arXiv 0907.34892009-07-20astro-ph.GA

椭圆星系中行星状星云的质量损失

Mass Loss From Planetary Nebulae in Elliptical Galaxies

Joel N. Bregman, Joel R. Parriott

备注：: 34 pages with 20 figures. Higher quality figures are in the ApJ version
发表信息：: ApJ, 699, 2009, 923-932
DOI：: 10.1088/0004-637X/699/2/923

摘要：

早期型星系拥有稀释的热（2- 10 E6 K）气体，可能是演化恒星质量损失的热化喷出物。我们研究了行星状星云事件中质量喷射的情况下，轨道恒星的质量损失与静止热气体相互作用的过程。流体动力学数值模拟表明，在第一，喷出物膨胀几乎对称，与上游的弓形激波在热的环境气体。在稍后的时间，通过喷出物的流动产生流体不稳定性，导致大约一半的喷出物分离，另一半在狭窄的尾流中向下游流动得更慢。当包括辐射冷却时，尾流中的大部分物质（>80%）保持在1 E5 K以下，而分离的喷出物更热（1 E5 - 1 E6 K）。分离出的喷出物的温度仍然小于环境介质温度的四分之一，并且其达到环境介质温度的唯一方式是通过湍流混合（在材料离开格栅之后）。这些计算表明，行星状星云喷出物的很大一部分可能不会成为周围热物质的一部分。这与我们之前对巨恒星持续质量损失的计算相反，在巨恒星中，大部分质量损失变成了热气。我们推测，可检测的OVI发射可能会产生，但更复杂的计算将需要确定的发射光谱，并更好地定义冷却材料的分数。

英文摘要：

Early-type galaxies possess a dilute hot (2-10E6 K) gas that is probably the thermalized ejecta of the mass loss from evolving stars. We investigate the processes by which the mass loss from orbiting stars interacts with the stationary hot gas for the case of the mass ejected in a planetary nebula event. Numerical hydrodynamic simulations show that at first, the ejecta expands nearly symmetrically, with an upstream bow shock in the hot ambient gas. At later times, the flow past the ejecta creates fluid instabilities that cause about half of the ejecta to separate and the other half to flow more slowly downstream in a narrow wake. When radiative cooling is included, most of the material in the wake (>80%) remains below 1E5 K while the separated ejecta is hotter (1E5-1E6 K). The separated ejecta is still less than one-quarter the temperature of the ambient medium and the only way it will reach the temperature of the ambient medium is through turbulent mixing (after the material has left the grid). These calculations suggest that a significant fraction of the planetary nebula ejecta may not become part of the hot ambient material. This is in contrast to our previous calculations for continuous mass loss from giant stars in which most of the mass loss became hot gas. We speculate that detectable OVI emission may be produced, but more sophisticated calculations will be required to determine the emission spectrum and to better define the fraction of cooled material.

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