arXiv subjects

Sang-Mok Cha

Publications and source records attributed to Sang-Mok Cha.

At least 145 records · Page 8Linked to original sources

arXiv2019

OGLE-2015-BLG-1771Lb: A Microlens Planet Orbiting an Ultracool Dwarf?

We report the discovery and the analysis of the short (tE < 5 days) planetary microlensing event, OGLE-2015-BLG-1771. The event was discovered by the Optical Gravitational Lensing Experiment (OGLE), and the planetary anomaly (at I ~ 19) was captured by The Korea Microlensing Telescope Network (KMTNet). The event has three surviving planetary models that explain the observed light curves, with planet-host mass ratio q \~ 5.4 * 10^{-3}, 4.5 * 10^{-3} and 4.5 * 10^{-2}, respectively. The first model is the best-fit model, while the second model is disfavored by Δχ^2 ~ 3. The last model is strongly disfavored by Δχ^2 ~ 15 but not ruled out. A Bayesian analysis using a Galactic model indicates that the first two models are probably composed of a Saturn-mass planet orbiting a late M dwarf, while the third one could consist of a super-Jovian planet and a mid-mass brown dwarf. The source-lens relative proper motion is mu_rel ~ 9 mas/yr, so the source and lens could be resolved by current adaptive-optics (AO) instruments in 2021 if the lens is luminous.

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arXiv2019

Candidate Brown-dwarf Microlensing Events with Very Short Timescales and Small Angular Einstein Radii

Short-timescale microlensing events are likely to be produced by substellar brown dwarfs (BDs), but it is difficult to securely identify BD lenses based on only event timescales $t_{\rm E}$ because short-timescale events can also be produced by stellar lenses with high relative lens-source proper motions. In this paper, we report three strong candidate BD-lens events found from the search for lensing events not only with short timescales ($t_{\rm E} \lesssim 6~{\rm days}$) but also with very small angular Einstein radii ($θ_{\rm E}\lesssim 0.05~{\rm mas}$) among the events that have been found in the 2016--2019 observing seasons. These events include MOA-2017-BLG-147, MOA-2017-BLG-241, and MOA-2019-BLG-256, in which the first two events are produced by single lenses and the last event is produced by a binary lens. From the Bayesian analysis conducted with the combined $t_{\rm E}$ and $θ_{\rm E}$ constraint, it is estimated that the lens masses of the individual events are $0.051^{+0.100}_{-0.027}~M_\odot$, $0.044^{+0.090}_{-0.023}~M_\odot$, and $0.046^{+0.067}_{-0.023}~M_\odot/0.038^{+0.056}_{-0.019}~M_\odot$ and the probability of the lens mass smaller than the lower limit of stars is $\sim 80\%$ for all events. We point out that routine lens mass measurements of short time-scale lensing events require survey-mode space-based observations.

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arXiv2019

Dwarf Galaxy Discoveries from the KMTNet Supernova Program II. The NGC 3585 Group and Its Dynamical State

We present our discovery and analysis of dwarf galaxies in the NGC 3585 galaxy group by the KMTNet Supernova Program. Using deep stack images reaching $\simeq$ 28 mag arcsec$^{-2}$ in $BVI$, we discovered 46 dwarf galaxy candidates distributed in a 7 square degree field. The dwarf galaxy candidates exhibit central surface brightness as faint as $μ_{0,V} = 26.2$ mag arcsec$^{-2}$, with effective radii larger than 150 pc and total absolute magnitudes brighter than $M_V \approx -10$ mag, if at the distance of NGC 3585. The dwarf galaxy surface number density decreases with projected distance from NGC 3585. We estimate the background contamination to be about 20% based both on the number density profile and on diffuse galaxy counts in a control field. The dwarf galaxy colors and Sersic structural parameters are consistent with those found for other dwarf galaxies. Unusually, there is no indication of a change of color or brightness in the dwarf galaxy candidates with projected distance from the group center. Approximately 20% of them contain an unresolved nucleus. The nucleated fraction is larger for brighter (and redder) galaxies but is independent of distance from the group center. We identify four ultra-diffuse galaxy candidates, all near the group center. We interpret these spatial properties as suggesting that the NGC 3585 group might be dynamically younger than the typical group. The galaxy luminosity function of the NGC 3585 group has a faint-end slope of $α\approx -1.39$, which is roughly consistent with the slopes found for other nearby groups. The possible dependence of the slope on global group properties is still unclear, and continues to motivate our homogeneous deep survey of dozens of nearby groups.

