Transient jets in the symbiotic prototype Z Andromedae

Abstract

We present the development of collimated bipolar jets from the symbiotic prototype Z And that appeared and disappeared during its 2006 outburst. We monitored the outburst with optical high-resolution spectroscopy and multicolor UBVRC photometry. In 2006 July, Z And reached its historical maximum at U 8.0. After 1 mag decline in mid-August, it kept its brightness at a high level of U 9 up to 2007 January. During this period, rapid photometric variations with Δm 0.06 mag on the timescale of hours developed. Simultaneously, high-velocity satellite components appeared on both sides of the Hα and Hβ emission line profiles. Their presence was transient, being detected to the end of 2006. They were launched asymmetrically with a red/blue velocity ratio of 1.2-1.3. From about mid-August onward they became symmetric at 1200 km s-1, reducing the velocity to 1100 km s-1 at their disappearance. The spectral properties of these satellite emissions indicated the ejection of bipolar jets collimated within an average opening angle of 61. If the jets were expelled at the escape velocity, then the mass of the accreting white dwarf is MWD 0.64 M⊙. We estimated the average outflow rate via jets to M⊙ yr-1, during their August-September maximum, which corresponds to the emitting mass in jets, Memjet 6 × 10-10(Rjet/1 AU)3/2 M⊙. During their lifetime, the jets released a total mass of Mtotaljet 7.4 × 10-7 M⊙. Evolution in the rapid photometric variability and asymmetric ejection of jets around the optical maximum can be explained by a disruption of the inner parts of the disk caused by radiation-induced warping of the disk.