* Astronomy

Title: OGLE-2012-BLG-0563Lb: a Saturn-mass Planet around an M Dwarf with the Mass Constrained by Subaru AO imaging
Author: A. Fukui, A. Gould, T. Sumi, D. P. Bennett, I. A. Bond, C. Han, D. Suzuki, J.-P. Beaulieu, V. Batista, A. Udalski, R. A. Street, Y. Tsapras, M. Hundertmark, F. Abe, M. Freeman, Y. Itow, C. H. Ling, N. Koshimoto, K. Masuda, Y. Matsubara, Y. Muraki, K. Ohnishi, L. C. Philpott, N. Rattenbury, T. Saito, D. J. Sullivan, P. J. Tristram, A. Yonehara, J.-Y. Choi, G. W. Christie, D. L. DePoy, Subo Dong, J. Drummond, B. S. Gaudi, K.-H. Hwang, A. Kavka, C. U. Lee, J. McCormick, T. Natusch, H. Ngan, H. Park, R. W. Pogge, I-G. Shin, T.-G. Tan, J. C. Yee, M. K. Szymanski, G. Pietrzynski, I. Soszynski, R. Poleski, S. Kozlowski, P. Pietrukowicz, K. Ulaczyk, L. Wyrzykowski D. M. Bramich, P. Browne, M. Dominik, K. Horne, S. Ipatov, N. Kains, C. Snodgrass, I. A. Steele

We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with the planet-star mass ratio ~1 x 10^{-3}. Intensive photometric observations of a high-magnification microlensing event allow us to detect a clear signal of the planet. Although no parallax signal is detected in the light curve, we instead succeed at detecting the flux from the host star in high-resolution JHK'-band images obtained by the Subaru/AO188 and IRCS instruments, allowing us to constrain the absolute physical parameters of the planetary system. With the help of a spectroscopic information of the source star obtained during the high-magnification state by Bensby et al. (2013), we find that the lens system is located at 1.3^{+0.6}_{-0.8} kpc from us, and consists of an M dwarf (0.34^{+0.12}_{-0.20} solar masses) orbited by a Saturn-mass planet (0.39^{+0.14}_{-0.23} Jupiter masses) at the projected separation of 0.74^{+0.26}_{-0.42} AU (close model) or 4.3^{+1.5}_{-2.5} AU (wide model). The probability of contamination in the host star's flux, which would reduce the masses by a factor of up to 3, is estimated to be 17%. This possibility can be tested by future high-resolution imaging. We also estimate the (J-Ks) and (H-Ks) colours of the host star, which are marginally consistent with a low-metallicity mid-to-early M dwarf, although further observations are required for the metallicity to be conclusive. This is the fifth sub-Jupiter-mass (0.2<m_p/Jupiter masses<1) microlensing planet around an M dwarf with the mass well constrained. The relatively rich harvest of sub-Jupiters around M dwarfs is contrasted with a possible paucity of ~1--2 Jupiter-mass planets around the same type of star, which can be explained by the planetary formation process in the core accretion scheme.

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