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arXiv2019

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

We report the discovery of 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 complex anomaly pattern can be decomposed into two parts produced by two binary-lens events, in which one binary pair has a very low mass ratio of $\sim 0.01$ between the lens components and the other pair has a mass ratio of $\sim 0.3$. 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 $\thetae$ (close solution), while the other solution has a separation greater than $\thetae$ (wide solution). From the Bayesian analysis with the constraints of the event time scale and angular Einstein radius together with the location of the source lying in the far disk behind the bulge, we find that the planet is a super-Jupiter with a mass of $4.4^{+3.0}_{-2.0}~M_{\rm J}$ and the stellar binary components are early and late M-type dwarfs with masses $0.42^{+0.29}_{-0.19}~M_\odot$ and $0.12^{+0.08}_{-0.05}~M_\odot$, respectively, and the planetary system is located at a distance of $D_{\rm L}=7.6^{+1.2}_{-0.9}~{\rm kpc}$. The planet is a circumstellar planet according to the wide solution, while it is a circumbinary planet according to the close solution. The projected primary-planet separation is $2.8^{+3.2}_{-2.5}~{\rm au}$ commonly for the close and wide solutions, but the primary-secondary binary separation of the close solution, $0.75^{+0.87}_{-0.66}~{\rm au}$, is widely different from the separation, $10.5^{+12.1}_{-9.2}~{\rm au}$, of the wide solution.

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arXiv2019

OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing

We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing campaign. This is a remarkable microlensing event because its source is photometrically bright and variable, which makes it possible to perform an asteroseismic analysis using ground-based data. We find that the source star is an oscillating red giant with average timescale of $\sim 9$ d. The asteroseismic analysis also provides us source properties including the source angular size ($\sim 27~μ{\rm as}$) and distance ($\sim 11.5$ kpc), which are essential for inferring the properties of the lens. When fitting the light curve, we test the feasibility of Gaussian Processes (GPs) in handling the correlated noise caused by the variable source. We find that the parameters from the GP model are generally more loosely constrained than those from the traditional $χ^2$ minimization method. We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source. With both finite-source effect and microlens parallax measured, we find that the lens is likely a $\sim 0.045~M_{\odot}$ brown dwarf at distance $\sim 9.0$ kpc, or a $\sim 0.073~M_{\odot}$ ultracool dwarf at distance $\sim 9.8$ kpc. Combining the estimated lens properties with a Bayesian analysis using a Galactic model, we find a $\sim 35$ per cent probability for the lens to be a bulge object and $\sim 65$ per cent to be a background disc object.

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arXiv2019

Spectroscopic Mass and Host-star Metallicity Measurements for Newly Discovered Microlensing Planet OGLE-2018-BLG-0740Lb

We report the discovery of the microlensing planet OGLE-2018-BLG-0740Lb. The planet is detected with a very strong signal of $Δχ^2\sim 4630$, but the interpretation of the signal suffers from two types of degeneracies. One type is caused by the previously known close/wide degeneracy, and the other is caused by an ambiguity between two solutions, in which one solution requires to incorporate finite-source effects, while the other solution is consistent with a point-source interpretation. Although difficult to be firmly resolved based on only the photometric data, the degeneracy is resolved in strong favor of the point-source solution with the additional external information obtained from astrometric and spectroscopic observations. The small astrometric offset between the source and baseline object supports that the blend is the lens and this interpretation is further secured by the consistency of the spectroscopic distance estimate of the blend with the lensing parameters of the point-source solution. The estimated mass of the host is $1.0\pm 0.1~M_\odot$ and the mass of the planet is $4.5\pm 0.6~M_{\rm J}$ (close solution) or $4.8\pm 0.6~M_{\rm J}$ (wide solution) and the lens is located at a distance of $3.2\pm 0.5$~kpc. The bright nature of the lens, with $I\sim 17.1$ ($V\sim 18.2$), combined with its dominance of the observed flux suggest that radial-velocity (RV) follow-up observations of the lens can be done using high-resolution spectrometers mounted on large telescopes, e.g., VLT/ESPRESSO, and this can potentially not only measure the period and eccentricity of the planet but also probe for close-in planets. We estimate that the expected RV amplitude would be $\sim 60\sin i ~{\rm m~s}^{-1}$.

