The California-Kepler Survey. I. High Resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets (1703.10400v2)

Abstract: The California-Kepler Survey (CKS) is an observational program 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 (Kp < 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 60 K in effective temperature, 0.10 dex in surface gravity, 0.04 dex in [Fe/H], and 1.0 km/s in projected rotational velocity. 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.

• The paper provides refined stellar parameters using high-resolution spectroscopy from Keck/HIRES, which leads to more accurate planetary measurements.
• It employs dual analysis pipelines (SpecMatch and SME) to derive key stellar properties such as temperature, gravity, metallicity, and rotational velocity with robust calibration.
• The study demonstrates significant improvements over earlier catalogs, deepening our understanding of exoplanet demographics and the impact of stellar characteristics on planetary systems.

The California-Kepler Survey: High-Resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets

The paper presents the California-Kepler Survey (CKS), an extensive observational campaign aimed at refining the properties of stars that host transiting exoplanets identified by NASA's Kepler Mission. This paper significantly contributes to exoplanetary science by leveraging high-resolution spectroscopy to achieve more accurate stellar and planetary parameters. The use of HIRES at the W. M. Keck Observatory offers improved precision over previous catalog-based studies such as the Kepler Input Catalog (KIC).

Key Components of the California-Kepler Survey

• Sample and Observations: The CKS focuses on \nstars stars, which include a magnitude-limited primary sample of \nstarsMaglim stars. These stars host a total of \nplanets transiting exoplanets. High-resolution spectra were obtained from the Keck/HIRES spectrometer to facilitate precise stellar characterization.
• Spectroscopic Analysis: The survey utilizes two spectroscopic analysis pipelines—SpecMatch and SME—to derive effective temperature (\teff), surface gravity (\logg), metallicity (\feh), and rotational velocity (\vsini). Both methods allow for cross-validation of results, ensuring consistency and enabling the identification of outliers.
• Calibration and Validation: The calibration of the spectroscopic parameters uses a robust comparison with well-characterized "platinum stars," providing confidence in the precision and systematic validity of the survey results. Uncertainties are reduced to \cksSigTeff~K in \teff, \cksSiglogg~dex in \logg, and \cksSigfeh~dex in \feh.
• Comparison with Prior Catalogs: The CKS results exhibit substantial improvements over earlier catalogs such as the KIC, yielding tighter constraints on stellar characterization. Discrepancies with previous catalogs are addressed, with systematic offsets noted particularly in metallicity measurements.

Implications and Future Directions

The CKS project represents a significant advancement in characterizing the host stars of Kepler's planetary candidates, with implications for the understanding of exoplanet demographics, the relationship between stellar and planetary properties, and the statistical occurrence of various types of planetary systems. The high-precision stellar parameters allow for refined calculations of planetary radii and orbit properties, crucial for evaluating habitability and other exoplanetary features.

With the CKS dataset being the largest of its kind using a homogeneous set of high-resolution spectra, subsequent analyses are expected to yield insights into the influence of stellar properties on planet occurrence. For instance, future papers in the CKS series aim to explore detailed distributions of planetary radii, paper metallicity trends among planet-hosting stars, and compare the properties of single and multi-planet systems.

The data provided are made publicly available, inviting further independent analysis and application across the astronomical community. As exoplanet discovery and observational capabilities progress, such comprehensive surveys will remain pivotal in refining theoretical models and guiding future observational strategies in the search for and paper of extrasolar worlds.