Titanium chemistry of WASP-121 b with ESPRESSO in 4-UT mode

¹ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Región Metropolitana, Chile
² Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
³ Laboratoire Lagrange, Observatoire de la Côte d’Azur, CNRS, Université Côte d’Azur, Nice, France
⁴ Space Telescope Science Institute, Baltimore, MD 21218, USA
⁵ School of Mathematical and Physical Sciences, Macquarie University, Sydney, NSW 2109, Australia
⁶ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁷ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁸ University of Bern, Physics Institute, Division of Space Research & Planetary Sciences, Gesellschaftsstr. 6, 3012 Bern, Switzerland
⁹ INAF – Osservatorio Astrofisico di Arcetri, Florence, Italy
¹⁰ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
¹¹ Département de Physique, Institut Trottier de Recherche sur les Exoplanètes, Université de Montréal, Montréal, Québec, H3T 1J4, Canada
¹² Observatoire de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
¹³ Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁴ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹⁵ Departamento de Física de la Tierra y Astrofísica & IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁶ Centro de Astrobiología, CSIC-INTA, Camino Bajo del Castillo, s/n, 28692 Villanueva de la Cañada, Madrid, Spain

^★ Corresponding author; bibiana.prinoth@fysik.lu.se

Received: 28 September 2024
Accepted: 2 December 2024

Abstract

Transit spectroscopy usually relies on the integration of one or several transits to achieve the signal-to-noise ratio (S/N) necessary to resolve spectral features. Consequently, high-S/N observations of exoplanet atmospheres, where we can forgo integration, are essential for disentangling the complex chemistry and dynamics beyond global trends. In this study, we combined two partial 4-UT transits of the ultrahot Jupiter WASP-121 b, observed with the ESPRESSO at the European Southern Observatory’s Very Large Telescope in order to revisit its titanium chemistry. Through cross-correlation analysis, we achieved detections of H I, Li I, Na I, K I, Mg I, Ca I, Ti I, V I, Cr I, Mn I, Fe I, Fe II, Co I, Ni I, Ba II, Sr I, and Sr II. Additionally, narrow-band spectroscopy allowed us to resolve strong single lines, resulting in significant detections of Hα, Hβ, Hγ, Li I, Na I, K I, Mg I, Ca II, Sr I, Sr II, and Mn I. Our most notable finding is the high-significance detection of Ti I (∼5σ per spectrum, and ∼19σ stacked in the planetary rest frame). Comparison with atmospheric models reveals that Ti I is indeed depleted compared to V I. We also resolve the planetary velocity traces of both Ti I and V I, with Ti I exhibiting a significant blueshift toward the end of the transit. This suggests that Ti I primarily originates from low-latitude regions within the super-rotating jet observed in WASP-121 b. Our observations suggest limited mixing between the equatorial jet and the mid-latitudes, in contrast with model predictions from General Circulation Models. We also report the non-detection of TiO, which we attribute to inaccuracies in the line list that could hinder its detection, even if present. Thus, the final determination of the presence of TiO must await space-based observations. We conclude that the 4-UT mode of ESPRESSO is an excellent testbed for achieving high S/N on relatively faint targets, paving the way for future observations with the Extremely Large Telescope.