4.2 Advanced Camera for Surveys (ACS)

As of July 4, 2006, ACS switched over to its Side-2 electronics and lowered its WFC setpoint temperature from -77 C to -81 C. This may result in slight discrepancies when comparing data from Side-1 to data from Side-2 until the ACS Team can fully characterize and calibrate the Side-2 performance. Updated reference files will be incorporated into the CALACS pipeline as soon as they are available. Observers should consult the ACS Instrument Handbook and ACS Web Page for current information.

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 to 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 25 arcsec field of view from 2000 to 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 21 x 21 µm pixels.

• The Solar Blind Channel (ACS/SBC):

The SBC has a 34 x 31 arcsec field of view from 1150 to 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 to 11,000Å in both the WFC and the HRC.
• Prism spectroscopy: Low resolution (R ~ 100 at 2000Å) near-UV spectroscopy from 2000 to 4000Å in the HRC.
• Prism spectroscopy: Low resolution (R ~ 100 at 1216Å) far-UV spectroscopy from 1150 to 1700Å in the SBC.
• Coronagraphy: Aberrated beam coronagraphy with the HRC from 2000 to 11,000Å with 1.8 arcsec and 3.0 arcsec diameter occulting spots. Use of the SBC with the Coronagraph is prohibited, for detector safety reasons.
• Imaging Polarimetry: Polarimetric imaging in the HRC and WFC with polarization angles of 0^o, 60^o, and 120^o.
• Ramp Filters: A set of ramp filters covering the wavelength range 3810 to 10,710A 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.