Chemical tracers of a highly eccentric AGB-main sequence star binary

TL;DR

This paper combines chemical and dynamical analysis to reveal a highly eccentric, long-period binary orbit in an AGB-main sequence star system, using novel astrochemical signatures to constrain orbital parameters.

Contribution

It introduces a new astrochemistry-based method to determine orbital parameters of long-period AGB binaries, demonstrated on W Aquilae.

Findings

Detection of anisotropic SiN emission

First detections of NS and SiC towards an S-type star

Density structures in CO emission linked to periastron interactions

Abstract

Binary interactions have been proposed to explain a variety of circumstellar structures seen around evolved stars, including asymptotic giant branch (AGB) stars and planetary nebulae. Studies resolving the circumstellar envelopes of AGB stars have revealed spirals, discs and bipolar outflows, with shaping attributed to interactions with a companion. For the first time, we have used a combined chemical and dynamical analysis to reveal a highly eccentric and long-period orbit for W Aquilae, a binary system containing an AGB star and a main sequence companion. Our results are based on anisotropic SiN emission, the first detections of NS and SiC towards an S-type star, and density structures observed in the CO emission. These features are all interpreted as having formed during periastron interactions. Our astrochemistry-based method can yield stringent constraints on the orbital parameters of long-period binaries containing AGB stars, and will be applicable to other systems.