Absolute astrometry with ultra-wide bandwidth synthesis
An exploratory project for testing a novel, economical way to determine
absolute position of radio sources with accuracy better than 0.1~mas
utilizing recent upgrade of VLBI hardware. It was shown that the core-shift
at 8 GHz is on average 0.2 mas. This sets the fundamental limit on
astrometric accuracy. The objective of this campaign is to test the
methodology that promises to overcome this limit. The novelty of the approach:
frequency switching C-band observations;
bandwidth synthesis within 4 GHz wide band;
observing triplets of near-by sources for determining
frequency-dependent core-shift;
using all tones of phase-cal signal;
4~hour blocks;
using outputs of high-resolution numerical weather models
for calibration for the contribution of slanted path delay the neutral
atmosphere;
using the empirical model of nutation.
Goals
The goal of proposed observations is to assess the level of systematic errors
and present evidence that claimed accuracy is achievable. If successful,
the methodology of determination of absolute positions with accuracies
0.05–0.1mas for less than 1/2 hours per triplet will be developed.
This will allow to refine on-demand positions of those sources for which
this level of accuracy is necessary.
)