Toward a Galactic Distribution of Planets. I. Methodology and Planet Sensitivities of the 2015 Highcadence Spitzer Microlens Sample
Abstract
We analyze an ensemble of microlensing events from the 2015 Spitzer microlensing campaign, all of which were densely monitored by groundbased highcadence survey teams. The simultaneous observations from Spitzer and the ground yield measurements of the microlensing parallax vector π_{E}, from which compact constraints on the microlens properties are derived, including ≲25% uncertainties on the lens mass and distance. With the current sample, we demonstrate that the majority of microlenses are indeed in the mass range of M dwarfs. The planet sensitivities of all 41 events in the sample are calculated, from which we provide constraints on the planet distribution function. In particular, assuming a planet distribution function that is uniform in log q, where q is the planettostar mass ratio, we find a 95% upper limit on the fraction of stars that host typical microlensing planets of 49%, which is consistent with previous studies. Based on this planetfree sample, we develop the methodology to statistically study the Galactic distribution of planets using microlensing parallax measurements. Under the assumption that the planet distributions are the same in the bulge as in the disk, we predict that ∼1/3 of all planet detections from the microlensing campaigns with Spitzer should be in the bulge. This prediction will be tested with a much larger sample, and deviations from it can be used to constrain the abundance of planets in the bulge relative to the disk.
 Publication:

The Astronomical Journal
 Pub Date:
 November 2017
 DOI:
 10.3847/15383881/aa8ef1
 arXiv:
 arXiv:1701.05191
 Bibcode:
 2017AJ....154..210Z
 Keywords:

 gravitational lensing: micro;
 methods: statistical;
 planetary systems;
 planets and satellites: dynamical evolution and stability;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 published on Astronomical Journal