MASADA: From Microlensing Planet Mass-Ratio Function to Planet Mass Function

Abstract

Using current technology, gravitational microlensing is the only method that can measure planet masses over the full parameter space of planet and stellar-host masses and at a broad range of planet-host separations. I present a comprehensive program to transform the $\sim 150$ planet/host mass ratio measurements from the first 6 full seasons of the KMTNet survey into planet mass measurements via late-time adaptive optics (AO) imaging on 30m-class telescopes. This program will enable measurements of the overall planet mass function, the planet frequency as a function of Galactic environment and the planet mass functions within different environments. I analyze a broad range of discrete and continuous degeneracies as well as various false positives and false negatives, and I present a variety of methods to resolve these. I analyze the propagation from measurement uncertainties to mass and distance errors and show that these present the greatest difficulties for host masses $0.13\lesssim(M/M_\odot)\lesssim 0.4$, i.e., fully convective stars supported by the ideal gas law, and for very nearby hosts. While work can begin later this decade using AO on current telescopes, of order 90% of the target sample must await 30m-class AO. I present extensive tables with information that is useful to plan observations of more than 100 of these planets and provide additional notes for a majority of these. Applying the same approach to two earlier surveys with 6 and 8 planets, respectively, I find that 11 of these 14 planets already have mass measurements by a variety of techniques. These provide suggestive evidence that planet frequency may be higher for nearby stars, $D_L\lesssim 4$ kpc compared to those in or near the Galactic bulge. Finally, I analyze the prospects for making the planet mass-function measurement for the case that current astronomical capabilities are seriously degraded.