Pre-launch model of Background

Three different thermal sources contribute to the NICMOS near infrared background. One is the thermal radiation from the Hubble Space Telescope (HST) itself, another is from the NICMOS optics, and the last one is the near infrared zodiacal background. The thermal radiation from both HST and the NICMOS optics can be simply characterized by a blackbody with temperatures of 293 Kelvin and 275 Kelvin respectively. The coefficients of the emissivity of HST and the NICMOS can be taken as 0.1 and 0.15 respectively. The efficiencies of thermal transmission are set as 72% for HST and 85% for NICMOS.

There are two different sources contributing to the near infrared zodiacal background. One is from the thermal radiation of the interplanetary dust (ZE), which can be characterized by a blackbody with a temperature of 265 Kelvin and an emissivity of 6.0$\times 10^{-8}$. The second background source is the scattered light from the dust (ZS). The quantitative description for this part is uncertain. Thompson (1996, private communication) suggests $10^{-9} \over \lambda^{1.69}$ photon/s/cm$^2/\mu$/sr. For the pre-launch version of Calnic C, Thompson's equation was used. At $\lambda \gt 3\mu$, the zodiacal background from the dust thermal emission (ZE) is much higher than the scattered light (ZS), however, at the shorter wavelength, such as J band, the zodiacal scattered light dominates.

The thermal radiation from HST dominates the near infrared background in K-band. In H-band, all three background sources are important, and in J, the zodiacal light contributes the most to the background calculation.