* Astronomy

Title: MOA-2010-BLG-311: A planetary candidate below the threshold of reliable detection
Authors: J.C. Yee, L.-W. Hung, I.A. Bond, W. Allen, L.A.G. Monard, M.D. Albrow, P. Fouque, M. Dominik, Y. Tsapras, A. Udalski, A. Gould, R. Zellem, the MicroFUN, MOA, OGLE, PLANET, RoboNet Collaborations, the MiNDSTEp Consortium

We analyse MOA-2010-BLG-311, a high magnification (A_max>600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event with both a point lens and a 2-body lens model and find that the 2-body lens model is a better fit but with only Delta chi²~140. The preferred mass ratio between the lens star and its companion is q=10^(-3.7±0.1), placing the candidate companion in the planetary regime. Despite the formal significance of the planet, we show that because of systematics in the data the evidence for a planetary companion to the lens is too tenuous to claim a secure detection. When combined with analyses of other high-magnification events, this event helps empirically define the threshold for reliable planet detection in high-magnification events, which remains an open question.

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