TASTE

V. A new ground-based investigation of orbital decay in the ultra-hot Jupiter WASP-12b^★

¹ Dipartimento di Fisica, Università di Trento, Via Sommarive 14, 38123 Povo, Italy
e-mail: pietro.leonardi@unitn.it
² Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
e-mail: pietro.leonardi.1@studenti.unipd.it
³ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
e-mail: valerio.nascimbeni@inaf.it
⁴ Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo” (CISAS), Università degli Studi di Padova, Via Venezia 15, 35131 Padova, Italy
⁵ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone, Italy
⁶ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁷ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy

Received: 23 October 2023
Accepted: 16 February 2024

Abstract

The discovery of the first transiting hot Jupiters (HJs), giant planets on orbital periods shorter than P ~ 10 days, was announced more than 20 years ago. As both ground- and space-based follow-up observations are piling up, we are approaching the temporal baseline required to detect secular variations in their orbital parameters. In particular, several recent studies have focused on constraining the efficiency of the tidal decay mechanism to better understand the evolutionary timescales of HJ migration and engulfment. This can be achieved by measuring a monotonic decrease in orbital period dP/dt < 0 due to mechanical energy being dissipated by tidal friction. WASP-12b was the first HJ for which a tidal decay scenario appeared convincing, even though alternative explanations have been hypothesized. Here we present a new analysis based on 28 unpublished high-precision transit light curves gathered over a 12-yr baseline and combined with all the available archival data, and an updated set of stellar parameters from HARPS-N high-resolution spectra, which are consistent with a main-sequence scenario, close to the hydrogen exhaustion in the core. Our values of dP/dt = −30.72 ± 2.67 and Q^′_* = (2.13 ± 0.18) × 10⁵ are statistically consistent with previous studies, and indicate that WASP-12 is undergoing fast tidal dissipation. We additionally report the presence of excess scatter in the timing data and discuss its possible origin.