scholarly journals The B Fields in OB Stars (BOB) Survey

2014 ◽  
Vol 9 (S307) ◽  
pp. 342-347 ◽  
Author(s):  
T. Morel ◽  
N. Castro ◽  
L. Fossati ◽  
S. Hubrig ◽  
N. Langer ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Lower Bound ◽  
Magnetic Fields ◽  
Field Strength ◽  
Massive Stars ◽  
Occurrence Rate ◽  
Early Type ◽  
Ob Stars ◽  
Early Type Stars ◽  
Field Formation

AbstractThe B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects.

scholarly journals Impact of rotation on the geometrical configurations of fossil magnetic fields

2014 ◽  
Vol 9 (S307) ◽  
pp. 373-374
Author(s):  
C. Emeriau ◽  
S. Mathis
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Large Scale ◽  
Massive Stars ◽  
Stellar Mass ◽  
Equilibrium States ◽  
Early Type ◽  
Mhd Equilibrium ◽  
Early Type Stars ◽  
Theoretical Results

AbstractThe MiMeS project demonstrated that a small fraction of massive stars (around 7%) presents large-scale, stable, generally dipolar magnetic fields at their surface. These fields that do not present any evident correlations with stellar mass or rotation are supposed to be fossil remnants of the initial phases of stellar evolution. They result from the relaxation to MHD equilibrium states, during the formation of stable radiation zones, of initial fields resulting from a previous convective phase. In this work, we present new theoretical results, where we generalize previous studies by taking rotation into account. The properties of relaxed fossil fields are compared to those obtained when rotation is ignored. Consequences for magnetic fields in the radiative envelope of rotating early-type stars and their stability are finally discussed.

scholarly journals The nature and origin of magnetic fields in early-type stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 255-264 ◽  
Author(s):  
Jonathan Braithwaite
Keyword(s):  
Field Theory ◽  
Magnetic Fields ◽  
Massive Stars ◽  
Current Knowledge ◽  
Magnetic Activity ◽  
Early Type ◽  
Strong Magnetic Fields ◽  
Early Type Stars

AbstractI review our current knowledge of magnetic fields in stars more massive than around 1.5 M⊙, in particular their nature and origin. This includes the strong magnetic fields found in a subset of the population and the fossil field theory invoked to explain them; the subgauss fields detected in Vega and Sirius and their possible origin; and what we can infer about magnetic activity in massive stars and how it might be linked to subsurface convection.

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 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.

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 A Comparison of Luminosity Calibrations for MK Classifications of OB Stars

1979 ◽  
Vol 47 ◽  
pp. 81-86
Author(s):  
Janet Rountree Lesh
Keyword(s):  
Main Sequence ◽  
Early Type ◽  
Class V ◽  
Ob Stars ◽  
Early Type Stars

It has been apparent for some time that there is a need for a single luminosity calibration to be used with modern MK types for early-type stars, at least from 0 through middle B. The widely used calibration of Blaauw (1963) has to be replaced because the refinement of the MK system - as reflected in the large collections of spectral types by Lesh (1968), Hiltner, Garrison, and Schild (1969) and Walborn (1971) - has led to a lower mean luminosity for most main sequence subgroups of early-type stars, as the higher luminosity stars tend to move out of class V. Thus the calibrations of Lesh (1968) and Walborn (1972, 1973) are systematically fainter than Blaauw’s

scholarly journals Terminal Velocities for a Large Sample of O Stars, B Supergiants, and Wolf-Rayet Stars

1991 ◽  
Vol 143 ◽  
pp. 317-317
Author(s):  
R. K. Prinja ◽  
M. J. Barlow ◽  
I. D. Howarth
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Early Type ◽  
Nuclear Mass ◽  
Ob Stars ◽  
Residual Intensity ◽  
The Mean ◽  
Effective Temperatures ◽  
Early Type Stars ◽  
Absorption Features

We argue that easily measured, reliable estimates of terminal velocities for early-type stars are provided (1) by the central velocity asymptotically approached by narrow absorption features in unsaturated UV P Cygni profiles, and (2) by the violet limit of zero residual intensity in saturated P Cygni profiles. We use these estimators and high resolution IUE data to determine terminal velocities, v∞, for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OB stars our values are typically 15-20% smaller than the extreme violet edge velocities, vedge, while for WR stars v∞ = 0.76vedge on average. We give new mass-loss rates for WR stars which are thermal radio emitters, taking into account our new terminal velocities and recent revisions to estimates of distances and to the mean nuclear mass per electron. We examine the relationships between v∞, the surface escape velocities, and effective temperatures.

scholarly journals Mass loss from early-type stars

1970 ◽  
Vol 36 ◽  
pp. 209-212
Author(s):  
J. B. Hutchings
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Stellar Evolution ◽  
Early Type ◽  
High Luminosity ◽  
Spectroscopic Evidence ◽  
Ob Stars ◽  
Early Type Stars ◽  
Very High ◽  
Hr Diagram

Following the detailed study of four very high luminosity OB stars, a survey has been made for spectroscopic evidence of mass loss in a number of early-type supergiants. A list of spectroscopic criteria is given and the mass loss estimates for 24 stars plotted on the HR diagram. The dependence of the phenomenon on spectral type and luminosity is discussed as well as its significance in terms of stellar evolution.

scholarly journals Magnetic fields, winds and X-rays of massive stars in the Orion nebula cluster

2010 ◽  
Vol 6 (S272) ◽  
pp. 208-209 ◽  
Author(s):  
Véronique Petit ◽  
Gregg A. Wade ◽  
Evelyne Alecian ◽  
Laurent Drissen ◽  
Thierry Montmerle ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Massive Stars ◽  
Theoretical Models ◽  
Magnetic Star ◽  
X Rays ◽  
Orion Nebula ◽  
X Ray ◽  
Ob Stars ◽  
The Impact ◽  
The Relationship

AbstractIn some massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind. Although theoretical models and MHD simulations are able to illustrate the dynamics of such a magnetized wind, the impact of this wind-field interaction on the observable properties of a magnetic star - X-ray emission, photometric and spectral variability - is still unclear. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars, by providing empirical observations and confronting theory. In conjunction with the COUP survey of the Orion Nebula Cluster, we carried out spectropolarimatric ESPaDOnS observations to determine the magnetic properties of massive OB stars of this cluster.

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