tokens: 2 (Lanzafame et al. 2018 ). The extended Kepler mission, K2 (Howell et al. 2014 ), has now observed more stars than the original Kepler sample, potentially doubling the number of high precision stellar rotation periods available. Similarly, by the end of the Gaia mission, Lanzafame et al. ( 2018 ) estimate that a sample of 3–20 million rotation periods will be recovered. The era of statistical studies in stellar rotation has therefore begun. Stellar rotation has long been noted as a means to possibly age-date stars due to their constant angular momentum loss via winds (Skumanich 1972 ). While studies of open clusters give hope that this “gyrochronology” model broadly works for solar-type and lower-mass stars, many uncertainties exist about the details of this spindown and its utility as a clock. These include questions about the initial rotation period distribution for stars (e.g., Barnes 2010 ; Matt et al. 2015 ), the specific analytic prescription for modeling the spindown (Angus et al. 2015 ), and exploring the efficiency of this angular momentum loss mechanism at older ages (van Saders et al. 2016 ). One of the most compelling results from the rotating star sample in Kepler is the discovery of a bimodal period distribution. McQuillan et al. ( 2013 ) first found a bimodality in the distribution of field M dwarfs with periods between ∼10 and ∼50 days. This feature was also found in the Kepler field K dwarfs in McQuillan et al. ( 2014 ), but was not seen in the bluer stars. Using Gaia DR1, Davenport ( 2017 ) was able to remove contaminating subgiants from the rotation sample, and found the bimodality extended to the G dwarfs as well. This bimodal surface rotation period distribution is either a new short-lived transition or instability phase of rapid angular momentum loss, or a signature of star formation history imprinted in the present-day rotation period distribution. However, as Davenport ( 2017 ) notes, this feature has only been observed in the Kepler rotation period catalog, and most critically only for stars within ∼300 pc. The faint M dwarfs in the Kepler sample studied in McQuillan et al. ( 2013 ) have an average distance of 250 pc. Gaia DR1 was also only able to provide precise distances for the nearest stars, and Davenport ( 2017 ) report a median distance of 285 pc for the blue stars in their sample. In this paper, we extend the work of Davenport ( 2017 ) in studying the Kepler rotation period distribution as a function of distance from the Sun using new astrometric data from the Gaia mission. By matching the McQuillan et al. ( 2014 ) rotation period catalog to the newest data from Gaia Data Release 2 (Gaia Collaboration et al. 2018b ), we can use precise distances for essentially every star in the McQuillan catalog to select the most-likely main-sequence dwarfs out to distances >2 kpc. Importantly, this filters out both subgiants, the main contaminant noted by Davenport ( 2017 ), and unresolved binary stars. Here we demonstrate
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