scholarly journals On the Theory of Rotating Magnetic Stars

1970 ◽  
Vol 4 ◽  
pp. 264-268
Author(s):  
G. A. E. Wright
Keyword(s):  
Magnetic Field ◽  
Low Energy ◽  
Early Type ◽  
Interstellar Gas ◽  
Yield Information ◽  
Magnetic Stars ◽  
Strong Surface ◽  
Early Type Stars ◽  
Surface Convection ◽  
Gas Cloud

AbstractAll observations of magnetic stars necessarily yield information only about their surface features. We are ignorant of the nature of the fields in the interiors of such stars, and equally we cannot be sure of the non-existence of interior fields in stars which are superficially non-magnetic. In fact, if we assume the truth of the ‘fossil’ theory – that the magnetic flux of an Ap star is a relic of the flux initially present in the gas cloud from which the star condensed – then it is surprising that magnetic stars are not observed to be much more common, since magnetic fields appear to be ubiquitous in interstellar gas clouds. For those stars with strong surface convection zones, we might expect that a fossil field of low energy would be expelled by the turbulence and would possibly be trapped in the interior. However, the majority of early-type stars with radiative envelopes also do not exhibit any observable magnetic field.

scholarly journals Magnetic Doppler imaging of early-type stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 166-171
Author(s):  
Oleg Kochukhov ◽  
Thomas Rivinius ◽  
Mary E. Oksala ◽  
Iosif Romanyuk
Keyword(s):  
Magnetic Field ◽  
Doppler Imaging ◽  
Early Type ◽  
Main Sequence Stars ◽  
Surface Mapping ◽  
B Stars ◽  
Magnetic Stars ◽  
Early Type Stars ◽  
Complex Magnetic Field ◽  
Fast Rotating

AbstractDoppler imaging of early-type magnetic stars is the most advanced method to interpret their line profile variations. DI allows us to study directly a complex interplay between chemical spots, magnetic fields, and the mass loss. Here we outline the general principles of the surface mapping of stars, discuss adaption of this technique to early-type stars and present several recent examples of the abundance and magnetic mapping performed for rapidly rotating early-B stars. In particular, we present the first Doppler images for the very fast rotating He-rich star HR 7355 and a reconstruction of magnetic field for the well-known Bp star σ Ori E. We also present new magnetic maps for the He-strong star HD 37776, which possesses one of the most complex magnetic field topologies among the upper main sequence stars.

scholarly journals Magnetic observations of pulsating B and Be stars with ESPaDOnS and Narval

2008 ◽  
Vol 4 (S259) ◽  
pp. 391-392
Author(s):  
James Silvester ◽  
C. Neiner ◽  
H. F. Henrichs ◽  
G. A. Wade ◽  
E. Alecian ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Critical Analysis ◽  
Be Stars ◽  
Early Type ◽  
Weak Magnetic Fields ◽  
Magnetic Stars ◽  
Early Type Stars ◽  
New Generation

AbstractDiscoveries of magnetic fields in pulsating B and Be stars have been claimed from low-resolution spectropolarimetric observations with FORS1 at VLT. We used the new generation of high-resolution spectropolarimeters, ESPaDOnS at CFHT and NARVAL at TBL, to check for the existence of these fields. We find that most of the claimed magnetic stars do not host a magnetic field. This work shows the importance of a critical analysis of FORS1 data when searching for weak magnetic fields in early-type stars and the advantage of using ESPaDOnS and NARVAL to study such type of stars.

scholarly journals Magnetic Archaeology of Early-type Stellar Dynamos

2021 ◽  
Vol 923 (1) ◽  
pp. 104
Author(s):  
Adam S. Jermyn ◽  
Matteo Cantiello
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Mass Loss ◽  
Bimodal Distribution ◽  
Early Type ◽  
Surface Magnetism ◽  
Near Surface ◽  
Early Type Stars ◽  
Slow Evolution ◽  
Weak Fields

