From pwl@herts.ac.uk Tue Oct 31 15:39:29 2006
Date: Mon, 30 Oct 2006 12:36:44 +0000 (GMT)
From: Phil Lucas <pwl@herts.ac.uk>
To: DIANE GREENING <DIANE.GREENING@pparc.ac.uk>
Subject: Report on G/07A/34

Report on G/07A/34: "Resolving the structure of debris disks
around 30-100 Myr A stars"

P.I. Mark Wyatt

Spatially resolved debris disc systems have rapidly increased
in number in recent years. These systems are important because
they provide perhaps the best available clues to understanding of
the mysterious process of planet formation.
This proposal aims to spatially resolve 2 debris disc systems
in the mid-IR that have greater ages than any previously imaged
in this waveband. Although debris disks have been resolved around 
some much older systems at submm and optical wavelengths
(eg. Kalas et al.2006, ApJLetters 637,57) the proposers argues that
mapping of mid-IR emission in relatively old systems could tell us 
something important. Since the reason for lack of spatially resolved
mid-IR emission in old systems is not known it is not clear that this 
is the case. Successful observations might provide some hint of how
the disc size changes with age, or detect clumps attributable
to collisions between protoplanets, as the proposers suggest.
As far as I can tell most debris disc systems have not yet been
imaged at high spatial reesolution in the mid-IR.

These observations are time consuming and the technical feasibility
seems questionable to me, since there is a long time delay (1.5 
hours) between observation of the targets and the PSF reference star, in 
which time the image profile could change significantly. The models
in Figure 1 do not appear to address the issue of PSF stability,
though it is stated in the science case that problems occurred with
the instrument during the previous Gemini run. 
While I am not a mid-IR observing expert, and the TAC may 
disagree, I would therefore suggest giving the minimum requested 
allocation (or half the total maybe) in order to observe only HD181296, 
since the predictions in Figure 1 show that the disc around this star is 
far more likely to be resolved than that around HD1438. HD1438
looks a bit marginal.

Grade: 3
Referee: Phil Lucas
Self Assessment: 2