NICMOS Calibration Challenges in the Ultra Deep Field

The reduction of NICMOS observations in the Hubble Ultra Deep Field required unique reduction and calibration techniques, not required for images containing brighter sources. This paper describes some of these techniques which may be useful in the reduction of other fields containing extremely faint sources. These techniques apply to NICMOS camera 3 which was the only NICMOS camera utilized in the observations. The absolute accuracy of the NICMOS camera 3 photometry was also investigated using the observations of the solar analog star P330-E. As a result the sensitivity of the camera in the F110W and F160W was found to be less than the sensitivities used in the construction of the Version 2.0 NICMOS Treasury catalog for the observations in the Hubble Ultra Deep Field. The catalog fluxes are too low by between 8 and 9%.