These are done after lunch to ensure the telescopes, instruments and image detectors (usually a CCD camera) are performing correctly. This also includes the mundane job of filling the CCD camera cryostats with liquid nitrogen. The INT has only one CCD camera these days (wide field imaging at prime focus), but the WHT depending on what instruments are in use may have several cryostats that need to be filled and this can be quite time consuming. If everything is ok, an entry is made in the telescope log book effectively handing over the systems for observing.
In the WHT control room (March 2002)
Me loading coordinate (RA and DEC) values into the Telescope Control System (TCS) to ensure that the telescope moves to the selected position and that finally tracking is achieved. This test also moves the dome. Its not been unknown that the dome aperture and the telescope can end up in different positions due to a problem... Not good for observing!
In the INT control room (March 2002)
Here I'm checking an image (a bias frame) from the prime focus Wide Field Camera. The image readout from the four large format CCD chips can be seen on the display monitor to the right.
Renee filling the INT Wide Field Camera cryostat with liquid nitrogen (July 2004)
The camera cryostats are topped up three times a day. By the observer (or the Telescope Operator in the WHT) before opening the dome. At dawn after the nights observing and after lunch by a member of the engineering staff. Its very important that the CCD cameras don't warm up else thermal noise will be introduced and saturate the images.Click here to read about some of my experiences working as a night duty engineer.
