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1

Massive compact binaries hosting supergiant stars  

NASA Astrophysics Data System (ADS)

In this review I first describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: i. Be circumstellar disk, ii. supergiant stellar wind, and iii. Roche lobe filling supergiants. I then report on the discovery of two new populations of HMXBs hosting supergiant stars, recently revealed by a wealth of new observations, coming from the high energy side (INTEGRAL, Swift, XMM, Chandra satellites), and complemented by multi-wavelength optical/infrared observations (mainly ESO facilities). The first population is constituted of obscured supergiant HMXBs, the second one of supergiant fast X-ray transients (SFXTs), exhibiting short and intense X-ray flares. I finally discuss the formation and evolution of HMXBs, constrain the accretion models (e.g. clumpy winds, transitory accretion disk, magneto-centrifugal barrier), show evidences suggesting the existence of an evolutionary link, include comparisons with population synthesis models, and finally build a consistent scenario explaining the various characteristics of these extreme celestial sources. Because they are the likely progenitors of Luminous Blue Variables (LBVs), and also of neutron star/black hole binary mergers, related to short/hard gamma-ray bursts, the knowledge of the nature, formation and evolution of these HMXB populations is of prime importance.

Chaty, Sylvain

2013-06-01

2

Spectral Classification of Cold IRAS Stars: Supergiants  

NASA Astrophysics Data System (ADS)

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

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

1994-12-01

3

Far-infrared circumstellar 'debris' shell of red supergiant stars  

NASA Technical Reports Server (NTRS)

An examination of IRAS data of red supergiant stars in the field and in galactic OB star associations indicates the presence of substantial amounts of 60-micron emitting material extending several arcminutes around many such sources. The characteristics of these large shells are discussed in terms of remnants of ongoing mass loss, and a simple model developed for the case of Alpha Orionis, in particular.

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

1988-01-01

4

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

5

Elemental abundances of the supergiant stars ? Cygnus and ? Leonis  

NASA Astrophysics Data System (ADS)

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

Tanr?verdi, Taner

2013-12-01

6

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

7

Near-infrared spectroscopy of candidate red supergiant stars in clusters  

E-print Network

Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. 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. We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks red supergiant stars with masses from 10 Msun to 15 Msun. Two red supergiants are located at Galactic coordinates (l,b)=(16.7deg,-0.63deg) and at a distance of about ~3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b)=(49.3deg,+0.72deg) and at a distance of ~7.0 kpc. Spectroscopic analysis of the brightest stars of detected overdensities and st...

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

2014-01-01

8

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

9

Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris  

E-print Network

LETTERS Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris L. M Canis Majoris (VY CMa). A variety of unexpected chemical com- pounds have been identified, including Na is further modified by interstellar ultraviolet radiation3,4 . Chemical compounds in these shells apparently

Ziurys, Lucy M.

10

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

11

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

12

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

13

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

14

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

15

Detection of a 1.59h Period in the B Supergiant Star HD 202850  

NASA Astrophysics Data System (ADS)

Photospheric lines of B-type supergiants show variability in their profile shapes. In addition, their widths are much larger than purely due to stellar rotation. This excess broadening is often referred to as macroturbulence. Both effects have been linked to stellar oscillations, however B supergiants have not been systematically searched yet for the presence of especially short-term variability caused by stellar pulsations. We obtained four time-series of high-quality optical spectra for the Galactic B supergiant HD 202850 with Ond?ejov 2-m telescope. The spectral coverage of about 500Å, around H_? encompasses the Si II (6347, 6371 Å) and He I (6678 Å) photospheric lines. Their time-series display a simultaneous, periodic variability in their profile shapes. Proper analysis using the moment method revealed a period of 1.59 hours in all three lines. This period is found to be stable with time over the observed span of 19 months. This period is much shorter than the rotation period of the star and might be ascribed to stellar oscillations. Since the star seems to fall outside the currently known pulsational instability domains, the nature of the discovered oscillation remains unclear.

Tomic, S.; Kraus, M.; Oksala, M.; Smole, M.

2013-05-01

16

Interacting supernovae from photoionization-confined shells around red supergiant stars  

E-print Network

Betelgeuse, a nearby red supergiant, is a runaway 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 significantly 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...

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

2014-01-01

17

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

E-print Network

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

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

2005-01-13

18

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

19

Isolated Wolf-Rayet Stars and O Supergiants in the Galactic Center Region Identified via Paschen-alpha Excess  

E-print Network

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 emission-line excess, following a narrowband imaging survey of the central 0.65 x 0.25 degress (l, b) around Sgr A* with the Hubble Space Telescope. Discoveries include 6 carbon-type (WC) and 5 nitrogen-type (WN) Wolf-Rayet stars, 6 O supergiants, and 2 Be 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 ...

Mauerhan, Jon; Dong, Hui; Morris, Mark; Wang, Daniel; Stolovy, Susan; Lang, Cornelia

2010-01-01

20

Long-period variables in the Magellanic Clouds - Supergiants, AGB stars, supernova precursors, planetary nebula precursors, and enrichment of the interstellar medium  

Microsoft Academic Search

IR JHK magnitudes and low dispersion red spectra for 90 long period variables (LPVs) in the Magellanic Clouds show the LPVs to fall into distinct groups of core He or C burning supergiants and asymptotic giant branch (AGB) stars. The existence of stars at the AGB limit provides direct evidence that the more massive AGB stars produce supernovae. Carbon star

P. R. Wood; M. S. Bessell; M. W. Fox

1983-01-01

21

Long-period variables in the Magellanic Clouds: Supergiants, AGB stars, supernova precursors, planetary nebula precursors, and enrichment of the interstellar medium  

Microsoft Academic Search

Infrared JHK magnitudes and low-dispersion red spectra have been obtained for 90 long-period variables (LPVs) in the Small and Large Magellanic Clouds. The LPVs fall into two distinct groups, core helium (or carbon) burning supergiants and stars on the asymptotic giant branch (AGB). The supergiants have small pulsation amplitudes in K (<0.25 mag) whereas the AGB stars have typical amplitudes

P. R. Wood; M. S. Bessell; M. W. Fox

1983-01-01

22

V838 Mon and the new class of stars erupting into cool supergiants (SECS)  

NASA Astrophysics Data System (ADS)

V838 Mon has undergone one of the most mysterious stellar outbursts on record. The spectrum at maximum closely resembled a cool AGB star, evolving toward cooler temperatures with time, never reaching optically thin conditions or showing increasing ionization and a nebular stage. The latest spectral type recorded is M8-9. The amplitude peaked at ?V=9 mag, with the outburst evolution being characterized by a fast rise, three maxima over four months, and a fast decay (possibly driven by dust condensation). BaII, LiI and s-element lines were prominent in the outburst spectra. Strong and wide (500 km/sec) P-Cyg profiles affected low ionization species, while Balmer lines emerged to modest emission only during the central phase of the outburst. A light-echo discovered expanding around the object constrains its distance to 790+/-30 pc, providing MV = +4.45 in quiescence and MV = -4.35 at optical maximum (dependent on the still uncertain EB-V=0.5 reddening). The visible progenitor resembles a somewhat under-luminous F0 main sequence star, that did not show detectable variability over the last half century. V838 Mon together with M31-RedVar and V4332 Sgr seems to define a new class of astronomical objects, Stars that Erupt into Cool Supergiants (SECS). They do not develop optically thin or nebular phases, and deep P-Cyg profiles denounce large mass loss at least in the early outburst phases. Their progenitors are photometrically located close to the Main Sequence, away from the post-AGB region. After the outburst, the remnants still closely resemble the precursors (same brightness, same spectral type). Many more similar objects could be buried among poorly studied variable stars that have been classified as Miras or SemiRegulars on the base of a single spectrum at maximum brightness.

Munari, U.; Henden, A.; Corradi, R. M. L.; Zwitter, T.

2002-11-01

23

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

24

The stars near the centre of supergiant shell LMC4: Further constraints on triggering scenarios  

E-print Network

The huge supergiant shell (SGS) LMC4, next to the giant HII region 30 Doradus the second most impressive feature of the Large Magellanic Cloud (LMC), has been the subject of many studies and was used to test various models of star forming mechanisms. In this paper we present a B, V photometry of the very centre of this SGS. The new data yield an age of 11(2)Myr and a colour excess E(B-V) = 0.10(3)mag. Additionally, the two clusters near the geometric centre are too old to be related to the formation of LMC4: HS343 being ~0.1Gyr and KMHK1000 being ~0.3Gyr of age. This and existing photometries support that the young stellar population covering the entire inner region is nearly coeval. We compare these findings with predictions of models proposed for the creation mechanism of SGSs. We conclude that the large-scale trigger, necessary to explain the observations, comes from hydrodynamic interaction of the galactic halo with gas in the leading edge of the moving LMC.

Jochen M. Braun; Klaas S. de Boer; Martin Altmann

2000-06-05

25

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

26

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

27

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

28

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

29

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

30

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

31

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

32

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

33

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

34

The supergiant shell with triggered star formation in the dwarf irregular galaxy IC 2574: neutral and ionized gas kinematics  

NASA Astrophysics Data System (ADS)

We analyse the ionized gas kinematics in the star formation regions of the supergiant shell (SGS) of the IC 2574 galaxy using observations made with the Fabry-Perot interferometer at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences; the data of the H I Nearby Galaxy Survey (THINGS) are used to analyse the neutral gas kinematics in the area. We perform the `derotation' of the H? and H I data cubes and show its efficiency in the kinematics analysis. We confirm the SGS expansion velocity of 25 km s-1 obtained previously and conclude that the SGS is located at the far side of the galactic disc plane. We determine the expansion velocities, kinematic ages and the required mechanical energy input rates for four star formation complexes in the walls of the SGS; for those remaining, we give the limiting values of the above parameters. A comparison with the age and energy input of the stellar population of the complexes shows that sufficient energy is fed to all H II regions except one. We discuss in detail the possible nature of this region and that of another region, which was believed to be a supernova remnant, according to radio observations. We have measured the expansion velocity of the latter and we can confirm its identification as an old supernova remnant. Our observations have allowed us to identify a faint diffuse H? emission inside the SGS, which was not been previously observed.

Egorov, O. V.; Lozinskaya, T. A.; Moiseev, A. V.; Smirnov-Pinchukov, G. V.

2014-10-01

35

Detection of the radial velocity curve of the B5-A0 supergiant companion star of Cir X-1?  

NASA Astrophysics Data System (ADS)

In this paper, we report on phase-resolved I-band optical spectroscopic and photometric observations of Cir X-1 obtained with the Very Large Telescope. The spectra are dominated by Paschen absorption lines at nearly all orbital phases except near phase zero (coinciding with the X-ray dip) when the absorption lines are filled in by broad Paschen emission lines. The radial velocity curve of the absorption lines corresponds to an eccentric orbit (e = 0.45) whose period and time of periastron passage are consistent with the period and phase predicted by the most recent X-ray dip ephemeris. We found that the I-band magnitude decreases from 17.6 to ~16.8 near phase 0.9-1.0 this brightening coincides in phase with the X-ray dip. Even though it is likely that the absorption-line spectrum is associated with the companion star of Cir X-1, we cannot exclude the possibility that the spectrum originates in the accretion disc. However, if the spectrum belongs to the companion star, it must be a supergiant of spectral type B5-A0. If we assume that the compact object does not move through the companion star at periastron, the companion star mass is constrained to <~10 Msolar for a 1.4-Msolar neutron star, whereas the inclination has to be . Alternatively, the measured absorption lines and their radial velocity curve can be associated with the accretion disc surrounding a 1.4-Msolar neutron star and its motion around the centre of mass. An absorption-line spectrum from an accretion disc is typically found when our line of sight passes through the accretion disc rim implying a high inclination. In this scenario, the companion star mass is found to be ~0.4 Msolar. However, from radio observations it was found that the angle between the line of sight and the jet axis is smaller than 5°. This would mean that the jet ploughs through the accretion disc in this scenario, making this solution less probable.

Jonker, P. G.; Nelemans, G.; Bassa, C. G.

2007-01-01

36

GALEX AND PAN-STARRS1 DISCOVERY OF SN IIP 2010aq: THE FIRST FEW DAYS AFTER SHOCK BREAKOUT IN A RED SUPERGIANT STAR  

SciTech Connect

We present the early UV and optical light curve of Type IIP supernova (SN) 2010aq at z = 0.0862, and compare it to analytical models for thermal emission following SN shock breakout in a red supergiant star. SN 2010aq was discovered in joint monitoring between the Galaxy Evolution Explorer (GALEX) Time Domain Survey (TDS) in the NUV and the Pan-STARRS1 Medium Deep Survey (PS1 MDS) in the g, r, i, and z bands. The GALEX and Pan-STARRS1 observations detect the SN less than 1 day after the shock breakout, measure a diluted blackbody temperature of 31, 000 {+-} 6000 K 1 day later, and follow the rise in the UV/optical light curve over the next 2 days caused by the expansion and cooling of the SN ejecta. The high signal-to-noise ratio of the simultaneous UV and optical photometry allows us to fit for a progenitor star radius of 700 {+-} 200R {sub sun}, the size of a red supergiant star. An excess in UV emission two weeks after shock breakout compared with SNe well fitted by model atmosphere-code synthetic spectra with solar metallicity is best explained by suppressed line blanketing due to a lower metallicity progenitor star in SN 2010aq. Continued monitoring of PS1 MDS fields by the GALEX TDS will increase the sample of early UV detections of Type II SNe by an order of magnitude and probe the diversity of SN progenitor star properties.

Gezari, S.; Huber, M. E.; Grav, T. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Rest, A.; Narayan, G. [Department of Physics, Harvard University, Cambridge, MA 20138 (United States); Forster, K.; Neill, J. D.; Martin, D. C. [California Institute of Technology, 1200 East California Blvd., Pasadena, CA 91125 (United States); Valenti, S.; Smartt, S. J. [Astrophysics Research Centre, School of Maths and Physics, Queen's University, BT7 1NN, Belfast (United Kingdom); Chornock, R.; Berger, E.; Soderberg, A. M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Mattila, S.; Kankare, E. [Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Fl-21500, Piikkioe (Finland); Burgett, W. S.; Chambers, K. C.; Dombeck, T.; Heasley, J. N.; Hodapp, K. W., E-mail: suvi@pha.jhu.ed [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)

2010-09-01

37

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

38

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

39

Luminosities and mass-loss rates of SMC and LMC AGB stars and red supergiants  

NASA Astrophysics Data System (ADS)

Context: Mass loss is one of the fundamental properties of Asymptotic Giant Branch (AGB) stars, and through the enrichment of the interstellar medium, AGB stars are key players in the life cycle of dust and gas in the universe. However, a quantitative understanding of the mass-loss process is still largely lacking, particularly its dependence on metallicity. Aims: To investigate the relation between mass loss, luminosity and pulsation period for a large sample of evolved stars in the Small and Large Magellanic Cloud. Methods: Dust radiative transfer models are presented for 101 carbon stars and 86 oxygen-rich evolved stars in the Magellanic Clouds for which 5-35 ?m Spitzer IRS spectra are available. The spectra are complemented with available optical and infrared photometry to construct the spectral energy distribution. A minimisation procedure is used to fit luminosity, mass-loss rate and dust temperature at the inner radius. Different effective temperatures and dust content are also considered. Periods from the literature and from new OGLE-III data are compiled and derived. Results: We derive (dust) mass-loss rates and luminosities for the entire sample. Based on luminosities, periods and amplitudes and colours, the O-rich stars are classified as foreground objects, AGB stars and Red Super Giants. For the O-rich stars silicates based on laboratory optical constants are compared to “astronomical silicates”. Overall, the grain type by Volk & Kwok (1988, ApJ, 331, 435) fits the data best. However, the fit based on laboratory optical constants for the grains can be improved by abandoning the small-particle limit. The influence of grain size, core-mantle grains and porosity are explored. A computationally convenient method that seems to describe the observed properties in the 10 ?m window are a distribution of hollow spheres with a large vacuum fraction (typically 70%), and grain size of about 1 ?m. Relations between mass-loss rates and luminosity and pulsation period are presented and compared to the predictions of evolutionary models, those by Vassiliadis & Wood (1993, ApJ, 413, 641) and their adopted mass-loss recipe, and those based on a Reimers mass-loss law with a scaling of a factor of five. The Vassiliadis & Wood models describe the data better, although there are also some deficiencies, in particular to the maximum adopted mass-loss rate. The derived mass-loss rates are compared to predictions by dynamical wind models and appear consistent with them at a level of a factor 2-4. A better understanding requires the determination of the expansion velocity from future observations from ALMA. The OGLE-III data reveal an O-rich star in the SMC with a period of 1749 days. Its absolute magnitude of M_bol= -8.0 makes it a good candidate for a super-AGB star. Complete Figs. 1-3 and 5-7 are only available in electronic form at http://www.aanda.org Complete Tables 1-4 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/506/1277

Groenewegen, M. A. T.; Sloan, G. C.; Soszy?ski, I.; Petersen, E. A.

2009-11-01

40

Carbon stars as possible members of open clusters. VII - The carbon star MZ CEP and the M-type supergiant MY CEP in the cluster NGC 7419 = C22252 + 605  

NASA Astrophysics Data System (ADS)

Two cool variable stars situated in the sky in or near the open cluster NGC 7419 have been photographically monitored in R(0,63)-, V- and B-passbands. Tables show individual magnitudes of both stars. The carbon star MZ Cep has irregular light variations with the V-amplitude of 0m.5 while the late-M-type supergiant shows semiregular light variations with the mean cycle length of about 395 days and the V-amplitude of more than 1m.1. The R(0,63)- and V-light curves for the two variables are shown in figures.

Alksne, Z.; Alksnis, A.

41

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

SciTech Connect

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

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

2011-01-15

42

NuSTAR Detection Of A Cyclotron Line In The Supergiant Fast X-ray Transient IGR J17544-2619  

E-print Network

We present NuSTAR spectral and timing studies of the Supergiant Fast X-ray Transient (SFXT) IGR J17544-2619. The spectrum is well-described by a ~1 keV blackbody and a hard continuum component, as expected from an accreting X-ray pulsar. We detect a cyclotron line at 17 keV, confirming that the compact object in IGR J17544-2619 is indeed a neutron star. This is the first measurement of the magnetic field in a SFXT. The inferred magnetic field strength, B = (1.45 +/- 0.03) * 10^12 G * (1+z) is typical of neutron stars in X-ray binaries, and rules out a magnetar nature for the compact object. We do not find any significant pulsations in the source on time scales of 1-2000 s.

Bhalerao, Varun; Tomsick, John; Natalucci, Lorenzo; Smith, David M; Bellm, Eric; Boggs, Steven E; Chakrabarty, Deepto; Christensen, Finn E; Craig, William W; Fuerst, Felix; Hailey, Charles J; Harrison, Fiona A; Krivonos, Roman A; Lu, Ting-Ni; Madsen, Kristin; Stern, Daniel; Younes, George; Zhang, William

2014-01-01

43

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

E-print Network

We investigate the formation of dust in a stellar wind during the red-supergiant (RSG) phase of a very massive Population III star with the zero-age main sequence mass of 500 M_sun. We show that, in a carbon-rich wind with a constant velocity, carbon grains can form with a lognormal-like size distribution, and that all of the carbon available for dust formation finally condense into dust for wide ranges of the mass-loss rate ((0.1-3)x10^{-3} M_sun yr^{-1}) and wind velocity (1-100 km s^{-1}). We also find that the acceleration of the wind driven by newly formed dust suppresses the grain growth but still allows more than half of gas-phase carbon to be finally locked up in dust grains. These results indicate that at most 1.7 M_sun of carbon grains can form in total during the RSG phase of 500 M_sun Population III stars. Such a high dust yield could place very massive primordial stars as important sources of dust at the very early epoch of the universe if the initial mass function of Population III stars was top...

Nozawa, Takaya; Maeda, Keiichi; Kozasa, Takashi; Nomoto, Ken'ichi; Langer, Norbert

2014-01-01

44

APERTURE SYNTHESIS OBSERVATIONS OF CO, HCN, AND 89 GHz CONTINUUM EMISSION TOWARD NGC 604 IN M33: SEQUENTIAL STAR FORMATION INDUCED BY A SUPERGIANT H II REGION  

SciTech Connect

We present the results from new Nobeyama Millimeter Array observations of CO(1-0), HCN(1-0), and 89 GHz continuum emission toward NGC 604, known as the supergiant H II region in the nearby galaxy M33. Our high spatial resolution images (4.''2 x 2.''6, corresponding to 17 pc x 11 pc physical size) of CO emission allowed us to uncover 10 individual molecular clouds that have masses of (0.8-7.4) x10{sup 5} M{sub sun} and sizes of 5-29 pc, comparable to those of typical Galactic giant molecular clouds. Moreover, we detected for the first time HCN emission in the two most massive clouds and 89 GHz continuum emission at the rims of the 'H{alpha} shells'. The HCN and 89 GHz continuum emission are offset from the CO peak and are distributed in the direction of the central cluster. Three out of ten CO clouds are well correlated with the H{alpha} shells both in spatial and velocity domains, implying an interaction between molecular gas and the expanding H II region. The CO clouds show varieties in star formation efficiencies (SFEs), which are estimated from the 89 GHz emission and combination of H{alpha} and Spitzer 24 {mu}m data. Furthermore, we found that the SFEs decrease with increasing projected distance measured from the heart of the central OB star cluster in NGC 604, suggesting radial changes in the evolutionary stages of the molecular clouds in the course of stellar cluster formation. Our results provide further support to the picture of sequential star formation in NGC 604 initially proposed by Tosaki et al. with the higher spatially resolved molecular clouds, in which an isotropic expansion of the H II region pushes gases outward, which accumulates to form dense molecular clouds, and then induces massive star formations.

Miura, Rie; Okumura, Sachiko K.; Kurono, Yasutaka; Nakanishi, Kouichiro [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Tosaki, Tomoka [Joetsu University of Education, Yamayashiki-machi, Joetsu, Niigata 943-8512 (Japan); Tamura, Yoichi [Department of Astronomy, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 133-0033 (Japan); Kuno, Nario; Kawabe, Ryohei [Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1805 (Japan); Sakamoto, Seiichi [Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara-shi, Kanagawa 252-5210 (Japan); Hasegawa, Takashi, E-mail: rie.miura@nao.ac.j [Gunma Astronomical Observatory, Nakayama, Takayama, Agatsuma, Gunma 377-0702 (Japan)

2010-12-01

45

Multiple ring nebulae around blue supergiants  

Microsoft Academic Search

Context: In the course of the life of a massive star, wind-wind interaction can give rise to the formation of circumstellar nebulae which are both predicted and observed in nature. Aims: We present generic model calculations to predict the properties of such nebulae for blue supergiants. Methods: From stellar evolution calculations including rotation, we obtain the time dependence of the

S. M. Chita; N. Langer; A. J. van Marle; G. García-Segura; A. Heger

2008-01-01

46

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

47

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

48

Observations of emission lines in M supergiants  

NASA Technical Reports Server (NTRS)

Copernicus observations of Mg 2 h and k emission lines from M giants and supergiants are described. Supergiants with extensive circumstellar gas shells show an asymmetric k line. The asymmetry is ascribed to superimposed lines of Fe 1 and Mn 1. The Mg 2 line width fit the Wilson-Bappu relation derived from observations of G and K Stars. Results of correlated ground-based observations include (1) the discovery of K 1 fluorescent emission from the Betelgeuse shell; (2) extimates of the mass-loss rates; and (3) the proposal that silicate dust grains must account for the major fraction of the Si atoms in the Betelgeuse shell.

Lambert, D. L.

1979-01-01

49

Multiple ring nebulae around blue supergiants  

NASA Astrophysics Data System (ADS)

Context: In the course of the life of a massive star, wind-wind interaction can give rise to the formation of circumstellar nebulae which are both predicted and observed in nature. Aims: We present generic model calculations to predict the properties of such nebulae for blue supergiants. Methods: From stellar evolution calculations including rotation, we obtain the time dependence of the stellar wind properties and of the stellar radiation field. These are used as input for hydro-calculations of the circumstellar medium throughout the star's life. Results: Here, we present the results for a rapidly rotating 12 {M}_? single star. This star forms a blue loop during its post main sequence evolution, at the onset of which its contraction spins it up close to critical rotation. Due to the consequent anisotropic mass loss, the blue supergiant wind sweeps up the preceding slow wind into an hourglass structure. Its collision with the previously formed spherical red supergiant wind shell forms a short-lived luminous nebula consisting of two polar caps and a central inner ring. With time, the polar caps evolve into mid-latitude rings which gradually move toward the equatorial plane while the central ring fades. These structures are reminiscent of the observed nebulae around the blue supergiant Sher 25 and the supernova 1987A. Conclusions: The simple model of an hourglass colliding with a spherical shell reproduces most of the intriguing nebula geometries discovered around blue supergiants, and suggests that they form an evolutionary sequence. Our results indicate that a binary system is not required to obtain them. Appendix A is only available in electronic form at http://www.aanda.org

Chita, S. M.; Langer, N.; van Marle, A. J.; García-Segura, G.; Heger, A.

2008-09-01

50

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

E-print Network

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 Varaibles (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-SN stages of very massive stars. We have begun a survey of the evolved and un stable 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, quiesc...

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

2014-01-01

51

The temperatures of Red Supergiants  

E-print Network

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 (a) the TiO bands, (b) line-free continuum regions of the spectral energy distributions (SEDs), and (c) the integrated fluxes. We show that the temperatures derived from fits to the TiO bands are systematically {\\it lower} than the other two 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. Afte...

Davies, Ben; Plez, Bertrand; Trager, Scott; Lancon, Ariane; Gazak, Zach; Bergemann, Maria; Evans, Chris; Chiavassa, Andrea

2013-01-01

52

Red supergiants around the obscured open cluster Stephenson 2  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

53

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

54

The chemistry of dust formation in red supergiants  

NASA Astrophysics Data System (ADS)

Massive stars in their late stages of evolution as Red Supergiants experience mass loss. The resulting winds show various degrees of dynamical and chemical complexity and produce molecules and dust grains. This review summarises our knowledge of the molecular and dust components of the wind of Red Supergiants, including VY CMa and Betelgeuse. We discuss the synthesis of dust as a non equilibrium process in stellar winds, and present the current knowledge of the chemistry involved in the formation of oxygen-rich dust such as silicates and metal oxides.

Cherchneff, I.

2013-05-01

55

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

56

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

57

X-ray Spectroscopy of O Supergiant Winds: Shock Physics, Clumping, and Mass-Loss Rates  

E-print Network

X-ray Spectroscopy of O Supergiant Winds: Shock Physics, Clumping, and Mass-Loss Rates David Cohen-ray emission: wind shocks 1. X-ray constraints on the shocked wind plasma 2. X-ray absorption as a mass. Adiabatic shocks Open questions: very dense winds (WR stars); low density winds (B stars); magnetic OB stars

Cohen, David

58

Magnetic Braking of Stellar Cores in Red Giants and Supergiants  

NASA Astrophysics Data System (ADS)

Magnetic configurations, stable on the long term, appear to exist in various evolutionary phases, from main-sequence stars to white dwarfs and neutron stars. The large-scale ordered nature of these fields, often approximately dipolar, and their scaling according to the flux conservation scenario favor a fossil field model. We make some first estimates of the magnetic coupling between the stellar cores and the outer layers in red giants and supergiants. Analytical expressions of the truncation radius of the field coupling are established for a convective envelope and for a rotating radiative zone with horizontal turbulence. The timescales of the internal exchanges of angular momentum are considered. Numerical estimates are made on the basis of recent model grids. The direct magnetic coupling of the core to the extended convective envelope of red giants and supergiants appears unlikely. However, we find that the intermediate radiative zone is fully coupled to the core during the He-burning and later phases. This coupling is able to produce a strong spin down of the core of red giants and supergiants, also leading to relatively slowly rotating stellar remnants such as white dwarfs and pulsars. Some angular momentum is also transferred to the outer convective envelope of red giants and supergiants during the He-burning phase and later.

Maeder, André; Meynet, Georges

2014-10-01

59

Red Supergiants and Post-Red Supergiants - the Evidence for High Mass Loss Events  

NASA Astrophysics Data System (ADS)

The complex circumstellar environments associated with several of the most luminous cool supergiants provide evidence for episodic high mass loss events. The origin of the high mass loss is not understood but circumstantial evidence strongly suggests that large scale surface activity and magnetic fields are responsible. I briefly review the observational evidence from multi-epoch imaging and spectroscopy for the high mass loss events and instabilities in these stars. New results from high-resolution AO near and mid-IR imaging of VY CMa, IRC +10420 and ? Cep is also presented.

Humphreys, R. M.

