5,509 research outputs found
High Precision Astrometric Millimeter VLBI Using a New Method for Atmospheric Calibration
We describe a new method which achieves high precision Very Long Baseline
Interferometry (VLBI) astrometry in observations at millimeter wavelengths. It
combines fast frequency-switching observations, to correct for the dominant
non-dispersive tropospheric fluctuations, with slow source-switching
observations, for the remaining ionospheric dispersive terms. We call this
method Source-Frequency Phase Referencing. Provided that the switching cycles
match the properties of the propagation media, one can recover the source
astrometry. We present an analytic description of the two-step calibration
strategy, along with an error analysis to characterize its performance. Also,
we provide observational demonstrations of a successful application with
observations using the Very Long Baseline Array at 86 GHz of the pairs of
sources 3C274 & 3C273 and 1308+326 & 1308+328, under various conditions. We
conclude that this method is widely applicable to millimeter VLBI observations
of many target sources, and unique in providing bona-fide astrometrically
registered images and high precision relative astrometric measurements in
mm-VLBI using existing and newly built instruments.Comment: Astronomical Journal, accepted for publicatio
Wide-angle energy-momentum spectroscopy
Light emission is defined by its distribution in energy, momentum, and
polarization. Here, we demonstrate a method that resolves these distributions
by means of wide-angle energy-momentum spectroscopy. Specifically, we image the
back focal plane of a microscope objective through a Wollaston prism to obtain
polarized Fourier-space momentum distributions, and disperse these
two-dimensional radiation patterns through an imaging spectrograph without an
entrance slit. The resulting measurements represent a convolution of individual
radiation patterns at adjacent wavelengths, which can be readily deconvolved
using any well-defined basis for light emission. As an illustrative example, we
use this technique with the multipole basis to quantify the intrinsic emission
rates for electric and magnetic dipole transitions in europium-doped yttrium
oxide (Eu:YO) and chromium-doped magnesium oxide
(Cr:MgO). Once extracted, these rates allow us to reconstruct the full,
polarized, two-dimensional radiation patterns at each wavelength.Comment: 4 pages, 4 figure
Role-playing as a technique for developing self-awareness and social growth in the elementary school
Call number: LD2668 .R4 1967 D5
- …