The GAPS Programme with HARPS-N at TNG

XIX. Atmospheric Rossiter-McLaughlin effect and improved parameters of KELT-9b^★,★★

¹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
e-mail: francesco.borsa@inaf.it; francesco.borsa@brera.inaf.it
² INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
³ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025, Pino Torinese, Italy
⁴ Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino, Italy
⁵ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
⁶ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123, Catania, Italy
⁷ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁸ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
¹⁰ Fundación Galileo Galilei – INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
¹¹ INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
¹² Department of Physics, University of Warwick, Coventry CV4 7AL, UK
¹³ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹⁴ Astronomy Department, 96 Foss Hill Drive, Van Vleck Observatory 101, Wesleyan University, Middletown, CT 06459, USA
¹⁵ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹⁶ Dipartimento di Fisica e Chimica Emilio Segré – Università di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
¹⁷ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4 - 28850 Torrejón de Ardoz, Madrid, Spain
¹⁸ Department of Physics, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
¹⁹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
²⁰ INAF – Osservatorio di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
²¹ Dipartimento di Fisica e Astronomia Galileo Galilei – Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
²² Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
²³ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
²⁴ Fondazione GAL Hassin, Via della Fontana Mitri, 90010 Isnello (PA), Italy

Received: 17 April 2019
Accepted: 23 July 2019

Abstract

Aims. In the framework of the GAPS project, we observed the planet-hosting star KELT-9 (A-type star, v sin i ~ 110 km s⁻¹) with the HARPS-N spectrograph at the Telescopio Nazionale Galileo. In this work we analyse the spectra and the extracted radial velocities to constrain the physical parameters of the system and to detect the planetary atmosphere of KELT-9b.

Methods. We extracted the mean stellar line profiles from the high-resolution optical spectra via an analysis based on the least-squares deconvolution technique. Then we computed the stellar radial velocities with a method optimised for fast rotators by fitting the mean stellar line profile with a purely rotational profile instead of using a Gaussian function.

Results. The new spectra and analysis led us to update the orbital and physical parameters of the system, improving in particular the value of the planetary mass to M_p = 2.88 ± 0.35 M_Jup. We discovered an anomalous in-transit radial velocity deviation from the theoretical Rossiter-McLaughlin effect solution, calculated from the projected spin-orbit angle λ = −85.78 ± 0.46 degrees measured with Doppler tomography. We prove that this deviation is caused by the planetary atmosphere of KELT-9b, thus we call this effect Atmospheric Rossiter-McLaughlin effect. By analysing the magnitude of the radial velocity anomaly, we obtained information on the extension of the planetary atmosphere as weighted by the model used to retrieve the stellar mean line profiles, which is up to 1.22 ± 0.02 R_p.

Conclusions. The Atmospheric Rossiter-McLaughlin effect will be observable for other exoplanets whose atmosphere has non-negligible correlation with the stellar mask used to retrieve the radial velocities, in particular ultra-hot Jupiters with iron in their atmospheres. The duration and amplitude of the effect will depend not only on the extension of the atmosphere, but also on the in-transit planetary radial velocities and on the projected rotational velocity of the parent star.