KMT-2022-BLG-2397: Brown Dwarf at the Upper Shore of the Einstein Desert

Abstract

We measure the Einstein radius of the single-lens microlensing event KMT-2022-BLG-2397 to be theta_E=24.8 +- 3.6 uas, placing it at the upper shore of the Einstein Desert, 9 < theta_E / uas < 25, between free-floating planets (FFPs) and bulge brown dwarfs (BDs). In contrast to the six BD (25 < theta_E < 50) events presented by Gould+22, which all had giant-star source stars, KMT-2022-BLG-2397 has a dwarf-star source, with angular radius theta_* ~ 0.9 uas. This prompts us to study the relative utility of dwarf and giant sources for characterizing FFPs and BDs from finite-source point-lens (FSPL) microlensing events. We find `dwarfs' (including main-sequence stars and subgiants) are likely to yield twice as many theta_E measurements for BDs and a comparable (but more difficult to quantify) improvement for FFPs. We show that neither current nor planned experiments will yield complete mass measurements of isolated bulge BDs, nor will any other planned experiment yield as many theta_E measurements for these objects as KMT. Thus, the currently anticipated 10-year KMT survey will remain the best way to study bulge BDs for several decades to come.

45 pages, 9 Figures, submitted to AAS Journals

References in corpus (14)

• The Gaia mission
• No large population of unbound or wide-orbit Jupiter-mass planets
• Microlens OGLE-2005-BLG-169 Implies Cool Neptune-Like Planets are Common
• The Exoplanet Mass-Ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass
• The Solar Neighborhood XXXVII: The Mass-Luminosity Relation for Main Sequence M Dwarfs
• An isolated mass gap black hole or neutron star detected with astrometric microlensing
• Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey II: Free-Floating Planet Detection Rates
• Planetary and Other Short Binary Microlensing Events from the MOA Short Event Analysis
• A terrestrial-mass rogue planet candidate detected in the shortest-timescale microlensing event
• PopSyCLE: A New Population Synthesis Code for Compact Object Microlensing Events
• Systematic errors as a source of mass discrepancy in black hole microlensing event OGLE-2011-BLG-0462
• Masses for Free-Floating Planets and Dwarf Planets
• WFIRST Ultra-Precise Astrometry I: Kuiper Belt Objects
• OGLE-2007-BLG-224L: Confirmation of Terrestrial Parallax

Cited by in corpus (3)

• Systematic Reanalysis of KMTNet microlensing events, Paper I: Updates of the Photometry Pipeline and a New Planet Candidate
• "Industrial-Scale" Black Hole Selection without a Satellite
• Prospects for Reconstructing the Free-floating Planet Mass Function at the Population Level with the Nancy Grace Roman Space Telescope