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XUV-driven mass loss from extrasolar giant planets orbiting active stars

XUV-driven mass loss from extrasolar giant planets orbiting active stars
XUV-driven mass loss from extrasolar giant planets orbiting active stars
Upper atmospheres of Hot Jupiters are subject to extreme radiation conditions that can result in rapid atmospheric escape. The composition and structure of the upper atmospheres of these planets are affected by the high-energy spectrum of the host star. This emission depends on stellar type and age, which are thus important factors in understanding the behaviour of exoplanetary atmospheres. In this study, we focus on Extrasolar Giant Planets (EPGs) orbiting K and M dwarf stars. XUV spectra for three different stars – ∊ Eridani, AD Leonis and AU Microscopii – are constructed using a coronal model. Neutral density and temperature profiles in the upper atmosphere of hypothetical EGPs orbiting these stars are then obtained from a fluid model, incorporating atmospheric chemistry and taking atmospheric escape into account. We find that a simple scaling based solely on the host star’s X-ray emission gives large errors in mass loss rates from planetary atmospheres and so we have derived a new method to scale the EUV regions of the solar spectrum based upon stellar X-ray emission. This new method produces an outcome in terms of the planet’s neutral upper atmosphere very similar to that obtained using a detailed coronal model of the host star. Our results indicate that in planets subjected to radiation from active stars, the transition from Jeans escape to a regime of hydrodynamic escape at the top of the atmosphere occurs at larger orbital distances than for planets around low activity stars (such as the Sun).
0019-1035
Chadney, Joshua
4209e45f-6092-4c9d-b46b-4b598269a0f3
Galand, Marina
083b2513-57ab-4b08-88e4-ba759f290c98
Unruh, Yvonne
c8e151aa-e9d2-43e1-bcde-c12a25f31368
Koskinen, Tommi
fd4b7af2-f84b-46ba-9dee-223eb741cf05
Sanz-Forcada, Jorge
ad1239b8-b31b-418b-a96c-23b44922cfc4
Chadney, Joshua
4209e45f-6092-4c9d-b46b-4b598269a0f3
Galand, Marina
083b2513-57ab-4b08-88e4-ba759f290c98
Unruh, Yvonne
c8e151aa-e9d2-43e1-bcde-c12a25f31368
Koskinen, Tommi
fd4b7af2-f84b-46ba-9dee-223eb741cf05
Sanz-Forcada, Jorge
ad1239b8-b31b-418b-a96c-23b44922cfc4

Chadney, Joshua, Galand, Marina, Unruh, Yvonne, Koskinen, Tommi and Sanz-Forcada, Jorge (2015) XUV-driven mass loss from extrasolar giant planets orbiting active stars. Icarus, 250. (doi:10.1016/j.icarus.2014.12.012).

Record type: Article

Abstract

Upper atmospheres of Hot Jupiters are subject to extreme radiation conditions that can result in rapid atmospheric escape. The composition and structure of the upper atmospheres of these planets are affected by the high-energy spectrum of the host star. This emission depends on stellar type and age, which are thus important factors in understanding the behaviour of exoplanetary atmospheres. In this study, we focus on Extrasolar Giant Planets (EPGs) orbiting K and M dwarf stars. XUV spectra for three different stars – ∊ Eridani, AD Leonis and AU Microscopii – are constructed using a coronal model. Neutral density and temperature profiles in the upper atmosphere of hypothetical EGPs orbiting these stars are then obtained from a fluid model, incorporating atmospheric chemistry and taking atmospheric escape into account. We find that a simple scaling based solely on the host star’s X-ray emission gives large errors in mass loss rates from planetary atmospheres and so we have derived a new method to scale the EUV regions of the solar spectrum based upon stellar X-ray emission. This new method produces an outcome in terms of the planet’s neutral upper atmosphere very similar to that obtained using a detailed coronal model of the host star. Our results indicate that in planets subjected to radiation from active stars, the transition from Jeans escape to a regime of hydrodynamic escape at the top of the atmosphere occurs at larger orbital distances than for planets around low activity stars (such as the Sun).

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Accepted/In Press date: 7 December 2014
e-pub ahead of print date: 19 December 2014
Published date: April 2015

Identifiers

Local EPrints ID: 415038
URI: https://eprints.soton.ac.uk/id/eprint/415038
ISSN: 0019-1035
PURE UUID: d95e6706-b026-45de-a109-67001d214427
ORCID for Joshua Chadney: ORCID iD orcid.org/0000-0002-5174-2114

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Date deposited: 23 Oct 2017 16:30
Last modified: 20 Jul 2019 00:33

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Contributors

Author: Joshua Chadney ORCID iD
Author: Marina Galand
Author: Yvonne Unruh
Author: Tommi Koskinen
Author: Jorge Sanz-Forcada

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