The structure of jets launched from post-AGB binary systems

Abstract

Context. In this paper, we focus on post-asymptotic giant branch (post-AGB) binaries and study the interaction between the different components of these complex systems. These components comprise the post-AGB primary, a main sequence secondary, a circumbinary disk, as well as a fast bipolar outflow (jet) launched by the companion. We obtained well-sampled time series of high resolution optical spectra over the last decade and these spectra provide the basis of our study. Aims. We aim to use the time-series data to quantify the velocity and density structure of the jets in nine of these post-AGB binaries. This complements our earlier work and this amounts to the analyses of 16 jet-launching systems in total. Methods. The jet is detected in absorption, at superior conjunction, when the line of sight towards the primary goes through the bipolar cone. Our spectral time series scan the jets during orbital motion. Our spatio-kinematic model is constrained by these dynamical spectra. We complement this with a radiative-transfer model in which the Balmer series are used to derive total mass-loss rates in the jets. Results. The jets are found to be wide (> 30°) and display an angle-dependent density structure with a dense and slower outer region near the jet cone and a fast inner part along the jet symmetry axes. The deprojected outflow velocities confirm that the companions are main sequence companions. The total mass-loss rates are large (10−8 − 10−5 M⊙ yr−1), from which we can infer that the mass-accretion rates onto the companion star must be high as well. The circumbinary disk is likely the main source for the accretion disk around the companion. All systems with full disks that start near the sublimation radius show jets, whereas for systems with evolved transition disks this lowers to a detection rate of 50%. Objects without an infrared excess do not show jets. Conclusions. We conclude that jet creation in post-AGB binaries is a mainstream process. Our geometric spatio-kinematic model is versatile enough to model the variety of spectral time series. The interaction between the circumbinary disks and the central binary provide the needed accretion flow, but the presence of a circumbinary disk does not seem to be the only prerequisite to launch a jet.