Simultaneous VLBI Astrometry of H2O and SiO Masers toward the Semiregular Variable R Crateris

TL;DR

This study presents the first astrometrically registered maps of H2O and SiO masers around R Crateris, revealing unique spatial distributions and dynamics that enhance understanding of circumstellar environments in semiregular variables.

Contribution

First simultaneous VLBI astrometric mapping of multiple maser species around R Crateris, showing distinct spatial structures and complex dynamics related to stellar pulsation modes.

Findings

SiO masers form a ring-like structure

H2O maser shows asymmetric outflow

86.2 GHz SiO masers are located inward compared to 43.1 GHz ones

Abstract

We obtained, for the first time, astrometrically registered maps of the 22.2 GHz H2O and 42.8, 43.1, and 86.2 GHz SiO maser emission toward the semiregular b-type variable (SRb) R Crateris, at three epochs (2015 May 21, and 2016 January 7 and 26) using the Korean Very-long-baseline Interferometry Network. The SiO masers show a ring-like spatial structure, while the H2O maser shows a very asymmetric one-side outflow structure, which is located at the southern part of the ring-like SiO maser feature. We also found that the 86.2 GHz SiO maser spots are distributed in an inner region, compared to those of the 43.1 GHz SiO maser, which is different from all previously known distributions of the 86.2 GHz SiO masers in variable stars. The different distribution of the 86.2 GHz SiO maser seems to be related to the complex dynamics caused by the overtone pulsation mode of the SRb R Crateris. Furthermore, we estimated the position of the central star based on the ring fitting of the SiO masers, which is essential for interpreting the morphology and kinematics of a circumstellar envelope. The estimated stellar coordinate corresponds well to the position measured by Gaia.