892 research outputs found
Planetary and Other Short Binary Microlensing Events from the MOA Short Event Analysis
We present the analysis of four candidate short duration binary microlensing
events from the 2006-2007 MOA Project short event analysis. These events were
discovered as a byproduct of an analysis designed to find short timescale
single lens events that may be due to free-floating planets. Three of these
events are determined to be microlensing events, while the fourth is most
likely caused by stellar variability. For each of the three microlensing
events, the signal is almost entirely due to a brief caustic feature with
little or no lensing attributable mainly to the lens primary. One of these
events, MOA-bin-1, is due to a planet, and it is the first example of a
planetary event in which stellar host is only detected through binary
microlensing effects. The mass ratio and separation are q = 4.9 +- 1.4 x
10^{-3} and s = 2.10 +- 0.05, respectively. A Bayesian analysis based on a
standard Galactic model indicates that the planet, MOA-bin-1Lb, has a mass of
m_p = 3.7 +- 2.1 M_{Jup}, and orbits a star of M_* = 0.75{+0.33 -0.41} M_solar
at a semi-major axis of a = 8.3 {+4.5 -2.7} AU. This is one of the most massive
and widest separation planets found by microlensing. The scarcity of such wide
separation planets also has implications for interpretation of the isolated
planetary mass objects found by this analysis. If we assume that we have been
able to detect wide separation planets with a efficiency at least as high as
that for isolated planets, then we can set limits on the distribution on
planets in wide orbits. In particular, if the entire isolated planet sample
found by Sumi et al. (2011) consists of planets bound in wide orbits around
stars, we find that it is likely that the median orbital semi-major axis is >
30 AU.Comment: 47 pages with 14 figure
Determining the Physical Lens Parameters of the Binary Gravitational Microlensing Event MOA-2009-BLG-016
We report the result of the analysis of the light curve of the microlensing
event MOA-2009-BLG-016. The light curve is characterized by a short-duration
anomaly near the peak and an overall asymmetry. We find that the peak anomaly
is due to a binary companion to the primary lens and the asymmetry of the light
curve is explained by the parallax effect caused by the acceleration of the
observer over the course of the event due to the orbital motion of the Earth
around the Sun. In addition, we detect evidence for the effect of the finite
size of the source near the peak of the event, which allows us to measure the
angular Einstein radius of the lens system. The Einstein radius combined with
the microlens parallax allows us to determine the total mass of the lens and
the distance to the lens. We identify three distinct classes of degenerate
solutions for the binary lens parameters, where two are manifestations of the
previously identified degeneracies of close/wide binaries and positive/negative
impact parameters, while the third class is caused by the symmetric cycloid
shape of the caustic. We find that, for the best-fit solution, the estimated
mass of the lower-mass component of the binary is (0.04 +- 0.01) M_sun,
implying a brown-dwarf companion. However, there exists a solution that is
worse only by \Delta\chi^2 ~ 3 for which the mass of the secondary is above the
hydrogen-burning limit. Unfortunately, resolving these two degenerate solutions
will be difficult as the relative lens-source proper motions for both are
similar and small (~ 1 mas/yr) and thus the lens will remain blended with the
source for the next several decades.Comment: 7 pages, 2 tables, and 5 figure
Recommended from our members
Application of value chain analysis in understanding the losses and wastes of cassava in Vietnam
To reduce post-harvest losses and foster development of cassava, it is necessary to evaluate the full range of activities required to bring fresh cassava root through different stages of production, processing, and marketing until it reaches the end-user. A Value Chain Analysis (VCA) provides the approach for such an understanding in that it is a process of tracing a product’s flow from the point of production to the point of consumption along with tracing the roles and relationships of different actors and stakeholder at different points in the value chain. This paper provides an overview of the main cassava value chains in Vietnam, and the extent and nature of losses and wastes in those value chains
MOA-2016-BLG-227Lb: A Massive Planet Characterized by Combining Light-curve Analysis and Keck AO Imaging
We report the discovery of a microlensing planet—MOA-2016-BLG-227Lb—with a large planet/host mass ratio of q ≃ 9 × 10−3. This event was located near the K2 Campaign 9 field that was observed by a large number of telescopes. As a result, the event was in the microlensing survey area of a number of these telescopes, and this enabled good coverage of the planetary light-curve signal. High angular resolution adaptive optics images from the Keck telescope reveal excess flux at the position of the source above the flux of the source star, as indicated by the light-curve model. This excess flux could be due to the lens star, but it could also be due to a companion to the source or lens star, or even an unrelated star. We consider all these possibilities in a Bayesian analysis in the context of a standard Galactic model. Our analysis indicates that it is unlikely that a large fraction of the excess flux comes from the lens, unless solar-type stars are much more likely to host planets of this mass ratio than lower mass stars. We recommend that a method similar to the one developed in this paper be used for other events with high angular resolution follow-up observations when the follow-up observations are insufficient to measure the lens–source relative proper motion
Microlensing Event MOA-2007-BLG-400: Exhuming the Buried Signature of a Cool, Jovian-Mass Planet
We report the detection of the cool, Jovian-mass planet MOA-2007-BLG-400Lb.
