Optical and Ultraviolet Spectrophotometry of the ONeMg Nova Herculis 1991

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Session 29 -- Novae and Supernovae
Display presentation, Tuesday, 9:30-6:30, Pauley Room

[29.03] Optical and Ultraviolet Spectrophotometry of the ONeMg Nova Herculis 1991

K.M.Vanlandingham (ASU), S.Starrfield (ASU), R.M.Wagner (OSU), S.N.Shore (GHRS/CSC), G.Sonneborn (LASP/GSFC)

\noindent Nova Herculis 1991 was a very fast ONeMg nova that was discovered on 24 March at V $\sim$ 5. Optical and ultraviolet (IUE) spectra were obtained and cover the period from March through July, when it became too faint to be observed. From our spectra, we have determined the reddening of Nova Her 91 to be in the range of E(B-V)$\sim$0.5-0.6, which agrees well with estimates made by other groups. Distance determinations using the $M_{V}-t_{3}$ relation yield results in the range of 5.4 to 8.3 kpc. Since these methods appear to overestimate the distance to fast ONeMg novae, we take these values as an upper limit. On the other hand, assuming Nova Her 91 was at the Eddington luminosity (L$_{ED} \sim 10^{38} erg s^{-1}$) at maximum light, we find a lower limit of the distance to be 1.8 kpc. We have been modeling the UV and optical spectra of Nova Her 91 using CLOUDY 80.06. We have concentrated on the spectra from 22-23 April, shortly after the UV became optically thin. In our models we have used a blackbody continuum for the remnant with an effective temperature of T=$2\times 10^{5}$K. The ejecta were assumed to have a number density of $3\times 10^{6}$cm$^{-3}$. The other parameters needed for the modeling will be listed on the poster. We also note that the shell is clearly filamentary and the filling factor is low at this time. Preliminary abundance estimates show enhanced C,N,Ne,Mg, and S, while O is underabundant (accounting for the lack of [OIII]$\lambda$1660, 1666, 4959, 5007 in the spectra). All other elements are assumed to have solar abundances. We are continuing to model both these and later spectra. The outburst of this nova will be compared with Nova Cygni 1992, the most recent and brightest ONeMg nova.

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