[论文解读] The low-mass stellar population in the young cluster Tr37: Disk evolution, accretion, and environment

A. Sicilia‐Aguilar, Jinyoung Serena Kim+4 more|Discovery Research Portal (University of Dundee)|Aug 1, 2013

Astrophysics and Star Formation Studies参考文献 87被引用 8

一句话总结

本研究利用多波段测光、光谱学和辐射转移建模，调查了400万年大的Tr 37星团中低质量M型恒星的盘面演化与吸积过程。研究发现尘埃与气体的演化密切相关，根据Sed类型和吸积状态可区分出不同的盘类；同时发现尘埃耗竭与内空洞形成主要是独立过程，显著受星团环境影响，而非仅由恒星质量决定。

ABSTRACT

We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr37. With a well-studied solar-type population, Tr37 is a benchmark for disk evolution. We used low-resolution spectroscopy to identify 141 members (78 new) and 64 probable members, mostly M-type stars. Hα emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the SEDs. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks. Including the new and previously known members, we confirm that a substantial fraction (~2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or as a more global evolution (low small-dust masses, dust settling, and weak/absent accretion signatures). Accretion is strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, and dust-depleted disks have weak (or undetectable) accretion signatures, especially among M-type stars. The analysis of accretion and disk structure suggests a parallel evolution of dust and gas. We find several distinct classes of evolved disks, based on SED type and accretion, pointing to different disk dispersal mechanisms and probably different evolutionary paths. Dust depletion and opening of inner holes appear to be independent processes: most transition disks are not dust-depleted, and most dust-depleted disks do not require inner holes. The differences in disk structure between M-type and solar-type stars in Tr37 (4 Myr) are not as remarkable as in the young, sparse, Coronet cluster (1-2 Myr), suggesting that other factors, like the environment/interactions, are likely to play a role in the disk evolution and dispersal. Finally, we also find some evidence of clumpy star formation or mini-clusters within Tr37.

研究动机与目标

• 理解在已充分研究的400万年大星团中，低质量M型恒星周围原行星盘的演化过程。
• 确定恒星质量、吸积与盘面结构在盘面消散机制中的作用。
• 探究密集星团（如Tr 37）中的环境因素是否与稀疏星团相比对盘面演化产生不同影响。
• 基于Sed和吸积特征对盘类（完整盘、过渡盘、预过渡盘、尘埃耗竭盘）进行分类。
• 探讨低质量恒星中尘埃演化与气体吸积之间的关系。

提出的方法

• 结合低分辨率光谱学识别141个星团成员（其中78个为新发现），并根据Hα发射线分类作为吸积的示踪指标。
• 收集从光学到中红外波段（2MASS、Spitzer、WISE）的多波段测光数据，构建光谱能量分布（SED）。
• 根据SED形态将源分类为：完整盘、过渡/预过渡盘、尘埃耗竭盘以及I类对象。
• 应用辐射转移模型解释盘面结构，包括内空洞、尘埃沉降及小颗粒尘埃质量较低的特征。
• 使用MARCS恒星大气模型进行光谱型比较与SED拟合。
• 在统计分析中排除存在测光污染或分类不确定的源。

实验结果

研究问题

• RQ1 在400万年大的Tr 37星团中，M型恒星与太阳型恒星的盘面演化有何不同？
• RQ2 吸积在多大程度上与盘面SED类型相关联，特别是在演化后的盘类中？
• RQ3 尘埃耗竭与盘面内空洞的存在是否为独立的演化路径？
• RQ4 与恒星质量相比，星团环境在塑造盘面消散机制中起何种作用？
• RQ5 能否在Tr 37中探测到星团子群或团块状恒星形成的证据？

主要发现

• Tr 37中约40%的盘面显示出演化的迹象，其中约一半的过渡盘未检测到明显的吸积信号。
• 尘埃耗竭盘表现出微弱或无法探测的吸积信号，尤其在M型恒星中，表明气体与尘埃演化存在脱耦现象。
• 尘埃耗竭与内空洞形成基本为独立过程：大多数过渡盘并非尘埃耗竭，且大多数尘埃耗竭盘并不要求存在内空洞。
• Tr 37中M型恒星与太阳型恒星在盘面结构上的差异，远小于年轻且稀疏的星团（如Coronet）中的差异，表明环境因素在盘面消散中起关键作用。
• 在Tr 37中发现团块状恒星形成或星团子群的证据，表明其局部恒星形成历史较为复杂。
• 辐射转移模型证实，演化后的盘类——过渡盘、预过渡盘与尘埃耗竭盘——代表了具有不同消散机制的独立演化路径。