K-line photometry of Southern A stars

The temperature dependence is well known; the abundance dependence appears as a correlation between the residual dK in K (after allowance for the temperature effect) and the difference from normal of the general metallicity index [m1] of Stromgren. Alternatively, it was shown in Paper I that the calcium abundance is probably the effective factor in producing the scatter in the relation between k and b-y by a process of elimination of other parameters (luminosity, etc.) that were found not to affect appreciably the value of k.

The value of k is, however, affected by a third parameter, namely, whether the star is an Am star or not. Many of the stars of Paper I were reobserved in order to tie in the new measurements with the old ones. An emphasis was laid on observing more Am stars, and on observing some stars that are of somewhat earlier spectral types than the earliest ones observed previously.

Simultaneously with the field-star measurements described here, extensive data were acquired for the A stars in five open clusters (Hyades, Pleiades, IC 2391, IC 2602, and NGC 6475) and one association (Orion), as described in Paper III (Hesser & Henry 1971ApJS...23..453H). The observations were made with the same instrument that was used to obtain the data for Paper I, and a description of the instrument may be found in that paper.