Repeated Transient Jets from a Warped Disk in the Symbiotic Prototype Z And: A Link to the Long-lasting Active Phase.
Authors:
A. Skopal, T. N. Tarasova, M. Wolf, P. Dubovsky, I. Kudzej
Image & caption:
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Image caption::
Simple illustration of the outburst of Z And with jets (left) and its observational justification (mid and right). A dense disk (yellow) expands from the burning WD (the red star), whose hard radiation powers a fast wind (blue; broad wings of the line profile – mid) and warps the inner disk (rapid light variability - right). Its material rapidly re-accretes, and thus sustains the high luminosity for a long time. The unused fraction of its mass is ejected in the form of jets (violet; satellite components in the line profile – mid). [Credit: A. Skopal]
Description:
Active phases of some symbiotic binaries survive for a long time of years to decades. Accretion process onto a white dwarf (WD) from its red giant companion sustaining long-lasting activity, sometimes leading to collimated ejection, is not well understood. During the 2009-10 outburst of the symbiotic prototype Z And we measured again the well-pronounced bipolar jets together with the simultaneous emergence of the rapid photometric variability on the time-scale of hours, as during the 2006 outburst. We explained these phenomena by the radiation-induced warping of the inner disk due to a significant increase of the burning WD luminosity. Ejection of transient jets by Z And around outbursts maxima signals a transient accretion at rates above the upper limit of the stable hydrogen burning on the WD surface, and thus proves the nature of Z And-type outbursts. The enhanced accretion through the disk warping, supplemented by the accretion from the giant's wind, can keep a high luminosity of the WD for a long time, until depletion of the disk. In this way the jets provide a link to long-lasting active phases of symbiotic stars.
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