Direct observational evidence for magnetic fields in hot stars

2008 ◽  
pp. 95-102 ◽  
Author(s):  
Gautier Mathys
Keyword(s):  
Magnetic Fields ◽  
Observational Evidence ◽  
Hot Stars

scholarly journals Direct Observational Evidence for Magnetic Fields in Hot Stars

1999 ◽  
Vol 169 ◽  
pp. 95-102
Author(s):  
Gautier Mathys
Keyword(s):  
Magnetic Fields ◽  
Observational Evidence ◽  
Hot Stars

AbstractAttempts at achieving direct detections of magnetic fields in hot stars are reviewed. The techniques used in these observations and their analysis are described, with emphasis on the physical situations to which they are relevant. Results of projects carried out in the last couple of years are reported, and prospects for future investigations are briefly considered.

Peculiarity Parameters

1976 ◽  
Vol 32 ◽  
pp. 233-254
Author(s):  
H. M. Maitzen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Theoretical Work ◽  
Observational Evidence ◽  
Rotator Model ◽  
Peculiar Behaviour ◽  
Field Spectrum ◽  
Oblique Rotator ◽  
Ap Stars ◽  
The Way

Ap stars are peculiar in many aspects. During this century astronomers have been trying to collect data about these and have found a confusing variety of peculiar behaviour even from star to star that Struve stated in 1942 that at least we know that these phenomena are not supernatural. A real push to start deeper theoretical work on Ap stars was given by an additional observational evidence, namely the discovery of magnetic fields on these stars by Babcock (1947). This originated the concept that magnetic fields are the cause for spectroscopic and photometric peculiarities. Great leaps for the astronomical mankind were the Oblique Rotator model by Stibbs (1950) and Deutsch (1954), which by the way provided mathematical tools for the later handling pulsar geometries, anti the discovery of phase coincidence of the extrema of magnetic field, spectrum and photometric variations (e.g. Jarzebowski, 1960).

scholarly journals Spots, Spot-Cycles, and Magnetic Fields of Late-Type Dwarfs

1983 ◽  
Vol 71 ◽  
pp. 137-156 ◽  
Author(s):  
Steven S. Vogt
Keyword(s):  
Magnetic Fields ◽  
Physical Characteristics ◽  
Observational Evidence ◽  
Late Type ◽  
Structural Morphology ◽  
Current State ◽  
Rs Cvn Stars ◽  
Activity Cycles ◽  
Observational Knowledge

AbstractA review is presented of the current state of observational knowledge concerning spots, spot-cycles and surface magnetic fields on active late-type dwarfs. The discussion centers primarily on the physical characteristics of starspots on BY Dra-type stars, including spot sizes, temperatures, structural morphology, migratory motions, and activity cycles. The discussion will also include some references to similar spot phenomena on the RS CVn stars. Observational evidence for surface magnetic fields on these stars, and on chromospherically-active G and K dwarfs, is also reviewed.

scholarly journals Conference Summary: The Demise of Spherical and Stationary Winds

1999 ◽  
Vol 169 ◽  
pp. 416-422
Author(s):  
Immo Appenzeller
Keyword(s):  
Spherical Symmetry ◽  
Theoretical Work ◽  
Observational Evidence ◽  
Stellar Structure ◽  
Hot Stars ◽  
Conference Summary ◽  
Time Variations

AbstractThe observational evidence and the theoretical work presented at this colloquium demonstrate that significant non-spherical effects and time variations are very common phenomena in the winds from hot stars. Hence, the assumptions of spherical symmetry and stationarity, while highly successful for the theory of stellar structure, appear to be inadequate for describing and understanding the winds of hot stars. This conclusion has significant consequences for the appearance and evolution of hot stars.

scholarly journals Magnetic fields in Planetary Nebulae: paradigms and related MHD frontiers

2008 ◽  
Vol 4 (S259) ◽  
pp. 35-46 ◽  
Author(s):  
Eric G. Blackman
Keyword(s):  
Magnetic Fields ◽  
Planetary Nebula ◽  
Large Scale ◽  
Rotational Energy ◽  
Observational Evidence ◽  
Supply Rate ◽  
Evolved Stars ◽  
Research Opportunity ◽  
Low Mass ◽  
Lower Luminosity

