BISTRO (B-Fields in Star-Forming Region Observations) JCMT Large Programme: First observing run

我们将使用POL-2来绘制我们之前用SCUBA-2和HARP-B绘制的所有古尔德带恒星形成区域的致密部分的偏振，以便追踪（通过Krasekhar-Fermi方法）所有这些区域中心的磁场方向和强度。这将回答目前在星星形成方面的悬而未决的问题，例如磁场和湍流对星星形成的相对重要性，并将使我们能够测试当前的星星形成模型，例如磁漏斗到细丝上的赫歇尔模型。JCMT上的POL-2和SCUBA-2是一个独特的设施，因为它是世界上唯一一个可以绘制附近恒星形成区域（如金牛座和蛇夫座）中~1000 Au尺度的冷密核心和细丝内磁场的设施。这个尺度对于测试类似于引力星星形成模型的模型是至关重要的，因为我们从其他研究中知道，大尺度场大致垂直于整个典型的暗条方向，但我们不知道暗条本身的致密气体中的场发生了什么，也不知道暗条中形成的核心中发生了什么。这对于理解正在发生的物理过程，以及区分正确包含磁场的星星形成过程模型至关重要。目前的假设是，场可能以螺旋方式缠绕在细丝周围，或者在致密气体中转向平行于细丝运行。我们将能够区分这两种情况。关于B场在原恒星形成后形成原恒星演化中所起的作用及其对双极外流的影响，存在争议。例如，最近的研究发现，在小于1000 Au的尺度上，外流和磁场方向之间没有相关性，而在~ 10，000 Au及以上的尺度上存在相关性。一种解释，这种明显的冲突，在外地形态使用详细的建模环形包裹的B-字段在中心的云。这已被用来解释早期磁盘形成的0类原恒星在最近的模型中，早期磁盘被假设为优先形成的领域与流出方向不一致。这种大规模同质数据集的遗产价值将是巨大的。未来所有关于磁场在星星形成中作用的模型都将被迫解释所有最近恒星形成区域的这些观测结果。

We will use POL-2 to map the polarization in the densest parts of all of the Gould Belt star-forming regions that we have previously mapped with SCUBA-2 and HARP-B, in order to trace (via the Chandrasekhar-Fermi method) the magnetic field direction and strength in the centres of all of these regions. This will answer currently open questions in star formation, such as the relative importance of magnetic fields and turbulence to star formation, and will allow us to test current models of star formation, such as the Herschel model of magnetic funnelling onto filaments.POL-2 with SCUBA-2 on JCMT is a unique facility, as it is the only facility world-wide that can map the magnetic field within cold dense cores and filaments on scales of ~1000 AU in nearby star-forming regions, such as Taurus and Ophiuchus. This size scale is crucial for testing models such as the filamentary star formation model, because we know from other studies that the large-scale field lies roughly perpendicular to the overall typical filament directions, but we do not know what happens to the field within the dense gas of the filaments themselves, nor what happens within the cores that form in the filaments. This is crucial to understanding the physical processes taking place, and to discriminating between the models of the star formation process that properly incorporate magnetic fields. The current hypotheses are either that the field may wrap around the filament in a helical manner, or else turn to run parallel to the filament in the densest gas. We will be able to distinguish between these two scenarios.There is debate about the role that the B-field plays in shaping proto-stellar evolution once proto-stars have formed and its effect on bipolar outflows. For example, recent studies find no correlation between outflow and magnetic field directions on scales less than 1000 AU, while there is correlation on scales of ~10,000 AU and above. One explanation of this apparent conflict in the field morphology uses detailed modelling of toroidally wrapped B-fields at the centres of clouds. This has been used to explain early disk formation in Class 0 proto-stars in a recent model in which early disks are hypothesized to be formed preferentially in fields misaligned with the outflow directions. The legacy value of this large-scale homogeneous data-set will be huge. All future models of the role of magnetic fields in star formation will be forced to explain these observations in all of the nearest star-forming regions.