AI 中文总结
研究发现盘碎裂与行星形成存在0.3 Z☉的金属丰度最佳点，此处盘冷却效率最高，形成的行星更多更快且初始质量更低，或可解释贫金属恒星周围宽轨道巨行星的轻微过剩。
AI 中文摘要
引力不稳定盘的碎裂为宽轨道上的气态巨行星和褐矮星提供了一种替代形成机制。金属丰度在从引力不稳定开始到行星形成的盘演化过程中起着关键作用。我们旨在确定金属丰度对盘碎裂以及盘不稳定行星性质的影响。我们使用光滑粒子流体动力学代码PHANTOM，对具有不同金属丰度（0.01-10 Z☉）的引力不稳定盘进行建模。我们的模拟显示，在0.3 Z☉处存在一个碎裂“最佳点”，此处冷却效率最高，而在更高和更低的金属丰度下，碎裂发生的剧烈程度较低。然而，远离该最佳点时，碎裂变得更加困难，最终在极端低和极端高金属丰度（分别为0.01 Z☉和10 Z☉）下被抑制，此时盘冷却效率低下。金属丰度接近最佳点的盘，每个盘形成的行星更多、速度更快，且初始质量比具有更高或更低金属丰度的碎裂盘更低。我们的结果或许可以解释观测到的贫金属恒星周围宽轨道巨行星的轻微过剩，这些行星可能是通过盘碎裂形成的。
英文摘要
Fragmentation of gravitationally unstable discs offers an alternate formation mechanism for gas giant planets and brown dwarfs on wide orbits. Metallicity plays a key role in disc evolution from the onset of gravitational instability to the formation of planets. We aim to determine the effect of metallicity on disc fragmentation and on the properties of disc-instability planets. We model gravitationally unstable discs with varying metallicity ($0.01-10 \,\rm Z_{\odot}$) using the Smoothed Particle Hydrodynamics code PHANTOM. Our simulations reveal a "sweet spot" for fragmentation at $0.3 \,\rm Z_{\odot}$, where cooling is most efficient, with fragmentation also happening less vigorously at higher and lower metallicities. However, further away from the sweet spot, fragmentation becomes more difficult and is eventually suppressed at extreme low and high metallicities ($0.01 \,\rm Z_{\odot}$ and $10 \,\rm Z_{\odot}$, respectively), where the disc cools inefficiently. Discs with metallicities close to the sweet spot form more planets per disc, faster, and with lower initial masses than fragmenting discs with higher or lower metallicities. Our results may explain the slight overabundance of wide-orbit giant planets observed around metal-poor stars; these planets may have formed via disc fragmentation.
Comments13 pages, 18 figures
