CaII triplet equivalent widths in 30 globulars

While the most fundamental way of determining GC abundances is by mean high-resolution spectroscopy, in practice this method is limited to only the brighter stars in the nearest and less reddened objects.

This restriction has, over the years, led to the development of a large number of techniques that measure the overall abundance indirectly from parameters that correlate with overall metallicity. One of the most efficient methods is measuring of the equivalent width (EW) of the calcium II triplet (CaT) at {lambda}~~8500{AA} in red giants, which are corrected for the luminosity and temperature effects using the V magnitude differences from the horizontal branch (HB).