KMT-2017-BLG-2820 and the Nature of the Free-floating Planet Population
Abstract
We report a new free-floating planet (FFP) candidate, KMT-2017-BLG-2820, with Einstein radius θE ≃ 6 μas, lens-source relative proper motion μrel ≃ 8 mas yr-1, and Einstein timescale tE = 6.5 hr. It is the third FFP candidate found in an ongoing study of giant-source finite-source point-lens (FSPL) events in the KMTNet database and the sixth FSPL FFP candidate overall. We find no significant evidence for a host. Based on their timescale distributions and detection rates, we argue that five of these six FSPL FFP candidates are drawn from the same population as the six point-source point-lens (PSPL) FFP candidates found by Mróz et al. in the OGLE-IV database. The θE distribution of the FSPL FFPs implies that they are either sub-Jovian planets in the bulge or super-Earths in the disk. However, the apparent "Einstein desert" (10 ≲ θE/μas ≲ 30) would argue for the latter. Whether each of the 12 (six FSPL and six PSPL) FFP candidates is truly an FFP or simply a very wide-separation planet can be determined at first adaptive optics (AO) light on 30 m telescopes, and earlier for some. If the latter, a second epoch of AO observations could measure the projected planet-host separation with a precision of ${ \mathcal O }(10\,\mathrm{au})$ . At the present time, the balance of evidence favors the unbound-planet hypothesis.
- Publication:
-
The Astronomical Journal
- Pub Date:
- March 2021
- DOI:
- 10.3847/1538-3881/abd55f
- arXiv:
- arXiv:2010.07527
- Bibcode:
- 2021AJ....161..126R
- Keywords:
-
- Gravitational microlensing;
- 672;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 35 pages, 7 figures, 1 Table