论文标题
锂和碳同位素比所追踪的现场巨人中混合混合的证据
Evidence of extra-mixing in field giants as traced by lithium and carbon isotope ratio
论文作者
论文摘要
尽管不是标准恒星演化预测的，但光元素的表面丰度（例如锂（Li），碳和氮）在红色巨型分支（RGB）期间变化而变化。这通常与RGB凹凸后的热盐混合作用有关。富含液化的RGB恒星也可能与外部来源的加混合或污染相关。我们在166个野外红色巨人的样本中测量了LI丰度和同位素比率为12C/13C，该样品由-0.3 <[Fe/H] <0.2，由Express Radial速度程序靶向，以分析额外混合的效果。系外行星检测所需的多个观测值用于减少在12C/13C测量中的矫治污染的影响。由于上限的流行，LI丰度模式很复杂，但RGB和Core Core燃烧的巨人之间的比较显示了与Thermohaline一致的混合效果。样品中最富含的巨型巨人，被归类为接近RGB凹凸的RGB恒星，其12c/13c低。鉴于12c/13c不应受到行星吞噬的影响，这似乎不是高利的来源。 RGB中质量和12C/13C之间的相关性降低，水平分支中的相关性越来越大，这再次与热盐混合一致。我们的数据还显示了12C/13C和[Fe/H]之间的相关性。二进制对LI或12C/13C的影响都没有明显的影响。我们的样本显示了与RGB凹凸后其他混合作用一致的行为。 12C/13C增加了新的线索来描述特级混合，并且很可能是研究红色巨人混合的最佳工具。在田间恒星中对12C/13C的其他测量将大大提高我们与模型和理解混合机制相比的能力。
Although not predicted by standard stellar evolution, the surface abundance of light elements, such as lithium (Li), carbon, and nitrogen, changes during the red giant branch (RGB) as a result of extra-mixing. This is associated usually with thermohaline mixing acting after the RGB bump. Peculiar Li-enriched RGB stars might also be related to either enhanced extra-mixing or pollution from external sources. We measure the Li abundance and carbon isotopic ratio 12C/13C in a sample of 166 field red giants with -0.3<[Fe/H]<0.2, targeted by the EXPRESS radial velocity program to analyze the effects of extra-mixing. Multiple-epoch observations needed for exoplanet detection are used to decrease the effects of telluric contamination in 12C/13C measurements. Due to the prevalence of upper limits, the Li abundance pattern is complicated to interpret, but the comparison between RGB and core-He burning giants shows effects of extra-mixing consistent with thermohaline. The most Li-enriched giant in the sample, classified as a RGB star close to the RGB bump, has low 12C/13C. Given that the 12C/13C should not be affected by planet engulfment, this does not seem to be the source of the high Li. There is a decreasing correlation between mass and 12C/13C in the RGB and an increasing correlation in the horizontal branch, which, once again, is consistent with thermohaline mixing. Our data also shows a correlation between 12C/13C and [Fe/H]. There is no evident impact of binarity either on Li or on 12C/13C. Our sample shows behavior consistent with additional mixing acting after the RGB bump. The 12C/13C adds new clues to describe extra-mixing, and could well be the best tool to study mixing in red giants. Additional measurements of 12C/13C in field stars would greatly improve our ability to compare with models and understand mixing mechanisms.
