arXiv 1902.052992019-02-14astro-ph.SRastro-ph.GA

用ALMA显示的前恒星核心的中心1000 AU。I. 1.3毫米波连续观测

The central 1000 AU of a pre-stellar core revealed with ALMA. I. 1.3 mm continuum observations

Paola Caselli, Jaime E. Pineda, Bo Zhao, Malcolm C. Walmsley, Eric Keto, Mario Tafalla, Ana Chacon-Tanarro, Tyler L. Bourke, Rachel Friesen, Daniele Galli, Marco Padovani

备注：: accepted for publication in The Astrophysical Journal
DOI：: 10.3847/1538-4357/ab0700

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摘要：

像我们的太阳这样的恒星形成于星际云中的自引力密集和寒冷的结构中，称为前恒星核心。虽然我们对原恒星启动前和启动后不久的致密云的物理结构了解很多，但前恒星核心的中心几千个天文单位（au）尚未探索。正是在这些中心区域内，恒星系统聚集和分裂可能发生，从而形成双星和多系统。本文介绍了8兆太阳前星核L1544尘埃连续辐射的ALMA波段6观测（ACA和12米阵列），角分辨率为2“× 1.6”（线分辨率270 au × 216 au）。在初级光束中，一个0.1兆太阳的紧凑区域，我们称之为“内核”，已经被揭开。核是细长的，具有半径Rker ~ 10“（~ 1400 au）的中心平坦区。Rker内的平均数密度约为1 x 10^6 cm^{-3}，可能有局部密度增强。Rker内的区域似乎已经破碎，但详细的分析表明，类似的子结构可以通过对具有类似中心平坦区的平滑中心集中致密核心的合成干涉观测来再现。在致密的核心中存在一个光滑的内核，这与对收缩云核的非理想磁流体动力学模拟结果一致，云核的峰值数密度为1 x 10^7 cm^{-3}。在模拟12米台阵观测时，中心密度较低的致密岩心被完全滤除。这些观测结果表明，动态演化的致密核的内核，可以在高角分辨率ALMA调查。

英文摘要：

Stars like our Sun form in self-gravitating dense and cold structures within interstellar clouds, called pre-stellar cores. Although much is known about the physical structure of dense clouds just before and soon after the switch-on of a protostar, the central few thousand astronomical units (au) of pre-stellar cores are unexplored. It is within these central regions that stellar systems assemble and fragmentation may take place, with the consequent formation of binaries and multiple systems. We present ALMA Band 6 observations (ACA and 12m array) of the dust continuum emission of the 8 Msun pre-stellar core L1544, with angular resolution of 2'' x 1.6'' (linear resolution 270 au x 216 au). Within the primary beam, a compact region of 0.1 Msun, which we call a "kernel", has been unveiled. The kernel is elongated, with a central flat zone with radius Rker ~ 10'' (~ 1400 au). The average number density within Rker is ~1 x 10^6 cm^{-3}, with possible local density enhancements. The region within Rker appears to have fragmented, but detailed analysis shows that similar substructure can be reproduced by synthetic interferometric observations of a smooth centrally concentrated dense core with a similar central flat zone. The presence of a smooth kernel within a dense core is in agreement with non-ideal magneto-hydro-dynamical simulations of a contracting cloud core with a peak number density of 1 x 10^7 cm^{-3}. Dense cores with lower central densities are completely filtered out when simulated 12m-array observations are carried out. These observations demonstrate that the kernel of dynamically evolved dense cores can be investigated at high angular resolution with ALMA.

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