VIMOS mask design on pre-image

Design of a Mask for Multi-Object Spectroscopy (MOS) observations with VIMOS. The mask serves to block, as far as possible, unwanted background light from the "night sky" (radiation from atoms and molecules in the Earth's upper atmosphere). During the set-up process for multi-object observations, the VIMOS software optimizes the position of the individual slits in the mask (one for each object for which a spectrum will be obtained) before these are cut. The photo shows an example of this fitting process, with the slit contours superposed on a short pre-exposure of the sky field to be observed.

Mask design made with the VMMPS tool, overlaying a pre-image. The selected objects are seen at the centre of the yellow squares, where a 1 arcsec slit is cut along the spatial X-axis. The rectangles in white represent the dispersion in wavelength of the spectra along the Y-axis. Masks are cut with the Mask Manufacturing Unit (MMU) built by the Virmos Consortium.