Three-dimensional hydrodynamic simulations of the upper atmosphere of $\pi$ Men c: comparison with Ly$\alpha$ transit observations

Abstract

Aims: We aim at constraining the conditions of the wind and high-energy emission of the host star reproducing the non-detection of Ly$\alpha$ planetary absorption. Methods: We model the escaping planetary atmosphere, the stellar wind, and their interaction employing a multi-fluid, three-dimensional hydrodynamic code. We assume a planetary atmosphere composed of hydrogen and helium. We run models varying the stellar high-energy emission and stellar mass-loss rate, further computing for each case the Ly$\alpha$ synthetic planetary atmospheric absorption and comparing it with the observations. Results: We find that a non-detection of Ly$\alpha$ in absorption employing the stellar high-energy emission estimated from far-ultraviolet and X-ray data requires a stellar wind with a stellar mass-loss rate about six times lower than solar. This result is a consequence of the fact that, for $\pi$ Men c, detectable Ly$\alpha$ absorption can be caused exclusively by energetic neutral atoms, which become more abundant with increasing the velocity and/or the density of the stellar wind. By considering, instead, that the star has a solar-like wind, the non-detection requires a stellar ionising radiation about four times higher than estimated. This is because, despite the fact that a stronger stellar high-energy emission ionises hydrogen more rapidly, it also increases the upper atmosphere heating and expansion, pushing the interaction region with the stellar wind farther away from the planet, where the planet atmospheric density that remains neutral becomes smaller and the production of energetic neutral atoms less efficient. Conclusions: Comparing the results of our grid of models with what is expected and estimated for the stellar wind and high-energy emission, respectively, we support the idea that the atmosphere of $\pi$ Men c is likely not hydrogen-dominated.

Accepted for publication in A&A. The abstract has been shortened to fit the arXiv form

References in corpus (7)

• Atmospheric Escape from Hot Jupiters
• Atmosphere Expansion and Mass Loss of Close-Orbit Giant Exoplanets heated by Stellar XUV. II. Effects of Planetary Magnetic Field, Structuring of inner Magnetosphere
• Global 3D hydrodynamic modeling of in-transit Lyα absorption of GJ436b
• Two regimes of interaction of a Hot Jupiter's escaping atmosphere with the stellar wind and generation of energized atomic hydrogen corona
• Lyα Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions
• Is pi Men c's atmosphere hydrogen-dominated? Insights from a non-detecton of Hy Ly-alpha absorption
• The XUV irradiation and likely atmospheric escape of the super-Earth $\pi$ Men c

Cited by in corpus (15)

• A Heavy Molecular Weight Atmosphere for the Super-Earth π Men c
• Constraints on the mass and atmospheric composition and evolution of the low-density young planet DS Tuc A b
• The impact of intrinsic magnetic field on the absorption signatures of elements probing the upper atmosphere of HD209458b
• The fundamentals of Lyman-alpha exoplanet transits
• Caught in the Act: Core-powered Mass-loss Predictions for Observing Atmospheric Escape
• The GAPS Programme at TNG. XXXII. The revealing non-detection of metastable HeI in the atmosphere of the hot Jupiter WASP-80b
• Global 3D simulation of the upper atmosphere of HD189733b and absorption in metastable HeI and Lyα lines
• A multi-wavelength look at the GJ 9827 system -- No evidence of extended atmospheres in GJ 9827 b and d from HST and CARMENES data
• Evolution of X-ray Activity in <25 Myr Old Pre-Main Sequence Stars
• Simulation of 10830 Å absorption with a 3D hydrodynamic model reveals the solar He abundance in upper atmosphere of WASP-107b
• Heating and ionization by non-thermal electrons in the upper atmospheres of water-rich exoplanets
• An efficient Monte Carlo model for the slowing down of photoelectrons. Application to H-$\alpha$ in exoplanet atmospheres
• Star-Planet Interactions: A Computational View
• Estimating the Mass Escaping Rates of Radius-valley-spanning Planets in the TOI-431 System via X-Ray and Ultraviolet Evaporation
• Comparative Analysis of the Model for Exoplanet Atmosphere Outflow