Pristine CNO abundances from Magellanic Cloud B stars - I. The LMC cluster NGC 2004 with UVES
Pristine CNO abundances from Magellanic Cloud B stars - I. The LMC cluster NGC 2004 with UVES
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DOI：
10.1051/0004-6361:20020116
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发表时间：
2002-01
影响因子：
6.5
通讯作者：
A. Korn;Stefan Keller;A. Kaufer;N. Langer;N. Przybilla;O. Stahl;B. Wolf
中科院分区：
文献类型：
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作者：
A. Korn;Stefan Keller;A. Kaufer;N. Langer;N. Przybilla;O. Stahl;B. Wolf
本文给出了大麦哲伦星云（LMC）年轻星团NGC 2004中四颗主序星B的化学丰度。除了H II区域，未演化的OB型恒星是目前唯一可获得的MC不被恒星演化改变的CNO丰度来源。在VLT上使用UVES，我们获得了足够分辨率（R = 20 000）和信噪比（S/N ≥ 100）的光谱，以推导各种元素（He，C，N，O，Mg和Si）的丰度与NLTE线形成。这项研究使LMC中具有详细化学丰度的主序星B的数量增加了一倍。更重要的是，与以前的研究相比，我们没有发现CNO丰度异常所带来的，例如，二元相互作用或旋转混合。因此，这是第一次，从大麦哲伦星云H II区的丰度可以合理地交叉检查对那些从B星排除进化的影响。我们确认H II区CNO丰度在误差范围内，特别是非常低的氮丰度e（N）= 7.0。从表面上看，星云的碳丰度比B星低0.16 dex，这可以用星际尘埃耗尽来解释。两个来源的氧丰度在0.03 dex以内。与MC金属丰度的银河系薄盘相比，麦哲伦云显然是氮贫乏的环境。
We present chemical abundances for four main sequence B stars in the young cluster NGC 2004 in the Large Magellanic Cloud (LMC). Apart from H II regions, unevolved OB-type stars are currently the only accessible source ofpresent-day CNO abundances for the MCs not altered by stellar evolution. Using UVES on the VLT, we obtained spectra of sufficient resolution (R = 20 000) and signal-to-noise (S/N ≥ 100) to derive abundances for a variety of elements (He, C, N, O, Mg and Si) with NLTE line formation. This study doubles the number of main sequence B stars in the LMC with detailed chemical abundances. More importantly and in contrast to previous studies, we find no CNO abundance anomalies brought on by e.g. binary interaction or rotational mixing. Thus, this is the first time that abundances from H II regions in the LMC can sensibly be cross-checked against those from B stars by excluding evolutionary effects. We confirm the H II-region CNO abundances to within the errors, in particular the extraordinarily low nitrogen abundance of e(N) ≃ 7.0. Taken at face value, the nebular carbon abundance is 0.16 dex below the B-star value which could be interpreted in terms of interstellar dust depletion. Oxygen abundances from the two sources agree to within 0.03 dex. In comparison with the Galactic thin disk at MC metallicities, the Magellanic Clouds are clearly nitrogen-poor environments.