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The stellar wind cycles and planetary radio emission of the τ Boo system

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1204.3843v1 (1.053Mb)
Date
11/07/2012
Author
Vidotto, Aline
Fares, Rim
Jardine, Moira Mary
Donati, J.-F.
Opher, M.
Moutou, C.
Catala, C.
Gombosi, T. I.
Funder
Science & Technology Facilities Council
Grant ID
ST/J001651/1
Keywords
MHD
Methods: Numerical
Stars: individual: Tau Bootis
Stars: magnetic field
Stars: winds, outflows
Radio continuum: planetary systems
QB Astronomy
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Abstract
Tau Boo is an intriguing planet-host star that is believed to undergo magnetic cycles similar to the Sun, but with a duration that is about one order of magnitude smaller than that of the solar cycle. With the use of observationally derived surface magnetic field maps, we simulate the magnetic stellar wind of Tau Boo by means of three-dimensional MHD numerical simulations. As the properties of the stellar wind depend on the particular characteristics of the stellar magnetic field, we show that the wind varies during the observed epochs of the cycle. Although the mass loss-rates we find (~2.7×10-12 Msun/yr-1) vary less than 3 per cent during the observed epochs of the cycle, our derived angular momentum loss-rates vary from 1.1 to 2.2×1032erg. The spin-down times associated to magnetic braking range between 39 and 78Gyr. We also compute the emission measure from the (quiescent) closed corona and show that it remains approximately constant through these epochs at a value of ~1050.6 cm-3. This suggests that a magnetic cycle of Tau Boo may not be detected by X-ray observations. We further investigate the interaction between the stellar wind and the planet by estimating radio emission from the hot-Jupiter that orbits at 0.0462 au from Tau Boo. By adopting reasonable hypotheses, we show that, for a planet with a magnetic field similar to Jupiter (~14G at the pole), the radio flux is estimated to be about 0.5-1 mJy, occurring at a frequency of 34MHz. If the planet is less magnetised (field strengths roughly Earths ionospheric cutoff. According to our estimates, if the planet is more magnetised than that and provided the emission beam crosses the observer line-of-sight, detection of radio emission from Tau Boo b is only possible by ground-based instruments with a noise level of ≤ 1 mJy, operating at low frequencies.
Citation
Vidotto , A , Fares , R , Jardine , M M , Donati , J-F , Opher , M , Moutou , C , Catala , C & Gombosi , T I 2012 , ' The stellar wind cycles and planetary radio emission of the τ Boo system ' , Monthly Notices of the Royal Astronomical Society , vol. 423 , no. 4 , pp. 3285-3298 . https://doi.org/10.1111/j.1365-2966.2012.21122.x
Publication
Monthly Notices of the Royal Astronomical Society
Status
Peer reviewed
DOI
https://doi.org/10.1111/j.1365-2966.2012.21122.x
ISSN
0035-8711
Type
Journal article
Rights
This is an author version of the article © 2012 The Authors Monthly Notices of the Royal Astronomical Society. The definitive version (c) 2012 RAS is available at www.blackwell-synergy.com
Description
15 pages, 10 figures
Collections
  • University of St Andrews Research
URL
http://arxiv.org/abs/1204.3843v1
URI
http://hdl.handle.net/10023/3256

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