A sub-Saturn Mass Planet, MOA-2009-BLG-319Lb

Miyake, N.; Sumi, T.; Dong, Subo; Street, R.; Mancini, Luigi; Gould, A.; Bennett, D. P.; Tsapras, Y.; Yee, J. C.; Albrow, M. D.; Bond, I. A.; Fouque, P.; Browne, P.; Han, C.; Snodgrass, C.; Finet, F.; Furusawa, K.; Harpsoe, K.; Allen, W.; Hundertmark, M.; Freeman, M.; Suzuki, D.; Abe, F.; Botzler, C. S.; Douchin, D.; Fukui, A.; Hayashi, F.; Hearnshaw, J. B.; Hosaka, S.; Itow, Y.; Kamiya, K.; Kilmartin, P. M.; Korpela, A.; Lin, W.; Ling, C. H.; Makita, S.; Masuda, K.; Matsubara, Y.; Muraki, Y.; Nagayama, T.; Nishimoto, K.; Ohnishi, K.; Perrott, Y. C.; Rattenbury, N.; Saito, T. O.; Skuljan, L.; Sullivan, D. J.; Sweatman, W. L.; Tristram, P. J.; Wada, K.; Yock, P. C. M.; The Moa Collaboration,; Bolt, G.; Bos, M.; Christie, G. W.; Depoy, D. L.; Drummond, J.; Gal Yam, A.; Gaudi, B. S.; Gorbikov, E.; Higgins, D.; Janczak, K. H. Hwang J.; Kaspi, S.; Lee, C. U.; Koo, J. R.; Kozlowski, S.; Lee, Y.; Mallia, F.; Maury, A.; Maoz, D.; Mccormick, J.; Monard, L. A. G.; Moorhouse, D.; Munoz, J. A.; Natusch, T.; Ofek, E. O.; Pogge, R. W.; Polishook, D.; Santallo, R.; Shporer, A.; Spector, O.; Thornley, G.; Allan, A.; Bramich, D. M.; Horne, K.; Kains, N.; Steele, I.; Bozza, Valerio; Burgdorf, M. J.; Calchi Novati, Sebastiano; Dominik, M.; Dreizler, S.; Glitrup, M.; Hessman, F. V.; Hinse, T. C.; Jørgensen, U. G.; Liebig, C.; Maier, G.; Mathiasen, M.; Rahvar, S.; Ricci, D.; Scarpetta, Gaetano; Skottfelt, J.; Southworth, J.; Surdej, J.; Wambsganss, J.; Zimmer, F.; Batista, V.; Beaulieu, J. P.; Brillant, S.; Cassan, A.; Cole, A.; Corrales, E.; Coutures, C. H.; Dieters, S.; Greenhill, J.; Kubas, D.; Menzies, J.

doi:10.1088/0004-637X/728/2/120

We report the gravitational microlensing discovery of a sub-Saturn mass planet, MOA-2009-BLG-319Lb, orbiting a K or M-dwarf star in the inner Galactic disk or Galactic bulge. The high cadence observations of the MOA-II survey discovered this microlensing event and enabled its identification as a high magnification event approximately 24 hours prior to peak magnification. As a result, the planetary signal at the peak of this light curve was observed by 20 different telescopes, which is the largest number of telescopes to contribute to a planetary discovery to date. The microlensing model for this event indicates a planet-star mass ratio of q = (3.95 +/- 0.02) x 10^{-4} and a separation of d = 0.97537 +/- 0.00007 in units of the Einstein radius. A Bayesian analysis based on the measured Einstein radius crossing time, t_E, and angular Einstein radius, \theta_E, along with a standard Galactic model indicates a host star mass of M_L = 0.38^{+0.34}_{-0.18} M_{Sun} and a planet mass of M_p = 50^{+44}_{-24} M_{Earth}, which is half the mass of Saturn. This analysis also yields a planet-star three-dimensional separation of a = 2.4^{+1.2}_{-0.6} AU and a distance to the planetary system of D_L = 6.1^{+1.1}_{-1.2} kpc. This separation is ~ 2 times the distance of the snow line, a separation similar to most of the other planets discovered by microlensing.