Atmospheric composition of WASP-85Ab with ESPRESSO/VLT observations

¹ CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Datun Road A20, Beijing 100101, PR China
e-mail: wangw@nao.cas.cn
² School of Astronomy and Space Science, University of Chinese Academy of Sciences, Yuquan Road, Beijing 100049, PR China
³ Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210033, PR China
⁴ Department of Astronomy, University of Science and Technology of China, JinZhai Road, Hefei 230026, PR China
⁵ Physics Department, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁶ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁷ Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
⁸ CAS South America Center for Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Datun Road A20, Beijing 100101, PR China

Received: 19 December 2022
Accepted: 5 July 2023

Abstract

Transit spectroscopy is the most frequently used technique to reveal the atmospheric properties of exoplanets. At high resolution, it has the added advantage of resolving the small Doppler shift of spectral lines and, thus, the trace signal of the exoplanet atmosphere can be extracted separately. We obtained the transmission spectra of the extrasolar planet WASP-85Ab, a hot Jupiter in a 2.655-day orbit around a G5, V = 11.2 mag host star, observed by the high-resolution spectrograph ESPRESSO at the Very Large Telescope array for three transits. We present an analysis of the Rossiter-McLaughlin (RM) effect on WASP-85A and determine a spin-orbit angle λ = −16.155°_−2.879^+2.916, suggesting that the planet is in a nearly aligned orbit. Combining the transmission spectra of three nights, we tentatively detected Hα and Call absorption with ⪆3σ via direct visual inspection of the transmission spectra with the center-to-limb variation and the Rossiter-McLaughlin effects removed; these absorptions still remain visible after excluding the cores of these strong lines with a 0.1Å mask. These spectral signals appear likely to have originated from the planetary atmosphere, but we cannot fully exclude a stellar origin. Via the cross-correlation analysis of a set of atoms and molecules, Li I is marginally detected at the ∼4σ level, suggesting that Li might be present in the atmosphere of WASP-85Ab.