ken sembach 27 october 2005 n.
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ACS Calibration Status. Ken Sembach 27-October-2005. ACS Website ACS Calibration Teams at STScI and ST-ECF. John Biretta Ralph Bohlin Marco Chiaberge Mauro Giavalisco Shireen Gonzaga Colin Cox Linda Dressel Andy Fruchter Ron Gilliland

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Ken Sembach 27-October-2005

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ken sembach 27 october 2005

ACS Calibration Status

Ken Sembach


ACS Website


ACS Calibration Teams at STScI and ST-ECF

John Biretta

Ralph Bohlin

Marco Chiaberge

Mauro Giavalisco

Shireen Gonzaga

Colin Cox

Linda Dressel

Andy Fruchter

Ron Gilliland

Vera Kozhurina-Platais

Jesús Maíz-Apellániz

Ray Lucas

Jennifer Mack

Max Mutchler

Cheryl Pavlovsky

Charles Proffitt

Adam Riess

Kailash Sahu

Ken Sembach

Marco Sirianni

Nolan Walborn


Richard Hook

Martin Kümmel

Sören Larsen

Jeremy Walsh

  • This talk is an overview of ACS calibration activities.
    • See the many talks/posters here for more details.
    • People listed below are good sources of information.
acs status operation
ACS Status / Operation
  • All modes continue to operate well
  • Two-gyro performance nominal
  • Calibration plan for Cycle 14
    • STScI team has reviewed plans from previous cycles
    • Continuing calibrations for most previous programs (ongoing usual calibration activities)
    • New programs to bring SBC calibrations up to the standard of HRC/WFC calibrations, to better characterize the ramp filters, ultraviolet narrow-band red leak, and to estimate T-dependence of QE, CTE, and hot pixel growth
  • ACS usage charted on STScI metrics page
    • Provides information about most frequently used modes
cycle 14 calibration orbit summary
Cycle 14 - Calibration Orbit Summary

* Two programs (PI = Dolphin): ACS zero point verification / Faint standard calibration

recent acs isrs

SBC flatfield

Recent ACS ISRs
  • Grism wavelength calibration
    • ISR 2005-08 (Larsen & Walsh)
  • CCD internal flat fields
    • ISR 2005-09 (Bohlin & Mack)
  • SBC pixel-pixel flat field
    • ISR 2005-04 (Bohlin & Mack)
  • Astrometric improvements
    • ISR 2005-06 (Koekemoer et al.)
  • HRC polarimetry
    • ISR 2005-10 (Kozhurina-Platais & Biretta)
  • Two-gyro calibrations
    • I. Pointing Stability (ISR 2005-07; Koekemoer et al.)
    • II. Coronagraphic Performance (ISR 2005-05; Cox & Biretta)

Complete list of ISRs at

acs high resolution channel
ACS High Resolution Channel
  • Typically accounts for ~15-20% of ACS observing time
  • Two-gyro checkout
    • PSF shape / stability
    • See poster by Pavlovsky
  • Updated internal flat fields
    • ISR 2005-09; Bohlin & Mack
    • See talk by Mack
  • Flats for use with polarizer filters
    • ISR 2005-10; Kozhurina-Platais & Biretta
  • PSFs and distortion corrections
    • ISR 2004-15; Anderson & King

(NASA, ESA, and J. Garvin (NASA/GSFC)

acs instrument performance in two gyro mode is excellent
ACS Instrument Performance in Two-Gyro Mode is Excellent

186 ACS/HRC exposures

Min (FWHM) = 1.89

Avg (FWHM) = 2.00

Max (FWHM) = 2.19

PSF analayses by M. Sirianni,

C. Pavlovsky, R. Lucas

Three-gyro historical data

Avg (FWHM) = 2.04±0.03

August 2005

114 exposures

3 clusters

- NGC 2298

- NGC 1891

- NGC 6752

October 2005

72 exposures

1 cluster (CVZ)

- NGC 6752

acs wide field channel
ACS Wide Field Channel
  • Typically accounts for ~75-80% of ACS observing time
  • Updated internal flat fields
    • ISR 2005-09; Bohlin & Mack
  • Astrometric accuracy using GSC2
    • See poster by Koekemoer, also ISR 2005-06
  • Photometric stability
    • ISR 2004-17; Riess
    • See also talk by Mack
  • PSFs and distortion corrections
    • See talk by Anderson

NASA, ESA and The Hubble Heritage Team (STScI/AURA)

acs solar blind channel

SBC flatfield

ACS Solar Blind Channel
  • Typically accounts for ~3% of ACS observing time
    • More attention w/ loss of STIS
  • New pixel-pixel flat field available
    • ISR 2005-04; Bohlin & Mack
  • Updated darks available
    • ISR 2004-14; Cox
  • New calibrations planned
    • Geometric distortion correction (see poster by Maíz-Apellániz)
    • Prism wavelength calibration
  • See SBC overview poster by Cox et al.
acs coronagraphy

