Spatial dependent systematic error correction and colour coefficients for the 2-m telescope of the Rozhen National Astronomical Observatory

Spatial dependent systematic error of the instrumental magnitudes on the CCD frames taken at the 2-m telescope of the Rozhen National Astronomical Observatory due to scattered light was present till mid-June 2009. We derive and discuss (U)BVRI spatial dependent systematic error correction, together with colour coefficients, on the basis of archival data. The simultaneous estimation of the two types of coefficients spatial and colour, ensures the detachment of the two effects, and, accordingly, the higher accuracy in the coefficient estimates. The application of the spatial dependent systematic error correction to the data in the period discussed would increase photometry accuracy. Key words: techniques: photometric