Congratulations to Paul Breuhan, who was the first to identify this motorcycles as an Aristos (also known as a Menos or Sterna).
Per the 1985 edition of The Illustrated Encyclopedia of Motorcycles by Erwin Tragatsch
“Designed by Johannes Passler, the 614cc Aristos was a very unorthodox machine with a watercooled flat twin sidevalve engine. The Mars-like frame was made of welded steel plates and allowed a low seat position. The Berlin-based company never developed this machine to the full. This led to more reorganisations and also to two more trade names for the Aristos inside of three years: Menos and Sterna. The differences between the three makes were small; they included, besides different tank transfers, the colour and the fork design.”
Here’s the original photo, without my removal of the company logo:
