A simple criterion for selecting disks with evidence for dust growth and settling

Dust growth and settling, as an initial step of planet formation in protoplanetary disks, have an important impact on the appearance of the spectral energy distribution (SED). Selecting a promising sample of disks with signs of these processes helps to guide future observations towards a better understanding of the initial conditions for planet formation and disk evolution. Using a standard flared disk model, we conducted a large parameter study to investigate the effects of various disk parameters on the overall shape of the SED. We found that the flaring index and scale height can be used to mimic the effects of dust evolution on the SED. The influences of these two parameters on the infrared excess are very similar to that caused by dust evolution which have been shown in previous simulations where grain growth and settling are treated directly. Based on a statistic analysis of all the models in our grid, we proposed a criterion of Psi >= 0.6 to diagnose signs of dust evolution, where Psi is a ratio defined by dividing a linearly interpolated (between 24 mu m and 1.3 mm) flux at 70 mu m by the observed 70 mu m photometry. We tested the applicability of our criterion with the class II disks in the Taurus star formation region.