Moa-2010-BLG-073L: An m-dwarf with a substellar companion at the planet/brown dwarf boundary

R. A. Street, J. Y. Choi, Y. Tsapras, C. Han*, K. Furusawa, M. Hundertmark, A. Gould, T. Sumi, I. A. Bond, D. Wouters, R. Zellem, A. Udalski, C. Snodgrass, K. Horne, M. Dominik, P. Browne, N. Kains, D. M. Bramich, D. Bajek, I. A. SteeleS. Ipatov, F. Abe, D. P. Bennett, C. S. Botzler, P. Chote, M. Freeman, A. Fukui, P. Harris, Y. Itow, C. H. Ling, K. Masuda, Y. Matsubara, N. Miyake, Y. Muraki, T. Nagayama, S. Nishimaya, K. Ohnishi, N. Rattenbury, To Saito, D. J. Sullivan, D. Suzuki, W. L. Sweatman, P. J. Tristram, K. Wada, P. C.M. Yock, M. K. Szymański, M. Kubiak, G. Pietrzyński, I. Soszyński, R. Poleski, K. Ulaczyk, Wyrzykowski, J. Yee, S. Dong, I. G. Shin, C. U. Lee, J. Skowron, L. Andrade De Almeida, D. L. Depoy, B. S. Gaudi, L. W. Hung, F. Jablonski, S. Kaspi, N. Klein, K. H. Hwang, J. R. Koo, D. Maoz, J. A. Muñoz, R. W. Pogge, D. Polishhook, A. Shporer, J. McCormick, G. Christie, T. Natusch, B. Allen, J. Drummond, D. Moorhouse, G. Thornley, M. Knowler, M. Bos, G. Bolt, J. P. Beaulieu, M. D. Albrow, V. Batista, S. Brillant, J. A.R. Caldwell, A. Cassan, A. Cole, E. Corrales, Ch Coutures, S. Dieters, D. Dominis Prester, J. Donatowicz, P. Fouqué, E. Bachelet, J. Greenhill, S. R. Kane, D. Kubas, J. B. Marquette, R. Martin, J. Menzies, K. R. Pollard, K. C. Sahu, J. Wambsganss, A. Williams, M. Zub, K. A. Alsubai, V. Bozza, M. J. Burgdorf, S. Calchi Novati, P. Dodds, S. Dreizler, F. Finet, T. Gerner, S. Hardis, K. Harpsøe, F. Hessman, T. C. Hinse, U. G. Jørgensen, E. Kerins, C. Liebig, L. Mancini, M. Mathiasen, M. T. Penny, S. Proft, S. Rahvar, D. Ricci, G. Scarpetta, S. Schäfer, F. Schönebeck, J. Southworth, J. Surdej

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010 March 18. This event was remarkable because the source was previously known to be photometrically variable. Analyzing the pre-event source light curve, we demonstrate that it is an irregular variable over timescales >200 days. Its dereddened color, (V-I)S, 0, is 1.221 ± 0.051 mag, and from our lens model we derive a source radius of 14.7 ± 1.3 R, suggesting that it is a red giant star. We initially explored a number of purely microlensing models for the event but found a residual gradient in the data taken prior to and after the event. This is likely to be due to the variability of the source rather than part of the lensing event, so we incorporated a slope parameter in our model in order to derive the true parameters of the lensing system. We find that the lensing system has a mass ratio of q = 0.0654 ± 0.0006. The Einstein crossing time of the event, tE = 44.3 ± 0.1 days, was sufficiently long that the light curve exhibited parallax effects. In addition, the source trajectory relative to the large caustic structure allowed the orbital motion of the lens system to be detected. Combining the parallax with the Einstein radius, we were able to derive the distance to the lens, DL = 2.8 ± 0.4 kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with ML,1 = 0.16 ± 0.03 M, while the companion has ML,2 = 11.0 ± 2.0 MJ, putting it in the boundary zone between planets and brown dwarfs.

Original languageEnglish
Article number67
JournalAstrophysical Journal
Issue number1
StatePublished - 20 Jan 2013


FundersFunder number
National Science Foundation0807444
Seventh Framework Programme268421, 246678
Science and Technology Facilities CouncilST/J001562/1, ST/G009465/1, ST/J001651/1, ST/H002391/1, PP/E001149/1, ST/G001987/1, ST/G002355/1, PP/F000057/1, ST/J001384/1, PP/D000955/1, ST/J001465/1, ST/J000035/1
Japan Society for the Promotion of Science23340044, 23340064, 23540339, 24253004, 23654082


    • brown dwarfs
    • gravitational lensing: micro
    • planetary systems
    • planets and satellites: formation
    • planets and satellites: general
    • techniques: photometric


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