Three K2 Campaigns Yield Rotation Periods for 1013 Stars in Praesepe

Abstract

Abstract We use three campaigns of K2 observations to complete the census of rotation in low-mass members of the benchmark, ≈670 Myr old open cluster Praesepe. We measure new rotation periods (P rot) for 220 ≲1.3 M ⊙ Praesepe members and recovery periods for 97% (793/812) of the stars with a P rot in the literature. Of the 19 stars for which we do not recover a P rot, 17 were not observed by K2. As K2’s three Praesepe campaigns took place over the course of 3 yr, we test the stability of our measured P rot for stars observed in more than one campaign. We measure P rot consistent to within 10% for >95% of the 331 likely single stars with ≥2 high-quality observations; the median difference in P rot is 0.3%, with a standard deviation of 2%. Nearly all of the exceptions are stars with discrepant P rot measurements in Campaign 18, K2’s last, which was significantly shorter than the earlier two (≈50 days rather than ≈75 days). This suggests that, despite the evident morphological evolution we observe in the light curves of 38% of the stars, P rot measurements for low-mass stars in Praesepe are stable on timescales of several years. A P rot can therefore be taken to be representative even if measured only once.