MOA-2011-BLG-262Lb : a sub-earth-mass moon orbiting a gas giant primary or a high velocity planetary system in the galactic bulge
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We present the first microlensing candidate for a free-floating exoplanet-exomoon system, MOA-2011-BLG-262, with a primary lens mass of M host ~ 4 Jupiter masses hosting a sub-Earth mass moon. The argument for an exomoon hinges on the system being relatively close to the Sun. The data constrain the product MLπrel where ML is the lens system mass and πrel is the lens-source relative parallax. If the lens system is nearby (large πrel), then ML is small (a few Jupiter masses) and the companion is a sub-Earth-mass exomoon. The best-fit solution has a large lens-source relative proper motion, μrel = 19.6 ± 1.6 mas yr–1, which would rule out a distant lens system unless the source star has an unusually high proper motion. However, data from the OGLE collaboration nearly rule out a high source proper motion, so the exoplanet+exomoon model is the favored interpretation for the best fit model. However, there is an alternate solution that has a lower proper motion and fits the data almost as well. This solution is compatible with a distant (so stellar) host. A Bayesian analysis does not favor the exoplanet+exomoon interpretation, so Occam's razor favors a lens system in the bulge with host and companion masses of M host = 0.12 +0.19-0.06 MΘ and mcomp = 18+28-10M⊕, at a projected separation of a⊥ = 0.84+0.25−0.14 AU. The existence of this degeneracy is an unlucky accident, so current microlensing experiments are in principle sensitive to exomoons. In some circumstances, it will be possible to definitively establish the mass of such lens systems through the microlensing parallax effect. Future experiments will be sensitive to less extreme exomoons.
Bennett , D P , Batista , V , Bond , I A , Bennett , C S , Suzuki , D , Beaulieu , J-P , Udalski , A , Donatowicz , J , Bozza , V , Abe , F , Botzler , C S , Freeman , M , Fukunaga , D , Fukui , A , Itow , Y , Koshimoto , N , Ling , C H , Masuda , K , Matsubara , Y , Muraki , Y , Namba , S , Ohnishi , K , Rattenbury , N J , Saito , T , Sullivan , D J , Sumi , T , Sweatman , W L , Tristram , P J , Tsurumi , N , Wada , K , Yock , P C M , Albrow , M D , Bachelet , E , Brillant , S , Caldwell , J A R , Cassan , A , Cole , A A , Corrales , E , Coutures , C , Dieters , S , Dominis Prester , D , Fouqué , P , Greenhill , J , Horne , K , Koo , J-R , Kubas , D , Marquette , J-B , Martin , R , Menzies , J W , Sahu , K C , Wambsganss , J , Williams , A , Zub , M , Choi , J Y , Depoy , D L , Dong , S , Gaudi , B S , Gould , A , Han , C , Henderson , C B , McGregor , D , Lee , C-U , Pogge , R W , Shin , I-G , Yee , J C , Szymański , M K , Skowron , J , Poleski , R , Kozłowski , S , Wyrzykowski , Ł , Kubiak , M , Pietrukowicz , P , Pietrzyński , G , Soszyński , I , Ulaczyk , K , Tsapras , Y , Street , R A , Dominik , M , Bramich , D M , Browne , P , Hundertmark , M , Kains , N , Snodgrass , C , Steele , I A , Dekany , I , Gonzalez , O A , Heyrovský , D , Kandori , R , Kerins , E , Lucas , P W , Minniti , D , Nagayama , T , Rejkuba , M , Robin , A C & Saito , A R 2014 , ' MOA-2011-BLG-262Lb : a sub-earth-mass moon orbiting a gas giant primary or a high velocity planetary system in the galactic bulge ' Astrophysical Journal , vol 785 , no. 2 . DOI: 10.1088/0004-637X/785/2/155
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D.P.B. was supported by grants NASA-NNX12AF54G, JPL-RSA 1453175 and NSF AST-1211875. This MOA project is supported by the grants JSPS18253002 and JSPS20340052. T.S. acknowledges the financial support from the JSPS, JSPS23340044, JSPS24253004. This work was partially supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. B.S.G. and A.G. were supported by NSF grant AST 110347. B.S.G., A.G., R.P.G. were supported by NASA grant NNX12AB99G. S.D. was partly supported through a Ralph E. and Doris M. Hansmann Membership at the IAS and by NSF grant AST-0807444. Work by J.C.Y. was performed in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. The OGLE project has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement No. 246678 to A.U. D.H. was supported by Czech Science Foundation grant GACR P209/10/1318. D.M.B., M.D., K.H., C.S., R.A.S., M.H. and Y.T. are supported by NPRP grant NPRP-09-476-1-78 from the Qatar National Research Fund (a member of the Qatar Foundation).
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