EXO 033319-2554.2

P. Giommi, L. Angelini, J. Osborne, L. Stella, and G. Tagliaferri, EXOSAT Observatory, report: "The soft X-ray source EXO 033319-2554.2, serendipitously discovered in two EXOSAT CMA observations at R.A. = 3h33m19.9, Decl. = -25 54'14" (equinox 1950.0; error radius 20"), shows a 100-percent modulation of its x-ray flux with a period of 127.6 +/- 3.0 min. The lightcurve displays an on-off behavior similar to that of VV Pup, with the bright part of the cycle lasting 0.56 in phase. It also shows an eclipse-like feature, lasting 8.0 +/- 0.5 min with unresolved ingress and egress, 0.13 in phase after maximum intensity. Bright phase countrates were 0.71 and 0.65 cts/s in 1983 Aug. (polypropylene filter) and 1986 Jan. (3000 lexan filter), respectively. The soft x-ray color is inconsistent with blackbody temperatures > 25 eV. No detection was achieved in the medium energy experiment (the 90-percent confidence upper limit to the bright phase countrate is 1.0 cts/s/half). K. Beuermann, Max-Planck-Institut fur Extraterrestrische Physik, Garching; and H.-C. Thomas, Max-Planck-Institut fur Astrophysik, Garching, report low resolution (2.0 nm FWHM) CCD spectrophotometry of the only candidate counterpart visible on the POSS plate, using the ESO/MPI 2.2-m telescope at La Silla on 1987 Oct. 20 and 22. The optical spectrum was characterized by a variable blue continuum, very weak Balmer emission lines (equivalent widths of H-alpha and H-beta were 1.0 and < 0.2 nm, respectively), and pronounced TiO features. The integrated flux showed recurrent dips which indicate a period of 126.5 +/- 0.5 min. The x-ray and optical properties of EXO 033319-2554.2 strongly suggest that this source is an AM-Her-type binary system which was in a low state at the time of the optical observations. In particular, the nature and position of the 8-min eclipse-like feature seen in the soft x-ray lightcurve suggests that this could be the second AM-Her system in which an eclipse by the companion occurs."