A new definition for the Ca4227 feature: Is calcium really underabundant in early-type galaxies?

We have investigated the abundance of calcium in early-type galaxies by measuring the strength of the Ca I lambda 4227 absorption line in their integrated spectra. The database used is the large sample of early-type galaxy integrated spectra in Caldwell and coworkers. We have measured Ca abundances from the Ca I lambda 4227 feature both by using the Lick Ca4227 index and by defining a new index, Ca4227(r), that avoids the CN4216 molecular band in the continuum on the blueward side of the line. With the new index definition we measure Ca abundances that are systematically similar to 0.3 dex higher than with the Lick Ca4227 index. The result is that with the new index definition we obtain higher [Ca/Fe] abundances in early-type galaxies, which are more consistent with their well-known [Mg/Fe] overabundances. Hence, we suggest that Ca might be slightly enhanced, relative to Fe, in early-type galaxies.