c 2008. Astronomical Society of Japan. JVN Observations of H2O Masers around the Evolved Star IRAS 22480+6002

We report on the H2O maser distributions around IRAS 22480+6002 ( = IRC+60370), observed with the Japanese VLBI Network (JVN) at three epochs spanning 2 months. This object was identified as a K-type supergiant in the 1970s, which was unusual as a stellar maser source. The spectrum of H2O masers consists of 5 peaks separated roughly equally by a few km s1 each. The H2O masers were spatially resolved into more than 15 features, which spread about 50 mas along the east–west direction. However, no correlation was found between the proper-motion vectors and their spatial positions; the velocity field of the envelope seems to be random. A statistical parallax method applied to the observed proper-motion data set gives a distance of 1:0 ˙ 0:4 kpc for this object, which is considerably smaller than previously thought. The distance indicates that this is an evolved star with L 5800 Lˇ. This star shows radio, infrared, and optical characteristics that are quite similar to those of population II post-AGB stars, such as RV Tau variables