Zero-metallicity stars

Abstract

Abstract.We present evolutionary models of zero-metallicity very massive objects, with initial masses in the range 120 M -1000 M , covering their quiescent evolution up to central carbon ignition. In the attempt of exploring the possible occurrence of mass loss by stellar winds, calculations are carried out with recently-developed formalisms for the mass-loss rates driven by radiation pressure (Kudritzki 2002) and stellar rotation . The study completes the previous analysis by Marigo et al. (2001) on the constant-mass evolution of primordial stars. Our results indicate that radiation pressure (assuming a minimum metallicity Z = 10 −4 × Z ) is not an efficient driving force of mass loss, except for very massive stars with M > ∼ 750 M . On the other hand, stellar rotation might play a crucial role in triggering powerful stellar winds, once the ΩΓ-limit is approached. However, this critical condition of intense mass loss can be maintained just for short, as the loss of angular momentum due to mass ejection quickly leads to the spinning down of the star. As by-product to the present work, the wind chemical yields from massive zero-metallicity stars are presented. The helium and metal enrichments, and the resulting ∆Y/∆Z ratio are briefly discussed.

Gamma-Ray Bursts and Population III Stars

“…Once the star reaches the critical rotation, mechanical mass shedding would occur, even when radiation-driven winds are very weak. This would be the dominant mode of mass-loss from massive Pop III stars (Marigo et al 2003;Ekström et al 2008;Yoon et al 2012). For very massive stars (M ∼ > 100 M ⊙ ), however, pulsationally driven winds during the red supergiant phase might also play an important role (Baraffe 2001;Moriya & Langer 2015).…”

“…Another necessary condition for long GRB progenitors is rapid rotation as mentioned above. Mass loss by radiation-driven winds is negligible for Pop III stars, and mass shedding due to rotation is not significant enough to remove the whole hydrogen envelope (Marigo et al 2003;Ekström et al 2008;Yoon et al 2012). This may raise a question of whether massive single Pop III stars can produce an ordinary long GRB.…”

“…The onset of this CNO boosting sensitively depends on the adopted overshooting parameter and the initial rotation speed, but it is usually found for Pop III stars in the mass range of about 10 -30 M ⊙ (C. Kye & S.-C. Yoon in prep). For more massive Pop III stars, the RSG solution seems to be generally favored (Marigo et al 2001(Marigo et al , 2003Ekström et al 2008;Yoon et al 2012 …”

“…By contrast, if ES circulations were the dominant mode of angular momentum transfer, the core and/or the envelope would retain a sufficient amount of angular momentum to produce a collapsar for a limited mass range of about 300 M ⊙ ∼ < M ∼ < 700 M ⊙ ). -The RSG solution is strongly favored for these very massive stars: it is most likely that Pop III stars with M > 260 M ⊙ end their lives as a RSG (Marigo et al 2003;Yoon et al 2012. Therefore, even if the core was rotating rapidly enough to produce a collapsar, the resultant relativistic jet would not be able to penetrate the envelope.…”

Masses of the Planetary Nebula Central Stars in the Galactic Globular Cluster System from HST Imaging and Spectroscopy∗

“…These include the opacity, molecular weight, nuclear reaction rates, chemical compositions, and stellar temperature (Marigo 2000). Thus, there is no simple core mass-luminosity relation to adopt for deriving a central star mass from a given luminosity.…”