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Early UV ingress in WASP-12b: measuring planetary magnetic fields

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vidotto2010astrophyjlettl168.pdf (263.2Kb)
Date
20/10/2010
Author
Vidotto, A. A.
Jardine, M.
Helling, Ch.
Keywords
Planet-star interactions
Planets and satellites: individual (WASP-12b)
Planets and satellites: magnetic fields
Stars: coronae
Stars: individual (WASP-12)
Stars: winds, outflows
Extrasolar planet
Mass
Evaporation
HD209458B
Exosphere
QC Physics
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Abstract
Recently, Fossati et al. observed that the UV transit of WASP-12b showed an early ingress compared with the optical transit. We suggest that the resulting early ingress is caused by a bow shock ahead of the planetary orbital motion. In this Letter, we investigate the conditions that might lead to the formation of such a bow shock. We consider two scenarios: (1) the stellar magnetic field is strong enough to confine the hot coronal plasma out to the planetary orbit and (2) the stellar magnetic field is unable to confine the plasma, which escapes in a wind. In both cases, a shock capable of compressing plasma to the observed densities will form around the planet for plasma temperatures T less than or similar to (4-5) x 10(6) K. In the confined case, the shock always forms directly ahead of the planet, but in the wind case the shock orientation depends on the wind speed and hence on the plasma temperature. For higher wind temperatures, the shock forms closer to the line of centers between the planet and the star. We conclude that shock formation leading to an observable early UV ingress is likely to be a common feature of transiting systems and may prove to be a useful tool in setting limits on planetary magnetic field strengths B-p. In the case of WASP-12b, we derive an upper limit of about B-p = 24 G.
Citation
Vidotto , A A , Jardine , M & Helling , C 2010 , ' Early UV ingress in WASP-12b: measuring planetary magnetic fields ' , Astrophysical Journal Letters , vol. 722 , no. 2 , pp. L168-L172 . https://doi.org/10.1088/2041-8205/722/2/L168
Publication
Astrophysical Journal Letters
Status
Peer reviewed
DOI
https://doi.org/10.1088/2041-8205/722/2/L168
ISSN
2041-8205
Type
Journal article
Rights
© 2010. The American Astronomical Society. All rights reserved.
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  • University of St Andrews Research
URL
http://adsabs.harvard.edu/abs/2010ApJ...722L.168V
URI
http://hdl.handle.net/10023/4738

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