A possible long-term activity cycle for ι Horologii: First results from SPI-HKα project

Abstract

In order to detect stellar activity cycles and study possiblestar-planet interactions (SPIs), we have been developing the HKαand SPI-HKα projects since 1999 and 2012 respectively. In thiswork, we present preliminary results of possible SPIs from studies ofchromospheric activity and look for possible correlations betweenstellar activity and stellar/planetary parameters. We find that forstars with a similar T_eff, stellar activity increases withthe mass of the planet, similar to results from previous works. However,stellar ages can also play a role, and a larger stellar sample is neededto verify these trends. We also note that some of these stars present aremarkably high level of chromospheric activity, comparable even withRSCvn or BY Dra active stars. In addition, we do not observe anycorrelation between stellar activity and semi-major axis. We present thefirst long-term activity study of the star ι Horologii, a youngsolar-type star that hosts a non-transiting Jovian planet and exhibits ahigh activity level. We analysed our own spectra, obtained between 2002and 2015, in conjunction with public HARPS (High Accuracy Radialvelocity Planet Searcher) observations. We calculated the Ca II indexesderived from the 987 Complejo Astronómico El Leoncito (CASLEO)and HARPS spectra and converted them to the Mt Wilson scale. We found along-term activity cycle of ?5 yr which fits the active sequenceof Böhm-Vitense. The amplitude of this longer cycle is irregular,as was also observed for the shorter cycle. This phenomenon could beattributable to an antisymmetric distribution of active regions on thestellar surface.