-
[show abstract]
[hide abstract]
ABSTRACT: The Galactic bulge shows a double red clump in sight lines with |b| > 5 deg
and -3 deg < l < 4 deg. It is interpreted as a signature of an X-shaped
structure seen almost edge-on. We measure the proper motions of the stars
belonging to the closer and the further arm of the X-shaped structure. The
intrinsic kinematic properties of the two arms are found by incorporating
information taken from the luminosity function. At b = -5 deg we find that the
proper motion difference between the two arms is a linear function of the
Galactic longitude for -0.1 deg < l < 0.5 deg, which we interpret as a
streaming motion of the stars within the X-shaped structure. Such a streaming
motion has not previously been reported. The proper motion difference is
constant for -0.8 deg < l < -0.1 deg, which gives us an estimate of bulge
rotation speed of 87.9 +/- 8.2 km/s/kpc.
04/2013;
-
R. Tylenda,
T. Kaminski,
A. Udalski,
I. Soszynski, R. Poleski,
M. K. Szymanski,
M. Kubiak,
G. Pietrzynski,
S. Kozlowski,
P. Pietrukowicz,
K. Ulaczyk,
L. Wyrzykowski
[show abstract]
[hide abstract]
ABSTRACT: OGLE-2002-BLG-360 was discovered as a microlensing candidate by the OGLE-III
project. The subsequent light curve however clearly showed that the brightening
of the object could not have resulted from the gravitational microlensing
phenomenon. We aim to explain the nature of OGLE-2002-BLG-360 and its eruption
observed in 2002--2006. The observational data primarily come from the archives
of the OGLE project, which monitored the object in 2001--2009. The archives of
the MACHO and MOA projects also provided us with additional data obtained in
1995--99 and 2000--2005, respectively. These data allowed us to analyse the
light curve of the object during its eruption, as well as the potential
variability of its progenitor. In the archives of several infrared surveys,
namely 2MASS, MSX, Spitzer, AKARI, WISE, and VVV, we found measurements of the
object, which allowed us to study the spectral energy distribution (SED) of the
object. We constructed a simple model of a star surrounded by a dusty envelope,
which was used to interpret the observed SED. Our analysis of the data clearly
shows that OGLE-2002-BLG-360 was most probably a red transient, i.e. an object
similar in nature to V838 Mon, whose eruption was observed in 2002. The SED in
all phases, i.e. progenitor, eruption, and remnant, was dominated by infrared
emission, which we interpret as evidence of dust formation in an intense mass
outflow. Since 2009 the object has been completely embedded in dust. We suggest
that the progenitor of OGLE-2002-BLG-360 was a binary, which had entered the
common-envelope phase a long time (at least decades) before the observed
eruption, and that the eruption resulted from the final merger of the binary
components. We point out similarities between OGLE-2002-BLG-360 and CK Vul,
whose eruption was observed in 1670--72, and this strengthens the hypothesis
that CK Vul was also a red transient.
04/2013;
-
G. Pietrzyński,
D. Graczyk,
W. Gieren,
I. B. Thompson,
B. Pilecki,
A. Udalski,
I. Soszyński,
S. Kozłowski,
P. Konorski,
K. Suchomska, [......],
R. Smolec,
D. Minniti,
M. Kubiak,
M. Szymański, R. Poleski,
Ł. Wyrzykowski,
K. Ulaczyk,
P. Pietrukowicz,
M. Górski,
P. Karczmarek
[show abstract]
[hide abstract]
ABSTRACT: In the era of precision cosmology it is essential to determine the Hubble
Constant with an accuracy of 3% or better. Currently, its uncertainty is
dominated by the uncertainty in the distance to the Large Magellanic Cloud
(LMC) which as the second nearest galaxy serves as the best anchor point of the
cosmic distance scale. Observations of eclipsing binaries offer a unique
opportunity to precisely and accurately measure stellar parameters and
distances. The eclipsing binary method was previously applied to the LMC but
the accuracy of the distance results was hampered by the need to model the
bright, early-type systems used in these studies. Here, we present distance
determinations to eight long-period, late- type eclipsing systems in the LMC
composed of cool giant stars. For such systems we can accurately measure both
the linear and angular sizes of their components and avoid the most important
problems related to the hot early-type systems. Our LMC distance derived from
these systems is demonstrably accurate to 2.2 % (49.97 +/- 0.19 (statistical)
+/- 1.11 (systematic) kpc) providing a firm base for a 3 % determination of the
Hubble Constant, with prospects for improvement to 2 % in the future.
