Planets and stellar activity : hide and seek in the CoRoT-7 system
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Since the discovery of the transiting super-Earth CoRoT-7b, several investigations have yielded different results for the number and masses of planets present in the system, mainly owing to the star's high level of activity. We re-observed CoRoT-7 in 2012 January with both HARPS and CoRoT, so that we now have the benefit of simultaneous radial-velocity and photometric data. This allows us to use the off-transit variations in the star's light curve to estimate the radial-velocity variations induced by the suppression of convective blueshift and the flux blocked by starspots. To account for activity-related effects in the radial velocities which do not have a photometric signature, we also include an additional activity term in the radial-velocity model, which we treat as a Gaussian process with the same covariance properties (and hence the same frequency structure) as the light curve. Our model was incorporated into a Monte Carlo Markov Chain in order to make a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We measure the masses of planets b and c to be 4.73 ± 0.95 and 13.56 ± 1.08 M⊕, respectively. The density of CoRoT-7b is (6.61 ± 1.72)(Rp/1.58 R⊕)−3 g cm−3, which is compatible with a rocky composition. We search for evidence of an additional planet d, identified by previous authors with a period close to 9 d. We are not able to confirm the existence of a planet with this orbital period, which is close to the second harmonic of the stellar rotation at ∼7.9 d. Using Bayesian model selection, we find that a model with two planets plus activity-induced variations is most favoured.
Haywood , R D , Cameron , A C , Queloz , D , Barros , S C C , Deleuil , M , Fares , R , Gillon , M , Lanza , A F , Lovis , C , Moutou , C , Pepe , F , Pollacco , D , Santerne , A , Segransan , D & Unruh , Y C 2014 , ' Planets and stellar activity : hide and seek in the CoRoT-7 system ' Monthly Notices of the Royal Astronomical Society , vol 443 , no. 3 , pp. 2517-2531 . DOI: 10.1093/mnras/stu1320
Monthly Notices of the Royal Astronomical Society
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2014 The Authors, Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
RDH acknowledges support from an STFC postgraduate research studentship. RF acknowledges support from STFC consolidated grant number ST/J001651/1. SCCB acknowledges support by CNES, grant number 98761. AS acknowledges the support by the European Research Council/European Community under the FP7 through Starting Grant agreement number 239953.
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