2013-05-01

60

An Observational Evaluation of Magnetic Confinement in the Winds of BA Supergiants  

E-print Network

Magnetic wind confinement has been proposed as one explanation for the complex wind structures of supergiant stars of spectral types B and A. Observational investigation of this hypothesis was undertaken using high-resolution ({\\lambda}/{\\Delta}{\\lambda} {\\sim} 65,000) circular polarization (Stokes V ) spectra of six late B and early A type supergiants ({\\beta} Ori, B8Iae; 4 Lac, B9Iab; {\\eta} Leo, A0Ib; HR1040, A0Ib; {\\alpha} Cyg, A2Iae; {\

Shultz, M; Petit, V; Grunhut, J; Neiner, C; Hanes, D

2013-01-01

61

Unveiling supergiant fast X-ray transient sources with INTEGRAL  

E-print Network

Supergiant high mass X-ray binaries (SGXBs) are believed to be rare objects, as stars in the supergiant phase have a very short lifetime and to date only about a dozen of them have been discovered. They are known to be persistent and bright X-ray sources. INTEGRAL is changing this classical picture as its observations are revealing the presence of a new subclass of SGXBs which have been labelled as supergiant fast X-ray transients (SFXTs) as they are strongly characterized by fast X-ray outbursts lasting less than a day, typically a few hours. We report on IBIS detections of newly discovered fast X-ray outbursts from 10 sources, four of which have been recently optically identified as supergiant high mass X-ray binaries. In particular for one of them, IGR J11215-5952, we observe fast X-ray transient behaviour for the first time. The remaining six sources (IGR J16479-4514, IGR J16418-4532, XTE J1743-363, IGR J16195-4945=AX J161929-4945, AX J1749.1-2733, IGR J17407-2808) are still unclassified, however they can be considered as candidate SFXTs because of their similarity to the known SFXTs.

V. Sguera; A. Bazzano; A. J. Bird; A. J. Dean; P. Ubertini; E. J. Barlow; L. Bassani; D. J. Clark; A. B. Hill; A. Malizia; M. Molina; J. B. Stephen

2006-03-28

62

The blue supergiant Sher 25 and its intriguing hourglass nebula  

E-print Network

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

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

2008-03-29

63

The blue supergiant Sher 25 and its intriguing hourglass nebula  

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

64

Red supergiants as tracers of Perseus Arm structure  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

65

Clump Accretion in Supergiant Fast X-Ray Transients  

NASA Astrophysics Data System (ADS)

Supergiant Fast X-Ray Transients (SFXTs) are a subclass of High-Mass X-Ray Binaries that consist of a neutron star and OB supergiant donor star. These systems display short, bright x-ray flares lasting a few minutes to a few hours with luminosities reaching 1036 erg/s, several orders of magnitude larger than the quiescent luminosities of 1032 erg/s. The clumpy wind hypothesis has been proposed as a possible mechanism for these transient flares; in this model, a portion of the stellar wind from the donor star forms into clumps and is accreted onto the neutron star, inducing flares. We use high-resolution 3D hydrodynamic simulations to test the clumpy wind hypothesis, tracking the mass and angular momentum accretion rates to infer properties of the resulting x-ray flare and secular evolution of the neutron star rotation. Our results are significantly different from the predictions of Hoyle-Lyttleton Accretion (HLA) theory, which assume steady, laminar, axisymmetric flow. For example, an off-axis clump initiated with an impact parameter greater than the clump radius (for which HLA predicts no effect) produces a small spike in mass accretion and induces a long period of disk-like flow that dramatically reduces the accretion rate below the steady HLA value. The result is a brief, weak flare with a net decrease in total accreted mass compared with steady wind accretion accompanied by a substantial accretion of angular momentum.

Chase, Eve; Raymer, E.; Blondin, J. M.

2014-01-01

66

NGC 7419 as a template for red supergiant clusters  

NASA Astrophysics Data System (ADS)

Context. The open cluster NGC 7419 is known to contain five red supergiants and a very high number of Be stars. However, there are conflicting reports about its age and distance that prevent a useful comparison with other clusters. Aims: We intend to obtain more accurate parameters for NGC 7419, using techniques different from those of previous authors, so that it may be used as a calibrator for more obscured clusters. Methods: We obtained Strömgren photometry of the open cluster NGC 7419, as well as classification spectroscopy of ~20 stars in the area. We then applied standard analysis and classification techniques. Results: We find a distance of 4 ± 0.4 kpc and an age of 14 ± 2 Myr for NGC 7419. The main-sequence turn-off is found at spectral type B1, in excellent agreement. We identify 179 B-type members, implying that there are more than 1200 M? in B stars at present. Extrapolating this to lower masses indicates an initial cluster mass of between 7000 and 10 000 M?, depending on the shape of the initial mass function. We find a very high fraction (?40%) of Be stars around the turn-off, but very few Be stars at lower masses. We also report for the first time a strong variability in the emission characteristics of Be stars. We verified that the parameters of the red supergiant members can be used to obtain accurate cluster parameters. Conclusions: NGC 7419 is sufficiently massive to serve as a testbed for theoretical predictions and as a template to compare more obscured clusters. The distribution of stars above the main-sequence turn-off is difficult to accommodate with current evolutionary tracks. Though the presence of five red supergiants is marginally consistent with theoretical expectations, the high number of Be stars and very low number of luminous evolved B stars hint at some unknown physical factor that is not considered in current synthesis models. Partially based on observations collected at the Nordic Optical Telescope and the William Herschel Telescope (La Palma) and at the 1.93-m telescope at Observatoire de Haute Provence (CNRS), France.Tables 1 and 2 are available in electronic form at http://www.aanda.orgTables 3, 4 and 7 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A92

Marco, A.; Negueruela, I.

2013-04-01

67

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

68

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

69

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

70

HD 50975: a yellow supergiant in a spectroscopic binary system  

NASA Astrophysics Data System (ADS)

Context. Recent detection of a yellow supergiant star as a possible progenitor of a supernova has posed serious questions about our understanding of the evolution of massive stars. Aims: The spectroscopic binary star HD 50975 with an unseen hot secondary was studied in detail with the main goal of estimating fundamental parameters of both components and the binary system. Methods: A comprehensive analysis and modeling of collected long-term radial velocity measurements, photometric data, and spectra was performed to calculate orbital elements, atmospheric parameters, abundances, and luminosities. The spectrum in an ultraviolet region was studied to clarify the nature of an unseen companion star. Results: The orbital period was found to be 190.22 ± 0.01 days. The primary star (hereafter HD 50975A) is a yellow supergiant with an effective temperature Teff = 5900 ± 150 K and a surface gravity of log (g) = 1.4 ± 0.3 (cgs). The atmosphere of HD 50975 A is slightly metal deficient relative to solar, [Fe/H] = -0.26 ± 0.06 dex. Abundances of Si and Ca are close to the scaled solar composition. The r-process element europium is enhanced, [Eu/H] = + 0.61 ± 0.07. The bolometric magnitude of the primary was estimated to be Mbol = -5.5 ± 0.3 mag and its mass to be 10.7 ± 2.0 M?. The secondary (hereafter HD 50975B) is a hot star of spectral type ~B2 near ZAMS with an effective temperature of Teff ? 21 000 K and a mass M ? 8.6 M?. The distance between HD 50975A and B is about 370 R?. The binary star is near a semi-detached configuration with a radius, RA ? 107 R?, and a radius of Roche lobe of about 120 R? for the primary star. The reduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/570/A3

Sperauskas, J.; Za?s, L.; Raudeli?nas, S.; Musaev, F.; Puzin, V.

2014-10-01

71

THE TYPE IIb SUPERNOVA 2011dh FROM A SUPERGIANT PROGENITOR  

SciTech Connect

A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star-with R {approx} 200 R{sub Sun }-is needed to reproduce the early light curve (LC) of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star. From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be Almost-Equal-To 2 M{sub Sun }, the explosion energy to be E = (6-10) Multiplication-Sign 10{sup 50} erg, and the {sup 56}Ni mass to be approximately 0.06 M{sub Sun }. The progenitor star was composed of a helium core of 3-4 M{sub Sun} and a thin hydrogen-rich envelope of Almost-Equal-To 0.1M{sub Sun} with a main-sequence mass estimated to be in the range of 12-15 M{sub Sun }. Our models rule out progenitors with helium-core masses larger than 8 M{sub Sun }, which correspond to M{sub ZAMS} {approx}> 25M{sub Sun }. This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

Bersten, Melina C.; Nomoto, Ken'ichi; Folatelli, Gaston; Maeda, Keiichi [Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan); Benvenuto, Omar G. [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, B1900FWA La Plata (Argentina); Ergon, Mattias; Sollerman, Jesper [The Oskar Klein Centre, Department of Astronomy, AlbaNova, SE-106 91 Stockholm (Sweden); Benetti, Stefano; Ochner, Paolo; Tomasella, Lina [INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova (Italy); Botticella, Maria Teresa [INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli (Italy); Fraser, Morgan; Kotak, Rubina, E-mail: melina.bersten@ipmu.jp [Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN (United Kingdom)

2012-09-20

72

The red supergiant and supernova rate problems: implications for core-collapse supernova physics  

NASA Astrophysics Data System (ADS)

Mapping supernovae to their progenitors is fundamental to understanding the collapse of massive stars. We investigate the red supergiant problem, which concerns why red supergiants with masses ˜16-30 M? have not been identified as progenitors of Type IIP supernovae, and the supernova rate problem, which concerns why the observed cosmic supernova rate is smaller than the observed cosmic star formation rate. We find key physics to solving these in the compactness parameter, which characterizes the density structure of the progenitor. If massive stars with compactness above ?2.5 ˜ 0.2 fail to produce canonical supernovae, (i) stars in the mass range 16-30 M? populate an island of stars that have high ?2.5 and do not produce canonical supernovae, and (ii) the fraction of such stars is consistent with the missing fraction of supernovae relative to star formation. We support this scenario with a series of two- and three-dimensional radiation hydrodynamics core-collapse simulations. Using more than 300 progenitors covering initial masses 10.8-75 M? and three initial metallicities, we show that high compactness is conducive to failed explosions. We then argue that a critical compactness of ˜0.2 as the divide between successful and failed explosions is consistent with state-of-the-art three-dimensional core-collapse simulations. Our study implies that numerical simulations of core collapse need not produce robust explosions in a significant fraction of compact massive star initial conditions.

Horiuchi, S.; Nakamura, K.; Takiwaki, T.; Kotake, K.; Tanaka, M.

2014-11-01

73

Population synthesis of massive stars  

NASA Astrophysics Data System (ADS)

This review deals with massive star population synthesis with a realistic population of binaries. We focus on the comparison between observed star numbers (as a function of metallicity) and theoretically predicted numbers of stellar populations in regions of continuous star formation and in starburst regions. Special attention is given to the O-type/WR/red supergiant stellar population, the population of blue supergiants, the pulsar and binary pulsar population, and the supernova rates. Finally, we consider massive double compact star mergers and the link with gravitational wave sources (the advanced LIGO II) and r-process element production sites.

Vanbeveren, Dany

2014-09-01

74

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

Microsoft Academic Search

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

Roberta M. Humphreys; Kris Davidson; Nathan Smith

2002-01-01

75

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

76

Physics of mass loss in massive stars  

E-print Network

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 from 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, J; Markova, N

2014-01-01

77

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

78

Investigating supergiant fast X-ray transients with LOFT  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

79

LBT Discovery of a Yellow Supergiant Eclipsing Binary in the Dwarf Galaxy Holmberg IX  

NASA Astrophysics Data System (ADS)

In a variability survey of M81 using the Large Binocular Telescope we have discovered a peculiar eclipsing binary (MV~-7.1) in the field of the dwarf galaxy Holmberg IX. It has a period of 271 days, and the light curve is well fit by an overcontact model in which both stars are overflowing their Roche lobes. It is composed of two yellow supergiants (V-I~=1 mag, Teff~=4800 K), rather than the far more common red or blue supergiants. Such systems must be rare. While we failed to find any similar systems in the literature, we did, however, note a second example. The SMC F0 supergiant R47 is a bright (MV~-7.5) periodic variable whose All Sky Automated Survey (ASAS) light curve is well fit as a contact binary with a 181 day period. We propose that these systems are the progenitors of supernovae like SN 2004et and SN 2006ov, which appeared to have yellow progenitors. The binary interactions (mass transfer, mass loss) limit the size of the supergiant to give it a higher surface temperature than an isolated star at the same core evolutionary stage. We also discuss the possibility of this variable being a long-period Cepheid. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is 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.

Prieto, J. L.; Stanek, K. Z.; Kochanek, C. S.; Weisz, D. R.; Baruffolo, A.; Bechtold, J.; Burwitz, V.; De Santis, C.; Gallozzi, S.; Garnavich, P. M.; Giallongo, E.; Hill, J. M.; Pogge, R. W.; Ragazzoni, R.; Speziali, R.; Thompson, D. J.; Wagner, R. M.

2008-01-01

80

No stellar age gradient inside supergiant shell LMC 4  

E-print Network

The youngest stellar populations of a 'J'-shaped region (400 pc strip E-W across LH 77 and 850 pc S-N) inside the supergiant shell (SGS) LMC 4 (with a diameter of 1.4 kpc) have been analysed with CCD photometry in B,V passbands. Isochrone fitting to the colour-magnitude diagrams yields ages in the range from 9 Myr to 16 Myr without correlation with the distance to the LMC 4 centre. We construct the luminosity function and the mass function of five regions to ensure that projection effects don't mask the results. The slopes lie in the expected range (gamma in [0.22;0.41] and Gamma in [-1.3;-2.4] respectively, with the Salpeter value of Gamma = -1.35). After our calculations a total of 5-7 10^3 supernovae has dumped the energy of 10^54.5 erg over the past 10 Myr into LMC 4, in fact enough to tear the original star-forming cloud apart in the time span between 5 and 8 Myr after the starformation burst, initiated by a large scale triggering event. We conclude that LMC 4 can have been formed without a contribution from stochastic self-propagating star formation (SSPSF).

Jochen M. Braun; Dominik J. Bomans; Jean-Marie Will; Klaas S. de Boer

1997-08-08

81

RED SUPERGIANTS IN THE ANDROMEDA GALAXY (M31)  

SciTech Connect

Red supergiants (RSGs) are a short-lived stage in the evolution of moderately massive stars (10-25 M{sub sun}), and as such their location in the H-R diagram provides an exacting test of stellar evolutionary models. Since massive star evolution is strongly affected by the amount of mass loss a star suffers, and since the mass-loss rates depend upon metallicity, it is highly desirable to study the physical properties of these stars in galaxies of various metallicities. Here we identify a sample of RSGs in M31, the most metal-rich of the Local Group galaxies. We determine the physical properties of these stars using both moderate resolution spectroscopy and broadband V - K photometry. We find that on average the RSGs of our sample are variable in V by 0.5 mag, smaller but comparable to the 0.9 mag found for Magellanic Cloud (MC) RSGs. No such variability is seen at K, also in accord with what we know of Galactic and MC RSGs. We find that there is a saturation effect in the model TiO band strengths with metallicities higher than solar. The physical properties we derive for the RSGs from our analysis with stellar atmosphere models agree well with the current evolutionary tracks, a truly remarkable achievement given the complex physics involved in each. We do not confirm an earlier result that the upper luminosities of RSGs depend upon metallicity; instead, the most luminous RSGs have log L/L{sub sun}{approx}5.2-5.3, broadly consistent but slightly larger than that recently observed by Smartt et al. as the upper luminosity limit to Type II-P supernovae, believed to have come from RSGs. We find that, on average, the RSGs are considerably more reddened than O and B stars, suggesting that circumstellar dust is adding a significant amount of extra extinction, {approx}0.5 mag, on average. This is in accord with our earlier findings on Milky Way and Magellanic Cloud stars. Finally, we call attention to a peculiar star whose spectrum appears to be heavily veiled, possibly due to scattering by an expanding dust shell.

Massey, Philip [Lowell Observatory, 1400 West Mars Hill Rd., Flagstaff, AZ 86001 (United States); Silva, David R.; Olsen, Knut A. G. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85748 (United States); Levesque, Emily M. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Plez, Bertrand [GRAAL, Universite Montpellier II, CNRS, 34095 Montpellier (France); Clayton, Geoffrey C. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Meynet, Georges; Maeder, Andre, E-mail: phil.massey@lowell.ed, E-mail: dsilva@noao.ed, E-mail: kolsen@noao.ed, E-mail: emsque@ifa.hawaii.ed, E-mail: bertrand.plez@graal.univ-montp2.f, E-mail: gclayton@fenway.phys.lsu.ed, E-mail: georges.meynet@unige.c, E-mail: andre.maeder@unige.c [Geneva University, Geneva Observatory, CH-1290 Versoix (Switzerland)

2009-09-20

82

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

83

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

84

Systematic detection of magnetic fields in massive, late-type supergiants  

NASA Astrophysics Data System (ADS)

We report the systematic detection of magnetic fields in massive (M > 5Msolar) late-type supergiants, using spectropolarimetric observations obtained with ESPaDOnS at the Canada-France-Hawaii Telescope. Our observations reveal detectable Stokes V Zeeman signatures in least-squares deconvolved mean line profiles in one-third of the observed sample of more than 30 stars. The signatures are sometimes complex, revealing multiple reversals across the line. The corresponding longitudinal magnetic field is seldom detected, although our longitudinal field error bars are typically 0.3 G (1?). These characteristics suggest topologically complex magnetic fields, presumably generated by dynamo action. The Stokes V signatures of some targets show clear time variability, indicating either rotational modulation or intrinsic evolution of the magnetic field. We also observe a weak correlation between the unsigned longitudinal magnetic field and the CaII K core emission equivalent width of the active G2Iab supergiant ? Dra and the G8Ib supergiant ? Gem. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France and the University of Hawaii. E-mail: Jason.Grunhut@rmc.ca

Grunhut, J. H.; Wade, G. A.; Hanes, D. A.; Alecian, E.

2010-11-01

85

Spectral atlas of O9.5-A1-Type supergiants  

NASA Astrophysics Data System (ADS)

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

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

2007-09-01

86

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

87

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

88

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

89

Young red supergiants and the near infrared light appearance of disk galaxies  

E-print Network

Disk galaxies often show prominent nonaxisymmetric features at near-infrared wavelengths. Such features may indicate variations in the surface density of stellar mass, contributions from young red supergiants in star forming regions, or substantial dust obscuration. To distinguish among these possibilities, we have searched for spatial variations in the 2.3 micron photometric CO index within the disks of three nearby galaxies (NGC 278, NGC 2649, & NGC 5713). This index measures the strength of the absorption bands of molecular CO in stellar atmospheres, and is strong in cool, low surface-gravity stars, reaching the largest values for red supergiants. We observe significant spatial CO index variations in two galaxies (NGC 278 & NGC 5713), indicating that the dominant stellar population in the near-infrared is not everywhere the same. Central CO index peaks are present in two galaxies; these could be due to either metallicity gradients or recent star formation activity. In addition, significant azimuthal CO index variations are seen in NGC 278. Because strong azimuthal metallicity gradients are physically implausible in disk galaxies, these features are most naturally explained by the presence of a young stellar population. The fraction of 2 micron light due to young stellar populations in star forming regions can be calculated from our data. Overall, young stellar populations can contribute ~3% of a (normal) galaxy's near infrared flux. Locally, this fraction may rise to ~33%. Thus, young stars do not dominate the total near infrared flux, but can be locally dominant in star forming regions, and can bias estimates of spiral arm amplitude or other nonaxisymmetric structures in galaxies' mass distributions.

James E. Rhoads

1997-10-17

90

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

91

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

92

Non-LTE studies of A-type supergiants  

NASA Astrophysics Data System (ADS)

The tenuous atmospheres of A-type supergiants are good sources for studying non-LTE physics. We present an overview of recent achievements in quantitative analyses of high-resolution spectra of Galactic A-type supergiants at optical and near-IR wavelengths, focusing on the nature and extent of non-LTE effects. We discuss their impact on determinations of atmospheric and fundamental stellar parameters and element abundances, and draw some conclusions regarding the evolutionary status of A-type supergiants.

Przybilla, N.; Butler, K.; Firnstein, M.

2014-11-01

93

Statistical properties of a sample of periodically variable B-type supergiants. Evidence for opacity-driven gravity-mode oscillations  

NASA Astrophysics Data System (ADS)

Aims:We have studied a sample of 28 periodically variable B-type supergiants selected from the HIPPARCOS mission and 12 comparison stars covering the whole B-type spectral range. Our goal is to test if their variability is compatible with opacity-driven non-radial oscillations. Methods: We have used the NLTE atmosphere code FASTWIND to derive the atmospheric and wind parameters of the complete sample through line profile fitting. We applied the method to selected H, He, and Si line profiles, measured with the high resolution CES spectrograph attached to the ESO CAT telescope in La Silla, Chile. Results: From the location of the stars in the (log T_eff, log g) diagram, we suggest that variability of our sample supergiants is indeed due to the gravity modes resulting from the opacity mechanism. We find nine of the comparison stars to be periodically variable as well, and suggest them to be new ? Cyg variables. We find marginal evidence of a correlation between the amplitude of the photometric variability and the wind density. We investigate the wind momentum-luminosity relation for the whole range of B spectral type supergiants, and find that the later types (>B5) perfectly follow the relation for A supergiants. Additionally, we provide a new spectral type - T_eff calibration for B supergiants. Conclusions: .Our results imply the possibility of probing internal structure models of massive stars of spectral type B through seismic tuning of gravity modes. Figures of the spectral line fits and discussion of the individual objects, Appendices A, B and Table 6 are only available in electronic form at http://www.aanda.org

Lefever, K.; Puls, J.; Aerts, C.

2007-03-01

94

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

95

Quantitative spectroscopy of Galactic BA-type supergiants. I. Atmospheric parameters  

NASA Astrophysics Data System (ADS)

Context. BA-type supergiants show a high potential as versatile indicators for modern astronomy. This paper constitutes the first in a series that aims at a systematic spectroscopic study of Galactic BA-type supergiants. Various problems will be addressed, including in particular observational constraints on the evolution of massive stars and a determination of abundance gradients in the Milky Way. Aims: The focus here is on the determination of accurate and precise atmospheric parameters for a sample of Galactic BA-type supergiants as prerequisite for all further analysis. Some first applications include a recalibration of functional relationships between spectral-type, intrinsic colours, bolometric corrections and effective temperature, and an exploration of the reddening-free Johnson Q and Strömgren [c1] and ?-indices as photometric indicators for effective temperatures and gravities of BA-type supergiants. Methods: An extensive grid of theoretical spectra is computed based on a hybrid non-LTE approach, covering the relevant parameter space in effective temperature, surface gravity, helium abundance, microturbulence and elemental abundances. The atmospheric parameters are derived spectroscopically by line-profile fits of our theoretical models to high-resolution and high-S/N spectra obtained at various observatories. Ionization equilibria of multiple metals and the Stark-broadened hydrogen and the neutral helium lines constitute our primary indicators for the parameter determination, supplemented by (spectro-)photometry from the UV to the near-IR. Results: We obtain accurate atmospheric parameters for 35 sample supergiants from a homogeneous analysis. Data on effective temperatures, surface gravities, helium abundances, microturbulence, macroturbulence and rotational velocities are presented. The interstellar reddening and the ratio of total-to-selective extinction towards the stars are determined. Our empirical spectral-type-Teff scale is steeper than reference relations from the literature, the stars are significantly bluer than usually assumed, and bolometric corrections differ significantly from established literature values. Photometric Teff-determinations based on the reddening-free Q-index are found to be of limited use for studies of BA-type supergiants because of large errors of typically ±5% (1? statistical) ±3% (1? systematic), compared to a spectroscopically achieved precision of 1-2% (combined statistical and systematic uncertainty with our methodology). The reddening-free [c1] -index and ? on the other hand are found to provide useful starting values for high-precision/accuracy analyses, with uncertainties of ±1% ± 2.5% in Teff, and ±0.04 ± 0.13 dex in log g (1?-statistical, 1?-systematic, respectively). Based on observations collected at the Centro Astronómico Hispano Alemán at Calar Alto (CAHA), 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 obtained at the European Southern Observatory, proposals 62.H-0176 and 079.B-0856(A). Additional data were adopted from the UVES Paranal Observatory Project (ESO DDT Program ID 266.D-5655).

Firnstein, M.; Przybilla, N.

2012-07-01

96

The impact of mass-loss on the evolution and pre-supernova properties of red supergiants  

E-print Network

The post main-sequence evolution of massive stars is very sensitive to many parameters of the stellar models. Key parameters are the mixing processes, the metallicity, the mass-loss rate and the effect of a close companion. We study how the red supergiant lifetimes, the tracks in the Hertzsprung-Russel diagram (HRD), the positions in this diagram of the pre-supernova progenitor as well as the structure of the stars at that time change for various mass-loss rates during the red supergiant phase (RSG), and for two different initial rotation velocities. The surface abundances of RSGs are much more sensitive to rotation than to the mass-loss rates during that phase. A change of the RSG mass-loss rate has a strong impact on the RSG lifetimes and therefore on the luminosity function of RSGs. At solar metallicity, the enhanced mass-loss rate models do produce significant changes on the populations of blue, yellow and red supergiants. When extended blue loops or blue ward excursions are produced by enhanced mass-loss...

Meynet, G; Ekström, S; Georgy, C; Granada, A; Groh, J; Maeder, A; Eggenberger, P; Levesque, E; Massey, P

2014-01-01

97

Swift's Christmas Burst From Blue Supergiant Star Explosion  

NASA Video Gallery

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

98

The Circumstellar Medium of Massive Stars in Motion  

E-print Network

The circumstellar medium around massive stars is strongly impacted by stellar winds, radiation, and explosions. We use numerical simulations of these interactions to constrain the current properties and evolutionary history of various stars by comparison with observed circumstellar structures. Two- and three-dimensional simulations of bow shocks around red supergiant stars have shown that Betelgeuse has probably only recently evolved from a blue supergiant to a red supergiant, and hence its bow shock is very young and has not yet reached a steady state. We have also for the first time investigated the magnetohydrodynamics of the photoionised H II region around the nearby runaway O star Zeta Oph. Finally, we have calculated a grid of models of bow shocks around main sequence and evolved massive stars that has general application to many observed bow shocks, and which forms the basis of future work to model the explosions of these stars into their pre-shaped circumstellar medium.

Mackey, Jonathan; Meyer, Dominique M -A; Gvaramadze, Vasilii V; Mohamed, Shazrene; Neilson, Hilding R; Mignone, Andrea

2014-01-01

99

The ring nebula around the blue supergiant SBW1: pre-explosion snapshot of an SN 1987A twin  

NASA Astrophysics Data System (ADS)

SBW1 is a B-type supergiant surrounded by a ring nebula that is a nearby twin of SN 1987A's progenitor and its circumstellar ring. We present images and spectra of SBW1 obtained with the Hubble Space Telescope (HST), the Spitzer Space Telescope and Gemini South. HST images of SBW1 do not exhibit long Rayleigh-Taylor (RT) fingers, which are presumed to cause the `hotspots' in the SN 1987A ring when impacted by the blast wave, but instead show a geometrically thin (?R/R ? 0.05) clumpy ring. The radial mass distribution and size scales of inhomogeneities in SBW1's ring closely resemble those in the SN 1987A ring, but the more complete disc expected to reside at the base of the RT fingers is absent in SBW1. This structure may explain why portions of the SN 1987A ring between the hotspots have not yet brightened, more than 15 years after the first hotspots appeared. The model we suggest does not require a fast wind colliding with a previous red supergiant wind, because a slowly expanding equatorial ring may be ejected by a rotating blue supergiant star or in a close binary system. More surprisingly, high-resolution images of SBW1 also reveal diffuse emission filling the interior of the ring seen in H? and in thermal-infrared (IR) emission; ˜190 K dust dominates the 8-20 ?m luminosity (but contains only 10-5 M? of dust). Cooler (˜85 K) dust resides in the equatorial ring itself (and has a dust mass of at least 5 × 10-3 M?). Diffuse emission extends inward to ˜1 arcsec from the central star, where a paucity of H? and IR emission suggests an inner hole excavated by the B-supergiant wind. We propose that diffuse emission inside the ring arises from an ionized flow of material photoevaporated from the dense ring, and its pressure prevents the B-supergiant wind from advancing in the equatorial plane. This inner emission could correspond to a structure hypothesized to reside around Sk-69°202 that was never directly detected. If this interpretation is correct, it would suggest that photoionization can play an important dynamical role in shaping the ring nebula, and we speculate that this might help explain the origin of the polar rings around SN 1987A. In effect, the photoevaporative flow shields the outer bipolar nebula at low latitudes, whereas the blue supergiant wind expands freely out the poles and clears away the polar caps of the nebula; the polar rings reside at the intersection of these two zones.

Smith, Nathan; Arnett, W. David; Bally, John; Ginsburg, Adam; Filippenko, Alexei V.

2013-02-01

100

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

101

On the possible existence of brightness spots on the Cyg X-1 supergiant  

NASA Astrophysics Data System (ADS)

A magnetic field was recently detected on the O9.7 Iab supergiant component of the Cyg X-1 X-ray binary system. This paper considers its impact upon the star's atmosphere. We have used the simple model of a unipolar cylindrically symmetric circumpolar magnetic spot in static approximation with the parallel magnetic force lines. In that model the Lorentz-force component related to the force line curvature can be neglected and the equation of hydrostatic equilibrium is nabla (P_{g}+P_{r}+{B^2}/{8?}) = ?{g} , where P_{g} and P_{r} are the gaseous and radiative pressures, respectively, B^2/8? is the isotropic magnetic pressure, g is the gravitation acceleration, and ? is the gas density. In the frame of this model, and of the model atmosphere that we calculated for the Cyg X-1 O-supergiant te{skb}, the magnetic pressure was found to be comparable with the model atmosphere gas and radiative pressures, and exceeded them in the area surrounding the magnetic poles. That condition should lead to the formation of circumpolar bright spots on the stellar surface. We estimate their brightness contrast to be 25 A dipolar or quadrupolar magnetic field can create large bright spots, which can be studied by ground-based optical photometry. If the magnetic field is inclined to the stellar rotation axis, the anticipated variability may reach about 1% can form spots of lesser size, and those may be revealed only by space telescopes. The spots may also be revealed through variability in spectral line profiles. The observation of spots can be considered an independent instrument for the analysis of magnetic fields in O-type supergiants such as that in Cyg X-1. The full text of this contribution has been published in te{kb}.

