JVN Observations of H2O Masers around the Evolved Star IRAS 22480+6002

Abstract

Abstract We report on the H$_2$O maser distributions around IRAS 22480$+$6002 ($=$ IRC$+$60370), observed with the Japanese VLBI Network (JVN) at three epochs spanning 2 months. This object was identified as a K-type supergiant in the 1970s, which was unusual as a stellar maser source. The spectrum of H$_2$O masers consists of 5peaks separated roughly equally by a fewkms$^{-1}$ each. The H$_2$O masers were spatially resolved into more than 15features, which spread about 50mas 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 $1.0\pm 0.4$kpc for this object, which is considerably smaller than previously thought. The distance indicates that this is an evolved star with $L\sim$5800$L_{\odot}$. 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.