scholarly journals Turbulence and magnetic spots at the surface of hot massive stars

2010 ◽  
Vol 6 (S273) ◽  
pp. 200-203
Author(s):  
Matteo Cantiello ◽  
Jonathan Braithwaite ◽  
Axel Brandenburg ◽  
Fabio Del Sordo ◽  
Petri Käpylä ◽  
...  
Keyword(s):  
Surface Properties ◽  
Line Profile ◽  
Convection Zone ◽  
Massive Stars ◽  
Convective Zone ◽  
Early Type ◽  
Line Broadening ◽  
Mhd Simulations ◽  
Early Type Stars ◽  
Thermal Line

AbstractHot luminous stars show a variety of phenomena in their photospheres and in their winds which still lack clear physical explanations at this time. Among these phenomena are non-thermal line broadening, line profile variability (LPVs), discrete absorption components (DACs), wind clumping and stochastically excited pulsations. Cantiello et al. (2009) argued that a convection zone close to the surface of hot, massive stars, could be responsible for some of these phenomena. This convective zone is caused by a peak in the opacity due to iron recombination and for this reason is referred to as the “iron convection zone” (FeCZ). 3D MHD simulations are used to explore the possible effects of such subsurface convection on the surface properties of hot, massive stars. We argue that turbulence and localized magnetic spots at the surface are the likely consequence of subsurface convection in early type stars.

scholarly journals The properties of early-type stars in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 325-336
Author(s):  
Christopher J. Evans
Keyword(s):  
Physical Properties ◽  
Mass Loss ◽  
Temperature Scale ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Early Type ◽  
The Past ◽  
The Galaxy ◽  
Stellar Temperature ◽  
Early Type Stars

AbstractThe past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.

scholarly journals The VLT-FLAMES survey of massive stars: mass loss and rotation of early-type stars in the SMC

2006 ◽  
Vol 456 (3) ◽  
pp. 1131-1151 ◽  
Author(s):  
M. R. Mokiem ◽  
A. de Koter ◽  
C. J. Evans ◽  
J. Puls ◽  
S. J. Smartt ◽  
...  
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Early Type ◽  
Early Type Stars

scholarly journals Steps to a New Calibration of the Spectral Type — Effective Temperature Relationship for Early-type Stars

1986 ◽  
Vol 116 ◽  
pp. 111-112
Author(s):  
B. Bohannan ◽  
D. C. Abbott ◽  
S. A. Voels ◽  
D. G. Hummer
Keyword(s):  
Spectral Type ◽  
Effective Temperature ◽  
Massive Stars ◽  
Temperature Relationship ◽  
Temperature Calibration ◽  
Early Type ◽  
Bolometric Luminosity ◽  
Early Type Stars

The spectral type - effective temperature calibration is a cornerstone of our understanding of massive stars and their environment. Any uncertainty in determining their effective temperature is directly reflected in an uncertainty in defining the bolometric luminosity and the number of ionizing photons. We suggest that previous calibrations of bolometric luminosity and the number of ionizing photons as a function of spectral type may be uncertain by at least a factor of 3 for the early 0-type stars (Table 1).

scholarly journals X-ray diagnostics of massive star winds

2016 ◽  
Vol 12 (S329) ◽  
pp. 151-155
Author(s):  
L. M. Oskinova ◽  
R. Ignace ◽  
D. P. Huenemoerder
Keyword(s):  
High Resolution ◽  
Stellar Wind ◽  
Massive Star ◽  
Massive Stars ◽  
Stellar Winds ◽  
X Rays ◽  
Early Type ◽  
Stellar Rotation ◽  
X Ray ◽  
Early Type Stars

AbstractObservations with powerful X-ray telescopes, such as XMM-Newton and Chandra, significantly advance our understanding of massive stars. Nearly all early-type stars are X-ray sources. Studies of their X-ray emission provide important diagnostics of stellar winds. High-resolution X-ray spectra of O-type stars are well explained when stellar wind clumping is taking into account, providing further support to a modern picture of stellar winds as non-stationary, inhomogeneous outflows. X-ray variability is detected from such winds, on time scales likely associated with stellar rotation. High-resolution X-ray spectroscopy indicates that the winds of late O-type stars are predominantly in a hot phase. Consequently, X-rays provide the best observational window to study these winds. X-ray spectroscopy of evolved, Wolf-Rayet type, stars allows to probe their powerful metal enhanced winds, while the mechanisms responsible for the X-ray emission of these stars are not yet understood.

scholarly journals Evolution of rotation in rapidly rotating early-type stars during the main sequence with 2D models

2019 ◽  
Vol 625 ◽  
pp. A89 ◽  
Author(s):  
D. Gagnier ◽  
M. Rieutord ◽  
C. Charbonnel ◽  
B. Putigny ◽  
F. Espinosa Lara
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Main Sequence ◽  
Massive Stars ◽  
Early Type ◽  
Wind Regime ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
Rotational Evolution ◽  
Early Type Stars

