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Reconstructing the high-energy irradiation of the evaporating hot Jupiter HD 209458b
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Louden, Tom M., Wheatley, Peter J. and Briggs, Kevin (2017) Reconstructing the high-energy irradiation of the evaporating hot Jupiter HD 209458b. Monthly Notices of the Royal Astronomical Society, 464 (2). pp. 2396-2402. doi:10.1093/mnras/stw2421 ISSN 0035-8711.
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Official URL: https://doi.org/10.1093/mnras/stw2421
Abstract
The atmosphere of the exoplanet HD 209458b is undergoing sustained mass loss, believed to be caused by X-ray and extreme-ultraviolet (XUV) irradiation from its star. The majority of this flux is not directly observable due to interstellar absorption, but is required in order to correctly model the photo-evaporation of the planet and photo-ionisation of the outflow. We present a recovered high energy spectrum for HD 209458 using a Differential Emission Measure (DEM) retrieval technique. We construct a model of the stellar corona and transition region for temperatures between 10^4.1 and 10^8 K which is constrained jointly by ultraviolet line strengths measured with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) and X-ray flux measurements from XMM-Newton. The total hydrogen ionising luminosity (λ<912 A) is found to be 10^28.26 erg s−1, which is similar to the value for the mean activity level of the Sun. This luminosity is incompatible with energy limited mass loss rates estimated from the same COS dataset, even the lower bound requires an uncomfortably high energetic efficiency of >40%. However, our luminosity is compatible with early estimates of the mass loss rate of HD 209458b based on results from the HST Space Telescope Imaging Spectrograph (STIS). Precisely reconstructed XUV irradiation is a key input to determining mass loss rates and efficiencies for exoplanet atmospheres.
Item Type: | Journal Article | |||||||||||||||
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Subjects: | Q Science > QB Astronomy | |||||||||||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | |||||||||||||||
Library of Congress Subject Headings (LCSH): | Extrasolar planets -- Atmospheres, Stellar activity, Stars -- Corona | |||||||||||||||
Journal or Publication Title: | Monthly Notices of the Royal Astronomical Society | |||||||||||||||
Publisher: | Oxford University Press | |||||||||||||||
ISSN: | 0035-8711 | |||||||||||||||
Official Date: | 11 January 2017 | |||||||||||||||
Dates: |
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Volume: | 464 | |||||||||||||||
Number: | 2 | |||||||||||||||
Page Range: | pp. 2396-2402 | |||||||||||||||
DOI: | 10.1093/mnras/stw2421 | |||||||||||||||
Status: | Peer Reviewed | |||||||||||||||
Publication Status: | Published | |||||||||||||||
Access rights to Published version: | Restricted or Subscription Access | |||||||||||||||
Date of first compliant deposit: | 10 July 2018 | |||||||||||||||
Date of first compliant Open Access: | 10 July 2018 | |||||||||||||||
RIOXX Funder/Project Grant: |
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