A Likely Detection of a Two-planet System in a Low-magnification Microlensing Event

Abstract

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 3.1 σ. The 2-planet model indicates that the first anomaly was caused by planet "b" with a mass ratio of q = (4.5 +0.7 −0.6 ) × 10 −4 and projected separation in unit of the A Microlensing Observations in Astrophysics (MOA) CollaborationEinstein radius, s = 0.753 ± 0.004. The second anomaly reveals planet "c" with a mass ratio of q 2 = (7.0 +2.3 −1.7 ) × 10 −4 with ∆χ 2 ∼ 170 compared to the single planet model. Its separation has two degenerated solutions: the separation of planet c is s 2 = 0.84 ± 0.03 and s 2 = 1.37 ± 0.04 for the close and wide models, respectively. Unfortunately, this event dose not show clear finite source and microlensing parallax effects, thus we estimated the physical parameters of the lens system from Bayesian analysis. This gives that the masses of planet b and c are m b = 56 +51 −33 M ⊕ and m c = 85 +86 −51 M ⊕ , respectively, and they orbit a late type star with a mass of M host = 0.40 +0.36 −0.24 M located at D L = 6.4 +1.3 −1.8 kpc from us. The projected distance between the host and planets are r ⊥,b = 1.5 ± 0.6 AU for planet b, and r ⊥,c = 1.7 +0.7 −0.6 AU and r ⊥,c = 2.7 +1.1 −1.0 AU for close and wide models of planet c. If the 2-planet model is true, then this is the third multiple planet system detected by using the microlensing method, and the first multiple planet system detected in the 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 6 year MOA microlensing survey (Suzuki et al. 2016) combined with the 4 year µFUN detection efficiency (Gould et al. 2010). It is estimated that 6 ± 2 % of stars host two cold giant planets.

OGLE-2018-BLG-0532Lb: Cold Neptune with Possible Jovian Sibling

“…Subsequently, Suzuki et al (2018b) showed that the OGLE-2014-BLG-1722 light curve has two unambiguous deviations from a Paczyński (1986) fit that are well explained by a 3L1S model with two planets. One deviation is a dip and so can only be due to a planet, but the other is a smooth bump, which could also in principle be caused by a second source.…”

OGLE-2018-BLG-1700L: Microlensing Planet in Binary Stellar System

“…By the time of writing this paper, there are nine published 3L1S events. Among them, five events were produced by multiplanet systems, including OGLE-2006-BLG-109 (Gaudi et al 2008Bennett et al 2010), OGLE-2012-BLG-0026 (Han et al 2013;Beaulieu et al 2016), OGLE-2014-BLG-1722(Suzuki et al 2018, OGLE-2018-BLG-0532 (Ryu et al 2019), and OGLE-2018-BLG-1011 (Han et al 2019a). 32 We note that all of these microlensing multiplanetary systems were detected through the channel of central perturbations, in which the source passes close to the central magnification region around the host star of the planets (Griest & Safizadeh 1998).…”

OGLE-2018-BLG-1011Lb,c: Microlensing Planetary System with Two Giant Planets Orbiting a Low-mass Star

“…For OGLE-2014-BLG-1722L, two planets with masses of ∼ 0.18 M J and ∼ 0.27 M J are orbiting a late-type star with a mass of ∼ 0.4 M ⊙ . The projected separations from the host are ∼ 1.5 au for the first planet and ∼ 1.7 au or ∼ 2.7 au for the second planet, and thus both planets are also located beyond the snow line (Suzuki et al 2018). OGLE-2018-BLG-0532L is the most recently reported candidate system, in which two planets with masses of ∼ 8 M ⊕ and ∼ 0.7 M J are located around an M-dwarf host having a mass of ∼ 0.25 M ⊙ with projected separations from the host of ∼ 1.4 au and 5.6 au, respectively (Ryu et al 2019).…”

“…OGLE-2018-BLG-0532L is the most recently reported candidate system, in which two planets with masses of ∼ 8 M ⊕ and ∼ 0.7 M J are located around an M-dwarf host having a mass of ∼ 0.25 M ⊙ with projected separations from the host of ∼ 1.4 au and 5.6 au, respectively (Ryu et al 2019). From the detection efficiency analysis of the MOA (Suzuki et al 2016) and µFUN (Gould et al 2010) surveys for the two microlensing multiplanetary systems OGLE-2006-BLG-109L and OGLE-2014-BLG-1722L, Suzuki et al (2018) estimated that the occurrence rate of systems with multiple cold gas giant systems was 6% ± 2%. We note that the multiple-planet signatures in the lensing light curves are securely detected for OGLE-2006-BLG-109L and OGLE-2012-BLG-0026L, but the signatures for OGLE-2014-BLG-1722L and OGLE-2018-BLG-0532L are less reliable.…”