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White Dwarfs in Globular Clusters

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). M4: the deepest WD cooling sequence.

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White Dwarfs in Globular Clusters

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

  2. 47 tuc (Zoccali et al 2001)

  3. M4 (Bedin et al. 2001)

  4. NGC 6397 (King et al. 1998)

  5. M4: the deepest WD cooling sequence Data obtained with the WFPC2on 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) 12.7"0.7 Gyr.

  6. WD Age from the CM-diagram: CIA connection

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

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

  9. Expected WD sequence in NGC6397 with ACS

  10. WD mass and progenitor mass function Synthetic NGC 6397 13 Gyr - Salpeter mass function

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

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

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

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

  15. Jp Ex (keV) ECM (keV) 10957 0- 10367 4+ 3195 2685 2+ 9847 9580 1- 2418 8872 2- Q = 7.162 MeV Gamow peack energies 7117 1- 12C+4He 6917 2+ -45 -245 6130 3- 0+ 6049 0 0+ 16O level scheme Na<s,v> (10-15 cm3mol-1s-1) for T9=0.2

  16. High rate 12C(a,g)16O Low rate White Dwarf interior: C and O profiles

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

  18. convective radiative He C/O induced overshooting (Castellani Giannone Renzini 1971) Core He-burning: the connection between Nuclear Reaction & Convection He (low k) -> C/O (high k)

  19. Radiative Zone CC SCZ Semi convective Zone RZ Convective Core Semiconvection

  20. a<0v…0 a<0v=0 a>0v…0 RCC + a Hp a=1 Mechanical overshooting

  21. 4 models for convection • same nuclear reaction rates • different convective scheme

  22. 16O MD WD internal composition is affected by core He burning convection

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