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arXiv 0805.4331astro-ph
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椭圆星系中演化恒星的质量损失

Mass Loss From Evolved Stars in Elliptical Galaxies

Joel R. Parriott, Joel N. Bregman

摘要:

早期型星系中的大多数X射线发射气体可能来自红巨星质量损失,在这里,我们模拟了这种恒星质量损失和热环境介质之间的相互作用。使用二维流体动力学模拟,我们采用的环境介质的温度为3E 6 K随着一系列的环境密度和恒星速度。当恒星的速度相对于周围的介质是超音速时,弓形激波会发生,伴随着一个被驱动到恒星喷出物中的激波,它只加热了一小部分气体。在弓形激波的后面,一个冷的尾流发展,但是热介质的快速流动导致开尔文-亥姆霍兹不稳定性增长,这些指状物受到冲击和加热(没有辐射冷却)。伴随着尾流物质与热介质的混合,大多数恒星喷出物在距离恒星2 pc的范围内被加热到接近热环境介质的温度。加上辐射冷却,一些尾流物质仍然很冷(<1 E5 K),占恒星质量损失的25%。当环境密度较低或恒星速度高于我们的参考情况时,冷却程度较低的气体会存活下来。这些结果表明,一些冷却的气体应该存在于具有热环境介质的早型星系的内部。这些计算可以解释观测到的分布光学发射线气体以及在早型星系的尘埃的存在。

英文摘要:

Most of the X-ray emitting gas in early-type galaxies probably originates from red giant mass loss and here we model the interaction between this stellar mass loss and the hot ambient medium. Using two-dimensional hydrodynamic simulations, we adopt a temperature for the ambient medium of 3E6 K along with a range of ambient densities and stellar velocities. When the stellar velocity is supersonic relative to the ambient medium, a bow shock occurs, along with a shock driven into the stellar ejecta, which heats only a fraction of the gas. Behind the bow shock, a cool wake develops but the fast flow of the hot medium causes Kelvin-Helmholtz instabilities to grow and these fingers are shocked and heated (without radiative cooling). Along with the mixing of this wake material with the hot medium, most of the stellar ejecta is heated to approximately the temperature of the hot ambient medium within 2 pc of the star. With the addition of radiative cooling, some wake material remains cool (< 1E5 K), accounting for up to 25% of the stellar mass loss. Less cooled gas survives when the ambient density is lower or when the stellar velocity is higher than in our reference case. These results suggest that some cooled gas should be present in the inner part of early-type galaxies that have a hot ambient medium. These calculations may explain the observed distributed optical emission line gas as well as the presence of dust in early-type galaxies.

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