Kepler Planet Occurrence Rates for Mid-type M Dwarfs as a Function of Spectral Type

Creators: Hardegree-Ullman, Kevin K.; Cushing, Michael C.; Muirhead, Philip S.; Christiansen, Jessie L.

Abstract

Previous studies of planet occurrence rates largely relied on photometric stellar characterizations. In this paper, we present planet occurrence rates for mid-type M dwarfs using spectroscopy, parallaxes, and photometry to determine stellar characteristics. Our spectroscopic observations have allowed us to constrain spectral type, temperatures, and, in some cases, metallicities for 337 out of 561 probable mid-type M dwarfs in the primary Kepler field. We use a random forest classifier to assign a spectral type to the remaining 224 stars. Combining our data with Gaia parallaxes, we compute precise (~3%) stellar radii and masses, which we use to update planet parameters and occurrence rates for Keplermid-type M dwarfs. Within the Kepler field, there are seven M3 V to M5 V stars that host 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 1.19^(+0.70)_(−0.49) planets per star. For M3 V, M4 V, and M5 V, we compute planet occurrence rates of 0.86^(+1.32)_(−0.68), 1.36^(+2.30)_(−1.02), and 3.07^(+5.49)_(−2.4) planets per star, respectively.

Additional Information

© 2019 The American Astronomical Society. Received 2018 August 30; revised 2019 April 16; accepted 2019 May 14; published 2019 July 19. We would like to thank WIYN observing assistants Amy Robertson, Anthony Paat, Christian Soto, Dave Summers, Doug Williams, Karen Butler, and Malanka Riabokin; DCT telescope operators Andrew Hayslip, Heidi Larson, Jason Sanborn, and Teznie Pugh; and IRTF telescope operators Brian Cabreira, Dave Griep, Eric Volquardsen, Greg Osterman, and Tony Matulonis. We would also like to thank NOAO observing support scientists Daryl Willmarth, Dianne Harmer, Mark Everett, and Susan Ridgway. K.H.-U. would like to thank Adam Schneider and Wayne Oswald for conducting some of the observations herein at the DCT and WIYN and Courtney Dressing, Gijs Mulders, and Jon Zink for informative discussions regarding planet occurrence rates and statistics. Data presented herein were obtained at the WIYN Observatory from telescope time allocated to NN-EXPLORE through the scientific partnership of the National Aeronautics and Space Administration, the National Science Foundation, and the National Optical Astronomy Observatory. This work was supported by a NASA WIYN PI Data Award, administered by the NASA Exoplanet Science Institute. These results made use of the Discovery Channel Telescope at Lowell Observatory. Lowell is a private, nonprofit institution dedicated to astrophysical research and public appreciation of astronomy and operates the DCT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University, and Yale University. The upgrade of the DeVeny optical spectrograph has been funded by a generous grant from John and Ginger Giovale. The Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work made use of the gaia-kepler.fun cross-match database created by Megan Bedell. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy; the University of Hawaii; the Pan-STARRS Project Office; the Max Planck Society and its participating institutes; the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching; Johns Hopkins University; Durham University; the University of Edinburgh; Queen's University Belfast; the Harvard-Smithsonian Center for Astrophysics; the Las Cumbres Observatory Global Telescope Network Incorporated; the National Central University of Taiwan; the Space Telescope Science Institute; the National Aeronautics and Space Administration under grant No. NNX08AR22G, issued through the Planetary Science Division of the NASA Science Mission Directorate; National Science Foundation grant No. AST-1238877; the University of Maryland; Eotvos Lorand University (ELTE); Los Alamos National Laboratory; and the Gordon and Betty Moore Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: WIYN (Hydra) - , DCT (DeVeny) - , IRTF (SpeX) - , NASA Exoplanet Archive. - Software: dustmaps (Green et al. 2018), IDL Astronomy User's Library (Landsman 1993), IRAF (Tody 1986, 1993), numpy (Oliphant 2015), scikit-learn (Pedregosa et al. 2011), Spextool (Cushing et al. 2004), xtellcor (Vacca et al. 2003).

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