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Register a new userKmt-2016-blg-1397b: Kmtnet-only discovery of a microlens giant planet
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We report the discovery of a giant planet in the KMT-2016-BLG-1397 microlensing event, which was found by The Korea Microlensing Telescope Network (KMTNet) alone. The time scale of this event is t_E = 40.0 +- 0.5 days and the mass ratio between the lens star and its companion is q = 0.016 +- 0.002. The planetary perturbation in the light curve is a smooth bump, resulting in the classical binary-lens/binary-source (2L1S/1L2S) degeneracy. We measure the V - I color of the (putative) two sources in the 1L2S model, and then effectively rule out the binary source solution. The finite-source effect is marginally detected. Combined with the limits on the blend flux and the probability distribution of the source size normalized by the Einstein radius rho, a Bayesian analysis yields the lens mass M_L = 0.45+0.33-0.28 M_sun, at distance of D_L = 6.60+1.10-1.30 kpc. Thus the companion is a super-Jupiter of a mass m_p = 7.0+5.2-4.3 M_J , at a projected separation r = 5.1+1.5-1.7 AU, indicating that the planet is well beyond the snow line of the host star.
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At $q=1.81pm 0.20 times 10^{-5}$, KMT-2018-BLG-0029Lb has the lowest planet-host mass ratio $q$ of any microlensing planet to date by more than a factor of two. Hence, it is the first planet that probes below the apparent pile-up at $q=5$--10 $times 10^{-5}$. The event was observed by {it Spitzer}, yielding a microlens-parallax $pi_{rm E}$ measurement. Combined with a measurement of the Einstein radius $theta_{rm E}$ from finite-source effects during the caustic crossings, these measurements imply masses of the host $M_{rm host}=1.14^{+0.10}_{-0.12}, M_odot$ and planet $M_{rm planet} = 7.59^{+0.75}_{-0.69},M_oplus$, system distance $D_L = 3.38^{+0.22}_{-0.26},,{rm kpc}$ and projected separation $a_perp = 4.27^{+0.21}_{-0.23},{rm au}$. The blended light, which is substantially brighter than the microlensed source, is plausibly due to the lens and could be observed at high resolution immediately.
We show that microlensing event KMT-2016-BLG-1107 displays a new type of degeneracy between wide-binary and close-binary Hollywood events in which a giant-star source envelops the planetary caustic. The planetary anomaly takes the form of a smooth, two-day bump far out on the falling wing of the light curve, which can be interpreted either as the source completely enveloping a minor-image caustic due to a close companion with mass ratio $q=0.036$, or partially enveloping a major-image caustic due to a wide companion with $q=0.004$. The best estimates of the companion masses are both in the planetary regime ($3.3^{+3.5}_{-1.8},M_{rm jup}$ and $0.090^{+0.096}_{-0.037},M_{rm jup}$) but differ by an even larger factor than the mass ratios due to different inferred host masses. We show that the two solutions can be distinguished by high-resolution imaging at first light on next-generation (30m) telescopes. We provide analytic guidance to understand the conditions under which this new type of degeneracy can appear.
KMT-2016-BLG-2605, with planet-host mass ratio $q=0.012pm 0.001$, has the shortest Einstein timescale, $t_e = 3.41pm 0.13,$days, of any planetary microlensing event to date. This prompts us to examine the full sample of 7 short ($t_e<7,$day) planetary events with good $q$ measurements. We find that six have clustered Einstein radii $theta_e = 115pm 20,muas$ and lens-source relative proper motions $mu_relsimeq 9.5pm 2.5,masyr$. For the seventh, these two quantities could not be measured. These distributions are consistent with a Galactic-bulge population of very low-mass (VLM) hosts near the hydrogen-burning limit. This conjecture could be verified by imaging at first adaptive-optics light on next-generation (30m) telescopes. Based on a preliminary assessment of the sample, planetary companions (i.e., below the deuterium-burning limit) are divided into genuine planets, formed in their disks by core accretion, and very low-mass brown dwarfs, which form like stars. We discuss techniques for expanding the sample, which include taking account of the peculiar anomaly dominated morphology of the KMT-2016-BLG-2605 light curve.
We report the discovery of KMT-2018-BLG-1292Lb, a super-Jovian $M_{rm planet} = 4.5pm 1.3,M_J$ planet orbiting an F or G dwarf $M_{rm host} = 1.5pm 0.4,M_odot$, which lies physically within ${cal O}(10,pc)$ of the Galactic plane. The source star is a heavily extincted $A_Isim 5.2$ luminous giant that has the lowest Galactic latitude, $b=-0.28^circ$, of any planetary microlensing event. The relatively blue blended light is almost certainly either the host or its binary companion, with the first explanation being substantially more likely. This blend dominates the light at $I$ band and completely dominates at $R$ and $V$ bands. Hence, the lens system can be probed by follow-up observations immediately, i.e., long before the lens system and the source separate due to their relative proper motion. The system is well characterized despite the low cadence $Gamma=0.15$--$0.20,{rm hr^{-1}}$ of observations and short viewing windows near the end of the bulge season. This suggests that optical microlensing planet searches can be extended to the Galactic plane at relatively modest cost.
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 Networks high-cadence observations (Gamma ~ 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_{-1.1}^{+1.9} M_{J} planet orbiting an M or K dwarf M_{rm host} = 0.49_{-0.25}^{+0.38} M_{Sun}, at a distance of D_{L} = 7.1_{-2.4}^{+0.8} kpc. The projected planet-host separation is 3.5^{+1.1}_{-0.9} AU, implying that the planet is located beyond the snowline 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 lesssim log q lesssim -3.0 for the 31 published KMTNet planets.
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