Revisiting the exoplanet radius valley with host stars from SWEET-Cat

Abstract

The radius valley,a deficit of planets near 2 ${\mathrm{R}}_{\oplus }$, was observed among exoplanets of radius $\lesssim$ 5 ${\mathrm{R}}_{\oplus }$ with periods $<$ 100 days by NASA's $Kepler$ mission. It separates super-Earths (rocky, $\lesssim 1.9$ ${\mathrm{R}}_{\oplus }$) from sub-Neptunes (volatile-rich, $\gtrsim 2$ ${\mathrm{R}}_{\oplus }$) and may arise from formation conditions or atmospheric loss. Disentangling these mechanisms has led to numerous studies of population-level trends, although the resulting interpretations remain sensitive to sample selection and the robustness of host-star parameters. We re-examine its existence, depth, and dependence on period, flux, stellar mass, and age. Using SWEET-Cat and MAISTEP tool, we derived stellar parameters for 1,221 main-sequence stars (1,405 planets), with effective temperatures 4400--7500 K and radii 0.62--2.75 ${\mathrm{R}}_{\odot }$, achieving 2\% precision in radius and mass. Planetary radii were recomputed from radius ratios, yielding 5\% median uncertainty. The valley is partially filled near 2 ${\mathrm{R}}_{\oplus }$ and depends on period, flux, and stellar mass, with slopes $-0.12_{-0.01}^{+0.02}$, $0.10_{-0.03}^{+0.02}$, and $0.19_{-0.07}^{+0.09}$. Sub-Neptunes show a stronger stellar mass-dependent trend than super-Earths ($0.17_{-0.04}^{+0.04}$ vs $0.11_{-0.05}^{+0.05}$). With stellar age, the super-Earth/sub-Neptune ratio rises from $0.51_{-0.08}^{+0.11}$ ($<3$ Gyr) to $0.64_{-0.11}^{+0.11}$ ($\gtrsim 3$ Gyr), and the valley becomes shallower and shifts to larger radii. A 4D fit shows consistent slopes with 2D analyses and a weaker age trend ($0.07_{-0.04}^{+0.03}$). These results suggest prolonged atmospheric loss, which is consistent with a core-powered mass loss scenario and emphasize the need for improved determinations, a goal expected to be achieved by future missions like PLATO.

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