Pruning the Lyman alpha forest of Q1331+170

We present a study of the Lyman alpha forest of the QSO 1331 + 170 in the range 1.67 <z(abs) < 2.10 at 18 km s(-1) resolution. Our analysis includes a careful search for previously unidentified heavy-element systems, and incorporates detailed deblending of Ly alpha forest lines from heavy-element lines. Various statistical properties of Ly alpha forest lines, such as distributions of equivalent widths, HI I column densities, Doppler parameters and pair-velocity separations, are computed. The effect on these properties of employing different limiting approaches to heavy-element deblending, and profile-fitting of the lines, is illustrated. Our data suggest that the N-HI distribution may not be fitted adequately by a single power law, i.e., that there may be a relative deficit of strong lines as compared with the predictions of a single power law. However, larger samples are required to verify this deficit. The median b value is approximate to 32 km s(-1). No significant correlation is observed between N-HI and b. An excess on the scale of similar to 100 km s(-1) is seen in the pair-velocity correlations, at the level of similar to 2.6 sigma for the conservative sample and at the level of similar to 4.9 sigma for the less conservative sample. Marginal excess correlation is seen in both the samples at the greater than or similar to 2 sigma level on scales of similar to 800-1000 km s(-1), and also on scales of similar to 6000 km s(-1).