Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21725403w&link_type=abstract
American Astronomical Society, AAS Meeting #217, #254.03; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
The COS FUV detector is composed of two micro-channel plate (MCP) segments with cross delay line anodes. The detector displays a variety of localized, non-uniformities in its response, including hexagonal and moire patterns, dead spots, gain variations, and shadows from the wire grid used to increase MCPs quantum efficiency. These features produce fixed-pattern noise in COS FUV spectra. Typically, such irregularities are eliminated by dividing the raw data by a flat field image. Ground testing of the prelaunch flats revealed that the S/N did not improve and consequently an attempt was made during SMOV to construct a flat field image from external targets. However, it did not result in a flat field of sufficient quality to be used for standard CALCOS processing. In contrast, it has been demonstrated that the fixed pattern features can be largely eliminated in high S/N data by using the iterative FP-SPLIT algorithm (similar to the one used for GHRS and FOS data) to obtain COS spectra with a S/N > 100. A product of this approach is a "1-D flat" which characterizes the contribution of fixed pattern noise to the spectrum. We have begun to explore various methods for utilizing these 1-D flats to correct unrelated, individual exposures. Initial results have been encouraging, and the results the our study will be discussed.
Ake Thomas B.
Béland Stephane
France Kevin
Massa Derck
McPhate Jason
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