scholarly journals Evidence for spots on hot stars suggests major revision of stellar physics

2019 ◽  
Vol 490 (2) ◽  
pp. 2112-2116 ◽  
Author(s):  
L A Balona
Keyword(s):  
Magnetic Fields ◽  
Hot Stars ◽  
B Stars ◽  
Considerable Fraction ◽  
Rotation Periods ◽  
Major Revision ◽  
Stellar Envelopes ◽  
Space Observations

ABSTRACT It has long been thought that starspots are not present in the A and B stars because magnetic fields cannot be generated in stars with radiative envelopes. Space observations show that a considerable fraction of these stars varies in light with periods consistent with the expected rotation periods. Here we show that the photometric periods are the same as the rotation periods and that starspots are the likely cause for the light variations. This discovery has wide-ranging implications and suggests that a major revision of the physics of hot stellar envelopes may be required.

scholarly journals Observations of Magnetic Fields in B Stars

1994 ◽  
Vol 162 ◽  
pp. 155-166
Author(s):  
David A. Bohlender
Keyword(s):  
Magnetic Fields ◽  
Radio Emission ◽  
Effective Temperature ◽  
Be Stars ◽  
Hot Stars ◽  
Photometric Variability ◽  
B Stars ◽  
Peculiar Stars ◽  
Thermal Radio Emission ◽  
Circumstellar Environments

Globally ordered magnetic fields are known to exist in non-degenerate stars with spectral types between approximately F0 and B2. Among the B stars, and in order of increasing effective temperature, these include the Bp Si stars, helium-weak stars, and the helium-strong stars. These rather remarkable objects present us with an excellent opportunity to quantitatively examine the possible effects of magnetic fields on the photospheres, winds, and circumstellar environments of hot stars. In this paper we review some of the observations of the magnetic fields and field geometries of magnetic B stars, and also briefly discuss the success of attempts to measure magnetic fields in hotter OB and Be stars. We point out some of the interesting observational similarities of the helium-weak and helium-strong stars to Be and other hot stars, including their spectroscopic and photometric variability, variable winds as demonstrated by the UV resonance lines of C IV and Si IV, and their non-thermal radio emission. Continuing work also suggests that a considerable fraction of the rapidly rotating magnetic helium-peculiar stars are in fact variable Be and Be shell stars.

scholarly journals Effect of a Dipole Magnetic Field on Stellar Mass-Loss

2016 ◽  
Vol 12 (S329) ◽  
pp. 242-245
Author(s):  
Chris Bard ◽  
Richard Townsend
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
Large Scale ◽  
Massive Star ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Local Environment ◽  
Surface Mass ◽  
B Stars ◽  
Dipole Magnetic Field

AbstractMassive star winds greatly influence the evolution of both their host star and local environment though their mass-loss rates, but current radiative line-driven wind models do not incorporate any magnetic effects. Recent surveys of O and B stars have found that about ten percent have large-scale, organized magnetic fields. These massive-star magnetic fields, which are thousands of times stronger than the Sun’s, affect the inherent properties of their own winds by changing the mass-loss rate. To quantify this, we present a simple surface mass-flux scaling over the stellar surface which can be easily integrated to get an estimate of the mass-loss rate for a magnetic massive star. The overall mass-loss rate is found to decrease by factors of 2-5 relative to the non-magnetic CAK mass-loss rate.

Mass Loss from Stars

1977 ◽  
Vol 3 (2) ◽  
pp. 96-96
Author(s):  
Donald C. Morton
Keyword(s):  
Mass Loss ◽  
Radiation Field ◽  
Excited States ◽  
Short Wavelength ◽  
Hot Stars ◽  
Short Wavelength Side ◽  
Far Ultraviolet ◽  
Wavelength Side ◽  
Space Observations

The visual spectra of some hot stars, including P Cygni, have emission with associated absorption troughs ˜ 102 km s-1 on the short-wavelength side (Beals 1929, 1951). These P Cygni profiles are easily understood in terms of mass flowing away from the star. Later, rocket observations of the far-ultraviolet resonance lines (Morton 1967) showed that the phenomenon is rather common among hot stars and the velocity shifts could be from 1000 to 3000 km s-1, demonstrating that the mass must be escaping from the star. Resonance lines provide the strongest absorption in the shell where neither the density nor the radiation field is high enough to leave many ions in excited states. Since the ion stages likely to be present around a hot star have their resonance lines shortward of the atmospheric cutoff, space observations are essential in this investigation. Figure 1 shows the P Cygni profile of O VI in ς Pup obtained with Copernicus satellite spectrometer.

