Systematic KMTNet Planetary Anomaly Search. VI. Complete Sample of 2018 Sub-Prime-Field Planets

TL;DR

This paper completes the analysis of 2018 sub-prime-field microlensing planets from KMTNet, identifying new planetary events and establishing a foundation for statistical analysis of planet mass ratios.

Contribution

It provides a complete sample of 2018 sub-prime-field planets, including new planetary solutions, and supports the first statistical study of planet mass-ratio distribution from KMTNet data.

Findings

6 new clear planetary events identified

Half of the 2018 planets have non-caustic-crossing anomalies

Semi-automated search is crucial for detecting low-mass-ratio planets

Abstract

We complete the analysis of all 2018 sub-prime-field microlensing planets identified by the KMTNet AnomalyFinder. Among the 9 previously unpublished events with clear planetary solutions, 6 are clearly planetary (KMT-2018-BLG-0030, KMT-2018-BLG-0087, KMT-2018-BLG-0247, OGLE-2018-BLG-0298, KMT-2018-BLG-2602, and OGLE-2018-BLG-1119), while the remaining 3 are ambiguous in nature. In addition, there are 8 previously published sub-prime field planets that were selected by the AnomalyFinder algorithm. Together with a companion paper (Gould et al. 2022) on 2018 prime-field planets, this work lays the basis for the first statistical analysis of the planet mass-ratio function based on planets identified in KMTNet data. As expected (Zhu et al. 2014), half (17/33) of the 2018 planets likely to enter the mass-ratio analysis have non-caustic-crossing anomalies. However, only 1 of the 5 non-caustic anomalies with planet-host mass ratio $q<10^{-3}$ was discovered by eye (compared to 7 of the 12 with $q>10^{-3}$), showing the importance of the semi-automated AnomalyFinder search.