Some Integrated Properties of Galactic Globular Clusters

The luminosities of globular clusters are found to correlate with theirhalf-light radii. The most luminous clusters have half-light radii r ~ 3 pc.Mean cluster luminosities are < Mv > = -6.64 +/- 0.26 for r < 2.0, < Mv > =-7.44 +/- 0.20 for 2.0 < r < 4.0 pc, and < Mv > = -6.57 +/- 0.21 for clusterswith r > 4.0 pc. An even fainter value < Mv > = -5.85 +/- 0.36 is found forlarge clusters with r > 8.0 pc. These results possibly weaken confidence in theconclusion that the peak of the globular cluster luminosity distribution is auniversal standard candle. In the outer Galactic halo globular clusters withred horizontal branches are fainter by about a factor of ten than are clusterswith blue and intermediate color horizontal branches. Among clusters withGalactocentric distances > 10 kpc there appears to be a clear dichotomy betweennormal clusters (which all have [Fe/H] < -1.2) and the anomalous relativelymetal-rich clusters Pal 1, Pal 12 and Ter 7, which are both unusually faint (Mv> -5) and relatively metal-rich ([Fe/H] > - 1.0). This suggests that theserelatively metal-rich halo clusters may have had an unusual evolutionaryhistory.