1 v 1 2 4 Ja n 19 94 – 1 – UPPER LIMITS ON METALS IN QUASAR LYMAN - ALPHA FOREST CLOUDS : ABSENCE OF C IV LINES IN ECHELLE SPECTRA 1

Recently Lu presented tentative evidence for C IV lines in QSO Lyα forest systems with strong lines. We have performed a similar search for C IV in our 10 km s −1 echelle spectra of the bright QSO HS 1946+7658. We shifted the spectra to align the expected positions of the C IV lines in 65 Lyα systems, then added them. The resulting composite spectrum, equivalent to 390 hours of exposure time on the Lick 3-m telescope, has a signal-to-noise ratio of 80 per 0.025Å in the rest frame of the absorbers. We do not see any C IV lines down to a 2σ limit of W(1548) ≤ 1.4 m ˚ A, about one-fifth of the strength of the lines seen by Lu.