Image-tube spectroscopic studies of rapid variables .II. Spectroscopic observations of WZ Sagittae during the 1978 december outburst.

Spectroscopic observations of WZ Sge during the outburst in 1978 December reveal the occurrence of a velocity variation with an amplitude of K₁ = 160 km s^-1 in the photometric period. This variation is interpreted as resulting from the orbital motion of the nova component and indicates: (1) that no outward expansion of the luminous material occurred during the outburst; (2) that the dwarf nova, or material immediately surrounding it, was the source of the outburst; (3) that the mass function of the system is f(M) = 0.024 M_sun. Various observational and theoretical constraints limit the range of possible masses of the dwarf nova to 0.004 ≤ M₁ ≤ 0.48 M_sun, the masses of the secondary star to 0.06 ≤ M₂ -≤ 0.25 M_sun, and the orbital inclination to 30° ≤ i ≤ 70°. With less certainty, these ranges are further limited to: 0.19 ≤ M₁ ≤ 0.48 M_sun and 0.15 ≤ M₂ ≤ 0.25 M_sun, if i = 70°, and to 0.004 ≤ M₁ ≤ 0.03 M_sun, 0.06 ≤ M₂ ≤ 0.07 M_sun, if 50° ≤ i ≤ 60°.

It is suggested: (1) that the primary is a white dwarf; (2) that the secondary star may be a normal late-type M dwarf and may be detectable spectroscopically at minimum light by observing in the infrared; (3) that improved spectroscopic observations at minimum light will confirm that the double emission from the accretion disk shows the same velocity variation as observed for the nova component during the outburst.

It is concluded that the outburst of WZ Sge more nearly resembles those observed in 55 Cyg than it does the explosions occurring in other novae and recurrent novae, and it appears possible that the masses of the component stars in these two systems are also rather similar.