Physics
Scientific paper
Oct 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008wfc..rept...21b&link_type=abstract
WFC3 Instrument Science Report 2008-21, 22 pages
Physics
Hubble Space Telescope, Hst, Space Telescope Science Institute, Wide Field Camera 3, Wfc3
Scientific paper
This report summarizes the behavior of the WFC3 calibration system in the UVIS channel, based upon data acquired during thermal-vacuum level tests performed in 2008 with the UVIS-1' flight detector. The results are evaluated in light of the calibration system require- ments. Tungsten: the new lamps satisfy the flux requirement of at least 16.7 e-/s/pix for all filters except in FQ436N and FQ437N (~9 and ~6 e-/s/pix, respectively, with tungsten lamp 3). Overall, the lamp output was found to be 1-2% higher when operated on side 1 of the instrument than it was on side 2. Of the four tungsten lamps, #4 has the highest flux, followed by #2 and #3; lamp #1 has the lowest output. Specifically, #3 is about 15-20% fainter than #4 and about 10-15% brighter than #1. A full evaluation of the short- and particularly long-term stability requirements will require more data. However, based on the flatfields obtained during TV3, the short-term stability requirement is met in the majority (80-90%) of cases. The long-term stability will not be met if the TV3 decline rates continue (typically 1-3% in 10-40 days), but there is some evidence that the rate of decline may be slowing. Over the large scale, the tungsten flatfields meet the uniformity specification (< factor of two over the full field of view) in all but three filters (F410M, F657N, and F658N); these exceptions, however, are due to the filters, not the lamps. Lamp lifetimes in the lab were 1960 hrs each, with some parts lasting more than 3000 hrs; if the flight lamps last this long, they will easily meet the lifetime requirement. Deuterium: the lamp satisfies the calsystem flux requirement except when used with FQ387N, FQ436N, and FQ437N (~16, ~14, and ~11 e-/s/pix, respectively). While the short-term stability is found to be generally good, the lamp will not meet the long-term requirement, having declined by 2-10%, depending upon filter, during the ~40 days of TV3. Over large scales across the FOV, the deuterium flatfields meet the uniformity specification. There are, however, small scale features (10-20 pix) where the flux can vary by more than a factor of two - but these features are due to residue on the CCD window, not the lamp.
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