and mass loss parameter $N=100$ during the hydrogen burning phase.[]{data-label="bar_fig1"}](figure1.eps){width="82mm"}

![Idem dito. Luminosity[]{data-label="bar_fig2"}](figure2.eps){width="82mm"}

![Idem dito. Effective temperature[]{data-label="bar_fig3"}](figure3.eps){width="82mm"}

![Idem dito. Radius[]{data-label="bar_fig4"}](figure4.eps){width="82mm"}

Population III stars are hotter than their metal enriched counterparts, and their locus in the HR-diagram is shifted to the left upper part; pregalactic stars are bluer than the galactic ones.

For a given stellar mass of main-sequence stars its location in the HR-diagram depends strongly on metallicity but also on the mass loss strength. During the hydrogen burning, the higher the mass loss rate, the greater the reduction in luminosity.

Our models exhibit a high production of ionizing photons. This confirms the important cosmological consequences of the first generation of stars for the reionization of the universe.

Depending on their initial mass and the mass loss rate the final fate of our models could be as supernovae or hypernovae explosions.

### a) Central density and temperature {#a-central-density-and-temperature .unnumbered}

Lower metallicity stars are denser than the enriched stars. At the beginning of the evolution, galactic and pregalactic stars have different central densities which increase with decreasing $Z$. The central density increases with decreasing stellar mass and it is higher for lower metallicity stars.

As the evolution goes on, the mean 