Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/institute/stuc/apr-2015/acs.pdf Дата изменения: Unknown Дата индексирования: Sun Apr 10 19:07:56 2016 Кодировка: Поисковые слова: 47 tuc

ACS Instrument Status
(N. Grogin and the ACS Team)

STUC ­ Apr 2015

1


ACS : Going Strong a3er 13 Years
· Usage of ACS increasing from Cycle 21 Ю 22:
ь ACS prime orbits : 13.1% Ю 16.8% ь Coordinated parallel orbits : 29.3% Ю 39.4% ь Doubling of SBC programs & orbits in Cyc 22

· ACS crucial in high-
impact GO/DD programs
ь E.g.: WFC & HFFs; SBC & Mars/comet fly-
by

· Net improvement of delivered WFC image quality b/c understanding is outpacing aging
ь E.g.: Geometric distorZon; CTE; etc.
STUC ­ Apr 2015 2


ACS Long-
Term Monitoring Programs
Ю WFC read noise stable for >2yrs since last glitch

WFC dark current ъ slowly but steadily worsening with Zme [Also, SBC filter sensiZviZes are steady for past >11 years]
STUC ­ Apr 2015 3


Long-
term Monitoring of WFC CTE
· Yearly imaging of 47 Tuc calibraZon field · Measurements of CTE loss as funcZons of:
­ WFC parallel transfers; background level; stellar flux; MJD of observaZon

· Comparisons between:
­ Uncorrected stellar photometry (FLTs) ­ Post-
hoc CTE photometric correcZon formula (FLTs) ­ Pixel-
based CTE correcZon (FLCs)
STUC ­ Apr 2015 4


Pixel-
based CTE correcZon (blue) vs Photometric correcZon formula (red) Cycles 18-
20-
21
CY18

CTE formula is more accurate than the pix-
CTE correcZon
STUC ­ Apr 2015 5


Pixel-
based CTE correcZon (blue) vs Photometric correcZon formula (red) Cycles 18-
20-
21
CY20

CTE formula is more accurate than the pix-
CTE correcZon
STUC ­ Apr 2015 6


Pixel-
based CTE correcZon (blue) vs Photometric correcZon formula (red) Cycles 18-
20-
21
CY21

CTE formula is more accurate than the pix-
CTE correcZon
STUC ­ Apr 2015 7


Refinements to WFC Geom. Dist.
· Leveraging 13yrs of 47 Tuc astrometry:
­ Dispersion of stars now limiZng astrometry (~0.1pix) ­ New reference catalog: includes proper moZons

· Fully generalized 2D non-
polynomial distorZon
­ Removes manufacturing anomalies in plate scale ­ Removes filter-
dependent residuals

· Sol'n cross-
validated with HFFs
­ Scaler reduced to ~0.02 pix (!)
STUC ­ Apr 2015 8


Geom. Dist.: Astrometric Residuals
0.02 pix

WFC2
Original SoluZon

WFC1

Including 47Tuc Proper MoZons
STUC ­ Apr 2015

Including 2D Detector/Filter ArZfacts
9


IlluminaJng the WFC Darks
· MoZvaZon:
­ ­ ­ ­ Low bkgnd. of calibraZon darks Ю severe CTE trailing Typical WFC use-
case has substanZal CTE-
miZgaZng bkgnd. HFF "self-
calibraZon" achieves 20% boost in sensiZvity WFC3 team already flashing UVIS darks for CTE miZgaZon

· Cycle 21 Pilot Program:
­ Supplemental calibraZon program, executed in Aug/Sep'14 ­ 16 internal orbits of biases/darks with LED FLASH=65e-


· Cycle 22 ImplementaZon:
­ 4Q14 : Superdark generaZon script revised/tested for FLASH ­ Jan'15 : Switch-
over to FLASH for most darks, half of biases
STUC ­ Apr 2015 10


Unflashed 1000sec Dark

Top of detector

Note that warm-
pixel structure seen at bolom of CCD is absent at top
Bolom of detector
STUC ­ Apr 2015 11


FLASH=65e- 1000sec Dark
(images already processed through bias subtracZon and flash subtracZon)

Top of detector

Э Noise increase is tolerable
UNFLASHED RMS = 1.6 e-
/ksec

FLASHED RMS = 2.5 e-
/ksec

Bolom of detector

STUC ­ Apr 2015

12


ScaMered-
Light Avoidance
[Coming AMracJon]

STUC ­ Apr 2015

13


For More InformaJon...
· ACS Instrument Handbook & Data Handbook:
ь www.stsci.edu/hst/acs/documents/handbooks/current/cover.html ь www.stsci.edu/hst/acs/documents/handbooks/currentDHB/acs_cover.html

· ACS Instrument Science Reports & Technical Instrument Reports:
ь www.stsci.edu/hst/acs/documents/isrs ь www.stsci.edu/hst/acs/documents/Zrs ь 6 new ISRs & 2 new TIRs in the last 12 months (April 2014 to March 2015)

· ACS Team Website (www.stsci.edu/instruments/acs/):
ь ь ь ь Links to Exposure Time Calculators (ETCs); CTE-
loss EsZmator; etc. Links to `acstools' stand-
alone Python codes & `selfcal' FORTRAN codes `acs_destripe_plus.py' : enhancements incl. 2K-
subarrays; post-
flash; masking Links to development versions of geometric distorZon reference files
STUC ­ Apr 2015 14