CO and HI emission from the circumstellar envelopes of some evolved stars

TL;DR

This paper investigates CO and HI radio emissions from evolved stars' circumstellar envelopes, revealing axial symmetry, bipolar outflows, and interactions with interstellar matter, using data from multiple radio telescopes.

Contribution

It provides new observational insights into the structure and dynamics of circumstellar envelopes of evolved stars, highlighting the role of bipolar outflows and extended HI emission.

Findings

Axial symmetry observed in CO emission for several stars.

Detection of bipolar outflows with enhanced polar wind velocities.

HI emission extends beyond CO, indicating interaction with interstellar matter.

Abstract

Studies of the CO and HI radio emission of some evolved stars are presented using data collected by the IRAM Plateau de Bure interferometer and Pico Veleta telescope, the Nan\c{c}ay Radio Telescope and the JVLA and ALMA arrays. Approximate axial symmetry of the physical and kinematic properties of the circumstellar envelope (CSE) are observed in CO emission, in particular, from RS Cnc, EP Aqr and the Red Rectangle. A common feature is the presence of a bipolar outflow causing an enhanced wind velocity in the polar directions. HI emission extends to larger radial distances than probed by CO emission and displays features related to the interaction between the stellar outflow and interstellar matter. With its unprecedented sensitivity, FAST will open a new window on such studies. Its potential in this domain is briefly illustrated.