The slit mechanism is driven by very stringent requirements in spectral stability and repeatability. The main requirements are:
-
Contribution of the slits to the flux error budget within the allocated value.
-
Contribution of the slits to the spectral stability error budget within the allocated value.
Slit repeatability to avoid acquiring slit position during observations.
A number of masks suitable to carry on a long slit, a MOS, or a long slit plus MOS observing program (thus easing queue observations) during the same night without changing masks.
The requeriments are achieved with a cassette with space to store as many as 13 multislit and long-slit masks. A mechanism of two degrees of freedom allows the selection of one of the masks by removing it from the cassette and positioning it in the telescope focal plane with the required repeatability.
See also:
Last update July 26, 2005, by Héctor Castañeda