ABSORPTION SPECTRA

At present, absorption lines are known to exist in the spectra of some 50 or so quasars. About half of them show a rich absorption spectrum. Such spectra have been interpreted on the redshift hypothesis by assuming multiple redshifts. The number of redshift systems proposed to account for these absorption lines is becoming comparable to the number of epicycles required (in a different era) to save the geocentric system of the solar system -- in one case (0237-23) as many as 45 redshift systems have been proposed and are discussed by Varshni (1981, 1983, 1988) he also discusses the spectra of 4C 05.34 in detail (1974a, 1974b, 1975) and has shown that the number and properties of the proposed absorption redshift systems are insignificantly different from those that would be expected from chance coincidences.

The absorption lines which occur in the spectra of quasars can be conveniently classified in four categories.

  1. Sharp and deep absorption lines, resembling those in a shell star.
  2. Unusually strong lines, quite often having several components.
  3. Very wide (about 30 Å) absorption lines.
  4. P Cygni lines, i.e., emission lines accompanied by shortward displaced absorption lines.
We have compared the expected shell spectrum of a quasar on the basis of the PLS model with observational data. The absorption lines arising from ordinary excited levels will be strongly underpopulated. The populations of metastable levels below the first ionization potential and those of the Wu levels will be enhanced due to the dilution of the stellar radiation. Consequently, lines arising from these levels are expected to be prominent. We expect that category 1 lines should mostly arise from transitions from metastable states below the first ionization potential. The ions and their levels which would be most important would, of course, depend on the degree of excitation of the shell. Lines due to metallic ions like Sc II, Ti II, Mn II, Fe II, Cr II etc. are known to occur frequently in spectra of 'classical' shell stars. In additions, He I and Fe III lines occur in some shells in which the ionization level is higher.

Extrapolating, we can expect the presence of He I, Fe III, Ti III, Ar II, Al III, Si III, Mn III, O II, O III etc. in the shells of quasars, if the ionization level is still higher.

For identifying spectral lines, one would like to have an accuracy of 0.1 Å or better in the observed wavelengths, and to have these data over a wide wavelength interval. However, most of the reported data are of poor accuracy - the claimed accuracy varies between 1 Å and 2 Å. When interpreting these data on the redshift hypothesis, usually most authors allow a discrepancy of ±2 Å and it would appear that most of the data have this sort of uncertainty. Also, in many cases, the mutual blending of lines is very severe. If one had a spectrum of an ordinary star of this quality, it would be prohibitively difficult to identify the lines, except those of hydrogen and Ca II. (Quasars, being deficient in hydrogen do not show the hydrogen lines). We may note here that He I 3389 Å, which is a prominent line in certain shell stars, also occurs in the spectra of PHL 957, 1331+170, 4C 25.05, PHL 5200, PKS 0237-23, and 1158+122. Lines arising from the Wu states will be difficult to identify as very few of these have been observed in the laboratory.

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