The color-magnitude ( CM ) diagram of cool dwarfs and brown dwarfs based on the recent astrometry data is compared with the CM diagram transformed from the theoretical evolutionary tracks via the unified cloudy models ( UCMs ) of L and T dwarfs .
A reasonable agreement between the models and observations is shown for the whole regime of ultracool dwarfs covering L and T dwarfs , and this is achieved , for the first time , with the use of a single grid of self-consistent nongray model photospheres accommodating dust cloud ( UCMs ; 700 \lesssim T _ { eff } \lesssim 2600 K ) .
A distinct brightening at the J band in the early T dwarfs revealed by the recent parallax measurements is explained as a natural consequence of the migration of the thin dust cloud to the inner region of the photosphere and should not necessarily be evidence for Burgasser et al. ’ s proposition that the dust cloud breaks up in the L/T dwarf transition .
Also , the rapid bluing from the late L to the early T dwarfs is a direct result of the transition of the thin dust cloud from the optically thin ( \tau < 1 ) to thick ( \tau \gtrsim 1 ) regimes while L _ { bol } and T _ { eff } lower only slightly .
Thus , the theoretical evolutionary models , the cloudy models of the photospheres ( UCMs ) , and the observed fundamental stellar parameters are brought into a consistent picture of the newly defined L and T dwarfs .