How does the chemical composition of stars influence planet formation?

原行星盘是行星的诞生地，主要由气体和少量尘埃组成。通过冰块的凝结和冷凝，尘埃颗粒可以成长为鹅卵石(毫米-厘米大小)。然后，这些鹅卵石可以形成行星体，然后通过附着其他星体或小鹅卵石来进一步生长，形成行星胚胎。一旦行星胚胎变得足够大(几个地球质量)，它们可以附着一个气态包层，最终形成气态巨星。在它们的生长过程中，行星通过圆盘移动。这个整个过程通常是在行星种群合成模拟中建模的。然而，仍然有几个大问题。行星形成中的一个大问题是：第一个小行星是在哪里形成的？最近的模拟似乎表明，水冰线可能是这种现象的主要位置，这也得益于水蒸气的凝结，在这些模拟中，通常假设水和岩石之间的比例为50：50。此外，行星的形成强烈依赖于可用于成长为更大物体的尘埃量。较高的尘气比或金属丰度可以促进生长，并使小行星和行星的形成更加有效。金属丰度是通过主星的丰度来确定的，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相同的方式发生整体变化。然而，从银河系的化学示踪和演化中我们知道，不同的元素(如C、O、Mg、Si、Fe)具有不同的富集性。结果表明，不同的元素比，如Mg/Fe、Si/Fe、C/O随[Fe/H]的变化有不同的斜率。从化学模型可以清楚地看出，与氢相比，氧更容易与碳结合。这意味着碳与一氧化碳和二氧化碳中的大量氧结合在一起，只有剩余的氧才能形成水。如果碳/氧比较大，则意味着可用于形成水的氧气较少。然而，如果可用的水更少，那么用于颗粒生长和小行星形成的水冷凝可能就不那么有效了。因此，这一提议旨在通过在单体和N体框架中模拟行星小星的生长和随后的行星形成(包括小行星和鹅卵石吸积)以及行星迁移来回答以下问题：1)不同的挥发性丰度(H2O、CO或CO2)如何影响鹅卵石和行星体的形成？2)元素的总体丰度对行星的化学组成有什么影响？3)对于化学成分不同的宿主恒星，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?