Stellar activity consequence on the retrieved transmission spectra through chromatic Rossiter-McLaughlin observations

¹ Institut für Astrophysik, Georg-August Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
e-mail: moshagh@astro.physik.uni-goettingen.de
² Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
³ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
⁴ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁵ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, R. Campo Alegre, 4169-007 Porto, Portugal
⁶ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de laAstronomía s/n, 18008 Granada, Spain
⁷ European Southern Observatory, Alonso de Córdova 3107, Santiago, Chile

Received: 26 December 2019
Accepted: 8 February 2020

Abstract

Mostly multiband photometric transit observations have been used so far to retrieve broadband transmission spectra of transiting exoplanets in order to study their atmosphere. An alternative method has been proposed and has only been used once to recover transmission spectra using chromatic Rossiter-McLaughlin observations. Stellar activity has been shown to potentially imitate narrow and broadband features in the transmission spectra retrieved from multiband photometric observations; however, there has been no study regarding the influence of stellar activity on the retrieved transmission spectra through chromatic Rossiter-McLaughlin. In this study with the modified SOAP3.0 tool, we consider different types of stellar activity features (spots and plages), and we generated a large number of realistic chromatic Rossiter-McLaughlin curves for different types of planets and stars. We were then able to retrieve their transmission spectra to evaluate the impact of stellar activity on them. We find that chromatic Rossiter-McLaughlin observations are also not immune to stellar activity, which can mimic broadband features, such as Rayleigh scattering slope, in their retrieved transmission spectra. We also find that the influence is independent of the planet radius, orbital orientations, orbital period, and stellar rotation rate. However, more general simulations demonstrate that the probability of mimicking strong broadband features is lower than 25% and that can be mitigated by combining several Rossiter-McLaughlin observations obtained during several transits.