Interpretation of the Spectra Originating from the Photospheres Contaminated with Dust - Experience in L and T Dwarfs

An essential feature of substellar dwarfs compared with the Sun and stars is the formation of dust in their photospheres (not in the outer envelope). It appears that the observed data could be understood if the dust exists in a form of thin cloud deep in the photosphere rather than in the cooler surface region. Recent observations also show that the dust column densities in the observable photosphere are quite different for the same effective temperature, gravity, and metallicity, but the reason for such a sporadic variation is unknown. Moreover, the effect of dust cloud is difficult to discriminate from those by other basic parameters such as the effective temperature which also has significant effect on the dust column density. For this reason, the spectra of dusty dwarfs were in fact misinterpreted by ourselves and will be reanalyzed in this contribution. Also, even the spectral classification is not free from such a difficulty, as is evidenced by an odd “brightening” of Mbol plotted against the L and T types.