Ndugu N, Abedigamba O P, Andama G
Centre for Space Research, Potchefstroom 2531, North-West University, South Africa.
Department of Physics, Mbarara University of Science and Technology, P.O.Box 1410, Mbarara, Uganda.
Mon Not R Astron Soc. 2022 Mar 3;512(1):861-873. doi: 10.1093/mnras/stac569. eCollection 2022 May.
Depending on the stellar densities, protoplanetary discs in stellar clusters undergo: background heating; disc truncation-driven by stellar encounter; and photoevaporation. Disc truncation leads to reduced characteristic sizes and disc masses that eventually halt gas giant planet formation. We investigate how disc truncation impacts planet formation via pebble-based core accretion paradigm, where pebble sizes were derived from the full grain-size distribution within the disc lifetimes. We make the best-case assumption of one embryo and one stellar encounter per disc. Using planet population synthesis techniques, we find that disc truncation shifts the disc mass distributions to the lower margins. This consequently lowered the gas giant occurrence rates. Despite the reduced gas giant formation rates in clustered discs, the encounter models mostly show as in the isolated field; the cold Jupiters are more frequent than the hot Jupiters, consistent with observation. Moreover, the ratio of hot to cold Jupiters depend on the periastron distribution of the perturbers with linear distribution in periastron ratio showing enhanced hot to cold Jupiters ratio in comparison to the remaining models. Our results are valid in the best-case scenario corresponding to our assumptions of: only one disc encounter with a perturber, ambient background heating, and less rampant photoevaporation. It is not known exactly of how much gas giant planet formation would be affected should disc encounter, background heating, and photoevaporation act in a concert. Thus, our study will hopefully serve as motivation for quantitative investigations of the detailed impact of stellar cluster environments on planet formations.
根据恒星密度，恒星团中的原行星盘会经历：背景加热；由恒星遭遇驱动的盘截断；以及光致蒸发。盘截断会导致特征尺寸和盘质量减小，最终阻碍气态巨行星的形成。我们通过基于卵石的核心吸积范式研究盘截断如何影响行星形成，其中卵石尺寸是根据盘寿命内的全粒度分布得出的。我们对每个盘做出一个胚胎和一次恒星遭遇的最佳情况假设。使用行星群体合成技术，我们发现盘截断将盘质量分布转移到较低边缘。这进而降低了气态巨行星的出现率。尽管聚集盘中气态巨行星的形成率降低，但遭遇模型大多与孤立场中的情况相同；冷木星比热木星更频繁，这与观测结果一致。此外，热木星与冷木星的比例取决于摄动体的近日点分布，近日点比例呈线性分布时，与其他模型相比，热木星与冷木星的比例会增加。我们的结果在与我们的假设相对应的最佳情况下是有效的：每个盘仅与一个摄动体遭遇、存在环境背景加热且光致蒸发不太剧烈。目前尚不清楚盘遭遇、背景加热和光致蒸发共同作用时气态巨行星的形成会受到多大影响。因此，我们的研究有望为定量研究恒星团环境对行星形成的详细影响提供动力。