Karitskaya, E. A.; Bochkarev, N. G.

2014-11-01

102

Hunting for Magnetars in High Mass X-ray Binaries. The Case of SuperGiant Fast X-Ray Transients  

E-print Network

In this paper we summarize some aspects of the wind accretion theory in high mass X-ray binaries hosting a magnetic neutron star and a supergiant companion. In particular, we concentrate on the different types of interaction between the inflowing wind matter and the neutron star magnetosphere that are relevant when accretion of matter onto the neutron star surface is largely inhibited; these include inhibition by the centrifugal and magnetic barriers. We show that very large luminosity swings (~10^4 or more on time scales as short as hours) can result from transitions across different regimes. This scenario is then applied to the activity displayed by supergiant fast X-ray transients (SFXTs), a new class of high mass X-ray binaries in our galaxy recently discovered with INTEGRAL. According to this interpretation we argue that SFXTs which display very large luminosity swings and host a slowly spinning neutron star are expected to be characterized by magnetar-like fields. Supergiant fast X-ray transients might thus provide a unique opportunity to detect and study accreting magnetars in binary systems.

E. Bozzo; M. Falanga; L. Stella

2008-11-06

103

Observed variations in the global longitudinal magnetic fields of stars  

NASA Astrophysics Data System (ADS)

Currently there are 218 stars for which the variation of the longitudinal magnetic field with phase has been determined. 172 of them have been classified as magnetic chemically peculiar stars (mCP), and the rest are stars of various spectral types, from the most massive hot Of?p supergiants to low-mass red dwarfs, and stars with planets. We review briefly the properties of the magnetic fields that have been detected in the various types of star.

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

2014-11-01

104

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

105

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

106

INTEGRAL and Swift observations of the supergiant fast X-ray transient AXJ1845.0-0433=IGRJ18450-0435  

E-print Network

Context: AXJ1845.0-0433 was discovered by ASCA in 1993 during fast outburst activity characterized by several flares on short timescales. Up to now, the source was not detected again by any X-ray mission. Its optical counterpart is suggested to be an O9.5I supergiant star, which is the only remarkable object found inside the ASCA error box. Aims: To detect and characterize new fast outbursts of AXJ1845.0-0433 and confirm its supergiant HMXB nature, using INTEGRAL and archival Swift XRT observations. Methods: We performed an analysis of INTEGRAL IBIS and JEM-X data with OSA 5.1 as well as an analysis of archive Swift XRT data. Results: We report on fast flaring activity from the source on timescales of a few tens of minutes, the first to be reported since its discovery in 1993. Two outbursts have been detected by INTEGRAL (Apr 2005 and Apr 2006) with similar peak fluxes and peak luminosities of 80 mCrab and 9.3X10^35 erg s^-1 (20--40 keV), respectively. Two other outbursts were detected by Swift XRT on Nov 2005 and Mar 2006. The refined Swift XRT position of AXJ1845.0-0433 confirms its association with the supergiant star previously proposed as optical counterpart. Conclusions: Our INTEGRAL and Swift results fully confirm the supergiant HMXB nature of AXJ1845.0-0433 which can therefore be classified as a supergiant fast X-ray transient. Moreover they provide for the first time evidence of its recurrent fast transient behaviour.

V. Sguera; A. J. Bird; A. J. Dean; A. Bazzano; P. Ubertini; R. Landi; A. Malizia; E. J. Barlow; D. J. Clark; A. B. Hill; M. Molina

2006-10-30

107

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

NASA Astrophysics Data System (ADS)

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

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

2006-10-01

108

Massive Star Generations  

NASA Astrophysics Data System (ADS)

This survey extends and enhances Chandra/ACIS studies of massive stars by sampling both very young O stars ionizing ultracompact HII regions (UCHIIRs) and the aged and evolved massive stars in Young Massive Clusters (YMCs). This will double the Chandra sample of UCHIIRs and provide dozens of X-ray spectra on older massive stars. We combine two new ACIS-I pointings with GTO and archival data to achieve an economical study of W42 and W33, nearby massive star-forming regions <1 Myr old, plus the much older and more distant YMCs Cl 1813-178 and Red Supergiant Cluster 1. These sensitive observations will also document pre-main sequence populations and trace the effects of massive star feedback by mapping diffuse X-rays from supernova remnants and wind-shocked plasma.

Townsley, Leisa

2014-09-01

109

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

110

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

E-print Network

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 even though the metal content of the envelopes is very small. 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 ~ 1e-4 - 1e-2 Msun/yr shortly before the explosions, which may create a dense circumstellar medium. Our results show that very massive stars with dense circumstellar media may originate from a wider initial mass range than that of 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 comp...

Moriya, Takashi J

2014-01-01

111

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

112

Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars  

NASA Astrophysics Data System (ADS)

We present a classification of 267 new variable B-type stars discovered by Hipparcos. We have used two different classification schemes and they both result in only a few new beta Cephei stars, a huge number of new slowly pulsating B stars, quite some supergiants with alpha Cyg-type variations and variable CP stars, and further some new periodic Be stars and eclipsing binaries. Our results clearly point out the biased nature towards short-period variables of earlier, ground-based surveys of variable stars. The position of the new beta Cephei stars and slowly pulsating B stars in the HR diagram is determined by means of Geneva photometry and is confronted with the most recent calculations of the instability strips for both groups of variables. We find that the new beta Cephei stars are situated in the blue part of the instability strip and that the new slowly pulsating B stars almost fully cover the theoretical instability domain determined for such stars. The supergiants with alpha Cyg-type variations are situated between the instability strips of the beta Cephei and the slowly pulsating B stars on the one hand and previously known supergiants that exhibit microvariations on the other hand. This suggests some connection between the variability caused by the kappa mechanism acting in a zone of partially ionised metals and the unknown cause of the variations in supergiants.

Waelkens, C.; Aerts, C.; Kestens, E.; Grenon, M.; Eyer, L.

1998-02-01

113

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

114

Measuring the angular diameters of stars  

Microsoft Academic Search

A difficult problem in observational optical astronomy is to measure the extremely small angles subtended at the Earth by the discs of stars. There are three techniques; Michelson's stellar interferometer, the stellar intensity interferometer at Narrabri, and lunar occultations. Michelson's interferometer has been used to measure a few cool giants and supergiants but, for technical reasons, attempts to develop it

R. H. Brown

1971-01-01

115

The superimposed photospheric and stellar wind variability of the O-type supergiant alpha Cam  

E-print Network

(Abridged) We provide empirical constraints on the different physical components that can act to yield temporal variability in predominantly or partially wind-formed optical lines of luminous OB stars, and thus potentially affect the reliable determination of fundamental parameters, including mass-loss rates via clumped winds. Using time-series spectroscopy from epochs spread over $\\sim$ 4 years, a case study of the O9.5 supergiant $\\alpha$ Cam is presented. We demonstrate that the He I 5876 (2$^3$P$^0$--3$^3$D) line is an important diagnostic for photospheric and wind variability in this star. The optical line profiles of $\\alpha$ Cam are affected by (i) deep-seated fluctuations close to, or at, the photosphere, (ii) atmospheric velocity gradients, and (iii) large-scale stellar wind structure. This study provides new empirical perspectives on accurate line-synthesis modelling of stellar wind signatures in massive luminous stars. Using a pure Halpha line-synthesis code we interpret maximum changes in the red-ward and peak emission of $\\alpha$ Cam in terms of mass-loss rate differences in the range $\\sim$ 5.1 $\\times$ 10$^{-6}$ to 6.5 $\\times$ 10$^{-6}$ M$_\\odot$ yr$^{-1}$. However, the models generally fail to reproduce the morphology of blueward (possibly absorptive) regions of the profiles.

R. K. Prinja; N. Markova; S. Scuderi; H. Markov

2006-06-29

116

Investigating the Powering Sources of Expanding Supergiant Shells in the Nearby Dwarf Galaxy IC 2574  

NASA Astrophysics Data System (ADS)

Using the unique resolving capability of the Hubble Space Telescope {HST} and the wide-field imaging capabilities of the ACS, we propose to perform a stellar population study of two prominent supergiant shells {SGS} in the nearby dwarf galaxy IC2574. By constructing the star formation history for those SGSs we will for the first time be able to test if past star formation created these impressive structures, as suggested by theory. We have carefully selected 2 SGSs; one is young {age: few 10^7yr, exhibiting a prominent central stellar association and the other is older {few 10^8yr}, with no obvious optical counterpart. The aim of this proposal is to determine the age and SF history of the central stellar associations of both SGSs by B, V, and I band imaging using HST's ACS. A primary goal is the comparison of the stellar ages with the age estimates from the HI kinematics. Using color magnitude diagrams, we will also estimate how many stars have evolved off the main sequence and exploded as SN, giving an estimate for the total mechanical energy deposited. A comparison with the values derived in other wavelengths is not only important for understanding these particular SGSs but will also set strong timing as well as energy constraints on the physical mechanisms which lie at the origin of SGSs in general.

Walter, Fabian

2003-07-01

117

Magnetic confinement, Alfven wave reflection, and the origins of X-ray and mass-loss 'dividing lines' for late-type giants and supergiants  

NASA Technical Reports Server (NTRS)

A simple qualitative model for the origin of the coronal and mass-loss dividing lines separating late-type giants and supergiants with and without hot, X-ray-emitting corona, and with and without significant mass loss is discussed. The basic physical effects considered are the necessity of magnetic confinement for hot coronal material on the surface of such stars and the large reflection efficiency for Alfven waves in cool exponential atmospheres. The model assumes that the magnetic field geometry of these stars changes across the observed 'dividing lines' from being mostly closed on the high effective temperature side to being mostly open on the low effective temperature side.

Rosner, R.; An, C.-H.; Musielak, Z. E.; Moore, R. L.; Suess, S. T.

1991-01-01

118

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

119

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

NASA Astrophysics Data System (ADS)

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

Ohnaka, K.

2014-01-01

120

Dense Molecular Clumps Associated with the Large Magellanic Cloud Supergiant Shells LMC 4 and LMC 5  

NASA Astrophysics Data System (ADS)

We investigate the effects of supergiant shells (SGSs) and their interaction on dense molecular clumps by observing the Large Magellanic Cloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC 4 and LMC 5. 12CO (J = 3-2, 1-0) and 13CO(J = 1-0) observations with the ASTE and Mopra telescopes have been carried out toward these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H2)) of the clumps are distributed from low to high density (103-105 cm–3) and their kinetic temperatures (T kin) are typically high (greater than 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of H?, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density H I envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high n(H2) and T kin, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.

Fujii, Kosuke; Minamidani, Tetsuhiro; Mizuno, Norikazu; Onishi, Toshikazu; Kawamura, Akiko; Muller, Erik; Dawson, Joanne; Tatematsu, Ken'ichi; Hasegawa, Tetsuo; Tosaki, Tomoka; Miura, Rie E.; Muraoka, Kazuyuki; Sakai, Takeshi; Tsukagoshi, Takashi; Tanaka, Kunihiko; Ezawa, Hajime; Fukui, Yasuo

2014-12-01

121

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

NASA Astrophysics Data System (ADS)

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

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

2002-11-01

122

Supergiant Fast X-ray Transients: A Case Study for LOFT  

NASA Astrophysics Data System (ADS)

LOFT, the Large Observatory For X-ray Timing, is a new space mission concept selected by ESA in February 2011 and currently competing for a launch of opportunity in 2022. LOFT will carry a coded mask Wide Field Monitor (WFM) and a 10-m^2 class collimated X-ray Large Area Detector (LAD) operating in the energy range 2-80 keV. The instruments on-board LOFT will dramatically deepen our knowledge of Supergiant Fast X-ray Transients, a class of High-Mass X-ray Binaries whose optical counterparts are O or B supergiant stars, and whose X-ray outbursts are about 4 orders of magnitude brighter than the quiescent state. The LAD and the WFM will provide simultaneous high S/N broad-band and time-resolved spectroscopy in several intensity states, long term monitoring that will yield new determinations of orbital periods, as well as spin periods. We show the results of an extensive set of simulations based on the Swift broad-band and detailed XMM-Newton observations we collected up to now. Our simulations describe the outbursts at several intensities (F(2-10 keV)=5.9E-9 to 5.5E-10 erg cm-2 s-1), the intermediate and most common state (1E-11 erg cm-2 s-1), and the low state (1.2E-12 to 5E-13 erg cm-2 s-1). We also considered large variations of NH and the presence of emission lines, as observed by Swift and XMM-Newton. We acknowledge financial contribution from ASI-INAF I/004/11/0 and I/021/12/0.

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

2013-04-01

123

The blue supergiant Sher 25 and its intriguing hourglass nebula  

Microsoft Academic Search

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

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

2008-01-01

124

The blue supergiant Sher 25 and its intriguing hourglass nebula  

Microsoft Academic Search

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

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

2008-01-01

125

Bow-shock induced star formation in the LMC?  

E-print Network

The structure of supergiant shells, in particular of LMC 4, is hard to explain with stochastic self-propagating star formation. A series of supergiant structures lies along the outer edge of the LMC and form a sequence increasing clockwise in age. We have considered the rotation of the LMC and its motion through the halo of the Milky Way and propose that these structures find their origin in star formation induced in the bow-shock formed at the leading edge of the LMC. Due to the rotation of the LMC these structures then move aside.

Klaas S. de Boer; Jochen M. Braun; Antonella Vallenari; Ulrich Mebold

1997-11-06

126

Neutral and ionized gas around the post-Red Supergiant IRC+10420 at au size scales  

E-print Network

IRC +10420 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. The star has an ionised wind and using the Br gamma hydrogen recombination emission we assess the mass-loss on spatial scales of order 1 au. We present new VLT Interferometer AMBER data which are combined with all other AMBER data in the literature. The final dataset covers a position angle range of 180 degrees and baselines up to 110 meters. The spectrally dispersed visibilities, differential phases and line flux are conjointly analyzed and modelled. We also present AMBER/FINITO observations which cover a larger wavelength range and allow us to observe the Na I doublet at 2.2 micron. The data are complemented by X-Shooter data, which provide a higher spectral resolution view. The Brackett gamma 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 gamma tra...

Oudmaijer, Rene

2012-01-01

127

Westerlund 1 as a Template for Massive Star Evolution  

E-print Network

With a dynamical mass M_dyn ~ 1.3x10e5 M_sun and a lower limit M_cl>5x10e4 M_sun from star counts, Westerlund 1 is the most massive young open cluster known in the Galaxy and thus the perfect laboratory to study massive star evolution. We have developed a comprehensive spectral classification scheme for supergiants based on features in the 6000-9000A range, which allows us to identify >30 very luminous supergiants in Westerlund 1 and ~100 other less evolved massive stars, which join the large population of Wolf-Rayet stars already known. Though detailed studies of these stars are still pending, preliminary rough estimates suggest that the stars we see are evolving to the red part of the HR diagram at approximately constant luminosity.

Ignacio Negueruela; J. Simon Clark; Paul A. Crowther; Lucy Hadfield

2008-02-28

128

BROADBAND ESO/VISIR-SPITZER INFRARED SPECTROSCOPY OF THE OBSCURED SUPERGIANT X-RAY BINARY IGR J16318-4848  

SciTech Connect

A new class of X-ray binaries has recently been discovered by the high-energy observatory INTEGRAL. It is composed of intrinsically obscured supergiant high-mass X-ray binaries, unveiled by means of multi-wavelength X-ray, optical, near- and mid-infrared observations, in particular, photometric and spectroscopic observations using ESO facilities. However, the fundamental questions about these intriguing sources, namely, their formation, evolution, and the nature of their environment, are still unsolved. Among them, IGR J16318-4848, a compact object orbiting around a supergiant B[e] star, seems to be one of the most extraordinary celestial sources of our Galaxy. We present here new ESO/Very Large Telescope (VLT) VISIR mid-infrared (MIR) spectroscopic observations of this source. First, line diagnostics allow us to confirm the presence of absorbing material (dust and cold gas) enshrouding the whole binary system, and to characterize the nature of this material. Second, by fitting broadband near- to mid-infrared spectral energy distribution, including ESO NTT/SofI, VLT/VISIR, and Spitzer data, with a phenomenological model for sgB[e] stars, we show that the star is surrounded by an irradiated rim heated to a temperature of {approx}3800-5500 K, along with a viscous disk component at an inner temperature of {approx}750 K. VISIR data allow us to exclude the spherical geometry for the dust component. This detailed study will allow us in the future to get better constraints on the formation and evolution of such rare and short-living high-mass X-ray binary systems in our Galaxy.

Chaty, S.; Rahoui, F., E-mail: sylvain.chaty@cea.fr, E-mail: frahoui@cfa.harvard.edu [AIM (UMR-E 9005 CEA/DSM-CNRS-Universite Paris Diderot) Irfu/Service d'Astrophysique, Centre de Saclay, FR-91191 Gif-sur-Yvette Cedex (France)

2012-06-01

129

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

130

Massive stars: Their lives in the interstellar medium; Proceedings of the Symposium, ASP Annual Meeting, 104th, Univ. of Wisconsin, Madison, June 23-25, 1992  

NASA Astrophysics Data System (ADS)

Various papers on massive stars and their relationship to the interstellar medium are presented. Individual topics addressed include: observations of newly formed massive stars, star formation with nonthermal motions, embedded stellar clusters in H II regions, a Milky Way concordance, NH3 and H2O masers, PIGs in the Trapezium, star formation in photoevaporating molecular clouds, massive star evolution, mass loss from cool supergiant stars, massive runaway stars, CNO abundances in three A-supergiants, mass loss from late-type supergiants, OBN stars and blue supergiant supernovae, the most evolved W-R stars, X-ray variability in V444 Cygni, highly polarized stars in Cassiopeia, H I bubbles around O stars, interstellar H I LY-alpha absorption, shocked ionized gas in 30 Doradus, wind mass and energy deposition. Also discussed are: stellar wind bow shocks, O stars giant bubbles in M33, Eridanus soft X-ray enhancement, wind-blown bubbles in ejecta medium, nebulae around W-R stars, highly ionized gas in the LMC, cold ionized gas around hot H II regions, initial mass function in the outer Galaxy, late stages in SNR evolution, possible LBV in NGC 1313, old SN-pulsar association, cold bright matter near SN1987A, starbursts in the nearby universe, giant H II regions, powering the superwind in NGC 253, obscuration effects in starburst Galactic nuclei, starburst propagation in dwarf galaxies, 30 Doradus, W-R content of NGC 595 and NGC 604, Cubic Cosmic X-ray Background Experiment.

Cassinelli, Joseph P.; Churchwell, Edward B.

1993-01-01

131

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

132

The Kinematics and Nature of Gould's Belt -- a 30 MYR Old Star Forming Region  

Microsoft Academic Search

For a sample of 2440 non-supergiant Hipparcos stars belonging to Stroemgren's `early group' luminosities, temperatures, ages and distances have been determined. 241 stars younger than 30 Myr with well determined ages and space velocities fall within the local flattened system, inclined 20deg to the galactic plane, called Gould's Belt. The system is dominated by a number of nearby prominent associations

P. O. Lindblad; J. Palous; K. Loden; L. Lindegren

1997-01-01

133

The reddening to the galaxy IC 342 from CCD BV photometry of its brightest stars  

Microsoft Academic Search

An attempt was made to estimate the reddening for the galaxy IC 342 on the basis of CCD BV photometry obtained for 117 stars brighter than V = 22.0 mag in a field centered near a spiral arm. At V = 19.4 mag, the plume of the main sequence and slightly evolved blue supergiant stars were detected. The plume is

Barry F. Madore; Wendy L. Freedman

1992-01-01

134

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

E-print Network

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

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

2014-01-01

135

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

136

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

NASA Astrophysics Data System (ADS)

We report on the results from observations of the most recent outbursts of XTE J1739-302 and IGR J17544-2619, which are considered to be the prototypes of the supergiant fast X-ray transient class. They triggered the Swift/Burst Alert Telescope on 2011 February 22 and March 24, respectively, and each time a prompt Swift slew allowed us to obtain the rich broad-band data we present. The X-ray Telescope light curves show the descending portion of very bright flares that reached luminosities of ˜2 × 1036 and ˜5 × 1036 erg s-1. The broad-band spectra, when fitted with the usual phenomenological models adopted for accreting neutron stars, yield values of both high-energy cut-off and e-folding energy consistent with those obtained from previously reported outbursts from these sources. In the context of more physical models, the spectra of both sources can be well fitted either with a two-blackbody model or with a single unsaturated Comptonization model. In the latter case, the model can be either a classical static Comptonization model, such as COMPTT, or the recently developed COMPMAG model, which includes thermal and bulk Comptonization for cylindrical accretion on to a magnetized neutron star. We discuss the possible accretion scenarios derived by the different models, and we also emphasize the fact that the electron density derived from the Comptonization models, in the regions where the X-ray spectrum presumably forms, is lower than that estimated using the continuity equation at the magnetospheric radius and the source X-ray luminosity, and we give some possible explanations.

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

2012-08-01

137

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

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

138

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

E-print Network

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

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

2008-03-26

139

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

140

Stellar Winds from Dme Stars  

NASA Astrophysics Data System (ADS)

Despite the fact that the most stars have low mass and lie on the main sequence, we know virtually nothing about their stellar winds. Existing measurements of stellar winds extend down only to a few times 1e-10 M_solar/yr and only apply to high-mass stars and red giants and supergiants. With Chandra's unparalleled imaging resolution, high sensitivity, and energy resolution, winds from nearby dwarf stars are now detectable via their X-ray emission from the charge exchange of stellar wind ions with neutral gas in the ISM. Our proposed observations of dwarf M flare stars will be capable of imaging stellar winds comparable to those of the Sun (mass loss rate 2e-14 M_solar/yr), and will provide information on wind and magnetosphere geometry, ion composition, and mass loss rates.

Wargelin, Bradford

2001-09-01

141

VizieR Online Data Catalog: Nature of the peculiar supergiant HD 101584 (Bakker+, 1996)  

NASA Astrophysics Data System (ADS)

We present a study of low- and high-resolution ultraviolet, high-resolution optical CAT/CES spectra and ultraviolet, optical and infrared photometry of the peculiar supergiant HD 101584. From the photometry we learn that the ultraviolet and optical energy distribution cannot be fitted in a consistent way and we need a model in which the UV and optical energy distribution are formed by different gas. The Geneva photometry is best fitted to a B9II Kurucz model, Teff=12000+/-1000K and logg=3.0+/-1.0, with an extinction of E(B-V)=0.49+/-0.05. The observed spectral features in the spectrum of HD 101584 are classified in eight different categories based on the velocity, shape of profile and the identification. The high-excitation HeI (?=20.87eV), NII (?=18.40eV), CII (?=14.39eV) and NI (?=10.29eV) optical absorption lines are formed in the photosphere of a late B-star (e.g. B8-9I-II). These absorption lines show radial velocity variations which are attributed to binary motion, with the secondary being a white dwarf or a low-mass main sequence object. The low-excitation P-Cygni lines in the optical and UV are formed in the wind. The number density of absorption lines in the UV is so large that the wind spectrum acts as an iron curtain in front of the B-star. The terminal velocity of the wind of v{infinity}=100+/-30km/s is consistent with the star being a low-mass post-AGB star and the low effective gravity is attributed to the presence of a nearby, unseen, secondary. We estimate a mass-loss rate of M?=~10-8M?/yr. Narrow absorption and emission lines are observed which are formed in a circumsystem disk with a typical radius of 102R*. (2 data files).

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

1995-07-01

142

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

143

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

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

144

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

NASA Astrophysics Data System (ADS)

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the H-R diagram. During their post-red supergiant evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semiforbidden region that de Jager and his collaborators have called the ``yellow void.'' We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long-slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double-peaked H? emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and mass-loss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently, the observed variations in apparent spectral type and inferred temperature are changes in the wind and do not necessarily mean that the underlying stellar radius and interior structure are evolving on such a short timescale. To explain the evidence for simultaneous outflow and infall of material near the star, we propose a ``rain'' model, in which blobs of gas condense in regions of lowered opacity outside the dense wind. With the apparent warming of its wind, the recent appearance of strong emission, and a decline in the mass-loss rate, IRC +10420 may be about to shed its opaque wind, cross the yellow void, and emerge as a hotter star. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

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

2002-08-01

145

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

146

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

147

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

148

Constraining Star Formation: Low Mass Companions of 5 Msun Stars  

NASA Astrophysics Data System (ADS)

Creating a binary/multiple system during star formation is an effective way to manipulate angular momentum, an important ingredient in the process, leaving binary parameters as a fingerprint. We have surveyed 69 Cepheids with the Hubble Space Telescope Wide Field Camera 3 (WFC3) survey, and identified 39 possible low-mass companions to these 5 Msun supergiants, which have the surprising characteristic that there are approximately as many F-G dwarfs as K dwarfs. X-rays are the key to determining whether they are physical companions or chance alignments, and this proposal is a pilot X-ray project to identify genuine companions to test this.

Remage Evans, Nancy

2011-10-01

149

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

150

ON THE PERIODIC VARIABILITY OF THE LONGITUDINAL MAGNETIC FIELDS OF STARS  

SciTech Connect

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

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

2013-10-01

151

A NEW DISTANCE TO M33 USING BLUE SUPERGIANTS AND THE FGLR METHOD  

SciTech Connect

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

U, Vivian; Urbaneja, Miguel A.; Kudritzki, Rolf-Peter; Jacobs, Bradley A.; Bresolin, Fabio [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Przybilla, Norbert, E-mail: vivian@ifa.hawaii.ed, E-mail: urbaneja@ifa.hawaii.ed, E-mail: kud@ifa.hawaii.ed, E-mail: bjacobs@ifa.hawaii.ed, E-mail: bresolin@ifa.hawaii.ed, E-mail: przybilla@sternwarte.uni-erlangen.d [Dr. Remeis-Sternwarte Bamberg, Sternwartstrasse 7, D-96049 Bamberg (Germany)

2009-10-20

152

ASPHERICAL CORE-COLLAPSE SUPERNOVAE IN RED SUPERGIANTS POWERED BY NONRELATIVISTIC JETS  

SciTech Connect

We explore the observational characteristics of jet-driven supernovae (SNe) by simulating bipolar-jet-driven explosions in a red supergiant (RSG) progenitor. We present results of four models in which we hold the injected kinetic energy at a constant 10{sup 51} erg across all jet models but vary the specific characteristics of the jets to explore the influence of the nature of jets on the structure of the SN ejecta. We evolve the explosions past shock-breakout and into quasi-homologous expansion of the SN envelope into a RSG wind. The simulations have sufficient numerical resolution to study the stability of the flow. Our simulations show the development of fluid instabilities that produce pristine helium clumps in the hydrogen envelope. The oppositely directed, nickel-rich jets give a large-scale asymmetry that may account for the nonspherical excitation and substructure of spectral lines such as H{alpha} and He I 10830 A. Jets with a large fraction of kinetic to thermal energy punch through the progenitor envelope and give rise to explosions that would be observed to be asymmetric from the earliest epochs, inconsistent with spectropolarimetric measurements of Type II SNe. Jets with higher thermal energy fractions result in explosions that are roughly spherical at large radii but are significantly elongated at smaller radii, deep inside the ejecta, in agreement with the polarimetric observations. We present shock-breakout light curves that indicate that strongly aspherical shock breakouts are incompatible with recent Galaxy Evolution Explorer observations of shock breakout from RSG stars. Comparison with observations indicates that jets must deposit their kinetic energy efficiently throughout the ejecta while in the hydrogen envelope. Thermal-energy-dominated jets satisfy this criterion and yield many of the observational characteristics of Type II SNe.

Couch, Sean M.; Wheeler, J. Craig; Milosavljevic, Milos [Department of Astronomy, University of Texas, Austin, TX 78712 (United States)], E-mail: smc@astro.as.utexas.edu

2009-05-01

153

Massive stars as important contributors to two micron light  

E-print Network

Near infrared light at 2 micrometers is relatively insensitive to the presence of hot young stars and dust in galaxies, and there has been recent interest in using it as a mass tracer in spiral galaxies. I present evidence that young, cool supergiant stars, whose presence is indicated by strong CO absorption in a 2.36 micrometer bandpass, dominate the 2 micrometer light from active star forming regions in the galaxy NGC 1309. The galaxy's quiescent regions, in contrast, do not show evidence of young supergiants. It follows that the 2 micrometer light comes from different stellar populations in different places, and large changes in the 2 micrometer surface brightness need not imply correspondingly large features in the galaxy's mass distribution.

