Multiwavelength modelling of the β Leo debris disc: One, two or three planetesimal populations?

In this paper we present a model of the β Leo debris disc, with an emphasis on modelling the resolved Photodetector Array Camera and Spectrometer (PACS) images obtained as a part of the Herschel key programme DEBRIS. We also present new Spectral and Photometric Imaging REceiver (SPIRE) images of the disc at 250μm, as well as new constraints on the disc from SCUBA-2, mid-infrared (mid-IR) and scattered light imaging. Combining all the available observational constraints, we find three possible models for the β Leo (HD 102647) debris disc: (i) a two-component model, comprised of a hot component at 2 au and a cold component from 15 to 70 au; (ii) a three-component model with hot dust at 2 au, warm dust at 9 au and a cold component from 30 to 70 au, is equally valid since the cold emission is not resolved within 30 au; (iii) a somewhat less likely possibility is that the system consists of a single very eccentric planetesimal population, with pericentres at 2 au and apocentres at 65 au. Thus, despite the wealth of observational constraints significant ambiguities remain; deep mid-IR and scattered light imaging of the dust distribution within 30 au seems to be the most promising method to resolve the degeneracy. We discuss the implications for the possible planetary system architecture, e.g. the two-component model suggests that planets may exist at 2-15 au, while the three-component model suggests planets between 2 and 30 au with a stable region containing the dust belt at 9 au, and there should be no planets between 2 and 65 au in the eccentric planetesimal model. We suggest that the hot dust may originate in the disintegration of comets scattered in the cold disc, and examine all A stars known to harbour both hot and cold dust to consider the possibility that the ratio of hot and cold dust luminosities is indicative of the intervening planetary system architecture.