  A synthetic spectrum-fitting analysis was applied to the Ca II line at
3933.68 A for 122 A-type stars (7000 <Te < 10000 K) in a wide range of
rotational velocity (10 < vsini < 300 km/s), in order to study the behaviors of
Ca abundances ([Ca/H]39) determined from this Ca II 3934 line, especially in
context of (i) how they are related with the Am phenomenon (often seen in slow
rotators) and (ii) whether they are consistent with the Ca abundances
([Ca/H]61) derived from the weaker Ca I 6162 line. It was confirmed that Ca
line strengths in Am stars tend to be weaker and associated abundances are
lower compared to non-Am stars at the same Te, indicating a deficiency of Ca in
the photosphere of Am stars. However, an appreciable fraction of cool Am stars
(Te < 8000 K) were found to show anomalous Ca II 3934 line feature (i.e.,
unusually broad for its weakness) which is hard to explain. Regarding the
comparison between [Ca/H]39 and [Ca/H]61, while both are roughly consistent for
hotter stars (Te > 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
"weak broad K line" objects, This fact suggests that some special mechanism
reducing the strength of Ca II 3934 line 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 line 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 line may
independently be operative.