James E. Rhoads

1995-03-20

154

An Upper Mass Limit on a Red Supergiant Progenitor for the Type II-Plateau Supernova SN 2006my  

E-print Network

We analyze two pre-supernova (SN) and three post-SN high-resolution images of the site of the Type II-Plateau supernova SN 2006my in an effort to either detect the progenitor star or to constrain its properties. Following image registration, we find that an isolated stellar object is not detected at the location of SN 2006my in either of the two pre-SN images. In the first, an I-band image obtained with the Wide-Field and Planetary Camera 2 on board the Hubble Space Telescope, the offset between the SN 2006my location and a detected source ("Source 1") is too large: > 0.08", which corresponds to a confidence level of non-association of 96% from our most liberal estimates of the transformation and measurement uncertainties. In the second, a similarly obtained V-band image, a source is detected ("Source 2") that has overlap with the SN 2006my location but is definitively an extended object. Through artificial star tests carried out on the precise location of SN 2006my in the images, we derive a 3-sigma upper bound on the luminosity of a red supergiant that could have remained undetected in our pre-SN images of log L/L_Sun = 5.10, which translates to an upper bound on such a star's initial mass of 15 M_Sun from the STARS stellar evolutionary models. Although considered unlikely, we can not rule out the possibility that part of the light comprising Source 1, which exhibits a slight extension relative to other point sources in the image, or part of the light contributing to the extended Source 2, may be due to the progenitor of SN 2006my. Only additional, high-resolution observations of the site taken after SN 2006my has faded beyond detection can confirm or reject these possibilities.

Douglas C. Leonard; Avishay Gal-Yam; Derek B. Fox; P. B. Cameron; Erik M. Johansson; Adam L. Kraus; David Le Mignant; Marcos A. van Dam

2008-09-10

155

The blue supergiant Sher 25 and its intriguing hourglass nebula  

E-print Network

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

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

2008-01-01

156

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

157

PACS and SPIRE Spectroscopy of the Red Supergiant VY CMa  

E-print Network

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

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

2010-01-01

158

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

159

Life Cycle of Stars  

NASA Technical Reports Server (NTRS)

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

1999-01-01

160

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

SciTech Connect

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

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

2010-02-15

161

HUBBLE SNAPSHOT CAPTURES LIFE CYCLE OF STARS  

NASA Technical Reports Server (NTRS)

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

2002-01-01

162

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

163

Properties of the CO and H$_2$O MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observations  

E-print Network

Context. Betelgeuse is the closest red supergiant (RSG), therefore it is well suited to study the complex processes in its atmosphere that lead to the chemical enrichment of the interstellar medium. Aims. We intend to investigate the shape and composition of the close molecular layer (also known as the MOLsphere) that surrounds the star. This analysis is part of a wider program that aims at understanding the dynamics of the circumstellar envelope of Betelgeuse. Methods. On January and February 2011, Betelgeuse was observed using the VLTI/AMBER interferometer in the H and K bands. Using the medium spectral resolution of the instrument ($R \\sim 1500$), we were able to investigate the carbon monoxide band heads and the water-vapor bands. We used two different approaches to analyse our data: model fitting both in the continuum and absorption lines and then fit with a RHD simulation. Results. Using the continuum data we derive a uniform disk diameter of $41.01 \\pm 0.41$ mas, a power law type limb-darkened disk dia...

Montargès, Miguel; Perrin, Guy; Ohnaka, Keiichi; Chiavassa, Andrea; Ridgway, Stephen T; Lacour, Sylvestre

2014-01-01

164

The very rich massive post-main-sequence star population of the open cluster Westerlund 1  

E-print Network

We report the discovery of a population of Wolf-Rayet stars in the young Galactic open cluster Westerlund 1. In an incomplete shallow spectroscopic survey, we find six nitrogen-rich (WN) and five carbon-rich (WC) WR stars. We also confirm the presence of a large population of yellow supergiants, some of which are candidate hypergiants. Given this population, Westerlund 1 is likely to be one of the most massive young clusters in the Local Group.

Ignacio Negueruela; J. Simon Clark

2002-08-23

165

Two years of monitoring supergiant fast X-ray transients with Swift  

NASA Astrophysics Data System (ADS)

We present results based on 2 yr of intense Swift monitoring of three supergiant fast X-ray transients (SFXTs), IGR J16479-4514, XTE J1739-302 and IGR J17544-2619, which we started in 2007 October. Our out-of-outburst intensity-based X-ray (0.3-10 keV) spectroscopy yields absorbed power laws characterized by hard photon indices (?˜ 1 -2). The broad-band (0.3-150 keV) spectra of these sources, obtained while they were undergoing new outbursts observed during the second year of monitoring, can be fitted well with models typically used to describe the X-ray emission from accreting neutron stars in high-mass X-ray binaries. We obtain an assessment of how long each source spends in each state using a systematic monitoring with a sensitive instrument. By considering our monitoring as a casual sampling of the X-ray light curves, we can infer that the time these sources spend in bright outbursts is between 3 and 5 per cent of the total. The most probable X-ray flux for these sources is ˜(1 -2) × 10-11 erg cm-2 s-1 (2-10 keV, unabsorbed), corresponding to luminosities of the order of a few 1033 to a few 1034 erg s-1 (two orders of magnitude lower than the bright outbursts). In particular, the duty-cycle of inactivity is ˜19, 39 and 55 per cent (˜5 per cent uncertainty) for IGR J16479-4514, XTE J1739-302 and IGR J17544-2619, respectively. We present a complete list of BAT onboard detections, which further confirm the continued activity of these sources. This demonstrates that true quiescence is a rare state and that these transients accrete matter throughout their life at different rates. Variability in the X-ray flux is observed at all time-scales and intensity ranges we can probe. Superimposed on the day-to-day variability is intraday flaring, which involves flux variations up to one order of magnitude that can occur down to time-scales as short as ˜1 ks, and which can be naturally explained by the accretion of single clumps composing the donor wind with masses Mcl˜ (0.3 -2) × 1019 g. Thanks to the Swift observations, the general picture we obtain is that, despite individual differences, common X-ray characteristics of this class are now well defined, such as outburst lengths well in excess of hours, with a multiple peaked structure, and a high dynamic range (including bright outbursts), up to approximately four orders of magnitude.

Romano, P.; La Parola, V.; Vercellone, S.; Cusumano, G.; Sidoli, L.; Krimm, H. A.; Pagani, C.; Esposito, P.; Hoversten, E. A.; Kennea, J. A.; Page, K. L.; Burrows, D. N.; Gehrels, N.

2011-01-01

166

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

167

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

SciTech Connect

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

Messineo, Maria [European Space Agency (ESA), The Astrophysics and Fundamental Physics Missions Division, Research and Scientific Support Department, Directorate of Science and Robotic Exploration, ESTEC, Postbus 299, 2200 AG Noordwijk (Netherlands); Davies, Ben; Figer, Donald F.; Trombley, Christine [Center for Detectors, Rochester Institute of Technology, 74 Lomb Memorial Drive, Rochester, NY 14623 (United States); Kudritzki, R. P. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Valenti, Elena [European Southern Observatory, Karl Schwarzschild-Strasse 2, D-85748 Garching bei Munchen (Germany); Najarro, F. [Centro de Astrobiologia (CSIC-INTA), Ctra. de Torrejon a Ajalvir km4, 28850, Torrejonde Ardoz, Madrid (Spain); Michael Rich, R., E-mail: messineo@mpifr-bonn.mpg.de [Physics and Astronomy Building, 430 Portola Plaza, Box 951547, Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States)

2011-05-20

168

Cold Dust in Three Massive Evolved Stars in the LMC  

E-print Network

Massive evolved stars can produce large amounts of dust, and far-infrared (IR) data are essential for determining the contribution of cold dust to the total dust mass. Using Herschel, we search for cold dust in three very dusty massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red supergiant. We model the spectral energy distributions using radiative transfer codes and find that these three stars have mass-loss rates up to 10^-3 solar masses/year, suggesting that high-mass stars are important contributors to the life-cycle of dust. We found far-IR excesses in two objects, but these excesses appear to be associated with ISM and star-forming regions. Cold dust (T stars.

Boyer, M L; van Loon, J Th; Srinivasan, S; Clayton, G C; Kemper, F; Smith, L J; Matsuura, M; Woods, Paul M; Marengo, M; Meixner, M; Engelbracht, C; Gordon, K D; Hony, S; Indebetouw, R; Misselt, K; Okumura, K; Panuzzo, P; Riebel, D; Roman-Duval, J; Sauvage, M; Sloan, G C

2010-01-01

169

Long-Lasting X-Ray Emission from Type IIb Supernova 2011dh and Mass-Loss History of The Yellow Supergiant Progenitor  

E-print Network

Type IIb Supernova (SN) 2011dh, with conclusive detection of an unprecedented Yellow Supergiant (YSG) progenitor, provides an excellent opportunity to deepen our understanding on the massive star evolution in the final centuries toward the SN explosion. In this paper, we report on detection and analyses of thermal X-ray emission from SN IIb 2011dh at ~500 days after the explosion on Chandra archival data, providing a solidly derived mass loss rate of an YSG progenitor for the first time. We find that the circumstellar media (CSM) should be dense, more than that expected from a Wolf-Rayet (WR) star by one order of magnitude. The emission is powered by a reverse shock penetrating into an outer envelope, fully consistent with the YSG progenitor but not with a WR progenitor. The density distribution at the outermost ejecta is much steeper than that expected from a compact WR star, and this finding must be taken into account in modeling the early UV/optical emission from SNe IIb. The derived mass loss rate is 3 x ...

Maeda, Keiichi; Bamba, Aya; Terada, Yukikatsu; Fukazawa, Yasushi

2014-01-01

170

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

NASA Astrophysics Data System (ADS)

The advent of Swift has allowed, for the first time, the possibility to give supergiant fast X-ray transients (SFXTs), the new class of high-mass X-ray binaries discovered by the International Gamma-Ray Astrophysics Laboratory, non-serendipitous attention throughout most phases of their life. In this paper, we present our results based on the first year of intense Swift monitoring of four SFXTs, IGR J16479-4514, XTE J1739-302, IGR J17544-2619 and AX J1841.0-0536. We obtain the first assessment of how long each source spends in each state using a systematic monitoring with a sensitive instrument. The duty-cycle of inactivity is ~17, 28, 39 and 55 per cent (~5per cent uncertainty), for IGR J16479-4514, AX J1841.0-0536, XTE J1739-302 and IGR J17544-2619, respectively, so that true quiescence, which is below our detection ability even with the exposures we collected in 1 yr, is a rare state, when compared with estimates from less sensitive instruments. This demonstrates that these transients accrete matter throughout their lifetime at different rates. AX J1841.0-0536 is the only source which has not undergone a bright outburst during our monitoring campaign. Although individual sources behave somewhat differently, common X-ray characteristics of this class are emerging, such as outburst lengths well in excess of hours, with a multiple peaked structure. A high dynamic range (including bright outbursts) of ~4 orders of magnitude has been observed in IGR J17544-2619 and XTE J1739-302, of ~3 in IGR J16479-4514 and of about 2 in AX J1841.0-0536 (this lowest range is due to the lack of bright flares). We also present a complete list of Burst Alert Telescope (BAT) on-board detections, which complements our previous work, and further confirms the continuous activity of these sources. We performed out-of-outburst intensity-based spectroscopy. In particular, spectral fits with an absorbed blackbody always result in blackbody radii of a few hundred metres, consistent with being emitted from a small portion of the neutron star surface, very likely the neutron star polar caps. We used the whole BAT data set, since the beginning of the mission, to search for periodicities due to orbital motion and found Porb = 3.32d for IGR J16479-4514, confirming previous findings. We also present the Ultraviolet/Optical Telescope (UVOT) data of these sources; we show the UVOT light curves of AX J1841.0-0536 and the ones of XTE J1739-302 before, during and after the outbursts.

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

2009-11-01

171

The pulsations and potential for seismology of B stars  

E-print Network

We review the nature of the oscillations of main-sequence and supergiant stars of spectral type B. Seismic tuning of the interior structure parameters of the $\\beta $Cep stars has been achieved since three years. The results are based on frequencies derived from long-term monitoring and progress in this area is rapid. Oscillations in mid-B stars as well as Be stars are well established by now, but we lack good mode identification to achieve seismic modelling. We provide recent evidence of g-mode pulsations in supergiant B stars. The spherical wavenumbers of their modes are yet unidentified, preventing seismic probing of such evolved hot stars at present. Improving the situation for the three groups of g-mode oscillators requires multi-site long-term high-resolution spectroscopy in combination with either space photometry or ground-based multicolour photometry. The CoRoT programme and its ground-based programme will deliver such data in the very near future.

C. Aerts

2006-11-13

172

Observation of winds in cool stars  

NASA Technical Reports Server (NTRS)

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

Dupree, A. K.

1983-01-01

173

Maps of the Molecular Emission Around 18 Evolved Stars  

E-print Network

We present maps at $20''$ resolution of the molecular emission around 18 evolved stars (14~asymptotic giant branch stars, one supergiant, two proto-planetary nebulae and one planetary nebula), mostly in the $^{12}$CO(3-2) line. Almost all molecular envelopes appear to be at least marginally resolved at this resolution. A substantial fraction of the molecular envelopes show clear deviations from spherical symmetry in the form of elliptical or bipolar envelopes. This indicates that there is a need to implement non-spherical mass loss in current scenarios of the late stages of stellar evolution, in particular on the asymptotic giant branch.

K. Z. Stanek; G. R. Knapp; K. Young; T. G. Phillips

1994-12-02

174

The population of M-type supergiants in the starburst cluster Stephenson 2  

NASA Astrophysics Data System (ADS)

The open cluster Stephenson 2 contains the largest collection of red supergiants known in the Galaxy, and at present is the second most massive young cluster known in the Milky Way. We have obtained multi-epoch, intermediate-resolution spectra around the Ca ii triplet for more than 30 red supergiants in Stephenson 2 and its surroundings. We find a clear separation between a majority of RSGs having spectral types M0-M2 and the brightest members in the NIR, which have very late spectral types and show strong evidence for heavy mass loss. The distribution of spectral types is similar to that of RSGs in other clusters, such as NGC 7419, or associations, like Per OB1. The cluster data strongly support the idea that heavy mass loss and maser emission is preferentially associated with late-M spectral types, suggesting that they represent an evolutionary phase.

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

2013-05-01

175

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

176

Line blocking factors in the ultraviolet spectra of 35 B6 to A0 stars  

NASA Technical Reports Server (NTRS)

Observed line-blocking factors for stars of spectral types B6 to A0 are presented which were measured on spectral tracings observed over the wavelength ranges from 2064 to 2158 A, 2496 to 2590 A, and 2775 to 2867 A with the S 59 spectrometer on the ESRO TD 1A satellite. Twenty-six stars having normal spectra were observed along with 12 stars having abnormal spectra. The results for normal and abnormal stars are compared to determine the changes in line blocking related to each type of spectral peculiarity. Detailed descriptions are given of the line-blocking factors in different spectral channels for a B8 supergiant, three Be stars, a shell star, two eclipsing binaries, an Hg-Mn star, and several peculiar B and A stars.

Underhill, A. B.; Van Der Hucht, K. A.

1977-01-01

177

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

178

SUPERGIANT SHELLS AND MOLECULAR CLOUD FORMATION IN THE LARGE MAGELLANIC CLOUD  

SciTech Connect

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

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

2013-01-20

179

Evolved star water maser cloud size determined by star size  

E-print Network

Cool, evolved stars undergo copious mass loss but the details of how the matter is returned to the ISM are still under debate. We investigated the structure and evolution of the wind at 5 to 50 stellar radii from Asymptotic Giant Branch and Red Supergiant stars. 22-GHz water masers around seven evolved stars were imaged using MERLIN, at sub-AU resolution. Each source was observed at between 2 and 7 epochs (several stellar periods). We compared our results with long-term Pushchino single dish monitoring. The 22-GHz emission is located in ~spherical, thick, unevenly filled shells. The outflow velocity doubles between the inner and outer shell limits. Water maser clumps could be matched at successive epochs separated by <2 years for AGB stars, or at least 5 years for RSG. This is much shorter than the decades taken for the wind to cross the maser shell, and comparison with spectral monitoring shows that some features fade and reappear. In 5 sources, most of the matched features brighten or dim in concert from...

Richards, A M S; Gray, M D; Lekht, E E; Mendoza-Torres, J E; Murakawa, K; Rudnitskij, G; Yates, J A

2012-01-01

180

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

181

Oxygen Isotopic Ratios in Cool R Coronae Borealis Stars  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

182

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

183

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

NASA Astrophysics Data System (ADS)

Long gamma-ray bursts (LGRBs) have a typical duration of ~30 s, and some of them are associated with hypernovae, such as Type Ic SN 1998bw. Wolf-Rayet stars are the most plausible LGRB progenitors, since the free fall time of the envelope is consistent with the duration, and the natural outcome of the progenitor is a Type Ic SN. While a new population of ultra-long GRBs (ULGRBs), GRB 111209A, GRB 101225A, and GRB 121027A, has a duration of ~104 s, two of them are accompanied by superluminous-supernova-like (SLSN-like) bumps, which are <~ 10 times brighter than typical hypernovae. Wolf-Rayet progenitors cannot explain ULGRBs because of durations that are too long and SN-like bumps that are too bright. A blue supergiant (BSG) progenitor model, however, can explain the duration of ULGRBs. Moreover, SLSN-like bumps can be attributed to the so-called cocoon fireball photospheric emissions (CFPEs). Since a large cocoon is inevitably produced during the relativistic jet piercing though the BSG envelope, this component can be smoking gun evidence of the BSG model for ULGRBs. In this paper, we examine u-, g-, r-, i-, and J-band light curves of three ULGRBs and demonstrate that they can be fitted quite well by our BSG model with the appropriate choices of the jet opening angle and the number density of the ambient gas. In addition, we predict that for 121027A, SLSN-like bump could have been observed for ~20-80 days after the burst. We also propose that some SLSNe might be CFPEs of off-axis ULGRBs without visible prompt emissions.

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

2013-11-01

184

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

185

XTE J1739-302 as a Supergiant Fast X-ray Transient  

E-print Network

XTE J1739-302 is a transient X-ray source with unusually short outbursts, lasting on the order of hours. Here we give a summary of X-ray observations we have made of this object in outburst with the Rossi X-ray Timing Explorer (RXTE) and at a low level of activity with the Chandra X-ray Observatory, as well as observations made by other groups. Visible and infrared spectroscopy of the mass donor of XTE J1739-302 are presented in a companion paper. The X-ray spectrum is hard both at low levels and in outburst, but somewhat variable, and there is strong variability in the absorption column from one outburst to another. Although no pulsation has been observed, the outburst data from multiple observatories show a characteristic timescale for variability on the order of 1500-2000 s. The Chandra localization (right ascension 17h 39m 11.58s, declination -30o 20' 37.6'', J2000) shows that despite being located less than 2 degrees from the Galactic Center and highly absorbed, XTE J1739-302 is actually a foreground object with a bright optical counterpart. The combination of a very short outburst timescale and a supergiant companion is shared with several other recently-discovered systems, forming a class we designate as Supergiant Fast X-ray Transients (SFXTs). Three persistently bright X-ray binaries with similar supergiant companions have also produced extremely short, bright outbursts: Cyg X-1, Vela X-1, and 1E 1145.1-6141.

D. M. Smith; W. A. Heindl; C. B. Markwardt; J. H. Swank; I. Negueruela; T. E. Harrison; L. Huss

2005-10-21

186

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

187

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

188

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

189

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

190

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

191

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

2006-04-05

192

Massive star evolution and SN 1987A  

NASA Technical Reports Server (NTRS)

The evolution of massive stars through hydrogen and helium burning is addressed. A set of stellar evolutionary sequences for mass/solar mass of 15, 20, and 25, and metallicity of 0.002, 0.005, 0.007, 0.010, and 0.20 are presented; semiconvection is restricted to operating slower than the local thermal time scale. Using these sequences, simple models of the massive star content of the LMC are found to agree moderately well with the new observational data of Fitzpatrick and Garmany (1990). LMC supergiants were detected only in their postmain-sequence phases, so that 5-10 times more massive stars are there but not identified as such. It is argued that SN 1987A exhibits the normal evolution of a single star of about 20 solar mases having LMC abundances. Despite the variety of envelope behavior, the structure of the core at collapse is rather similar for the stars of a given mass. Variations due to different rates of mass loss are likely to be larger than those due to composition.

Arnett, David

1991-01-01

193

VizieR Online Data Catalog: Catalogue of Late-type Stars with Maser Emission (Engels, 1979)  

NASA Astrophysics Data System (ADS)

The systematic literature search is complete up to January 1, 1979. The catalogue ends with a reference list containing all objects followed by a code number and a list containing the literature belonging to each code number. The literature cited for each object contains all data used, except data from the general catalogue of variable stars, the two-micron sky survey and the AFCRL infrared sky survey. See the source reference for additional information. The catalogued stars are divided in six groups M-supergiant stars Type I OH/IR stars Type II OH/IR stars H2O/IR stars without detected OH-emission SiO/IR stars Objects undetected in the optical or infrared (6 data files).

Engels, D.

1995-11-01

194

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

E-print Network

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, disk-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 I. Prominent spectral features, such as the Brackett gamma 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 LBV candidate (MWC314), one supergiant B[e] candidate with 13CO (MWC137) and in two cases (MWC623 and AS 381) indications for th...

Liermann, A; Kraus, M; Kreplin, A; Arias, M L; Cidale, L S

2014-01-01

195

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

196

Pulsations of B stars: A review of observations and theories  

SciTech Connect

The observational and theoretical status are discussed for several classes of variable B stars. The older classes now seem to be better understood in terms of those stars that probably have at least one radial mode and those that have only nonradial modes. The former are the ..beta.. Cephei variables, and the latter are the slowly rotating 53 Persei and the rapidly rotating zeta Ophiuchi variables. It seems that in this last class there are also some Be stars that show nonradial pulsations from the variations of the line shapes and their light. Among the nonradial pulsators, we must also include the supergiants which show pulsations with very short lifetimes. A review of the present observational and theoretical problems is given. The most persistent problem of the cause for the pulsations is briefly discussed, and many proposed mechanisms plus some new thoughts are presented. 57 refs., 4 figs.

Cox, A.N.

1986-01-01

197

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

NASA Technical Reports Server (NTRS)

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

Underhill, A. B.

1981-01-01

198

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

199

Extreme Helium Stars: Model Atmospheres and a NLTE analysis of BD+10°2179  

NASA Astrophysics Data System (ADS)

Extreme helium stars are hydrogen-deficient supergiants of spectral type A and B. They are believed to result from mergers in double degenerate systems, if one white dwarf is of C/O-type and the other of He-type. We calculate a new grid of model atmospheres accounting for metal line blanketing with ATLAS12 and compare it to the benchmark code STERNE. Synthetic spectra are calculated accounting for NLTE effects for many ions and applied to high-quality optical spectra of the prototype extreme helium star BD+10°2179.

Kupfer, T.; Heber, U.; Przybilla, N.; Jeffery, C. S.; Behara, N. T.; Butler, K.

2010-11-01

200

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

E-print Network

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

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

2006-12-20

201

On the massive stellar population of the Super Star Cluster Westerlund 1  

E-print Network

We present new spectroscopic and photometric observations of the young Galactic open cluster Westerlund 1 (Wd 1) that reveal a unique population of massive evolved stars. We identify ~200 cluster members and present spectroscopic classifications for ~25% of these. We find that all stars so classified are unambiguously post-Main Sequence objects, consistent with an apparent lack of an identifiable Main Sequence in our photometric data to V~20. We are able to identify rich populations of Wolf Rayet stars, OB supergiants and short lived transitional objects. Of these, the latter group consists of both hot (Luminous Blue Variable and extreme B supergiants) and cool (Yellow Hypergiant and Red Supergiant) objects - we find that half the known Galactic population of YHGs resides within Wd1. We obtain a mean V-M_V ~25 mag from the cluster Yellow Hypergiants, implying a Main Sequence turnoff at or below M_V =-5 (O7 V or later). Based solely on the masses inferred for the 53 spectroscopically classified stars, we determine an absolute minimum mass of \\~1.5 x 10^3 Msun for Wd 1. However, considering the complete photometrically and spectroscopically selected cluster population and adopting a Kroupa IMF we infer a likely mass for Wd 1 of ~10^5 Msun, noting that inevitable source confusion and incompleteness are likely to render this an underestimate. As such, Wd 1 is the most massive compact young cluster yet identified in the Local Group, with a mass exceeding that of Galactic Centre clusters such as the Arches and Quintuplet. Indeed, the luminosity, inferred mass and compact nature of Wd 1 are comparable with those of Super Star Clusters - previously identified only in external galaxies - and is consistent with expectations for a Globular Cluster progenitor.

J. S. Clark; I. Negueruela; P. A. Crowther; S. P. Goodwin

2005-04-15

202

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

203

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

NASA Technical Reports Server (NTRS)

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

Stothers, R.; Frogel, J. A.

1974-01-01

204

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

205

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

206

Radiative Transfer Modeling of the Winds and Circumstellar Environments of Hot and Cool Massive Stars  

NASA Astrophysics Data System (ADS)

We present modeling research work of the winds and circumstellar environments of a variety of prototypical hot and cool massive stars using advanced radiative-transfer calculations. This research aims at unraveling the detailed physics of various mass-loss mechanisms of luminous stars in the upper portion of the H-R diagram. Very recent 3D radiative-transfer calculations, combined with hydrodynamic simulations, show that radiatively-driven winds of OB supergiants are structured due to large-scale density and velocity fields caused by rotating bright spots at the stellar equator. The mass-loss rates computed from matching Discrete Absorption Components (DACs) in IUE observations of HD 64760 (B Ib) do not reveal appreciable changes from the rates of unstructured (smooth) wind models. Intermediate yellow supergiants (such as the yellow hypergiant ? Cas, F-G Ia0), on the other hand, show prominent spectroscopic signatures of strongly increased mass-loss rates during episodic outbursts that cause dramatic changes of the stellar photospheric conditions. Long-term high-resolution spectroscopic monitoring of cool hypergiants near the Yellow Evolutionary Void reveals that their mass-loss rates and wind-structure are dominated by photospheric eruptions and large-amplitude pulsations that impart mechanical momentum to the circumstellar environment by propagating acoustic (shock) waves. In massive red supergiants, however, clear evidence for mechanical wave propagation from the sub-photospheric convection zones is lacking, despite their frequently observed spectroscopic and photometric variability. Recent spatially resolved HST-STIS observations inside Betelgeuse's (M Iab) very extended chromosphere and dust envelope show evidence of warm chromospheric gas far beyond the dust-condensation radius of radiative-transfer models. Models for these long-term spectroscopic observations demonstrate that the chromospheric pulsations are not spherically symmetric. The STIS observations point to the importance of mechanical wave propagation for heating and sustaining chromospheric conditions in the extended winds of red supergiants.

Lobel, A.

2010-06-01

207

OXYGEN ISOTOPIC RATIOS IN COOL R CORONAE BOREALIS STARS  

SciTech Connect

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

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

2010-05-01

208

New very massive stars in Cygnus OB2  

E-print Network

The compact association Cygnus OB2 is known to contain a large population of massive stars, but its total mass is currently a matter of debate. While recent surveys have uncovered large numbers of OB stars in the area around Cyg OB2, detailed study of the optically brightest among them suggests that most are not part of the association. We observed an additional sample of optically faint OB star candidates, with the aim of checking if more obscured candidates are correspondingly more likely to be members of Cyg OB2. Low resolution spectra of 9 objects allow the rejection of one foreground star and the selection of four O-type stars, which were later observed at higher resolution. In a subsequent run, we observed three more stars in the classification region and three other stars in the far red. We identify five (perhaps six) new evolved very massive stars and three main sequence O-type stars, all of which are likely to be members of Cyg OB2. The new findings allow a much better definition of the upper HR diagram, suggesting an age ~2.5Myr for the association and hinting that the O3-5 supergiants in the association are blue stragglers, either younger or following a different evolutionary path from other cluster members. Though the bulk of the early stars seems to belong to an (approximately) single-age population, there is ample evidence for the presence of somewhat older stars at the same distance. Our results suggest that, even though Cyg OB2 is unlikely to contain as many as 100 O-type stars, it is indeed substantially more massive than was thought prior to recent infrared surveys.

Ignacio Negueruela; Amparo Marco; Artemio Herrero; Simon Clark

2008-06-17

209

Stars and Star Myths.  

ERIC Educational Resources Information Center

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

Eason, Oliver

210

1-D Imaging of the Dynamical Atmosphere of the Red Supergiant Betelgeuse in the CO First Overtone Lines with VLTI/AMBER  

NASA Astrophysics Data System (ADS)

We present high-spatial and high-spectral resolution observations of the red supergiant Betelgeuse in the CO first overtone lines near 2.3?m with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). Our AMBER observations in 2008 spatially resolved the gas motions in a stellar atmosphere (photosphere and extended molecular outer atmosphere) for the first time other than the Sun. From our second observations one year later, we have reconstructed 1-D images in the individual CO lines with an angular resolution of 9.8 mas and a spectral resolution of 6000 by applying the self-calibration technique to restore the Fourier phase from the differential phase measurements. The reconstructed 1-D images reveal that the star appears different in the blue and red wing of the individual CO lines. In the blue wing, the star shows a pronounced, asymmetrically extended component at least up to 1.3 R?, while such a component does not appear in the red wing 1-D image. This can be explained by a model in which the CO gas patch (or clump) more than half as large as the star is moving slightly outward with 0–5 km s-1, while the gas in the remaining region is infalling fast with 20–30 km s-1. Comparison between the CO line data taken in 2008 and 2009 shows a significant time variation in the dynamics of the photosphere and outer atmosphere. However, the 1-D images in the continuum show only a slight deviation from a limb-darkened disk with an angular diameter of 42.49±0.06 mas, which leads to an effective temperature of 3690± 54 K. Moreover, the continuum data taken in 2008 and 2009 reveal no or only marginal time variations, much smaller than the maximum variation predicted by the current 3-D convection simulation. The derived continuum diameter also shows that the near-IR size of Betelgeuse has been nearly constant over the last 18 years, in marked contrast to the recently reported noticeable decrease in the mid-IR size.

