关于轻元素一次加工（LEPP）的需要
On the need of the Light Elements Primary Process (LEPP)
摘要：
现存的化学演化模型低估了银河系中Sr、Y和Zr的产生，以及太阳系中90<A<130的纯s同位素的丰度。为了解决这个问题，调用了一个额外的（未知的）过程，即所谓的LEPP（轻元素主过程）。在本文中，我们研究可能的替代解决方案。基于全网络恒星演化计算，我们研究了一些通常被忽略的物理过程（如旋转）的包含或对流过冲，质量损失和核过程的效率的处理的变化对太阳系s-唯一分布的影响。我们的主要发现是：（1）在太阳系形成时期，我们的参考模型在整个s-唯分布范围内，甚至在90<A<130范围内，都产生了超太阳丰度，（2）在误差范围内，s-唯分布相对于~（150）Sm是平坦的; 3）小质量AGB星的s过程贡献（M<1.5 M_SUN）以及更大质量的（M> 4.0M_SUN）可忽略不计; 4）包含旋转意味着整个分布的向下移动对于重的仅S同位素具有更高的效率，导致更平坦的仅S分布; 5）关于对流或质量损失的不同规定产生整个分布的几乎刚性的移位。总之，AGB核合成标准范例的变化将允许协调模型预测与太阳系s-唯一丰度。尽管如此，LEPP并不能被完全排除，因为恒星和银河系化学演化模型仍然受到不确定性的影响。
英文摘要：
Extant chemical evolution models underestimate the Galactic production of Sr, Y and Zr as well as the Solar System abundances of s-only isotopes with 90<A<130. To solve this problem, an additional (unknown) process has been invoked, the so-called LEPP (Light Element Primary Process). In this paper we investigate possible alternative solutions. Basing on Full Network Stellar evolutionary calculations, we investigate the effects on the Solar System s-only distribution induced by the inclusion of some commonly ignored physical processes (e.g. rotation) or by the variation of the treatment of convective overshoot, mass-loss and the efficiency of nuclear processes. Our main findings are: 1) at the epoch of the formation of the Solar System, our reference model produces super-solar abundances for the whole s-only distribution, even in the range 90<A<130; 2) within errors, the s-only distribution relative to 150Sm is flat; 3) the s-process contribution of the less massive AGB stars (M<1.5 M_SUN) as well as of the more massive ones (M>4.0 M_SUN) are negligible; 4) the inclusion of rotation implies a downward shift of the whole distribution with an higher efficiency for the heavy s-only isotopes, leading to a flatter s-only distribution; 5) different prescriptions on convection or mass-loss produce nearly rigid shifts of the whole distribution. In summary, a variation of the standard paradigm of AGB nucleosynthesis would allow to reconcile models predictions with Solar System s-only abundances. Nonetheless, the LEPP cannot be definitely ruled out, because of the uncertainties still affecting stellar and Galactic chemical evolution models.
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