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Tips for Observing with the Cross-disperser

Here are some practical tips for observing with the Cross-disperser.

• Focusing is best done with a R1200Y grating and the Copper Neon lamp.
• There is no software to extract the orders on-line, however, FOS software can be used afterwards to extract about three orders. This is easily done because they are straight lines (see figure 4.10).
• Wavelength calibration is rather difficult due to the lack of a lamp with wide wavelength coverage. A planetary nebula (such as NGC 7027) can be used. Figure 4.10 shows maps of the CCD images for grating angles of 60.75 , 60 and 59.25 with enough lines even in the ultraviolet. See also Table 3.3.
• Do not use a grating angle outside the range 60 1 , otherwise the efficiency falls off rapidly.
• The FOS-dekker is best used, in order to ensure that there is no overlap of orders in the spatial direction. It has a 24.5 arcsec long slit which is ideal for use with the cross-disperser.

(a) A spectrum using the IDS cross-disperser and a grating angle 60.75\DEG . Orders (3) to (8) can be seen.

(b) A spectrum using the IDS cross-disperser and a grating angle 60.\DEG . Orders (3) to 8 can be seen.