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arXiv 1812.03065astro-ph.SR
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黄超巨星绕增二的新爆发

A new outburst of the yellow hypergiant star Rho Cas

Michaela Kraus, Indrek Kolka, Anna Aret, Dieter H. Nickeler, Grigoris Maravelias, Tõnis Eenmäe, Alex Lobel, Valentina G. Klochkova

摘要:

黄超巨星是已经演化到后红超巨星阶段的大质量恒星。后红超巨星演化回赫兹-罗素图的蓝色、热的一面,可以穿过一个温度域,在这个温度域中,它们的大气层对脉动变得不稳定(黄空或黄墙),恒星可以经历短暂但猛烈的大规模爆发。黄色超巨星罗·卡斯以其历史和最近的爆发而闻名,在此期间,恒星发展出一种非常短暂但质量损失率很高的冷的光学厚风,导致光变曲线突然下降。在这里,我们报告了一个新的爆发的Rho Cas发生在2013年,伴随着温度下降~3000 K和亮度下降0.6马格。在爆发期间出现TiO带,以及许多低激发金属大气线的特征,后来的光谱类型。随着这次新的爆发,似乎单个事件之间的时间间隔缩短,这可能表明Rho Cas正在准备一次大爆发,这可能有助于恒星穿过黄色虚空。我们还分析了在最大亮度阶段出现的发射特征,发现它们与突出的[CaII]线的发射同步变化。我们的结论是,偶尔检测到的发射光谱中的Rho Cas,以及某些不对称的低到中等激发电位的吸收线,是拱星的性质,我们讨论了这种材料的可能来源。

英文摘要:

Yellow hypergiants are evolved massive stars that were suggested to be in post-red supergiant stage. Post-red supergiants that evolve back to the blue, hot side of the Hertzsprung-Russell diagram can intersect a temperature domain in which their atmospheres become unstable against pulsations (the Yellow Void or Yellow Wall), and the stars can experience outbursts with short, but violent mass eruptions. The yellow hypergiant Rho Cas is famous for its historical and recent outbursts, during which the star develops a cool, optically thick wind with a very brief but high mass-loss rate, causing a sudden drop in the light curve. Here we report on a new outburst of Rho Cas which occurred in 2013, accompanied by a temperature decrease of ~3000 K and a brightness drop of 0.6 mag. During the outburst TiO bands appear, together with many low excitation metallic atmospheric lines characteristic for a later spectral type. With this new outburst, it appears that the time interval between individual events decreases, which might indicate that Rho Cas is preparing for a major eruption that could help the star to pass through the Yellow Void. We also analysed the emission features that appear during phases of maximum brightness and find that they vary synchronous with the emission in the prominent [CaII] lines. We conclude that the occasionally detected emission in the spectra of Rho Cas, as well as certain asymmetries seen in the absorption lines of low to medium-excitation potential, are circumstellar in nature, and we discuss the possible origin of this material.

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