03/2013;
-
G Pietrzyński,
D Graczyk,
W Gieren,
I B Thompson,
B Pilecki,
A Udalski,
I Soszyński,
S Kozłowski,
P Konorski,
K Suchomska, [......],
R Smolec,
D Minniti,
M Kubiak,
M K Szymański, R Poleski,
L Wyrzykowski,
K Ulaczyk,
P Pietrukowicz,
M Górski,
P Karczmarek
[show abstract]
[hide abstract]
ABSTRACT: In the era of precision cosmology, it is essential to determine the Hubble constant to an accuracy of three per cent or better. At present, its uncertainty is dominated by the uncertainty in the distance to the Large Magellanic Cloud (LMC), which, being our second-closest galaxy, serves as the best anchor point for the cosmic distance scale. Observations of eclipsing binaries offer a unique opportunity to measure stellar parameters and distances precisely and accurately. The eclipsing-binary method was previously applied to the LMC, but the accuracy of the distance results was lessened by the need to model the bright, early-type systems used in those studies. Here we report determinations of the distances to eight long-period, late-type eclipsing systems in the LMC, composed of cool, giant stars. For these systems, we can accurately measure both the linear and the angular sizes of their components and avoid the most important problems related to the hot, early-type systems. The LMC distance that we derive from these systems (49.97 ± 0.19 (statistical) ± 1.11 (systematic) kiloparsecs) is accurate to 2.2 per cent and provides a firm base for a 3-per-cent determination of the Hubble constant, with prospects for improvement to 2 per cent in the future.
Nature 03/2013; 495(7439):76-9. · 36.28 Impact Factor
-
N. Kains,
R. Street,
J. -Y. Choi,
C. Han,
A. Udalski,
L. A. Almeida,
F. Jablonski,
P. Tristram,
U. G. Jorgensen,
M. K. Szymanski, [......],
S. R. Kane,
D. Kubas,
J. -B. Marquette,
R. Martin,
P. Meintjes,
J. Menzies,
K. R. Pollard,
A. Williams,
D. Wouters,
M. Zub
[show abstract]
[hide abstract]
ABSTRACT: We present the analysis of the gravitational microlensing event
OGLE-2011-BLG-0251. This anomalous event was observed by several survey and
follow-up collaborations conducting microlensing observations towards the
Galactic Bulge. Based on detailed modelling of the observed light curve, we
find that the lens is composed of two masses with a mass ratio q=1.9 x 10^-3.
Thanks to our detection of higher-order effects on the light curve due to the
Earth's orbital motion and the finite size of source, we are able to measure
the mass and distance to the lens unambiguously. We find that the lens is made
up of a planet of mass 0.53 +- 0.21,M_Jup orbiting an M dwarf host star with a
mass of 0.26 +- 0.11 M_Sun. The planetary system is located at a distance of
2.57 +- 0.61 kpc towards the Galactic Centre. The projected separation of the
planet from its host star is d=1.408 +- 0.019, in units of the Einstein radius,
which corresponds to 2.72 +- 0.75 AU in physical units. We also identified a
competitive model with similar planet and host star masses, but with a smaller
orbital radius of 1.50 +- 0.50 AU. The planet is therefore located beyond the
snow line of its host star, which we estimate to be around 1-1.5 AU.
03/2013;
-
J. -Y. Choi,
C. Han,
A. Udalski,
T. Sumi,
B. S. Gaudi,
A. Gould,
D. P. Bennett,
M. Dominik,
J. -P. Beaulieu,
Y. Tsapras, [......],
J. Greenhill,
D. Kubas,
J. -B. Marquette,
J. W. Menzies,
K. C. Sahu,
M. Zub,
D. M. Bramich,
K. Horne,
I. A. Steele,
R. A. Street
[show abstract]
[hide abstract]
ABSTRACT: Although many models have been proposed, the physical mechanisms responsible
for the formation of low-mass brown dwarfs are poorly understood. The
multiplicity properties and minimum mass of the brown-dwarf mass function
provide critical empirical diagnostics of these mechanisms. We present the
discovery via gravitational microlensing of two very low-mass, very tight
binary systems. These binaries have directly and precisely measured total
system masses of 0.025 Msun and 0.034 Msun, and projected separations of 0.31
AU and 0.19 AU, making them the lowest-mass and tightest field brown-dwarf
binaries known. The discovery of a population of such binaries indicates that
brown dwarf binaries can robustly form at least down to masses of ~0.02 Msun.
