A study on evolved stars by simultaneous observations of H₂O and SiO masers using KVN

Abstract

The Korean VLBI Network (KVN) is a unique millimeter VLBI system which is consisted of three 21 m telescopes with relatively short baselines. We present the preliminary results of simultaneous monitoring observations of the 22.2 GHz H2O and 43.1/42.8/86.2/129.3 GHz SiO masers based on the KVN Key Science Project (KSP). We obtained the astrometrically registered maps of the H2O and SiO masers toward nine evolved stars using the source frequency phase referencing method (SFPR). The SFPR maps of the H2O and SiO masers enabled us to investigate the spatial structure and kinematics from the SiO to H2O maser regions including the development of an outward motion from the ring-like or elliptical structures of SiO masers to the asymmetric structures of the 22.2 GHz H2O maser features. In particular, the 86.2/129.3 GHz SiO (v=1, J=2–1 and J=3–2) masers were clearly imaged toward several objects for the first time. The SiO v=1, J=3–2 maser shows different distributions compared to those of the SiO v=1, 2, J=1–0 and v=1, J=2–1 masers implying a different physical condition.

Astrometrically registered maps of H2O and SiO masers toward VX Sagittarii

“…H 2 O and SiO maser maps and their morphological differences. Figure 1 shows the astrometrically registered integrated intensity map of the H 2 O and SiO maser lines observed on March 27, 2016 (optical phase φ = 0.67) toward VX Sgr 14 . The distributions of the SiO masers show a typical ring-like structure, while that of the H 2 O maser shows an asymmetric structure spread slightly in the NW and SE direction in ~350 mas and relatively dense distributions in the NE and SW direction in ~270 mas.…”

“…Histograms represent the radial distribution of the maser spots with respect to the central star. The ring radius and FWHM derived from the Gaussian fitting are represented in each panel Variation of the SiO ring radius with the optical light curve (in press manuscript14 ). The gray cross indicates the optical light curve from American Association of Variable Star Observers (AAVSO; https://www.aavso.org).…”