Status Report from Andrew Bennett, Jan 2002

This was supposed to be an end-of-year report from the Bennett independent processing effort but things were going so badly that I put it off.

1. Dark/Flat processing is back working again after some very depressing bug chasing. At last, with the dome flats and lots of averaging, processed data has lower noise than raw. A major improvement, Tom: let's keep on doing it this way!

2. I finally got tired of retuning my matching routines every time Tom kicked the mount - it took 3 sessions of tuning to get through the 3 days of data the first time. I took a fortnight off and translated Michael Richmond's matching routines into Pascal. Better. They went through the whole of Data Set 20 starting from the RA and Dec in the FITS header and with no further tuning, without missing one image. At 0.3 seconds/image they are both faster and more reliable than what I was using.

3. I am now managing to keep some image data, like "median" and "sigma" accessible to the photometry program. Yes - I know IRAF does all this sort of thing automatically but this is an *independent* effort. Read *pig-headed* if you like. I am using simple pruning criteria like median or sigma less than 150% of darkest, quietest image and thus manage to throw away all the data for Days 2239 and 2246 leaving only 2199. Looking at the raw photometry suggests that this is a good idea but it does rather cut down on the ability to detect variables!

4. Even after throwing away all this data, things don't look too good. The V-band noise floor is perhaps a little better than before - at least I have got it below 0.01 mags; some of the results before I got the bugs out of Dark/Flat processing were running more like 0.1 mags ... But the I-band is not as good as I got with Data Set Tom. It should be a lot better because stars are measured in more less the same place on the CCD each time instead of scattered randomly.

5. I have the first version of Ensemble Photometry running but the results are awful so far. Using only *good* sets for which the same ensemble of calibration stars is available in every case drastically reduces the amount of data and looks worse than the raw data! I will keep looking for the bugs ... but I fear that the problem is the small number of ensemble sources that are clean on every image: the increased statistical scatter from using fewer sources outweighs the improvement in systematic error from using the same sources each time. Or, as I said, I still have bugs.