Wavelength calibration and absolute flux determination procedures require some auxiliary data. Some tables are provided by the system, but the user can modify or include new information using the available table commands (Vol. A, Chapter 5). In addition to columns of interest to the user, user-supplied tables must have the columns and column labels required by the various MIDAS commands they are to be used with.
For the purpose of the reduction of spectral data, there are three basic table structures:
a) Line identification tables, used in the wavelength calibration step. One column must contain the laboratory (if the reference frame is to be used) wavelengths in the units desired for the calibrated spectrum. A sample table with comparison lines of the spectrum He-Ar is available in MID_ARC:hear.tbl it contains lines in the range from 3600 Å to 9300 Å and is suitable for data with dispersions between about 5 and 10 Å /mm.
b) Flux tables, used for flux calibration and rectification of spectra. These tables contain at least three columns defining for each entry central wavelength, bin width and flux, with labels :WAVE, :BIN_W, :FLUX_W. When composing your own tables, take care that the wavelength unit is the same for all three quantities and agrees with the one used for the wavelength calibration. Some sample flux tables are available in the directory MID_STANDARD. If you are still preparing your observations, note that the data available for the various stars is very inhomogeneous whereas the quality of the calibrations depends very sensitively on the number and spacing of entries within the spectral range to be observed.
c) Sample atmospheric and interstellar extinction
laws are contained in directory MID_EXTINCTION. All
interstellar laws are normalised to 
at 5500 Å,
and interpolated and rebinned to a constant step in wavelength (10
Å or nm). Note that the wavelength coverage is very different for
various data sets.
Table: Standard Stars for Absolute Flux Calibration in system area MID_STANDARD.
Table: Extinction Tables in directory MID_EXTINCTION