Closing down

Now that all the calculations to produce accurate positions of the holes which will host the fibres have been executed, you can proceed to a part of the process which is undoubtedly much more trivial but nonetheless vital both for having the holes actually drilled on the plate and for the subsequent work at the telescope.

First of all, you can obtain a map of the final coordinates of your objects and guide stars by using the command:

PLOT/OPTOPUS [table] [label] [EW_flag],

where [table] is the table output by REFRACTION/OPTOPUS. Recall that before using this command it is necessary to assign the plotter you want to use with the command:

ASSIGN/PLOT device

and then, after successful completion of PLOT/OPTOPUS, the plot is sent to the assigned device.

The option provided by the EW_flag allows the user to choose between two possible orientations of the map. Normally, only the (default) unflipped version, corresponding to the appearance of the starplate from the machined side, is needed. If direct comparisons will be made with photographic plates where east is to the right, a flipped map should be requested. The default version of the map has north at the top and east to the left, and will be extremely helpful at the telescope, to ensure identical numbering of both objects and fibers. If the two are not uniquely correlated, the observer will not know which spectrum comes from which object!

Once on La Silla, holes will have to be labelled using the provided self-adhesive labels, in the same way as they are numbered on the maps produced by PLOT/OPTOPUS (i.e. according to the consecutive numbers assigned by the REFRACTION/OPTOPUS command). In order to avoid object misidentifications at a later stage, and for a cross identification between object identifiers and hole numbers, it is recommended to bring a printout of the table output created by the command REFRACTION/OPTOPUS to the telescope. Also definitely needed at the telescope is the printout of the descriptors of this fundamental table. An example can be found in Table H.3.

We remind users less familiar with MIDAS, that both the table and its descriptors may be printed out by first assigning the output ASCII file with:

ASSIGN/PRINTER FILE filename

then using the MIDAS commands PRINT/TAB and PRINT/DESCRIPTOR for the table and the descriptors respectively.

The last command to be used in an Optopus session generally is

DRILL/OPTOPUS in_table [out_file]

to transform the object coordinates taken from the output file of REFRACTION/OPTOPUS into a long sequence of machine instructions, correctly formatted for the programmable milling machine on La Silla. These will be output in [out_file] in ASCII format.

At the end of the operations with the Optopus package, all the instruction files created by DRILL/OPTOPUS, together with a copy of the plots produced by PLOT/OPTOPUS, have to handed over to the Garching staff. They will take care of the transfer to La Silla.