EDP Sciences
Free access
Volume 413, Number 2, January II 2004
Page(s) 657 - 667
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20031565

A&A 413, 657-667 (2004)
DOI: 10.1051/0004-6361:20031565

Magnetic activity in HD 111456, a young F5-6 main-sequence star

R. Freire Ferrero1, A. Frasca2, E. Marilli2 and S. Catalano2

1  Observatoire Astronomique, 11 rue de l'Université, 67000 Strasbourg, France
2  INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy

(Received 21 November 2002 / Accepted 30 September 2003)

We present spectroscopic and photometric observations of the young F5-6 V field star HD 111456 which exhibits emission cores in the $\ion{Ca}{ii}$ H and K lines and a filling in the H $\alpha$ line. Absorption lines of $\ion{He}{i}$ D 3 and $\ion{Li}{i}$ are clearly detected and we give a new value of $v\sin i=41.5$ km s -1. Although the limit of magnetic activity detectability at optical wavelengths occurs around F5-6 spectral types, HD 111456 shows unusual chromospheric activity. High UV fluxes in the $\ion{C}{ii}$, $\ion{C}{iv}$, $\ion{Si}{ii}$ and $\ion{Si}{iv}$ lines and a strong X-ray emission confirm that HD 111456 is one of the most active F5-6 V star. The $\ion{Ca}{ii}$ and H $\alpha$ chromospheric emission fluxes do not show any detectable variation on time scales of few days, as well as uvby photometry. A possible explanation in terms of a very high level of magnetic activity and a homogeneous distribution of active regions, both at chromospheric and photospheric level, or a very low inclination of the rotation axis with respect to the line of sight is proposed. From 1998 to 2001 the radial velocity varies indicating a possible binary system, but the spectral distribution of HD 111456 is better reproduced by a single normal F5 V star, and composite spectra simulations ( $\ion{Ca}{ii}$, H $\alpha$) with a normal inactive F star and a very active low-mass K-M star are not able to reproduce the observed emissions.

Key words: stars: activity -- stars: individual: HD 111456

Offprint request: R. Freire Ferrero, freire@cluster.u-strasbg.fr

SIMBAD Objects in preparation

© ESO 2004