Spectroscopic observations of the X-ray nova A 0620-00.

Spectroscopic observations of the X-ray nova A0620-00 are reported which cover the interval from September 8, 1975, to May 5, 1976, inclusive. The features seen in the spectrum include emission lines of H-alpha, H-beta, H-gamma, He I, He II, and N III, broad absorption underlying the Balmer emission, and interstellar absorption lines. The H-alpha emission is sometimes double, with variable velocity separation and equivalent widths. The spectrum has some similarity in its later stage to that of a dwarf nova, but at no time so far has it resembled the spectrum of a common nova. The source's distance is either about 1 or 15 kpc; the smaller value is favored. Models of the outburst event in terms of a binary system, involving accretion on to a neutron star or runaway nuclear burning on a white dwarf, are briefly discussed with regard to periodicities, X-ray heating, and evolutionary origin.