Future microlensing surveys will measure a mass-selected sample of brown-dwarf
binary systems, which can then be directly compared to similar samples of
stellar binaries.
02/2013;
-
A Gould,
J ~C Yee,
I ~A Bond,
A Udalski,
C Han,
U ~G Jørgensen,
J Greenhill,
Y Tsapras,
M ~H Pinsonneault,
T Bensby, [......],
C ~B Henderson,
D Kubas,
J -B Marquette,
R Martin,
J ~W Menzies,
B Shappee,
A Williams,
J Saders,
M Zub,
The PLANET Collaboration
apj. 02/2013; 763:141.
-
S. Kozlowski,
A. Udalski,
L. Wyrzykowski, R. Poleski,
P. Pietrukowicz,
M. K. Szymanski,
M. Kubiak,
G. Pietrzynski,
I. Soszynski,
K. Ulaczyk,
J. Skowron
[show abstract]
[hide abstract]
ABSTRACT: We analyze two years (mid-2010 to mid-2012) of OGLE-IV data covering ~65
deg^2 of the Magellanic Bridge (the area between the Magellanic Clouds) and
find 130 transient events including 126 supernovae (SNe), two foreground dwarf
novae and another two SNe-like transients that turned out to be active galactic
nuclei (AGNs). We show our SNe detection efficiency as a function of SN peak
magnitude based on available SNe rate estimates. It is 100% for SNe peak
magnitudes I<18.8 mag and drops to 50% at I=~19.7 mag. With our current
observing area between and around the Magellanic Clouds (~600 deg^2), we expect
to find 24 SNe peaking above I<18 mag, 100 above I<19 mag, and 340 above I<20
mag, annually. We briefly introduce our on-line near-real-time detection system
for SNe and other transients, the OGLE Transient Detection System.
Acta Astronomica -Warsaw and Cracow- 01/2013; · 1.68 Impact Factor
-
C. P. Nicholls,
C. Melis,
I. Soszyński,
A. Udalski,
M. K. Szymański,
M. Kubiak,
G. Pietrzyński, R. Poleski,
K. Ulaczyk,
Ł. Wyrzykowski,
S. Kozłowski,
P. Pietrukowicz
[show abstract]
[hide abstract]
ABSTRACT: We present mid-IR photometry and spectra of the merged binary V1309 Sco taken
between 18 and 23 months after outburst. Strong mid-IR emission and a solid
state absorption feature indicate the presence of a significant amount of dust
in the circumstellar environment. The absence of detectable mid-IR emission
before the outburst suggests this dust was produced in the eruptive merger
event.
Model fits to the solid state absorption feature constrain the constituent
species and column density of the dust around V1309 Sco. We find the absorption
feature can be reproduced by large (3 micron) amorphous pyroxene grains at a
temperature of 800 K. This grain size, if confirmed with longer wavelength
spectroscopy and modelling, would be suggestive of dust processing in the
circumstellar environment. The data in hand do not allow us to discriminate
between disk or shell configurations for the dusty material.
01/2013;
-
I -G Shin,
C Han,
A Gould,
A Udalski,
T Sumi,
M Dominik,
J -P Beaulieu,
Y Tsapras,
V Bozza,
M ~K Szyma'nski, [......],
J -B Marquette,
R Martin,
P Meintjes,
J Menzies,
K ~R Pollard,
K ~C Sahu,
J Wambsganss,
A Williams,
C Vinter,
M Zub
The Astrophysical Journal 12/2012; 760:116. · 6.02 Impact Factor
-
R. A. Street,
J. -Y. Choi,
Y. Tsapras,
C. Han,
K. Furusawa,
M. Hundertmark,
A. Gould,
T. Sumi,
I. A. Bond,
D. Wouters, [......],
M. Mathiasen,
M. T. Penny,
S. Proft,
S. Rahvar,
D. Ricci,
G. Scarpetta,
S. Schafer,
F. Schonebeck,
J. Southworth,
J. Surdej
[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073,
announced by the Microlensing Observations in Astrophysics survey on
2010-03-18.
