... clusters

Based on observations collected at the European Southern Observatory, Cerro Paranal, Chile (ESO No. 66.B-0131).

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... pixel

The S/N is determined as an average over the observed wavelength range. The minimum S/N per resolution element is $\approx$25.

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...$\langle$Fe$\rangle$

$\mbox{$\langle$ Fe$\rangle$ }= ( {\rm Fe5270} + {\rm Fe5335})/2$  (González 1993).

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... [MgFe]

${\rm [MgFe]} = \sqrt{\mbox{Mg~{\it b}}\times ( {\rm Fe5270} + {\rm Fe5335})/2}$  (González 1993).

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