2004/02/16 by Takashi Tsuji, Tadashi Nakajima, Kenshi Yanagisawa · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/383300
published as Astrophys.J. 607 (2004) 499-510 · 43 pages, 13 figures, to appear in Astrophys. J. (May 20, 2004) Some minor corrections including the address of our web site, which is now ready
arxiv created 2004/02/16 · openalex publication_date 2004/05/17 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We report an attempt to interpret the spectra of L and T dwarfs with the use of the unified cloudy model (UCM). For this purpose, we extend the grid of the UCMs to cases of log g = 4.5 and 5.5. The dust column density relative to the gas column density in the observable photosphere is larger at higher gravities, and molecular line intensity is generally smaller at higher gravities. The overall spectral energy distributions (SEDs) are f J < f H < f K in middle and late L dwarfs, f J < f H > f K in early T dwarfs (L/T transition objects), and finally f J > f H > f K in middle and late T dwarfs, where f J , f H , and f K are the peak fluxes at J , H , and K bands, respectively, in f ν units. This tendency is the opposite of what is expected for the temperature effect, but it can be accounted for as the effect of thin dust clouds formed deep in the photosphere together with the effect of the gaseous opacities, including H 2 (collision-induced absorption), H 2 O, CH 4 , and K I. Although the UCMs are semiempirical models based on a simple assumption that thin dust clouds form in the region of T cr ≲ T ≲ T cond ( T cr ≈ 1800 K is only an empirical parameter, while T cond ≈ 2000 K is fixed by the thermodynamical data), the major observations, including the overall SEDs and the strengths of the major spectral features, are consistently accounted for throughout L and T dwarfs. In view of the formidable complexities of the cloud formation, we hope that our UCM can be of some use as a guide for future modeling of ultracool dwarfs and for interpretation of observed data of L and T dwarfs.