In this paper, we report the structural dynamics of polycrystalline bismuth (Bi) thin films in response to photoexcitation, visualized by mega-electron-volt ultrafast electron diffraction. The data ...reveal that the carrier–phonon scattering process involves phonon squeezing within sub-picoseconds (ps) and lattice thermalization within a few ps. Through the time-resolved pair distribution function analysis, we directly observe the changes in the interatomic distance of adjacent Bi atoms in real space, which can be explained by phonon softening and subsequent phonon squeezing.
Abstract
We measure the Einstein radius of the single-lens microlensing event KMT-2022-BLG-2397 to be
θ
E
= 24.8 ± 3.6
μ
as, placing it at the upper shore of the Einstein Desert, 9 ≲
θ
E
/
μ
as ≲ 25, ...between free-floating planets (FFPs) and bulge brown dwarfs (BDs). In contrast to the six BD (25 ≲
θ
E
≲ 50) events presented by Gould et al. (2022), which all had giant-star source stars, KMT-2022-BLG-2397 has a dwarf-star source, with angular radius
θ
ast
∼ 0.9
μ
as. This prompts us to study the relative utility of dwarf and giant sources for characterizing FFPs and BDs from finite-source point-lens (FSPL) microlensing events. We find “dwarfs” (including main-sequence stars and subgiants) are likely to yield twice as many
θ
E
measurements for BDs and a comparable (but more difficult to quantify) improvement for FFPs. We show that neither current nor planned experiments will yield complete mass measurements of isolated bulge BDs, nor will any other planned experiment yield as many
θ
E
measurements for these objects as the Korea Microlensing Telescope (KMT). Thus, the currently anticipated 10 yr KMT survey will remain the best way to study bulge BDs for several decades to come.
Aims.
We systematically inspected the microlensing data acquired by the KMTNet survey during the previous seasons in order to find anomalous lensing events for which the anomalies in the lensing ...light curves cannot be explained by the usual binary-lens or binary-source interpretations.
Methods.
From the inspection, we find that interpreting the three lensing events OGLE-2018-BLG-0584, KMT-2018-BLG-2119, and KMT-2021-BLG-1122 requires four-body (lens+source) models, in which either both the lens and source are binaries (2L2S event) or the lens is a triple system (3L1S event). Following the analyses of the 2L2S events presented in our previous work, here we present the 3L1S analysis of the KMT-2021-BLG-1122.
Results.
It is found that the lens of the event KMT-2021-BLG-1122 is composed of three masses, in which the projected separations (normalized to the angular Einstein radius) and mass ratios between the lens companions and the primary are (
s
2
,
q
2
)∼(1.4, 0.53) and (
s
3
,
q
3
)∼(1.6, 0.24). By conducting a Bayesian analysis, we estimate that the masses of the individual lens components are (
M
1
,
M
2
,
M
3
)∼(0.47
M
⊙
, 0.24
M
⊙
, 0.11
M
⊙
). The companions are separated in projection from the primary by (
a
⊥, 2
,
a
⊥, 3
)∼(3.5, 4.0) AU. The lens of KMT-2018-BLG-2119 is the first triple stellar system detected via microlensing.
Aims.
We present the analysis of the microlensing event KMT-2018-BLG-1743. The analysis was conducted as a part of the project, in which previous lensing events detected in and before the 2019 season ...by the KMTNet survey were reinvestigated with the aim of finding solutions of anomalous events with no suggested plausible models.
Methods.
The light curve of the event, with a peak magnification
A
peak
~ 800, exhibits two anomaly features, one around the peak and the other on the falling side of the light curve. An interpretation with a binary lens and a single source (2L1S) cannot describe the anomalies. By conducting additional modeling that includes an extra lens (3L1S) or an extra source (2L2S) relative to a 2L1S interpretation, we find that 2L2S interpretations with a planetary lens system and a binary source best explain the observed light curve with Δ
χ
2
~ 188 and ~91 over the 2L1S and 3L1S solutions, respectively. Assuming that these Δ
χ
2
values are adequate for distinguishing the models, the event is the fourth 2L2S event and the second 2L2S planetary event. The 2L2S interpretations are subject to a degeneracy, resulting in two solutions with
s
> 1.0 (wide solution) and
s
< 1.0 (close solution).
Results.
The masses of the lens components and the distance to the lens are (
M
host
/
M
⊙
,
M
planet
/
M
J
,
D
L
/kpc)~(0.19
−0.111
+0.27
,0.25
−0.14
+0.34
,6.48
−1.03
+0.94
) and ~(0.42
−0.25
+0.34
,1.61
−0.97
+1.30
,6.04
−1.27
+0.93
) according to the wide and close solutions, respectively. The source is a binary composed of an early G dwarf and a mid M dwarf. The values of the relative lens-source proper motion expected from the two degenerate solutions,
μ
wide
~ 2.3 mas yr
−1
and
μ
close
~ 4.1 mas yr
−1
, are substantially different, and thus the degeneracy can be broken by resolving the lens and source from future high-resolution imaging observations.
Aims.
We search for microlensing planets with signals exhibiting no caustic-crossing features, considering the possibility that such signals may be missed due to their weak and featureless nature.
...Methods.
For this purpose, we reexamine the lensing events found by the KMTNet survey before the 2019 season. From this investigation, we find two new planetary lensing events, KMT-2018-BLG-1976 and KMT-2018-BLG-1996. We also present the analysis of the planetary event OGLE-2019-BLG-0954, for which the planetary signal was known but no detailed analysis had previously been presented. We identify the genuineness of the planetary signals by checking various interpretations that can generate short-term anomalies in lensing light curves.
