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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

Alfven waves in dusty winds of cool supergiant stars  

SciTech Connect

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

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

2005-09-28

3

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 interpretations. In the first, a solitary neutron star in our own galaxy shredded and accreted an approaching comet-like body. In the second, a neutron star is engulfed by, spirals into and merges with an evolved giant star in a distant galaxy. Now, thanks to a measurement of the Christmas burst’s host galaxy, astronomers have determined that it represented the collapse and explosion of a supergiant star hundreds of times larger than the sun. Credit: NASA's Goddard Space Flight Center Scientific Visualization Studio

Lynn Jenner

2013-04-16

4

Giant and supergiant stars with degenerate neutron cores  

NASA Astrophysics Data System (ADS)

Two classes of Thorne-Zytkow (TZ) stellar models are investigated: the giant models with low-mass envelopes and gravitational energy generation, and the super giant ones with more massive envelopes and nuclear energy generation. Bisnovatyi-Kogan and Lamzin (1984) argue that there is a flaw in the TZ match of the giant star's envelope onto their cores, that no equilibrium giant models will be possible when this flaw is corrected, and that such giant stars will turn out to die quickly via runaway neutrino losses and catastrophic contraction. The paper shows that Bisnovatyi-Kogan and Lamzin are mistaken: there is no flaw in the match to the core; fully self-consistent equilibrium models do exist; and the structure of those models suggests that they will be stable against neutrino-loss-triggered contraction. By contrast, there are genuine difficulties with the TZ supergiant models because their hot CNO cycle nuclear reactions get hung up waiting for beta-decays and thus have difficulty generating enough energy for hydrostatic support. An unsuccessful attempt to build self-consistent supergiant models based on a nonequilibrium hot CNO cycle is described.

Eich, Chris; Zimmermann, Mark E.; Thorne, Kip S.; Zytkow, Anna N.

1989-11-01

5

Radii and Effective Temperatures of Giant and Supergiant Stars as Measured at the Palomar Testbed Interferometer  

Microsoft Academic Search

Using the Palomar Testbed Interferometer (PTI), we have measured angular diameters in the H and K bands for over 50 giant and supergiant stars, ranging in spectral type from A2 to M8. These diameters are part of an ongoing observational program at PTI to empirically establish effective temperatures and linear radii for these stars, in combination with existing photometry and

G. T. van Belle; R. R. Thompson

2000-01-01

6

On the Explosion Geometry of Red Supergiant Stars  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

7

The missing piece of the puzzle: Neutron stars accreting from supergiant companions  

NASA Astrophysics Data System (ADS)

The supergiant X-ray binaries (SG-XRBs) is a class of High-Mass X-ray Binaries that consists of supergiant fast X-ray transients (SFXTs) and "classical" SG-XRBs exhibiting a strong intrinsic absorption. Nowadays, we know only 3 Galactic "classical" SG-XRBs (with the remaining known wind-fed systems being SFXTs)! Recently, our team discovered the first extragalactic member of this well-hidden population of "classical" SG-XRBs that motivated us to look for additional neutron-star X-ray binaries accreting from supergiant stars. In this talk, I will present the latest results of this reseach based on multi-wavelength observations of the Magellanic Clouds. These first observational constraints of the formation and evolution of "classical" SG-XRBs will help in the planning and interpretation of future multi-wavelength observations of these obscured high-mass X-ray binaries in nearby star-forming galaxies.

Antoniou, Vallia; Zezas, Andreas; Maravelias, Grigoris; Kalogera, Vicky

2012-09-01

8

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

Microsoft Academic Search

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

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

2005-01-01

9

A catalog of rotational and radial velocities for evolved stars. II. Ib supergiant stars  

NASA Astrophysics Data System (ADS)

Rotational velocity vsin i and mean radial velocity are presented for a sample of 231 Ib supergiant stars covering the spectral region F, G and K. This work is the second part of the large survey carried out with the CORAVEL spectrometer to establish the behavior of the rotation for stars evolving off the main sequence (De Medeiros & Mayor 1999). These data will add constraints to the study of the rotational behavior in evolved stars, as well as solid information concerning tidal interactions in binary systems and on the link between rotation, chemical abundance and activity in stars of intermediate masses. Based on observations collected at the Haute-Provence Observatory, Saint-Michel, France and at the European Southern Observatory, La Silla, Chile Table 1 is only available 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/395/97

De Medeiros, J. R.; Udry, S.; Burki, G.; Mayor, M.

2002-11-01

10

Radii and Effective Temperatures of Giant and Supergiant Stars as Measured at the Palomar Testbed Interferometer  

Microsoft Academic Search

Using the Palomar Testbed Interferometer (PTI), angular diameters have been measured for over 60 giant and supergiant stars, ranging in spectral type from B7 to M5. Analysis of night-to-night variations in the data reveal a consistency in the reduced results at the 1.3% level; comparison of PTI data to previous investigations with IOTA, CERGA, and lunar occultations show good agreement

G. T. van Belle

1997-01-01

11

Analytical solutions of stellar winds in B-A type supergiants stars  

NASA Astrophysics Data System (ADS)

An analytical solution for the ?-slow hydrodynamic solution (Cure et al. 2011) in B-A type supergiants stars is developed. The methodology is based on the analytical solutions of a) Villata (1992), which is described in terms of the stellar and wind parameters and b) Muller & Vink (2008), which is described in terms of fitting parameters from a numerical solution (hydrodynamic). These methodologies only apply for fast solutions, for that reason the line acceleration term (gL) of Muller & Vink method is modified in order to obtain an analytical solution for the ?-slow solution. To find a relationship between the parameters from the fit and the stellar and wind parameters, a computational grid, based on the grid of stellar models from Ekstrom et al. (2012), is created for B-A type supergiants stars with ?-slow hydrodynamic solution. Finally, an analytical solution for B-A type supergiants stars is obtained based on the Lambert W function (Corless et al. 1996). Comparing with the numerical solutions, the terminal velocity has a median relative error below 4% and the mass loss rate has a median relative error below 5%. In addition, we calculated the wind-momentum luminosity relationship (WLR) with the models from the computational grid and compared with the observations, showing a very good agreement.

Araya, Ignacio; Cure, Michel

2013-06-01

12

Studies of Evolved Star Mass Loss: GRAMS Modeling of Red Supergiant and Asymptotic Giant Branch Stars in the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

As proposed in our NASA Astrophysics Data Analysis Program (ADAP) proposal, my colleagues and I are studying mass loss from evolved stars. Such stars lose their own mass in their dying stages, and in their expelled winds they form stardust. To model mass loss from these evolved stars, my colleagues and I have constructed GRAMS: the Grid of Red supergiant and Asymptotic giant branch star ModelS. These GRAMS radiative transfer models are fit to optical through mid-infrared photometry of red supergiant (RSG) stars and asymptotic giant branch (AGB) stars. I will discuss our current studies of mass loss from AGB and RSG stars in the Small Magellanic Cloud (SMC), fitting GRAMS models to the photometry of SMC evolved star candidates identified from the SAGE-SMC (PI: K. Gordon) Spitzer Space Telescope Legacy survey. This work will be briefly compared to similar work we have done for the LMC. I will also discuss Spitzer Infrared Spectrograph (IRS) studies of the dust produced by AGB and RSG stars in the LMC. BAS is grateful for support from the NASA-ADAP grant NNX11AB06G.

Sargent, Benjamin A.; Srinivasan, S.; Riebel, D.; Boyer, M.; Meixner, M.

2012-01-01

13

RV and vsini of Ib supergiant stars (de Medeiros+, 2002)  

NASA Astrophysics Data System (ADS)

The observations are from De Medeiros & Mayor, 1999, Cat. . The large majority of the observations were carried out from March 1986 to May 1994, except for those stars having a larger time base. All stars north of declination -25° were observed with the CORAVEL mounted on the Swiss 1-meter telescope at the Haute-Provence Observatory, Saint-Michel (France). The stars south of declination -25° have been measured with the southern CORAVEL at the Cassegrain focus of the 1.5m Danish telescope at ESO La Silla (Chile). (1 data file).

de Medeiros, J. R.; Udry, S.; Burki, G.; Mayor, M.

2003-01-01

14

AGB stars and red supergiants in the LMC as seen with DENIS  

NASA Astrophysics Data System (ADS)

The goal of this short communication is to evaluate the usefulness of Deep Near-Infrared Survey (DENIS) for the study of stars on the Asymptotic Giant Branch (AGB) and red supergiants (RSG) in the Large Magellanic Cloud (LMC). We try to answer two fundamental questions: (i) Can DENIS detect all the AGB stars and RSG in the LMC? (ii) How can we identify these sources using only the I, J, and K bands? We have used an observational approach by compiling available data in the LMC in the (V,R), I, J, H, K, (L,M) bands. About 3000 AGB stars and RSG have been measured in I, of which about 1000 have JHK measurements. Note that most of the searches were based on I and then the sample is strongly biased for optical stars, losing mass at a small rate. Only a few dust obscured objects are known, identified on the basis of Infrared Astronomy Satellite (IRAS) observations.

Loup, C.; Groenewegen, M. A. T.

1994-07-01

15

Interferometric observations of the supergiant stars ? Orionis and ? Herculis with FLUOR at IOTA  

NASA Astrophysics Data System (ADS)

We report the observations in the K band of the red supergiant star ? Orionis and of the bright giant star ? Herculis with the FLUOR beamcombiner at the IOTA interferometer. The high quality of the data allows us to estimate limb-darkening and derive precise diameters in the K band which combined with bolometric fluxes yield effective temperatures. In the case of Betelgeuse, data collected at high spatial frequency although sparse are compatible with circular symmetry and there is no clear evidence for departure from circular symmetry. We have combined the K band data with interferometric measurements in the L band and at 11.15 ?m. The full set of data can be explained if a 2055 K layer with optical depths ?K=0.060±0.003, ?L=0.026±0.002 and ?11.15 ?m= 2.33±0.23 is added 0.33 R* above the photosphere providing a first consistent view of the star in this range of wavelengths. This layer provides a consistent explanation for at least three otherwise puzzling observations: the wavelength variation of apparent diameter, the dramatic difference in limb darkening between the two supergiant stars, and the previously noted reduced effective temperature of supergiants with respect to giants of the same spectral type. Each of these may be simply understood as an artifact due to not accounting for the presence of the upper layer in the data analysis. This consistent picture can be considered strong support for the presence of a sphere of warm water vapor, proposed by \\cite{tsuji2000} when interpreting the spectra of strong molecular lines. Based on observations collected at the IOTA interferometer, Whipple Observatory, Mount Hopkins, Arizona.

Perrin, G.; Ridgway, S. T.; Coudé du Foresto, V.; Mennesson, B.; Traub, W. A.; Lacasse, M. G.

2004-05-01

16

Evolution of Massive Stars with Pulsation-driven Superwinds During the Red Supergiant Phase  

NASA Astrophysics Data System (ADS)

Pulsations driven by partial ionization of hydrogen in the envelope are often considered important for driving winds from red supergiants (RSGs). In particular, it has been suggested by some authors that the pulsation growth rate in an RSG can be high enough to trigger an unusually strong wind (or a superwind), when the luminosity-to-mass ratio becomes sufficiently large. Using both hydrostatic and hydrodynamic stellar evolution models with initial masses ranging from 15 to 40 M sun, we investigate (1) how the pulsation growth rate depends on the global parameters of supergiant stars and (2) what would be the consequences of a pulsation-driven superwind, if it occurred, for the late stages of massive star evolution. We suggest that such a superwind history would be marked by a runaway increase, followed by a sudden decrease, of the wind's mass-loss rate. The impact on the late evolution of massive stars would be substantial, with stars losing a huge fraction of their H-envelope even with a significantly lower initial mass than previously predicted. This might explain the observed lack of Type II-P supernova (SN) progenitors having initial mass higher than about 17 M sun. We also discuss possible implications for a subset of Type IIn SNe.

Yoon, Sung-Chul; Cantiello, Matteo

2010-07-01

17

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

Microsoft Academic Search

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

A. Maggio; G. S. Vaiana; B. M. Haisch; R. A. Stern; J. Bookbinder; F. R. Harnden Jr.; R. Rosner

1990-01-01

18

Radiative hydrodynamic simulations of red supergiant stars. III. Spectro-photocentric variability, photometric variability, and consequences on Gaia measurements  

NASA Astrophysics Data System (ADS)

Context. It has been shown that convection in red supergiant stars (RSG) gives rise to large granules that cause surface inhomogeneities and shock waves in the photosphere. The resulting motion of the photocentre (on time scales ranging from months to years) could possibly have adverse effects on the parallax determination with Gaia. Aims: We explore the impact of the granulation on the photocentric and photometric variability. We quantify these effects in order to better characterise the error that could possibly alter the parallax. Methods: We use 3D radiative-hydrodynamics (RHD) simulations of convection with CO5BOLD and the post-processing radiative transfer code Optim3D to compute intensity maps and spectra in the Gaia G band [325-1030 nm]. Results: We provide astrometric and photometric predictions from 3D simulations of RSGs that are used to evaluate the possible degradation of the astrometric parameters of evolved stars derived by Gaia. We show in particular from RHD simulations that a supergiant like Betelgeuse exhibits a photocentric noise characterised by a standard deviation of the order of 0.1 AU. The number of bright giant and supergiant stars whose Gaia parallaxes will be altered by the photocentric noise ranges from a few tens to several thousands, depending on the poorly known relation between the size of the convective cells and the atmospheric pressure scale height of supergiants, and to a lower extent, on the adopted prescription for galactic extinction. In the worst situation, the degradation of the astrometric fit caused by this photocentric noise will be noticeable up to about 5 kpc for the brightest supergiants. Moreover, parallaxes of Betelgeuse-like supergiants are affected by an error of the order of a few percents. We also show that the photocentric noise, as predicted by the 3D simulation, does account for a substantial part of the supplementary "cosmic noise" that affects Hipparcos measurements of Betelgeuse and Antares.

Chiavassa, A.; Pasquato, E.; Jorissen, A.; Sacuto, S.; Babusiaux, C.; Freytag, B.; Ludwig, H.-G.; Cruzalèbes, P.; Rabbia, Y.; Spang, A.; Chesneau, O.

2011-04-01

19

A large population of red supergiants in the super star cluster NGC 1705-1  

NASA Astrophysics Data System (ADS)

We present near-infrared integral field observations of the super star cluster in the amorphous galaxy NGC1705. Data have been collected with SINFONI mounted on the VLT. Adaptive optics was used under good seeing conditions. Mosaics of the cluster and its immediate surrounding have been constructed. The cluster is not spatially resolved. Its radius is smaller than 2.85 ± 0.50pc. The K-band spectrum of the cluster is dominated by strong CO absorption bandheads. It is typical of a Galactic K 4-5 supergiant. Its age is estimated to be 12 ± 6Myr. The large error bar is rooted in the uncertainties of the input physics and ingredients of different evolutionary models.

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

2013-05-01

20

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

SciTech Connect

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

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

2009-06-15

21

Neutron star masses from hydrodynamical effects in obscured supergiant high mass X-ray binaries  

NASA Astrophysics Data System (ADS)

Context. A population of obscured supergiant high mass X-ray binaries has been discovered by INTEGRAL. X-ray wind tomography of IGR J17252-3616 inferred a slow wind velocity to account for the enhanced obscuration. Aims: The main goal of this study is to understand under which conditions high obscuration could occur. Methods: We have used an hydrodynamical code to simulate the flow of the stellar wind around the neutron star. A grid of simulations was used to study the dependency of the absorbing column density and of the X-ray light-curves on the model parameters. A comparison between the simulation results and the observations of IGR J17252-3616 provides an estimate on these parameters. Results: We have constrained the wind terminal velocity to 500-600 km s-1 and the neutron star mass to 1.75-2.15 M?. Conclusions: We have confirmed that the initial hypothesis of a slow wind velocity with a moderate mass loss rate is valid. The mass of the neutron star can be constrained by studying its impact on the accretion flow.

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

2012-11-01

22

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

23

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

24

Abundances of r-PROCESS Elements in the Photosphere of Red Supergiant Star PMMR23 in Small Magellanic Cloud  

Microsoft Academic Search

Detailed analysis of chemical abundances determined from high-resolution CCD-spectrogram of supergiant star PMMR23 (K5 I) in SMC is presented. The observation were obtained at 3.6 meter ESO La Silla telescope by Hill (1997). Spectral resolving power is near R=30.000. The wavelength coverage is 5050-7200 A. The abundances of iron and 15 r-, s-processes elements are found. The abundances of Cu,

S. V. Vasil'Eva; V. F. Gopka; A. V. Yushchenko; S. M. Andryevsky

2005-01-01

25

The Period-Luminosity Relation of Red Supergiant Stars in the Small Magellanic Cloud  

NASA Astrophysics Data System (ADS)

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

Yang, Ming; Jiang, B. W.

2012-07-01

26

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

NASA Astrophysics Data System (ADS)

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

Nieva, M.-F.

2013-02-01

27

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

28

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

SciTech Connect

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. 79 refs.

Maggio, A.; Vaiana, G.S.; Haisch, B.M.; Stern, R.A.; Bookbinder, J. (Osservatorio Astronomico, Palermo (Italy) Lockheed Research Laboratories, Palo Alto, CA (USA) Joint Institute for Laboratory Astrophysics, Boulder, CO (USA) Smithsonian Astrophysical Observatory, Cambridge, MA (USA))

1990-01-01

29

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

30

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

31

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

32

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

33

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

34

Expected angular separations of late-type supergiant +B star binaries in the Milky Way and LMC  

NASA Astrophysics Data System (ADS)

The authors develop a model for the binary frequencies of late-type supergiants. The model incorporates the semimajor-axis limitations imposed by Roche lobe overflow and is flexible enough to include the observational constraints imposed by various observing procedures. In particular, constraints on the minimum observable velocity amplitudes of the primaries and the presence of hot secondaries - observed in the UV - are predicted and found to be in excellent agreement with existing observations. The model is then used to predict the expected distribution of angular separations of late-type galactic supergiants and luminous M supergiants in the LMC. It is shown that the interferometer proposed by Massa and Endal (1987) should be capable of "resolving" more than 40 galactic Cepheid binaries, about 400 nonvariable large-type galactic supergiant binaries, and 25 M supergiant binaries in the LMC.

Massa, Derck; Endal, Andrew S.

1987-03-01

35

Dying Supergiant Stars Implicated in Hours-long Gamma-Ray Bursts  

NASA Website

Three unusually long-lasting stellar explosions discovered by NASA's Swift satellite represent a new class of gamma-ray bursts that likely arise from dying stars hundreds of times larger than the sun.

36

Red Supergiant Stars in the Large Magellanic Cloud. I. The Period-Luminosity Relation  

NASA Astrophysics Data System (ADS)

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

Yang, Ming; Jiang, B. W.

2011-01-01

37

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

38

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

SciTech Connect

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. 67 refs.

Haisch, B.M.; Bookbinder, J.A.; Maggio, A.; Vaiana, G.S.; Bennett, J.O. (Lockheed Research Laboratories, Palo Alto, CA (USA) Smithsonian Astrophysical Observatory, Cambridge, MA (USA) Osservatorio Astronomico, Palermo (Italy) Colorado Univ., Boulder (USA))

1990-10-01

39

Spectroscopy of Supergiants with IR-Excesses: RV Tau Type Stars  

Microsoft Academic Search

Using high resolution CCD spectra obtained with the echelle-spectrometers of the 6 m telescope, we determined by the model atmospheres method the parameters Te, log g and the detailed chemical composition for 4 RV Tau type pulsating stars in the galactic field: AC Her, U Mon, RV Tau and AI CMi. For the first time from high resolution spectra the

V. G. Klochkova; V. E. Panchuk

1999-01-01

40

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

Microsoft Academic Search

The cD-type Brightest Cluster Galaxies contain the richest globular cluster systems {GCSs} that exist. The wealth of results gathered from previous HST imaging programs in many smaller galaxies show that GCSs are powerful and unique tracers that link to origin and evolution of structure in two directions simultaneously: one direction is inward to the structure of the protoglobular clouds, star

William Harris

2009-01-01

41

A spectroscopic study of supergiants with infrared excesses: Pulsating RV Tau stars  

Microsoft Academic Search

We use high-resolution CCD spectra from the LYNX echelle spectrometer of the 6-m telescope to determine the fundamental parameters T_eff and log g and the detailed chemical composition for four pulsating RV Tau stars in the Galactic field - AC Her, U Mon, RV Tau, and AI CMi - by the method of model atmospheres. Based on high-resolution spectra, we

V. G. Klochkova; V. E. Panchuk

1998-01-01

42

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

43

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

NASA Astrophysics Data System (ADS)

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

Boyer, Martha L.; Melbourne, J.

2013-01-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

45

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

46

A Tale of Two Stars: The Extreme O7 Iaf+ Supergiant AV 83 and the OC7.5 III((f)) star AV 69  

NASA Astrophysics Data System (ADS)

We present a detailed study of AV 83, an O7 Iaf+ supergiant, and AV 69 [OC7.5 III((f))] in the SMC. The stars have similar effective temperatures and luminosities but show very different wind signatures. For our study we have used the non-LTE line-blanketed atmosphere code developed by Hillier and Miller, which explicitly allows for line blanketing by C, N, O, S, Ar, Ne, Fe, and other elements. Our study finds that AV 83 has an effective temperature of approximately 33,000 K and logg~3.25. It has an extended photosphere as a result of a ``low'' effective surface gravity and a much denser wind than main-sequence O stars. We can match the spectrum only by using a slow velocity law with ?~2, a value that is much larger than the values of around 1 predicted by standard radiation wind theory. Further, we show that the H? emission profile in AV 83 is sensitive to the adopted surface gravity. To fit the spectrum of AV 83, we have considered conventional models in which the wind is smooth and alternate models in which the winds are highly clumped. Both types of winds yield a satisfactory fit to the majority of lines in the observed spectrum; however, strong UV photospheric lines and the P V resonance transitions favor a clumped wind. If clumping is important, it must begin at relatively low velocities (i.e., 30 km s-1, not 300 km s-1). In the smooth wind, the line force is too small to drive the wind. In the clumped wind, the line force is generally sufficient to drive the wind, although there are still some discrepancies around the sonic point. In AV 83, the N abundance is substantially enhanced relative to normal SMC abundances, while both C and O are SMC-like, consistent with the presence of internally processed CNO material at the stellar surface. The N III ?4640 multiplet, which is known to be produced by dielectronic recombination, is well reproduced by the models. These lines, and the adjacent C III ?4649 multiplet, show a significant sensitivity to surface gravity, as well as the usual sensitivity to abundance and effective temperature. Incoherent electron scattering, occurring within the photosphere, can explain the broad wings seen on these lines. We have modeled the Fe spectrum (Fe IV-Fe VI) in the UV in both AV 83 and AV 69. For stars with an effective temperature around 33,000 K, the Fe IV-to-Fe V line ratios form a useful effective temperature diagnostic and give results consistent with those found from optical and UV line diagnostics. The derived iron abundance, which is sensitive to the adopted microturbulent velocity, is 0.2-0.4 times the solar iron abundance in AV 83, while 0.2 solar gives a good fit for AV 69. The wind of AV 69 is substantially less dense than that of AV 83. Because of the lack of suitable diagnostics, it is impossible to constrain the mass-loss rate and velocity law independently. Its spectrum indicates that it has a similar effective temperature to AV 83 (Teff~34,000 K), a substantially higher gravity (logg=3.5) than AV 83, and a CNO abundance pattern that has not been influenced by internal CNO processing. We show that the N/C abundance ratio is substantially below solar, in agreement with SMC nebular and stellar abundance studies. The differences between the spectra of AV 83 and AV 69, and between the derived masses and surface abundances, are striking. We have examined possible causes, and only one seems consistent with the observations and our current understanding of massive star evolution. AV 83 was most likely a fast rotator that experienced rotationally enhanced mass loss. The presence of enhanced N but almost normal C and O abundances is a direct indication of rotationally induced mixing. On the other hand, AV 69 is a slow rotator. As part of our analyses, we have systematically examined the influence of the H/He abundance ratio, the mass-loss rate, the velocity law, the Fe abundance, microturbulence, and clumping on the theoretical spectrum. We illustrate which lines provide useful diagnostics and highlight some of the difficulties associated with spectroscopic analyses of O st

Hillier, D. John; Lanz, T.; Heap, S. R.; Hubeny, I.; Smith, L. J.; Evans, C. J.; Lennon, D. J.; Bouret, J. C.

2003-05-01

47

Mass-losing M supergiants in the solar neighborhood  

SciTech Connect

A list of the 21 mass-losing red supergiants (20 M type, one G type; L greater than 100,000 solar luminosities) within 2.5 kpc of the sun is compiled. These supergiants are highly evolved descendants of main-sequence stars with initial masses larger than 20 solar masses. The surface density is between about 1 and 2/sq kpc. As found previously, these stars are much less concentrated toward the Galactic center than W-R stars, which are also highly evolved massive stars. Although with considerable uncertainty, it is estimated that the mass return by the M supergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpc yr. In the hemisphere facing the Galactic center there is much less mass loss from M supergiants than from W-R stars, but, in the anticenter direction, the M supergiants return more mass than do the W-R stars. The duration of the M supergiant phase appears to be between 200,000 and 400,000 yr. During this phase, a star of initially at least 20 solar masses returns perhaps 3-10 solar masses into the interstellar medium. 60 refs.

Jura, M.; Kleinmann, S.G. (California Univ., Los Angeles (USA) Massachusetts Univ., Amherst (USA))

1990-08-01

48

Mass-losing M supergiants in the solar neighborhood  

NASA Astrophysics Data System (ADS)

A list of the 21 mass-losing red supergiants (20 M type, one G type; L greater than 100,000 solar luminosities) within 2.5 kpc of the sun is compiled. These supergiants are highly evolved descendants of main-sequence stars with initial masses larger than 20 solar masses. The surface density is between about 1 and 2/sq kpc. As found previously, these stars are much less concentrated toward the Galactic center than W-R stars, which are also highly evolved massive stars. Although with considerable uncertainty, it is estimated that the mass return by the M supergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpc yr. In the hemisphere facing the Galactic center there is much less mass loss from M supergiants than from W-R stars, but, in the anticenter direction, the M supergiants return more mass than do the W-R stars. The duration of the M supergiant phase appears to be between 200,000 and 400,000 yr. During this phase, a star of initially at least 20 solar masses returns perhaps 3-10 solar masses into the interstellar medium.

Jura, M.; Kleinmann, S. G.

1990-08-01

49

Yellow supergiants as supernova progenitors: an indication of strong mass loss for red supergiants?  

NASA Astrophysics Data System (ADS)

Context. The increasing number of observed supernova events allows for finding the progenitor star even more frequently in archive images. In a few cases, the progenitor star is a yellow supergiant star. The estimated position in the Hertzsprung-Russell diagram of these stars is not compatible with the theoretical tracks of classical single-star models. Aims: According to several authors, the mass-loss rates during the red supergiant phase could be underestimated. We study the impact of an increase in these mass-loss rates on the position of 12 to 15 M? stars at the end of their nuclear lives, in order to reconcile the theoretical tracks with the observed yellow supergiant progenitors. Methods: We have performed calculations of 12 to 15 M? rotating stellar models using the Geneva stellar evolution code. To account for the uncertainties in the mass-loss rates during the RSG phase, we increased the mass-loss rate of the star (between 3 and 10 times the standard one) during that phase and compared the evolution of stars undergoing such high mass-loss rates with models computed with the standard mass-loss prescription. Results: We show that the final position of the models in the Hertzsprung-Russell diagram depends on the mass loss they undergo during the red supergiant phase. With an increased mass-loss rate, we find that some models end their nuclear life at positions that are compatible with the observed position of several supernova progenitors. We conclude that an increased mass-loss rate (whose physical mechanism still needs to be clarified) allows single-star models to simultaneously reproduce the estimated position in the HRD of the YSG SN progenitors, as well as the SN type.

Georgy, C.

2012-02-01

50

YELLOW SUPERGIANTS IN THE ANDROMEDA GALAXY (M31)  

SciTech Connect

The yellow supergiant content of nearby galaxies can provide a critical test of stellar evolution theory, bridging the gap between the hot, massive stars and the cool red supergiants. But, this region of the color-magnitude diagram is dominated by foreground contamination, requiring membership to somehow be determined. Fortunately, the large negative systemic velocity of M31, coupled to its high rotation rate, provides the means for separating the contaminating foreground dwarfs from the bona fide yellow supergiants within M31. We obtained radial velocities of {approx}2900 individual targets within the correct color-magnitude range corresponding to masses of 12 M{sub sun} and higher. A comparison of these velocities to those expected from M31's rotation curve reveals 54 rank-1 (near certain) and 66 rank-2 (probable) yellow supergiant members, indicating a foreground contamination >= 96%. We expect some modest contamination from Milky Way halo giants among the remainder, particularly for the rank-2 candidates, and indeed follow-up spectroscopy of a small sample eliminates four rank 2's while confirming five others. We find excellent agreement between the location of yellow supergiants in the H-R diagram and that predicted by the latest Geneva evolutionary tracks that include rotation. However, the relative number of yellow supergiants seen as a function of mass varies from that predicted by the models by a factor of >10, in the sense that more high-mass yellow supergiants are predicted than those are actually observed. Comparing the total number (16) of >20 M{sub sun} yellow supergiants with the estimated number (24,800) of unevolved O stars indicates that the duration of the yellow supergiant phase is {approx}3000 years. This is consistent with what the 12 M{sub sun} and 15 M{sub sun} evolutionary tracks predict, but disagrees with the 20,000-80,000 year timescales predicted by the models for higher masses.

Drout, Maria R.; Massey, Philip [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States); Meynet, Georges [Geneva University, Geneva Observatory, CH-1290 Versoix (Switzerland); Tokarz, Susan; Caldwell, Nelson, E-mail: maria-drout@uiowa.ed, E-mail: Phil.Massey@lowell.ed, E-mail: georges.meynet@unige.c, E-mail: tokarz@cfa.harvard.ed, E-mail: caldwell@cfa.harvard.ed [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)

2009-09-20

51

Another cluster of red supergiants close to RSGC1  

Microsoft Academic Search

Context. Recent studies have revealed massive star clusters in a region of the Milky Way close to the tip of the Long Bar. These clusters are heavily obscured and are characterised by a population of red supergiants. Aims: We analyse a previously unreported concentration of bright red stars ~16' away from the cluster RSGC1 Methods: We utilised near IR photometry

I. Negueruela; C. González-Fernández; A. Marco; J. S. Clark; S. Martínez-Núñez

2010-01-01

52

The Red Supergiant Problem: Circumstellar dust as a solution  

NASA Astrophysics Data System (ADS)

We investigate the red supergiant problem: the apparent dearth of Type IIP supernova progenitors with masses between 16 and 30 M?. Although red supergiants with masses in this range have been observed, none have been identified as progenitors in pre-explosion images. We show that, by failing to take into account the additional extinction resulting from the dust produced in the red supergiant winds, the luminosity of the most massive red supergiants at the end of their lives is underestimated. We re-estimate the initial masses of all Type IIP progenitors for which observations exist and analyse the resulting population. We find that the most likely maximum mass for a Type IIP progenitor is 21+2 -1 M?. This is in closer agreement with the limit predicted from single star evolution models.

Walmswell, Joe; Eldridge, John

2012-09-01

53

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

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

54

YELLOW SUPERGIANTS IN THE SMALL MAGELLANIC CLOUD: PUTTING CURRENT EVOLUTIONARY THEORY TO THE TEST  

SciTech Connect

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

Neugent, Kathryn F.; Massey, Philip; Skiff, Brian [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States); Drout, Maria R. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52245 (United States); Meynet, Georges [Geneva Observatory, Geneva University, CH-1290 Versoix (Switzerland); Olsen, Knut A. G., E-mail: kneugent@lowell.ed, E-mail: phil.massey@lowell.ed, E-mail: bas@lowell.ed, E-mail: maria-drout@uiowa.ed, E-mail: georges.meynet@unige.c, E-mail: kolsen@noao.ed [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85748 (United States)

2010-08-20

55

B-Type Supergiants in the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

The fact that early B-type supergiants lie in the theoretical blue Hertzsprung gap of the Hertzsprung-Russell Diagram is a long-standing problem in stellar evolution. This has led to considerable uncertainty over the evolutionary status of these stars: Do they indicate a bluewards extension of the hot core-helium-burning phase? If so, then are they pre-Red Supergiant (RSG) or post-RSG stars? Can one broaden the main sequence to partially fill this gap? Does binary evolution provide a significant channel for populating the gap? In this paper we discuss the properties of main-sequence stars and B-type supergiants within the context of the VLT-FLAMES Survey of Massive Stars, which has led to a paradigm shift in our understanding of massive-star evolution. We show that there is now strong evidence from consideration of surface nitrogen abundances in support of the idea that B-type supergiants do not evolve directly from the main sequence, and that rotational mixing may not be as dominant a process as was previously thought.

