A Planetary Microlensing Event with an Unusually Red Source Star: MOA-2011-BLG-291

David P. Bennett, Andrzej Udalski, Ian A. Bond, Daisuke Suzuki, Yoon Hyun Ryu, Fumio Abe, Richard K. Barry, Aparna Bhattacharya, Martin Donachie, Akihiko Fukui, Yuki Hirao, Kohei Kawasaki, Iona Kondo, Naoki Koshimoto, Man Cheung Alex Li, Yutaka Matsubara, Shota Miyazaki, Yasushi Muraki, Masayuki Nagakane, Koji OhnishiClément Ranc, Nicholas J. Rattenbury, Haruno Suematsu, Takahiro Sumi, Paul J. Tristram, Atsunori Yonehara, Michał K. Szymański, Igor Soszyński, Łukasz Wyrzykowski, Krzysztof Ulaczyk, Radek Poleski, Szymon Kozłowski, Paweł Pietrukowicz, Jan Skowron, Yossi Shvartzvald, Dan Maoz, Shai Kaspi, Matan Friedmann, Virginie Batista, Darren Depoy, Subo Dong, B. Scott Gaudi, Andrew Gould, Cheongho Han, Richard W. Pogge, Thiam Guan Tan, Jennifer C. Yee

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


We present the analysis of the planetary microlensing event MOA-2011-BLG-291, which has a mass ratio of q = (3.8 ± 0.7) × 10-4 and a source star that is redder (or brighter) than the bulge main sequence. This event is located at a low Galactic latitude in the survey area that is currently planned for NASA's Wide Field Infrared Survey Telescope (WFIRST) exoplanet microlensing survey. This unusual color for a microlensed source star implies that we cannot assume that the source star is in the Galactic bulge. The favored interpretation is that the source star is a lower main-sequence star at a distance of D S = 4.9 ± 1.3 kpc in the Galactic disk. However, the source could also be a turn-off star on the far side of the bulge or a subgiant in the far side of the Galactic disk if it experiences significantly more reddening than the bulge red clump stars. However, these possibilities have only a small effect on our mass estimates for the host star and planet. We find host star and planet masses of and from a Bayesian analysis with a standard Galactic model, under the assumption that the planet hosting probability does not depend on the host mass or distance. However, if we attempt to measure the host and planet masses with host star brightness measurements from high angular resolution follow-up imaging, the implied masses will be sensitive to the host star distance. The WFIRST exoplanet microlensing survey is expected to use this method to determine the masses for many of the planetary systems that it discovers, so this issue has important design implications for the WFIRST exoplanet microlensing survey.

Original languageEnglish
Article number113
JournalAstronomical Journal
Issue number3
StatePublished - Sep 2018


FundersFunder number
US-Israel Binational Science Foundation2017R1A4A1015178
National Science Foundation1516842
National Aeronautics and Space AdministrationNASA-80NSSC18K0274
Science and Technology Facilities CouncilST/P000495/1
Japan Society for the Promotion of Science17H02871, 16H05732, 18J00897, 16H06287, 17J02146
National Research Foundation of Korea
Israel Science Foundation1829/12
Narodowe Centrum NaukiMAESTRO 2014/14/A/ST9/00121
Israeli Centers for Research Excellence


    • gravitational lensing: micro
    • planetary systems


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