Structure of the hot object in the symbiotic binary Z Andromedae.
Authors:
A. Skopal, A.A. Vittone, L. Errico, M. Otsuka, S. Tamura, M. Wolf, V.G. Elkin
Image & caption:
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Image caption::
FUSE spectra of Z And from the maximum of its optical brightness during the 2000-03 outburst. The solid line represents the Rayleigh attenuated blackbody radiation from the hot stellar source at 28000 K, while the dotted line is not attenuated. The presence of emission lines from highly ionized elements signals the presence of a very hot ionizing source in the system. This composite spectrum suggests a disk-like structure of the hot active object in Z And during its active phase.
Description:
The key problem in investigation of symbiotic stars is the nature of their outburst. Observations show an increase of the active object luminosity to 10 000 Suns, a dramatical decrease of its temperature from 200 000 to only 20 000 K, whereas the spectrum indicates the presence of a hot body capable of ionizing hydrogen and helium. Understanding the geometrical structure of the active object, which is currently not well known, can significantly contribute to our understanding the nature of outbursts. The aim of our study was to reconstruct structure of the active object in Z And. Analyzing the high-resolution spectroscopy, multi-colour photometry and the ultraviolet spectroscopy as measured by the satellite Far Ultraviolet Spectroscopic Explorer, we inferred the structure of its active object. We found that the hot object consisted of an optically thick, slowly-expanding (100-200 km/s) disk-like material encompassing the accretor at the orbital plane and a fast (2 500 km/s) optically thin stellar wind over the remainder of the accretor. The result contributes to our understanding the physical processes responsible for the outbursts.
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