An asteroseismic view of the radius valley: stripped cores, not born rocky. Issue 4 (6th July 2018)

• Record Type: Journal Article
• Authors: Van Eylen, V; Agentoft, Camilla; Lundkvist, M S; Kjeldsen, H; Owen, J E; Fulton, B J; Petigura, E; Snellen, I
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 479:Issue 4(2018)
• Page Start: 4786
• Page End: 4795
• Publication Date: 2018-07-06
• Subjects: planets and satellites: composition -- planets and satellites: formation -- planets and satellites: fundamental parameters -- planets and satellites: physical evolution; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty1783
• Languages: English
• ISSNs: 0035-8711

Abstract

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 ${\approx } 2\, \text{R}_\oplus$ . 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 (${\approx } 1.5\, \text{R}_\oplus$ ) and sub-Neptunes (≈2.5 R⊕ ) separated by a deficiency around $2\, \text{R}_\oplus$ . We furthermore characterize the slope of the valley as a power law R ∝ P γ with $\gamma = {-0.09^{+0.02}_{-0.04}}$ . 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.