Central Bureau for Astronomical Telegrams
IAUC 3537: SN IN NGC 6946
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Read IAUC 3538
Circular No. 3537
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-864-5758
SUPERNOVA IN NGC 6946
N. Panagia, on behalf of the ESA-SRC Team for Supernova Observations,
communicates: "Low-resolution IUE observations have been
made at the Vuspa Station with the short-wavelength (Oct. 30, Nov.
2 and 5) and the long-wavelength (Oct. 30, Nov. 1, 2 and 5) cameras.
At all epochs the spectrum is found to consist of a strong continuum
on which several absorption lines are superimposed. No emission
line can be discerned at any time. Preliminary examination of the
spectra leads to the identification of absorption lines with resonance
transitions of neutral and once-ionized atoms, i.e. O I, C I,
C II, Si II, S II, Fe II, Mn II, Al II, Mg I and Mg II, as well as
some highly-ionized species, namely Si IV, C IV and Al III. All
features are rather narrow and appear not to vary with time, suggesting
an interstellar origin, either in the disk or the halo of
both our galaxy and NGC 6946. In addition, a broad absorption
feature centered around 220 nm is clearly seen. From this a color
excess E(B-V) of 0.32 is estimated. Allowing for this reddening the
color temperature between 160 and 520 nm was found to be 13.5, 13.3
and 12.1 kK on Oct. 30, Nov. 2 and 5, respectively. The absolute
flux also decreased with time. The variations relative to the Oct.
30 observations amounted to 0.13 and 0.58 mag in the 125-190-nm
band and to 0.07 and 0.36 mag in the 190-320-nm band for Nov. 2 and
5, respectively. The FeS magnitude (520 nm) was measured to be
11.56, 11.56, 11.59, 11.57 and 11.62 on Oct. 30, 31 and Nov. 1, 2
and 5, respectively. Adopting a distance of 3.2 Mpc the total
luminosity on Oct. 30 and Nov. 2 and 5 was 4.4 x 10**35, 4.3 x 10**35 and
3.6 x 10**35 J/s."
R. Barbon, F. Ciatti and L. Rosino, Asiago Astrophysical
Observatory, report: "Preliminary photographic UBV photometry
indicates: Oct. 29, B = 11.8; 30, U = 11.1; Nov. 2, B = 11.75, V =
11.55; 7, B = 12.1, V = 11.6; 8, U = 11.45, B = 12.0. Spectrograms
(range 380-760 nm) on Nov. 7 and 8 show an almost featureless
continuum well extended in the blue region, with no clear indication
of emission bands. Some faint absorptions are possibly present,
similar to those recorded for last year's Type II supernova in M100
at comparably early phases. The lack of the typical Type I signature
at 615 nm strongly suggests that the new supernova is of Type
II. This seems to be confirmed by the very blue color, as shown by
the U-B index, and by the absolute magnitude, estimated as MB ~
17.6 (assuming a distance of 4.2 Mpc)."
1980 November 13 (3537) Brian G. Marsden
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