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arXiv2019

OGLE-2018-BLG-1011L\lowercase{b,c}: Microlensing Planetary System with Two Giant Planets Orbiting a Low-mass Star

We report a multiplanetary system found from the analysis of microlensing event OGLE-2018-BLG-1011, for which the light curve exhibits a double-bump anomaly around the peak. We find that the anomaly cannot be fully explained by the binary-lens or binary-source interpretations and its description requires the introduction of an additional lens component. The 3L1S (3 lens components and a single source) modeling yields three sets of solutions, in which one set of solutions indicates that the lens is a planetary system in a binary, while the other two sets imply that the lens is a multiplanetary system. By investigating the fits of the individual models to the detailed light curve structure, we find that the multiple-planet solution with planet-to-host mass ratios $\sim 9.5\times 10^{-3}$ and $\sim 15\times 10^{-3}$ are favored over the other solutions. From the Bayesian analysis, we find that the lens is composed of two planets with masses $1.8^{+3..4}_{-1.1}~M_{\rm J}$ and $2.8^{+5.1}_{-1.7}~M_{\rm J}$ around a host with a mass $0.18^{+0.33}_{-0.10}~M_\odot$ and located at a distance $7.1^{+1.1}_{-1.5}~{\rm kpc}$. The estimated distance indicates that the lens is the farthest system among the known multiplanetary systems. The projected planet-host separations are $a_{\perp,2}=1.8^{+2.1}_{-1.5}~{\rm au}$ ($0.8^{+0.9}_{-0.6}~{\rm au}$) and $a_{\perp,3}=0.8^{+0.9}_{-0.6}~{\rm au}$, where the values of $a_{\perp,2}$ in and out the parenthesis are the separations corresponding to the two degenerate solutions, indicating that both planets are located beyond the snow line of the host, as with the other four multiplanetary systems previously found by microlensing.

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arXiv2019

OGLE-2015-BLG-1670Lb: A Cold Neptune beyond the Snow Line in the Provisional WFIRST Microlensing Survey Field

We present the analysis of the microlensing event OGLE-2015-BLG-1670, detected in a high-extinction field, very close to the Galactic plane. Due to the dust extinction along the line of sight, this event was too faint to be detected before it reached the peak of magnification. The microlensing light-curve models indicate a high-magnification event with a maximum of $A_\mathrm{max}\gtrsim200$, very sensitive to planetary deviations. An anomaly in the light curve has been densely observed by the microlensing surveys MOA, KMTNet, and OGLE. From the light-curve modeling, we find a planetary anomaly characterized by a planet-to-host mass ratio, $q=\left(1.00^{+0.18}_{-0.16}\right)\times 10^{-4}$, at the peak recently identified in the mass-ratio function of microlensing planets. Thus, this event is interesting to include in future statistical studies about planet demography. We have explored the possible degeneracies and find two competing planetary models resulting from the $s\leftrightarrow1/s$ degeneracy. However, because the projected separation is very close to $s=1$, the physical implications for the planet for the two solutions are quite similar, except for the value of $s$. By combining the light-curve parameters with a Galactic model, we have estimated the planet mass $M_2=17.9^{+9.6}_{-8.8}\,\mathrm{M}_\oplus$ and the lens distance $D_\mathrm{L}=6.7^{+1.0}_{-1.3}\,\mathrm{kpc}$, corresponding to a Neptune-mass planet close to the Galactic bulge. Such events with a low absolute latitude ($|b|\approx 1.1\,\mathrm{deg}$) are subject to both high extinction and more uncertain source distances, two factors that may affect the mass measurements in the provisional Wide Field Infrared Survey Telescope fields. More events are needed to investigate the potential trade-off between the higher lensing rate and the difficulty in measuring masses in these low-latitude fields.

