Asymmetric distributions of H₂O and SiO masers towards V627 Cas

Abstract

We performed simultaneous observations of the $\rm H_2O$ 6_1,6 - 5_2,3 (22.235080 GHz) and SiO V = 1, 2, J = 1 → 0, SiO V = 1, J = 2 → 1, 3 → 2 (43.122080, 42.820587, 86.243442, and 129.363359 GHz) masers towards the suspected D-type symbiotic star, V627 Cas, using the Korean VLBI Network. Here, we present astrometrically registered maps of the $\rm H_2O$ and SiO V = 1, 2, J = 1 → 0, SiO V = 1, J = 2 → 1 masers for five epochs from January 2016 to June 2018. Distributions of the SiO maser spots do not show clear ring-like structures, and those of the $\rm H_2O$ maser are biased towards the north-north-west to west with respect to the SiO maser features according to observational epochs. These asymmetric distributions of $\rm H_2O$ and SiO masers are discussed based on two scenarios of a bipolar outflow and the presence of the hot companion, a white dwarf, in V627 Cas. We carried out ring fitting of SiO V = 1, and V = 2 masers and estimated the expected position of the cool red giant. The ring radii of the SiO V = 1 maser are slightly larger than those of the SiO V = 2 maser, as previously known. Our assumption for the physical size of the SiO maser ring of V627 Cas to be the typical size of a SiO maser ring radius (∼4 au) of red giants yields the distance of V627 Cas to be ∼1 kpc.