Unified Model Photospheres for Ultracool Dwarfs of Types L and T

摘要: The presence of the two distinct groups ultracool dwarfs (UCDs), ‘L’ and ‘T’ types, is now well established: L are thought to be dusty while T show strong bands methane (CH4) but little evidence for dust in their spectra. So far, different model sequences, which we referred as (or case B) dust-segregated C) have been considered dwarfs. We propose instead that these UCDs may understood a temperature effect unique sequence photospheres always exists only restricted region (where 1800 ≲ 2000 K) an active zone cloud). This natural consequence considering not formation also its segregation process photosphere. By this sequence, dust-column density observable photosphere first increases cooler objects infrared colours become redder from late M On other hand, decreases than latest moves optically thick deep turn blueward towards coolest In way, observed spectra through types can explained consistently by single grid unified photospheres. More generally, important conclusion photospheric effective warmer regions. contrary general belief forms surface