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White Dwarfs in Globular Clusters O. Straniero, P. Prada Moroni, I. Dominguez, G. Imbriani, L. Piersanti G. De Marchi P. Bergeron
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47 tuc (Zoccali et al 2001)
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M4 (Bedin et al. 2001)
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NGC 6397 (King et al. 1998)
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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.
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WD Age from the CM-diagram: CIA connection
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Age from luminosity function Crystallization phase Debye cooling Convective coupling WD cooling
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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
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Expected WD sequence in NGC6397 with ACS
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WD mass and progenitor mass function Synthetic NGC 6397 13 Gyr - Salpeter mass function
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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
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Thermal conductivity by degenerate electrons From Prada Moroni & Straniero 2002 C/O Core He-rich Mantel
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WD progenitors Case B no-AGB Case B1 Post-AGB with final thermal pulse Case B2 classical Post- AGB Case C Post RGB
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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+
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E x (keV) JJ 10957 10367 9847 9580 8872 7117 6917 6130 6049 0 0-0- 4+4+ 2+2+ 1-1- 2-2- 1-1- 2+2+ 3-3- 0+0+ 0+0+ 12 C+ 4 He 2418 2685 3195 E CM (keV) Gamow peack energies -45 -245 16 O 16 O level scheme Q = 7.162 MeV LowAdop.high Kunz et al 2001 5.257.5810.2 Buchman n 1996 3.047.0413.04 NACRE 5.449.1112.8 CF88 4.74 CF85 11.3 N a (10 -15 cm 3 mol -1 s -1 ) for T 9 =0.2
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White Dwarf interior: C and O profiles 12 C( ) 16 O High rate Low rate
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cooling is affected by the internal chemical stratification high rate low rate
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Core He-burning: the connection between Nuclear Reaction & Convection He (low ) -> C/O (high ) C/OHe induced overshooting (Castellani Giannone Renzini 1971) convectiveradiative
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Semiconvection Convective Core Semi convective Zone Radiative Zone CCSCZRZ
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Mechanical overshooting a>0 v … 0 a<0 v … 0 a<0 v=0 R CC + H p =1
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4 models for convection same nuclear reaction rates different convective scheme
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WD internal composition is affected by core He burning convection MDMD 16 O
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