Central Bureau for Astronomical Telegrams
IAUC 6918: 1998bw; 1998bu
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Circular No. 6918
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 1998bw IN ESO 184-G82
F. Patat, European Southern Observatory (ESO); and A.
Piemonte, Pontificia Universidad Catolica, report on their
observations of SN 1998bw with the ESO 1.5-m telescope (+ Boller &
Chivens spectrograph; 45-min exposure, range 315-1015 nm,
resolution 1.5 nm) on May 23.39 UT at La Silla: "A full reduction
of the CCD spectrogram shows no clear traces of He I lines (such as
those at 587.6 and 667.8 nm), which were clearly detected in the
type-Ib SN 1984L, a few weeks after maximum light (Harkness et al.
1987, Ap.J. 317, 355). Therefore, SN 1998bw should be classified
rather as a type-Ic event. Nevertheless, there are some
differences between SN 1998bw and known type-Ic supernovae. In
particular, the whole spectrum strongly peaks around 540.0 nm, the
O I 777.4-nm absorption is much broader than all other absorptions,
and the Fe II features are weak, making this object unique. The
most prominent features are identified as Ca II H and K, Si II
635.5-nm (possibly blended with C II 658.0-nm), O I 777.4-nm, the
Ca II triplet (at 849.8, 854.2, and 866.2 nm), and a number of Fe
II lines. The expansion velocities deduced from the minima of Ca
II H and K and Si II 635.5-nm are 11 700 and 9100 km/s,
respectively."
SUPERNOVA 1998bu IN NGC 3368
M. Centurion, Instituto de Astrofisica de Canarias; P.
Bonifacio, Osservatorio Astronomico di Trieste; N. Walton, Isaac
Newton Group of Telescopes; and D. King, Royal Greenwich
Observatory, report: "A high-resolution (about 50 000) CCD
spectrum of SN 1998bu was obtained by the Extra-solar Planet
Observational Research Team with the Utrecht echelle spectrograph
on the 4.2-m William Herschel telescope at La Palma on May 18.61
UT. Preliminary reduction reveals two interstellar components of
the Ca II doublet (K and H) from M96 at heliocentric radial
velocities of +743 km/s (equivalent width of K, EW_K = 0.0107 nm),
in agreement with the velocity of the stronger component of Na I
also reported by Munari et al. on IAUC 6902, and +750 km/s (EW_K =
0.0060 nm), which is not observed in Na I. A weak Na I component
at +722 km/s is also observed in our spectrum. Five components of
Ca II originating in the galactic interstellar medium are observed
at heliocentric radial velocities of -26 km/s (EW_K = 0.0077 nm),
-8 km/s (EW_K = 0.0154 nm), +7 km/s (EW_K = 0.0016 nm), +48 km/s
(EW_K = 0.0012 nm), and +53 km/s (EW_K = 0.0022 nm). A single
component is observed in Na I at -8 km/s, in agreement with Munari
et al. (op.cit.)."
(C) Copyright 1998 CBAT
1998 May 26 (6918) Daniel W. E. Green
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