VLA and NOEMA Views of Bok Globule CB 17: The Starless Nature of a Proposed First Hydrostatic Core Candidate
VLA and NOEMA Views of Bok Globule CB 17: The Starless Nature of a Proposed First Hydrostatic Core Candidate
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DOI：
10.3847/1538-4357/ac3083
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发表时间：
2021-11
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通讯作者：
Stephanie Spear;María José Maureira;H. Arce;J. Pineda;M. Dunham;P. Caselli;D. Segura-Cox
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作者：
Stephanie Spear;María José Maureira;H. Arce;J. Pineda;M. Dunham;P. Caselli;D. Segura-Cox
为了揭示600-1100 au尺度的尘埃结构和气体性质，并限定其演化阶段，我们利用3 mm连续体北方扩展毫米阵列和NH3甚大阵列对第一流体静力核（FHSC）候选者CB 17 MMS进行了观测。尽管期望最小信噪比为9，但我们没有在先前确定的1.3 mm点源中检测到任何紧凑源。NH3示踪的气体表现为亚音速运动，平均温度为10.4 K。由氨辐射得到的径向柱密度曲线的拟合发现一个半径为~ 1800 au的平坦内区，中心密度为~ 6 × 105 cm−3。维里尔和密度结构分析表明，核是边缘结合的（α维里尔= 0.73）。该区域与年轻的无恒星核心完全一致，因此排除了CB 17 MMS作为FHSC候选者的可能性。此外，岩心呈现出与长轴一致的速度梯度，在位置-速度图中呈现出圆弧状结构，并在两个不同的速度峰引起的离中心区域具有高速度色散。这些特征可能是由于与附近的流出物相互作用，由于NH3柱密度峰值附近的致密气体而出现偏转。我们研究了无恒星核心的特定角动量分布，发现它与先前在0类源中类似的径向分布的研究密切相关。这种与更进化的天体的相似性表明，1000天文单位尺度的运动是由大尺度的致密云运动决定的，并且可能在恒星形成的早期阶段被保存下来。
We use 3 mm continuum NOrthern Extended Millimeter Array and NH3 Very Large Array observations toward the First Hydrostatic Core (FHSC) candidate CB 17 MMS in order to reveal the dust structure and gas properties to 600–1100 au scales and to constrain its evolutionary stage. We do not detect any compact source at the previously identified 1.3 mm point source, despite expecting a minimum signal-to-noise ratio of 9. The gas traced by NH3 exhibits subsonic motions, with an average temperature of 10.4 K. A fit of the radial column density profile derived from the ammonia emission finds a flat inner region of radius ∼1800 au and a central density of ∼6 × 105 cm−3. Virial and density structure analysis reveals the core is marginally bound (α vir = 0.73). The region is entirely consistent with that of a young starless core, hence ruling out CB 17 MMS as an FHSC candidate. Additionally, the core exhibits a velocity gradient aligned with the major axis, showing an arc-like structure in the position–velocity diagram and an off-center region with high velocity dispersion, caused by two distinct velocity peaks. These features could be due to interactions with the nearby outflow, which appears to deflect due to the dense gas near the NH3 column density peak. We investigate the specific angular momentum profile of the starless core, finding that it aligns closely with previous studies of similar radial profiles in Class 0 sources. This similarity to more evolved objects suggests that motions at 1000 au scales are determined by large-scale dense cloud motions, and may be preserved throughout the early stages of star formation.