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^(+0.79)_(-0.25) M_J) orbiting a late M dwarf (M = 0.14^(+0.20)_(-0.06) M⊙) at a distance of (D_L = 1.23^(+1.06)_(-0.43) kpc, and projected at 2.6 ± 0.6 times the snow line distance, i.e., a_(snow) ≡ 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.