This event was remarkable because the source was previously known to be
photometrically variable. Analyzing the pre-event source lightcurve, we
demonstrate that it is an irregular variable over time scales >200d. Its
dereddened color, $(V-I)_{S,0}$, is 1.221$\pm$0.051mag and from our lens model
we derive a source radius of 14.7$\pm$1.3 $R_{\odot}$, suggesting that it is a
red giant star.
We initially explored a number of purely microlensing models for the event
but found a residual gradient in the data taken prior to and after the event.
This is likely to be due to the variability of the source rather than part of
the lensing event, so we incorporated a slope parameter in our model in order
to derive the true parameters of the lensing system.
We find that the lensing system has a mass ratio of q=0.0654$\pm$0.0006. The
Einstein crossing time of the event, $T_{\rm{E}}=44.3$\pm$0.1d, was
sufficiently long that the lightcurve exhibited parallax effects. In addition,
the source trajectory relative to the large caustic structure allowed the
orbital motion of the lens system to be detected. Combining the parallax with
the Einstein radius, we were able to derive the distance to the lens,
$D_L$=2.8$\pm$0.4kpc, and the masses of the lensing objects. The primary of the
lens is an M-dwarf with $M_{L,p}$=0.16$\pm0.03M_{\odot}$ while the companion
has $M_{L,s}$=11.0$\pm2.0M_{\rm{J}}$ putting it in the boundary zone between
planets and brown dwarfs.
11/2012;
-
J. C. Yee,
L. -W. Hung,
I. A. Bond,
W. Allen,
L. A. G. Monard,
M. D. Albrow,
P. Fouque,
M. Dominik,
Y. Tsapras,
A. Udalski, [......],
S. Rahvar,
D. Ricci,
K. C. Sahu,
G. Scarpetta,
S. Schafer,
F. Schonebeck,
C. Snodgrass,
J. Southworth,
J. Surdej,
J. Wambsgans
[show abstract]
[hide abstract]
ABSTRACT: We analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing
event with complete data coverage over the peak, making it very sensitive to
planetary signals. We fit this event with both a point lens and a 2-body lens
model and find that the 2-body lens model is a better fit but with only Delta
chi^2~140. The preferred mass ratio between the lens star and its companion is
$q=10^(-3.7+/-0.1), placing the candidate companion in the planetary regime.
Despite the formal significance of the planet, we show that because of
systematics in the data the evidence for a planetary companion to the lens is
too tenuous to claim a secure detection. When combined with analyses of other
high-magnification events, this event helps empirically define the threshold
for reliable planet detection in high-magnification events, which remains an
open question.
10/2012;
-
A. Gould,
J. C. Yee,
I. A. Bond,
A. Udalski,
C. Han,
U. G. Jorgensen,
J. Greenhill,
Y. Tsapras,
M. H. Pinsonneault,
T. Bensby, [......],
P. Fouque,
C. B. Henderson,
D. Kubas,
J. -B Marquette,
R. Martin,
J. W. Menzies,
B. Shappee,
A. Williams,
J. van Saders,
M. Zub
[show abstract]
[hide abstract]
ABSTRACT: The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations
from a standard microlensing lightcurve near the peak of an Amax ~ 265
high-magnification microlensing event. The deviations originally seemed
consistent with expectations for a planetary companion to the principal lens.
We combine long-term photometric monitoring with a previously published
high-resolution spectrum taken near peak to demonstrate that this is an RS CVn
variable, so that planetary microlensing is not required to explain the
lightcurve deviations. This is the first spectroscopically confirmed RS CVn
star discovered in the Galactic bulge.
10/2012;
-
K. Ulaczyk,
M. K. Szymanski,
A. Udalski,
M. Kubiak,
G. Pietrzynski,
I. Soszynski,
L. Wyrzykowski, R. Poleski,
W. Gieren,
A. Walker,
A. Garcia-Varela
[show abstract]
[hide abstract]
ABSTRACT: We present photometric maps based on data from the shallow survey in the
Large Magellanic Cloud performed as the supplementary project during the third
phase of the Optical Gravitational Lensing Experiment. They cover about 40
square degrees in the LMC and contain mean calibrated VI photometry and
astrometry of about 1.7 million stars. The magnitudes of the registered objects
range from 9.1 to 18.5.