Ohnaka, K.

2014-09-01

211

Red-Eye Astronomy: 15 Years of V-band and Near-IR Tio Photometry of the Red Supergiants Alpha Orionis And TV Geminorum.  

NASA Astrophysics Data System (ADS)

V-band and narrow to intermediate-band Wing TiO-band (719 nm, 754 nm), and near-IR 1024 nm pseudo-bolometric photometric observations of the SRc M2 Iab supergiants Alpha Orionis and TV Geminorum have been conducted for the past 15 years. The goals are to monitor brightness and temperature-dependent TiO-band variations, ascertain any resulting periodicities and amplitudes, and estimate variations of basic stellar parameters such as temperature, luminosity, and radius. Preliminary results for both stars indicate similar long-term V-mag periods of 6.5 years with imposed shorter-term V-mag periods of 1.2 years. The V-magnitude amplitudes were 0.8 for Alpha Ori and 1.3 for TV Gem. For both stars the temperature and luminosity variations correlate well with the V-mag changes. However, inverse radii correlations with respect to temperature and luminosity variations were not seen in either star. In Alpha Ori the the radii changes were approximately in direct correlation with the temperature and luminosity changes. In TV Gem there was a combination of correlation/inverse correlation effects. Causes for these variations are speculative, but may be due to highly convective super-granulations occurring at irregular intervals rather than fundamental mode pulsation or harmonic oscillations. Based in part on an updated RSG temperature scale and a new VLA/Hipparchos distance estimate (197 PC), the Alpha Ori temperatures ranged from 3550 K to 3730 K, with ranges in solar luminosities and radii of L = 90,000 to 115,000 and R = 760 to 820, respectively. The slightly more dynamical TV Gem underwent temperature variations from 3500 K to 3850 K with ranges in solar luminosity and radii of L = 65,000 to 90,000 and R = 620 to 720 respectively. Discussions of the observations, data reduction methods, and analysis of the data will be presented. This research is supported by NASA grant NNX10AI85G and NSF grants AST 10-09903 and AST 05-07542.

Wasatonic, Richard P.; Guinan, E.; Engle, S.

2011-05-01

212

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

213

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

214

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

215

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

216

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

217

On the evolutionary stage of the unclassified B[e] star CD-42o11721  

E-print Network

The star CD-42o11721 is a curious B[e] star sometimes pointed as an evolved B[e] supergiant and sometimes as a young HAeBe star, due to very uncertain or even unknown stellar parameters, especially the distance. In this paper, we present new data gained from high-resolution optical spectroscopy and a detailed description of IR data of this star. We present a qualitative study of the numerous emission lines in our optical spectra and the classification of their line profiles, which indicate a non-spherically symmetric circumstellar environment. The first real detection of numerous [Fe II] emission lines and of many other permitted and forbidden emission lines is reported. From our optical data, we derive an effective temperature of 14000 K, a radius of 17.3 +/- 0.6 Rsun, as well as a luminosity of 1.0 +/- 0.3 x 10^{4} Lsun. We advocate that CD-42o11721 might be a post-main sequence object, even though a pre-main sequence nature cannot be ruled out due to the uncertain distance. We further found that the SED in the optical and infrared can best be fitted with an outflowing disk-forming wind scenario rather than with a spherical symmetric envelope or with a flared disc, supporting our tentative classification as a B[e] supergiant.

Marcelo Borges Fernandes; Michaela Kraus; Silvia Lorenz Martins; Francisco X. de Araujo

2007-03-22

218

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

219

Combining observational techniques to constrain convection in evolved massive star models  

E-print Network

Recent stellar evolution computations indicate that massive stars in the range ~ 20 - 30 Msun 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 (alpha 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 r...

Georgy, C; Meynet, G

2014-01-01

220

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

221

The VLT-FLAMES survey of massive stars: atmospheric parameters and rotational velocity distributions for B-type stars in the Magellanic Clouds  

E-print Network

We provide atmospheric parameters and rotational velocities of a large sample (~400) of O- and early B-type stars, analysed in a homogeneous and consistent manner, for use in constraining theoretical models. Comparison of the rotational velocities with evolutionary tracks suggest that the end of core hydrogen burning occurs later than currently predicted. We also show that the large number of the luminous blue supergiants observed in the fields are unlikely to have directly evolved from main-sequence massive O-type stars as neither their low rotational velocities or position on the H-R diagram are predicted. We suggest that blue-loops or mass-transfer binary systems may populate the blue supergiant regime. By comparing the rotational velocity distributions of the Magellanic Cloud stars to a similar Galactic sample we find that (at 3sigma confidence level) massive stars (above 8Msun) in the SMC rotate faster than those in the solar neighbourhood. However there appears to be no significant difference between the rotational velocity distributions in the Galaxy and the LMC. We find that the vsini distributions in the SMC and LMC can modelled with an intrinsic rotational velocity distribution which is a Gaussian peaking at 175km/s (SMC) and 100km/s (LMC). We find that in NGC346 in the SMC, the 10-25Msun main-sequence stars appear to rotate faster than their higher mass counterparts. Recently Yoon et al. (2006) have determined rates of GRBs by modelling rapidly rotating massive star progenitors. Our measured rotational velocity distribution for the 10-25Msun stars is peaked at slightly higher velocities than they assume, supporting the idea that GRBs could come from rapid rotators with initial masses as low as 14Msun at low metallicities. (abridged).

I. Hunter; D. J. Lennon; P. L. Dufton; C. Trundle; S. Simon-Diaz; S. J. Smartt; R. S. I. Ryans; C. J. Evans

2007-11-14

222

Sharp Vision Reveals Intimacy of Stars  

NASA Astrophysics Data System (ADS)

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

2005-11-01

223

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

224

Evolution of massive stars in very young clusters and associations  

NASA Technical Reports Server (NTRS)

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

Stothers, R. B.

1985-01-01

225

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

NASA Astrophysics Data System (ADS)

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

Mcley, Liron; Soker, Noam

2014-05-01

226

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

227

Stochastic accretion and the variability of supergiant fast X-ray transients  

E-print Network

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 the accretion of a single clump, and derive a stochastic differential equation (SDE) for the accretion powered luminosity $L(t)$. We put the SDE in the equivalent form of an equation for the flares' luminosity distribution (FLD), and discuss its solution in the stationary case. As a case study, we apply our formalism to the analysis of the FLDs of Super-Giant Fast X-ray Transients (SFXTs), a peculiar sub-class of High Mass X-ray Binary Systems (HMXBs). 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 fairly agrees with the observed distributions, and allows to predict some properties of the stellar wind. Finally, we discus...

Pizzolato, Fabio

2012-01-01

228

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

229

NUCLEOSYNTHESIS AND EVOLUTION OF MASSIVE METAL-FREE STARS  

SciTech Connect

The evolution and explosion of metal-free stars with masses 10-100 M{sub sun} are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. Such stars would have been the first to form after the big bang and may have left a distinctive imprint on the composition of the early universe. When the supernova yields are integrated over a Salpeter initial mass function (IMF), the resulting elemental abundance pattern is qualitatively solar, but with marked deficiencies of odd-Z elements with 7 {<=} Z {<=} 13. Neglecting the contribution of the neutrino wind from the neutron stars that they form, no appreciable abundances are made for elements heavier than germanium. The computed pattern compares favorably with what has been observed in metal-deficient stars with [Z] {approx}< -3. The amount of ionizing radiation from this generation of stars is {approx}2.16 MeV per baryon (4.15 B per M{sub sun}; where 1 B = 1 Bethe = 10{sup 51} erg) for a Salpeter IMF, and may have played a role in reionizing the universe. Neglecting rotation, most of the stars end their lives as blue supergiants and form supernovae with distinctive light curves resembling SN 1987A, but some produce primary nitrogen due to dredge-up and become red supergiants. These make brighter supernovae like typical Type IIp's. For the lower mass supernovae considered, the distribution of remnant masses clusters around typical modern neutron star masses, but above 20-30 M{sub sun}, with the value depending on explosion energy, black holes are copiously formed by fallback, with a maximum hole mass of {approx}40 M{sub sun}. A novel automated fitting algorithm is developed for determining optimal combinations of explosion energy, mixing, and IMF in the large model database to agree with specified data sets. The model is applied to the low-metallicity sample of Cayrel et al. and the two ultra-iron-poor stars HE0107-5240 and HE1327-2326. Best agreement with these very low metallicity stars is achieved with very little mixing, and none of the metal-deficient data sets considered show the need for a high-energy explosion component. In contrast, explosion energies somewhat less than 1.2 B seem to be preferred in most cases.

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

2010-11-20

230

The MiMeS Survey of Magnetism in Massive Stars: CNO surface abundances of Galactic O stars  

E-print Network

The evolution of massive stars is still partly unconstrained. Mass, metallicity, mass loss and rotation are the main drivers of stellar evolution. Binarity and magnetic field may also significantly affect the fate of massive stars. Our goal is to investigate the evolution of single O stars in the Galaxy. For that, we use a sample of 74 objects comprising all luminosity classes and spectral types from O4 to O9.7. We rely on optical spectroscopy obtained in the context of the MiMeS survey of massive stars. We perform spectral modelling with the code CMFGEN. We determine the surface properties of the sample stars, with special emphasis on abundances of carbon, nitrogen and oxygen. Most of our sample stars have initial masses in the range 20 to 50 Msun. We show that nitrogen is more enriched and carbon/oxygen more depleted in supergiants than in dwarfs, with giants showing intermediate degrees of mixing. CNO abundances are observed in the range of values predicted by nucleosynthesis through the CNO cycle. More ma...

Martins, F; Bouret, J -C; Marcolino, W; Wade, G A; Neiner, C; Alecian, E; Grunhut, J; Petit, V

2014-01-01

231

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

232

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

233

The Massive Star Content of NGC 3603  

NASA Astrophysics Data System (ADS)

We investigate the massive star content of NGC 3603, the closest known giant H II region. We have obtained spectra of 26 stars in the central cluster using the Baade 6.5 m telescope (Magellan I). Of these 26 stars, 16 had no previous spectroscopy. We also obtained photometry of all of the stars with previous or new spectroscopy, primarily using archival HST Advanced Camera for Surveys/High-Resolution Camera images. The total number of stars that have been spectroscopically classified in NGC 3603 now stands at 38. The sample is dominated by very early O-type stars (O3); there are also several (previously identified) H-rich WN+abs stars. We derive E(B - V) = 1.39, and find that there is very little variation in reddening across the cluster core, in agreement with previous studies. Our spectroscopic parallax is consistent with the kinematic distance only if the ratio of total to selective extinction is anomalously high within the cluster, as argued by Pandey et al. Adopting their reddening, we derive a distance of 7.6 kpc. We discuss the various distance estimates to the cluster, and note that although there has been a wide range of values in the recent literature (6.3-10.1 kpc) there is actually good agreement with the apparent distance modulus of the cluster—the disagreement has been the result of the uncertain reddening correction. We construct our H-R diagram using the apparent distance modulus with a correction for the slight difference in differential reddening from star to star. The resulting H-R diagram reveals that the most massive stars are highly coeval, with an age of 1-2 Myr, and of very high masses (120 Msun). The three stars with Wolf-Rayet features are the most luminous and massive, and are coeval with the non-WRs, in accord with what was found in the R136 cluster. There may be a larger age spread (1-4 Myr) for the lower mass objects (20-40 Msun). Two supergiants (an OC9.7 I and the B1 I star Sher 25) both have an age of about 4 Myr. We compare the stellar content of this cluster to that of R136, finding that the number of very high luminosity (Mbol <= -10) stars is only about 1.1-2.4× smaller in NGC 3603. The most luminous members in both clusters are H-rich WN+abs stars, basically "Of stars on steroids," relatively unevolved stars whose high luminosities results in high-mass loss rates, and hence spectra that mimic that of evolved WNs. To derive an initial-mass function for the massive stars in NGC 3603 requires considerably more spectroscopy; we estimate from a color-magnitude diagram that less than a third of the stars with masses above 20 Msun have spectral types known. This paper is based on data gathered with the 6.5 m Magellan telescopes located at Las Campanas Observatory, Chile.

Melena, Nicholas W.; Massey, Philip; Morrell, Nidia I.; Zangari, Amanda M.

2008-03-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

235

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

236

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

237

Geological and geochemical controls on the formation and distribution of supergiant gas fields in the Russian sedimentary basins  

SciTech Connect

The West Siberian, Barents Sea and Northern Caspian sedimentary basins are the most prolific Russian gas producing regions and include 15 supergiant gas fields each of them content identified gas reserves between 1 x 10[sup 12] m[sup 3] to 11 x 10[sup 12] m[sup 3]. They are Urengoi, Yarnburg, Bovanenkov, Zapoljarnoye, Medvezhie, Charasavey, Kruzenshtern, N.Urengoi, S.Tambey, S.Russkoye, Rusanov, Shtockmanov, Lunin, Astrachan and Orenburg. The gas reserves in these basins exceed 70 x 10[sup 12] m[sup 3] and about 65% of them concentrated in supergiant fields. Among the geological prerequisites for largest gas accumulations note big size of trap (Urengoi 40x300 km[sup 2]; Astrachan l80x200 km[sup 2]), anticline type of tectonic structure (swell, megaswell, dome, arch) with amplitude from 110 m to 800 in. These tectonic structure were active long time include the latest period. The main gas productive reservoirs are slightly consulted non-marine sandstones of Cenomanian or Middle Jurassic ages (West Siberia and Barents Sea) or Middle Carboniferous reef carbonate buildups (Northern Caspian basin). The next geochemical parameters controlled of the gas accumulation histories: (1) West Siberia and Barents Sea regions gas genetically connect with dispersed or concentrated non-marine coal type kerogen distributed into productive complex under lower maturity conditions (before or early oil window zone). This is dry gas almost pure methane with [delta][sup 13] C[sub 1] between -44,40[per thousand]. In this case we observe widely distributed mainly sandstones reservoirs at same time gas source rocks also; (2) the Northern Caspian basin found supergiant wet gas-condensate accumulations into local distributed reef carbonate buildups. Gas source rocks is marine kerogen type II, which has a low concentration in marlaceous facies. It is gas high maturity zone.

Lopatin, N. (VNIIgeosystem, Moscow (Russian Federation))

1996-01-01

238

Geological and geochemical controls on the formation and distribution of supergiant gas fields in the Russian sedimentary basins  

SciTech Connect

The West Siberian, Barents Sea and Northern Caspian sedimentary basins are the most prolific Russian gas producing regions and include 15 supergiant gas fields each of them content identified gas reserves between 1 x 10{sup 12} m{sup 3} to 11 x 10{sup 12} m{sup 3}. They are Urengoi, Yarnburg, Bovanenkov, Zapoljarnoye, Medvezhie, Charasavey, Kruzenshtern, N.Urengoi, S.Tambey, S.Russkoye, Rusanov, Shtockmanov, Lunin, Astrachan and Orenburg. The gas reserves in these basins exceed 70 x 10{sup 12} m{sup 3} and about 65% of them concentrated in supergiant fields. Among the geological prerequisites for largest gas accumulations note big size of trap (Urengoi 40x300 km{sup 2}; Astrachan l80x200 km{sup 2}), anticline type of tectonic structure (swell, megaswell, dome, arch) with amplitude from 110 m to 800 in. These tectonic structure were active long time include the latest period. The main gas productive reservoirs are slightly consulted non-marine sandstones of Cenomanian or Middle Jurassic ages (West Siberia and Barents Sea) or Middle Carboniferous reef carbonate buildups (Northern Caspian basin). The next geochemical parameters controlled of the gas accumulation histories: (1) West Siberia and Barents Sea regions gas genetically connect with dispersed or concentrated non-marine coal type kerogen distributed into productive complex under lower maturity conditions (before or early oil window zone). This is dry gas almost pure methane with {delta}{sup 13} C{sub 1} between -44,40{per_thousand}. In this case we observe widely distributed mainly sandstones reservoirs at same time gas source rocks also; (2) the Northern Caspian basin found supergiant wet gas-condensate accumulations into local distributed reef carbonate buildups. Gas source rocks is marine kerogen type II, which has a low concentration in marlaceous facies. It is gas high maturity zone.

Lopatin, N. [VNIIgeosystem, Moscow (Russian Federation)

1996-12-31

239

The Luminous Starburst Ring in NGC 7771: Sequential Star Formation?  

E-print Network

Only two of the twenty highly luminous starburst galaxies analyzed by Smith et al. exhibit circumnuclear rings of star formation. These galaxies provide a link between 10^11 L_sun systems and classical, less-luminous ringed systems. We report the discovery of a near-infrared counterpart to the nuclear ring of radio emission in NGC 7771. A displacement between the ~10 radio bright clumps and the ~10 near-infrared bright clumps indicates the presence of multiple generations of star formation. The estimated thermal emission from each radio source is equivalent to that of ~35000 O6 stars. Each near-infrared bright knot contains ~5000 red supergiants, on average. The stellar mass of each knot is estimated to be ~10^7 M_sun. The implied time-averaged star formation rate is \\~40 M_sun per yr. Several similarities are found between the properties of this system and other ringed and non-ringed starbursts. Morphological differences between NGC 7771 and the starburst + Seyfert 1 galaxy NGC 7469 suggest that NGC 7771 may not be old enough to fuel an AGN, or may not be capable of fueling an AGN. Alternatively, the differences may be unrelated to the presence or absence of an AGN and may simply reflect the possibility that star formation in rings is episodic.

Denise A. Smith; Terry Herter; Martha P. Haynes; Susan G. Neff

1998-08-28

240

Sea Stars  

NSDL National Science Digital Library

At first glance, starfish, more properly called sea stars, arenât doing much of anything. In this video, Jonathanâs 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.

Productions, Jonathan B.

2010-10-06

241

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

242

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

243

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

244

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

245

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

NASA Technical Reports Server (NTRS)

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

Linsky, J. L.

1981-01-01

246

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

SciTech Connect

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

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

2010-07-15

247

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

SciTech Connect

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

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

2012-03-10

248

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

SciTech Connect

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

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

2010-02-20

249

Near-IR spectroscopic ages of massive star clusters in M82  

E-print Network

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

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

2008-12-29

250

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

251

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

252

Ultraviolet spectroscopy of the brightest supergiants in M31 and M33  

NASA Technical Reports Server (NTRS)

Ultraviolet spectroscopy from the IUE, in combination with groundbased visual and infrared photometry, are to determine the energy distributions of the luminous blue variables, the Hubble-Sandage variables, in M31 and M33. The observed energy distributions, especially in the ultraviolet, show that these stars are suffering interstellar reddening. When corrected for interstellar extinction, the integrated energy distributions yield the total luminosities and black body temperatures of the stars. The resulting bolometric magnitudes and temperatures confirm that these peculiar stars are indeed very luminous, hot stars. They occupy the same regions of the sub B01 vs. log T sub e diagram as do eta Car, P Cyg and S Dor in our galaxy and the LMC. Many of the Hubble-Sandage variables have excess infrared radiation which is attributed to free-free emission from their extended atmospheres. Rough mass loss estimates from the infrared excess yield rates of 0.00001 M sub annual/yr. The ultraviolet spectra of the H-S variables are also compared with similar spectra of eta Car, P Cyg and S For.

Humphreys, R. M.; Blaha, C.; Dodorico, S.; Gull, T. R.; Benevenuti, P.

1983-01-01

253

The VLT-FLAMES survey of massive stars: rotation and nitrogen enrichment as the key to understanding massive star evolution  

E-print Network

Rotation has become an important element in evolutionary models of massive stars, specifically via the prediction of rotational mixing. Here, we study a sample of stars, including rapid rotators, to constrain such models and use nitrogen enrichments as a probe of the mixing process. Chemical compositions (C, N, O, Mg and Si) have been estimated for 135 early B-type stars in the Large Magellanic Cloud with projected rotational velocities up to ~300km/s using a non-LTE TLUSTY model atmosphere grid. Evolutionary models, including rotational mixing, have been generated attempting to reproduce these observations by adjusting the overshooting and rotational mixing parameters and produce reasonable agreement with 60% of our core hydrogen burning sample. We find (excluding known binaries) a significant population of highly nitrogen enriched intrinsic slow rotators vsini less than 50km/s incompatible with our models ~20% of the sample). Furthermore, while we find fast rotators with enrichments in agreement with the models, the observation of evolved (log g less than 3.7dex) fast rotators that are relatively unenriched (a further ~20% of the sample) challenges the concept of rotational mixing. We also find that 70% of our blue supergiant sample cannot have evolved directly from the hydrogen burning main-sequence. We are left with a picture where invoking binarity and perhaps fossil magnetic fields are required to understand the surface properties of a population of massive main sequence stars.

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

2007-11-14

254

Neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars are laboratories for dense matter and gravitational physics. Observations of neutron stars from sources such as radio pulsars, low-mass X-ray binaries, X-ray bursts and thermally-emitting neutron stars are setting bounds to neutron star masses, radii, rotation rates, temperatures and ages. Mass measurements constrain the equation of state at the highest densities and set firm bounds to the highest possible density of cold matter. Radii constrain the equation of state in the vicinity of the nuclear saturation density and yield information about the density dependence of the nuclear symmetry energy. Laboratory measurements and theoretical studies of pure neutron matter are in remarkable agreement with observational bounds.

Lattimer, James M.

2014-05-01

255

Stars equilibrium  

NSDL National Science Digital Library

What causes the fusion reaction in a star's core? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to processes inside a star. Students read about the equilibrium process in a star, in which outward gas pressure equals inward gravitational pressure. Then, an interactive lab activity offers students the opportunity to predict temperature, pressure, and gravity changes that occur during equilibrium. The chemical reactions of the fusion process are presented, and more specific detailed reactions are available in a pop-up box. Student practice quizzes about the equilibrium process and pressure and gravity interactions inside the star are included, as are answers. Copyright 2005 Eisenhower National Clearinghouse

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

2003-01-01

256

Star fruit  

Microsoft Academic Search

The carambola or star fruit belongs to the Oxalidaceae family, species Averrhoa carambola. Slices cut in cross-section have the form of a star (Figure 1). It is believed to have originated in Ceylon and the Moluccas\\u000a but it has been cultivated in southeast Asia and Malaysia for many centuries. It is commonly grown in some provinces in southern\\u000a China, in

Miguel M. Neto; Ruither O. Carolino; Norberto P. Lopes; Norberto Garcia-Cairasco

257

HV2112, a Thorne-Zytkow Object or a Super Asymptotic Giant Branch Star  

E-print Network

The very bright red star HV2112 in the Small Magellanic Cloud could be a massive Thorne-Zytkow Object, a supergiant-like star with a degenerate neutron core. With its luminosity of over $10^5\\,\\rm L_\\odot$, it could also be a super asymptotic giant branch star, a star with an oxygen/neon core supported by electron degeneracy and undergoing thermal pulses with third dredge up. Both TZOs and SAGB stars are expected to be rare. Abundances of heavy elements in HV2112's atmosphere, as observed to date, do not allow us to distinguish between the two possibilities based on the latest models. Molybdenum and rubidium can be enhanced by both the irp-process in a TZO or by the s-process in SAGB stars. Lithium can be generated by hot bottom burning at the base of the convective envelope in either. HV2112's enhanced calcium could thus be the key determinant. A SAGB star is not able to synthesise its own calcium but it may be possible to produce this in the final stages of the process that forms a TZO, when the degenerate ...

Tout, Christopher A; Church, Ross P; Lau, Herbert H B

2014-01-01

258

Spitzer IRAC Observations of Star Formation in N159 in the LMC  

E-print Network

We present observations of the giant HII region complex N159 in the LMC using IRAC on the {\\it Spitzer Space Telescope}. One of the two objects previously identified as protostars in N159 has an SED consistent with classification as a Class I young stellar object (YSO) and the other is probably a Class I YSO as well, making these two stars the youngest stars known outside the Milky Way. We identify two other sources that may also be Class I YSOs. One component, N159AN, is completely hidden at optical wavelengths, but is very prominent in the infrared. The integrated luminosity of the entire complex is L $\\approx 9\\times10^6$L$_{\\odot}$, consistent with the observed radio emission assuming a normal Galactic initial mass function (IMF). There is no evidence for a red supergiant population indicative of an older burst of star formation. The N159 complex is 50 pc in diameter, larger in physical size than typical HII regions in the Milky Way with comparable luminosity. We argue that all of the individual components are related in their star formation history. The morphology of the region is consistent with a wind blown bubble $\\approx 1-2Myr-old that has initiated star formation now taking place at the rim. Other than its large physical size, star formation in N159 appears to be indistinguishable from star formation in the Milky Way.

Terry J. Jones; Charles E. Woodward; Martha L. Boyer; Robert D. Gehrz; Elisha Polomski

2004-10-28

259

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

260

Spontaneous and Induced Star Formation in the LMC  

NASA Astrophysics Data System (ADS)

The Large Magellanic Cloud is the best site in the Universe to investigate star formation processes not connected with the spiral arms. This is because the galaxy is close, nearly pole-on, and has only a small depth on the line of sight (unlike the SMC). This give the best possible opportunity to learn about large-scale properties of star formation. Spontaneous star formation in turbulent gas implies hierarchical structure in the distribution of young stars. This is indeed observed as sequences of embedded young star groups, from mini-clusters to clusters to associations, aggregates, and complexes. Quantitative evidence for such a sequence is also present in the stellar ages, as follows from the data for the LMC clusters. The average age differences between clusters increases with their separation, from about 100 pc to 1000 pc throughout the LMC. From this we infer that the duration of star formation increases with the size of the region. The time - size relation also implies that the size of a young stellar group is determined by its age. This explains the characteristic size of an OB-association, which is always about ~80 pc because the age is about 10-15 Myrs. OB associations are only one level in a continuous hierarchy of structures. The Cepheids data with new period - age relation based on the same age scale as for the LMC clusters (with mild overshooting) display the similar separation - age difference relation, which is worse based statistically than this for clusters, however. There is at least one region in the LMC where triggered star formation has been suggested by many investigators: the Constellation III/LMC4 region. There has not been any agreement, though, on the mechanism of triggering and no age gradient has been found. We find that the 600 pc-long arc of young stars and clusters commonly called Constellation III was probably swept up by a central source of pressure that was associated with a visible cluster of six A-type supergiant stars having an age of ~30 My. The expansion of a bubble around these and other stars in the same cluster could have triggered the formation of the arc at the right time and place. The LMC4 superbubble and giant HI shell surround this arc, and probably formed by the continued expansion of the cavity following star formation in the arc and the associated new pressures. The whole situation is similar to that in Gould's Belt, where the old dispersed Cas-Tau association is considered to be the triggering event for the Lindblad ring and associated young stars in Orion, Perseus and Sco-Cen. Triggered shells and holes are so large in LMC-type galaxies because there is very little shear and the disk thickness is large. Also, the old idea on Super-SN explosion as the trigger of LMC4 supershell may be revived now, after indentification of GRBs, these events are able to produce supergiant shells and are plausibly in regions of star formation.

Efremov, Y. N.; Elmegreen, B. G.

261

Near-IR Spectroscopy and Population Synthesis of Super Star Clusters in NGC 1569  

E-print Network

We present H- and K-band NIRSPEC spectroscopy of super star clusters (SSCs) in the irregular starburst galaxy NGC 1569, obtained at the Keck Observatory. We fit these photospheric spectra to NextGen model atmospheres to obtain effective spectral types of clusters, and find that the information in both H- and K-band spectra is necessary to remove degeneracy in the fits. The light of SSC B is unambiguously dominated by K0 supergiants (T_eff=4400 +- 100 K, log g=0.5 +- 0.5). The double cluster SSC A has higher T_eff (G5) and less tightly constrained surface gravity (log g=1.3 +- 1.3), consistent with a mixed stellar population dominated by blue Wolf-Rayet stars and red supergiants. We predict the time evolution of infrared spectra of SSCs using Starburst99 population synthesis models coupled with empirical stellar spectral libraries (at solar metallicity). The resulting model sequence allows us to assign ages of 15-18 Myr for SSC B and 18-21 Myr for SSC A.

