The Open University ’ s repository of research publications and other research outputs Can eccentric debris disks be long - lived ? A first

Context. Imaging of debris disks has found evidence for both eccentric and offset disks. One hypothesis is that these provide evidence for massive perturbers, for example planets or binary companions, that sculpt the observed structures. One such disk was recently observed in the far-IR by the Herschel Space Observatory around ζ2 Reticuli. In contrast with previously reported systems, the disk is significantly eccentric, and the system is Gyr-old. Aims. We aim to investigate the long-term evolution of eccentric structures in debris disks caused by a perturber on an eccentric orbit around the star. We hypothesise that the observed eccentric disk around ζ2 Reticuli might be evidence of such a scenario. If so we are able to constrain the mass and orbit of a potential perturber, either a giant planet or binary companion. Methods. Analytical techniques are used to predict the effects of a perturber on a debris disk. Numerical N-body simulations are used to verify these results and further investigate the observable structures that could be produced by eccentric perturbers. The long-term evolution of the disk geometry is examined, with particular application to the ζ2 Reticuli system. In addition, synthetic images of the disk are produced for direct comparison with Herschel observations. Results. We show that an eccentric companion can produce both the observed offsets and eccentric disks. Such effects are not immediate and we characterise the timescale required for the disk to develop to an eccentric state (and any spirals to vanish). For the case of ζ2 Reticuli, we place limits on the mass and orbit of the companion required to produce the observations. Synthetic images show that the pattern observed around ζ2 Reticuli can be produced by an eccentric disk seen close to edge-on, and allow us to bring additional constraints on the disk parameters of our model (disk flux, extent). Conclusions. We determine that eccentric planets or stellar companions can induce long-lived eccentric structures in debris disks. Observations of such eccentric structures, thus, provide potential evidence of the presence of such a companion in a planetary system. We consider the specific example of ζ2 Reticuli, whose observed eccentric disk can be explained by a distant companion (at tens of AU), on an eccentric orbit (ep & 0.3).