Ly α Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions
- Space Research Institute, Austrian Academy of Sciences, Graz (Austria)
- Institute of Laser Physics SB RAS, Novosibirsk (Russian Federation)
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.
- OSTI ID:
- 22679795
- Journal Information:
- Astrophysical Journal, Vol. 847, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
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