SIMBAD references

Physical conditions and element abundances in the optically thin shells of 11 classical novae with outbursts between 1978 and 1989 were determined from an analysis of UV and optical spectra obtained during the nebular stage. Eight novae were studied on the basis of new optical and UV spectra: PW Vul (1984), QU Vul (1984), V842 Cen (1986), V827 Her (1987), QV Vul (1987), V2214 Oph (1988), V977 Sco (1989), and V443 Sct (1989), while three other novae - V1668 Cyg (1978), V693 CrA (1981), and V1370 Aql (1982) - were reinvestigated using the same spectral analysis techniques. In the case of PW Vul results of Andreae et al. (1991) are included. The accuracy of the element abundances depends on whether or not simultaneous UV spectra were available to determine individual ionization stage dependent gas temperatures. Generally, slightly higher than solar abundances of helium and pronounced overabundances of the heavier elements were found. QU Vul turned out to be an ONeMg nova, while the other objects belong to the class of CO novae. The nature of V2214 Oph could not be completely clarified. The novae V1668 Cyg (1978), V693 CrA (1981), and V1370 Aql (1982), for which published element abundances exist, were reanalyzed to check the consistency of our spectral analysis approach. Satisfactory agreement of the results was found. Photoionization calculations were carried out for PW Vul using the code of Aldrovandi, Pequignot, and Stasinska. A synthetic spectrum was generated for the parameters derived from the analysis of the UV and optical spectra, which is in very good agreement with the observations. The spectral analysis technique was then applied to the model spectrum and reproduced the model parameters well. Electron temperatures for the C²⁺ and C³⁺ ions between 7500 and 12000K and for N⁴⁺ between 12000 and 16000K were derived. For PW Vul and QU Vul these temperatures remained relatively constant over several months. The decline in density of the ejected shells with time could be investigated for V842 Cen, QV Vul, V977 Sco, and V443 Sct, and was found to deviate from the relation N_e∝t^–2 for free expansion of a shell in a different way for each object. A possible explanation may be the complex density structure of the shells. This suspicion is supported by high resolution spectra (ESO 3.6m telescope + CASPEC): the emission line profiles show a complex structure with numerous sharp subcomponents possibly correlated with local condensations in clumpy shells.