超音速中微子驱动风中的r过程：风终端激波的滚转
The r-Process in Supersonic Neutrino-Driven Winds: The Roll of Wind Termination Shock
摘要：
最近对核心坍缩超新星的流体动力学研究表明，初生中子星的中微子加热喷出物发展为超音速外流。这些超音速风受到来自前一颗超新星喷出物的反向激波的影响，形成了风终止激波。我们研究了中微子驱动风中的终止激波及其滚转对r过程的影响。超音速外流计算与半解析中微子驱动的风模式。随后的终端冲击，亚音速外流得到应用朗肯-Hugoniot关系。我们发现了一些与r过程相关的效应。第一种是由于风的终止而使温度下降的突然减缓。第二个是由终止激波加热引起的熵跳变，可达几百NAk。核合成计算得到的风进行检查这些影响的r-过程。我们发现：1）温度下降的减缓对r过程丰度曲线的确定起着决定性的作用。这是由于核合成路径在r-过程冻结阶段对温度的强烈依赖性。我们的结果表明，只有相对较小的激波半径（~ 500公里）的终止激波风与大部分太阳r过程丰度（A~100-180）有关。然而，太阳r过程曲线中最重的部分（A~180-200）可以在冲击风和非冲击风中重现。这些结果可能有助于限制与r过程相关的超新星祖先的质量范围。另一方面，我们发现熵跳在r过程中的作用可以忽略不计。这是因为相当大的熵增加只发生在一个大的激波半径（~10，000 km），在那里r-过程已经停止。
英文摘要：
Recent hydrodynamic studies of core-collapse supernovae imply that the neutrino-heated ejecta from a nascent neutron star develops to supersonic outflows. These supersonic winds are influenced by the reverse shock from the preceding supernova ejecta, forming the wind termination shock. We investigate the effects of the termination shock in neutrino-driven winds and its roll on the r-process. Supersonic outflows are calculated with a semi-analytic neutrino-driven wind model. Subsequent termination-shocked, subsonic outflows are obtained by applying the Rankine-Hugoniot relations. We find a couple of effects that can be relevant for the r-process. First is the sudden slowdown of the temperature decrease by the wind termination. Second is the entropy jump by termination-shock heating, up to several 100NAk. Nucleosynthesis calculations in the obtained winds are performed to examine these effects on the r-process. We find that 1) the slowdown of the temperature decrease plays a decisive roll to determine the r-process abundance curves. This is due to the strong dependences of the nucleosynthetic path on the temperature during the r-process freezeout phase. Our results suggest that only the termination-shocked winds with relatively small shock radii (~500km) are relevant for the bulk of the solar r-process abundances (A~100-180). The heaviest part in the solar r-process curve (A~180-200), however, can be reproduced both in shocked and unshocked winds. These results may help to constrain the mass range of supernova progenitors relevant for the r-process. We find, on the other hand, 2) negligible roles of the entropy jump on the r-process. This is a consequence that the sizable entropy increase takes place only at a large shock radius (~10,000km) where the r-process has already ceased.
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