The atmospheric composition of the ultra-hot Jupiter WASP-178 b observed with ESPRESSO^★

¹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
e-mail: yuricd2001@gmail.com
² Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Región Metropolitana, Chile
⁴ Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
⁵ Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁶ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁸ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁹ Centro de Astrobiología, CSIC-INTA, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹⁰ Center for Space and Habitability, University of Bern, Gesellsschaftsstr. 6, 3012 Bern, Switzerland
¹¹ Département de Physique, Institut Trottier de Recherche sur les Exoplanètes, Université de Montréal, Montréal, Québec, H3T 1J4, Canada
¹² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹³ INAF – Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143, Trieste, Italy
¹⁴ Centre Vie dans l’Univers, Faculté des sciences de l’Université de Genève, Quai Ernest-Ansermet 30, 1205 Geneva, Switzerland
¹⁵ Centro de Astrobiología, CSIC-INTA, Crta. Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
¹⁶ Centro de Astrobiología (CAB, CSIC-INTA), ESAC campus, 28692, Villanueva de la Cañada (Madrid), Spain
¹⁷ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁸ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

Received: 25 March 2024
Accepted: 3 June 2024

Abstract

Context. Ultra-hot Jupiters (UHJ) have emerged as ideal testbeds for new techniques for studying exoplanet atmospheres. Only a limited number of them are currently well studied, however.

Aims. We search for atmospheric constituents for the UHJ WASP-178 b with two ESPRESSO transits. Additionally, we show parallel photometry that we used to obtain updated and precise stellar, planetary, and orbital parameters.

Methods. The two transits we obtained were analysed with narrow-band transmission spectroscopy and with the cross-correlation technique to provide detections at different altitude levels. We focused on searching for Na I, Hα, Hβ, Hγ, Mg I, and Li I lines in narrow-band data, as well as Fe I and Fe II, and attempted to confirm Mg I with the cross-correlation technique. We corrected for the Rossiter-McLaughlin effect and regions with a low signal-to-noise ratio due to Na I absorption in the interstellar medium. We then verified our results via bootstrapping.

Results. We report the resolved line detections of Na I (5.5σ and 5.4σ), Hα (13σ), Hβ (7.1σ), and tentatively Mg I (4.6σ). With a cross-correlation, we confirm the Mg I detection (7.8 σ and 5.8 σ), and we additionally report the detections of Fe I (12σ and 10σ) and Fe II (11σ and 8.4σ) on both nights separately. The detection of Mg I remains tentative, however, because the results on the two nights differ. The results also differ compared with the properties derived from the narrow-band data.

Conclusions. None of our resolved spectral lines probing the middle to upper atmosphere shows significant shifts relative to the planetary rest frame. Hα and Hβ exhibit a respective line broadening of 39.6 ± 2.1 km s⁻¹ and 27.6 ± 4.6 km s⁻¹, however, indicating the onset of possible escape. WASP-178 b differs from similar UHJ by its lack of strong atmospheric dynamics in the upper atmosphere. The broadening seen for Fe I (15.66 ± 0.58 km s⁻¹) and Fe II (11.32 ± 0.52 km s⁻¹) might indicate the presence of winds in the mid-atmosphere, however. Future studies of the impact of the flux variability caused by the host star activity might shed more light on the subject. Previous work indicated the presence of SiO cloud-precursors in the atmosphere of WASP-178 b and a lack of Mg I and Fe II. However, our results suggest that a scenario in which the planetary atmosphere is dominated by Mg I and Fe II is more likely. In light of our results, we encourage future observations to further elucidate these atmospheric properties.