ABSTRACT. We present a spectral analysis of a sample of late L dwarfs. We use our latest model atmospheres and synthetic spectra and optical and K-band spectra to determine effective temperatures. We derive effective temperatures of 1400-1700 K for L8-L6 dwarfs. The analysis demonstrates that our recent models that rain out the formed dust completely are applicable to optical spectra of late L dwarfs and that more consistent models are needed for intermediate L dwarfs and for infrared spectra. We compare the results for the effective temperatures with the temperatures of the onset of methane formation. Our models predict methane absorption at 3.3 μm to occur at temperatures about 400 K higher than methane absorption at 2.2 μm. This is consistent with our data and previous observations, which show methane absorption at 3.3 μm, but not at 2.2 μm, in late L dwarfs.

Subject headings: molecular processes; stars: atmospheres; stars: fundamental parameters; stars: low-mass, brown dwarfs

Print publication: Issue 1 (2002 February 10)
Received 2001 July 13, accepted for publication 2001 October 11