Central Bureau for Astronomical Telegrams
IAUC 7054: 1998et; 1998es
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Circular No. 7054
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 1998et IN ANONYMOUS GALAXY
J. Mueller reports her discovery of a supernova (mag about 18)
on a red plate taken on Nov. 17 UT with the 1.2-m Oschin Schmidt
Telescope in the course of the second Palomar Sky Survey. SN
1998et is located at R.A. = 6h59m18s.74, Decl. = +57o44'41".0
(equinox 2000.0), which is 5".4 west and 5".4 north of the host
galaxy's center. There is no object at this position on a Palomar
Sky Survey red plate taken on 1989 Dec. 5 or on the Digitized Sky
Survey. S. Nakano, Sumoto, Japan, reports the following position
end figures measured by Y. Kushida from an unfiltered CCD image
taken in bad seeing by R. Kushida, Yatsugatake South Base
Observatory, with a 0.40-m f/6.3 Schmidt-Cassegrain telescope on
Nov. 18.773 UT, when the supernova's magnitude was measured as
18.0: 18s.36, 41".2. P. Garnavich, P. Challis, S. Jha, and R.
Kirshner, Harvard-Smithsonian Center for Astrophysics, report that
a spectrum of SN 1998et was obtained by P. Berlind with the 1.5-m
Tillinghast telescope on Nov. 19.4 UT, showing this to be a type-II
supernova exhibiting strong Balmer and helium emission lines, but
with a weak continuum and no P-Cyg absorption. The H-alpha line
has a width of 1700 km/s (FWHM), and the supernova is a member of
the peculiar type-IIn subclass. The host galaxy has a redshift of
12 100 km/s, based on the observed wavelength of narrow [O III]
500.7-nm emission.
SUPERNOVA 1998es IN NGC 632
S. Jha, P. Garnavich, P. Challis, and R. Kirshner, Harvard-
Smithsonian Center for Astrophysics, report that a spectrum of SN
1998es was taken by M. Calkins on Nov. 14.2 UT at the F. L. Whipple
Observatory 1.5-m telescope (+ FAST spectrograph). The spectrum
features a blue continuum with strong absorption features at 374,
429, and 498 nm, and a weak, broad feature at 610 nm. The spectrum
is generally similar to that of the peculiar type-Ia SN 1991T seven
days before maximum light (Filippenko et al. 1992, Ap.J. 384, L15),
with the exception of the absorption at 374 nm. The 374-nm
absoprtion was seen in the SN 1991T-like supernova 1998ab (IAUC
6858) and is presumably due to Ca II H and K. Adopting the
NASA/IPAC Extragalactic Database (NED) recession velocity of 3168
km/s for NGC 632 implies a supernova expansion velocity of 19 000
km/s, measured using the Ca II H and K feature. The NED
morphological classification of NGC 632 (Mrk 1002) is 'S0?', but it
has a nuclear starburst with a diameter of 18" (Pogge and Eskridge
1993, A.J. 106, 1405), and the position of SN 1998es is projected
near the edge of the star-forming region."
(C) Copyright 1998 CBAT
1998 November 19 (7054) Daniel W. E. Green
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