Charge Transfer Efficiency of the STIS CCD:The time dependence of charge loss and centroid shiftsfrom Internal Sparse Field data

Goudfrooij, Paul; Maíz-Apellániz, Jesús; Brown, Tom; Kimble, Randy
Instrument Science Report STIS 2006-01, 11 pages


We describe the Internal Sparse Field test used to characterize relevant aspects of the decreasing Charge TransferEf ciency (CTE) of the STIS CCD with elapsed on-orbit time. We measure two main observational effectsof CTE: Fractional signal loss and centroid shift, using arti cial point-source spectra read out by ampli ersat both serial registers. We derive time constants of the increases of fractional signal loss (21.8% yr-1) and centroid shift (16.0% yr-1) due to CTE effects, and a very tight relation between the two. This relationshould be useful for science programs requiring sub-pixel astrometric accuracy. Finally, we compare results inthe two supported gain settings of the STIS CCD (gain=1 and gain= 4).