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Planet Signatures in Collisionally Active Debris Discs: scattered light images

Planet perturbations are often invoked as a potential explanation for many spatial structures that have been imaged in debris discs. So far this issue has been mostly investigated with collisionless N-body numerical models. We numerically investigate how the coupled effect of collisions and radiation pressure can affect the formation and survival of radial and azimutal structures in a disc perturbed by a planet. We consider two set-ups: a planet embedded within an extended disc and a planet exterior to an inner debris ring. We use the DyCoSS code of Thebault(2012) and derive synthetic images of the system in scattered light. The planet's mass and orbit, as well as the disc's collisional activity are explored as free parameters. We find that collisions always significantly damp planet-induced structures. For the case of an embedded planet, the planet's signature, mostly a density gap around its radial position, should remain detectable in head-on images if M_planet > M_Saturn. If the system is seen edge-on, however, inferring the presence of the planet is much more difficult, although some planet-induced signatures might be observable under favourable conditions. For the inner-ring/external-planet case, planetary perturbations cannot prevent collision-produced small fragments from populating the regions beyond the ring: The radial luminosity profile exterior to the ring is close to the one it should have in the absence of the planet. However, a Jovian planet on a circular orbit leaves precessing azimutal structures that can be used to indirectly infer its presence. For a planet on an eccentric orbit, the ring is elliptic and the pericentre glow effect is visible despite of collisions and radiation pressure, but detecting such features in real discs is not an unambiguous indicator of the presence of an outer planet.