FAR-UV SPECTRAL VARIABILITY IN THE GRAVITATIONAL LENS CANDIDATE UM-425

A comparison of recently acquired far-UV spectra with data obtained ne arly 10 months earlier indicates changes have occurred in both absorpt ion and ionization levels associated with Broad Absorption Line (BAL) structure in the QSO UM 425, a candidate gravitationally lensed system . These observations are compared with the initial discovery of O VI a nd N V BAL structure previously found with the international Ultraviol et Explorer (IUE), that suggests outflow of highly ionized material wi th speeds up to similar to -12,000 km s(-1) in the QSO (z = 1.471) res t frame. Discrete absorption components in the O VI BAL trough, occurr ing at velocity intervals of similar to 2100 km s(-1) up to the termin al speed, are also evident in the Lyman-alpha lambda 1216 line profile , which is affected by similar absorption structures within the veloci ty-broadened N V lambda 1240 BAL trough. The greatest temporal change in relative optical depth occurs at velocity intervals which correspon d to the BAL absorption components. Significantly, a decrease in O VI BAL absorption over the entire BAL velocity range was accompanied by b oth an increase in ionization level, indicated by enhanced O VI emissi on, and by a strengthening of other moderate-to high-excitation emissi on lines, that include S VI(1) lambda lambda 937,945, C III(1) lambda 977, N III(1) lambda 990, and S IV(1) lambda lambda 1063,1073. These o bservations are relevant to time-delay studies of UM 425 because the t emporal changes observed in intrinsic QSO ionization are small compare d with the estimated delay time between the images in the system.