scholarly journals X-ray Emission from Isolated Be Stars

2000 ◽  
Vol 175 ◽  
pp. 156-169 ◽  
Author(s):  
David H. Cohen
Keyword(s):  
High Flux ◽  
Be Stars ◽  
B Stars ◽  
X Ray ◽  
Ob Stars ◽  
Spectral Diagnostics ◽  
Survey Results ◽  
New Generation

AbstractI discuss the X-ray observations of Be stars, and how their properties compare to non-emission B stars. I focus on several specific stars that show high flux levels and variability but also report on several interesting survey results. The Be X-ray properties are discussed in the context of wind-shock X-ray emission from normal OB stars as well as in the context of general mechanisms that have been proposed to explain the Be phenomenon. Finally, I conclude with a discussion of the spectral diagnostics that will be available from the new generation of X-ray telescopes.

scholarly journals Chromospheres, Coronae, and Mass Loss in Stars Hotter than the Sun

1980 ◽  
Vol 5 ◽  
pp. 525-531 ◽  
Author(s):  
Theodore P. Snow
Keyword(s):  
Mass Loss ◽  
Main Sequence ◽  
Emission Lines ◽  
Be Stars ◽  
Main Sequence Stars ◽  
B Stars ◽  
X Ray ◽  
Ob Stars ◽  
F Stars ◽  
Simple Dependence

AbstractReviews of the mass-loss characteristics of OB stars have been published recently, and the present review therefore emphasizes the A and F stars and very recent results on O and B stars. For the F stars, chromospheric indicators are present in the form of emission lines, seen in visible and ultraviolet wavelengths. Winds are present in A supergiants, but not in main sequence stars, although at least a few of the latter are X-ray sources, indicating the possible existence of coronae. Most OB supergiants are X-ray sources as well, indicating, along with the presence of super-ionization, that these stars have coronae. On the main sequence, the O stars and some B stars (including Be stars in many cases) have mass loss with highly-ionized species in the wind. The winds in the O and B stars are commonly variable. The mass-loss rates do not show a simple dependence on luminosity, contrary to the predictions for radiatively-driven winds.

scholarly journals Strange Among the Strange: The B-emission Star γ Cassiopeiæ

2002 ◽  
Vol 187 ◽  
pp. 221-237 ◽  
Author(s):  
P. Harmanec
Keyword(s):  
Unsolved Problem ◽  
Central Star ◽  
Time Variability ◽  
Be Stars ◽  
Iras Source ◽  
B Stars ◽  
X Ray ◽  
Spectroscopic Binary ◽  
Present Understanding

Abstractγ Cas (HD 5394) is an important representative of Be stars, hot B stars exhibiting Balmer and other emission lines in their spectra at certain epochs. Its emission spectrum was observed as early as in 1863 and has undergone spectacular changes since then. γ Cas is also extremely interesting because it qualifies for several phenomenologically defined groups: it is a light and colour variable, long-term radial-velocity variable, X-ray source, IRAS source, rapid line-profile variable, a single-line spectroscopic binary and a central star of a reflection nebula.A critical compilation of the wealth of observational data on the star, with emphasis on its time variability on several time scales, as well as an estimate of the most probable values of all basic physical properties of the object is presented. It is pointed out that in spite of a large quantity of data, systematic and well-calibrated observations are still rather rare. The present understanding of the object is put into perspective of the more general – and as yet unsolved – problem of the formation of Be envelopes.

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

2010 ◽  
Vol 6 (S272) ◽  
pp. 254-259
Author(s):  
Alceste Z. Bonanos ◽  
Danny J. Lennon ◽  
Derck L. Massa ◽  
Marta Sewilo ◽  
Fabian Köhlinger ◽  
...  
Keyword(s):  
Magellanic Clouds ◽  
Spectral Energy ◽  
Be Stars ◽  
Energy Distributions ◽  
Photometric Variability ◽  
B Stars ◽  
Ob Stars ◽  
Luminous Blue Variables ◽  
Red Supergiants ◽  
Be Star

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

scholarly journals The Chandra survey of Carina OB stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 608-609
Author(s):  
Marc Gagné ◽  
Garrett Fehon ◽  
Michael R. Savoy ◽  
David H. Cohen ◽  
Leisa K. Townsley ◽  
...  
Keyword(s):  
Time Variability ◽  
B Stars ◽  
X Ray ◽  
Ob Stars ◽  
High Shock

AbstractWe have combined 22 deep Chandra ACIS-I pointings to map over one square degree of the Carina complex. Our x-ray survey detects 69 of 70 known O-type stars and 61 of 130 known early B stars. The majority of single O stars display soft X-ray spectra and have a mean log LX/Lbol ≈ −7.5 suggesting shocks embedded in the O-star winds. Over OB stars show unusually high X-ray luminosities, high shock temperatures or time variability, not predicted for embedded wind shocks.

