infrared pre-explosion images that allow a meaningful search for the progenitor stars. In five cases they are clearly red supergiants, one case is unconstrained, two fall on compact coeval star clusters and the other twelve have no progenitor detected. We review and update all the available data for the host galaxies and SN environments (distance, metallicity and extinction) and determine masses and upper mass estimates for these 20 progenitor stars using the STARS stellar evolutionary code and a single consistent homogeneous method. A maximum likelihood calculation suggests that the minimum stellar mass for a Type II-P to form is mmin = 8.5+1-1.5Msolar and the maximum mass for II-P progenitors is mmax = 16.5 +/- 1.5Msolar, assuming a Salpeter initial mass function holds for the progenitor population (in the range ? = -1.35+0.3-0.7). The minimum mass is consistent with current estimates for the upper limit to white dwarf progenitor masses, but the maximum mass does not appear consistent with massive star populations in Local Group galaxies. Red supergiants in the Local Group have masses up to 25Msolar and the minimum mass to produce a Wolf-Rayet star in single star evolution (between solar and LMC metallicity) is similarly 25-30Msolar. The reason we have not detected any high-mass red supergiant progenitors above 17Msolar is unclear, but we estimate that it is statistically significant at 2.4? confidence. Two simple reasons for this could be that we have systematically underestimated the progenitor masses due to dust extinction or that stars between 17-25Msolar produce other kinds of SNe which are not II-P. We discuss these possibilities and find that neither provides a satisfactory solution. We term this discrepancy the `red supergiant problem' and speculate that these stars could have core masses high enough to form black holes and SNe which are too faint to have been detected. We compare the 56Ni masses ejected in the SNe to the progenitor mass estimates and find that low-luminosity SNe with low 56Ni production are most likely to arise from explosions of low-mass progenitors near the mass threshold that can produce a core-collapse.

Smartt, S. J.; Eldridge, J. J.; Crockett, R. M.; Maund, J. R.

2009-05-01

352

MASER OBSERVATIONS OF WESTERLUND 1 AND COMPREHENSIVE CONSIDERATIONS ON MASER PROPERTIES OF RED SUPERGIANTS ASSOCIATED WITH MASSIVE CLUSTERS  

SciTech Connect

We report the results of Australia Telescope Compact Array observations of the Westerlund 1 (Wd1) region in the SiO v = 1, J = 1-0, and H{sub 2}O 6{sub 16}-5{sub 23} maser lines, and we also report the analysis of maser properties of red supergiants (RSGs) associated with six massive clusters including Wd1. The primary purpose of this research is to explore possibilities of using maser emission for investigating the nature of massive clusters and associated RSGs. The SiO v = 1, J = 1-0, and H{sub 2}O 6{sub 16}-5{sub 23} maser lines are detected toward two of four known RSGs in Wd1. The large velocity ranges of maser emission are consistent with the RSG status. RSGs with maser emission tend to exhibit redder log (F {sub 21}/F {sub 12}) and [K-12.13] colors compared to RSGs with no maser emission. The mass-loss rates derived from dust radiative transfer modeling suggest that RSGs with maser emission tend to exhibit larger mass-loss rates compared to RSGs with no maser emission. In an extended sample of 57 RSGs in six massive clusters, detections in the SiO line tend to homogeneously distribute in absolute luminosity L, whereas those in the H{sub 2}O line tend to distribute in a region with large L values.

Fok, Thomas K. T.; Nakashima, Jun-ichi; Yung, Bosco H. K.; Hsia, Chih-Hao [Department of Physics, University of Hong Kong, Pokfulam Road (Hong Kong); Deguchi, Shuji, E-mail: junichi@hku.hk [Nobeyama Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Minamisaku, Nagano 384-1305 (Japan)

2012-11-20

353

CHARA/MIRC Observations of Two M Supergiants in Perseus OB1: Temperature, Bayesian Modeling, and Compressed Sensing Imaging  

NASA Astrophysics Data System (ADS)

Two red supergiants (RSGs) of the Per OB1 association, RS Per and T Per, have been observed in the H band using the Michigan Infra-Red Combiner (MIRC) instrument at the CHARA array. The data show clear evidence of a departure from circular symmetry. We present here new techniques specially developed to analyze such cases, based on state-of-the-art statistical frameworks. The stellar surfaces are first modeled as limb-darkened disks based on SATLAS models that fit both MIRC interferometric data and publicly available spectrophotometric data. Bayesian model selection is then used to determine the most probable number of spots. The effective surface temperatures are also determined and give further support to the recently derived hotter temperature scales of RSGs. The stellar surfaces are reconstructed by our model-independent imaging code SQUEEZE, making use of its novel regularizer based on Compressed Sensing theory. We find excellent agreement between the model-selection results and the reconstructions. Our results provide evidence for the presence of near-infrared spots representing about 3%-5% of the stellar flux.

Baron, F.; Monnier, J. D.; Kiss, L. L.; Neilson, H. R.; Zhao, M.; Anderson, M.; Aarnio, A.; Pedretti, E.; Thureau, N.; ten Brummelaar, T. A.; Ridgway, S. T.; McAlister, H. A.; Sturmann, J.; Sturmann, L.; Turner, N.

2014-04-01

354

H? line profiles for a sample of supergiant HII regions. II. Broad, low intensity components  

NASA Astrophysics Data System (ADS)

We analyze the broad, low intensity, high velocity components that are seen in the H? line profiles for a sample of HII regions. These HII regions are chosen from among the brightest and most isolated in a sample of spiral galaxies for which we have photometric and spectroscopic data: NGC 157, NGC 3631, NGC 6764, NGC 3344, NGC 4321, NGC 5364, NGC 5055, NGC 5985, and NGC 7479. We confirm that the line profiles of most of these bright, giant extragalactic HII regions contain broad kinematic components of low intensity, but high velocity, that we denote as wings. We analyze these components, deriving emission measures, central velocities, and velocity dispersions of the blue and red features, which are similar. We interpret these components as expanding shells within the HII regions and produced by the stellar winds from the ionizing stars. We compare the kinetic energies of these expanding shells with the kinetic energy available from the stellar winds. If we allow for the hypothesis that the brightest HII regions are density bounded, we show that, for these HII regions, the stellar wind mechanism can explain the observed shell kinetic energies.

Rozas, M.; Richer, M. G.; López, J. A.; Relaño, M.; Beckman, J. E.

