Computer Science
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002acs..rept....1b&link_type=abstract
Instrument Science Report ACS 02-01, 17 pages
Computer Science
Hubble Space Telescope, Hst, Space Telescope Science Institute, Advanced Camera For Surveys, Acs, Stsci
Scientific paper
The ACS has three ramp filters in each of five filter wheel-2 slots. The five middle segments are available to the HRC, while all 15 ramps cover portions of the WFC field of view. Therefore, each pipeline WFC ramp pixel-to-pixel P-flat is composed of three segments, where each segment is from the broadband LP-flat that is nearest to the central wavelengths of each ramp segment. Since the P-flats vary slowly with wavelength, the surrogate P-flats for the ramp filters generally reduce the intrinsic CCD rms noise from 1% to ~0.2%. Along the ramps, the transmitted wavelengths are a function of position; and the large-scale relative response depends on the shape of the continuum flux distribution. Instead of an L-flat measured by a laboratory lamp, ramp filters will have an absolute sensitivity as a function of wavelength defined for pipeline flux calibration. Across the ramps, i.e. perpendicular to the direction of changing wavelength, a traditional L-flat could be applied; however, any variation in the total throughput integrated over the bandpass along this axis causes this L-flat to differ for the cases of monochromatic and continuum illumination.
Bohlin Ralph Charles
Hartig George
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