Classifying the secondary component of the binary star W Aquilae

TL;DR

This study characterizes the faint companion of the binary star W Aquilae, identifying it as a main sequence star and constraining the system's stellar masses through spectral and photometric analysis.

Contribution

The paper provides new spectral and photometric data that identify the companion as a main sequence star and refine the mass estimates of the binary system.

Findings

Companion classified as F8 to G0 main sequence star

Mass of AGB component constrained to 1.04-3 M_sun

System mass estimated at 2.1-4.1 M_sun

Abstract

AIMS: The object W Aql is an asymptotic giant branch (AGB) star with a faint companion. By determining more carefully the properties of the companion, we hope to better constrain the properties of the AGB star. METHODS: We present new spectral observations of the binary star W Aql at minimum and maximum brightness and new photometric observations of W Aql at minimum brightness. RESULTS: The composite spectrum near minimum light is predominantly from the companion at wavelengths $\lambda$ < 6000 $\AA$. This spectrum can be classified as F8 to G0, and the brightness of the companion is that of a dwarf star. Therefore, it can be concluded that the companion is a main sequence star. From this, we are able to constrain the mass of the AGB component to 1.04 - 3 $M_\odot$ and the mass of the W Aql system to 2.1 - 4.1 $M_\odot$ . Our photometric results are broadly consistent with this classification and suggest that the main sequence component suffers from approximately 2 mag of extinction in the V band primarily due to the dust surrounding the AGB component.