Abstract Early-type stars show a bimodal distribution of magnetic field strengths, with some showing very strong fields (≳1 kG) and others very weak fields (≲10 G). Recently, we proposed that this reflects the processing or lack thereof of fossil fields by subsurface convection zones. Stars with weak fossil fields process these at the surface into even weaker dynamo-generated fields, while in stars with stronger fossil fields magnetism inhibits convection, allowing the fossil field to remain as is. We now expand on this theory and explore the timescales involved in the evolution of near-surface magnetic fields. We find that mass loss strips near-surface regions faster than magnetic fields can diffuse through them. As a result, observations of surface magnetism directly probe the frozen-in remains of the convective dynamo. This explains the slow evolution of magnetism in stars with very weak fields: these dynamo-generated magnetic fields evolve on the timescale of the mass loss, not that of the dynamo.

Fossil magnetic fields and rotation of early-type stars

1994 ◽  
Vol 162 ◽  
pp. 184-185
Author(s):  
A.E. Dudorov
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Main Sequence ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars ◽  
Quadrupole Magnetic Field ◽  
Interstellar Molecular Clouds

Observational data of the last 10 years allow two main conclusions:a) Main sequence stars can be separated in two classes: - magnetic (Bp) stars with surface strengths of a dipole or quadrupole magnetic field of Bs ≈ n · (102 − 103) G, n = 2,3,4…7, and - normal main sequence stars (F-O) with magnetic fields Bs ≈ 1 − 100 G (< 300 G);b) Typical star formation takes place in interstellar molecular clouds with magnetic field strengths B ≈ 10-5 G (See Dudorov 1990).

scholarly journals Radio Detection of Colliding Wind Binaries

2006 ◽  
Vol 23 (1) ◽  
pp. 50-63 ◽  
Author(s):  
Paula Benaglia ◽  
Bärbel Koribalski ◽  
Juan F. Albacete Colombo
Keyword(s):  
Magnetic Field ◽  
Thermal Emission ◽  
Stellar Systems ◽  
Early Type ◽  
X Ray ◽  
High Energies ◽  
Radio Detection ◽  
Early Type Stars ◽  
The Magnetic Field ◽  
Compact Array

AbstractFour massive, early-type stars, three of which are confirmed binaries, have been observed with the Australia Telescope Compact Array at 1.4, 2.4, 4.8, and 8.6 GHz. The earliest star cataloged so far, HD 93129A, was also observed at 17.8 and 24.5 GHz. Here we present an analysis of the spectra as well as the structure of the stellar systems. All four spectra show clear evidence of non-thermal emission, indicative of a binary system with a colliding wind region. We discuss the magnetic field of the emitting region of HD 93129A and make predictions on the radiation at high energies. Archive X-ray observations towards the target sources are also investigated and interpreted in the light of the non-thermal emission detected.

scholarly journals Doppler Imaging of Variable Early-Type Stars

1988 ◽  
Vol 132 ◽  
pp. 193-198
Author(s):  
Dietrich Baade
Keyword(s):  
Surface Chemistry ◽  
Doppler Imaging ◽  
Driving Mechanism ◽  
Early Type ◽  
Wide Spread ◽  
Inhomogeneous Surface ◽  
Magnetic Stars ◽  
Bona Fide ◽  
Early Type Stars ◽  
Nonradial Pulsation

Line profile–variability (LPV) is very wide–spread among early–type stars. With the exception of inhomogeneous surface abundance distributions associated with magnetic fields, the LPV of bona fide non–magnetic stars is consistent with (often only with) nonradial pulsation (NRP). Peculiar surface chemistry and NRP may even be mutually exclusive, and there are other indications that in spite of the ubiquity of NRPs the distribution of their characterizing parameters in the HRD is far from being uniform. This may be important for uncovering the driving mechanism of NRPs in early–type stars.

scholarly journals Detection of magnetic field in the B2 star ρ Ophiuchi A with ESO FORS2

