Spectrophotometry of Solar Analog Stars and Nicmos Grism Calibration

Details Spectrophotometry of Solar Analog Stars and Nicmos Grism Calibration Spectrophotometry of Solar Analog Stars and Nicmos Grism Calibration

Jul 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004hst..prop10385b&link_type=abstract

HST Proposal ID #10385

Physics

Hst Proposal Id #10385

Scientific paper

NICMOS IR Standards {4 orbits} In cycle 12, 24 orbits were used to measure the NICMOS grism mode sensitivities and to establish a set of IR flux standards with a goal of 1% accuracy. However, the G096 setting shows up to 5% peak-to-peak range among the sensitivities derived from the three primary WD standards, as shown in Figure 1 {for the Phase 1 proposal}. The possible causes of this large scatter include changes in the flat field, a systematic change of sensitivity with time, and a fundamental limitation of the repeatability for stars at the WD flux levels. The same residuals for STIS in the 0.8-1.0 micron overlap range are <1%, so that the problem is not with the fluxes for the three primary standard stars. Either there is a systematic trend in the Nicmos grism data that can be removed with more monitoring; or alternatively, repeating the cycle 12 observations should reduce the error in the mean sensitivity by sqrt{2}, if the deviations among the stars are random instrumental fluctuations. The NICMOS cycle 13 calibration program includes 2 orbits to repeat the observations of the bright standard BD+17d4708, which has a very high S/N, so that any change in its response should reflect an instrumental sensitivity difference between cycle 12 and 13. The four Nicmos orbits in this program include one each for GD71 and GD153 in G096 and G141, while two orbits are required for the repeat of G191B2B, where the G206 mode is also included.

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