2006-08-01

355

Circumstellar medium around rotating massive stars at solar metallicity  

NASA Astrophysics Data System (ADS)

Aims: Observations show nebulae around some massive stars but not around others. If observed, their chemical composition is far from homogeneous. Our goal is to put these observational features into the context of the evolution of massive stars and their circumstellar medium (CSM) and, more generally, to quantify the role of massive stars for the chemical and dynamical evolution of the ISM. Methods: Using the A-MAZE code, we perform 2d-axisymmetric hydrodynamical simulations of the evolution of the CSM, shaped by stellar winds, for a whole grid of massive stellar models from 15 to 120 M? and following the stellar evolution from the zero-age main-sequence to the time of supernova explosion. In addition to the usual quantities, we also follow five chemical species: H, He, C, N, and O. Results: We show how various quantities evolve as a function of time: size of the bubble, position of the wind termination shock, chemical composition of the bubble, etc. The chemical composition of the bubble changes considerably compared to the initial composition, particularly during the red-supergiant (RSG) and Wolf-Rayet (WR) phases. In some extreme cases, the inner region of the bubble can be completely depleted in hydrogen and nitrogen, and is mainly composed of carbon, helium, and oxygen. We argue why the bubble typically expands at a lower rate than predicted by self-similarity theory. In particular, the size of the bubble is very sensitive to the density of the ISM, decreasing by a factor of ~2.5 for each additional dex in ISM density. The bubble size also decreases with the metallicity of the central star, because low-metallicity stars have weaker winds. Our models qualitatively fit the observations of WR ejecta nebulae.

Georgy, Cyril; Walder, Rolf; Folini, Doris; Bykov, Andrei; Marcowith, Alexandre; Favre, Jean M.

2013-11-01

356

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.

357

PG1323-086 and PG1704+222 - two post-AGB stars at high galactic latitudes  

E-print Network

Two high galactic latitude B-type stars, PG1323-086 and PG1704+222, are analysed from low and medium resolution optical spectra and Stroemgren photometry. A differential abundance analysis for He, C, N, O, Mg, Al, and Si reveals that the He abundance is close to solar while metal underabundances relative to the solar value of typically 1.3 and 1.2 dex for PG1323-086 and PG1704+222, respectively, are found. For both stars, carbon is even more depleted. The atmospheric parameters are consistent with evolutionary tracks for stars evolving from the asymptotic giant branch (AGB) with a stellar mass of 0.55 solar masses. The anomalous compositions are compatible with those of other high galactic latitude post-AGB stars. Hence, PG1323-086 and PG1704+222 are low mass post-AGB stars in an evolutionary stage between those of A- and F-type supergiants of low mass and central stars of planetary nebulae. From kinematic data and distances a population II membership is probable for both stars.

S. Moehler; U. Heber

1998-05-20

358

GIANT CONVECTION CELL TURNOVER AS AN EXPLANATION OF THE LONG SECONDARY PERIODS IN SEMIREGULAR RED VARIABLE STARS  

SciTech Connect

Giant convection cells in the envelopes of massive red supergiants turn over in a time comparable in order of magnitude with the observed long secondary periods in these stars, according to a theory proposed some years ago by Stothers and Leung. This idea is developed further here by using improved theoretical data, especially a more accurate convective mixing length and a simple calculation of the expected radial-velocity variations at the stellar surface. The theory is applied to the two best-observed red supergiants, Betelgeuse and Antares, with more success than in the earlier study. The theory can also explain the long secondary periods seen in the low-mass red giants, thus providing a uniform and coherent picture for all of the semiregular red variables. How the turnover of a giant convection cell might account for the observed slow light and radial-velocity variations, their relative phasing, and the absence of these variations in certain stars is discussed here in a qualitative way, but follows naturally from the theory.

Stothers, Richard B. [NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 (United States)

2010-12-10

359

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

360

Star formation and the ages of stars  

NASA Astrophysics Data System (ADS)

In this contribution we illustrate how the knowledge of the ages of stars is important to constrain star formation processes. We focus on two specific cases: star formation around the supermassive black hole at the center of the Galaxy and triggered star formation on the borders of Hii regions.

Martins, F.

2014-11-01

361

Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars  

NASA Astrophysics Data System (ADS)

Our understanding of massive star evolution is in flux due to recent upheavals in our view of mass loss and observations of a high binary fraction among O-type stars. Mass-loss rates for standard metallicity-dependent winds of hot stars are lower by a factor of 2-3 compared with rates adopted in modern stellar evolution codes, due to the influence of clumping on observed diagnostics. Weaker hot star winds shift the burden of H-envelope removal to the winds, pulsations, and eruptions of evolved supergiants, as well as binary mass transfer. Studies of stripped-envelope supernovae, in particular, require binary mass transfer. Dramatic examples of eruptive mass loss are seen in Type IIn supernovae, which have massive shells ejected just a few years earlier. These eruptions are a prelude to core collapse, and may signify severe instabilities in the latest nuclear burning phases. We encounter the predicament that the most important modes of mass loss are also the most uncertain, undermining the predictive power of single-star evolution models. Moreover, the influence of winds and rotation has been evaluated by testing single-star models against observed statistics that, it turns out, are heavily influenced by binary evolution. Altogether, this may alter our view about the most basic outcomes of massive-star mass loss—are Wolf-Rayet stars and Type Ibc supernovae the products of winds, or are they mostly the result of binary evolution and eruptive mass loss? This is not fully settled, but mounting evidence points toward the latter. This paradigm shift impacts other areas of astronomy, because it changes predictions for ionizing radiation and wind feedback from stellar populations, it may alter conclusions about star-formation rates and initial mass functions, it affects the origin of compact stellar remnants, and it influences how we use supernovae as probes of stellar evolution across cosmic time.

