Stellar activity and Lithium abundances in exoplanets host stars

MAUAS, P. J. D.; BUCCINO, A. P.; SAFFE, C.; FLORES TRIVIGNO, M.

Moscú

Conferencia; COSPAR 2014; 2014

To date, the developed theory proposes that the star-planetinteractions (SPI) could be of magnetic origin, through themagnetosphere of the exoplanet, or mechanical origin, where tidalforces are involved in the interactions. Both processes could increasethe stellar activity level in the host stars.  However, there is notfull agreement in the literature associated with the increase in theactivity level shown by the host star. As a contribution on this discussion, we analyzed thepossible relation between stellar activity and some planetaryparameters (semi-major axis, planets masses). Our observations weremade at the 2.15 m telescope of the Complejo Astron´omico El Leoncito(CASLEO), which is located at 2552 m above sea level, in theArgentinean Andes. We used the REOSC spectrograph to obtain a seriesof mid-resolution spectra (R$sim$13000). We studied the long-termactivity of stars with planets. We used as activity indicator thewell-known Mount Wilson index (S). Furthermore, we tookcuasisimultaneous spectra of stars without planets with the samespectral class, to compare activity levels. Moreover, we also focused on study the possible excess ofLithium (Li) depletion, found in stars with planets when they arecompared with stars without planets of similar parameters (such asTeff and log g), and its possible relation with the stellar activity.It is believed, that the stellar rotation is the mostimportant parameter to determine the surface Li content, because theLi loss mechanism caused by the mixing envelope operates moreefficiently as stellar rotation decreases. If this interpretation iscorrect, would be possible to explain the apparent excess of Lidepletion in stars with planets when they are compared with fieldstars. A planetary system may alter the evolution of the angularmomentum of the star and the surface convective mixing, thus causingthe excess of Li depletion.To do so, we used high-resolution spectra (R$sim$110.000)of FGK stars with and without planets taken with the HARPS (HighAccuracy Radial velocity Planet Searcher) spectrograph, installed atthe 3.6 m ESO telescope. Then, we ajust the Li (6707.8 AA) line bysynthetic spectra calculated with SYNTHE for the stars with andwithout planets from our sample.