Andrea M. Gilbert; James R. Graham

2000-12-05

262

COMPUTING THE DUST DISTRIBUTION IN THE BOW SHOCK OF A FAST-MOVING, EVOLVED STAR  

SciTech Connect

We study the hydrodynamical behavior occurring in the turbulent interaction zone of a fast-moving red supergiant star, where the circumstellar and interstellar material collide. In this wind-interstellar-medium collision, the familiar bow shock, contact discontinuity, and wind termination shock morphology form, with localized instability development. Our model includes a detailed treatment of dust grains in the stellar wind and takes into account the drag forces between dust and gas. The dust is treated as pressureless gas components binned per grain size, for which we use 10 representative grain size bins. Our simulations allow us to deduce how dust grains of varying sizes become distributed throughout the circumstellar medium. We show that smaller dust grains (radius <0.045 {mu}m) tend to be strongly bound to the gas and therefore follow the gas density distribution closely, with intricate fine structure due to essentially hydrodynamical instabilities at the wind-related contact discontinuity. Larger grains which are more resistant to drag forces are shown to have their own unique dust distribution, with progressive deviations from the gas morphology. Specifically, small dust grains stay entirely within the zone bound by shocked wind material. The large grains are capable of leaving the shocked wind layer and can penetrate into the shocked or even unshocked interstellar medium. Depending on how the number of dust grains varies with grain size, this should leave a clear imprint in infrared observations of bow shocks of red supergiants and other evolved stars.

Van Marle, A. J.; Meliani, Z.; Keppens, R. [Centre for Plasma Astrophysics, K. U. Leuven, Celestijnenlaan 200B, Heverlee, B-3001 (Belgium); Decin, L. [Institute of Astronomy, K. U. Leuven, Celestijnenlaan 200D, Heverlee, B-3001 (Belgium)

2011-06-20

263

An Intermediate Luminosity Transient in NGC300: The Eruption of a Dust-Enshrouded Massive Star  

E-print Network

[abridged] We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC300. We find that the transient (NGC300 OT2008-1) has a peak absolute magnitude of M_bol~-11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km/s) hydrogen Balmer lines and CaII emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect broad CaII H&K absorption with an asymmetric red wing extending to ~1000 km/s, indicative of gas infall onto a massive and relatively compact star (blue supergiant or Wolf-Rayet star); an extended red supergiant progenitor is unlikely. The origin of the inflowing gas may be a previous eje...

Berger, E; Chevalier, R A; Fransson, C; Foley, R J; Leonard, D C; Debes, J H; Diamond-Stanic, A M; Dupree, A K; Ivans, I I; Simmerer, J; Thompson, I B; Tremonti, C A

2009-01-01

264

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

SciTech Connect

A detailed study of the blue supergiant UIT 005 (B2-2.5Ia{sup +}) in M 33 is presented. The results of our quantitative spectral analysis indicate that the star is a very luminous (log L/L{sub sun} {approx} 5.9 dex) and massive (M {approx} 50 M{sub sun}) object, showing a very high nitrogen-to-oxygen ratio in its surface (N/O{approx}8, by mass). Based on the derived Mg and Si abundances, we argue that this high N/O ratio cannot be the result of an initial low O content due to its location on the disk of M 33, a galaxy known to present a steep metallicity gradient. In combination with the He abundance, the most plausible interpretation is that UIT 005 is in an advanced stage of evolution, showing in its surface N enrichment and O depletion resulting from mixing with CNO processed material from the stellar interior. A comparison with the predictions of current stellar evolutionary models indicates that there are significant discrepancies, in particular with regard to the degree of chemical processing, with the models predicting a much lower degree of O depletion than observed. At the same time, the mass-loss rate derived in our analysis is an order of magnitude lower than the values considered in the evolutionary calculations. Based on a study of the surrounding stellar population and the nearby cluster, NGC 588, using Hubble Space Telescope/WFPC2 photometry, we suggest that UIT 005 could be in fact a runaway star from this cluster. Regardless of its origin, the derived parameters place the star in a region of the Hertzsprung-Russell diagram where luminous blue variables (LBVs) are usually found, but we find no evidence supporting photometric or spectroscopic variability, except for small H{alpha} changes, otherwise observed in Galactic B-type supergiants. Whether UIT 005 is an LBV in a dormant state or a regular blue supergiant could not be discerned in this study. Subsequent monitoring would help us to improve our knowledge of the more massive stars, bridging the gap between regular and more exotic blue supergiants.

Urbaneja, M. A. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Herrero, A. [Instituto de Astrofisica de Canarias, VIa Lactea S/N, E-38200 La Laguna, Canary Islands (Spain); Lennon, D. J. [ESA, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Corral, L. J. [Instituto de AstronomIa y MetereologIa, Universidad de Guadalajara, Avda. Vallarta 2602, Guadalajara, Jalisco, C.P. 44130 (Mexico); Meynet, G. [Geneva Observatory, Ch. des Mailettes 51, 1290 Sauverny (Switzerland)

2011-07-01

265

Spectroscopy of the M Supergiant ? Ori in the 1 2.5 ?m Region  

NASA Astrophysics Data System (ADS)

The study of elemental abundances in cool stars via atomic lines in the optical region is made di.cult by stellar molecular absorption. At infrared wavelengths this problem is diminished, but ground-based observations suffer from absorption by the earth’s atmosphere. Fortunately, there are spectral windows through which we can observe. We have explored several such windows in the spectral region from 1 2.5 ?m, coinciding with the wavelength domain of the new VLT instrument CRIRES, for atomic lines suitable for the study of cool luminous stars, in particular ? Ori (M2Iab). We present preliminary results from this search along with our first results on abundances of iron and the weak s-process elements Sr, Y, Zr.

Lundqvist, Martin; Wahlgren, Glenn

266

Kinematic Masses of Super Star Clusters in M82 from High-Resolution Near-Infrared Spectroscopy  

E-print Network

Using high-resolution (R~22,000) near-infrared (1.51 -- 1.75 microns) spectra from Keck Observatory, we measure the kinematic masses of two super star clusters in M82. Cross-correlation of the spectra with template spectra of cool evolved stars gives stellar velocity dispersions of sigma_r=15.9 +/- 0.8 km/s for MGG-9 and sigma_r=11.4 +/- 0.8 km/s for MGG-11. The cluster spectra are dominated by the light of red supergiants, and correlate most closely with template supergiants of spectral types M0 and M4.5. We fit King models to the observed profiles of the clusters in archival HST/NICMOS images to measure the half-light radii. Applying the virial theorem, we determine masses of 1.5 +/- 0.3 x 10^6 M_sun for MGG-9 and 3.5 +/- 0.7 x 10^5 M_sun for MGG-11. Population synthesis modelling suggests that MGG-9 is consistent with a standard initial mass function, whereas MGG-11 appears to be deficient in low-mass stars relative to a standard IMF. There is, however, evidence of mass segregation in the clusters, in which case the virial mass estimates would represent lower limits.

Nate McCrady; Andrea M. Gilbert; James R. Graham

2003-06-18

267

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

268

A- and B-type star pulsations in the Kepler and CoRoT era: theoretical considerations  

NASA Astrophysics Data System (ADS)

Among A-type main-sequence variables, pulsations of ? Sct and ? Dor variables are driven in the He II ionization zone, while H-ionization zone and strong magnetic fields seem to play roles in the excitation of high-order p-modes in rapidly oscillating Ap (roAp) stars. Pulsations in B-type variables, ? Cephei and slowly pulsating B (SPB) stars are excited by the ?-mechanism at the Fe-opacity bump at T? 2×10^5K. In addition, the strange-mode instability seems responsible for the excitation of pulsations in luminous AB supergiants (? Cygni variables). We discuss excitation mechanisms for pulsations in A- and B-type variable stars.

Saio, H.

2014-11-01

269

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

270

The friendly stars  

NASA Astrophysics Data System (ADS)

Describes prominent stars such as Vega, Arcturus, and Antares and means of identifying them, discusses the constellations in which they are located, and explains star names, stellar light, distances between stars, and types of stars.

Martin, Martha Evans

271

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

272

SN 2011hs: a fast and faint Type IIb supernova from a supergiant progenitor  

NASA Astrophysics Data System (ADS)

Observations spanning a large wavelength range, from X-ray to radio, of the Type IIb supernova (SN) 2011hs are presented, covering its evolution during the first year after explosion. The optical light curve presents a narrower shape and a fainter luminosity at peak than previously observed for Type IIb SNe. High expansion velocities are measured from the broad absorption H I and He I lines. From the comparison of the bolometric light curve and the time evolution of the photospheric velocities with hydrodynamical models, we found that SN 2011hs is consistent with the explosion of a 3-4 M? He-core progenitor star, corresponding to a main-sequence mass of 12-15 M?, that ejected a mass of 56Ni of about 0.04 M?, with an energy of E = 8.5 × 1050 ERG. Such a low-mass progenitor scenario is in full agreement with the modelling of the nebular spectrum taken at ˜215 d from maximum. From the modelling of the adiabatic cooling phase, we infer a progenitor radius of ?500-600 R?, clearly pointing to an extended progenitor star. The radio light curve of SN 2011hs yields a peak luminosity similar to that of SN 1993J, but with a higher mass-loss rate and a wind density possibly more similar to that of SN 2001ig. Although no significant deviations from a smooth decline have been found in the radio light curves, we cannot rule out the presence of a binary companion star.

Bufano, F.; Pignata, G.; Bersten, M.; Mazzali, P. A.; Ryder, S. D.; Margutti, R.; Milisavljevic, D.; Morelli, L.; Benetti, S.; Cappellaro, E.; Gonzalez-Gaitan, S.; Romero-Cañizales, C.; Stritzinger, M.; Walker, E. S.; Anderson, J. P.; Contreras, C.; de Jaeger, T.; Förster, F.; Gutierrez, C.; Hamuy, M.; Hsiao, E.; Morrell, N.; Olivares E., F.; Paillas, E.; Parker, S.; Pian, E.; Pickering, T. E.; Sanders, N.; Stockdale, C.; Turatto, M.; Valenti, S.; Fesen, R. A.; Maza, J.; Nomoto, K.; Phillips, M. M.; Soderberg, A.

2014-04-01

273

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

274

SMARTS Monitoring of the Exotic Variable Star V838 Monocerotis  

NASA Astrophysics Data System (ADS)

In recent years, several luminous red stellar transients have been discovered, with maximum brightnesses lying between those of novae and supernovae. A prototype is the Galactic star V838 Monocerotis, whose 2002 outburst illuminated a spectacular light echo, extensively imaged by HST. Polarimetric imaging of the echo with HST has yielded a geometric distance of 6.2 kpc, making V838 Mon at maximum intermediate in luminosity between a classical nova and a subluminous Type II SN. Possibly related intermediate-luminosity transients have been discovered recently in the nearby galaxies M31, NGC 300 (two such events), M85, M99, and NGC 6946. Unlike a nova, V838 Mon remained a luminous red supergiant throughout its outburst. Recently, the slowly expanding dusty photosphere of V838 Mon has ingested a B-type companion star, leading to spectacular photometric and spectroscopic variability. X rays were detected at that time, but it remains unclear whether these were related to the interaction with the B star, or were due to flaring on a rotating merged binary. I propose to continue to monitor these changes using synoptic service observing with the SMARTS 1.3m (photometry) and 1.5m (spectroscopy) telescopes.

Bond, Howard E.

2011-02-01

275

Predicted magnitudes and colors from cool-star model atmospheres  

NASA Technical Reports Server (NTRS)

An intercomparison of model stellar atmospheres and observations of real stars can lead to a better understanding of the relationship between the physical properties of stars and their observed radiative flux. In this spirit we have determined wide-band and narrow-band magnitudes and colors for a subset of models of K and M giant and supergiant stars selected from the grid of 40 models by Johnson, Bernat and Krupp (1980) (hereafter referred to as JBK). The 24 models selected have effective temperatures of 4000, 3800, 3600, 3400, 3200, 3000, 2750 and 2500 K and log g = 0, 1 or 2. Emergent energy fluxes (erg/ sq cm s A) were calculated at 9140 wavelengths for each model. These computed flux curves were folded through the transmission functions of Wing's 8-color system (Wing, 1971; White and Wing, 1978) and through Johnson's (1965) wide-band (BVRIJKLM) system. The calibration of the resultant magnitudes was made by using the absolute calibration of the flux curve of Vega by Schild, et al. (1971).

Johnson, H. R.; Steiman-Cameron, T. Y.

1981-01-01

276

Pre-Supernova Evolution of Massive Stars  

E-print Network

We present the preliminary results of a detailed theoretical investigation on the hydrodynamical properties of Red Supergiant (RSG) stars at solar chemical composition and for stellar masses ranging from 10 to 20 M_sun. We find that the main parameter governing their hydrodynamical behavior is the effective temperature, and indeed when moving from higher to lower effective temperatures the models show an increase in the dynamical perturbations. Also, we find that RSGs are pulsationally unstable for a substantial portion of their lifetimes. These dynamical instabilities play a key role in driving mass loss, thus inducing high mass loss rates (up to several 1e-4 M_sun/yr) and considerable variations of the mass loss activity over timescales of the order of 10,000 years. Our results are able to account for the variable mmass loss rates as implied by radio observations of type II supernovae, and we anticipate that comparisons of model predictions with observed circumstellar phenomena around SNII will provide valuable diagnostics about their progenitors and their evolutionary histories.

Nino Panagia; Giuseppe Bono

2000-03-14

277

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

278

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

279

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.

Television, Twin C.

2010-01-01

280

Obscured AGB stars in the Magellanic Clouds II. Near-infrared and mid-infrared counterparts  

E-print Network

We have carried out an infrared search for obscured AGB stars in the Magellanic Clouds. The survey uncovered a number of obscured AGB stars as well as some supergiants with infrared excess. We present photometry of the sources and discuss the colour diagrams and bolometric luminosities. Most of the AGB stars are luminous, often close to the classical limit of $M_{\\rm bol}=-7.1$. To determine whether the stars are oxygen-rich or carbon-rich, we have acquired narrow-band mid-infrared photometry with the ESO TIMMI camera for several sources. All but one are found to show the silicate feature and therefore to have oxygen-rich dust: the colours of the remaining source are consistent with either an oxygen-rich or a carbon-rich nature. A method to distinguish carbon and oxygen stars based on H$-$K versus K$-$[12] colours is presented. We discuss several methods of calculating the mass-loss rate: for the AGB stars the mass-loss rates vary between approximately 5 times 10**-4 and 5 times 10**-6 solar masses per year, depending on assumed dust-to-gas mass ratio. We present a new way to calculate mass-loss rates from the OH-maser emission. We find no evidence for a correlation of the mass-loss rates with luminosity in these obscured stars. Neither do the mass-loss rates for the LMC and SMC stars differ in any clear systematic way from each other. Expansion velocities appear to be slightly lower in the LMC than in the Galaxy. Period determinations are discussed for two sources: the periods are comparable to those of the longer-period galactic OH/IR stars. All of the luminous stars for which periods are available, have significantly higher luminosities than predicted from the period--luminosity relations.

Albert A. Zijlstra; Cecile Loup; L. B. F. M. Waters; P. A. Whitelock; Jacco Th. van Loon; F. Guglielmo

1995-10-13

281

The rotation rates of massive stars. How slow are the slow ones?  

NASA Astrophysics Data System (ADS)

Context. Rotation plays a key role in the life cycles of stars with masses above ~8 M?. Hence, accurate knowledge of the rotation rates of such massive stars is critical for understanding their properties and for constraining models of their evolution. Aims: This paper investigates the reliability of current methods used to derive projected rotation speeds vsini from line-broadening signatures in the photospheric spectra of massive stars, focusing on stars that are not rapidly rotating. Methods: We use slowly rotating magnetic O-stars with well-determined rotation periods to test the Fourier transform (FT) and goodness-of-fit (GOF) methods typically used to infer projected rotation rates of massive stars. Results: For our two magnetic test stars with measured rotation periods longer than one year, i.e., with vsini ? 1 km s-1, we derive vsini ? 40-50 km s-1 from both the FT and GOF methods. These severe overestimates are most likely caused by an insufficient treatment of the competing broadening mechanisms referred to as microturbulence and macroturbulence. Conclusions: These findings warn us not to rely uncritically on results from current standard techniques to derive projected rotation speeds of massive stars in the presence of significant additional line broadening, at least when vsini ? 50 km s-1. This may, for example, be crucial for i) determining the statistical distribution of observed rotation rates of massive stars; ii) interpreting the evolutionary status and spin-down histories of rotationally braked B-supergiants; and iii) explaining the deficiency of observed O-stars with spectroscopically inferred vsini ? 0 km s-1. Further investigations of potential shortcomings of the above techniques are presently under way. Final reduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/559/L10

Sundqvist, J. O.; Simón-Díaz, S.; Puls, J.; Markova, N.

2013-11-01

282

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.

283

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

284

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

285

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

NASA Astrophysics Data System (ADS)

We present an analysis of the far-infrared and submillimetre molecular emission-line spectrum of the luminous M-supergiant VY CMa, observed with the Spectral and Photometric Imaging Receiver (SPIRE) and Photodetector Array Camera and Spectrometer for Herschel spectrometers aboard the Herschel Space Observatory. Over 260 emission lines were detected in the 190-650 ?m SPIRE Fourier Transform Spectrometer spectra, with one-third of the observed lines being attributable to H2O. Other detected species include CO, 13CO, H_2^{18}O, SiO, HCN, SO, SO2, CS, H2S and NH3. Our model fits to the observed 12CO and 13CO line intensities yield a 12C/13C ratio of 5.6 ± 1.8, consistent with measurements of this ratio for other M-supergiants, but significantly lower than previously estimated for VY CMa from observations of lower-J lines. The spectral line energy distribution for 20 SiO rotational lines shows two temperature components: a hot component at ˜1000 K, which we attribute to the stellar atmosphere and inner wind, plus a cooler ˜200 K component, which we attribute to an origin in the outer circumstellar envelope. We fit the line fluxes of 12CO, 13CO, H2O and SiO, using the SMMOL non-local thermodynamic equilibrium (LTE) line transfer code, with a mass-loss rate of 1.85 × 10-4 M? yr-1 between 9R* and 350R*. We also fit the observed line fluxes of 12CO, 13CO, H2O and SiO with SMMOL non-LTE line radiative transfer code, along with a mass-loss rate of 1.85 × 10-4 M? yr-1. To fit the high rotational lines of CO and H2O, the model required a rather flat temperature distribution inside the dust condensation radius, attributed to the high H2O opacity. Beyond the dust condensation radius the gas temperature is fitted best by an r-0.5 radial dependence, consistent with the coolant lines becoming optically thin. Our H2O emission-line fits are consistent with an ortho:para ratio of 3 in the outflow.

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

2014-01-01

286

Christmas star.  

NASA Astrophysics Data System (ADS)

There are continuous attempts to identify the legendary Christmas Star with a real astronomical event accompanying the birth of Jesus from Nazareth. Unfortunately, the date of birth is difficult to establish on the basis of historical records with better accuracy than a few years. During that period a number of peculiar astronomical events were observed and it seem to be impossible to identify the right one unambiguously.

Bia?a, J.

287

Integrated Near-Infrared Colors of Star Clusters: Analysis of the Stochastic Effects on the Initial Mass Function  

NASA Astrophysics Data System (ADS)

In this paper we examine the influence of stochastic effects on the integrated near-infrared light of star clusters with ages between 7.5 < log t < 9.25. To do this, we use stellar evolution models and a Monte Carlo technique to simulate the effects of stochastic variations in the numbers of main sequence, giant, and supergiant stars for single-generation stellar populations. The fluctuations in the integrated light produced by such variations are evaluated for the VJHK bands. We show that the VJHK light of the star clusters can be strongly affected by plausible stochastic fluctuations in the numbers of bright but scarce stars. In particular, the inclusion of thermally pulsing asymptotic giant branch (AGB) stars in the stellar evolution models yields integrated colors with values in agreement with the spread seen for Large Magellanic Cloud clusters that are known to have significant numbers of AGB stars. Implications of this analysis are important for studies of the integrated light of stellar populations where it is not possible to resolve individual stars.

Santos, João F. C., Jr.; Frogel, Jay A.

1997-04-01

288

Planck stars  

E-print Network

A star that collapses gravitationally can reach a further stage of its life, where quantum-gravitational pressure counteracts weight. The duration of this stage is very short in the star proper time, yielding a bounce, but extremely long seen from the outside, because of the huge gravitational time dilation. Since the onset of quantum-gravitational effects is governed by energy density --not by size-- the star can be much larger than planckian in this phase. The object emerging at the end of the Hawking evaporation of a black hole can can then be larger than planckian by a factor $(m/m_{\\scriptscriptstyle P})^n$, where $m$ is the mass fallen into the hole, $m_{\\scriptscriptstyle P}$ is the Planck mass, and $n$ is positive. The existence of these objects alleviates the black-hole information paradox. More interestingly, these objects could have astrophysical and cosmological interest: they produce a detectable signal, of quantum gravitational origin, around the $10^{-14} cm$ wavelength.

Rovelli, Carlo

2014-01-01

289

Planck stars  

E-print Network

A star that collapses gravitationally can reach a further stage of its life, where quantum-gravitational pressure counteracts weight. The duration of this stage is very short in the star proper time, yielding a bounce, but extremely long seen from the outside, because of the huge gravitational time dilation. Since the onset of quantum-gravitational effects is governed by energy density ---not by size--- the star can be much larger than planckian in this phase. The object emerging at the end of the Hawking evaporation of a black hole can then be larger than planckian by a factor $(m/m_{\\scriptscriptstyle P})^n$, where $m$ is the mass fallen into the hole, $m_{\\scriptscriptstyle P}$ is the Planck mass, and $n$ is positive. We consider arguments for $n=1/3$ and for $n=1$. There is no causality violation or faster-than-light propagation. The existence of these objects alleviates the black-hole information paradox. More interestingly, these objects could have astrophysical and cosmological interest: they produce a detectable signal, of quantum gravitational origin, around the $10^{-14} cm$ wavelength.

Carlo Rovelli; Francesca Vidotto

2014-01-25

290

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

291

Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane  

NASA Astrophysics Data System (ADS)

At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional axisymmetric hydrodynamical simulations following the evolution of the circumstellar medium of these stars in the Galactic plane from the main sequence to the red supergiant phase. We find that thermal conduction is an important process governing the shape, size and structure of the bow shocks around hot stars, and that they have an optical luminosity mainly produced by forbidden lines, e.g. [O III]. The H? emission of the bow shocks around hot stars originates from near their contact discontinuity. The H? emission of bow shocks around cool stars originates from their forward shock, and is too faint to be observed for the bow shocks that we simulate. The emission of optically thin radiation mainly comes from the shocked ISM material. All bow shock models are brighter in the infrared, i.e. the infrared is the most appropriate waveband to search for bow shocks. Our study suggests that the infrared emission comes from near the contact discontinuity for bow shocks of hot stars and from the inner region of shocked wind for bow shocks around cool stars. We predict that, in the Galactic plane, the brightest, i.e. the most easily detectable bow shocks are produced by high-mass stars moving with small space velocities.

Meyer, D. M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V. V.; Mignone, A.; Izzard, R. G.; Kaper, L.

2014-11-01

292

Boron Abundances in A and B-type Stars  

NASA Technical Reports Server (NTRS)

Boron abundances in A- and B-type stars may be a successful way to track evolutionary effects in these hot stars. The light elements - Li, Be, and B - are tracers of exposure to temperatures more moderate than those in which the H-burning CN-cycle operates. Thus, any exposure of surface stellar layers to deeper layers will affect these light element abundances. Li and Be are used in this role in investigations of evolutionary processes in cool stars, but are not observable in hotter stars. An investigation of boron, however, is possible through the B II 1362 A resonance line. We have gathered high resolution spectra from the IUE database of A- and B-type stars near 10 solar mass for which nitrogen abundances have been determined. The B II 1362 A line is blended throughout; the temperature range of this program, requiring spectrum syntheses to recover the boron abundances. For no star could we synthesize the 1362 A region using the meteoritic/solar boron abundance of log e (B) = 2.88; a lower boron abundance was necessary which may reflect evolutionary effects (e.g., mass loss or mixing near the main-sequence), the natal composition of the star forming regions, or a systematic error in the analyses (e.g., non-LTE effects). Regardless of the initial boron abundance, and despite the possibility of non-LTE effects, it seems clear that boron is severely depleted in some stars. It may be that the nitrogen and boron abundances are anticorrelated, as would be expected from mixing between the H-burning and outer stellar layers. If, as we suspect, a residue of boron is present in the A-type supergiants, we may exclude a scenario in which mixing occurs continuously between the surface and the deep layers operating the CN-cycle. Further exploitation of the B II 1362 A line as an indicator of the evolutionary status of A- and B-type stars will require a larger stellar sample to be observed with higher signal-to-noise as attainable with the Hubble Space Telescope.

Lambert, David L.

1997-01-01

293

A New Method for Measuring Metallicities of Young Super Star Clusters  

E-print Network

We demonstrate how the metallicities of young super star clusters can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of super star clusters older than ~6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z]= +0.28 +/- 0.14 dex using a moderate resolution (R~3500) J-band spectrum and in NGC 6496 we report [Z]= -0.32 +/- 0.20 dex from a low resolution spectrum of R~1800. Recently commissioned low resolution multiplexed spectrographs on the VLT (KMOS) and Keck (MOSFIRE) will allow accurate measurements of super star cluster metallicities across the disks of star-forming galaxies up to distances of 70 Mpc with single night observation campaigns using the method presented in this letter.

Gazak, J Zachary; Bastian, Nate; Kudritzki, Rolf; Bergemann, Maria; Plez, Bertrand; Evans, Chris; Patrick, Lee; Bresolin, Fabio; Schinnerer, Eva

2014-01-01

294

IUE low-dispersion spectra of six luminous stars in symmetric nebulae  

NASA Technical Reports Server (NTRS)

The stars and nebulae are HD 156738 and HDE 319703A, respectively centered in a pair of symmetric nebulae among the NGC 6334 group, AG Car in its nebula, HDE 250550 in nebula 8 of a catalog by Herbig, 209 BAC in Ml-67, and HD 89358 in NGC 3199. These include two O stars, two WN stars, an unstable B supergiant, and a ZAMS B star. Four of them are additions to a previous similar study, and the information about AG CAR and 209 BAC/Ml-67 is extended from that study. The objects are interpreted with Weaver et al.'s (1977) theory of the interaction of a stellar wind with the ambient interstellar medium, except where the short lifetime of the HDE 250550 nebula has forestalled such analysis. Spectral line identifications and types, and several parameters of mass loss, are tabulated. When the present mass loss rates are compared with previous results from other methods, there is an outstanding difference only for WN stars, since 1-3 x 10 to the -7th solar masses/year is derived here.

Johnson, H. M.

1982-01-01

295

Following the rapid evolution of the central star of the Stingray Nebula in real time  

NASA Astrophysics Data System (ADS)

SAO 244567 is an unusually fast evolving star. Within twenty years only, it has turned from a B-type supergiant into the central star of the Stingray nebula. Space and ground-based observations obtained over the last decades have revealed that its spectrum changes noticeably over just a few years, showing stellar evolution in real time. Previous analysis indicates it must be a low mass star and thus the observed fast evolution is in strong contradiction with canonical post-asymptotic giant branch (AGB) evolution. A late He-shell flash is able to account for the rapid evolution. This scenario would predict an evolution back to the AGB, e.g. a decrease of the effective temperature (which is already indicated by the FUSE observations in 2006) and an increase of luminosity. With COS spectroscopy we want to follow the evolution of the surface properties of SAO 244567 to verify this thesis. The very compact nebula of SAO 244567 makes it impossible to derive these parameters from optical spectra, because most of the photospheric lines are blended by nebular emission lines thus they are not suitable for a spectral analysis. The derived surface parameters will establish constraints for late thermal pulse evolutionary calculations. With these calculations we aim not only to explain the nature of SAO 244567, but they also will provide a deeper insight in the formation process of hydrogen deficient stars, which make up 25% of the post AGB-stars and white dwarfs.

Reindl, Nicole

2014-10-01

296

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

297

When Stars Collide  

E-print Network

When two stars collide and merge they form a new star that can stand out against the background population in a starcluster as a blue straggler. In so called collision runaways many stars can merge and may form a very massive star that eventually forms an intermediate mass blackhole. We have performed detailed evolution calculations of merger remnants from collisions between main sequence stars, both for lower mass stars and higher mass stars. These stars can be significantly brighter than ordinary stars of the same mass due to their increased helium abundance. Simplified treatments ignoring this effect give incorrect predictions for the collision product lifetime and evolution in the Hertzsprung-Russell diagram.

E. Glebbeek; O. R. Pols

2007-10-09

298

IGR J17354-3255 as bench test for investigation of ?-ray emission from Supergiant Fast X-ray Transients  

NASA Astrophysics Data System (ADS)

Among the different types of sources shining in the high energy sky, gamma-ray binaries are rapidly becoming the subject of major interest. In fact, in the last few years a number of High Mass X-ray Binaries (HMXBs) have been firmly detected from MeV to TeV energies, providing secure evidences that particles can be efficiently accelerated up to very high energies in such galactic systems. Similarly to this general and emerging class of gamma-ray binaries, in principle Supergiant Fast X-ray Transients (SFXTs) have all the "ingredients" to be transient high energy emitters. In this context, the SFXT IGR J17354-3255 is a good bench test and we present intriguing hints likely suggesting that it is a transient gamma-ray source flaring on short timescales. If fully confirmed by further studies, the implications stemming are huge, both theoretically and observationally, and would add a further extreme characteristic to the already extreme class of SFXTs.

Sguera, V.

