Main-Sequence Stars

Abstract

We present spectroscopic and photometric observations of the young F5-6 V field star HD 111456 which exhibits emission cores in the Ca  H and K lines and a filling in the Hα line. Absorption lines of He  D 3 and Li  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 C , C , Si  and Si  lines and a strong X-ray emission confirm that HD 111456 is one of the most active F5-6 V star. The Ca  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 (Ca , Hα) with a normal inactive F star and a very active low-mass K-M star are not able to reproduce the observed emissions.