VIPS Astrometry

1127 compact extragalactic sources were observed under the VLBA Imaging and Polarimetry Survey. By July 2010, positions of 647 of these sources were determined using observations under other absolute astrometry VLBA programs, and positions of 480 othere sources were known from VLA with low accuracy.

I analyzed the first VIPS experiment, bt085a, in order to learn whether we can use VIPS observations for determining source positions. I also tested for the first time the mode of my fringing fitting software PIMA when RR and LL polarizations data are coherenly combined.

Listing of BT085a solution that used RR polarization data.

Listing of BT085a solution that used combined RR and LL polarization data.

I examined coherence losses in combining RR+LL data defined as Ampl(RR+LL)/sqrt(Amp(RR)^2 + Amp(LL)^2). Value 1.0 means no losses.

The plot of losses as a function of SNR is shown is shown here.

The average loss factor is 0.97. Reduction of the loss factors at very high SNR is presumably due to imperfection of complex RR and LL bandpass calibration.

Conclcusions

  1. Combined RR+LL fringe fitting mode passed the test.

  2. Absolute astrometry of VIPS data is feasible and highly desirable.

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This page was prepared by Leonid Petrov ()
Last update: 2010.08.30_08:02:04