6.3 The observations

To verify this hypothesis, that the equivalent width of a spectral line may increase with increased disc density, Strömgren photometry of the entire representative sample was obtained on the nights of April 24-25 2001 using the Jacobus Kapyten Telescope (JKT) equipped with the JAG CCD detector. The filters used were the Strömgren uvby. Standard stars were taken from Fabregat and Torrejon (1998) and were observed at high and low air masses at approximately 60 minute intervals. The observations were reduced using the Liverpool Telescope pipe-line, see Section 6.4 for more details.