6,070 research outputs found
Constraining the Location of Microlensing Objects by using the Finite Source Effect in EAGLE events
We propose a new method to constrain the location of microlensing objects
using EAGLE (Extremely Amplified Gravitational LEnsing) events. We have
estimated the rate of EAGLE events by taking the finite-source effect in to
account. We found that the EAGLE event rate for using a 1-m class telescope w
hose limiting magnitude is is the same as or higher than that of
the ordinary microlensing events which have been found to date. We have also
found that the fraction of transit EAGLE events is large enough to detect:
between depending on the lens location. Since the lens proper
motion can be measured for a transit event, one can distinguish whether the
lens is a MACHO (MAssive Compact Halo Object) in our hal o or one of the known
stars in the Large Magellanic Cloud (LMC) from the proper motion measurement
for each transit EAGLE event. Moreover, we show that the fraction of transit
EAGLEs in all EAGLE events signif icantly depends on the lensing locations: the
transit EAGLE fraction for the sel f-lensing case is times larger
than that for halo MACHOs. Thus, one can constrain the location of lens objects
by the statistics of the tr ansit events fraction. We show that we can
reasonably expect transit events out of 21 EAGLE events in 3 years.
We can also constrain the lens population properties at a gre ater than 99%
confidence level depending on the number of transit events de tected. We also
present the duration of EAGLE events, and show how an hourly ob servational
mode is more suitable for an EAGLE event search program.Comment: 18 pages, 4 figures, accepted for publication in Ap
Renormalized transport of inertial particles in surface flows
Surface transport of inertial particles is investigated by means of the
perturbative approach, introduced by Maxey (J. Fluid Mech. 174, 441 (1987)),
which is valid in the case the deflections induced on the particle trajectories
by the fluid flow can be considered small. We consider a class of compressible
random velocity fields, in which the effect of recirculations is modelled by an
oscillatory component in the Eulerian time correlation profile. The main issue
we address here is whether fluid velocity fluctuations, in particular the
effect of recirculation, may produce nontrivial corrections to the streaming
particle velocity. Our result is that a small (large) degree of recirculation
is associated with a decrease (increase) of streaming with respect to a
quiescent fluid. The presence of this effect is confirmed numerically, away
from the perturbative limit. Our approach also allows us to calculate the
explicit expression for the eddy diffusivity, and to compare the efficiency of
diffusive and ballistic transport.Comment: 18 pages, 13 figures, submitted to JF
Observation of Microlensing towards the Galactic Spiral Arms. EROS II 2 year survey
We present the analysis of the light curves of 8.5 million stars observed
during two seasons by EROS (Experience de Recherche d'Objets Sombres), in the
galactic plane away from the bulge. Three stars have been found that exhibit
luminosity variations compatible with gravitational microlensing effects due to
unseen objects. The corresponding optical depth, averaged over four directions,
is 0.38 (+0.53, -0.15) 10^{-6}. All three candidates have long Einstein radius
crossing times ( 70 to 100 days). For one of them, the lack of evidence
for a parallax or a source size effect enabled us to constrain the lens-source
% geometric configuration. Another candidate displays a modulation of the
magnification, which is compatible with the lensing of a binary source.
The interpretation of the optical depths inferred from these observations is
hindered by the imperfect knowledge of the distance to the target stars. Our
measurements are compatible with expectations from simple galactic models under
reasonable assumptions on the target distances.Comment: 11 pages, 13 figures, accepted by A&A in Aug 9
Labour productivity in state-owned enterprises
In the aftermath of the Global and Financial Crisis (GFC), between 2013 and 2015, the Portuguese government revoked four holidays for both public sector and private employees. We test whether the revocation had an effect on labour productivity in State-Owned Enterprises (SOEs) in Portugal. Moreover, we also study whether such effects are different taking into account the SOEs managed by the Central Government or the Local and Regional Governments. Our results show that revocation of holidays did not impact labour productivity for either central or local and regional government managed SOEs. Though revocation of holidays espoused to improve productivity, the policy seems to have served a ceremonial purpose, but not an economic oneinfo:eu-repo/semantics/publishedVersio
MACHO Mass Determination Based on Space Telescope Observation
We investigate the possibility of lens mass determination for a caustic
crossing microlensing event based on a space telescope observation. We
demonstrate that the parallax due to the orbital motion of a space telescope
causes a periodic fluctuation of the light curve, from which the lens distance
can be derived. Since the proper motion of the lens relative to the source is
also measurable for a caustic crossing event, one can find a full solution for
microlensing properties of the event, including the lens mass. To determine the
lens mass with sufficient accuracy, the light curve near the caustic crossing
should be observed within uncertainty of 1%. We argue that the Hubble
Space Telescope observation of the caustic crossing supplied with ground-based
observations of the full light curve will enable us to determine the mass of
MACHOs, which is crucial for understanding the nature of MACHOs.Comment: 9 pages + 3 figures, accepted for publication in ApJ Letter
Astrometric Resolution of Severely Degenerate Binary Microlensing Events
We investigate whether the "close/wide" class of degeneracies in
caustic-crossing binary microlensing events can be broken astrometrically.
Dominik showed that these degeneracies are particularly severe because they
arise from a degeneracy in the lens equation itself rather than a mere
"accidental" mimicking of one light curve by another. A massive observing
campaign of five microlensing collaborations was unable to break this
degeneracy photometrically in the case of the binary lensing event MACHO
98-SMC-1. We show that this degeneracy indeed causes the image centroids of the
wide and close solutions to follow an extremely similar pattern of motion
during the time when the source is in or near the caustic. Nevertheless, the
two image centroids are displaced from one another and this displacement is
detectable by observing the event at late times. Photometric degeneracies
therefore can be resolved astrometrically, even for these most severe cases.Comment: 11 pages, including 4 figures. Submitted to Ap
Microjansky sources at 1.4 GHz
We present a deep 1.4 GHz survey made with the Australia Telescope Compact
Array (ATCA), having a background RMS of 9 microJy near the image phase centre,
up to 25 microJy at the edge of a 50' field of view. Over 770 radio sources
brighter than 45 microJy have been catalogued in the field. The differential
source counts in the deep field provide tentative support for the growing
evidence that the microjansky radio population exhibits significantly higher
clustering than found at higher flux density cutoffs. The optical
identification rate on CCD images is approximately 50% to R=22.5, and the
optical counterparts of the faintest radio sources appear to be mainly single
galaxies close to this optical magnitude limit.Comment: 6 pages, 4 figures, accepted by ApJ Letters 4 May 199
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