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The problematic modelling of RCrB atmospheres

The problematic modelling of RCrB atmospheres. Hydrogen-Deficient Stars T übingen, September 2007. Bengt Gustafsson Department of Astronomy and Space Physics Uppsala University. Standard MARCS models. 1D (plane-parallel or spherically symmetric) Detailed blanketing LTE

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The problematic modelling of RCrB atmospheres

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  1. The problematic modelling of RCrB atmospheres Hydrogen-Deficient Stars Tübingen, September 2007 Bengt Gustafsson Department of Astronomy and Space Physics Uppsala University

  2. Standard MARCS models • 1D (plane-parallel or spherically symmetric) • Detailed blanketing • LTE • Mixing-Length Convection See Asplund, Gustafsson, Kiselman & Eriksson (1997): A&A 318, 521 Asplund, Gustafsson, Lambert & Rao (2000): A&A 353, 287 as well as Eriksson, Edvardsson, Gustafsson & Plez (2007), in preparation

  3. No HI and H - opacity => Heavy blanketing => Steepened grad T

  4. Increasing Teff => increasing  => decreasing and Pg, unaltered Pe.

  5. Increasing Teff => increasing  => decreasing and Pg, unaltered Pe.

  6. Model-structure variations with fundamental parameters

  7. Density inversion -- Super Eddington? , /

  8. Density inversion -- Super Eddington? , / >1 < 0 < 0 in ioniz. zone

  9. Density inversion -- Super Eddington? , / >1 < 0 < 0 in ioniz. zone => < 0 Density inversion occurs (first) due to ionization -- not radiative force

  10. Yet,  >1 does not automatically lead to mass flows -- a positive pressure grandient may balance • Additional effects due to Pdyn • Instabilities deserve further studies! Border case at = 1?

  11. Super-Eddington luminosities cause RCB declines? Yet very uncertain whether effect works, See Asplund (1998), A&A 330, 641 Effects of spheriicity and convection! RCB:s evolve from right to left: Expansion => Cooling => Stability LBV:s from left to right: Expansion => Cooling => Instability From Asplund & Gustafsson (1996), ASP Conf. 96, 39

  12. Low H increases line blanketing from CI and other atoms => flux pushed redwards. So does also CI continuum

  13. Dominating opacity sources Total e- C I N I He- Mg He I See also Pavlenkos talk!

  14. A reasonable fit to observed fluxes

  15. CI lines at 5000-7000Å ~ 8.5 eV gf values from TOP data base W ~ l/ mainly from CI bf, ~ 9.2 eV Data also from TOP Incidently, also other opacities (He-, C- , e- ) reflect C abundance since most electrons come from C

  16. C = [C]pred - [C]obs

  17. C = [C]pred - [C]obs A real problem! ”The Carbon Problem”

  18. What could be the reason? • Errors in FP:s?No! • Errors in codes etc?No! • W? No! • Extra-photospheric flux? (> 3x photosp., No!) • Basic atomic data for CI in error? (~10-30%, much too little!) • CI opacity not dominant? (C/He = 1%, must be lowered by more than x 20, inconsistent with hot RCrB stars and EHe stars) • NLTE? (~ 2%, Asplund & Ryde 1996, No (?)) • Model atmospheres? - incomplete opacities? - sphericity? - dep. from hydrostatic equilibrium? Hardly! - temperature inhomogeneities? Not per se - errors in structures due, e.g. due to dynamical fluxes

  19. New Marcs models (Eriksson et al. 2007, in prep) , • New better opacities • More heavy blanketing • Steeper grad T Sphericity => Steeper grad T Effects on abundances : ~ ± 0.1 dex New MARCS Goes the wrong way for C I!

  20. Decrease grad T in CI-line forming layers! This works reasonably well but requires Fheat ~ 4P (4T3T)s ~ 10% Ftot Compare to Fmech ~ vturb3 vturb ~ 40 km/s

  21. C problem also for [CI]Pandey et al. (2004), MNRAS 353, 143

  22. … however not for CII (?) To do: • C2? • CI and C2 in IR (He- takes over in ) • Explore accurately normal supergiants • 3D HD simulations

  23. No real progress in 8 years. Errors in abundances at least x2 - x4 in absolute numbers. Time to resolve this now?

  24. ”Truth is the daughter of time, and I feel no shame of being her midwife” Johannes Kepler No real progress in 8 years. Errors in abundances at least x2 - x4 in absolute numbers. Time to resolve this now?

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