Science with an ngVLA: Probing Strong Binary Interactions and Accretion in AGB stars with the ngVLA

TL;DR

This paper discusses how the next-generation Very Large Array (ngVLA) can be used to study binary interactions and accretion processes in AGB stars, shedding light on their role in stellar evolution and nebula formation.

Contribution

It proposes a survey with the ngVLA to detect and characterize radio emissions from AGB stars, testing the hypothesis of active binarity and accretion during the late AGB phase.

Findings

Detection of variable non-thermal radio emission from fuvAGB stars.

Support for the hypothesis that these stars have actively accreting companions.

Potential to distinguish between binary/accretion-related and single-star chromospheric emissions.

Abstract

Understanding strong binary interactions is of wide astrophysical importance, and the deaths of most stars in the Universe that evolve in a Hubble time could be fundamentally affected by such interactions. These stars end their lives, evolving from Asymptotic Giant Branch stars with extensive mass-loss into planetary nebulae with a spectacular array of morphologies. Binarity, and the associated formation of accretion disks (that drive collimated, fast jets) during the very late AGB or early post-AGB phase is believed to produce this dramatic morphological transformation. But the evidence for binarity and accretion during the AGB phase has been hard to obtain due to observational limitations. However, recent observations at UV and X-ray wavelengths have broken thru the observational barrier -- our studies using GALEX reveal a candidate population of AGB stars, generally with strongly-variable far-ultraviolet (FUV) emission (fuvAGB stars), and our follow-up studies with XMM-Newton, Chandra, and HST of a few key objects supports our hypothesis that these objects have companions that are actively accreting material from the primary. The most prominent fuvAGB star has been detected with the VLA, showing the presence of variable non-thermal emission. The ngVLA, with its unprecedented sensitivity, is needed to survey a statistical sample of fuvAGB stars over the ~3-90 Ghz range to search for and characterize the nature of the radio emission from fuvAGB stars and test our binarity+accretion hypothesis. Such a survey will distinguish between binarity/accretion-related radio emission that is expected to have both thermal and non-thermal components and display significantly time-variable on short time-scales (minutes to weeks), and single-star chromospheric emission from the primary that is expected to be thermal, possibly with time-variability, but only on long time-scales (many months to a year).