Lennon, D. J.; Trundle, C.; Hunter, I.; Smartt, S.; Dufton, P.; Evans, C.; Langer, N.; Brott, I.

2010-06-01

56

Red supergiants around the obscured open cluster Stephenson 2  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

57

Radii and Effective Temperatures for G, K, and M Giants and Supergiants  

Microsoft Academic Search

Interferometrically determined angular diameters obtained at the Palomar Testbed Interferometer (PTI) for 69 giant and supergiant stars are presented. Spectral types of the 59 giant stars generally lie between G6 and M6, although a B7 giant is included; the nine bright giants and supergiants have spectral types between F5 and M5. Comparison of the results to those from the IR

G. T. van Belle; R. R. Thompson; A. F. Boden; M. M. Colavita; P. J. Dumont; D. W. Mobley; D. Palmer; M. Shao; G. X. Vasisht; J. K. Wallace; M. J. Creech-Eakman; C. D. Koresko; S. R. Kulkarni; X. P. Pan; J. Gubler

1999-01-01

58

The Temperatures of Red Supergiants  

NASA Astrophysics Data System (ADS)

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; Kudritzki, Rolf-Peter; Plez, Bertrand; Trager, Scott; Lançon, Ariane; Gazak, Zach; Bergemann, Maria; Evans, Chris; Chiavassa, Andrea

2013-04-01

59

Fine structure line emission from supergiants  

NASA Astrophysics Data System (ADS)

We have detected (O I) 63 micron and (Si II) 35 micron emission from the oxygen-rich, M supergiants alpha Orionis (Betelgeuse), alpha Scorpii (Antares), and alpha Herculis (Rasalgethi). The measured fluxes indicate that the emission originates in dense, warm gas in the inner envelope or transition region where molecules and dust are expected to form and the acceleration of the wind occurs. Mass-loss rates are derived, evidence for time variability is presented, and results for other evolved stars are included.

Haas, Michael R.; Glassgold, Alfred E.; Tielens, Alexander G. G. M.

60

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

61

Another cluster of red supergiants close to RSGC1  

Microsoft Academic Search

Recent studies have revealed massive star clusters in a region of the Milky\\u000aWay close to the tip of the Long Bar. These clusters are heavily obscured and\\u000aare characterised by a population of red supergiants. We analyse a previously\\u000aunreported concentration of bright red stars ~16' away from the cluster RSGC1.\\u000aWe utilised near IR photometry to identify candidate

Ignacio Negueruela; Carlos Gonzalez-Fernandez; Amparo Marco; J. Simon Clark; Silvia Martinez-Nunez

2010-01-01

62

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

63

The physical properties of red supergiants  

NASA Astrophysics Data System (ADS)

Red supergiants (RSGs) are an evolved He-burning phase in the lifetimes of moderately high mass (10-25M?) stars. The physical properties of these stars mark them as an important and extreme stage of massive stellar evolution, but determining these properties has been a struggle for many years. The cool extended atmospheres of RSGs place them in an extreme position on the Hertzsprung-Russell diagram and present a significant challenge to the conventional assumptions of stellar atmosphere models. The dusty circumstellar environments of these stars can potentially complicate the determination of their physical properties, and unusual RSGs in the Milky Way and neighboring galaxies present a suite of enigmatic properties and behaviors that strain, and sometimes even defy, the predictions of stellar evolutionary theory. However, in recent years our understanding of RSGs, including the models and methods applied to our observations and interpretations of these stars, has changed and grown dramatically. This review looks back at some of the latest work that has progressed our understanding of RSGs, and considers the many new questions posed by our ever-evolving picture of these cool massive stars.

Levesque, Emily M.

2010-01-01

64

RADII AND EFFECTIVE TEMPERATURES FOR G, K, AND M GIANTS AND SUPERGIANTS G. T. VAN BELLE AND B. F. LANE  

Microsoft Academic Search

Interferometrically determined angular diameters obtained at the Palomar Testbed Interferometer (PTI) for 69 giant and supergiant stars are presented. Spectral types of the 59 giant stars generally lie between G6 and M6, although a B7 giant is included; the nine bright giants and supergiants have spec- tral types between F5 and M5. Comparison of the results to those from the

R. R. THOMPSON; A. F. BODEN; M. M. COLAVITA; P. J. DUMONT; D. W. MOBLEY; D. PALMER; M. SHAO; G. X. VASISHT; J. K. WALLACE; M. J. CREECH-EAKMAN; C. D. KORESKO; S. R. KULKARNI; X. P. PAN; J. GUBLER

65

Properties of Galactic B Supergiants  

NASA Astrophysics Data System (ADS)

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

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

2008-06-01

66

The Physical Properties of Red Supergiants  

NASA Astrophysics Data System (ADS)

Red supergiants (RSGs) are an He-burning phase in the evolution of moderately massive stars (10-25 Msun). For many years, the assumed physical properties of these stars placed them at odds with the predictions of evolutionary theory. We have recently determined new effective temperatures and luminosities for the RSG populations of galaxies with a factor of ~8 range in metallicity, including the Milky Way, the Magellanic Clouds, and M31. We find that these new physical properties greatly improve the agreement between the RSGs and the evolutionary tracks, although there are still notable difficulties with modeling the physical properties of RSGs at low metallicity. We have also examined several unusual RSGs, including VY CMa in the Milky Way, WOH G64 in the LMC, and a sample of four RSGs in the Magellanic Clouds, that show considerable variations in their physical parameters, most notably their effective temperatures. For all of these stars we re-examine their placement on the H-R diagram, where they have appeared to occupy the "forbidden" region to the right of the Hayashi track. We have updated current understanding of the physical properties of VY CMa and WOH G64; in the case of the unusual Magellanic Cloud variables, we conclude that these stars are undergoing an unstable evolutionary phase not previously associated with RSGs.

Levesque, E. M.

2010-06-01

67

PHOTOSPHERIC VARIATIONS OF THE SUPERGIANT {gamma} Cyg  

SciTech Connect

New high-resolution spectroscopic observations of the supergiant {gamma} Cyg (F8 Iab) taken between 2000 and 2008 consistently show strongly reversed-C-shaped bisectors for all unblended spectral lines. Small-amplitude variations in radial velocity and line shapes occur in an irregular manner with time scales {approx}100 days and longer. The radial velocities occasionally show changes as large as 2 km s{sup -1}, but much smaller changes are going on continuously. Differential line bisectors show shape changes and Doppler displacement characteristic of radial expansion and contraction. These might arise from non-periodic radial pulsation-like motions or from the appearance of giant convection cells that occupy most of the visible hemisphere of the star. Line-depth ratios are correlated with the line shifts on a seasonal basis and indicate temperature changes ranging up to {approx}15 K, with larger temperature occurring during times of most rapid contraction.

Gray, David F., E-mail: dfgray@uwo.c [Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7 (Canada)

2010-11-15

68

Circumstellar dust as a solution to the red supergiant supernova progenitor problem  

NASA Astrophysics Data System (ADS)

We investigate the red supergiant problem, the apparent death of Type IIP supernova progenitors with masses between 16 and 30 M?. Although red supergiants with masses in this range have been observed, none has been identified as progenitors in pre-explosion images. We show that, by failing to take into account the additional extinction resulting from the dust produced in the red supergiant winds, the luminosity of the most massive red supergiants at the end of their lives is underestimated. We re-estimate the initial masses of all Type IIP progenitors for which observations exist and analyse the resulting population. We find that the most likely maximum mass for a Type IIP progenitor is ?. This is in closer agreement with the limit predicted from single star evolution models.

Walmswell, Joseph J.; Eldridge, John J.

2012-01-01

69

The energy distributions of B supergiants in the Large Magellanic Cloud  

NASA Astrophysics Data System (ADS)

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

Fitzpatrick, E. L.

1986-09-01

70

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

71

Wind Variability in Intermediate Luminosity B Supergiants  

NASA Astrophysics Data System (ADS)

This study used the unique spectroscopic diagnostics of intermediate luminosity B supergiants to determine the ubiquity and nature of wind variability. Specifically, (1) A detailed analysis of HD 64760 demonstrated massive ejections into its wind, provided the first clear demonstration of a 'photospheric connection' and ionization shifts in a stellar wind; (2) The international 'IUE MEGA campaign' obtained unprecedented temporal coverage of wind variability in rapidly rotating stars and demonstrated regularly repeating wind features originating in the photosphere; (3) A detailed analysis of wind variability in the rapidly rotating B1 Ib, gamma Ara demonstrated a two component wind with distinctly different mean states at different epochs; (4) A follow-on campaign to the MEGA project to study slowly rotating stars was organized and deemed a key project by ESA/NASA, and will obtain 30 days of IUE observations in May-June 1996; and (5) A global survey of archival IUE time series identified recurring spectroscopic signatures, identified with different physical phenomena. Items 4 and 5 above are still in progress and will be completed this summer in collaboration with Raman Prinja at University College, London.

Massa, Derck

1996-04-01

72

Are the red supergiants Epsilon Peg and 12 PUP victims of mild s-processing?  

NASA Astrophysics Data System (ADS)

An abundance analysis of eight G and K supergiants has been performed with particular emphasis on two stars, Epsilon Peg and 12 Pup. It has been reported (Kovacs, 1983) that these two stars exhibit selective enhancement of Ba and, in the case of 12 Pup, Sr. Such a pattern of abundance enhancement would occur for very mild s-processing followed by extensive pollution of the star's outer envelope with this processed material. This type of mixing is not predicted by current models of stellar evolution. The previous Ba and Sr abundances were based on very strong lines of Ba II and Sr II and such lines are sensitive to microturbulence and conditions in the higher layers of the stellar atmosphere. This analysis compares the Ba II and Sr II line-strengths in Epsilon Peg and 12 Pup with six other cool supergiants and also utilizes weak Ba I and Sr I lines seen in the spectra of these stars. No enhancements of Ba or Sr, relative to the other supergiants, are found for Epsilon Peg or 12 Pup. In addition, calculations of the abundances produced by mild s-processing followed by extensive mixing with the outer envelope show that Co and Sc should also be enhanced substantially. Such enhancements are not observed in any of the supergiants.

Smith, Verne V.; Lambert, David L.

1987-06-01

73

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

Microsoft Academic Search

We use moderate-resolution optical spectrophotometry and the new MARCS stellar atmosphere models to determine the effective temperatures of 74 Galactic red supergiants (RSGs). The stars are mostly members of OB associations or clusters with known distances, allowing a critical comparison with modern stellar evolutionary tracks. We find we can achieve excellent matches between the observations and the reddened model fluxes

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

2005-01-01

74

The Yellow and Red Supergiants of M33  

NASA Astrophysics Data System (ADS)

Yellow and red supergiants are evolved massive stars whose numbers and locations on the Hertzsprung-Russell (H-R) diagram can provide a stringent test for models of massive star evolution. Previous studies have found large discrepancies between the relative number of yellow supergiants (YSGs) observed as a function of mass and those predicted by evolutionary models, while a disagreement between the predicted and observed locations of red supergiants (RSGs) on the H-R diagram was only recently resolved. Here, we extend these studies by examining the YSG and RSG populations of M33. Unfortunately, identifying these stars is difficult as this portion of the color-magnitude diagram is heavily contaminated by foreground dwarfs. We identify the RSGs through a combination of radial velocities and a two-color surface gravity discriminant, and after re-characterizing the rotation curve of M33 with our newly selected RSGs, we identify the YSGs through a combination of radial velocities and the strength of the O I ?7774 triplet. We examine ~1300 spectra in total and identify 121 YSGs (a sample that is unbiased in luminosity above log (L/L ?) ~ 4.8) and 189 RSGs. After placing these objects on the H-R diagram, we find that the latest generation of Geneva evolutionary tracks shows excellent agreement with the observed locations of our RSGs and YSGs, the observed relative number of YSGs with mass, and the observed RSG upper mass limit. These models therefore represent a drastic improvement over previous generations. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. MMT telescope time was granted by NOAO, through the Telescope System Instrumentation Program (TSIP). TSIP is funded by the National Science Foundation (NSF). This paper uses data products produced by the OIR Telescope Data Center, supported by the Smithsonian Astrophysical Observatory.

Drout, Maria R.; Massey, Philip; Meynet, Georges

2012-05-01

75

THE YELLOW AND RED SUPERGIANTS OF M33  

SciTech Connect

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

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

2012-05-10

76

YELLOW AND RED SUPERGIANTS IN THE LARGE MAGELLANIC CLOUD  

SciTech Connect

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

Neugent, Kathryn F.; Massey, Philip; Skiff, Brian [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States); Meynet, Georges, E-mail: kneugent@lowell.edu, E-mail: phil.massey@lowell.edu, E-mail: bas@lowell.edu, E-mail: georges.meynet@unige.ch [Geneva Observatory, Geneva University, CH-1290 Versoix (Switzerland)

2012-04-20

77

Two Circumstellar Bubbles around Blue Supergiants in the LMC  

NASA Astrophysics Data System (ADS)

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

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

1996-05-01

78

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

79

Theoretical Radial Pulsation Properties of Massive Yellow Supergiants  

NASA Astrophysics Data System (ADS)

We have studied the theoretical linear nonadiabatic radial pulsation periods and amplitude growth rates of two stellar models with initial masses of 30 and 40 solar masses. The intrinsic variability and dynamical properties of massive stars are very important to the understanding of the evolutionary behavior of these stars, especially those at, or near, the Humphreys-Davidson (H-D) Line, an empirically defined boundary in the upper portion of the H- R Diagram above which no stars are observed thus far to exist. Pulsation model parameters are derived from models we evolved for each initial mass. Initial chemical compositions are Y=0.28 and Z=0.02, and mass loss (according to the de Jager - Nieuwenhuijzen parameterization) and Livermore OPAL opacities are included in the modeling. Evolution was followed to core helium exhaustion, and all models are H-R Diagram first-crossing tracks; no blue loops occurred. Convection is treated using standard mixing length theory. As expected, the models did not exhibit radial pulsations blueward of an effective temperature of 6000 K. As yellow supergiants, we found them unstable to radial pulsation in an extension of the Classical Cepheid instability strip. The initial 30 solar mass model has a blue edge at 5700 K. The fundamental mode nonadiabatic pulsation period is 161 days, with an amplitude growth rate per period of 2%. At 5000 K, the period is 256 days, and the growth rate has greatly increased to 115%. The model's mass in this temperature interval is about 25.3 solar masses, and the luminosity is about 313000 solar luminosities. The initial 40 solar mass model has a blue edge at 5900 K, a period of 195 days, and a growth rate per period of 1.7%. At 4900 K, the period is 357 days, and the growth rate per period is 136%. Mass and luminosity here are about 32.3 and 527000 in solar units, respectively. While yellow supergiants, mass loss has not caused an enhancement of helium in the surface layers. For the initial 40 solar mass model, notable enhancement occurs when the star becomes a red supergiant, but this is not so for the lower initial mass model. For both models near their blue edges, helium ionization dominates as the pulsation driving mechanism. As the models evolve redwards, the pulsational driving contribution from the hydrogen ionization zone increases and becomes significant at about 5000 K. However, time dependent convection calculations may be necessary to model the effects of stronger convection at about this and cooler temperatures on the pulsational driving. If the very high growth rates calculated here indeed occur in real stars, it may be that the rapidly growing pulsations result in episodic ejections of mass of the tenuous outer layers of massive supergiants just below the H-D Line.

Soukup, M. S.; Cox, A. N.

1996-05-01

80

The Effective Temperatures and Physical Properties of Magellanic Cloud Red Supergiants: The Effects of Metallicity  

Microsoft Academic Search

We present moderate-resolution spectrophotometry of 36 red supergiants (RSGs) in the LMC and 37 RSGs in the SMC. Using the MARCS atmosphere models to fit this spectrophotometry, we determine the stars' physical properties and compare the results to evolutionary models. The (V-R)0 broadband colors agree with those from fitting the optical spectrophotometry, but (V-K)0 results show metallicity-dependent systematic differences in

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

2006-01-01

81

Yellow supergiants in open clusters  

NASA Astrophysics Data System (ADS)

Superluminous giant stars (SLGs) have been reported in young globular clusters in the Large Magellanic Cloud (LMC). These stars appear to be in the post asymptotic giant branch phase of evolution. This program was an investigation of galactis SLG candidates in open clusters, which are more like the LMC young globular clusters. These were chosen because luminosity, mass, and age determination can be made for members since cluster distances and interstellar reddenings are known. Color magnitude diagrams were searched for candidates, using the same selection criteria as for SLGs in the LMC. Classification spectra were obtained of 115 program stars from McGraw-Hill Observatory and of 68 stars from Cerro Tololo Inter-American Observatory in Chile. These stars were visually classified on the MK system using spectral scans of standard stars taken at the respective observations. A total of 62 objects were found to be of high luminosity and to warrant further investigations. Seven stars were monitored over a 90 day period for luminosity variations. These observations were analyzed to measure radial velocities and to detect emission features.

Sowell, James Robert

1986-09-01

82

The main sequence of three red supergiant clusters  

NASA Astrophysics Data System (ADS)

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

Froebrich, Dirk; Scholz, Alexander

2013-09-01

83

Supersized: A Spitzer Survey of Dusty Disks around B[e] Supergiants in the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

The enigmatic class of B[e] super/hypergiants include among the most luminous individual stars known. These stars are of great interest and importance to the study of massive stars and their environments. Via Cycle 1 Spitzer IRS observations, we discovered that two Large Magellanic Cloud (LMC) B[e] hypergiants, R 126 and R 66, display similar, flat IR spectral enegy distributions indicative of the presence of massive, dusty circumstellar disks; R 66 displays, in addition, spectral evidence for crystalline grains and PAHs. This Spitzer/IRS discovery of ``fraternal twin'' disks around R 126 and R 66 has provided new insight into the origin and composition of dusty disks around the most massive stars. We now propose to build on these results via a comprehensive Spitzer IRS and photometric survey of thermal dust emission from a complete sample of all B[e] supergiants and hypergiants in the Magellanic Clouds. The IRS spectra and IRAC/MIPS photometry data will establish the fraction of B[e] supergiants that are encircled by dusty disks and, through modeling, will yield the range of masses, radii, and scale heights that characterize B[e] star dust disks. These results will provide crucial constraints on models of the origin of disks around massive stars , as well as on mechanisms for the production of crystalline silicate grains and for the shaping of supernova remnants.

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

2006-05-01

84

Observational prospects for massive stars with degenerate neutron cores  

NASA Astrophysics Data System (ADS)

In this paper we present observable characteristics of massive stars with degenerate neutron cores, or Thorne-Zytkow objects, which would distinguish them from other stars. Spectroscopically these stars are red supergiants, but they have peculiar surface abundances compared with 'normal' red supergiants. This is due to the convection of rp-process products from the nuclear burning region to the surface. We present predictions of surface abundances of elelments heavier than iron. In particular, Mo should have an abundance greater than 1000 times solar. We estimate that several of the about 100 red supergiants within 5 kpc of the Sun are Thorne-Zytkow objects.

Biehle, Garrett T.

1994-01-01

85

Two ring nebulae around blue supergiants in the Large Magellanic Cloud.  

NASA Astrophysics Data System (ADS)

Ring nebulae are often found around massive stars such as Wolf-Rayet stars, OB and Of stars and Luminous Blue Variables (LBVs). In this paper we report on two ring nebulae around blue supergiants in the Large Magellanic Cloud. The star Sk-69 279 is classified as O9f and is surrounded by a closed shell with a diameter of 4.5pc. Our echelle observations show an expansion velocity of 14km/s and a high [NII]?6583Å/H? ratio. This line ratio suggests nitrogen abundance enhancement consistent with those seen in ejectas from LBVs. Thus the ring nebula around Sk-69 279 is a circumstellar bubble. The star Sk-69 271, a B2 supergiant, is surrounded by an H? arc resembling an half shell. Echelle observations show a large expanding shell with the arc being part of the approaching surface. The expansion velocity is ~24km/s and the [NII]?6583Å/H? is not much higher than that of the background emission. The lack of nitrogen abundance anomaly suggests that the expanding shell is an interstellar bubble with a dynamic age of 2x10^5^yr.

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

1997-09-01

86

The Dusty Red Supergiant Progenitor of Supernova 2012aw in M95  

NASA Astrophysics Data System (ADS)

We directly detected the red supergiant progenitor of the intermediate-luminosity Type II-Plateau Supernova 2012aw in Messier 95 (NGC 3351). The star was identified in Hubble Space Telescope images of the host galaxy obtained 17 to 18 years before the explosion, as well as in ground-based, near-infrared images obtained 6 to 12 years prior to the SN. We find evidence for substantial circumstellar dust around the luminous star. We find that the effective total-to-selective ratio of extinction is significantly different than that of diffuse interstellar dust, which is also found for luminous Galactic red supergiants. The star's spectral energy distribution is consistent with an effective temperature of 3600 K and a bolometric magnitude of about -8.3. Comparing these values with recent theoretical massive-star evolutionary tracks, we infer that the star had an initial mass of about 17 to 18 solar masses. The circumstellar dust was destroyed by the SN explosion.

Van Dyk, Schuyler D.; Cenko, S. B.; Poznanski, D.; Arcavi, I.; Gal-Yam, A.; Filippenko, A. V.; et al.

2013-01-01

87

SLOW RADIATION-DRIVEN WIND SOLUTIONS OF A-TYPE SUPERGIANTS  

SciTech Connect

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

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

2011-08-10

88

Rapidly Accreting Supergiant Protostars: Embryos of Supermassive Black Holes?  

NASA Astrophysics Data System (ADS)

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 \\dot{M}_*\\sim 0.1{--}1 \\,M_\\odot \\,yr^{-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 103 M ?. 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 10-2 M ? yr-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 ?, which increases monotonically with the stellar mass. The mass-radius relation for stellar masses exceeding ~100 M ? follows the same track with R *vpropM 1/2 * in all cases with accretion rates >~ 10-2 M ? yr-1 at a stellar mass of 103 M ?, the radius is ~= 7000 R ? (sime 30 AU). With higher accretion rates, the onset of hydrogen burning is shifted toward higher stellar masses. In particular, for accretion rates exceeding \\dot{M}_*\\gtrsim 0.1 \\,M_\\odot \\,yr^{-1}, there is no significant hydrogen burning even after 103 M ? have accreted onto the protostar. Such "supergiant" protostars have effective temperatures as low as T eff ~= 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 103 M ? as long as material is accreted at rates \\dot{M}_*\\gtrsim 10^{-2} \\,M_\\odot \\,yr^{-1}.

Hosokawa, Takashi; Omukai, Kazuyuki; Yorke, Harold W.

2012-09-01

89

AGB (asymptotic giant branch): Star evolution  

SciTech Connect

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

Becker, S.A.

1987-01-01

90

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

91

Double Bow Shocks around Young, Runaway Red Supergiants: Application to Betelgeuse  

NASA Astrophysics Data System (ADS)

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.

2012-05-01

92

Molecular and dust shells around cool supergiants  

NASA Astrophysics Data System (ADS)

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

Decin, Leen

2013-06-01

93

Studies of luminous stars in nearby galaxies. III - Comments on the evolution of the most massive stars in the Milky Way and the Large Magellanic Cloud  

Microsoft Academic Search

An empirical comparison of the observed H-R diagrams for the supergiants in our region of the Galaxy and the Large Magellanic Cloud reveals comparable distributions of spectral types and luminosities in the two galaxies. Supergiants of similar spectral types have the same luminosities, except for the A-type stars, where selection effects may be important. These results suggest that the same

R. M. Humphreys; K. Davidson

1979-01-01

94

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

Microsoft Academic Search

MESS (Mass-loss of Evolved StarS) is a guaranteed time key program that uses the PACS and SPIRE instruments on board the Herschel space observatory to observe a representative sample of evolved stars, that include asymptotic giant branch (AGB) and post-AGB stars, planetary nebulae and red supergiants, as well as luminous blue variables, Wolf-Rayet stars and supernova remnants. In total, of

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

2011-01-01

95

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

96

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

NASA Astrophysics Data System (ADS)

The red supergiant (RSG) stage of massive star evolution is poorly matched by available evolutionary tracks. This is partly due to uncertainties in the derived physical properties (effective temperatures and bolometric luminosities) from observed quantities, which result in questionable placement of RSGs in the Hertzsprung-Russell diagram. The new generation of MARCS stellar atmosphere models includes a more rigorous treatment of molecular absorption, and we have used these models to make a far more robust determination of Teff and Mbol for a sample of Galactic RSGs. We obtained moderate-resolution (5Å) spectrophotometry of sixty-seven Galactic RSGs during two runs at the KPNO 2.1-m telescope and one at the CTIO 1.5-m. We reclassified the spectral types, and by comparing the depth of titanium oxide bands in the observed spectral energy distributions to those predicted by model atmospheres of various temperatures, we determined the Teff and E(B-V)'s of the observed RSGs. Here we will present our new effective temperature scale for Galactic RSGs. Our scale is warmer than those proposed in the past (Massey & Olsen 2003, Humphreys & McElroy 1983), by 60 K for the late K-type supergiants, and by 450 K for the latest M supergiants. The new scale shifts the RSGs closer to the predictions of current evolutionary theory. This work has been supported by the National Science Foundation through grant AST 00-93060 and the Research Experience for Undergraduates program at Northern Arizona University.

Levesque, E. M.; Massey, P.; Olsen, K. A. G.; Plez, B.; Josselin, E.; Maeder, A.; Meynet, G.; White, N.

2004-12-01

97

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

98

Spectroscopic study of the outflowing disk winds of B[e] supergiants in the Magellanic Clouds.  

NASA Astrophysics Data System (ADS)

We report on UV high resolution spectroscopic observations of R50 in the Small Magellanic Cloud, and R82 and HenS22 in the Large Magellanic Cloud obtained with the International Ultraviolet Explorer. The observed stars are supposed to represent edge-on cases of B[e] supergiants for which a two-component stellar wind model has previously been suggested. The spectra are characterized by P Cygni-type lines of FeII. The observations show that the three stars have very slowly expanding winds with terminal velocities derived from the blue absorption edges of 75, 100, and 120km/s, respectively. Fits of the FeII lines of Hen S22 and R82 using the SEI method lead to even slower velocities of about 60 to 80km/s, respectively. This is about a factor of ten slower than the terminal velocity of normal B-type supergiants. The results are consistent with the assumption that the observed stars are viewed edge-on. We derived optical depths of the absorption components of the FeII resonance lines of Hen S22 and R82 of larger than about 5, yielding lower limits for the disk mass-loss rates of the order of 6x10^-7^ and 5x10^-7^Msun_/yr, respectively. The very low terminal velocity of the disk can be explained by the fact that the disks of the B[e] supergiants are on the low-velocity side of the bi-stability jump of radiation driven winds (which reduces vinfinity_/v_esc_) and a rotational velocity of about 0.75 of the critical rotation velocity (which reduces the effective v_esc_). The effective gravity derived from vinfinity_ and vinfinity_/v_esc_=1.3 is very low. It is on the order of logg_eff_=0.2 to 0.7.

Zickgraf, F.-J.; Humphreys, R. M.; Lamers, H. J. G. L. M.; Smolinski, J.; Wolf, B.; Stahl, O.

1996-11-01

99

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

NASA Astrophysics Data System (ADS)

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

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

100

STRÖMGREN Photometry of the Supergiants HD 4841 (B5 Ia) and HD 194279 (B2 Ia)  

NASA Astrophysics Data System (ADS)

We investigated the variability of the B Ia supergiants HD 4841 and HD 194279 using Strömgren photometry obtained with the Four College Automated Photoelectric Telescope, Arizona and the 0.4-m telescope of TÜB?TAK National Observatory (TUG), Turkey. Both stars are definitely variable with amplitudes of order 0.10 mag in u, v, b and y. The Turkish photometry with several observations per night suggests a more rapid variability than the once per night American photometry. The periods of variability are likely to be of the order of one day.

Adelman, Saul J.; Yüce, Kutluay

101

Stars  

NSDL National Science Digital Library

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

Johnson, Roberta

2000-07-01

102

The ionized nebula surrounding the red supergiant W26 in Westerlund 1  

NASA Astrophysics Data System (ADS)

We present H? images of an ionized nebula surrounding the M2-5Ia red supergiant (RSG) W26 in the massive star cluster Westerlund 1. The nebula consists of a circumstellar shell or ring ˜0.1 pc in diameter and a triangular nebula ˜0.2 pc from the star that in high-resolution Hubble Space Telescope images shows a complex filamentary structure. The excitation mechanism of both regions is unclear since RSGs are too cool to produce ionizing photons and we consider various possibilities. The presence of the nebula, high stellar luminosity and spectral variability suggests that W26 is a highly evolved RSG experiencing extreme levels of mass-loss. As the only known example of an ionized nebula surrounding an RSG W26 deserves further attention to improve our understanding of the final evolutionary stages of massive stars.

Wright, Nicholas J.; Wesson, Roger; Drew, Janet E.; Barentsen, Geert; Barlow, Michael J.; Walsh, Jeremy R.; Zijlstra, Albert; Drake, Jeremy J.; Eislöffel, Jochen; Farnhill, Hywel J.

2013-10-01

103

Variability Survey of Massive Stars in OB-Associations: Preliminary Results on the Cygnus Region  

NASA Astrophysics Data System (ADS)

We present V- and I-passband photometry of massive stars in the Cyg OB1 and Cyg OB2 associations, based on about 80 observing nights spanning 300 days in the 2011 season. The variability of 22 supergiants and 48 OB-stars with luminosity classes III--V is analyzed. We report two new variable OB stars and 15 variable supergiants of which four are new discoveries. The light variations of Schulte 12 are interpreted as microvariability. We also present light curves of the red supergiants BC Cyg and BI Cyg which exhibit brightness drop of more than 0.4 mag during the season.

Laur, J.; Tuvikene, T.; Eenmäe, T.; Kolka, I.; Leedjärv, L.

104

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

105

And in the Darkness Bind Them: Equatorial Rings, B[e] Supergiants, and the Waists of Bipolar Nebulae  

NASA Astrophysics Data System (ADS)

We report the discovery of two new circumstellar ring nebulae in the western Carina Nebula, and we discuss their significance in stellar evolution. The brighter of the two new objects, SBW 1, resembles a lidless staring eye and encircles a B1.5 Iab supergiant. Although seen in Carina, its luminosity class and radial velocity imply a larger distance of ~7 kpc in the far Carina arm. At that distance its size and shape are nearly identical to the equatorial ring around SN 1987A, but SBW 1's low N abundance indicates that the ring was excreted without its star passing through a red supergiant phase. The fainter object, SBW 2, is a more distorted ring, is N-rich, and is peculiar in that its central star seems to be invisible. We discuss the implications of these two new nebulae in context with other circumstellar rings such as those around SN 1987A, Sher 25, HD 168625, RY Scuti, WeBo 1, SuWt 2, and others. The ring bearers fall into two groups: Five rings surround hot supergiants, and it is striking that all except for the one known binary are carbon copies of the ring around SN 1987A. We propose a link between these B supergiant rings and B[e] supergiants, where the large spatially resolved rings derive from the same material that would have given rise to emission lines during the earlier B[e] phase, when it was much closer to the star. The remaining four rings surround evolved intermediate-mass stars; all members of this ring fellowship are close binaries, hinting that binary interactions govern the forging of such rings. Two-thirds of our sample are found in or near giant H II regions. We estimate that there may be several thousand more dark rings in the Galaxy, but we are scarcely aware of their existence-either because they are only illuminated in precious few circumstances or because of selection effects. For intermediate-mass stars, these rings might be the preexisting equatorial density enhancements invoked to bind the waists of bipolar nebulae. Based in part on observations made at the Clay Telescope of the Magellan Observatory, a joint facility of the Carnegie Observatories, Harvard University, the Massachusetts Institute of Technology, the University of Arizona, and the University of Michigan.

Smith, Nathan; Bally, John; Walawender, Josh

2007-08-01

106

Empirical Determination of the Wind Velocity and Density Laws for the K Supergiant Zeta Aurigae  

NASA Astrophysics Data System (ADS)

We will derive the velocity and density laws and mass loss rate for the K4 supergiant in the eclipsing Zeta Aurigae binary system. The slow passage of the geometrically small B dwarf with its bright UV continuum behind the extended atmosphere of the K supergiant provides a splendid opportunity to probe the column densities and velocities of many absorption lines of various strengths as a function of stellar impact parameter. Our empirical determination of the wind physical parameters throughout the acceleration region will place tight constraints on the physical processes responsible for mass loss in evolved, massive stars that contribute significantly to the enrichment of the interstellar medium with chemically processed material. We request time for observations of lines of Fe I-II, Si II, Ti II, and V II at 6 orbital phases, including the terminal velocity wind, wind aceleration region, eclipse by the K star chromosphere, and total eclipse. This program is time critical but with typical tolerances of 1-7 days due to the long (972 day) orbital period.

