56 research outputs found
Adaptive Optics Imaging Breaks the Central Caustic Cusp Approach Degeneracy in High Magnification Microlensing Events
We report new results for the gravitational microlensing target
OGLE-2011-BLG-0950 from adaptive optics (AO) images using the Keck observatory.
The original analysis by Choi et al. 2012 reports degenerate solutions between
planetary and stellar binary lens systems. This is due to a degeneracy in high
magnification events where the shape of the light curve peak can be explained
by a source approach to two different cusp geometries with different source
radius crossing times. This particular case is the most important type of
degeneracy for exoplanet demographics, because the distinction between a
planetary mass or stellar binary companion has direct consequences for
microlensing exoplanet statistics. The 8 and 10-year baselines between the
event and the Keck observations allow us to directly measure a relative proper
motion of mas/yr, which confirms the detection of the lens star
system and directly rules out the planetary companion models that predict a
smaller relative proper motion. The combination of the lens
brightness and close stellar binary light curve parameters yield primary and
secondary star masses of and at a distance of kpc, and a primary-secondary projected separation of
AU. Since this degeneracy is likely to be common, the
high resolution imaging method described here will be used to disentangle the
central caustic cusp approach degeneracy for events observed by the
\textit{Roman} exoplanet microlensing survey using the \textit{Roman} images
taken near the beginning or end of the survey.Comment: Revised version, 19 pages, 8 figures. AJ, 164, 21
Keck Observations Confirm a Super-Jupiter Planet Orbiting M Dwarf OGLE-2005-BLG-071L
We present adaptive optics imaging from the NIRC2 instrument on the Keck II telescope that resolves the exoplanet host (and lens) star as it separates from the brighter source star. These observations yield the K-band brightness of the lens and planetary host star, as well as the lens-source relative proper motion, µ_(rel,H), in the heliocentric reference frame. The µ_(rel,H) measurement allows for the determination of the microlensing parallax vector, π_E, which had only a single component determined by the microlensing light curve. The combined measurements of µ_(rel,H) and K L provide the masses of the host star, M_(host) = 0.426 ± 0.037 M⊙, and planet, m_p = 3.27 ± 0.32M_(Jupiter) with a projected separation of 3.4 ± 0.5 au. This confirms the tentative conclusion of a previous paper that this super-Jupiter mass planet, OGLE-2005-BLG-071Lb, orbits an M dwarf. Such planets are predicted to be rare by the core accretion theory and have been difficult to find with other methods, but there are two such planets with firm mass measurements from microlensing, and an additional 11 planetary microlens events with host mass estimates <0.
0.5M⊙ and planet mass estimates >2 Jupiter masses that could be confirmed by high angular follow-up observations. We also point out that OGLE-2005-BLG-071L has separated far enough from its host star that it should be possible to measure the host-star metallicity with spectra from a high angular resolution telescope such as Keck, the Very Large Telescope, the Hubble Space Telescope, or the James Webb Space Telescope
Free-Floating planet Mass Function from MOA-II 9-year survey towards the Galactic Bulge
We present the first measurement of the mass function of free-floating
planets (FFP) or very wide orbit planets down to an Earth mass, from the MOA-II
microlensing survey in 2006-2014. Six events are likely to be due to planets
with Einstein radius crossing times, days, and the shortest has
days and an angular Einstein radius of as. We measure the detection efficiency depending on both
and with image level simulations for the first
time. These short events are well modeled by a power-law mass function,
dexstar with for . This implies a total of FFP or very wide orbit
planets of mass per star, with a total mass of
per star. The number of FFPs is
times the number of planets in wide orbits (beyond the snow line), while the
total masses are of the same order. This suggests that the FFPs have been
ejected from bound planetary systems that may have had an initial mass function
with a power-law index of , which would imply a total mass of
star. This model predicts that Roman Space
Telescope will detect FFPs with masses down to that of
Mars (including with ). The
Sumi(2011) large Jupiter-mass FFP population is excluded.Comment: 17 pages, 7 figures, accepted for publication in A
MOA-2020-BLG-135Lb: A New Neptune-class Planet for the Extended MOA-II Exoplanet Microlens Statistical Analysis
We report the light-curve analysis for the event MOA-2020-BLG-135, which
leads to the discovery of a new Neptune-class planet, MOA-2020-BLG-135Lb. With
a derived mass ratio of and separation
, the planet lies exactly at the break and likely peak of the
exoplanet mass-ratio function derived by the MOA collaboration (Suzuki et al.
2016). We estimate the properties of the lens system based on a Galactic model
and considering two different Bayesian priors: one assuming that all stars have
an equal planet-hosting probability and the other that planets are more likely
to orbit more massive stars. With a uniform host mass prior, we predict that
the lens system is likely to be a planet of mass
and a host star of mass
, located at a distance
. With a prior that holds that planet
occurrence scales in proportion to the host star mass, the estimated lens
system properties are ,
, and . This planet qualifies for inclusion in the extended MOA-II
exoplanet microlens sample.Comment: 22 pages, 6 figures, 4 tables, submitted to the AAS Journal
KMT-2021-BLG-1077L: The fifth confirmed multiplanetary system detected by microlensing
The high-magnification microlensing event KMT-2021-BLG-1077 exhibits a subtle
and complex anomaly pattern in the region around the peak. We analyze the
lensing light curve of the event with the aim of revealing the nature of the
anomaly. We test various models in combination with several interpretations. We
find that the anomaly cannot be explained by the usual three-body (2L1S and
1L2S) models. The 2L2S model improves the fit compared to the three-body
models, but it still leaves noticeable residuals. On the other hand, the 3L1S
interpretation yields a model explaining all the major anomalous features in
the lensing light curve. According to the 3L1S interpretation, the estimated
mass ratios of the lens companions to the primary are and , which correspond to and
times the Jupiter/Sun mass ratio, respectively, and therefore the
lens is a multiplanetary system containing two giant planets. With the
constraints of the event time-scale and angular Einstein radius, it is found
that the host of the lens system is a low-mass star of mid-to-late M spectral
type with a mass of , and it hosts
two gas giant planets with masses of and . The planets lie beyond
the snow line of the host with projected separations of and . The planetary system resides in the
Galactic bulge at a distance of . The
lens of the event is the fifth confirmed multiplanetary system detected by
microlensing following OGLE-2006-BLG-109L, OGLE-2012-BLG-0026L,
OGLE-2018-BLG-1011L, and OGLE-2019-BLG-0468L.Comment: 9 pages, 8 figure
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
Systematic KMTNet Planetary Anomaly Search. IX. Complete Sample of 2016 Prime-Field Planets
As a part of the ``Systematic KMTNet Planetary Anomaly Search" series, we
report five new planets (namely, OGLE-2016-BLG-1635Lb, MOA-2016-BLG-532Lb,
KMT-2016-BLG-0625Lb, OGLE-2016-BLG-1850Lb, and KMT-2016-BLG-1751Lb) and one
planet candidate (KMT-2016-BLG-1855), which were found by searching
KMTNet prime fields. These planets show a wide range of masses from
Earth--class to Super--Jupiter--class, and are located in both the disk and the
bulge. The ultimate goal of this series is to build a complete planet sample.
Because our work provides a complementary sample to other planet detection
methods, which have different detection sensitivities, our complete sample will
help us to obtain a better understanding of planet demographics in our Galaxy.Comment: 38 pages, 17 figures, 12 Tables, submitted to the AAS journa
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
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
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