Transmission spectroscopy of MASCARA-1b with ESPRESSO: Challenges of overlapping orbital and Doppler tracks^★

¹ Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
e-mail: barris@strw.leidenuniv.nl
² INAF – Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, Italy
³ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁵ Department of Physics, and Institute for Research on Exoplanets, Université de Montréal, Montréal H3T 1J4, Canada
⁶ Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51b, Sauverny, CH-1290, Switzerland
⁷ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁸ Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
⁹ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
¹⁰ INAF – Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy
¹¹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹² Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal
¹³ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁴ Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
¹⁵ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
¹⁶ European Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
¹⁷ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy

Received: 30 December 2021
Accepted: 5 May 2022

Abstract

Atmospheric studies at high spectral resolution have shown the presence of molecules, neutral and ionised metals, and hydrogen in the transmission spectrum of ultra-hot Jupiters, and have started to probe the dynamics of their atmospheres. We analyse the transmission spectrum of MASCARA-1b, one of the densest ultra-hot Jupiters orbiting a bright (V = 8.3) star. We focus on the CaII H&K, NaI doublet, LiI, Hα, and KI D1 spectral lines and on the cross-correlated FeI, Fe II, CaI, YI, VI, VII, CaH, and TiO lines. For those species that are not present in the stellar spectrum, no detections are reported, but we are able to measure upper limits with an excellent precision (~10 ppm for particular species) thanks to the signal-to-noise ratio (S/N) achieved with Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) observations. For those species that are present in the stellar spectrum and whose planet-occulted spectral lines induce spurious features in the planetary transmission spectrum, an accurate modelling of the Rossiter-McLaughlin effect (RM) and centre-to-limb variations (CLV) is necessary to recover possible atmospheric signals. In the case of MASCARA-1b, this is difficult due to the overlap between the radial velocities of the stellar surface regions occulted by MASCARA-1b and the orbital track along which the planet atmospheric signal is expected to be found. To try to disentangle a possible planetary signal, we compare our results with models of the RM and CLV effects, and estimate the uncertainties of our models depending on the different system parameters. Unfortunately, more precise measurements of the spin-orbit angle are necessary to better constrain the planet-occulted track and correct for the transit effects in the transmission spectrum with enough precision to be able to detect or discard possible planetary absorptions. Finally, we discuss the possibility that non-detections are related to the low absorption expected for a high surface gravity planet such as MASCARA-1b. Other techniques such as emission spectroscopy may be more useful for exploring their atmospheric composition.