American Association of Variable Star Observers (AAVSO)
Fri, 12/25/2020 - 18:16

What is the proper way to deal with SR images from BSM systems when using VPhot?  I've found that "renaming" SR images to R from the Available Images window allows VPhot processing to proceed normally, but I don't know if we can assume that SR transforms to R.  

Please advise.



American Association of Variable Star Observers (AAVSO)
SR Filter Transformation to R magnitude in VPhot


1. In the case where there is an SR filter present instead of an R filter on a specific telescope, I have normally generated transformation coefficients which transform the SR magnitude to an R magnitude, entered them in VPhot and added a note to that effect.

2. This means that if you collect both an SR image and another filter image like V, you should use these available coeffs to provide both a transformed R mag and a transformed V mag.

3. In order to do that, you do first rename the SR filter image to R. Then you run two color transformation as normal. The magnitude generated is calculated as and is to be reported as an R mag. This will also work for TA in the cases where you renamed multiple SR images to R images.

4. I hope this is understandable. Questions?

5. HOWEVER, IF you are only using an SR image (single filter photometry not color photometry), it is NOT appropriate to rename an SR image to an R image, conduct non-transformed photometry, and report the magnitude as R mag. The image was taken with an SR filter. In this case you MUST obtain an SR comp(s) magnitude from the APASS database and edit your sequence to include this SR magnitude. This obviously requires knowledge and additional effort! I recommend using BVI filters for most of your multi-color photometry.

6. These issues will frankly only be resolved when Sloan Magnitudes are appended to the AAVSO Comp Database.