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Sylvie Vauclair Institut de Recherches en Astrophysique et Planétologie, OMP, CNRS,

Stellar microphysics Atomic diffusion , accretion , thermohaline convection, links with asteroseismology. Sylvie Vauclair Institut de Recherches en Astrophysique et Planétologie, OMP, CNRS, Université de Toulouse, Institut universitaire de France.

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Sylvie Vauclair Institut de Recherches en Astrophysique et Planétologie, OMP, CNRS,

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  1. Stellar microphysics Atomic diffusion, accretion, thermohaline convection, links with asteroseismology Sylvie Vauclair Institut de Recherches en Astrophysique et Planétologie, OMP, CNRS, Université de Toulouse, Institut universitaire de France Séminaire M2 , Toulouse, 14 novembre 2011

  2. Element Diffusion in Stars (Stars are non-uniform multi-component gases) • Basics of stellarphysics: twokinds of processes in competition • « microscopicprocesses » (atomic diffusion) • « macroscopicprocesses » (mixing, mass loss, etc.) • Importance of precisemicrophysics for stellar structure and evolution • gravitationalsettling • thermal diffusion • concentration gradients • radiative accelerations • Large data basis on atomicphysics, in relation withopacityprojects: • OPAL , OP… • Helio and asteroseismic tests • e.g. helium gradients below convective zones and manyotherconsequences

  3. The development of knowledge • Beginning of 20th century: • basics of stellarphysicsincluding discussions on atomic diffusion… • Eddington 1916, 1926; Chapman 1917; etc • and macroscopicprocesses • Von Zeipel 1924; Vogt 1925; Eddington 1929; Sweet 1950; etc. • 1950 to 1970: • discussions of diffusion in white dwarfs, and in the Sun • Schatzman 1944, 1945, 1958; Aller and Chapman 1960, etc. • In the 1970s: • first explanations of chemicallypeculiar stars by atomic diffusion… • F. Praderie 1967; G. Michaud 1970; W.D. Watson 1971 • andcompetitionwithmacroscopicprocesses: MCV2; V2SM; V2M, etc. • also: instabilities INDUCED by atomic diffusion??? (Ed. Spiegel) • Now: • Helio and asteroseismic tests • detailedstudies of the inducedinstabilities

  4. Chapman-Enskog description Treatment of collisions (Boltzmann integro-differentialequation): [f(c+Fdt, r+cdt, t+dt) – f(c,r,t)] = (collision term) f (c,r,t) is the distribution function of the particles, i.e. the number of particles in the volume element (r, r+dr) withvelocities in the range (c, c+dc) at time t Maxwellian ( ) : in the presence of gradients ( ) : Compute the collision integralsas a development in terms of smallknudsennumberk= l/L=tmic/tmac / 0 0 /

  5. Results: Diffusion equation: with: for test atoms: (includingmixing coefficient Dth) Approximate expressions (not used in codes but interesting for physical discussions):

  6. Burgers diffusion equations (see Hu 2011)

  7. Orders of magnitude • Atomic diffusion is a very slow but efficient process • Vdincreases and tddecreasestowards the surface • Below the solar convective zone: td ~ 1010yrs • In atmospheres: td ~ 102 ~ 104yrs • At the bottom of the second convective zone in Am stars: • Dm ~ 100 cm2/sec , td ~106yr, vd ~ 10-6 cm/sec, tcol ~10-10 sec • Competitionwithmacroscopic motions : selective vs homogenizingprocesses

  8. Radiative accelerations : unsaturated line saturated line gradindependent of N gradwhen N

  9. 1982

  10. Radiative accelerations in an A star, 1.7Msun, 403 Myr fractional radius (TGEC code, Théado & Vauclair, in prep.)

  11. Examples of colorintensity codedelements concentrations afterpure diffusion : 3Msun, 70Myr (Richer et al. 1999) • Possible macroscopicconsequences of atomic diffusion: • (otherthanobservedabundances) • dynamical convection • thermohaline convection • stellar oscillations

  12. Richard, Michaud, Richer 2001

  13. Thermohaline convection: the ocean case Stern 1960,Kato 1966, Veronis 1965, Turner 1973, Turner and Veronis 2000, Wells 2001, Piacsek and Toomre 1980, Shen and Veronis 1997,Yoshida and Nagashima 2003, Gargett and Ruddick 2003

  14. The stellar case m = dlnm/dlnP plays the role of the salinity gradient; rad- plays the role of the temperaturegradient « fingers » form if : with: and t = km / kT = tT / tm For R0<1, dynamical convection For R0=1/t, dissipation Simulations by Traxler, Garaud, Stellmach 2011 R0 = 1.45 and 9.1 ; 1/t = 10

  15. Thermohaline diffusion coefficients Ulrich 1972, Kippenhahn et al. 1980 o o o o o o o Denissenkov 2010 o o Traxler et al. 2011 seeThéado & Vauclair 2011, arXiv 1109.4238

  16. Théado, Vauclair, Alecian, Leblanc 2009 log (M/M) log (M/M) many applications: SPB/bCeph, sdB, g Dor, etc.

  17. Exoplanets host stars 119 planet-host stars (dashed) ; 94 comparison stars (solid) 22 planet-host stars in binary systems (solid) ; dashed : single planet-host stars Santos et al. 2005

  18. But!!! Santos et al 2003 heavyelements and… problem of Y

  19. Israelian et al, Nature 2010

  20. TV-2011- thermohaline after accretion in EHS 0.03 Mjup, 1.10 Msun, 2, 25, 54, 89 Myrs

  21. Conclusions • Importance of chemical stratification for stellar structure and evolution, • and for helio and asteroseismology • Abundances modifications inside stars can trigger or prevent oscillations • Competitionbetween micro and macroscopic motions studied for manyyears • But :importance of the instabilitiesinduced by the stratification itself: still • lot of work to do !

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