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Pakuranga, New Zealand

Freeman M.,University of Auckland | Philpott L.C.,University of British Columbia | Abe F.,Nagoya University | Albrow M.D.,University of Canterbury | And 21 more authors.
Astrophysical Journal | Year: 2015

Recently Sumi et al. reported evidence for a large population of planetary-mass objects (PMOs) that are either unbound or orbit host stars in orbits ≤10 AU. Their result was deduced from the statistical distribution of durations of gravitational microlensing events observed by the MOA collaboration during 2006 and 2007. Here we study the feasibility of measuring the mass of an individual PMO through microlensing by examining a particular event, MOA-2011-BLG-274. This event was unusual as the duration was short, the magnification high, the source-size effect large, and the angular Einstein radius small. Also, it was intensively monitored from widely separated locations under clear skies at low air masses. Choi et al. concluded that the lens of the event may have been a PMO but they did not attempt a measurement of its mass. We report here a re-analysis of the event using re-reduced data. We confirm the results of Choi et al. and attempt a measurement of the mass and distance of the lens using the terrestrial parallax effect. Evidence for terrestrial parallax is found at a 3σ level of confidence. The best fit to the data yields the mass and distance of the lens as 0.80 ± 0.30 MJ and 0.80 ± 0.25 kpc respectively. We exclude a host star to the lens out to a separation ∼40 AU. Drawing on our analysis of MOA-2011-BLG-274 we propose observational strategies for future microlensing surveys to yield sharper results on PMOs including those down to super-Earth mass. © 2015. The American Astronomical Society. All rights reserved. Source


Bennett D.P.,University of Notre Dame | Rhie S.H.,University of Notre Dame | Nikolaev S.,Lawrence Livermore National Laboratory | Gaudi B.S.,Ohio State University | And 73 more authors.
Astrophysical Journal | Year: 2010

We present a new analysis of the Jupiter+Saturn analog system, OGLE-2006-BLG-109Lb,c, which was the first double planet system discovered with the gravitational microlensing method. This is the only multi-planet system discovered by any method with measured masses for the star and both planets. In addition to the signatures of two planets, this event also exhibits a microlensing parallax signature and finite source effects that provide a direct measure of the masses of the star and planets, and the expected brightness of the host star is confirmed by Keck AO imaging, yielding masses of M * = 0.51+0.05?0.04 M⊙ Mb = 231 ± 19M, and Mc = 86 ± 7M. The Saturn-analog planet in this system had a planetary light-curve deviation that lasted for 11 days, and as a result, the effects of the orbital motion are visible in the microlensing light curve. We find that four of the six orbital parameters are tightly constrained and that a fifth parameter, the orbital acceleration, is weakly constrained. No orbital information is available for the Jupiter-analog planet, but its presence helps to constrain the orbital motion of the Saturn-analog planet. Assuming co-planar orbits, we find an orbital eccentricity of ε = 0.15+0.17?0.10 and an orbital inclination of i = 64° +4°?7° . The 95% confidence level lower limit on the inclination of i> 49° implies that this planetary system can be detected and studied via radial velocity measurements using a telescope of ≳30m aperture. © 2010. The American Astronomical Society. Source


Ryu Y.-H.,Chungbuk National University | Han C.,Chungbuk National University | Hwang K.-H.,Las Cumbres Observatory Global Telescope Network | Street R.,University of Warsaw | And 118 more authors.
Astrophysical Journal | Year: 2010

We report the result of the analysis of a dramatic repeating gravitational microlensing event OGLE-2009-BLG-092/MOA-2009-BLG-137, for which the light curve is characterized by two distinct peaks with perturbations near both peaks. We find that the event is produced by the passage of the source trajectory over the central perturbation regions associated with the individual components of a wide-separation binary. The event is special in the sense that the second perturbation, occurring ∼100 days after the first, was predicted by the real-time analysis conducted after the first peak, demonstrating that real-time modeling can be routinely done for binary and planetary events.With the data obtained from follow-up observations covering the second peak, we are able to uniquely determine the physical parameters of the lens system.We find that the event occurred on a bulge clump giant and itwas produced by a binary lens composed of a K- and M-type main-sequence stars. The estimated masses of the binary components are M1 = 0.69±0.11M⊙ and M2 = 0.36±0.06M⊙, respectively, and they are separated in projection by r⊥ = 10.9±1.3AU. The measured distance to the lens is DL = 5.6 ± 0.7 kpc. We also detect the orbital motion of the lens system. © 2010. The American Astronomical Society. Source


Shin I.-G.,Chungbuk National University | Han C.,Chungbuk National University | Gould A.,Ohio State University | Udalski A.,University of Warsaw | And 171 more authors.
Astrophysical Journal | Year: 2012

Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation histories. In this paper, we present the candidate binaries with brown dwarf companions that are found by analyzing binary microlensing events discovered during the 2004-2011 observation seasons. Based on the low mass ratio criterion of q < 0.2, we found seven candidate events: OGLE-2004-BLG-035, OGLE-2004-BLG-039, OGLE-2007-BLG-006, OGLE-2007-BLG-399/MOA-2007-BLG-334, MOA-2011-BLG-104/OGLE-2011-BLG-0172, MOA-2011-BLG-149, and MOA-201-BLG-278/OGLE- 2011-BLG-012N. Among them, we are able to confirm that the companions of the lenses of MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149 are brown dwarfs by determining the mass of the lens based on the simultaneous measurement of the Einstein radius and the lens parallax. The measured masses of the brown dwarf companions are 0.02 ± 0.01 M and 0.019 ± 0.002 M for MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149, respectively, and both companions are orbiting low-mass M dwarf host stars. More microlensing brown dwarfs are expected to be detected as the number of lensing events with well-covered light curves increases with new-generation searches. © 2012. The American Astronomical Society. All rights reserved. Source


Street R.A.,LCOGT | Choi J.-Y.,Chungbuk National University | Tsapras Y.,LCOGT | Tsapras Y.,Queen Mary, University of London | And 134 more authors.
Astrophysical Journal | Year: 2013

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. © 2013 The American Astronomical Society. All rights reserved. Source

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