AAS 202nd Meeting, May 2003
Session 4 Instrumentation: Space Missions
Poster, Monday, May 26, 2003, 9:20am-6:30pm, West Exhibit Hall

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[4.07] Flux Calibration of the STIS CCD: Correcting for Charge Transfer Inefficiency and Time-Dependent Sensitivity

J. Davies, P. Goudfrooij, R.C. Bohlin, D.J. Stys, T.M. Brown, N.R. Walborn (STScI), C.R. Proffitt (STScI/CSC)

A variety of on-orbit imaging and spectroscopic observations have been used to characterize the Charge Transfer Efficiency (CTE) of the Charge-Coupled Device (CCD) of the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. A set of formulae has been developed to correct aperture photometry and spectrophotometry of point sources for CTE-related loss, with dependencies on X and Y positions, the source signal, the background counts, and the time of observation. Application of the new formulae leads to a CCD flux calibration that is accurate to within one percent, independent of source signal.

The analysis of the STIS Sensitivity Monitor observations from 1997 through January 2003 shows continuing sensitivity trends correlated with time for all first-order, low- and medium resolution spectroscopic modes as well as a temperature dependance in the FUV and recently in the CCD detectors. The newly available CTE corrections allow for the proper determination of time-dependent sensitivity (TDS) trends in CCD modes. The wavelength-averaged rates of sensitivity loss for the CCD modes range from ~0%/yr (G750L grating) to ~1.5%/yr (G230LB grating). These sensitivity losses are wavelength dependent and will be corrected for within the STIS data reduction pipeline by means of the delivery of new reference files.

The author(s) of this abstract have provided an email address for comments about the abstract: goudfroo@stsci.edu

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.