841 research outputs found
The POINT-AGAPE Microlensing Survey: First Constraint on MACHOs towards M31
To reveal the galactic dark matter in the form of MACHOs ("Massive
Astrophysical Compact Halo Objects"), the POINT-AGAPE collaboration is carrying
out a search for gravitational microlensing towards M31. A clear microlensing
signal is detected. The high-threshold analysis of 3-year data leads to 7
bright and short microlensing candidates. The preliminary estimation of the
detection efficiency implies that less than 25% (60%) of standard halos can be
composed of objects with masses between 10^{-4} and 10^{-1} (10^{-1} and 1)
solar mass at the 95% C.L. This result is compatible with previous microlensing
results towards the Magellanic Clouds and gives the first constraints on MACHOs
for a distant spiral galaxy.Comment: 4 pages, 2 figures, to appear in the proceedings of the XXXIXth
Rencontres de Moriond "Exploring the Universe", La Thuile, Italy, March
28-April 4, 200
Microlensing Parallax for Observers in Heliocentric Motion
Motivated by the ongoing Spitzer observational campaign, and the forecoming
K2 one, we revisit, working in an heliocentric reference frame, the geometrical
foundation for the analysis of the microlensing parallax, as measured with the
simultaneous observation of the same microlensing event from two observers with
relative distance of order AU. For the case of observers at rest we discuss the
well known fourfold microlensing parallax degeneracy and determine an equation
for the degenerate directions of the lens trajectory. For the case of observers
in motion, we write down an extension of the Gould (1994) relationship between
the microlensing parallax and the observable quantities and, at the same time,
we highlight the functional dependence of these same quantities from the
timescale of the underlying microlensing event. Furthermore, through a series
of examples, we show the importance of taking into account the motion of the
observers to correctly recover the parameters of the underlying microlensing
event. In particular we discuss the cases of the amplitude of the microlensing
parallax and that of the difference of the timescales between the observed
microlensing events, key to understand the breaking of the microlensing
parallax degeneracy. Finally, we consider the case of the simultaneous
observation of the same microlensing event from ground and two satellites, a
case relevant for the expected joint K2 and Spitzer observational programs in
2016.Comment: Accepted for publication in Ap
Newtonian Limit of Induced Gravity
We discuss the weak-field limit of induced gravity and show that results
directly depend on the coupling and self-interaction potential of the scalar
field. A static spherically symmetric exact solution is found and its conformal
properties are studied. As an application, it is shown that the light
deflection angle and the microlensing quantities can be parametrized by the
coupling of the theory.Comment: 15 pages, LATEX, to appear in Grav & Cos
Pixel lensing: Microlensing towards M31
Pixel lensing is gravitational microlensing of unresolved stars. The main
target explored up to now has been the nearby galaxy of Andromeda, M31. The
scientific issues of interest are the search for dark matter in form of compact
halo objects, the study of the characteristics of the luminous lens and source
populations and the possibility of detecting extra-solar (and extra-galactic)
planets. In the present work we intend to give an updated overview of the
observational status in this field.Comment: Invited article for the GRG special issue on gravitational lensing
(Ph. Jetzer, Y. Mellier and V. Perlick Eds.
MiNDSTEp differential photometry of the gravitationally lensed quasars WFI 2033-4723 and HE 0047-1756: microlensing and a new time delay
Aims. We present V and R photometry of the gravitationally lensed quasars WFI 2033-4723 and HE 0047-1756. The data were taken by the MiNDSTEp collaboration with the 1.54 m Danish telescope at the ESO La Silla observatory from 2008 to 2012.
Methods. Differential photometry has been carried out using the image subtraction method as implemented in the HOTPAnTS package, additionally using GALFIT for quasar photometry.
Results. The quasar WFI 2033-4723 showed brightness variations of order 0.5 mag in V and R during the campaign. The two lensed components of quasar HE 0047-1756 varied by 0.2–0.3 mag within five years. We provide, for the first time, an estimate of the time delay of component B with respect to A of Δt = (7.6 ± 1.8) days for this object. We also find evidence for a secular evolution of the magnitude difference between components A and B in both filters, which we explain as due to a long-duration microlensing event. Finally we find that both quasars WFI 2033-4723 and HE 0047-1756 become bluer when brighter, which is consistent with previous studies
OGLE-2013-BLG-0911Lb: A Secondary on the Brown-dwarf Planet Boundary around an M Dwarf
We present the analysis of the binary-lens microlensing event OGLE-2013-BLG-0911. The best-fit solutions indicate the binary mass ratio of q 0.03, which differs from that reported in Shvartzvald et al. The event suffers from the well-known close/wide degeneracy, resulting in two groups of solutions for the projected separation normalized by the Einstein radius of s ~ 0.15 or s ~ 7. The finite source and the parallax observations allow us to measure the lens physical parameters. The lens system is an M dwarf orbited by a massive Jupiter companion at very close (M_(host) = 0.30^(+0.08)_(-0.06)M⊙, M_(comp) = 10.1^(+2.9)_(-2.2)M_(Jup), a_(exp) = 0.40^(+0.05)_(-0.04) au) or wide (M_(host) = 0.28^(+0.10)_(-0.08) M⊙, M_(comp) = 9.9^(+3.8)_(-3.5)M_(Jup), a(exp) = 18.0^(+3.8)_(3.5) au) separation. Although the mass ratio is slightly above the planet-brown dwarf (BD) mass-ratio boundary of q = 0.03, which is generally used, the median physical mass of the companion is slightly below the planet-BD mass boundary of 13M_(Jup). It is likely that the formation mechanisms for BDs and planets are different and the objects near the boundaries could have been formed by either mechanism. It is important to probe the distribution of such companions with masses of ~13M_(Jup) in order to statistically constrain the formation theories for both BDs and massive planets. In particular, the microlensing method is able to probe the distribution around low-mass M dwarfs and even BDs, which is challenging for other exoplanet detection methods
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