Circular No. 5408 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Postal Address: Central Bureau for Astronomical Telegrams Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. Telephone 617-495-7244/7440/7444 (for emergency use only) TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505 MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN SUPERNOVA 1991bg IN NGC 4374 M. Della Valle, J. Danziger, and C. Gouiffes, European Southern Observatory, communicate: "A CCD spectrogram (range 400-840 nm, resolution about 2 nm) of SN 1991bg was obtained on Dec. 15.4 UT with the 3.54-m New Technology Telescope (+ EMMI) at La Silla. The spectrum is dominated by strong absorptions of Si II (635.5, 597.2, 564.0, 545.4 nm) and Fe II (492.4 nm), indicating a type-Ia superno- va. The expansion velocity deduced from the minima of the Si II 635.5-nm absorption is 10 200 km/s. Preliminary photometric mea- surements give V = 14.11 +/- 0.02 and B = 14.87 +/- 0.03. This im- plies E(B-V) about 0.7-0.9 and B(0) = 11.9 at maximum light if it is a normal type-Ia object. This compares with Bmax = 12.2 for SN 1957B in the same galaxy. Alverado and Wenderoth (IIT) report simi- lar colors obtained from CCD photometry on the 0.90-m Dutch tele- scope for Dec. 16.3. If the SN is normal, all these measurements are consistent (within +/- 0.2 mag), with the age at Dec. 15 being 0-7 days past maximum and with significant reddening." M. M. Phillips and M. Hamuy, Cerro Tololo Interamerican Obser- vatory, report: "Low-dispersion CCD spectrophotometry (range 350.0- 730.0 nm) of SN 1991bg was obtained by J. Maza (University of Chile) on Dec. 15.35 UT with the CTIO 4.0-m telescope. The spectrum resem- bles that of a type-Ia event within about 1 week of maximum, but with clear peculiarities (cf. IAUC 5403, 5405). The following mag- nitudes were synthesized from an observation obtained through a 7" slit: V = 14.03, B-V = +0.86. Direct CCD images were obtained by N. Caldwell (F. L. Whipple Observatory) on Dec. 17.35 UT with the CTIO 0.91-m telescope. A preliminary reduction of these data yields V = 14.05 and B-V = +0.89, suggesting that the supernova is near maximum. The red color is also unusual for a type-Ia supernova at maximum. Although NGC 4374 has a small dust lane near its nucleus (see Gallagher 1986, PASP 98, 81), the supernova is located well outside this region. Because of this and the lack of evidence for interstellar Na I D absorption lines in Maza's low-dispersion spec- trum, we consider it unlikely that the supernova magnitudes and col- ors have been affected significantly by dust extinction. Hence, if SN 1991bg has actually reached maximum, it would appear to be as much as 3 mag fainter in B than the type-I SN 1957B which occurred in the same galaxy." Visual magnitude estimates: Dec. 14.167 UT, 13.8 (S. Pesci, Milan, Italy); 15.52, 13.9 (W. Johnson, Anza, CA). 1991 December 18 Daniel W. E. Green