High Carbon in I Zwicky 18: New Results from Hubble Space Telescope Spectroscopy
High Carbon in I Zwicky 18: New Results from Hubble Space Telescope Spectroscopy
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I Zwicky 18 中的高碳：哈勃太空望远镜光谱的新结果
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发表时间：
1996
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影响因子：
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通讯作者：
G. Shields
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作者：
D. Garnett;E. Skillman;R. Dufour;G. Shields
我们使用哈勃太空望远镜上的微弱天体摄谱仪，基于两个 H II 区域的紫外光谱，提出了对极度贫金属矮不规则星系 I Zw 18 的西北 (NW) 和东南 (SE) 部分气相 C/O 丰度比的新测量。我们确定 NW 分量的 log C/O = -0.63 ± 0.10 的值，以及 SE 分量的 log C/O = -0.56 ± 0.09 的值。相比之下，太阳中的 log C/O = -0.37，而 Garnett 等人测量的三个金属最贫乏的不规则星系中的 log C/O = -0.85 ± 0.07。我们的测量结果表明，I Zw 18 中的 C/O 明显高于其他相对贫金属的不规则星系，并且高于对大质量恒星核合成的预期 C/O 的预测。这些结果表明，I Zw 18 中的碳已被早期的低质量产碳恒星所增强；这一想法得到了 I Zw 18 及其伴星的恒星光度测量的支持，这表明当前的大质量恒星爆发并不是第一次。尽管金属丰度非常低，但 I Zw 18 很可能不是一个“原始”星系。
We present new measurements of the gas-phase C/O abundance ratio in both the northwest (NW) and southeast (SE) components of the extremely metal-poor dwarf irregular galaxy I Zw 18, based on ultraviolet spectroscopy of the two H II regions using the Faint Object Spectrograph on the Hubble Space Telescope. We determine values of log C/O = -0.63 ± 0.10 for the NW component and log C/O = -0.56 ± 0.09 for the SE component. In comparison, log C/O = -0.37 in the Sun, while log C/O = -0.85 ± 0.07 in the three most metal-poor irregular galaxies measured by Garnett et al. Our measurements show that C/O in I Zw 18 is significantly higher than in other comparably metal-poor irregular galaxies and above predictions for the expected C/O from massive star nucleosynthesis. These results suggest that carbon in I Zw 18 has been enhanced by an earlier population of lower-mass carbon-producing stars; this idea is supported by stellar photometry of I Zw 18 and its companion, which demonstrate that the current bursts of massive stars were not the first. Despite its very low metallicity, it is likely that I Zw 18 is not a “primeval” galaxy.