Doppler's 1842 paper discussed the colored light of which kind of stars?

Doppler’s 1842 paper discussed the colored light of binary stars.

Christian Doppler introduced his principle in a treatise commonly known in English as “On the Coloured Light of the Binary Stars and Some Other Stars of the Heavens.” He proposed that the observed color of a star could change when the star moved toward or away from an observer, much as a moving sound source changes the apparent pitch of its sound.

The title refers especially to binary, or double, stars because their orbital motion offered a possible explanation for alternating color shifts. Doppler connected his idea with stellar aberration, an earlier phenomenon identified by James Bradley in 1728. The work appeared in a preliminary form in 1842, while some bibliographies give 1843 for its publication in the proceedings of the Bohemian Society of Sciences.

A common mix-up is to associate the paper with red giants, white dwarfs, or neutron stars. Those are later stellar classifications; Doppler’s original discussion concerned binary stars and stellar motion in general, before modern astrophysical categories existed.