Probing the extent of WASP-52 b’s atmosphere

High-resolution observations and 3D modeling insights

¹ Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
² Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, MS-51, Cambridge, MA 02138, USA
³ Ludwig Maximilian University, Faculty of Physics, University Observatory, Scheinerstr. 1, Munich 81679, Germany
⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁵ Institut für Astrophysik und Geophysik, Georg-August-Universität, Friedrich Hund Platz 1, 37077 Göttingen, Germany
⁶ Planetary Exploration, Technical University Delft, Kluyverweg 1 2629 HS Delft, The Netherlands

^★ Corresponding author: fabienne.nail@gmail.com

Received: 21 May 2025
Accepted: 22 August 2025

Abstract

WASP-52 b is an inflated hot Jupiter with a large Roche lobe filling fraction, positioned in the hot Neptune desert. Previous in-transit observations of the helium triplet at 10 833 Å have reported a range of excess absorption values (1.5–5.5%) and a lack of net blueshift relative to the planet’s rest frame, distinguishing it from other escaping atmospheres. This study investigates the extent and morphology of material escaping from WASP-52 b, and we assessed whether its outflow resembles a stream-like structure, as suggested for HAT-P-67 b and HAT-P-32 b. We obtained high-resolution spectra with CRIRES⁺ and CARMENES, covering a broader orbital phase range (φ ≈ ±0.1, ±0.2, 0.5) than previous studies. By analyzing the He I 10 833 Å line as a tracer of escape, we searched for extended absorption beyond transit. Additionally, we explored possible outflow morphologies with three-dimensional (3D) hydrodynamic simulations, coupled with an improved radiative transfer approach, assessing the He I 10 833 Å triplet. The helium line shows no significant evidence of planetary material at the orbital phases observed in this work, though 3D modeling suggests such a structure could exist below observational detection limits. We conclude that the atmospheric outflow of WASP-52 b can be characterized by an intermediate hydrodynamic escape parameter, placing it in a transitional regime between cold outflows forming a stream-like morphology and hot outflows forming a tail. Additionally, the absence of a detectable in-transit blueshift in the helium line rules out a strong day-to-nightside anisotropy scenario.