Arne, Maurice and Seiichiro, Thanks for the comments. Unfortunately it appears that I've scrapped all the images except one of V803 Centauri. This is attached. I hope you can use ST6 images. The effect is not large in this image, although it's greater in some of the ones I can't locate. It seems to be about 20% of the background sky brightness which is not normally large. I'm at a very dark site in the Far North of NZ with the only towns - Awanui 300 people at 7 miles and Kaitaia 7500 at 10 miles. There is little night time lighting in either. The telescope in the BVRI configuration is a Meade LX6, which is 8" f6.3. The filters are from Mike Bessell and have been described by him in a publication, CCD Astronomy I think it was. These are 25mm in diameter and there is severe vignetting in this telescope due to the large filter-detector distance. I don't use any optical devices - focal reducers or Barlows - and the corrector plate on this telescope is not heated. My BVRI work is largely a summertime pursuit when dewing is not much of a problem. I don't see the effect in unfiltered images, but here it would be about 10 times less if it were purely an IR effect. In the summer the ambient night temperatures are probably 15C to 23C. In my naive way I would have thought the various components would radiate at close to 1 micron at that level. I'm suffering from a bad summer cold at present so won't be able to get at the telescope for a night or two. But I'll try the ideas suggested by Arne as soon as possible. I'd given up the idea of I photometry and decided on just BVR measures because of this problem. But one other interest - and it's largely why I asked - is that the unfiltered photometry might be improved by putting the IR blocking filter back in the system. Since I'm looking at CVs with the CBA there's not really a need for IR sensitivity. Regards, Stan ---------- > From: aah@nofs.navy.mil > To: vsnet-chat@kusastro.kyoto-u.ac.jp > Subject: [vsnet-chat 2492] Re: ST6 - IR Blocking Filter
V803-i.011 (011 File)
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