The Ultraviolet and Optical Spectra of Metal‐deficient O Stars in the Small Magellanic Cloud
The Ultraviolet and Optical Spectra of Metal‐deficient O Stars in the Small Magellanic Cloud
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小麦哲伦星云中缺金属 O 星的紫外光谱和光谱
DOI：
10.1086/316617
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发表时间：
2000
影响因子：
3.5
通讯作者：
J. Parker
中科院分区：
文献类型：
--
作者：
N. Walborn;D. Lennon;S. Heap;D. Lindler;Linda J. Smith;C. Evans;J. Parker
提出并描述了小麦哲伦星云（SMC）中15颗0型恒星的紫外光谱图。该梯队数据具有104阶的解析能力；它们是用哈勃太空望远镜的紫外成像光谱仪和英澳望远镜或欧洲南方天文台的3.6米光学波段获得的。最终目标是开发金属缺乏模板来解释遥远的恒星爆发，但在这里我们讨论SMC恒星本身有趣的新特性，这些特性是由这些高质量的数据揭示的。SMC金属缺乏在整个O主序上以及在中等光度处产生异常微弱的恒星风剖面；给出了SMC第一个中间Si iv λ1400风廓线。SMC中第二颗已知的Of星显示出与它的光谱同族相同的风特性，同样可能是由于较低的系统金属丰度。一些天体显示出明显的CNO异常，包括在O型光谱中首次出现没有niii λ4640的ciii λ4650发射。在年轻星团ngc346中，N/C比值似乎随着质量、远离零年龄主序的演化程度和/或旋转速度的增加而增加。此外，Onfp （Oef）和of ？在SMC中发现了p谱（后者只是已知的其特殊壳类的第四个成员）。这些天体的紫外线风特征与其光学特性相关。所有这些光谱现象提供了对缺金属大质量恒星演化状态的诊断。
An ultraviolet and optical spectral atlas of 15 O stars in the Small Magellanic Cloud (SMC) is presented and described. The echelle data have resolving powers of order 104; they were obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph in the UV, and at the Anglo‐Australian Telescope or the European Southern Observatory 3.6 m in the optical. The ultimate objective is to develop metal‐deficient templates for the interpretation of distant starbursts, but here we discuss interesting new properties of the SMC stars themselves, revealed by the high quality of these data. The SMC metal deficiency produces anomalously weak stellar‐wind profiles along the entire O main sequence, as well as at intermediate luminosities; the first intermediate Si iv λ1400 wind profile in the SMC is shown. The second known Of star in the SMC displays wind peculiarities that are identical to those of its spectral classmate, again likely due to the low systemic metallicity. Several objects display marked CNO anomalies, including the first cases of C iii λ4650 emission without N iii λ4640 in O‐type spectra. The N/C ratio appears to increase with mass, extent of evolution away from the zero‐age main sequence, and/or rotational velocity in the young cluster NGC 346. In addition, the first examples of Onfp (Oef) and Of?p spectra in the SMC have been found (the latter being only the fourth member of its peculiar shell category known anywhere). The UV wind characteristics of these objects correlate with their optical peculiarities. All these spectroscopic phenomena provide diagnostics of the evolutionary status of metal‐deficient massive stars.