scholarly journals A Simple Spectropolarimetric Temperature Diagnostic for Circumstellar Disks

2000 ◽  
Vol 175 ◽  
pp. 603-606 ◽  
Author(s):  
Karen S. Bjorkman ◽  
Jon E. Bjorkman ◽  
Kenneth Wood
Keyword(s):  
Scattered Light ◽  
Circumstellar Disks ◽  
Spectral Lines ◽  
Polarization Spectrum ◽  
Be Stars ◽  
Light Spectrum ◽  
Temperature Estimate ◽  
Disk Material ◽  
Be Star ◽  
Temperature Diagnostic

AbstractWe describe a technique for estimating average temperatures of Be star disks from analysis of ultraviolet spectropolarimetry. The technique utilizes the fact that the spectrum of the scattered starlight is sensitive to the circumstellar opacity, and hence temperature, since the signature of the disk material is imprinted on the scattered light spectrum. Analysis of the polarization spectrum thus allows us to disentangle the relative contributions of the star and disk, and thereby obtain an estimate of the average disk opacity as a function of wavelength. Using an LTE line-blanketed model (containing about 106 spectral lines) for the opacity, we determine a theoretical opacity as a function of temperature. By comparing this to the opacity deduced from the spectropolarimetry, we can estimate the average disk temperature. For classical Be stars, the relative strengths of the Fe II and Fe III multiplets at around 2400Å and 1900Å, respectively, are a sensitive temperature diagnostic, so that the temperature estimate can be made within ±1000K. We demonstrate our technique with analysis of UV spectropolarimetry (from WUPPE) of the classical Be star ζ Tau, for which we infer an isothermal disk temperature of14000K.

scholarly journals X-Ray Observations of B-Emission Stars (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 291-308 ◽  
Author(s):  
E.P.J. van den Heuvel ◽  
S. Rappaport
Keyword(s):  
Review Paper ◽  
Circumstellar Disks ◽  
Close Binaries ◽  
Be Stars ◽  
X Ray ◽  
Blue Stragglers ◽  
Galactic Clusters ◽  
Be Star ◽  
Emission Stars ◽  
X Ray Binaries

Most evidence on X-ray emission from the vicinity of Be stars concerns the Be/X-ray binaries. Presently some 20 of these systems are known, making them the most numerous class of massive X-ray binaries. Evidence for the binary nature of these systems comes from (i) Doppler modulation of X-ray pulse periods, (ii) periodic X-ray flaring behavior, and (iii) correlated optical and X-ray variability. The correlation between X-ray pulse period and orbital period found by Corbet (1984) can potentially provide important information on the densities and velocities in the circumstellar disks of Be stars.Evolutionary models indicate that the Be/X-ray binaries represent a later stage in the evolution of normal close binaries with initial primary masses predominantly in the the range 8 to 15 M⊙ . These models indicate that also a class of slightly less massive Be star binaries should exist in which the compact companions are white dwarfs. Be-type blue stragglers in galactic clusters may be such systems.

scholarly journals Continuous spectra of circumstellar envelopes of Be stars

1994 ◽  
Vol 162 ◽  
pp. 425-426
Author(s):  
D. Rohe-Koths ◽  
J. Dachs
Keyword(s):  
Line Emission ◽  
Circumstellar Disks ◽  
Balmer Line ◽  
Be Stars ◽  
Continuous Emission ◽  
Circumstellar Envelopes ◽  
Recombination Radiation ◽  
Infrared Spectral ◽  
Be Star ◽  
Central Stars

Line emission in Be star spectra is accompanied by continuous emission both in the Balmer continuum and in the infrared spectral region, due to the same process that is responsible for Balmer line emission, i.e. to recombination radiation from ionized hydrogen in the extended circumstellar disks surrounding the hot central stars.

scholarly journals Global oscillations in Be star envelopes: observational evidence

1994 ◽  
Vol 162 ◽  
pp. 384-385
Author(s):  
R. W. Hanuschik ◽  
W. Hummel ◽  
O. Dietle ◽  
J. Dachs ◽  
E. Sutorius
Keyword(s):  
Full Range ◽  
Observational Evidence ◽  
Spectral Lines ◽  
Emission Lines ◽  
Be Stars ◽  
Intrinsic Structure ◽  
Be Star

