[论文解读] The VLT-FLAMES Tarantula Survey - XI. A census of the hot luminous stars and their feedback in 30 Doradus

E. Doran, P. A. Crowther+17 more|UvA-DARE (University of Amsterdam)|Aug 15, 2013

Stellar, planetary, and galactic studies参考文献 115被引用 72

一句话总结

本研究利用VLT-FLAMES Tarantula巡天的多 epoch 光谱数据，首次对大麦哲伦云中30 Doradus星暴区域内的炽热明亮恒星进行了全面普查。研究发现，大质量恒星——尤其是初始质量 >100 M⊙ 以及 W-R/Of/WN 型恒星——在电离辐射和恒星风反馈中贡献了不成比例的份额，约6%的电离光子逃逸出该区域，且标准模型如Starburst99在反馈估算上存在2至9倍的低估。

ABSTRACT

We compile the first comprehensive census of hot luminous stars in the 30 Doradus (30 Dor) star forming region of the LMC. The census extends to a radius of 10arcmin (150pc) from the central cluster, R136. Stars were selected photometrically and combined with the latest spectral types. 1145 candidate hot luminous stars were identified of which >700 were considered genuine early type stars that contribute to feedback. We assess the spectroscopic completeness to be 85% in outer regions (>5pc) but fall to 35% in the vicinity of R136, giving a total of 500 hot luminous stars with spectroscopy. Stellar calibrations and models were used to obtain their physical parameters before integrated values were compared to global observations and the population synthesis code, Starburst99. The 31 W-R and Of/WN stars made large contributions to the total ionising and wind luminosities of ~40% and ~50%, respectively. Stars with Minit>100Msun also showed high contributions to the global feedback, ~25% in both cases. Such massive stars are not accounted for by the current Starburst99 code, which underestimated the ionising and wind luminosities of R136 by factors of ~2 and ~9, respectively. The census inferred a SFR of 0.073+/-0.04Msun/yr for 30 Dor, typically higher than results from popular SFR calibrations. However, it remained consistent with a far-UV luminosity tracer and a combined Halpha and mid-infrared tracer, but only after correcting for Halpha extinction. The global ionising output exceeded measurements from the associated gas and dust, suggesting ~6(+55/-6)% of ionising photons escape the region. When studying very luminous star forming regions, it is therefore essential to include the most massive stars to ensure a reliable energy budget. If 30 Dor is typical of other large star forming regions, estimates of the SFR will be underpredicted if this escape fraction is not accounted for.(abridged)

研究动机与目标

• 编制30 Doradus区域内炽热明亮恒星的完整普查，重点关注早型星与大质量恒星。
• 评估光谱采样完整性，并识别最重最亮的恒星，包括W-R和Of/WN型。
• 测量总电离光度与恒星风光度，以重新评估恒星形成率（SFR）与电离光子逃逸分数。
• 检验如Starburst99等群体合成模型在重现极端H II区观测反馈方面的准确性。
• 确定初始质量 >100 M⊙ 的最重恒星对区域总能量预算的贡献。

提出的方法

• 结合光度选择与VLT-FLAMES Tarantula巡天的多 epoch 光谱数据，识别炽热明亮恒星。
• 应用恒星大气模型与校准方法（如Martins & Pleijel 2006），从光谱类型与光度数据推导物理参数。
• 利用基于K波段光度测量获得的消光律（R_V = 3.5–4.2）校正尘埃消光，并估算固有星等。
• 从单颗恒星贡献计算总电离光度与风光度，并与整体紫外至亚毫米波观测进行比较。
• 通过与群体合成模型（Starburst99）及观测示踪剂（远紫外、Hα、中红外）对比，验证结果可靠性。
• 通过比较总恒星输出与气体相电离测量，估算电离光子逃逸分数。

实验结果

研究问题

• RQ1 30 Doradus区域内炽热明亮恒星的完整普查结果如何，特别是在密集的R136星团中？
• RQ2 对早型星的光谱采样在拥挤的中心区域有多完整？
• RQ3 最重恒星（>100 M⊙）及W-R/Of/WN型恒星对总电离光度与风光度的贡献占比是多少？
• RQ4 标准群体合成模型如Starburst99在多大程度上低估了极端H II区中大质量恒星的反馈？
• RQ5 30 Doradus的全局电离光子逃逸分数是多少，其对SFR估算有何影响？

主要发现

• 普查共识别出1,145颗炽热明亮恒星候选体，其中500颗通过光谱确认，其中超过700颗为真实早型星。
• 在R136附近，光谱采样完整性下降至35%，但在 >5 pc 处达到85%，表明星团核心区域存在显著的不完整采样。
• 尽管仅31颗，W-R与Of/WN型恒星贡献了约40%的总电离光度与约50%的风光度。
• 初始质量 >100 M⊙ 的恒星（主要为H丰富的WN型）对电离光度与风光度的贡献各约25%。
• Starburst99因缺少极高质量恒星，导致对R136电离光度的估算低估约2倍，对风光度的估算低估约9倍。
• 推算出的恒星形成率为 0.073 ± 0.04 M⊙ yr⁻¹，仅在修正Hα消光后与远紫外及Hα+中红外示踪剂一致，暗示光子逃逸分数约为6%（6⁺⁵⁵₋₆%），表明存在显著的电离输出泄漏。