Spectroscopy of the massive interacting binary UU Cassiopeiae

TL;DR

This study analyzes spectra of the massive interacting binary UU Cas over several years to understand the accretion process, circumstellar matter, and their variability, revealing a disk wind and dynamic circumstellar structures.

Contribution

It provides a detailed spectral analysis of UU Cas, including disentangling spectra over years and modeling the physical parameters of the stars and circumstellar matter.

Findings

Detection of a disk wind emanating above the orbital plane.

Variability in Hα emission indicates changing circumstellar structures.

Spectral analysis shows the dominant influence of the donor star and circumstellar matter.

Abstract

Context. The eclipsing close binary UU Cas is an interacting massive double-periodic system with a gainer star partly hidden in an accretion disk. Aims. In order to study the physics of the accretion process in greater detail, along with the structure and dynamics of the circumstellar matter in the system, we supplement our previous results obtained from photometry with an analysis of the spectra of UU Cas. Methods. We collected all available spectra used in previous publications on UU Cas and we acquired new ones. The method of disentangling was applied to this set of spectra spanning the years 2008-2021. The orbital parameters were disentangled and a fit of the separated component spectra by synthetic ones has been used to determine the physical parameters of the component stars. We compared the results to models of the evolution of interacting binaries. Results. We found that in addition to the dominant role of the donor star and a weak contribution of the gainer, the line profiles are strongly influenced by the circumstellar matter. The absorption lines reveal a presence of a disk wind emanating above the orbital plane. The variability of H{\alpha} emission yields evidence of changes in the structure of the circumstellar matter on a timescale of several orbital periods.