AbstractMany, if not all, post AGB stellar systems swiftly transition from a spherical to a powerful aspherical pre-planetary nebula (pPNE) outflow phase before waning into a PNe. The pPNe outflows require engine rotational energy and a mechanism to extract this energy into collimated outflows. Just radiation and rotation are insufficient but a symbiosis between rotation, differential rotation and large scale magnetic fields remains promising. Present observational evidence for magnetic fields in evolved stars is suggestive of dynamically important magnetic fields, but both theory and observation are rife with research opportunity. I discuss how magnetohydrodynamic outflows might arise in pPNe and PNe and distinguish different between approaches that address shaping vs. those that address both launch and shaping. Scenarios involving dynamos in single stars, binary driven dynamos, or accretion engines cannot be ruled out. One appealing paradigm involves accretion onto the primary post-AGB white dwarf core from a low mass companion whose decaying accretion supply rate owers first the pPNe and then the lower luminosity PNe. Determining observational signatures of different MHD engines is a work in progress. Accretion disk theory and large scale dynamos pose many of their own fundamental challenges, some of which I discuss in a broader context.

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.

scholarly journals The evolution of magnetic fields in hot stars

2016 ◽  
Vol 12 (S329) ◽  
pp. 141-145
Author(s):  
Mary E. Oksala ◽  
Coralie Neiner ◽  
Cyril Georgy ◽  
Norbert Przybilla ◽  
Zsolt Keszthelyi ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Stellar Structure ◽  
Surface Magnetism ◽  
Hot Stars ◽  
Life Project ◽  
Surface Magnetic Field ◽  
First Order ◽  
Structure Changes ◽  
The Impact

AbstractOver the last decade, tremendous strides have been achieved in our understanding of magnetism in main sequence hot stars. In particular, the statistical occurrence of their surface magnetism has been established (~10%) and the field origin is now understood to be fossil. However, fundamental questions remain: how do these fossil fields evolve during the post-main sequence phases, and how do they influence the evolution of hot stars from the main sequence to their ultimate demise? Filling the void of known magnetic evolved hot (OBA) stars, studying the evolution of their fossil magnetic fields along stellar evolution, and understanding the impact of these fields on the angular momentum, rotation, mass loss, and evolution of the star itself, is crucial to answering these questions, with far reaching consequences, in particular for the properties of the precursors of supernovae explosions and stellar remnants. In the framework of the BRITE spectropolarimetric survey and LIFE project, we have discovered the first few magnetic hot supergiants. Their longitudinal surface magnetic field is very weak but their configuration resembles those of main sequence hot stars. We present these first observational results and propose to interpret them at first order in the context of magnetic flux conservation as the radius of the star expands with evolution. We then also consider the possible impact of stellar structure changes along evolution.

A fresh view of magnetic fields and cosmic ray electrons in halos of spiral galaxies

2018 ◽  
Vol 14 (A30) ◽  
pp. 315-318
Author(s):  
Ralf-Jürgen Dettmar ◽  
Volker Heesen ◽  
Keyword(s):  
Magnetic Fields ◽  
Spiral Galaxies ◽  
Numerical Models ◽  
Cosmic Ray ◽  
Observational Evidence ◽  
Radio Continuum ◽  
Galactic Halos ◽  
Star Forming ◽  
Polarization Studies ◽  
Disc Galaxies

AbstractRecent numerical models of the multiphase ISM underline the importance of cosmic rays and magnetic fields for the physics of the ISM in disc galaxies. Observations of properties of the ISM in galactic halos constrain models of the expected exchange of matter between the star-forming disc and the environment (circumgalactic medium, CGM). We present new observational evidence from radio-continuum polarization studies of edge-on galaxies on magnetic field strength and structure as well as cosmic ray electron transport in galactic halos. The findings are discussed in the context of the disk-halo interaction of the interstellar medium. In addition, it is also briefly demonstrated how recent LOFAR observations of edge-on galaxies further constrain the extent of magnetic fields in galactic halos.

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