TY - JOUR
T1 - The California-Kepler Survey. X. the Radius Gap as a Function of Stellar Mass, Metallicity, and Age
AU - Petigura, Erik A.
AU - Rogers, James G.
AU - Isaacson, Howard
AU - Owen, James E.
AU - Kraus, Adam L.
AU - Winn, Joshua N.
AU - Macdougall, Mason G.
AU - Howard, Andrew W.
AU - Fulton, Benjamin
AU - Kosiarek, Molly R.
AU - Weiss, Lauren M.
AU - Behmard, Aida
AU - Blunt, Sarah
N1 - Funding Information:
E.A.P. acknowledges support from the following sources: Hubble Fellowship grant HST-HF2-51365.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS 5-26555; a NASA Keck PI Data Award (80NSSC20K0308), administered by the NASA Exoplanet Science Institute; a NASA Astrophysics Data Analysis Program (ADAP) grant (80NSSC20K0457); and the Alfred P. Sloan Foundation.
Funding Information:
The data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency’s scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.
PY - 2022/4/1
Y1 - 2022/4/1
N2 - In 2017, the California-Kepler Survey (CKS) published its first data release (DR1) of high-resolution optical spectra of 1305 planet hosts. Refined CKS planet radii revealed that small planets are bifurcated into two distinct populations, super-Earths (smaller than 1.5 R ⊕) and sub-Neptunes (between 2.0 and 4.0 R ⊕), with few planets in between (the "radius gap"). Several theoretical models of the radius gap predict variation with stellar mass, but testing these predictions is challenging with CKS DR1 due to its limited M ∗ range of 0.8-1.4 M ⊙. Here we present CKS DR2 with 411 additional spectra and derived properties focusing on stars of 0.5-0.8 M ⊙. We found that the radius gap follows R p ∝ P m with m = -0.10 ± 0.03, consistent with predictions of X-ray and ultraviolet- and core-powered mass-loss mechanisms. We found no evidence that m varies with M ∗. We observed a correlation between the average sub-Neptune size and M ∗. Over 0.5-1.4 M ⊙, the average sub-Neptune grows from 2.1 to 2.6 R ⊕, following Rp∝M∗α with α = 0.25 ± 0.03. In contrast, there is no detectable change for super-Earths. These M ∗-R p trends suggest that protoplanetary disks can efficiently produce cores up to a threshold mass of M c , which grows linearly with stellar mass according to M c ≈ 10 M ⊕(M ∗/M ⊙). There is no significant correlation between sub-Neptune size and stellar metallicity (over -0.5 to +0.5 dex), suggesting a weak relationship between planet envelope opacity and stellar metallicity. Finally, there is no significant variation in sub-Neptune size with stellar age (over 1-10 Gyr), which suggests that the majority of envelope contraction concludes after ∼1 Gyr.
AB - In 2017, the California-Kepler Survey (CKS) published its first data release (DR1) of high-resolution optical spectra of 1305 planet hosts. Refined CKS planet radii revealed that small planets are bifurcated into two distinct populations, super-Earths (smaller than 1.5 R ⊕) and sub-Neptunes (between 2.0 and 4.0 R ⊕), with few planets in between (the "radius gap"). Several theoretical models of the radius gap predict variation with stellar mass, but testing these predictions is challenging with CKS DR1 due to its limited M ∗ range of 0.8-1.4 M ⊙. Here we present CKS DR2 with 411 additional spectra and derived properties focusing on stars of 0.5-0.8 M ⊙. We found that the radius gap follows R p ∝ P m with m = -0.10 ± 0.03, consistent with predictions of X-ray and ultraviolet- and core-powered mass-loss mechanisms. We found no evidence that m varies with M ∗. We observed a correlation between the average sub-Neptune size and M ∗. Over 0.5-1.4 M ⊙, the average sub-Neptune grows from 2.1 to 2.6 R ⊕, following Rp∝M∗α with α = 0.25 ± 0.03. In contrast, there is no detectable change for super-Earths. These M ∗-R p trends suggest that protoplanetary disks can efficiently produce cores up to a threshold mass of M c , which grows linearly with stellar mass according to M c ≈ 10 M ⊕(M ∗/M ⊙). There is no significant correlation between sub-Neptune size and stellar metallicity (over -0.5 to +0.5 dex), suggesting a weak relationship between planet envelope opacity and stellar metallicity. Finally, there is no significant variation in sub-Neptune size with stellar age (over 1-10 Gyr), which suggests that the majority of envelope contraction concludes after ∼1 Gyr.
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U2 - 10.3847/1538-3881/ac51e3
DO - 10.3847/1538-3881/ac51e3
M3 - Article
AN - SCOPUS:85127329133
SN - 0004-6256
VL - 163
JO - Astronomical Journal
JF - Astronomical Journal
IS - 4
M1 - 179
ER -