The GAPS programme at TNG

XLIV. Projected rotational velocities of 273 exoplanet-host stars observed with HARPS-N^★,★★

¹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi, 46, 23807 Merate (LC), Italy
e-mail: monica.rainer@inaf.it
² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio, 5, 35122 Padova (PD), Italy
³ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese (TO), Italy
⁴ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁵ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone (Roma), Italy
⁶ INAF – Osservatorio Astrofisico di Catania, Via S.Sofia 78, 95123 Catania, Italy
⁷ INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
⁸ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁹ INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
¹⁰ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS34229, 06304 Nice Cedex 4, France
¹¹ Department of Physics, University of Rome “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Rome, Italy
¹² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹³ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹⁴ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹⁵ INAF – Fundación Galileo Galilei, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja (TF), Spain
¹⁶ INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy

Received: 28 November 2022
Accepted: 22 June 2023

Abstract

Context. The leading spectrographs used for exoplanets’ search and characterization offer online data reduction softwares (DRS) that yield, as an ancillary result, the full-width at half-maximum (FWHM) of the cross-correlation function (CCF) that is used to estimate the radial velocity of the host star. The FWHM also contains information on the stellar projected rotational velocity v_eq sin i_★, if appropriately calibrated.

Aims. We wanted to establish a simple relationship to derive the v_eq sin i_★ directly from the FWHM computed by the HARPS-N DRS in the case of slow-rotating solar-like stars. This may also help to recover the stellar inclination i_★, which in turn affects the exoplanets’ parameters.

Methods. We selected stars with an inclination of the spin axis compatible with 90 deg by looking at exoplanetary transiting systems with known small sky-projected obliquity: for these calibrators, we can presume that v_eq sin i_★ is equal to stellar equatorial velocity v_eq. We derived their rotational periods from photometric and spectroscopic time series and their radii from the spectral energy distribution (SED) fitting. This allowed us to recover their v_eq, which could be compared to the FWHM values of the CCFs obtained both with G2 and K5 spectral-type masks.

Results. We obtained an empirical relation for each mask: this can be used to derive v_eq sin i_★ directly from FWHM values for slow rotators (FWHM < 20 km s⁻¹). We applied our relations to 273 exoplanet-host stars observed with HARPS-N, obtaining homogeneous v_eqsin i_★ measurements. When possible, we compared our results with the literature ones to confirm the reliability of our work. We were also able to recover or constrain i_★ for 12 objects with no prior v_eq sin i_★ estimation.

Conclusions. We provide two simple empirical relations to directly convert the HARPS-N FWHM obtained with the G2 and K5 mask to a v_eq sin i_★ value. We tested our results on a statistically significant sample, and we found a good agreement with literature values found with more sophisticated methods for stars with log ɡ > 3.5. We also tried our relation on HARPS and SOPHIE data, and we conclude that it can be used as it is also on FWHM derived by HARPS DRS with the G2 and K5 mask, and it may be adapted to the SOPHIE data as long as the spectra are taken in high-resolution mode.