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 (inoperable)	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	2%	3%	5%	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)

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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. It shows the layout of the instrument entrance apertures in the telescope focal plane as projected onto the sky. The scale in arc seconds is indicated. 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. (Based on an experiment performed with Fe55) 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: ACS Model PSFs in central 5x5 pixel region (SBC). 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