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

2. courtesy by M. Di Criscienzo

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

4. Canuto & Mazzitelli 1991

5. Canuto & Mazzitelli 1991

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

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

8. FST more efficient
MLT more efficient

10. Canuto & Mazzitelli 1992

11. Photometry of NGC 6791 (Kalirai et al. 1997)
[Fe/H]=

12. 1.2MSun
Z=0.04
FST (b=0.2)
MLT (a=1.9)

13. 1.2MSun
Parallel paths
FST
MLT
500K !
different slopes!

14. 1.2MSun
FST
MLT

15. FST more
efficient

16. Δ - Δ ad
Log P

17. FST
MLT Δ - Δ
rad ad
Log P

18. FST
MLT
Log T
Log P

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

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

22. 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

23. Log Teff
Time

24. 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

25. 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 ( Myr) depend on the modality
with which overshooting is modelled: a diffusive
approach favours longer staying in the blue