The planet was detected in a high-magnification microlensing event (with peak
magnification A_max = 628) in which the primary lens transited the source,
resulting in a dramatic smoothing of the peak of the event. The angular extent
of the region of perturbation due to the planet is significantly smaller than
the angular size of the source, and as a result the planetary signature is also
smoothed out by the finite source size. Thus the deviation from a single-lens
fit is broad and relatively weak (~ few percent). Nevertheless, we demonstrate
that the planetary nature of the deviation can be unambiguously ascertained
from the gross features of the residuals, and detailed analysis yields a fairly
precise planet/star mass ratio of q = 0.0026+/-0.0004, in accord with the large
significance (\Delta\chi^2=1070) of the detection. The planet/star projected
separation is subject to a strong close/wide degeneracy, leading to two
indistinguishable solutions that differ in separation by a factor of ~8.5.
Upper limits on flux from the lens constrain its mass to be M < 0.75 M_Sun
(assuming it is a main-sequence star). A Bayesian analysis that includes all
available observational constraints indicates a primary in the Galactic bulge
with a mass of ~0.2-0.5 M_Sun and thus a planet mass of ~ 0.5-1.3 M_Jupiter.
The separation and equilibrium temperature are ~0.6-1.1AU (~5.3-9.7AU) and
~103K (~34K) for the close (wide) solution. If the primary is a main-sequence
star, follow-up observations would enable the detection of its light and so a
measurement of its mass and distance.Comment: 30 pages, 6 figures, Submitted to Ap
Improving the Prospects for Detecting Extrasolar Planets in Gravitational Microlensing in 2002
Gravitational microlensing events of high magnification have been shown to be
promising targets for detecting extrasolar planets. However, only a few events
of high magnification have been found using conventional survey techniques.
Here we demonstrate that high magnification events can be readily found in
microlensing surveys using a strategy that combines high frequency sampling of
target fields with online difference imaging analysis. We present 10
microlensing events with peak magnifications greater than 40 that were detected
in real-time towards the Galactic Bulge during 2001 by MOA. We show that Earth
mass planets can be detected in future events such as these through intensive
follow-up observations around the event peaks. We report this result with
urgency as a similar number of such events are expected in 2002.Comment: 11 pages, 3 embedded ps figures including 2 colour, revised version
accepted by MNRA
OGLE-2009-BLG-023/MOA-2009-BLG-028: Characterization of a Binary Microlensing Event Based on Survey Data
We report the result of the analysis of the light curve of a caustic-crossing
binary-lens microlensing event OGLE-2009-BLG-023/MOA-2009-BLG-028. Even though
the event was observed solely by survey experiments, we could uniquely
determine the mass of the lens and distance to it by simultaneously measuring
the Einstein radius and lens parallax. From this, we find that the lens system
is composed of M-type dwarfs with masses and
located in the Galactic disk with a distance of kpc toward the Galactic bulge direction. The event demonstrates that
physical lens parameters of binary-lens events can be routinely determined from
future high-cadence lensing surveys and thus microlensing can provide a new way
to study Galactic binaries.Comment: 8 pages, 5 figure
On Planetary Companions to the MACHO-98-BLG-35 Microlens Star
We present observations of microlensing event MACHO-98-BLG-35 which reached a
peak magnification factor of almost 80. These observations by the Microlensing
Planet Search (MPS) and the MOA Collaborations place strong constraints on the
possible planetary system of the lens star and show intriguing evidence for a
low mass planet with a mass fraction . A giant planet with is excluded from 95%
of the region between 0.4 and 2.5 from the lens star, where is the
Einstein ring radius of the lens. This exclusion region is more extensive than
the generic "lensing zone" which is . For smaller mass planets,
we can exclude 57% of the "lensing zone" for and 14% of
the lensing zone for . The mass fraction corresponds to an Earth mass planet for a lensing star of mass \sim
0.3 \msun. A number of similar events will provide statistically significant
constraints on the prevalence of Earth mass planets. In order to put our limits
in more familiar terms, we have compared our results to those expected for a
Solar System clone averaging over possible lens system distances and
orientations. We find that such a system is ruled out at the 90% confidence
level. A copy of the Solar System with Jupiter replaced by a second Saturn mass
planet can be ruled out at 70% confidence. Our low mass planetary signal (few
Earth masses to Neptune mass) is significant at the confidence
level. If this planetary interpretation is correct, the MACHO-98-BLG-35 lens
system constitutes the first detection of a low mass planet orbiting an
ordinary star without gas giant planets.Comment: ApJ, April 1, 2000; 27 pages including 8 color postscript figure
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