Two nearly identical instruments named SHOC are available for use on the SAAO 1.9-m and 1.0-m telescopes, and on the new 1.0-m telescope, Lesedi. SHOC 1 and 2 are high-speed, visible-wavelength systems, mounted at Cassegrain focus and using the existing filter wheels employed by the SAAO CCDs. The SHOC cameras allowed the UCT CCD camera to be decommissioned in 2012.
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.
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:
|Telescope||Field of View (arcmin)||Platescale (arcsec/pixel)|
|1.9 m||1.29 x 1.29||0.076|
|1.9 m + focal reducer||2.79 x 2.79||0.163|
|1.0 m||2.85 x 2.85||0.167|
|Lesedi||5.72 x 5.72||0.335|
The cameras have 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 1 and 2 systems contain identical components, except that the cameras have slightly different technical properties (read noise, well depth, etc.). See the SHOC 1 camera specification sheet and the SHOC 2 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 open for general use. The software has been overhauled and integrated during the two years following commissioning, and is now running on a web-based platform with js9 display. Please note the following:
- 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.
- External start mode with the 3 MHz amplifier is not currently available on SHOC 2. Please instead use External timing, a different amplifier, or specifically request SHOC 1.
Observers are invited to apply for time using SHOC on the 1.9-m and 1.0-m telescopes. SHOC 2 is currently mounted on the new 1.0-m telescope at all times. Those new to SHOC must request assistance for the first night of their run; students must be accompanied by their supervisor. Please reference the SHOC instrument paper in your publications (see below).
For the 1.9-m and original 1.0-m telescopes, the available filter sets are listed below (click on filter name to view 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
Please be sure to list every filter you require for your program 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.
Selected publications from commissioning:
- SHOC instrument paper: Coppejans, R. et al., 2013, Characterizing and Commissioning the Sutherland High-Speed Optical Cameras (SHOC), PASP, 125, 976-988
- P. Woudt, et. al., 2012, CC Sculptoris: a superhumping intermediate polar, MNRAS, 427, 1004-1013
- D. Coppejans, et al. 2013, High-speed photometry of faint cataclysmic variables -VIII. Targets from the Catalina Real-time Transient Survey, MNRAS, 437, 510-523
- A.N. Semena, et al., 2014, On the area of accretion curtains from fast aperiodic time variability of intermediate polar EX Hya, MNRAS, 442, 1123-1132.
- D. de Martino et al., 2014, Unveiling the redback nature of the low-mass X-ray binary XSS J1227.0-4859 through optical observations, MNRAS, 444, 3004-3014.