Transiting Exoplanets From The CoRoT Space Mission: XXVI. CoRoT-24: a transiting multiplanet system
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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 11.76 d 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 +/- 0.4 and 5.0 +/- 0.5 R-circle plus, respectively. Several radial velocities serve to provide an upper limit of 5.7 M-circle plus for the 5.11 d signal and to tentatively measure a mass of 28(-11)(+11); M-circle plus 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 serves to estimate the probability that the observations are caused by transiting Neptune-sized planets as much as over 26 times higher than a blend scenario involving only one transiting planet and as much as over 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 AU from the host, but more data are required to determine the precise orbital parameters of this companion.