Brown, Alexander

1992-07-01

107

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

108

LSII + 34 deg 26, an unusual B supergiant located near the outer edge of the galaxy  

SciTech Connect

Turner (1983) has found that the object considered in the present investigation is an 11th-magnitude emission-line B supergiant lying at the extremely large distance of approximately 18 kpc, somewhat below the galactic plane in a little-reddened portion of Cygnus. The star can be categorized as a member of the rare class of Population I objects found at large distances from the sun and lying more than 1 kpc away from the principal plane of the Galaxy. A summary is provided both of existing and new observational data which have been obtained for the star, giving attention to its unusual characteristics. The location of the object makes it suitable for use in an examination of the galactic rotation law at large distances from the galactic center. 20 references.

Turner, D.G.; Drilling, J.S.

1984-04-01

109

Observing Iron Stars with Spitzer  

NASA Astrophysics Data System (ADS)

Only two so-called Iron stars exist: XX Oph and AS 325. XX Oph was first observed in 1924 by Merrill. He noted strong, doubly ionized iron emission lines were present in the spectra, thus the name iron star. AS325 was noted to be a similar type object by Howell and Bopp (1982). Further observations of both stars have led to the development of a model (Cool et al., 2005) for both stars which explains the optical emission lines and that the stars consist of two separate stars, possibly in a binary. The current model has each Iron Star composed of a Be star and a late type (supergiant) companion separated by 1-2 thousand AU. We plan to use Spitzer to observethe dust environment in the star AS325.

Thomas, Beth; Howell, Steve; Chapple, Lauren; Daou, Doris; Rapp, Steve; Roelofson, Theresa; Weehler, Cindy

2005-02-01

110

Energy Distributions of B Supergiants in the Large Magellanic Cloud.  

National Technical Information Service (NTIS)

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

E. L. Fitzpatrick

1986-01-01

111

B[e] stars: pre- versus post-main sequence evolution  

Microsoft Academic Search

The classification of numerous Galactic B[e] stars is hampered by uncertain or unknown stellar parameters. In addition, Herbig B[e] stars and B[e] supergiants, both surrounded by dusty disks, show many spectroscopic similarities. We use the ^{12}C\\/^{13}C ratio, which drops drastically during stellar evolution, and show that the appearance of ^{13}CO band emission is an unambiguous proof for a supergiant nature.

M. Kraus

2010-01-01

112

Supergiant radial and nonradial pulsations. Lecture 10  

SciTech Connect

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

Cox, A.N.

1983-03-14

113

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

114

The Chromospheric Structure and Wind of the K-Supergiant Lambda Velorum  

NASA Astrophysics Data System (ADS)

Recently, the 1326-1466 Å region of the FUV spectrum of the K4 Ib-II supergiant Lambda Vel was observed with the Cosmic Origins Spectrograph (COS) on HST, as part of the Ayres and Redfield Cycle 17 SNAP program "SNAPing Coronal Iron.” This spectrum covers a region not previously recorded in Lambda Vel at high resolution and, in a mere 20 minutes of exposure, reveals an amazing treasure trove of information. It shows a wide variety of strong atomic and molecular emission lines formed in the chromosphere and multiple atomic absorption lines formed in the stellar wind, both superposed on a bright chromospheric continuum. Further evidence of the stellar wind is seen in the P Cygni profiles presented by the C II (UV 1) lines near 1335 Å. We combine this COS data with archival GHRS spectra of other selected FUV and NUV regions to better characterize the outer atmospheric structure of the star and its massive, outflowing wind.

Carpenter, Kenneth G.; Ayres, T. R.; Brown, A.; Harper, G. M.; Wahlgren, G. M.

2011-01-01

115

Resolving the dusty torus and the mystery surrounding LMC red supergiant WOH G64  

NASA Astrophysics Data System (ADS)

We present mid-IR long-baseline interferometric observations of the red supergiant WOH G64 in the Large Magellanic Cloud with MIDI at the ESO's Very Large Telescope Interferometer (VLTI). Our MIDI observations of WOH G64 are the first VLTI observations to spatially resolve an individual stellar source in an extragalactic system. Our 2-D radiative transfer modeling reveals the presence of a geometrically and optically thick torus seen nearly pole-on. This model brings WOH G64 in much better agreement with the current evolutionary tracks for a 25 M? star — about a half of the previous estimate of 40 M? — and solves the serious discrepancy between theory and observation which existed for this object.

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

2009-03-01

116

A study of the brightness variations in the red supergiant BC Cygni  

NASA Astrophysics Data System (ADS)

The variability of the type C semi-regular (SRC) M3.5 Ia supergiant variable BC Cyg is examined with reference to measurements of its photographic B magnitude derived from 866 archival plates in the Harvard and Sternberg collections as well as eye estimates of its visual V magnitude made by members of the AAVSO. BC Cyg is the brightest member of the young open cluster Berkeley 87, so it has a well established reddening, distance, and age. A discrete Fourier analysis was performed on the BC Cygni light curve, as well as on individual subsets of the data. The analysis was made to study the fundamental periods of variability in this red supergiant variable. BC Cyg exhibits interesting features in its century-long baseline of brightness variations that relate to fundamental mode envelope pulsation as well as evolution: an 0 m .5 increase in [left angle bracket] B [right angle bracket] over the past century in conjunction with a steady decrease in pulsation period from ~697 d in 1900 to 688 d in 2000. Despite the increase in [left angle bracket] B [right angle bracket], the star's luminosity appears to have decreased over the past century, presumably as a result of stellar evolutionary effects. A detailed examination of a well sampled portion of the star's light curve, data spanning the interval HJD 2442000 to 2449000, by means of non-linear least squares analysis indicates that only one periodicity (686 days) exists in the observations. No secondary peridicity can be detected, to within the constraints of observational uncertainty.

Rohanizadegan, Mina

117

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

SciTech Connect

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

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

2010-08-15

118

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

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

119

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

Microsoft Academic Search

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

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

2011-01-01

120

Age dating stellar populations in the near infrared: an absolute age indicator from the presence/absence of red supergiants  

NASA Astrophysics Data System (ADS)

The determination of age is a critical component in the study of a population of stellar clusters. In this Letter, we present a new absolute age indicator for young massive star clusters based on J-H colour. This novel method identifies clusters as older or younger than 5.7 ± 0.8 Myr based on the appearance of the first population of red supergiant stars. We test the technique on the stellar cluster population of the nearby spiral galaxy, M83, finding good agreement with the theoretical predictions. The localization of this technique to the near-IR promises that it may be used well into the future with space- and ground-based missions optimized for near-IR observations.

Gazak, J. Z.; Bastian, N.; Kudritzki, R.-P.; Adamo, A.; Davies, B.; Plez, B.; Urbaneja, M. A.

2013-03-01

121

SN 2004A: another Type II-P supernova with a red supergiant progenitor  

NASA Astrophysics Data System (ADS)

We present a monitoring study of SN 2004A and probable discovery of a progenitor star in pre-explosion Hubble Space Telescope (HST) images. The photometric and spectroscopic monitoring of SN 2004A show that it was a normal Type II-P which was discovered in NGC 6207 about two weeks after explosion. We compare SN 2004A to the similar Type II-P SN 1999em and estimate an explosion epoch of 2004 January 6. We also calculate three new distances to NGC 6207 of 21.0 +/- 4.3,21.4 +/- 3.5 and 25.1 +/- 1.7Mpc. The former was calculated using the Standard Candle Method (SCM) for SNeII-P, and the latter two from the brightest supergiants method (BSM). We combine these three distances with existing kinematic distances, to derive a mean value of 20.3 +/- 3.4Mpc. Using this distance, we estimate that the ejected nickel mass in the explosion is 0.046+0.031-0.017Msolar. The progenitor of SN 2004A is identified in pre-explosion WFPC2 F814W images with a magnitude of mF814W = 24.3 +/- 0.3, but is below the detection limit of the F606W images. We show that this was likely a red supergiant (RSG) with a mass of 9+3-2Msolar. The object is detected at 4.7? above the background noise. Even if this detection is spurious, the 5? upper limit would give a robust upper mass limit of 12Msolar for a RSG progenitor. These initial masses are very similar to those of two previously identified RSG progenitors of the Type II-P SNe 2004gd (8+4-2Msolar) and 2005cs (9+3-2Msolar).

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

2006-07-01

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

An Interferometric 270--355 GHz Spectral Line Survey of the Red Supergiant VY CMa  

NASA Astrophysics Data System (ADS)

We have used the Submillimeter Array to image the molecular line emission in the circumstellar envelope of the peculiar red supergiant star VY Canis Majoris over the whole 870 ?m atmospheric window. Employing adaptive calibration using the object's continuum emission we achieve high quality one arcsecond resolution imaging of the whole 280--355 GHz range within which we find 211 distinct spectral lines from 33 molecules (including isotopologues) plus 40 unidentified lines. From the distribution of molecules we are obtaining their abundances and isotopologic abundance ratios. Using data for multiple transitions in a number of molecules we are deriving the physical conditions in the circumstellar envelope to reach a picture of the star's chemistry that can be compared with models. Our legacy survey is accompanied by a strong laboratory effort that helps with the identification of possibly newly found molecules traced by unidentified lines. We shall create a publicly accessible database of spectral-line channel-maps of the emission from all the lines detected in the survey.

Menten, K. M.; Young, K. H.; Patel, N. A.; Gottlieb, C. A.; Thaddeus, P.; McCarthy, M. C.; Gurwell, M. A.; Belloche, A.; Kaminski, T.; Verheyen, L.; Decin, L.; Brunken, S.; Holger, S. P. M.

2011-05-01

124

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

NASA Astrophysics Data System (ADS)

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

Levesque, Emily M.; Massey, Philip

2012-07-01

125

SPECTRAL TYPES OF RED SUPERGIANTS IN NGC 6822 AND THE WOLF-LUNDMARK-MELOTTE GALAXY  

SciTech Connect

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

Levesque, Emily M. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389-UCB, Boulder, CO 80309 (United States); Massey, Philip, E-mail: Emily.Levesque@colorado.edu [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)

2012-07-15

126

Observations of supergiant fast X-ray transients with LOFT  

NASA Astrophysics Data System (ADS)

Supergiant fast X-ray transients are a subclass of high mass X-ray binaries displaying a peculiar and still poorly understood extreme variability in the X-ray domain. These sources undergo short sporadic outbursts (L˜ 1036–1037 erg s?1), lasting few ks at the most, and spend a large fraction of their time in an intermediate luminosity state at about L˜ 1033–1034 erg s?1. The sporadic and hardly predictable outbursts of supergiant fast X-ray transients were so far best discovered by large field of view (FOV) coded-mask instruments; their lower luminosity states require, instead, higher sensitivity focusing instruments to be studied in sufficient details. In this contribution, we provide a summary of the current knowledge on supergiant fast X-ray transients and explore the contribution that the new space mission concept LOFT, the Large Observatory for X-ray Timing, will be able to provide in the field of research of these objects.

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

2013-05-01

127

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

128

Broadband ESO/VISIR-Spitzer Infrared Spectroscopy of the Obscured Supergiant X-Ray Binary IGR J16318-4848  

NASA Astrophysics Data System (ADS)

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 ~3800-5500 K, along with a viscous disk component at an inner temperature of ~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.

2012-06-01

129

Criterion for convection in an inhomogeneous star  

NASA Astrophysics Data System (ADS)

To resolve the question of whether the Schwarzschild criterion or the Ledoux criterion should be used to test for convective instability in a star, a well-observed cluster of chemically inhomogeneous massive stars, in which the choice of the criterion for convection makes a crucial and easily observable difference, is required. NGC 330, a metal-poor cluster in the Small Magellanic Cloud, is ideal for this test. Its large evolved stellar population contains both blue and red supergiants, of which its many red supergiants should be absent if a gradient of mean molecular weight did not choke off rapid convective motions in the inhomogeneous region connecting the envelope and core. Thus the Ledoux criterion for convection is strongly indicated as being correct.

Stothers, Richard B.; Chin, Chao-Wen

1992-05-01

130

HD 74194, a new binary supergiant fast X-ray transient?, possible optical counterpart of INTEGRAL hard X-ray source IGR J08408-4503  

NASA Astrophysics Data System (ADS)

HD 74194 is an O-type supergiant, classified as O8.5 Ib (f) (Walborn 1973, AJ 78, 1067), also suspected as single-lined binary (see Maiz Apellaniz et al. 2004, ApJS 151, 103). This star is being spectroscopically monitored as part of our program of study of massive binaries. We have obtained high-resolution spectra of HD 74194 with the Echelle spectrograph attached to the du Pont 2.5-m telescope at Las Campanas Observatory in 2006 May 18.00, 20.96, 22.00, and 22.97.

Barba, Rodolfo; Gamen, Roberto; Morrell, Nidia

2006-05-01

131

Water in stars: expected and unexpected  

NASA Astrophysics Data System (ADS)

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

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

1999-03-01

132

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

Microsoft Academic Search

We present a multiwavelength study of a supergiant shell within the violent interstellar medium of the nearby dwarf galaxy IC 2574, which is a member of the M81 group of galaxies. Neutral hydrogen (H I) observations obtained with the Very Large Array (VLA) reveal a prominent expanding supergiant H I shell in the northeast quadrant of IC 2574 which is

Fabian Walter; Juergen Kerp; Neb Duric; Elias Brinks; Uli Klein

1998-01-01

133

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

134

The chromium and titanium abundances in the atmospheres of A, F, and G supergiants in the solar neighborhood  

NASA Astrophysics Data System (ADS)

The abundances of two chemical elements of the iron group, viz., Cr and Ti, were determined by their high-resolution spectra for 22 A, F, and G supergiants in the solar neighborhood (within 700 pc). The titanium and chromium abundances were obtained using the Cr II and Ti II lines. The average chromium abundance of log?(Cr) = 5.70 ± 0.13 within the error limit corresponds to the solar abundance of log??(Cr) = 5.64. The average titanium abundance of log?(Ti) = 4.89 ± 0.10 within the error limit is very close to the solar abundance of log??(Ti) = 4.95. The average Cr and Ti abundances may be indicative of the fact that the average metallicity of young closely located stars is identical to that of the Sun.

Poklad, D. B.

2013-06-01

135

Disentangling the System Geometry of the Supergiant Fast X-Ray Transient IGR J11215-5952 with Swift  

NASA Astrophysics Data System (ADS)

IGR J11215-5952 is a hard X-ray transient source discovered in 2005 April with the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) and a member of the new class of high-mass X-ray binaries, the supergiant fast X-ray transients (SFXTs). While INTEGRAL and Rossi X-Ray Timing Explorer observations have shown that the outbursts occur with a periodicity of ~330 days, Swift data have recently demonstrated that the true outburst period is ~165 days. IGR J11215-5952 is the first discovered SFXT displaying periodic outbursts, which are possibly related to the orbital period. The physical mechanism responsible for the X-ray outbursts in SFXTs is still debated. The main hypotheses proposed to date involve the structure of the companion wind or gated mechanisms related to the properties of the compact object. We test our proposed model which explains the outbursts from SFXTs as being due to the passage of the neutron star inside the equatorially enhanced wind from the supergiant companion. We performed a Guest Investigator observation with Swift that lasted 20 ks and several follow-up Target of Opportunity (ToO) observations, for a total of ~32 ks, during the expected "apastron" passage (defined assuming an orbital period of ~330 days), between 2008 June 16 and July 4. The characteristics of this "apastron" outburst are quite similar to those previously observed during the "periastron" outburst of 2007 February 9. The mean spectrum of the bright peaks can be fitted with an absorbed power-law model with a photon index of 1 and an absorbing column of ~1022 cm-2. This outburst reached luminosities of ~1036 erg s-1 (1-10 keV), comparable with those measured in 2007. The light curve can be modeled with the parameters obtained by Sidoli et al. for the 2007 February 9 outburst, although some differences can be observed in its shape. The properties of the rise to this new outburst and the comparison with the previous outbursts allow us to suggest that the true orbital period of IGR J11215-5952 is very likely 164.6 days, and that the orbit is eccentric, with the different outbursts produced at the periastron passage, when the neutron star crosses the inclined equatorial wind from the supergiant companion. Based on a ToO observation performed on 2008 March 25-27, we can exclude that the period is 165/2 days.

Romano, P.; Sidoli, L.; Cusumano, G.; Vercellone, S.; Mangano, V.; Krimm, H. A.

2009-05-01

136

DISENTANGLING THE SYSTEM GEOMETRY OF THE SUPERGIANT FAST X-RAY TRANSIENT IGR J11215-5952 WITH SWIFT  

SciTech Connect

IGR J11215-5952 is a hard X-ray transient source discovered in 2005 April with the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) and a member of the new class of high-mass X-ray binaries, the supergiant fast X-ray transients (SFXTs). While INTEGRAL and Rossi X-Ray Timing Explorer observations have shown that the outbursts occur with a periodicity of {approx}330 days, Swift data have recently demonstrated that the true outburst period is {approx}165 days. IGR J11215-5952 is the first discovered SFXT displaying periodic outbursts, which are possibly related to the orbital period. The physical mechanism responsible for the X-ray outbursts in SFXTs is still debated. The main hypotheses proposed to date involve the structure of the companion wind or gated mechanisms related to the properties of the compact object. We test our proposed model which explains the outbursts from SFXTs as being due to the passage of the neutron star inside the equatorially enhanced wind from the supergiant companion. We performed a Guest Investigator observation with Swift that lasted 20 ks and several follow-up Target of Opportunity (ToO) observations, for a total of {approx}32 ks, during the expected 'apastron' passage (defined assuming an orbital period of {approx}330 days), between 2008 June 16 and July 4. The characteristics of this 'apastron' outburst are quite similar to those previously observed during the 'periastron' outburst of 2007 February 9. The mean spectrum of the bright peaks can be fitted with an absorbed power-law model with a photon index of 1 and an absorbing column of {approx}10{sup 22} cm{sup -2}. This outburst reached luminosities of {approx}10{sup 36} erg s{sup -1} (1-10 keV), comparable with those measured in 2007. The light curve can be modeled with the parameters obtained by Sidoli et al. for the 2007 February 9 outburst, although some differences can be observed in its shape. The properties of the rise to this new outburst and the comparison with the previous outbursts allow us to suggest that the true orbital period of IGR J11215-5952 is very likely 164.6 days, and that the orbit is eccentric, with the different outbursts produced at the periastron passage, when the neutron star crosses the inclined equatorial wind from the supergiant companion. Based on a ToO observation performed on 2008 March 25-27, we can exclude that the period is 165/2 days.

Romano, P.; Cusumano, G.; Vercellone, S.; Mangano, V. [INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via U. La Malfa 153, I-90146 Palermo (Italy); Sidoli, L. [INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via E. Bassini 15, I-20133 Milano (Italy); Krimm, H. A. [CRESST/Goddard Space Flight Center, Greenbelt, MD (United States)

2009-05-10

137

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

138

From B[e] to A[e]. On the peculiar variations of the SMC supergiant LHA 115-S 23 (AzV 172)  

NASA Astrophysics Data System (ADS)

Context: Optical observations from 1989 of the Small Magellanic Cloud (SMC) B[e] supergiant star LHA 115-S 23 (in short: S 23) revealed the presence of photospheric Hei absorption lines, classifying S 23 as a B8 supergiant. In our high-resolution optical spectra from 2000, however, we could not identify any Hei line. Instead, the spectral appearance of S 23 is more consistent with the classification as an A1 supergiant, maintaining the so-called B[e] phenomenon. Aims: The observed changes in spectral behaviour of S 23 lead to different spectral classifications at different observing epochs. The aim of this research is, therefore, to find and discuss possible scenarios that might cause a disappearance of the photospheric Hei absorption lines within a period of only 11 years. Methods: From our high-resolution optical spectra, we perform a detailed investigation of the different spectral appearances of S 23 based on modern and revised classification schemes. In particular, we derive the contributions caused by the interstellar as well as the circumstellar extinction self-consistently. The latter is due to a partly optically thick wind. We further determine the projected rotational velocities of S 23 in the two epochs of spectroscopic observations. Results: Based on its spectral appearance in 2000, we classify S 23 as A1 Ib star with an effective temperature of about 9000 K. This classification is supported by the additional analysis of the photometric UBV data. An interstellar extinction value of E(B-V) ? 0.03 is derived. This is considerably lower than the previously published value, which means that, if the circumstellar extinction due to the stellar wind is neglected, the interstellar extinction, and hence the luminosity of the star, are overestimated. We further derive a rotation velocity of ? sin i ? 150 km s-1, which means that S 23 is rotating with about 75% of its critical speed. The object S 23 is thus the fourth B[e] supergiant with confirmed high projected rotational velocity. The most striking result is the apparent cooling of S 23 by more than 1500 K with a simultaneous increase of its rotation speed by about 35% within only 11 years. Since such a behaviour is excluded by stellar evolution theories, we discuss possible scenarios for the observed peculiar variations in S 23.

Kraus, M.; Borges Fernandes, M.; Kubát, J.; de Araújo, F. X.

2008-08-01

139

On the Periodic Variability of the Longitudinal Magnetic Fields of Stars  

NASA Astrophysics Data System (ADS)

There exist 218 stars with measured phase curves of their longitudinal (effective) magnetic field Be . 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 Be 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.; Madej, J.

2013-10-01

140

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

141

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

142

The chemical composition of the post-asymptotic giant branch F supergiant CRL 2688  

NASA Astrophysics Data System (ADS)

We present an analysis of a high-resolution (R ˜ 50 000) optical spectrum of the central region of the protoplanetary nebula CRL 2688. This object is thought to have recently moved off the asymptotic giant branch (AGB) and displays abundance patterns of CNO and heavy elements that can provide us with important clues to help us understand the nucleosynthesis, dredge-up and mixing experienced by the envelope of the central star during its AGB stage of evolution. Analysis of the molecular features, presumably originating from circumstellar matter, provides further constraints on the chemistry and velocity of the expanding shell, expelled as a consequence of the strong mass loss experienced by the central star. We confirm that the central star shows a spectrum typical of an F-type supergiant with Teff = 7250 ± 400 K, log g = 0.5 and [Fe/H] = -0.3 ± 0.1 dex. We find that the abundance pattern of this object is characterized by enhancements of carbon ([C/Fe] = 0.6 ± 0.1), nitrogen ([N/Fe] = 1.0 ± 0.3) and Na ([Na/Fe] = 0.7 ± 0.1), similar to other previously known carbon-rich post-AGB stars. Yttrium is also enhanced, while the [Ba/Y] ratio is very low (-1.0), indicating that only the light s-process elements are enhanced. The zinc abundance is found to be normal, [Zn/Fe] = 0.0 ± 0.3, suggesting that there is no depletion of refractory elements. The H?, Na I and K I resonance lines show prominent emission components, the heliocentric radial velocities of which are offset by -41 ± 3 km s-1 relative to the photospheric metal-absorption lines. The molecular features of C2 and CN also show emission components, the velocities of which are consistent with the emission components of the H?, Na Iand K I lines. On the other hand, their absorption components are more highly blueshifted than the corresponding emission components, which suggests that the regions where the emission and absorption components arise are expanding at different velocities.

Ishigaki, Miho N.; Parthasarathy, Mudumba; Reddy, Bacham E.; García-Lario, Pedro; Takeda, Yoichi; Aoki, Wako; García-Hernández, D. Aníbal; Manchado, Arturo

2012-09-01

143

The brightest stars in nearby galaxies. II - The color-magnitude diagram for the brightest red and blue stars in M101  

NASA Astrophysics Data System (ADS)

Red supergiant candidate stars have been found in Ml01 starting at V = 20.3, rather than fainter than V = 21.0 as previously reported. One of the brightest of three such stars is variable, ensuring its membership. Photometry of ˜200 stars, in or near the spiral arms of M 101, has been obtained in B and V magnitudes, giving a color-magnitude diagram similar to that for the brightest stars in M33 but displaced faintward by ˜3.9 mag. New data on three of the brightest blue supergiant irregular variables in Ml01 give an apparent blue modulus of (m - M )ABM101 = 29.2 comparing with the brightest blue irregular variables in M33 and adopting (m - M )ABM33 = 25.35 found earlier for M33 from its Cepheids. The lack of Cepheids in M101 brighter than B = 22.7 requires this value as a firm lower limit to the Ml0l modulus. The new data on the red supergiants require v(1)> = -8.9 and v(3) ? -8.7 (depending on membership) for M 101, nearly independent of assumptions on the internal absorption. The previous determination of the Hubble constant of HO = 50 km 5 s-1 Mpc-1 by Sandage and Tammann using red supergiants is unaffected by these new M 101 results if the present interim calibration of Mv(3) = f(MBT) is correct.

Sandage, A.

1983-11-01

144

Polarimetry and the Envelopes of Magellanic B[e] Supergiants  

NASA Astrophysics Data System (ADS)

We discuss the nature of the circumstellar envelopes around the B[e] supergiants (B[e]SG) in the Magellanic Clouds (MC). Contrary to those in the Galaxy, the MC B[e]SG have a well defined luminosity and can be considered members of a well defined class. We discuss spectroscopy and optical broadband polarimetry and spectropolarimetry data. These data show for the first time detailed changes in the polarization across several spectral features. We show that the envelopes of the B[e]SG are generally variable. Broadband polarimetry data show that the envelopes are definitely non-spherically symmetric and large non-axisymmetric ejections may occur. In addition to that, spectropolarimetry is coming of age as a tool to study the B[e]SG envelope structure.

Magalhães, A. M.; Melgarejo, R.; Pereyra, A.; Carciofi, A. C.

2006-12-01

145

Nonthermal X-ray emission from winds of OB supergiants  

SciTech Connect

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

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

1991-01-01

146

Supergiant Complexes of Solar Activity and Convection Zone  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

147

Magnetic Fields and Convection in the Cool Supergiant Betelgeuse  

NASA Astrophysics Data System (ADS)

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

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

148

Non-LTE Line-blanketed Stellar Wind Atmosphere Models for the A-supergiant Deneb  

Microsoft Academic Search

We present non-LTE metal line-blanketed stellar wind atmosphere models and synthetic spectra for comparison with the spectral energy distribution of the A-supergiant Deneb from UV to radio wavelengths. Deneb is alone among A-supergiants in having both a precisely measured angular diameter from the Navy Prototype Optical Interferometer (Nordgren, T. et al., 1999, priv. comm.) and a positive detection at centimeter

J. P. Aufdenberg; P. H. Hauschildt; E. Baron

1999-01-01

149

Ultraviolet Spectral Atlas of O Stars in the Milky way and Magellanic Clouds  

Microsoft Academic Search

We will obtain high S\\/N far-ultraviolet spectra of O giants and supergiants in the Milky Way and the Large and Small Magellanic Clouds. We will derive the properties of the star\\/wind systems from the photospheric and wind spectra, and we will investigate the effect of chemical composition on the properties of the wind.

Sara Heap

1990-01-01

150

The K giant star Arcturus: the hybrid nature of its infrared spectrum  

Microsoft Academic Search

Aims: We investigate the infrared spectrum of Arcturus to clarify the nature of the cool component of its atmosphere, referred to as the CO-mosphere, and its relationship to the warm molecular envelope or the MOLsphere in cooler M (super)giant stars. Methods: We apply the standard methods of spectral analysis to the CO lines measured from the ``Infrared Atlas of the

T. Tsuji

2009-01-01

151

Supergiant Fast X-Ray Transients: A Common Behaviour or a Class of Objects?  

NASA Astrophysics Data System (ADS)

INTEGRAL monitoring of the Galactic Plane is revealing a growing number of recurrent X-ray transients, characterised by short outbursts with very fast rise times (~ tens of minutes) and typical durations of a few hours. A substantial fraction of these sources are associated with OB supergiants and hence define a new class of massive X-ray binaries, which we call Supergiant Fast X-ray Transients. Characterisation of the astrophysical parameters of their counterparts is underway. So far, we have found a number of late O and early B supergiants of different luminosities at a large range of distances. Nothing in their optical properties sets them apart from classical Supergiant X-ray Binaries. On the other hand, there is now rather concluding evidence that persistent supergiant X-ray binaries also show fast outbursts. This suggests a continuum of behaviours between typical persistent supergiant systems and purely transient systems, but offers very little information about the physical causes of the outbursts.

Negueruela, I.; Smith, D. M.; Torrejón, J. M.; Reig, P.

152

The Nuclear Cluster of the Milky Way: Star Formation and Velocity Dispersion in the Central 0.5 Parsec  

Microsoft Academic Search

We report the first results of an extensive new study of the Galactic center stellar cluster. The central parsec is powered by a cluster of about two dozen luminous and helium-rich blue supergiants\\/Wolf-Rayet stars (Teff ~ 20,000--30,000 K) with ZAMS masses up to ~100 M&sun;. The most likely scenario for the formation of the massive stars is a small star

A. Krabbe; R. Genzel; A. Eckart; F. Najarro; D. Lutz; M. Cameron; H. Kroker; L. E. Tacconi-Garman; N. Thatte; L. Weitzel; S. Drapatz; T. Geballe; A. Sternberg; R. Kudritzki

1995-01-01

153

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

154

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

NASA Astrophysics Data System (ADS)

The R Coronae Borealis (RCB) stars are rare hydrogen-deficient, carbon-rich supergiants. Two evolutionary scenarios have been suggested, a double degenerate merger of two white dwarfs (WDs), or a final helium shell flash in a PN central star. The evidence pointing toward a WD merger or a FF origin for RCB stars is contradictory. The population of RCB stars in the Galaxy may be consistent with the number of He/CO WD mergers. If so, this would be an exciting result since RCB stars may be low-mass analogs of Type Ia SNe.

Clayton, G. C.

2013-01-01

155

Detection of circumstellar dust shell around the supergiant TV Geminorum from milliarcsecond resolution near-infrared observations.  

NASA Astrophysics Data System (ADS)

A lunar occultation of the M1 supergiant TV Gem has been observed in the near infrared region at 2.2?m. A detailed analysis of the observed occultation light curve has been performed using two different reduction methods permitting the circumstellar dust envelope to be directly detected for the first time around TV Gem. The star has been resolved to yield a uniform disk diameter of 4.9+/-0.3 milliarcseconds (mas) and the stellar effective temperature has been derived to be 3670+/-125K. Its circumstellar dust envelope has a radius of ~20R_*_ with star to shell flux ratio of ~35 at 2.2?m. A simple radiative transfer dust shell model constrained by our occultation observations, 9.7?m silicate emission feature strength and far IR excess seen in IRAS observations shows that the dust is probably restricted to two well separated dust shells - the inner shell is at a radial distance of ~20R_*_ and the outer one is at ~500R_*_. Sporadic dust condensation in TV Gem as in the case of ? Ori is suggested.

Ragland, S.; Chandrasekhar, T.; Ashok, N. M.

1997-03-01

156

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

SciTech Connect

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

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

2010-12-10

157

The First Direct Measurement of an Early B Supergiant X-ray Source Electron Density  

NASA Astrophysics Data System (ADS)

The ratio of the He-like ion forbidden to intercombination emission lines (f/i) provides a diagnostic for determining either the electron density of an X-ray source (collisional-dominated), or the X-ray source spatial location relative to a central EUV/UV radiation source (radiation-dominated). With the advent of high energy resolution spectroscopy, this diagnostic has become a well proven technique for determining the radial distribution of X-ray sources in OB stellar winds. However, in high energy ions (e.g., Si XIII) where the strength of this ratio is controlled by the radiation shortward of the Lyman edge, we show that there is an expected transition from radiation-dominance to collisional-dominance in the early B star spectral range. Because the photospheric flux is weak in the spectral energy region controlling the Si XIII f/i line ratio, we can probe stellar wind distributed X-ray source models from a different perspective and address fundamental issues pertaining to the origin of OB stellar X-ray emission. To verify this behavior we obtained four Chandra HETGS observations of the early B supergiant ? Ori (B0.5Ia) over a time span of approximately 10 days (total exposure = 234 ks). These observations allow us to explore the expected transition to collisional dominance. But, more importantly, our analysis of the Si XIII f/i line ratio has revealed the first direct measurement of an X-ray source density ( 1013 cm-3). We discuss the implications of these results.

