Accretion phase of star formation in clouds with different metallicities
Accretion phase of star formation in clouds with different metallicities
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不同金属丰度云中恒星形成的吸积阶段
DOI：
10.1093/mnras/stu2633
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发表时间：
2015
影响因子：
4.8
通讯作者：
Teppei
中科院分区：
文献类型：
--
作者：
Machida;Masahiro N.; Nakamura;Teppei
在0≤Z≤Z⊙不同金属丰度的云团中研究了恒星形成的主要吸积阶段，解析了原恒星半径。从接近平衡的恒星前云开始，我们计算了第一颗原恒星形成后约100年的云演化。在金属丰度较低（Z≤10−4Z⊙）和较高（Z> 10−4Z⊙）的云之间，恒星的形成有很大的不同。碎片经常发生，许多原恒星在低金属丰度云中出现时没有稳定的星周盘。在这些云中，虽然原恒星相互作用，有些被从云中心喷射出来，但许多仍然是一个小的恒星团。相比之下，金属丰度更高的云产生了一颗原恒星，它被一个几乎稳定的旋转支撑的圆盘包围。在这些云团中，虽然偶尔会出现碎片，但碎片会向内迁移，最终落在中心的原恒星上。云演化的差异是由于不同的热演化和质量吸积速率。云的热演化决定了第一个核心的出现和寿命。在金属丰度较高的云团中，第一核心先于原恒星形成，而在金属丰度较低的云团中没有（明显的）第一核心。第一个核心演变成一个螺旋形的星周圆盘，有效地将角动量向外转移，抑制了频繁的碎裂。在金属丰度较低的云中，较高的质量吸积率在很短的时间内增加了盘的表面密度，使盘在自重力作用下变得不稳定，并引起剧烈的碎裂。
The main accretion phase of star formation is investigated in clouds with different metallicities in the range 0 ≤Z≤ Z⊙, resolving the protostellar radius. Starting from a near-equilibrium prestellar cloud, we calculate the cloud evolution up to ∼100 yr after the first protostar forms. Star formation differs considerably between clouds with lower (Z≤ 10−4Z⊙) and higher (Z> 10−4Z⊙) metallicities. Fragmentation frequently occurs and many protostars appear without a stable circumstellar disc in lower-metallicity clouds. In these clouds, although protostars mutually interact and some are ejected from the cloud centre, many remain as a small stellar cluster. In contrast, higher-metallicity clouds produce a single protostar surrounded by a nearly stable rotation-supported disc. In these clouds, although fragmentation occasionally occurs in the disc, the fragments migrate inwards and finally fall on to the central protostar. The difference in cloud evolution is due to different thermal evolutions and mass accretion rates. The thermal evolution of the cloud determines the emergence and lifetime of the first core. The first core develops prior to the formation of a protostar in higher-metallicity clouds, whereas no (obvious) first core appears in lower-metallicity clouds. The first core evolves into a circumstellar disc with a spiral pattern, which effectively transfers the angular momentum outwards and suppresses frequent fragmentation. In lower-metallicity clouds, the higher mass accretion rate increases the disc surface density within a very short time, rendering the disc unstable to self-gravity and inducing vigorous fragmentation.