Spectroscopic monitoring of the jet in the symbiotic star MWC 560

Abstract

Abstract. 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, 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. 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 components ≈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-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 of ≈900−1300 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 , which can be considered as terminal velocities v∞ 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•...

Orbital eccentricity of the symbiotic star MWC 560

“…The jet (orbit) inclination angle to the line of sight is i < 16 • , and the white dwarf accretes at a rateṀ acc ≈ 5 × 10 −7 M ⊙ (Schmid et al 2001). …”

“…In the case of MWC 560, we can estimate from the rate of accretion on the white dwarf,Ṁ acc ≈ 5 × 10 −7 M ⊙ (Schmid et al 2001), that it will take 10 6 yr to accrete ∼ 0.5 M ⊙ from the envelope of the red giant companion. Because the giant also losses mass via stellar wind, we find that the lifetime of the symbiotic phase of MWC 560 should be τ ss < ∼ 10 6 yr.…”

“…Using the value for v sin i= 8.2 ± 1.5 km s −1 (Sect.2), R g = 140 ± 7 R ⊙ , and i = 12 • − 16 • (Schmid et al 2001), we calculate P rot = 144 − 306 days. This value is considerably less than the orbital period, P orb = 1931 ± 162 days.…”

Detection of X-rays from the jet-driving symbiotic star MWC 560

“…Thus the absorption must be caused by material close to the central white dwarf. Our own calculations showed that the column density of the jet is only of the order of 10 22 cm −2 Schmid et al 2001) or below, thus the high column density derived from our data cannot be attributed to the jet.…”

“…While these two objects are seen at high inclinations, in MWC 560 (or V694 Mon) the jet axis is practically parallel to the line of sight (Tomov et al 1990;Schmid et al 2001). This special orientation allows one to observe the outflowing gas as line absorption in the source spectrum.…”