The role of convection on the RGB modelling P. Ventura F. D’Antona Observatory of Rome R. Carini M. Di Criscienzo

courtesy by M. Di Criscienzo

Two local models for convection FST (Canuto & Mazzitelli 1991) All eddies L=z+bHp MLT (Vitense 1953) L=d=aHp

Canuto & Mazzitelli 1991

Canuto & Mazzitelli 1991

ΔT ~ 100K for Δb=100% ΔT ~ 250K for Δa=24% 0.8MSun Z=10-4 L=z+bHp

Overadiabaticity peak 0.8 Msun Δ - Δ ad FST more efficient in the interior! Overadiabaticity peak higher and narrower Log P

FST more efficient MLT more efficient

Canuto & Mazzitelli 1992

Photometry of NGC 6791 (Kalirai et al. 1997) [Fe/H]=+0.3-0.4

1.2MSun Z=0.04 FST (b=0.2) MLT (a=1.9)

1.2MSun Parallel paths FST MLT 500K ! different slopes!

1.2MSun FST MLT

FST more efficient

Δ - Δ ad Log P

FST MLT Δ - Δ rad ad Log P

FST MLT Log T Log P

FST ATMOSPHERE NEEDED! recombination Δ ad t=10 Log P

Distribution of clump stars in NGC 1866 (Testa et al. 1999) NB ~ NR

Synthetic diagrams (no dispersion!) using isochrones where mixing was treated in the instantaneous and diffusion-like modality The extensions of the loops are similar, but the diffusive scheme predicts a blue clump more populated

Log Teff Time

YC Time In the diffusive case helium is consumed more slowly in the core YC Time In the instantaneous mixing scheme the helium is consumed faster, which favours a quick return to the red

Conclusions * The morphology of the RGB of high Z clusters depend on the treatment of convection modelling * At any luminosity, the MLT model is cooler in the interior, enters the region of molecular recombination, with the consequent lowering of the adiabatic gradient, and the increase in the overadiabaticity: the track results much cooler than the FST counterpart * The distribution of stars in the clump of relatively young clusters (150-200 Myr) depend on the modality with which overshooting is modelled: a diffusive approach favours longer staying in the blue