An asteroseismic view of the radius valley: stripped cores, not born rocky

October 2018 • 2018MNRAS.479.4786V

Authors • Van Eylen, V. • Agentoft, Camilla • Lundkvist, M. S. • Kjeldsen, H. • Owen, J. E. • Fulton, B. J. • Petigura, E. • Snellen, I.

Abstract • 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_\oplus. 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_\oplus) and sub-Neptunes (≈2.5 R_⊕) separated by a deficiency around 2 R_\oplus. 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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2018MNRAS.479.4786V
• PDF http://academic.oup.com/mnras/pdf-lookup/doi/10.1093/mnras/sty1783
• PREPRINT http://arxiv.org/abs/1710.05398
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2018MNRAS.479.4786V
• ELECTR https://doi.org/10.1093%2Fmnras%2Fsty1783