THE ASTRONOMER Electronic Circular No 510 1991 Apr 16 20.35UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP, England. Telephone: (0256)471074 Int:+44256471074 Telex: 9312111261 Answerback: TA G JANET BOXES: GMH at UK.AC.CAM.ASTRONOMY.STARLINK or GUYH at UK.AC.SUSSEX.CLUSTER TELECOM GOLD: 10074:MIK2885 PRESTEL 256471074 ------------------------------------------------------------------- SUPERNOVA 1991T IN NGC 4527 E. Waagen, AAVSO, reports the discovery of a supernova by Stephen Knight, Waterford, ME, in NGC 4527 (R.A. = 12h31m.6, Decl. =+2 56', equinox 1950.0). The object has been independently reported by Robert O. Evans, Hazelbrook, N.S.W.; by M. Villi and G. Cortini, Monte Colombo, Italy; and by Wayne Johnson, Anza, CA. Visual magnitude estimates: Apr. 4.48 UT, [15 (Evans); 9.9, [15 (Villi and Cortini); 13.17, 14 (Knight); 14.14, 13.6 (Knight); 15.6, 13 (Evans);15.9, 13.0 (Villi and Cortini); 16.26, 13.5 (Johnson).The following position was measured by R. H. McNaught, Anglo-Australian Observatory, from an Uppsala Southern Schmidt photo taken Apr.15.5: R.A. = 12h31m36s.91, Decl. = +2 56'28".3; offsets from the nucleus are 25".7 east, 44".4 north. A nearby star of mag about 16 is located at R.A. = 12h31m42s.80, Decl. = +2 55'15".1. J. Mueller, Palomar Observatory, reports that an IVN (near-infrared) plate taken Apr.10 with the Oschin Schmidt Telescope failed to show the supernova. E. Cappellaro, Padua Observatory, reports: "G. Cutispoto (Catania Observatory) obtained the following photometry under non- photometric conditions with the European Southern Observatory 1-m telescope on Apr. 16.35 UT, V = 12.9, B-V = +0.1, U-B = -0.6, V-R = +0.1. A CCD spectrogram (range 350-830 nm) obtained by F. La Franca (Padua University) and C. Goldschmidt (Edinburgh University) at the ESO 2.2-m telescope shows a blue, almost featureless continuum, with only two strong lines having P-Cyg profile and absorption measured at 424 and 494 nm. The bright magnitude, the blue color, and the lack of the Balmer lines seem to indicate a type-I SN before maximum." R. P. Kirshner,Harvard-Smithsonian Center for Astrophysics, notes that the feature from 424 to 494 nm is also present on a spectrum obtained on Apr.16.18 UT by J. Peters with the 1.5-m reflector at the Whipple Observatory. The spectrum is highly unusual but is certainly not that of a classic type-II or type-Ia supernova near maximum; it could well be that of a type-I supernova in its very early stages. IAUC 5239 Editor: The initial alert was received from Rob McNaught on Apr 15 and relayed by cable. Denis Buczynski responded with photographic confirmation the same day. Mirko Villi's observation represents the *first supernova discovery,* pre-announcement, made by a member of UK Nova/Supernova Patrol since the programme's formation. DWARF NOVA IN OPHIUCHUS F. M. Bateson, Variable Star Section, Royal Astronomical Society of New Zealand, reported (via A. C. Gilmore, Mt. John University Observatory) the discovery on Apr. 11.62 UT of a possible nova of mag about 10 by P. Camilleri, Cobram, Victoria. A measurement by P. M. Kilmartin of a 0.15-m astrograph film taken by Gilmore on Apr. 14.72 yields the following accurate position: R.A. = 17h17m14s.01, Decl. = -26 43'28".8 (equinox 1950.0). M. Wagner, Ohio State University and Lowell Observatory, reports that his examination of a spectrogram obtained Apr. 14 UT by D. Hunter reveals strong and broad H-alpha absorption characteristic of a dwarf nova at maximum; there were two bright objects in the spectrograph's field-of-view, this object being the brighter one. Available magnitude estimates, visual unless otherwise noted: Mar. 23, [12 (Camilleri; photographic); Apr. 12.55, 10.7: (D. A. J. Seargent, The Entrance, N.S.W.); 13.46 UT, 10.5 (A. Jones and D. Lester, Nelson, N.Z.); 13.55, 10.5 (P. Williams, Heathcote, N.S.W.); 13.56, 10.5 (Seargent); 15.46, 9.9 (Jones); 15.56, 11.0 (Seargent). IAUC 5238 Guy M Hurst