Post common envelope binary

A PCEB will continue to lose angular momentum via magnetic braking and gravitational waves and will eventually begin mass-transfer, resulting in a cataclysmic variable.

A planetary nebula formed by a common envelope system usually shows a bipolar structure.

The remaining hydrogen envelope of HD 101584 was ejected during the interaction between the red giant and the companion and it now forms the circumstellar medium around the binary.

While orbiting exoplanets are often proposed as the cause of these variations, planetary models often fail to predict subsequent changes in eclipse timing.

Other proposed causes, such as the Applegate mechanism, often cannot fully explain the observed eclipse timing variations either.

HD 101584 is a suspected post-common envelope binary. The engulfed companion triggered an outflow of gas, creating the nebula seen by ALMA .
Key stages in a common envelope phase. Top: A star fills its Roche lobe . Middle: The companion is engulfed; the core and companion spiral towards one another inside a common envelope . Bottom: The envelope is ejected and forms a PCEB or the two stars merge .