Smith, Nathan

2014-08-01

362

Stars : the end of a star  

NSDL National Science Digital Library

What happens during the death of a star? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to the final processes of stars. Here students read about low-mass, medium-mass, and massive stars. Low-mass stars produce white dwarfs. A pop-up window describes how white dwarfs form. Medium-mass stars produce neutron stars and supernova. Pop-up information explains the supernova process. Massive stars undergo carbon burning. An interactive lab activity presents students the opportunity to predict temperature, pressure, and gravity changes that occur during carbon fusion. In a final lab activity, students compare initial star size with the type of death that occurs. Activity questions about star death are provided for each star size and are recordable and printable. Copyright 2005 Eisenhower National Clearinghouse

University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)

2003-01-01

363

Molecular Clouds and Star Formation in the Magellanic System by NANTEN  

NASA Astrophysics Data System (ADS)

The Magellanic System offers an ideal laboratory to study how the interstellar medium evolves and how stars are formed at the unrivalled closeness to us. In order to elucidate star formation in the Magellanic System, surveys of the molecular clouds were carried out by NANTEN. In this work, we compare the giant molecular clouds (GMCs) with young clusters and H II regions identified by optical or radio. We find that about 76 % of the GMCs are actively forming stars or clusters, while 24 % show no signs of massive star or cluster formation. Effects of supergiant shells (SGSs) on the formation of GMCs and stars are also studied. The number and surface mass densities of the GMCs are higher by a factor of 1.5-2 at the edge of the SGSs than elsewhere. It is also found that young stellar clusters are more actively formed in the GMCs facing to the center of the SGSs. These results are consistent with the previous studies by Yamaguchi et al. and suggest the formation of the GMCs and the cluster is triggered by dynamical effects of the SGSs. We will also present a result from a comparison of the GMCs with YSO candidates from SAGE.

Kawamura, Akiko; Onishi, T.; Minamidani, T.; Mizuno, Y.; Mizuno, N.; Mizuno, A.; Fukui, Y.; Meixner, M.; Vijh, U.; Leitherer, C.; Whitney, B.; Meade, M.; Babler, B.; Indebetouw, R.; Hora, J.; Gordon, K.; Engelbracht, C.; For, B.; Block, M.; Misselt, K.; Madden, S.; Bernard, J.; Paladini, R.; Reach, W.; SAGE Team

2006-12-01

364

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-bands. The cluster age is determined from isochrone main-sequence (MS) and pre-MS fitting. We derive stellar parameters for eight of the stellar members, using a full non-LTE modeling of the obtained spectra. Mercer 23 is a very young cluster, with age of t=2-4 Myr. The cluster suffers reddening of E(J-Ks)=1.35, Av = 7.2 mag. The derived distance is d=6.5 +/- 0.2 kpc. Our spectral modeling allows us to conclude that the three most luminous member are evolved, highly massive stars: a WR star, and two mid-O supergiant stars, based on their derived luminosity. Mercer 23, is not a super-massive cluster, such as those recently recognized to exist in the Milky Way. However, its mass estimate of 4-6 x 103 Msun puts it in the unique class of young, very massive Galactic clusters hosting WR stars.

Hanson, Margaret M.; Kurtev, R.; Borissova, J.; Georgiev, L.; Ivanov, V. D.; Hillier, D. J.; Minniti, D.

2010-05-01

365

VLTI observations of the dust geometry around R Coronae Borealis stars  

E-print Network

We are investigating the formation and evolution of dust around the hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim to determine the connection between the probable merger past of these stars and their current dust-production activities. We carried out high-angular resolution interferometric observations of three RCB stars, namely RY Sgr, V CrA, and V854 Cen with the mid-IR interferometer, MIDI on the VLTI, using two telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the dusty environment at very small spatial scales (~ 50 mas or 400 stellar radii). The observations of the RCB star dust environments were interpreted using both geometrical models and one-dimensional radiative transfer codes. From our analysis we find that asymmetric circumstellar material is apparent in RY Sgr, may also exist in V CrA, and is possible for V854 Cen. Overall, we find that our observations are consistent with dust forming in clumps ejected randomly around the RCB star so tha...

Bright, S N; Clayton, G C; De Marco, O; Leão, I C; Nordhaus, J; Gallagher, J S

2011-01-01

366

Very Large Telescope Interferometer observations of the dust geometry around R Coronae Borealis stars  

NASA Astrophysics Data System (ADS)

We are investigating the formation and evolution of dust around the hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim to determine the connection between the probable merger past of these stars and their current dust-production activities. We carried out high angular resolution interferometric observations of three RCB stars, namely RY Sgr, V CrA and V854 Cen, with the mid-infrared interferometer (MIDI) on the Very Large Telescope Interferometer (VLTI), using two telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the dusty environment at very small spatial scales (˜50 mas or 400R?). The observations of the RCB star dust environments were interpreted using both geometrical models and one-dimensional radiative transfer codes. From our analysis, we find that asymmetric circumstellar material is apparent in RY Sgr, may also exist in V CrA and is possible for V854 Cen. Overall, we find that our observations are consistent with dust forming in clumps ejected randomly around the RCB star so that over time they create a spherically symmetric distribution of dust. However, we conclude that the determination of whether there is a preferred plane of dust ejection must wait until a time series of observations are obtained. Based on observations made with the Very Large Telescope Interferometer at Paranal Observatory under programme 079.D-0415.

Bright, S. N.; Chesneau, O.; Clayton, G. C.; De Marco, O.; Leão, I. C.; Nordhaus, J.; Gallagher, J. S.

2011-06-01

367

Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams  

E-print Network

Color-magnitude diagrams (CMDs) are presented for the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the Large Magellanic Cloud (LMC). IRAC and MIPS 24 um epoch one data are presented. These data represent the deepest, widest mid-infrared CMDs of their kind ever produced in the LMC. Combined with the 2MASS survey, the diagrams are used to delineate the evolved stellar populations in the Large Magellanic Cloud as well as Galactic foreground and extragalactic background populations. Some 32000 evolved stars brighter than the tip of the red giant branch are identified. Of these, approximately 17500 are classified as oxygen-rich, 7000 carbon-rich, and another 1200 as ``extreme'' asymptotic giant branch (AGB) stars. Brighter members of the latter group have been called ``obscured'' AGB stars in the literature owing to their dusty circumstellar envelopes. A large number (1200) of luminous oxygen--rich AGB stars/M supergiants are also identified. Finally, there is strong evidence from the 24 um MIPS channel that previously unexplored, lower luminosity oxygen-rich AGB stars contribute significantly to the mass loss budget of the LMC (1200 such sources are identified).

