Varshni,Y.P.: 1978, 'The Ta-You Wu Festschrift: Science of Matter', ed. S. Fujita (Gordon and Breach, 1978) p.285

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The plasma laser star (PLS) model for quasars proposed by the author, is applied to explain the absorption spectra of quasars. The following topics are briefly reviewed (a) Shell stars, especially gamma Cas. The role of the metastable states. He I 3889 . (b) High Rydberg states. (c) Multiply-excited states of atoms (and ions) which lie above the first ionization potential, especially the Wu states (metastable states which cannot autoionize by Coulomb interactions or decay radiatively. Prototype 1s2s2p P quartet state of the Li I sequence). (d) Dielectronic recombination. The expected shell spectrum of a quasar on the basis of the PLS model is compared with the observational data. The absorption lines arising from ordinary excited levels will be very weak as these levels will be strongly underpopulated (bn < < 1). The populations of metastable levels below the first ionization potential and those of the Wu levels will be enhanced due to the dilution of stellar radiation. Consequently, lines arising from these levels are expected to be prominently. Those arising from the Wu states will be difficult to identify as very few of these have been observed in the laboratory. The difficulties in the identification of observed lines due to the blending of lines due to the rather large uncertainties in the measured wavelengths are discussed. The presence of He I 3889 in the spectra of PHL 957, 1331+170, 4C 25.05, PHL 5200, PKS 0237-23 and 1158+122 is noted. A very reasonable explanation of the absorption 'hole' at 4020 in the spectrum of PHL 957 is that it is due to a transition from a Wu level to an autoionizing level. Also, there is no need of assuming redshifts in the spectra of two BL Lac objects, namely 0725+178 and AO 0235+164.

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