Hydrodynamical interaction of stellar and planetary winds: effects of charge exchange and radiation pressure on the observed Ly$alpha$ absorption. (arXiv:1907.04933v1 [astro-ph.EP])

Hydrodynamical interaction of stellar and planetary winds: effects of charge exchange and radiation pressure on the observed Ly$alpha$ absorption. (arXiv:1907.04933v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Esquivel_A/0/1/0/all/0/1">A. Esquivel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schneiter_M/0/1/0/all/0/1">M. Schneiter</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+DAngelo_C/0/1/0/all/0/1">C. Villarreal D&#x27;Angelo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sgro_M/0/1/0/all/0/1">M. A. Sgr&#xf3;</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Krapp_L/0/1/0/all/0/1">L. Krapp</a>

Lyman $alpha$ observations of the transiting exoplanet HD 209458b enable the
study of exoplanets exospheres exposed to stellar EUV fluxes, as well as the
interacting stellar wind properties. In this study we present 3D hydrodynamical
models for the stellar-planetary wind interaction including radiation pressure
and charge exchange, together with photoionization, recombination and
collisional ionization processes. Our models explore the contribution of the
radiation pressure and charge exchange on the Ly$alpha$ absorption profile in
a hydrodynamical framework, and for a single set of stellar wind parameters
appropriate for HD 209458. We find that most of the absorption is produced by
the material from the planet, with a secondary contribution of neutralized
stellar ions by charge exchange. At the same time, the hydrodynamic shock heats
up the planetary material, resulting in a broad thermal profile. Meanwhile, the
radiation pressure yielded a small velocity shift of the absorbing material.
While neither charge exchange nor radiation pressure provide enough neutrals at
the velocity needed to explain the observations at $-100~mathrm{km~s^{-1}}$
individually, we find that the two effects combined with the broad thermal
profile are able to explain the observations.

Lyman $alpha$ observations of the transiting exoplanet HD 209458b enable the
study of exoplanets exospheres exposed to stellar EUV fluxes, as well as the
interacting stellar wind properties. In this study we present 3D hydrodynamical
models for the stellar-planetary wind interaction including radiation pressure
and charge exchange, together with photoionization, recombination and
collisional ionization processes. Our models explore the contribution of the
radiation pressure and charge exchange on the Ly$alpha$ absorption profile in
a hydrodynamical framework, and for a single set of stellar wind parameters
appropriate for HD 209458. We find that most of the absorption is produced by
the material from the planet, with a secondary contribution of neutralized
stellar ions by charge exchange. At the same time, the hydrodynamic shock heats
up the planetary material, resulting in a broad thermal profile. Meanwhile, the
radiation pressure yielded a small velocity shift of the absorbing material.
While neither charge exchange nor radiation pressure provide enough neutrals at
the velocity needed to explain the observations at $-100~mathrm{km~s^{-1}}$
individually, we find that the two effects combined with the broad thermal
profile are able to explain the observations.

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