Re: Andrew's analysis of data set T

[Andrew Bennett <andrew.bennett@ns.sympatico.ca>]

On Sat, 3 Mar 2001 10:37:41 -0700, Arne
<aah@nofs.navy.mil> wrote:

>Could Andrew or someone remind me of what the exposure
>times were for the analyzed frames?  I don't see it in
>his memo. 
Right. The times are not there; I remarked
somewhere that I had not got round to parsing
Tom's log files ... hoping somebody else would
do it for me! I have used all the data: this includes
runs with short and long exposures and the long
exposures varied from time to time. A range of nearly
2 magnitudes. Most were around 100 seconds, I think.

> The I-band photometric error plot looks just
>like the bright end contains saturated stars.  Andrew
>says they are not, but does not give an explanation of
>how he decides saturataion level (it isn't always
>65535 ADU, for example).

Again you are right- I need to go back and look at this.

I looked at some earlier images and picked a value that
was close to saturation in the worst case. In those days,
saturation varied a lot across the images. Since then, Tom
has improved things greatly and the saturation value varies 
much less than it did before. I have used the same constant
value throughout. This should be very safe for all the recent
images but may be marginal in one corner of the older images.
As you say, it certainly looks like saturation.

>  Another possibility is the transformation for the
>Tycho stars used for the I-band calibration, since this
>transformation is nonlinear and highly luminosity class
>dependent.

The standard deviation I measured is the internal value
for the TASS data. It is quite independent of Tycho.

Andrew Bennett, Avondale Vineyard