- ID:
- ivo://CDS.VizieR/J/AJ/154/108
- Title:
- California-Kepler Survey (CKS). II. Properties
- Short Name:
- J/AJ/154/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar and planetary properties for 1305 Kepler Objects of Interest hosting 2025 planet candidates observed as part of the California-Kepler Survey. We combine spectroscopic constraints, presented in Paper I, with stellar interior modeling to estimate stellar masses, radii, and ages. Stellar radii are typically constrained to 11%, compared to 40% when only photometric constraints are used. Stellar masses are constrained to 4%, and ages are constrained to 30%. We verify the integrity of the stellar parameters through comparisons with asteroseismic studies and Gaia parallaxes. We also recompute planetary radii for 2025 planet candidates. Because knowledge of planetary radii is often limited by uncertainties in stellar size, we improve the uncertainties in planet radii from typically 42% to 12%. We also leverage improved knowledge of stellar effective temperature to recompute incident stellar fluxes for the planets, now precise to 21%, compared to a factor of two when derived from photometry.
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- ID:
- ivo://CDS.VizieR/J/AJ/154/107
- Title:
- California-Kepler Survey (CKS). I. 1305 stars
- Short Name:
- J/AJ/154/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The California-Kepler Survey (CKS) is an observational program developed to improve our knowledge of the properties of stars found to host transiting planets by NASA's Kepler Mission. The improvement stems from new high-resolution optical spectra obtained using HIRES at the W. M. Keck Observatory. The CKS stellar sample comprises 1305 stars classified as Kepler objects of interest, hosting a total of 2075 transiting planets. The primary sample is magnitude-limited (K_p_<14.2) and contains 960 stars with 1385 planets. The sample was extended to include some fainter stars that host multiple planets, ultra-short period planets, or habitable zone planets. The spectroscopic parameters were determined with two different codes, one based on template matching and the other on direct spectral synthesis using radiative transfer. We demonstrate a precision of 60K in T_eff_, 0.10dex in logg, 0.04dex in [Fe/H], and 1.0km/s in Vsini. In this paper, we describe the CKS project and present a uniform catalog of spectroscopic parameters. Subsequent papers in this series present catalogs of derived stellar properties such as mass, radius, and age; revised planet properties; and statistical explorations of the ensemble. CKS is the largest survey to determine the properties of Kepler stars using a uniform set of high-resolution, high signal-to-noise ratio spectra. The HIRES spectra are available to the community for independent analyses.
- ID:
- ivo://CDS.VizieR/J/AJ/156/264
- Title:
- California-Kepler Survey. VII. Planet radius gap
- Short Name:
- J/AJ/156/264
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of planet sizes encodes details of planet formation and evolution. We present the most precise planet size distribution to date based on Gaia parallaxes, Kepler photometry, and spectroscopic temperatures from the California-Kepler Survey. Previously, we measured stellar radii to 11% precision using high-resolution spectroscopy; by adding Gaia astrometry, the errors are now 3%. Planet radius measurements are, in turn, improved to 5% precision. With a catalog of ~1000 planets with precise properties, we probed in fine detail the gap in the planet size distribution that separates two classes of small planets, rocky super-Earths and gas-dominated sub-Neptunes. Our previous study and others suggested that the gap may be observationally under-resolved and inherently flat-bottomed, with a band of forbidden planet sizes. Analysis based on our new catalog refutes this; the gap is partially filled in. Two other important factors that sculpt the distribution are a planet's orbital distance and its host-star mass, both of which are related to a planet's X-ray/UV irradiation history. For lower-mass stars, the bimodal planet distribution shifts to smaller sizes, consistent with smaller stars producing smaller planet cores. Details of the size distribution including the extent of the "sub-Neptune desert" and the width and slope of the gap support the view that photoevaporation of low-density atmospheres is the dominant evolutionary determinant of the planet size distribution.
