Paper

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

Zapatero-Osorio, M R, González Hernández, J I, Sousa, S G, Steiner, M, Ehrenreich, D, Esparza-Borges, E, Micela, G, Santos, N C, C J A P Martins, Alibert, Y, Stangret, M, Damasceno, Y C, Seidel, J V, Psaridi, A, Pallé, E, Zhao, Y, Allart, R, Prinoth, B, Vaulato, V, Lendl, M, Pepe, F, Cristo, E, Herrero-Cisneros, E, Cointepas, M, P Di Marcantonio, Lillo-Box, J, T Azevedo Silva, Costa Silva, A R

2024

Overview

We search for atmospheric constituents for the UHJ WASP-178 b with two ESPRESSO transits using the narrow-band and cross-correlation techniques, focusing on the detections of NaI, H\\(\\alpha\\), H\\(\\beta\\), H\\(\\gamma\\), MgI, FeI and FeII. Additionally, we show parallel photometry used to obtain updated and precise stellar, planetary and orbital parameters. We report the resolved line detections of NaI (5.5 and 5.4 \\(\\sigma\\)), H\\(\\alpha\\) (13 \\(\\sigma\\)), H\\(\\beta\\) (7.1 \\(\\sigma\\)), and tentatively MgI (4.6 \\(\\sigma\\)). In cross-correlation, we confirm the MgI detection (7.8 and 5.8 \\(\\sigma\\)) and additionally report the detections of FeI (12 and 10 \\(\\sigma\\)) and FeII (11 and 8.4 \\(\\sigma\\)), on both nights separately. The detection of MgI remains tentative, however, due to the differing results between both nights, as well as compared with the narrow-band derived properties. None of our resolved spectral lines probing the mid- to upper atmosphere show significant shifts relative to the planetary rest frame, however H\\(\\alpha\\) and H\\(\\beta\\) exhibit line broadenings of 39.6 \\(\\pm\\) 2.1 km/s and 27.6 \\(\\pm\\) 4.6 km/s, respectively, indicating the onset of possible escape. WASP-178 b differs from similar UHJ with its lack of strong atmospheric dynamics in the upper atmosphere, however the broadening seen for FeI (15.66 \\(\\pm\\) 0.58 km/s) and FeII (11.32 \\(\\pm\\) 0.52 km/s) could indicate the presence of winds in the mid-atmosphere. Future studies on 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 MgI and FeII. However, our results suggest that a scenario where the planetary atmosphere is dominated by MgI and FeII is more likely. In light of our results, we encourage future observations to further elucidate these atmospheric properties.

• Publisher: Cornell University Library, arXiv.org
• Subject: Atmospheric composition / Cross correlation / Extrasolar planets / Gas giant planets / Jupiter / Line spectra / Planetary atmospheres / Upper atmosphere