A Second Method to Photometrically Align Multi-Site Microlensing Light Curves: Source Color in Planetary Event MOA-2007-BLG-192

TL;DR

This paper introduces a second photometric alignment method using common field stars, improving source color estimation in microlensing events, exemplified by the MOA-2007-BLG-192 planetary event.

Contribution

The paper presents a novel technique for photometrically aligning microlensing light curves using field star photometry, enhancing source color determination.

Findings

Refined source color estimate: V-I=2.36 ± 0.03

Method resolves ambiguities in event prediction

Application to MOA-2007-BLG-192 improves lens mass estimates

Abstract

At present, microlensing light curves from different telescopes and filters are photometrically aligned by fitting them to a common model. We present a second method based on photometry of common field stars. If two spectral responses are similar (or the color of the source is known) then this technique can resolve important ambiguities that frequently arise when predicting the future course of the event, and that occasionally persist even when the event is over. Or if the spectral responses are different, it can be used to derive the color of the source when that is unknown. We present the essential elements of this technique and apply it to the case of MOA-2007-BLG-192, an important planetary event for which the system may be a terrestrial planet orbiting a brown dwarf or very low mass star. The refined estimate of the source color that we derive here, V-I=2.36 +- 0.03, will aid in making the estimate of the lens mass more precise.