Barium stars also show enhanced spectral features of carbon, the bands of the molecules CH, CN and C2.
The class was originally recognized and defined by William P. Bidelman and Philip Keenan.
[1] Initially, after their discovery, they were thought to be red giants, but the same chemical signature has been observed in main-sequence stars[2][3] as well.
These systems are being observed at an indeterminate amount of time after the mass transfer event, when the donor star has long been a white dwarf.
[11][12] Depending on the initial properties of the binary system, the polluted star can be found at different evolutionary stages.