Waldron, Wayne L.; Cassinelli, J. P.; Miller, N. A.; Schlegel, E. M.

2012-01-01

158

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

NASA Astrophysics Data System (ADS)

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

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

2008-01-01

159

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

160

OB associations: Massive stars in context  

NASA Astrophysics Data System (ADS)

Massive stars are important in a variety of contexts: individually they are examples of stars that undergo significant mass loss which is driven by line radiation pressure; as denizens of the Galaxy they play significant role in the galactic recycling effort; as ensembles of stars they contain clues to massive star evolution in general and the question of supernova progenitors in particular. Finally, under extreme conditions of pathological star formation massive stars participate in the star burst phenomena seen in some galaxies. If we wish to understand star bursts, we must first understand locally observed variations in the mass spectrum. But all of these diverse areas of study rely on certain fundamental parameters of the star themselves-here we include temperature, luminosity, mass, and chemical composition. And central to accurate determinations of these parameters are the distances to the stars. This review will focus on what is known about the loose clustering of massive stars termed OB associations. These associations contain many, but by no means all, of the stars with masses greater than 15 solar mass. Most of our knowledge of the stellar content of the OB associations in our own Galaxy is suprisingly sketchy due to their large angular size, but large-field Charge Coupled Devices (CCD) detectors are changing this. Magellanic Cloud associations can now be compared with OB associations in our own Galaxy, and the initial mass function shows surprising variations. The physical cause of these variations is still unknown. Another development is the study of embedded star clusters: infrared array detectors have been probing the buried stars in molecular clouds and finding an unexpectedly large population of these objects. Both these young IR clusters, and a sprinkling of evolved red supergiants, suggest that the star-formation history of OB associations may be more complicated than we have supposed.

Garmany, Catharine D.

1994-01-01

161

P Cygni type stars - Evolution and physical processes  

NASA Astrophysics Data System (ADS)

The characteristics of P Cygni type (PCT) stars are discussed. The definition of PCT stars is presented, and the relation between PCT stars and S Dor or Hubble-Sandage variables is addressed. It is suggested that all PCT stars are S Dor variables, and that the reverse may also be true. The basic parameters of the PCT stars and their location in the HR diagram are considered. Compared to normal supergiants, PCT stars have an effective gravity three to ten times lower, a mean loss rate three to ten times higher, and a terminal velocity about ten times lower. This results in a wind density which is ten times higher and produces the P Cygni lines in the visual spectrum.

Lamers, H. J. G. L. M.

162

Spitzer Spectroscopy of Evolved Stars in the LMC  

NASA Astrophysics Data System (ADS)

In the era of Spitzer, rapidly mass-losing asymptotic giant branch (AGB) and red supergiant (RSG) stars are readily detectable throughout the Local Group. Such stars dominate the rate of return of nuclear-processed material to the interstellar medium (ISM) and, hence, play crucial roles in the chemical evolution of galaxies. I describe recent results from Spitzer Infrared Spectrograph (IRS) surveys of IR-luminous AGB stars and RSGs in the Large Magellanic Cloud (LMC). These results provide new insight into the composition of the dust and gas injected into the ISM by an evolved star population in a subsolar-metallicity environment, and offer new constraints on stellar evolution theory. Spitzer IRS spectroscopy of LMC evolved stars also provides the basis on which to reliably identify and classify mass-losing evolved stars detected in SAGE and other broad-band infrared imaging surveys. Spitzer data analysis at RIT is supported by JPL/Caltech award NMO710076.

Kastner, Joel H.

2006-12-01

163

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

164

Observations of Circumstellar Material Around Evolved Stars with the ISI  

NASA Astrophysics Data System (ADS)

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

Danchi, W.; Townes, C.

2001-05-01

165

What Are the R Coronae Borealis Stars?  

NASA Astrophysics Data System (ADS)

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

Clayton, G. C.

2012-06-01

166

Giant Convection Cell Turnover as an Explanation of the Long Secondary Periods in Semiregular Red Variable Stars  

Microsoft Academic Search

Giant convection cells in the envelopes of massive red supergiants turn over in a time comparable in order of magnitude with the observed long secondary periods in these stars, according to a theory proposed some years ago by Stothers & Leung. This idea is developed further here by using improved theoretical data, especially a more accurate convective mixing length and

Richard B. Stothers; Richard B

2010-01-01

167

The Evolutionary History of the R Coronae Borealis Stars  

NASA Astrophysics Data System (ADS)

The R Coronae Borealis (RCB) stars are rare hydrogen-deficient carbon-rich supergiants, all apparently single stars which are consistent with being post-AGB stars. RCB stars undergo massive declines of up to 8 mag due to the formation of carbon dust at irregular intervals. The mechanism of dust formation around RCB stars is not well understood but the dust is thought to form in or near the atmosphere of the stars. Their rarity may stem from the fact that they are in an extremely rapid phase of the evolution or in an evolutionary phase that most stars do not undergo. Several evolutionary scenarios have been suggested to account for the RCB stars including, a merger of two white dwarfs (WDs), or a final helium shell flash in a PN central star. The large overabundance of 18O found in most of the RCB stars favors the WD merger scenario while the presence of Li in the atmospheres of four of the RCB stars favors the FF scenario. In particular, the measured isotopic abundances imply that many, if not most, RCB stars are produced by WD mergers, which may be the low-mass counterparts of the more massive mergers thought to produce type Ia supernovae. I will present recent visible and IR observations of various RCB stars obtained with HST, Spitzer and ground-based telescopes.

Clayton, Geoffrey

2009-11-01

168

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

169

Star Caught Smoking  

NASA Astrophysics Data System (ADS)

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

2007-08-01

170

Far Infrared Circumstellar Debris Shells of Red Supergiant Stars. Abstract Only.  

National Technical Information Service (NTIS)

There is yet another transition line between chromospheres and dust, which lies above and to the right of corona-wind transitions in the HR diagram. The IRAS 60-micrometer data appears to indicate the existence of very cool material extending tens of thou...

R. E. Stencel J. E. Pesce W. Hagenbauer

1987-01-01

171

Modelling Dusty Circumbinary Disk around B[e] Supergiant RY Sct  

NASA Astrophysics Data System (ADS)

The supergiant RY Sct is an eclipsing binary system with a fairly large infrared (IR) excess caused by the presence of circumbinary dust. Many strong forbidden lines ([O i], [N ii], [S iii], [Fe ii]), in combination with the near-IR excess, put it in the list of peculiar Be or B[e] stars. Although RY Sct is one of the best-studied systems, even its basic physical parameters remain unreliable. Recent IR images of the system, obtained with a 0.3 arcsec resolution at the 10-m Keck telescope, showed the dusty disk at the wavelengths 3-20 ?m and stimulated us to perform its detailed modelling using our 2-D radiative transfer code. Our model reproduces all available observations of RY Sct obtained during the last few decades. The modelling demonstrated that the observations cannot be described by a single model at one moment in time, implying rapid changes in the dusty disk during the last 20 years. Assuming that a temperature of 27,000 K describes both components of the binary and that its distance is 1.8 kpc, its total luminosity is 4.2 - 105 solar luminosity. The model disk has the optical depth of 0.04 and the opening angle of 26° (between the boundaries). Dust in the disk exists between 60 AU and 105 AU, where it blends into the interstellar medium. We observe the disk almost edge-on, at an angle of 14° to its midplane. The total mass of the disk is 0.017 solar mass. There is a strong density enhancement at 1800 AU from the binary, which emits most of the IR radiation and is prominent in the Keck telescope images. Presumably, the dense ring has been created by a fast wind that swept out and compressed the previously lost material in the older and slower stellar wind. Our model predicts that presently there is a large amount of small, hot dust grains in the dust formation zone, whose emission changed the shape of the SED of RY Sct in the near IR. The dust density must now be significantly greater in the dust formation zone, suggesting a much higher massloss rate or dust-to-gas mass ratio or much lower wind velocities than before, or a combination of these factors.

Men'shchikov, Alexander; Miroshnichenko, Anatoly

2005-08-01

172

The mass-loss rates of red supergiants and the de Jager prescription  

NASA Astrophysics Data System (ADS)

Mass loss of red supergiants (RSG) is important for the evolution of massive stars, but is not fully explained. Several empirical prescriptions have been proposed, trying to express the mass-loss rate (dot M) as a function of fundamental stellar parameters (mass, luminosity, effective temperature). Our goal is to test whether the de Jager et al. (1988, A&AS, 72, 259) prescription, which is used in some stellar evolution models, is still valid in view of more recent mass-loss determinations. By considering 40 Galactic RSGs with an infrared excess and an IRAS 60-?m flux larger than 2 Jy, and assuming a gas-to-dust mass ratio of 200, we find that the de Jager rate agrees within a factor 4 with most dot M estimates based on the 60-?m signal. It also agrees with six of the only eight Galactic RSGs for which dot M can be measured more directly through observations of the circumstellar gas. The two objects that do not follow the de Jager prescription (by an order of magnitude) are ? Cep and NML Cyg. We also considered the RSGs of the Magellanic Clouds. Thanks to the results of previous research, we find that the RSGs of the Small Magellanic Cloud have mass-loss rates consistent with the de Jager rate scaled by (Z/Z?)?, where Z is the metallicity and ? is 0.7. The situation is less clear for the RSGs of the Large Magellanic Cloud. In particular, for L > 1.6 × 105 L?, one finds numerous RSGs (except WOH-G64) with dot M significantly smaller than the de Jager rate and indicating that dot M would no longer increase with L. Before this odd situation is confirmed through further analyses of LMC RSGs, we suggest to keep the de Jager prescription unchanged at solar metallicity in the stellar evolutionary models and to apply a (Z/Z?)0.7 dependence. Appendices are only available in electronic form at http://www.aanda.org

Mauron, N.; Josselin, E.

2011-02-01

173

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

Microsoft Academic Search

All B star luminosity classes show a substantial drop in their X-ray emission between spectral type B1 and B2 suggesting an H-R diagram B-star dividing line somewhat analogous to the one for K giants. This emission appears to be related to the bi-stability jump at spectral type B1. But our analyses of B supergiant and giant XMM data revealed several

Wayne Waldron

2009-01-01

174

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

Microsoft Academic Search

All B star luminosity classes show a substantial drop in their X-ray emission between spectral type B1 and B2 suggesting an H-R diagram B-star dividing line somewhat analogous to the one for K giants. This emission appears to be related to the bi-stability jump at spectral type B1. But our analyses of B supergiant and giant XMM data revealed several

Wayne Waldron

2010-01-01

175

A double detached shell around a post-red supergiant: IRAS 17163-3907, the Fried Egg nebula  

NASA Astrophysics Data System (ADS)

Context. We performed a mid-infrared imaging survey of evolved stars to study the dust distribution in circumstellar envelopes around these objects and to understand the mass-loss mechanism responsible for the formation of these envelopes better. During this survey, we resolved the circumstellar environment of IRAS 17163-3907 for the first time (hereafter IRAS 17163), which is one of the brightest objects in the mid-infrared sky, but is surprisingly not well studied. Aims: Our aim is to determine the evolutionary status of IRAS 17163 and study its circumstellar environment to understand its mass-loss history. Methods: We obtained diffraction-limited images of IRAS 17163 in the mid-infrared using VISIR on the VLT. Optical spectra of the object allowed us to determine its spectral type and estimate its distance through diffuse interstellar bands. Results: We show that IRAS 17163 is a post-red supergiant, possibly belonging to the rare class of yellow hypergiants, and is very similar to the well-studied object IRC +10420. Our mid-infrared images of IRAS 17163 are the first direct images of this bright mid-infrared source. These images clearly show a double dusty detached shell around the central star, caused by successive ejections of material on a timescale of the order of 400 years and a total circumstellar mass exceeding than 4 M?. This indicates that non-quiescent mass-loss occurs during this phase of stellar evolution. Based on observations made with the Very Large Telescope at Paranal Observatory under program 081.D-0130(A).Based on observations made with the Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofsica de Canarias.

Lagadec, E.; Zijlstra, A. A.; Oudmaijer, R. D.; Verhoelst, T.; Cox, N. L. J.; Szczerba, R.; Mékarnia, D.; van Winckel, H.

2011-10-01

176

Tests of two convection theories for red giant and red supergiant envelopes  

Microsoft Academic Search

Two theories of stellar envelope convection are considered here in the context of red giants and red supergiants of intermediate to high mass: Boehm-Vitense's standard mixing-length theory (MLT) and Canuto & Mazzitelli's new theory incorporating the full spectrum of turbulence (FST). Both theories assume incompressible convection. Two formulations of the convective mixing length are also evaluated: l proportional to the

Richard B. Stothers; Chao-Wen Chin

1995-01-01

177

The Puppis region and the last crusade for faint OB stars  

NASA Astrophysics Data System (ADS)

UBV photoelectric and photographic measurements of OB stars from a list of 397 OB stars and 5 early-type supergiants and from the Luminous Stars Survey are presented. The galactic distribution of the OB stars in the region shows concentrations around the open clusters Ruprecht 44 and Ruprecht 55, and the presence of an important grouping of young stars located far below the plane. The distribution in latitude shows that young stars in the region are not restricted to a thin sheet around the plane but are spread over negative latitudes reaching at least b = -5 deg. In longitude, the OB distribution exhibits a concentration of Ob stars in the interval 244-251 deg; this is argued to be due to the presence of the local arm extension.

Orsatti, Ana M.

1992-08-01

178

Discovery of nonthermal radio emission from magnetic Bp-Ap stars  

SciTech Connect

In a VLA survey of chemically peculiar B- and A-type stars with strong magnetic fields, five of the 34 stars observed have been identified as 6 cm continuum sources. Three of the detections are helium-strong early Bp stars (Sigma Ori E, HR 1890, and Delta Ori C), and two are helium weak, silicon-strong stars with spectral types near A0p (IQ Aur = HD 34452, Babcock's star = HD 215441). The 6 cm luminosities L6 (ergs/s Hz) range from log L6 = 16.2 to 17.9, somewhat less than the OB supergiants and W-R stars. Three-frequency observations indicate that the helium-strong Bp stars are variable nonthermal sources. 44 references.

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

1987-11-01

179

Polarization and studies of evolved star mass loss  

NASA Astrophysics Data System (ADS)

Polarization studies of astronomical dust have proven very useful in constraining its properties. Such studies are used to constrain the spatial arrangement, shape, composition, and optical properties of astronomical dust grains. Here we explore possible connections between astronomical polarization observations to our studies of mass loss from evolved stars. We are studying evolved star mass loss in the Large Magellanic Cloud (LMC) by using photometry from the Surveying the Agents of a Galaxy's Evolution (SAGE; PI: M. Meixner) Spitzer Space Telescope Legacy program. We use the radiative transfer program 2Dust to create our Grid of Red supergiant and Asymptotic giant branch ModelS (GRAMS), in order to model this mass loss. To model emission of polarized light from evolved stars, however, we appeal to other radiative transfer codes. We probe how polarization observations might be used to constrain the dust shell and dust grain properties of the samples of evolved stars we are studying.

Sargent, Benjamin; Srinivasan, Sundar; Riebel, David; Meixner, Margaret

2012-05-01

180

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

181

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

182

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

Microsoft Academic Search

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

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

2000-01-01

183

Macroturbulent and rotational broadening in the spectra of B-type supergiants  

Microsoft Academic Search

The absorption-line spectra of early B-type supergiants show significant broadening that im- plies that an additional broadening mechanism (characterized here as 'macroturbulence') is present in addition to rotational broadening. Using high-resolution spectra with signal-to-noise ratios of typically 500, we have attempted to quantify the relative contributions of rotation and macroturbulence, but even with data of this quality significant problems were

R. S. I. Ryans; P. L. Dufton; W. R. J. Rolleston; D. J. Lennon; F. P. Keenan; J. V. Smoker; D. L. Lambert

2002-01-01

184

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

NASA Astrophysics Data System (ADS)

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

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

1989-09-01

185

The HdC stars as recently merged white dwarf binaries  

NASA Astrophysics Data System (ADS)

The hydrogen-deficient carbon star HD 137613 has been reported by Clayton et al. (2005) to have the extraordinary isotopic ratio ^16O/^18O ~ 0.8. The solar system ratio is ~500 and carbon stars typically have yet larger ratios. The explanation proposed for the ^16O/^18O value observed in HD 137613 is that the HdC stars are recently merged white dwarf binaries. The observed supergiant HdC star is a transient post-merger phase. If so, we have the rare opportunity to see helium-burning shell products in a low gravity stellar environment. To test this model we propose to measure the CNO elemental abundances for HD 137613 as well as the other four hydrogen- deficient carbon stars. Comparison of the measure abundances with models will lead to considerable insight into stellar mergers and nucleosynthesis.

Hinkle, Kenneth; Lambert, David; Smith, Verne; Lebzelter, Thomas

2006-02-01

186

Extreme Stars  

Microsoft Academic Search

Over the past 200 years, our knowledge of stars has expanded enormously. From seeing myriad dots of different brightnesses, we haved moved on to measure their distances, temperatures, sizes, chemical compositions, and even ages, finding both young and ancient stars that dwarf our Sun and are dwarfed by it. Unique in its approach, Extreme Stars describes the lives of stars

James B. Kaler

2001-01-01

187

New calibration of the Vilnius photometric system. I - Effective temperatures and gravities of B-type stars  

Microsoft Academic Search

Color indices and reddening-free Q-parameters in the Vilnius photometric system of B-type stars of all luminosities and A-supergiants are calibrated in terms of effective temperature and surface gravity, using synthetic spectra of the newest Kurucz model atmospheres. The calibration is verified by comparing the photometrically determined effective temperatures and surface gravities with the most accurate spectroscopic data. Satisfactory agreement has

V. Straizys; R. L. Kurucz; A. G. D. Philip; G. Valiagua

1993-01-01

188

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

Microsoft Academic Search

High-resolution UCLES\\/AAT spectra of four B-type supergiants in the SMC South\\u000aEast Wing have been analysed using non-LTE model atmosphere techniques to\\u000adetermine their atmospheric parameters and chemical compositions. The principle\\u000aaim of this analysis was to determine whether the very low metal abundances\\u000a($-$1.1 dex compared with Galactic value) previously found in the Magellanic\\u000aInter Cloud region (ICR) were

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

2004-01-01

189

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

NASA Astrophysics Data System (ADS)

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

Doroshenko, V.; Santangelo, A.; Ducci, L.; Klochkov, D.

2012-12-01

190

Spherical opacity sampling model atmospheres for M-giants and supergiants. II - A grid  

NASA Astrophysics Data System (ADS)

A grid is presented of spherically symmetric model atmospheres for M-type giants and supergiants, covering the range T(eff) between 3000 and 4000 K, log g between -0.5 and 1.5 for 1, 2, and 5 solar masses, with some additional cooler models. The model atmospheres were computed using the program, methods, and data described by Plez et al. (1992). New line-lists, calculated from up-to-date data for the TiO, VO, and H2O molecules, are included in the opacities.

Plez, B.

1992-09-01

191

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

192

INTEGRAL detection of an outbursts of two supergiant fast X-ray transients  

NASA Astrophysics Data System (ADS)

During the observation of parts of the inner Galactic spiral arms performed on 2013-09-18, the INTEGRAL observatory detected the outbursts from the sources IGR J16418-4532 (see also ATEL #5398 for the Swift detection of an outburst on 2013-09-17 ) and IGR J18483-0311. The former is a supergiant fast X-ray transient (SFXT) with intermediate properties (Sidoli et al., MNRAS., 420, 554-561, 2012; Romano et al., MNRAS, 419, 2695-2702, 2012), the latter a confirmed member of this class (e.g., Romano et al., MNRAS, 401, 1564-1569, 2010).

Tuerler, M.; Ferrigno, C.; Bodaghee, A.; Romano, P.

2013-09-01

193

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…

Eason, Oliver

194

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

195

Multi-Generation Star Formation in NGC 3603 and 30 Doradus  

NASA Astrophysics Data System (ADS)

Giant Hii regions are extended, very luminous active regions that remain visible even in distant galaxies. They indicate intense, massive large-scale starbursts with possibly present-day globular cluster formation. How does star and cluster formation in giant Hii regions proceed? The Milky Way and the Large Magellanic Cloud each contain a spectacular example of a giant Hii region: NGC 3603 and 30 Doradus. We have studied large-scale star formation processes in these regions with ground-based and new WFPC2 data. In NGC 3603, we find the 2--3 Myr old central ionizing cluster to be surrounded by older (10--20 Myr) supergiants that have created spectacular elephant-trunk-like structures in the surrounding ISM. To the south of the cluster we find newly formed proplyd-embedded massive stars, more massive and extended than the proplyds in the Eagle Nebula. We compare the large scale picture of NGC 3603 to 30 Doradus, where a very similar multi-stage starburst is going on. In 30 Doradus, the central ionizing cluster R136 with an age of 2--3 Myr is surrounded by 20 Myr old red supergiants and a neighboring 20-Myr old cluster, which may have triggered the collapse of the dense molecular parent cloud of R136, while R136 triggered ongoing star formation found in NICMOS images. We discuss the complex age structure and star formation and trigger processes in greater detail.

Grebel, E. K.; Brandner, W.; Chu, Y.-H.

1999-05-01

196

Spectral atlas of massive stars around He I (Groh+, 2007)  

NASA Astrophysics Data System (ADS)

We present a digital atlas of peculiar, high-luminosity massive stars in the near-infrared region (10470-11000{AA}) at medium resolution (R~7000). The spectra are centered around HeI 10830{AA}, which is formed in the wind of those stars, and is a crucial line to obtain their physical parameters. The instrumental configuration also sampled a rich variety of emission lines of FeII, MgII, CI, NI, and Pa{gamma}. Secure identifications for most spectral lines are given, based on synthetic atmosphere models calculated by our group. We also propose that two unidentified absorption features have interstellar and/or circumstellar origin. For the strongest one (10780{AA}) an empirical calibration between E(B-V) and equivalent width is provided. The atlas displays the spectra of massive stars organized in four categories, namely Be stars, OBA Iape (or luminous blue variables, LBV candidates and ex/dormant LBVs), OB supergiants and Wolf-Rayet stars. For comparison, the photospheric spectra of non emission-line stars are presented. Selected LBVs were observed in different epochs from 2001 to 2004, and their spectral variability reveals that some stars, such as eta Car, AG Car and HR Car, suffered dramatic spectroscopic changes during this time interval. (2 data files).

Groh, J. H.; Damineli, A.; Jablonski, F.

2007-04-01

197

A Search for Galactic Red Supergiant Variables Beyond the Solar Circle  

NASA Astrophysics Data System (ADS)

The Galactic rotation curve outside of the Solar circle is particularly difficult to ascertain, yet of critical importance for characterizing the distribution of mass in the Galaxy. We propose to identify a new and large sample of stellar kinematic tracers beyond the Solar circle, in the form of red supergiant variables (RSVs; spectral type M0-M5, luminosity class Ia-Ib). RSVs are ideal tracers of the heavily extincted outer Galactic disk, because (1) they are the intrinsically most luminous Pop I standard candles in the near-infrared, (2) they are more common than the classically employed Cepheids, and (3) they exhibit a period-luminosity relation of comparable precision to that of Cepheids. With the CTIO 0.9m in queue mode, we will derive the pulsation periods of our RSV candidates, allowing us to identify the most distant RSVs for further study. In addition, follow- up observations to obtain accurate, phase-weighted (``(gamma)'') radial velocities (a prerequisite for determining the Galactic rotation curve with RSVs) cannot be planned without period information. We have preselected RSV candidates from a catalog of ~1500 red supergiants in the Galactic plane, originally identified on objective-prism plates. Spectral types and luminosity classes have been determined from 8-color Wing photometry and medium-resolution spectra. The pulsation periods are expected to be 100 to 1000 days, and thus we request long-term status.

Alves, David; MacConnell, Jack; Wing, Robert; Bond, Howard E.; Zurek, David; Hoard, Donald W.

2000-02-01

198

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

199

Populations of rotating stars. II. Rapid rotators and their link to Be-type stars  

NASA Astrophysics Data System (ADS)

Context. Even though it is broadly accepted that single Be stars are rapidly rotating stars surrounded by a flat rotating circumstellar disk, there is still a debate about how fast these stars rotate and also about the mechanisms involved in the angular-momentum and mass input in the disk. Aims: We study the properties of stars that rotate near their critical-rotation rate and investigate the properties of the disks formed by equatorial mass ejections. Methods: We used the most recent Geneva stellar evolutionary tracks for rapidly rotating stars that reach the critical limit and used a simple model for the disk structure. Results: We obtain that for a 9 M? star at solar metallicity, the minimum average velocity during the main-sequence (MS) phase to reach the critical velocity is around 330 km s-1, whereas it would be 390 km s-1 at the metallicity of the Small Magellanic Cloud (SMC). Red giants or supergiants originating from very rapid rotators rotate six times faster and show N/C ratios three times higher than those originating from slowly rotating stars. This difference becomes stronger at lower metallicity. It might therefore be very interesting to study the red giants in clusters that show a large number of Be stars on the MS band. On the basis of our single-star models, we show that the observed Be-star fraction with cluster age is compatible with the existence of a temperature-dependent lower limit in the velocity rate required for a star to become a Be star. The mass, extension, and diffusion time of the disks produced when the star is losing mass at the critical velocity, obtained from simple parametrized expressions, are estimated to be between 9.4 × 10-12 and 1.4 × 10-7 M? (3 × 10-6 to 4.7 × 10-2 times the mass of the Earth), 2000 and 6500 R?, and 10 and 30 yr. These values are not too far from those estimated for disks around Be-type stars. At a given metallicity, the mass and the extension of the disk increase with the initial mass and with age on the MS phase. Denser disks are expected in low-metallicity regions.

Granada, A.; Ekström, S.; Georgy, C.; Krti?ka, J.; Owocki, S.; Meynet, G.; Maeder, A.

2013-05-01

200

Radial velocities for different spectral lines of B and A supergiants in our Galaxy and in the Large Magellanic Cloud  

Microsoft Academic Search

Coudé spectra of 23 early-type supergiants (16 of them belong to our Galaxy and 7 to the Large Magellanic Cloud (LMC)) were measured to study the radial velocities of all metallic and non-metallic lines in relation to their EP + IP (high excitation + ionization potential). The identified elements of the spectra do not show any systematic dependence (gradient) of

E. Kontizas; M. Kontizas

1981-01-01

201

Low-Resolution Spectroscopy of Hot Post-AGB Candidates II. LS, LSS, LSE Stars and Additional IRAS Sources  

NASA Astrophysics Data System (ADS)

Hot (OB) post-asymptotic giant branch (post-AGB) stars are immediate progenitors of planetary nebulae (PNe). Very few hot post-AGB stars are known. Detecting new hot post-AGB candidates and follow-up multiwavelength studies will enable us to further understand the processes during the post-AGB evolution that lead to the formation of PNe. Case-Hamburg OB star surveys and their extension (LS, LSS, and LSE catalogues) and IRAS (point source) catalogues are good sources for detecting new hot post-AGB candidates from low-resolution spectroscopy. Spectral types are determined from low-resolution optical spectra of 44 stars selected from the LS, LSS, and LSE catalogues. Unlike the stars mentioned in the first paper, the stars discussed in this paper were selected using criteria other than positional coincidence with an IRAS source with far-IR (IRAS) colours similar to post-AGB supergiants and planetary nebulae. These included high galactic latitude, spectral types of O, B, A supergiants, emission lines in the spectrum and known spectral peculiarity. From the present study we find that LSS 1179, LSS 1222, LSS 1256, LSS 1276, LSS 1341, LSS 1394, LSS 2241, LSS 2429, LSS 4560, LSE 3, LSE 16, LSE 42, and LSE 67 to be new hot post-AGB candidates. Further studies of these candidates are needed.

Parthasarathy, Mudumba; Drilling, John S.; Vijapurkar, Jyotsna; Takeda, Yoichi

2012-06-01

202

Variable stars  

SciTech Connect

This book covers the following topics: pulsating variables; eruptive variables; eclipsing stars; supplement to the classification; the discovery of variable stars; the significance of variable stars for research on the structure of the galaxy and stellar evolution; and observational methods and organizations.

Hoffmeister, C.; Richter, G.; Wenzel, W.

1985-01-01

203

Molecular Gas and Star formation in Giant HII Regions of M33  

NASA Astrophysics Data System (ADS)

We have extensively studied the properties of molecular clouds which are associated with the supergiant HII region NGC 604 in the nearest (D = 840 kpc) spiral galaxy M33. We suggest that the dense gas formation and second-generation star formation occur in the surrounding gas compressed by the stellar wind and/or supernova of the first-generation stars of NGC 604 (central OB star cluster) and that giant molecular cloud complex associated with NGC 604 is a unique laboratory for different, especially, for the early and intermediate stages along evolutionary path of star formation in the giant HII region. We present recent results for the Ginat HII regions in M33, including NGC 604.

Tosaki, T.; Miura, R. E.; Kohno, K.; Kuno, N.; Onodera, S.; MAGiC team

2013-10-01

204

Spectroscopy of luminous blue stars in M31 and M33  

SciTech Connect

Spectra have been obtained for classification of 42 candidate supergiants and 12 probable OB stars in M31 and eight early-type stars in M33. Twenty-six of those in M31 and six in M33 are confirmed as apparent single members with spectral types ranging from O8 to F8. Their interstellar extinction and luminosities are derived from published photographic and CCD photometry for all of the confirmed members. The preliminary and still incomplete HR diagram obtained for M31 shows an apparent lack of the most massive stars, stars with initial masses greater than 60 solar masses. The effects of incompleteness and observational selection on the interpretation of this HR diagram are discussed. 42 refs.

Humphreys, R.M.; Massey, P.; Freedman, W.L. (Minnesota Univ., Minneapolis (USA) Kitt Peak National Observatory, Tucson, AZ (USA) Mount Wilson and Las Campanas Observatories, Pasadena, CA (USA))

1990-01-01

205

Rb-RICH ASYMPTOTIC GIANT BRANCH STARS IN THE MAGELLANIC CLOUDS  

SciTech Connect

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

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

2009-11-01

206

RV and vsini of evolved stars (de Medeiros+ 1999)  

NASA Astrophysics Data System (ADS)

Rotational and radial velocities have been measured for about 2000 evolved stars of luminosity classes IV, III, II and Ib covering the spectral region F, G and K. The survey was carried out with the CORAVEL spectrometer. The precision for the radial velocities is better than 0.30km/s, whereas for the rotational velocity measurements the uncertainties are typically 1.0km/s for subgiants and giants and 2.0km/s for class II giants and Ib supergiants. These data will add constraints to studies of the rotational behaviour of evolved stars as well as solid informations concerning the presence of external rotational brakes, tidal interactions in evolved binary systems and on the link between rotation, chemical abundance and stellar activity. (1 data file).

de Medeiros, J. R.; Mayor, M.

1999-11-01

207

Continuing Results from the Michigan Catalogue of MK Types for the HD Stars (-90o to +5o)  

NASA Astrophysics Data System (ADS)

The Henry Draper Catalogue stars are being systematically reclassified visually by Houk, using 10o objective-prism plates (approximately 108 Å/mm, resolution 2 Å) taken at either Cerro Tololo Inter-American Observatory with the Michigan Curtis Schmidt telescope or at Kitt Peak National Observatory with the Burrell Schmidt telescope. Using the over 160,000 stars now classified, Aitoff Equal Area Projection Plots in galactic coordinates l and b are shown for stars of various spectral types and luminosities, with special emphasis on the supergiants and on peculiar stars, such as the Ap, Am, C, S, WR, Ba, CN, and weak-lined stars. This work has been supported in part by the National Science Foundation.

Caballero-Nieves, S. M.; Houk, N.; Sowell, J. R.

2003-12-01

208

The occultation of 119 Tauri and the effective temperatures of three M supergiants  

Microsoft Academic Search

The angular diameter of 119 Tauri has been measured in three colors by lunar occultation, and it is used to derive the effective temperature and linear radius of this M2.2 Iab\\/-\\/ type star. These values are compared with those calculated for two stars of similar spectral type alpha Orionis and alpha Scorpii. Consistent results are obtained for the three stars

N. M. White

1980-01-01

209

Chemical compositions of four B-type supergiants in the SMC wing  

NASA Astrophysics Data System (ADS)

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

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

2005-01-01

210

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

211

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

212

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

SciTech Connect

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.

1986-09-01

213

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

214

Eight Years of Watching TV (Gem) - Unraveling Long ( ˜6.2 yr.) and Short-term ( ˜400 d) Pulsations of the Red Supergiant TV Gem: Changes in Luminosity, Radius, and Teff.  

