Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html Phone 617-495-7244/7440/7444 (for emergency use only) Circular No. 6899 1998 May 10 (6899) Daniel W. E. Green SUPERNOVA 1998bu IN NGC 3368 Mirko Villi, Forli, Italy, reports his discovery on CCD images taken on May 9.9 UT of an apparent supernova (mag about 13) located about 60" north of the center of NGC 3368 = M96. Villi notes that a previous CCD image taken on Apr. 21.9 shows no object in this position, neither is anything visible on several atlases of galaxy images. S. Nakano, Sumoto, Japan, reports that M. Aoki (Toyama) has obtained a CCD image of SN 1998bu (V = 11.8) on May 10.618 with a 0.43-m reflector in bad weather conditions, from which the following precise position was measured: R.A. = 10h46m46s.03, Decl. = +11o50'07".1 (equinox 2000.0), which is 4".3 east and 55".3 north of the center of NGC 3368. No star was visible on previous frames of this galaxy taken by Aoki. B. A. Skiff, Lowell Observatory, reports that he viewed the apparent supernova on May 10.33 UT at visual mag perhaps 12.0-12.5. D. Hanzl, Brno, Czech Republic, reports that he imaged SN 1998bu on May 10.835 at V = 12.37 with a 0.40-m reflector + CCD; he gave the offset as 49" north of the galaxy's center. Circular No. 6902 1998 May 13 (6902) Daniel W. E. Green SUPERNOVA 1998bu IN NGC 3368 U. Munari, R. Barbon, L. Tomasella, and M. Rejkuba, Asiago Astrophysical Observatory, communicate: "Echelle CCD spectra of SN 1998bu obtained with the Asiago 1.82-m telescope during May 11.81- 11.90 UT reveal strong interstellar Na I D absorption. The Na I absorption from M96 is seen at heliocentric radial velocity +744.8 +/- 0.3 km/s, with an equivalent width for the Na I D_1 of 0.035 nm, which corresponds to E(B-V) = 0.15 according to the Munari and Zwitter (1997, A.Ap. 318, 269) calibration. The Na I absorption arising inside our Galaxy is seen at heliocentric radial velocity -6 +/- 1.5 km/s, with a Na I D_1 equivalent width of 0.019 nm and corresponding E(B-V) = 0.06." R. Evans and W. Wild, University of Chicago, report the following photometric magnitudes obtained with the Yerkes 1-m reflector during May 11.13-11.15 UT: B = 13.1, V = 12.7, R = 12.3, I = 12.2 (comparison star HR 1433). L. Boschini, Bergamo, Italy, reports the following position for SN 1998bu (cf. IAUC 6899) from an unfiltered CCD image obtained on May 10.84 UT with a 0.25-m telescope: R.A. = 10h46m46s.01, Decl. = +11o50'07".5 (equinox 2000.0), mag 12.6. Identical positions have been measured by D. Hanzl, Brno, Czech Republic, and by G. Masi, Ceccano, Italy; Masi's unfiltered CCD image, obtained on May 10.821, yields mag 12.6. Visual magnitude estimates: May 11.83 UT, 11.9 (A. Baransky, Kiev, Ukraine); 11.88, 12.0 (K. Hornoch, Lelekovice, Czech Republic); 12.72, 12.2 (B. Monard, Pretoria, South Africa); 12.8, 12.2 (L. Kiss, Szeged, Hungary); 12.82, 12.0 (Baransky). Circular No. 6905 1998 May 14 (6905) Daniel W. E. Green SUPERNOVA 1998bu IN NGC 3368 K. Ayani, Bisei Astronomical Observatory (BAO); H. Nakatani, Fuchu, Hiroshima, Japan; and H. Yamaoka, Kyushu University, report that a wide-band spectrogram (range 400-750 nm) of SN 1998bu (IAUC 6899, 6902) was obtained with the BAO 1.01-m telescope on May 