摘要：We report on the analysis of a microlensing event, OGLE-2014-BLG-1722, that showed two distinct short-term anomalies. The best-fit model to the observed light curves shows that the two anomalies are explained with two planetary mass ratio companions to the primary lens. Although a binary-source model is also able to explain the second anomaly, it is marginally ruled out by 3.1σ. The two-planet model indicates that the first anomaly was caused by planet “b” with a mass ratio of q 4.5 0.6 10 = 0.7 ´ 4 - ( + ) - and projected separation in units of the Einstein radius, s=0.753±0.004. The second anomaly reveals planet “c” with a mass ratio of q2 7.0 1.7 10 = 2.3 ´ 4 - ( + ) - with Δχ2∼170 compared to the single-planet model. Its separation has two degenerated solutions: the separation of planet c is s2=0.84±0.03 and 1.37±0.04 for the close and wide models, respectively. Unfortunately, this event does not show clear finite-source and microlensing parallax effects; thus, we estimated the physical parameters of the lens system from Bayesian analysis. This gives the masses of planets b and c as mb 56 33 = 51 - + and m 85 M c 51 = 86 - + Å, respectively, and they orbit a late-type star with a mass of Mhost = 0.40 0.24 M 0.36 - + located at DL 6.4 1.8 kpc = 1.3 - + from us. The projected distances between the host and planets are r^,b = 1.5 0.6 au for planet b and r ,c 1.7 0.6 au = 0.7 ^ - + and r 2.7 au ,c 1.0 = 1.1 ^ - + for the close and wide models of planet c. If the two-planet model is true, then this is the third multiple-planet system detected using the microlensing method and the first multiple-planet system detected in low-magnification events, which are dominant in the microlensing survey data. The occurrence rate of multiple cold gas giant systems is estimated using the two such detections and a simple extrapolation of the survey sensitivity of the 6 yr MOA microlensing survey combined with the 4 yr μFUN detection efficiency. It is estimated that 6%±2% of stars host two cold giant planets.
关键词：gravitational lensing: micro;planetary systems
