Microlensing by Kuiper, Oort, and Free-Floating Planets

TL;DR

This paper discusses how current and future telescopes can detect and constrain the presence of host stars around free-floating planet candidates through microlensing, extending the search to distant planetary systems.

Contribution

It demonstrates the feasibility of using adaptive optics and next-generation telescopes to identify host stars of free-floating planets at large separations, beyond current limits.

Findings

Current AO techniques can constrain hosts at Oort Cloud distances.

Next-generation telescopes will enable probing Kuiper Belt separations.

Future observations will routinely vet FFP candidates for host stars.

Abstract

Microlensing is generally thought to probe planetary systems only out to a few Einstein radii. Microlensing events generated by bound planets beyond about 10 Einstein radii generally do not yield any trace of their hosts, and so would be classified as free floating planets (FFPs). I show that it is already possible, using adaptive optics (AO), to constrain the presence of potential hosts to FFP candidates at separations comparable to the Oort Cloud. With next-generation telescopes, planets at Kuiper-Belt separations can be probed. Next generation telescopes will also permit routine vetting for all FFP candidates, simply by obtaining second epochs 4-8 years after the event. At present, the search for such hosts is restricted to within the "confusion limit" of theta_confus ~ 250 mas, but future WFIRST observations will allow one to probe beyond this confusion limit as well.