H0139-68

P. C. Agrawal and A. R. Rao, Tata Institute of Fundamental Research; G. R. Riegler, Jet Propulsion Laboratory; and A. J. Pickles and N. Visvanathan, Mount Stromlo and Siding Spring Observatories, telex: "We have discovered a new variable soft x-ray source, H0139-68, and its optical identification with an AM-Her-like cataclysmic variable. The x-ray source, originally detected with the low-energy detectors of the HEAO A-2 experiment, was found to be highly variable over periods as short as 3 hr, with maximum flux of ~ 6 x 10**-14 J m**-2 s**-1 in the band 0.15-0.4 keV. No flux was detected above 0.4 keV, indicating a very soft spectrum (i.e., < 3 x 10**6 K). Observation of the H0139-68 error box with the image proportional counter of the Einstein Observatory confirmed a bright variable x-ray source and yielded the following position (equinox 1950.0): R.A. = 1h39m36s, Del. = -68o07'57". During IPC observations lasting for 1800 s, the source count-rate decreased from ~ 2 cts/s to ~ 1 ct/s. There is indication of flickering on a timescale of 20 s or less. The x-ray source has been identified with a star at R.A. = 1h39m37s.5, Decl. = -68o08'32", which is within 36" of the x-ray source position. Time-resolved spectrophotometry of the star over 3 hr with the PCA on the Mt. Stromlo 1.9-m telescope shows a variation between V = 14.9 and V = 16.4 with a period of 110 min. Spectra are dominated by emission lines of H I, He I 447.1 and 587.5 nm, He II 468.5 and 541.1 nm, C III and N III 464.7 nm throughout the period. The mean radial-velocity curve of the emission lines varies from +340 to -150 km/s, leading the light curve by 0.1 period. The continuum changes with phase and is reddest at maximum."