White Dwarfs in Globular Clusters O. Straniero, P. Prada Moroni, I. Dominguez, G. Imbriani, L. Piersanti G. De Marchi P. Bergeron

47 tuc (Zoccali et al 2001)

M4 (Bedin et al. 2001)

NGC 6397 (King et al. 1998)

Data obtained with the WFPC2 on board the HST (Hansen et al. 2002, Richer et al. 2002). The target is a region located  5’ E of the center of M4 and has been imaged through the: F606W (98 x 1300 sec) F814W (148 x 1300 sec) M4: the deepest WD cooling sequence 12.7 " 0.7 Gyr.

WD Age from the CM-diagram: CIA connection

Age from luminosity function Crystallization phase Debye cooling Convective coupling WD cooling

Good match between theory and observation Good description of the high density matter behavior Bad: only a lower limit for the age can be set:  9 Gyr The observed WD Luminosity function Good: smaller dependence on the distance

Expected WD sequence in NGC6397 with ACS

WD mass and progenitor mass function Synthetic NGC Gyr - Salpeter mass function

98% C-O core 2% He mantel (<10 -2 M À ) 0.01% H envelope (<10 -4 M À ) no conduction e - highly degenerateisothermal envelope core energy reservoir C-O ions main energy reservoir e - non-degenerate thermal insulator DA White Dwarf

Thermal conductivity by degenerate electrons From Prada Moroni & Straniero 2002 C/O Core He-rich Mantel

WD progenitors Case B no-AGB Case B1 Post-AGB with final thermal pulse Case B2 classical Post- AGB Case C Post RGB

4 He 16 O 12 C 5 M  Z=0.02 Y=0.28 He-burning: the competition between 3  -> 12 C and 12 C+  -> 16 O+ 

E x (keV) JJ C+ 4 He E CM (keV) Gamow peack energies O 16 O level scheme Q = MeV LowAdop.high Kunz et al Buchman n NACRE CF CF N a ( cm 3 mol -1 s -1 ) for T 9 =0.2

White Dwarf interior: C and O profiles 12 C(  ) 16 O High rate Low rate

cooling is affected by the internal chemical stratification high rate low rate

Core He-burning: the connection between Nuclear Reaction & Convection He (low  ) -> C/O (high  ) C/OHe induced overshooting (Castellani Giannone Renzini 1971) convectiveradiative

Semiconvection Convective Core Semi convective Zone Radiative Zone CCSCZRZ

Mechanical overshooting a>0 v … 0 a<0 v … 0 a<0 v=0 R CC +  H p  =1

4 models for convection same nuclear reaction rates different convective scheme

WD internal composition is affected by core He burning convection MDMD 16 O