[论文解读] A census of molecular hydrogen outflows and their sources along the Orion A molecular ridge: characteristics and overall distribution

C. J. Davis, D. Froebrich+10 more|ArXiv.org|Dec 19, 2008

Astrophysics and Star Formation Studies参考文献 74被引用 40

一句话总结

本研究利用近红外WFCAM成像、斯皮策空间望远镜中红外测光以及亚毫米波尘埃连续谱图，对猎户座A分子脊中的116个分子氢（H₂）喷流进行了全面普查。结果证实，H₂喷流源主要为0型或I型原恒星，具有平坦或正的谱指数；同时发现H₂喷流阶段迅速衰减，持续时间短于原恒星阶段，表明喷流阶段动态短暂，且在原恒星演化为预主序星之前即已显著减弱。

ABSTRACT

We present wide-field near-IR images of Orion A. K and H2 1-0S(1) images of a contiguous 8 sqr degree region are compared to photometry from Spitzer and dust-continuum maps obtained with MAMBO and SCUBA. We also measure proper motions for H2 features in 33 outflows. We increase the number of known H2 outflows in Orion A to 116. A total of 111 H2 flows were observed with Spitzer; outflow sources are identified for at least 72 of them. The MAMBO 1200 micron maps cover 97 H2 flows; 57 of them are associated with Spitzer sources and dust cores or extended emission. The H2 jets are widely distributed and randomly orientated; the jets do not appear to be orthogonal to large-scale filaments or even to the small-scale cores. Moreover, H2 jet lengths and opening angles are not obviously correlated with indicators of outflow source age - source spectral index or (sub)millimetre core flux. We demonstrate that H2 jet sources are predominantly protostellar with flat or positive spectral indices, rather than disk-excess (or T Tauri) stars. Most protostars in molecular cores drive H2 outflows. However, not all molecular cores are associated with protostars or H2 jets. On statistical grounds, the H2 jet phase may be marginally shorter than the protostellar phase, though must be considerably shorter than the prestellar phase. In terms of their spectral index, H2 jet sources are indistinguishable from protostars. The few true protostars without H2 jets are almost certainly more evolved than their H2-jet-driving counterparts. We also find that protostars that power molecular outflows are no more (nor no less) clustered than protostars that do not. The H2 emission regions in outflows from young stars clearly weaken and fade very quickly, before the source evolves from protostar to pre-main-sequence star.

研究动机与目标

• 识别并表征猎户座A巨大分子云中所有分子氢喷流。
• 利用多波段数据，将每个H₂喷流与其中源原恒星及其相关分子核关联。
• 确定H₂喷流在空间上的分布、取向及其动力学特性与原恒星演化阶段的关系。
• 评估H₂喷流阶段持续时间相对于其他原恒星演化阶段的长短。
• 评估H₂发射作为喷流长度、张角及源年龄示踪器的可靠性。

提出的方法

• 利用英国红外望远镜（UKIRT）上的WFCAM获取了覆盖约8平方度猎户座A区域的宽场近红外K波段及H₂ 1-0 S(1)窄带成像，以绘制H₂喷流分布。
• 利用斯皮策空间望远镜的中红外测光识别原恒星和具有盘状过剩的源，提供谱指数α等谱谱能分布（SED）指标。
• 利用MAMBO和SCUBA的亚毫米波尘埃连续谱图追踪致密分子核及其与喷流源的关联。
• 测量33个喷流中H₂特征的自行运动，以优化喷流-源关联关系并推断动力学年龄。
• 应用统计分析，包括最近邻（NN）分析，比较H₂喷流源与其他原恒星及盘状过剩源的空间聚集性。
• 通过多波段交叉识别与形态比较，将H₂喷流与原恒星源及尘埃核关联。

实验结果

研究问题

• RQ1 猎户座A分子脊中分子氢喷流的总数及其空间分布如何？
• RQ2 H₂喷流如何与原恒星源及致密分子核相关联？
• RQ3 H₂喷流参数（长度、张角）与源年龄指标（如谱指数α或1200 μm核通量）之间存在何种关系？
• RQ4 H₂喷流是否存在相对于大尺度丝状结构或小尺度核对齐的优选取向？
• RQ5 H₂喷流阶段持续时间相对于原恒星阶段和预主序阶段有多长？

主要发现

• 本研究在猎户座A中识别出116个H₂喷流，包括43个新发现，显著增加了该区域已知喷流数量。
• 在观测到的111个H₂喷流中，72个（65%）可确凿关联至原恒星源，另有12个存在可能关联，证实H₂喷流主要由0型或I型原恒星驱动。
• H₂喷流源的聚集程度并不高于其他原恒星，表明H₂喷流阶段短暂且在原恒星演化过程中迅速衰减。
• H₂喷流长度或张角与源谱指数α或1200 μm核通量之间无显著相关性，表明H₂发射作为动力学生长时间或喷流大小的示踪器效果较差。
• H₂喷流阶段的持续时间可能比原恒星阶段短一个数量级，表明随着原恒星向预主序星演化，H₂发射迅速减弱。
• 尽管大量原恒星驱动H₂喷流，但仍有少数演化程度较高的原恒星未表现出H₂喷流，表明存在一个H₂发射迅速减弱的短暂过渡阶段。