船底座矮星系的核合成和不均匀化学演化
Nucleosynthesis and the Inhomogeneous Chemical Evolution of the Carina Dwarf Galaxy
摘要：
船底座dSph中9颗明亮的RGB恒星中23种元素的详细丰度是基于VLT和麦哲伦望远镜收集的高分辨率光谱。使用标准方法将球形模型大气分析应用于380至680 nm范围内的光谱。分析中的恒星范围为-2.9 < [Fe/H] <-1.3，并采用Lemasle等人（2012）确定的年龄，我们能够检查船底座老年和中年人口的化学演化。这项工作的主要结果之一是在船底座的非均匀混合的证据;[Mg/Fe]的大离散表明老年人口的混合较差，老年人口和中年人口之间[α/Fe]比值的偏移（当与先前发表的结果进行检查时）表明，第二次恒星形成事件发生在富含α的气体中，一颗恒星，Car-612，似乎是在SN Ia/II产物增强的口袋中形成的。后一颗恒星提供了矮星系中超新星Ia/II比值增强的恒星与外星系晕中超新星Ia/II比值增强的恒星形成之间的第一个直接联系（Ivans et al. 2003）。另一个重要的结果是SN II驱动风的潜在证据。我们发现，在船底座的非常贫金属的恒星并没有在AGB或SN Ia产品的增强，因此，他们非常低的[Sr/Ba]的比例表明，早期SNe II的贡献的损失。其中两颗恒星的[Na/Fe]、[Mn/Fe]和[Cr/Fe]比值较低，支持了这一假设，另外一颗恒星的[Zn/Fe]上限也较低。有趣的是，船底座中贫金属恒星的化学成分与银河系、大多数其他dSphs或UFD中的不相似，这表明船底座可能处于临界质量，在那里一些化学富集事件通过SN II驱动的风而丢失。
英文摘要：
The detailed abundances of 23 elements in nine bright RGB stars in the Carina dSph are presented based on high resolution spectra gathered at the VLT and Magellan telescopes. A spherical model atmospheres analysis is applied using standard methods to spectra ranging from 380 to 680 nm. The stars in this analysis range from -2.9 < [Fe/H] < -1.3, and adopting the ages determined by Lemasle et al. (2012), we are able to examine the chemical evolution of Carina's old and intermediate-aged populations. One of the main results from this work is the evidence for inhomogeneous mixing in Carina; a large dispersion in [Mg/Fe] indicates poor mixing in the old population, an offset in the [alpha/Fe] ratios between the old and intermediate-aged populations (when examined with previously published results) suggests that the second star formation event occurred in alpha-enriched gas, and one star, Car-612, seems to have formed in a pocket enhanced in SN Ia/II products. This latter star provides the first direct link between the formation of stars with enhanced SN Ia/II ratios in dwarf galaxies to those found in the outer Galactic halo (Ivans et al. 2003). Another important result is the potential evidence for SN II driven winds. We show that the very metal-poor stars in Carina have not been enhanced in AGB or SN Ia products, and therefore their very low ratios of [Sr/Ba] suggests the loss of contributions from the early SNe II. Low ratios of [Na/Fe], [Mn/Fe], and [Cr/Fe] in two of these stars support this scenario, with additional evidence from the low [Zn/Fe] upper limit for one star. It is interesting that the chemistry of the metal-poor stars in Carina is not similar to those in the Galaxy, most of the other dSphs, or the UFDs, and suggests that Carina may be at the critical mass where some chemical enrichment events are lost through SN II driven winds.
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