2011MNRAS.410....2C

Two-thirds of the F star members of the 12 Myr old β Pictoris moving group (BPMG) show significant excess emission in the mid-infrared, several million years after the expected dispersal of the protoplanetary disc. Theoretical models of planet formation suggest that this peak in the mid-infrared emission could be due to the formation of Pluto-sized bodies in the disc, which ignite the collisional cascade and enhance the production of small dust. Here we present resolved mid-infrared imaging of the disc of HD 191089 (F5V in the BPMG) and consider its implications for the state of planet formation in this system. HD 191089 was observed at 18.3 µm using T-ReCS on Gemini South and the images were compared to models of the disc to constrain the radial distribution of the dust. The emission observed at 18.3 µm is shown to be significantly extended beyond the point spread function (PSF) at a position angle of 80°. This is the first time dust emission has been resolved around HD 191089. Modelling indicates that the emission arises from a dust belt from 28 to 90 au, inclined at 35° from edge on with very little emission from the inner 28 au of the disc, indicating the presence of an inner cavity. The steep slope of the inner edge is more consistent with truncation by a planet than with ongoing stirring. A tentative brightness asymmetry F_W/F_E= 0.80±0.12 (1.8σ) between the two sides of the disc could be evidence for perturbations from a massive body on an eccentric orbit in the system.