Photometric Monitoring of NICMOS

The photometric stability of NIC1 and NIC2 detectors was monitored once a month from August 1997 through November 1998. Images of one HST standard (the solar analog P330E through a subset of filters (5 for NIC1 and 6 for NIC2, covering the entire wavelength range of the NICMOS cameras, are obtained at three or four different positions. The countrate is computed as the average value of the countrates measured at the separated positions in the detector. All the measurements for a given filter have been normalized to the mean countrate for that filter.

In addition to the images obtained as part of the photometric monitoring program, results from images obtained as part of other calibration programs have also been included in the plots shown below.

All the images have been flat-fieldedd with the best flats at the time of the final calibration. The reference files and pedigree for the flats used in the calibrations are indicated below. Typical uncertainties in the measurements are at the 1-2% level. Large uncertainties (4-5% found in some measurements are mostly due to calibrations with non-optimal flats, i.e. ground flats or on-orbit flats taken during the early phases of SMOV.

Below are listed, for each target/camera/filter combination, the flat field reference file used in the data reduction and its pedigree.

Photemetric Monitoring Measurements: