Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/423

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Offsets in correlation lines in two-color diagrams can be caused by many diverse effects. Easiest to detect because it is so large are differences in Fraunhofer line blanketing (blocking and backwarming) due to variations in metallicity. An early statement of the blanketing effect for various metallicities was made by Sandage & Eggen (1959) where the concept of blanketing lines in a U-B, B-V diagram was introduced. The blocking effect was measured by Wildey et al. (1962) and was first calibrated in terms of metal abundance by Wallerstein & Carlson (1960). It was studied for the guillotine problem in the ultraviolet-excess data for subdwarfs by Sandage (1969). Other effects producing smaller differences in two-color diagrams include variations of surface gravity and the scale of atmospheric microturbulence (eg. SBT, Table 6).

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