2013-06-01

299

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

300

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

301

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

302

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

2005-09-13

303

THE NUCLEOSYNTHETIC IMPRINT OF 15-40 M{sub sun} PRIMORDIAL SUPERNOVAE ON METAL-POOR STARS  

SciTech Connect

The inclusion of rotationally induced mixing in stellar evolution can alter the structure and composition of pre-supernova stars. We survey the effects of progenitor rotation on nucleosynthetic yields in Population III and II supernovae (SNe) using the new adaptive mesh refinement code CASTRO. We examine piston-driven spherical explosions in 15, 25, and 40 M{sub sun} stars at Z = 0 and 10{sup -4} Z{sub sun} with three explosion energies and two rotation rates. Rotation in the Z = 0 models resulted in primary nitrogen production and a stronger hydrogen burning shell which led all models to die as red supergiants (in contrast to the blue supergiant progenitors made without rotation). On the other hand, the Z = 10{sup -4} Z{sub sun} models that included rotation ended their lives as compact blue stars. Because of their extended structure, the hydrodynamics favors more mixing and less fallback in the metal-free stars than the Z = 10{sup -4} models. As expected, higher energy explosions produce more enrichment and less fallback than do lower energy explosions, and at constant explosion energy, less massive stars produce more enrichment and leave behind smaller remnants than do more massive stars. We compare our nucleosynthetic yields to the chemical abundances in the three most iron-poor stars yet found and reproduce the abundance pattern of one, HE 0557-4840, with a zero metallicity, 15 M{sub sun}, 2.4 x 10{sup 51} erg SN. A Salpeter IMF-averaged integration of our yields for Z = 0 models with explosion energies of 2.4 x 10{sup 51} erg or less is in good agreement with the abundances observed in larger samples of extremely metal-poor (EMP) stars, provided 15 M{sub sun} stars are included. Since the abundance patterns of EMP stars likely arise from a representative sample of progenitors, our yields suggest that 15-40 M{sub sun} core-collapse SNe with moderate explosion energies contributed the bulk of the metals to the early universe.

Joggerst, C. C.; Woosley, S. E. [Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95060 (United States); Almgren, A.; Bell, J. [Computational Research Division, Lawrence Berkeley National Lab, Berkeley, CA 94720 (United States); Heger, Alexander [School of Physics and Astronomy, University of Minnesota, Twin Cities, Minneapolis, MN 55455 (United States); Whalen, Daniel, E-mail: cchurch@ucolick.or [Theoretical Astrophysics (T-2), Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2010-01-20

304

A new calibration of stellar parameters of Galactic O stars  

E-print Network

We present new calibrations of stellar parameters of O stars at solar metallicity taking non-LTE, wind, and line-blanketing effects into account. Gravities and absolute visual magnitudes are derived from results of recent spectroscopic analyses. Two types of effective temperature scales are derived: one from a compilation based on recent spectroscopic studies of a sample of massive stars - the ``observational scale'' - and the other from direct interpolations on a grid of non-LTE spherically extended line-blanketed models computed with the code CMFGEN (Hillier & Miller 1998) - the ``theoretical scale''. These Teff scales are then further used together with the grid of models to calibrate other parameters (bolometric correction, luminosity, radius, spectroscopic mass and ionising fluxes) as a function of spectral type and luminosity class. Compared to the earlier calibrations of Vacca et al. (1996) the main results are: 1) the effective temperature scales are cooler by 2000 to 8000 K, the reduction being the largest for early supergiants; 2) bolometric corrections are lower by 0.1 mag for a given temperature, and are lower by 0.3 - 0.6 mag for a given spectral type; 3) luminosities are reduced by 0.20 to 0.35 dex; 4) Lyman ionising fluxes are lower by 0.20 to 0.80 dex. We provide calibration tables for each luminosity class and for both types of Teff scales.

F. Martins; D. Schaerer; D. J. Hillier

2005-03-16

305

Large-scale star formation in the Magellanic Clouds  

E-print Network

In this contribution I will present the current status of our project of stellar population analyses and spatial information of both Magellanic Clouds (MCs). The Magellanic Clouds - especially the LMC with its large size and small depth (<300pc) - are suitable laboratories and testing ground for theoretical models of star formation. With distance moduli of 18.5 and 18.9mag for the LMC and SMC, respectively, and small galactic extinction, their stellar content can be studied in detail from the most massive stars of the youngest populations (<25Myr) connected to H-alpha emission down to the low mass end of about 1/10 of a solar mass. Based on broad-band photometry (U,B,V) I present results for the supergiant shell (SGS) SMC1, some regions at the LMC east side incl. LMC2 showing different overlapping young populations and the region around N171 with its large and varying colour excess, and LMC4. This best studied SGS shows a coeval population aged about 12Myr with little age spread and no correlation to distance from LMC4's centre. I will show that the available data are not compatible with many of the proposed scenarios like SSPSF or a central trigger (like a cluster or GRB), while a large-scale trigger like the bow-shock of the rotating LMC can do the job.

Jochen M. Braun

2001-08-03

306

The FEROS--Lick/SDSS observational database of spectral indices of FGK stars for stellar population studies  

E-print Network

We present FEROS--Lick/SDSS, an empirical database of Lick/SDSS spectral indices of FGK stars to be used in population synthesis projects for discriminating different stellar populations within the integrated light of galaxies and globular clusters. From about 2500 FEROS stellar spectra obtained from the ESO Science Archive Facility we computed line--strength indices for 1085 non--supergiant stars with atmospheric parameter estimates from the AMBRE project. Two samples of 312 {\\it dwarfs} and of 83 {\\it subgiants} with solar chemical composition and no significant $\\alpha$--element abundance enhancement are used to compare their observational indices with the predictions of the Lick/SDSS library of synthetic indices. In general, the synthetic library reproduces very well the behaviour of observational indices as a function of temperature, but in the case of low temperature ($T_{\\rm eff}$ $\\lesssim $5000\\,K) dwarfs; low temperature subgiants are not numerous enough to derive any conclusion. Several possible ca...

Franchini, M; Di Marcantonio, P; Malagnini, M L; Chavez, M

2014-01-01

307

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

308

The ultraviolet spectrum of noncoronal late-type stars - The Gamma Crucis (M3.4 III) reference spectrum  

NASA Technical Reports Server (NTRS)

A guide is presented to the UV spectrum of M-type giants and supergiants whose outer atmospheres contain warm chromospheres but not coronae. The M3 giant Gamma Crucis is taken as the archetype of the cooler, oxygen-rich, noncoronal stars. Line identifications and integrated line flux measurements of the chromospheric emission features seen in the 1200-3200 A range of IUE high-resolution spectra are presented. The major fluorescence processes operating in the outer atmosphere of Gamma Crucis, including eight previously unknown pumping processes and 21 new fluorescent line products, are summarized, and the enhancements of selected line strengths by 'line leakage' is discussed. A set of absorption features toward the longer wavelength end of this range is identified which can be used to characterize the radial velocity of the stellar photospheres. The applicability of the results to the spectra of noncoronal stars with different effective temperatures and gravities is discussed.

Carpenter, Kenneth G.; Pesce, Joseph E.; Stencel, Robert E.; Brown, Alexander; Johansson, Sveneric

1988-01-01

309

Star formation - An overview  

NASA Technical Reports Server (NTRS)

Methods for studying star formation are reviewed. Stellar clusters and associations, as well as field stars, provide a fossil record of the star formation process. Regions of current star formation provide a series of snapshots of different epochs of star formation. A simplified picture of individual star formation as it was envisioned in the late 1970s is contrasted with the results of recent observations, in particular the outflow phenomenon.

Evans, N. J., II

1985-01-01

310

Influence of extreme ultraviolet radiation on the P V ionization fraction in hot star winds  

NASA Astrophysics Data System (ADS)

Different diagnostics of hot star wind mass-loss rates provide results that are difficult to reconcile with each other. The widely accepted presence of clumping in hot star winds implies a significant reduction of observational mass-loss rate estimates from diagnostics that depend on the square of the density. Moreover, the ultraviolet P V resonance lines indicate a possible need for an even stronger reduction of hot star mass-loss rates, provided that P V is a dominant ionization stage of phosphorus, at least in some hot stars. The latter assumption is challenged by the possible presence of extreme ultraviolet (XUV) radiation. Here, we study the influence of XUV radiation on the P V ionization fraction in hot star winds. Using a detailed solution of the hydrodynamical radiative transfer and statistical equilibrium equations, we confirm that a sufficiently strong XUV radiation source might decrease the P V ionization fraction, possibly depreciating the P V lines as a reliable mass-loss rate indicator. However, the XUV radiation also influences the ionization fraction of heavier ions that drive the wind, leading to a decrease of the wind terminal velocity. Consequently, we conclude that XUV radiation alone cannot bring theory and observations into agreement. We fit our predicted wind mass-loss rates using a suitable formula and we compare the results with the observational mass-loss rate diagnostics. We show that for supergiants and giants the theoretical predictions do not contradict the mass-loss rate estimates based on X-ray line profiles or density-squared diagnostics. However, for main-sequence stars, the predicted mass-loss rates are still significantly higher than those inferred from P V or X-ray lines. This indicates that the 'weak wind problem' recently detected in low-luminosity main-sequence stars might also occur, to some extent, for stars with higher luminosity.

Krti?ka, Ji?í; Kubát, Ji?í

2012-11-01

311

The Abundance of Boron in Evolved A- and B-Type Stars  

E-print Network

Boron abundances in A- and B-type stars may be a successful way to track evolutionary effects in these hot stars. The light elements -- Li, Be, and B -- are tracers of exposure to temperatures more moderate than those in which the H-burning CN-cycle operates. Thus, any exposure of surface stellar layers to deeper layers will affect these light element abundances. Li and Be are used in this role in investigations of evolutionary processes in cool stars, but are not observable in hotter stars. An investigation of boron, however, is possible through the B II 1362=C5 resonance line. We have gathered high resolution spectra from the IUE database of A- and B-type stars near 10~M$_\\odot$ for which nitrogen abundances have been determined (by Gies & Lambert, 1992, and Venn 1995). The B II 1362=C5 line is blended throughout the temperature range of this program, requiring spectrum syntheses to recover the boron abundances. For no star could we synthesize the 1362=C5 region using the meteoritic/solar boron abundance of log(B) =3D 2.88 (Anders & Grevesse 1989); a lower boron abundance was necessary which may reflect evolutionary effects (e.g., mass loss or mixing near the main-sequence), the natal composition of the star forming regions, or a systematic error in the analyses (e.g., non-LTE effects). Regardless of the initial boron abundance, and despite the possibility of non-LTE effects, it seems clear that boron is severely depleted in some stars. It may be that the nitrogen and boron abundances are anticorrelated, as would be expected from mixing between the H-burning and outer stellar layers. If, as we suspect, a residue of boron is present in the A-type supergiants, we may exclude a scenario in which mixing occurs continuously between the surface and the deep

Kim A. Venn; David L. Lambert; Michael Lemke

1995-08-01

312

VizieR Online Data Catalog: B6-B9.5 stars abundance analysis (Niemczura+, 2009)  

NASA Astrophysics Data System (ADS)

The observational material consists of the high-resolution (R~40000-50000) spectroscopic observations of B-type stars obtained with the ELODIE and FEROS spectrographs. The ELODIE spectrograph was attached to the 1.93m telescope at the Observatoire de Haute-Provence, France. The FEROS spectrograph was installed on the 1.52m and 2.2m telescopes at La Silla, Chile. Both instruments are cross-dispersed, fibre-fed echelle spectrographs. Typical signal-to-noise ratios of the spectra range from 100 to 150 at 550nm. The wavelength intervals covered are 390-680nm and 380-910nm for ELODIE and FEROS, respectively. In our initial sample, we have 160 FEROS spectra and 62 ELODIE spectra of B-type stars. Only the spectroscopic observations of the B6-B9.5 stars available in the GAUDI archive are analysed in this paper. We also excluded Be stars, supergiants and spectroscopic binaries for which the lines of two stars were visible in the spectra. Basic information about the analysed stars, including spectral type, name of the spectrograph, observation date in UT, V magnitude, interstellar reddening, indications of binarity, and abundance determinations in the literature are given in Table 1. (4 data files).

Niemczura, E.; Morel, T.; Aerts, C.

2009-10-01

313

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

314

On stars and Steiner stars Adrian Dumitrescu  

E-print Network

On stars and Steiner stars Adrian Dumitrescu Csaba D. T´oth Guangwu Xu§ March 9, 2009 Abstract A Steiner star for a set P of n points in Rd connects an arbitrary point in Rd to all points of P, while a star connects one of the points in P to the remaining n - 1 points of P. All connections are realized

Dumitrescu, Adrian

315

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

316

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

317

Ultraviolet spectroscopy of F and G supergiants with IUE. II - The hot companions of HR 2786 and HR 2859  

NASA Technical Reports Server (NTRS)

Hot companion stars in two binary systems are analyzed by means of IUE low-dispersion spectra. HR 2859B is found to be a B2 IV or V star, and analysis of ultraviolet to near-infrared photometry indicates the primary to be an early G star only one magnitude brighter in V with a magnitude of -4.0. A third star probably associated with this system was classified B9p Hg a probable visual absolute magnitude of about -1.6 is obtained for it. HR 2786 is now confirmed to have a hot secondary, for which a spectral class of B9-9.5 is obtained. With an assumed luminosity for this component, the G2 Ib primary then has a magnitude of -3.8.

Parsons, S. B.

1982-01-01

318

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

319

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

320

Massive star populations and the IMF in metal-rich starbursts  

E-print Network

We present new spectroscopic observations of Mkn 309, a starburst galaxy with one of the largest WR populations known. A highly super solar metallicity is derived. Using additional objects we analyse a sample of five metal-rich WR galaxies with the main goal of constraining the basic properties of the massive star populations (IMF slope, M_up) and the star formation history (age, burst duration) of these objects by quantitative comparisons with evolutionary synthesis models. The following main results are obtained: 1) The observations are well explained by extended bursts of star formation or a superposition of several bursts. Ages and burst durations are estimated. This naturally explains both the observed WR populations (including WN and WC stars) and the presence of red supergiants. 2) The fitted SEDs indicate that the stellar light suffers from a smaller extinction than that of the gas, confirming independent earlier findings. 3) All the considered observational constraints are compatible with a Salpeter IMF extending to masses >~ 40 Msun. Adopting a conservative approach we derive a LOWER LIMIT of Mup >~ 30 Msun for the Salpeter IMF. From more realistic assumptions on the metallicity and SF history we favour a lower limit Mup >~ 30-40 Msun, which is also in agreement with Hbeta equivalent width measurements of metal-rich HII regions in spiral galaxies indicating an upper mass cut-off of at least ~ 35 - 50 Msun. Steep IMF slopes (alpha >~ 3.3) are very unlikely. (abridged/modified abstract)

Daniel Schaerer; Natalia G. Guseva; Yuri I. Izotov; Trinh X. Thuan

2000-08-31

321

A multiwavelength study of evolved massive stars in the Galactic Centre  

NASA Astrophysics Data System (ADS)

The central region of the Milky Way Galaxy provides a unique laboratory for a systematic, spatially resolved population study of evolved massive stars of various types in a relatively high-metallicity environment. We have conducted a multiwavelength data analysis of 180 such stars or candidates, most of which were drawn from a recent large-scale Hubble Space Telescope (HST)/Near-Infrared Camera and MultiObject Spectrometer (NICMOS) narrow-band Paschen ? survey, plus additional 14 Wolf-Rayet stars identified in earlier ground-based spectroscopic observations of the same field. The multiwavelength data include broad-band infrared (IR) photometry measurements from HST/NIC2, Simultaneous three-colour InfraRed Imager for Unbiased Surveys (SIRIUS), Two-Micron All-Sky Survey (2MASS), Spitzer/IRAC and X-ray observations from Chandra. We correct for extinctions towards individual stars, improve the Paschen ? line equivalent width measurements, quantify the substantial mid-IR dust emission associated with carbon sequence Wolf-Rayet (WC) stars and find X-ray counterparts. In the process, we identify 10 foreground sources, some of which may be nearby cataclysmic variables. The nitrogen sequence Wolf-Rayet (WN) stars in the Arches and Central clusters show correlations between the Paschen ? equivalent width and the adjacent continuum emission. However, the WN stars in the latter cluster are systematically dimmer than those in the Arches cluster, presumably due to the different ages of the two clusters. In the equivalent width-magnitude plot, late-type nitrogen sequence Wolf-Rayet (WNL) stars, WC stars and OB supergiants roughly fall into three distinct regions. We estimate that the dust mass associated with individual WC stars in the quintuplet cluster can reach 10-5 M?, or more than one order of magnitude larger than previous estimates. Thus, WC stars could be a significant source of dust in the galaxies of the early Universe. Nearly half of the evolved massive stars in the Galactic Centre are located outside the three known massive stellar clusters. The ionization of several compact H II regions can be accounted for by their enclosed individual evolved massive stars, which thus likely formed in isolation or in small groups.

Dong, H.; Wang, Q. D.; Morris, M. R.

2012-09-01

322

Counting Your Lucky Stars  

NSDL National Science Digital Library

In this activity, learners sample a star field to estimate the number of stars in the universe. This activity simulates how astronomers use sampling instead of census (counting) to more easily collect data in space. Learners predict, count, approximate, and average the number of stars in a Star Field Sheet.

Ricles, Shannon; Hatok, Tim; Taylor, Berlina

2013-01-30

323

Extragalactic Star Clusters: the Resolved Star Approach  

NASA Astrophysics Data System (ADS)

The physical processes leading to the dissolution of star clusters is a topic barely studied and still not understood. We started a pilot project to develop a new approach to directly detect and study the properties of stellar clusters while they are being destroyed. Our technique currently under development makes use of the exceptional spatial resolution and sensitivity of the ACS camera onboard HST to resolve individual stars in nearby galaxies. PSF stellar photometry and color-magnitude diagrams allows us to separate the most massive stars (more likely to be in clusters) from the star field background. While applying the method to the normal spiral galaxy NGC1313, we found that the method of studying star clusters through resolved stars in nearby galaxies is even more powerful than we first expected. The stellar maps obtained for NGC1313 show that a large fraction of early B-type stars contained in the galaxy are already part of the star field background rather that being in star clusters. Such stars live for 5 to 25 Myr. Since most stars form in clusters, the presence of such massive stars in the field means that they must have left their birthplace very rapidly. It also means that the processes involved in the dissolution of the clusters are extremely efficient. The only plausible explanation for so many young stars to be in the field background is the infant mortality of star clusters. We will present the latest results on the two galaxies NGC 1313 and IC 2475 and discuss the potential of the new approach for studying extragalactic stellar clusters.

Pellerin, Anne; Meyer, M. J.; Jason, H.; Calzetti, D.

2006-12-01

324

IntrAst2 (Petrovay) Variable stars VARIABLE STARS  

E-print Network

IntrAst2 (Petrovay) Variable stars VARIABLE STARS Definitions: (a) Stars displaying brightness variations (in the optical domain) All stars are variables (a matter of sensitivity only). (b) Stars) A variable star is what is listed in GCVS or VSX GCVS: General Catalogue of Variable Stars; http

Petrovay, Kristóf

325

Radial-Velocity Analysis of the Post-AGB Star, HD101584  

NASA Astrophysics Data System (ADS)

This project concerns the analysis of the periodicity of the radial velocity of the peculiar emission-line supergiant star HD 101584 (F0 Ia), and also we propose a physical model to account for the observations. From its peculiarities, HD 101584 is a star that is in the post-AGB phase. This study is considered as a key to clarify the multiple aspects related with the evolution of the circum-stellar layer associated with this star's last phase. The star shows many lines with P Cygni profiles, including H-alpha, Na D lines in the IR Ca triplet, indicating a mass outflow. For HD 101584 we have performed a detailed study of its radial-velocity variations, using both emission and absorption lines over a wide range of wavelength. We have analyzed the variability and found a periodicity for all types of lines of 144 days, which must arise from the star's membership in a binary system. The data span a period of five consecutive years and were obtained using the 1-m telescope of Mt John Observatory, in New Zealand., with the echelle and Hercules high resolution spectrographs and CCD camera. HD101584 is known to be an IRAS source, and our model suggests it is a proto-planetary nebula, probably with a bipolar outflow and surrounded by a dusty disk as part of a binary system. We have found no evidence for HD101584 to contain a B9 star as found by Bakker et al (1996). A low resolution IUE spectrum shows the absence of any strong UV continuum that would be expected for a B star to be in this system.

Díaz, F.; Hearnshaw, J.; Rosenzweig, P.; Guzman, E.; Sivarani, T.; Parthasarathy, M.

2007-08-01

326

Massive stars dying alone: Extremely remote environments of SN2009ip and SN2010jp  

NASA Astrophysics Data System (ADS)

We propose an imaging study of the astonishingly remote environments of two recent supernovae (SNe): SN2009ip and SN2010jp. Both were unusual Type IIn explosions that crashed into dense circumstellar material (CSM) ejected by the star shortly before explosion. The favored progenitors of these SNe are very massive luminous blue variable (LBV) stars. In fact, SN2009ip presents an extraordinay case where the LBV-like progenitor was actually detected directly in archival HST data, and where we obtained spectra and photometry for numerous pre-SN eruptions. No other SN has this treasure trove of detailed information about the progenitor (not even SN1987A). SN2010jp represents a possible collapsar-powered event, since it showed evidence of a fast bipolar jet in spectra and a low 56Ni mass; this would be an analog of the black-hole forming explosions that cause gamma ray bursts, but where the relativistic jet is damped by a residual H envelope on the star. In both cases, the only viable models for these SNe involve extremely massive (initial masses of 40-100 Msun) progenitor stars. This seems at odds with their extremely remote environments in the far outskirts of their host galaxies, with no detected evidence for an underlying massive star population in ground-based data (nor in the single shallow WFPC2/F606W image of SN2009ip). Here we propose deep UV HST images to search for any mid/late O-type stars nearby, deep red images to detect any red supergiants, and an H-alpha image to search for any evidence of ongoing star formation in the vicinity. These observations will place important and demanding constraints on the initial masses and ages of these progenitors.

Smith, Nathan

2014-10-01

327

SURVEYING THE AGENTS OF GALAXY EVOLUTION IN THE TIDALLY STRIPPED, LOW METALLICITY SMALL MAGELLANIC CLOUD (SAGE-SMC). II. COOL EVOLVED STARS  

SciTech Connect

We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled 'Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity SMC', or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at IR wavelengths (3.6-160 {mu}m). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute {approx}20% of the global SMC flux (extended + point-source) at 3.6 {mu}m, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies. The equivalent SAGE survey of the higher-metallicity Large Magellanic Cloud (SAGE-LMC) allows us to explore the influence of metallicity on dust production. We find that the SMC RSG stars are less likely to produce a large amount of dust (as indicated by the [3.6] - [8] color). There is a higher fraction of carbon-rich stars in the SMC, and these stars appear to reach colors as red as their LMC counterparts, indicating that C-rich dust forms efficiently in both galaxies. A preliminary estimate of the dust production in AGB and RSG stars reveals that the extreme C-rich AGB stars dominate the dust input in both galaxies, and that the O-rich stars may play a larger role in the LMC than in the SMC.

Boyer, Martha L.; Meixner, Margaret; Gordon, Karl D.; Shiao, Bernie [STScI, Baltimore, MD 21218 (United States); Srinivasan, Sundar [Institut d'Astrophysique de Paris, CNRS UPR 341, Paris F-75014 (France); Van Loon, Jacco Th. [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom); McDonald, Iain; Kemper, F. [Jodrell Bank Centre for Astrophysics, University of Manchester, M13 9PL (United Kingdom); Zaritsky, Dennis; Block, Miwa; Engelbracht, Charles W.; Misselt, Karl [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Babler, Brian; Bracker, Steve; Meade, Marilyn; Whitney, Barbara [Department of Astronomy, University of Wisconsin, Madison, Madison, WI 53706-1582 (United States); Hora, Joe; Robitaille, Thomas [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138-1516 (United States); Indebetouw, Remy [Department of Astronomy, University of Virginia, Charlottesville, VA 22903-0818 (United States); Sewilo, Marta, E-mail: mboyer@stsci.edu [Department of Physics and Astronomy, The Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States)

2011-10-15

328

THE MASS-LOSS RETURN FROM EVOLVED STARS TO THE LARGE MAGELLANIC CLOUD. VI. LUMINOSITIES AND MASS-LOSS RATES ON POPULATION SCALES  

SciTech Connect

We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to {approx}30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 Multiplication-Sign 10{sup -5} M{sub Sun} yr{sup -1}, equivalent to a total mass injection rate (including the gas) into the ISM of {approx}6 Multiplication-Sign 10{sup -3} M{sub Sun} yr{sup -1}. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K{sub s} band as a function of J - K{sub s} color, BC{sub K{sub s}}= -0.40(J-K{sub s}){sup 2} + 1.83(J-K{sub s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (M-dot{sub d}) from C-rich AGB stars, such as log M-dot{sub d} = (-18.90/((K{sub s}-[8.0])+3.37) - 5.93. We find that a larger fraction of AGB stars exhibiting the 'long-secondary period' phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.

Riebel, D.; Meixner, M. [Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Srinivasan, S. [UPMC-CNRS UMR7095, Institut d'Astrophysique de Paris, F-75014 Paris (France); Sargent, B., E-mail: driebel@pha.jhu.edu [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

2012-07-01

329

Herschel's Star Gages  

NSDL National Science Digital Library

The EJS Herschel's Star Gages Model illustrates William Herschel's methods of "star gages" by which he attempted to map out the shape of our galaxy in 1785. Herschel's star gages (sic) relied on two important assumptions: that Herschel's telescope (his "large 20 foot" with an 18.5 inch aperture) could see to the ends of the galaxy, and that within the galactic system stars are distributed uniformly. If the first assumption holds then the stars seen in the telescope all lie within a conical region of space with the apex at the telescope and the base at the edge of the galaxy. If the second assumption holds then the number of stars seen in the telescope is proportional to the volume of this cone. Since the volume of the cone is proportional to the cube of its height, the distance to the galactic edge in any direction is proportional to the cube root of the number of stars seen in that direction. This simulation allows the user to use Herschel's method of star gages to map out the shape of an artificial "star system" for which Herschel's assumptions are valid. One window shows the view through a telescope, with a slider to change the telescopes direction (around a single fixed axis). Another window shows a 3D view of the star system, showing either all of the stars in the system or only those stars visible through the telescope. A third window shows a plot of the star gages. Plotting star gages for many different directions maps out a cross-section of the star system. An optional slider allows the user to decrease the distance to at which stars are no longer visible, and a menu allows the user to select a star system in which the stars are not distributed uniformly. These options let the user explore how violations of Herschel's two fundamental assumptions invalidate his star gage method.

Timberlake, Todd

2011-05-28

330

A Bake-off between CMFGEN and FASTWIND: Modeling the Physical Properties of SMC and LMC O-type Stars  

NASA Astrophysics Data System (ADS)

The model atmosphere programs FASTWIND and CMFGEN are both elegantly designed to perform non-LTE analyses of the spectra of hot massive stars, and include sphericity and mass-loss. The two codes differ primarily in their approach toward line blanketing, with CMFGEN treating all of the lines in the co-moving frame and FASTWIND taking an approximate approach which speeds up execution times considerably. Although both have been extensively used to model the spectra of O-type stars, no studies have used the codes to independently model the same spectra of the same stars and compare the derived physical properties. We perform this task on 10 O-type stars in the Magellanic Clouds. For the late-type O supergiants, both CMFGEN and FASTWIND have trouble fitting some of the He I lines, and we discuss causes and cures. We find that there is no difference in the average effective temperatures found by the two codes for the stars in our sample, although the dispersion is large, due primarily to the various difficulties each code has with He I. The surface gravities determined using FASTWIND are systematically lower by 0.12 dex compared to CMFGEN, a result we attribute to the better treatment of electron scattering by CMFGEN. This has implications for the interpretation of the origin of the so-called mass discrepancy, as the masses derived by FASTWIND are on average lower than inferred from stellar evolutionary models, while those found by CMFGEN are in better agreement.

Massey, Philip; Neugent, Kathryn F.; Hillier, D. John; Puls, Joachim

2013-05-01

331

Anatomy of a Young Massive Star Cluster: NGC 1569-B  

E-print Network

We present new H-band echelle spectra, obtained with the NIRSPEC spectrograph at Keck II, for the massive star cluster "B" in the nearby dwarf irregular galaxy NGC 1569. From spectral synthesis and equivalent width measurements we obtain abundances and abundance patterns. We derive an Fe abundance of [Fe/H]=-0.63+/-0.08, a super-solar [alpha/Fe] abundance ratio of +0.31+/-0.09, and an O abundance of [O/H]=-0.29+/-0.07. We also measure a low 12C/13C = 5+/-1 isotopic ratio. Using archival imaging from the Advanced Camera for Surveys on board HST, we construct a colour-magnitude diagram (CMD) for the cluster in which we identify about 60 red supergiant (RSG) stars, consistent with the strong RSG features seen in the H-band spectrum. The mean effective temperature of these RSGs, derived from their observed colours and weighted by their estimated H-band luminosities, is 3790 K, in excellent agreement with our spectroscopic estimate of Teff = 3800+/-200 K. From the CMD we derive an age of 15-25 Myr, slightly older than previous estimates based on integrated broad-band colours. We derive a radial velocity of -78+/-3 km/s and a velocity dispersion of 9.6+/-0.3 km/s. In combination with an estimate of the half-light radius of 0.20"+/-0.05" from the HST data, this leads to a dynamical mass of (4.4+/-1.1)E5 Msun. The dynamical mass agrees very well with the mass predicted by simple stellar population models for a cluster of this age and luminosity, assuming a normal stellar IMF. The cluster core radius appears smaller at longer wavelengths, as has previously been found in other extragalactic young star clusters.

