The Kepler Mission revolutionized exoplanet science and stellar astrophysics by obtaining highly precise photometry of over 200,000 stars over 4 yr. A critical piece of information to exploit Kepler data is its selection function, since all targets had to be selected from a sample of half a million stars on the Kepler CCDs using limited information. Here we use Gaia DR2 to reconstruct the Kepler selection function and explore possible biases with respect to evolutionary state, stellar multiplicity, and kinematics. We find that the Kepler target selection is nearly complete for stars brighter than Kp < 14 mag and was effective at selecting main-sequence stars, with the fraction of observed stars decreasing from 95% to 60% between 14 < Kp < 16 mag. We find that the observed fraction for subgiant stars is only 10% lower, confirming that a significant number of subgiants selected for observation were believed to be main-sequence stars. Conversely we find a strong selection bias against low-luminosity red giant stars (R ≈ 3–5R _⊙, T _eff≈ 5500 K), dropping from 90% at Kp = 14 mag to below 30% at Kp = 16 mag, confirming that the target selection was efficient at distinguishing dwarfs from giants. We compare the Gaia Re-normalized Unit Weight Error (RUWE) values of the observed and nonobserved main-sequence stars and find a difference in elevated (>1.2) RUWE values at ∼σ significance, suggesting that the Kepler target selection shows some bias against either close or wide binaries. We furthermore use the Gaia proper motions to show that the Kepler selection function was unbiased with respect to kinematics.

开普勒任务通过在 4 年内获得超过 200,000 颗恒星的高精度光度测量，彻底改变了系外行星科学和恒星天体物理学。利用开普勒数据的一个关键信息是它的选择功能，因为必须使用有限的信息从开普勒 CCD 上的 50 万颗恒星样本中选择所有目标。在这里，我们使用 Gaia DR2 来重建开普勒选择函数，并探索关于演化状态、恒星多样性和运动学的可能偏差。我们发现，对于比Kp < 14 mag更亮的恒星，开普勒目标选择几乎完成，并且在选择主序星方面是有效的，在 14 < Kp之间观察到的恒星比例从 95% 下降到 60%< 16 倍。我们发现次巨星的观测比例仅低 10%，这证实了大量被选择用于观测的次巨星被认为是主序星。相反，我们发现对低光度红巨星（R ≈ 3–5 R _⊙，T _eff ≈ 5500 K）有很强的选择偏差，从Kp = 14 mag 时的90% 下降到Kp = 16 mag 时的30% 以下，证实目标选择在区分矮人和巨人方面是有效的。我们比较了观测到的和未观测到的主序星的 Gaia Re-normalized Unit Weight Error (RUWE) 值，并发现在 ∼ σ处升高 (>1.2) RUWE 值的差异意义，表明开普勒目标选择显示出对近或宽二进制的一些偏见。我们进一步使用 Gaia 自身运动来表明开普勒选择函数在运动学方面是无偏的。