3.5 ACS Quick Reference Guide

Field of View

202 × 202 arcsec²

29 × 26 arcsec²

34.6 × 30.5 arcsec²

Plate Scale

~0.05 × 0.05 arcsec²/pixel

~0.028 × 0.025 arcsec²/pixel

~0.034 × 0.030 arcsec²/pixel

Pixel Size

15 × 15 μm²

21 × 21 μm²

25 × 25 μm²

Image Format

2 × 2048 × 4096 pixels

1024 × 1024 pixels

1024 × 1024 pixels

Spectral Response

~3500 Å to 11,000 Å

~1700 Å to 11,000 Å

~1150 Å to 1700 Å

Detector

SITe CCDs thinned backside illuminated, anti-reflection coated, multiphased pinned

SITe CCD thinned backside illuminated, anti-reflection coated, multiphased pinned

CsI MCP with MAMA readout

Detector
Efficiency ^[a]

~75% at 4000 Å
~81% at 6000 Å
~66% at 8000 Å

~32% at 2500 Å
~69% at 6000 Å
~53% at 8000 Å

~34% @ 1216 Å

Peak Total System Efficiency ^[a]

47% at ~6700 Å ^[c]

27% at ~6400 Å

8.5% at ~1260 Å

Read Noise

3.75 e– to 5.65 e^–

4.7 e^–

0 counts

Dark Current ^[a]

0.0161 e^–/s/pixel ^[c]

0.0058 e^–/s/pixel

8.52 × 10^–6 counts/s/pixel when instrument temperature < 25°C ^[d]

Saturation Level ^[b]

~77,400 ± 5000 e^{– [c]}

~155,000 ± 10,000 e^–

Detector count rate linearity limit: 200,000 counts/sec
Pixel count-rate linearity limit: ~22 counts/sec/pixel ^[e]

Gain

0.5, 1.0, 1.4, and
2.0 e^–/DN
(Max 65,535 DN)

1,2,4 and 8 e^–/DN
(Max 65,535 DN)

n/a

Operating Temperature

−81°C ^[c]

−80°C

n/a

Distortion Solution Accuracy

0.1 pixel

0.1 pixel

0.13 pixel
 

Calibration & stability of 
geometric distortion ^[a]

Absolute Astrometry

0.2" to 0.5"

0.2" to 0.5"

0.2" to 0.5"

Guide Star Catalog uncertainties ^[b]

Absolute Photometry

2%

3%

5%^[c]

Absolute flux of standard stars

Relative Photometry 
within an Image

1%

1%

2%

Flat-field characterization or 
characterization of geometric distortion.

Repeated Photometry of Same Star

0.3%

0.3%

1%

Stability of flat field

Transformation to 
Standard
Magnitude Systems

0.02 mag SDSS
0.025 mag WFPC2
0.03 mag BVRI

0.02 mag SDSS
0.025 mag WFPC2
0.03 mag BVRI

n/a

DQE curve determination
Color terms

Polarimetry

1%

1%

n/a

Wavelength Calibration

20 Å grism

12 Å grism

1 pixel prisms

Accuracy of dispersion solution

Spectrophotometry

6% (Grism)

10% (Grism)

20% (Prism)

Broadband

Sloan Digital Sky Survey (SDSS): F475W, F625W, F775W, F850LP 

WFC/HRC

B, V, Medium V, Wide V, I: F435W, F555W, F550M, F606W, F814W

WFC/HRC

Near-UV: F220W, F250W, F330W 

HRC

No Filter: CLEAR

WFC/HRC

Narrowband

Hα (2%), [OIII] (1%), [NII] (1%): F658N, F502N, F660N 

WFC/HRC

NeV (3440 Å): F344N

HRC

Methane (8920 Å): F892N

HRC/[WFC^[a]]

Ramp filters

2% bandpass (3700–10,700 Å): FR388N, FR505N, FR656N

WFC/HRC

2% bandpass (3700–10,700 Å): FR423N, FR462N, FR716N, FR782N, FR853N, FR931N, FR1016N, FR551N, FR601N 

