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arXiv 0901.0710astro-ph.HE
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NGC300中的中等亮度瞬变:一颗被尘埃笼罩的大质量恒星的爆发

An Intermediate Luminosity Transient in NGC300: The Eruption of a Dust-Enshrouded Massive Star

E. Berger, A. M. Soderberg, R. A. Chevalier, C. Fransson, R. J. Foley, D. C. Leonard, J. H. Debes, A. M. Diamond-Stanic, A. K. Dupree, I. I. Ivans, J. Simmerer,… 展开作者

E. Berger, A. M. Soderberg, R. A. Chevalier, C. Fransson, R. J. Foley, D. C. Leonard, J. H. Debes, A. M. Diamond-Stanic, A. K. Dupree, I. I. Ivans, J. Simmerer, I. B. Thompson, C. A. Tremonti

摘要:

我们提出了多时期高分辨率光谱学,紫外/无线电/X射线成像,以及最近在附近星系NGC300中发现的中等光度光学瞬变的哈勃和斯皮策档案观测。我们发现瞬变(NGC300 OT 2008 - 1)的峰值绝对星等为M_bol~-11.8 mag,介于新星和超新星之间,与最近的M85 OT 2006 - 1和SN 2008 S事件相似。我们的高分辨率光谱是这一事件的第一个,主要是中速(~200 - 1000 km/s)氢巴耳末线和CaII发射和吸收线,指向一个复杂的星周环境,让人想起黄色超巨星IRC +10420。特别是,我们检测到广泛的CaII H & K吸收,不对称的红翼延伸到~1000 km/s,表明气体流入大质量和相对紧凑的恒星(蓝超巨星或沃尔夫-拉叶星);扩展的红超巨星祖星是不可能的。流入气体的来源可能是前一次从母星或大质量双星伴星的风中喷出。低光度,中等速度,以及与已知爆发恒星的总体相似性表明,该事件并没有导致祖先的完全破坏。我们确定的祖先在档案斯皮策观测,深上限从哈勃数据。光谱能量分布表明这是一颗被尘埃遮蔽的恒星,光度约为6 × 10^4 L_sun,代表着一个~10 - 20 M_sun的祖先(或双星系统)。这一结论与我们对爆发和星周性质的解释是一致的。在瞬态光谱中没有明显的消光表明,围绕着祖先的尘埃被爆发清除了。

英文摘要:

[abridged] We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC300. We find that the transient (NGC300 OT2008-1) has a peak absolute magnitude of M_bol~-11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km/s) hydrogen Balmer lines and CaII emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect broad CaII H&K absorption with an asymmetric red wing extending to ~1000 km/s, indicative of gas infall onto a massive and relatively compact star (blue supergiant or Wolf-Rayet star); an extended red supergiant progenitor is unlikely. The origin of the inflowing gas may be a previous ejection from the progenitor or the wind of a massive binary companion. The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6x10^4 L_sun, indicative of a ~10-20 M_sun progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst.

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