14 research outputs found
Brown dwarf companions in binaries detected from the 2021 season high-cadence microlensing surveys
As a part of the project aiming to build a homogeneous sample of binary-lens
(2L1S) events containing brown-dwarf (BD) companions, we investigate the 2021
season microlensing data collected by the Korea Microlensing Telescope Network
(KMTNet) survey. For this purpose, we first identify 2L1S events by conducting
systematic analyses of anomalous lensing events. We then select candidate
BD-companion events by applying the criterion that the mass ratio between the
lens components is less than . From this procedure, we find
four binary-lens events including KMT-2021-BLG-0588, KMT-2021-BLG-1110,
KMT-2021-BLG-1643, and KMT-2021-BLG-1770, for which the estimated mass ratios
are , 0.07, 0.08, and 0.15, respectively. The event
KMT-2021-BLG-1770 is selected as a candidate despite the fact that the mass
ratio is slightly greater than because the lens mass expected from
the measured short time scale of the event, ~days, is small.
From the Bayesian analyses, we estimate that the primary and companion masses
are for KMT-2021-BLG-0588L, for KMT-2021-BLG-1110L, for KMT-2021-BLG-1643L, and for KMT-2021-BLG-1770L. It is estimated that the
probabilities of the lens companions being in the BD mass range are 82\%, 85\%,
91\%, and 59\% for the individual events. For confirming the BD nature of the
lens companions found in this and previous works by directly imaging the lenses
from future high-resolution adaptive-optics (AO) followup observations, we
provide the lens-source separations expected in 2030, which is an approximate
year of the first AO light on 30~m class telescopes.Comment: 11 pages, 10 tables, 8 figure
KMT-2021-BLG-1150Lb: Microlensing planet detected through a densely covered planetary-caustic signal
Recently, there have been reports of various types of degeneracies in the
interpretation of planetary signals induced by planetary caustics. In this
work, we check whether such degeneracies persist in the case of well-covered
signals by analyzing the lensing event KMT-2021-BLG-1150, for which the light
curve exhibits a densely and continuously covered short-term anomaly. In order
to identify degenerate solutions, we thoroughly investigate the parameter space
by conducting dense grid searches for the lensing parameters. We then check the
severity of the degeneracy among the identified solutions. We identify a pair
of planetary solutions resulting from the well-known inner-outer degeneracy,
and find that interpreting the anomaly is not subject to any degeneracy other
than the inner-outer degeneracy. The measured parameters of the planet
separation (normalized to the Einstein radius) and mass ratio between the lens
components are for the inner
solution and for the outer
solution. According to a Bayesian estimation, the lens is a planetary system
consisting of a planet with a mass
and its host with a mass lying toward
the Galactic center at a distance ~kpc. By
conducting analyses using mock data sets prepared to mimic those obtained with
data gaps and under various observational cadences, it is found that gaps in
data can result in various degenerate solutions, while the observational
cadence does not pose a serious degeneracy problem as long as the anomaly
feature can be delineated.Comment: 9 pages, 8 figure
KMT-2021-BLG-1547Lb: Giant microlensing planet detected through a signal deformed by source binarity
We investigate the previous microlensing data collected by the KMTNet survey
in search of anomalous events for which no precise interpretations of the
anomalies have been suggested. From this investigation, we find that the
anomaly in the lensing light curve of the event KMT-2021-BLG-1547 is
approximately described by a binary-lens (2L1S) model with a lens possessing a
giant planet, but the model leaves unexplained residuals. We investigate the
origin of the residuals by testing more sophisticated models that include
either an extra lens component (3L1S model) or an extra source star (2L2S
model) to the 2L1S configuration of the lens system. From these analyses, we
find that the residuals from the 2L1S model originate from the existence of a
faint companion to the source. The 2L2S solution substantially reduces the
residuals and improves the model fit by with respect to the
2L1S solution. The 3L1S solution also improves the fit, but its fit is worse
than that of the 2L2S solution by . According to the 2L2S
solution, the lens of the event is a planetary system with planet and host
masses lying at a distance \D_{\rm L}
=5.07^{+0.98}_{-1.50}~kpc, and the source is a binary composed of a subgiant
primary of a late G or an early K spectral type and a main-sequence companion
