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Evidence for an increase in the occurrence rate of hot sub-Neptunes at young ages with K2

Presentation #403.07 in the session Exoplanets Formation & Evolution (Oral Presentation)

Published onOct 23, 2023
Evidence for an increase in the occurrence rate of hot sub-Neptunes at young ages with K2

The NASA K2 mission obtained high precision time-series photometry of four young clusters, including the 600–700 My-old Praesepe cluster. Using our automated transit detection pipeline, we recover 10 planet candidates from the ~1000 members of the Praesepe cluster, seven of which are already confirmed planets. We find an occurrence rate of 79–107% for small (1.7-4.0 Re), short-period (1-10 days) hot sub-Neptunes orbiting GKM stars. This is 2.5–3.5 sigma higher than the occurrence rate of 16.54+0.0100−0.0098% for the same planets orbiting >Gyr-old GKM field stars observed by K2, even after accounting for the slightly super-solar metallicity ([Fe/H]~0.2 dex) of the Praesepe cluster. We examine the effect of adding ~100 targets from the 600-700 Myr-old Hyades cluster, and extending the planet parameter space under examination, and find similarly high occurrence rates. The significantly higher occurrence rate of hot sub-Neptunes in these young clusters could indicate one of two things: either, that these planets are undergoing some evolution as they age, or, that the planets forming in these clusters have primordial formation differences. Under the assumption of the planet evolution scenario, a significantly higher occurrence rate of these planets at intermediate ages strongly favors the core-powered mass loss scenario as sculpting the population of hot sub-Neptunes, as compared to the photoevaporation scenario.

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