Stellar evolution and the 'O-rich AGB sequence'
  The `O-rich AGB sequence' is a well defined area occupied by oxygen-rich AGB stars (OH/IR) in the IRAS two-colour diagram [12]-[25] vs [25]-[60]. This sequence is interpreted in terms of evolutionary stage and/or progenitor mass with the aim to link observed classes of AGB stars and Planetary Nebulae (PNe). 
F.M. Jimenez-Esteban, D. Engels, and P. Garcia-Lario