Other
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997nicm.rept...32d&link_type=abstract
Instrument Science Report NICMOS-97-032, 8 pages
Other
Hubble Space Telescope, Hst, Space Telescope Science Institute, Nicmos
Scientific paper
This Instrument Science Report presents the results of the analysis of the South Atlantic Anomaly (SAA) contour test executed in June 1997 during SMOV. The goal of the test is to determine the optimal SAA limits for the NICMOS detectors operations, and the orbital radiation effects on the NICMOS dark current during passages and when coming out of the SAA. The data show that the most external SAA contour (Model 5) is the most appropriate for NICMOS science operations; inside the contour there is a steep increase in the number of pixels affected by cosmic rays (CRs), by factors in the range 5 to 40. CR counts go back to nominal within 4 minutes of leaving the contour defined by Model 5. If the NICMOS detectors are kept on and reading during SAA crossings, the average dark counts do not show variations before and after the crossing. However, in one SAA passage the detectors were switched off, and in this case the average dark counts measured after leaving the SAA show the post-SAA pedestal effect, namely the exponentially decreasing trend already observed in other NICMOS dark frames. These results suggest to: 1. keep the NICMOS detectors on as much as possible; 2. determine a new SAA contour intermediate between Model 5 and the inner Model 2, for the purpose of reducing the effects of the post-SAA pedestal. NICMOS science operations should still be performed only outside the current SAA Model 5.
Calzetti Daniela
Daou Doris
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