Installation of the ACS Guido De Marchi – TIPS meeting – Guido De Marchi - ESA/STScI - ACS Group The ACS was installed on board the HST on the 6th of March replacing the ageing FOC No problems encountered by astronauts during installation Aliveness test proved that the camera can boot properly Functional test run soon after to verify ability to provide science grade data

ACS functional test Guido De Marchi – TIPS meeting – After switch on, both CCD cooled rapidly to -67 C Both filter wheels moved properly to position A set of bias and dark frames was taken for both CCD with several combinations of amplifiers and lamps The ACS IDT and ACS group at STScI analysed the data simultaneously but independently: same results!

ACS functional test: bias frames Guido De Marchi – TIPS meeting – Read noise found to be at nominal values: WFC: ~5 e- rms; HRC: ~4 e- rms Fourier analysis reveals no correlated noise Large number of cosmic ray hits seen in bias frames, non uniformly distributed (gradient). Reason: long read out time! One might benefit from CR-SPLIT for exposures shorter than a few minutes [Sirianni] Cosmic ray events show no tails (i.e. no deferred charge) thus proving good CTE [Riess]

ACS functional test: flat frames Guido De Marchi – TIPS meeting – No cosmetic degradation apparent (WFC, HRC), no new large dust particles nor shifting of existing ones [Riess] Illumination levels consistently higher (~20%) than on the ground for all lamps. Could be due to higher operating temperature in vacuum. Planned internal flat fields will need shorter exposure times [Hartig] Shadow cast by coronographic finger suggests a shift occurred during flight. Similar shifts seen when moving the camera on the ground [Hartig] Cycle HRC/SBC fold mirror to ensure nominal position

ACS SMOV programme Guido De Marchi – TIPS meeting – On-board memory tested for bit flips during SAA passa- ges: only 8 bits flipped in 6x34 million bytes [De Marchi] Both CCD (WFC, HRC) cooled rapidly to operating tem- peratures and remain stable there (–77 C, –80 C) [Cox] GSFC/Ball are reviewing the thermal models for opportu- nity to further lower operating temperatures Dark rate stable to within +/-1 at ~7.5 e-/px/hr, well below specifications (< 25 e-/px/hr) [Sirianni, Mutchler, Cox]

ACS SMOV programme: WFC bias Guido De Marchi – TIPS meeting – After CCD activation, bias level gracefully decays and stabilises at ~20 e- down after a few hours [Pavlovsky] Level of WFC amplifier B shows larger scatter, with variations of up to ~ +/- 10 e-, but RN still 5 e- [Sirianni] This is not a problem because the offset (i.e. the differen- ce between the bias level in the image and in the physi- cal overscan) is constant to within +/- 0.3 e- [Sirianni] Correct bias level can be determined from overscan