Imperial College London
Dr Yvonne Unruh

DrYvonneUnruh

Faculty of Natural Sciences, Department of Physics

Reader in Astrophysics
 
 
 
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Contact

 

y.unruh Website

 
 
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Location

 

1114Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Citation

BibTex format

@article{Chadney:2017:0004-6361/201731129,
author = {Chadney, JM and Koskinen, TT and Galand, M and Unruh, YC and Sanz-Forcada, J},
doi = {0004-6361/201731129},
journal = {Astronomy and Astrophysics},
title = {Effect of stellar flares on the upper atmospheres of HD 189733b and HD  209458b},
url = {http://dx.doi.org/10.1051/0004-6361/201731129},
volume = {608},
year = {2017}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - Stellar flares are a frequent occurrence on young low-mass stars around whichmany detected exoplanets orbit. Flares are energetic, impulsive events, andtheir impact on exoplanetary atmospheres needs to be taken into account wheninterpreting transit observations. We have developed a model to describe theupper atmosphere of Extrasolar Giant Planets (EGPs) orbiting flaring stars. Themodel simulates thermal escape from the upper atmospheres of close-in EGPs.Ionisation by solar radiation and electron impact is included and photochemicaland diffusive transport processes are simulated. This model is used to studythe effect of stellar flares from the solar-like G star HD209458 and the youngK star HD189733 on their respective planets. A hypothetical HD209458b-likeplanet orbiting the active M star AU Mic is also simulated. We find that theneutral upper atmosphere of EGPs is not significantly affected by typicalflares. Therefore, stellar flares alone would not cause large enough changes inplanetary mass loss to explain the variations in HD189733b transit depth seenin previous studies, although we show that it may be possible that an extremestellar proton event could result in the required mass loss. Our simulations dohowever reveal an enhancement in electron number density in the ionosphere ofthese planets, the peak of which is located in the layer where stellar X-raysare absorbed. Electron densities are found to reach 2.2 to 3.5 times pre-flarelevels and enhanced electron densities last from about 3 to 10 hours after theonset of the flare. The strength of the flare and the width of its spectralenergy distribution affect the range of altitudes that see enhancements inionisation. A large broadband continuum component in the XUV portion of theflaring spectrum in very young flare stars, such as AU Mic, results in a broadrange of altitudes affected in planets orbiting this star.
AU  - Chadney,JM
AU  - Koskinen,TT
AU  - Galand,M
AU  - Unruh,YC
AU  - Sanz-Forcada,J
DO  - 0004-6361/201731129
PY  - 2017///
SN  - 0004-6361
TI  - Effect of stellar flares on the upper atmospheres of HD 189733b and HD  209458b
T2  - Astronomy and Astrophysics
UR  - http://dx.doi.org/10.1051/0004-6361/201731129
UR  - http://hdl.handle.net/10044/1/54913
VL  - 608
ER  -
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