Abstract
The PRime-focus Infrared Microlensing Experiment (PRIME) will be the first to conduct a dedicated near-infrared microlensing survey by using a 1.8 m telescope with a wide field of view of ...1.45 deg
2
at the South African Astronomical Observatory. The major goals of the PRIME microlensing survey are to measure the microlensing event rate in the inner Galactic bulge to help design the observing strategy for the exoplanet microlensing survey by the Nancy Grace Roman Space Telescope and to make a first statistical measurement of exoplanet demographics in the central bulge fields where optical observations are very difficult owing to the high extinction in these fields. Here we conduct a simulation of the PRIME microlensing survey to estimate its planet yields and determine the optimal survey strategy, using a Galactic model optimized for the inner Galactic bulge. In order to maximize the number of planet detections and the range of planet mass, we compare the planet yields among four observation strategies. Assuming the Cassan et al. mass function as modified by Penny et al., we predict that PRIME will detect planetary signals for 42–52 planets (1–2 planets with
M
p
≤ 1
M
⊕
, 22−25 planets with mass 1
M
⊕
<
M
p
≤ 100
M
⊕
, 19–25 planets 100
M
⊕
<
M
p
≤ 10, 000
M
⊕
), per year depending on the chosen observation strategy.
Abstract
We present the first measurement of the mass function of free-floating planets (FFPs), 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
t
E
< 0.5 days, and the shortest has
t
E
= 0.057 ± 0.016 days and an angular Einstein radius of
θ
E
= 0.90 ± 0.14
μ
as. We measure the detection efficiency depending on both
t
E
and
θ
E
with image-level simulations for the first time. These short events are well modeled by a power-law mass function,
dN
4
/
d
log
M
=
(
2.18
−
1.40
+
0.52
)
×
(
M
/
8
M
⊕
)
−
α
4
dex
−1
star
−1
with
α
4
=
0.96
−
0.27
+
0.47
for
M
/
M
⊙
< 0.02. This implies a total of
f
=
21
−
13
+
23
FFPs or very wide orbit planets of mass 0.33 <
M
/
M
⊕
< 6660 per star, with a total mass of
80
−
47
+
73
M
⊕
star
−1
. The number of FFPs is
19
−
13
+
23
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
α
∼ 0.9, which would imply a total mass of
171
−
52
+
80
M
⊕
star
−1
. This model predicts that Roman Space Telescope will detect
988
−
566
+
1848
FFPs with masses down to that of Mars (including
575
−
424
+
1733
with 0.1 ≤
M
/
M
⊕
≤ 1). The Sumi et al. large Jupiter-mass FFP population is excluded.
Abstract
We report the discoveries of low-mass free-floating planet (FFP) candidates from the analysis of 2006–2014 MOA-II Galactic bulge survey data. In this data set, we found 6111 microlensing ...candidates and identified a statistical sample consisting of 3535 high-quality single-lens events with Einstein radius crossing times in the range 0.057 <
t
E
/days < 757, including 13 events that show clear finite-source effects with angular Einstein radii of 0.90 <
θ
E
/
μ
as < 332.54. Two of the 12 events with
t
E
< 1 day have significant finite-source effects, and one event, MOA-9y-5919, with
t
E
= 0.057 ± 0.016 days and
θ
E
= 0.90 ± 0.14
μ
as, is the second terrestrial-mass FFP candidate to date. A Bayesian analysis indicates a lens mass of
0.75
−
0.46
+
1.23
M
⊕
for this event. The low detection efficiency for short-duration events implies a large population of low-mass FFPs. The microlensing detection efficiency for low-mass planet events depends on both the Einstein radius crossing times and the angular Einstein radii, so we have used image-level simulations to determine the detection efficiency dependence on both
t
E
and
θ
E
. This allows us to use a Galactic model to simulate the
t
E
and
θ
E
distribution of events produced by the known stellar populations and models of the FFP distribution that are fit to the data. Methods like this will be needed for the more precise FFP demographics determinations from Nancy Grace Roman Space Telescope data.
Aims.
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.
Methods.
We test various models in combination with several interpretations: that the lens is a binary (2L1S), the source is a binary (1L2S), both the lens and source are binaries (2L2S), or the lens is a triple system (3L1S). We search for the best-fit models under the individual interpretations of the lens and source systems.
Results.
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 ~1.56 × 10
−3
and ~1.75 × 10
−3
, which correspond to ~1.6 and ~1.8 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 amass of
M
h
= 0.14
−0.07
+0.19
M
Θ
, and it hosts two gas giant planets with masses of
M
p1
= 0.22
−0.12
+0.31
M
J
and
M
p2
= 0.25
−0.13
+0.35
. The planets lie beyond the snow line of the host with projected separations of
a
⊥,p1
= 1.26
−1.08
+1.41
AU and
a
⊥,p2
= 0.93
−0.80
+1.05
AU. The planetary system resides in the Galactic bulge at a distance of
D
L
= 8.24
−1.16
+1.02
kpc. 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.
