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IAUC 4949: 1990B; N LMC 1990

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                                                  Circular No. 4949
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505

     On behalf of the Berkeley Automated Supernova Search, S. Perlmutter
and C. Pennypacker report the discovery of a mag 16 supernova in NGC
4568 (R.A. = 12h34m02s, Decl. = +11d30'.9, equinox 1950.0), in five images
obtained during Jan. 20.47 and 21.47-21.51 UT.  The supernova
is 6" west and 10" north of the galaxy's nucleus and was not present to
limiting magnitude 18 (95-percent confidence limit) on 1989 Dec. 23. NGC
4568 should not be confused with NGC 4567, which is 23" to the west and
66" to the north.

     S. Shore, Computer Sciences Corporation/GHRS; G. Sonneborn,
NASA/Goddard Space Flight Center; C. Shrader, Computer Sciences
Corporation/IUE; and S. Starrfield, Arizona State University, report:
"Analysis of IUE ultraviolet spectra from Jan. 18.05 UT shows
many high-excitation emission lines, including N V 124.0 nm,
Si IV 140.0, C IV 155.0, He II 164.0, Al III 186.0 and Al II 267.0, not
low-temperature absorption systems (cf. IAUC 4947).  The C IV, Si IV
and Al III lines have strong P-Cyg emission profiles with flat-bottomed
absorption troughs extending to -8000, -7500 and -6000 km/s,
respectively.  Mg II 280.0 nm shows emission with FWHM 4800 km/s with no
P Cyg absorption.  This remarkable spectrum and the large expansion
velocities are very similar to those seen in early ultraviolet outburst
spectra of N V693 CrA 1981 (an oxygen-neon-magnesium nova) and N U Sco
1979 (a recurrent nova).  Like these objects, N LMC 1990 may fade very
rapidly.  The total ultraviolet flux (120-330 nm) on Jan. 18.05 is
2.4 x 10**-10 erg cm-2 s-1.  With correction for typical LMC extinction
(non-30 Dor) of E(B-V) = 0.15 and a distance of 55 kpc the observed
ultraviolet luminosity is 2.8 x 10**38 erg/s.  This is approximately the
Eddington luminosity for a one solar-mass object.

     A. C. Gilmore and P. M. Kilmartin, Mount John University
Observatory, provide the following photoelectric photometry, obtained
with a 0.61-m Cassegrain reflector: Jan. 18.57 UT, V = 13.55, U-B =
-0.92, B-V = -0.34, V-R = +0.89; 20.47, 13.92, -0.84, -0.33, +0.94;
22.60, 14.52, -0.88, -0.45, +0.86.  The nearby star SAO 249266 has the
following approximate magnitude and colors: V = 9.42, U-B = +0.72, B-V
= +0.99, V-R = +0.52, V-I = +1.00.

1990 January 23                (4949)              Brian G. Marsden

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