Structure of the hot object in the symbiotic prototype Z Andromedae during its 2000–03 active phase

¹ Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranská Lomnica, Slovakia
² INAF Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
³ Okayama Astrophysical Observatory, NAOJ, Kamogata, Okayama 719-0232, Japan
⁴ Astronomical Institute, Tohoku University, Sendai 980-8578, Japan
⁵ Astronomical Institute, Charles University Prague, 18000 Praha 8, V Holešovičkách 2, Czech Republic
⁶ Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK

Received: 22 February 2005
Accepted: 2 March 2006

Abstract

Aims.To investigate structure of the hot object in the symbiotic prototype Z And during its major 2000-03 active phase.

Methods.Analysis of the far ultraviolet, optical low- and high-resolution spectroscopy and  photometry. Reconstruction of the spectral energy distribution (SED) during the outburst. The Raman scattering process.

Results.At the initial stages of the outburst the hot object was characterized by the two-temperature spectrum (a warm stellar radiation and a strong nebular emission) with signatures of a mass-outflow at moderate (~100-200 km s^-1) and very high (≈1000-2000 km s^-1) velocities. The corresponding structure of the hot object consists of an optically thick, slowly-expanding disk-like material encompassing the accretor at the orbital plane and a fast optically thin wind over the remainder of the star. The disk-like shell persisted around the central star until 2002 August as was indicated by the eclipse effect. Then, a significant dilution of the optically thick material and evolution of a fast wind from the hot star, concentrated more at the orbital plane, were detected. A striking similarity of [] λ6087 and Raman λ6825 profiles at/after the dilution of the disk suggests their origin within the interaction zone where the winds from the binary components collide.