Kepler Planet Occurrence Rates for Mid-Type M Dwarfs as a Function of Spectral Type
2018 • 2018PhDT.......140H
Abstract • Previous studies of planet occurrence rates largely relied on photometric stellar characterizations. We present spectroscopic observations of 337 out of 561 probable mid-type M dwarfs in the primary Kepler field. Our observations have allowed us to constrain spectral type, temperatures, and in some cases metallicities for these stars. We use a random forest classifier to spectral type the remaining 224 targets. Combining our data with Gaia parallaxes, we have computed precise ( 3%) stellar radii, which we use to update planet parameters and planet occurrence rates for Kepler mid-type M dwarfs. Within the Kepler field, there are seven M3 V to M5 V stars which host a total of 13 confirmed planets between 0.5 and 2.5 Earth radii and at orbital periods between 0.5 and 10 days. For this population, we compute a planet occurrence rate of 1.27+0.140.28 planets per star. With our spectral classifications, we compute planet occurrence rates for each spectral sub-type which yields 0.78+0.53-0.40, 1.23+1.14-0.75, and 2.51+2.87-1.51 planets per star for M3 V, M4 V, and M5 V, respectively. Our updated planet parameters show Kepler-1649 b to be an Earth sized planet receiving insolation flux similar to Earth. We also use our data to compute stellar mass, identify active stars with Halpha emission, and identify binary candidates. Our observations with the multi-object spectrograph Hydra on the WIYN telescope allowed us to observe 1,083 other Kepler stars, which will be useful in future studies.
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