VERA内部測地観測へのK帯の適用とその効果

抄録

We changed the observation frequency band adopted by the geodetic VLBI (Very Long Baseline Interferometry) observations bounded within the VERA (VLBI Exploration of Radio Astrometry) network from S/X- to K-band (2.2 and 8.2 GHz to 22 GHz) aiming at improving precision of the antenna coordinates. Since performance of the VERA observing system has been demonstrated best in K-band, fringe detection sensitivity increases by a factor of 8.9 in comparison with that in X-band, leading to reduction of scan length needed for fringe detection. Thanks to the sensitivity improvement, the number of scans increased to more than 800, i.e., the number that is twice of that of geodetic VLBI using S/X bands in VERA. 90 radio sources which are sufficient in quantity to be used for regular observations have been secured, and more than a half of the sources have higher peak flux density in K-band than in X-band. Experimental observations were carried out for two years from January 2006. The coordinates of the VERA antenna reference points and the baseline lengths were estimated with errors of a few mm. The increase in the number of scans thus led effectively to reduction of the standard deviations of the estimated coordinates of antennas by typically 1.64 times in one session. The distribution of post-fit residual delays in K-band and in X-band is similar. The magnitude of error in K-band is 7.14 picoseconds smaller than that in X-band. The inaccuracy of a coherence loss factor is one of the candidates of the additional error sources. Secular variations were detected from the time series of observed baseline lengths. In these baseline lengths and their temporal variations, clear differences are not found between S/X- and K-band.