Physics
Scientific paper
Jun 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011acs..rept....3b&link_type=abstract
Instrument Science Report ACS 2011-03, 16 pages
Physics
Hubble Space Telescope, Hst, Space Telescope Science Institute, Acs
Scientific paper
The flux calibration of HST instruments is normally specified after removal of artifacts such as a decline in charge transfer efficiency (CTE) for CCD detectors and optical throughput degradation. This ACS ISR deals with the HRC and WFC losses in sensitivity from polymerization of contaminants on the optical surfaces. Prior to the demise of the ACS CCD channels on 2007 Jan. 27, the losses are less than ∼0.003 mag/year, except for the two short wavelength HRC filters F220W and F250W. The measurements of the sensitivity loss rates using a set of observations of WD flux standards has a precision of ∼0.0008 mag/year, while the sensitivity loss rates using repeated observations of the globular cluster 47 Tuc are probably consistent within their currently lower precision. Following the revival of ACS WFC during the Servicing Mission 4 (SM4) in 2009 May, the gain of the new electronics was set so that the measured signal in electrons s-1 matched the signal for the same 47 Tuc field as measured in 2002 with the F606W filter. However, a longer time baseline is required to reliably determine the post-SM4 loss rates.
Bohlin Ralph Charles
Mack Jennifer
Ubeda Leonardo
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