Volume 543, July 2012
|Number of page(s)||6|
|Section||Stellar structure and evolution|
|Published online||12 July 2012|
The quest for companions to post-common envelope binaries
III. A reexamination of HW Virginis
Institut für Astrophysik, Georg-August-Universität,
2 Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, CT2 7NH, UK
Received: 11 April 2012
Accepted: 11 June 2012
We report new mid-eclipse times of the short-period sdB/dM binary HW Virginis, which differ substantially from the times predicted by a previous model. The proposed orbits of the two planets in that model are found to be unstable. We present a new secularly stable solution, which involves two companions orbiting HW Vir with periods of 12.7 yr and 55 ± 15 yr. For orbits coplanar with the binary, the inner companion is a giant planet with mass M3 sin i3 ≃ 14 MJup and the outer one a brown dwarf or low-mass star with a mass of M4 sin i4 = 30−120 MJup. Using the mercury6 code, we find that such a system would be stable over more than 107 yr, in spite of the sizeable interaction. Our model fits the observed eclipse-time variations by the light-travel time effect alone, without invoking any additional process, and provides support for the planetary hypothesis of the eclipse-time variations in close binaries. The signature of non-Keplerian orbits may be visible in the data.
Key words: planets and satellites: detection / binaries: close / binaries: eclipsing / subdwarfs / stars: individual: HW Virginis
© ESO, 2012
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