14 Ceti: a probable Ap-star-descendant entering the Hertzsprung gap
Abstract
Context. 14 Ceti is a subgiant star of F spectral class that displays variations in the S-index of its Ca ii H & K lines and an X-ray emission that is stronger than the mean observed for its spectral class, which may be due to some magnetic activity.
Aims: We attempt to Zeeman-detect and study the magnetic field of 14 Ceti and to infer its origin.
Methods: We used the spectropolarimeter Narval at the Telescope Bernard Lyot, Pic du Midi Observatory, and the least squares deconvolution method to create high signal-to-noise ratio Stokes V profiles. We derived the surface-averaged longitudinal magnetic field Bl. We also measured the S-index, and the radial velocity for each observation.
Results: 14 Ceti is Zeeman-detected for the 30 observed dates spanning from August 2007 to January 2012. The average longitudinal magnetic field does not reverse its sign, reaches about -35 G, and shows some month-long-timescale variations in our 2008 and 2011-2012 observations. The S-index follows the same long-term trend as Bl. 14 Ceti is confirmed as a single star without H-K emission cores. The strength of the observed surface magnetic field of 14 Ceti is one order of magnitude greater than the observed one for late F main-sequence stars, and is comparable to the values measured in the active late F pre-main-sequence star HR 1817. On the other hand, taking into account the post-main-sequence evolution of an Ap star, an oblique rotator model can explain the strength of the magnetic field of 14 Ceti. The variations with a timescale of months observed for both the Bl and S-index could be due to the rotation.
Conclusions: The most probable scenario to explain our observations appears to be that 14 Ceti is the descendant of a cool Ap star.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 2012
- DOI:
- 10.1051/0004-6361/201219324
- arXiv:
- arXiv:1205.6962
- Bibcode:
- 2012A&A...543A.118A
- Keywords:
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- stars: individual: 14 Ceti;
- stars: magnetic field;
- stars: late-type;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Accepted for publication in Astronomy &