9,673 research outputs found
Discovery of Blue Luminescence in the Red Rectangle: Possible Fluorescence from Neutral Polycyclic Aromatic Hydrocarbon Molecules?
Here we report our discovery of a band of blue luminescence (BL) in the Red
Rectangle (RR) nebula. This enigmatic proto-planetary nebula is also one of the
brightest known sources of extended red emission as well as of unidentified
infra-red (UIR) band emissions. The spectrum of this newly discovered BL is
most likely fluorescence from small neutral polycyclic aromatic hydrocarbon
(PAH) molecules. PAH molecules are thought to be widely present in many
interstellar and circumstellar environments in our galaxy as well as in other
galaxies, and are considered likely carriers of the UIR-band emission. However,
no specific PAH molecule has yet been identified in a source outside the solar
system, as the set of mid-infra-red emission features attributed to these
molecules between the wavelengths of 3.3 micron and 16.4 micron is largely
insensitive to molecular sizes. In contrast, near-UV/blue fluorescence of PAHs
is more specific as to size, structure, and charge state of a PAH molecule. If
the carriers of this near-UV/blue fluorescence are PAHs, they are most likely
neutral PAH molecules consisting of 3-4 aromatic rings such as anthracene
(C14H10) and pyrene (C16H10). These small PAHs would then be the largest
molecules specifically identified in the interstellar medium.Comment: 4 pages, 4 figures, Accepted for publication in ApJL (LaTeX, uses
emulateapj.sty
Assessing parental risk in parenting plan (child custody) evaluation cases involving internet sexual behavior
One type of claim in parenting assessment (child custody)1 cases is that one parent, typically the father, is alleged to be engaging in improper or compulsive sexual behavior via the Internet. The sexual behavior at issue can range from frequent sexually explicit chats with other adults to compulsive viewing of adult pornography. In more extreme cases, the problematic behavior may involve viewing child pornography, and in some cases the parent faces actual criminal charges in this regard. The present article reviews the current scientific knowledge base for evaluation of risk in such parenting evaluation cases and provides some guidelines and recommendations for an evaluator in the assessment process
Analytic Time Delays and H_0 Estimates for Gravitational Lenses
We study gravitational lens time delays for a general family of lensing
potentials, which includes the popular singular isothermal elliptical potential
and singular isothermal elliptical density distribution but allows general
angular structure. Using a novel approach, we show that the time delay can be
cast in a very simple form, depending only on the observed image positions.
Including an external shear changes the time delay proportional to the shear
strength, and varying the radial profile of the potential changes the time
delay approximately linearly. These analytic results can be used to obtain
simple estimates of the time delay and the Hubble constant in observed
gravitational lenses. The naive estimates for four of five time delay lenses
show surprising agreement with each other and with local measurements of H_0;
the complicated Q 0957+561 system is the only outlier. The agreement suggests
that it is reasonable to use simple isothermal lens models to infer H_0,
although it is still important to check this conclusion by examining detailed
models and by measuring more lensing time delays.Comment: 16 pages with 2 embedded figures; submitted to Ap
Expansion of the Planet Detection Channels in Next-Generation Microlensing Surveys
We classify various types of planetary lensing signals and the channels of
detecting them. We estimate the relative frequencies of planet detections
through the individual channels with special emphasis on the new channels to be
additionally provided by future lensing experiments that will survey wide
fields continuously at high cadence by using very large-format imaging cameras.
From this investigation, we find that the fraction of wide-separation planets
that would be discovered through the new channels of detecting planetary
signals as independent and repeating events would be substantial. We estimate
that the fraction of planets detectable through the new channels would comprise
~15 -- 30% of all planets depending on the models of the planetary separation
distribution and mass ratios of planets. Considering that a significant
fraction of planets might exist in the form of free-floating planets, the
frequency of planets to be detected through the new channel would be even
higher. With the expansion of the channels of detecting planet, future lensing
surveys will greatly expand the range of planets to be probed.Comment: 6 pages, 3 figures, one tabl
Detection Rates for Close Binaries Via Microlensing
Microlensing is one of the most promising methods of reconstructing the
stellar mass function down to masses even below the hydrogen-burning limit. The
fundamental limit to this technique is the presence of unresolved binaries,
which can in principle significantly alter the inferred mass function. Here we
quantify the fraction of binaries that can be detected using microlensing,
considering specifically the mass ratio and separation of the binary. We find
that almost all binary systems with separations greater than of
their combined Einstein ring radius are detectable assuming a detection
threshold of . For two M dwarfs, this corresponds to a limiting separation
of \gsim 1 \au. Since very few observed M dwarfs have companions at
separations \lsim 1 \au, we conclude that close binaries will probably not
corrupt the measurements of the mass function. We find that the detectability
depends only weakly on the mass ratio. For those events for which individual
masses can be determined, we find that binaries can be detected down to .Comment: 19 pages including 6 figures. Uses phyyzx format. Send requests for
higher quality figures to [email protected]
Lensing Properties of Cored Galaxy Models
A method is developed to evaluate the magnifications of the images of
galaxies with lensing potentials stratified on similar concentric ellipses. A
simple contour integral is provided which enables the sums of the
magnifications of even parity or odd parity or the central image to be easily
calculated. The sums for pairs of images vary considerably with source
position, while the signed sums can be remarkably uniform inside the tangential
caustic in the absence of naked cusps. For a family of models in which the
potential is a power-law of the elliptic radius, the number of visible images
is found as a function of flattening, external shear and core radius. The
magnification of the central image depends on the core radius and the slope of
the potential. For typical source and lens redshifts, the missing central image
leads to strong constraints; the mass distribution in the lensing galaxy must
be nearly cusped, and the cusp must be isothermal or stronger. This is in
accord with the cuspy cores seen in high resolution photometry of nearby,
massive, early-type galaxies, which typically have the surface density falling
like distance^{-1.3} outside a break radius of a few hundred parsecs. Cuspy
cores by themselves can provide an explanation of the missing central images.
Dark matter at large radii may alter the slope of the projected density;
provided the slope remains isothermal or steeper and the break radius remains
small, then the central image remains unobservable. The sensitivity of the
radio maps must be increased fifty-fold to find the central images in
abundance.Comment: 42 pages, 11 figures, ApJ in pres
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
Exceptional Superconformal Algebras
Reductive W-algebras which are generated by bosonic fields of spin-1, a
single spin-2 field and fermionic fields of spin-3/2 are classified. Three new
cases are found: a `symplectic' family of superconformal algebras which are
extended by , an and an superconformal algebra.
The exceptional cases can be viewed as arising a Drinfeld-Sokolov type
reduction of the exceptional Lie superalgebras and , and have an
octonionic description. The quantum versions of the superconformal algebras are
constructed explicitly in all three cases.Comment: 16 page
Exotic Statistics for Ordinary Particles in Quantum Gravity
Objects exhibiting statistics other than the familiar Bose and Fermi ones are
natural in theories with topologically nontrivial objects including geons,
strings, and black holes. It is argued here from several viewpoints that the
statistics of ordinary particles with which we are already familiar are likely
to be modified due to quantum gravity effects. In particular, such
modifications are argued to be present in loop quantum gravity and in any
theory which represents spacetime in a fundamentally piecewise-linear fashion.
The appearance of unusual statistics may be a generic feature (such as the
deformed position-momentum uncertainty relations and the appearance of a
fundamental length scale) which are to be expected in any theory of quantum
gravity, and which could be testable.Comment: Awarded an honourable mention in the 2008 Gravity Research Foundation
Essay Competitio
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