The atoll source 4U 1608-52 is not a Z source
  We have studied the spectral and timing behaviour of the atoll source 4U 1608-52. We find that the timing behaviour of 4U 1608-52 is almost identical to that of the atoll sources 4U 0614+09 and 4U 1728-34. Recently Muno, Remillard & Chakrabarty (2002) and Gierlinski & Done (2002) suggested that the atoll sources trace out similar three-branch patterns as the Z sources. The timing behaviour is not consistent with the idea that 4U 1608-52 traces out a three-branched Z shape in the color-color diagram along which the timing properties vary gradually. 
S. van Straaten (1), M. van der Klis (1) and M. Mendez (2) ((1) Univ.   Amsterdam, (2) SRON)