The Maser Emitting Structure and Time Variability of the SIS Lines J = 14 - 13 and 15 - 14 in IRC+10216.

Abstract

We present new high angular resolution interferometer observations of the υ = 0 J = 14 - 13 and 15 - 14 SiS lines towards IRC+10216, carried out with CARMA and ALMA. The maps, with angular resolutions of reveal (1) an extended, roughly uniform, and weak emission with a size of (2) a component elongated approximately along the East-West direction peaking at at both sides of the central star, and (3) two blue- and red-shifted compact components peaking around to the NW of the star. We have modeled the emission with a 3D radiation transfer code finding that the observations cannot be explained only by thermal emission. Several maser clumps and one arc-shaped maser feature arranged from 5 to 20R⋆ from the central star, in addition to a thin shell-like maser structure at ≃ 13R⋆ are required to explain the observations. This maser emitting set of structures accounts for 75% of the total emission while the other 25% is produced by thermally excited molecules. About 60% of the maser emission comes from the extended emission and the rest from the set of clumps and the arc. The analysis of a time monitoring of these and other SiS and 29SiS lines carried out with the IRAM 30 m telescope from 2015 to present suggests that the intensity of some spectral components of the maser emission strongly depends on the stellar pulsation while other components show a mild variability. This monitoring evidences a significant phase lag of ≃ 0.2 between the maser and NIR light-curves.