Prof Suzanne Aigrain

Abstract:

This paper presents the case of CoRoT LRa02-E2-0121, which was initially classified as a Neptune-size transiting-planet candidate on a relatively wide orbit of 36.3 days. Follow-up observations were performed with UVES, Sandiford, SOPHIE, and HARPS. These observations revealed a faint companion in the spectra. To find the true nature of the system we derived the radial velocities of the faint companion using TODMOR-a two-dimensional correlation technique, applied to the SOPHIE spectra. Modeling the lightcurve with EBAS we discovered a secondary eclipse with a depth of∼0.07%, indicating a diluted eclipsing binary. Combined MCMC modeling of the lightcurve and the radial velocities suggested that CoRoT LRa02-E2-0121 is a hierarchical triple system with an evolved G-type primary and an A-type:F-type grazing eclipsing binary. Such triple systems are difficult to discover. © 2011 ESO.

Abstract:

We report the detection of CoRoT-18b, a massive hot Jupiter transiting in front of its host star with a period of 1.9000693 ± 0.0000028 days. This planet was discovered thanks to photometric data secured with the CoRoT satellite combined with spectroscopic and photometric ground-based follow-up observations. The planet has a mass Mp = 3.47 ± 0.38M Jup, a radius Rp = 1.31 ± 0.18RJup, and a density ρp = 2.2 ± 0.8 g cm-3. It orbits a G9V star with a mass M = 0.95 ± 0.15 M, a radius R = 1.00 ± 0.13 R, and arotation period Prot = 5.4 ± 0.4 days. The age of the system remains uncertain, with stellar evolution models pointing either to a few tens Ma or several Ga, while gyrochronology and lithium abundance point towards ages of a few hundred Ma. This mismatch potentially points to a problem in our understanding of the evolution of young stars, with possibly significant implications for stellar physics and the interpretation of inferred sizes of exoplanets around young stars. We detected the Rossiter-McLaughlin anomaly in the CoRoT-18 system thanks to the spectroscopic observation of a transit. We measured the obliquity ψ = 20° ± 20° (sky-projected value λ =-10° ± 20°), indicating that the planet orbits in the same way as the star is rotating and that this prograde orbit is nearly aligned with the stellar equator. © 2011 ESO.