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Thermohaline mixing in low mass giants

Thermohaline mixing in low mass giants. Matteo Cantiello N. Langer and H. Hoekstra Astronomical Institute Utrecht. Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008. Outline of the talk.

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Thermohaline mixing in low mass giants

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  1. Thermohaline mixing in low mass giants Matteo Cantiello N. Langer and H. Hoekstra Astronomical Institute Utrecht Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  2. Outline of the talk • The physics of thermohaline mixing • Thermohaline mixing in stars • Methods • Results of our models • Discussion Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  3. Thermohaline instability • Double diffusive instability • Plays an important role in the oceans (salt fingers thermohaline circulation) • Mixing occurs on a thermal timescale Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  4. Thermohaline mixing in the kitchen t ~15 m t = 0 t ~ 5 m Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  5. Thermohaline mixing in stars • Accreting binary system (Wellstein et al. 2001, Stancliffe et al. 2007) • Accreting star during planetary formation (Vauclair 2004) • Off-center ignition in semi-degenerate cores • Low mass giants(Eggleton et al. 2006, Charbonnel & Zahn 2007a) Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  6. 3He+3He 2 1H+4He • (Ulrich 1972, Eggleton et al. 2006) • Needs • Reservoir of 3He RGB , Core He burning, AGB Thermohaline mixing in red giants Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  7. Stellar models Z = 0.02 • 1D-Hydrodynamic code • Mixing treated as a diffusive process • Rotational mixing(Heger et al. 2000) • Magnetic mixing(Spruit, 2002) • Thermohaline mixing(Wellstein et al. 2001, Kippenhahn et al. 1980) 1, 1.5, 2, 3 MSun @ ZSun (Suijs et al. 2008) Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  8. Results: mixing during the RGB and beyond - 1MSun Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  9. Log(L/LSun) Surface abundances evolution Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  10. Results: mixing during the RGB and beyond - 2MSun Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  11. 3He+3He 2 1H+4He (1 - 6/7) 1 2 3 Halting Thermohaline mixing (7/6 - 4/3) 3He + 4He 7Be + 7Be + -e 7Li + 7Li + 1H 2 4He 1 23 Controlled by ratio3He/ 4He after 1Dup,which decreases with M (e.g. Boothroyd & Sackmann 1999) Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  12. Thermally-pulsingAGB (TP-AGB) Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  13. Mass (MSun) 1 Thermal pulse Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  14. Li surface abundace Th. Mixing 3DUP Li-rich, low mass AGB stars(Uttenthaler et al. 2007) Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  15. Thermohaline mixing VsRotational mixing and B fields Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  16. Rotational Mixing and B fields 1 MSun Vi= 10km/s Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  17. A mass threshold for Th.Mixing • Th. mixing working in M < Mth ~ 1.5MSun • Mth sensitive to mixing efficiency parameter • ~ 4% of low mass stars avoid thermohaline mixing(Charbonnel & Do Nascimento 1998) • Mass threshold ? • Fossil B fields ?(Charbonnel & Zahn 2007b) Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  18. Efficiency of thermohaline mix • Controversy: Ulrich vs Kippenhahn • Theory (Kippenhahn 1980) and simulations (e.g. Merryfield 1995) suggest no fingers in stars • Ulrich (long fingers) needed to explain RGB abundances(Charbonnel & Zahn 2007a) • Interaction of th.mix and shear maybe important • Need further study / realistic hydro simulations! Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  19. Conclusions • Thermohaline mixing can efficiently burn 3He during the RGB in stars below ~ 1.5MSun • Th.mix can occur also during core He burning and on the AGB and TP-AGB • Rotational instabilities and magnetic mixing have lower diffusion coefficients than Th.mix • The interaction of rotation and B fields with thermohaline mixing need to be investigated to determine the efficiency parameter of th.mix Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

  20. Thank you ! Matteo Cantiello Thermohaline Mixing in low-mass giants IAU252 Sanya - April 2008

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