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 absorp tions in the symbiotic system MWC 560, obtained with the FEROS echelle spec trograph 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 ou t owing 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, He I, Na I, Ca II 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. Therefor e they can be attributed to the irradiated (chromospheric) layers of the ne utral part of the accretion disk. The fluxes of forbidden emission lines ar e practically constant because they originate in a much larger volume. The structure and variability of the jet absorptions indicate the presence of t hree distinct out ow 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 out ow region co vering the continuum source and up to about half of the line emission from the disk. This region shows repeatedly high velocity components <approximat e to>1800-2500 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-correlate d and therefore closely related to the low velocity absorptions of region I . The life time of the high velocity components suggests that region II ext ends to about one to a few AU from the jet source; III. A steady ow at an i ntermediate velocity of <approximate to>900-1300 km s(-1) at a distance of the order similar to 10 AU from the jet source. This component covers the h ot 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), which can be considered as terminal velocities v(infinity) of the j et out ow. The components disappear during the following several weeks as e xpected for the end of an occultation phase of the red giant by the collima ted jet occuring probably regularly once per binary orbit. Several fast mov ing (1300-1700 km s(-1)), narrow absorptions are present in the Ca II reson ance lines. The high speed, low column density, and the long life time (sim ilar to months) suggest that these are radiative bow shocks in the jet coco on generated by the collision of the transient high velocity components wit h slower moving jet material. A geometric model for the jet out ow in MWC 5 60 is presented. System parameters are derived based on our spectroscopic d ata and previous studies. Beside other parameters a binary separation of th e order 4 AU, a jet inclination of <16<degrees>, a mass accretion rate of 5 x 10(-7) M. yr(-1) and a jet out ow rate larger than 7 x 10(9) M. yr(-1) a re derived.