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

We measure the Einstein radius of the single-lens microlensing event KMT-2022-BLG-2397 to beθE= 24.8 ± 3.6μas, placing it at the upper shore of the Einstein Desert, 9 ≲θE/μas ≲ 25, between free-floating planets (FFPs) and bulge brown dwarfs (BDs). In contrast to the six BD (25 ≲θE≲ 50) events presented by Gould et al. (2022), which all had giant-star source stars, KMT-2022-BLG-2397 has a dwarf-star source, with angular radiusθast∼ 0.9μas. 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 manyθEmeasurements 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 manyθEmeasurements for these objects as the Korea Microlensing Telescope (KMT). Thus, the currently anticipated 10 yr KMT survey will remain the best way to study bulge BDs for several decades to come.

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DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astronomical Journal
Medium: X Size: Article No. 100
["Article No. 100"]
Sponsoring Org:
National Science Foundation
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