NuGrid计划中钌同位素组成的预测
Isotopic Compositions of Ruthenium Predicted from the NuGrid Project
摘要：
钌（Ru）的同位素组成测量从前太阳能碳化硅（SiC）颗粒。在一个流行的场景中，太阳前SiC颗粒形成于渐近巨星分支（AGB）恒星的外围，以恒星风的形式离开恒星，并加入太阳前分子云，从而形成太阳系。Ru同位素在恒星内部形成，在AGB阶段移动到恒星表面，并被锁定在SiC颗粒中。在这种情况下，我们分析了NuGrid数据，该数据提供了一组初始质量和金属丰度范围广泛的恒星的Ru同位素在恒星风中的丰度。我们应用C>O（碳丰度大于氧丰度）条件，这是通常采用的SiC在恒星风中形成的条件。NuGrid的数据证实，SiC颗粒不会在大质量恒星的风中形成。低质量恒星风中Ru的同位素组成可以解释测量结果。我们发现低金属丰度（Z=0.0001）的低质量恒星（$1.65~M_\odot$和$2~M_\odot$）可以解释大部分Ru的同位素组成。我们确认，丰富的${^{99}}$ Ru内的前太阳晶粒包括从原位衰变的${^{99}}$ Tc的贡献。我们还验证了我们的结论，通过比较的同位素组成的Ru集成在所有的脉冲与计算在个别脉冲。
英文摘要：
The isotopic compositions of ruthenium (Ru) are measured from presolar silicon carbide (SiC) grains. In a popular scenario, the presolar SiC grains formed in the outskirt of an asymptotic giant branch (AGB) star, left the star as a stellar wind, and joined the presolar molecular cloud from which the solar system formed. The Ru isotopes formed inside the star, moved to the stellar surface during the AGB phase, and were locked into the SiC grains. Following this scenario, we analyze the NuGrid data which provide the abundances of the Ru isotopes in the stellar wind for a set of stars in a wide range of initial masses and metallicities. We apply the C>O (carbon abundance larger than the oxygen abundance) condition which is commonly adopted for the condition of the SiC formation in the stellar wind. The NuGrid data confirm that SiC grains do not form in the winds of massive stars. The isotopic compositions of Ru in the winds of low-mass stars can explain measurements. We find that lower-mass stars ($1.65~M_\odot$ and $2~M_\odot$) with low metallicity (Z=0.0001) can explain most of the measured isotopic compositions of Ru. We confirm that the abundance of ${^{99}}$Ru inside the presolar grain includes the contribution from the in-situ decay of ${^{99}}$Tc. We also verify our conclusion by comparing the isotopic compositions of Ru integrated over all the pulses with those calculated at individual pulses.
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