Modelling the He I triplet absorption at 10 830 Å in the atmosphere of HD 209458 b

• Verfasst von: Lampón, Manuel [VerfasserIn]
• Verfasst von: López-Puertas, M. [VerfasserIn]
• Verfasst von: Lara, L. M. [VerfasserIn]
• Verfasst von: Sánchez López, Alejandro [VerfasserIn]
• Verfasst von: Salz, M. [VerfasserIn]
• Verfasst von: Czesla, Stefan [VerfasserIn]
• Verfasst von: Sanz-Forcada, J. [VerfasserIn]
• Verfasst von: Molaverdikhani, Karan [VerfasserIn]
• Verfasst von: Alonso Floriano, Francisco J. [VerfasserIn]
• Verfasst von: Nortmann, L. [VerfasserIn]
• Verfasst von: Caballero, José A. [VerfasserIn]
• Verfasst von: Bauer, F. F. [VerfasserIn]
• Verfasst von: Pallé, Enric [VerfasserIn]
• Verfasst von: Montes, D. [VerfasserIn]
• Verfasst von: Quirrenbach, Andreas [VerfasserIn]
• Verfasst von: Nagel, E. [VerfasserIn]
• Verfasst von: Ribas, Ignasi [VerfasserIn]
• Verfasst von: Reiners, Ansgar [VerfasserIn]
• Verfasst von: Amado, P. J. [VerfasserIn]
• Titel: Modelling the He I triplet absorption at 10 830 Å in the atmosphere of HD 209458 b
• Verf.angabe: M. Lampón, M. López-Puertas, L.M. Lara, A. Sánchez-López, M. Salz, S. Czesla, J. Sanz-Forcada, K. Molaverdikhani, F.J. Alonso-Floriano, L. Nortmann, J.A. Caballero, F.F. Bauer, E. Pallé, D. Montes, A. Quirrenbach, E. Nagel, I. Ribas, A. Reiners, and P.J. Amado
• E-Jahr: 2020
• Jahr: 07 April 2020
• Umfang: 14 S.
• Fussnoten: Gesehen am 20.10.2020
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2020
• Band/Heft Quelle: 636(2020) Artikel-Nummer A13, 14 Seiten
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201937175
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1700732749

Abstract

HD 209458 b is an exoplanet with an upper atmosphere undergoing blow-off escape that has mainly been studied using measurements of the Ly<i>α<i/> absorption. Recently, high-resolution measurements of absorption in the He I triplet line at 10 830 Å of several exoplanets (including HD 209458 b) have been reported, creating a new opportunity to probe escaping atmospheres.<i>Aims.<i/> We aim to better understand the atmospheric regions of HD 209458 b from where the escape originates.<i>Methods.<i/> We developed a 1D hydrodynamic model with spherical symmetry for the HD 209458 b thermosphere coupled with a non-local thermodynamic model for the population of the He I triplet state. In addition, we performed high-resolution radiative transfer calculations of synthetic spectra for the helium triplet lines and compared them with the measured absorption spectrum in order to retrieve information about the atmospheric parameters.<i>Results.<i/> We find that the measured spectrum constrains the [H]/[H<sup>+<sup/>] transition altitude occurring in the range of 1.2 <i>R<i/><sub>P<sub/>-1.9 <i>R<i/><sub>P<sub/>. Hydrogen is almost fully ionised at altitudes above 2.9 <i>R<i/><sub>P<sub/>. We also find that the X-ray and extreme ultraviolet absorption takes place at effective radii from 1.16 to 1.30 <i>R<i/><sub>P<sub/>, and that the He I triplet peak density occurs at altitudes from 1.04 to 1.60 <i>R<i/><sub>P<sub/>. Additionally, the averaged mean molecular weight is confined to the 0.61-0.73 g mole<sup>−1<sup/> interval, and the thermospheric H/He ratio should be larger than 90/10, and most likely approximately 98/2. We also provide a one-to-one relationship between mass-loss rate and temperature. Based on the energy-limited escape approach and assuming heating efficiencies of 0.1-0.2, we find a mass-loss rate in the range of (0.42-1.00) ×10<sup>11<sup/> g s<sup>−1<sup/> and a corresponding temperature range of 7125-8125 K.<i>Conclusions.<i/> The analysis of the measured He I triplet absorption spectrum significantly constrains the thermospheric structure of HD 209458 b and advances our knowledge of its escaping atmosphere.