* Astronomy

Title: A sub-Saturn Mass Planet, MOA-2009-BLG-319Lb
Authors: N. Miyake, T. Sumi, Subo Dong, R. Street, L. Mancini, A. Gould, D. P. Bennett, Y. Tsapras, J. C. Yee, M. D. Albrow, I. A. Bond, P. Fouque, P. Browne, C. Han, C. Snodgrass, F. Finet, K. Furusawa, K. Harpsoe, W. Allen, M. Hundertmark, M. Freeman, D. Suzuki, F. Abe, C. S. Botzler, D. Douchin, A. Fukui, F. Hayashi, J. B. Hearnshaw, S. Hosaka, Y. Itow, K. Kamiya, P. M. Kilmartin, A. Korpela, W. Lin, C. H. Ling, S. Makita, K. Masuda, Y. Matsubara, Y. Muraki, T. Nagayama, K. Nishimoto, K. Ohnishi, Y. C. Perrott, N. Rattenbury, To. Saito, L. Skuljan, D. J. Sullivan, W. L. Sweatman, P. J. Tristram, K. Wada, P. C. M. Yock, The MOA Collaboration, G. Bolt, M. Bos, G.W. Christie, D.L. DePoy, J. Drummond, A. Gal-Yam, B.S. Gaudi, E. Gorbikov, D. Higgins, K.-H. Hwang J. Janczak, S. Kaspi, C.-U. Lee, J.-R. Koo, S. Koz lowski, Y. Lee, F. Mallia, A. Maury, D. Maoz, J. McCormick, L.A.G. Monard, D. Moorhouse, J. A. Mu~noz, T. Natusch, E.O. Ofek, R.W. Pogge, D. Polishook, R. Santallo, A. Shporer, O. Spector, G. Thornley, The Micro FUN Collaboration, A. Allan, D. M. Bramich, K. Horne, N. Kains, I. Steele, The RoboNet Collaboration, V. Bozza, M. J. Burgdorf, S. Calchi Novati, M. Dominik, S. Dreizler, M. Glitrup, F. V. Hessman, T. C. Hinse, U. G. Jorgensen, C. Liebig, G. Maier, M. Mathiasen, S. Rahvar, D. Ricci, G. Scarpetta, J. Skottfelt, J. Southworth, J. Surdej, J. Wambsganss, F. Zimmer, The MiNDSTEp Consortium, V. Batista, J. P. Beaulieu, S. Brillant, A. Cassan, A. Cole, E. Corrales, Ch. Coutures, S. Dieters, J. Greenhill, D. Kubas, J. Menzies, The PLANET Collaboration
et al. (57 additional authors not shown)
(Version v2)

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.

Read more (172kb, PDF)