Central Bureau for Astronomical Telegrams
IAUC 4435: 1987A; N Cyg 1986
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Circular No. 4435
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 617-495-7244/7440/7444
SUPERNOVA 1987A IN THE LARGE MAGELLANIC CLOUD
R. Kirshner, Center for Astrophysics; G. Sonneborn, IUE
Observatory, Goddard Space Flight Center; A. Cassatella, R. Gilmozzi,
and W. Wamsteker, ESA IUE Observatory; and N. Panagia, Space
Telescope Science Institute (for the European Target-of-Opportunity
team) report: "Measurements with the Fine Error Sensor on the IUE
satellite show that the rapid decline in visual light (which followed
the maximum on May 20) ended on about June 25 at m(FES) = 4.2
+/- 0.1. Since then, more than 40 measurements show that the decline
has been linear with a slope of -0.0093 +/- 0.001 mag/day. This is
in good accord with the interpolated slope reported by Suntzeff and
Hamuy (IAUC 4427) and contains measures on 11 dates during the
interval of bad weather in Chile. The observed decline rate coincides
with the average for SN II-P at late times and may be related
to radioactive energy sources. Photometric behavior in the ultraviolet
is quite different: the band from 270-320 nm reached a maximum
near May 20 and declined by a factor of two by June 25, but
has not shared the subsequent linear decline of the optical emission.
This band increased by 0.2 mag through Aug. 10. The short-
wavelength ultraviolet continuum (180-195 nm) also showed a gradual
increase of about 0.4 mag from May 24 through Aug. 10. As reported
earlier by Wamsteker et al. (IAUC 4410), at the shortest UV
wavelengths (180 nm), the increase is due principally to the emergence
of narrow (FWHM < 1500 km/s) emission lines, including N V (124.0
nm), Si IV (139.7 nm) blended with O IV (140.5 nm), N IV] (148.5
nm), He II (164.0 nm), N III] (175.0 nm) and possibly C III] (190.9
nm). The N III] line is the strongest: it was not detectable on
May 19 and barely visible on May 30. All these lines have grown
stronger with time through Aug. 3, when the N III] had an observed
flux of about 5 x 10E-13 erg/cm2/s. The presence of narrow lines from a
gas which is nitrogen-rich suggests circumstellar material
photoionized by the UV burst from the SN and raises the possibility of
future interaction between the expanding debris and this material."
NOVA CYGNI 1986
Visual magnitude estimates (cf. IAUC 4419): June 29.93 UT,
13.0 (M. Verdenet, Bourbon-Lancy, France); July 3.93, 12.6 (G. M.
Hurst, Basingstoke, England); 5.03, 12.8 (S. Korth, Duesseldorf, W.
Germany); 16.94, 13.8 (R. Monella, Covo, Italy); 25.92, 12.5
(Hurst); Aug. 2.9, 12.6 (M. V. Zanotta, Milan, Italy).
1987 August 14 (4435) Daniel W. E. Green
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