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Register a new userThe 2L1S/1L2S Degeneracy for Two Microlensing Planet Candidates Discovered by the KMTNet Survey in 2017
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We report two microlensing planet candidates discovered by the KMTNet survey in $2017$. However, both events have the 2L1S/1L2S degeneracy, which is an obstacle to claiming the discovery of the planets with certainty unless the degeneracy can be resolved. For KMT-2017-BLG-0962, the degeneracy cannot be resolved. If the 2L1S solution is correct, KMT-2017-BLG-0962 might be produced by a super Jupiter-mass planet orbiting a mid-M dwarf host star. For KMT-2017-BLG-1119, the light curve modeling favors the 2L1S solution but higher-resolution observations of the baseline object tend to support the 1L2S interpretation rather than the planetary interpretation. This degeneracy might be resolved by a future measurement of the lens-source relative proper motion. This study shows the problem of resolving 2L1S/1L2S degeneracy exists over a much wider range of conditions than those considered by the theoretical study of Gaudi (1998).
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We report two microlensing events, KMT-2017-BLG-1038 and KMT-2017-BLG-1146 that are caused by planetary systems. These events were discovered by KMTNet survey observations from the $2017$ bulge season. The discovered systems consist of a planet and host star with mass ratios, $5.3_{-0.4}^{+0.2} times 10^{-3}$ and $2.0_{-0.1}^{+0.6} times 10^{-3}$, respectively. Based on a Bayesian analysis assuming a Galactic model without stellar remnant hosts, we find that the planet, KMT-2017-BLG-1038Lb, is a super Jupiter-mass planet ($M_{rm p}= 2.04_{-1.15}^{+2.02},M_{rm J}$) orbiting a mid-M dwarf host ($M_{rm h}= 0.37_{-0.20}^{+0.36}, M_{odot}$) that is located at $6.01_{-1.72}^{+1.27}$ kpc toward the Galactic bulge. The other planet, KMT-2017-BLG-1146Lb, is a sub Jupiter-mass planet ($M_{rm p}= 0.71_{-0.42}^{+0.80},M_{rm J}$) orbiting a mid-M dwarf host ($M_{rm h}= 0.33_{-0.20}^{+0.36},M_{odot}$) at a distance toward the Galactic bulge of $6.50_{-2.00}^{+1.38}$ kpc. Both are potentially gaseous planets that are beyond their hosts snow lines. These typical microlensing planets will be routinely discovered by second-generation microlensing surveys, rapidly increasing the number of detections.
We report the discovery of microlensing planet OGLE-2017-BLG-0373Lb. We show that while the planet-host system has an unambiguous microlens topology, there are two geometries within this topology that fit the data equally well, which leads to a factor 2.5 difference in planet-host mass ratio, i.e., $q=1.5times 10^{-3}$ vs. $q=0.6times 10^{-3}$. We show that this is an accidental degeneracy in the sense that it is due to a gap in the data. We dub it the caustic-chirality degeneracy. We trace the mathematical origins of this degeneracy, which should enable similar degenerate solutions to be easily located in the future. A Bayesian estimate, based on a Galactic model, yields a host mass $M=0.25^{+0.30}_{-0.15} M_odot$ at a distance $D_L=5.9^{+1.3}_{-1.95}$ kpc. The lens-source relative proper motion is relatively fast, $mu=9$ mas/yr, which implies that the host mass and distance can be determined by high-resolution imaging after about 10 years. The same observations could in principle resolve the discrete degeneracy in $q$, but this will be more challenging.
We analyze the combined Spitzer and ground-based data for OGLE-2017-BLG-1140 and show that the event was generated by a Jupiter-class $(m_psimeq 1.6,M_{rm jup})$ planet orbiting a mid-late M dwarf $(Msimeq 0.2,M_odot)$ that lies $D_{LS}simeq 1.0,mathrm{kpc}$ in the foreground of the microlensed, Galactic-bar, source star. The planet-host projected separation is $a_perp simeq 1.0,mathrm{au}$, i.e., well-beyond the snow line. By measuring the source proper motion ${mathbf{mu}}_s$ from ongoing, long-term OGLE imaging, and combining this with the lens-source relative proper motion ${mathbf{mu}}_mathrm{rel}$ derived from the microlensing solution, we show that the lens proper motion ${mathbf{mu}}_l={mathbf{mu}}_mathrm{rel} + {mathbf{mu}}_s$ is consistent with the lens lying in the Galactic disk, although a bulge lens is not ruled out. We show that while the Spitzer and ground-based data are comparably well fitted by planetary (i.e., binary-lens, 2L1S) models and by binary-source (1L2S) models, the combination of Spitzer and ground-based data decisively favor the planetary model. This is a new channel to resolve the 2L1S/1L2S degeneracy, which can be difficult to break in some cases.
We report the discovery of HATS-1b, a transiting extrasolar planet orbiting the moderately bright V=12.05 G dwarf star GSC 6652-00186, and the first planet discovered by HATSouth, a global network of autonomous wide-field telescopes. HATS-1b has a period P~3.4465 d, mass Mp~1.86MJ, and radius Rp~1.30RJ. The host star has a mass of 0.99Msun, and radius of 1.04Rsun. The discovery light curve of HATS-1b has near continuous coverage over several multi-day periods, demonstrating the power of using a global network of telescopes to discover transiting planets.
We report a giant exoplanet discovery in the microlensing event OGLE-2017-BLG-1049, which is a planet-host star mass ratio of $q=9.53pm0.39times10^{-3}$ and has a caustic crossing feature in the Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of $theta_{rm E}=0.52 pm 0.11 {rm mas}$. However, the microlens parallax is not measured because of the time scale of the event $t_{rm E}simeq 29 {rm days}$, which is not long enough in this case to determine the microlens parallax. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. From this, we find that the lens system has a star with mass $M_{rm h}=0.55^{+0.36}_{-0.29} M_{odot}$ hosting a giant planet with $M_{rm p}=5.53^{+3.62}_{-2.87} M_{rm Jup}$, at a distance of $D_{rm L}=5.67^{+1.11}_{-1.52} {rm kpc}$. The projected star-planet separation in units of the Einstein radius $(theta_{rm E})$ corresponding to the total mass of the lens system is $a_{perp}=3.92^{+1.10}_{-1.32} rm{au}$. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is $mu_{rm rel}sim 7 rm{mas yr^{-1}}$, thus the lens and source will be separated from each other within 10 years. Then the flux of the host star can be measured by a 30m class telescope with high-resolution imaging in the future, and thus its mass can be determined.
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