He-rich and He-poor populations in RGB stars. Results on a sample of 19 globular clusters

We use about 1400 red giant branch stars observed in 19 Galactic Globular Clusters (GCs) to compare colours, metallicities, and RGB bump luminosities of stars assigned to first and second generations. We find subtle differences which we attribute to the different He content. In general these differences are visible only when we consider the extreme second generation stars, with the exception of NGC 2808. When using various indicators, the implied helium enhancements are similar, but the absolute calibration is still uncertain.