Centre de Recherche Astronomique de Lyon (CRAL),
Ecole Normale Supérieure de Lyon, Lyon, Cedex 07, 69364 France
E-Mail: fallard@ens-lyon.fr
Dept. of Physics and Astronomy & Centre for Simulational Physics,
University of Georgia, Athens, GA 30602-2451
Email: yeti@hal.physast.uga.edu
Dept. of Physics, Wichita State University,
Wichita, KS 67260-0032
E-Mail: dra@twsuvm.uc.twsu.edu
Dept. of Physics and Astronomy,
University of Georgia, Athens, GA 30602-2451
Email: andy@physast.uga.edu
We find that silicate dust grains can form abundantly in the outer atmospheric layers of red and brown dwarfs with spectral type later than M8. The greenhouse effects of dust opacities provide a natural explanation for the peculiarly red spectroscopic distribution of the latest M dwarfs and young brown dwarfs. The grainless (Cond) models on the other hand, correspond closely to methane brown dwarfs such as Gliese 229B. We also recover that the 5891,5897Å Na I D and 7687,7701Å K I resonance doublets plays a critical role in T dwarfs where their red wing define the pseudo-continuum from the I to the Z bandpass.
low mass stars,brown dwarfs,grains,fundamental parameters