Properties of massive Population III and metal-poor stars

We review the properties of massive Population III and very metal-poor stars, including briefly their formation, IMF, their main sequence evolution, possible mass loss mechanisms, atmosphere modeling etc. For detailed predictions concerning the properties of these stars we refer to Schaerer (2002) and Schaerer (2002) and references therein. Extending these calculations, Schaerer (2007) present new calculations concerning the ionizing power, Ly-α strength and related properties for different metallicities as well as for a range of power-law and log-normal IMFs. For illustrations from these studies see the Figures below. New detailed calibrations for solar metallicity O-type stars have recently been presented by Martins et al. (2005).