标题： JCMT POL-2 和 BISTRO 调查对 L1689 分子云中磁场的观测 显示英文标题

标题： JCMT POL-2 and BISTRO Survey observations of magnetic fields in the L1689 molecular cloud

摘要： 我们展示了对L1689分子云的850$\mu$米极化观测数据，L1689是附近Ophiuchus分子云复合体的一部分，观测使用了詹姆斯·克拉克·麦克斯韦望远镜（JCMT）上的POL-2偏振计。 我们观测了L1689的三个区域：包含IRAS 16293-2422原恒星系统的云团L1689N，无恒星的云团SMM-16，以及无恒星的核心L1689B。 我们使用Davis-Chandrasekhar-Fermi方法估计了L1689N中的平面磁场强度为$366\pm 55$ $\mu$ G，SMM-16中的为$284\pm 34$ $\mu$ G，以及L1689B中的为$72\pm 33$ $\mu$ G，这是基于我们采用的尘埃光学厚度的参考值。 这些数值表明这三个区域很可能是磁临界状态，并且湍流速度低于阿尔芬速度。 在所有三个区域，推断出的平均磁场方向大致垂直于在$Herschel$空间望远镜观测中识别出的局部丝状结构方向。 L1689N 和 L1689B 的核心尺度磁场形态与$Planck$空间观测站测量的云尺度磁场形态一致，表明对于这些源，物质可以从大尺度自由流动到小尺度。 基于这些磁场测量结果，我们认为从云向 L1689N 和 L1689B 的吸积可能是磁力调控的。 然而，在 SMM-16 中，团块尺度的磁场几乎垂直于$Planck$观测到的云尺度磁场，表明它可能无法有效地从周围环境中吸积更多物质。 显示英文摘要

摘要： We present 850$\mu$m polarization observations of the L1689 molecular cloud, part of the nearby Ophiuchus molecular cloud complex, taken with the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). We observe three regions of L1689: the clump L1689N which houses the IRAS 16293-2422 protostellar system, the starless clump SMM-16, and the starless core L1689B. We use the Davis-Chandrasekhar-Fermi method to estimate plane-of-sky field strengths of $366\pm 55$ $\mu$G in L1689N, $284\pm 34$ $\mu$G in SMM-16, and $72\pm 33$ $\mu$G in L1689B, for our fiducial value of dust opacity. These values indicate that all three regions are likely to be magnetically trans-critical with sub-Alfv\'{e}nic turbulence. In all three regions, the inferred mean magnetic field direction is approximately perpendicular to the local filament direction identified in $Herschel$ Space Telescope observations. The core-scale field morphologies for L1689N and L1689B are consistent with the cloud-scale field morphology measured by the $Planck$ Space Observatory, suggesting that material can flow freely from large to small scales for these sources. Based on these magnetic field measurements, we posit that accretion from the cloud onto L1689N and L1689B may be magnetically regulated. However, in SMM-16, the clump-scale field is nearly perpendicular to the field seen on cloud scales by $Planck$, suggesting that it may be unable to efficiently accrete further material from its surroundings.