You Shall Not Pass (Without Modeling): High-resolution Analysis of KMT-2019-BLG-0253 using MORIA

We present the Microlensing Object high-Resolution Imaging Analysis pipeline, or MORIA . This is an automated procedure to reduce high-resolution Hubble Space Telescope (HST) images of microlensing targets, build empirical point-spread function (PSF) models from the data, and perform simultaneous multistar PSF fitting to blended sources, lenses, and neighbor stars. We have developed and tested this pipeline using HST observations of the microlensing event KMT-2019-BLG-0253, which shows clear evidence of three highly blended stars in HST. Under our assumed source and lens identification, we determine a host mass of M host = 0.65 ± 0.04 M ⊙ . We have reduced the number of possible solutions for this target by a factor of 2, with the remaining solution subject to the well-known close/wide degeneracy. We determine a planet mass of m p = 7.18 ± 0.40 M ⊕ (close) or m p = 9.48 ± 1.13 M ⊕ (wide), and distance to the lens system of D L = 2.64 ± 0.22 kpc. This target lies within the upcoming Roman Telescope Galactic Bulge Time Domain Survey (GBTDS) field. Future analysis of the Roman data for this event can confirm or reject the initial source and lens identifications presented in this work. Finally, this work demonstrates the importance of using an automated high-resolution imaging tool to inform lightcurve modeling for microlensing planets found during the GBTDS.