Deep-sky infrared imaging by reduction of the background light .1. Sources of the background and potential suppression of the OH emission

The major components of the infrared background in astronomical applications are reviewed and the improvement that can be obtained by removing the OH emission is calculated. An instrument that removes ideally chosen wavelengths could suppress the OH emission lines for the atmosphere without removing most of the light from an observed source, resulting in a marked improvement of the signal-to-noise ratio (SNR). New calculations of methods to reduce the OH background, using a new technique for determining the optimum background filter, are reported. The OH emission-line blocking required to give the highest SNR is described. Ground-based methods would result in a background reduction of at least a factor of 9 in the J band, 18 in H, and 3 in K, but which could be as high as 100 in J, 520 in H, and 260 in K, depending on the air and telescope temperature and which estimate of the background emission is used. In the band from 0.7-1.1 mu m, the results show a background reduction between 5 and 12. The results also show that the NICMOS camera on the Hubble Space Telescope should give a background reduction of a factor of 185 in J and 220 in H; this is 6 times higher in J and 3 in H than reported in previous estimates. For the K band, it is shown that a telescope located at middle latitudes employing a cooled background reducer would give better improvement than an antarctic telescope of the same size unless it also uses a background reducer.