The maser emitting structure and time variability of the SiS lines J=14-13 and 15-14 in IRC+10216

TL;DR

This study uses high-resolution interferometry to analyze SiS maser emission structures and their variability in IRC+10216, revealing complex spatial features and a phase lag with stellar pulsation.

Contribution

It provides the first detailed modeling of SiS maser structures in IRC+10216, combining high-resolution imaging with time monitoring to understand their spatial distribution and variability.

Findings

Maser emission accounts for 75% of total SiS emission.

Maser structures include clumps, an arc, and a shell at ~13 stellar radii.

Maser intensity varies with stellar pulsation, showing a phase lag of ~0.2.

Abstract

We present new high angular resolution interferometer observations of the v=0 J=14-13 and 15-14 SiS lines towards IRC+10216, carried out with CARMA and ALMA. The maps, with angular resolutions of ~0.25"and 0.55", reveal (1) an extended, roughly uniform, and weak emission with a size of ~0.5", (2) a component elongated approximately along the East-West direction peaking at ~0.13" and 0.17" at both sides of the central star, and (3) two blue- and red-shifted compact components peaking around 0.07" 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 30m 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.