* Astronomy

Title: Planetary and Other Short Binary Microlensing Events from the MOA Short Event Analysis
Authors: D. P. Bennett, T. Sumi, I. A. Bond, K. Kamiya, F. Abe, C. S. Botzler, A. Fukui, K. Furusawa, Y. Itow, A. V. Korpela, P. M. Kilmartin, C. H. Ling, K. Masuda, Y. Matsubara, N. Miyake, Y. Muraki, K. Ohnishi, N. J. Rattenbury, To. Saito, D. J. Sullivan, D. Suzuki, W. L. Sweatman, P. J. Tristram, K. Wada, P. C. M. Yock (The MOA Collaboration)

We present the analysis of four candidate short duration binary microlensing events from the 2006-2007 MOA Project short event analysis. These events were discovered in an analysis designed to find short timescale single lens events that may be due to free-floating planets. Three of these events are determined to be microlensing events, while the fourth is most likely caused by stellar variability. For each of the three microlensing events, the signal is almost entirely due to a brief caustic feature with little or no lensing attributable mainly to the lens primary. One of these events, MOA-bin-1, is due to a planet, and it is the first example of a planetary event in which stellar host is only detected through binary microlensing effects. The mass ratio, q = 4.9 ±1.4 x 10^{-3}, is relatively large for a planetary system, and the star-planet separation, s = 2.10 ±0.05, is the largest ever for a low magnification microlensing event. The planet MOA-bin-1Lb has a mass of m_p = 3.7 ±2.1 M_Jup, and orbits a star of M_\ast = 0.75 (+0.33 -0.41) M_solar at a semi-major axis of a = 8.3 (+4.5 -2.7) AU, according to a Bayesian analysis based on a standard Galactic model. This is one of the most massive planets found by microlensing. The scarcity of such wide separation planets also has implications for interpretation of the isolated planetary mass objects found by this analysis. If these planets are actually bound in wide orbits around host stars, then it is likely that the median orbital semi-major axis is > 30 AU.

Read more (2186kb, PDF)