S. S. Larsen; L. Origlia; J. P. Brodie; J. S. Gallagher III

2007-10-02

332

Spherically Extended Model Atmospheres of Hot Luminous Stars  

NASA Astrophysics Data System (ADS)

Spherical, hydrostatic, non-local thermodynamic equilibrium (non-LTE) metal line-blanketed model atmospheres have been employed to reproduce the spectral energy distributions of the bright B-type giant stars Beta and Epsilon Canis Majoris, including the extreme ultraviolet where previous models have failed. (Aufdenberg, J.P., et al. 1999, MNRAS, 302, 599; Aufdenberg, J.P. et al., 1998, ApJ, 498, 837). The combination of spherical geometry and line-blanketing produces significantly different model temperature structures and synthetic extreme ultraviolet spectra relative to otherwise similar plane-parallel geometry models. In addition, a full grid of O- and early B-type model stellar atmospheres has been constructed and comparisons with hydrostatic, plane-parallel, LTE line-blanketed models show that our models predict consistently higher ionizing fluxes, particularly at lower effective temperatures. Models for hot, luminous stars and their winds have been developed which unify the inner hydrostatic layers with the outer dynamic layers of the atmosphere into a single structure. These models include the effects of full non-LTE metal line-blanketing in both the computation of the model atmosphere plus wind and the synthetic spectrum. Models of this type have been developed for comparison with the spectral energy distribution and detailed spectrum of the A-type supergiant Deneb. Synthetic spectra have been computed which are able to match reasonably well Deneb's observed spectral energy distribution between 120 nm to 3.6 cm. These models predict that Deneb's expanding envelope is only partially ionized, which leads to a steeper spectral slope at millimeter and radio wavelengths than predicted by a fully ionized model commonly applied to hotter O- and B-type stars. Non-LTE model structures and line formation in the ultraviolet indicate mass-loss rates 50 times larger than in our LTE studies.

Aufdenberg, J. P.

2000-12-01

333

Multi-dimensional models of circumstellar shells around evolved massive stars  

NASA Astrophysics Data System (ADS)

Context. Massive stars shape their surrounding medium through the force of their stellar winds, which collide with the circumstellar medium. Because the characteristics of these stellar winds vary over the course of the evolution of the star, the circumstellar matter becomes a reflection of the stellar evolution and can be used to determine the characteristics of the progenitor star. In particular, whenever a fast wind phase follows a slow wind phase, the fast wind sweeps up its predecessor in a shell, which is observed as a circumstellar nebula. Aims: We make 2D and 3D numerical simulations of fast stellar winds sweeping up their slow predecessors to investigate whether numerical models of these shells have to be 3D, or whether 2D models are sufficient to reproduce the shells correctly. Methods: We use the MPI-AMRVAC code, using hydrodynamics with optically thin radiative losses included, to make numerical models of circumstellar shells around massive stars in 2D and 3D and compare the results. We focus on those situations where a fast Wolf-Rayet star wind sweeps up the slower wind emitted by its predecessor, being either a red supergiant or a luminous blue variable. Results: As the fast Wolf-Rayet wind expands, it creates a dense shell of swept up material that expands outward, driven by the high pressure of the shocked Wolf-Rayet wind. These shells are subject to a fair variety of hydrodynamic-radiative instabilities. If the Wolf-Rayet wind is expanding into the wind of a luminous blue variable phase, the instabilities will tend to form a fairly small-scale, regular filamentary lattice with thin filaments connecting knotty features. If the Wolf-Rayet wind is sweeping up a red supergiant wind, the instabilities will form larger interconnected structures with less regularity. The numerical resolution must be high enough to resolve the compressed, swept-up shell and the evolving instabilities, which otherwise may not even form. Conclusions: Our results show that 3D models, when translated to observed morphologies, give realistic results that can be compared directly to observations. The 3D structure of the nebula will help to distinguish different progenitor scenarios.

van Marle, A. J.; Keppens, R.

2012-11-01

334

VLTI/MIDI observations of 7 classical Be stars  

NASA Astrophysics Data System (ADS)

Context: Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar envelope that is responsible for the observed IR-excess and emission lines. The origin of this envelope, its geometry, and kinematics have been debated for some time. Aims: We measured the mid-infrared extension of the gaseous disk surrounding seven of the closest Be stars in order to constrain the geometry of their circumstellar environments and to try to infer physical parameters characterizing these disks. Methods: Long baseline interferometry is the only technique that enables spatial resolution of the circumstellar environment of classical Be stars. We used the VLTI/MIDI instrument with baselines up to 130 m to obtain an angular resolution of about 15 mas in the N band and compared our results with previous K band measurements obtained with the VLTI/AMBER instrument and/or the CHARA interferometer. Results: We obtained one calibrated visibility measurement for each of the four stars, p Car, ? Tau, ? CMa, and ? Col, two for ? Cen and ? CMi, and three for ? Ara. Almost all targets remain unresolved even with the largest VLTI baseline of 130 m, evidence that their circumstellar disk extension is less than 10 mas. The only exception is ? Ara, which is clearly resolved and well-fitted by an elliptical envelope with a major axis a=5.8±0.8 mas and an axis ratio a/b=2.4±1 at 8 ?m. This extension is similar to the size and flattening measured with the VLTI/AMBER instrument in the K band at 2 ?m. Conclusions: The size of the circumstellar envelopes for these classical Be stars does not seem to vary strongly on the observed wavelength between 8 and 12 ?m. Moreover, the size and shape of ? Ara's disk is almost identical at 2, 8, and 12 ?m. We expected that longer wavelengths probe cooler regions and correspondingly larger envelopes, but this is clearly not the case from these measurements. For ? Ara this could come from to disk truncation by a small companion; however, other explanations are needed for the other targets. Based on observations made with ESO Telescopes at Paranal under programs 073.A-9014G, 077.D-0097 and 082.D-0189.

Meilland, A.; Stee, Ph.; Chesneau, O.; Jones, C.

2009-10-01

335

VizieR Online Data Catalog: Far-UV spectral atlas of O-type stars (Smith, 2012)  

NASA Astrophysics Data System (ADS)

In this paper, we present a spectral atlas covering the wavelength interval 930-1188Å for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188Å. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas (Cat. J/ApJS/186/175), to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. (4 data files).

Smith, M. A.

2012-10-01

336

Astronomy: A Star Party  

NSDL National Science Digital Library

This lesson is designed to teach students about the functions of a telescope, the daylight uses of a telescope, the parts of the telescope, and to identify and view certain stars and planets during a star party at night.

337

Stars in Nutrition & Cancer  

Cancer.gov

Stars in Nutrition & Cancer Soy and Cancer: Wish You Were Young Again Star Speaker Stephen Barnes, PhD Professor, Department of Pharmacology and Toxicology University of Alabama Birmingham Birmingham, Alabama Meeting Date Monday, October 04, 2010

338

Open Star Clusters  

NSDL National Science Digital Library

This site offers information about the formation of star clusters, the pleiades, how to calculate star cluster distances, and much more. There are also some great images that techers can use on this website.

2005-02-11

339

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

E-print Network

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the HR diagram. During their post--RSG evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semi--forbidden region, that de Jager and his collaborators have called the `yellow void'. We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double--peaked Halpha emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and mass loss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently the observed variations in apparent spectral type and inferred temperature are changes in the wind and do not necessarily mean that the underlying stellar radius and interior structure are evolving on such a short timescale. To explain the evidence for simultaneous outflow and infall of material near the star, we propose a `rain' model in which blobs of gas condense in regions of lowered opacity outside the dense wind. With the apparent warming of its wind, the recent appearance of strong emission, and a decline in the mass loss rate, IRC +10420 may be about to shed its opaque wind, cross the `yellow void', and emerge as a hotter star.

Roberta M. Humphreys; Kris Davidson; Nathan Smith

2002-05-15

340

R Coronae Borealis Stars in M31 from the Palomar Transient Factory  

NASA Astrophysics Data System (ADS)

We report the discovery of R Coronae Borealis (RCB) stars in the Andromeda galaxy (M31) using the Palomar Transient Factory (PTF). RCB stars are rare hydrogen-deficient, carbon-rich supergiant variables, most likely the merger products of two white dwarfs. These new RCBs, including two confirmed ones and two candidates, are the first to be found beyond the Milky Way and the Magellanic Clouds. All of M31 RCBs showed >1.5 mag irregular declines over timescales of weeks to months. Due to the limiting magnitude of our data (R ? 21-22 mag), these RCB stars have R ? 19.5-20.5 mag at maximum light, corresponding to MR = -4 to -5, making them some of the most luminous RCBs known. Spectra of two objects show that they are warm RCBs, similar to the Milky Way RCBs RY Sgr and V854 Cen. We consider these results, derived from a pilot study of M31 variables, as an important proof-of-concept for the study of rare bright variables in nearby galaxies with the PTF or other synoptic surveys.

Tang, Sumin; Cao, Yi; Bildsten, Lars; Nugent, Peter; Bellm, Eric; Kulkarni, Shrinivas R.; Laher, Russ; Levitan, David; Masci, Frank; Ofek, Eran O.; Prince, Thomas A.; Sesar, Branimir; Surace, Jason

2013-04-01

341

An Empirical UBV RI JHK Color-Temperature Calibration for Stars  

NASA Astrophysics Data System (ADS)

A collection of Johnson/Cousins photometry for stars with known [Fe/H] is used to generate color-color relations that include the abundance dependence. Literature temperature and bolometric correction (BC) dependences are attached to the color relations. The JHK colors are transformed to the Bessell & Brett homogenized system. The main result of this work is the tabulation of seven colors and the V-band BC as a function of T eff, log g, and [Fe/H] for -1.06 < V - K < 10.2 and an accompanying interpolation program. Improvements to the present calibration would involve filling photometry gaps, obtaining more accurate and on-system photometry, knowing better log g and [Fe/H] values, improving the statistics for data-impoverished groups of stars such as metal-poor K dwarfs, applying small tweaks in the processing pipeline, and obtaining better empirical temperature and BC relations, especially for supergiants and M stars. A way to estimate dust extinction from M dwarf colors is pointed out.

Worthey, Guy; Lee, Hyun-chul

2011-03-01

342

R CORONAE BOREALIS STARS IN M31 FROM THE PALOMAR TRANSIENT FACTORY  

SciTech Connect

We report the discovery of R Coronae Borealis (RCB) stars in the Andromeda galaxy (M31) using the Palomar Transient Factory (PTF). RCB stars are rare hydrogen-deficient, carbon-rich supergiant variables, most likely the merger products of two white dwarfs. These new RCBs, including two confirmed ones and two candidates, are the first to be found beyond the Milky Way and the Magellanic Clouds. All of M31 RCBs showed >1.5 mag irregular declines over timescales of weeks to months. Due to the limiting magnitude of our data (R Almost-Equal-To 21-22 mag), these RCB stars have R Almost-Equal-To 19.5-20.5 mag at maximum light, corresponding to M{sub R} = -4 to -5, making them some of the most luminous RCBs known. Spectra of two objects show that they are warm RCBs, similar to the Milky Way RCBs RY Sgr and V854 Cen. We consider these results, derived from a pilot study of M31 variables, as an important proof-of-concept for the study of rare bright variables in nearby galaxies with the PTF or other synoptic surveys.

Tang Sumin; Bildsten, Lars [Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States); Cao Yi; Bellm, Eric; Kulkarni, Shrinivas R.; Levitan, David; Prince, Thomas A.; Sesar, Branimir [Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Nugent, Peter [Computational Cosmology Center, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720 (United States); Laher, Russ; Surace, Jason [Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States); Masci, Frank [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Ofek, Eran O. [Benoziyo Center for Astrophysics and the Helen Kimmel Center for Planetary Science, Weizmann Institute of Science, 76100 Rehovot (Israel)

2013-04-20

343

Large-scale asymmetries in the winds of (binary) AGB stars  

NASA Astrophysics Data System (ADS)

Observations of 78 Asymptotic Giant Branch (AGB) stars and Red Supergiants were carried out with the PACS photometer on-board Herschel as part of the MESS (Mass loss of Evolved StarS) program. For about 60% of these objects, the dusty wind differs from spherically symmetric and reveals a complex morphology. The majority of these asymmetries are caused by a rather simple incident, the interaction of the stellar wind with the interstellar medium. A bow shock is formed in direction of the stellar motion where the two media interact. However, also much more irregular shapes are encountered in the sample. These structures are often related to the binarity of the stellar system. Accreted material by the companion can cause nova outbursts or bipolar outflows which are relatively common. A rather rare encounter are Archimedean spirals that are imprinted in the wind which are now found for a handful of objects, among W Aquilae observed with Herschel and R Sculptoris with ALMA. The most complicated structures in the MESS sample indicate the interplay of multiple interacting influences. A prominent case is o Ceti (Mira). Its exceptionally high space motion produces a strong bow shock and its white dwarf companion drags an Archimedean spiral into the deformed stellar wind bubble and pierces it with a fast bipolar outflow.

Mayer, A.; Jorissen, A.; Kerschbaum, F.; Ottensamer, R.; Nowotny, W.; Aringer, B.; Paladini, C.; Mecina, M.; Pourbaix, D.; Groenewegen, M.; Mohamed, S.

2014-04-01

344

Dynamical Young Star Masses  

NASA Astrophysics Data System (ADS)

Mass is a star's most important property, once composition has been established, and determines the entire life trajectory of an object. Only a couple dozen young stars have absolute dynamical mass measurements, and many of those are imprecise. We propose to observe ~17 young close visual binaries in the Taurus star forming region to advance our knowledge of young star masses. We will use NIRSPEC in high-resolution mode behind the adaptive optics system on the Keck II telescope.

Prato, Lisa; Schaefer, Gail; Simon, Michal

2013-08-01

345

Extragalactic Stellar Astronomy with the Brightest Stars in the Universe  

E-print Network

A supergiants are objects in transition from the blue to the red (and vice versa) in the uppermost HRD. They are the intrinsically brightest "normal" stars at visual light with absolute visual magnitudes up to -9. They are ideal to study young stellar populations in galaxies beyond the Local Group to determine chemical composition and evolution, interstellar extinction, reddening laws and distances. We discuss most recent results on the quantitative spectral analysis of such objects in galaxies beyond the Local Group based on medium and low resolution spectra obtained with the ESO VLT and Keck. We describe the analysis method including the determination of metallicity and metallicity gradients. A new method to measure accurate extragalactic distances based on the stellar gravities and effective temperatures is presented, the flux weighted gravity - luminosity relationship (FGLR). The FGLR is a purely spectroscopic method, which overcomes the untertainties introduced by interstellar extinction and variations of metallicity, which plague all photometric stellar distance determination methods. We discuss the perspectives of future work using the giant ground-based telescopes of the next generation such as the TMT, the GMT and the E-ELT.

R. -P. Kudritzki; M. A. Urbaneja; F. Bresolin; N. Przybilla

2008-03-26

346

Eclipsing Binary Stars  

NSDL National Science Digital Library

Eclipsing Binary Stars model simulates the detection of eclipsing binary stars. In this method, the light curve from the combination of the two stars, and how it changes over time due to each star transiting (or being occulted or eclipsing the other), is observed and then analyzed. In this simulation each star orbits the other in circular motion via Kepler's third law.  When one star passes in front of the other (transits), it blocks part of the starlight of the other star. This decrease in starlight is shown on the graph.  In the simulation the binary star system is shown as seen from Earth (edge on view) and from overhead, but magnified greatly, and with the star sizes not shown to the scale of the orbit. The mass, radius, and temperature of each star can be changed. The simulation uses either simple 3D or Java 3D (if installed) to render the view the stars. If Java 3D is not installed, the simulation defaults to simple 3D using Java. The Eclipsing Binary Stars model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_astronomy_eclipsing_binaries.jar file will run the program if Java is installed.

Belloni, Mario

2010-07-15

347

America's Star Libraries  

ERIC Educational Resources Information Center

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

Lyons, Ray; Lance, Keith Curry

2009-01-01

348

Massive stars and star clusters in the Antennae galaxies  

E-print Network

Large numbers of young stars are formed in merging galaxies, such as the Antennae galaxies. Most of these stars are formed in compact star clusters (i.e., super star clusters), which have been the focus of a large number of studies. However, an increasing number of projects are beginning to focus on the individual stars as well. In this contribution, we examine a few results relevant to the triggering of star and star cluster formation; ask what fraction of stars form in the field rather than in clusters; and begin to explore the demographics of both the massive stars and star clusters in the Antennae.

Bradley C. Whitmore

2006-12-22

349

Vega-like stars  

NASA Astrophysics Data System (ADS)

The results on Vega-like stars obtained with ISO are discussed. We find that the incidence of Vega-like disks is approximately 21% on average, with some dependency upon the spectral type. While young stars do more frequently show disks than old stars, there is no clear trend in the amount of dust seen at different ages. We also discuss the discovery of a Vega-like disk associated with ?1Cnc, a star which is know to be orbited by a planet. Finally we show preliminary results on HD 207129, an old G star with a very prominent IR excess.

Dominik, C.; Habing, H. J.; Laureijs, R. J.; Jourdain de Muizon, M.; Bouchet, P.; Heske, A.; Kessler, M. F.; Leech, K.; Metcalfe, L.; Salama, A.; Siebenmorgen, R.; Trams, N. R.

1999-03-01

350

The most luminous stars.  

PubMed

Stars with individual luminosities more than a million times that of the sun are now being studied in a variety of contexts. Observational and theoretical ideas about the most luminous stars have changed greatly in the past few years. They can be observed spectroscopically even in nearby galaxies. They are not very stable; some have had violent outbursts in which large amounts of mass were lost. Because of their instabilities, these stars do not evolve to become red superglants as less luminous stars do. Theoretical scenarios for the evolution of these most massive stars depend on the effects of turbulence and mixing combined with high radition densities. PMID:17801579

Humphreys, R M; Davidson, K

1984-01-20

351

Stars and Constellations  

NSDL National Science Digital Library

This site from Jim Kaler, a Professor of Astronomy at the University of Illinois, is geared toward amateur and budding astronomers. Kaler offers detailed but non-technical descriptions of selected stars and a link to a photo of their respective constellations. Another section of the site, The Natures of Stars, consists of basic overviews of key concepts. The star descriptions are interesting to beginner and avid starwatchers alike, but the photos would benefit perhaps from superimposed arrows or other finding aids. The Stars site grows by one celestial body each week: the Star of the Week from Kaler's other site, Skylights.

Kaler, James, B.

352

Neutron Star Collision  

NSDL National Science Digital Library

Systems of orbiting neutron stars are born when the cores of two old stars collapse in supernova explosions. Neutron stars have the mass of our Sun but are the size of a city, so dense that boundaries between atoms disappear. Einsteins theory of general relativity predicts that the orbit shrinks from ripples of space-time called gravitational waves. After about 1 billion simulation years, the two neutron stars closely circle each other at 60,000 revolutions per minute. The stars finally merge in a few milliseconds, sending out a burst of gravitational waves.

Bock, Dave; Shalf, John; Swesty, Doug; Calder, Alan; Wang, Ed

1999-01-21

353

The K-Band Spectrum of the Hot Star in IRS 8: An Outsider in the Galactic Center?  

NASA Astrophysics Data System (ADS)

Using adaptive optics at the Gemini North telescope, we have obtained a K-band spectrum of the star near the center of the luminous Galactic center bow shock IRS 8, as well as a spectrum of the bow shock itself. The stellar spectrum contains emission and absorption lines characteristic of an O5-O6 giant or supergiant. The wind from such a star is fully capable of producing the observed bow shock. However, both the early spectral type and the apparently young age of the star, if it is single, mark it as unique among hot stars within 1 pc of the center. Based on data 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 (US), the Particle Physics and Astronomy Research Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).

Geballe, T. R.; Najarro, F.; Rigaut, F.; Roy, J.-R.

2006-11-01

354

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

E-print Network

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the HR diagram. During their post--RSG evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semi--forbidden region, that de Jager and his collaborators have called the `yellow void'. We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double--peaked Halpha emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and mass loss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently the observed var...

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

2002-01-01

355

Evolution of variable stars  

SciTech Connect

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

Becker, S.A.

1986-08-01

356

Stars main sequence  

NSDL National Science Digital Library

What happens during most of a star's life? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to the main sequence phase of a star's existence. This phase is where a star lives out the majority of its life. In an interactive lab activity, students predict the length of the main sequence for four different stars. The predictions can be printed for later evaluation. Students view diagrams that compare the size and color of stars to human lives, and equilibrium within a star is stressed. Finally, students choose between two hypotheses about the length of life of a star. Students write a one- to three-sentence explanation for their hypotheses. The correct answer is provided. Copyright 2005 Eisenhower National Clearinghouse

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

2003-01-01

357

Ponderable soliton stars  

NASA Astrophysics Data System (ADS)

The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.

Chiu, Hong-Yee

1990-12-01

358

Red Eyes on Wolf-Rayet Stars: New Discoveries via Infrared Color Selection  

NASA Astrophysics Data System (ADS)

We summarize the latest results form our infrared, color-based survey for Galactic Wolf-Rayet (WR) stars. Using photometry from the Spitzer/GLIMPSE and 2MASS databases, we select WRs via a method that exploits their unique infrared colors, which is mainly the result of excess radiation generated by free-free scattering within their dense ionized winds. The selection criterion results in a WR detection rate of ?20% in spectroscopic follow-up of candidates that comprise a broad color space defined by the color distribution of all known WRs having B > 14 mag, although there are smaller regions within this color space which yield WRs at a rate of >50%. Cross-correlation with archival X-ray catalogs increases the WR detection rate of the broad color space to ?40%, although with significant bias toward WN types. Although the majority of the new WRs have no obvious association with stellar clusters, two WC8 stars reside in a previously unknown massive-star cluster, in which five OB supergiants were also identified. In addition, two WC and four WN stars, all but one of which are X-ray sources, were identified in association with the stellar clusters Danks 1 and 2. Our 60 latest WR discoveries (out of nearly 100 to date) include 38 WN types and 22 WC types, bringing the total number of known Galactic WRs close to 500, or ?8% of the total empirically estimated population. An examination of their Galactic distribution reveals an approximate tracing of spiral arms and an enhanced WR surface density toward several massive-star formation sites.

Mauerhan, J. C.; Van Dyk, S.; Morris, P.

2012-12-01

359

The Search for Acoustically-Driven Mass-Loss in Evolved Stars  

NASA Astrophysics Data System (ADS)

Recent ab-initio calculations of stochastic stellar wind models by Cuntz (1992 in Cool Stars VII, ASP Conf. Ser. 26, p.383) have proven remarkably robust in predicting observed chromospheric flow patterns including possible variabilities with time in selected cool, evolved stars. The calculations solve the equations of hydrodynamics using the method of characteristics and assume: (i) saw-tooth shock wave profiles, and (ii) wave periods were changed stochastically while keeping the wave amplitudes constant (see Cuntz 1990 Ap.J. 349, p.141). Among the results of fitting chromospheric flow velocities is the implication that the permitted range of acoustic wave periods for a given star is constrained. We made use of the IUE satellite during August and September 1992 to repeatedly observe two stars, the yellow giant Aldebaran (K5 III) and the red supergiant, Betelgeuse (M2 Iab), in order to sample variations in their atmospheres on timescales of ~ 10(4) to ~ 10(6) seconds, which bracket the predicted mean acoustic wave periods for these objects. In particular, we obtained deep exposures in order to measure density-sensitive line ratios within the C II] intercombination features near 2325A (cf. Lennon et al. 1985 Ap.J. 294, p.200) to test the hypothesis that density fluctuations could be measured as a consequence of these acoustic waves. The results of these observations will be presented and discussed in terms of the number and amplitude of acoustic waves contributing to chromospheric heating and mass loss from these stars, as well as the wave origins in the evolving oscillatory structure of these stellar interiors. We are pleased to acknowledge IUE--NASA grant NAG5-2103 for partial support of this effort.

Stencel, R. E.; Brown, A.; Carpenter, K. G.; Cuntz, M.; Judge, P.

1992-12-01

360

The donor star winds in High-Mass X-ray Binaries  

NASA Astrophysics Data System (ADS)

High-mass X-ray binaries (HMXBs) are essential astrophysical laboratories. These objects represent an advanced stage in the evolution of massive binary systems, after the initially more massive star has already collapsed in a supernova explosion, but its remnant, a neutron star or black hole, remains gravitationally bound. The stellar wind from the OB-type donor is partially accreted onto its compact companion powering its relatively high X-ray luminosity. Since HMXBs accrete from the stellar wind, parameters such as the donor's mass-loss rate, the velocity of the wind, and its clumpiness are of fundamental importance.This proposal takes advantage of the unique capabilities of HST/STIS for UV spectroscopy. We focus on the most populous in the Galaxy class of those HMXBs where the stellar wind of the OB donor is directly accreted onto a neutron star. Recently, a new sub-class of HMXBs - "supergiant fast X-ray transients" - was discovered. It has been proposed that these enigmatic objects can be explained by the specific properties of their donor-star winds. The only way to validate or disprove this hypothesis is by a studying the wind diagnostics lines in the UV spectra of donor stars. The observations proposed here will, for the first time, provide the UV spectra of this important new type of accreting binaries. Our state-of-the art non-LTE expanding stellar atmospheres and 3-D stellar wind simulations allow thorough exploitation of the STIS spectra. As a result we will obtain the wind parameters for a representative sample of six Galactic HMXBs, thus heightening our knowledge thereof considerably.

Oskinova, Lida

2014-10-01

361
362

Massive Star and Star Cluster Formation  

E-print Network

I review the status of massive star formation theories: accretion from collapsing, massive, turbulent cores; competitive accretion; and stellar collisions. I conclude the observational and theoretical evidence favors the first of these models. I then discuss: the initial conditions of star cluster formation as traced by infrared dark clouds; the cluster formation timescale; and comparison of the initial cluster mass function in different galactic environments.

Jonathan C. Tan

2006-10-16

363

Massive stars, disks, and clustered star formation  

NASA Astrophysics Data System (ADS)

The formation of an isolated massive star is inherently more complex than the relatively well-understood collapse of an isolated, low-mass star. The dense, clustered environment where massive stars are predominantly found further complicates the picture, and suggests that interactions with other stars may play an important role in the early life of these objects. In this thesis we present the results of numerical hydrodynamic experiments investigating interactions between a massive protostar and its lower-mass cluster siblings. We explore the impact of these interactions on the orientation of disks and outflows, which are potentially observable indications of encounters during the formation of a star. We show that these encounters efficiently form eccentric binary systems, and in clusters similar to Orion they occur frequently enough to contribute to the high multiplicity of massive stars. We suggest that the massive protostar in Cepheus A is currently undergoing a series of interactions, and present simulations tailored to that system. We also apply the numerical techniques used in the massive star investigations to a much lower-mass regime, the formation of planetary systems around Solar- mass stars. We perform a small number of illustrative planet-planet scattering experiments, which have been used to explain the eccentricity distribution of extrasolar planets. We add the complication of a remnant gas disk, and show that this feature has the potential to stabilize the system against strong encounters between planets. We present preliminary simulations of Bondi-Hoyle accretion onto a protoplanetary disk, and consider the impact of the flow on the disk properties as well as the impact of the disk on the accretion flow.

Moeckel, Nickolas Barry

364

Touchstone Stars: Highlights from the Cool Stars 18 Splinter Session  

E-print Network

We present a summary of the splinter session on "touchstone stars" -- stars with directly measured parameters -- that was organized as part of the Cool Stars 18 conference. We discuss several methods to precisely determine cool star properties such as masses and radii from eclipsing binaries, and radii and effective temperatures from interferometry. We highlight recent results in identifying and measuring parameters for touchstone stars, and ongoing efforts to use touchstone stars to determine parameters for other stars. We conclude by comparing the results of touchstone stars with cool star models, noting some unusual patterns in the differences.

Mann, Andrew W; Boyajian, Tabetha; Gaidos, Eric; von Braun, Kaspar; Feiden, Gregory A; Metcalfe, Travis; Swift, Jonathan J; Curtis, Jason L; Deacon, Niall R; Filippazzo, Joseph C; Gillen, Ed; Hejazi, Neda; Newton, Elisabeth R

2014-01-01

365

59Death Stars Our sun is an active star that  

E-print Network

- Suppose that searches for planets orbiting red dwarf stars have studied 1000 stars for a total of 480 % Problem 3 - Suppose that searches for planets orbiting red dwarf stars have studied 1000 stars for a total dwarf stars. To two significant figures, about how long would inhabitants on each planet have to wait

366

A DETAILED FAR-ULTRAVIOLET SPECTRAL ATLAS OF O-TYPE STARS  

SciTech Connect

In this paper, we present a spectral atlas covering the wavelength interval 930-1188 A for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188 A. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of 'missed' features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas, to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. We discuss the statistics of line populations among the various elemental ionization states. Also, as an aid to users we list those isolated lines that can be used to determine stellar temperatures and the presence of possible chemical anomalies. Finally, we have prepared FITS files that give pairs of merged spectra for stars in our population sequences, for access via MAST.

Smith, Myron A., E-mail: msmith@stsci.edu [Catholic University of America, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2012-10-15

367