Planets and stellar activity: hide and seek in the CoRoT-7 system

R. D. Haywood*, A. Collier Cameron, D. Queloz, S. C. C. Barros, M. Deleuil, R. Fares, M. Gillon, A. F. Lanza, C. Lovis, C. Moutou, F. Pepe, D. Pollacco, A. Santerne, D. Segransan, Y. C. Unruh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

213 Citations (Scopus)
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Abstract

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.

Original languageEnglish
Pages (from-to)2517-2531
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Volume443
Issue number3
Early online date31 Jul 2014
DOIs
Publication statusPublished - 21 Sept 2014

Keywords

  • Techniques: radial velocities
  • Stars: activity
  • Stars: individual: CoRoT-7
  • Planetary systems
  • Radial-velocity variations
  • Super-Earths
  • Sum
  • Star
  • Mass
  • Periodogram
  • Impact
  • Spots

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