of a K spectral type. The event demonstrates the need of sophisticated modeling
for unexplained anomalies for the construction of a complete microlensing
planet sample.Comment: 9 pages, 4 tables, 7 figure
Four microlensing giant planets detected through signals produced by minor-image perturbations
Funding: Work by C.H. was supported by the grants of National Research Foundation of Korea (2019R1A2C2085. This research was supported by the Korea Astronomy and Space Science Institute under the R&D program (Project No. 2023-1-832-03) supervised by the Ministry of Science and ICT. The MOA project is supported by JSPS KAKENHI Grant Number JP24253004, JP26247023, JP23340064, JP15H00781, JP16H06287, JP17H02871 and JP22H00153. J.C.Y., I.G.S., and S.J.C. acknowledge support from NSF Grant No. AST-2108414. Y.S. acknowledges support from NSF Grant No. 2020740. C.R. was supported by the Research fellowship of the Alexander von Humboldt Foundation. This work was authored by employees of Caltech/IPAC under Contract No. 80GSFC21R0032 with the National Aeronautics and Space Administration. V.B. is supported by PRIN 2022 CUP D53D23002590006. R.F.J. acknowledges support for this project provided by ANIDâs Millennium Science Initiative through grant ICN12_009, awarded to the Millennium Institute of Astrophysics (MAS), and by ANIDâs Basal project FB210003. This project has received funding from the European Unionâs Horizon 2020 research and innovation program under grant agreement No. 101004719 (OPTICON - RadioNet Pilot). This work is supported by the Polish MNiSW grant DIR/WK/2018/12.Aims. We investigated the nature of the anomalies appearing in four microlensing events KMT-2020-BLG-0757, KMT-2022-BLG-0732, KMT-2022-BLG-1787, and KMT-2022-BLG-1852. The light curves of these events commonly exhibit initial bumps followed by subsequent troughs that extend across a substantial portion of the light curves. Methods. We performed thorough modeling of the anomalies to elucidate their characteristics. Despite their prolonged durations, which differ from the usual brief anomalies observed in typical planetary events, our analysis revealed that each anomaly in these events originated from a planetary companion located within the Einstein ring of the primary star. It was found that the initial bump arouse when the source star crossed one of the planetary caustics, while the subsequent trough feature occurred as the source traversed the region of minor image perturbations lying between the pair of planetary caustics. Results. The estimated masses of the host and planet, their mass ratios, and the distance to the discovered planetary systems are (Mhost/Mâ, Mplanet/MJ, q/10â3, DL/kpc) = (0.58â0.30+0.33, 10.71â5.61+6.17, 17.61 ± 2.25, 6.67â1.30+0.93) for KMT-2020-BLG-0757, (0.53â0.31+0.31, 1.12â0.65+0.65, 2.01 ± 0.07, 6.66â1.84+1.19) for KMT-2022-BLG-0732, (0.42â0.23+0.32, 6.64â3.64+4.98, 15.07 ± 0.86, 7.55â1.30+0.89) for KMT-2022-BLG-1787, and (0.32â0.19+0.34, 4.98â2.94+5.42, 8.74 ± 0.49, 6.27â1.15+0.90) for KMT-2022-BLG-1852. These parameters indicate that all the planets are giants with masses exceeding the mass of Jupiter in our solar system and the hosts are low-mass stars with masses substantially less massive than the Sun.Peer reviewe
Systematic KMTNet Planetary Anomaly Search. V. Complete Sample of 2018 Prime-Field
We complete the analysis of all 2018 prime-field microlensing planets
identified by the KMTNet AnomalyFinder. Among the 10 previously unpublished
events with clear planetary solutions, 8 are either unambiguously planetary or
are very likely to be planetary in nature: OGLE-2018-BLG-1126,
KMT-2018-BLG-2004, OGLE-2018-BLG-1647, OGLE-2018-BLG-1367, OGLE-2018-BLG-1544,
OGLE-2018-BLG-0932, OGLE-2018-BLG-1212, and KMT-2018-BLG-2718. Combined with
the 4 previously published new AnomalyFinder events and 12 previously published
(or in preparation) planets that were discovered by eye, thismakes a total of
24 2018 prime-field planets discovered or recovered by AnomalyFinder. Together
with a paper in preparation on 2018 sub-prime planets, this work lays the basis
for the first statistical analysis of the planet mass-ratio function based on
planets identified in KMTNet data. By systematically applying the heuristic
analysis of Hwang et al. (2022) to each event, we identify the small
modification in their formalism that is needed to unify the so-called
close/wide and inner/outer degeneracies, as conjectured byComment: 22 pages, 14 tables, 15 figure
Brown dwarf companions in microlensing binaries detected during the 2016â2018 seasons
Aims. With the aim of finding microlensing binaries containing brown dwarf (BD) companions, we investigate the microlensing survey data collected during the 2016â2018 seasons.
