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Title: Ly α Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions

Abstract

To shed more light on the nature of the observed Ly α absorption during transits of HD 209458b and to quantify the major mechanisms responsible for the production of fast hydrogen atoms (the so-called energetic neutral atoms, ENAs) around the planet, 2D hydrodynamic multifluid modeling of the expanding planetary upper atmosphere, which is driven by stellar XUV, and its interaction with the stellar wind has been performed. The model self-consistently describes the escaping planetary wind, taking into account the generation of ENAs due to particle acceleration by the radiation pressure and by the charge exchange between the stellar wind protons and planetary atoms. The calculations in a wide range of stellar wind parameters and XUV flux values showed that under typical Sun-like star conditions, the amount of generated ENAs is too small, and the observed absorption at the level of 6%–8% can be attributed only to the non-resonant natural line broadening. For lower XUV fluxes, e.g., during the activity minima, the number of planetary atoms that survive photoionization and give rise to ENAs increases, resulting in up to 10%–15% absorption at the blue wing of the Ly α line, caused by resonant thermal line broadening. A similar asymmetric absorption canmore » be seen under the conditions realized during coronal mass ejections, when sufficiently high stellar wind pressure confines the escaping planetary material within a kind of bowshock around the planet. It was found that the radiation pressure in all considered cases has a negligible contribution to the production of ENAs and the corresponding absorption.« less

Authors:
; ; ; ;  [1]; ; ; ;  [2];  [3]
  1. Space Research Institute, Austrian Academy of Sciences, Graz (Austria)
  2. Institute of Laser Physics SB RAS, Novosibirsk (Russian Federation)
  3. Department of Astrophysics, University of Vienna (Austria)
Publication Date:
OSTI Identifier:
22679795
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 847; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTRA; ASYMMETRY; ATOMS; EXTREME ULTRAVIOLET RADIATION; HYDRODYNAMICS; HYDROGEN; LINE BROADENING; LYMAN LINES; MASS; PHOTOIONIZATION; PLANETS; PLASMA; PROTONS; RADIATION PRESSURE; SATELLITE ATMOSPHERES; SATELLITES; SIMULATION; STAR EVOLUTION; STELLAR WINDS; VISIBLE RADIATION

Citation Formats

Khodachenko, M. L., Lammer, H., Kislyakova, K. G., Fossati, L., Arkhypov, O. V., Shaikhislamov, I. F., Berezutsky, A. G., Miroshnichenko, I. B., Posukh, V. G., and Johnstone, C. P., E-mail: maxim.khodachenko@oeaw.ac.at. Ly α Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA88AD.
Khodachenko, M. L., Lammer, H., Kislyakova, K. G., Fossati, L., Arkhypov, O. V., Shaikhislamov, I. F., Berezutsky, A. G., Miroshnichenko, I. B., Posukh, V. G., & Johnstone, C. P., E-mail: maxim.khodachenko@oeaw.ac.at. Ly α Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions. United States. doi:10.3847/1538-4357/AA88AD.
Khodachenko, M. L., Lammer, H., Kislyakova, K. G., Fossati, L., Arkhypov, O. V., Shaikhislamov, I. F., Berezutsky, A. G., Miroshnichenko, I. B., Posukh, V. G., and Johnstone, C. P., E-mail: maxim.khodachenko@oeaw.ac.at. Sun . "Ly α Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions". United States. doi:10.3847/1538-4357/AA88AD.
@article{osti_22679795,
title = {Ly α Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions},
author = {Khodachenko, M. L. and Lammer, H. and Kislyakova, K. G. and Fossati, L. and Arkhypov, O. V. and Shaikhislamov, I. F. and Berezutsky, A. G. and Miroshnichenko, I. B. and Posukh, V. G. and Johnstone, C. P., E-mail: maxim.khodachenko@oeaw.ac.at},
abstractNote = {To shed more light on the nature of the observed Ly α absorption during transits of HD 209458b and to quantify the major mechanisms responsible for the production of fast hydrogen atoms (the so-called energetic neutral atoms, ENAs) around the planet, 2D hydrodynamic multifluid modeling of the expanding planetary upper atmosphere, which is driven by stellar XUV, and its interaction with the stellar wind has been performed. The model self-consistently describes the escaping planetary wind, taking into account the generation of ENAs due to particle acceleration by the radiation pressure and by the charge exchange between the stellar wind protons and planetary atoms. The calculations in a wide range of stellar wind parameters and XUV flux values showed that under typical Sun-like star conditions, the amount of generated ENAs is too small, and the observed absorption at the level of 6%–8% can be attributed only to the non-resonant natural line broadening. For lower XUV fluxes, e.g., during the activity minima, the number of planetary atoms that survive photoionization and give rise to ENAs increases, resulting in up to 10%–15% absorption at the blue wing of the Ly α line, caused by resonant thermal line broadening. A similar asymmetric absorption can be seen under the conditions realized during coronal mass ejections, when sufficiently high stellar wind pressure confines the escaping planetary material within a kind of bowshock around the planet. It was found that the radiation pressure in all considered cases has a negligible contribution to the production of ENAs and the corresponding absorption.},
doi = {10.3847/1538-4357/AA88AD},
journal = {Astrophysical Journal},
number = 2,
volume = 847,
place = {United States},
year = {Sun Oct 01 00:00:00 EDT 2017},
month = {Sun Oct 01 00:00:00 EDT 2017}
}