2005ApJ...627L..49K

We have measured the annual parallax of the Mira-type variable star UX Cyg at {piv}=0.54±0.06 mas from phase-referencing VLBI observations of its circumstellar water masers with the VLBA. The corresponding distance is 1.85^+0.25_–0.19kpc. This is the first measurement of an annual parallax based on observations of water masers. It is important to calibrate the period-luminosity relation of Mira variables because it is an important distance indicator in astronomy. We discuss the distance to the Large Magellanic Cloud by comparing our results with the period-luminosity relation in the Large Magellanic Cloud. We obtained the three-dimensional position and velocity of UX Cyg in our Galaxy: (R,θ,z)=(8.20±0.01 kpc, 12°.4^+1°.7_–1°.3, -0.30^+0.03_–0.04 kpc), (V_R,V_θ,V_z)=(-81.6^+14.0_–15.3, 204.0^+3.6_–3.4, -12.1^+10.2_–10.3) km/s. We also discuss the origin of UX Cyg.