WFC

9% bandpass (3700–10,700 Å): FR459M, FR914M

WFC/HRC

9% bandpass (3700–10,700 Å): FR647M

WFC

Spectroscopic

Grism: G800L

WFC/HRC

Prism: PR200L

HRC

Polarizers

Visible (0°, 60°,120°): POL0V, POL60V, POL120V

HRC/[WFC ^[a]]

Near-UV (0°, 60°, 120°): POL0UV, POL60UV, POL120UV

HRC/[WFC ^[a]]

Medium Band

Lyman-Alpha: F122M

SBC

Long Pass

MgF₂, CaF₂, BaF₂, Quartz, Fused Silica: F115LP, F125LP, F140LP, F150LP, F165LP

SBC

Prisms

LiF, CaF₂: PR110L, PR130L

SBC

POL0UV
POL60UV
POL120UV

F220W

unavailable

HRC NUV short

F250W

unavailable

HRC NUV long

F330W 

unavailable

HRC U

F435W 

available

Johnson B

F660N ^[a]

available

F814W 

available

Broad I

POL0V
POL60V
POL120V

F475W ^[a]

supported

SDSS g

F502N

available

F550M

available

F555W

available

Johnson V

F606W ^[a]

supported

Johnson V Wide

F625W

available

SDSS r

F658N ^[a]

available

Hα

F775W ^[a]

supported

SDSS i

G800L

supported

Grism

G800L

WFC

1st order: 5500 to 10500

100 @ 8000 Å

39.8 ^[b]

–2

2nd order: 5000 to 8500

200 @ 8000 Å

20.7 ^[b]

–2

HRC

1st order: 5500 to 10500

140 @ 8000 Å

23.9 ^[c]

–38

2nd order: 5500 to 8500

280 @ 8000 Å

12.0 ^[c]

–38

PR200L

HRC

1700 to 3900

59 @ 2500 Å

21.3

–1

PR110L

SBC

1150 to 1800

79 @ 1500 Å

9.5

0

PR130L

SBC

1250 to 1800

96 @ 1500 Å

7.8

0

Proposal 
Preparation 
Tips

Table 7.1: Science decision guide.
Table 7.2: Science feasibility guide.
Table 9.1: Useful quantities for the ACS WFC, at -81C (since July 2006).
Table 9.2: Useful quantities for the ACS SBC.
Figure 7.1: Defining an ACS observation.

Overheads 

Table 8.1: Science Exposure Overheads: General.
Table 8.2: ACS Science Exposure Overhead Times (Minutes).

Aperture 
Parameters 

Table 7.7: WFC aperture parameters.
Table 7.8: Ramp filter apertures.
Table 7.9: HRC aperture parameters.
Table 7.10: SBC aperture parameters
Figure 3.1: The HST field of view with the locations of the SI and the FGS apertures in the (U2,U3) focal plane.
Figure 5.10: WFC and HRC filter wheels layout.
Figure 5.12: SBC Filter wheel layout.
Figure 7.8: Aperture and image feature orientation.
Figure 7.9: ACS apertures in the V2/V3 reference frame.

Detector 
Characteristics 

Table 2.1: WFC Performance Summary.
Table 3.1: Instrument characteristics.
Table 4.1: WFC amplifier gain and read noise after installation of the CEB-R (valid after May 2009).
Table 4.7: SBC detector performance characteristics.

SBC Bright
Object 
Protection 
Limits

Table 7.3: Absolute SBC count rate screening limits for nonvariable and variable objects.
Table 7.4: Bright limit V-band magnitudes for observations with the SBC filters and prisms (no reddening).
Table 7.5: Bright object protection policy for SBC observations.

Hot, Warm, and Unstable 
Pixels

Table 2.1: WFC Performance Summary.
Table 4.4: Creation rate of new hot, warm, and unstable pixels (% of detector per year).
Table 4.5: Hot and Warm Pixel Flags Over the History of ACS.
Figure 4.7: Hot Pixel Growth Rate for HRC.
Figure 4.8: Pixel Stability and Hot Pixel Growth in WFC.

Charge 
Transfer 
Efficiency

Table 4.6: Charge transfer efficiency measurements of the ACS CCDs prior to installation from Fe55 experiments (Sirianni et al. 2000, Proc. SPIE 4008)

Geometric 
Distortion

Figure 10.111: The geometric distortion map for the ACS/WFC, which shows only the non-linear component to the solution.
Figure 10.113: The geometric distortion map for the HRC.
Figure 10.115: The geometric distortion map for the ACS/SBC.
Figure 10.116: The map of the effective pixel areas of the ACS/SBC. The areas are normalized to 0.025 arcsecond square pixels.

