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2013•The Astrophysical JournalOpen access

MOA-2010-BLG-073L: AN M-DWARF WITH A SUBSTELLAR COMPANION AT THE PLANET/BROWN DWARF BOUNDARY

Rachel A. Street, J.-Y. Choi, Yiannis Tsapras, Cheongho Han, K. Furusawa, M. Hundertmark, Andrew P. Gould, T. Sumi, I. A. Bond, D. Wouters, Robert T. Zellem, Andrzej Udalski, C. Snodgrass, K. Horne, M. Dominik, Paul Browne, N. Kains, D. M. Bramich, David Bajek, Iain A. Steele, Sergei I. Ipatov, F. Abe, D. P. Bennett, C. S. Botzler, Paul Robin Brian Chote, M. Freeman, Akihiko Fukui, P. Harris, Y. Itow, C. H. Ling, Kento Masuda, Y. Matsubara, N. Miyake, Y. Muraki, T. Nagayama, S. Nishimaya, Koji Ohnishi, Nicholas James Rattenbury, To. Saito, Denis J. Sullivan, Daisuke Suzuki, Winston LeMay Sweatman, Paul . J. Tristram, K. Wada, P. C. M. Yock, Michał K. Szymański, Marcin Kubiak, Grzegorz Pietrzyński, I. Soszyński, R. Poleski, Krzysztof Ulaczyk, Ł. Wyrzykowski, Jennifer C. Yee, Subo Dong, In-Gu Shin, Chung‐Uk Lee, J. Skowron, L. A. Almeida, Darren L. DePoy, B. S. Gaudi, Li-Wei Hung, F. Jablonski, S. Kaspi, N. Klein, Kyu‐Ha Hwang, J.-R. Koo, Dan Maoz, Jose A. Muñoz, Richard W. Pogge, D. Polishhook, Avi Shporer, J. McCormick, Grant I. G. Christie, T. Natusch, Branden E. Allen, J. Drummond, D. Moorhouse, G. Thornley, M. Knowler, Marc Bos, Greg Bolt, Jean‐Philippe Beaulieu, Michael D. Albrow, V. Batista, S. Brillant, J. A. R. Caldwell, A. Cassan, Andrew A. Cole, Elizabeth Corrales, C. Coutures, S. Dieters, D. Dominis Prester, J. Donatowicz, Pascal Fouqué, E. Bachelet, J. G. Greenhill, Stephen R. Kane, D. Kubas, J. B. Marquette, Roland Martín, John W. Menzies, Karen R. Pollard, K. C. Sahu, Joachim Wambsganß, Andrew J. Williams, M. Zub, MiNDSTEp, Khalid A. Alsubai, V. Bozza, Martin Jörg Burgdorf, S. Calchi Novati, P. Dodds, S. Dreizler, F. Finet, T. Gerner, S. Hardis, K. Harpsøe, F. V. Hessman, T. C. Hinse, Uffe Gråe Jørgensen, Eamonn J. Kerins, Christine Liebig, Luigi Mancini, M. Mathiasen, Matthew T. Penny, S. Proft, S. Rahvar, D. Ricci, GAETANO SCARPETTA, Sebastian Schäfer, F. Schönebeck, John H. Southworth, J. Surdej

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Abstract

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, t E = 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, D L = 2.8 ± 0.4 kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with M L , 1 = 0.16 ± 0.03 M ☉ , while the companion has M L , 2 = 11.0 ± 2.0 M J , putting it in the boundary zone between planets and brown dwarfs.

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What this paper is about

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, t E = 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, D L = 2.8 ± 0.4 kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with M L , 1 = 0.16 ± 0.03 M ☉ , while the companion has M L , 2 = 11.0 ± 2.0 M J , putting it in the boundary zone between planets and brown dwarfs.

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Available abstract

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, t E = 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, D L = 2.8 ± 0.4 kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with M L , 1 = 0.16 ± 0.03 M ☉ , while the companion has M L , 2 = 11.0 ± 2.0 M J , putting it in the boundary zone between planets and brown dwarfs.

Key concepts: Gravitational microlensing, Physics, Einstein radius, Astrophysics, Planet, Light curve, Einstein ring, Caustic (mathematics)

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