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 λ < 6000 A˚. 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⊙ and the mass of the W Aql system to 2.1 - 4.1 M⊙ . 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.
@article{arxiv.1501.00863,
title = {Classifying the secondary component of the binary star W Aquilae},
author = {T. Danilovich and G. Olofsson and J. H. Black and K. Justtanont and H. Olofsson},
journal= {arXiv preprint arXiv:1501.00863},
year = {2015}
}