The understanding of the rotational evolution of early-type stars is deeply related to that of anisotropic mass and angular momentum loss. In this paper, we aim to clarify the rotational evolution of rapidly rotating early-type stars along the main sequence (MS). We have used the 2D ESTER code to compute and evolve isolated rapidly rotating early-type stellar models along the MS, with and without anisotropic mass loss. We show that stars with Z = 0.02 and masses between 5 and 7 M⊙ reach criticality during the main sequence provided their initial angular velocity is larger than 50% of the Keplerian one. More massive stars are subject to radiation-driven winds and to an associated loss of mass and angular momentum. We find that this angular momentum extraction from the outer layers can prevent massive stars from reaching critical rotation and greatly reduce the degree of criticality at the end of the MS. Our model includes the so-called bi-stability jump of the Ṁ − Teff relation of 1D-models. This discontinuity now shows up in the latitude variations of the mass-flux surface density, endowing rotating massive stars with either a single-wind regime (no discontinuity) or a two-wind regime (a discontinuity). In the two-wind regime, mass loss and angular momentum loss are strongly increased at low latitudes inducing a faster slow-down of the rotation. However, predicting the rotational fate of a massive star is difficult, mainly because of the non-linearity of the phenomena involved and their strong dependence on uncertain prescriptions. Moreover, the very existence of the bi-stability jump in mass-loss rate remains to be substantiated by observations.

scholarly journals Mass-loss predictions and stellar masses of early-type stars

2003 ◽  
Vol 212 ◽  
pp. 164-165 ◽  
Author(s):  
Alex de Koter ◽  
Jorick S. Vink
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Spectroscopic Binaries ◽  
Evolution Theory ◽  
Early Type ◽  
Direct Measurements ◽  
Wind Theory ◽  
Early Type Stars ◽  
Stellar Masses

We show that the stellar masses implied by our predictions of the wind properties of massive stars are in agreement with masses derived from evolution theory and from direct measurements using spectroscopic binaries, contrary to previous attempts to derive masses from wind theory.

scholarly journals Stellar Winds from Massive Stars: The Influence of X-Rays on the Dynamics

1991 ◽  
Vol 143 ◽  
pp. 318-318
Author(s):  
I. Stevens ◽  
G. Cooper ◽  
S. Owocki
Keyword(s):  
Theoretical Investigation ◽  
Massive Stars ◽  
Stellar Winds ◽  
X Rays ◽  
Early Type ◽  
Early Type Stars

We report on a theoretical investigation of the X-rays observed from early type stars on the global wind dynamics.

scholarly journals NRP Modes in a Be Star Zeta Oph

1995 ◽  
Vol 155 ◽  
pp. 301-302
Author(s):  
E. Kambe ◽  
R. Hirata ◽  
M. Kato ◽  
H. Ando ◽  
E. J. Kennelly ◽  
...  
Keyword(s):  
Line Profile ◽  
Early Type ◽  
Period Analysis ◽  
Be Star ◽  
Early Type Stars ◽  
Almost All

AbstractTwo large sinusoidal variations with periods of 3.337 hrs and 2.018 hrs and other smaller variations have been detected from the period analysis of Hel Λ 6678 spectra obtained by our multi-site campaign for ζ Oph in May, 1993. The resultant periodgram is considerably improved (aliasing free) from those in previous publications. The periodicity may be consistent with previous studies except ambiguities of aliasing. It is surprising that almost all detected periods have a common superperiodicity of about 10.05 hrs. We emphasise the importance of multi-site campaign for the study of line-profile variations (lpv) in early-type stars.

scholarly journals Astero-Oscillometry: Gauging Stars with Oscillations

2002 ◽  
Vol 185 ◽  
pp. 222-225 ◽  
Author(s):  
M. Maintz ◽  
Th. Rivinius ◽  
D. Baade ◽  
S. Štefl
Keyword(s):  
Line Profile ◽  
Stellar Evolution ◽  
Physical Modeling ◽  
New Method ◽  
Early Type ◽  
Rapid Rotation ◽  
Early Type Stars ◽  
Conventional Methods ◽  
Nonradial Pulsation

AbstractAstero-oscillometry is presented as a new method for deriving stellar parameters on the basis of a physical modeling of line profile variability (lpv) caused by nonradial pulsation (nrp). First applications to rapidly rotating B-type stars show that the method is able to yield reasonable stellar parameters. The radii are systematically smaller compared to those derived by conventional methods. This could be attributed to possible effects of rapid rotation on stellar evolution. Since the method requires only one or a few pulsation modes to be excited, it is ideally suited to investigating early-type stars.

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