14 Ceti: a probable Ap-star-descendant entering the Hertzsprung gap⋆
1 Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie, 31400 Toulouse France
e-mail: email@example.com; firstname.lastname@example.org; email@example.com; firstname.lastname@example.org; thierry.roudier]@irap.omp.eu
2 CNRS, Institut de Recherche en Astrophysique et Planétologie, 14 av. Edouard Belin, 31400 Toulouse, France
3 Institute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko shose, 1784 Sofia, Bulgaria
4 Geneva Observatory, University of Geneva, 51 Chemin des Maillettes, 1290 Versoix, Switzerland
5 Institut d’Astrophysique, Université libre de Bruxelles, Campus Plaine – CP 226, 1050 Bruxelles, Belgium
Received: 1 April 2012
Accepted: 17 May 2012
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.
Key words: stars: individual: 14 Ceti / stars: magnetic field / stars: late-type
© ESO, 2012