THE DENSITY STRUCTURE OF THE PROTOSTELLAR DISK - A POWER-LAW DISTRIBUTION OF THE DUST AROUND GGD-27-IRS

We have made submillimeter continuum observations toward GGD 27 IRS, a well-defined bipolar outflow plus dense disk system. Photometry was done in the wavelength range of 350 μm to 1.1 mm toward the peak, and spatial distributions at 450 and 800 μm were measured. Both emissions consist of a very compact (FWHM ∼ 20″) core and a diffuse component which is aligned to the previously known dense molecular disk. A numerical model calculation that fits to the current data favors power-law radial distributions of dust density and temperature, with exponents of α = 1.8-2.2 and γ = 0.2-0.4 and a spectral index of the dust emissivity β= 1.5. The dust distribution, and hence, the total mass distribution thus derived reproduce the nature of the simulated model of the rotating isothermal cloud. The total gas and dust mass of the disk is estimated to be about 100 M⊙ within the radius of 30″ (0.25 pc), assuming a dust emissivity of 3.9 cm2 g-1 at 400 μm and a gas-to-dust ratio of 100.