R. D. Blum; J. R. Mould; K. A. Olsen; J. A. Frogel; M. Werner; M. Meixner; F. Markwick-Kemper; R. Indebetouw; B. Whitney; M. Meade; B. Babler; E. B. Churchwell; K. Gordon; C. Engelbracht; B. -Q. For; K. Misselt; U. Vijh; C. Leitherer; K. Volk; S. Points; W. Reach; J. L. Hora; J. -P. Bernard; F. Boulanger; S. Bracker; M. Cohen; Y. Fukui; J. Gallagher; V. Gorjian; J. Harris; D. Kelly; A. Kawamura; W. B. Latter; S. Madden; A. Mizuno; N. Mizuno; A. Nota; M. S. Oey; T. Onishi; R. Paladini; N. Panagia; P. Perez-Gonzalez; H. Shibai; S. Sato; L. Smith; L. Staveley-Smith; A. G. G. M. Tielens; T. Ueta; S. Van Dyk; D. Zaritsky

2006-08-08

368

Mining the HST Treasury: The ASTRAL Reference Spectra for Evolved M Stars  

NASA Technical Reports Server (NTRS)

The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres) is an HST Cycle 18 Treasury Program designed to collect a definitive set of representative, high-resolution (R greater than 100,000) and high signal/noise (S/N greater than 100) UV spectra of eight F-M evolved cool stars. These extremely high-quality STIS UV echelle spectra are available from the HST archive and through the University of Colorado (http://casa.colorado.edu/ayres/ASTRAL/) portal and will enable investigations of a broad range of problems -- stellar, interstellar. and beyond -- for many years. In this current paper, we concentrate on producing a roadrnap to the very rich spectra of the two evolved M stars in the sample, the M3.4 giant Gamma Crucis (GaCrux) and the M2Iab supergiant Alpha Orionis (Betelgeuse) and illustrate the huge increase in coverage and quality that these spectra provide over that previously available from IUE and earlier HST observations. These roadmaps will facilitate the study of the spectra, outer atmospheres, and winds of not only these stars. but also numerous other cool, low-gravity stars and make a very interesting comparison to the already-available atlases of the K2III giant Arcturus.

Carpenter, K. G.; Ayres, T.; Harper, G.; Kober, G.; Wahlgren, G. M.

2012-01-01

369

Non-LTE analysis of the Ofpe/WN9 star HDE 269227 (R84)  

NASA Technical Reports Server (NTRS)

The paper presents the results of a spectral analysis of the Ofpe/WN9 star HD 269227 (R84), which assumes a spherically expanding atmosphere to find solutions for equations of radiative transfer. The spectra of hydrogen and helium were predicted with a non-LTE model. Six stellar parameters were determined for R84. The shape of the velocity law is empirically found, since it can be probed from the terminal velocity of the wind. The six stellar parameters are further employed in a hydrodynamic model where stellar wind is assumed to be directed by radiation pressure, duplicating the mass-loss rate and the terminal wind velocity. The velocity laws found by computation and analysis are found to agree, supporting the theory of radiation-driven stellar wind. R84 is surmised to be a post-red supergiant which lost half of its initial mass, possibly during the red-supergiant phase. This mass loss is also suggested by its spectroscopic similarity to S Doradus.

Schmutz, Werner; Leitherer, Claus; Hubeny, Ivan; Vogel, Manfred; Hamann, Wolf-Rainer

1991-01-01

370

Near-infrared spectroscopy of the super star cluster in NGC 1705  

NASA Astrophysics Data System (ADS)

Aims: We study the near-infrared properties of the super star cluster NGC 1750-1 to constrain its spatial extent, its stellar population, and its age. Methods: We used adaptive-optics assisted integral field spectroscopy with SINFONI on the Very Large Telescope. We estimated the spatial extent of the cluster and extracted its K-band spectrum from which we constrained the age of the dominant stellar population. Results: Our observations have an angular resolution of about 0.11'', providing an upper limit on the cluster radius of 2.85 ± 0.50 pc depending on the assumed distance. The K-band spectrum is dominated by strong CO absorption bandheads typical of red supergiants. Its spectral type is equivalent to a K4-5I star. Using evolutionary tracks from the Geneva and Utrecht groups, we determine an age of 12 ± 6 Myr. The large uncertainty is rooted in the large difference between the Geneva and Utrecht tracks in the red supergiants regime. The absence of ionized gas lines in the K-band spectrum is consistent with the absence of O and/or Wolf-Rayet stars in the cluster, as expected for the estimated age. Based on observations collected at the ESO/VLT under program 384.D-0301(A).The FITS file of the reduced cluster spectrum is 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/547/A17

Martins, F.; Förster Schreiber, N. M.; Eisenhauer, F.; Lutz, D.

2012-11-01

371

The VLT-FLAMES Tarantula Survey X: Evidence for a bimodal distribution of rotational velocities for the single early B-type stars  

E-print Network

Aims: Projected rotational velocities (\\vsini) have been estimated for 334 targets in the VLT-FLAMES Tarantula survey that do not manifest significant radial velocity variations and are not supergiants. They have spectral types from approximately O9.5 to B3. The estimates have been analysed to infer the underlying rotational velocity distribution, which is critical for understanding the evolution of massive stars. Methods: Projected rotational velocities were deduced from the Fourier transforms of spectral lines, with upper limits also being obtained from profile fitting. For the narrower lined stars, metal and non-diffuse helium lines were adopted, and for the broader lined stars, both non-diffuse and diffuse helium lines; the estimates obtained using the different sets of lines are in good agreement. The uncertainty in the mean estimates is typically 4% for most targets. The iterative deconvolution procedure of Lucy has been used to deduce the probability density distribution of the rotational velocities. R...

Dufton, P L; Dunstall, P R; Evans, C J; Brott, I; de Mink, S E; Howarth, I D; Kennedy, M; McEvoy, C; Potter, A T; Ramírez-Agudelo, O H; Sana, H; Simón-Díaz, S; Taylor, W; Vink, J S

2012-01-01

372

Observational constraints for the circumstellar disk of the B[e] star CPD-52 9243  

NASA Astrophysics Data System (ADS)

