Previous: How to get the masks made
Up: How to get the masks made
Next: Alternative methods
Previous Page: How to get the masks made
Next Page: Alternative methods
A numerically controled Bridgeport INTERACT-4 milling machine is used to cut the slits and acquisition holes in a brass disk mounted on a special jig on the X-Y machine table. The cutting head consists of a cutting tool held in a chuck on a rotating spindle which moves in the Z direction. The slits have a V-shaped profile which avoids defocussing at the slit edge. The nominal width is 320m which corresponds to about 1.5 arcsec on the sky. In principle, the width of the slits can be varied by altering the depth at which the cutting head is set, however there is no guarantee that the quality of the slit edge would be optimal for these other slit widths. The slits have rounded ends with radius equal to half the slit width. A reproduction of a slit made with INTERACT-4 is shown in Fig 8. The mask is machined as a unit within its cell so that no positional uncertainty is introduced by mounting the mask in the cell at a later stage.
Curved slits can be made by connecting short slits between a number of user-specified points. However, this will not, in general, result in a constant slit width in the dispersion direction. Please note that the interface specification for INTERACT-4 (as used in the .MFR files) does not have provision for specifying curved slits so it would be necessary to make special arrangements with the observatory.
To get the masks made, check with the observatory for details of when they want the files and the desired physical format of the data. They will require the .MFR file produced by LEXT using the WRITE/MAN command. Since this is in ASCII format, it may be E-mailed to the observatory or sent by any other means appropriate to the transfer of ASCII data.
The elapsed time to make a mask depends on the availability of trained staff at the observatory and reference should therefore be made to the technical staff via your Support Astronomer. The system has been designed with the aim of producing masks within 30 minutes of generating the .MFR file.