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Title: OGLE-2016-BLG-1195 AO: Lens, Companion to Lens or Source, or None of the Above?

We systematically investigate Vandorou et al.’s claim to have detected the host star of the low-mass-ratio (q< 10−4) microlensing planet OGLE-2016-BLG-1195Lb, via Keck adaptive optics (AO) measurements Δt= 4.12 yr after the event’s peak (t0). If correct, this measurement would contradict the microlens-parallax measurement derived from Spitzer observations taken neart0. We show that this host identification would be in 4σconflict with the original ground-based relative lens–source proper-motion measurements. By contrast, Gould estimated a probabilityp= 10% that the “other star” resolved by single-epoch late-time AO would be a companion to the host or the microlensed source, which is much more probable than a 4σstatistical fluctuation. Independent of this proper-motion discrepancy, the kinematics of this host identification are substantially less probable than those of the Spitzer solution. Hence, this identification should not be accepted, pending additional observations that would either confirm or contradict it, which could be taken in 2023. Motivated by this tension, we present two additional investigations. We explore the possibility that Vandorou et al. identified the wrong “star” for their analysis. Astrometry of KMT and Keck images favors a star (or asterism) lying about 175 mas northwest of Vandorou et al.’s star. We also present event parameters from a combined fit to all survey data, which yields a more precise mass ratio,q= (4.6 ± 0.4) × 10−5. Finally, we discuss the broader implications of minimizing such false positives for the first measurement of the planet mass function, which will become possible when AO on next-generation telescopes are applied to microlensing planets.

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Author(s) / Creator(s):
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DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astronomical Journal
Medium: X Size: Article No. 145
["Article No. 145"]
Sponsoring Org:
National Science Foundation
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