An important ingredient of both planning and data reduction is a set of standard stars. These can serve double duty as extinction stars, and are used for this by the planning program. They are obviously essential in data reduction.
If more than one table is used, the user must be careful not to intermix data that are not on the same system. For example, the Cousins E-region standards are clearly not on the same ``UBV'' system as the Landolt equatorial standards. Likewise, several distinct ``RI'' systems are in use.
Sometimes it is useful to include ``catalog'' stars in an observing program. These are stars that have been observed in (supposedly) the same system as the standard stars, but are of lower quality and are not suitable for use as standards. However, they are not obviously variable, and may be useful both as extinction stars and for checking transformations.
In addition, we need tables of program stars. These usually will contain at least a magnitude, which is used to confirm identifications but is not used in data reduction.
Different types of star (standard, catalog, and program) should be put in separate table files. You can have several tables of each type, but you should not try to mix different types in the same file.
These star tables all require the following data
( above the line in Table 
):