THE ACCURACY OF INFRARED PHOTOMETRY WITH ARRAYS

The photometric accuracy and repeatability of an InSb array in the infrared camera IRCAM is investigated. Measurements of standard stars are described; these were made using the United Kingdom Infrared 3.8-m Telescope (UKIRT) over five nights in May 1988, as part of an observational program on globular clusters. Observations were made at wavelengths of 1.25-mu-m (J) and 2.2-mu-m (K). The results show clearly that the camera-array combination is capable of a photometric accuracy of better than 1% when the standard-star images obtained with short on-chip exposure (0.5 sec) are flat fielded with long on-chip exposure (7-50 sec) sky flats. Linearity corrections determined in the laboratory were applied to the data and there was no evidence of residual nonlinearity of > 2% over the magnitude range 6.m5-13.m0. The range of mean nightly zero points at K during the five nights was 0.m03, showing that both the site and the camera system were very stable over this period. At J the zero points were less well determined and had twice this range during three nights.