The GAPS Programme at TNG

XXVII. Reassessment of a young planetary system with HARPS-N: is the hot Jupiter V830 Tau b really there?^★,★★

¹ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese (TO), Italy
e-mail: mario.damasso@inaf.it
² INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
³ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁴ Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, CB3 0HE Cambridge, UK
⁵ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁶ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁷ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone (RM), Italy
⁸ Dipartimento di Fisica e Astronomia “G. Galilei”– Università degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁹ Aix-Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹⁰ INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi, 5, 50125 Firenze, Italy
¹¹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
¹² INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
¹³ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
¹⁴ Fundación Galileo Galilei – INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
¹⁵ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹⁶ Department of Physics, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy
¹⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁸ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius (CA), Italy
¹⁹ Dipartimento di Fisica, Università di Roma La Sapienza, P.le A. Moro 5, 00185 Roma, Italy
²⁰ INAF – Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
²¹ Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy

Received: 8 July 2020
Accepted: 17 August 2020

Abstract

Context. Detecting and characterising exoworlds around very young stars (age ≤10 Myr) are key aspects of exoplanet demographic studies, especially for understanding the mechanisms and timescales of planet formation and migration. Any reliable theory for such physical phenomena requires a robust observational database to be tested. However, detection using the radial velocity method alone can be very challenging because the amplitude of the signals caused by the magnetic activity of such stars can be orders of magnitude larger than those induced even by massive planets.

Aims. We observed the very young (~2 Myr) and very active star V830 Tau with the HARPS-N spectrograph between October 2017 and March 2020 to independently confirm and characterise the previously reported hot Jupiter V830 Tau b (K_b = 68 ± 11 m s⁻¹; m_b sin i_b = 0.57 ± 0.10 M_Jup; P_b = 4.927 ± 0.008 d).

Methods. Because of the observed ~1 km s⁻¹ radial velocity scatter that can clearly be attributed to the magnetic activity of V830 Tau, we analysed radial velocities extracted with different pipelines and modelled them using several state-of-the-art tools. We devised injection-recovery simulations to support our results and characterise our detection limits. The analysis of the radial velocities was aided by a characterisation of the stellar activity using simultaneous photometric and spectroscopic diagnostics.

Results. Despite the high quality of our HARPS-N data and the diversity of tests we performed, we were unable to detect the planet V830 Tau b in our data and cannot confirm its existence. Our simulations show that a statistically significant detection of the claimed planetary Doppler signal is very challenging.

Conclusions. It is important to continue Doppler searches for planets around young stars, but utmost care must be taken in the attempt to overcome the technical difficulties to be faced in order to achieve their detection and characterisation. This point must be kept in mind when assessing their occurrence rate, formation mechanisms, and migration pathways, especially without evidence of their existence from photometric transits.