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 qp = (1.26 0.19) × 10−3 to the primary. ...The mass ratio of the two stars is qs = 0.289 0.011, and their projected separation is ss = 2.1 0.7 au, while the projected separation of the planet from the primary is sp = 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 , , and , and the K-band magnitude of the combined brightness of the host stars is . 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.
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 q=1.52+0.39-0.31x10-4 ...and separation s ≈ 1, the planet lies exactly at the break and likely peak of the exoplanet mass-ratio function derived by the Microlensing Observations in Astrophysics (MOA) Collaboration. 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 mplanet= 11.3 +19.2 -6.9M⨁ and a host star of mass Mhost=0.23+0.39-0.14M⨀, located at a distance 𝐃𝐋=7.9+1.0-1.0 kpc. With a prior that holds that planet occurrence scales in proportion to the host-star mass, the estimated lens system properties are mplanet=25+22 -15 M⨁, M Mhost=0.53+0.42 -0,32 M⨀, and DL=8.3+0.9-1.0.This planet qualifies for inclusion in the extended MOA-II exoplanet microlens sample.
The Microlensing Observations in Astrophysics (MOA-II) survey has performed high cadence, wide field observations of the Galactic Bulge from New Zealand since 2005. The hourly cadence of the survey ...during eight months of the year, across nearly 50 deg2 of sky, provides an opportunity to sample asteroid lightcurves in the broad MOA-R filter. We perform photometry of a subset of bright asteroids numbered observed by the survey. We obtain 26 asteroid rotation periods, including for two asteroids where no prior data exist, and present evidence for the possible non-principal axis rotation of (2011) Veteraniya. This archival search could be extended to several thousands of asteroids brighter than 22nd magnitude.
Characterizing a planet detected by microlensing is hard if the planetary signal is weak or the lens-source relative trajectory is far from caustics. However, statistical analyses of planet ...demography must include those planets to accurately determine occurrence rates. As part of a systematic modelling effort in the context of a >10-yr retrospective analysis of MOA’s survey observations to build an extended MOA statistical sample, we analyse the light curve of the planetary microlensing event MOA-2014-BLG-472. This event provides weak constraints on the physical parameters of the lens, as a result of a planetary anomaly occurring at low magnification in the light curve. We use a Bayesian analysis to estimate the properties of the planet, based on a refined Galactic model and the assumption that all Milky Way’s stars have an equal planet-hosting probability. We find that a lens consisting of a 1.9(+2.2,−1.2)M(J) giant planet orbiting a 0.31(+0.36,−0.19)Mꙩ host at a projected separation of 0.75±0.24au is consistent with the observations and is most likely, based on the Galactic priors. The lens most probably lies in the Galactic bulge, at 7.2(+0.6,−1.7)kpc from Earth. The accurate measurement of the measured planet-to-host star mass ratio will be included in the next statistical analysis of cold planet demography detected by microlensing.
We report the discovery of a gas-giant planet orbiting a low-mass host star in the microlensing event MOA-bin-29 that occurred in 2006. We find five degenerate solutions with the planet/host-star ...mass ratio of q ∼ 10−2. The Einstein radius crossing time of all models are relatively short (∼4-7 days), which indicates that the mass of host star is likely low. The measured lens-source proper motion is 5-9 mas yr−1 depending on the models. Since only finite source effects are detected, we conduct a Bayesian analysis in order to obtain the posterior probability distribution of the lens physical properties. As a result, we find the lens system is likely to be a gas-giant orbiting a brown dwarf or a very late M-dwarf in the Galactic bulge. The probability distributions of the physical parameters for the five degenerate models are consistent within the range of error. By combining these probability distributions, we conclude that the lens system is a gas giant with a mass of orbiting a brown dwarf with a mass of at a projected star-planet separation of . The lens distance is , i.e., likely within the Galactic bulge.
We present the analysis of five black hole candidates identified from gravitational microlensing surveys. Hubble Space Telescope astrometric data and densely sampled light curves from ground-based ...microlensing surveys are fit with a single-source, single-lens microlensing model in order to measure the mass and luminosity of each lens and determine if it is a black hole. One of the five targets (OGLE-2011-BLG-0462/MOA-2011-BLG-191 or OB110462 for short) shows a significant >1 mas coherent astrometric shift, little to no lens flux, and has an inferred lens mass of 1.6–4.4 M⨀. This makes OB110462 the first definitive discovery of a compact object through astrometric microlensing and it is most likely either a neutron star or a low-mass black hole. This compact-object lens is relatively nearby (0.70–1.92 kpc) and has a slow transverse motion of <30 kms-1. OB110462 shows significant tension between models well fit to photometry versus astrometry, making it currently difficult to distinguish between a neutron star and a black hole. Additional observations and modeling with more complex system geometries, such as binary sources, are needed to resolve the puzzling nature of this object. For the remaining four candidates, the lens masses are <2M⨀, and they are unlikely to be black holes; two of the four are likely white dwarfs or neutron stars. We compare the full sample of five candidates to theoretical expectations on the number of black holes in the Milky Way (∼108 ) and find reasonable agreement given the small sample size.
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