Repeated transient jets from a warped disk in the symbiotic prototype Z And: A link to the long-lasting active phase

TL;DR

This study documents repeated collimated jets from Z And during its prolonged active phase, linking jet ejections to disk warping and enhanced accretion processes that sustain long-term activity.

Contribution

It reveals the connection between transient jets, disk warping, and long-lasting activity in symbiotic binaries, supported by high-resolution spectroscopy and photometry.

Findings

Jets re-emerged during 2009-10 outburst with similar properties to 2006.

Jet ejections coincide with rapid photometric variability on hour timescales.

Disk warping caused by increased luminosity likely triggers jet formation.

Abstract

Active phases of some symbiotic binaries survive for a long time from years to decades. The accretion process onto a white dwarf (WD) sustaining long-lasting activity, and sometimes leading to collimated ejection, is not well understood. We present the repeated emergence of highly collimated outflows (jets) from the symbiotic prototype Z And during its 2008 and 2009-10 outbursts and suggest their link to the current long-lasting (from 2000) active phase. We monitored Z And with the high-resolution spectroscopy, multicolor $UBVR_{\rm C}$ and high-time-resolution photometry. The well-pronounced bipolar jets were ejected again during the 2009-10 outburst together with the simultaneous emergence of the rapid photometric variability ($\Delta m \approx 0.06$ mag) on the timescale of hours, showing similar properties as those during the 2006 outburst. These phenomena and the measured disk-jets connection could be caused 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 outburst maxima signals a transient accretion at rates above the upper limit of the stable hydrogen burning on the WD surface. 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 Z And.