The effect of diffusion on the red giant luminosity function 'bump'

This paper investigates the effect of microscopic diffusion of helium and heavy elements on the location of the red giant branch (RGB) luminosity function bump in Population II stellar models. To this aim, updated evolutionary models taking into account diffusion from the main sequence until the zero-age horizontal branch (ZAHB) are computed. The observational luminosity difference between the RGB bump and the ZAHB (Delta V-hb(bump)), as collected for a sample of Galactic globular clusters, is compared with the corresponding theoretical values obtained by adopting both canonical and diffusive models. We find that the effect of diffusion, even if slightly improving the agreement between observations and theory, is negligible with respect to the observational uncertainties. In any case, the theoretical predictions for Delta V-hb(bump) models with and without diffusion appear in agreement with the observational results within the estimated errors. Thus canonical models can be still safely adopted, at least until much more accurate observational data become available.