A&A 540, A82 (2012) Astronomy DOI: 10.1051/0004-6361/201118247 & c ESO 2012 Astrophysics Evidence for enhanced chromospheric Ca II H and K emission in stars with close-in extrasolar planets T. Krejcovᡠ1 and J. Budaj2 1 Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlárskᡠ2, 61137 Brno, Czech Republic e-mail:
[email protected] 2 Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovak Republic e-mail:
[email protected] Received 11 October 2011 / Accepted 13 February 2012 ABSTRACT Context. The planet-star interaction is manifested in many ways. It has been found that a close-in exoplanet causes small but mea- surable variability in the cores of a few lines in the spectra of several stars, which corresponds to the orbital period of the exoplanet. Stars with and without exoplanets may have different properties. Aims. The main goal of our study is to search for the influence that exoplanets might have on atmospheres of their host stars. Unlike the previous studies, we do not study changes in the spectrum of a host star or differences between stars with and without exoplanets. We aim to study a large number of stars with exoplanets and the current level of their chromospheric activity and to look for a possible correlation with the exoplanetary properties. Methods. To analyse the chromospheric activity of stars, we exploited our own and publicly available archival spectra, measured the equivalent widths of the cores of Ca II H and K lines, and used them to trace their activity. Subsequently, we searched for their dependence on the orbital parameters and the mass of the exoplanet.