Since 1982, we are performing a long-term spectroscopic observing programme of emission-lines in Be stars (Hanuschik 1987, Hanuschik et al. 1988, Dachs et al. 1992, Sutorius 1992, Dietle 1993). We are using ESO's 1.4m CAT, at resolution R ≥ 50 000 and S/N = 100–1000. Spectral lines chosen are the optically thick Hα, Hβ lines and the optically thin Fe ii λ5317 line. The latter line is an extremely sharp tracer (Δvth = 2 km s−1) for the kinematics in the disks. We believe that our atlas shows the full range of intrinsic structure of these emission lines.

scholarly journals Interferometric survey of Be stars with the CHARA array

2010 ◽  
Vol 6 (S272) ◽  
pp. 634-635 ◽  
Author(s):  
Yamina N. Touhami ◽  
Douglas R. Gies ◽  
Gail H. Schaefer ◽  
Noel D. Richardson ◽  
Stephen J. Williams ◽  
...  
Keyword(s):  
Rotational Velocity ◽  
Circumstellar Disks ◽  
Geometrical Parameters ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Disk Model ◽  
Spatially Resolved ◽  
Near Ir ◽  
Be Star ◽  
Chara Array

AbstractWe present the first spatially resolved observations of circumstellar envelopes of 25 bright northern Be stars. The survey was performed with the CHARA Array interferometer in the K-band at intermediate and long baselines. The interferometric visibilities are well fitted by a viscous disk model where the gas density steeply decreases with the radius. Physical and geometrical parameters such as the density profile, the inclination, and the position angles of the circumstellar disks are determined. We find that the density radial exponent ranges between n ≈ 2.4 − 3.2, which is consistent with previous IRAS measurements. We have also obtained simultaneous optical and near-IR spectrophotometric measurements, and found that the model reproduces well the observed disk IR-continuum excess emission. By combining the projected rotational velocity of the Be star with the disk inclination derived from interferometry, we give estimates of the equatorial rotational velocities of these Be stars.

scholarly journals HEROS Be Star Campaigns

2000 ◽  
Vol 175 ◽  
pp. 356-363 ◽  
Author(s):  
S. Štefl ◽  
T. Rivinius
Keyword(s):  
High Frequency ◽  
Spectroscopic Data ◽  
Spectral Lines ◽  
Frequency Resolution ◽  
High Spectral Resolution ◽  
Data Sets ◽  
Strong Impact ◽  
Be Stars ◽  
Be Star ◽  
Different Parts

AbstractSystematic Be star observations with the HEROS spectrograph have been carried out in several long observing runs and seasons, mainly at the ESO La Silla Observatory. The HEROS data represents one of the most extended spectroscopic data sets for the Be star research. More complete and efficient diagnostics and a higher frequency resolution in analyses of periodic spectral variations were achieved, thanks to a combination of relatively high spectral resolution, a large sample of monitored spectral lines of different formation properties, long observing runs, and a relatively high frequency of observations of main targets.Important results concerning different parts of the extended atmospheres of Be stars and having strong impact on our understanding of these objects have been achieved.

Linear Polarization and the Dynamics of Circumstellar Disks of Classical Be Stars

2014 ◽  
Vol 9 (S307) ◽  
pp. 377-378
Author(s):  
Robbie J. Halonen ◽  
Carol E. Jones
Keyword(s):  
Linear Polarization ◽  
Polarized Light ◽  
Circumstellar Disks ◽  
Be Stars ◽  
Stellar Radiation ◽  
Circumstellar Gas ◽  
Linearly Polarized ◽  
Spherically Symmetric Distribution ◽  
Be Star ◽  
Dynamical Nature

AbstractThe intrinsic linearly polarized light arising from electron scattering of stellar radiation in a non-spherically symmetric distribution of gas is a characterizing feature of classical Be stars. The distinct polarimetric signature provides a mean for directly probing the physical and geometric properties of the gaseous material enveloping these rapidly-rotating massive stars. Using a Monte Carlo radiative transfer computation and a self-consistent radiative equilibrium solution for the circumstellar gas, we explore the role of this observable signature in investigating the dynamical nature of classical Be star disks. In particular, we focus on the potential for using linearly polarized light to develop diagnostics of mass-loss events and to trace the evolution of the gas in a circumstellar disk. An informed context for interpreting the observed linear polarization signature can play an important role in identifying the physical process(es) which govern the formation and dissipation of the gaseous disks surrounding classical Be stars.

