The GAPS Programme at TNG

LI. Investigating the correlations between transiting system parameters and host chromospheric activity

¹ INAF – Osservatorio Astronomico di Padova, vicolo Osservatorio, 5, 35122 Padova, Italy
e-mail: riccardo.claudi@oapd.inaf.it
² Dipartimento di Matematica e Fisica, Università Roma Tre, Via della Vasca Navale 84, 00146 Roma, Italy
³ INAF-Osservatorio Astrofisico di Catania, via S. Sofia, 78, 95123 Catania, Italy
⁴ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
⁵ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁶ INAF – Osservatorio Astronomico di Roma, Via Frascati, 33, 00078 Monte Porzio (RM), Italy
⁷ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
⁸ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁹ INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
¹⁰ Instituto de Astrofísica de Andalucìa, CSIC, Glorieta de la Astronomía, 18080 Granada, Spain
¹¹ Sorbonne Universités, UPMC Université Paris 6 et CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
¹² Dipartimento di Fisica e Astronomia Galileo Galilei, Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova (Pd), Italy
¹³ Dipartimento di Fisica, Università di Roma ‘Tor Vergata’, Via della Ricerca Scientifica 1, 00133 Rome, Italy
¹⁴ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁵ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
¹⁶ Fundaciòn Galileo Galilei – INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
¹⁷ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131, Napoli, Italy
¹⁸ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047, Selargius (CA), Italy

Received: 2 June 2023
Accepted: 14 November 2023

Abstract

Context. Stellar activity is the most relevant types of astrophysical noise that affect the discovery and characterization of extrasolar planets. On the other hand, the amplitude of stellar activity could hint at an interaction between the star and a close-in giant planet. Progress has been made in recent years in understanding how to deal with stellar activity and search for observational evidence of star-planet interactions.

Aims. The aim of this work is to characterize the chromospheric activity of stars hosting short-period exoplanets by studying the correlations between the chromospheric emission (CE) in the Ca II H&K and the planetary parameters.

Methods. We measured CE in the Ca II H&K lines using more than 1900 high-resolution spectra of a sample composed of 76 targets, observed with the HARPS-N spectrograph between 2012 and 2020. We transformed the fluxes into bolometric- and photospheric-corrected chromospheric emission ratios, R′_HK. Furthermore, we completed the sample of hosts digging for data in previous works. Stellar parameters T_eff, B–V, and V were retrieved homogeneously from the Gaia DR3. Then, M_★, R_★, and ages were determined from isochrone fitting. We retrieved planetary data from the literature and catalogs. The search for correlations between the log(R′_HK) and planetary parameters have been performed through both Spearman’s rank and its statistics as well as the more sophisticated Gaussian mixture model method.

Results. We found that the distribution of log(R′_HK) for the transiting planet hosts is different from the distribution of field main-sequence and sub-giant stars. The log(R′_HK) of planetary hosts is correlated with planetary parameters proportional to the planetary radius to the power of n (R_Pⁿ, indicating a common origin for the correlations. The statistical analysis has also highlighted four clusters of host stars with different behavior in terms of their stellar activity with respect to the planetary surface gravity. Some of the host stars have a value of log(R′_HK) that is lower than the basal level of activity for main sequence stars. The planets of these systems are very close to filling their Roche lobe, suggesting that they evaporate through hydrodynamic escape under the strong irradiation of the host star, creating shrouds that absorb the core of the chromospheric resonance lines.