DUNES: DUst around NEarby Stars
A Herschel Key Programme

A debris disc is the by-product of a planet formation process around another star. These discs are composed of dust grains ranging in size from microns to millimetres, and usually observed at far infra-red wavelengths as emission in excess of that predicted from the stellar photosphere. Although more than 200 of these debris disc systems have been identified through surveys by (for example) IRAS and Spitzer, only a handful of the discs have been resolved. Imaging these systems is vital if a connection is to be made between the visible dust disc and any larger bodies in the system. This is due to the degeneracy between physical parameters of the dust grains and their spatial location in modelling the emission from these systems. In several systems where the disc has been imaged, evidence suggesting the dynamical influence of an unseen planetary mass body working on the dust has been observed, e.g. the warp in the Beta Pictoris disc or the positional offset of the disc around Fomalhaut.

The Herschel DUNES program has observed a volume limited (< 20pc) sample of 133 sun-like (FGK spectral type) stars with the PACS and SPIRE instruments, of which 19 are known to be host to one or more exoplanets. Several of these have also been identified as debris disc systems, both from previous Spitzer surveys and new Herschel/DUNES detections. The key factor is the ability of Herschel to resolve the physical extent of the dust disc, uniquely constraining the dust location and thereby breaking the model degeneracy based on unresolved emission alone.

I will present results of the DUNES observations of these exoplanet host stars, focussing on two specific examples, HIP7978 and HIP15371, where the observed dust spatial distribution implies the existence of an unseen exoplanet shaping the debris disc.