Steady-state evolution of debris discs around solar-type stars

Abstract

We present an analysis of debris disk data around Solar-type stars (spectral types F0-K5) using the steady-state analytical model of Wyatt et al. (2007a). Models are fitted to published data from the FEPS (Meyer et al. 2006b) project and various GTO programs obtained with MIPS on the Spitzer Space Telescope at 24�m and 70�m, and compared to a previously published analysis of debris disks around A stars using the same evolutionary model. We find that the model reproduces most features found in the data sets, noting that the model disk parameters for solar-type stars are different to those of A stars. Although this could mean that disks around Solar-type stars have different properties from their counterparts around earlier-type stars, it is also possible that the properties of disks around stars of different spectral types appear more different than they are because the blackbody disk radius underestimates the true disk radius by a factor Xr which varies with spectral type. We use results from realistic grain modelling to quantify this effect for solar-type stars and for A stars. Our results imply that planetesimals around solar-type stars are on average larger than around A stars by a factor of a few but that the mass of the disks are lower for disks around FGK stars, as expected. We also suggest that discrepancies between the evolutionary timescales of 24�m statistics predicted by our model and that observed in previous surveys could be explained by the presence of two-component disks in the samples of those surveys, or by transient events being responsible for the 24�m emission of cold disks beyond a few Myr. Further study of the prevalence of two component disks, and of constraints on Xr, and increasing the size of the sample of detected disks, are important for making progress on interpreting the evolution of disks around solar-type stars.