Multiwavelength analyses of the extraordinary nova LMC 1991

LMC 91 was a very fast, classical nova and the brightest nova ever observed in the Large Magellanic Cloud. It was extensively observed during both its early optically thick and its nebular evolution in the optical and UV wave length regions. We successfully fit all the optically thick spectra using a grid of spherically symmetric, non-LTE, line-blanketed, expanding syntheti c spectra created with the model atmosphere code PHOENIX. The emission line s of the nebular spectra have been fitted using an optimization technique f or the emission-line luminosities predicted by the photoionization code CLO UDY. Our analyses show the following: the bolometric luminosity was super-E ddington before visual maximum and reached LBolmax similar to 6x10(5) L-., the ejected mass was similar to 3x10(-4) M-., and nuclear burning on the wh ite dwarf ceased after similar to 100 days. The elemental abundances (by nu mber) with respect to solar of the ejecta are He/H=0.8 +/-0.2, C/H=5(-2)(+2 .5) N/H=85(-17)(+22) O/H=6.5(-1.5)(+2.5) and all other elements similar to0 .1. These abundances were determined from both the optically thick and nebu lar analyses. The extreme luminosity, high ejected mass, rapid turn-off tim e, and low metallicity (except for enhanced CNO) represent the extreme valu es of observational nova parameters and thus present interesting challenges for understanding the nature of the outburst of LMC 91.