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 Å. 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.
Authors: T. Danilovich, G. Olofsson, J. H. Black, K. Justtanont, H. Olofsson