- ID:
- ivo://CDS.VizieR/J/AJ/156/254
- Title:
- California-Kepler Survey.VI. Kepler multis & singles
- Short Name:
- J/AJ/156/254
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The California-Kepler Survey (CKS) catalog contains precise stellar and planetary properties for the Kepler planet candidates, including systems with multiple detected transiting planets ("multis") and systems with just one detected transiting planet ("singles", although additional planets could exist). We compared the stellar and planetary properties of the multis and singles in a homogeneous subset of the full CKS-Gaia catalog. We found that sub-Neptune-sized singles and multis do not differ in their stellar properties or planet radii. In particular: (1) The distributions of stellar properties M_*_, [Fe/H], and vsini for the Kepler sub-Neptune-sized singles and multis are statistically indistinguishable. (2) The radius distributions of the sub-Neptune-sized singles and multis with P>3 days are indistinguishable, and both have a valley at ~1.8 R_{Earth}_. However, there are significantly more detected short-period (P<3 days), sub-Neptune-sized singles than multis. The similarity of the host-star properties, planet radii, and radius valley for singles and multis suggests a common origin. The similar radius valley, which is likely sculpted by photo-evaporation from the host star within the first 100 Myr, suggests that planets in both singles and multis spend much of the first 100 Myr near their present, close-in locations. One explanation that is consistent with the similar fundamental properties of singles and multis is that many of the singles are members of multi-planet systems that underwent planet-planet scattering.
- ID:
- ivo://CDS.VizieR/J/ApJ/770/90
- Title:
- Candidate planets in the habitable zones
- Short Name:
- J/ApJ/770/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A key goal of the Kepler mission is the discovery of Earth-size transiting planets in "habitable zones" where stellar irradiance maintains a temperate climate on an Earth-like planet. Robust estimates of planet radius and irradiance require accurate stellar parameters, but most Kepler systems are faint, making spectroscopy difficult and prioritization of targets desirable. The parameters of 2035 host stars were estimated by Bayesian analysis and the probabilities p_HZ_ that 2738 candidate or confirmed planets orbit in the habitable zone were calculated. Dartmouth Stellar Evolution Program models were compared to photometry from the Kepler Input Catalog, priors for stellar mass, age, metallicity and distance, and planet transit duration. The analysis yielded probability density functions for calculating confidence intervals of planet radius and stellar irradiance, as well as p_HZ_. Sixty-two planets have p_HZ_>0.5 and a most probable stellar irradiance within habitable zone limits. Fourteen of these have radii less than twice the Earth; the objects most resembling Earth in terms of radius and irradiance are KOIs 2626.01 and 3010.01, which orbit late K/M-type dwarf stars. The fraction of Kepler dwarf stars with Earth-size planets in the habitable zone ({eta}_{Earth}_) is 0.46, with a 95% confidence interval of 0.31-0.64. Parallaxes from the Gaia mission will reduce uncertainties by more than a factor of five and permit definitive assignments of transiting planets to the habitable zones of Kepler stars.
- ID:
- ivo://CDS.VizieR/J/AJ/130/1177
- Title:
- C and N abundances for M15 stars
- Short Name:
- J/AJ/130/1177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of a large sample of moderate-resolution Keck Low Resolution Imaging Spectrometer spectra of subgiants and stars at the base of the red giant branch (RGB) in the Galactic globular cluster (GC) M15 (NGC 7078), most within the range 16.5<V<19.5 (1.2<M_V_<4.2), with the goal of deriving C abundances (from the G band of CH) and N abundances (from the NH band at 3360{AA}).
