The ultraviolet spectrum of 2S 0921‐630

An ultraviolet spectrum of the long‐period low‐mass x‐ray binary 2S 0921‐630 was obtained with IUE near the time of partial eclipse of the accretion disk by its G‐giant companion star. The short‐wavelength spectrum shows a very weak continuum, with emission lines of N v, Si iv, C iv, and He iv. The strength of these lines during eclipse implies that the volume of the line‐emitting region must be larger than that which is eclipsed in the optical light curve. The UV spectrum is similar to that of Cyg X‐2 (when it is on the x‐ray flaring branch of x‐ray color‐color plots) although the weakness of N v may indicate a lower abundance for that element. Alternatively, the apparent absence of N iii and N iv in 2S 0921‐630 suggests the upper portion of the accretion disk in 2S 0921‐630 may be hotter than that in Cyg X‐2.