[论文解读] Results from DROXO. II. - [Ne II] and X-ray emission from Rho Ophiuchi young stellar objects

E. Flaccomio, B. Stelzer+4 more|arXiv (Cornell University)|Jun 25, 2009

Astrophysics and Star Formation Studies参考文献 54被引用 16

一句话总结

本研究利用斯皮策IRS和XMM-牛顿X射线数据，调查了猎户座Ophiuchi星云中28个年轻恒星物体（YSOs）的[Ne II]和[Ne III]发射线。研究发现，[Ne II]的光度比X射线照射盘模型的预测高出1–3个量级，且与X射线光度无显著相关性，表明吸积驱动的紫外辐射或喷流等额外激发机制在I类源中对发射线的产生起着关键作用。

ABSTRACT

The infrared [Ne II] and [Ne III] fine structure lines at 12.81um and 15.55um are predicted to trace the circumstellar disk gas subject to X-ray heating and ionization. We investigate the origin of these lines by comparing observations with models of X-ray irradiated disks and by searching for empirical correlations between the line luminosities and stellar and circumstellar parameters. We measure neon line fluxes and X-ray luminosities for 28 young stellar objects in the Rho Ophiuchi star formation region for which good quality infrared spectra and X-ray data have been obtained, the former with the Spitzer IRS and the latter with the Deep Rho Ophiuchi XMM-Newton Observation. We detect the [Ne II] and the [Ne III] lines in 10 and 1 cases, respectively. Line luminosities show no correlation with X-ray emission. The luminosity of the [Ne II] line for one star, and that of both the [Ne II] and [Ne III] lines for a second star, match the predictions of published models of X-ray irradiated disks; for the remaining 8 objects the [Ne II] emission is 1-3 dex higher than predicted on the basis of their L_X. Class I objects show significantly stronger [Ne II] lines than Class II and Class III ones. A correlation is moreover found between the [Ne II] line emission and the disk mass accretion rates. This might point toward a role of accretion-generated UV emission in the generation of the line or to other mechanisms related to mass inflows from circumstellar disks and envelopes and/or to the associated mass outflows (winds and jets). We conclude that the X-ray luminosity is not the only parameter that determines the [Ne II] emission. Explaining the strong [Ne II] emission of Class I objects likely requires the inclusion in the models of additional physical components such as the envelope, inflows, and outflows.

研究动机与目标

• 检验电离氖细结构线（[Ne II] 12.81 μm，[Ne III] 15.55 μm）是否在年轻恒星物体中反映X射线照射的原行星盘，如理论模型所预测。
• 确定X射线光度是否单独决定[Ne II]发射线，还是其他恒星和原行星环境参数也参与其中。
• 探讨吸积、盘质量及包层喷流在I、II、III类YSO中驱动[Ne II]发射线的作用。
• 通过将理论X射线照射盘模型的预测与一个特征明确的YSO样本的观测发射线光度进行比较，评估该理论模型的有效性。

提出的方法

• 从猎户座Ophiuchi星云中选取28个具有高质量斯皮策IRS红外光谱和XMM-牛顿X射线数据的YSO。
• 测量[Ne II]和[Ne III]发射线的流量，并计算了考虑消光校正后的光度，包括未检测到源的上限值。
• 将观测到的发射线光度与X射线照射盘模型（如MGN 08、GH 08）的理论预测进行比较。
• 利用从光学到毫米波段的光谱能量分布（SED）拟合，采用恒星/盘/包层模型，推导出恒星和原行星环境参数。
• 分析[Ne II]光度与X射线光度、盘吸积速率以及12.81 μm波长连续谱流量之间的相关性。
• 评估演化阶段（I、II、III类）对发射线的影响，并评估喷流和包层吸积的作用。

实验结果

研究问题

• RQ1 YSO中的[Ne II]发射是否主要由X射线照射原行星盘驱动，如理论模型所预测？
• RQ2 在一个特征明确的YSO样本中，观测到的[Ne II]光度与X射线光度之间存在何种关系？
• RQ3 盘吸积速率和原行星包层特性与[Ne II]发射线光度之间有何相关性？
• RQ4 为何一些YSO的[Ne II]光度显著高于X射线照射模型的预测值？
• RQ5 除了X射线照射之外，哪些物理机制可解释观测到的[Ne II]发射，特别是在I类YSO中？

主要发现

• 在28个YSO样本中，[Ne II] 12.81 μm线在10个源中被检测到，[Ne III] 15.55 μm线在1个源中被检测到。
• 对于大多数YSO，观测到的[Ne II]光度比X射线照射盘模型的预测高出1–3个量级，即使X射线光度匹配。
• 在样本中未发现[Ne II]发射线光度与X射线光度之间存在显著相关性。
• I类YSO的[Ne II]发射显著强于II类和III类YSO，表明其可能与包层吸积或喷流有关。
• 发现[Ne II]光度与12.81 μm波长的连续谱流量以及由SED拟合估算的盘吸积速率之间存在强相关性。
• 两个源，DoAr 25（II类）和WL 5/GY 246（III类），其[Ne II]和[Ne III]光度与X射线照射模型一致，表明在特定恒星和盘条件下模型有效。