HD 130948A 3-gyro F625W

HD 130948A 2-gyro F625W

HD 216149 2-gyro F625W

ACS Coronagraphy

3.0” spot

  • Typically ~3-4% of ACS observing time
  • Coronagraphic flat fields
    • ISR 2004-16; Krist
  • Two-gyro coronagraphy performance
    • ISR 2005-05; Cox & Biretta

1.8” spot

acs grism prism spectroscopy
ACS Grism/Prism Spectroscopy
  • In Cycle 14
    • ~25% of HRC observing time
    • ~9% of WFC observing time
    • ~23% of SBC observing time
  • Slitless spectroscopy with ACS
    • Talks by Kümmel, Meurer, and Maíz-Apellániz
  • Grism spectroscopy
    • WFC/G800L wavelength calibration (ISR 2005-08; Larsen & Walsh)
    • WFC and HRC G800L flat field and sensitivity (ISR 2005-02; Walsh & Pirzkal)
  • Prism spectroscopy
    • Prisms used more since shutdown of STIS
    • New wavelength/flux calibrations (see poster by Larsen)
  • Software improvements
    • aXe spectral extraction of prism/grism data (see poster by Walsh)
qe cte temperature dependence
QE & CTE Temperature Dependence
  • 12 orbit study to determine T-dependence of CTE, QE, hot pixel growth, etc., has relevance for
    • Performance of ACS in the coming years (T may increase)
    • Future CTE temperature/time dependent corrections
    • Aft-Shroud Cooling System considerations for SM4
  • Test scheduled for November (47 Tuc, GOODS-N) fields) will obtain data at the current operating temperature and colder/hotter temperatures
    • WFC: -81˚, -77˚ (current), and -74˚ C
    • HRC: -86˚, -80˚ (current), and -76˚ C
charge transfer efficiency

Serial Readout





Charge Transfer Efficiency

Degradation of the Charge Transfer Efficiency (CTE) is a well known problem for space-operated CCDs.

Even if only a very small part of the charge packet is left behind in each pixel-to-pixel transfer the effect is severe:

CTE=99.99 % after 2048 transfers results in loss of ~19% of the signal

Current parallel CTE (@1620 e-) is 99.997%

Effects of poor CTE:

- Signal is lost during the readout

Lower S/N

Degraded detection limit

- Some trapped charge is released

on short time scales, creating tails

Increased noise

PSF alteration

- CTE depends on the signal level, position, background, and time

Low number of transfers

High number of transfers

acs ccd hot pixel growth




ACS CCD Hot Pixel Growth

Hot pixels continue to increase

because of radiation damage

to the CCDs.

Effects of hot pixels can be

reduced by dithering exposures.

Monthly anneals heal most of

the hot pixels (see poster by

Marco Sirianni).

acs pipeline calibrations see talk by max mutchler
ACS Pipeline Calibrations (see talk by Max Mutchler)

WFC Bias

  • Most recent ACS pipeline improvements
  • Emphasis on bias and dark calibrations, including hot pixels
  • Reference file production and delivery
  • Data quality flagging and monitoring
  • Ramifications for downstream data reductions, e.g. drizzling

WFC Dark


Automated ACS Bias and Dark Reference File Production,

and Improved Detector Trend Analysis

Ray A. Lucas (STScI), Mike Swam (STScI), Max Mutchler (STScI), and Marco Siriarnni (ESA/STScI)


Automatic Copy of Daily Darks and

Statistics to Storage Disk for Long-

Term Trend Analysis

Files Delivered to OPUS and Archive

For Use in Pipeline and OTFC

Automated Retrieval of

Raw Data From STScI

Data Archive

Automated Processing to

Make Reference Biases and

Darks from Raw Data

Automatic Triggering

Based on HST Schedule

acs documentation
ACS Documentation
  • Cycle 15 Instrument Handbook streamlining and updates
    • Length reduced by ~15% (310 pages trimmed to 262) w/o loss of content
    • Some calibration plan reference material moved to ACS website
    • Indexing update to make information easier to access in both paper and electronic versions of handbook
    • Released with Cycle 15 Call for Proposals
  • Cycle 15 Data Handbook update planned
    • Minor updates to wording in various places and syntax in examples
acs press releases comets planets and stars

Hubble Makes Movie of

Neptune's Dynamic Atmosphere

Scattered Light from the Boomerang Nebula

Hubble/Chandra Image SNR N132D in the LMC

Hubble Pinpoints Doomed Supernova Progenitor

Comet 9P/Tempel 1

Before and After Deep Impact

Hubble Spies a Zoo of Galaxies

Black Hole in Search of a Home

"Big Baby" Galaxies in the Newborn Universe

Hubble Tracks Ceres

Debris Ring Reshaped By

Planet Around Nearby Star

ACS Press Releases(Comets, Planets, and Stars)

ACS Press Releases(Black Holes and Supernovae)

ACS Press Releases(Nebulae and Galaxies)