The axisymmetric envelopes of RS Cnc and EP Aqr

TL;DR

This study presents high-resolution observations of two AGB stars, revealing axisymmetric outflows with different velocities in equatorial and polar regions, suggesting a potential link to stellar companions and advancing understanding of mass loss mechanisms.

Contribution

It provides detailed interferometric and single-dish observations showing axisymmetric morpho-kinematics in AGB stars, highlighting the role of companions in shaping stellar outflows.

Findings

Matter flows out at ~2 km/s in equatorial planes.

Matter flows out at ~8 km/s along polar axes.

Axisymmetric outflows are common in early AGB stars with composite CO profiles.

Abstract

We report on observations obtained at IRAM on two semi-regular variable Asymptotic Giant Branch (AGB) stars, RS Cnc and EP Aqr, undergoing mass loss at an intermediate rate of ~ 10^-7 solar mass per year. Interferometric data obtained with the Plateau-de-Bure interferometer (NOEMA) have been combined with On-The-Fly maps obtained with the 30-m telescope in the CO(1-0) and (2-1) rotational lines. The spectral maps of spatially resolved sources reveal an axisymmetric morphology in which matter is flowing out at a low velocity (~ 2 km/s) in the equatorial planes, and at a larger velocity (~ 8 km/s) along the polar axes. There are indications that this kind of morpho-kinematics is relatively frequent among stars at the beginning of their evolution on the Thermally-Pulsing AGB, in particular among those that show composite CO line profiles, and that it might be caused by the presence of a companion. We discuss the progress that could be expected for our understanding of the mass loss mechanisms in this kind of sources by increasing the spatial resolution of the observations with ALMA or NOEMA.