Planet Hunters Talk

The Kepler Dichotomy among the M Dwarfs: Half of Systems Contain Five or More Coplanar Planets

  • JeanTate by JeanTate

    That's the title of an astro-ph preprint which appeared on the arXiv server yesterday, arXiv:1410.4192; here's the abstract:

    We present a statistical analysis of the Kepler M dwarf planet hosts, with a particular focus on the fractional number of systems hosting multiple transiting planets. We manufacture synthetic planetary systems within a range of planet multiplicity and mutual inclination for comparison to the Kepler yield. We recover the observed number of systems containing between 2 and 5 transiting planets if every M dwarf hosts 6.1+/-1.9 planets with typical mutual inclinations of 2.0 +4.0-2.0 degrees. This range includes the Solar System in its coplanarity and multiplicity. However, similar to studies of Kepler exoplanetary systems around more massive stars, we report that the number of singly-transiting planets found by Kepler is too high to be consistent with a single population of multi-planet systems: a finding that cannot be attributed to selection biases. To account for the excess singleton planetary systems we adopt a mixture model and find that 55 +23-12% of planetary systems are either single or contain multiple planets with large mutual inclinations. Thus, we find that the so-called "Kepler dichotomy" holds for planets orbiting M dwarfs as well as Sun-like stars. Additionally, we compare stellar properties of the hosts to single and multiple transiting planets. For the brightest subset of stars in our sample we find intriguing, yet marginally significant evidence that stars hosting multiply-transiting systems are rotating more quickly, are closer to the midplane of the Milky Way, and are comparatively metal poor. This preliminary finding warrants further investigation.

    I hadn't heard of the "Kepler dichotomy" before (perhaps I simply haven't been keeping up); if it pans out, it's pretty amazing, don't you think?

    Also got me wondering: what if the 'singletons' are, in fact, multi-planet systems, but the other planets are too small to see (a logical possibility, in addition to the 'contain multiple planets with large mutual inclinations')? I.e. that the dichotomy (if it turns out to be real) has more to do with a dichotomy in planet size distribution than singleton vs multi-planet systems.

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