Encircled 
Energy

Table 9.3: Encircled energy comparison for WFC/F850LP.
Figure 4.15: MAMA point spread function. Solid lines are from observations, dashed lines are from Tiny Tim models.
Figure 5.13: Encircled energy for the CCD channels.
Figure 5.14: Encircled energy for the SBC. Solid lines correspond to observations, dashed lines correspond to Tiny Tim models.

PSF

Table 5.9: ACS Model PSFs in central 5 × 5 pixel region (SBC).
Figure 4.15: MAMA point spread function. Solid lines are from observations, dashed lines are from Tiny Tim models.
Figure 5.13: Encircled energy for the CCD channels.
Figure 5.14: Encircled energy for the SBC. Solid lines correspond to observations, dashed lines correspond to Tiny Tim models.

Filters

Table 3.3: ACS filters.
Table 3.5: ACS dispersers.
Table 5.1: ACS WFC/HRC filters in Filter Wheel #1.
Table 5.2: ACS WFC/HRC filters in Filter Wheel #2.
Table 5.3: ACS SBC filter complement.
Table 5.5: In-band flux as a percentage of the total flux.
Table 5.6: Visible-light rejection of the SBC F115LP imaging mode.

Polarizers

Table 3.4: ACS polarizers.
Table 6.1: Filters that can be used in conjunction ion with the ACS polarizers.
Table 6.2: Examples of polarizer and non-polarizer exposures in a Phase II proposal. HRC apertures are no longer available but are shown for archival purposes.

Photometry

Table 5.4: V detection limits for ACS, HRC, and SBC direct imaging.
Table 9.1: Useful quantities for the ACS WFC, at -81C (since July 2006).
Table 9.2: Useful quantities for the ACS SBC.
Table 10.1 Color corrections ABv to go from Johnson V magnitude to AB magnitude for the WFC.
Table 10.2: Color corrections ABv to go from Johnson V magnitude to AB magnitude for the HRC.
Table 10.3: Color corrections ABv to go from Johnson V magnitude to AB magnitude for the SBC.
Table 10.4: Color corrections to go from GALEX NUV AB magnitude to AB magnitude for the SBC.
Table 10.5: Color corrections to go from GALEX FUV AB magnitude to AB magnitude for the SBC.

Limiting 
Magnitudes
for Direct
Imaging

Table 5.4: V detection limits for ACS, HRC, and SBC direct imaging.
Figure 5.8: HST Limiting Magnitude for point sources in 10 hours, as a function of wavelength.
Figure 5.9: HST total integration time needed to attain ABMAG=26 for extended sources.

Spectroscopy

Table 6.3: Optical parameters of ACS dispersers.
Table 6.4: V detection limits for the ACS grism/prism modes.
Figure 6.16: Sensitivity versus pixel position for WFC G800L.
Figure 6.18: Sensitivity versus wavelength for HRC G800L.
Figure 6.19: Sensitivity versus pixel position for HRC G800L.
Figure 6.21: Sensitivity versus wavelength for HRC/PR200L.
Figure 6.22: Sensitivity versus wavelength for SBC PR110L.
Figure 6.24: Sensitivity versus wavelength for SBC/PR130L.

Sky 
Backgrounds

Table 9.4: Approximate zodiacal sky background as a function of ecliptic latitude and ecliptic longitude. (In V magnitudes per square arcseconds.)
Table 9.5: Geocoronal emission lines.
Table 9.6: High sky backgrounds.
Figure 9.1: High sky background intensity as a function of wavelength.
Figure 9.2: Background contributions in V magnitude per arcseconds².
Figure 9.3: Extinction versus wavelength.

Calibration 
Accuracies

Table 3.2: Calibration accuracies.
Figure 4.7: Hot Pixel Growth Rate for HRC.
Figure 4.8: Pixel Stability and Hot Pixel Growth in WFC.
Figure 4.9: ACS/WFC Dark Current Histograms.