Type-II Cepheids contains different sub-classes of variables depending on period. The W Vir class are thought to be related to AGB evolution. The peculiar W Vir have been suggested to be in binary systems, while the RV Tau are thought to be post-AGB stars.

In recent works Groenewegen and Jurkovic constructed and analyses the SEDs of all OGLE-III Type-II and Anomalous Cepheids in the Magellanic Clouds. Stars with IR excess were found at luminosities incompatible with single-star evolution.

In addition the light-time travel effect was investigated to look for new binary candidates.
Some were found, and also stars that apparently show large period changes.