Obituary: ApJ 4, 80 (1896); AJ 16, 112 (1896); AN 140, 193 (1896)

Krüger worked with Schönfeld for the Bonner Durchmusterung; the catalogue contains 97 NGC-objects. He measured the stars of the double cluster in Perseus NGC 869/884; the results were published 1865 in Finnland.