The spectral MLTY transition: the role of convection in cloud formation

1. The spectral MLTY transition:the role of convection in cloud formation F. Allard (CRAL-ENS, Lyon, France)

2. MLT Spectral Sequenceoptical to red spectral rangeBurgasser CS13 2003 Burgasser et al. (2001) Kirkpatrick et al. ‘99 VO CrH,FeH TiO, VO H FeH NaID,K H2O CaH Hyd, alk Rb Rb,Cs  CH4 • K Li CrH Cs H2O Martín et al ‘99 wraps in L4-L8 in only 2 extra subtypes (to L6) 1/3 of 2MASS field L dwarfs but ZERO T dwarfs show Li 6708Å Hundreds of L dwarfs and at least 30 T dwarfs known

3. MLT Spectral Sequencenear-IR spectral rangeBurgasser, CS12, 2003 H2,CH4 CO KI  no FeH H2 Changes in H2O bands behavior due to dust DO NOT define M-L transition L-T transition defined by onset of CH4 in H and K bandpasses

10. Grain extinction cross-section (Mie) per particle as a function of wavelength for species we include. The monoatomiques monomers such as the metals only contribute as diffusion (dotted lines) in the UV to visual, while corundum, magnesium spinel, CaTiO3, silicates absorb (full, dashed and dotted bleue lines) in the IR.

11. Mg2Si04 Al203 Mg2Si04 Extinction profile for a grain size distribution of 1, 2, 10, and 100 times that of the ISM, for conditions prevailing in the photospheric layers (T1300K) of our AMES-Dusty model at Teff = 1800K. Spectral features seen above 8.5 m are due to Mg2SiO3 and MgAl2O4.

12. Model Grids name dust handling reference NextGen none Allard et al. (1996) Dusty/CondEquilibrium Allard et al. (2001)

13. 2 models to bracket de solution Allard et al. (2001)

15. Phenomenological Model: • Chemical equilibrium • Dust monomers in equilibrium with gas phase • Cloud bottom set to its hottest CE condensation level • Cloud extension controlled by convective turbulent updraft refueling cloud layers with refractory material • Hydrostatic equilibrium  T, Pgas (done independently before) We solve layer by layer outwards: • Grain diffusion (cond., sed., mix.)  Ngrain , rgrain • Revised elemental abundances • Chemical equilibrium • Go back to 1) and repeat until no more grain forms B. Radiative transfer, spectrum, model iteration, and back to A) till model converged General Principle

16. Quasi-Static Cloud Model Refractory Elements

17. Microphysical and convective characteristic time scales as a function of mean particle radius Grain growth: • Convection transports condensable gas up • Sedimentation (rain) brings dust particles down • Condensation increases radii of small particles • Coalescence brings large particles together Last 3 timescales estimated using Rossow (1978)

19. Surface convection in late M dwarfLudwig, Allard, Hauschildt, ApJ 2002 • RHD simulation • Teff =2800K, logg=5.0 • Vertically: • timescale=100 sec • velocities=240 m/s • Horizontally: • cell size = 80 km • contrast 1.1%

20. Mass exchange frequency as a function of Pressure for various degrees of subsonic filtering

21. Considered Mixing Options • Phenomenological model i.e.with NO free parameter • mix   conv Hp /inside the convection zone. • mix  parabola of same opening above the convection zone.

22. New Model Grids New alkali line profiles for NaI D & KI by Allard N. F. et al. (2003, 2005) New solar abundances by Asplund, Grevesse & Sauval (2005, astro-ph/04102v2) New cloud model by Allard et al. (2003, IAU 211, ASP, p.325) New line data for CaH & VO C-X systems (B. Plez GRAAL) Update on QTiO( X 3 or 0.5 dex too large!)  X 3 larger TiO opacity!  weaker contrast to lines! name dust handling reference NextGen none Allard et al. (1996) Dusty/Cond Equilibrium Allard et al. (2001) Settl Cloud Model Allard et al. (2003) to replace Dusty Rainout Full Sedimentation to replace Cond

23. Tsuji et al. (1999, 2002)  Tcr Ackerman & Marley (2001)  frain Cooper et al. (2002)  Smax

24. Metals’ Depletion

25. “Parabolic” Cloud Model Allard, Guillot, Ludwig et al. (2003)

26. Tmix & Ngrains vs Tau1,2 Ludwig, Allard, Hauschildt (2002) IN Ngrains Tmix OUT

27. LAH02 Model Constant gravity locus: logg=5.0

28. Conclusions MLT and perhaps Y transition is highly sensitive to turbulence !  3D RHD convection simulations needed to study the range and type of turbulence dependence upon optical depth, Teff, and surface gravity. Project for the next 3 yrs: modeling cloud formation with 3D RHD COBOLD models in BDs  import Phoenix’s opacities and CE into COBOLD  import cloud model into COBOLD

29. Gravity Effect? Constant gravity locii: 5.0 & 5.5

31. Évolution de Phoenixpériode 2005 - 2015 • Transfert radiatif 3Dvs1D en symétrie sphérique PHH • Diffusion géométriquevsisotropie JP • Croissance des grainsvstaux de condensation (Rossow ‘78) CH • Diffusion des grainsvssolution linéaire au 1er ordre FA • Photochimie vséquilibre chimique de gaz idéal FS • Chimie non-idéale (SC)vs équilibre chimique de gaz idéal FA • Profiles de raies unifiésvs profiles de Lorentz NFA • Extension de nos calculs d’équilibre chimique jusqu’à 10K FA • Complétion de nos bases d’opacités moléculaires jusqu’à 10K JF PHH= P. H. Hauschildt (Obs. de Hamburg); NFA= Nicole F. Allard (IAP) JP = Jimmy Paillet (CRAL, PhD ss ma dir.); CH= C. Helling (Univ. T. de Berlin) FS = Franck Selsis (CRAL, CR2 ss ma dir.); JF= Jason Ferguson (WSU)