Context. The formation and evolution of gas and dust environments around B[e] supergiants are still open issues. Aims: We intend to study the geometry, kinematics and physical structure of the circumstellar environment (CE) of the B[e] supergiant CPD-52 9243 to provide further insights into the underlying mechanism causing the B[e] phenomenon. Methods: The influence of the different physical mechanisms acting on the CE (radiation pressure, rotation, bi-stability or tidal forces) is somehow reflected in the shape and kinematic properties of the gas and dust regions (flaring, Keplerian, accretion or outflowing disks). To investigate these processes we mainly used quasi-simultaneous observations taken with high spatial resolution optical long-baseline interferometry (VLTI/MIDI), near-IR spectroscopy of CO bandhead features (Gemini/Phoenix and VLT/CRIRES) and optical spectra (CASLEO/REOSC). Results: High angular resolution interferometric measurements obtained with VLTI/MIDI provide strong support for the presence of a dusty disk(ring)-like structure around CPD-52 9243, with an upper limit for its inner edge of ~8 mas (~27.5 AU, considering a distance of 3.44 kpc to the star). The disk has an inclination angle with respect to the line of sight of 46 ± 7°. The study of CO first overtone bandhead evidences a disk structure in Keplerian rotation. The optical spectrum indicates a rapid outflow in the polar direction. Conclusions: The IR emission (CO and warm dust) indicates Keplerian rotation in a circumstellar disk while the optical line transitions of various species are consistent with a polar wind. Both structures appear simultaneously and provide further evidence for the proposed paradigms of the mass-loss in supergiant B[e] stars. The presence of a detached cold CO ring around CPD-52 9243 could be due to a truncation of the inner disk caused by a companion, located possibly interior to the disk rim, clearing the center of the system. More spectroscopic and interferometric data are necessary to determine a possible binary nature of the star. Based on observations taken with: 1) Telescopes at Paranal ESO Observatory under the program 085.D-0454 and 385.D-0513A; 2) Gemini South/Phoenix instrument, science program GS-2010A-Q-41; 3) J. Sahade Telescope at Complejo Astronómico El Leoncito (CASLEO), operated under an agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, the Secretaría de Ciencia y Tecnología de la Nación and the National Universities of La Plata, Córdoba and San Juan.

Cidale, L. S.; Borges Fernandes, M.; Andruchow, I.; Arias, M. L.; Kraus, M.; Chesneau, O.; Kanaan, S.; Curé, M.; de Wit, W. J.; Muratore, M. F.

2012-12-01

373

Integration of geology, geostatistics, well logs and pressure data to model a heterogeneous supergiant field in Iran  

SciTech Connect

The geological reservoir study of the supergiant Ahwaz field significantly improved the history matching process in many aspects, particularly the development of a geostatistical model which allowed a sound basis for changes and by delivering much needed accurate estimates of grid block vertical permeabilities. The geostatistical reservoir evaluation was facilitated by using the Heresim package and litho-stratigraphic zonations for the entire field. For each of the geological zones, 3-dimensional electrolithofacies and petrophysical property distributions (realizations) were treated which captured the heterogeneities which significantly affected fluid flow. However, as this level of heterogeneity was at a significantly smaller scale than the flow simulation grid blocks, a scaling up effort was needed to derive the effective flow properties of the blocks (porosity, horizontal and vertical permeability, and water saturation). The properties relating to the static reservoir description were accurately derived by using stream tube techniques developed in-house whereas, the relative permeabilities of the grid block were derived by dynamic pseudo relative permeability techniques. The prediction of vertical and lateral communication and water encroachment was facilitated by a close integration of pressure, saturation data, geostatistical modelling and sedimentological studies of the depositional environments and paleocurrents. The nature of reservoir barriers and baffles varied both vertically and laterally in this heterogeneous reservoir. Maps showing differences in pressure between zones after years of production served as a guide to integrating the static geological studies to the dynamic behaviour of each of the 16 reservoir zones. The use of deep wells being drilled to a deeper reservoir provided data to better understand the sweep efficiency and the continuity of barriers and baffles.

Samimi, B.; Bagherpour, H.; Nioc, A. [and others

1995-08-01

374

Hubble Space Telescope/NICMOS Observations of I Zw 18: A Population of Old Asymptotic Giant Branch Stars Revealed.  

PubMed

I present the first results from a Hubble Space Telescope/NICMOS imaging study of the most metal-poor blue compact dwarf galaxy, I Zw 18. The near-infrared color-magnitude diagram (CMD) is dominated by two populations, one 10-20 Myr population of red supergiants and one 0.1-5 Gyr population of asymptotic giant branch stars. Stars older than 1 Gyr are required to explain the observed CMD at the adopted distance of 12.6 Mpc, showing that I Zw 18 is not a young galaxy. The results hold also if the distance to I Zw 18 is significantly larger. This rules out the possibility that I Zw 18 is a truly young galaxy formed recently in the local universe. PMID:10835308

Östlin

2000-06-01

375

Triggered Star Formation by Massive Stars  

NASA Astrophysics Data System (ADS)

We present our diagnosis of the role that massive stars play in the formation of low- and intermediate-mass stars in OB associations (the ? Ori region, Ori OB1, and Lac OB1 associations). We find that the classical T Tauri stars and Herbig Ae/Be stars tend to line up between luminous O stars and bright-rimmed or comet-shaped clouds; the closer to a cloud the progressively younger they are. Our positional and chronological study lends support to the validity of the radiation-driven implosion mechanism, where the Lyman continuum photons from a luminous O star create expanding ionization fronts to evaporate and compress nearby clouds into bright-rimmed or comet-shaped clouds. Implosive pressure then causes dense clumps to collapse, prompting the formation of low-mass stars on the cloud surface (i.e., the bright rim) and intermediate-mass stars somewhat deeper in the cloud. These stars are a signpost of current star formation; no young stars are seen leading the ionization fronts further into the cloud. Young stars in bright-rimmed or comet-shaped clouds are likely to have been formed by triggering, which would result in an age spread of several megayears between the member stars or star groups formed in the sequence.

Lee, Hsu-Tai; Chen, W. P.

2007-03-01

376

Triggered Star Formation by Massive Stars  

E-print Network

We present our diagnosis of the role that massive stars play in the formation of low- and intermediate-mass stars in OB associations (the Lambda Ori region, Ori OB1, and Lac OB1 associations). We find that the classical T Tauri stars and Herbig Ae/Be stars tend to line up between luminous O stars and bright-rimmed or comet-shaped clouds; the closer to a cloud the progressively younger they are. Our positional and chronological study lends support to the validity of the radiation-driven implosion mechanism, where the Lyman continuum photons from a luminous O star create expanding ionization fronts to evaporate and compress nearby clouds into bright-rimmed or comet-shaped clouds. Implosive pressure then causes dense clumps to collapse, prompting the formation of low-mass stars on the cloud surface (i.e., the bright rim) and intermediate-mass stars somewhat deeper in the cloud. These stars are a signpost of current star formation; no young stars are seen leading the ionization fronts further into the cloud. Young stars in bright-rimmed or comet-shaped clouds are likely to have been formed by triggering, which would result in an age spread of several megayears between the member stars or star groups formed in the sequence.