We discuss the quality of data and present color--magnitude diagrams of
selected fields. The maps together with the main LMC photometric maps are
available to the astronomical community from the OGLE Internet archive.
10/2012;
-
I. -G. Shin,
T. Sumi,
A. Udalski,
J. -Y. Choi,
C. Han,
A. Gould,
F. Abe,
D. P. Bennett,
I. A. Bond,
C. S. Botzler, [......],
M. K. Szymański,
M. Kubiak,
I. Soszyński,
G. Pietrzyński, R. Poleski,
K. Ulaczyk,
P. Pietrukowicz,
S. Kozłowski,
J. Skowron,
Ł. Wyrzykowski
[show abstract]
[hide abstract]
ABSTRACT: Microlensing can provide an important tool to study binaries, especially
those composed of faint or dark objects. However, accurate analysis of
binary-lens light curves is often hampered by the well-known degeneracy between
close (s<1) and wide (s>1) binaries, which can be very severe due to an
intrinsic symmetry in the lens equation. Here s is the normalized projected
binary separation. In this paper, we propose a method that can resolve the
close/wide degeneracy using the effect of a lens orbital motion on lensing
light curves. The method is based on the fact that the orbital effect tends to
be important for close binaries while it is negligible for wide binaries. We
demonstrate the usefulness of the method by applying it to an actually observed
binary-lens event MOA-2011-BLG-040/OGLE-2011-BLG-0001, which suffers from
severe close/wide degeneracy. From this, we are able to uniquely specify that
the lens is composed of K and M-type dwarfs located at ~3.5 kpc from the Earth.
10/2012;
-
C. Han,
A. Udalski,
J. -Y. Choi,
J. C. Yee,
A. Gould,
G. Christie,
T. -G. Tan,
M. K. Szymański,
M. Kubiak,
I. Soszyński, [......],
C. -U. Lee,
J. -R. Koo,
J. McCormick,
L. A. G. Monard,
T. Natusch,
H. Ngan,
H. Park,
R. W. Pogge,
Ian Porritt,
I. -G. Shin
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a planetary system from observation of the
high-magnification microlensing event OGLE-2012-BLG-0026. The lensing light
curve exhibits a complex central perturbation with multiple features. We find
that the perturbation was produced by two planets located near the Einstein
ring of the planet host star. We identify 4 possible solutions resulting from
the well-known close/wide degeneracy. By measuring both the lens parallax and
the Einstein radius, we estimate the physical parameters of the planetary
system. According to the best-fit model, the two planet masses are ~0.11
M_Jupiter and 0.68 M_Jupiter and they are orbiting a G-type main sequence star
with a mass ~0.82 M_Sun. The projected separations of the individual planets
are beyond the snow line in all four solutions, being ~3.8 AU and 4.6 AU in the
best-fit solution. The deprojected separations are both individually larger and
possibly reversed in order. This is the second multi-planet system with both
planets beyond the snow line discovered by microlensing. This is the only such
a system (other than the Solar System) with measured planet masses without
sin(i) degeneracy. The planetary system is located at a distance 4.1 kpc from
the Earth toward the Galactic center. It is very likely that extra light from
stars other than the lensed star comes from the lens itself. If this is
correct, it will be possible to obtain detailed information about the
planet-host star from follow-up observation.
10/2012;
-
I. Soszynski,
A. Udalski, R. Poleski,
S. Kozlowski,
L. Wyrzykowski,
P. Pietrukowicz,
M. K. Szymanski,
M. Kubiak,
G. Pietrzynski,
K. Ulaczyk,
J. Skowron
[show abstract]
[hide abstract]
ABSTRACT: We present a comprehensive analysis of the Gaia South Ecliptic Pole (GSEP)
field, 5.3 square degrees area around the South Ecliptic Pole on the outskirts
of the LMC, based on the data collected during the fourth phase of the Optical
Gravitational Lensing Experiment, OGLE-IV. The GSEP field will be observed
during the commissioning phase of the ESA Gaia space mission for testing and
calibrating the Gaia instruments.
