29,598 research outputs found
Photometric redshift of the GRB 981226 host galaxy
No optical afterglow was found for the dark burst GRB 981226 and hence no
absorption redshift has been obtained. We here use ground-based and space
imaging observations to analyse the spectral energy distribution (SED) of the
host galaxy. By comparison with synthetic template spectra we determine the
photometric redshift of the GRB 981226 host to be z_phot = 1.11+/-0.06 (68%
confidence level). While the age-metallicity degeneracy for the host SED
complicates the determination of accurate ages, metallicity, and extinction,
the photometric redshift is robust. The inferred z_phot value is also robust
compared to a Bayesian redshift estimator which gives z_phot=0.94+/-0.13. The
characteristics for this host are similar to other GRB hosts previously
examined. Available low resolution spectra show no emission lines at the
expected wavelengths. The photometric redshift estimate indicates an isotropic
energy release consistent with the Amati relation for this GRB which had a
spectrum characteristic of an X-ray flash.Comment: Accepted for publication in ApJ Letter
En route position and time control of aircraft using Kalman filtering of radio aid data
Fixed-time-of-arrival (FTA) guidance and navigation is investigated as a possible technique capable of operation within much more stringent en route separation standards and offering significant advantages in safety, higher traffic densities, and improved scheduling reliability, both en route and in the terminal areas. This study investigated the application of FTA guidance previously used in spacecraft guidance. These FTA guidance techniques have been modified and are employed to compute the velocity corrections necessary to return an aircraft to a specified great-circle reference path in order to exercise en route time and position control throughout the entire flight. The necessary position and velocity estimates to accomplish this task are provided by Kalman filtering of data from Loran-C, VORTAC/TACAN, Doppler radar, radio or barometric altitude,and altitude rate. The guidance and navigation system was evaluated using a digital simulation of the cruise phase of supersonic and subsonic flights between San Francisco and New York City, and between New York City and London
Verifying the mass-metallicity relation in damped Lyman-alpha selected galaxies at 0.1<z<3.2
A scaling relation has recently been suggested to combine the galaxy
mass-metallicity (MZ) relation with metallicities of damped Lyman-alpha systems
(DLAs) in quasar spectra. Based on this relation the stellar masses of the
absorbing galaxies can be predicted. We test this prediction by measuring the
stellar masses of 12 galaxies in confirmed DLA absorber - galaxy pairs in the
redshift range 0.1<z<3.2. We find an excellent agreement between the predicted
and measured stellar masses over three orders of magnitude, and we determine
the average offset = 0.44+/-0.10 between absorption
and emission metallicities. We further test if could depend on the
impact parameter and find a correlation at the 5.5sigma level. The impact
parameter dependence of the metallicity corresponds to an average metallicity
difference of -0.022+/-0.004 dex/kpc. By including this metallicity vs. impact
parameter correlation in the prescription instead of , the scatter
reduces to 0.39 dex in log M*. We provide a prescription how to calculate the
stellar mass (M*,DLA) of the galaxy when both the DLA metallicity and DLA
galaxy impact parameter is known. We demonstrate that DLA galaxies follow the
MZ relation for luminosity-selected galaxies at z=0.7 and z=2.2 when we include
a correction for the correlation between impact parameter and metallicity.Comment: 15 pages, 6 figures. Major revision. Accepted for publication in
MNRA
What controls the large-scale magnetic fields of M dwarfs?
Observations of active M dwarfs show a broad variety of large-scale magnetic
fields encompassing dipole-dominated and multipolar geometries. We detail the
analogy between some anelastic dynamo simulations and spectropolarimetric
observations of 23 M stars. In numerical models, the relative contribution of
inertia and Coriolis force in the global force balance -estimated by the
so-called local Rossby number- is known to have a strong impact on the magnetic
field geometry. We discuss the relevance of this parameter in setting the
large-scale magnetic field of M dwarfs.Comment: 4 pages, 3 figures, conference proceeding, IAUS 302 'Magnetic Fields
Throughout the Stellar Evolution', (26-30 Aug 2013, Biarritz, France
What controls the magnetic geometry of M dwarfs?
