Issue |
A&A
Volume 695, March 2025
|
|
---|---|---|
Article Number | A186 | |
Number of page(s) | 10 | |
Section | Planets, planetary systems, and small bodies | |
DOI | https://doi.org/10.1051/0004-6361/202452740 | |
Published online | 18 March 2025 |
Cold dayside winds shape large leading streams in evaporating exoplanet atmospheres
1
Anton Pannekoek Institute for Astronomy, University of Amsterdam,
1090 GE
Amsterdam,
The Netherlands
2
Center for Astrophysics,
Harvard & Smithsonian 60 Garden Street, MS-16,
Cambridge,
MA
02138,
USA
3
Department of Astronomy, The University of Texas at Austin,
2515 Speedway,
Austin,
TX
78712,
USA
4
Department of Astronomy and Astrophysics, University of California, Santa Cruz,
Santa Cruz,
CA
95064,
USA
★ Corresponding author; f.nail@uva.nl
Received:
24
October
2024
Accepted:
10
February
2025
Recent observations of planetary atmospheres in HAT-P-32 b and HAT-P-67 b reveal extensive outflows reaching up to hundreds of planetary radii. The helium 1083 nm light curves for these planets, captured across their full orbits, show notable asymmetries: both planets display more pronounced pre-transit than post-transit absorptions, with HAT-P-67 b being the more extreme case. Using 3D hydrodynamic simulations, we identified the key factors influencing the formation of a dense leading outflow stream and characterized its morphology. Our models suggest that such a geometry of escaped material is caused by a relatively cold outflow with a high mass-loss rate, launched preferentially from the planet’s dayside. From the simulations we calculated synthetic He I 1083 nm spectra that show large absorption depths and irregular line profiles due to complex gas kinematics. We find that the measurements of the He I 1083 nm equivalent width and the velocity shift relative to the planet’s rest frame, observed over a significant portion of the planet’s orbital phase, can provide important constraints on the outflow properties and its interaction with the stellar wind.
Key words: hydrodynamics / radiative transfer / planets and satellites: atmospheres / planet-star interactions
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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