Mining the Kepler Field: Atmospheric Parameters, Bolometric Corrections, and Luminosities

Technical Deep Dive: Mining the Kepler Field

Overview

This work provides a comprehensive catalog of atmospheric parameters, bolometric corrections, and luminosities for the ~200,000 stars observed by the Kepler mission. By crossmatching the Kepler stars with several modern spectroscopic and spectro-photometric surveys, the authors have assembled a dataset that enables detailed astrophysical explorations of the Kepler field.

Problem & Context

The Kepler mission has provided unprecedented data on stars across a wide range of astrophysical fields, from exoplanets to stellar activity. To fully leverage this rich dataset, thorough stellar characterizations are needed. While knowledge of Kepler targets has grown over the past decade, the advent of new spectroscopic and photometric surveys allows the authors to push the limits of stellar parameter determinations even further.

Methodology

The authors:

• Crossmatched the ~200,000 Kepler stars with various spectroscopic and spectro-photometric surveys to obtain atmospheric parameters (T_eff, log(g), [M/H]).
• Used these atmospheric parameters to calculate bolometric corrections, which were then combined with Gaia DR3 data to derive self-consistent luminosities.
• Applied quality cuts to the survey data to ensure reliability.
• Compared atmospheric parameters across surveys, finding varying levels of agreement.

Data & Experimental Setup

• Target sample: 196,762 Kepler stars with Gaia DR3 counterparts
• Surveys used for atmospheric parameters:
  • High-resolution: Gaia-ESO, Kepler CFOP
  • Medium-resolution: APOGEE, Gaia DR3 gspspec
  • Low-resolution: LAMOST MRS and LRS
  • Spectro-photometric: XGBoost, Berger et al. (2020)
• Bolometric corrections calculated using the gaiadr3_bcg function, which interpolates MARCS synthetic spectra.
• Luminosities derived from Gaia DR3 absolute magnitudes and the computed bolometric corrections.

Results

• Compiled a catalog of atmospheric parameters, bolometric corrections, and luminosities for the Kepler stars, publicly available online.
• Presented Kiel and Hertzsprung-Russell diagrams showing the surveyed Kepler sample, with heterogeneities due to the different sources of atmospheric parameters.
• Found good overall agreement between luminosities and literature values (e.g., 93% of LAMOST LRS luminosities within 3σ of Gaia DR3).

Interpretation

• The assembled dataset provides a valuable resource for further astrophysical explorations of the Kepler field, enabling refined studies of exoplanets, asteroseismology, stellar rotation/activity, and more.
• The survey-to-survey variations in atmospheric parameters highlight the challenges of homogenizing such a large, heterogeneous dataset, which the authors note is beyond the scope of this work.

Limitations & Uncertainties

• Around 100 stars had atmospheric parameters outside the input range of the bolometric correction calculation, lacking those values.
• The authors caution about the use of XGBoost-derived atmospheric parameters, especially for main-sequence stars, due to limitations in the training set.
• Inter-survey differences in atmospheric parameters, while examined, were not fully homogenized.

What Comes Next

The authors make the compiled catalog publicly available, expecting it to serve as a valuable resource for further explorations of the Kepler field. Future work could focus on homogenizing the atmospheric parameters across surveys and investigating the origins of the observed survey-to-survey variations.