Context: observations of rapidly rotating M dwarfs show a broad variety of
large-scale magnetic fields encompassing dipole-dominated and multipolar
geometries. In dynamo models, the relative importance of inertia in the force
balance -- quantified by the local Rossby number -- is known to have a strong
impact on the magnetic field geometry. Aims: we aim to assess the relevance of
the local Rossby number in controlling the large-scale magnetic field geometry
of M dwarfs. Methods: we explore the similarities between anelastic dynamo
models in spherical shells and observations of active M-dwarfs, focusing on
field geometries derived from spectropolarimetric studies. To do so, we
construct observation-based quantities aimed to reflect the diagnostic
parameters employed in numerical models. Results: the transition between
dipole-dominated and multipolar large-scale fields in early to mid M dwarfs is
tentatively attributed to a Rossby number threshold. We interpret late M dwarfs
magnetism to result from a dynamo bistability occurring at low Rossby number.
By analogy with numerical models, we expect different amplitudes of
differential rotation on the two dynamo branches.Comment: 4 pages, 4 figures, accepted for publication in A&
Generation and detection of a sub-Poissonian atom number distribution in a one-dimensional optical lattice
We demonstrate preparation and detection of an atom number distribution in a
one-dimensional atomic lattice with the variance dB below the Poissonian
noise level. A mesoscopic ensemble containing a few thousand atoms is trapped
in the evanescent field of a nanofiber. The atom number is measured through
dual-color homodyne interferometry with a pW-power shot noise limited probe.
Strong coupling of the evanescent probe guided by the nanofiber allows for a
real-time measurement with a precision of atoms on an ensemble of some
atoms in a one-dimensional trap. The method is very well suited for
generating collective atomic entangled or spin-squeezed states via a quantum
non-demolition measurement as well as for tomography of exotic atomic states in
a one-dimensional lattice
An assessment of two decades of contaminant monitoring in the Nationâs Coastal Zone.
Executive Summary:
Information found in this report covers the years 1986 through 2005. Mussel Watch began monitoring a suite of trace metals and organic contaminants such as DDT, PCBs and PAHs. Through time additional chemicals were added, and today approximately 140 analytes are monitored. The Mussel Watch Program is the longest running estuarine and coastal pollutant monitoring effort conducted in the United States that is national in scope each year. Hundreds of scientific journal articles and technical reports based on Mussel Watch data have been written; however, this report is the first that presents local, regional and national findings
across all years in a Quick Reference format, suitable for use by policy makers, scientists, resource managers and the general public.
Pollution often starts at the local scale where high concentrations point to a specific source of contamination, yet some contaminants such as PCBs are atmospherically transported across regional and national scales, resulting in contamination far from their origin. Findings presented here showed few national trends for trace metals and decreasing trends for most organic contaminants; however, a wide variety of trends, both increasing and decreasing, emerge at regional and local levels. For most organic contaminants, trends have resulted from state and
federal regulation. The highest concentrations for both metal and organic contaminants are found near urban and industrial areas.
In addition to monitoring throughout the nationâs coastal shores and Great Lakes, Mussel Watch samples are stored in a specimen bank so that trends can be determined retrospectively for new and emerging contaminants of
concern. For example, there is heightened awareness of a group of flame retardants that are finding their way into the marine environment. These compounds, known as polybrominated diphenyl ethers (PBDEs), are now being studied using historic samples from the specimen bank and current samples to determine their spatial distribution. We will continue to use this kind of investigation to assess new contaminant threats.
We hope you find this document to be valuable, and that
you continue to look towards the Mussel Watch Program
for information on the condition of your coastal waters. (PDF contains 118 pages
MCMC Exploration of Supermassive Black Hole Binary Inspirals
The Laser Interferometer Space Antenna will be able to detect the inspiral
and merger of Super Massive Black Hole Binaries (SMBHBs) anywhere in the
Universe. Standard matched filtering techniques can be used to detect and
characterize these systems. Markov Chain Monte Carlo (MCMC) methods are ideally
suited to this and other LISA data analysis problems as they are able to
efficiently handle models with large dimensions. Here we compare the posterior
parameter distributions derived by an MCMC algorithm with the distributions
predicted by the Fisher information matrix. We find excellent agreement for the
extrinsic parameters, while the Fisher matrix slightly overestimates errors in
the intrinsic parameters.Comment: Submitted to CQG as a GWDAW-10 Conference Proceedings, 9 pages, 5
figures, Published Versio
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