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arXiv2019

KSP-SN-2016kf: a long-rising H-rich Type II Supernova with unusually high $^{56}$Ni mass discovered in the KMTNet Supernova Program

We present the discovery and the photometric and spectroscopic study of H-rich Type II supernova (SN) KSP-SN-2016kf (SN2017it) observed in the KMTNet Supernova Program in the outskirts of a small irregular galaxy at $z\simeq0.043$ within a day from the explosion. Our high-cadence, multi-color ($BVI$) light curves of the SN show that it has a very long rise time ($t_\text{rise}\simeq 20$ days in $V$ band), a moderately luminous peak ($M_V\simeq -$17.6 mag), a notably luminous and flat plateau ($M_V\simeq -$17.4 mag and decay slope $s\simeq0.53$ mag per 100 days), and an exceptionally bright radioactive tail. Using the color-dependent bolometric correction to the light curves, we estimate the $^{56}$Ni mass powering the observed radioactive tail to be $0.10\pm0.01$ M$_\odot$, making it a H-rich Type II SN with one of the largest $^{56}$Ni masses observed to date. The results of our hydrodynamic simulations of the light curves constrain the mass and radius of the progenitor at the explosion to be $\sim$15 M$_\odot$ (evolved from a star with an initial mass of $\sim$ 18.8 M$_\odot$) and $\sim1040$ R$_\odot$, respectively, with the SN explosion energy of $\sim 1.3\times 10^{51}$ erg s$^{-1}$. The above-average mass of the KSP-SN-2016kf progenitor, together with its low metallicity $ Z/Z_\odot \simeq0.1-0.4$ obtained from spectroscopic analysis, is indicative of a link between the explosion of high-mass red supergiants and their low-metallicity environment. The early part of the observed light curves shows the presence of excess emission above what is predicted in model calculations, suggesting there is interaction between the ejecta and circumstellar material. We further discuss the implications of the high progenitor initial mass and low-metallicity environment of KSP-SN-2016kf on our understanding of the origin of Type II SNe.

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arXiv2019

KSP-OT-201611a: A Distant Population II Dwarf Nova Candidate Discovered by the KMTNet Supernova Program

We present a multi-color, high-cadence photometric study of a distant dwarf nova KSP-OT-201611a discovered by the Korea Microlensing Telescope Network Supernova Program. From October 2016 to May 2017, two outbursts, which comprises a super/long outburst followed by a normal/short outburst separated by $\sim$91 days, were detected in the $BVI$ bands. The shapes and amplitudes of the outbursts reveal the nature of KSP-OT-201611a to be an SU UMa- or U Gem-type dwarf nova. Color variations of periodic humps in the super/long outburst possibly indicate that KSP-OT-201611a is an SU UMa-type dwarf nova. The super and normal outbursts show distinctively different color evolutions during the outbursts due most likely to the difference of time when the cooling wave is formed in the accretion disk. The outburst peak magnitudes and the orbital period of the dwarf nova indicate that it is at a large Galactocentric distance ($\sim$13.8 kpc) and height ($\sim$1.7 kpc) from the Galactic plane. KSP-OT-201611a, therefore, may provide a rare opportunity to study the accretion disk process of Population II dwarf novae.

astro-ph.SR↗

arXiv2019

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

We report the discovery of the planet OGLE-2018-BLG-0532Lb, with very obvious signatures in the light curve that lead to an estimate of the planet-host mass ratio $q=M_{\rm planet}/M_{\rm host}\simeq 1\times10^{-4}$. Although there are no obvious systematic residuals to this double-lens/single-source (2L1S) fit, we find that $χ^2$ can be significantly improved by adding either a third lens (3L1S, $Δχ^2=81$) or second source (2L2S, $Δχ^2=65$) to the lens-source geometry. After thorough investigation, we conclude that we cannot decisively distinguish between these two scenarios and therefore focus on the robustly-detected planet. However, given the possible presence of a second planet, we investigate to what degree and with what probability such additional planets may affect seemingly single-planet light curves. Our best estimates for the properties of the lens star and the secure planet are: a host mass $M\sim 0.25\,M_\odot$, system distance $D_L\sim 1\,$kpc and planet mass $m_{p,1}= 8\,M_\oplus$ with projected separation $a_{1,\perp}=1.4\,$au. However, there is a relatively bright $I=18.6$ (and also relatively blue) star projected within $<50\,$mas of the lens, and if future high-resolution images show that this is coincident with the lens, then it is possible that it is the lens, in which case, the lens would be both more massive and more distant than the best-estimated values above.

