Selecting doubles from the WDS catalogue with required values for separation, magnitude delta etc. is a good approach for session planning - but besides the unavoidable errors in the advertised data there are also sometimes unexpected changes in the meaning of the listed values. Notably while one would expect consistent visual magnitude values here as the concept of magnitude seems explicitly a visual one there are often values in the infrared band given. So you have suddenly doubles with +8mag primaries on your list but you will find this star on no amateur star map because this magnitude is not visual.
It helps when you check the code columns after selecting - note code "K" means infrared and "R" means "red" magnitudes.
Besides the potential troubles with the magnitude values exist other traps hidden in the note codes "I" and "X" for probably bogus doubles.
Reason for this post are several Köhler doubles in Taurus with infrared magnitudes I got during my session planning for the next clear night in January I hope for.
Traps for selecting doubles from the WDS catalogue
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