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IAUC 5362: N LMC 1991; 1991n

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                                                  Circular No. 5362
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

     S. Shore, Computer Sciences Corporation and Goddard Space
Flight Center; S. Starrfield, Arizona State University; and G.
Sonneborn, Goddard Space Flight Center, report:  "Low-dispersion
spectra (115.0-200.0 nm, resolution 0.6 nm) of Nova LMC 1991 were
obtained with the International Ultraviolet Explorer satellite on
Sept. 2.29 and 29.61 UT, when the integrated ultraviolet fluxes
(120-195 nm) were 9.27 and 7.87 x 10E-12 erg sE-1 cmE-2, respectively.
The value on Sept. 29 corresponds to a dereddened ultraviolet
luminosity of 2000 L(sun) [assuming E(B-V) = 0.15 and a distance to
the LMC of 55 kpc].  The ultraviolet spectrum obtained on Sept. 29
shows strong nebular emission lines with the following integrated
fluxes (10E-12 erg sE-1 cmE-2):  N V 120-nm, 22.9; N IV 149-nm,
12.1; C IV 155-nm, 12.9; N III] 175-nm, 6.66; and C III] 190-nm,
3.87.  The FWHM of the stronger lines is 2700 km/s.  He II 164-nm
was absent on the Sept. 2 spectrum and weakly present on Sept. 29.
The appearance of He II suggests that the far-ultraviolet optical
depth of the ejected shell is decreasing.  O III] 167-nm is also
present but was too weak to measure.  The changes in the emission
line fluxes over the past few weeks indicate that the ionization is
continuing to increase, as both the N IV/N III and C IV/C III emission
line ratios have increased by 20 +/- 7 percent since Sept. 2,
but N V/N IV has remained constant.  The increase in ionization is
expected from our previous studies of novae emission lines.  Since
the source became optically thin in Fe II about 100 days prior to
these spectra, the integrated ultraviolet flux has remained virtually
constant even though the ionization state has steadily increased.
We are continuing our IUE observations, and urge continued
monitoring of this star by ground-based observers."

     Total visual magnitude estimates (cf. IAUC 5356): Oct. 3.09 UT,
10.2 (A. Pereira, Cabo da Roca, Portugal, 0.15-m reflector); 4.89,
9.9 (A. Boattini, Florence, Italy, 0.33-m reflector); 6.27, 9.8 (C.
S. Morris, Lockwood Valley, CA, 0.51-m reflector; 10' tail in p.a.
about 250 deg); 8.29, 9.6 (C. Spratt, Victoria, BC, 0.20-m reflector);
9.11, 9.9 (J. E. Bortle, Stormville, NY, 0.32-m reflector).

1991 October 10                (5362)             Daniel W. E. Green

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