How does the chemical composition of stars influence planet formation?

原行星盘是行星的诞生地，主要由气体和一小部分尘埃组成。通过冰的凝结和凝结，尘埃颗粒可以成长为鹅卵石（mm-cm大小）。这些鹅卵石可以形成星子，然后通过吸积其他星子或小鹅卵石进一步生长，形成行星胚胎。一旦行星胚胎变得足够大（几个地球质量），它们就会吸积一个气体包层，最终形成气态巨行星。在它们的成长过程中，行星通过圆盘迁移。整个过程通常在行星人口综合模拟中进行模拟。然而，几个大问题仍然存在。行星形成的一个大问题是：第一批星子是在哪里形成的？最近的模拟似乎表明，水冰线可能是这一点的主要位置，也有水蒸气凝结的帮助，在这些模拟中，通常假设水和岩石的比例为50:50。此外，行星的形成在很大程度上取决于形成更大天体所需的尘埃数量。较高的尘气比或金属丰度促进了生长，并允许更有效的小行星和行星形成。金属丰度是通过主星丰度来确定的，主要是通过铁的测量，[Fe/H]。在过去的行星形成模型中，[Fe/H]的变化意味着所有元素以同样的方式发生了总体变化。然而，我们从星系化学示踪和进化中知道，不同的元素（如C、O、Mg、Si、Fe）富集的因素不同。因此，Mg/Fe、Si/Fe、C/O等不同元素比随[Fe/H]的变化斜率不同。从化学模型可以清楚地看出，氧比氢更容易与碳结合。这意味着碳在CO和CO2中结合了大量的氧，只有剩余的氧才能形成水。如果碳氧比大，就意味着形成水的氧气较少。然而，如果可用的水较少，那么用于晶粒生长的水凝结和因此形成的星子可能不会有效地工作。因此，本提案旨在通过在单个和n体框架中模拟星子的生长和随后的行星形成，包括星子和鹅卵石的吸积以及行星的迁移，来回答以下问题：1)不同的挥发丰度（H2O， CO或CO2）如何影响鹅卵石和星子的形成？2)元素的总体丰度对行星的化学成分有什么影响？3)不同化学成分的主恒星形成的行星的可观测性质是否不同？

Protoplanetary discs, the birth places of planets, consist of mainly of gas and to a small fraction of dust. The dust grains can grow to pebbles (mm-cm in size) through coagulation and condensation of ices. These pebbles can then form planetesimals, which can then grow further by accreting other planetesimals or the small pebbles to form planetary embryos. Once the planetary embryos become big enough (several Earth masses), they can accrete a gaseous envelop to form eventually gas giants. During their growth, the planets migrate through the disc. This whole process is normally modeled in planet population synthesis simulations. However, several big questions remain.One of the big questions in planet formation is: where do the first planetesimals form? Recent simulations seem to indicate that the water ice line could be the prime location for this, also aided by condensation of water vapor, where usually a 50:50 ratio between water and rock is assumed in these simulations.In addition, planet formation depends strongly on the amount of dust available to grow to bigger objects. A higher dust-to-gas ratio or metallicity enhances growth and allows more efficient planetesimal and planet formation. The metallicity is determined through the host star abundance, mainly through the iron measurements, [Fe/H].In planet formation models in the past, a change of [Fe/H] implied an overall change of all elements in the same fashion. However, we know from galactic chemical tracing and evolution that different elements (e.g. C, O, Mg, Si, Fe) are enriched with different factors. As a consequence, different element ratios, e.g. Mg/Fe, Si/Fe, C/O have different slopes as function of [Fe/H].From chemical models it is clear that oxygen binds preferably with carbon compared to hydrogen. This implies that carbon binds large quantities of oxygen in CO and CO2, and only the remaining oxygen can form water. If the C/O ratio is large, it implies that less oxygen is available to form water. However, if less water is available, water condensation for grain growth and thus planetesimal formation might not work as efficiently. This proposal thus aims to answer the following questions by modeling the growth of planetesimals and subsequent planet formation including planetesimal and pebble accretion as well as planet migration in a single and N-body framework:1) How do the different volatile abundances (H2O, CO or CO2) influence the formation of pebbles and planetesimals?2) What influences do the overall abundances of elements have on the chemical composition of planets?3) Are the observable properties of formed planets different for host stars with different chemical composition?