14.5 UT. Preliminary reduction reveals that it has deep and broad SI II absorption at 612 nm (at the rest frame of NGC 3368), which indicates that SN 1998bu is of type Ia. Other broad absorption lines are seen at 575, 544, 527, 486, and 427 nm. The expansion velocity derived from the shift of the Si II absorption minimun is about 11 000 km/s. P. Meikle, M. Hernandez, and A. Fassia, Imperial College, London, report: "A spectrum of SN 1998bu was obtained by J. Iglesias with the William Herschel Telescope of the Isaac Newton Group, La Palma, on May 12.9 UT. The ISIS spectrograph (range 315- 898 nm, resolution 0.8 nm) yields a spectrum of a type-Ia supernova a few days before maximum light. It is similar to the spectrum of SN 1990N at one week before B maximum (Leibundgut et al. 1991, Ap.J. 371, L23). The Si II absorption minimum is at 611.5 nm (host galaxy rest frame, adopting the heliocentric radial velocity +744.8 km/s for M96 given by Munari et al. on IAUC 6902). B. A. Skiff, Lowell Observatory, reports that C. Faranda, Jr., Lauderhill, FL, obtained a frame of NGC 3368 on May 3.14 UT (0.25-m reflector + unfiltered CCD) that shows a prediscovery image of SN 1998bu at mag 16.5 +/- 0.3 (using a V-band comparison-star sequence). Visual magnitude estimates: May 13.22 UT, 12.1 (C. E. Spratt, Victoria, BC); 13.86, 12.2 (A. Baransky, Kiev, Ukraine); 13.90, 11.8 (K. Hornoch, Lelekovice, Czech Republic). Circular No. 6921 1998 May 28 (6921) Daniel W. E. Green UPERNOVA 1998bu IN NGC 3368 R. Evans and W. Wild, University of Chicago, report additional magnitudes (cf. IAUC 6902) for SN 1998bu, obtained with the Yerkes 1-m telescope (estimated error +/- 0.15 mag): May 21.10 UT, I = 12.0; 21.11, R = 11.8; 21.13, B = 12.4, V = 12.0. Absolute calibration was done using HR 1433, HR 4983, and HR 3427. CCD photometry by D. Hanzl, Brno, Czech Republic (0.40-m reflector), based on comparison star GSC 849.733 (Tycho magnitudes V = 9.73 +/- 0.03, B-V = +0.636 +/- 0.04): May 10.835 UT, V = 12.83 +/- 0.04 (revision of value on IAUC 6899); 11.861, V = 12.59 +/- 0.02; 14.848, V = 12.25 +/- 0.02, B-V = +0.40 +/- 0.02; 20.857, V = 12.01 +/- 0.04, B-V = +0.48 +/- 0.04. Circular No. 6926 1998 June 2 (6926) Daniel W. E. Green SUPERNOVA 1998bu IN NGC 3368 B. E. Schaefer, Yale University, reports the following magnitudes obtained with the 3.5-m WIYN telescope and based on ten Landolt comparison stars: May 23.18 UT, B = 12.34 +/- 0.04, V = 11.92 +/- 0.03; 26.14, 12.44 +/- 0.04, 11.94 +/- 0.03. Schaefer remarks: "Using these and other reported magnitudes (IAUC 6899, 6902, 6905, 6921), standard-template fits to the light curves of type-Ia supernovae (Schaefer 1996, Ap.J. 460, L19) suggest that peak magnitudes occurred on May 21.0 +/- 0.3, with B = 12.36 +/- 0.05, V = 11.93 +/- 0.04, and a decline rate in B from peak to 15 days later of 0.95 +/- 0.05." Circular No. 6937 1998 June 12 (6937) Daniel W. E. Green SUPERNOVA 1998bu IN NGC 3368 Additional CCD photometry by Hanzl (cf. IAUC 6921): May 28.844 UT, V = 12.28 +/- 0.01, B-V = +0.64 +/- 0.02; 29.862, 12.38 +/- 0.01, +0.71 +/- 0.09; 31.873, 12.51 +/- 0.01, +0.75 +/- 0.02; June 2.872, 12.63 +/- 0.02, +0.73 +/- 0.03; 7.870, 12.84 +/- 0.02, -; 9.860, 12.94 +/- 0.01, +1.2 +/- 0.2.