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Sub-Saturn planet MOA-2008-BLG-310Lb: Likely to be in the galactic bulge


Janczak, J and Fukui, A and Dong, S and Monard, LAG and Kozlowski, S and Gould, A and Beaulieu, JP and Kubas, D and Marquette, JB and Sumi, T and Bond, IA and Bennett, DP and Abe, F and Furusawa, K and Hearnshaw, JB and Hosaka, S and Itow, Y and Kamiya, K and Korpela, AV and Kilmartin, PM and Lin, W and Ling, CH and Makita, S and Masuda, K and Matsubara, Y and Miyake, N and Muraki, Y and Nagaya, M and Nagayama, T and Nishimoto, K and Ohnishi, K and Perrott, YC and Rattenbury, NJ and Sako, T and Saito, T and Skuljan, L and Sullivan, DJ and Sweatman, WL and Tristram, PJ and Yock, PCM and An, JH and Christie, GW and Chung, SJ and DePoy, DL and Gaudi, BS and Han, C and Lee, CU and Mallia, F and Natusch, T and Park, BG and Pogge, RW and Anguita, T and Calchi Novati, S and Dominik, M and Jorgensen, UG and Masi, G and Mathiasen, M and Batista, V and Brilliant, S and Cassan, A and Cole, A and Corrales, E and Coutures, C and Dieters, S and Fouque, P and Greenhill, J, Sub-Saturn planet MOA-2008-BLG-310Lb: Likely to be in the galactic bulge, Astrophysical Journal , 711, (2) pp. 731-743. ISSN 0004-637X (2010) [Refereed Article]

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Copyright 2010 The American Astronomical Society

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DOI: doi:10.1088/0004-637X/711/2/731


We report the detection of sub-Saturn-mass planet MOA-2008-BLG-310Lb and argue that it is the strongest candidate yet for a bulge planet. Deviations from the single-lens fit are smoothed out by finite-source effects and therefore are not immediately apparent from the light curve. Nevertheless, we find that a model in which the primary has a planetary companion is favored over the single-lens model by 2 ~ 880 for an additional 3 degrees of freedom. Detailed analysis yields a planet/star mass ratio q = (3.3 0.3) 10C4 and an angular separation between the planet and star within 10% of the angular Einstein radius. The small angular Einstein radius, E = 0.155 0.011 mas, constrains the distance to the lens to be DL >6.0 kpc if it is a star (ML >0.08 M ). This is the only microlensing exoplanet host discovered so far that must be in the bulge if it is a star. By analyzing VLT NACO adaptive optics images taken near the baseline of the event, we detect additional blended light that is aligned to within 130 mas of the lensed source. This light is plausibly from the lens, but could also be due to a companion to the lens or source, or possibly an unassociated star. If the blended light is indeed due to the lens, we can estimate the mass of the lens, ML = 0.67 0.14 M , planet mass m = 74 17 M , and projected separation between the planet and host, 1.25 0.10 AU, putting it right on the "snow line." If not, then the planet has lower mass, is closer to its host and is colder. To distinguish among these possibilities on reasonable timescales would require obtaining Hubble Space Telescope images almost immediately, before the source-lens relative motion of U=5 mas yr -1 causes them to separate substantially.

Item Details

Item Type:Refereed Article
Keywords:Galaxy: bulge; gravitational lensing: micro; planets and satellites: detection
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Galactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Cole, A (Associate Professor Andrew Cole)
UTAS Author:Greenhill, J (Dr John Greenhill)
ID Code:63621
Year Published:2010
Web of Science® Times Cited:82
Deposited By:Physics
Deposited On:2010-05-18
Last Modified:2011-03-23
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