Hsu-Tai Lee; W. P. Chen

2009-02-03

377

Three-micron spectroscopy of highly reddened field stars  

NASA Technical Reports Server (NTRS)

Broad absorption features centered at 3.45 microns and at 3.0-3.0 microns towards a number of late-type supergiants in the vicinity of the galactic center were repeatedly reported. Here, 2.0 to 2.5 and 3.0 to 4.0 micron spectra are presented for field late-type highly reddened (A sub V is approximately 17-27) stars located in different regions of the galactic plane more than 20 deg away from the galactic center direction. The observations, made with the 3.6, 2.2, and 1.0 m ESO telescopes at La Silla, Chile, consists of CVF spectra with resolution lambda/delta lambda is approximately or equal to 100 and IRSPEC spectra with resolution lambda/delta lambda is approximately or equal to 700. In the direction of the most highly reddened stars, definitive detections of the 3.45 and the 3.0 to 3.1 micron absorption features are reported. The 3.45 micron feature was attributed to absorption arising in a vibrational transition resulting from the C-H stretching in organic compounds, while the 3.0 to 3.1 micron broader feature are tentatively attributed to O-H bonds. The observations strongly support that the agent producing the 3.45 micron feature, presumably organic molecules, is an important component of the diffuse interstellar medium and is not characteristic only of the galactic center environment.

Tapia, Mauricio; Persi, P.; Roth, M.; Ferrari-Toniolo, M.

1989-01-01

378

Evolved stars: a combined view from interferometry and spectroscopy  

NASA Astrophysics Data System (ADS)

In this thesis, we combine infrared spectroscopic and interferometric observations to study the atmospheres and dusty stellar winds of evolved (RGB, AGB and RSG) giant and super giant stars. We focus on (1) the exact mechanism driving the mass loss, e.g. the dust condensation sequence, and (2) the origin of the asymmetries seen later on in Planetary Nebulae. Extensive data sets are presented for the giant Arcturus, the supergiant Betelgeuse and the OH/IR star OH26.5+0.6. While the spectroscopic data on Arcturus can be well modelled using a single MARCS model atmosphere, the interferometric data suggest emission far out from the photosphere. We suggest this to be a subgiant companion at small (projected) separation. In Betelgeuse we find strong evidence for a thin layer of alumina dust grains only 0.5 stellar radii above the photosphere. This is the first time the dust condensation sequence is spatially resolved and confirms the crucial role of alumina. OH26.5+0.6 is found to have an asymmetric superwind, indicating that deviations from spherical symmetry already occur in the AGB phase. Moreover, the observed angular size throughout the N-band is not compatible with a spherical outflow model. Lastly, as a more practical contribution to the field of IR interferometry, we present a new network of mid-IR interferometric calibrators with new optical and near-IR photometry and accurate diameter estimates.

Verhoelst, T.

2005-03-01

379

IGR J17544-2619 IN DEPTH WITH SUZAKU: DIRECT EVIDENCE FOR CLUMPY WINDS IN A SUPERGIANT FAST X-RAY TRANSIENT  

SciTech Connect

We present direct evidence for dense clumps of matter in the companion wind in a Supergiant Fast X-ray Transient (SFXT) binary. This is seen as a brief period of enhanced absorption during one of the bright, fast flares that distinguish these systems. The object under study was IGR J17544-2619, and a total of 236 ks of data were accumulated with the Japanese satellite Suzaku. The activity in this period spans a dynamic range of almost 10{sup 4} in luminosity and gives a detailed look at SFXT behavior.

Rampy, Rachel A.; Smith, David M. [Physics Department and Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA (United States); Negueruela, Ignacio, E-mail: rrampy@ucsc.ed [Departamento de Fisica, IngenierIa de Sistemas y TeorIa de la Senal, Universidad de Alicante, Apartado 99 E03080, Alicante (Spain)

2009-12-10

380

A Suzaku X-ray Observation of One Orbit of the Supergiant Fast X-ray Transient IGR J16479-4514  

NASA Technical Reports Server (NTRS)

We report on a 250 ks long X-ray observation of the supergiant fast X-ray transient (SFXT) IGR J16479-4514 performed with Suzaku in 2012 February. During this observation, about 80% of the short orbital period (P(sub orb) approximates 3.32 days) was covered as continuously as possible for the first time. The source light curve displays variability of more than two orders of magnitude, starting with a very low emission state (10(exp -13) erg / sq cm/s; 1-10 keV) lasting the first 46 ks, consistent with being due to the X-ray eclipse by the supergiant companion. The transition to the uneclipsed X-ray emission is energy dependent. Outside the eclipse, the source spends most of the time at a level of 6-7X10)(exp-12) erg/sq. cm/s) punctuated by two structured faint flares with a duration of about 10 and 15 ks, respectively, reaching a peak flux of 3-4X10(exp -11) erg/sq. cm./S, separated by about 0.2 in orbital phase. Remarkably, the first faint flare occurs at a similar orbital phase of the bright flares previously observed in the system. This indicates the presence of a phase-locked large scale structure in the supergiant wind, driving a higher accretion rate onto the compact object. The average X-ray spectrum is hard and highly absorbed, with a column density, NH, of 10*exp 23)/sq cm, clearly in excess of the interstellar absorption. There is no evidence for variability of the absorbing column density, except that during the eclipse, where a less absorbed X-ray spectrum is observed. A narrow Fe K-alpha emission line at 6.4 keV is viewed along the whole orbit, with an intensity which correlates with the continuum emission above 7 keV. The scattered component visible during the X-ray eclipse allowed us to directly probe the wind density at the orbital separation, resulting in rho(sub w)=7X10(exp -14) g/cubic cm. Assuming a spherical geometry for the supergiant wind, the derived wind density translates into a ratio M(sub w)/v(sub infinity) = 7X10(exp -17) Solar M/km which, assuming terminal velocities in a large range 500-3000 km/s, implies an accretion luminosity two orders of magnitude higher than that observed. As a consequence, a mechanism should be at work reducing the mass accretion rate. Different possibilities are discussed.

Sidoli, L.; Esposito, P.; Sguera, V.; Bodaghee, A.; Tomsick, J. A.; Pottschmidt, K.; Rodriguez, J.; Ramano, P.; Wilms, J.