Methods. For this purpose, we first modeled lensing events with light curves exhibiting anomaly features that are likely to be produced by binary lenses. We then sorted out BD companion binary-lens events by applying the criterion that the companion-to-primary mass ratio is qââČâ0.1. With this procedure, we identify six binaries with candidate BD companions: OGLE-2016-BLG-0890L, MOA-2017-BLG-477L, OGLE-2017-BLG-0614L, KMT-2018-BLG-0357L, OGLE-2018-BLG-1489L, and OGLE-2018-BLG-0360L.
Results. We estimated the masses of the binary companions by conducting Bayesian analyses using the observables of the individual lensing events. According to the Bayesian estimation of the lens masses, the probabilities for the lens companions of the events OGLE-2016-BLG-0890, OGLE-2017-BLG-0614, OGLE-2018-BLG-1489, and OGLE-2018-BLG-0360 to be in the BD mass regime are very high with PBDâ>â80%. For MOA-2017-BLG-477 and KMT-2018-BLG-0357, the probabilities are relatively low with PBDâ=â61% and 69%, respectively
MOA-2022-BLG-249Lb: Nearby microlensing super-Earth planet detected from high-cadence surveys
Aims. We investigate the data collected by the high-cadence microlensing surveys during the 2022 season in search of planetary signals appearing in the light curves of microlensing events. From this search, we find that the lensing event MOA-2022-BLG-249 exhibits a brief positive anomaly that lasted for about one day, with a maximum deviation of ~0.2 mag from a single-source, single-lens model.
Methods. We analyzed the light curve under the two interpretations of the anomaly: one originated by a low-mass companion to the lens (planetary model) and the other originated by a faint companion to the source (binary-source model).
Results. We find that the anomaly is better explained by the planetary model than the binary-source model. We identified two solutions rooted in the inner-outer degeneracy and for both of them, the estimated planet-to-host mass ratio, q ~ 8 Ă 10â5, is very small. With the constraints provided by the microlens parallax and the lower limit on the Einstein radius, as well as the blend-flux constraint, we find that the lens is a planetary system, in which a super-Earth planet, with a mass of (4.83 ± 1.44) Îâ, orbits a low-mass host star, with a mass of (0.18 ± 0.05) Mâ, lying in the Galactic disk at a distance of (2.00 ± 0.42) kpc. The planet detection demonstrates the elevated microlensing sensitivity of the current high-cadence lensing surveys to low-mass planets
Probable brown dwarf companions detected in binary microlensing events during the 2018-2020 seasons of the KMTNet survey
We inspect the microlensing data of the KMTNet survey collected during the
2018--2020 seasons in order to find lensing events produced by binaries with
brown-dwarf companions. In order to pick out binary-lens events with candidate
BD lens companions, we conduct systematic analyses of all anomalous lensing
events observed during the seasons. By applying the selection criterion with
mass ratio between the lens components of , we
identify four binary-lens events with candidate BD companions, including
KMT-2018-BLG-0321, KMT-2018-BLG-0885, KMT-2019-BLG-0297, and KMT-2019-BLG-0335.
For the individual events, we present the interpretations of the lens systems
and measure the observables that can constrain the physical lens parameters.
The masses of the lens companions estimated from the Bayesian analyses based on
the measured observables indicate that the probabilities for the lens
companions to be in the brown-dwarf mass regime are high: 59\%, 68\%, 66\%, and
66\% for the four events respectively.Comment: 10 pages, 8 figure
KMT-2022-BLG-0475Lb and KMT-2022-BLG-1480Lb: Microlensing ice giants detected via the non-caustic-crossing channel
Aims. We investigate the microlensing data collected in the 2022 season from high-cadence microlensing surveys in order to find weak signals produced by planetary companions to lenses.
Methods. From these searches, we find that two lensing events, KMT-2022-BLG-0475 and KMT-2022-BLG-1480, exhibit weak short-term anomalies. From a detailed modeling of the lensing light curves, we determine that the anomalies are produced by planetary companions with a mass ratio to the primary of q ~ 1.8 Ă 10â4 for KMT-2022-BLG-0475L and q ~ 4.3 Ă 10â4 for KMT-2022-BLG-1480L.
Results. We estimate that the host and planet masses and the projected planet-host separation are (Mh/Mâ, Mp/MU, aâ„/au) = (0.43â0.23+0.35, 1.73â0.92+1.42, 2.03â0.38+0.25) for KMT-2022-BLG-0475L and (0.18â0.09+0.16, 1.82â0.92+1.60, 1.22â0.14+0.15) for KMT-2022-BLG-1480L, where MU denotes the mass of Uranus. The two planetary systems have some characteristics in common: the primaries of the lenses are early-mid M dwarfs that lie in the Galactic bulge, and the companions are ice giants that lie beyond the snow lines of the planetary systems