Understanding Mass-Loss and the late Evolution of Intermediate Mass Stars: Jets, Disks, Binarity, Dust and Magnetic Fields

TL;DR

This paper reviews the complex late evolutionary stages of intermediate-mass stars, focusing on mass loss, jets, disks, binarity, dust, and magnetic fields, highlighting recent observational discoveries and unresolved questions.

Contribution

It summarizes current understanding and identifies key unsolved problems in the mass-loss processes and morphological features of evolved intermediate-mass stars.

Findings

Discovery of jets and disks in unexpected stellar environments

Recognition of multipolar and point-symmetric nebulae

Identification of major unresolved issues in stellar mass-loss mechanisms

Abstract

Almost all stars in the 1-8 Msun range evolve through the Asymptotic Giant Branch (AGB), preplanetary nebula (PPN) and planetary nebula (PN) evolutionary phases. Most stars that leave the main sequence in a Hubble time will end their lives in this way. The heavy mass loss which occurs during the AGB phase is important across astrophysics, and the particulate matter crucial for the birth of new solar systems is made and ejected by AGB stars. Yet stellar evolution from the beginning of the AGB phase to the PN phase remains poorly understood. We do not understand how the mass-loss (rate, geometry, temporal history) depends on fundamental stellar parameters or the presence of a binary companion. While the study of evolved non-massive stars has maintained a relatively modest profile in recent decades, we are nonetheless in the midst of a quiet but exciting revolution in this area, driven by new observational results, such as the discovery of jets and disks in stellar environments where these were never expected, and by the recognition of new symmetries such as multipolarity and point-symmetry occuring frequently in the nebulae resulting from the outflows. In this paper we summarise the major unsolved problems in this field, and specify the areas where allocation of effort and resources is most likely to help make significant progress.