Central Bureau for Astronomical Telegrams
IAUC 7058: 1998S; 1997ab, 1998S, 1998et; C/1998 P1
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Circular No. 7058
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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SUPERNOVA 1998S IN NGC 3877
P. Garnavich, S. Jha, and R. Kirshner, Harvard-Smithsonian
Center for Astrophysics; and C. Gerardy and R. Fesen, Dartmouth
College, write: "Spectra taken with the MDM 2.4-m telescope on Oct.
27 and the 1.5-m Mt. Hopkins telescope by M. Calkins on Nov. 14
show prominent H-alpha emission with a flux of 3.6 x 10E-13 erg
cmE-2 sE-1. The H-alpha emission has a full width at the base of
14 400 km/s and three sharp and well resolved peaks at -4650, -400,
and +3700 km/s. The H-alpha line has a very different structure
than seen in the ultraviolet emission (cf. IAUC 7047), but the
H-alpha profile is also seen in He I 587.6- and 1083.0-nm and
Paschen-beta lines, and may be indicative of a strong interaction
with a circumstellar ring or disk. Photometry obtained with the
Mt. Hopkins 1.2-m telescope by A. Szentgyorgyi gives the following
magnitudes: Nov. 10.6 UT, J = 16.25, H = 14.85, K = 13.44; Nov.
14.5, U = 18.67, B = 19.09, V = 18.65, R = 17.18, I = 17.59
(uncertainties of 0.05 mag). The V-K color of > 5 magnitudes
indicates that a large infrared excess has developed, suggestive of
dust formation within the ejecta and consistent with the observed
blueshifted metal line profiles. A Tillinghast spectrum taken on
Nov. 21.5 shows a 15-percent decline in the flux of the redshifted
side of H-alpha emission relative to the blue side, when compared
to the Nov. 14 spectrum, implying continuing dust formation."
SUPERNOVAE 1997ab, 1998S, 1998et
B. E. Schaefer and B. Roscherr, Yale University, report on
photometry from three Type-IIn supernovae obtained with the 3.5-m
WIYN telescope on Nov. 21.4 UT: "SN 1997ab has B = 20.02, V =
19.92, and R = 18.74. The event was near maximum on 1996 Apr. 11
at B = 14.7 (Hagen et al. 1997, A.Ap. 324, L29), so our observation
is 954 days later with an average decline rate of 0.56 mag per 100
days. SN 1997ab provides a near-unique opportunity to observe a
supernova at a reasonable brightness at extremely late times. SN
1998S has U = 19.42, B = 19.06, V = 18.68, R = 17.23, and I =
17.73, with the R magnitude perhaps indicative of a bright H-alpha
line. SN 1998et is just past peak, with U = 18.91, B = 20.25, V =
20.19, R = 19.22, and I = 19.38. Galaxy background uncertainties
are of order 0.1 mag."
COMET C/1998 P1 (WILLIAMS)
Visual m_1 estimates by A. Hale, Cloudcroft, NM: Nov. 15.51
UT, 10.1: (0.2-m reflector; low altitude); 22.51, 9.4 (Hale, 10x70
binoculars).
(C) Copyright 1998 CBAT
1998 November 24 (7058) Daniel W. E. Green
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