3.5 ACS Quick Reference Guide

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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 mm	21 ¥ 21 mm	25 ¥ 25 mm
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
Readnoise	5.0 e–	4.7 e–	0 counts
Dark Current2	0.0029 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/second Pixel count-rate linearity limit: ~22 counts/second/pixel
Gain	1,2,4 and 8 e–/DN (Max 65,535 DN)	1,2,4 and 8 e–/DN (Max 65,535 DN)	n/a
Operating Temperature2	-80×C	-81×C	n/a

1Loss of linearity occurs at count rates larger than these values. For more information, please see Section 4.5.6. 2Average 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	0.5" to 1"	1"	1"	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)

1Anderson & King, ISR 04-15 (http://www.stsci.edu/hst/acs/documents/isrs/isr0415.pdf) 2Koekemoe, 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	Ha (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

1Limited 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 Ha 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
Proposal Preparation Tips	Table 6.1: Examples of polarizer and non-polarizer exposures in a Phase II proposal. Table 7.1: Science decision guide. Table 7.2: Science feasibility guide. Table 9.1: Useful quantities for the ACS WFC. Table 9.2: Useful quantities for the ACS HRC. Table 9.3: Useful quantities for the ACS SBC.
Overheads	Table 8.1: Science exposure overheads: general. Table 8.2: ACS science exposure overhead times (minutes).
Auto-parallels	Table 7.12: Filter combinations for auto-parallels in the two cases of (i) HRC camera prime and (ii) WFC camera prime. Table 7.13: Minimum primary exposure time (seconds) to attach an auto-parallel for CR-SPLIT=n.
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 Table 7.11: 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. The scale in arcsec 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: CCD gain and readout noise (e- rms) under SIDE-1 operation (03/2002->06/2006). Table 4.2: CCD gain and readout noise (e- rms) under SIDE-2 operation (07/2006-01/2007). 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 limit J- and F-band magnitudes of an unreddened O5 star for observations with the SBC filters and prisms. Table 7.6: Bright object protection policy for SBC observations.
Hot and Warm Pixels	Table 4.3: Creation rate of new hot pixels (pixel/day). Table 4.4: Annual permanent hot pixel growth (%).. Figure 4.12: Growth of permanent warm and hot pixel population as a function of time (WFC top, HRC bottom).
Charge Transfer Efficiency	Table 4.5: Charge transfer efficiency measurements for the ACS CCDs at installation time (Fe55 test at 1620 e–). Table 4.6: Example of science applications and their assumed parameters. Figure 4.15: Projected CTE losses in WFC (and 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. Note that this figure is rotated 180× with respect to the pipeline calibration products, where WFC2 is the lower half of the detector. Figure 10.128: The map of the effective pixel areas of the ACS/WFC chips. Figure 10.129: The geometric distortion map for the HRC. Figure 10.130: The map of the effective pixel areas of 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.
Encircled Energy	Table 5.4: Encircled energy measurements for the ACS channels. Table 9.4: Encircled energy comparison for WFC/F850LP. Figure 4.18: MAMA point spread function. Figure 5.9: Encircled energy for the CCD channels. Figure 5.10: Encircled energy for the SBC.
PSF	Figure 5.8: Kernels representing CCD pixel functions for HRC and WFC. Table 5.10: Model ACS SBC PSFs. Figure 5.9: Encircled energy for the CCD channels.
Plate Scale	Table 7.11: 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: Examples of polarizer and non-polarizer exposures in a Phase II proposal. Table 6.2: Filters that can be used in conjunction with the ACS polarizers.
Photometry	Table 5.5: V detection limits for ACS, HRC, and SBC direct imaging. Table 9.1: Useful quantities for the ACS WFC. Table 9.2: Useful quantities for the ACS HRC. Table 9.3: 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.
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. Figure 6.22: Sensitivity versus wavelength for SBC PR110L. Figure 6.24: Sensitivity versus wavelength for SBC/PR130L.
Sky Backgrounds	Table 9.5: Approximate zodiacal sky background as a function of ecliptic latitude and ecliptic longitude (in V magnitudes per square arcseconds). Table 9.6: Geocoronal emission lines. Table 9.7: 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 due to the zodiacal light, Moon, and the sunlit Earth, as a function of angle between the target and the limb of the Earth or Moon. Figure 9.3: Extinction versus wavelength.
Calibration Accuracies	Table 3.2: Calibration accuracies. Figure 4.5: Dark rate trend with time for the WFC CCDs. Figure 4.6: Dark current as a function of time for the HRC Figure 4.7: Histogram of WFC dark frames taken before and after the change in temperature.