Analysis of the public HARPS/ESO spectroscopic archive — Ca II H&K time series for the HARPS radial velocity database

The identification and elimination of instrumental effects increases the precision of exoplanet detection via the radial velocity (RV) technique. However, even inactive stars such as our Sun exhibit radial velocity jitter of the order of~1 m/s caused by active regions on the stellar surface. Time series of chromospheric activity indicators such as the Ca II H&K lines can contribute to mitigating this influence of RV jitter.

We present an update of the HARPS-RVBANK published by Trifonov et al. (2020) and extend it with the relative emission in the Ca II H&K lines, R'_HK, in order to provide the community with an additional tool to understanding the influence of stellar magnetic activity on HARPS RV time series. R'_HK is determined both from the individual spectra, as well as co-added templates, with the help of PHOENIX models (Husser et al. 2013) using the method described by Perdelwitz et al. (2021). Stellar parameters of all ~5000 targets, necessary as input for the approach, were derived with the SPECIES code (Soto & Jenkins 2018; Soto et al. 2021).

The resulting new version of the HARPS RV database has a total of 180000 values of R'_HK, which corresponds to ~85% of all spectra contained in the HARPS-RVBANK.