Extreme count rates linearity test for NICMOS

Details Extreme count rates linearity test for NICMOS Extreme count rates linearity test for NICMOS

Jul 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004hst..prop10454d&link_type=abstract

HST Proposal ID #10454

Computer Science

Hst Proposal Id #10454

Scientific paper

This NICMOS calibration proposal tests the linearity of the detectors at count rates falling at the low and high extremes of what is feasible. This program is a response to the discovery that grism observations obtained with NIC3 show a systematic offset from spectra taken with STIS and ACS in the 0.8-1.0 micron overlap region. The observations are consistent with a NIC3 sensitivity that depends on incident flux, i.e. count rate. By observing one bright star {BD+17D4708, the Sloan Digital Sky Survey absolute standard} and two faint stars {SNAP-2, a solar analog star; WD1657+343, a white dwarf} in a number of filters we will check whether this is an intrinsic feature of the all NICMOS detectors, something intrinsic to NIC3, or a result of a not understood effect of the grism observations. We will furthermore be able to test whether the effect has a wavelength dependence. The data will be reduced in exactly the same fashion as has been done before for the photometric calibration program, so a direct comparison with previous data can be made. In addition, we will obtain extra spectroscopic data on WD1657+343, the faintest and best modeled white dwarf of the stars on which the original discovery of the non-linearity was made. This will reduce the errors in this spectrum from 5% to 2% and will allow a better estimate of the effect. In order to ease scheduling, there are no time constraints specified in the proposal. However, because of the potentially important implications of this effect, it is very important that these orbits be scheduled as soon as possible. They could be critical for the proper calibration of NICMOS The targets have visibility 1} BD+17D4708: 16 Apr - 17 Jan 2} SNAP-2: 3 Feb-1 Mar 3} WD1657+343: 3 Feb-26 Feb

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