KMT-2018-BLG-1990Lb: A Nearby Jovian Planet From A Low-cadence Microlensing Field

We report the discovery of KMT-2018-BLG-1990Lb, a Jovian planet ({m}_p={0.57}_-0.25^+0.79 {M}_J) orbiting a late M dwarf (M={0.14}_-0.06^+0.20 {M}_⊙ ) at a distance of ({D}_L={1.23}_-0.43^+1.06 {kpc}), and projected at 2.6 ± 0.6 times the snow line distance, i.e., {a}_snow}\equiv 2.7 {au}(M/{M}_⊙ ). This is the second Jovian planet discovered by the Korea Microlensing Telescope Network (KMTNet) in its low-cadence (0.4 hr^-1) fields, demonstrating that this population can be probed based on relatively low-cadence survey-only microlensing data. However, while many Jovian-planet microlensing events will not have caustic crossings (e.g., the previous case, KMT-2016-BLG-1397) and some that do will be well characterized by low-cadence survey observations (e.g., the current case), in general higher-cadence follow-up observations of the caustic crossings are preferable. Such follow-up observations require microlensing alerts, which KMTNet now provides.