The elusive atmosphere of WASP–12 b

High-resolution transmission spectroscopy with CARMENES

¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
e-mail: sczesla@tls-tautenburg.de
² Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
³ Universitäts-Sternwarte, Ludwig-Maximilians-Universität München, Scheinerstrasse 1, 81679 München, Germany
⁴ Exzellenzcluster Origins, Boltzmannstrasse 2, 85748 Garching, Germany
⁵ Institut für Astrophysik und Geophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁶ Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna, 38206 Tenerife, Spain
⁸ Centro de Astrobiología (CSIC-INTA), ESAC, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹¹ Department of Astronomy, University of Science and Technology of China, Hefei 230026, PR China
¹² Centro Astronómico Hispano en Andalucía, Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almería, Spain
¹³ Departamento de Física de la Tierra y Astrofísica and IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁴ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, c/ de Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
¹⁵ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
¹⁶ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

Received: 28 September 2023
Accepted: 26 December 2023

Abstract

To date, the hot Jupiter WASP–12 b has been the only planet with confirmed orbital decay. The late F-type host star has been hypothesized to be surrounded by a large structure of circumstellar material evaporated from the planet. We obtained two high-resolution spectral transit time series with CARMENES and extensively searched for absorption signals by the atomic species Na, H, Ca, and He using transmission spectroscopy, thereby covering the He I λ10833 Å triplet with high resolution for the first time. We apply SYSREM for atomic line transmission spectroscopy, introduce the technique of signal protection to improve the results for individual absorption lines, and compare the outcomes to those of established methods. No transmission signals were detected and the most stringent upper limits as of yet were derived for the individual indicators. Nonetheless, we found variation in the stellar Hα and He I λ10833 Å lines, the origin of which remains uncertain but is unlikely to be activity. To constrain the enigmatic activity state of WASP–12, we analyzed XMM-Newton X-ray data and found the star to be moderately active at most. We deduced an upper limit for the X-ray luminosity and the irradiating X-ray and extreme ultraviolet (XUV) flux of WASP–12 b. Based on the XUV flux upper limit and the lack of the He I λ10833 Å signal, our hydrodynamic models slightly favor a moderately irradiated planet with a thermospheric temperature of ≲12 000 K, and a conservative upper limit of ≲4 × 10¹² g s⁻¹ on the mass-loss rate. Our study does not provide evidence for an extended planetary atmosphere or absorption by circumstellar material close to the planetary orbit.