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arXiv2019

$Spitzer$ Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M-dwarf

We report the discovery of a $Spitzer$ microlensing planet OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio $q \sim 2\times10^{-4}$. The planetary signal, which is characterized by a short $(\sim 1~{\rm day})$ "bump" on the rising side of the lensing light curve, was densely covered by ground-based surveys. We find that the signal can be explained by a bright source that fully envelops the planetary caustic, i.e., a "Hollywood" geometry. Combined with the source proper motion measured from $Gaia$, the $Spitzer$ satellite parallax measurement makes it possible to precisely constrain the lens physical parameters. The preferred solution, in which the planet perturbs the minor image due to lensing by the host, yields a Uranus-mass planet with a mass of $M_{\rm p} = 13.9\pm1.6~M_{\oplus}$ orbiting a mid M-dwarf with a mass of $M_{\rm h} = 0.23\pm0.03~M_{\odot}$. There is also a second possible solution that is substantially disfavored but cannot be ruled out, for which the planet perturbs the major image. The latter solution yields $M_{\rm p} = 1.2\pm0.2~M_{\oplus}$ and $M_{\rm h} = 0.15\pm0.02~M_{\odot}$. By combining the microlensing and $Gaia$ data together with a Galactic model, we find in either case that the lens lies on the near side of the Galactic bulge at a distance $D_{\rm L} \sim 6\pm1~{\rm kpc}$. Future adaptive optics observations may decisively resolve the major image/minor image degeneracy.

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arXiv2019

KMT-2018-BLG-1990Lb: A Nearby Jovian Planet From A Low-Cadence Microlensing Field

We report the discovery and characterization of KMT-2018-BLG-1990Lb, a Jovian planet $(m_p=0.57_{-0.25}^{+0.79}\,M_J)$ orbiting a late M dwarf $(M=0.14_{-0.06}^{+0.20}\,M_\odot)$, at a distance $(D_L=1.23_{-0.43}^{+1.06}\,\kpc)$, and projected at $2.6\pm 0.6$ times the snow line distance, i.e., $a_{\rm snow}\equiv 2.7\,\au (M/M_\odot)$, This is the second Jovian planet discovered by KMTNet in its low cadence ($0.4\,{\rm hr}^{-1}$) fields, demonstrating that this population will be well characterized based on survey-only microlensing data.

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arXiv2019

KMT-2018-BLG-1292: A Super-Jovian Microlens Planet in the Galactic Plane

We report the discovery of KMT-2018-BLG-1292Lb, a super-Jovian $M_{\rm planet} = 4.5\pm 1.3\,M_J$ planet orbiting an F or G dwarf $M_{\rm host} = 1.5\pm 0.4\,M_\odot$, which lies physically within ${\cal O}(10\,\pc)$ of the Galactic plane. The source star is a heavily extincted $A_I\sim 5.2$ 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 $Γ=0.15$--$0.20\,{\rm hr^{-1}}$ 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.

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arXiv2019

Spitzer Microlensing parallax reveals two isolated stars in the Galactic bulge

We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a $0.60 \pm 0.03 M_{\odot}$ star with $D_{\rm LS} = 0.53 \pm 0.11~\text{kpc}$, where $D_{\rm LS}$ is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a $0.51^{+0.12}_{-0.10} M_{\odot}$ star with $D_{\rm LS} = 0.40 \pm 0.12~\text{kpc}$ or a $0.38^{+0.13}_{-0.12} M_{\odot}$ star with $D_{\rm LS} = 0.53 \pm 0.19~\text{kpc}$. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite-source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurrence in single lens events.

