The blue supergiant Sher 25 and its intriguing hourglass nebula
The blue supergiant Sher 25 and its intriguing hourglass nebula
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蓝色超巨星 Sher 25 及其迷人的沙漏星云
DOI：
10.1111/j.1365-2966.2008.13347.x
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发表时间：
2008
影响因子：
4.8
通讯作者：
Hendry M
中科院分区：
文献类型：
--
作者：
Hendry M
蓝色超巨星Sher 25被一个不对称的沙漏状环绕星云包围。它的结构和动力学已经通过高分辨率成像和光谱进行了研究，它看起来动态地类似于SN1987A周围的环结构。在这里，我们展示了Sher 25周围的星周星云和主星系团NGC 3603的背景星云的长缝光谱。我们进行了详细的星云丰度分析，以测量氧、氮、硫、霓虹和Ar的气相丰度。星周星云的氧丰度(12+logO/H=8.61±0.13Dex)与背景星云的氧丰度(8.56±0.07)相似，表明主体星团的组成在太阳附近。然而，我们确认该星云富含氮，其丰度为8.91±0.15，而背景值为7.47±0.18。用快风模式大气代码对恒星光谱的最新分析表明，SHER 25的光球氮和氧丰度与星云的结果是一致的。虽然氮的丰度很高，但与恒星演化模型相比，它们并不能明确证实这颗恒星在之前的红超巨星阶段经历了对流清理。我们认为，更有可能的情况是，该星云是在恒星处于蓝色超巨星阶段时被喷出的。这颗恒星的初始质量约为50M⊙，对于它来说，作为一颗红超巨星，它的对流包络阶段太高了。旋转的恒星模型会导致核处理过的物质在核氢燃烧过程中混合到恒星表面，它可以定量地将恒星结果与星云的丰度进行匹配。
The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here, we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log O/H = 8.61 ± 0.13 dex) is similar to that in the background nebula (8.56 ± 0.07), suggesting that the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 ± 0.15, compared to the background value of 7.47 ± 0.18. A new analysis of the stellar spectrum with thefastwindmodel atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher 25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models, they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50 M⊙, which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances.
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DOI：
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发表时间：
2003
期刊：
影响因子：
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作者：
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DOI：
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发表时间：
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期刊：
影响因子：
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作者：
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DOI：
10.1086/305350
发表时间：
1998-03
期刊：
The Astrophysical Journal
影响因子：
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影响因子：
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作者：
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通讯作者：
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作者：
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通讯作者：
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