Inferring the size scales of planetary systems using resolved debris discs

Circumstellar debris discs are tenuous remnant rings of icy and rocky material left over from planet(esimal) formation processes around their host stars. Possible relationships between stellar luminosity and disc parameters have been examined. Based on analysis of a sample of 39 spatially resolved debris discs at infrared wavelengths by Herschel, a trend between stellar luminosities (L_star ) and the ratio of the discs' resolved radii (R_d) to blackbody radii (R_bb) was noted. We have examined a larger sample of resolved debris discs from archival far-infrared Herschel observations in order to determine the fidelity of that trend. We further examine whether the inferred extents of these discs are consistent with self-stirring models or may be indicative of dynamical perturbation by a planetary companion. Disc radii were determined by fitting the source brightness profiles with simple annular disc models convolved with a PSF. We obtain good agreement between the resolved extent of debris discs as measured at millimetre wavelengths and the estimates based on L_star and R_d/R_bb at far-infrared wavelengths, suggesting that the measured trend is a fair, albeit imperfect, predictor of actual disc extent. In future work we will apply this revised relationship to the larger sample of unresolved debris discs in an attempt to identify systems that exhibit evidence of stirring by a planetary companion.