  We use abundances of Ca, O, Na, Al from high resolution UVES spectra of 200
red giants in 17 globular clusters (GCs) to investigate the correlation found
by Lee et al. (2009) between chemical enrichment from SN II and star-to-star
variations in light elements in GC stars. We find that (i) the [Ca/H]
variations between first and second generation stars are tiny in most GCs
(~0.02-0.03 dex, comparable with typical observational errors). In addition,
(ii) using a large sample of red giants in M 4 with abundances from UVES
spectra from Marino et al. (2008), we find that Ca and Fe abundances in the two
populations of Na-poor and Na-rich stars are identical. These facts suggest
that the separation seen in color-magnitude diagrams using the U band or hk
index (as observed in NGC 1851 by Han et al. 2009) are not due to Ca
variations. Small differences in [Ca/H] as associated to hk variations might be
due to a small systematic effect in abundance analysis, because most
O-poor/Na-rich (He-rich) stars have slightly larger [Fe/H] (by 0.027 dex on
average, due to decreased H in the ratio) than first generation stars and are
then located at redder positions in the V,hk plane. While a few GCs (M 54,
omega Cen, M 22, maybe even NGC 1851) do actually show various degree of
metallicity spread, our findings eliminate the need of a close link between the
enrichment by core-collapse SNe with the mechanism responsible for the Na-O
anticorrelation.
