Probing the Protosolar Cloud: Characterization of the Solar System’s circumstellar building blocks at the sub-micrometer scale

所有的恒星都以电离原子的形式失去质量，要么是持续的恒星风，要么是爆发性的新星和超新星。在演化的恒星周围，这些原子最终凝聚成固体颗粒，这些颗粒携带着关于凝聚条件的信息，以及母星星本身的元素和同位素组成。今天在原始太阳系物质（陨石，行星际尘埃，彗星物质）中发现的所谓“前太阳”星尘被纳入分子尘埃和气体云，太阳和我们的行星系统在大约45.7亿年前形成。前太阳颗粒可以通过其高度异常的同位素组成与太阳系起源的固体区分开来。太阳前尘埃的研究不仅为实验室研究来自太阳以外的恒星（现已灭绝）的物质提供了独特的可能性，而且这些星尘颗粒也代表了我们太阳系的最初组成部分。在这个项目中，我将专注于恒星的起源和岩石形成元素钙、钛和铁的同位素组成，以及它们如何受到银河系化学演化的影响。对太阳前硅酸盐和氧化物中的微量元素Sr、Zr、Mo和Ba的研究将提供有关颗粒凝聚的更多信息，并将有助于回答这些元素是由富含O的太阳前颗粒引入原太阳星云的问题，还是主要由碳质尘埃提供的问题。最终，所有这些研究将允许更好地限制为新生太阳系贡献物质的不同类型的恒星源，例如，低质量渐近巨星分支（AGB）星，核心坍缩超新星，大质量AGB星，新星，其他类型的超新星），并将为Ca和Ti同位素的分类方案提供基础。这甚至可能为太阳前Ca和Ti载体之间的潜在联系提供线索，以及富含钙铝的包裹体（CAIs）的同位素组成，这是太阳星云中形成的第一种固体。他们将结合共振电离质谱（RIMS）的铁和微量元素同位素从合适的颗粒和研究选定的前太阳硅酸盐和氧化物的透射电子显微镜（TEM）技术，以表征其矿物学和监测程度的变化通过监测分布和氧化态的铁。将对太阳前硅酸盐宿主地点进行高精度的氧同位素调查，以确定它们各自的蚀变程度。在西姆斯分析之前，将通过扫描电子显微镜（SEM）和基于SEM的能量色散X射线光谱（SEM-EDS）对样品进行表征，以确定有希望的目标区域。

All stars lose mass in the form of ionized atoms, either continuously as stellar winds, or in explosive scenarios like novae and supernovae. Around evolved stars, these atoms eventually condense into solid particles, which carry information about the condensation conditions, and the elemental and isotopic composition of the parent star itself. So-called “presolar” stardust that is found today in primitive Solar System materials (meteorites, interplanetary dust, cometary matter) was incorporated into the molecular dust and gas cloud from which the Sun and our planetary system formed some 4.57 billion years ago. Presolar grains can be distinguished from solids of Solar System origin by their highly anomalous isotopic compositions. The study of presolar dust offers not only a unique possibility for the laboratory-based investigation of material from – now extinct – stars other than the Sun; these stardust grains also represent initial building blocks of our Solar System.In this project, I will focus on the stellar origins and isotopic compositions of the rock-forming elements calcium, titanium, and iron, and how they are affected by Galactic Chemical Evolution. Investigation of the trace elements Sr, Zr, Mo, and Ba in presolar silicates and oxides will provide additional information on grain condensation, and will help to answer the question if these elements were introduced into the protosolar nebula by O-rich presolar grains, or if they were mainly provided by carbonaceous dust. Ultimately, all these studies will allow to better constrain the different types of stellar sources that contributed material to the nascent Solar System, e.g., low-mass asymptotic giant branch (AGB) stars, core-collapse supernovae, massive AGB stars, novae, other types of supernovae), and will provide a groundwork for a classification scheme for Ca and Ti isotopes. This might even provide hints for potential connections between the presolar carriers of Ca and Ti, and the isotopic compositions of calcium-aluminum-rich inclusions (CAIs), the first solids that formed in the Solar nebula.The isotopic and trace element measurements of presolar grains will be carried out by NanoSIMS ion imaging. They will be combined with resonance ionization mass spectrometry (RIMS) of Fe and trace element isotopes from suitable grains and studies by transmission electron microscopic (TEM) techniques of selected presolar silicates and oxides, to characterize their mineralogy and monitor the degree of alteration by monitoring the distribution and oxidation state of Fe. High-precision O-isotopic investigations of presolar silicate host sites will be carried out to determine their respective degrees of alteration. Samples will be characterized by scanning electron microscopy (SEM) and SEM-based energy-dispersive x-ray spectroscopy (SEM-EDS) prior to SIMS analysis to identify promising target areas.