Results.
From Bayesian analyses conducted with the constraint from available observables, we find that the host and planet masses are (
M
1
,
M
2
) ~ (0.65
M
⊙
, 2
M
J
) for KMT-2018-BLG-1976L, ~(0.69
M
⊙
, 1
M
J
) for KMT-2018-BLG-1996L, and ~(0.80
M
⊙
, 14
M
J
) for OGLE-2019-BLG-0954L. The estimated distance to OGLE-2019-BLG-0954L, 3.63
−1.64
+1.22
kpc, indicates that it is located in the disk, and the brightness expected from the mass and distance matches the brightness of the blend well, indicating that the lens accounts for most of the blended flux. The lens of OGLE-2019-BLG-0954 may be resolved from the source by conducting high-resolution follow-up observations in and after 2024.
Abstract
We continue our program of publishing all planets (and possible planets) found by eye in 2021 Korea Microlensing Telescope Network (KMTNet) online data. We present four planets ...(KMT-2021-BLG-0712Lb, KMT-2021-BLG-0909Lb, KMT-2021-BLG-2478Lb, and KMT-2021-BLG-1105Lb), with planet-to-host mass ratios in the range
−
3.3
≲
log
q
≲
−
2.2
. This brings the total of secure, by-eye, 2021 KMTNet planets to 16, including 8 in this series. The by-eye sample is an important check of the completeness of semiautomated detections, which are the basis for statistical analyses. One of the planets, KMT-2021-BLG-1105Lb, is blended with a relatively bright (
I
,
V
) ∼ (18.9, 21.6) star that may be the host. This could be verified immediately by high-resolution imaging. If so, the host is an early G dwarf, and the planet could be characterized by radial velocity observations on 30 m class telescopes.
Abstract
We analyze the microlensing event OGLE-2019-BLG-0304, whose light curve exhibits two distinctive features: a deviation in the peak region and a second bump appearing ∼61 days after the main ...peak. Although a binary-lens model can explain the overall features, it leaves subtle but noticeable residuals in the peak region. We find that the residuals can be explained by the presence of either a planetary companion located close to the primary of the binary lens (3L1S model) or an additional close companion to the source (2L2S model). Although the 3L1S model is favored over the 2L2S model, with Δ
χ
2
∼ 8, securely resolving the degeneracy between the two models is difficult with the currently available photometric data. According to the 3L1S interpretation, the lens is a planetary system, in which a planet with a mass
0.51
−
0.23
+
0.51
M
J
is in an S-type orbit around a binary composed of stars with masses
0.27
−
0.12
+
0.27
M
⊙
and
0.10
−
0.04
+
0.10
M
⊙
. According to the 2L2S interpretation, however, the source is composed of G- and K-type giant stars and the lens is composed of a low-mass M dwarf and a brown dwarf with masses
0.12
−
0.05
+
0.12
M
⊙
and
0.045
−
.019
+
0.045
M
⊙
, respectively. The event illustrates the need for thorough model testing in the interpretation of lensing events with complex features in light curves.
Abstract
With a planet–host mass ratio
q
= 0.012 ± 0.001, KMT-2016-BLG-2605 has the shortest Einstein timescale,
t
E
= 3.41 ± 0.13 days, of any planetary microlensing event to date. This prompts us ...to examine the full sample of seven short (
t
E
< 7 days) planetary events with good
q
measurements. We find that six have clustered Einstein radii
θ
E
= 115 ± 20
μ
as and lens–source relative proper motions
μ
rel
≃ 9.5 ± 2.5 mas yr
−1
. For the seventh, these two quantities could not be measured. These distributions are consistent with a Galactic bulge population of very low mass (VLM) hosts near the hydrogen-burning limit. This conjecture could be verified by imaging at first adaptive optics light on next-generation (30 m) telescopes. Based on a preliminary assessment of the sample, “planetary” companions (i.e., below the deuterium-burning limit) are divided into “genuine planets,” formed in their disks by core accretion, and VLM brown dwarfs, which form like stars. We discuss techniques for expanding the sample, which include taking account of the peculiar “anomaly-dominated” morphology of the KMT-2016-BLG-2605 light curve.
Aims.
We analyze the microlensing event KMT-2019-BLG-0797. The light curve of the event exhibits two anomalous features from a single-lens single-source model, and we aim to reveal the nature of the ...anomaly.
Methods.
It is found that a model with two lenses plus a single source (2L1S model) can explain one feature of the anomaly, but the other feature cannot be explained. We test various models and find that both anomalous features can be explained by introducing an extra source to a 2L1S model (2L2S model), making the event the third confirmed case of a 2L2S event, following MOA-2010-BLG-117 and OGLE-2016-BLG-1003. It is estimated that the extra source comprises ∼4% of the
I
-band flux from the primary source.
Results.
Interpreting the event is subject to a close–wide degeneracy. According to the close solution, the lens is a binary consisting of two brown dwarfs with masses (
M
1
,
M
2
) ∼ (0.034, 0.021)
M
⊙
, and it is located at a distance of
D
L
∼ 8.2 kpc. According to the wide solution, on the other hand, the lens is composed of an object at the star–brown dwarf boundary and an M dwarf with masses (
M
1
,
M
2
) ∼ (0.06, 0.33)
M
⊙
located at
D
L
∼ 7.7 kpc. The source is composed of a late G dwarf to early K dwarf primary and an early-to-mid M dwarf companion.
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