Evolved stars of initial mass 8-10 to about 40 Mo. They are shell-hydrogen burning. Their spectral type is F/G, their luminosity type is I. They are rapidly (lifetime = a few thousands years) evolving towards the red supergiant phase (helium burning). When crossing the instability strip they can be observed as classical Cepheid variables.

-- CecileLoup - 2014-02-20