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Abstract The gravitational microlensing method of discovering exoplanets and multi-star systems can produce degenerate solutions, some of which require in-depth analysis to uncover. We propose a new parameter space that can be used to sample potential solutions more efficiently and is more robust at finding all degenerate solutions for the “central-resonant” caustic degeneracy. We identified two new parameters,kandh, that can be sampled in place of the mass ratios and separations of the systems under analysis to identify degenerate solutions. The parameterkis related to the size of the central caustic, Δξ_c, whilehis related to the distance of a point along thekcontour from log(s) = 0, wheresis the projected planet-host separation. In this work, we present the characteristics of these parameters and the tests we conducted to prove their efficacy. 

Abstract To exhume the buried signatures of free-floating planets (FFPs) with small angular Einstein radiusθ_E, we build a new full-frame difference image pipeline for the Korean Microlensing Telescope Network (KMTNet) survey based on the newly optimized pySIS package. We introduce the detailed processes of the new pipeline, including frame registration, difference image analysis, and light curve extraction. To test this pipeline, we extract one-year light curves for 483,068 stars withI ≲ 17 and conduct a model-independent search for microlensing events. The search finds 36 microlensing events, including five new events and six events discovered by other collaborations but missed by previous KMTNet searches. We find that the light curves from the new pipeline are precise enough to be sensitive to FFPs withθ_E ∼ 1μas. Using the new pipeline, a complete FFP search on the eight-year KMTNet images can be finished within six months and then yield the FFP mass function. The new pipeline can be used for a new KMTNet AlertFinder system, with significantly reduced false positives. 

Abstract 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.