2013-01-01

381

IGR J17544-2619 in Depth With Suzaku: Direct Evidence for Clumpy Winds in a Supergiant Fast X-ray Transient  

NASA Astrophysics Data System (ADS)

We present direct evidence for dense clumps of matter in the companion wind in a Supergiant Fast X-ray Transient (SFXT) binary. This is seen as a brief period of enhanced absorption during one of the bright, fast flares that distinguish these systems. The object under study was IGR J17544-2619, and a total of 236 ks of data were accumulated with the Japanese satellite Suzaku. The activity in this period spans a dynamic range of almost 104 in luminosity and gives a detailed look at SFXT behavior.

Rampy, Rachel A.; Smith, David M.; Negueruela, Ignacio

2009-12-01

382

Binary stars.  

PubMed

Most stars in the solar neighborhood are either double or multiple systems. They provide a unique opportunity to measure stellar masses and radii and to study many interesting and important phenomena. The best candidates for black holes are compact massive components of two x-ray binaries: Cygnus X-1 and LMC X-3. The binary radio pulsar PSR 1913 + 16 provides the best available evidence for gravitational radiation. Accretion disks and jets observed in close binaries offer a very good testing ground for models of active galactic nuclei and quasars. PMID:17749544

Paczynacuteski, B

1984-07-20

383

Modelling Evolved Stars Detected by the Spitzer LMC Survey (SAGE)  

NASA Astrophysics Data System (ADS)

The Spitzer photometric survey of the Large Magellanic Cloud (SAGE) has the sensitivity to detect all evolved stars of luminosity 1000 L ? or higher. In order to estimate the global mass return to the interstellar medium for these stars we will need to (a) classify the type of object based upon the available photometry from Spitzer, and 2MASS where available; and (b) estimate the dust shell properties directly from these observations. This will require calculating a grid of dust radiative transfer models to cover the range of parameters suitable for stars in the LMC and having an automatic algorithm for selecting the best fit model for each observed object. Given the lower metallicity of the LMC compared to the Galaxy we need to study some of the brighter objects in detail including fitting of spectroscopy observations to understand the basic dust properties for both oxygen-rich objects with silicate dust and carbon-rich objects with amorphous carbon and silicon-carbide dust. The dust to gas mass ratio must also be estimated, as it is expected to be somewhat higher than the values derived for galactic objects. We will show some preliminary results of the modelling work for a small number of the brighter AGB stars or M-type supergiants in the LMC, as well as discussing the identification of groups of objects in the multi-color space defined by the Spitzer IRAC, Spitzer MIPS, and 2MASS observations. The SAGE Project is supported by NASA/Spitzer grant 1275598 and NASA NAG5-12595.

Volk, Kevin; Meixner, M.; Srinivasan, S.; Markwick-Kemper, F.; Whitney, B.; Blum, R. D.; Meade, M.; Babler, B.; Indebetouw, R.; Hora, J.; Gordon, K.; Engelbracht, C.; For, B.; Block, M.; Misselt, K.; Vijh, U.; Leitherer, C.; SAGE Team

2006-12-01

384

THE STELLAR POPULATION OF h AND {chi} PERSEI: CLUSTER PROPERTIES, MEMBERSHIP, AND THE INTRINSIC COLORS AND TEMPERATURES OF STARS  

SciTech Connect

From photometric observations of {approx} 47,000 stars and spectroscopy of {approx} 11,000 stars, we describe the first extensive study of the stellar population of the famous Double Cluster, h and {chi} Persei, down to subsolar masses. By analyzing optical spectra and optical/infrared photometry, we constrain the distance moduli (dM), reddening (E(B - V)), and ages for h Persei, {chi} Persei, and the low-density halo population surrounding both cluster cores. With the exception of mass and spatial distribution, the clusters are nearly identical in every measurable way. Both clusters have E(B - V) {approx} 0.52-0.55 and dM = 11.8-11.85; the halo population, while more poorly constrained, likely has identical properties. As determined from the main-sequence turnoff, the luminosity of M supergiants, and pre-main-sequence isochrones, ages for h Persei, {chi} Persei, and the halo population all converge on {approx}14 Myr, thus showing a stunning agreement between estimates based on entirely different physics. From these data, we establish the first spectroscopic and photometric membership lists of cluster stars down to early/mid M dwarfs. At minimum, there are {approx} 5000 members within 10' of the cluster centers, while the entire h and {chi} Persei region has at least {approx} 13,000 and as many as 20,000 members. The Double Cluster contains {approx} 8400 M {sub sun} of stars within 10' of the cluster centers. We estimate a total mass of at least 20,000 M {sub sun}. We conclude our study by outlining outstanding questions regarding the past and present properties of h and {chi} Persei. From comparing recent work, we compile a list of intrinsic colors and derive a new effective temperature scale for O-M dwarfs, giants, and supergiants.

Currie, Thayne; Irwin, Jonathan; Kenyon, Scott J.; Tokarz, Susan [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hernandez, Jesus [Centro de Investigaciones de Astronomica (CIDA), Apdo. Postal 264, Merida 5101-A (Venezuela, Bolivarian Republic of); Balog, Zoltan [MPIA-Heidelberg, Heidelberg (Germany); Bragg, Ann [Department of Physics, Marietta College, Marietta, OH (United States); Berlind, Perry; Calkins, Mike [Fred Lawrence Whipple Observatory, Tucson, AZ (United States)], E-mail: tcurrie@cfa.harvard.edu, E-mail: jirwin@cfa.harvard.edu, E-mail: jhernan@umich.edu

2010-02-01

385

New R Coronae Borealis stars discovered in OGLE-III Galactic Bulge fields from their mid- and near- infrared properties  

E-print Network

An R Coronae Borealis (RCB) star is a rare type of supergiant star that is increasingly thought to be the evolved merger product of two white dwarfs. Recently, many of them have been found distributed in a thin disk structure embedded inside the Galactic Bulge. This unexpected high density can give us more insight into the nature and age of RCB stars. We applied and tested successfully a new technique to find RCB stars based on the particular infrared emission. We demonstrated that RCB stars can now be found without the need of a light curve analysis, and therefore outside optically monitored fields. The selection of RCB candidates was based on their near-infrared excess and on particular mid-infrared emission of RCB shells, using photometric data from the 2MASS and Spitzer/GLIMPSE surveys. The OGLE light curves of all RCB candidates were then inspected visually and the ones presenting large and fast declines were followed-up spectroscopically . We discovered two new R Coronae Borealis stars, but also propose...

