Spectroscopic observations of the interacting massive binary AQ\,Cassiopea

TL;DR

This paper presents spectroscopic and photometric analysis of the binary star AQ Cassiopeia, revealing details about its components, mass transfer effects, and distance, with implications for stellar evolution models.

Contribution

It provides new spectroscopic data and detailed modeling of AQ Cassiopeia, including the effects of mass transfer and stream distortion on observed light curves.

Findings

Primary star: 17.63 M☉, 13.48 R☉, spectral type B0.5 II-III

Secondary star: 12.56 M☉, 23.55 R☉, spectral type B3 II

System distance estimated at 4150±240 pc

Abstract

New spectroscopic observations of the double-lined eclipsing binary AQ\,Cas are presented. All available spectroscopic and photometric observations have been analysed for the fundamental properties of the components. Analyses show that the system consists of a massive primary with a mass of 17.63$\pm$0.91 M$_{\odot}$ and radius of 13.48$\pm$0.64R$_{\odot}$ and a secondary with 12.56$\pm$0.81 M$_{\odot}$ and radius of 23.55$\pm$0.73 R$_{\odot}$, corresponding spectral types of B0.5($\pm$2) II-III + B3($\pm$1) II. The secondary star fills its corresponding Roche lobe and mass transfer to the primary star is going on. This stream considerably does affect the photometric observations both starting from the second quarter up to the first contact of primary eclipse and just at the second maximum. Thus, the light curve is distorted and tightly depended on the wavelength of the observations. The available multi passband light curves have been analysed by taking the stream effects, as either hot or cool spots, into account. The comparison of the models and observations in the $\log(L/L_{\odot})$ - $\log T_{eff}$ and $\log g - \log T_{eff}$ diagrams clearly shows that the more massive star is consistent with models and is predicted to be close to the phase of hydrogen shell ignition. Average distance to the system is estimated as 4150$\pm$240 pc using the BVJHK magnitudes and V-passband extinction.