15,151 research outputs found
Inversion of polarimetric data from eclipsing binaries
We describe a method for determining the limb polarization and limb darkening
of stars in eclipsing binary systems, by inverting photometric and polarimetric
light curves.
Because of the ill-conditioning of the problem, we use the Backus-Gilbert
method to control the resolution and stability of the recovered solution, and
to make quantitative estimates of the maximum accuracy possible. Using this
method we confirm that the limb polarization can indeed be recovered, and
demonstrate this with simulated data, thus determining the level of
observational accuracy required to achieve a given accuracy of reconstruction.
This allows us to set out an optimal observational strategy, and to critcally
assess the claimed detection of limb polarization in the Algol system.
The use of polarization in stars has been proposed as a diagnostic tool in
microlensing surveys by Simmons et al. (1995), and we discuss the extension of
this work to the case of microlensing of extended sources.Comment: 10pp, 5 figures. To appear in A&
Polarimetric variations of binary stars. II. Numerical simulations for circular and eccentric binaries in Mie scattering envelopes
We present numerical simulations of the periodic polarimetric variations
produced by a binary star placed at the center of an empty spherical cavity
inside a circumbinary ellipsoidal and optically thin envelope made of dust
grains. Mie single-scattering is considered along with pre- and post-scattering
extinction factors which produce a time-varying optical depth and affect the
morphology of the periodic variations. We are interested in the effects that
various parameters will have on the average polarization, the amplitude of the
polarimetric variations, and the morphology of the variability. We show that
the absolute amplitudes of the variations are smaller for Mie scattering than
for Thomson scattering. Among the four grain types that we have studied, the
highest polarizations are produced by grains with sizes in the range 0.1-0.2
micron. In general, the variations are seen twice per orbit. In some cases,
because spherical dust grains have an asymmetric scattering function, the
polarimetric curves produced also show variations seen once per orbit.
Circumstellar disks produce polarimetric variations of greater amplitude than
circumbinary envelopes.
Another goal of these simulations is to see if the 1978 BME (Brown, McLean, &
Emslie, ApJ, 68, 415) formalism, which uses a Fourier analysis of the
polarimetric variations to find the orbital inclination for Thomson-scattering
envelopes, can still be used for Mie scattering. We find that this is the case,
if the amplitude of the variations is sufficient and the true inclinations is
i_true > 45 deg. For eccentric orbits, the first-order coefficients of the
Fourier fit, instead of second-order ones, can be used to find almost all
inclinations.Comment: 23 pages, 5 figures, to be published in Astronomical Journa
Probing the Atmospheres of Planets Orbiting Microlensed Stars via Polarization Variability
We present a new method to identify and probe planetary companions of stars
in the Galactic Bulge and Magellanic Clouds using gravitational microlensing.
While spectroscopic studies of these planets is well beyond current
observational techniques, monitoring polarization fluctuations during high
magnification events induced by binary microlensing events will probe the
composition of the planetary atmospheres, an observation which otherwise is
currently unattainable even for nearby planetary systems.Comment: 7 pages, 2 figures. To appear in Astrophysical Journal Letter
A new methodology for the quantitative visualization of coherent flow structures in alluvial channels using multibeam echo-sounding (MBES)
In order to investigate the interactions between turbulence and suspended sediment transport in natural aqueous environments, we ideally require a technique that allows simultaneous measurement of fluid velocity and sediment concentration for the whole flow field. Here, we report on development of a methodology using the water column acoustic backscatter signal from a multibeam echo sounder to simultaneously quantify flow velocities and sediment concentrations. The application of this new technique is illustrated with reference to flow over the leeside of an alluvial sand dune, which allows, for the first time in a field study, quantitative visualization of large-scale, whole flow field, turbulent coherent flow structures associated with the dune leeside that are responsible for suspending bed sediment. This methodology holds great potential for use in a wide range of aqueous geophysical flows
Larger testes are associated with a higher level of polyandry, but a smaller ejaculate volume, across bushcricket species (Tettigoniidae)
