Spectroscopic monitoring of the jet in the symbiotic star MWC 560 - I. Spectroscopic properties, general outflow structure and system parameters

We present the results of an intensive monitoring program of the jet absorptions in the symbiotic system MWC 560, obtained with the FEROS echelle spectrograph at the ESO 1.5 m Telescope. MWC 560 is a unique jet source because the line of sight lies practically parallel to the jet axis so that the outflowing gas is seen as absorption in the continuum of the accreting object, in the emission line spectrum of the accretion disk and temporary also in the spectrum of the red giant companion. Highly variable, blue-shifted jet absorption components, due to H i ,H ei ,N ai ,C aii and Fe ii are observed, which are detached from the undisplaced, narrow emission line components. The allowed emission lines from neutral and singly ionized heavy elements vary simultaneously with the strongly variable continuum emission. Therefore they can be attributed to the irradiated (chromospheric) layers of the neutral part of the accretion disk. The fluxes of forbidden emission lines are practically constant because they originate in a much larger volume. The structure and variability of the jet absorptions indicate the presence of three distinct outflow regions along the jet axis: i. An initial acceleration region above the disk with low velocities <600 km s 1 which covers only partly the central continuum source; ii. A highly variable outflow region covering the continuum source and up to about half of the line emission from the disk. This region shows repeatedly high velocity components1800 2500 km s 1 which are decelerated to <1500 km s 1 within one to a few days. The appearance of high velocity components is anti-correlated and therefore closely related to the low velocity absorptions of region i. The life time of the high velocity components suggests that region ii extends to about one to a few AU from the jet source; iii. A steady flow at an intermediate velocity of900 1300 km s 1 at a distance of the order 10 AU from the jet source. This component covers the hot continuum source and the entire narrow line region of the accretion disk. At the beginning of our campaign region iii covers also the extended red giant companion with two absorption components at 1250 km s 1 and 1140 km s 1 ,w hich can be considered as terminal velocities v1 of the jet outflow. The components disappear during the following several weeks as expected for the end of an occultation phase of the red giant by the collimated jet occuring probably regularly once per binary orbit. Several fast moving (1300 1700 km s 1 ), narrow absorptions are present in the Ca ii resonance lines. The high speed, low column density, and the long life time (months) suggest that these are radiative bow shocks in the jet cocoon generated by the collision of the transient high velocity components with slower moving jet material. A geometric model for the jet outflow in MWC 560 is presented. System parameters are derived based on our spectroscopic data and previous studies. Beside other parameters a binary separation of the order 4 AU, a jet inclination of <16, a mass accretion rate of 5 10 7 M yr 1 and a jet outflow rate larger than 7 10 9 M yr 1 are derived.