# Mapping the circumstellar SiO maser emission in R Leo

## TL;DR

This paper uses high-resolution interferometry to map SiO maser emissions around R Leo, revealing spatial distributions that challenge existing maser pumping theories and providing insights into the star's circumstellar environment.

## Contribution

First detailed mapping of 29SiO v=0 J=1-0 emission in R Leo, comparing spatial distributions of multiple SiO maser lines at different frequencies.

## Key findings

- 28SiO v=2 maser is closer to the star than v=1.
- 86 GHz maser occurs in a farther shell than 43 GHz.
- Observed distributions differ from theoretical predictions.

## Abstract

The study of the innermost circumstellar layers around AGB stars is crucial to understand how these envelopes are formed and evolve. The SiO maser emission occurs at a few stellar radii from the central star, providing direct information on the stellar pulsation and on the chemical and physical properties of these regions. Our data also shed light on several aspects of the SiO maser pumping theory that are not well understood yet. We aim to determine} the relative spatial distribution of the 43 GHz and 86 GHz SiO maser lines in the oxygen-rich evolved star R Leo. We have imaged with milliarcsecond resolution, by means of Very Long Baseline Interferometry, the 43 GHz (28SiO v=1, 2 J=1-0 and 29SiO v=0 J=1-0) and 86 GHz (28SiO v=1 J=2-1 and 29SiO v=0 J=2-1) masing regions. We confirm previous results obtained in other oxygen-rich envelopes. In particular, when comparing the 43 GHz emitting regions, the 28SiO v=2 transition is produced in an inner layer, closer to the central star. On the other hand, the 86 GHz line arises in a clearly farther shell. We have also mapped for the first time the 29SiO v=0 J=1-0 emission in R Leo. The already reported discrepancy between the observed distributions of the different maser lines and the theoretical predictions is also found in R Leo.