Chromospheric activity and lithium line variations in the spectra of the spotted star LQ Hydrae^⋆,⋆⋆

Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: mflores@aip.de; kstrassmeier@aip.de; mweber@aip.de

Received: 16 October 2014
Accepted: 12 January 2015

Abstract

Context. Although the relationship between lithium abundance in stars and their magnetic activity is commonly accepted, it is still unclear how the different phenomena related to it can increase the amount of Li, reduce its depletion, or be a source of bias for the measurements.

Aims. We study the rotational modulation of chromospheric and photospheric parameters of the young, active, single K2 dwarf LQ Hya and their connection with the variability of the Li i 6708 Å line.

Methods. A total of 199 high-resolution STELLA spectra and quasi-simultaneous photometry were used to compute effective temperature, gravity, and chromospheric activity indicators such as Hα and Hβ emission, Balmer decrement, and chromospheric electron density, as a function of the rotational phase. The variation of the Li i 6708 Å line was characterized in terms of equivalent width, abundance, and of ⁶Li/⁷Li isotopic ratio in the form of line shifts.

Results. Photospheric and chromospheric parameters show clear rotational modulation. Effective temperatures and continuum variations reveal a higher concentration of cool spots on the side of the star on which we also detect stronger chromospheric activity. Increased electron densities and the modulation of the He i D₃ line suggest that the source of this activity can be a combination of plages and repeated low-intensity flares. The Li line and other temperature-sensitive lines are clearly enhanced by the spots located on the most active side of the star. Li abundances calculated taking into account the temperature variations simultaneously show, although with high dispersion, a small overabundance of this element that correlates well with the surface magnetic activity. In addition, the Li line center is more intensely redshifted than in the other hemisphere, which might be interpreted as a weak enrichment of ⁶Li.