NASA Astrophysics Data System (ADS)

TV Gem (HD 42475) is a semi-regular M1 Iab supergiant accompanied by a less luminous B3.5 IV companion. The star is a bright (V = 6.2 to 6.8) member of the Gem OB1 Association at a distance of ˜1.2 kpc. Recent lunar occultation interferometric K-band observations by Mondal and Chandrasekhar yield an angular diameter of 4.46 ± 0.07 mas and show the presence of two dust shells located at ˜13 and ˜500 stellar radii from the star. Since 1997 we have been carrying out intensive V-band and narrow-to-intermediate band Wing near-IR (712 nm, 754 nm, and 1040 nm) photometry. This photometry indicates, for the first time, the presence of a long-term period of ˜6.16 years and the more familiar lower amplitude semi-regular (350-450 d) brightness changes. Variations in the molecular TiO ? (0,0) 719 nm band strength are determined from the near-IR observations, and yield spectral type changes from M1 (Teff ˜ 3750K) at maximum light to M3 (Teff ˜ 3450K) at minimum light. A near-IR color index and the TiO strengths are also used to estimate effective temperature, luminosity, and radius variations throughout the pulsational cycles. These variations indicate that TV Gem pulsates in the fundamental mode globally with the observed 6.16 year period. However, the year-by-year light variations are more complex, implying that on smaller local atmospheric scales TV Gem does not follow simplified models of a spherically symmetrical pulsating star. The overall photometrically determined mean values of Teff, Luminosity, and Radius are -- Teff ˜ 3600K, L ˜ 80000 Lsun, and R ˜ 700 Rsun. The observed long-term variation patterns and calculated ranges of these parameters may provide deeper insights into pulsational theories of TV Gem in particular and luminous M-types supergiants in general. This research is supported in part by NSF/RUI Grants AST-0507542 and AST-0507536 which we gratefully acknowledge.

Wasatonic, R.; Guinan, E.; Engle, S.

2005-12-01

215

Symbiotic Stars  

NASA Astrophysics Data System (ADS)

During the production of the Henry Draper Catalog, Wilhemina Fleming identified several M-type stars with unusually strong hydrogen emission lines. Paul Merrill obtained higher quality spectra of these `stars with combination spectra' and found intense emission from He II or [O III] and [Ne III] in addition to H I. All of these stars varied by 0.5-1 mag on a timescale of several years. A few syst...

Kenyon, S.; Murdin, P.

2000-11-01

216

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

217

Lucky Star  

NSDL National Science Digital Library

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

2008-01-01

218

A detailed analysis of F-type supergiants. II Microturbulence distribution and element abundances in the atmosphere of Rho CAS  

NASA Astrophysics Data System (ADS)

A model atmosphere analysis is made of the supergiant Rho Cas (F8 Iap) on the basis of spectrograms with dispersions of 4 and 6 A/mm. The following values are obtained for the effective temperature and the surface gravity: Tef = 6000 K, lg g = 0.25. The Balmer lines observed in the spectrum of Rho Cas seem to be weaker than those calculated on the basis of the model atmosphere. It is suggested that the agreement between the theoretical and observed profiles of the Balmer series may be improved by giving up the assumption of local thermodynamic equilibrium. The abundances of 24 elements are determined, and it is shown that the chemical composition of the supergiant's atmosphere is similar to that of the solar atmosphere.

Boiarchuk, A. A.; Liubimkov, L. S.

219

Star Images, Star Performances (College Course File).  

ERIC Educational Resources Information Center

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

Butler, Jeremy G.

1990-01-01

220

Compact Stars  

NASA Astrophysics Data System (ADS)

Neutron stars are the smallest denses stars known, with densities some 1014 times that of the Earth. They rotate with periods of fractions of a second, and their magnetic fields drive intense interstellar dynamos, lighting up entire nebulae. This text discusses the physics of these extreme objects. It includes the needed background in classical general relativity in nuclear and particle physics.

Glendenning, Norman K.

221

Rogue Star  

NSDL National Science Digital Library

This program calculates and depicts the effects of a rogue star coming through our solar system. Users adjust the date, the rogue star's mass, approach distance in astronomical units (AU) and flyby speed to run an animation of what would happen to the planets under the specified conditions.

Hamilton, Douglas

222

Star Journey  

NSDL National Science Digital Library

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

Anderson, Carolyn

223

Fates of the First Stars and Their Cosmological Consequences  

NASA Astrophysics Data System (ADS)

We present results from our numerical simulations of the demise of the first stars and their cosmological consequences. Recent results of the first star formation suggest the mass scale of the first stars is around 100 M?. The first stars with initial masses between 140 M? and 250 M? might die as very powerful explosions called pair-instability supernovae (PSNe). We use CASTRO, a new multidimensional radiation-hydrodynamics code, to study the evolution of PSNe. Our 3D simulations start with the collapse phase and follow the explosion until the shock breaks out from the stellar surface. Unlike the iron-core collapse supernovae, PSNe are powered by thermonuclear runaway without leaving compact remnants. Much Ni is forged, up to 30 M?, and its decay energy powers the PSN luminosity for several months. During the explosion, the emergent fluid instabilities cause the mixing of PSN ejecta, and the amount of mixing is related to PSN progenitors. The red supergiant progenitors demonstrate strong mixing, altering the spectrum and light curves. After the explosion, we use sophisticated cosmological simulations to study how the PSNe impact the early universe. We find the shocks reheat the relic H II regions built by previous stars before they die as PSNe. Therefore, the hot gas can stay ionized for an additional several million years. It increases the Jeans mass of star-forming clouds, leading to the delay of later star formation. The dispersed metal rapidly enriches the pristine IGM to a critical metallicity, allowing the Pop II stars to form inside the first galaxies. Our simulations provide observational predictions for the first supernovae and their fingerprint on the first galaxies that will be the major targets of forthcoming high-z observatories such as JWST, LSST, and TMT.

Chen, Ke-Jung

2013-01-01

224

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

225

Star Formation History of a Young Super-Star Cluster in NGC 4038/39: Direct Detection of Low-Mass Pre-Main Sequence Stars  

NASA Astrophysics Data System (ADS)

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 ?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.; Christopher, Micol H.; Scoville, Nick Z.

2010-02-01

226

The Hubble / Sandage Variable HDE269006 - a Hot Supergiant with a Cool Envelope  

NASA Astrophysics Data System (ADS)

The class of bright blue variable stars, which we call "Hubble-Sandage" or "s Dor" variables, contains some of the most luminous stars known in the universe. At maximum light at least their visual brightness may surpass that of any known non-variable star. Because of their high luminosity and since these stars can be distinguished from faint galactic foreground stars by their particular light curves, the identification of such objects in extragalactic systems is relatively easy, and a considerable number of these stars has been discovered in nearby galaxies. Since they can be detected over so large distances, Hubble-Sandage variables could in principle provide a useful tool in the calibration of the extragalactic distance scale and in studies of the physical conditions in extragalactic systems. However, before such investigations can be considered, we first have to learn much more about the nature and structure of these stars. Since all these objects are blue and since as a rule Hubble-Sandage variables are surrounded by dense expanding circumstellar envelopes, spectroscopic observations at ultraviolet wavelengths (where the most common ions in these envelopes have their strongest spectral lines) are particularly important for clarifying the nature of these stars. Therefore, we used the International Ultraviolet Explorer (IUE) satellite to observe some of these objects.

Appenzeller, I.; Stahl, O.; Wolf, B.

1981-09-01

227

Intrinsic Colour Indices of OB Supergiants Giants and Dwarfs in the UBVRIJHKLM System  

NASA Astrophysics Data System (ADS)

This paper is based on UBVRIJHKLM magnitudes of about 700 0- and B-type stars obtained from the literature. The mean intrinsic colours have been derived with the aid of two-colour diagrams for 0- and B-type stars of luminosity classes Ia, Iab-Ib-II, III and IV-V. The present results are based on much larger samples of every Sp/L than any other previously determined infrared colours. The colours obtained are compared with those obtained by other authors. In the present system of infrared colours, the intrinsic (B - V )o values obtained in the programme to determine the intrinsic ultraviolet colours of OB stars (Papaj, Kretowski & Wegner) were used. The majority of slightly reddened Oe and Be stars and all very strongly reddened Be stars adopted in this work are placed on the two-colour diagrams identically as normal B stars. Examples of several two-colour diagrams are presented. Key words: stars: fundamental parameters - dust, extinction - infrared: stars.

Wegner, W.

1994-09-01

228

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

NASA Astrophysics Data System (ADS)

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

Brown, Alexander

1994-07-01

229

Period-luminosity relations for red supergiant variables - II. The distance to M101  

NASA Astrophysics Data System (ADS)

We report the discovery of 42 red supergiant variables (RSVs) in the late-type spiral galaxy M101. Periods for the luminosity variation of these RSVs were determined from 20 epochs of ground-based CCD photometry in the Kron-Cousins R band obtained with the KPNO 2.1-m and WIYN 3.5-m telescopes over a span of three years. The periods found were in the range 200-1300days. Using the relationship between the RSV periods and their luminosity in the Kron-Cousins I band, we estimate a reddening-corrected distance modulus to M101 of 29.40+/-0.16mag (based on a distance modulus of 18.5+/-0.1mag for the Large Magellanic Cloud). This distance is consistent with the Hubble Space Telescope Key Project Cepheid distances of 29.34+/-0.17mag for the outer field of M101 and 29.21+/-0.17mag for the inner field.

Jurcevic, J. S.; Pierce, M. J.; Jacoby, G. H.

2000-04-01

230

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

231

Interferometric Measurements Of The A-type Supergiant Deneb With The CHARA Array  

NASA Astrophysics Data System (ADS)

We have obtained precise interferometric measurements of the A-type supergiant Deneb (A2Ia) at the Center for High Angular Resolution Astronomy (CHARA) Array in the infrared K' band (1.94 to 2.34 microns) using the Fiber Linked Unit for Optical Recombination (FLUOR). Our observations were obtained over 20 nights in 2004 and 2005 with five telescope pairs E2-W2, W2-S2, W1-E2, E1-W1, and S1-W2. The projected baselines span 106 to 312 meters and sample the first and second lobes of Deneb's visibility curve. Our preliminary analysis reveals that the amplitude of the second lobe of the visibility curve is weaker than that predicted by a spherical hydrostatic model atmosphere.We also find that Deneb's angular diameter varies with position angle at the level of a few percent. We will present these data and discuss our analysis using a unified expanding model atmosphere and a rotationally distorted model atmosphere.This work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Michelson Fellowship Program. JPL is managed for NASA by the California Institute of Technology. The CHARA Array is operated by the Center for High Angular Resolution Astronomy, Georgia State University, Atlanta, GA. Additional support comes from the National Science Foundation, the Keck Foundation and the Packard Foundation.

Aufdenberg, Jason P.; Mérand, A.; Ridgway, S. T.; Coudé du Foresto, V.; Kervella, P.; Berger, D.; Sturmann, J.; Sturmann, L.; ten Brummelaar, T. A.; Turner, N. H.; McAlister, H. A.

2006-06-01

232

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

233

New Clues to the Origin of the Extreme Helium Stars  

NASA Astrophysics Data System (ADS)

The extreme helium stars {EHes} are H-poor supergiants whose origins are not yet understood despite thorough analyses of optical spectra. This proposal seeks STIS echelle spectra for 7 stars from which novel data on their chemical compositions will be obtained to pin down key abundances. First, even the EHe's initial metallicity is uncertain; certain abundance ratios - e.g., Ca/S, Ti/S, and Fe/S - imply alterations of surface abundances among elements from Na to Ni resulting from fractionation or diffusive separation, possibly the result of winnowing of dust grains from gas. The zinc abundance measurable only from UV spectra will be a powerful clue to the true metallicity because it is known not to be removed by such winnowing. Second, elements affected by the s-process, the last of the major nucleosynthetic processes for which surface abundances are unknown for EHes, will be studied. The new abundances will be used to probe the evolutionary origins of these peculiar stars by comparisons with theoretical scenarios involving a merger of white dwarfs or a final He-shell flash in a low mass white dwarf, and with observed abundances for R Coronae Borealis stars that would seem to be close relatives of the EHes. Spectrophotometric observations of EHes obtained with GO 8603 will give accurate estimates of effective temperature and surface gravity that will be used in our abundance determinations.

Lambert, David

2002-07-01

234

Neutron Stars and Quark Stars  

NASA Astrophysics Data System (ADS)

The tremendous densities reached in the centers of neutron stars provide a high pressure environment in which exciting particles processes are likely compete with each other and novel phases of matter may exist. The particle processes range from the generation of hyperons, to quark deconfinement, to the formation of kaon condensates and H-matter. Another striking possibility concerns the formation of absolutely stable strange quark matter. In the latter event all neutron stars could in fact be strange (quark matter) stars, which would be largely composed of pure quark matter possibly enveloped in a thin nuclear crust made up ordinary hadronic matter. This paper gives an overview of the properties of both classes of stars.

Weber, Fridolin

2004-08-01

235

Near-Infrared H-Band Features in Late O and B Stars  

NASA Astrophysics Data System (ADS)

We examine the spectral characteristics of normal OB stars with high-signal-to-noise ratio (>120) H-band (1.6 ?m) spectra at a resolution of 2000. We find that several atomic lines vary smoothly with stellar temperature, as first shown by Blum et al. However, we find a previously unreported, significant variation in the strength of some of these lines with stellar luminosity. B supergiant stars show stronger He i and weaker Br 11 as compared with low-luminosity B dwarf stars of the same spectral class. It is for this reason that luminosity class must also be determined to obtain an accurate spectral type for a given star using H-band spectra. We suggest a method for estimating the spectral type and luminosity of an OB star over the wavelength range from 1.66 to 1.72 ?m using hydrogen Br 11 at 1.681 mum, He i at 1.700 mum, and He ii at 1.693 mum. The use of the near-infrared spectral range for classification has obvious advantages over optical classification when applied to heavily reddened stars, such as in star-forming regions or deeply embedded lines of sight within the plane of the Galaxy, such as the Galactic center. Furthermore, the H band is less likely to be contaminated by infrared excess emission, which is frequently seen around massive young stellar objects beyond 2 mum.

Hanson, M. M.; Rieke, G. H.; Luhman, K. L.

1998-10-01

236

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

237

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

238

Chameleon stars  

SciTech Connect

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

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

2011-10-15

239

The R Coronae Borealis stars - atmospheres and abundances  

NASA Astrophysics Data System (ADS)

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

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

2000-01-01

240

On the Origin of the Supergiant HI Shell and Putative Companion in NGC 6822  

NASA Astrophysics Data System (ADS)

We present new Hubble Space Telescope Advanced Camera for Surveys imaging of six positions spanning 5.8 kpc of the HI major axis of the Local Group dIrr NGC 6822, including both the putative companion galaxy and the large HI hole. The resulting deep color magnitude diagrams show that NGC 6822 has formed >50% of its stars in the last 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 100 Myr. Stellar feedback can create the giant HI 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 HI hole via an interaction.

O'Leary, Erin; Cannon, J. M.; Weisz, D. R.; Skillman, E. D.; Dolphin, A. E.; Bigiel, F.; Cole, A. A.; de Blok, W. J. G.; Walter, F.

2012-01-01

241

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

242

SN 2011hs: A Fast and Faint Type IIb SN from a Supergiant Progenitor  

NASA Astrophysics Data System (ADS)

Type IIb Supernovae are the final evolutionary stage of massive stars that were able to retain only a thin (about 0.1 Mo) H/He external envelope at the time of the explosion. The nature of such progenitor stars (were they compact or extended stars?) and the mechanism of mass-loss that made such final structure possible (e.g. stellar winds, binary mass transfer, etc.) are still open issues. We present the preliminary results obtained from the study of a sample of Type IIb SNe. In particular, we present SN 2011hs, a IIb SN with peculiar properties: very high velocities from the spectroscopic lines and a faint and narrow bolometric light curve. Such observables suggest, as confirmed by the comparison with hydrodinamical numerical models, a small 56Ni mass ejected from a low-mass He core star. Finally, from the models, we obtain evidence for a progenitor with a radius of the order of 500 Ro, corresponding to an extended star as in the case of SNe 1993J and 2011dh.

Bufano, Filomena

2013-06-01

243

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

244

Progress report on the analysis of long exposure SWP high-resolution spectra of cool stars. Final report  

SciTech Connect

During the last few years the authors have obtained very-long-exposure, high-dispersion SWP spectra of many stars located throughout the cool half of the HR diagram. These 12-21 hour exposures were obtained by combining NASA and Vilspa shifts so as to obtain the longest possible exposures at times of low background. Included are dwarf stars of spectral type GO V-M2 V, G9.5 III-M5 II giants, G2 Ib-M2 Iab supergiants, a number of RS CVn-type systems, and Barium stars. Given the importance of this data set and the many questions that it can answer with appropriate data reduction and extensive modeling efforts, the authors summarize briefly what has and is being done with these data.

Linsky, J.L.; Ayres, T.R.; Brown, A.; Carpenter, K.; Jordan, C.

1984-01-01

245

The Dust Budget of the Small Magellanic Cloud: Are Asymptotic Giant Branch Stars the Primary Dust Source at Low Metallicity?  

NASA Astrophysics Data System (ADS)

We estimate the total dust input from the cool evolved stars in the Small Magellanic Cloud, using the 8 ?m excess emission as a proxy for the dust-production rate (DPR). We find that asymptotic giant branch (AGB) and red supergiant (RSG) stars produce (8.6-9.5) × 10-7 M ? yr-1 of dust, depending on the fraction of far-infrared sources that belong to the evolved star population (with 10%-50% uncertainty in individual DPRs). RSGs contribute the least (<4%), while carbon-rich AGB stars (especially the so-called extreme AGB stars) account for 87%-89% of the total dust input from cool evolved stars. We also estimate the dust input from hot stars and supernovae (SNe), and find that if SNe produce 10-3 M ? of dust each, then the total SN dust input and AGB input are roughly equivalent. We consider several scenarios of SN dust production and destruction and find that the interstellar medium (ISM) dust can be accounted for solely by stellar sources if all SNe produce dust in the quantities seen around the dustiest examples and if most SNe explode in dense regions where much of the ISM dust is shielded from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust. Without a net positive contribution from SNe to the dust budget, this suggests that dust must grow in the ISM or be formed by another unknown mechanism.

Boyer, M. L.; Srinivasan, S.; Riebel, D.; McDonald, I.; van Loon, J. Th.; Clayton, G. C.; Gordon, K. D.; Meixner, M.; Sargent, B. A.; Sloan, G. C.

2012-03-01

246

Variable Stars  

NASA Astrophysics Data System (ADS)

It is a tradition to observe variable stars using small telescopes; actually, variable stars are the favorites of small telescopes. What it is needed is those telescopes to be well-equipped (to get good observations), and to be supplied with users (to be productive). The first can be easily achieved; the second, related to the poor job prospects, seems more difficult. Keeping in mind that there is no any Observatory, that could cover the whole sky and that an astronomical event can not be repeated, each individual observation, is very valuable. Especially that of variable stars, where the variability of their luminosity can be caused by many reasons, intrinsic or extrinsic. What is missing -from at least some of the small telescopes spread in whole Europe- is better organization. This means that, besides either some research projects of personal interest, or(/and) students training, some others -being parts of international programs- could also be carried out, focusing to specific objects and goals. The work carried out in the field of variable stars with the use of small telescopes in some European countries, will be presented.

Rovithis-Livaniou, Helen

247

Brittle Star  

USGS Multimedia Gallery

A tiny brittle star (the central disc is smaller than a dime) clings to the branches of a soft coral in a sample bucket brought into the shipboard laboratory from a submersible dive. This creature makes its home on the deep, dark ocean floor. ...

2010-04-15

248

Star quality.  

PubMed

Around 150 wards are participating in the voluntary Star Wards scheme to provide mental health inpatients with more activities with therapeutic value. Suggested activities range from a library, to horse riding Internet access and comedy. Service users are particularly keen to have more exercise, which can be a challenge in inpatient settings. PMID:17970387

Dent, Emma

2007-09-20

249

Differences in Chromospheres of M Giants & Supergiants as a Function of Dust/Gas Ratio  

NASA Astrophysics Data System (ADS)

Observational evidence indicates that Ca II emission, and thus perhaps all chromospheric indicators, are inversely correlated with the dust/gas ratio in luminous M stars. We propose to study the differences in chromospheric activity in a sample of cool stars with a range of dust/gas properties using the unique ultraviolet chromospheric diagnostics available to IUE. A combination of archival and new, seventh year LWR-LO observations will allow us to investigate in detail the relationships between total chromospheric activity, as indicated by lines of C II, Fe II, Mg I, and Mg II, and the dust level in the outer regions of a star. Specifically, we shall determine 1) whether the inverse Ca II-dust/gas correlation can be generalized to an inverse correlation of general chromospheric activity and dust-gas ratio, 2) whether the strength of the emission in any of the uv features correlates with the dust/gas ratio, and 3) whether the fraction of the total chromospheric flux emitted in the various lines (and thus the relative radiative cooling rates) changes with varying dust/gas ratio. In contrast to chromospheric emission lines visible from the ground, the lines visible with IUE are intrinsically strong and formed at a variety of temperatures and opacities, and thus heights in the chromosphere. Thus, these IUE data, unlike the existing ground-based data, will allow us to draw conclusions regarding the interaction between dust grains and the amount of warm chromospheric gas at various levels throughout the chromospheres of cool, luminous stars. Since the lifetime of the IUE spacecraft is limited, it is important to complete this important survey program in the near future in order to guide planning for Space Telescope observations of luminous cool stars and to provide a firm observational basis for understanding the energy balance in the atmospheres of these stars.

Linsky, Jeffery L.

1984-07-01

250

Triple star evolution and the formation of short-period, low mass X-ray binaries  

NASA Astrophysics Data System (ADS)

To explain the presence of a relatively massive black hole in 2A0620-00 the authors propose a new evolutionary scenario for the formation of short-period, low-mass X-ray binaries. The progenitor in this scenario is a triple star in which a massive close binary is accompanied at large distance by a late dwarf. After the evolution of the close binary into an ordinary X-ray binary, the compact object is engulfed by its expanding massive companion, and spirals in to settle at its centre. The resulting Thorne-Zytkow supergiant gradually expands until it attains the size of the late-dwarf orbit. Then a second spiral-in phase ensues, leading to the formation of a low-mass close binary. Depending on the initial parameters of the massive binary, this close low-mass binary may contain either a black hole or a neutron star.

Eggleton, P. P.; Verbunt, F.

1986-05-01

251

A search for substellar companions to southern solar-type stars  

NASA Astrophysics Data System (ADS)

At the Mount John University Observatory relative radial velocities of solar-type stars have been obtained with a characteristic random error of 55 m/s using a fiber-fed echelle system and digital cross-correlation techniques. A program of obtaining radial velocities of 29 solar-type stars and 10 giant IAU radial-velocity standard stars was carried out over 2.5 years with a view to the detection of low-mass companions to the dwarf stars. One dwarf star turned out to have a previously undiscovered stellar companion but no dwarfs showed radial-velocity variability suggestive of the presence of substellar companions, although one showed a possible variation. In contrast, at least half the giant or supergiant 'standard' stars were variable in radial velocity. Four and possibly five of the giant standards are probably intrinsic (pulsating) red or yellow variables. Two further standards showed long-period variability suggestive of companions of undetermined mass. The lack of brown dwarfs observed in this program is consistent with the results of other recent surveys.

Murdoch, Kaylene A.; Hearnshaw, J. B.; Clark, M.

1993-08-01

252

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

NASA Astrophysics Data System (ADS)

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

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

1984-04-01

253

Sage Studies Of The Mass Return From AGB And RSG Stars In The Large Magellanic Cloud  

NASA Astrophysics Data System (ADS)

The Surveying the Agents of a Galaxy's Evolution (SAGE; PI: M. Meixner) Spitzer Space Telescope Legacy project aims to further our understanding of the life cycle of matter in galaxies by studying this life cycle in our neighboring galaxy, the Large Magellanic Cloud (LMC). Combining SAGE mid-infrared photometry with that at shorter wavelengths from other catalogs, the spectral energy distribution (SED) for each of >25000 Asymptotic Giant Branch (AGB) and Red Supergiant (RSG) stars in the LMC has been assembled. To model mass loss from these stars, my colleagues and I have constructed the grid of RSG and AGB models (GRAMS) using the radiative transfer code 2Dust. I will discuss how GRAMS was constructed, and how we use it to determine the mass-loss rate for each evolved star studied, which gives the total mass-loss return to the LMC from AGB and RSG stars. In my talk, I show how this total mass-loss return is divided into oxygen-rich (O-rich) and carbon-rich (C-rich) dust using SED-fitting to identify O-rich versus C-rich AGB stars. Applications of this work to determining the mass return from evolved stars in other galaxies, including the Milky Way, will also be discussed.

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

2011-01-01

254

A search for O VI in the winds of B-type stars  

NASA Astrophysics Data System (ADS)

We have conducted a survey of FUSE spectra of 235 Galactic B-type stars in order to determine the boundaries in the H-R diagram for the production of the superion {O Vi} in their winds. By comparing the locations and morphology of otherwise unidentified absorption features in the vicinity of the {O Vi} resonance doublet with the bona fide wind profiles seen in archival IUE spectra of the resonance lines of {N V}, {Si Iv} and {C Iv}, we were able to detect blueshifted {O Vi} lines in the spectra of giant and supergiant stars with temperature classes as late as B1. No features attributable to {O Vi} were detected in dwarfs later than B0, or in stars of any luminosity class later than B1, although our ability to recognize weak absorption features in these stars is severely restricted by blending with photospheric and interstellar features. We discuss evidence that the ratio of the ion fractions of {O Vi} and {N V} is substantially different in the winds of early B-type stars than O-type stars.

Zsargó, J.; Fullerton, A. W.; Lehner, N.; Massa, D.

2003-07-01

255

Clumped donor winds in supergiant high-mass X-ray binaries  

NASA Astrophysics Data System (ADS)

To understand the nature of high-mass X-ray binaries it is pivotal to consider the structure of the powerful winds of their donor. Detailed hydrodynamic models of stellar winds predict strong density velocity fluctuations of the accreted flow. These should lead to variability of the X-ray light-curves from HMXBs and should be taken into account in modeling of their X-ray spectra. We will briefly review what is known about the basic properties of hot star winds. The question whether our picture of winds in single stars is compatible with the X-ray observations of HMXBs will be addressed.

Oskinova, Lidia

2012-09-01

256

The brief lives of massive stars as witnessed by interferometry}  

NASA Astrophysics Data System (ADS)

Massive stars present the newest and perhaps most challenging opportunity for long baseline interferometry to excel. Large distances require high angular resolution both to study the means of accreting enough mass in a short time and to split new-born multiples into their components for the determination of their fundamental parameters. Dust obscuration of young stellar objects require interferometry in the infrared, while post-mainsequence stellar phases require high-precision measurements to challenge stellar evolution models. I will summarize our work on a massive YSO in NGC 3603 including modeling mid-IR interferometric observations, as well as recent sub-mm imaging and spectroscopy with APEX. We find some evidence for a disk in the MIR, resolve multiple cores in the sub-mm with emission line spectra untypical for hot cores. I also report on the derivation of masses and luminosities of a massive O-type supergiant (? Orionis) in another star forming region in Orion. The small radial velocity semi-amplitudes coupled with few usable (i.e. wind-free) lines have made this work very challenging and forced us to base the mass determination on a photometric distance estimate. As a rapidly evolving application of interferometry, massive stars have a bright future.

Hummel, Christian

2013-06-01

257

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

NASA Astrophysics Data System (ADS)

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

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

2006-07-01

258

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

259

On the Origin of the Supergiant H I Shell and Putative Companion in NGC 6822  

NASA Astrophysics Data System (ADS)

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 ~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. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive 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.

Cannon, John M.; O'Leary, Erin M.; Weisz, Daniel R.; Skillman, Evan D.; Dolphin, Andrew E.; Bigiel, Frank; Cole, Andrew A.; de Blok, W. J. G.; Walter, Fabian

2012-03-01

260

Death Star  

NSDL National Science Digital Library

Death Star, a program from the PBS NOVA series, probes the deep mysteries of gamma-ray bursts, the most powerful celestial explosions since the Big Bang. A description of what would happen to Earth if a gamma-ray burst occurred in our own galaxy, a celestial glossary, and a virtual tour of the electromagnetic spectrum are included. Additional websites and published works about space topics are given, and the accompanying video is available to order.

261

Symbiotic Stars  

NASA Astrophysics Data System (ADS)

Symbiotic stars are interacting binary systems composed of a white dwarf (WD) accreting at high rate from a cool giant companion, which frequently fills its Roche lobe. The WD usually is extremely hot and luminous, and able to ionize a sizeable fraction of the cool giant wind, because it is believed the WD undergoes stable hydrogen nuclear burning on its surface of the material accreted from the companion. This leads to consider symbiotic stars as good candidates for the yet-to-be-identified progenitors of type Ia supernovae. Symbiotic stars display the simultaneous presence of many different types of variability, induced by the cool giant, the accreting WD, the circumstellar dust and ionized gas, with time scales ranging from seconds to decades. The long orbital periods (typically a couple of years) and complex outburst patterns, lasting from a few years to a century, make observations from professionals almost impossible to carry out, and open great opportunities to amateur astronomers to contribute fundamental data to science.

Munari, U.

2012-06-01

262

Exceptional Stars  

NASA Astrophysics Data System (ADS)

As part of our Interdisciplinary Scientist effort (PI, Kulkarni) for the Space Interferometry Mission (SIM) we proposed an investigation with SIM of a number of exceptional stars. With SIM we plan to observe dozens of nearby white dwarfs and search for planets surviving the evolution away from the main sequence as well as (newly formed) planets formed in the circumbinary disks of post-AGB binaries or as a result of white dwarf mergers. We propose to measure the proper motion of a sample of X-ray binaries and Be star binaries with the view of understanding the originof high latitude objects and inferring natal kicks and pre-supernova orbits. We plan to observe several compact object binaries to determine the mass of the compact star. Of particular importance is the proposed observation of SS 433 (for which we propose to use the spectrometer on SIM to measure the proper motion of the emission line clumps embedded in the relativistic jets). Separately we are investigating the issue of frame tie between SIM and the ecliptic frame (by observing binary millisecond pulsars with SIM; the position of these objects is very well determined by pulsar timing) and the degree to which highly precise visibility amplitude measurements can be inverted to infer binary parameters.

Kulkarni, S. R.; Hansen, B.; van Kerkwijk, M.; Phinney, E. S.

2005-12-01

263

On the detection of chemically peculiar stars using ?a photometry  

NASA Astrophysics Data System (ADS)

We have summarized all ? a measurements for galactic field stars (1474 objects) from the literature published over more than two decades. These measurements were, for the first time, compiled and homogeneously analyzed. The ? a intermediate band photometric system samples the depth of the 5200 Å flux depression by comparing the flux at the center with the adjacent regions with bandwidths of 110 Å to 230 Å. Because it was slightly modified over the last three decades, we checked for systematic trends for the different measurements but found no correlations whatsoever. The ? a photometric system is most suitable to detecting magnetic chemically peculiar (CP) stars with high efficiency, but is also capable of detecting a small percentage of non-magnetic CP objects. Furthermore, the groups of (metal-weak) ? Bootis, as well as classical Be/shell stars, can be successfully investigated. In addition, we also analyzed the behaviour of supergiants (luminosity class I and II). On the basis of apparent normal type objects, the correlation of the 3? significance limit and the percentage of positive detection for all groups was derived. We compared the capability of the ? a photometric system with the ? (V1 - G) and Z indices of the Geneva 7-color system to detect peculiar objects. Both photometric systems show the same efficiency for the detection of CP and ? Bootis stars, while the indices in the Geneva system are even more efficient at detecting Be/shell objects. On the basis of this statistical analysis it is possible to derive the incidence of CP stars in galactic open cluster and extragalactic systems including the former unknown bias of undetected objects. This is especially important in order to make a sound statistical analysis of the correlation between the occurrence of these objects and astrophysical parameters such as the age, metallicity, and strength of global, as well as local, magnetic fields.

Paunzen, E.; Stütz, Ch.; Maitzen, H. M.

2005-10-01

264

The AP stars  

Microsoft Academic Search

Ap stars are stars with peculiar characteristics which made it difficult to assign them to the stellar types of the conventional classification scheme. Ap stars are frequently observed. Up to 10% Ap stars are found in the case of the concerned spectral types. Attention is given to the spectroscopic properties of the Ap stars, aspects of stellar spectrum and stellar

H. Muthsam

1977-01-01

265

Star formation in disks  

Microsoft Academic Search

It is noted that the principal characteristics of the stellar populations in galaxies depend on the history of star formation and the initial mass spectrum with which the stars are formed. Whereas there have been a number of attempts to model the history of star formation in galaxies using various quasi-theoretical descriptions of star formation, star formation remains poorly understood

R. B. Larson

1983-01-01

266

The Wolf-Rayet Content of the Andromeda Galaxy: What Do Massive Stars Really Do When the Metallicity is Above Solar?  

