MassRadius Relationship for M Dwarf Exoplanets: Comparing Nonparametric and Parametric Methods
Abstract
Though they are the most abundant stars in the Galaxy, M dwarfs form only a small subset of known stars hosting exoplanets with measured radii and masses. In this paper, we analyze the massradius (MR) relationship of planets around M dwarfs using MR measurements for 24 exoplanets. In particular, we apply both parametric and nonparametric models and compare the two different fitting methods. We also use these methods to compare the results of the M dwarf MR relationship with that from the Kepler sample. Using the nonparametric method, we find that the predicted masses for the smallest and largest planets around M dwarfs are smaller than similar fits to the Kepler data, but that the distribution of masses for 3 R _{⊕} planets does not substantially differ between the two data sets. With future additions to the M dwarf MR relation from the Transiting Exoplanet Survey Satellite and instruments like the Habitable Zone Planet Finder, we will be able to characterize these differences in more detail. We release a publicly available Python code called MRExo (https://github.com/shbhuk/mrexo) that uses the nonparametric algorithm introduced by Ning et al. to fit the MR relationship. Such a nonparametric fit does not assume an underlying powerlaw fit to the measurements and hence can be used to fit an MR relationship that is less biased than a power law. In addition, MRExo offers a tool to predict mass from radius posteriors, and vice versa.
 Publication:

The Astrophysical Journal
 Pub Date:
 September 2019
 DOI:
 10.3847/15384357/ab334c
 arXiv:
 arXiv:1903.00042
 Bibcode:
 2019ApJ...882...38K
 Keywords:

 methods: statistical;
 planets and satellites: composition;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 Received 2019 February 21