scholarly journals The ST3 Mission, and its Capabilities for Be Star Observations

2000 ◽  
Vol 175 ◽  
pp. 141-144 ◽  
Author(s):  
R. P. Linfield
Keyword(s):  
Angular Resolution ◽  
Circumstellar Disks ◽  
Brightness Distribution ◽  
Fourier Transform Spectrometer ◽  
Be Stars ◽  
Optical Interferometer ◽  
Visual Magnitude ◽  
Be Star ◽  
Spectrally Resolved ◽  
Heliocentric Orbit

AbstractThe ST3 mission will launch a space optical interferometer into heliocentric orbit, for observation of 50–100 sources on baselines of 40–200 m, during a time span of 3–4.5 months. The angular resolution in the 450–900 nm passband will be ≈ 500 microarcseconds. For Be stars, a velocity resolution of 50–100 km/s can be achieved by operating the interferometer in a Fourier Transform Spectrometer mode. This should allow spectrally resolved measurements of the brightness distribution in circumstellar disks, but will be limited to stars brighter than a visual magnitude of ≈ 5.

scholarly journals Line Profile Modeling of Disks

2000 ◽  
Vol 175 ◽  
pp. 396-408 ◽  
Author(s):  
W. Hummel
Keyword(s):  
Line Profile ◽  
Spectral Lines ◽  
Three Dimensions ◽  
Emission Lines ◽  
Be Stars ◽  
Short Overview ◽  
Be Star ◽  
Line Transfer ◽  
Profile Modeling

AbstractIn this talk I give a short overview of models for spectral lines in Be stars disks which I think are quite instructive. I then examine the arguments for my own model assumptions and discuss selected topics concerning radiative line transfer calculations in three dimensions. We show that symmetric Hα emission lines of Be stars can be understood in terms of Keplerian disks. It is also demonstrated that one-armed global disk oscillations provide the best available solution to understand the long-term V/R variations in Be star emission lines.

scholarly journals Investigating the continuum linear polarization of Be stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 394-395
Author(s):  
Robbie J. Halonen ◽  
Frances E. Mackay ◽  
Carol E. Jones ◽  
T. A. Aaron Sigut
Keyword(s):  
Chemical Composition ◽  
Thermal Structure ◽  
Circumstellar Disks ◽  
Theoretical Models ◽  
Be Stars ◽  
Astronomical Observations ◽  
Self Consistent ◽  
Be Star ◽  
Best Fit ◽  
The Continuum

AbstractIn order to understand the mechanisms that govern the development of circumstellar disks surrounding classical Be stars, we use computational codes to create theoretical models of these particular objects with their gaseous environments and we compare the predicted observables to astronomical observations. In this study, we present the use of the non-LTE radiative transfer code of Sigut & Jones (2007) to examine the effect of a self-consistent thermal structure and realistic chemical composition on the polarization of the classical Be star γ Cassiopeia. Primarily, we investigate the effect of several improvements on the pioneering work of Poeckert & Marlborough (1978) in calculating the polarization levels of γ Cas. We establish best-fit models for the same observations and analyze the implications of the differences between our results and those obtained by Poeckert & Marlborough.

Dynamics of Self-Accreting Disks in Be Stars

1997 ◽  
Vol 163 ◽  
pp. 494-497 ◽  
Author(s):  
P. Kroll ◽  
R.W. Hanuschik
Keyword(s):  
Angular Momentum ◽  
Critical Velocity ◽  
Stellar Surface ◽  
Ejection Velocity ◽  
Be Stars ◽  
Stellar Matter ◽  
High Angular Momentum ◽  
Viscous Forces ◽  
Disk Material ◽  
Be Star

AbstractBe star disks are formed by ejection of stellar matter from the surface of a B star rotating at almost critical velocity. In SPH simulations we find that most of the ejected particles fall back on the stellar surface but those with sufficient angular momentum are able to feed a disk-like structure. Owing to viscous interaction some particles are lifted to larger radii where they carry high angular momentum. Viscous forces also cause a thinning of the initially geometrically thick disk and the final accretion of most of the disk material. Different simulations show how the formation and the extension of the decretion disk depend on the ejection velocity, the viscous parameter α and on how long the source is active. After the outburst the disk thins out more and more, over a timescale much longer than the outburst time.The simulations are compared to Hα observations of the Be star µ Cen.

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