JVN observations of H2O masers around the evolved star IRAS 22480+6002

TL;DR

This study uses VLBI observations to analyze H2O maser distributions around the evolved star IRAS 22480+6002, revealing a complex velocity field, a closer distance estimate, and characteristics similar to post-AGB stars.

Contribution

First detailed VLBI analysis of H2O masers around IRAS 22480+6002, providing new distance measurement and insights into its stellar nature.

Findings

H2O masers spread over 50 mas with no clear proper motion correlation.

Distance estimated at 1.0+-0.4 kpc, smaller than previous estimates.

Star exhibits properties similar to post-AGB stars.

Abstract

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 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/s 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 distributions; the velocity field of the envelope seems 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, that is considerably smaller than previously thought. The distance indicates that this is an evolved star with L~5800 Lsun. This star shows radio, infrared, and optical characteristics quite similar to those of the population II post-AGB stars such as RV Tau variables.