Study of Inhomogeneities on the Surface of Magnetic CP Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100091338 ◽

1986 ◽

Vol 90 ◽

pp. 125-132

Author(s):

V.L. Khokhlova

Keyword(s):

Magnetic Field ◽

Inverse Problem ◽

Stokes Parameters ◽

Abundance Distribution ◽

Peculiar Star ◽

Chemically Peculiar ◽

Field Geometry

AbstractThe formulation and solution of the inverse problem to determine local Stokes parameters on the surface of a star, in particular magnetic chemically peculiar star, and hence to determine surface abundance distribution and magnetic field geometry is reviewed.

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Magnetic field topology of the unique chemically peculiar star CU Virginis

Astronomy and Astrophysics ◽

10.1051/0004-6361/201423472 ◽

2014 ◽

Vol 565 ◽

pp. A83 ◽

Cited By ~ 50

Author(s):

O. Kochukhov ◽

T. Lüftinger ◽

C. Neiner ◽

E. Alecian ◽

MiMeS collaboration

Keyword(s):

Magnetic Field ◽

Peculiar Star ◽

Magnetic Field Topology ◽

Chemically Peculiar

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Magnetic field topology and chemical abundance distributions of the young, rapidly rotating, chemically peculiar star HR 5624

Astronomy and Astrophysics ◽

10.1051/0004-6361/201730919 ◽

2017 ◽

Vol 605 ◽

pp. A13 ◽

Cited By ~ 14

Author(s):

O. Kochukhov ◽

J. Silvester ◽

J. D. Bailey ◽

J. D. Landstreet ◽

G. A. Wade

Keyword(s):

Magnetic Field ◽

Peculiar Star ◽

Chemical Abundance ◽

Magnetic Field Topology ◽

Chemically Peculiar

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Magnetic field topologies of the bright, weak-field Ap stars θ Aurigae andεUrsae Majoris

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834279 ◽

2019 ◽

Vol 621 ◽

pp. A47 ◽

Cited By ~ 14

Author(s):

O. Kochukhov ◽

M. Shultz ◽

C. Neiner

Keyword(s):

Magnetic Field ◽

Weak Field ◽

Spectral Lines ◽

Stokes Parameters ◽

Local Magnetic Field ◽

Chemical Abundance ◽

Circular Polarisation ◽

Chemically Peculiar ◽

Peculiar Stars ◽

Chemically Peculiar Stars

Context.The brightest magnetic chemically peculiar stars θ Aur andεUMa were targeted by numerous studies of their photometric and spectroscopic variability. Detailed maps of chemical abundance spots were repeatedly derived for both stars. However, owing to the weakness of their surface magnetic fields, very little information on the magnetic field geometries of these stars is available.Aims.In this study we aim to determine detailed magnetic field topologies of θ Aur andεUMa based on modern, high-resolution spectropolarimetric observations.Methods.Both targets were observed in all four Stokes parameters using the Narval and ESPaDOnS spectropolarimeters. A multi-line technique of least-squares deconvolution was employed to detect polarisation signatures in spectral lines. These signatures were modelled with a Zeeman-Doppler imaging code.Results.We succeed in detecting variable circular and linear polarisation signatures for θ Aur. Only circular polarisation was detected forεUMa. We obtain new sets of high-precision longitudinal magnetic field measurements using mean circular polarisation metal line profiles as well as hydrogen line cores, which are consistent with historical data. Magnetic inversions revealed distorted dipolar geometries in both stars. The Fe and Cr abundance distributions, reconstructed simultaneously with magnetic mapping, do not show a clear correlation with the local magnetic field properties, with the exception of a relative element underabundance in the horizontal field regions along the magnetic equators.Conclusions.Our study provides the first ever detailed surface magnetic field maps for broad-line, weak-field chemically peculiar stars, showing that their field topologies are qualitatively similar to those found in stronger field stars. The Fe and Cr chemical abundance maps reconstructed for θ Aur andεUMa are at odds with the predictions of current theoretical atomic diffusion calculations.

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Strong variable linear polarization in the cool active star II Peg

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314002518 ◽

2013 ◽

Vol 9 (S302) ◽

pp. 369-372

Author(s):

Lisa Rosén ◽

Oleg Kochukhov ◽

Gregg A. Wade

Keyword(s):

Magnetic Field ◽

Circular Polarization ◽

Linear Polarization ◽

Transverse Component ◽

Doppler Imaging ◽

Stokes Parameters ◽

Limited Information ◽

Magnetic Imaging ◽

Field Geometry ◽

The Magnetic Field

AbstractMagnetic fields of cool active stars are currently studied polarimetrically using only circular polarization observations. This provides limited information about the magnetic field geometry since circular polarization is only sensitive to the line-of-sight component of the magnetic field. Reconstructions of the magnetic field topology will therefore not be completely trustworthy when only circular polarization is used. On the other hand, linear polarization is sensitive to the transverse component of the magnetic field. By including linear polarization in the reconstruction the quality of the reconstructed magnetic map is dramatically improved. For that reason, we wanted to identify cool stars for which linear polarization could be detected at a level sufficient for magnetic imaging. Four active RS CVn binaries, II Peg, HR 1099, IM Peg, and σ Gem were observed with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope. Mean polarization profiles in all four Stokes parameters were derived using the multi-line technique of least-squares deconvolution (LSD). Not only was linear polarization successfully detected in all four stars in at least one observation, but also, II Peg showed an extraordinarily strong linear polarization signature throughout all observations. This qualifies II Peg as the first promising target for magnetic Doppler imaging in all four Stokes parameters and, at the same time, suggests that other such targets can possibly be identified.

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