标题： 低金属丰度下伽马射线暴前身星的演化 显示英文标题

标题： Evolution of Gamma-Ray Burst Progenitors at Low Metallicity

摘要： 尽管越来越多的证据表明长伽马射线暴（GRBs）与沃尔夫-拉叶星的死亡有关，但大质量恒星演化为GRBs的路径以及GRB前身星的确切性质仍然知之甚少。 然而，最近的大质量恒星演化模型指出——对于足够低的金属丰度——初始非常快速旋转的恒星可以满足坍缩星形成的条件。 即使这些模型中包含了磁场扭矩，但由于由旋转混合引起的准化学均匀演化，强的核心自转减速得以避免。 在这里，我们探讨了对于初始质量和自转范围而言，Z=Zsun/20的单颗恒星预计会产生GRBs。 我们进一步发现GRB前身星的化学结构存在二分性，其中较低初始质量的恒星以富含大量氦且仍含有一些氢的包层结束生命，而较高初始质量的恒星则以富含C/O且不含氢的大气爆炸。 显示英文摘要

摘要： Despite the growing evidence that long Gamma-Ray Bursts (GRBs) are associated with deaths of Wolf-Rayet stars, the evolutionary path of massive stars to GRBs and the exact nature of GRB progenitors remained poorly known. However, recent massive star evolutionary models indicate that -- for sufficiently low metallicity -- initially very rapidly rotating stars can satisfy the conditions for collapsar formation. Even though magnetic torques are included in these models, a strong core spin-down is avoided through quasi-chemically homogeneous evolution induced by rotational mixing. Here, we explore for which initial mass and spin-range single stars of Z=Zsun/20 are expected to produce GRBs. We further find a dichotomy in the chemical structure of GRB progenitors, where lower initial masses end their lives with a massive helium envelope which still contains some amounts of hydrogen, while higher initial masses explode with C/O-dominated hydrogen-free atmospheres.