Spectroscopy of the massive interacting binary UU Cassiopeiae

¹ Astronomical Institute of the Academy of Sciences of the Czech Republic, Boční II 1401/1, 141 00 Praha 4, Czech Republic
e-mail: had@asu.cas.cz
² Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
³ Astronomical Observatory Belgrade, Volgina 7, Serbia
⁴ Universidad de Concepción, Departamento de Astronomía, Casilla 160-C, Concepción, Chile
⁵ Kourovka Astronomical Observatory, Ural Federal University, Mira str., 19, Yekaterinburg 620002, Russia
⁶ Astronomical Institute of Charles University, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
⁷ Institute of Astronomy and NAO, Bulgarian Academy of Sciences, Sofia, Bulgaria
⁸ Universidad Nacional Autónoma de México, Instituto de Astronomía, AP 106, Ensenada, 22860 BC, Mexico

Received: 28 October 2021
Accepted: 7 January 2022

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 Hα emission yields evidence of changes in the structure of the circumstellar matter on a timescale of several orbital periods.