[论文解读] Star formation in Perseus: III. Outflows

J. Hatchell, G. A. Fuller+1 more|ArXiv.org|Jun 12, 2007

Astrophysics and Star Formation Studies参考文献 34被引用 55

一句话总结

本研究对御夫座分子云中51个亚毫米波长核心的12 CO 3–2辐射进行了映射，以识别分子喷流并评估原恒星活动。研究发现，基于喷流判断，65%的核心为原恒星，且Class 0与Class I源的动量通量无显著差异，挑战了早期演化过程中喷流能量下降的既定假设。喷流导致的核心破坏 timescale 超过观测到的原恒星寿命，表明需要额外的质量损失机制。

ABSTRACT

We present a search for outflows towards 51 submillimetre cores in Perseus. With consistently derived outflow properties from a large homogeneous dataset within one molecular cloud we can investigate further the mass dependence and time evolution of protostellar mass loss. Of the 51 cores, 37 show broad linewings indicative of molecular outflows. In 13 cases, the linewings could be due to confusion with neighbouring flows but 9 of those sources also have near-infrared detections confirming their protostellar nature. The total fraction of protostars in our sample is 65%. All but four outflow detections are confirmed as protostellar by Spitzer IR detections and only one Spitzer source has no outflow, showing that outflow maps at this sensitivity are equally good at identifying protostars as Spitzer. Outflow momentum flux correlates both with source luminosity and with core mass but there is considerable scatter even within this one cloud despite the homogeneous dataset. We fail to confirm the result of Bontemps et al. (1996) that Class I sources show lower momentum fluxes on average than Class 0 sources, with a KS test showing a significant probability that the momentum fluxes for both Class 0s and Class Is are drawn from the same distribution. We find that outflow power may not show a simple decline between the Class 0 to Class I stages. Our sample includes low momentum flux, low-luminosity Class 0 sources, possibly at a very early evolutionary stage. If the only mass loss from the core were due to outflows, cores would last for 10^5-10^8 years, longer than current estimates of 1.5-4 x 10^5 years for the mean lifetime for the embedded phase. Additional mechanisms for removing mass from protostellar cores may be necessary.

研究动机与目标

• 通过探测分子喷流，在御夫座分子云中识别原恒星。
• 利用单一分子云内统一的数据集，推导一致的喷流性质。
• 研究原恒星质量损失的依赖性及其随时间的演化。
• 检验喷流动量通量从Class 0到Class I阶段下降的假设。
• 评估喷流驱动的质量损失是否足以解释核心破坏 timescale 与观测到的原恒星寿命之间的关系。

提出的方法

• 使用詹姆斯·克拉克·马克斯韦尔望远镜在345 GHz波段对12 CO 3–2进行映射， beam 尺寸为14″，采样间隔5″，覆盖51个亚毫米波长核心中心的2'×2'区域。
• 通过12 CO 3–2谱线中展宽的线翼识别分子喷流，利用10倍因子校正光学厚度和倾角影响。
• 利用速度积分线强度计算喷流动量通量，并假设喷流温度为50 K。
• 通过与斯必泽红外探测结果交叉比对，确认原恒星性质，并减少邻近喷流引起的混淆。
• 使用柯尔莫哥洛夫-斯米尔诺夫（K-S）检验比较Class 0与Class I源的动量通量分布。
• 通过将核心质量（由亚毫米波发射推导）除以喷流质量损失率，估算核心破坏 timescale。

实验结果

研究问题

• RQ1 御夫座中亚毫米波长核心的原恒星比例是多少，由分子喷流指示？
• RQ2 Class 0与Class I原恒星的喷流动量通量是否存在显著差异？
• RQ3 仅靠喷流驱动的质量损失率是否足以解释观测到的核心破坏 timescale，与估算的1.5–4×10⁵年原恒星寿命相比？
• RQ4 在单一、统一的云样本中，喷流动量通量如何与原恒星光度和核心质量相关联？
• RQ5 喷流图谱在识别原恒星方面是否与斯必泽红外观测同样有效？

主要发现

• 51个亚毫米波长核心中有37个（72.5%）显示出指示分子喷流的展宽线翼，其中33个经斯必泽探测确认为原恒星。
• 样本中原恒星比例为65%，仅有一个斯必泽探测到的源未检测到可分辨喷流。
• 喷流动量通量与总辐射光度及核心质量显著相关，但存在较大离散度。
• Class 0与Class I源之间动量通量无统计显著差异（K-S检验p值 > 0.05），与Bontemps等人（1996年）的早期发现相矛盾。
• 基于恒定喷流质量损失率的核心破坏 timescale 范围为10⁵至10⁸年，超过估算的1.5–4×10⁵年原恒星寿命。
• 该差异表明喷流本身不足以解释核心消散，暗示存在其他质量损失机制，如碎片化、电离或引力解体。