A TRIGONOMETRIC PARALLAX OF Sgr B2

We have measured the positions of H2O masers in Sgr B2, a massive star forming region in the Galactic center, relative to an extragalactic radio source with the Very Long Baseline Array. The positions measured at 12 epochs over a time span of one year yield the trigonometric parallax of Sgr B2 and hence a distance to the Galactic center of R0 = 7.9 +0.8 −0.7 kpc. The proper motion of Sgr B2 relative to Sgr A * suggests that Sgr B2 is ≈ 0.13 kpc nearer than the Galactic center, assuming a low-eccentricity Galactic orbit. Subject headings: Galaxy: fundamental parameters, structure, kinematics and dynamics, halo — stars: formation — astrometry