Advanced Camera
for Surveys:
Status Update
Roeland
van der Marel
Team News


Mark Clampin on Sabbatical (Nov 4)
Thanks for a job well done!
Team Retreat (Oct 11)



Calibration Workshop (Oct 17/18)


Facilitate transition to a new Team Lead
Discuss current status ACS and future priorities
Summarize ACS status to the community & solicit feedback
Recognition


STScI Achievement Award: Jennifer Mack
GSFC SM3b awards
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
SMOV Closure Review
(Sep 30)

ACS Requirements



Nearly all specs were met, many were exceeded.
Exception: misalignment/drift coronagraphic spots/mask
Coronagraphy




GTO and GO programs on hold
Commanding improvements implemented to minimize positional
inaccuracies that affect scientific performance
[Welty, Cox, Krist, Clampin]
New strategies still to be tested
Scheduling problem: prevent insertion of calibration observations
(dark/bias) in a coronagraphy sequence.
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
Minor Instrument Anomalies

Image quality:





Long-wavelength halo WFC
PSF in UV has an asymmetric extension
SBC encircled energy slightly lower than hoped
(due to unrealistic hopes [Hartig])
Image drift: up to 5 mas/hr
Ghosts (low-level):


WFC CCD amplifier cross-talk: electronic ghosts
Optical ghosts
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
Minor Anomalies

Bias:


Variable offset between overscan and detector
Scattered Light:

Peculiar scattered light feature detected in some individual
dark frames [reported by GOODS]
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
Hot Pixels

WFC Anneal Rate lower than for other HST CCDs



80-85 % : WFPC2, STIS, ACS/HRC
60-65 % : ACS/WFC
Continues to be monitored closely
[Riess, van Orsow, Mutchler]
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
Measured Anneal Rate

Rate levels off as function of number of anneals
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
Hot Pixel Growth Rate

Long-term growth
approximately
linear.
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
Hot Pixel Predictions
(fairly uncertain)
1 hot pixel per
4x4 box
WFPC2
STIS
no hot pixels
2002
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
2010
Hot Pixel Impact


In the long-term, careful dithering will be essential
Hot pixels are always easier to remove than cosmic
rays: you know where they are!
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
Hot Pixel Actions

Why is the anneal rate lower?


Possible cause [Clampin]: Integration in MPP mode, Readout in non-MPP mode? ( no WFC3 impact)
What can be done about it?

Lower temperature (ASCS) ?



Tests will be done at higher T
Different annealing process (more often? longer? …)
Planned: Meeting of Detector Experts
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel
Calibration



SIAF Tables updated (FGS re-alignment) [Cox]
Improved procedure for dark/bias frame creation
[Mutchler, van Orsow]
Ongoing analysis of calibration data
Roeland van der Marel - Space Telescope Science Institute
marel@stsci.edu
http://www.stsci.edu/~marel