Why is Tau Ceti a G-type star and Toliman (Alpha Cen B) a K-type?

In terms of mass, Tau Ceti is actually the lighter one (78% of the
Sun's mass vs. 90% for Toliman.) So you'd expect the opposite..

https://en.wikipedia.org/wiki/Tau_Ceti
https://en.wikipedia.org/wiki/Alpha_...pha_Centauri_B

--
Jos

[[Mod. note -- One plausible reason is that stars change in spectral
type as they age. Wikipedia gives Tau Ceti's age as 5.8 Gyr, Alpha Cen B
as 5.3 Gyr. The two stars also have somewhat different metallicities
(which affect spectral types).
-- jt]]