Abstract
A synthetic spectrum-fitting analysis was applied to the Ca II at 3933.68 A for 122 A-type stars (7000 8000 K), the former tends to be lower (by up to -1 dex or even more) than the latter for cooler A stars (Te < 8000 K) including those broad K line objects, This fact suggests that some special mechanism reducing the strength of Ca II 3934 is involved at Te < 8000 K where [Ca/H]39 would be no more reliable. Whereas atomic diffusion causing the deficit of Ca in the photosphere as a result of element segregation in the deeper radiative envelope may be regarded as a promising explanation because it seems to fit in the qualitative trend of [Ca/H]61 in A-type stars, the well-known feature of considerably weak Ca II K in classical Am stars should not necessarily be attributed to only this element diffusion scenario, for which some unknown weakening mechanism specific to this resonance may independently be operative.
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