A ug 1 99 5 Aperture Synthesis Imaging of the Circumstellar Dust Disk Around DO Tauri

We have detected the T Tauri star, DO Tauri, in a 0.6 ′′-resolution VLA map of 43.3 GHz (λ = 7 mm) continuum emission. The 43 GHz flux density lies on the same power-law slope defined by 89 to 232 GHz measurements, F ν ∝ ν α with index α = 2.39±0.23, confirming that the 43.3 GHz emission is thermal radiation from circumstellar dust. Upper limits to the flux densities at 8.4 and 22.5 GHz constrain the contribution of free-free emission from a compact ionized wind to less than 49%. The dust emissivity index, β, is 0.39±0.23, if the emission is optically thin. Fitting a model of a thin circumstellar disk to the observed spectral energy distribution gives β = 0.6 ± 0.3, consistent with the power-law derivation. Both values are substantially lower than is generally accepted for the interstellar medium, suggesting grain growth. Given the youth of DO Tau and the early evolutionary state of its circumstellar disk, this result implies that mm-size grains have already formed by the early T-Tauri phase.