SHOC: Sutherland High Speed Optical Cameras

Two nearly identical instruments named SHOC (Sutherland High Speed Optical Camera) are available for use on the 1.0-m telescope. SHOCnAwe and SHOCnDisbelief are high-speed, visible-wavelength systems, mounted at Cassegrain focus and accommodating two filter wheels, making up to 14 filters available at any time. They were previously available on the 1.9-m and Lesedi telescopes as well. The 1.9m now has its own dedicated camera, SHOCnWonder, while Lesedi’s Nasmyth ports are both occupied by other permanently-mounted instruments.

The SHOC design is based on POETS (Portable Occultation, Eclipse, and Transit Systems; developed by a collaboration between groups at the Massachusetts Institute of Technology (MIT) and Williams College) and MORIS (MIT Optical Rapid Imaging System) at NASA’s 3-m IRTF on Mauna Kea, Hawaii.

SHOC mounted with the focal reducer on the 1.9m telescope. The large blue rectangle near the centre of the image is the box containing the SHOC computer and electronics; the camera is the small grey object at the end of the long, black focal reducer tube.

Technical Specifications

The SHOC instruments employ Andor iXon 888 EM CCD cameras, which have an electron-multiplying (EM) capability. They are 2048×1024 13-μm pixel detectors, operated in frame-transfer mode (imaging area 1024×1024 pixels). The following characteristics apply (although SHOC is now only available on the 1.0m):

The cameras have a selection of amplifiers (four different speeds; two conventional and four EM), each having multiple electron to ADU gain settings.  Binning and subframing are also user selectable. Operating at the lowest readout speed (lowest read noise) with appropriate binning for Sutherland’s median seeing, a minimum cycle time of ~0.5 seconds is typical. With further binning, windowing and higher readout speed, the cycle time can be decreased to 0.01 seconds. The SHOC systems contain identical components, except that the cameras have slightly different technical properties (read noise, well depth, etc.). See the SHOCnAwe camera specification sheet and the SHOCnDisbelief camera specification sheet.

There is an online calculator to help with estimating observing times, signal-to-noise ratios, and limiting magnitudes.

Current Status & Availability

The instruments are now over 10 years old and are starting to present with some issues. SHOCnAwe can no longer reliably cool below -40°C, so for programmes using long exposures please request SHOCnDisbelief.   SHOCnDisbelief has an issue with the 1MHz readout mode, in which a variable number of rows have a different bias level from the rest of the detector.  With SHOCnDisbelief it is therefore recommended only to use the 3MHz mode.

Please note that use of EM mode is prohibited unless demonstrated competence of this mode is provided, due to the risk of permanent damage to the CCD.  Future software will incorporate safeguards to protect the detector in EM mode. In the meantime, observing in EM mode is highly regulated.

Observers are invited to apply for time using SHOC on the 1.0-m telescope. Those new to SHOC must request assistance for the first night of their run; students must be accompanied by their supervisor.  Please cite the SHOC instrument paper in your publications (see below).

Filters

The available filter sets are listed below (click on filter name to view the transmission curve); there is also an empty slot in each filter wheel for white light observations:

• Bessell U B V R I
• SDSS u’ g’ r’ i’ z’
• Hα wide (20 nm)
• Hα narrow (3 nm)
• Redshifted Hα at 667, 681 & 686 nm
• [O III] 501 nm
• BG38
• Z

Please be sure to list every filter you require for your programme in the GRATINGS AND FILTERS field of the SAAO Telescope Time Application form.  This will ensure that your desired filters are scheduled for your run.

Visitor filters up to 51 mm square and 10 mm thick can also be accommodated.  Visitors wishing to use their own filters should contact the Head of Telescope Operations (rrs at saao.ac.za) to discuss this when applying for telescope time.

Further Information

Further information can be found on the online user manual.  Available here are links to the SHOC commissioning website and the SHOC data reduction pipeline (start with the README!).

Selected publications from commissioning: