  60% of the A star members of the 12 Myr old beta Pictoris moving group (BPMG)
show significant excess emission in the mid-infrared, several million years
after the proto-planetary disk is thought to disperse. Theoretical models
suggest this peak may coincide with the formation of Pluto-sized planetesimals
in the disk, stirring smaller bodies into collisional destruction. Here we
present resolved mid-infrared imaging of the disk of eta Tel (A0V in the BPMG)
and consider its implications for the state of planet formation in this system.
eta Tel was observed at 11.7 and 18.3um using T-ReCS on Gemini South. The
resulting images were compared to simple disk models to constrain the radial
distribution of the emitting material. The emission observed at 18.3um is shown
to be significantly extended beyond the PSF along a position angle 8 degrees.
This is the first time dust emission has been resolved around eta Tel.
Modelling indicates that the extension arises from an edge-on disk 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 18um
emission comes from an unresolved dust component at ~4 AU. The radial structure
of the eta Tel debris disk is reminiscent of the Solar System, suggesting that
this is a young Solar System analogue. For an age of 12Myr, both the radius and
dust level of the extended cooler component are consistent with self-stirring
models for a protoplanetary disk 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.
