Maser Studies in Evolved Stars

TL;DR

This paper reviews recent advances in high-resolution observations and modeling of maser emissions in evolved stars, highlighting progress in understanding circumstellar environments and the potential of new instruments and techniques.

Contribution

It emphasizes the need for comprehensive models that integrate all maser characteristics, driven by high-quality data and improved observational methods.

Findings

Progress in astrometrically aligned multi-transition maser observations

Development of models to explain maser spatial distribution and variability

Potential of new instruments and techniques to enhance understanding

Abstract

High resolution maps of maser emission provide very detailed information on processes occurring in circumstellar envelopes of late-type stars. A particularly detailed picture of the innermost shells around AGB stars is provided by SiO masers. Considerable progress is being made to provide astrometrically aligned multi-transition simultaneous observations of these masers, which are needed to better constrain the models. In view of the large amount of high quality data available, models should now be developed to fully explain all maser characteristics together (spatial distribution, variability, etc). New generation instruments (VERA, VSOP-2), new observational techniques (frequency-phase transfer), and new models promise important improvements of our knowledge on this topic.