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Electron densities and alkali atoms in exoplanet atmospheres | Panayotis Lavvas
; Tommi Koskinen
; Roger V. Yelle
; | Date: |
29 Oct 2014 | Abstract: | We describe a detailed study on the properties of alkali atoms in extrasolar
giant planets, and specifically focus on their role in generating the
atmospheric free electron densities, as well as their impact on the transit
depth observations. We focus our study on the case of HD 209458 b, and we show
that photoionization produces a large electron density in the middle atmosphere
that is about two orders of magnitude larger than the density anticipated from
thermal ionization. Our purely photochemical calculations though result in a
much larger transit depth for K than observed for this planet. This result does
not change even if the roles of molecular chemistry and excited state chemistry
are considered for the alkali atoms. In contrast, the model results for the
case of exoplanet XO-2 b are in good agreement with the available observations.
Given these results we discuss other possible scenarios, such as changes in the
elemental abundances, changes in the temperature profiles, and the possible
presence of clouds, which could potentially explain the observed HD 209458 b
alkali properties. We find that most of these scenarios can not explain the
observations, with the exception of a heterogeneous source (i.e. clouds or
aerosols) under specific conditions, but we also note the discrepancies among
the available observations. | Source: | arXiv, 1410.8102 | Services: | Forum | Review | PDF | Favorites |
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