INDICATIONS FOR GRAIN GROWTH AND MASS DECREASE IN COLD DUST DISKS AROUND CLASSICAL T TAURI STARS IN THE MBM 12 YOUNG ASSOCIATION

摘要

We report the detection of continuum emission at λ = 850 and 450 μm from disks around four classical T Tauri stars in the MBM 12 (L1457) young association. Using a simple model, we infer masses of 0.0014―0.012 solar mass for the disk of LkHα 263 ABC, 0.005―0.021 solar mass for S18 ABab, 0.03―0.18 solar mass for LkHα 264 A, and 0.023―0.23 solar mass for LkHα 262. The disk mass found for LkHα 263 ABC is consistent with the 0.0018 solar mass inferred from the scattered-light image of the edge-on disk around component C. Comparison to earlier ~(13)CO line observations indicates CO depletion by up to a factor of 300 with respect to dark-cloud values. The spectral energy distributions (SEDs) suggest grain growth, possibly to sizes of a few hundred microns, but our spatially unresolved data cannot rule out opacity as an explanation for the SED shape. Our observations show that these T Tauri stars are still surrounded by significant reservoirs of cold material at an age of 1―5 Myr. We conclude that the observed differences in disk mass are likely explained by binary separation affecting the initial value. With available accretion rate estimates we find that our data are consistent with theoretical expectations for viscously evolving disks having decreased their masses by ～30%.