Modeling the spectral energy distributions of L dwarfs

Mechanisms for the formation of the optical (λλ500–950 nm) spectra of L dwarfs—stars and sub-stellar objects with Teff<2200 K—are discussed. Their spectral energy distributions are determined primarily by the K I and Na I resonance-doublet absorption lines. The equivalent widths of these absorption lines formally computed using the dusty model atmospheres of Tsuji can reach several thousand angstroms. In this case, the extended wings of these lines form a pseudo-continuum for weaker absorption lines and even molecular bands. Mechanisms for the broadening of alkali-element lines in the atmospheres of late-type stars due to interactions between neutral atoms and hydrogen molecules are analyzed. The computed optical spectral energy distributions of several L dwarfs are compared with their observed spectra.