93 research outputs found
Direct Detection of Giant Close-In Planets Around the Source Stars of Caustic-Crossing Microlensing Events
We propose a direct method to detect close-in giant planets orbiting stars in
the Galactic bulge. This method uses caustic-crossing binary microlensing
events discovered by survey teams monitoring the bulge to measure light from a
planet orbiting the source star. When the planet crosses the caustic, it is
more magnified than the source star; its light is magnified by two orders of
magnitude for Jupiter size planets. If the planet is a giant close to the star,
it may be bright enough to make a significant deviation in the light curve of
the star. Detection of this deviation requires intensive monitoring of the
microlensing light curve using a 10-meter class telescope for a few hours after
the caustic. This is the only method yet proposed to directly detect close-in
planets around stars outside the solar neighborhood.Comment: 4 pages, 2 figures. Submitted to ApJ Letter
Gravitational lensing as folds in the sky
We revisit the gravitational lensing phenomenon using a new visualization
technique. It consists in projecting the observers sky into the source plane,
what gives rise to a folded and stretched surface. This provides a clear
graphical tool to visualize some interesting well-known effects, such as the
development of multiple images of a source, the structure of the caustic
curves, the parity of the images and their magnification as a function of the
source position.Comment: 11 pages, 8 figure
Microlensing of gamma ray bursts by stars and MACHOs
The microlensing interpretation of the optical afterglow of GRB 000301C seems
naively surprising, since a simple estimate of the stellar microlensing rate
gives less than one in four hundred for a flat Omega_Lambda=0.7 cosmology,
whereas one event was seen in about thirty afterglows. Considering baryonic
MACHOs making up half of the baryons in the universe, the microlensing
probability per burst can be roughly 5% for a GRB at redshift z=2. We explore
two effects that may enhance the probability of observing microlensed gamma-ray
burst afterglows: binary lenses and double magnification bias. We find that the
consideration of binary lenses can increase the rate only at the ~15% level. On
the other hand, because gamma-ray bursts for which afterglow observations exist
are typically selected based on fluxes at widely separated wavebands which are
not necessarily well correlated (e.g. localization in X-ray, afterglow in
optical/infrared), magnification bias can operate at an enhanced level compared
to the usual single-bias case. We find that existing estimates of the slope of
the luminosity function of gamma-ray bursts, while as yet quite uncertain,
point to enhancement factors of more than three above the simple estimates of
the microlensing rate. We find that the probability to observe at least one
microlensing event in the sample of 27 measured afterglows can be 3-4% for
stellar lenses, or as much as 25 Omega_lens for baryonic MACHOs. We note that
the probability to observe at least one event over the available sample of
afterglows is significant only if a large fraction of the baryons in the
universe are condensed in stellar-mass objects. (ABRIDGED)Comment: 22 pages, 4 figures, 2 table
Beyond Caustic Crossings: Properties of Binary Microlensing Light Curves
Binary microlensing light curves have a variety of morphologies. Many are
indistinguishable from point lens light curves. Of those that deviate from the
point lens form, caustic crossing light curves have tended to dominate
identified binary lens events. Other distinctive signatures of binary lenses
include significant asymmetry, multiple peaks, and repeating events. We have
quantified, using high resolution simulations, the theoretically expected
relative numbers of each type of binary lens event, based on its measurable
characteristics. We find that a microlensing survey with current levels of
photometric uncertainty and sampling should find at least as many non-caustic
crossing binary lens events as caustic crossing events; in future surveys with
more sensitive photometry, the contribution of distinctive non-caustic crossing
events will be even greater. To try to explain why caustic crossing light
curves appear to be so dominant among the published binary lensing events, we
investigate the influence of several physical effects, including blending,
sampling rate, and various binary populations.Comment: 17 pages, 17 figures, submitted to Ap
On Multiple Einstein Rings
A number of recent surveys for gravitational lenses have found examples of
double Einstein rings. Here, we investigate analytically the occurrence of
multiple Einstein rings. We prove, under very general assumptions, that at most
one Einstein ring can arise from a mass distribution in a single plane lensing
a single background source. Two or more Einstein rings can therefore only occur
in multi-plane lensing. Surprisingly, we show that it is possible for a single
source to produce more than one Einstein ring. If two point masses (or two
isothermal spheres) in different planes are aligned with observer and source on
the optical axis, we show that there are up to three Einstein rings. We also
discuss the image morphologies for these two models if axisymmetry is broken,
and give the first instances of magnification invariants in the case of two
lens planes.Comment: MNRAS, in press (extra figure included
Kältevasokonstriktion, Kältedilatation und reaktive Hyperämie der Haut, dargestellt anhand der Laser-Doppler-Flußmessung
Der Einsatz der Laser-Doppler-Flußmessung hat sich auch in der hydrotherapeutischen
Forschung zur Frage der Objektivierung von thermisch ausgelösten Effekten im kutanen
Gefäßsystem bewährt. Die in der vorliegenden Arbeit dargestellten Versuchsergebnisse
beruhen auf kleinflächigen lokalen Abkühlungen mittels einer mit verschieden temperiertem
Wasser perfundierten Thermode. Dabei wurden an definierten Meßstellen periphere gefäßregulatorische
Vorgänge, wie Kältevasokonstriktion, -dilatation und reaktive Hyperämie,
sowie Durchblutungsgrad und Vasomotion an 10 gesunden Versuchspersonen untersucht
Images for a Binary Gravitational Lens from a Single Real Algebraic Equation
It is shown that the lens equation for a binary gravitational lens being a
set of two coupled real fifth-order algebraic equations (equivalent to a single
complex equation of the same order) can be reduced to a single real fifth-order
algebraic equation, which provides a much simpler way to study lensing by
binary objects.Comment: 4 pages; accepted for publication in A&A Letter
A direct cerebello-telencephalic projection in an electrosensory mormyrid fish
After injections of the posterior part of the lateral zone of the area dorsalis telencephali (Dlp) with either horseradish peroxidase or the newly available carbocyanine dye DiI, efferent cells were labeled in the valvula cerebelli of the mormyrid fish,Gnathonemus petersii. This may be a unique connection for this group of electrosensory teleosts, since no other vertebrate has ever been reported before to have a direct cerebello-telencephalic projection
- …