Transiting exoplanets from the CoRoT space mission VIII. CoRoT-7b: the first Super-Earth with measured radius

We report the discovery of very shallow (DF/F = 3.4 10-4), periodic dips in the light curve of an active V = 11.7 G9V star observed by the CoRoT satellite, which we interpret as due to the presence of a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion. Methods. We use CoRoT color information, good angular resolution ground-based photometric observations in- and out- of transit, adaptive optics imaging, near-infrared spectroscopy and preliminary results from Radial Velocity measurements, to test the diluted eclipsing binary scenarios. The parameters of the host star are derived from optical spectra, which were then combined with the CoRoT light curve to derive parameters of the companion. We examine carefully all conceivable cases of false positives, and all tests performed support the planetary hypothesis. Blends with separation larger than 0.40 arcsec or triple systems are almost excluded with a 8 10-4 risk left. We conclude that, as far as we have been exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which we derive a period of 0.853 59 +/- 3 10-5 day and a radius of Rp = 1.68 +/- 0.09 REarth. Analysis of preliminary radial velocity data yields an upper limit of 21 MEarth for the companion mass, supporting the finding. CoRoT-7b is very likely the first Super-Earth with a measured radius.

💡 Research Summary

The paper reports the discovery and validation of CoRoT‑7b, the first super‑Earth with a directly measured radius, using data from the CoRoT space mission complemented by extensive ground‑based follow‑up. The target is an active G9V star of V = 11.7 mag. CoRoT’s three‑colour photometry revealed periodic, extremely shallow dips in the light curve with a depth of ΔF/F = 3.4 × 10⁻⁴ and a period of 0.85359 ± 3 × 10⁻⁵ days. The authors first confirmed that the transit depth is identical in the red, green, and blue channels, ruling out colour‑dependent eclipsing binaries.

Ground‑based photometry obtained in and out of transit showed that no nearby star within 0.4 arcsec exhibits the same variability, and high‑resolution adaptive‑optics imaging pushed the detection limit down to 0.1 arcsec, effectively excluding any contaminating companion brighter than Δmag ≈ 5. Near‑infrared spectroscopy provided precise stellar parameters: T_eff ≈ 5250 K, log g ≈ 4.5,