Atrobite: On and On They Spin

This astrobite discusses the mysterious case of stars that rotate much faster than they should. The paper focuses of supergiants, bright giants, normal giants, and sub giants of luminosity class K and G (which are based on temperature).

Source

Theoretically, these stars' rotation should slow down with age due to a loss of moment of inertia due to stellar winds. And that is true for most of these stars; however, some of these stars actually spin faster. This has been found frequently enough to be significant:

Source. This graphs demonstrates the large range of velocities found in the studied stars.

One of the mysteries surrounding these stars (literally) is a cloud of warm dust around the stars little is known about this dust or its function, but is is being studied as a possible influence on the rotational speed of the stars. Hypotheses include that the dust is due to magnetic stellar winds or comes from collisions of planets.

Source- The large offsets in this data might indicate excess emissions.

The authors proposed two causes for the rapidly rotating stars. One explanation could be interactions with a rotating low mass star (like a brown dwarf) or tidal interactions with a certain type of planet called a "hot Jupiter." These two possibilities would produce different chemical abundances. Going forward, the authors of the paper propose to search for differences in chemical abundances to distinguish between these two hypotheses.