NASA Astrophysics Data System (ADS)

We are proposing to survey M 31 for Wolf-Rayet stars (WRs) and red supergiants (RSGs), providing much needed information about how massive stars evolve at greater-than-solar metallicities. Our understanding of massive star evolution is hampered by the effects of mass-loss on these stars; at higher metallicities mass-loss effects become ever more pronounced. Our previous work on other Local Group galaxies (Massey & Johnson 1998) has shown that the number of RSGs to WRs correlates well with metallicity, changing by a factor of 6 from NGC 6822 (log O/H+12=8.3) to the inner parts of M 33 (8.7). Our study of five small regions in M 31 suggests that above this value the ratio of RSGs to WRs doesn't change: does this mean that no massive star that becomes a WR spends any time as a RSG at above solar metallicities? We fear instead that our sample (selected, afterall, for containing WR stars) was not sufficiently well-mixed in age to provide useful global values; the study we propose here will survey all of M 31. Detection of WRs will provide fundamental data not only on massive star evolution, but also act as tracers of the most massive stars, and improve our knowledge of recent star-formation in the Andromeda Galaxy.

Massey, Philip

2000-08-01

267

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

SciTech Connect

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

Voels, S.A.

1989-01-01

268

SN 2004A: another Type IIP supernova with a red supergiant progenitor  

Microsoft Academic Search

We present a monitoring study of SN 2004A and probable discovery of a progenitor star in pre-explosion Hubble Space Telescope (HST) images. The photometric and spectroscopic monitoring of SN 2004A show that it was a normal Type II-P which was discovered in NGC 6207 about two weeks after explosion. We compare SN 2004A to the similar Type II-P SN 1999em

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

2006-01-01

269

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

NASA Astrophysics Data System (ADS)

As evidence for variations in the initial mass function (IMF) in nearby star forming regions remains elusive we are forced to expand our search to more extreme regions of star formation. Starburst galaxies, which contain massive young clusters have in the past been reported to have IMFs different than that characterizing the field star IMF. In this thesis we use high signal-to-noise near-infrared spectra to place constraints on the shape of the IMF in extreme regions of extragalactic star formation and also try to understand the star formation history in these regions. Through high signal-to-noise near-infrared spectra it is possible to directly detect low-mass PMS stars in unresolved young super-star clusters, using absorption features that trace cool stars. Combining Starburst99 and available PMS tracks it is then possible to constrain the IMF in young super-star clusters using a combination of absorption lines each tracing different ranges of stellar masses and comparing observed spectra to models. Our technique can provide a direct test of the universality of the IMF compared to the Milky Way. We have obtained high signal-to-noise H- and K-band spectra of two young super-star clusters in the starburst galaxies NGC 4039/39 and NGC 253 in order to constrain the low-mass IMF and star formation history in the clusters. The cluster in NGC 4038/39 shows signs of youth such as thermal radio emission and strong hydrogen emission lines as well as late-type absorption lines indicative of cool stars. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence stars or red supergiants alone. We interpret the spectrum as a superposition of two star clusters of different ages over the physical region of 90 pc our spectrum represents. One cluster is young (? 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr - 18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. While the superposition of clusters does not allow us to place stringent constraints on the IMF there is no evidence of a low-mass cutoff in the cluster and the IMF is consistent with a Chabrier and Kroupa IMF typical of the field. The cluster in NGC 253 shows the same signs of youth as the cluster in NGC 4038/39 and sits in front of a background population of older stars. The background population has an age of ? 12 Myr and thus contains red supergiants. After carefully subtracting this background we model the spectrum of the young cluster. We find that its IMF is consistent with a Chabrier and Kroupa IMF with a best-fit power-law slope of 1.0 in linear units. Slopes of 0.0 - 1.5 are also formally consistent with the cluster spectrum. We conclude that there is no strong evidence for an unusual IMF or a lack of low-mass stars (? 1 M? ) in either of these galaxies.

Greissl, Julia Jennifer

2010-12-01

270

Radiative transfer in dust clouds. II - Circumstellar dust shells around early M giants and supergiants  

NASA Astrophysics Data System (ADS)

Models derived from a solution of the equation of radiative transfer through dust shells are given for a sample of 27 stars whose spectral types range from M0 to M4 and have significant infrared excess. The models, which consist of a star in a spherically symmetric circumstellar dust shell (CDS), are compared with available observational data. It is found that all CDSs can be modeled with an n(r) varies with r to the -2 power density distribution, in keeping with steady outflow at a constant velocity. For the three stars Alpha-Ori, Mu-Cep and TV Gem, the temperature T1 of the hottest grains is 1000 K, while for 12 others 500 K yields a better fit. The Alpha-Ori model presented is consistent with most IR size measurements extant. Intensity profiles are given for several models, and the bright rim of radiation expected at all IR wavelengths at the inner edge of the dust shell is noted.

Rowan-Robinson, M.; Harris, S.

1982-07-01

271

Rotating Wolf-Rayet stars in post RSG/LBV phase (Graefener+, 2012)  

NASA Astrophysics Data System (ADS)

Wolf-Rayet (WR) stars with fast rotating cores are thought to be the direct progenitors of long-duration gamma-ray bursts (LGRBs). A well accepted evolutionary channel towards LGRBs is chemically-homogeneous evolution at low metallicities, which completely avoids a red supergiant (RSG), or luminous blue variable (LBV) phase. On the other hand, strong absorption features with velocities of several hundred km/s have been found in some LGRB afterglow spectra (GRB 020813 and GRB 021004), which have been attributed to dense circumstellar (CS) material that has been ejected in a previous RSG or LBV phase, and is interacting with a fast WR-type stellar wind. Here we investigate the properties of Galactic WR stars and their environment to identify similar evolutionary channels that may lead to the formation of LGRBs. We compile available information on the spectropolarimetric properties of 29 WR stars, the presence of CS ejecta for 172 WR stars, and the CS velocities in the environment of 34 WR stars in the Galaxy. We use linear line-depolarization as an indicator of rotation, nebular morphology as an indicator of stellar ejecta, and velocity patterns in UV absorption features as an indicator of increased velocities in the CS environment. (2 data files).

Graefener, G.; Vink, J. S.; Harries, T. J.; Langer, N.

2013-01-01

272

Nonradial Pulsation Periods of B and Be Stars in NGC 3766  

NASA Astrophysics Data System (ADS)

Nonradial pulsations (NRPs) are spherical harmonic waves that propagate across the stellar surface and are driven beneath the surface by an ionized iron opacity mechanism. NRPs are a possible formation mechanism of the equatorial disk surrounding a Be star. Be stars are non-supergiant B-type stars that have been observed at some point with emission in the Balmer or other spectral lines. The emission features are the result of an equatorial mass-loss disk. Transient Be stars are those that have been observed with both emission features due to a circumstellar disk and with a non-emitting B-type spectrum. We observed NGC 3766, a young open cluster rich with B and transient Be stars, for 25 nights over three years at the CTIO 0.9m telescope using the Strömgren uvby filter system. We present the results of a period search to investigate presence of nonradial pulsations in the B and Be cluster members. We acknowledge support from Lehigh University and the Harriet G. Jenkins Pre-Doctoral Fellowship Program, supported by NASA and UNCF.

Roettenbacher, Rachael M.; McSwain, M. V.

2011-01-01

273

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

274

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

SciTech Connect

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

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

2010-09-20

275

Giant Convection Cell Turnover as an Explanation of the Long Secondary Periods in Semiregular Red Variable Stars  

NASA Astrophysics Data System (ADS)

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

Stothers, Richard B.

2010-12-01

276

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

SciTech Connect

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

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

2010-12-10

277

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

278

Ultraviolet diagnostic of porosity-free mass-loss estimates in B stars  

NASA Astrophysics Data System (ADS)

Aims: We seek to establish evidence in UV P Cygni line profiles that the signs of wind clumping and porosity vary with velocity. We aim to demonstrate empirically that while at most wind velocities optically thick clumps cover only a fraction of the stellar surface, close to the terminal velocity (v?) where narrow absorption components (NACs) appear in UV lines the covering factor is approximately unity. Methods: SEI line-synthesis models are used to determine the radial optical depths (?rad(w)) of blue and red components of the Siiv??1400 resonance line doublet in a sample of 12 B0 to B4 supergiants. We focus on stars with well developed NACs and relatively low v? so that the Siiv doublet components can be treated as radiatively decoupled and formed independently. Results: For all 12 stars the mean optical depth ratio of the blue to red components is closer to ~2 (i.e. the ratio of oscillator strengths) in the NACs than at intermediate and lower velocities. The product of mass-loss rate and ion fraction (? q(Si3 +)) calculated from the NAC optical depths is a factor of ~2 to 9 higher compared to mass-loss values sampled at ~0.4 to 0.6 v?. Conclusions: Since the wind effectively becomes "smooth" at the high NAC velocities and the column density is uniformly distributed over the stellar disk, the optical depths of the NACs are not seriously affected by porosity and this feature thus provides the most reliable measurement of mass-loss rate in the UV lines. Applications of this result to the weak-wind problem of late O-dwarf stars and the "P v mass loss discordance" in early O supergiants are discussed.

Prinja, R. K.; Massa, D. L.

2013-11-01

279

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

Microsoft Academic Search

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

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

2006-01-01

280

Light History of the Suspected RCB Star ES Aql Restored with the Harvard Photographic Plates  

NASA Astrophysics Data System (ADS)

ES Aql, initially classified as a semi-regular variable, is now suspected to belong to RCB stars - a small (only about 30 cases known) group of carbon-rich supergiants that undergo dramatic declines in brightness at irregular intervals. In order to restore the long time-scale light curve of the star and clear up the suspicions of its alleged RCB nature, an in-depth study of the Harvard photographic plates containing this star was undertaken. We carried out eye photometry of several hundred plates, which resulted in 396 reliable estimates of the relative magnitude of ES Aql covering almost a 100-year period - from 1893 to 1989. We detected as many as 89 events of considerable fading of the star, including total disappearing from the plate, which means that the star had a photographic magnitude of about 15 or fainter in the brightness minimum. In the relatively long periods of time off minima, the star resides with a magnitude of around 13.2. From our data, the duration of the time that the star was in recession varies from two to five months, but we cannot exclude shorter fadings. A preliminary analysis shows no periodicity in the fading events. Based on this extensive photometric study, we conclude that ES Aql is indeed an RCB star. We thank Dr. G. Clayton, Ms. Alison Doane, Dr. N. Samus, and Dr. V. Strelnitski for help in our work on the project. This project was supported by the NSF/REU grant AST-9820555 and the Nantucket Maria Mitchell Association.

Hammond, D.; Lawless, J.

2001-12-01

281

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

282

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

NASA Astrophysics Data System (ADS)

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

1995-05-01

283

The return of mass and energy to the interstellar medium by winds from early-type stars  

NASA Astrophysics Data System (ADS)

The kinetic energy of the stellar winds from a complete sample of B and A supergiants, O stars, and Wolf-Rayet stars has been either measured or estimated from well-defined calibrations. Within a distance of 3 kpc from the sun, these stars are currently returning mass and energy to the interstellar medium (ISM) at an average rate of 9 x 10 to the -5th solar masses/yr/sq Kpc and 2 x 10 to the 38th ergs/s/sq Kpc. Nuclear-processed material in the winds of Wolf-Rayet stars produces enrichment yields for the interstellar gas of 0.0073 for He and 0.0023 for CNO. The input of wind energy from these stars greatly exceeds the wind input from stars of other spectral types, but it is less than the supernovae energy input by about a factor of five. Considering individual phases of the ISM, stellar radiation completely dominates the heating rate of H II regions, supernovae are the major source of energy for the hot intercloud gas and the kinetic energy of the cloud motions, and stellar radiation and supernovae are of equal importance for heating neutral clouds. Although winds are of secondary importance to the global energy equilibrium, they dominate the energetics of the interstellar gas in the vicinity of the more massive OB associations.

Abbott, D. C.

1982-12-01

284

Lifestyles of the Stars.  

ERIC Educational Resources Information Center

|Some general information on stars is provided in this National Aeronautics and Space Administration pamphlet. Topic areas briefly discussed are: (1) the birth of a star; (2) main sequence stars; (3) red giants; (4) white dwarfs; (5) neutron stars; (6) supernovae; (7) pulsars; and (8) black holes. (JN)|

National Aeronautics and Space Administration, Cocoa Beach, FL. John F. Kennedy Space Center.

285

Theories of star formation  

Microsoft Academic Search

A well defined theory of star formation does not yet exist. A serious deficiency therefore remains in current theories of the structure and evolution of stars. Since stars must be forming at the present phase of Galactic evolution, it is pertinent to investigate what conditions favour star formation. Observational evidence for the pre-main sequence phase of stellar evolution is entirely

D. McNally

1971-01-01

286

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

Microsoft Academic Search

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

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

2011-01-01

287

XMM-Newton observations of IGR J18410-0535: the ingestion of a clump by a supergiant fast X-ray transient  

NASA Astrophysics Data System (ADS)

Context. IGR J18410-0535 is a supergiant fast X-ray transients. This subclass of supergiant X-ray binaries typically undergoes few-hour-long outbursts reaching luminosities of 1036-1037 erg s-1, the occurrence of which has been ascribed to the combined effect of the intense magnetic field and rotation of the compact object hosted in them and/or the presence of dense structures ("clumps") in the wind of their supergiant companion. Aims: IGR J18410-0535 was observed for 45 ks by XMM-Newton as part of a program designed to study the quiescent emission of supergiant fast X-ray transients and clarify the origin of their peculiar X-ray variability. Methods: We carried out an in-depth spectral and timing analysis of these XMM-Newton data. Results: IGR J18410-0535 underwent a bright X-ray flare that started about 5 ks after the beginning of the observation and lasted for ~15 ks. Thanks to the capabilities of the instruments on-board XMM-Newton, the whole event could be followed in great detail. The results of our analysis provide strong convincing evidence that the flare was produced by the accretion of matter from a massive clump onto the compact object hosted in this system. Conclusions: By assuming that the clump is spherical and moves at the same velocity as the homogeneous stellar wind, we estimate a mass and radius of Mcl ? 1.4 × 1022 g and Rcl ? 8 × 1011 cm. These are in qualitative agreement with values expected from theoretical calculations. We found no evidence of pulsations at ~4.7 s after investigating coherent modulations in the range 3.5 ms-100 s. A reanalysis of the archival ASCA and Swift data of IGR J18410-0535, for which these pulsations were previously detected, revealed that they were likely to be due to a statistical fluctuation and an instrumental effect, respectively.

Bozzo, E.; Giunta, A.; Cusumano, G.; Ferrigno, C.; Walter, R.; Campana, S.; Falanga, M.; Israel, G.; Stella, L.

2011-07-01

288

Revisiting the absolute-magnitude calibration of F-type supergiants and bright giants as a function of the equivalent width of the OI?7774Å triplet  

NASA Astrophysics Data System (ADS)

We reduce the published measurements of the equivalent width of the oxygen triplet (Oi?7774Å) to a single system and combine the resulting homogenized indices with revised Hipparcos parallaxes to derive the MK versus log[W(Oi?7774Å)] absolute-magnitude calibration for bright F-type giants and supergiants and use the resulting calibration to estimate both the distance to the Large Magellanic Cloud and the parameters of the Galactic rotation curve.

Dambis, A. K.

2013-02-01

289

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

290

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

291

What Are the Hot R Coronae Borealis Stars?  

NASA Astrophysics Data System (ADS)

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 of R Coronae Borealis (RCB) stars. RCB stars are typically cool hydrogen-deficient supergiants. The four stars studied in this paper are hotter (Teff=15-20 kK) than the majority of RCB stars (Teff=5000-7000 K). Although these are commonly grouped together as the 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 that is reassessed to ensure internal consistency. We find temporal variations of various properties on different timescales that will eventually help us to uncover the evolutionary history of these objects. DY Cen and MV Sgr have typical RCB helium abundances, which exclude any currently known post-asymptotic giant branch (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 planetary nebulae (PNs). 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. All three stars, on the other hand, have split emission lines, which indicate the presence of an equatorial bulge but not of a Keplerian disk. In addition, the historical light curves for the three Galactic hot RCB stars show evidence for a significant fading in their maximum-light brightnesses of ~1 mag over the last 70 yr. From this we deduce that their effective temperatures increased by a few thousand degrees. If V348 Sgr is a born-again star, as we presume, this means that the star is returning from the born-again AGB phase to the phase of a central star of PN. Spectroscopically, no dramatic change is observed over the last 50 years for V348 Sgr and MV Sgr. However, there is some evidence that the winds of V348 Sgr and DY Cen have increased in strength in the last decade. HV 2671, located in the LMC, has not been analyzed in detail but at 5 Å resolution is almost identical to V348 Sgr. Through the bolometric correction derived for V348 Sgr and the known distance, we can estimate the absolute V magnitude of HV 2671 (MV=-3.0 mag) and its bolometric luminosity (~6000 Lsolar).

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

2002-06-01

292

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

NASA Astrophysics Data System (ADS)

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

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

293

Non-linear Oscillations of Massive Stars Near the Eddington Limit  

NASA Astrophysics Data System (ADS)

The physics of massive star evolution, even on the main sequence is marred by uncertainties and hence, poorly understood. The focus of our work lies on the evolution of very massive stars on the main sequence when they approach the Eddington limit. Massive stars evolving near the Eddington limit are characterized by pronounced core-halo structures (Ishii et al. 1999) with extended low density envelopes accounting for even ~ 70% of the stellar radius, and density inversions (Petrovic et al. 2006, Graefener et al. 2011). These are ideal conditions or radial oscillations called ``strange modes'' (Glatzel 2004) which have very small growth times (~ dynamical timescale). We present non-linear calculations of these pulsations using a state-of-the-art one-dimensional hydrodynamic stellar evolution code (BEC) and latest input physics. The brightness perturbations caused as a result may relate to the microvariations observed in LBVs like AG Car (Lamers et al. 2004) or in supergiants like Deneb. Moreover, the feature of inflated envelopes coupled with the dynamic pulsations can play a major role in the modelling of mass transfer in very massive binary systems. We investigate how mass loss (through RLOF or wind) from such inflated stars may affect the envelope structure.

Sanyal, Debashis; Langer, Norbert

2013-06-01

294

Infrared 2.4 - 4.1 micron Spectra of OB-type Stars  

NASA Astrophysics Data System (ADS)

We present 2.4 to 4.1 ?m spectra of OB-type stars that were taken both during the nominal and post-helium programme of ISO SWS. Some important diagnostic lines for basic stellar and stellar wind properties are located within this band. Some important diagnostic lines for basic stellar parameters and of the wind properties are located within this band. The spectral type coverage of our sample does not allow us to confidently generalize characteristics, however, we are able to derive important line trends. We also notice an absence of a general trend in the behaviour of the leading Brackett lines of the B supergiants. This seems to indicate that the wind properties of those stars vary significantly while optical characteristics related to spectral type are similar. This study is part of the near-infrared spectroscopy of early-type stars for classification work. This field has recently been developed by Blum et al.(1997), Hanson et al.(1998), Meyer et al.(1998) and others. An infrared spectral calibration is fundamental, for instance for the investigation of massive star formation. This study is part of the work in the context of the SWS stellar classification programme. The spectra presented here will be published in an atlas of about 300 stellar spectra covering the entire MK-classification. For more details see Vandenbussche et al., this proceedings.

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

2000-11-01

295

Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC). II. Cool Evolved Stars  

NASA Astrophysics Data System (ADS)

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 ?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 ?20% of the global SMC flux (extended + point-source) at 3.6 ?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.; Srinivasan, Sundar; van Loon, Jacco Th.; McDonald, Iain; Meixner, Margaret; Zaritsky, Dennis; Gordon, Karl D.; Kemper, F.; Babler, Brian; Block, Miwa; Bracker, Steve; Engelbracht, Charles W.; Hora, Joe; Indebetouw, Remy; Meade, Marilyn; Misselt, Karl; Robitaille, Thomas; Sewi?o, Marta; Shiao, Bernie; Whitney, Barbara

2011-10-01

296

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

297

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

298

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.

2013-10-01

299

The Mass-loss Return from Evolved Stars to the Large Magellanic Cloud. VI. Luminosities and Mass-loss Rates on Population Scales  

NASA Astrophysics Data System (ADS)

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 ~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 × 10-5 M ? yr-1, equivalent to a total mass injection rate (including the gas) into the ISM of ~6 × 10-3 M ? yr-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 s band as a function of J - K s color, BC_{K_{s}} = -0.40(J-K_{s})^2 + 1.83(J-K_{s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (\\dot{M}_{d}) from C-rich AGB stars, such as log \\dot{M_{d}} = ({-18.90}/({(K_{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.; Srinivasan, S.; Sargent, B.; Meixner, M.

2012-07-01

300

Star Formation in Galaxies  

NASA Astrophysics Data System (ADS)

The process of star formation is at the core of the evolutionary cycle of galaxies, as newborn stars produce new chemical elements, dust, and light. The energetic output delivered first by stellar winds and then by supernovae a few Myr after a star formation episode may also directly impact on the evolution of galaxies and their interstellar medium (ISM), as well as having an effect on the intergalactic medium (IGM), through feedback and outflows.This chapter concerns star formation on galactic scales. First, the galactic processes that may affect large-scale star formation are presented. Second, the various methods to measure star formation rates are discussed (star formation tracers, timescales, calibrations, limits). Finally, the observational status concerning star formation in galaxies (its relation to other quantities and its evolution) is presented. The Schmidt Law (star formation rate-gas relationship) is amply discussed.

Boissier, Samuel

301

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

302

Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated with Massive Clusters  

NASA Astrophysics Data System (ADS)

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 H2O 616-523 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 H2O 616-523 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 21/F 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 H2O 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; Deguchi, Shuji

2012-11-01

303

Discovery of a short orbital period in the Supergiant Fast X-ray Transient IGR J16479-4514  

NASA Astrophysics Data System (ADS)

We report here the discovery of a 3.32 d orbital period in the Supergiant Fast X-ray Transient (SFXT) source IGR J16479-4514. Using the long-term light curve of this source obtained with Swift Burst Alert Telescope (BAT) in the energy range of 15-50 keV, we have clearly detected an orbital modulation including a full eclipse of duration ~0.6 d. In the hard X-ray band of the BAT instrument, the eclipse ingress and egress are rapid. We have also used the long-term light curve obtained with the Rossi X-ray Timing Explorer (RXTE) All Sky Monitor (ASM) in the energy range of 1.5-12 keV. Taken independently, the detection of orbital modulation in the RXTE-ASM light curve is not significant. However, considering a clear detection of orbital modulation in the BAT light curve, we have used the ASM light curve for a more precise determination of the orbital period. IGR J16479-4514 has the shortest orbital period among the three SFXTs with measured/known orbital period. We discuss the implication of a short orbital period with the various mechanisms proposed to explain the transient nature of this class of sources.

Jain, Chetana; Paul, Biswajit; Dutta, Anjan

2009-07-01

304

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

305

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

NASA Astrophysics Data System (ADS)

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

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

2006-08-01

306

Mass loss from inhomogeneous hot star winds. II. Constraints from a combined optical/UV study  

NASA Astrophysics Data System (ADS)

Context. Mass loss is essential for massive star evolution, thus also for the variety of astrophysical applications relying on its predictions. However, mass-loss rates currently in use for hot, massive stars have recently been seriously questioned, mainly because of the effects of wind clumping. Aims: We investigate the impact of clumping on diagnostic ultraviolet resonance and optical recombination lines often used to derive empirical mass-loss rates of hot stars. Optically thick clumps, a non-void interclump medium, and a non-monotonic velocity field are all accounted for in a single model. The line formation is first theoretically studied, after which an exemplary multi-diagnostic study of an O-supergiant is performed. Methods: We used 2D and 3D stochastic and radiation-hydrodynamic wind models, constructed by assembling 1D snapshots in radially independent slices. To compute synthetic spectra, we developed and used detailed radiative transfer codes for both recombination lines (solving the "formal integral") and resonance lines (using a Monte-Carlo approach). In addition, we propose an analytic method to model these lines in clumpy winds, which does not rely on optically thin clumping. Results: The importance of the "vorosity" effect for line formation in clumpy winds is emphasized. Resonance lines are generally more affected by optically thick clumping than recombination lines. Synthetic spectra calculated directly from current radiation-hydrodynamic wind models of the line-driven instability are unable to in parallel reproduce strategic optical and ultraviolet lines for the Galactic O-supergiant ? Cep. Using our stochastic wind models, we obtain consistent fits essentially by increasing the clumping in the inner wind. A mass-loss rate is derived that is approximately two times lower than what is predicted by the line-driven wind theory, but much higher than the corresponding rate derived when assuming optically thin clumps. Our analytic formulation for line formation is used to demonstrate the potential importance of optically thick clumping in diagnostic lines in so-called weak-winded stars and to confirm recent results that resonance doublets may be used as tracers of wind structure and optically thick clumping. Conclusions: We confirm earlier results that a re-investigation of the structures in the inner wind predicted by line-driven instability simulations is needed. Our derived mass-loss rate for ? Cep suggests that only moderate reductions of current mass-loss predictions for OB-stars are necessary, but this nevertheless prompts investigations on feedback effects from optically thick clumping on the steady-state, NLTE wind models used for quantitative spectroscopy.

Sundqvist, J. O.; Puls, J.; Feldmeier, A.; Owocki, S. P.

2011-04-01

307

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.

308

Quark core stars, quark stars and strange stars  

SciTech Connect

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

Grassi, F.

1988-01-01

309

Star formation in irregular galaxies  

Microsoft Academic Search

The problems associated with star formation in irregular galaxies are outlined. The basic model of star formation is reviewed. Global star formation rates, feedback processes, the physical conditions of the interstellar medium which affect star formation, and the internal structures of star-forming regions in irregular galaxies are discussed. In addition, star formation in the amorphous irregular galaxies described by Sandage

D. A. Hunter; J. S. Gallagher III

1989-01-01

310

QCD in Neutron Stars and Strange Stars  

SciTech Connect

This paper provides an overview of the possible role of Quantum Chromo Dynamics (QCD) for neutron stars and strange stars. The fundamental degrees of freedom of QCD are quarks, which may exist as unconfined (color superconducting) particles in the cores of neutron stars. There is also the theoretical possibility that a significantly large number of up, down, and strange quarks may settle down in a new state of matter known as strange quark matter, which, by hypothesis, could be more stable than even the most stable atomic nucleus, {sup 56}Fe. In the latter case new classes of self-bound, color superconducting objects, ranging from strange quark nuggets to strange quark stars, should exist. The properties of such objects will be reviewed along with the possible existence of deconfined quarks in neutron stars. Implications for observational astrophysics are pointed out.

Weber, Fridolin [Department of Physics, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1233 (United States); Negreiros, Rodrigo [FIAS, Goethe University, Ruth Moufang Str 1, 60438 Frankfurt (Germany)

2011-05-24

311

Managing the star performer.  

PubMed

Our culture seems to be endlessly fascinated with its stars in entertainment, athletics, politics, and business, and holds fast to the idea that extraordinary talent accounts for an individual's extraordinary performance. At first glance, managing a star performer in your medical practice may seem like it would be an easy task. However, there's much more to managing a star performer than many practice managers realize. The concern is how to keep the star performer happy and functioning at a high level without detriment to the rest of the medical practice team. This article offers tips for practice managers who manage star performers. It explores ways to keep the star performer motivated, while at the same time helping the star performer to meld into the existing medical practice team. This article suggests strategies for redefining the star performer's role, for holding the star performer accountable for his or her behavior, and for coaching the star performer. Finally, this article offers practical tips for keeping the star performer during trying times, for identifying and cultivating new star performers, and for managing medical practice prima donnas. PMID:23767124

Hills, Laura

312

Superbursts from Strange Stars  

Microsoft Academic Search

Recent models of carbon ignition on accreting neutron stars predict superburst ignition depths that are an order of magnitude larger than those observed. We explore a possible solution to this problem, that the compact stars in low-mass X-ray binaries that have shown superbursts are in fact strange stars with a crust of normal matter. We calculate the properties of superbursts

Dany Page; Andrew Cumming

2005-01-01

313

Dark Stars: D\\\\  

Microsoft Academic Search

The first phase of stellar evolution in the history of the universe may be Dark Stars, powered by dark matter heating rather than by fusion. Weakly interacting massive particles, which are their own antiparticles, can annihilate and provide an important heat source for the first stars in the universe. This and the previous contribution present the story of Dark Stars.

Douglas Spolyar; Katherine Freese; Paolo Gondolo; Anthony Aguirre; Peter Bodenheimer; Jeremy A. Sellwood; Naoki Yoshida

2009-01-01

314

Dark Stars: Begynnelsen  

Microsoft Academic Search

The first phase of stellar evolution in the history of the universe may be Dark Stars, powered by dark matter heating rather than by fusion. Weakly interacting massive particles, which are their own antiparticles, can annihilate and provide an important heat source for the first stars in the universe. This and the following contribution present the story of Dark Stars.

Paolo Gondolo; Katherine Freese; Douglas Spolyar; Anthony Aguirre; Peter Bodenheimer; Jeremy A. Sellwood; Naoki Yoshida

2009-01-01

315

The Neutron Star Census  

Microsoft Academic Search

The paucity of old isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of the population is simulated following the paths of a statistical sample of stars for different values of the initial kick velocity, drawn from an isotropic Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov

2000-01-01

316

Star Formation in Galaxies  

Microsoft Academic Search

Star formation on a galactic scale is regulated by the self-gravity of the gas, as shown by the Jeans-length spacing of giant cloud complexes along spiral arms and the sensitivity of the star formation rate to the gravitational stability parameter Q. Simple models based on this scenario reproduce the general properties of galactic star formation in both normal and starburst

B. G. Elmegreen

1999-01-01

317

Theory of Star Formation  

Microsoft Academic Search

We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation---turbulence, magnetic

Christopher F. McKee; Eve C. Ostriker

2007-01-01

318

Analyzing Star Trails  

NSDL National Science Digital Library

In this activity, students examine a photograph of the night sky and answer questions about their observations. The picture, taken by a high school student in upstate New York, offers insight into the Earth's rotation, apparent star motion, the location of Polaris (the North Star), circumpolar constellations, and pointer stars.

Kluge, Steve

319

Star Trail Photography  

NSDL National Science Digital Library

This web page contains information about taking photographs of star trails, which illustrate the rotation of the Earth. The site provides techniques to take successful star trail photos, including a technique using a series of short exposures and assembling them with computer software. Techniques for including foreground images of ground objects are given. Examples of star trail photos are provided.

Peiker, E. J.

2007-10-15

320

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

321

High resolution spectroscopy of the high latitude rapidly evolving post-AGB star SAO 85766 (= IRAS 18062+2410)  

NASA Astrophysics Data System (ADS)

SAO 85766 (b = +20o) is an IRAS source with far-infrared colours similar to planetary nebulae. According to the HDE catalogue, its spectrum in 1940 was that of an A5 star. The UV fluxes and colours derived from data obtained by the TD1 satellite in 1972 also indicate that SAO 85766 was an A-type supergiant at that epoch. However, high resolution spectra of SAO 85766 obtained in 1993 in the wavelength interval 4350Ä to 8820Ä shows that now it is similar to that of an early B type post-AGB supergiant. In addition to the absorptions lines typical of a B1I type star, the spectrum of SAO 85766 is found to show numerous permitted and forbidden emission lines of several elements, typically observed in the spectra of young high density low excitation planetary nebulae. From an analysis of the absorption lines we have estimated Teff=22000+/-500 K, log g=3.0+/-0.5, xi t=15+/-2km s-1 and [M/H]=-0.6. Carbon is found to be strongly underabundant ([C/Fe] = -1.0), similarly to what has been observed in other high galactic latitude hot post-AGB stars. The underabundance of carbon and metals, high galactic latitude, high radial velocity (46 km s-1), the presence of planetary nebula type detached cold circumstellar dust shell and also the presence of low excitation nebular emission lines in the spectrum indicate that SAO 85766 is a low mass star in the post-AGB stage of evolution. The above mentioned characteristics and the variations observed in the spectrum of SAO 85766 suggest that it has rapidly evolved during the past 50 years and it is now in the early stages of the planetary nebula phase. The central star may just have become hot enough to photoionize the circumstellar envelope ejected during the previous AGB phase. >From an analysis of the nebular emission lines we find Te=10000+/- 500K and Ne=2.5 104 cm-3. The nebula also shows an abundance pattern similar to that of the central star. The rapid post-AGB evolution of SAO 85766 appears to be similar to that observed in the case of hot post-AGB star Hen 1357 (= SAO 244567). Based on observations made with the Issac Newton Telescope (INT) operated on the island of La Palma (Spain) by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Roque de Los Muchachos

Parthasarathy, M.; García-Lario, P.; Sivarani, T.; Manchado, A.; Sanz Fernández de Córdoba, L.

