48 research outputs found
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
A Gas Giant Planet in the OGLE-2006-BLG-284L Stellar Binary System
We present the analysis of microlensing event OGLE-2006-BLG-284, which has a
lens system that consists of two stars and a gas giant planet with a mass ratio
of to the primary. The mass ratio of the
two stars is , and their projected separation is AU, while the projected separation of the planet from the primary
is AU. For this lens system to have stable orbits, the
three-dimensional separation of either the primary and secondary stars or the
planet and primary star must be much larger than that these projected
separations. Since we do not know which is the case, the system could include
either a circumbinary or a circumstellar planet. Because there is no
measurement of the microlensing parallax effect or lens system brightness, we
can only make a rough Bayesian estimate of the lens system masses and
brightness. We find host star and planet masses of , , and
, and the -band magnitude of the combined
brightness of the host stars is . The separation
between the lens and source system will be mas in mid-2020, so it
should be possible to detect the host system with follow-up adaptive optics or
Hubble Space Telescope observations
A Gas Giant Planet in the OGLE-2006-BLG-284L Stellar Binary System
We present the analysis of microlensing event OGLE-2006-BLG-284, which has a lens system that consists of two stars and a gas giant planet with a mass ratio of q_p = (1.26 ± 0.19) Ă 10â»Âł to the primary. The mass ratio of the two stars is q_s = 0.289 ± 0.011, and their projected separation is s_s = 2.1 ± 0.7 au, while the projected separation of the planet from the primary is s_p = 2.2 ± 0.8 au. For this lens system to have stable orbits, the three-dimensional separation of either the primary and secondary stars or the planet and primary star must be much larger than the projected separations. Since we do not know which is the case, the system could include either a circumbinary or a circumstellar planet. Because there is no measurement of the microlensing parallax effect or lens system brightness, we can only make a rough Bayesian estimate of the lens system masses and brightness. We find host star and planet masses of, M_(L1) = 0.35^(+0.30)_(â0.20) Mâ, M_(L2) = 0.10^(+0.09)_(â0.06) Mâ, and m_p = 144^(+126)_(â82) Mâ, and the K-band magnitude of the combined brightness of the host stars is K_L = 19.7^(+0.7)_(â1.0). The separation between the lens and source system will be ~90 mas in mid-2020, so it should be possible to detect the host system with follow-up adaptive optics or Hubble Space Telescope observations
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
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-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
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
Mass Production of 2021 KMTNet Microlensing Planets III: Analysis of Three Giant Planets
We present the analysis of three more planets from the KMTNet 2021
microlensing season. KMT-2021-BLG-0119Lb is a planet
orbiting an early M-dwarf or a K-dwarf, KMT-2021-BLG-0192Lb is a planet orbiting an M-dwarf, and KMT-2021-BLG-0192Lb is a planet orbiting a very--low-mass M dwarf or a brown dwarf.
These by-eye planet detections provide an important comparison sample to the
sample selected with the AnomalyFinder algorithm, and in particular,
KMT-2021-BLG-2294, is a case of a planet detected by-eye but not by-algorithm.
KMT-2021-BLG-2294Lb is part of a population of microlensing planets around
very-low-mass host stars that spans the full range of planet masses, in
contrast to the planet population at au, which shows a strong
preference for small planets.Comment: 17 pages, 12 figures, 7 tables. Accept for publication in The
Astronomical Journa