A Spectroscopic Analysis of the California-Kepler Survey Sample: I. Stellar Parameters, Planetary Radii and a Slope in the Radius Gap

Abstract

We present results from a quantitative spectroscopic analysis conducted on archival Keck/HIRES high-resolution spectra from the California-$Kepler$ Survey (CKS) sample of transiting planetary host stars identified from the $Kepler$ mission. The spectroscopic analysis was based on a carefully selected set of Fe I and Fe II lines, resulting in precise values for the stellar parameters of effective temperature (T${}_{\mathrm{eff}}$) and surface gravity (log $g$). Combining the stellar parameters with $Gaia$ DR2 parallaxes and precise distances, we derived both stellar and planetary radii for our sample, with a median internal uncertainty of 2.8$\%$ in the stellar radii and 3.7$\%$ in the planetary radii. An investigation into the distribution of planetary radii confirmed the bimodal nature of this distribution for the small radius planets found in previous studies, with peaks at: $\sim$1.47 $\pm$ 0.05 R${}_{\oplus }$ and $\sim$2.72 $\pm$ 0.10 R${}_{\oplus }$, with a gap at $\sim$ 1.9R${}_{\oplus }$. Previous studies that modeled planetary formation that is dominated by photo-evaporation predicted this bimodal radii distribution and the presence of a radius gap, or photo-evaporation valley. Our results are in overall agreement with these models. The high internal precision achieved here in the derived planetary radii clearly reveal the presence of a slope in the photo-evaporation valley for the CKS sample, indicating that the position of the radius gap decreases with orbital period; this decrease was fit by a power law of the form R${}_{pl}$ $\propto$ P${}^{-0.11}$, which is consistent with photo-evaporation and Earth-like core composition models of planet formation.

33 pages, 13 figures

References in corpus (11)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The Dartmouth Stellar Evolution Database
• Most 1.6 Earth-Radius Planets are not Rocky
• Accurate, Empirical Radii and Masses of Planets and their Host Stars with Gaia Parallaxes
• Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation
• Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes
• ARES v2 - new features and improved performance
• A Statistical Reconstruction of the Planet Population Around Kepler Solar-Type Stars
• The First APOKASC Catalog of Kepler Dwarf and Subgiant Stars
• A Super-Solar Metallicity For Stars With Hot Rocky Exoplanets
• Metallicities of Planet Hosting Stars: A Sample of Giants and Subgiants

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• A Spectroscopic Analysis of the California-Kepler Survey Sample: II. Correlations of Stellar Metallicities with Planetary Architectures
• Rotation periods of TESS Objects of Interest from the Magellan-TESS Survey with multiband photometry from Evryscope and TESS
• Identifying Exo-Earth Candidates in Direct Imaging Data through Bayesian Classification
• Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting planets I. Detailed characterization of multi-planet systems Kepler-278 and Kepler-391
• A super-Earth and a mini-Neptune around Kepler-59
• The Mass Budgets and Spatial Scales of Exoplanet Systems and Protoplanetary Disks