Elemental abundance pattern and temperature inversion on the dayside of HAT-P-70b observed with CARMENES and PEPSI

¹ Department of Astronomy, University of Science and Technology of China, Hefei 230026, China
² Institut für Astrophysik und Geophysik, Georg-August-Universitåt, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁵ Universitåts-Sternwarte, Ludwig-Maximilians-Universitåt München, Scheinerstrasse 1, 81679 München, Germany
⁶ Exzellenzcluster Origins, Boltzmannstrasse 2, 85748 Garching bei München, Germany
⁷ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁸ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁰ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
¹¹ Universitåt Potsdam, Institut für Physik und Astronomie, Karl-Liebknecht-Str. 24/25, 14476 Potsdam-Golm, Germany
¹² INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
¹³ Freie Universitåt Berlin, Institute of Geological Sciences, Malteserstrasse 74-100, 12249 Berlin, Germany
¹⁴ Centro de Astrobiología (CSIC-INTA), Camino Bajo del Castillo s/n, Campus ESAC, 28692 Villanueva de la Cañada, Madrid, Spain
¹⁵ Landessternwarte, Zentrum für Astronomie der Universitåt Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹⁶ Institut de Ciències de l’Espai (CSIC), c/ de Can Magrans s/n, Campus UAB, 08193 Bellaterra, Barcelona, Spain
¹⁷ Institut d’Estudis Espacials de Catalunya, 08860 Castelldefels, Barcelona, Spain
¹⁸ Departamento de Física de la Tierra y Astrofísica & IPARCOS Instituto de Física de Partículas y del Cosmos, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, Plaza de Ciencias 1, 28400 Madrid, Spain
¹⁹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²⁰ Centro Astronómico Hispano en Andalucía, Observatorio Astronómico de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almería, Spain
²¹ Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721, USA
²² Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

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Received: 28 October 2025
Accepted: 14 December 2025

Abstract

Ground-based high-resolution spectroscopic observations have identified various chemical species in the atmosphere of numerous ultra-hot Jupiters (UHJs), including neutral and ionized metals. These detections have offered valuable insights into planet formation mechanisms via abundance measurements of refractory elements. We observed the dayside thermal emission spectrum of UHJ HAT-P-70b using the high-resolution spectrographs CARMENES and PEPSI. Through our cross-correlation analysis, we detected emission signals for Al I, AlH, Ca II, Cr I, Fe I, Fe II, Mg I, Mn I, and Ti I, marking the first detection of Al I and AlH in an exoplanetary atmosphere. Tentative signals of C I, Ca I, Na I, NaH, and Ni i were also identified. Based on those detections, we were able to perform atmospheric retrievals to constrain the thermal profile and elemental abundances of the planet’s dayside hemisphere. The retrieved temperature-pressure profile reveals a strong temperature inversion layer. The chemical free retrieval yielded a metallicity of [Fe/H] = 0.38_−1.11^+0.74, while the chemical equilibrium retrieval resulted in [Fe/H] = 0.23_−0.98^+1.08, with both values consistent with the solar metallicity. We also tentatively found an enriched abundance of Ni, which could result from the accretion of Ni-rich planetesimals during the planet’s formation. On the other hand, elements with condensation temperatures above 1400 K(e.g., Ca, Ti, and V) appear to be slightly depleted, possibly due to cold-trapping on the planet’s nightside. However, Al, with the highest condensation temperature at 1653 K, displays a solar-like abundance, which might reflect the formation-related enrichment of Al. Our retrieval indicates extremely high volume mixing ratios of metal ions (Fe II and Ca II), which are significantly inconsistent with predictions from chemical equilibrium models. This disequilibrium suggests that the atmosphere is likely undergoing significant hydrodynamic escaping, which enhances the atmospheric density at high altitudes where the ionic lines are formed.