KMT-2019-BLG-1339L: An M Dwarf with a Giant Planet or a Companion near the Planet/Brown Dwarf Boundary

Abstract

We analyze KMT-2019-BLG-1339, a microlensing event with an obvious but incompletely resolved brief anomaly feature around the peak of the light curve. Although the origin of the anomaly is identified to be a companion to the lens with a low mass ratio q, the interpretation is subject to two different degeneracy types. The first type is the ambiguity in ρ, representing the angular source radius scaled to the angular radius of the Einstein ring, θ E , and the other is the s ↔ s −1 degeneracy. The former type, "finite-source degeneracy," causes ambiguities in both s and q, while the latter induces an ambiguity only in s. Here, s denotes the separation (in units of θ E) in projection between the lens components. We estimate that the lens components have masses~-+-+  according to the two solutions subject to the finite-source degeneracy, indicating that the lens comprises an M dwarf and a companion with a mass around the planet/brown dwarf boundary or a Jovianmass planet. It is possible to lift the finite-source degeneracy by conducting future observations utilizing a highresolution instrument because the relative lens-source proper motion predicted by the solutions is widely different.

Three microlensing planets with no caustic-crossing features

“…For random source trajectories going through the Einstein ring, the cross sections of the first two type are small because central caustics and minorimage planetary caustics are small. Indeed, it was the small size 2 There exist six cases of binary microlenses with companion masses at around this boundary including MOA-2010-BLG-073L (Street et al 2013), OGLE-2013-BLG-0102L (Jung et al 2015), MOA-2015-BLG-337L (Miyazaki et al 2018), OGLE-2016-BLG-1190L (Ryu et al 2018, OGLE-2017-BLG-1375L (Han et al 2020b), and KMT-2019-BLG-1339L (Han et al 2020a of the planetary caustic in OGLE-2019-BLG-0954 that led to it entering our sample: small gaps in relatively dense and continuous coverage meant that there was no coverage over the short cusp crossing. However, as Yee et al (2021) have pointed out, resonant and near-resonant (defined as having "magnificationdeviation ridges" of at least 10% extending from the central to planetary caustic) have much larger cross sections, and they account for a large fraction of all planetary detections.…”

Three microlensing planets with no caustic-crossing features

“…For random source trajectories going through the Einstein ring, the cross sections of the first two type are small because central caustics and minorimage planetary caustics are small. Indeed, it was the small size 2 There exist six cases of binary microlenses with companion masses at around this boundary including MOA-2010-BLG-073L (Street et al 2013), OGLE-2013-BLG-0102L (Jung et al 2015), MOA-2015-BLG-337L (Miyazaki et al 2018), OGLE-2016-BLG-1190L (Ryu et al 2018), OGLE-2017-BLG-1375L (Han et al 2020b), and KMT-2019-BLG-1339L (Han et al 2020a of the planetary caustic in OGLE-2019-BLG-0954 that led to it entering our sample: small gaps in relatively dense and continuous coverage meant that there was no coverage over the short cusp crossing. However, as Yee et al (2021) have pointed out, resonant and near-resonant (defined as having "magnificationdeviation ridges" of at least 10% extending from the central to planetary caustic) have much larger cross sections, and they account for a large fraction of all planetary detections.…”

Three faint-source microlensing planets detected via the resonant-caustic channel

“…The first planet was KMT-2018-BLG-0748Lb (Han et al 2020b), for which the planetary signal had been missed due to the faintness of the source combined with relatively large finite-source effects. This discovery was followed by the detections of: KMT-2016-BLG-2364Lb, KMT-2016-BLG-2397Lb, OGLE-2017-BLG-0604Lb, and OGLE-2017, for all of which the lensing events involved faint source stars (Han et al 2021a); KMT-2019-BLG-1339Lb, for which the planetary signal was partially covered (Han et al 2020a); KMT-2018-BLG-1976Lb, OGLE-2019-BLG-0954Lb, and KMT-2018, for which the planetary signals were produced through a non-caustic-crossing channel and were thus weak (Han et al 2021b); and KMT-2018-BLG-1025Lb, for which the planetary signal had been missed due to the low mass ratio of the planet (q ∼ 0.8 × 10 −4 or 1.6 × 10 −4 for two degenerate solutions) together with the non-caustic-crossing nature of its planetary signal (Han et al 2021c). Visually inspecting missing planets can provide various types of planetary signals that are prone to being missed and thus can help to develop a more complete algorithm for automatized planet detections.…”