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arXiv2019

RR Lyrae Stars in the Field of Sagittarius II

We present the detection of RR Lyrae variable stars in the field of the Sagittarius II (Sgr II) ultra-faint dwarf (UFD) galaxy. Using B, V time-series photometry obtained with the Korea Microlensing Telescope Network (KMTNet) 1.6 m telescope at CTIO and G-band data from Gaia Data Release 2 (DR2), we identified and characterized two ab-type and four c-type RR Lyrae variables. Five out of the six stars are clustered within three half-light radii (~4.8') of the galaxy indicating their association with Sgr II, while the RRab star V4 is located ~22' from the galaxy center. By excluding V4, the high c-type fraction (0.8) and the period of the only RRab star V3 (P_V3 = 0.666 days) suggest an Oosterhoff II (Oo II) classification for Sgr II. Located close to the locus of Oo II clusters in the period-amplitude diagram, V3 is similar to RRab stars in other UFDs having Oosterhoff-intermediate and Oo II properties. Sgr II is, however, more compact than usual UFDs, placed in between star clusters and dwarf galaxies in the size-luminosity plane, and therefore spectroscopic studies are eventually required to ascertain the true nature of this stellar system. We derive the metallicity ([Fe/H]_RRab = -2.1 +- 0.3) and heliocentric distance (~64 +- 3 kpc) of Sgr II from the RR Lyrae stars, and estimate its age (~12 Gyr) based on our stellar population models. The Oosterhoff properties of UFDs can be explained with the evolution effect of RR Lyrae stars in the instability strip.

astro-ph.GA↗

arXiv2019

Spitzer Microlensing of MOA-2016-BLG-231L : A Counter-Rotating Brown Dwarf Binary in the Galactic Disk

We analyze the binary microlensing event MOA-2016-BLG-231, which was observed from the ground and from Spitzer. The lens is composed of very low-mass brown dwarfs (BDs) with $M_1 = 21^{+12}_{-5} \ M_J$ and $M_2 = 9^{+5}_{-2}\ M_J$, and it is located in the Galactic disk $D_{\rm L} = 2.85^{+0.88}_{-0.50}\ {\rm kpc}$. This is the fifth binary brown dwarf discovered by microlensing, and the BD binary is moving counter to the orbital motion of disk stars. Constraints on the lens physical properties come from late time, non-caustic-crossing features of the Spitzer light curve. Thus, MOA-2016-BLG-231 shows how Spitzer plays a crucial role in resolving the nature of BDs in binary BD events with short timescale ($\lesssim 10$ days).

astro-ph.SR↗

arXiv2019

OGLE-2016-BLG-0156: Microlensing Event With Pronounced Microlens-Parallax Effects Yielding Precise Lens Mass Measurement

We analyze the gravitational binary-lensing event OGLE-2016-BLG-0156, for which the lensing light curve displays pronounced deviations induced by microlens-parallax effects. The light curve exhibits 3 distinctive widely-separated peaks and we find that the multiple-peak feature provides a very tight constraint on the microlens-parallax effect, enabling us to precisely measure the microlens parallax $π_{\rm E}$. All the peaks are densely and continuously covered from high-cadence survey observations using globally located telescopes and the analysis of the peaks leads to the precise measurement of the angular Einstein radius $θ_{\rm E}$. From the combination of the measured $π_{\rm E}$ and $θ_{\rm E}$, we determine the physical parameters of the lens. It is found that the lens is a binary composed of two M dwarfs with masses $M_1=0.18\pm 0.01\ M_\odot$ and $M_2=0.16\pm 0.01\ M_\odot$ located at a distance $D_{\rm L}= 1.35\pm 0.09\ {\rm kpc}$. According to the estimated lens mass and distance, the flux from the lens comprises an important fraction, $\sim 25\%$, of the blended flux. The bright nature of the lens combined with the high relative lens-source motion, $μ=6.94\pm 0.50\ {\rm mas}\ {\rm yr}^{-1}$, suggests that the lens can be directly observed from future high-resolution follow-up observations.

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