mass loss rate, its evolution can be different.

![Evolutionary tracks in the HR-diagram for $100$, $120$, $150$, $200$ and $250\,M_{\odot}$ galactic Population III stars with metallicity $Z=10^{-6}$ and mass loss parameter $N=50$, during the hydrogen and helium burning phases.[]{data-label="bar_fig11"}](figure11.eps){width="72mm"}

![Idem dito. Mass loss parameter $N=100$.[]{data-label="bar_fig12"}](figure12.eps){width="70mm"}

![Evolutionary tracks in the HR-diagram for $100$, $120$, $150$, $200$ and $250\,M_{\odot}$ pregalactic Population III stars, metallicity $Z=10^{-9}$, and mass loss parameter $N=50$, during the hydrogen and helium burning phases.[]{data-label="bar_fig13"}](figure13.eps){width="72mm"}

![Idem dito. Mass loss parameter $N=100$.[]{data-label="bar_fig14"}](figure14.eps){width="70mm"}

During hydrogen burning, the luminosity of a star without mass loss increases while a helium core is formed. Then, as the star evolves, the luminosity remains almost constant while the effective temperature decreases. However, for different stars their luminosity and effective temperature decrease with decreasing mass and increasing metallicity. The luminosity is lower for mass losing stars than for stars without mass loss.

Different stars evolve with different lifetimes. Depending on the mass loss rate, both the initial hydrogen and helium burning phases take place at the blue side of the HR diagram. When the stars evolve with assumed mass loss rates they move toward the red, like in the conservative case. With and without mass loss the stars 