scholarly journals Magnetic fields of slowly pulsating B stars and β Cep variables: Comparing results from FORS1/2 and ESPaDOnS

2012 ◽  
Author(s):  
Matt Shultz ◽  
Gregg Wade ◽  
Stefano Bagnulo ◽  
John Landstreet ◽  
Jason Grunhut ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
B Stars

scholarly journals The Strömgren Four-Color System and the Log Teff, Log G Diagram

1978 ◽  
Vol 80 ◽  
pp. 443-446
Author(s):  
Lawrence J. Relyea ◽  
A.G. Davis Philip
Keyword(s):  
Spectral Range ◽  
Hot Stars ◽  
Stellar Spectrum ◽  
Temperature Index ◽  
B Stars ◽  
Color System ◽  
Early Type Stars ◽  
Set Up ◽  
F Stars ◽  
The Many

Strömgren (1966) set up the four-color system of photometry as a means of studying early-type stars in the spectral range 0 through F. In this spectral range one of the important measures that can be made of a stellar spectrum is the magnitude of the Balmer jump. For stars of a given (b-y) color the discontinuity is very large for stars of high luminosity and small for low luminosity stars. For very hot stars (0 and B stars) this luminosity effect becomes too small to be used as a luminosity indicator, but because of this insensitivity to luminosity changes the magnitude of the Balmer discontinuity becomes a temperature indicator (see Philip and Newell 1974 and Davis and Shobbrook 1977). Photoelectric measures of the strength of the Hßline can be used in a similar, but reverse, manner. For the B and O stars the index is a measure of luminosity; for late A and F stars the index is a good temperature index. In the spectral range A0-A3 both the Balmer jump and the Beta index are functions of temperature and luminosity. For a bibliography of the many uses of Strömgren four-color and Hßphotometry see the paper prepared by Philip and Perry (1977).

scholarly journals X-Ray Emission from Magnetically Confined Winds

1999 ◽  
Vol 169 ◽  
pp. 187-190
Author(s):  
Jacques Babel
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Hot Stars ◽  
X Ray ◽  
Magnetically Confined ◽  
Circumstellar Environment

AbstractWe consider the effect of large scale magnetic fields on the circumstellar environment of hot stars. In these stars, magnetic fields of order of 100 G lead to magnetically confined wind shocks (MCWS) and then to the existence of large X-ray emitting region. MCWS lead also to the presence of corotating cooling disks around hot stars.We discuss the case of θ1 Ori C, which is perhaps the hottest analog to Bp stars and consider the effect from rotation and instabilities. We finally discuss the case of the Herbig Ae-Be HD 104237 and show that MCWS might also explain the X-ray emission from this star.

EUV Radiation from Hot Star Photospheres: Theory Versus Observations

1996 ◽  
Vol 152 ◽  
pp. 381-388
Author(s):  
Ivan Hubeny ◽  
Thierry Lanz
Keyword(s):  
Ultraviolet Radiation ◽  
White Dwarfs ◽  
Extreme Ultraviolet ◽  
Theoretical Interest ◽  
Paper Briefly ◽  
Hot Stars ◽  
B Stars ◽  
Theory Versus ◽  
Stellar Photosphere ◽  
Extreme Ultraviolet Radiation

The only stars other than white dwarfs whose photospheric extreme ultraviolet radiation has been detected are ϵ and β CMa. It is therefore of considerable theoretical interest to compare the EUVE observations of these two giant B stars to predicted spectra. However, both LTE and non-LTE very sophisticated line blanketed model atmospheres fail to match the observed flux. This failure leaves the stellar photosphere theory, even for seemingly “simple” objects as normal B giants were believed to be, in a rather dubious position. This paper briefly summarizes possible reasons for the failure of existing models to describe the EUVE observations of hot stars. In particular, we discuss the effects of uncertainties in the line blanketing, and the effects of the photosphere-wind interaction.

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