Abstract
We have measured D A , the mean relative depression of quasar continuum between Lyα and Lyβ emission, for a large sample of quasars. We have carried out the measurements by simply adding the Lyα lines (excluding the lines in identified systems) together. The big advantage of this approach over the conventional method is that the continuum is fitted locally by employing high S/N and relatively high resolution spectra, and this leads to a more reliable estimate of the continuum level in the Lyα forest region. Also, the contamination of D A by metal lines is easily removed. Extending the method proposed by Zuo (1993) and Lu & Zuo (1993), we have determined γ int , the intrinsic evolutionary rate exponent of Lyα forest lines
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