All Figures

Figure 1: FORS2 red optical spectrum of the T1 dwarf  Indi Ba (solid), compared to our synthetic spectra for a 1.3 Gyr (dashed) and 2 Gyr (dotted) model. To highlight the various sources of opacity, spectra obtained when the K and Na D doublets are omitted (dot-dashed), and when dust grains involving Ca and other refractory species are prevented from forming and raining out (upper dotted line) are also shown. All molecular bands but CaH and H2O have been omitted from the latter spectrum for clarity. The EFOSC spectrum of  Indi Ba,b is shown from 8600-10 000 Å (light [magenta] solid line) against a composite model of both T dwarfs.

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In the text

Figure 2: Effective temperature sequence of log g = 5.0 Settl models with (solid) and without (dashed) CaH band opacity. The synthetic spectra have been degraded to 5 Å resolution for comparison with L dwarf spectra (thick [red] lines) observed with the Keck LRIS spectrograph (Martín et al. 1999; Reid et al. 2001,2000). Spectral subtypes of the L dwarfs are given in the optical classification system of Kirkpatrick et al. (1999, in prep.); note that DENIS J 0255-4700 has been typed L6 in the system of Martín et al. (1999). The sharp CaH band head near 7075 Å vanishes in both observed and model spectra between about L5 and L8, and a distinctive absorption feature emerges that extends well to the red of the original CaH band head. The models have Li abundance reduced to 1% (solid) and 0.1% (dashed), indicating strong Li depletion in all these field L dwarfs.

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In the text

	Figure 3: Partial pressures of principal Ca-bearing species versus optical depth in the Settl model for  K (thick lines) and 1600 K (thin lines). Gas temperature is shown (dotted lines) with the convection zones indicated (crosses), right scale.
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In the text