A Double Periodic Variable (DPV) is a type of binary star. As the name implies, the systems vary in brightness not only due to eclipses of one star by the other, but also on a cycle of roughly 33 times longer than the orbit. The star gaining mass from the other has a thick disk of material surrounding it, and the systems apparently lose mass cyclically into the interstellar medium over time. The cause for the secondary longer variability still is not established. The stars are rare, with 21 systems found in the Galaxy and more than 170 in the Magellanic Clouds (Abril 2016).
List
Catalogues of Double Periodic Variables are given by Mennickent, Otero and Kołaczkowski (2016), Pawlak et al. (2013) and Poleski et al. (2010). Some few examples are given below.
The following list contains selected double periodic variables that are of interest to amateur or professional astronomy. Unless otherwise noted, the given magnitudes are in the V-band.