Magnetic field topologies of the bright, weak-field Ap stars theta Aurigae and epsilon Ursae Majoris. (arXiv:1811.04928v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kochukhov_O/0/1/0/all/0/1">O. Kochukhov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shultz_M/0/1/0/all/0/1">M. Shultz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Neiner_C/0/1/0/all/0/1">C. Neiner</a>
The brightest magnetic chemically peculiar stars theta Aur and eps UMa were
targeted by numerous studies of their photometric and spectroscopic
variability. Detailed maps of chemical abundance spots were repeatedly derived
for both stars. However, very little information on the magnetic field
geometries of these stars is available. In this study we aim to determine
detailed magnetic field topologies of theta Aur and eps UMa based on modern,
high-resolution spectropolarimetric observations. 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. We succeeded in detecting variable circular and
linear polarisation signatures for theta Aur. Only circular polarisation was
detected for eps UMa. We obtained 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. 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 theta Aur and eps UMa are at odds
with the predictions of current theoretical atomic diffusion calculations.
The brightest magnetic chemically peculiar stars theta Aur and eps UMa were
targeted by numerous studies of their photometric and spectroscopic
variability. Detailed maps of chemical abundance spots were repeatedly derived
for both stars. However, very little information on the magnetic field
geometries of these stars is available. In this study we aim to determine
detailed magnetic field topologies of theta Aur and eps UMa based on modern,
high-resolution spectropolarimetric observations. 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. We succeeded in detecting variable circular and
linear polarisation signatures for theta Aur. Only circular polarisation was
detected for eps UMa. We obtained 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. 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 theta Aur and eps UMa are at odds
with the predictions of current theoretical atomic diffusion calculations.
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