OPTICAL AND ULTRAVIOLET SPECTROPHOTOMETRY OF THE ONEMG NOVA V838 HERCULIS 1991

We present an analysis of-optical and UV spectra of the fast nova V838 Herculis 1991. IUE observations began on 1991 March 25 and continued through 1991 August 20, while optical observations began on 1991 March 29 and continued through 1991 August 20. We determine a value for the reddening of E(B-V)similar to 0.5+/-0.1 and a distance of similar to 3+/-1 kpc based both on our own observations and on those of other gro ups. This nova was remarkable in being both fast and optically thick i n the UV at maximum light. Our spectra show strong lines of helium, ne on, sulphur and nitrogen. In contrast, oxygen lines were never present in our UV spectra and very weak in our optical spectra. We use a new optimization method to perform an abundance analysis of the spectra, a nd find that carbon, nitrogen, neon, silicon and sulphur are overabund ant with respect to solar material by factors ranging from 5 to 37, wh ile helium and oxygen are both underabundant by a factor of 0.3. Our b est model is obtained with a luminosity for the central source of 5.1 x 10(36) erg s(-1), indicating that this nova may have turned off by t wo months after outburst. We also find an ejected mass for this nova o f M(ej) similar to 1.8 x 10(-4) M(.). Based on both the characteristic s of the outburst and our observed abundances, we suggest that this ou tburst occurred on a very massive ONeMg white dwarf.