MOA-2006-BLG-074: recognizing xallarap contaminants in planetary microlensing

TL;DR

This paper demonstrates that xallarap effects, caused by binary sources, can mimic planetary signals in microlensing events, emphasizing the need to account for them in planetary detection analyses.

Contribution

It reveals that xallarap can explain certain microlensing anomalies previously attributed to planets, highlighting its importance in accurate planetary demographics.

Findings

Xallarap can mimic planetary signals in microlensing.

Binary source orbital motion can be well characterized from light curves.

Xallarap effects must be considered in planetary microlensing surveys.

Abstract

MOA-2006-BLG-074 was selected as one of the most promising planetary candidates in a retrospective analysis of the MOA collaboration: its asymmetric high-magnification peak can be perfectly explained by a source passing across a central caustic deformed by a small planet. However, after a detailed analysis of the residuals, we have realized that a single lens and a source orbiting with a faint companion provides a more satisfactory explanation for all the observed deviations from a Paczynski curve and the only physically acceptable interpretation. Indeed the orbital motion of the source is constrained enough to allow a very good characterization of the binary source from the microlensing light curve. The case of MOA-2006-BLG-074 suggests that the so-called xallarap effect must be taken seriously in any attempts to obtain accurate planetary demographics from microlensing surveys.