[Previous] | [Session 101] | [Next]
G.J. Schwarz, S. Starrfield (Arizona State University), P.H. Hauschildt (University of Georgia, Athens), S.N. Shore (Indiana University South Bend)
Nova LMC 1991 (hereafter LMC 91) was the intrisically most luminous nova, and one of the fastest (t3 = 6 ± 1 days), yet observed. It was discovered on 18.3 April, 1991 (Liller, IAUC 5244) at mv = 12, although UK Schmidt J (4000 - 5400Å) plates show that LMC 91 steadily increased in brightness from a possible pre-outburst magnitude of mV ~ 20.5 in early April. It reached mVmax ~ 9 on 24 April. The slow rise to maximum was very unusual, showing behavior more closely resembling a slow nova. The combination of the rapid discovery announcement and a very slow pre-maximum rise permitted many IUE and optical observations. The 20.0 April optical spectrum showed strong hydrogen and iron multiplet P Cygni lines; most other novae with pre-maximum spectra (with the exception of DQ Her) show only blue shifted absorption lines. The IUE spectrum on that date, the earliest UV spectrum ever obtained of a nova in outburst, showed the bulk of the flux being emitted below 2300Å. By 22.8 April, the UV spectral peak had shifted to \lambda > 2500 Å\ and the spectrum was similar to the pre-maximum spectra seen in Nova Cyg 1992.
The best agreement between the observations and the synthetic spectra (calculated with spherical, NLTE, line-blanketed {\tt PHOENIX} model atmospheres) requires a metallicity Z = 0.1Z\odot. This is significantly lower metallicity than the canonical LMC value of 1/3 used to successfully model nova LMC 1988 #1 (Schwarz et al. 1998, MNRAS, in press). The extreme brightness and low metallicity of LMC 91 may confirm recent hydrodynamic calculations that metallicity is inversely correlates with luminosity if mixing occurs during the thermonuclear runaway (Starrfield et al. 1998, MNRAS, 296, 502).
The author(s) of this abstract have provided an email address for comments about the abstract: schwarz@hydro.la.asu.edu