SAAO CCD Camera
Introduction
The SAAO CCD camera is available for direct imaging on the 1.0-m and 1.9-m telescopes. Two SITe back-illuminated detectors are available: either a 1024x1024 pixel CCD (designated STE4) or a 512x512 pixel chip (STE3). The CCD control software manual for use with the 1.0-m telescope is available here. The instrument is controlled by a DOS PC when mounted on the 1.9-m.
The detector is contained within a cryostat mounted at the Cassegrain focus, together with a remotely-operated filter box and an autoguider. Software is available at the telescope for determining guide star positions. This setup is describe in the TCS manual for each telescope.
Filters
The following filters are available for use with the SAAO CCD and are installed at all times:
- Bessell UBVRI
- Z
- Hα
There is also an empty slot in the filter wheel for white light observations. A BG38 filter is available on request. Visitor filters up to 51 mm square and 10 mm thick can be accommodated. Visitors wishing to use their own filters should contact the Head of Telescope Operations to discuss this when applying for telescope time.
Detector Properties
The table below gives the properties of STE4. STE3 has very similar attributes.
| Device Name | STE4 |
|---|---|
| Manufacturer | SITe |
| Chip Type | Back-illuminated |
| Number of Pixels | 1024 x 1024 |
| Pixel size | 24 microns square |
| Scale (1.0-m) | 0.31 arcsec/pix |
| Scale (1.9-m) | 0.14 arcsec/pix |
| Field of view (1.0-m) | 317 x 317 arcsecs squared |
| Field of view (1.9-m) | 146 x 146 arcsec squared |
| Read Noise | 6.5 electrons |
| Scale Factor | 2.8 electrons/ADU |
| Linear Count Limit | 65535 ADU |
| Readout Time | 43 sec |
| U zero point (1ADU/sec)(1.0-m) | 19.20 mag |
| B | 22.00 mag |
| V | 22.35 mag |
| I | 21.80 mag |
Data reduction
There are computers located in the domes for image processing using IRAF and a pipeline based on DoPHOT. The latter can be used for real-time reductions, to obtain reduced CCD photometry of stellar fields while observing. As each image is written to disc, the program picks out the correct flatfield, cleans and flatfields the frame and writes it out as a FITS file. It then runs DoPHOT on the image to produce aperture and profile-fitted magnitudes. If you are observing the same field repeatedly, DoPHOT will display differential profile-fitted magnitudes as a function of time. The results from DoPHOT can be further processed using routines in STAR to produce the final results.
Observers may also, by arrangement, use machines in Cape Town to carry out reductions on their data.
Data backup & archiving
Observers can backup their data to their laptop, or transfer it to their home institute via ftp. Alternatively, observers may arrange with IT staff to write their data to DVD for them. The computers in the domes to not have DVD-writing facilities, nor functioning USB ports.
