Context :

Aims : We study the effects of moderate deviations from solar abundances upon the atmospheric structure and colours of typical Mira variables .

Methods : We present two model series of dynamical opacity-sampling models of Mira variables which have ( 1 ) \frac { 1 } { 3 } solar metallicity and ( 2 ) “ mild ” S-type C/O abundance ratio ( [ C/O ] =0.9 ) with typical Zr enhancement ( solar +1.0 ) .
These series are compared to a previously studied solar-abundance series which has similar fundamental parameters ( mass , luminosity , period , radius ) that are close to those of o Cet .

Results : Both series show noticeable effects of abundance upon stratifications and infrared colours but cycle-to-cycle differences mask these effects at most pulsation phases , with the exception of a narrow-water-filter colour near minimum phase .

Conclusions :