The effects of rotation on stellar evolution are particularly important at low metallicity , when mass loss by stellar winds diminishes and the surface enrichment due to rotational mixing becomes relatively more pronounced than at high metallicities .
Here we investigate the impact of rotation and metallicity on stellar evolution .
Using a similar physics as in our previous large grids of models at Z = 0.002 and Z = 0.014 , we compute stellar evolution models with the Geneva code for rotating and nonrotating stars with initial masses ( M _ { ini } ) between 1.7 and 120 M _ { \odot } and Z = 0.0004 ( 1/35 solar ) .
This is comparable to the metallicities of the most metal poor galaxies observed so far , such as I Zw 18 .
Concerning massive stars , both rotating and nonrotating models spend most of their core-helium burning phase with an effective temperature higher than 8000 \mathrm { K } .
Stars become red supergiants only at the end of their lifetimes , and few red supergiants are expected .
Our models predict very few to no classical Wolf-Rayet stars as a results of weak stellar winds at low metallicity .
The most massive stars end their lifetimes as luminous blue supergiants or luminous blue variables , a feature that is not predicted by models with higher initial metallicities .
Interestingly , due to the behavior of the intermediate convective zone , the mass domain of stars producing pair-instability supernovae is smaller at Z=0.0004 than at Z=0.002 .
We find that during the main sequence ( MS ) phase , the ratio between nitrogen and carbon abundances ( N/C ) remains unchanged for nonrotating models .
However , N/C increases by factors of 10-20 in rotating models at the end of the MS. Cepheids coming from stars with M _ { ini } > 4 - 6 ~ { } M _ { \odot } are beyond the core helium burning phase and spend little time in the instability strip .
Since they would evolve towards cooler effective temperatures , these Cepheids should show an increase of the pulsation period as a function of age .