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Post Info TOPIC: MOA-2011-BLG-293Lb
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RE: MOA-2011-BLG-293Lb
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Title: MOA-2011-BLG-293Lb: First Microlensing Planet possibly in the Habitable Zone
Author: V. Batista, J.-P. Beaulieu, A. Gould, D.P. Bennett, J.C Yee, A. Fukui, B.S. Gaudi, T. Sumi, A. Udalski

We used Keck adaptive optics observations to identify the first planet discovered by microlensing to lie in or near the habitable zone, i.e., at projected separation r_t=1.1±0.1AU from its ML=0.86±0.06 solar masses host, being the highest microlensing mass definitely identified. The planet has a mass mp=4.8±0.3 Jupiter masses, and could in principle have habitable moons. This is also the first planet to be identified as being in the Galactic bulge with good confidence: DL=7.7±0.44 kpc. The planet/host masses and distance were previously not known, but only estimated using Bayesian priors based on a Galactic model (Yee et al. 2012). These estimates had suggested that the planet might be a super-Jupiter orbiting an M dwarf, a very rare class of planets. We obtained high-resolution JHK images using Keck adaptive optics to detect the lens and so test this hypothesis. We clearly detect light from a G dwarf at the position of the event, and exclude all interpretations other than that this is the lens with high confidence (95%), using a new astrometric technique. The calibrated magnitude of the planet host star is HL=19.16±0.13. We infer the following probabilities for the three possible orbital configurations of the gas giant planet: 53% to be in the habitable zone, 35% to be near the habitable zone, and 12% to be beyond the snow line, depending on the atmospherical conditions.

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Title: MOA-2011-BLG-293Lb: A testbed for pure survey microlensing planet detections
Authors: J. C. Yee, Y. Shvartzvald, A. Gal-Yam, I. A. Bond, A. Udalski, S. Kozlowski, C. Han, A. Gould, J. Skowron, D. Suzuki, the MOA Collaboration, the OGLE Collaboration, the MicroFUN Collaboration

Microlensing planet searches are transitioning from "survey+followup" mode to "pure survey" mode, wherein events will be monitored without reference to the presence of planets, which will enable a more rigorous statistical interpretation. Such surveys will be able to monitor many more events but at a lower cadence than typical followup observations, meaning that the significance of the planets detected in this manner will be lower. It would be useful to test these pure survey detections to ensure that even with sparser data, the planets can be reliably detected. MOA-2011-BLG-293 provides one such test. This planet is robustly detected in survey+followup data (DeltaChi˛~5400). The planet/host mass ratio is q=5.1 ±0.2*10^(-3). The best fit projected separation is s=0.545 ±0.005 Einstein radii. However, due to the s -> 1/s degeneracy, projected separations of 1/s are only marginally disfavoured at DeltaChi˛=2. A Bayesian estimate of the host mass gives M_L = 0.44^{+0.27}_{-0.17} solar masses, with a sharp upper limit of M_L < 1.2 solar masses from upper limits on the lens flux. Hence, the best estimate of the planet mass is m_p=2.4^{+1.4}_{-0.9} Jupiter masses, and the physical projected separation is either r_perp ~ 1.0 AU or r_perp ~ 3.5 AU. We show that survey data alone correctly predict this solution and are able to characterise the planet even though the signal from the planet is close to the limit of detectability (DeltaChi^2~500). Analysing a large sample of events like MOA-2011-BLG-293, which have both followup data and high cadence survey data, will provide a guide for the interpretation of pure survey microlensing data.

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