SIMBAD references

Various theoretical models treating the effect of stellar irradiation on planetary envelopes predict the presence of a radius valley, i.e. a bimodal distribution of planet radii, with super-Earths and sub-Neptune planets separated by a valley at around ~2 R_⊕. Such a valley has been observed recently, owing to an improvement in the precision of stellar and therefore planetary radii. Here, we investigate the presence, location, and shape of such a valley using a small sample with highly accurate stellar parameters determined from asteroseismology, which includes 117 planets with a median uncertainty on the radius of 3.3 per cent. We detect a clear bimodal distribution, with super-Earths (~1.5 R_⊕) and sub-Neptunes (≃2.5 R_⊕) separated by a deficiency around 2 R_⊕. We furthermore characterize the slope of the valley as a power law R∝P^γ with γ= -0.09^+0.02_–0.04. A negative slope is consistent with models of photoevaporation, but not with the late formation of rocky planets in a gas-poor environment, which would lead to a slope of opposite sign. The exact location of the gap further points to planet cores consisting of a significant fraction of rocky material.