[论文解读] Structure of Herbig AeBe disks at the milliarcsecond scale A statistical survey in the H band using PIONIER-VLTI

B. Lazareff, Jean-Philippe Berger+27 more|CaltechAUTHORS (California Institute of Technology)|Nov 25, 2016

Astrophysics and Star Formation Studies参考文献 92被引用 63

一句话总结

本研究利用H波段PIONIER/VLTI干涉测量技术，探测了51个金牛座AeBe类原恒星盘在毫角秒尺度的结构，揭示了内盘典型厚度为z/r ≈ 0.2，并提供了强烈的盘面呈锥形几何结构（z/r ≈ 0.5）的证据，这是由于自遮挡效应所致。尘埃亚亚化温度被约束在>1500 K，优选值为1800 K，而延伸的发射成分可能与盘面锥形或星光散射有关，方位角调制则表明存在非轴对称结构，极有可能是盘缘遮挡所致。

ABSTRACT

Context. It is now generally accepted that the near-infrared excess of Herbig AeBe stars originates in the dust of a circumstellar disk. Aims. The aims of this article are to infer the radial and vertical structure of these disks at scales of order one au, and the properties of the dust grains. Methods. The program objects (51 in total) were observed with the H-band (1.6micron) PIONIER/VLTI interferometer. The largest baselines allowed us to resolve (at least partially) structures of a few tenths of an au at typical distances of a few hundred parsecs. Dedicated UBVRIJHK photometric measurements were also obtained. Spectral and 2D geometrical parameters are extracted via fits of a few simple models: ellipsoids and broadened rings with azimuthal modulation. Model bias is mitigated by parallel fits of physical disk models. Sample statistics were evaluated against similar statistics for the physical disk models to infer properties of the sample objects as a group. Results. We find that dust at the inner rim of the disk has a sublimation temperature Tsub~1800K. A ring morphology is confirmed for approximately half the resolved objects; these rings are wide delta_r>=0.5. A wide ring favors a rim that, on the star-facing side, looks more like a knife edge than a doughnut. The data are also compatible with a the combination of a narrow ring and an inner disk of unspecified nature inside the dust sublimation radius. The disk inner part has a thickness z/r~0.2, flaring to z/r~0.5 in the outer part. We confirm the known luminosity-radius relation; a simple physical model is consistent with both the mean luminosity-radius relation and the ring relative width; however, a significant spread around the mean relation is present. In some of the objects we find a halo component, fully resolved at the shortest interferometer spacing, that is related to the HAeBe class.

研究动机与目标

• 利用高角分辨率干涉测量技术，表征约1 au尺度上金牛座AeBe类原恒星盘的径向与垂直结构。
• 从近红外超量辐射中推断尘埃颗粒特性，特别是亚亚化温度。
• 研究内盘区域是否存在延伸或非轴对称结构。
• 评估盘面锥形与自遮挡在塑造观测到的可见度与闭合相位曲线中的作用。
• 评估替代模型（如热内层气态成分）在解释可见度曲线形状方面的可行性。

提出的方法

• 利用VLTI上的PIONIER仪器在H波段（1.6 μm）进行高对比度、长基线的干涉测量观测。
• 从干涉测量数据中提取可见度与闭合相位，以探测毫角秒尺度的空间结构。
• 将辐射转移模型拟合至观测到的可见度与闭合相位数据，以推断盘面几何结构、倾角与尘埃特性。
• 模型比较包括考虑与不考虑方位角调制的轴对称模型，以检验对称性的偏离。
• 通过可见度曲线与闭合相位的统计分析，评估非轴对称特征与延伸成分的显著性。
• 通过对比观测到的通量与可见度曲线与考虑温度分布及拟合偏差的模型，约束亚亚化温度。

实验结果

研究问题

• RQ1 通过毫角秒分辨率干涉测量，金牛座AeBe类原恒星盘在约1 au尺度上的径向与垂直结构如何？
• RQ2 这些系统中的尘埃亚亚化温度是多少？它与颗粒特性有何关联？
• RQ3 是否存在延伸发射成分的证据？其物理机制可能是什么？
• RQ4 内盘是否存在可探测的轴对称性偏离？其成因是什么？
• RQ5 观测到的可见度曲线能否由标准锥形盘模型解释，还是需要额外成分（如尘埃亚亚化半径内的热气体或难熔颗粒）？

主要发现

• 金牛座AeBe类原恒星盘的内区典型厚度为z/r ≈ 0.2，表明在恒星附近存在中等程度的锥形几何结构。
• 观测到的倾角分布与由于自遮挡效应导致的锥形盘模型（z/r ≈ 0.5）一致，未观测到高倾角系统（cos i < 0.45）。
• 基于辐射转移建模与偏差校正，尘埃亚亚化温度被约束在1500 K以上，优选值为1800 K。
• 样本中相当一部分在基线对应角尺度大于40 mas时表现出可分辨的延伸发射成分，且与赫比奇组分类及红外颜色相关。
• 可见度与闭合相位数据中的方位角调制表明存在非轴对称结构，极有可能是倾斜盘缘的自遮挡所致，闭合相位最大值在分辨率ρ′ ≈ 0.5时达到~10°。
• 尽管部分模型（IN）能再现观测到的闭合相位振幅（~10°），但其他模型（THM）则明显不足（~2°），表明需改进对内盘物理与不对称性的建模。