Spatially resolved images of dust belt(s) around the planet-hosting subgiant kappa CrB

We present Herschel spatially resolved images of the debris disc orbiting the subgiant kappa Coronae Borealis (kappa CrB). Not only are these the first resolved images of a debris disc orbiting a subgiant, but kappa CrB is a rare example of an intermediate mass star where a detailed study of the structure of the planetary system can be made, including both planets and planetesimal belt(s). The only way to discover planets using the radial velocity technique around such stars is to observe 'retired' A stars, which are cooler and slower rotators compared to their main-sequence counterparts. A planetary companion has already been detected orbiting the subgiant kappa CrB, with revised parameters of m sin i = 2.1 M-J and a(pl) = 2.8 au (Johnson et al. 2008). We present additional Keck I HIRES (High Resolution Echelle Spectrometer) radial velocity measurements that provide evidence for a second planetary companion, alongside Keck II adaptive optics imaging that places an upper limit on the mass of this companion. Modelling of our Herschel images shows that the dust is broadly distributed, but cannot distinguish between a single wide belt (from 20 to 220 au) or two narrow dust belts (at around 40 and 165 au). Given the existence of a second planetary companion beyond similar to 3 au it is possible that the absence of dust within similar to 20 au is caused by dynamical depletion, although the observations are not inconsistent with depletion of these regions by collisional erosion, which occurs at higher rates closer to the star.