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

We report a planet in a binary that was discovered from the analysis of the microlensing event OGLE-2018-BLG-1700. We identify the triple nature of the lens from the fact that the anomaly pattern can be decomposed into two parts produced by two binary-lens events, in which one binary pair has a mass ratio of ~0.01 between the lens components and the other pair has a mass ratio of ~0.3. We find two sets of degenerate solutions, in which one solution has a projected separation between the primary and its stellar companion less than the angular Einstein radius θ_E (close solution), while the other solution has a separation greater than θ_E (wide solution). From the Bayesian analysis with the constraints of the event timescale and angular Einstein radius, we find that the planet has a mass of 4.4^(+3.0)_(−2.0) M_J and the stellar binary components have masses of 0.42^(+0.29)_(−0.19) M_⊙ and 0.12^(+0.08)_(−0.05) M_⊙, respectively, and the distance to the lens is D_L=7.6^(+1.2)_(−0.9) kpc. The planet is a circumstellar planet according to the wide solution, while it is a circumbinary planet according to the close solution

MOA-2016-BLG-319Lb: Microlensing Planet Subject to Rare Minor-image Perturbation Degeneracy in Determining Planet Parameters

We present the analysis of the planetary microlensing event MOA-2016-BLG-319. The event light curve is characterized by a brief (~3 days) anomaly near the peak produced by minor-image perturbations. From modeling, we find two distinct solutions that describe the observed light curve almost equally as well. From the investigation of the lens-system configurations, we find that the confusion in the lensing solution is caused by the degeneracy between the two solutions resulting from the source passages on different sides of the planetary caustic. These degeneracies can be severe for major-image perturbations, but it is known that they are considerably less severe for minor-image perturbations. From the comparison of the lens-system configuration with those of two previously discovered planetary events, for which similar degeneracies were reported, we find that the degeneracies are caused by the special source trajectories that passed the star–planet axes at approximately right angles. By conducting a Bayesian analysis, it is estimated that the lens is a planetary system in which a giant planet with a mass M_p = 0.62^(+1.16)_(-0.33) M_J (0.65^(+1.21)_(-0.35) M_J) is orbiting a low-mass M-dwarf host with a mass M_h = 0.15^(+0.28)_(-0.08) M⊙ . Here the planet masses in and out of the parentheses represent the masses for the individual degenerate solutions. The projected host-planet separations are a⊥ ~ 0.95 and ~1.05 au for the two solutions. The identified degeneracy indicates the need to check similar degeneracies in future analyses of planetary lensing events with minor-image perturbations

KMT-2016-BLG-1836Lb: A Super-Jovian Planet from a High-cadence Microlensing Field

We report the discovery of a super-Jovian planet in the microlensing event KMT-2016-BLG-1836, which was found by the Korea Microlensing Telescope Network (KMTNet) high-cadence observations (Γ ~ 4 hr^⁻¹). The planet–host mass ratio q ~ 0.004. A Bayesian analysis indicates that the planetary system is composed of a super-Jovian M_(planet) = 2.2^(+1.9)_(-1.1)M_J planet orbiting an M or K dwarf, M_(host) = 0.49^(+0.38)_(-0.25) M_⊙, at a distance of D_L = 7.1^(+0.8)_(-2.4) kpc. The projected planet–host separation is 3.5^(+1.1)_(-0.9) au, implying that the planet is located beyond the snow line of the host star. Future high-resolution images can potentially strongly constrain the lens brightness and thus the mass and distance of the planetary system. Without considering detailed detection efficiency, selection, or publication biases, we find a potential mass-ratio desert at −3.7 ≾ log q ≾ −3.0 for the 31 published KMTNet planets

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

We report a planet in a binary that was discovered from the analysis of the microlensing event OGLE-2018-BLG-1700. We identify the triple nature of the lens from the fact that the anomaly pattern can be decomposed into two parts produced by two binary-lens events, in which one binary pair has a mass ratio of ~0.01 between the lens components and the other pair has a mass ratio of ~0.3. We find two sets of degenerate solutions, in which one solution has a projected separation between the primary and its stellar companion less than the angular Einstein radius θ_E (close solution), while the other solution has a separation greater than θ_E (wide solution). From the Bayesian analysis with the constraints of the event timescale and angular Einstein radius, we find that the planet has a mass of 4.4^(+3.0)_(−2.0) M_J and the stellar binary components have masses of 0.42^(+0.29)_(−0.19) M_⊙ and 0.12^(+0.08)_(−0.05) M_⊙, respectively, and the distance to the lens is D_L=7.6^(+1.2)_(−0.9) kpc. The planet is a circumstellar planet according to the wide solution, while it is a circumbinary planet according to the close solution

