Performance of VERA in the Phase-Referencing Astrometry
Abstract
In order to evaluate the performance of VERA in the phase-referencing astrometry, we review the details of the calibrations and data reductions in VERA's astrometry. We present examples of phase-referencing data as well as the results of data reductions, especially focusing on the phase residuals after the phase-referencing. We show that once the calibration processes are carried out in a proper manner, the phase residual after the phase-referencing becomes white-phase noise for nearly full track (i.e., 8 hour), confirming and extending the previous findings for a shorter range (~hour). We also discuss the astrometric accuracy that can be achieved with VERA by considering various sources of errors including both calibration errors in the observing system and the structural effects of objects. In the absence of the structural effect, we show that the tropospheric zenith delay is the dominant source of astrometric error, and also show that parallax measurements at 10 nas level are feasible for sources under good observing conditions (i.e., bright source, close separation, and relatively high declination). On the other hand, based on the most up-to-date results from VERA, we find that the maser structure effect is also significant in many cases, limiting the parallax accuracy at 5-15% level, especially for nearby sources within a few kpc from the Sun.
- Publication:
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Publications of the National Astronomical Observatory of Japan
- Pub Date:
- June 2011
- Bibcode:
- 2011PNAOJ..13...57H