Analysis of the X-ray emission of OB stars II: B stars

2019 ◽  
Vol 19 (8) ◽  
pp. 120 ◽  
Author(s):  
Elizaveta Ryspaeva ◽  
Alexander Kholtygin
Keyword(s):  
B Stars ◽  
X Ray ◽  
Ob Stars

scholarly journals Inter-Division IV/V WG on Active OB Stars

2005 ◽  
Vol 1 (T26A) ◽  
pp. 241-242
Author(s):  
Stan Owocki ◽  
Conny Aerts ◽  
Juan Fabregat ◽  
Doug Gies ◽  
Huib Henrichs ◽  
...  
Keyword(s):  
Stellar Structure ◽  
Be Stars ◽  
Early Type ◽  
B Stars ◽  
Ob Stars ◽  
Circumstellar Material

Our group studies active early-type (OB) stars, with historical focus on classical Be stars, but extending in recent years to include Slowly Pulsating B-stars (SPB), Beta-Cephei stars, the strongly magnetic Bp stars, Luminous Blue Vairiable (LBV) stars, and B[e] stars. An overall goal is to understand the nature, origin, and consequences of this activity, in terms of both the stellar structure and evolution, as well as the distribution and dynamics of circumstellar material and mass outflows.

scholarly journals A Search for White Dwarf Companions of Be Stars

1992 ◽  
Vol 151 ◽  
pp. 347-350
Author(s):  
A.J.M. Piters ◽  
E.J.A. Meurs ◽  
J. Coté ◽  
M.H. Van Kerkwijk ◽  
J. Van Paradijs ◽  
...  
Keyword(s):  
White Dwarf ◽  
Close Binary ◽  
Be Stars ◽  
Infrared Photometry ◽  
B Stars ◽  
X Ray ◽  
Bolometric Luminosity ◽  
Sky Survey ◽  
Multi Wavelength ◽  
Binary Evolution

Preliminary results of an extended multi-wavelength study of bright B- and Be-type stars are presented. This project aims at finding evidence for the existence of white-dwarf companions to Be stars which are predicted as the result of close binary evolution. Comparison of ROSAT all-sky survey data with simultaneous measurements of Hα profiles and infrared photometry suggests that there is no difference in the X-ray behaviour of Be stars with respect to that of normal B stars. The ROSAT X-ray luminosities of B and Be stars range from 10−8 to 10−5 times the bolometric luminosity.

scholarly journals ROSAT Observations of B and Be Stars

1994 ◽  
Vol 162 ◽  
pp. 189-199
Author(s):  
Joseph P. Cassinelli ◽  
David H. Cohen
Keyword(s):  
Large Fraction ◽  
Emission Measure ◽  
X Rays ◽  
Be Stars ◽  
Hard Component ◽  
B Stars ◽  
X Ray ◽  
Wind Speeds ◽  
Sky Survey ◽  
Wind Theory

We present results from a survey of X-ray emission properties of near main-sequence B stars, including several Be and β Cephei stars. The main conclusions of our survey are: 1) The X-rays are soft, probably because the shock velocity jumps are small since the terminal wind speeds are small. 2) A major fraction of the wind emission measure is hot, assuming wind theory estimates for the density distribution. A large fraction of the wind is not expected to be hot in current wind shock models. 3) A hard component is found to be present in τ Sco; possible causes are discussed. 4) For the Be stars, the X-rays emission is from a normal B-star wind that is coming from the poles as in the WCD model of Be stars. 5) None of the stars, including the β Cep stars, show noticeable variability in their X-rays. For the normal B stars we conclude from the lack of variability that the shocks are in the form of fragments in the wind instead of spherical shells. 6) Our observations suggest that all B stars are X-ray sources and that there is a basal amount of X-ray luminosity of about 10-8.5Lboi. The hot component in τ Sco and the high X-ray luminosity of B stars detected in the all-sky survey suggests that there is a source of X-ray emission in addition to wind shocks in some B stars.

scholarly journals Hot stars observed by XMM-Newton

2018 ◽  
Vol 619 ◽  
pp. A148 ◽  
Author(s):  
Yaël Nazé ◽  
Christian Motch
Keyword(s):  
Spectral Analysis ◽  
Main Sequence ◽  
Be Stars ◽  
Hot Stars ◽  
X Ray ◽  
Ob Stars ◽  
Wide Range

We perform a survey of Oe and Be stars in the X-ray range. To this aim, we cross-correlated XMM-Newton and Chandra catalogs of X-ray sources with a list of Be stars, finding 84 matches in total. Of these, 51 objects had enough counts for a spectral analysis. This paper provides the derived X-ray properties (X-ray luminosities, and whenever possible, hardness ratios, plasma temperatures, and variability assessment) of this largest ever sample of Oe and Be stars. The targets display a wide range in luminosity and hardness. In particular, the significant presence of very bright and hard sources is atypical for X-ray surveys of OB stars. Several types of sources are identified. A subset of stars display the typical characteristics of O-stars, magnetic OB stars, or pre-main-sequence (PMS) objects: their Be nature does not seem to play an important role. However, another subset comprises γ Cas analogs, which are responsible for the luminous and hard detections. Our sample contains seven known γ Cas analogs, but we also identify eight new γ Cas analogs and one γ Cas candidate. This nearly doubles the sample of such stars.

scholarly journals Asteroseismic observations of OB stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 433-444 ◽  
Author(s):  
Peter De Cat ◽  
Katrien Uytterhoeven ◽  
Juan Gutiérrez-Soto ◽  
Pieter Degroote ◽  
Sergio Simón-Díaz
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Space Missions ◽  
High Order ◽  
Be Stars ◽  
B Stars ◽  
Ob Stars ◽  
Pulsating Stars ◽  
Different Types

AbstractThe region of the hot end of the main-sequence is hosting pulsating stars of different types and flavours. Pulsations are not only observed for Slowly pulsating B stars (mid to late B-type stars; high order g-modes) and β Cephei stars (early B-type stars; low order p/g-modes) but are also causing variability in Be stars and OB-supergiants. In this review we give an overview of the asteroseismic observations that are currently available for these types of stars. The first asteroseismic results were solely based on ground-based observations. Recently, the arrival of space-based data gathered by space missions like most, corot and kepler has led to important discoveries for massive stars, highlighting their excellent asteroseismic potential. We show that, despite the unprecedented precision of the space-based data, there is still a clear need for ground-based follow-up observations.

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