While early models of ejaculate allocation predicted that both relative testes and ejaculate size should increase with sperm competition intensity across species, recent models predict that ejaculate size may actually decrease as testes size and sperm competition intensity increase, owing to the confounding effect of potential male mating rate. A recent study demonstrated that ejaculate volume decreased in relation to increased polyandry across bushcricket species, but testes mass was not measured. Here, we recorded testis mass for 21 bushcricket species, while ejaculate ( ampulla) mass, nuptial gift mass, sperm number and polyandry data were largely obtained from the literature. Using phylogenetic-comparative analyses, we found that testis mass increased with the degree of polyandry, but decreased with increasing ejaculate mass. We found no significant relationship between testis mass and either sperm number or nuptial gift mass. While these results are consistent with recent models of ejaculate allocation, they could alternatively be driven by substances in the ejaculate that affect the degree of polyandry and/or by a trade-off between resources spent on testes mass versus non-sperm components of the ejaculate
Analysis of Uncharacterized mKiaa1211 Expression during Mouse Development and Cardiovascular Morphogenesis
Mammalian Kiaa1211 and Kiaa1211-like are a homologous pair of uncharacterized, highly conserved genes cloned from fetal and adult brain cDNA libraries. Herein we map the in utero spatiotemporal expression of mKiaa1211 and mKiaa1211L mRNA and their expression patterns in postnatal testis, skin, gastrointestinal, and adipose progenitor tissues. Significantly, mKiaa1211 is present throughout the early stages of mouse heart development, particularly in the second heart field (SHF) lineage as it differentiates from mesenchymal cells into cardiomyocytes. We also show that mKiaa1211 is expressed within several early neuronal tissues destined to give rise to central, peripheral, and sympathetic nervous system structures. Expression profiling revealed that the paralog mKiaa1211L is not expressed during the normal developmental process and that mKiaa1211 expression was noticeably absent from most adult terminally differentiated tissues. Finally, we confirm that a previously uncharacterized CRISPR/CAS-generated mKiaa1211 mouse mutant allele is hypomorphic
The Accuracy of Morphological Decomposition of Active Galactic Nucleus Host Galaxies
In order to assess the accuracy with which we can determine the morphologies
of AGN host galaxies, we have simulated more than 50,000 ACS images of galaxies
with z < 1.25, using image and noise properties appropriate for the GOODS
survey. We test the effect of central point-source brightness on host galaxy
parameter recovery with a set of simulated AGN host galaxies made by adding
point sources to the centers of normal galaxies. We extend this analysis and
also quantify the recovery of intrinsic morphological parameters of AGN host
galaxies with a set of fully simulated inactive and AGN host galaxies.
We can reliably separate good from poor fit results using a combination of
reasonable error cuts, in the regime where L_{host}:L_{PS} > 1:4. We give
quantitative estimates of parameter errors as a function of
host-to-point-source ratio. In general, we separate host and point-source
magnitudes reliably at all redshifts; point sources are well recovered more
than 90% of the time, although spurious detection of central point sources can
be as high as 25% for bulge-dominated sources. We find a general correlation
between Sersic index and intrinsic bulge-to-total ratio, such that a host
galaxy with Sersic n < 1.5 generally has at least 80% of its light from a disk
component. Likewise, "bulge-dominated" galaxies with n > 4 typically derive at
least 70% of their total host galaxy light from a bulge, but this number can be
as low as 55%. Single-component Sersic fits to an AGN host galaxy are
statistically very reliable to z < 1.25 (for ACS survey data like ours). In
contrast, two-component fits involving separate bulge and disk components tend
to over-estimate the bulge fraction by ~10%, with uncertainty of order 50%.Comment: 45 pages, 20 figures, submitted to ApJ ; Accepted Version --
additions to introduction and conclusions; title changed, was "Simulations of
AGN Host Galaxy Morphologies
What does it mean to find the Face of the Franchise? Physical Attractiveness and the Evaluation of Athletic Performance
Previous research has shown how more attractive people reap more rewards in a variety of settings. We show that attractiveness as measured by facial symmetry leads to greater rewards in professional sports. National Football League quarterbacks who are more attractive are paid greater salaries and this premium persists after controlling for player performance.
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