A catalogue of activity indicators from telluric-corrected CARMENES spectra

Between 2016 and 2020, the CARMENES spectrographs at the 3.5 m telescope of the Calar Alto Observatory in Almería, Spain, collected almost 20 000 visible-light and near-infrared spectra of 362 M dwarfs during guaranteed time observations (GTO) in its quest to find planet-induced radial velocity (RV) modulations. However, activity phenomena can affect the shape of the spectral lines in a way that also leads to periodic variations in the measured RV. From each CARMENES GTO spectrum, we derived two sets of activity indicators based on different kinds of spectral features: indices of molecular absorption bands formed in the photosphere and pseudo-equivalent widths of atomic lines that may show a chromospheric component. By stacking generalised Lomb-Scargle periodograms of the photospheric and the chromospheric activity indicators for each star, we search for periodic variations and compare them to known rotation periods of the stars. We show that using spectra that were corrected for absorption lines formed in the Earth’s atmosphere mitigates strong modulations with a period of one year and its integer fractions. Our catalogue of activity indicators is not only a valuable trove of information to study the activity of low-mass stars, but can also help to discriminate planet-induced Doppler-shift modulations from activity-induced modulations.