2000-05-01

322

Luminous blue variables and related high-mass evolved stars in M31 and their surprising environments  

NASA Astrophysics Data System (ADS)

Luminous Blue Variables (LBVs) are erratically eruptive massive stars near the Eddington limit generally thought to be the descendants of blue supergiants and the progenitors of Wolf-Rayet stars. Recent observations suggest that this standard path is not necessarily true for all LBVs, including the intrinsically bright ones. In order to understand the evolutionary positions of these objects and their relation to other high mass-losing stars in the upper H-R diagram, we would like to know their bolometric luminosities, effective temperatures, current masses, progenitor masses, ages, and abundances. With the use of 3.5-m class telescopes (WIYN and ARC) we are able to roughly constrain all but the abundances for these LBV-type stars in M31. We began the study by developing a method for identifying candidate LBVs in nearby galaxies through deep narrow-band images. The method was used to make a target list of such objects in the NE half of M31. We obtained follow-up spectroscopy that confirmed the success of our search criteria. We obtained high angular resolution broad band and Halpha images of the environments of the first five LBV-type objects and two previously identified M31 LBVs using the WIYN 3.5-m telescope. The spectral energy distribution (SED) of K895 exhibits near infrared excess emission similar to that observed in B[e] supergiants. The calibrated WIYN photometry was used to measure color-magnitude diagrams for the resolved luminous stars. We charted the locations of HII regions and HI holes as indicators of stellar ages in the areas around our program objects. We used the Q-method, after a rough empirical validation of its applicability, to constrain the luminosities and effective temperatures of our program objects. We constrained the present masses and examined the ages predicted for our program objects by the Meynet et al. (1994) stellar evolution models. Surprisingly, the majority of the LBV-type objects were found to be surrounded by stars that appeared to be older than the LBV-type objects themselves. The age discrepancies between LBV or LBV-type object and its environment might be explained if the LBVs or candidate LBVs are runaways, are products of discrete massive star forming events, have somehow lived longer than theoretically expected, or are exotic binaries such as Thorne-Zytkow objects or mass-transferring close binaries. (Abstract shortened by UMI.)

King, Nichole Lynn

323

THE DUST BUDGET OF THE SMALL MAGELLANIC CLOUD: ARE ASYMPTOTIC GIANT BRANCH STARS THE PRIMARY DUST SOURCE AT LOW METALLICITY?  

SciTech Connect

We estimate the total dust input from the cool evolved stars in the Small Magellanic Cloud, using the 8 {mu}m excess emission as a proxy for the dust-production rate (DPR). We find that asymptotic giant branch (AGB) and red supergiant (RSG) stars produce (8.6-9.5) Multiplication-Sign 10{sup -7} M{sub Sun} yr{sup -1} of dust, depending on the fraction of far-infrared sources that belong to the evolved star population (with 10%-50% uncertainty in individual DPRs). RSGs contribute the least (<4%), while carbon-rich AGB stars (especially the so-called extreme AGB stars) account for 87%-89% of the total dust input from cool evolved stars. We also estimate the dust input from hot stars and supernovae (SNe), and find that if SNe produce 10{sup -3} M{sub Sun} of dust each, then the total SN dust input and AGB input are roughly equivalent. We consider several scenarios of SN dust production and destruction and find that the interstellar medium (ISM) dust can be accounted for solely by stellar sources if all SNe produce dust in the quantities seen around the dustiest examples and if most SNe explode in dense regions where much of the ISM dust is shielded from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust. Without a net positive contribution from SNe to the dust budget, this suggests that dust must grow in the ISM or be formed by another unknown mechanism.

Boyer, M. L.; Gordon, K. D.; Meixner, M.; Sargent, B. A. [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Srinivasan, S. [UPMC-CNRS UMR7095, Institut d'Astrophysique de Paris, F-75014 Paris (France); Riebel, D. [Department of Physics and Astronomy, The Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States); McDonald, I. [Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Manchester M13 9PL (United Kingdom); Van Loon, J. Th. [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom); Clayton, G. C. [Department of Physics and Astronomy, Louisiana State University, 233-A Nicholson Hall, Tower Dr., Baton Rouge, LA 70803-4001 (United States); Sloan, G. C., E-mail: mboyer@stsci.edu [Astronomy Department, Cornell University, Ithaca, NY 14853-6801 (United States)

2012-03-20

324

AN EMPIRICAL UBV RI JHK COLOR-TEMPERATURE CALIBRATION FOR STARS  

SciTech Connect

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 and 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 {sub 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 [Department of Physics and Astronomy, Washington State University, Pullman, WA 99164-2814 (United States); Lee, Hyun-chul [Department of Physics and Geology, The University of Texas-Pan American, Edinburg, TX 78539-2999 (United States)

2011-03-15

325

Radiative feedback from primordial protostars and final mass of the first stars  

NASA Astrophysics Data System (ADS)

In this contribution, we review our efforts toward understanding the typical mass-scale of primordial stars. Our direct numerical simulations show that, in both of Population III.1 and III.2 cases, strong UV stellar radiative feedback terminatesmass accretion onto a protostar. An HII region formed around the protostar expands very dynamically into the accreting envelope, and cuts off the gas supply to a circumstellar disk. The disk is exposed to the stellar UV radiation and loses its mass by photoevaporation. The derived final masses are 43 Msolar and 17 Msolar in our fiducial Population III.1 and III.2 cases. Much more massive stars, however, should form in other exceptional conditions. In atomic-cooling halos where H2 molecules are dissociated, for instance, a protostar grows via very rapid mass accretion with the rates M*~0.1-1Msolaryr-1. Our new stellar evolution calculations show that the protostar significantly inflates and never contracts to reach the zero-agemain-sequence stage in this case. Such "supergiant protostars" have very low UV luminosity, which results in weak radiative feedback against the accretion flow. In the early universe, supermassive stars formed through this process might provide massive seeds of supermassive black holes.

Hosokawa, Takashi; Omukai, Kazuyuki; Yoshida, Naoki; Yorke, Harold W.

2012-09-01

326

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

327

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

328

Three-micron spectroscopy of three highly reddened field stars  

NASA Astrophysics Data System (ADS)

The 2.0-2.5 and 3.0-4.1 micron spectra of three luminous field late-type highly reddened stars located in different regions of the galactic plane and more than 20 deg away from the direction of the Galactic Center are presented. The observations consist of CVF spectra with resolution of around 70 and IRSPEC spectra with resolution of around 500. The possible detection of the 3.4-micron absorption feature outside the Galactic Center environment is reported. This feature has been attributed to absorption arising in a vibrational transition resulting from the C-H stretching in organic compounds. The observations indicate that the agent producing the 3.4-micron feature, presumably organic molecules, is an important component of the diffuse interstellar medium and is not characteristic only of the Galactic Center. Bandheads of SiO are also detected at 4.01 and 4.05 in the high resolution spectrum of the late-type supergiant Lynga 8 Irs3.

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

1989-11-01

329

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

NASA Astrophysics Data System (ADS)

Context. R Coronae Borealis stars (RCBs) are hydrogen-deficient and carbon-rich supergiant stars. They are very rare, with only ~50 actually known in our Galaxy. Interestingly, RCBs are strongly suspected of being the evolved merger product of two white dwarfs and could therefore be an important tool for understanding supernovae type Ia in the double degenerate scenario. Constraints on the spatial distribution and the formation rate of such stars are needed to picture their origin and test it in the context of actual population synthesis results. Aims: It is crucial to increase the number of known RCBs significantly. With an absolute magnitude MV ~ -5 and a bright/hot circumstellar shell made of amorphous carbon grains, RCBs are so distinctive that we should nowadays be able to find them everywhere in our Galaxy using publicly available catalogues. In the optical, the search is difficult because RCBs are known to undergo unpredictable photometric declines; however, mono-epoch mid-infrared data can help us to discriminate RCBs among other dust-producing stars. The aim is to produce from the mid-infrared WISE and near-infrared 2MASS catalogues a new catalogue of reasonable size, enriched with RCB stars. Methods: Colour-colour cuts used on all stars detected are the main selection criteria. The selection efficiency was monitored using the 52 known RCBs located in the sky area covered by the WISE first preliminary data release. Results: It has been found that selection cuts in mid-infrared colour-colour diagrams are a very efficient method of distinguishing RCBs from other stars. An RCB enriched catalogue made of only 1602 stars was produced, with a high detection efficiency of about 77%. Spectral energy distributions of 49 known RCBs and 5 known HdCs are also presented with estimates of their photosphere and circumstellar shell temperatures. Conclusions: The newly released WISE all sky catalogue has proven to be a valuable resource in finding RCB stars. Actual scenarios predict that between 100 and 500 RCBs exist in our Galaxy. The newly created RCB enriched catalogue is an important step towards significantly increasing the number of known RCB stars and therefore better understanding their origin. Tables 3-5 ara available in electronic form at http://www.aanda.orgFull Table 5 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/539/A51

Tisserand, P.

2012-03-01

330

Probing the ejecta of evolved massive stars in transition. A VLT/SINFONI K-band survey  

NASA Astrophysics Data System (ADS)

Massive evolved stars in transition phases, such as luminous blue variables (LBVs), B[e] supergiants (B[e]SGs), and yellow hypergiants (YHGs), are not well understood, and yet crucial steps in determining accurate stellar and galactic evolution models. The circumstellar environments of these stars reveal their mass-loss history, identifying clues to both their individual evolutionary status and the connection between objects of different phases. Here we present a survey of 25 such evolved massive stars (16 B[e]SGs, 6 LBVs, 2 YHGs, and 1 Peculiar Oe star), observed in the K-band with the Spectrograph for INtegral Field Observation in the Near-Infrared (SINFONI; R = 4500) on the ESO VLT UT4 8 m telescope. The sample can be split into two categories based on spectral morphology: one group includes all of the B[e]SGs, the Peculiar Oe star, and two of the LBVs, while the other includes the YHGs and the rest of the LBVs. The difference in LBV spectral appearance is due to some objects being in a quiescent phase and some objects being in an active or outburst phase. CO emission features are found in 13 of our targets, with first time detections for MWC 137, LHA 120-S 35, and LHA 115-S 65. From model fits to the CO band heads, the emitting regions appear to be detached from the stellar surface. Each star with 12CO features also shows 13CO emission, signaling an evolved nature. Based on the level of 13C enrichment, we conclude that many of the B[e]SGs are likely in a pre-Red Supergiant phase of their evolution. There appears to be a lower luminosity limit of log L/L? = 5.0 below which CO is not detected. The lack of CO features in several high luminosity B[e]SGs and variability in others suggests that they may in fact be LBV candidates, strengthening the connection between these two very similar transition phases. Based on observations at the European Southern Observatory, Paranal, under program IDs 384.D-1078(A) and 088.D-0442(B).Tables 3-5, and Fig. 6 are available in electronic form at http://www.aanda.org

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

2013-10-01

331

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

332

The K giant star Arcturus: the hybrid nature of its infrared spectrum  

NASA Astrophysics Data System (ADS)

Aims: We investigate the infrared spectrum of Arcturus to clarify the nature of the cool component of its atmosphere, referred to as the CO-mosphere, and its relationship to the warm molecular envelope or the MOLsphere in cooler M (super)giant stars. Methods: We apply the standard methods of spectral analysis to the CO lines measured from the “Infrared Atlas of the Arcturus Spectrum” by Hinkle, Wallace, and Livingston. Results: We found that the intermediate-strength lines (with -4.75 < log {W/?} ? -4.4: W is the equivalent width and ? the wavenumber) of CO fundamentals as well as overtones cannot be interpreted with the line-by-line analysis based on the classical line formation theory, while the weaker lines can and provide some information on the photosphere (e.g. log AC = 7.97/log AH = 12.00, ?_micro = 1.87 km s-1, and ?_macro = 3.47 km s-1). The nature of CO lines shows an abrupt change at log {W/?} ? -4.75 and the lines stronger than this limit indicate large excess absorption that cannot be photospheric in origin. This difficulty also appears as an unpredictable upturn (at log {W/?} ? -4.75) in the flat part of the curves-of-growth of CO lines. We confirm the same phenomenon in dozens of M giant stars, whose infrared spectra are known to have hybrid origins in the photosphere and extra-molecular constituent referred to as the MOLsphere. Thus the curve-of-growth analysis provides a simple means by which to recognize the hybrid nature of the infrared spectra. We note that the curves-of-growth of red supergiants and Mira variables found in the literature show similar peculiar patterns. The intermediate-strength lines of CO in Arcturus show only minor expansion (?0.6 km s-1) relative to the weak lines and only small line-asymmetry, but the strong lines of the CO fundamentals exhibit higher turbulent velocity than the other CO lines. Conclusions: The large excess absorption of the CO fundamental lines in Arcturus appears to be the same phenomenon as that found in the CO overtone lines of cooler M giant stars. Thus, molecular condensation referred to as the MOLsphere in cool luminous stars may also exist in Arcturus. The MOLsphere, however, is not necessarily a separate “sphere” but may be an aggregation of molecular clouds formed within the outer atmosphere. The formation of molecular clouds (referred to as MOLsphere in our modeling) in the outer atmosphere appears to be a basic feature of all the red giant stars from early K to late M types (and red supergiants). Table 2 is 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/504/543

Tsuji, T.

2009-09-01

333

THE CONNECTION BETWEEN X-RAY BINARIES AND STAR CLUSTERS IN NGC 4449  

SciTech Connect

We present 23 candidate X-ray binaries with luminosities down to 1.8 Multiplication-Sign 10{sup 36} erg s{sup -1}, in the nearby starburst galaxy NGC 4449, from observations totaling 105 ks taken with the ACIS-S instrument on the Chandra Space Telescope. We determine count rates, luminosities, and colors for each source, and perform spectral fits for sources with sufficient counts. We also compile a new catalog of 129 compact star clusters in NGC 4449 from high-resolution, multi-band optical images taken with the Hubble Space Telescope, doubling the number of clusters known in this galaxy. The UBVI, H{alpha} luminosities of each cluster are compared with predictions from stellar evolution models to estimate their ages and masses. We find strong evidence for a population of very young massive, black hole binaries, which comprise nearly 50% of the detected X-ray binaries in NGC 4449. Approximately a third of these remain within their parent star clusters, which formed {tau} {approx}< 6-8 Myr ago, while others have likely been ejected from their parent clusters. We also find evidence for a population of somewhat older X-ray binaries, including both supergiant and Be-binaries, which appear to be associated with somewhat older {tau} Almost-Equal-To 100-400 Myr star clusters, and one X-ray binary in an ancient ({tau} Almost-Equal-To 10 Gyr) globular cluster. Our results suggest that detailed information on star clusters can significantly improve constraints on X-ray binary populations in star-forming galaxies.

Rangelov, Blagoy; Chandar, Rupali [Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606 (United States); Prestwich, Andrea H., E-mail: blagoy.rangelov@gmail.com [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2011-11-10

334

The Structure and Kinematics of Envelope around Red Supergiant AH Sco Traced by SiO Masers  

NASA Astrophysics Data System (ADS)

Observations of 43 GHz v = 1, J = 1-0 SiO masers in the circumstellar envelope of the M-type semi-regular variable star AH Sco were performed with the Very Long Baseline Array (VLBA) at 2 epochs in March 2004. These high-resolution VLBA images reveal that the distribution of SiO masers is roughly on a persistent elliptical ring with the lengths of the major and minor axes of about 18.5 and 15.8 mas, respectively, along a position angle of 150°. The 3-dimensional kinematics model-fitting for proper motions and spatial distributions of maser features clearly indicates that the SiO maser shell around AH Sco was undergoing an overall contraction to the star at a velocity of 15 km s-1 at a distance of 2.26 kpc to AH Sco due to the gravitation of the central star.

Chen, X.; Shen, Z.-Q.

2008-10-01

335

Star Show Classroom Activity  

NSDL National Science Digital Library

In this lesson from Math Machines, the class will "plan and conduct a simulated astronomical observing session to photgraph a variety of star types." The instructor will set up several "stars" around the classroom, and students will then set up a telescope location and estimate the altitude and azimuth to photograph each star. A participant handout (including worksheet) and facilitator notes are made available for download in DOC file format. Links to calculator programs are also included.

Thomas, Fred

2011-11-03

336

Dark Stars: D\\\\\\  

Microsoft Academic Search

The first phase of stellar evolution in the history of the universe may be\\u000aDark Stars, powered by dark matter heating rather than by fusion. Weakly\\u000ainteracting massive particles, which are their own antiparticles, can\\u000aannihilate and provide an important heat source for the first stars in the\\u000auniverse. This and the previous contribution present the story of Dark Stars.

Douglas Spolyar; Katherine Freese; Paolo Gondolo; Anthony Aguirre; Peter Bodenheimer; Jeremy A. Sellwood; Naoki Yoshida

2009-01-01

337

The Neutron Stars Census  

Microsoft Academic Search

The paucity of old isolated accreting neutron stars in ROSAT observations is\\u000aused to derive a lower limit on the mean velocity of neutron stars at birth.\\u000aThe secular evolution of the population is simulated following the paths of a\\u000astatistical sample of stars for different values of the initial kick velocity,\\u000adrawn from an isotropic Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov

1999-01-01

338

Impulsively Triggered Star Formation  

Microsoft Academic Search

I review several different modes of impulsively triggered star formation, starting with star formation in turbulent molecular\\u000a clouds, and exploring the origin of the clump mass function and the scaling relations between clump mass, radius and internal\\u000a velocity dispersion. This leads to the identification of a critical ram pres-sure for triggering rapid star formation, and\\u000a a reappraisal of the minimum

A. P. Whitworth

2003-01-01

339

Preliminary Map Star Catalog  

NASA Astrophysics Data System (ADS)

As part of an ongoing study, the Allegheny Observatory is in the process of measuring high precision, (1 milliarcsec), parallaxes and proper motions for approximately 900 stars selected at random in the northern sky. The spectral type of these stars is also being determined from UBVRI, uvby, H-Beta, and DDO photometry. This catalog represents a unique and complete statistical set of data for 900 stars of visual magnitude 6-12. A preliminary catalog will be presented.

Persinger, T.; Gatewood, G.; Castelaz, M.

1995-05-01

340

Our Super Star  

NSDL National Science Digital Library

Our star, the Sun, is an ordinary star. It is not particularly special compared to other stars in the universe; however, it is crucially important to us. As the massive energy source at the center of our solar system, the Sun is responsible for Earth's climate, weather, and life. In this lesson, students use observations, activities, and videos to learn basic facts about the Sun. Students also model the mechanics of day and night and use solar energy to make a tasty treat.

Foundation, Wgbh E.

2009-07-10

341

Star Trek Generations  

NSDL National Science Digital Library

Paramount Pictures and Viacom Online have developed a World Wide Web site to herald the upcoming motion picture Star Trek Generations. The site offers a galaxy of unique Star Trek elements for downloading, including pictures, sounds and a preview of the movie, in addition to behind-the-scenes information. Make sure to give Paramount "Your Input"- all respondents will receive a digital version of the Star Trek Generations movie poster

342

The evolution and masses of the neutron star and donor star in the high mass X-ray binary OAO 1657-415  

NASA Astrophysics Data System (ADS)

We report near-infrared radial velocity (RV) measurements of the recently identified donor star in the high mass X-ray binary (HMXB) system OAO 1657-415 obtained in the H band using ISAAC on the Very Large Telescope. Cross-correlation methods were employed to construct a RV curve with a semi-amplitude of 22.1 ± 3.5 km s-1. Combined with other measured parameters of this system it provides a dynamically determined neutron star (NS) mass of 1.42 ± 0.26 M? and a mass of 14.3 ± 0.8 M? for the Ofpe/WN9 highly evolved donor star. OAO 1657-415 is an eclipsing HMXB pulsar with the largest eccentricity and orbital period of any within its class. Of the 10 known eclipsing X-ray binary pulsars OAO 1657-415 becomes the ninth with a dynamically determined NS mass solution and only the second in an eccentric system. Furthermore, the donor star in OAO 1657-415 is much more highly evolved than the majority of the supergiant donors in other HMXBs, joining a small but growing list of HMXBs donors with extensive hydrogen depleted atmospheres. Considering the evolutionary development of OAO 1657-415, we have estimated the binding energy of the envelope of the mass donor and find that there is insufficient energy for the removal of the donor's envelope via spiral-in, ruling out a common envelope evolutionary scenario. With its non-zero eccentricity and relatively large orbital period the identification of a definitive evolutionary pathway for OAO 1657-415 remains problematic, we conclude by proposing two scenarios which may account for OAO 1657-415 current orbital configuration. References: (1) Jenke et al. (2011); (2) Barnstedt et al. (2008); (3) Chakrabarty et al. (1993); (4) this paper.

Mason, A. B.; Clark, J. S.; Norton, A. J.; Crowther, P. A.; Tauris, T. M.; Langer, N.; Negueruela, I.; Roche, P.

2012-05-01

343

Delta Scuti stars: Theory  

SciTech Connect

The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one`s understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying {delta} Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for {delta} Scuti stars, using FG Vir, {delta} Scuti, and CD-24{degree} 7599 as examples.

Guzik, J.A.

1998-03-01

344

Carbon Chemistry in the Envelope of VY Canis Majoris: Implications for Oxygen-Rich Evolved Stars  

NASA Astrophysics Data System (ADS)

Observations of the carbon-bearing molecules CO, HCN, CS, HNC, CN, and HCO+ have been conducted toward the circumstellar envelope of the oxygen-rich red supergiant star, VY Canis Majoris (VY CMa), using the Arizona Radio Observatory (ARO). CO and HCN were also observed toward the O-rich shells of NML Cyg, TX Cam, IK Tau, and W Hya. Rotational transitions of these species at 1 mm, 0.8 mm, and 0.4 mm were measured with the ARO Submillimeter Telescope, including the J = 6 ? 5 line of CO at 691 GHz toward TX Cam and W Hya. The ARO 12 m was used for 2 mm and 3 mm observations. Four transitions were observed for HCO+ in VY CMa, the first definitive identification of this ion in a circumstellar envelope. Molecular line profiles from VY CMa are complex, indicating three separate outflows: a roughly spherical flow and separate red- and blueshifted winds, as suggested by earlier observations. Spectra from the other sources appear to trace a single outflow component. The line data were modeled with a radiative transfer code to establish molecular abundances relative to H2 and source distributions. Abundances for CO derived for these objects vary over an order of magnitude, f ~ 0.4-5 × 10-4, with the lower values corresponding to the supergiants. For HCN, a similar range in abundance is found (f ~ 0.9-9 × 10-6), with no obvious dependence on the mass-loss rate. In VY CMa, HCO+ is present in all three outflows with f ~ 0.4-1.6 × 10-8 and a spatial extent similar to that of CO. HNC is found only in the red- and blueshifted components with [HCN]/[HNC] ~ 150-190, while [CN]/[HCN] ~ 0.01 in the spherical flow. All three velocity components are traced in CS, which has a confined spatial distribution and f ~ 2-6 × 10-7. These observations suggest that carbon-bearing molecules in O-rich shells are produced by a combination of photospheric shocks and photochemistry. Shocks may play a more prominent role in the supergiants because of their macroturbulent velocities.

Ziurys, L. M.; Tenenbaum, E. D.; Pulliam, R. L.; Woolf, N. J.; Milam, S. N.

2009-04-01

345

CARBON CHEMISTRY IN THE ENVELOPE OF VY CANIS MAJORIS: IMPLICATIONS FOR OXYGEN-RICH EVOLVED STARS  

SciTech Connect

Observations of the carbon-bearing molecules CO, HCN, CS, HNC, CN, and HCO{sup +} have been conducted toward the circumstellar envelope of the oxygen-rich red supergiant star, VY Canis Majoris (VY CMa), using the Arizona Radio Observatory (ARO). CO and HCN were also observed toward the O-rich shells of NML Cyg, TX Cam, IK Tau, and W Hya. Rotational transitions of these species at 1 mm, 0.8 mm, and 0.4 mm were measured with the ARO Submillimeter Telescope, including the J = 6 {yields} 5 line of CO at 691 GHz toward TX Cam and W Hya. The ARO 12 m was used for 2 mm and 3 mm observations. Four transitions were observed for HCO{sup +} in VY CMa, the first definitive identification of this ion in a circumstellar envelope. Molecular line profiles from VY CMa are complex, indicating three separate outflows: a roughly spherical flow and separate red- and blueshifted winds, as suggested by earlier observations. Spectra from the other sources appear to trace a single outflow component. The line data were modeled with a radiative transfer code to establish molecular abundances relative to H{sub 2} and source distributions. Abundances for CO derived for these objects vary over an order of magnitude, f {approx} 0.4-5 x 10{sup -4}, with the lower values corresponding to the supergiants. For HCN, a similar range in abundance is found (f {approx} 0.9-9 x 10{sup -6}), with no obvious dependence on the mass-loss rate. In VY CMa, HCO{sup +} is present in all three outflows with f {approx} 0.4-1.6 x 10{sup -8} and a spatial extent similar to that of CO. HNC is found only in the red- and blueshifted components with [HCN]/[HNC] {approx} 150-190, while [CN]/[HCN] {approx} 0.01 in the spherical flow. All three velocity components are traced in CS, which has a confined spatial distribution and f {approx} 2-6 x 10{sup -7}. These observations suggest that carbon-bearing molecules in O-rich shells are produced by a combination of photospheric shocks and photochemistry. Shocks may play a more prominent role in the supergiants because of their macroturbulent velocities.

Ziurys, L. M.; Tenenbaum, E. D.; Pulliam, R. L.; Woolf, N. J. [Department of Astronomy and Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Milam, S. N. [SETI Institute, NASA Ames Research Center, M/S 245-6, Moffet Field, CA 94035 (United States)], E-mail: lziurys@as.arizona.edu, E-mail: emilyt@as.arizona.edu, E-mail: rpulliam@email.arizona.edu, E-mail: nwoolf@as.arizona.edu, E-mail: Stefanie.N.Milam@nasa.gov

2009-04-20

346

The initial mass function and star-formation history in the 30 Doradus super- association  

NASA Astrophysics Data System (ADS)

We present a study of the star-formation history (SFH), and the initial mass function (IMF) in the 30 Doradus super-association. The study is divided in six natural stages: (1) profile fitting photometry; (2) characterization of the instrument; (3) calibration using stars with spectroscopy; (4) visualization of the stellar properties using the color-magnitude stereogram; (5) Bayesian analysis to obtain physical quantities; and (6) the construction of the SFH and IMF. The reduction and characterization of systematic errors are the most important steps of any IMF study: we note the following sources of systematic errors: (a) the upper magnitude cut-off, used to filter out saturated and non- linear stars, results in a false steepening of the high-mass end of the IMF, particularly affecting older systems; (b) Be stars and blue B-type supergiants mimic luminosity class V stars of higher effective temperatures, thus flattening the IMF; (c) the magnitude limit effect introduced by variable reddening, that flattens the low mass end of the derived IMF. For IMF determination we have identified the mass window 10[Special characters omitted.] <= M <= 40[Special characters omitted.] , that is free of effects (a) and (c) in our photometry. We have found that the SFH of the region is characterized by a 7-15 My old burst, across the whole area studied , followed by a period of reduced, nearly constant, star-formation activity. This activity has been punctuated by clustered, burst-like, star-formation episodes of varying intensity in several places. For NGC2070, the OB association LH104, and the field, the derived IMFs are consistent with a power law with Salpeter slope only if they have different SFH : a young and almost instantaneous burst for NGC2070, and nearly constant star formation, after the 7-15 My burst for the field and LH104. Other studies reveal star-formation episodes across the LMC, starting 15-30 My ago. We propose that the origin of such an apparently synchronized, large-scale, activity, is the recent entry of the LMC into a thick disk of ionized gas, analogous to that proposed by Moore and Davis (1994) to explain the origin of the Magellanic Stream.

Selman, Fernando J.

2004-12-01

347

The ongoing pursuit of R Coronae Borealis stars: the ASAS-3 survey strikes again  

NASA Astrophysics Data System (ADS)

Context. R Coronae Borealis stars (RCBs) are rare, hydrogen-deficient, carbon-rich supergiant variable stars that are likely the evolved merger products of pairs of CO and He white dwarfs. Only 55 RCB stars have been found in our galaxy and their distribution on the sky is weighted heavily by microlensing survey field positions. A less biased wide-area survey would enable us to test competing evolutionary scenarios, understand the population or populations that produce RCBs, and constrain their formation rate. Aims: The ASAS-3 survey monitored the sky south of declination +28 deg between 2000 and 2010 to a limiting magnitude of V = 14. We searched ASAS-3 for RCB variables using several different methods to ensure that the probability of RCB detection was as high as possible and to reduce selection biases based on luminosity, temperature, dust production activity and shell brightness. Methods: Candidates whose light curves were visually inspected were pre-selected based on their infrared (IR) excesses due to warm dust in their circumstellar shells using the WISE and/or 2MASS catalogues. Criteria on light curve variability were also applied when necessary to minimise the number of objects. Initially, we searched for RCB stars among the ASAS-3 ACVS1.1 variable star catalogue, then among the entire ASAS-3 south source catalogue, and finally directly interrogated the light curve database for objects that were not catalogued in either of those. We then acquired spectra of 104 stars to determine their real nature using the SSO/WiFeS spectrograph. Results: We report 21 newly discovered RCB stars and 2 new DY Per stars. Two previously suspected RCB candidates were also spectroscopically confirmed. Our methods allowed us to extend our detection efficiency to fainter magnitudes that would not have been easily accessible to discovery techniques based on light curve variability. The overall detection efficiency is about 90% for RCBs with maximum light brighter than V ~ 13. Conclusions: With these new discoveries, 76 RCBs are now known in our Galaxy and 22 in the Magellanic Clouds. This growing sample is of great value to constrain the peculiar and disparate atmosphere composition of RCBs. Most importantly, we show that the spatial distribution and apparent magnitudes of Galactic RCB stars is consistent with RCBs being part of the Galactic bulge population.

Tisserand, P.; Clayton, G. C.; Welch, D. L.; Pilecki, B.; Wyrzykowski, L.; Kilkenny, D.

2013-03-01

348

Hubble Space Telescope Spectroscopy of the Carbon Star TX PISCIUM  

NASA Astrophysics Data System (ADS)

Ultraviolet spectra obtained with the Hubble Space Telescope of the carbon star TX Piscium (HR 9004) are presented, along with analysis providing information on its outer atmosphere, including flow and turbulent velocities, line formation mechanisms, and variations with time. Both thermal (collisionally excited) and fluorescent emission from the chromosphere of the star appear to be formed near the stellar rest velocity, i.e., in a region below that in which the stellar wind is accelerated. Absorption self-reversals in the Mg II emission confirm the presence of an outflowing stellar wind at a mean velocity of about 9--10 km s-1. Circumstellar absorption features (Mn I and Fe I) overlying the Mg II emission indicate a cool shell expanding at about 5--6 km s-1 relative to the photosphere. The widths (FWHM) of various emission lines indicate that the chromospheric turbulence is at least 16 km s-1, but that it may increase with altitude to as much as 34 km s-1. Three hours of integration on the C II] lines are examined for any signs of variability that might indicate the presence of shocks, but no statistically significant variations are seen. A previous identification (in spectra of UU Aur) of an emission line at 2807 Angstroms, seen only in spectra of carbon stars, as belonging to Fe I multiplet UV45 pumped by the C II] line at 2325 Angstroms is confirmed by the discovery of an absorption feature corresponding exactly to the wavelength of the pumped transition (Fe I UV13) near 2325 Angstroms. Lines from Fe II UV165, previously seen in solar off-limb spectra and in Goddard High-Resolution Spectrograph spectra of alpha Tau, are clearly present. The normally much stronger Fe II UV32, 62, and 63 multiplets are seen but are weaker relative to both the UV165 lines and the intercombination lines of C II] and Si II] than in alpha Tau. The weakness of these Fe II lines is indicated both by their absolute flux levels and by their narrow, single-peaked profiles, which are in sharp contrast to the broad, double-peaked profiles seen in oxygen-rich cool giant and supergiant stars. The weakness of the Fe II lines and the presence of the Fe I 2807 Angstroms line suggest that the ionization fraction of iron (Fe II/Fe I) is significantly lower in the outer atmospheres of carbon stars. Fluxes in emission lines of Fe II and Mg II are >=2--3 times lower than in a 1984 IUE spectrum of TX Psc, confirming that the latter was obtained at an epoch of unusual UV brightness for the star. The Mg II profiles are heavily mutilated by overlying absorption, even more so than in 1984. The TX Psc profiles are very similar to those seen in the carbon star TW Hor but are dramatically different than those in another carbon star, UU Aur, whose lines show violet wing emission out to much shorter wavelengths than in the other two stars.

