4.2 Advanced Camera for Surveys (ACS)

The ACS is designed to advance the survey capabilities of HST, defined as the product (Throughput x DETECTOR AREA), by a factor of ~10 in the visual and near infrared. This instrument comprises three channels, each optimized for a specific goal:

• The Wide Field Channel (ACS/WFC):
• The WFC has a 202 x 202 arcsec field of view from 3700-11,000Å, and a peak efficiency of 48% (including the OTA). The plate scale is ~0.05 arcsec/pixel, providing critical sampling at 11,600Å. The detector consists of a mosaic of two 2048 x 4096 Scientific Imaging Technologies (SITe) CCDs, with 15 x 15 µm pixels.
• The High Resolution Channel (ACS/HRC):
• The HRC has a 29 x 26 arcsec field of view from 2000-11,000Å and a peak efficiency of 31%. The plate scale is ~0.027 arcsec/pixel, providing critical sampling at 6300Å. The detector is a 1024 x 1024 Scientific Image Technologies (SITe) CCD, with 21x 21 µm pixels.
• The Solar Blind Channel (ACS/SBC):
• The SBC has a 35 x 31 arcsec field of view from 1150-1700Å, and a peak efficiency of 6%. The plate scale is ~0.032 arcsec/pixel. The detector is a solar-blind CsI MAMA, with 25 x 25 µm pixels.

In addition to these three prime capabilities, ACS also provides:

• Grism spectroscopy: Low resolution (R~100) wide field spectroscopy from 5500-11,000Å in both the WFC and the HRC.
• Objective prism spectroscopy: Low resolution (R~100 at 2000Å) near-UV spectroscopy from 2000-4000Å in the HRC.
• Objective prism spectroscopy: Low resolution (R~100 at 1216Å) far-UV spectroscopy from 1150-1700Å in the SBC.
• Coronagraphy: Aberrated beam coronagraphy in the HRC from 2000-11,000Å with 1.8 arcsec and 3.0 arcsec diameter occulting spots.
• Imaging Polarimetry: Polarimetric imaging in the HRC and WFC with polarization angles of 0^o, 60o and 120o.
• Ramp Filters: A set of ramp filters covering the wavelength range 3810-10710A at 2% and 9% bandwidth. There are five ramp units which each have inner, middle, and outer segments. WFC can use all three segments, providing 15 ramp filters, while HRC can only use the 3 middle ramp filters. ACS ramp filters have a higher throughput than those in WFPC2.