Ultraviolet and coordinated ground-based observations of Z Andromedae

Spectrophotometric observations of symbiotic stars and related objects

“…The ultraviolet spectrum of Z And has been discussed by Friedjung (1980) and by Altamore et al (1981). A very rich emission-line spectrum was observed in the ultraviolet, with excitation ranging from O i and Mg ii up to N v, O v, and Mg v. The weak continuum is inferred to arise from a hot subdwarf (T eff « 4x10 4 K, R « 2 X10 10 cm).…”

Models for symbiotic stars in the light of the data

“…The study of Z And by Altamore et al (1981) as well as new addition al arguments of mine given here for Z And and CI Cyg, suggest formation of high ionization ultraviolet lines far from the hot component of stars of this type, and can most easily be interpreted by formation around the cool component. It may be noted that emission lines of singly ionized metals also may be produced by photoionization in the atmosphere of the cool component, as for instance suggested by Boyarchuk (1967) for AG Peg.…”

“…In particular his model gives a boundary layer temperature of <! 35000°K for Z And, not very different from the black body temperature of 43000°K found by Altamore et al (1981). The flux of photons able to doubly ionize helium would be a factor of 1CF too small to produ ce the observed 1640 A flux of Z And for the latter temperature; the tern perature required in fact would be near 80000°K.…”

“…Information about normal cool giant velocities is given by Reimers (1980), where one sees that velocities can be of the order of 10 km s " , much less than the stellar surface escape velocity. Using the Altamore et al (1981) data, one finds that for the Hell 1640 A line to be formed in a wind, a mass loss rate of about 3-8x10 -' M w yr -' is required. Taking the Kudritzki and Reimers (1978) constant for the red giant mass loss formula, the expected mass loss rate of the cool star of Z And if it was single is 3x10~°M yr -1 , when the star is supposed to have a mass of 3 M 9 .…”

Z Andromedae: the prototype?

“…At high resolution the emission lines appear narrow. The relative intensity of intercombination lines of CIII, NIII and OIV suggests an electron density of about 2x10''^cm (Altamore et al 1981). At low resolution ( Figure 1) a weak continuum is detectable with a depre£ sion near 2200 A suggesting an interstellar extinction of E(B-v) = 0.35» According to results we have just obtained, the continuum of the deredden ed spectrum ( Figure 2) can be fitted by the sum of two components: (a) a hot black body with T~105 0 K, and (b) a nebular type continuum with T * 1 ,5x10^°K, for which free-free, bound-free and two photon (negligie .…”