2018 ◽  
Vol 610 ◽  
pp. L3 ◽  
Author(s):  
I. Pillitteri ◽  
L. Fossati ◽  
N. Castro Rodriguez ◽  
L. Oskinova ◽  
S. J. Wolk
Keyword(s):  
Magnetic Field ◽  
Longitudinal Component ◽  
Early Type ◽  
Stellar Rotation ◽  
X Ray ◽  
Very Large Telescope ◽  
Surface Spot ◽  
Early Type Stars ◽  
Magnetic Origin ◽  
The Magnetic Field

Circumstantial evidence suggests that magnetism and enhanced X-ray emission are likely correlated in early B-type stars: similar fractions of them (~10%) are strong and hard X-ray sources and possess strong magnetic fields. It is also known that some B-type stars have spots on their surface. Yet up to now no X-ray activity associated with spots on early-type stars was detected. In this Letter we report the detection of a magnetic field on the B2V star ρ Oph A. Previously, we assessed that the X-ray activity of this star is associated with a surface spot, herewith we establish its magnetic origin. We analyze spectra of ρ Oph A obtained with the FORS2 spectrograph at ESO Very Large Telescope (VLT) at two epochs, and detect a longitudinal component of the magnetic field of the order of ~500 G in one of the datasets. The detection of the magnetic field only at one epoch can be explained by stellar rotation which is also invoked to explain observed periodic X-ray activity. From archival HARPS ESO VLT high resolution spectra we derived the fundamental stellar parameters of ρ Oph A and further constrained its age. We conclude that ρ Oph A provides strong evidence for the presence of active X-ray emitting regions on young magnetized early type stars.

scholarly journals Magnetic fields in early-type stars

2014 ◽  
Vol 10 (S305) ◽  
pp. 53-60 ◽  
Author(s):  
Jason H. Grunhut ◽  
Coralie Neiner
Keyword(s):  
Magnetic Field ◽  
Magnetic Properties ◽  
Magnetic Fields ◽  
Imaging Techniques ◽  
Doppler Imaging ◽  
Small Scale ◽  
Early Type ◽  
Surface Magnetic Field ◽  
Detailed Surface ◽  
Early Type Stars

AbstractFor several decades we have been cognizant of the presence of magnetic fields in early-type stars, but our understanding of their magnetic properties has recently (over the last decade) expanded due to the new generation of high-resolution spectropolarimeters (ESPaDOnS at CFHT, Narval at TBL, HARPSpol at ESO). The most detailed surface magnetic field maps of intermediate-mass stars have been obtained through Doppler imaging techniques, allowing us to probe the small-scale structure of these stars. Thanks to the effort of large programmes (e.g. the MiMeS project), we have, for the first time, addressed key issues regarding our understanding of the magnetic properties of massive (M> 8M⊙) stars, whose magnetic fields were only first detected about fifteen years ago. In this proceedings article we review the spectropolarimetric observations and statistics derived in recent years that have formed our general understanding of stellar magnetism in early-type stars. We also discuss how these observations have furthered our understanding of the interactions between the magnetic field and stellar wind, as well as the consequences and connections of this interaction with other observed phenomena.

Environs of HII Regions

1983 ◽  
Vol 5 (2) ◽  
pp. 158-162 ◽  
Author(s):  
R. S. Roger
Keyword(s):  
Molecular Clouds ◽  
Hii Regions ◽  
Low Density ◽  
Dust Grains ◽  
Early Type ◽  
Hydrogen Atoms ◽  
Interstellar Gas ◽  
Early Type Stars ◽  
Stable Surfaces ◽  
Dust Absorption

It is generally agreed that early-type stars, and hence their HII regions, appear to develop preferentially in dense concentrations within molecular clouds. These parent molecular clouds owe their existence in two ways to the dust grains in the interstellar gas, a component which comprises about 1% by mass. First, dust grains provide stable surfaces upon which hydrogen atoms can come together to form molecules. Then, once formed, the molecules are protected in cloud interiors by dust absorption of the dissociating ultraviolet radiation which pervades the low-density interstellar medium.

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