We analyzed 3 years of data from the Kepler space mission to derive rotation periods of mainsequence stars below 6500 K. Our automated autocorrelation-based method detected rotation periods between 0.2 and 70 days for 34,030 (25.6%) of the 133,030 main-sequence Kepler targets (excluding known eclipsing binaries and Kepler Objects of Interest), making this the largest sample of stellar rotation periods to date. In this paper we consider the detailed features of the now well-populated period-temperature distribution and demonstrate that the period bimodality, first seen by McQuillan, Aigrain & Mazeh (2013) in the M-dwarf sample, persists to higher masses, becoming less visible above 0.6 M ⊙ . We show that these results are globally consistent with the existing ground-based rotationperiod data and find that the upper envelope of the period distribution is broadly consistent with a gyrochronological age of 4.5 Gyrs, based on the isochrones of Barnes (2007), Mamajek & Hillenbrand (2008) and Meibom et al. (2009). We also performed a detailed comparison of our results to those of Reinhold et al. (2013) and Nielsen et al. (2013), who have measured rotation periods of field stars observed by Kepler. We examined the amplitude of periodic variability for the stars with detected rotation periods, and found a typical range between ∼ 950 ppm (5 th percentile) and ∼ 22, 700 ppm (95 th percentile), with a median of ∼ 5, 600 ppm. We found typically higher amplitudes for shorter periods and lower effective temperatures, with an excess of low-amplitude stars above ∼ 5400 K.

We present the Coordinated Synoptic Investigation of NGC 2264, a continuous 30-day multiwavelength photometric monitoring campaign on more than 1000 young cluster members using 16 telescopes. The unprecedented combination of multi-wavelength, high-precision, high-cadence, and long-duration data opens a new window into the time domain behavior of young stellar objects. Here we provide an overview of the observations, focusing on results from Spitzer and CoRoT. The highlight of this work is detailed analysis of 162 classical T Tauri stars for which we can probe optical and mid-infrared flux variations to 1% amplitudes and sub-hour timescales. We present a morphological variability census and then use metrics of periodicity, stochasticity, and symmetry to statistically separate the light curves into seven distinct classes, which we suggest represent different physical processes and geometric effects. We provide distributions of the characteristic timescales and amplitudes, and assess the fractional representation within each class. The largest category (>20%) are optical "dippers" having discrete fading events lasting ∼1-5 days. The degree of correlation between the optical and infrared light curves is positive but weak; notably, the independently assigned optical and infrared morphology classes tend to be different for the same object. Assessment of flux variation behavior with respect to (circum)stellar properties reveals correlations of variability parameters with Hα emission and with effective temperature. Overall, our results point to multiple origins of young star variability, including circumstellar obscuration events, hot spots on the star and/or disk, accretion bursts, and rapid structural changes in the inner disk. Subject headings:Electronic address: amc@ipac.caltech.edu * Based on data from the Spitzer and CoRoT missions. The CoRoT space mission was developed and is operated by the French space agency CNES, with particpiation of ESA's RSSD

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We present a large sample of stellar rotation periods for Kepler Objects of Interest (KOIs), based on three years of public Kepler data. These were measured by detecting periodic photometric modulation caused by star spots, using an algorithm based on the autocorrelation function (ACF) of the light curve, developed recently by McQuillan, Aigrain & Mazeh (2013). Of the 1919 main-sequence exoplanet hosts analyzed, robust rotation periods were detected for 737. Comparing the detected stellar periods to the orbital periods of the innermost planet in each system reveals a notable lack of close-in planets around rapid rotators. It appears that only slowly spinning stars, with rotation periods longer than 5-10 days, host planets on orbits shorter than 3 days, although the mechanism(s) that lead(s) to this is not clear.

Among the available methods for dating stars, gyrochronology is a powerful one because it requires knowledge of only the star's mass and rotation period. Gyrochronology relations have previously been calibrated using young clusters, with the Sun providing the only age dependence, and are therefore poorly calibrated at late ages. We used rotation period measurements of 310 Kepler stars with asteroseismic ages, 50 stars from the Hyades and Coma Berenices clusters and 6 field stars (including the Sun) with precise age measurements to calibrate the gyrochronology relation, whilst fully accounting for measurement uncertainties in all observable quantities. We calibrated a relation of the form Pwhere P is rotation period in days, A is age in Myr, B and V are magnitudes and a, b and n are the free parameters of our model. We found a = 0.40 +0.3 −0.05 , b = 0.31 +0.05 −0.02 and n = 0.55 +0.02 −0.09 . Markov Chain Monte Carlo methods were used to explore the posterior probability distribution functions of the gyrochronology parameters and we carefully checked the effects of leaving out parts of our sample, leading us to find that no single relation beween rotation period, colour and age can adequately describe all the subsets of our data. The Kepler asteroseismic stars, cluster stars and local field stars cannot all be described by the same gyrochronology relation. The Kepler asteroseismic stars may be subject to observational biases, however the clusters show unexpected deviations from the predicted behaviour, providing concerns for the overall reliability of gyrochronology as a dating method.