Resolved debris disc emission aroundηTelescopii: a young solar system or ongoing planet formation?

Abstract

Aims. Sixty percent of the A 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 proto-planetary disc is thought to disperse. Theoretical models suggest this peak may coincide with the formation of Pluto-sized planetesimals in the disc, stirring smaller bodies into collisional destruction. Here we present resolved mid-infrared imaging of the disc of η Tel (A0V in the BPMG) and consider its implications for the state of planet formation in this system. Methods. The source was observed at 11.7 and 18.3 μm using T-ReCS on Gemini South. The resulting images were compared to simple disc models to constrain the radial distribution of the emitting material. Results. The emission observed at 18.3 μm is shown to be significantly extended beyond the PSF along a position angle 8 ◦ . This is the first time dust emission has been resolved around η Tel. Modelling indicates that the extension arises from an edge-on disc of radius 0.5 arcsec (∼24 AU). Combining the spatial constraints from the imaging with those from the spectral energy distribution shows that >50% of the 18 μm emission comes from an unresolved dust component at ∼ 4A U. Conclusions. The radial structure of the η Tel debris disc is reminiscent of the Solar System, suggesting that this is a young Solar System analogue. For an age of 12 Myr, both the radius and dust level of the extended cooler component are consistent with selfstirring models for a protoplanetary disc of 0.7 times minimum mass solar nebula. The origin of the hot dust component may arise in an asteroid belt undergoing collisional destruction or in massive collisions in ongoing terrestrial planet formation.