Circular No. 2794 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Postal Address: Central Bureau for Astronomical Telegrams Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. Cable Address: SATELLITES, NEWYORK Western Union: RAPID SATELLITE CAMBMASS 3U 0900-40 S. Rappaport and J. McClintock, Massachusetts Institute of Technology, report that the SAS-3 group has discovered a 282s.9 +/- 0s.4 periodicity in the x-ray intensity of the x-ray/optical binary system 3U 0900-40/HD 71581. The source was detected between June 18.8 and 24.5 UT in the energy range 1.5-30 keV. The light curve has an asymmetric double pulsed structure with at least a 60 percent modulation. The source exhibited an extremely hard spectrum and a high degree of irregular variability, on time scales from seconds to hours, in addition to the periodic phenomenon. The identification is based on a positional coincidence within an uncertainty area of 0.15 square degrees (90-percent confidence) and the absence of any signal during a predicted eclipse of 3U 0900-40. The available data are not yet sufficient to define the Doppler effect due to orbital motion. CYGNUS X-3 E. Kendz Orra, W. Pietsch, R. Staubert and J. Trumper, Astronomisches Institut, Tubingen, report: "Cyg X-3 was observed on Feb. 20.64 UT using a balloon borne hard x-ray telescope launched from Palestine, Texas. In the energy range 29-70 keV an intensity variation was detected that is in phase with the low energy 4h.8 sinusoidal variation. The relative amplitude at 29-70 keV is 0.37 +/- 0.19. Comparing this value with the results of Uhuru (2-6 keV) and OSO-7 (7-10 keV), there is no indication for an energy dependence of the relative amplitude." HD 87643 W. Wamsteker, European Southern Observatory, reports: "Recent observations of the star HD 87643 (R.A. = 10h02m49s, Decl. = -58o25'.4, equinox 1950.0; spectral type Be) give a visual magnitude V = 7.40. This is one magnitude brighter than in 1968 (Hiltner et al. 1968, Astrophys. Lett. 2, 153). The infrared flux also seems to have changed by Delta-(K - L) = +0.72 compared with Allen (1973, Monthly Notices Roy. Astron. Soc. 161, 145). Spectrum scans indicate an increase in expansion velocity. This star might be in an active phase as a slow nova, possibly representing the formation of an eta Car-type object. Observations of this object in any mode could therefore be of great interest." 1975 June 30 (2794) Brian G. Marsden
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