Transiting exoplanets from the CoRoT space mission: XXVI. CoRoT-24: A transiting multi-planet system

TL;DR

This paper reports the discovery of a multi-planet transiting system around a K1V star from the CoRoT mission, with detailed photometric and spectroscopic analysis supporting the planetary nature of the signals.

Contribution

First detection of a multiply-transiting system in the CoRoT mission, with detailed analysis confirming two Neptune-sized planets and a possible additional giant planet.

Findings

Two transiting objects of 3.7 and 5.0 Earth radii detected.

Radial velocity data suggest low-density, gaseous Neptune-sized planets.

Evidence for a possible 1.5 Jupiter-mass planet at 1.8 AU.

Abstract

We present the discovery of a candidate multiply-transiting system, the first one found in the CoRoT mission. Two transit-like features with periods of 5.11 and 11.76d are detected in the CoRoT light curve, around a main sequence K1V star of r=15.1. If the features are due to transiting planets around the same star, these would correspond to objects of 3.7$\pm$0.4 and 5.0$\pm$0.5 R_earth respectively. Several radial velocities serve to provide an upper limit of 5.7 M_earth for the 5.11~d signal, and to tentatively measure a mass of 28$^{+11}_{-11}$ M_earth for the object transiting with a 11.76~d period. These measurements imply low density objects, with a significant gaseous envelope. The detailed analysis of the photometric and spectroscopic data serve to estimate the probability that the observations are caused by transiting Neptune-sized planets as $>$26$\times$ higher than a blend scenario involving only one transiting planet, and $>$900$\times$ higher than a scenario involving two blends and no planets. The radial velocities show a long term modulation that might be attributed to a 1.5 M_jup planet orbiting at 1.8~A.U. from the host, but more data are required to determine the precise orbital parameters of this companion.