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

Abstract

To detect stellar activity cycles and study the possible star-planet interactions (SPI's), we have developed both HK$α$ and SPI-HK$α$ projects since 1999 and 2012 respectively. In this work, we present preliminary results of possible SPI's studying the chromospheric activity and look for possible correlations between stellar activity and stellar/planetary parameters. We find that for stars with similar T$_{eff}$, stellar activity increases with the mass of the planet, similar to previous works. However, stellar ages can also play a role and a larger stellar sample is needed to verify these trends. We also note that some of these stars present a remarkably high level of chromospheric activity, even comparable with RSCvn or BY Dra active stars. In addition, we do not observe any correlation between stellar activity and semi-major axis. We present the first long-term activity study of the star $ι$ Horologii, a young solar-type star which hosts a non-transiting Jovian planet and presents a high activity level. We analyze our own spectra, obtained between 2002 and 2015, combined with public HARPS observations. We calculate the Ca II indexes derived from the 987 CASLEO and HARPS spectra and convert them to the Mount-Wilson scale. We found a long-term activity cycle of $\sim$ 5 years which fits the active sequence of Bohm-Vitense. The amplitude of this longer cycle is irregular, as was also observed for the shorter one. This fact could be attributed to an antisymmetric distribution of active regions on the stellar surface.