Inverting the m sin i RV exoplanet distribution and comparison with some synthetic population models predictions
Résumé
The detection of an exoplanet orbiting another star with the radial velocity (RV) method allows to determine only a minimum mass of the planet, m sin i, m being the true mass and i the angle of inclination of the planet orbital polar axis with the line-of-sight. Given an observed discretized distribution of m sin i apparent masses f0(m sin i) we have designed a simple algorithm to find a unique true mass distribution f(m) that would reproduce exactly the observed distribution f0(m sin i) . The algorithm will be briefly described. It was applied to the latest sample of RV discovered planets containing 909 planets. The resulting mass distribution is bi-modal, with one peak at ∼8-16 Mearth and the other of giant planets at ∼1,5-3 Mjup. The first peak is an artefact due to non-detection of lighter planets that are below the ∼1 m/s threshold of current best RV surveys. The true mass distribution is most likely increasing with decreasing mass. The second peak is mainly due to a quite populated cluster of planets in the range ∼1,5-3 Mjup and periods in the range ∼100 to 10,000 days. When limiting the mass distribution to periods <100 days, there is a clear so-called sub-Saturn desert, a depleted mass range 0.1 to 0.2 Mjup ( ∼32 to 64 Mearth) seen first in the raw m sin i distribution, and even amplified in the inverted true mass distribution. The addition of the strongly populated cluster of giants in the range ∼0.5-10 Mjup with periods >100 days enhances the sub-Saturn desert. A comparison with a recent synthetic population model indicates the absence in the model of the sub-Saturn desert and of the strongly populated cluster of giants. Focusing on lighter planets, we found a gap of planets in the observed m sin i distribution in the narrow range of 13.7 to 15.2 Mearth which contains Uranus (14.5 Mearth ) and seems to be statistically significant.