An HI 21-cm line survey of evolved stars

TL;DR

This paper discusses a survey of the 21 cm hydrogen line around evolved stars, aiming to understand their circumstellar environments and the interaction with the interstellar medium, with recent focus on S-type stars.

Contribution

It presents new observational data from a large-scale HI survey of evolved stars, highlighting progress and emphasizing findings related to S-type stars.

Findings

Detection of HI emission around evolved stars.

Insights into the kinematics of circumstellar shells.

Differences observed in S-type stars' circumstellar environments.

Abstract

The HI line at 21 cm is a tracer of circumstellar matter around AGB stars, and especially of the matter located at large distances (0.1-1 pc) from the central stars. It can give unique information on the kinematics and on the physical conditions in the outer parts of circumstellar shells and in the regions where stellar matter is injected into the interstellar medium. However this tracer has not been much used up to now, due to the difficulty of separating the genuine circumstellar emission from the interstellar one. With the Nancay Radiotelescope we are carrying out a survey of the HI emission in a large sample of evolved stars. We report on recent progresses of this long term programme, with emphasis on S-type stars.