Surface Rotation and Photometric Activity for Kepler Targets. II. G and F Main-sequence Stars and Cool Subgiant Stars

Dark magnetic spots crossing the stellar disk lead to quasiperiodic brightness variations, which allow us to constrain stellar surface rotation and photometric activity. The current work is the second of this series, where we analyze the Kepler long-cadence data of 132,921 main-sequence F and G stars and late subgiant stars. Rotation-period candidates are obtained by combining wavelet analysis with autocorrelation function. Reliable rotation periods are then selected via a machine-learning (ML) algorithm, automatic selection, and complementary visual inspection. The ML training data set comprises 26,521 main-sequence K and M stars from Paper I. To supplement the training, we analyze in the same way as Paper I, i.e., automatic selection and visual inspection, 34,100 additional stars. We finally provide rotation periods P-rot and associated photometric activity proxy S-ph for 39,592 targets. Hotter stars are generally faster rotators than cooler stars. For main-sequence G stars, S-ph spans a wider range of values with increasing effective temperature, while F stars tend to have smaller S-ph values in comparison with cooler stars. Overall for G stars, fast rotators are photometrically more active than slow rotators, with S-ph saturating at short periods. The combined outcome of the two papers accounts for average P-rot and S-ph values for 55,232 main-sequence and subgiant FGKM stars (out of 159,442 targets), with 24,182 new P-rot detections in comparison with McQuillan et al. The upper edge of the P-rot distribution is located at longer P (rot) than found previously.

Automated summary

The study analyzed Kepler data of 132,921 main-sequence F and G stars and late subgiant stars, identifying rotation-period candidates and selecting reliable rotation periods using a machine-learning algorithm. The research also found that hotter stars generally rotate faster and that the photometric activity of main-sequence G stars varies with increasing effective temperature.