We provide the photometric maps of the GSEP region containing the mean VI
photometry of all detected stellar objects and their equatorial coordinates. We
show the quality and completeness of the OGLE-IV photometry and color-magnitude
diagrams of this region.
We conducted an extensive search for variable stars in the GSEP field leading
to the discovery of 6789 variable stars. In this sample we found 132 classical
Cepheids, 686 RR Lyr type stars, 2819 long-period, and 1377 eclipsing
variables. Several objects deserving special attention were also selected,
including a new classical Cepheid in a binary eclipsing system.
To provide empirical data for the Gaia Science Alert system we also conducted
a search for optical transients. We discovered two firm type Ia supernovae and
nine additional supernova candidates. To facilitate future Gaia supernovae
detections we prepared a list of more than 1900 galaxies to redshift about 0.1
located in the GSEP field.
Finally, we present the results of astrometric study of the GSEP field. With
the 26 months time base of the presented here OGLE-IV data, proper motions of
stars could be detected with the accuracy reaching 2 mas/yr. Astrometry allowed
to distinguish galactic foreground variable stars detected in the GSEP field
from LMC objects and to discover about 50 high proper motion stars (proper
motion >100 mas/yr). Among them three new nearby white dwarfs were found.
Acta Astronomica -Warsaw and Cracow- 10/2012; · 1.68 Impact Factor
-
J ~C Yee,
L -W Hung,
I ~A Bond,
W Allen,
L ~A ~G Monard,
M ~D Albrow,
P Fouque,
M Dominik,
Y Tsapras,
A Udalski, [......],
S Rahvar,
D Ricci,
K ~C Sahu,
G Scarpetta,
S Schafer,
F Schonebeck,
C Snodgrass,
J Southworth,
J Surdej,
J Wambsgans
ArXiv e-prints. 10/2012;
-
J ~C Yee,
L -W Hung,
I ~A Bond,
W Allen,
L ~A ~G Monard,
M ~D Albrow,
P Fouque,
M Dominik,
Y Tsapras,
A Udalski, [......],
S Rahvar,
D Ricci,
K ~C Sahu,
G Scarpetta,
S Schafer,
F Schonebeck,
C Snodgrass,
J Southworth,
J Surdej,
J Wambsgans
ArXiv e-prints. 10/2012;
-
I. -G. Shin,
C. Han,
A. Gould,
A. Udalski,
T. Sumi,
M. Dominik,
J. -P. Beaulieu,
Y. Tsapras,
V. Bozza,
M. K. Szymański, [......],
J. -B. Marquette,
R. Martin,
P. Meintjes,
J. Menzies,
K. R. Pollard,
K. C. Sahu,
J. Wambsganss,
A. Williams,
C. Vinter,
M. Zub
[show abstract]
[hide abstract]
ABSTRACT: Brown dwarfs are important objects because they may provide a missing link
between stars and planets, two populations that have dramatically different
formation history. In this paper, we present the candidate binaries with brown
dwarf companions that are found by analyzing binary microlensing events
discovered during 2004 - 2011 observation seasons. Based on the low mass ratio
criterion of q < 0.2, we found 7 candidate events, including OGLE-2004-BLG-035,
OGLE-2004-BLG-039, OGLE-2007-BLG-006, OGLE-2007-BLG-399/MOA-2007-BLG-334,
MOA-2011-BLG-104/OGLE-2011-BLG-0172, MOA-2011-BLG-149, and
MOA-201-BLG-278/OGLE-2011-BLG-012N. Among them, we are able to confirm that the
companions of the lenses of MOA-2011-BLG-104/OGLE-2011-BLG-0172 and
MOA-2011-BLG-149 are brown dwarfs by determining the mass of the lens based on
the simultaneous measurement of the Einstein radius and the lens parallax. The
measured mass of the brown dwarf companions are (0.02 +/- 0.01) M_Sun and
(0.019 +/- 0.002) M_Sun for MOA-2011-BLG-104/OGLE-2011-BLG-0172 and
MOA-2011-BLG-149, respectively, and both companions are orbiting low mass M
dwarf host stars. More microlensing brown dwarfs are expected to be detected as
the number of lensing events with well covered light curves increases with new
generation searches.
08/2012;
