Stellar masks and bisector's shape for M-type stars observed in the GAPS Programme with HARPS-N at TNG

Abstract

The HARPS/HARPS-N Data Reduction Software (DRS) relies on the cross-correlation between the observed spectra and a suitable stellar mask to compute a cross-correlation function (CCF) to be used both for the radial velocity (RV) computation and as an indicator of stellar lines asymmetry, induced for example by the stellar activity. Unfortunately the M2 mask currently used by the HARPS/HARPS-N DRS for M-type stars results in heavily distorted CCFs. We created several new stellar masks in order to decrease the errors in the RVs and to improve the reliability of the activity indicators as the bisector's span. We obtained very good results with a stellar mask created from the theoretical line list provided by the VALD3 database for an early M-type star (T${}_{\mathrm{eff}}$=3500~K and $\log g=4.5$). The CCF's shape and relative activity indicators improved and the RV time-series allowed us to recover known exoplanets with periods and amplitudes compatible with the results obtained with HARPS-TERRA.

13 pages, 8 figures Accepted for publication in Experimental Astronomy

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• A HARPS-N mass for the elusive Kepler-37d: a case study in disentangling stellar activity and planetary signals
• Long-term stellar activity variations and their effect on radial-velocity measurements
• The GAPS programme at TNG XLIV. Projected rotational velocities of 273 exoplanet-host stars observed with HARPS-N
• A super-Earth on a close-in orbit around the M1V star GJ 740. A HADES and CARMENES collaboration
• The CARMENES search for exoplanets around M dwarfs. Line-by-line sensitivity to activity in M dwarfs
• The GAPS programme at TNG. XLVI. Deep search for low-mass planets in late-dwarf systems hosting cold Jupiters
• The GAPS programme at TNG XLIII. A massive brown dwarf orbiting the active M dwarf TOI-5375
• HADES RV programme with HARPS-N at TNG XIV. A candidate super-Earth orbiting the M-dwarf GJ 9689 with a period close to half the stellar rotation period
• The Interpolation Constraint in the RV Analysis of M-Dwarfs Using Empirical Templates