Elemental Abundances for Nova Hercules 1991 Determined from Combined Ultraviolet and Optical Spectrophotometry

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Session 46 -- Novae
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[46.06] Elemental Abundances for Nova Hercules 1991 Determined from Combined Ultraviolet and Optical Spectrophotometry

K.M.Vanlandingham, S.Starrfield (ASU), R.M.Wagner (OSU), S.N.Shore (IUSB), G.Sonneborn (NASA/GSFC)

\noindent Nova V838 Her was discovered in outburst on 24 March 1991 and we began IUE observations on 25 March 1991, continuing through 12 June 1991. Optical observations began on 29 March 1991 and continued through 20 August 1991. This nova was remarkable in being both fast and optically thick in the UV at maximum light. Our spectra show strong lines of helium, neon, sulfur, and nitrogen. Oxygen lines were never present in our UV spectra and very weak in our optical spectra. We have used two methods to determine the reddening to Nova Her 91. First, Nova Her 91 was very similar to V1500 Cyg both in the rate of decay of the light curve, as well as the early spectral evolution. Because of this similarity we have assumed Nova Her 91 to have the same intrinsic B-V color at maximum as V1500 Cyg. Using this intrinsic color and the measured B-V color at maximum, we have determined E(B-V)$\sim$0.4. The Balmer decrement from our spectra implies E(B-V)$\sim$0.6. This result agrees well with that of Starrfield et al (1992) determined by comparing the UV flux of Nova Her 91 with that of LMC90-1. Our estimates of the distance to Nova Her 91 lie in the range from 2.9-5.1 kpc. Starrfield et al (1992) obtained a distance of 3 kpc using their comparison to LMC90-1. Woodward et al (1992) also find a distance of 3 kpc from their IR observations. As this value lies within our determined range, we adopt a distance of $\simeq$3kpc. We have performed an abundance analysis of our combined IUE and optical spectra, using CLOUDY 84, and find that helium, carbon, nitrogen, neon, and sulfur are overabundant with respect to solar material by 1.2, 12, 60, 35, 15 times respectively. Oxygen is underabundant by 0.15 times solar. The large neon over-abundance supports the idea that Nova Her 91 is a member of the ONeMg class of novae. From the results of Starrfield et al (1992) the high N/O ratio, in addition to the enhanced sulfur abundance, suggests that this outburst occurred on a massive ONeMg white dwarf.

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