Proceedings of the International Astronomical Union

Table of Contents - January 2012 - Volume 8, Symposium S287 (Cosmic Masers - from OH to H0)  

Contributed Papers

Astrometry of water masers in post-AGB stars

Hiroshi Imaia1 and VERA collaborationa1a2

a1 Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan email: hiroimai@sci.kagoshima-u.ac.jp

a2 Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-12 Hoshigaoka, Mizusawa-Ku, Oshu-shi, Iwate 023-0861, Japan

Abstract

Measurements of trigonometric parallaxes and secular motions of evolved stars, especially post-AGB stars including central objects of planetary nebulae and water fountain sources as well as peculiar or unclassified stars, provide unambiguous source distance scales and information on their orbits in the Milky Way Galaxy. True source luminosities and kinematical properties should lead us to elucidate the true characteristics and evolutional tracks of these stars. Here we present the recent results of astrometry towards H2O maser sources with the VLBI Exploration of Radio Astormetry (VERA). The target sources include a planetary nebula (K3–35), a pre-PN (IRAS 19312+1950), a water fountain (IRAS 18286−0959) and a K-type star (IRAS 22480+6002). We have demonstrated that parental stars of the former three sources should be intermediate-mass stars from their luminosities and orbits in the Milky Way. It is suggested that IRAS 22480+6002 should be a K-type supergiant previously suggested rather than an RV Tau variable star.

Keywords

  • masers;
  • stars:distances;
  • individuals (K3–35, IRAS 19312+1950, IRAS 18286−0959, IRAS 22480+6002)