KMT-2016-BLG-1836Lb: A Super-Jovian Planet from a High-cadence Microlensing Field

We report the discovery of a super-Jovian planet in the microlensing event KMT-2016-BLG-1836, which was found by the Korea Microlensing Telescope Network (KMTNet) high-cadence observations (Γ ~ 4 hr^⁻¹). The planet–host mass ratio q ~ 0.004. A Bayesian analysis indicates that the planetary system is composed of a super-Jovian M_(planet) = 2.2^(+1.9)_(-1.1)M_J planet orbiting an M or K dwarf, M_(host) = 0.49^(+0.38)_(-0.25) M_⊙, at a distance of D_L = 7.1^(+0.8)_(-2.4) kpc. The projected planet–host separation is 3.5^(+1.1)_(-0.9) au, implying that the planet is located beyond the snow line of the host star. Future high-resolution images can potentially strongly constrain the lens brightness and thus the mass and distance of the planetary system. Without considering detailed detection efficiency, selection, or publication biases, we find a potential mass-ratio desert at −3.7 ≾ log q ≾ −3.0 for the 31 published KMTNet planets

Two new free-floating or wide-orbit planets from microlensing

Planet formation theories predict the existence of free-floating planets that have been ejected from their parent systems. Although they emit little or no light, they can be detected during gravitational microlensing events. Microlensing events caused by rogue planets are characterized by very short timescales t_E (typically below two days) and small angular Einstein radii θ_E (up to several μas). Here we present the discovery and characterization of two ultra-short microlensing events identified in data from the Optical Gravitational Lensing Experiment (OGLE) survey, which may have been caused by free-floating or wide-orbit planets. OGLE-2012-BLG-1323 is one of the shortest events discovered thus far (t_E = 0.155 ± 0.005 d, θ_E = 2.37 ± 0.10μas) and was caused by an Earth-mass object in the Galactic disk or a Neptune-mass planet in the Galactic bulge. OGLE-2017-BLG-0560 (t_E = 0.905 ± 0.005 d, θ_E = 38.7 ± 1.6μas) was caused by a Jupiter-mass planet in the Galactic disk or a brown dwarf in the bulge. We rule out stellar companions up to a distance of 6.0 and 3.9 au, respectively. We suggest that the lensing objects, whether located on very wide orbits or free-floating, may originate from the same physical mechanism. Although the sample of ultrashort microlensing events is small, these detections are consistent with low-mass wide-orbit or unbound planets being more common than stars in the Milky Way

A Planetary Microlensing Event with an Unusually Red Source Star: MOA-2011-BLG-291

We present the analysis of the planetary microlensing event MOA-2011-BLG-291, which has a mass ratio of q = (3.8 ± 0.7) × 10−4 and a source star that is redder (or brighter) than the bulge main sequence. This event is located at a low Galactic latitude in the survey area that is currently planned for NASA's Wide Field Infrared Survey Telescope (WFIRST) exoplanet microlensing survey. This unusual color for a microlensed source star implies that we cannot assume that the source star is in the Galactic bulge. The favored interpretation is that the source star is a lower main-sequence star at a distance of D_S = 4.9 ± 1.3 kpc in the Galactic disk. However, the source could also be a turn-off star on the far side of the bulge or a subgiant in the far side of the Galactic disk if it experiences significantly more reddening than the bulge red clump stars. However, these possibilities have only a small effect on our mass estimates for the host star and planet. We find host star and planet masses of M_(host) = 0.15^(+0.27)_(-0.10) M⊙ and m_p = 18^(+34)_(-12) M⊕ from a Bayesian analysis with a standard Galactic model, under the assumption that the planet hosting probability does not depend on the host mass or distance. However, if we attempt to measure the host and planet masses with host star brightness measurements from high angular resolution follow-up imaging, the implied masses will be sensitive to the host star distance. The WFIRST exoplanet microlensing survey is expected to use this method to determine the masses for many of the planetary systems that it discovers, so this issue has important design implications for the WFIRST exoplanet microlensing survey