Tisserand, P; Wood, P R; Udalski, A; Szyma?ski, M K; Kubiak, M; Pietrzy?ski, G; Soszy?ski, I; Szewczyk, O; Ulaczyk, K; Poleski, R

2010-01-01

386

Double core evolution. 7: The infall of a neutron star through the envelope of its massive star companion  

NASA Technical Reports Server (NTRS)

Binary systems with properties similar to those of high-mass X-ray binaries are evolved through the common envelope phase. Three-dimensional simulations show that the timescale of the infall phase of the neutron star depends upon the evolutionary state of its massive companion. We find that tidal torques more effectively accelerate common envelope evolution for companions in their late core helium-burning stage and that the infall phase is rapid (approximately several initial orbital periods). For less evolved companions the decay of the orbit is longer; however, once the neutron star is deeply embedded within the companion's envelope the timescale for orbital decay decreases rapidly. As the neutron star encounters the high-density region surrounding the helium core of its massive companion, the rate of energy loss from the orbit increases dramatically leading to either partial or nearly total envelope ejection. The outcome of the common envelope phase depends upon the structure of the evolved companion. In particular, it is found that the entire common envelope can be ejected by the interaction of the neutron star with a red supergiant companion in binaries with orbital periods similar to those of long-period Be X-ray binaries. For orbital periods greater than or approximately equal to 0.8-2 yr (for companions of mass 12-24 solar mass) it is likely that a binary will survive the common envelope phase. For these systems, the structure of the progenitor star is characterized by a steep density gradient above the helium core, and the common envelope phase ends with a spin up of the envelope to within 50%-60% of corotation and with a slow mass outflow. The efficiency of mass ejection is found to be approximately 30%-40%. For less evolved companions, there is insufficient energy in the orbit to unbind the common envelope and only a fraction of it is ejected. Since the timescale for orbital decay is always shorter than the mass-loss timescale from the common envelope, the two cores will likely merge to form a Thorne-Zytkow object. Implications for the origin of Cyg X-3, an X-ray source consisting of a Wolf-Rayet star and a compact companion, and for the fate of the remnant binary consisting of a helium star and a neutron star are briefly discussed.

Terman, James L.; Taam, Ronald E.; Hernquist, Lars

1995-01-01

387

First supernova companion star found  

NASA Astrophysics Data System (ADS)

Supernova 1993J exploding hi-res Size hi-res: 222 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Supernova 1993J exploding (artist’s impression) New observations with the Hubble Space Telescope allow a look into a supernova explosion under development. In this artist’s view the red supergiant supernova progenitor star (left) is exploding after having transferred about 10 solar masses of hydrogen gas to the blue companion star (right). This interaction process happened over about 250 years and affected the supernova explosion to such an extent that SN 1993J was later known as one of the most peculiar supernovae ever seen. Supernova 1993J exploding hi-res Size hi-res: 4200 kb Credits: ESA and Justyn R. Maund (University of Cambridge) The site of the Supernova 1993J explosion A virtual journey into one of the spiral arms of the grand spiral Messier 81 (imaged with the Isaac Newton Telescope on La Palma, left) reveals the superb razor-sharp imaging power of the NASA/ESA Hubble Space Telescope (Hubble’s WFPC2 instrument, below). The close-up (with Hubble’s ACS, to the right) is centred on the newly discovered companion star to Supernova 1993J that itself is no longer visible. The quarter-circle around the supernova companion is a so-called light echo originating from sheets of dust in the galaxy reflecting light from the original supernova explosion. Supernova 1993J explosing site hi-res Size hi-res: 1502 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Close-up of the Supernova 1993J explosion site (ACS/HRC image) This NASA/ESA Hubble Space Telescope image shows the area in Messier 81 where Supernova 1993J exploded. The companion to the supernova ‘mother star’ that remains after the explosion is seen in the centre of the image. The image is taken with Hubble’s Advanced Camera for Surveys and is a combination of four exposures taken with ACS’ High Resolution Camera. The exposures were taken through two near-UV filters (250W, 2100 seconds and 330W, 1200 seconds) shown in purple and blue, a deep blue filter (435W, 1000 seconds) shown in green and a green filter (555W, 1120 seconds) shown in red. The quarter-circle around the supernova companion is a so-called light echo originating from sheets of dust in the galaxy reflecting light from the original supernova explosion. The timing of the appearance of these echoes can be used to map out the dust structure around the supernova. The light echo was detected in late 2002 and early 2003 by two competing groups of scientists. Messier 81 spiral arm (WFPC2 image) hi-res Size hi-res: 1502 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Messier 81 spiral arm (WFPC2 image) This NASA/ESA Hubble Space Telescope image shows a small portion of one of Messier 81’s spiral arms. It extends about 0.03 x 0.03 degrees. The supernova companion is the bluish star in the upper right hand corner. Dust lanes in the spiral arms of the galaxy are seen, as well as many other stars and a few star forming nebulae. The image is composed of four separate exposures from the ESO/ST-ECF Archive through a blue filter, a green filter, a red filter and a near-infrared filter. The image was taken with Hubble’s Wide Field and Planetary Camera 2. Acknowledgement: Bob Kirshner (Harvard University, USA) Grand Spiral Messier 81 (ground-based) hi-res Size hi-res: 1502 kb Credits: ESA/INT/DSS2 Grand Spiral Messier 81 (ground-based) This ground-based image shows the spiral galaxy Messier 81 in its entirety. The image is a combination of exposures from the Isaac Newton Telescope on La Palma (courtesy of Jonathan Irwin) and Digitized Sky Survey 2 images. The dynamic duo, Messier 81 and 82 (ground-based) hi-res Size hi-res: 1502 kb Credits: Robert Gendler (http://www.robgendlerastropics.com) The dynamic duo, Messier 81 and 82 (ground-based) This wide-angle image taken by astrophotographer Robert Gendler shows the amazing duo of Messier 81 (right) and Messier 82 (left). These two mighty galaxies in the Plough (Ursa Major) belong to some of the most famous and beloved

2004-01-01

388

Star Search  

NSDL National Science Digital Library

In this online activity, learners can test their skills at finding constellations in the northern hemisphere's night sky. Learners can choose during which season to look, and then look for four constellations in that season. The simulation shows a simple representation of the night sky with key stars highlighted. Use this as a practice before going outside or just to give learners an idea of the difficulties involved in identifying constellations. When learners set up a free account at Kinetic City, they can answer bonus questions at the end of the activity as a quick assessment. As a larger assessment, learners can complete the Smart Attack game after they've completed several activities.

Science, American A.

2009-01-01