New approach to diagnosing properties of protoplanetary disks

In this paper we suggest that subjecting the observationally derived proper ties of protoplanetary disks to the evolutionary interpretation yields new insights into the working of those disks, and offers valuable constraints o n their models. We propose that the global properties of individual disks, such as their accretion rates and disk masses, sorted by the mass of the ce ntral star, can be indexed by the age of the star to simulate the evolution of a single disk. Using data from published surveys of T Tauri stars, we s how that accretion rate data, and disk mass data for the lowest mass stars, form well-defined evolutionary tracks. The higher mass stars show a defini tive negative correlation between accretion rates and star ages. We use the time-dependent alpha-disk model of the Viscous protoplanetary disk to link the theory to observations. The data are consistent with the standard theo retical paradigm, but not with the layered accretion model. The best fits t o the data are obtained for the standard models that start with disks that are about one-third of the mass of the central star and have their angular momenta, j, and alpha-coefficients linked by the relationship j proportiona l to M-*(3/2) alpha(1/3). The proportionality constant in this relationship , when derived from the accretion rate data, differs from the constant deri ved from the disk mass data. We argue that the accretion rate data are more reliable. Taking into account typical values of the specific angular momen tum of disk-forming matter, we obtain alpha greater than or equal to 10(-2) . A complete time-dependent standard disk model, built on the parameters de termined from the best-fit procedure, is presented. Such a model constitute s a good point of departure for various theoretical studies aimed at the is sue of formation of planetary systems and the character of protoplanetary d isks.