Distance to Orion KL Measured with VERA

Abstract

We present the initial results of multiepoch VLBI observations of 22 GHz H$_{2}$O masers in the Orion KL region with VERA (VLBI Exploration of Radio Astrometry). With the VERA dual-beam receiving system, we carried out phase-referencing VLBI astrometry, and successfully detected the annual parallax of Orion KL to be 2.29$\;\pm\;$0.10 mas, corresponding to a distance of 437$\;\pm\;$19 pc from the Sun. The distance to Orion KL was determined for the first time with the trigonometric parallax method in these observations. Although this value is consistent with that previously reported, 480$\;\pm\;$80 pc, which was estimated from a statistical parallax method using the proper motions and radial velocities of the H$_{2}$O maser features, our new results provide a much more accurate value with an uncertainty of only 4%. In addition to the annual parallax, we detected an absolute proper motion of the maser feature, suggesting an outflow motion powered by the radio source I along with the systematic motion of source I itself.