First ultraviolet observations of two new cataclysmic variables 1E 0643-1648 and 4U 1849-31.

Abstract

The two hard X-ray sources 1 E0643-1648 and 4U 1849-31 have been observed in the range 1200-3200 Å with I.U.E.. They show ultraviolet spectra typical of cataclysmic variables. The distances inferred from the ultraviolet interstellar extinction are 300 pc and 600 pc respectively for 1 E0643-1648 and 4U 1849-31.

The line spectrum is characterized for both sources by strong resonance lines in emission. In addition 1 E0643-t648 shows intercombination lines more typical of classical and recurrent novae.

The energy distribution from ultraviolet to optical is predicted correctly for the two sources by standard optically thick accretion disc models, with derived disc accretion rates implying the existence of a large soft X-ray emission. Ultraviolet and optical data suggest that both sources could be intermediate between "polar" and non-magnetic systems.