Distance of W3(OH) by VLBI annual parallax measurement
Abstract
The most powerful tool for measuring distances within our Galaxy is the annual parallax. We carried out phase-referencing VLBI observations of H2O masers in the star forming region W3(OH) with respect to the extragalactic continuum source ICRF 0244+624 to measure their absolute proper motions. The measured annual parallax is 0.484 0.004 milli-arcseconds which corresponds to a distance of 2.07+0.01-0.02$ kpc from the sun. This distance is consistent with photometric and kinematic distances from previous observations.
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