3.5 ACS Quick Reference Guide

Please check for updates on the ACS website. Information regarding the HRC is provided for archival purposes only.

Table 3.1: Instrument characteristics.


 

WFC

HRC (inoperable)

SBC

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

× 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

~76% at 4000 Å
~82% at 6000 Å
~66% at 8000 Å

~32% at 2500 Å
~69% at 6000 Å
~54% at 8000 Å

~35% @ 1216 Å

Peak Efficiency

47% at ~6700 Å [a]

28% at ~6400 Å

8.8% at ~1260 Å

Read Noise

3.75 e– to 5.05 e

4.7 e

0 counts

Dark Current

0.0132 e/s/pixel [a]

0.0058 e/s/pixel

8.11 × 106 counts/s/pixel when instrument temperature < 25°C [b]

Full Well

84,700 e [a]

155,000 e

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

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 [a]

−80°C

n/a

a Average value for WFC1 and WFC2.
b ACS ISR 2017-04
c Loss of linearity occurs at count rates larger than these values. For more information, please see Section 4.5.7.


Table 3.2: Calibration accuracies

Attribute

WFC 

HRC 

SBC 

Limiting factor

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)


 

ACS ISR 2015-06ACS ISR 2008-02; ACS ISR 2004-15
ACS ISR 2005-06
c ACS ISR 2019-05


Table 3.3: ACS filters. 

Filter type

Filter description

Camera

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

a Limited field of view (72 × 72 arcsec2) for these filters using WFC.

Table 3.4: ACS polarizers. 

Polarizer set

Filters

Availability

Filter comments

POL0UV
POL60UV
POL120UV

F220W 
F250W 
F330W 
F435W 
F660N [a]
F814W 

unavailable
unavailable
unavailable
available
available
available

HRC NUV short
HRC NUV long
HRC U
Johnson B
 
Broad I

POL0V
POL60V
POL120V

F475W [a]
F502N
F550M
F555W
F606W [a]
F625W
F658N [a]
F775W [a]
G800L

supported
available
available
available
supported
available
available
supported
supported

SDSS g
 
 
Johnson V
Johnson V Wide
SDSS r

SDSS i

a These filters are part of an ACS program to calibrate the polarizer/filter combination to 1% or better


Table 3.5: ACS dispersers. 

Disperser

Channel

Wavelength range (Å)

Resolving power

G800L

WFC

1st order: 5500 to 10,500

100 @ 8000 Å

G800L

WFC

2nd order: 5000 to 8500

200 @ 8000 Å

G800L

HRC

1st order: 5500 to 10,500

140 @ 8000 Å

G800L

HRC

2nd order: 5500 to 8500

280 @ 8000 Å

PR200L

HRC

1700 to 3900

59 @ 2500 Å

PR110L

SBC

1150 to 1800

79 @ 1500 Å

PR130L

SBC

1250 to 1800

96 @ 1500 Å


Table 3.6: Useful tables and figures list.  

Topics

Tables/Figures

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 5.11: 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 5.12: Encircled energy for the CCD channels.
Figure 5.13: 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 5.12: Encircled energy for the CCD channels.
Figure 5.13: 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.