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