A Spectroscopic Analysis of the California-Kepler Survey Sample: I. Stellar Parameters, Planetary Radii and a Slope in the Radius Gap. (arXiv:1903.00174v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Martinez_C/0/1/0/all/0/1">Cintia F. Martinez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cunha_K/0/1/0/all/0/1">Katia Cunha</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ghezzi_L/0/1/0/all/0/1">Luan Ghezzi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_V/0/1/0/all/0/1">Verne V. Smith</a>
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$_{rm eff}$) 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.
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$_{rm eff}$) 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.
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