Key points are not available for this paper at this time.
The authors measured the proper motions of many H2O maser spots associated with the star-forming region, Sgr B2 (N), which lies close to the Galactic Center. They used five VLBI observations spanning 1. 5 yr and achieved relative positional accuracies of about 20 microarcseconds (μas) across a 4arcsec field. The proper motion information shows that the dominant motions of the Sgr B2 (N) masers are expansion, with evidence for some rotation. The expansion velocity is ≡45 km s-1. The rotation velocity at a radial distance of 1arcsec is ≡20 km s-1, indicating a mass enclosed by the 2arcsec masing region of ≡2×104Mₛun;. The authors find the distance to the Sgr B2 (N) H2O masers, and hence the distance to the Galactic Center (R0), to be 7. 1 kpc with a one standard deviation uncertainty, including systematic sources of error, of 1. 5 kpc.
Reid et al. (Fri,) studied this question.