TRIGONOMETRIC PARALLAXES FOR 1507 NEARBY MID-TO-LATE M DWARFS

Abstract

The MEarth survey is a search for small rocky planets around the smallest, nearest stars to the Sun as identified by high proper motion with red colors. We augmented our planetary search time series with lower cadence astrometric imaging and obtained two million images of approximately 1800 stars suspected to be mid-to-late M dwarfs. We fit an astrometric model to MEarth's images for 1507 stars and obtained trigonometric distance measurements to each star with an average precision of 5 mas. Our measurements, combined with the Two Micron All Sky Survey photometry, allowed us to obtain an absolute K[subscript s] magnitude for each star. In turn, this allows us to better estimate the stellar parameters than those obtained with photometric estimates alone and to better prioritize the targets chosen to monitor at high cadence for planetary transits. The MEarth sample is mostly complete out to a distance of 25 pc for stars of type M5.5V and earlier, and mostly complete for later type stars out to 20 pc. We find eight stars that are within 10 pc of the Sun for which there did not exist a published trigonometric parallax distance estimate. We release with this work a catalog of the trigonometric parallax measurements for 1507 mid-to-late M dwarfs, as well as new estimates of their masses and radii.