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.

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.

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 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 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 Analysis of the X-ray emission from OB stars III: low-resolution spectra of OB stars

2020 ◽  
Vol 20 (7) ◽  
pp. 108
Author(s):  
Elizaveta Ryspaeva ◽  
Alexander Kholtygin
Keyword(s):  
Low Resolution ◽  
X Ray ◽  
Ob Stars

Fractal X-ray time variability and spectral invariance of the Seyfert galaxy NGC5506

Nature ◽  
1987 ◽  
Vol 325 (6106) ◽  
pp. 696-698 ◽  
Author(s):  
Ian McHardy ◽  
Bozena Czerny
Keyword(s):  
Seyfert Galaxy ◽  
Time Variability ◽  
Spectral Invariance ◽  
X Ray

STRUCTURE AND EMISSION OF COMPACT BLAZAR JETS

2012 ◽  
Vol 08 ◽  
pp. 151-162 ◽  
Author(s):  
ALAN P. MARSCHER
Keyword(s):  
Millimeter Wave ◽  
Position Angle ◽  
Turbulent Plasma ◽  
Time Variability ◽  
Relativistic Jets ◽  
X Ray ◽  
The Core ◽  
Central Engine ◽  
Conical Shock ◽  
Jet Plasma

Relativistic jets in blazars on parsec scales can now be explored with direct imaging at radio wavelengths as well as observations of time variability of flux and linear polarization at various wavebands. The results thus far suggest that the millimeter-wave "core" is usually a standing, conical shock and that the jet plasma is turbulent. Disturbances and turbulent plasma crossing the standing shock can explain much of the observed variability, as well as the appearance of bright knots moving down the jet at superluminal apparent speeds. The core, located parsecs downstream of the central engine, appears to be the site of many of the outbursts observed at optical, X-ray, and γ-ray energies. Rotations in the optical polarization position angle prior to the passage of a knot through the millimeter-wave core provide evidence for helical magnetic fields that accelerate and collimate the jet before turbulence tangles the fields.

scholarly journals Achromatic late-time variability in thermonuclear X-ray bursts

2010 ◽  
Vol 525 ◽  
pp. A111 ◽  
Author(s):  
J. J. M. in ’t Zand ◽  
D. K. Galloway ◽  
D. R. Ballantyne
Keyword(s):  
Time Variability ◽  
Late Time ◽  
X Ray

scholarly journals New Results on Pulsating OB Stars

1995 ◽  
Vol 155 ◽  
pp. 44-55 ◽  
Author(s):  
Paweł Moskalik
Keyword(s):  
Data Model ◽  
Physical Mechanism ◽  
High Order ◽  
Early Type ◽  
Instability Strip ◽  
Model Calculations ◽  
B Stars ◽  
Ob Stars ◽  
Early Type Stars ◽  
Theoretical Results

AbstractUntil very recently the physical mechanism driving oscillations in β Cep and other early type stars has been a mystery. The breakthrough came with the publication of new OPAL and OP opacity data. Model calculations with the new opacities have demonstrated that the pulsations are driven by the familiar K-mechanism, acting in the metal opacity bump at T ≈ 2 × 105K. The mechanism excites the low order p- and g-modes in the upper part of the instability strip and the high order g-modes in the lower part of the strip. The theoretical instability domains agree well with the observed domains of the β Cep and the SPB stars. In this review I present these recent theoretical results and discuss their consequences for our understanding of B stars pulsations.

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