3.5 ACS Quick Reference Guide

 

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

Table 3.1: Instrument characteristics.

	WFC	HRC	SBC
Field of View	202"× 202"	29"× 26"	34.6"× 30.8"
Plate Scale	~0.05"/pixel	~0.028 × 0.025"/pixel	~0.034 × 0.030"/pixel
Pixel Size	15 × 15 μm	21 × 21 μm	25 × 25 μm
Image Format	2 × 2048 × 4096 pixels	1024 × 1024 pixel	1024 × 1024 pixel
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	~77% at 4000 Å ~83% at 6000 Å ~67% at 8000 Å	~33% at 2500 Å ~69% at 6000 Å ~53% at 8000 Å	~19.2% @ 1216 Å
Peak Efficiency2	48% at ~7000 Å	29% at ~6500 Å	7.5% at ~1250 Å
Read Noise	4.2 e–	4.7 e–	0 counts
Dark Current2	0.0062 e–/s/pixel	0.0058 e–/s/pixel	1.241 × 10−5 e–/s/pixel
Full Well2	84,700 e–	155,000 e–	1Detector count rate linearity limit: 200,000 counts/sec Pixel count-rate linearity limit: ~22 counts/sec/pixel
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 Temperature2	−81°C	−80°C	n/a

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1

Loss of linearity occurs at count rates larger than these values. For more information, please see Section 4.5.6.

2

Average value for WFC1 and WFC2

Table 3.2: Calibration accuracies.

Attribute	WFC	HRC	SBC	Limiting factor
Distortion Solution Accuracy	0.1 pixel	0.1 pixel	0.25 pixel	Calibration & stability of geometric distortion1
Absolute Astrometry	0.2" to 0.5"	0.2" to 0.5"	0.2" to 0.5"	Guide Star Catalog uncertainties2
Absolute Photometry	3%	2%	5%	Absolute calibration, standards
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)

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1

Anderson & King, ISR 04-15 (http://www.stsci.edu/hst/acs/documents/isrs/isr0415.pdf)

2

Koekemoer et al., ISR 05-06 (http://www.stsci.edu/hst/acs/documents/isrs/isr0506.pdf)

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/[WFC1]
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/[WFC1]
	Near-UV (0°, 60°, 120°): POL0UV, POL60UV, POL120UV	HRC/[WFC1]
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

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1

Limited field of view (72" x 72") for these filters using WFC

Table 3.4: ACS polarizers.

Polarizer set	Filters	Filter comments
POL0UV, POL60UV, POL120UV	F220W F250W F330W F435W F814W	HRC NUV short HRC NUV long HRC U Johnson B Broad I
POL0V, POL60V, POL120V	F475W F606W F625W F658N F775W	SDSS g Johnson V SDSS r Hα SDSS i

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 Table 9.2: Useful quantities for the ACS SBC.
Overheads	Table 8.1: Science exposure overheads: general. Table 8.2: ACS science exposure overhead times (minutes).
Aperture Parameters	Table 7.6: WFC aperture parameters. Table 7.7: Ramp filter apertures. Table 7.8: HRC aperture parameters. Table 7.9: SBC aperture parameters Table 7.10: Plate scales and axis angles for the 3 ACS channels. 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 7.8: Aperture and image feature orientation. Figure 7.9: ACS apertures in the V2/V3 reference frame.
Detector Characteristics	Table 3.1: Instrument characteristics. Table 4.1: WFC amplifier gain and read noise after installation of the CEB-R (valid after May 2009). Values apply to dual-slope integrator mode of pixel sampling. 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 and Warm Pixels	Table 4.4: Creation rate of new hot pixels (pixel/day). Table 4.5: Annual permanent hot pixel growth (%). Figure 4.5: Hot Pixel Growth Rate for HRC and WFC
Charge Transfer Efficiency	Table 4.6: Charge transfer efficiency measurements for the ACS CCDs after installation in March 2002 Figure 4.10: Projected CTE losses in WFC (equivalently, the size of corrections)
Geometric Distortion	Figure 10.127: The geometric distortion map for the ACS/WFC, which shows only the non-linear component to the solution. Figure 10.129: The geometric distortion map for the HRC. Figure 10.131: The geometric distortion map for the ACS/SBC. Figure 10.132: The map of the effective pixel areas of the ACS/SBC. The areas are normalized to 0.025 arcsecond square pixels..
Encircled Energy	Table 5.4: Encircled energy measurements for the ACS channels. Table 9.3: Encircled energy comparison for WFC/F850LP. Figure 4.13: MAMA point spread function. Figure 5.11: Encircled energy for the CCD channels. Figure 5.12: Encircled energy for the SBC.
PSF	Figure 5.10: Kernels representing CCD pixel functions for HRC and WFC. Table 5.10: Model ACS SBC PSFs. Figure 5.11: Encircled energy for the CCD channels.
Plate Scale	Table 7.10: Plate scales and axis angles for the 3 ACS channels.
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 5.6: In-band flux as a percentage of the total flux. Table 5.7: 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 with the ACS polarizers. Table 6.2: Examples of polarizer and non-polarizer exposures in a Phase II proposal.
Photometry	Table 5.5: V detection limits for ACS, HRC, and SBC direct imaging. Table 9.1: Useful Quantities for the ACS WFC, at -81C Table 9.2: Useful quantities for the ACS SBC. Table 10.1: Color corrections ABn to go from Johnson V magnitude to AB magnitude for the WFC. Table 10.2: Color corrections ABn to go from Johnson V magnitude to AB magnitude for the HRC. Table 10.3: Color corrections ABn to go from Johnson V magnitude to AB magnitude for the SBC.
Limiting Magnitudes for Direct Imaging	Table 5.5: 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. Point source limiting magnitude achieved with a signal to noise of 5 in a 10 hour long exposure with optimal extraction. Figure 5.9: HST Limiting Magnitude for extended sources in 10 hours, as a function of wavelength.
Spectroscopy	Table 6.3: Optical parameters of ACS dispersers. Table 6.4: V detection limits for the ACS grism/prism modes. Figure 6.15: Sensitivity versus wavelength for WFC G800L. 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. The numbers indicate the resolving power (R) and the offset from the direct image in pixels (Dx) as functions of wavelength. Figure 6.22: Sensitivity versus wavelength for SBC PR110L. The numbers indicate the resolving power (R) and the offset from the direct image in pixels (Dx) as functions of wavelength. Figure 6.24: Sensitivity versus wavelength for SBC/PR130L. The numbers indicate the resolving power (R) and the offset from the direct image in pixels (Dx) as functions of wavelength.
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 4.5: Hot Pixel Growth Rate for HRC and WFC Figure 4.6: WFC Dark Current Histogram for Chip 1