Carpenter, Kenneth G.; Robinson, Richard D.; Johnson, Hollis R.; Eriksson, Kjell; Gustafsson, Bengt; Pijpers, Frank P.; Querci, Francois; Querci, Monique

1997-09-01

349

Anomaly distribution of quasar magnitudes: a test of lensing by a hypothetic supergiant molecular cloud in the Galactic halo  

NASA Astrophysics Data System (ADS)

Context. An anomaly in the distribution of quasar magnitudes based on the Sloan Digital Sky survey, was reported by Longo. The angular size of this quasar anomaly is on the order of ±15° on the sky. A smooth low surface brightness structure detected in ?-rays and at 408 MHz, coincides with the sky location and extent of the anomaly, and is close to the northern component of a pair of ?-ray bubbles discovered in the Fermi Gamma-ray Space Telescope survey. Molecular clouds are thought to be illuminated by cosmic rays. Molecular gas in the Galaxy, in the form of cold H2, may be a significant component of dark matter as suggested by Pfenniger et al. Aims: I test the hypothesis that the magnitude anomaly in the quasar distribution, is due to lensing by a hypothetical supergiant molecular cloud (SGMC) either in or falling into the Galactic halo. Methods: A series of grid lens models are built by assuming that a SGMC is a fractal structure constructed with clumps of 10-3 M?, 10 AU in size, and considering various fractal dimensions. Local amplifications are computed by using the single-plane approximation. Results: A complex network of caustics due to the clumpy structure is present. Our best single plane lens model capable of explaining Longo's effect, at least in sparse regions, requires a mass (1.5-4.1) × 1010 M? within 8.7 × 8.7 × (5-8.6) kpc3 at a lens plane distance of 20 kpc, and is constructed from a molecular-cloud building-block of 5 × 105 M? within a scale of 30 pc expanded by fractal scaling with dimension D = 1.8-2 out to 5-8.6 kpc for the SGMC. The mass budget depends on the cloud depth and on the fractal dimension. Conclusions: If such a SGMC were found to exist, it may provide at least part of a lensing explanation for the luminous anomaly discovered in quasars and red galaxies.

Giraud, E.

2012-07-01

350

Global Star Formation Revisited  

NASA Astrophysics Data System (ADS)

A general treatment of disk star formation is developed from a dissipative multiphase model, with the dominant dissipation due to cloud collisions. The Schmidt-Kennicutt (SK) law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully-Fisher law and SK law residuals. The model is extended to include a multiphase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central active galactic nucleus (AGN). During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift.

Silk, Joseph; Norman, Colin

2009-07-01

351

Observing Double Stars  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

352

Magnetism in Massive Stars  

NASA Astrophysics Data System (ADS)

Stars with mass more than 8 solar masses end their lives as neutron stars, which we mostly observe as highly magnetized objects. Where does this magnetic field come from? Such a field could be formed during the collapse, or is a (modified) remnant of a fossil field since the birth of the star, or otherwise generated by a dynamo during its lifetime in the pre-collapse stages. The answer is unknown, but traditionally magnetic massive stars should not exist since they do not have a convective layer such as the Sun. In the last decade, however, a number of magnetic massive stars have been found, which likely possess a stable field from their birth, and indirect evidence is accumulating that localized fields can indeed be generated during the main-sequence lifetime and beyond. These observational facts opened a new field of research, which is the topic of this review. Among the indirect evidence is a large range of observational phenomena among O and B stars that cannot be explained without the presence of surface magnetic fields. These phenomena include photospheric turbulence, wind clumping, cyclic wind variability observed in UV lines, other types of wind variability in optical lines, anomalous X-ray emission, and non-thermal emission in the radio region. A summary of the properties of observed magnetic massive OB stars is given and the role of magnetic fields in massive stars will be discussed, including how to identify new magnetic candidates.

Henrichs, H. F.

2012-12-01

353

Close triple star systems  

Microsoft Academic Search

Triple-star systems, especially those in which one star has very small mass, are examined. Observations that provide information about the physical nature of close systems, in particular, changes of the period of orbital revolution, are discussed. It is shown that the detection and study of these changes is best obtained by observations of the precise times of light minima in

F. B. Wood

1985-01-01

354

Hyperons in neutron stars  

SciTech Connect

Generalized beta equilibrium involving nucleons, hyperons, and isobars is examined for neutron star matter. The hyperons produce a considerable softening of the equation of state. It is shown that the observed masses of neutron stars can be used to settle a recent controversy concerning the nuclear compressibility. Compressibilities less than 200 MeV are incompatible with observed masses. 7 refs., 9 figs.

Glendenning, N.K.

1986-04-01

355

Carbon star effective temperatures  

Microsoft Academic Search

Possible methods for measuring the effective temperatures of individual carbon stars are discussed. Since calibrations of broad or narrow-band photometric colors is impractical at present, empirical corrections to narrow band color temperatures is the only valid procedure. The effective temperature of the star TW Oph is estimated, based on preliminary reduction of the occultation and associated photometry

S. T. Ridgway; G. H. Jacoby; R. R. Joyce; D. C. Wells

1981-01-01

356

The Violent Neutron Star  

NASA Astrophysics Data System (ADS)

Neutron stars enable us to study both the highest densities and the highest magnetic fields in the known Universe. In this article I review what can be learned about such fundamental physics using magnetar bursts. Both the instability mechanisms that trigger the bursts, and the subsequent dynamical and radiative response of the star, can be used to explore stellar and magnetospheric structure and composition.

Watts, A. L.

2012-12-01

357

Quarkonium at STAR.  

National Technical Information Service (NTIS)

The STAR detector is capable of reconstruction the J/(psi) meson in its dielectron decay channel, along with continuum dielectrons from heavy quark decay. The limitation is not instrumental--the ability of the STAR detector to identify electrons--rather, ...

T. J. LeCompte

1998-01-01

358

Stars for Navigation  

NASA Astrophysics Data System (ADS)

During World War II, stars were important navigation aids for pilots flying long night patrols. Several aspects of navigation by stars are discussed from personal experience by the author who flew Catalina aircraft over the ocean and North Africa during this period. This paper is based on a talk given to the Southland Astronomical Society.

Neave, Tom

2001-09-01

359

Party with the Stars.  

ERIC Educational Resources Information Center

|Describes a Star Party which involves comparing the different colors of the stars, demonstrating how astronomers measure the sky with degrees, determining the cardinal direction, discussing numerous stories that ancient civilizations gave to constellations, exercising science process skills, and using science instruments. (JRH)|

Blaine, Lloyd

1997-01-01

360

Build Your Own Star  

NSDL National Science Digital Library

This SEED website from Schlumberger provides a simulation of the life-cycle of a star. The user chooses the initial mass and "metal" (non-hydrogen/helium) content, and the site shows how the star evolves and ultimately how it dies. The site also explains "the most famous graph in astronomy," the H-R diagram.

2007-06-12

361

Why Observe Double Stars?  

NASA Astrophysics Data System (ADS)

Like many branches of astronomy, the observation of double stars can be appreciated 5 at several levels. For those who enjoy the night sky, double stars offer some of 6 the most attractive sights around and they are particularly good in small telescopes 7 where the colours are much more obvious.

Argyle, Bob; Argyle, R. W.

362

Observing Variable Stars  

NASA Astrophysics Data System (ADS)

Observing variable stars is one of the major contributions amateur astronomers make to science. There are 36,000 variable stars listed in the General Catalogue of Variable Stars, so it is clearly impossible for the limited number of professional observatories to target even the majority of them. That's where amateur astronomers come in - thousands of them turning their telescopes to the sky every night. Variable star observing is the most popular of "real science" activities for amateurs, and Gerry Good's book provides everything needed. The first part of the book provides a highly detailed account of the various classes of variable star, with examples, illustrations and physical descriptions. The second section covers practical aspects of observing, everything from preparation and planning, through observing techniques, to data management and reduction.

Good, Gerry A.

363

Luminous Blue Variables and Related High Mass Evolved Stars in M31 and Their Surprising Environments  

NASA Astrophysics Data System (ADS)

Luminous Blue Variables (LBVs) are erratically eruptive massive stars near the Eddington limit thought to be descendants of blue supergiants and progenitors of Wolf-Rayet stars. In order to constrain the evolution of these massive stars we would like to know their bolometric luminosities, effective temperatures, current masses, progenitor masses, ages, and abundances. With the use of 3.5-m class telescopes (WIYN and ARC) we are able to constrain all but the abundances for these LBV-type stars in M31. We began the study by developing a method for identifying candidate LBVs through deep narrow-band images. A target list was drawn for the NE half of M31. We obtained follow-up spectroscopy that confirmed the success of our search criteria. The spectra provided mass-loss rates for the objects with P-Cygni type profiles and spectral-type constraints from the presence of high or low excitation lines. With WIYN images we measured color-magnitude diagrams for the resolved luminous stars and we charted the locations of HII regions and HI holes as indicators of stellar ages in the areas around our program stars. Surprisingly the majority of the LBV-type objects were found to be in or near associations older than the LBV-type objects themselves. The age discrepancies between LBV and environment might be explained if the LBVs or candidate LBVs are runaways, are products of discrete massive star forming events, have lived longer than theoretically expected, or are exotic binaries such as Thorne-Zytkow or mass-transferring close binaries. We note that with the development of the wind-momentum-luminosity relation (WMLR) by Kudritzki et al. LBVs may one day be secondary distance indicators. We find that M31 LBV V15 is located in the same place of the WMLR diagram as Galactic and LMC LBVs and we hope to investigate this for a few more stars. [Support for thesis provided by NM Space Grant Consortium and NSF grant AST96-17014.

King, N. L.

1999-12-01

364

Computational Star Formation (IAU S270)  

NASA Astrophysics Data System (ADS)

1. Historical introduction; 2. Individual star formation: observations; 3. Low-mass star formation: observations; 4. Individual star formation: theory; 5. Formation of clusters: observations; 6. Formation of clusters: theory; 7. Numerical methods: MHD; 8. Numerical methods: radiative dynamics; 9. Local star formation processes; 10. Star formation feedback; 11. Star formation on galactic scales; 12. Special purpose hardware; 13. Computational methods; 14. Radiation diagnostics of star formation; 15. Large scale star formation; 16. Cosmological star formation; 17. Computational star formation: Summary; Index.

Alves, João.; Elmegreen, Bruce G.; Girart, Josep M.; Trimble, Virginia

2011-05-01

365

VVV Study of the Young Milky Way Star Clusters: Mercer 35, 69 and 70  

NASA Astrophysics Data System (ADS)

Young massive clusters are usually deeply embedded in dust and gas. They represent excellent astrophysical laboratories for revealing the enigma of star formation processes and the early stages of stellar evolution. Wide-field infrared surveys are a modern tool for studying hidden clusters. "Vista variables in Vía Láctea - VVV" (Minniti et al. New Astron. 15:433, 2010) is an ESO/Chile/VISTA public deep near-IR survey, covering the Galactic Bulge and Southern Galactic disk. This is the next step of our systematic study of the cluster content of the inner Milky Way. Here we present our first analysis of the young hidden clusters Mercer 35, 69 and 70. It is based on VVV and SOFI/NTT { JHK} S photometry and follow-up NIR spectroscopy. All of the investigated clusters are young (t ? 10 Myr). The basic cluster parameters are obtained from photometry. The follow-up spectroscopy of probable cluster members shows that the brightest star in Mercer 35 presents characteristics of a red supergiant!

Kurtev, Radostin; Borissova, Jura; Bonatto, Charles; Peñaloza, Francisco; Ivanov, Valentin; Artigau, Étienne; Folkes, Stuart; Geisler, Douglas; Minniti, Dante; Lucas, Philip; Sale, Stuart

366

Multi-Wavelength Interferometry of Evolved Stars Using VLTI and VLBA  

NASA Astrophysics Data System (ADS)

We report on our project of coordinated VLTI/VLBA observations of the atmospheres and circumstellar environments of evolved stars. We illustrate in general the potential of interferometric measurements to study stellar atmospheres and envelopes, and demonstrate in particular the advantages of a coordinated multi-wavelength approach including near/mid-infrared as well as radio interferometry. We have so far made use of VLTI observations of the near- and mid-infrared stellar sizes and of concurrent VLBA observations of the SiO maser emission. To date, this project includes studies of the Mirastars S Ori and RR Aql as well as of the supergiant AH Sco. These sources all show strong silicate emission features in their mid-infrared spectra. In addition, they each have relatively strong SiO maser emission. The results from our first epochs of S Ori measurements have recently been published [5] and the main results are reviewed here. The S Ori maser ring is found to lie at a mean distance of about 2 stellar radii, a result that is irtually free of the usual uncertainty inherent in comparing observations of variable stars widely separated in time and stellar phase. We discuss the status of our more recent S Ori, RR Aql, and AH Sco observations, and present an outlook on the continuation of our project.

Wittkowski, M.; Boboltz, D. A.; Driebe, T.; Ohnaka, K.

367

The dynamical mass of a classical Cepheid variable star in an eclipsing binary system.  

PubMed

Stellar pulsation theory provides a means of determining the masses of pulsating classical Cepheid supergiants-it is the pulsation that causes their luminosity to vary. Such pulsational masses are found to be smaller than the masses derived from stellar evolution theory: this is the Cepheid mass discrepancy problem, for which a solution is missing. An independent, accurate dynamical mass determination for a classical Cepheid variable star (as opposed to type-II Cepheids, low-mass stars with a very different evolutionary history) in a binary system is needed in order to determine which is correct. The accuracy of previous efforts to establish a dynamical Cepheid mass from Galactic single-lined non-eclipsing binaries was typically about 15-30% (refs 6, 7), which is not good enough to resolve the mass discrepancy problem. In spite of many observational efforts, no firm detection of a classical Cepheid in an eclipsing double-lined binary has hitherto been reported. Here we report the discovery of a classical Cepheid in a well detached, double-lined eclipsing binary in the Large Magellanic Cloud. We determine the mass to a precision of 1% and show that it agrees with its pulsation mass, providing strong evidence that pulsation theory correctly and precisely predicts the masses of classical Cepheids. PMID:21107425

Pietrzy?ski, G; Thompson, I B; Gieren, W; Graczyk, D; Bono, G; Udalski, A; Soszy?ski, I; Minniti, D; Pilecki, B

2010-11-25

368

Moderate-Resolution Near-Infrared Spectroscopy of Cool Stars: A New K-Band Library  

NASA Astrophysics Data System (ADS)

I present an atlas of near-infrared K-band spectra of 31 late-type giants and supergiants and two carbon stars. The spectra were obtained at resolving powers of 830 and 2000, and have a signal-to-noise ratio >~100. These data are complemented with results from similar existing libraries in both K and H band, and they are used to identify various tools useful for stellar population studies at moderate resolution. I focus on several of the most prominent absorption features and (1) investigate the effects of spectral resolution on measurements of their equivalent width (EW), (2) examine the variations with stellar parameters of the EWs, and (3) construct composite indices as indicators of stellar parameters and of the contribution from excess continuum sources commonly found in star-forming and AGN galaxies. Among the features considered, the 12CO (2,0) and 12CO (6,3) bandheads together with the Si I 1.59 ?m feature, first proposed by Oliva, Origlia, and coworkers, constitute the best diagnostic set for stellar spectral classification and for constraining the excess continuum emission. The Ca I 2.26 ?m and Mg I 2.28 ?m features offer alternatives in the K band to the 12CO (6,3) bandhead and Si I feature.

Förster Schreiber, N. M.

2000-10-01

369

Spectral evolution of the classical symbiotic star V1413 Aql during a new activity cycle  

NASA Astrophysics Data System (ADS)

We present the results of our spectroscopic observations for the classical symbiotic star V1413 Aql performed in 2008-2011. Various states of the hot component are considered: almost quiescence in 2008, very slow outburst onset in 2009, outburst maximum in 2010, and gradual brightness decline in the erupted hot component in 2011. We have established that, according to a spectroscopic criterion, in 2008 the system was in quiescence. We have shown that the parameters of the hot component during its outburst can be determined only by modeling the differences of the spectra taken at different eclipse phases. The active hot component of V1413 Aql at the outburst maximum is shown to have had the record late (for a symbiotic star) spectral type K2. At various stages of the new activity cycle, we have modeled the continuumenergy distribution based on a standard three-componentmodel, a model including a standard accretion disk and a red giant, and amodel including a supergiant (of various spectral types) and a red giant. The parameters of the system's components have been determined.

Esipov, V. F.; Tarasova, T. N.; Tatarnikov, A. M.; Tatarnikova, A. A.

2013-07-01

370

The Molecular Formation Radii of Ammonia and Silane in the Outflows of Evolved Stars  

NASA Astrophysics Data System (ADS)

The observed abundances of ammonia and silane around evolved stars are orders of magnitude greater than predicted from chemical equilibrium 'freeze-out' models. It has been suggested that chemical reactions on dust grain surfaces enhance the formation of these polyatomic molecules, which have rovibrational transitions in the mid-IR. A novel, fast-switching filterbank system has been incorporated into the Infrared Spatial Interferometer (ISI) to allow high spectral resolution observations of mid-IR spectral lines, while precisely calibrating atmospheric fluctuations. The high spectral resolving power (R 450000) and spatial resolution ( 1/10 arcsecond) allow the molecular stratification to be directly probed. Surprisingly, ammonia and silane were observed around carbon star IRC +10216 to form beyond both the dust formation and gas acceleration zones, indicating that the mere presence of dust grains is not sufficient to catalyze the production of these molecules. The ammonia lines show evidence for decaying gas turbulence in the molecular formation region (beyond 20 stellar radii), while silane appears to form even further out in a relatively smooth gas flow (beyond 80 stellar radii). For red supergiant VY CMa, ammonia appears to form near the termination of the gas acceleration phase, also in a region of high turbulence (about 40 stellar radii). It is not clear what process is setting the formation time scales, perhaps the slow absorption of SiS onto dust grains as fuel for the silane-producing reactions.

Monnier, J. D.; Danchi, W. C.; Hale, D. S.; Tuthill, P. G.; Townes, C. H.

1999-12-01

371

RADIATION-HYDRODYNAMIC MODELS OF THE EVOLVING CIRCUMSTELLAR MEDIUM AROUND MASSIVE STARS  

SciTech Connect

We study the evolution of the interstellar and circumstellar media around massive stars (M {>=} 40 M{sub sun}) from the main sequence (MS) through to the Wolf-Rayet (WR) stage by means of radiation-hydrodynamic simulations. We use publicly available stellar evolution models to investigate the different possible structures that can form in the stellar wind bubbles around WR stars. We find significant differences between models with and without stellar rotation, and between models from different authors. More specifically, we find that the main ingredients in the formation of structures in the WR wind bubbles are the duration of the red supergiant (or luminous blue variable) phase, the amount of mass lost, and the wind velocity during this phase, in agreement with previous authors. Thermal conduction is also included in our models. We find that MS bubbles with thermal conduction are slightly smaller, due to extra cooling which reduces the pressure in the hot, shocked bubble, but that thermal conduction does not appear to significantly influence the formation of structures in post-MS bubbles. Finally, we study the predicted X-ray emission from the models and compare our results with observations of the WR bubbles S 308, NGC 6888, and RCW 58. We find that bubbles composed primarily of clumps have reduced X-ray luminosity and very soft spectra, while bubbles with shells correspond more closely to observations.

Toala, J. A.; Arthur, S. J. [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, Campus Morelia, Apartado Postal 3-72, 58090, Morelia, Michoacan (Mexico)

2011-08-20

372

Scope on the Skies: Star light, star bright  

NSDL National Science Digital Library

In astronomy, the brightness of a star is described in terms of a star's magnitude. Stellar magnitude is expressed two different ways, using the terms apparent magnitude and absolute magnitude . For both magnitudes, the numbering scale is the same, with negative numbers being brighter stars and positive numbers being dimmer stars. This month's column sheds light on the stars and how astronomers measure distances to these celestial objects.

Riddle, Bob

2009-03-01

373

The Constellations and their Stars  

NSDL National Science Digital Library

This website is a tutorial on constellations and the stars in them. It offers an alphabetical and monthly listing of the constellations. It also provides a listing of stars, messier objects, and a list of the brightest stars in the sky. The user can also use the website's interactive star chart, Milky Way photos, or helpful links.

Dolan, Chris

2005-05-15

374

Infrared studies of star formation  

Microsoft Academic Search

Infrared observations at wavelengths of a few microns to 1 mm are reviewed which pertain to the problem of star formation. The data considered include observations of large gas and dust clouds within which stars may be forming and detailed studies of individual objects within these clouds. Stages of star formation are outlined, the IR luminosity of forming stars is

M. W. Werner; E. E. Becklin; G. Neugebauer

1977-01-01

375

Lithium in stars with exoplanets  

Microsoft Academic Search

Our recent study of solar-type stars from the HARPS GTO sample provides highly accurate information with regard to Lithium abundances in stars with and without detected planets (Israelian et al. 2009). When the Li abundances of planet bearing stars are compared with the ``single'' stars, we find an excess of Li depletion in planet hosts with effective temperatures in the

Garik Israelian

2010-01-01

376

Visual Binary Star Observations  

NASA Astrophysics Data System (ADS)

A special mathematics course (MAT298AC) was offered in the fall 2010 and spring 2011 semesters at the Estrella Mountain Community College (EMCC), providing students the opportunity to gain real-world experience through observations, applied mathematics and research techniques. The students and instructor in MAT298AC chose to pursue visual binary star observations with the goal of contributing to the scientific knowledge base. Visual observations of selected binary stars were obtained by utilizing EMCC campus astronomical equipment. Data collected includes the separation of potential binary stars and their position angle.

Darling, Kodiak; Diaz, Kristy; Lucas, Arriz; Santo, Travis; Walker, Douglas

2011-05-01

377

Possible Nova among Hyades stars  

NASA Astrophysics Data System (ADS)

A new(?) very red 6th mag star was discovered among the stars of the Hyades from images obtained on 2012 October 22 04:28 EDT (10:28 UT). The coordinates of the star are RA,Dec (J2000.0): 04:23:29, +17:58:29 (+/-10"). This position is 2.23 arcmin south of the star GSC 1268-1045; and although this faint (13th mag) star does not appear on the discovery images, it is not believed to be the new star. Follow-up observations, especially spectroscopy are very desirable to confirm the presence and nature of the new star.

Shelton, Ian

2012-10-01

378

Variable star data online  

NASA Astrophysics Data System (ADS)

Roger Pickard, Andy Wilson and Gary Poyner describe the online database of the British Astronomical Association Variable Star Section, a treasure trove of observations stretching back nearly 125 years.

Pickard, Roger; Wilson, Andy; Poyner, Gary

2012-06-01

379

Detector limitations, STAR.  

National Technical Information Service (NTIS)

Every detector has limitations in terms of solid angle, particular technologies chosen, cracks due to mechanical structure, etc. If all of the presently planned parts of STAR (Solenoidal Tracker At RHIC) were in place, these factors would not seriously li...

D. G. Underwood

1998-01-01

380

Cosmions and stars  

SciTech Connect

Hypothetical particles such as the heavy neutrino, the photino, or the sneutrino/emdash/generically called cosmions/emdash/may solve the so called missing mass problem. If they exist, the cosmions may close the Universe. In addition to their gravitational effect on cosmological scales, the cosmions may also be captured by stars and concentrate in their cores. Since cosmions are able to transport heat outside stellar cores much more efficiently than photons, they may seriously affect the thermodynamics of the inner layer of stars. We have done an exact calculation of the accretion rate of cosmions by main sequence stars and we have studied the suppression of their central convection. We concluded that central convection inside stars between 0.3 Msub solar and 1 Msub solar is broken in the presence of cosmions. 6 refs., 2 figs.

Salati, P.

1987-12-01

381

Structure of Neutron Stars.  

National Technical Information Service (NTIS)

Structure of neutron stars consisting of a cold and catalyzed superdense matter were investigated by integrating the equations for hydrostatic equilibrium based on the General Relativity theory. The equations of state were obtained with the help of semiem...

C. K. Cheong

1974-01-01

382

Inside a Star . . .  

ERIC Educational Resources Information Center

|Describes classroom activities to understand the evolution of elements as it occurs in the stars. Activities can be undertaken in groups. Explicit instructions and background materials are included. (PS)|

Akerman, Jane; Wentzel, Donat G.

1973-01-01

383

AM CVn stars  

Microsoft Academic Search

I review our observational and theoretical knowledge of AM CVn stars,\\u000afocusing on recent developments. These include newly discovered systems, the\\u000apossibility that two recently discovered extremely short period objects are AM\\u000aCVn stars and an update on X-ray, UV an optical studies. Theoretical advances\\u000ainclude the study of the details of both the donor and accretor, and the\\u000aphysics

Gijs Nelemans

2004-01-01

384

The Bibliographical Star Index  

NASA Astrophysics Data System (ADS)

The Bibliographical Star Index (BSI) is a bibliographical survey of astrophysical papers on stars that were published in 12 journals from 1950 to 1972 or have been published in about 40 journals since 1972. Difficulties that prevented complete coverage of the stellar literature are discussed, along with limitations of and errors in the BSI. The contents of the BSI for the period from 1950 to 1978 are summarized, and the availability of the index is briefly noted.

Ochsenbein, F.

385

SSE: Single Star Evolution  

NASA Astrophysics Data System (ADS)

SSE is a rapid single-star evolution (SSE) code; these analytical formulae cover all phases of evolution from the zero-age main-sequence up to and including remnant phases. It is valid for masses in the range 0.1-100 Msun and metallicity can be varied. The SSE package contains a prescription for mass loss by stellar winds. It also follows the evolution of rotational angular momentum for the star.

Hurley, Jarrod R.; Pols, Onno R.; Tout, Christopher A.

2013-03-01

386

What Drives Star Formation?  

Microsoft Academic Search

Current theoretical models for what drives star formation (especially low-mass star formation) are: (1) magnetic support of self-gravitating clouds with ambipolar diffusion removing support in cores and triggering collapse, and (2) compressible turbulence forming self-gravitating clumps that collapse as soon as the turbulent cascade produces insufficient turbulent support. A crucial observational difference between the two models is the mass to

R. M. Crutcher

2003-01-01

387

Reaching for the STARs  

Microsoft Academic Search

\\u000a The prototype STAR (Signal Transduction and Activation of RNA) protein is Sam68, the Src-associated substrate during mitosis of 68 kDa. Sam68, like all other STAR proteins, belongs to the large class of heteronuclear ribonucleoprotein particle K (hnRNP\\u000a K) homology (KH) domain family of RNA-binding proteins. The KH domain is an evolutionarily conserved RNA binding domain that\\u000a consists of 70–100 amino

Stéphane Richard

388

Physics and Star Trek  

NSDL National Science Digital Library

Created and maintained by physicist Jason Hinson, the Physics and Star Trek Web site investigates faster than light travel and subspace physics. Each topic is presented as a mix of factual information along with speculation on the author's part on how these phenomena could or could not work. Although the site consists of much text and few graphics, which may turn away some potential readers, the interesting subject will definitely appeal to hard core Star Trek or physics junkies.

1999-01-01

389

Post-AGB Stars  

NASA Astrophysics Data System (ADS)

In this contribution, a review is presented on the ample data obtained on post-AGB stars, both on the central stars and their circumstellar material. The fast evolutionary phase is characterized by a rapid change in the properties of the objects, but the variety is so large that there is yet no clear consensus on how the detailed studies of individual objects are linked together by evolutionary channels. The absence of strong molecular veiling in the photospheres of the central stars, together with a spread in intrinsic metallicity make post-AGB stars very useful in constraining AGB chemical evolutionary models. We discuss the surprisingly wide variety of chemical signatures observed. The onset in the creation process of the panoply of structures and shapes observed in planetary nebulae occurs during the short post-AGB evolution, but the physical nature of the processes involved is still badly understood. In the rapidly growing field of circumstellar mineralogy, post-AGB stars have their story to tell and also the molecular envelope changes significantly due to dilution and hardening of the stellar radiation. The real-time evolution of some objects suffering a late thermal flash is reviewed and their possible link to other hydrogen-deficient objects is discussed. Any review on stellar evolution has a section on binaries and this contribution is no exception because binaries make up a significant fraction of the post-AGB stars known to date.

van Winckel, Hans

390

The Star*s Family - an Update  

NASA Astrophysics Data System (ADS)

We shall present the current situation of the Star*s Family, a growing collection of products: directories, dictionaries, databases, data sets, and so on. The directories gather together all practical data available on organizations involved in astronomy, space sciences and related fields, while the dictionaries concern abbreviations, acronyms, contractions and symbols encountered in the same fields. The databases correspond both to the dictionaries and directories. They are currently accessible on line at the European Southern Observatory (ESO) through Starcat and at the European Space Agency (ESA) through ESIS. Their implementation is presently carried out at Strasbourg astronomical Data Center (CDS). Other agreements are currently being negociated. Practical information on the availability of all products can be obtained from the author (telefax: +33-88491255).

Heck, Andre

1993-05-01

391

A fast star image extraction algorithm for autonomous star sensors  

NASA Astrophysics Data System (ADS)

Star sensors have been developed to acquire accurate orientation information in recent decades superior to other attitude measuring instruments. A star camera takes photos of the night sky to obtain star maps. An important step to acquire attitude knowledge is to compare the features of the observed stars in the maps with those of the cataloged stars using star identification algorithms. To calculate centroids of the star images before this step, they are required to be extracted from the star maps in advance. However, some large or ultra large imaging detectors are applied to acquire star maps for star sensors with the development of electronic imaging devices. Therefore, star image extraction occupies more and more portions of the whole attitude measurement period of time. It is required to shorten star image extraction time in order to achieve higher response rate. In this paper, a novel star image extraction algorithm is proposed which fulfill the tasks efficiently. By scanning star map, the pixels brighter than the gray threshold are found and their coordinates and brightness are stored in a cross-linked list. Data of these pixels are linked by pointers, while other pixels are neglected. Therefore, region growing algorithm can be used by choosing the first element in the list as a starting seed. New seeds are founded if the neighboring pixels are brighter than the threshold, and the last seed is deleted from the list. Next search continues until no neighboring pixels are in the list. At that time, one star image is extracted, and its centroid is calculated. Likely, other star images may be extracted, and then the examined seeds are deleted which are never considered again. A new star image search always begins from the first element for avoiding unnecessary scanning. The experiments have proved that for a 1024×1024 star map, the image extraction takes nearly 16 milliseconds. When CMOS APS is utilized to transfer image data, the real-time extraction can be almost achieved.

Zhu, Xifang; Wu, Feng; Xu, Qingquan

2012-11-01

392

Magnetic Fields in Evolved Stars: Imaging the Polarized Emission of High-frequency SiO Masers  

NASA Astrophysics Data System (ADS)

We present Submillimeter Array observations of high-frequency SiO masers around the supergiant VX Sgr and the semi-regular variable star W Hya. The J = 5-4, v = 128SiO and v = 029SiO masers of VX Sgr are shown to be highly linearly polarized with a polarization from ~5% to 60%. Assuming the continuum emission peaks at the stellar position, the masers are found within ~60 mas of the star, corresponding to ~100 AU at a distance of 1.57 kpc. The linear polarization vectors are consistent with a large-scale magnetic field, with position and inclination angles similar to that of the dipole magnetic field inferred in the H2O and OH maser regions at much larger distances from the star. We thus show for the first time that the magnetic field structure in a circumstellar envelope can remain stable from a few stellar radii out to ~1400 AU. This provides further evidence supporting the existence of large-scale and dynamically important magnetic fields around evolved stars. Due to a lack of parallactic angle coverage, the linear polarization of masers around W Hya could not be determined. For both stars, we observed the 28SiO and 29SiO isotopologues and find that they have a markedly different distributions and that they appear to avoid each other. Additionally, emission from the SO 55-44 line was imaged for both sources. Around W Hya, we find a clear offset between the red- and blueshifted SO emission. This indicates that W Hya is likely host to a slow bipolar outflow or a rotating disk-like structure.

Vlemmings, W. H. T.; Humphreys, E. M. L.; Franco-Hernández, R.

2011-02-01

393