- ID:
- ivo://CDS.VizieR/J/ApJ/791/58
- Title:
- C and O abundances across the Hertzsprung gap
- Short Name:
- J/ApJ/791/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derived atmospheric parameters and spectroscopic abundances for C and O for a large sample of stars located in the Hertzsprung gap in the Hertzsprung-Russell diagram in order to detect chemical peculiarities and get a comprehensive overview of the population of stars in this evolutionary state. We have observed and analyzed high-resolution spectra (R = 60,000) of 188 stars in the mass range 2-5 M_{sun}_ with the 2.7 m Harlan J. Smith Telescope at the McDonald Observatory including 28 stars previously identified as Am/Ap stars. We find that the C and O abundances of the majority of stars in the Hertzsprung gap are in accordance with abundances derived for local lower-mass dwarfs but detect expected peculiarities for the Am/Ap stars. The C and O abundances of stars with T_eff_< 6500 K are slightly lower than for the hotter objects but the C/O ratio is constant in the analyzed temperature domain. No indication of an alteration of the C and O abundances of the stars by mixing during the evolution across the Hertzsprung gap could be found before the homogenization of their atmospheres by the first dredge-up.
- ID:
- ivo://CDS.VizieR/J/ApJ/778/132
- Title:
- C and O abundances in 55 Cnc
- Short Name:
- J/ApJ/778/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The super-Earth exoplanet 55 Cnc e, the smallest member of a five-planet system, has recently been observed to transit its host star. The radius estimates from transit observations, coupled with spectroscopic determinations of mass, provide constraints on its interior composition. The composition of exoplanetary interiors and atmospheres are particularly sensitive to elemental C/O ratio, which to first order can be estimated from the host stars. Results from a recent spectroscopic study analyzing the 6300{AA}[OI] line and two CI lines suggest that 55 Cnc has a carbon-rich composition (C/O=1.12+/-0.09). However, oxygen abundances derived using the 6300{AA}[OI] line are highly sensitive to a Ni I blend, particularly in metal-rich stars such as 55 Cnc ([Fe/H]=0.34+/-0.18). Here, we further investigate 55 Cnc's composition by deriving the carbon and oxygen abundances from these and additional C and O absorption features. We find that the measured C/O ratio depends on the oxygen lines used. The C/O ratio that we derive based on the 6300{AA}[OI] line alone is consistent with the previous value. Yet, our investigation of additional abundance indicators results in a mean C/O ratio of 0.78+/-0.08. The lower C/O ratio of 55 Cnc determined here may place this system at the sensitive boundary between protoplanetary disk compositions giving rise to planets with high (>0.8) versus low (<0.8) C/O ratios. This study illustrates the caution that must applied when determining planet host star C/O ratios, particularly in cool, metal-rich stars.
- ID:
- ivo://CDS.VizieR/J/A+A/568/A25
- Title:
- C and O abundances in stellar populations
- Short Name:
- J/A+A/568/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- C and O abundances are determined for 151 F and G main-sequence stars with metallicities in the range -1.6<[Fe/H]<+0.4. The C abundances are determined from the CI lines at 5052 and 5380{AA} and oxygen abundances from the OI triplet at 7774{AA} and the forbidden [OI] line at 6300{AA}.
- ID:
- ivo://CDS.VizieR/J/A+A/548/A55
- Title:
- C and O isotopic ratios in Arcturus and Aldebaran
- Short Name:
- J/A+A/548/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We re-analyzed the carbon and oxygen isotopic ratios in the atmospheres of the two bright K giants Arcturus ({alpha} Boo) and Aldebaran ({alpha} Tau). These stars are in the evolutionary stage following the first dredge-up (FDU). Previous determinations (dating back more than 20 years) of their ^16^O/^18^O ratios showed a rough agreement with FDU expectations; however, the estimated ^16^O/^17^O and ^12^C/^13^C ratios were lower than in the canonical predictions for red giants. Today these anomalies are interpreted as signs of the occurrence of non-convective mixing episodes. We therefore re-investigated this problem to verify whether the observed data can be reproduced in this scenario and if the fairly well determined properties of the two stars can help us in fixing the uncertain parameters that characterize non-convective mixing and in constraining its physical nature.