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Hα Absorption in Transiting Exoplanet Atmospheres

Published online by Cambridge University Press:  06 January 2014

Duncan Christie ,
Phil Arras  and
Zhi-Yun Li
Duncan Christie
Affiliation:
Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, Virginia, USA email: dac5zm@virginia.edu, pla7y@virginia.edu, zl4h@virginia.edu
Phil Arras
Affiliation:
Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, Virginia, USA email: dac5zm@virginia.edu, pla7y@virginia.edu, zl4h@virginia.edu
Zhi-Yun Li
Affiliation:
Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, Virginia, USA email: dac5zm@virginia.edu, pla7y@virginia.edu, zl4h@virginia.edu
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Abstract

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Recent observations by Jensen et al. of Hα absorption by the upper atmosphere of HD189733b have motivated the need for a theoretical understanding of the distribution of n=2 hydrogen within hot Jupiter atmospheres. With this in mind, we model the n=2 state of atomic hydrogen in a hydrostatic atmosphere in thermal and photoionization equilibrium. Both collisional and radiative transitions are included in the calculation of the n = 2 state level population. In our model, the Hα absorption is dominated by a τ ~ 1 shell composed of metastable 2s hydrogen located within the neutral atomic layer, with the contribution coming roughly uniformly throughout the layer instead of from a specific impact parameter. An ionization rate an order of magnitude over the expected value can reproduce the observed transit depth.

Keywords

line: formation – planets and satellites: atmospheres – stars: individual (HD 189733, HD 209458)

References

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Trammell, G. B., Arras, P., & Li, Z.-Y. 2011, ApJ, 728, 152Google Scholar
Vidal-Madjar, A., Lecavelier des Etangs, A., Désert, J.-M., et al. 2003, Nature, 422, 143Google Scholar