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

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

Corresponding author: R. Freire Ferrero, freire@cluster.u-strasbg.fr

Received: 21 November 2002
Accepted: 30 September 2003

Abstract

We present spectroscopic and photometric observations of the young F5–6 V field star HD 111456 which exhibits emission cores in the H and K lines and a filling in the Hα line. Absorption lines of D₃ and are clearly detected and we give a new value of 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 , , and lines and a strong X-ray emission confirm that HD 111456 is one of the most active F5–6 V star. The and Hα 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 (, Hα) with a normal inactive F star and a very active low-mass K-M star are not able to reproduce the observed emissions.