Invited Presentation

Properties of circumstellar envelope of WX Psc observed by ALMA and KVN

Author(s): Youngjoo Yun, Se-Hyung Cho, Dong-Hwan Yoon, Haneul Yang

Presenter: Youngjoo Yun (KASI)

We present the results of ALMA and KVN observations toward WX Psc (IRC+10011) which is a long-period variable OH/IR star. These observations aim to study the development of asymmetric outward motions during the late stage of asymptotic giant branch (AGB), which are closely related to the copious mass-loss rates of AGB stars. The 1 mm SiO masers of J=5-4 rotational transition and H2O v2=1, 5(5,0)-6(4,3) masers were observed together with the continuum emission at ALMA Band 6 in October 2017 (Cycle 5). The strong SiO and H2O maser features are detected around the continuum emission peak, and a detached shell-like structure is also found from SiO v=0, J=5-4 thermal component. The clumpy structures and the asymmetric morphology of the circumstellar envelope (CSE) of this source are clearly shown by the spatial distributions of the masers and the thermal components. The detached shell-like structure surrounds the maser regions and its size is about 100 mas that corresponds to the dust layer around this object. The detached shells are known to be developed through an episodic mass eruption associated with a thermal pulse, thus they give a crucial information related to the mass loss history of the late AGB stars. While the spatial resolution 20 mas of this ALMA observation cannot clearly resolve the individual maser spot at the inner part of the CSE, the KVN observations show the detailed spatial distributions of the v=1 J=1-0, J=2-1, J=3-2 SiO masers emitted from the inner regions of CSE. Therefore, the KVN observations help us to study the physical properties of the inner CSE, which are closely linked to the initial stage of development of the stellar winds. The bipolar outflow feature is also found from the KVN results of 22 GHz H2O maser and the direction of the outflow axis, NW-SE, seems to be coincident with the void regions of the detached shell-like structure found in this ALMA observation. Our results show the synergy of the combined observations of ALMA and KVN for the study of stellar evolution.