considerations and only an indirect evidence can be gained from observations of later generations of stars. E.g., the abundances of elements and isotopes observed in metal-poor halo stars [@Beers2005] suggest that these stars were formed from an interstellar matter enriched by mass lost during the H- and He- burning in the first stars rather than by debris of pair-instability supernovae (SNe) expected to be the final stage of the first VMS evolution [@Hirschi2007; @Cescutti2010].

Stellar winds
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The mass loss via stellar winds influences significantly the evolution of massive Population I and II stars and contributes a great deal to the enrichment of interstellar matter by heavy elements.

For cool winds of Population I red giants on the RGB [@Reimers1975; @Reimers1977] found an empirical relation giving the mass loss rate as

$$\label{Reimers}
 \dot{M}\sim \frac{L}{gR}\sim \frac{LR}{M}\; ,$$

where $L$, $R$, $M$ and $g$ are the luminosity, radius, mass and surface gravity of the star. [@Schroder2005] obtained a semi-empirical generalization of the Reimers’ relation.

The stellar winds are significantly enhanced at the early-type stars by radiative pressure either in continuum or especially in lines. The dependence of the mass loss rate due to CAK-wind on the metallicity has been scaled by the 