Photometric calibration of the CCD camera of 1-m telescope at VBO

Abstract

Calibration of the CCD camera of the 1-m telescope at the Vainu Bappu Observatory, Kavalur, to the BVR system is reported here based on the observations of stars in the 'dipper asterism' in the open cluster M 67 (NGC 2682). Transformations involving B and V have negligible color terms, while those involving R are slightly color dependent. The possibility of using scaled-down R band fluxes to estimate the continuum flux at H-alpha is investigated by comparing the counts in R band with those through an interference filter center at H-alpha. The scaling factor is found to remain constant over a wide range of colors. The sensitivity of the telescope-filter-CCD combination is estimated to be 2.0 percent, 8.3 percent and 9.7 percent in B, V and R bands, respectively. The star F117 appears to be a small-amplitude (about 0.05 mag) variable