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Published online by Cambridge University Press: 03 August 2017
The objective of the present study is to clarify the tests, checks and clues one may employ to determine whether a feature on a one century old plate is probably identical to a feature on a recent Schmidt plate. A test region of 40′ × 40′ around star HD 42088 was selected in order to detect a variability in nebulosities around Gem OB 1 stars.