From: Rachel G. (gibbo@panisse.lbl.gov)
Date: Thu Mar 13 2003 - 13:24:03 PST
Rob,
I'll post on Monday some minor comments I have
concerning wording, and where I think some description could
be beefed up. But right now, I do have a few (possibly more
important) comments regarding the use of TinyTim PSFs.
I think there should be a short description of how
the model PSFs were produced - for instance, what spectral
energy distribution you used, etc.
Second, I know TinyTim works best for the NIC1 and
2 cameras where the PSF is well-sampled, but PSFs across the
WFPC2 are supposedly harder to model because of
undersampling. I don't know what this means in terms of how
it should be accounted for in the photometric errors (was
it?). Perhaps none of this matters at a measureable level
due to the faintness of the objects in this sample, but I
think it would be nice to simply be able to state that - if
you remember any specifics about the tests you did.
And if it hasn't already been done I would be
willing to run some comparisons between TinyTim models and
stellar images from our WFPC2 data, to get you something
quantitative on how small this measurement error is. I
remember doing this with STIS data and found TinyTim PSFs to
be consistently too narrow compared to empirical point
source images - at least for the models I was interested in.
To put your mind at ease, the differences were not
significant and possibly minimal, although I can't quote a
number for you now. Anyway, this should be one additional
line in the paper.
I'll also get the TinyTim reference for you - I know
John Krist and Richard Hook developed the software, but I
haven't looked at this stuff in a long time.
Rachel
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