On the Origin of the UV Upturn in Elliptical Galaxies. I. Sensitivity of UV Population Synthesis to Various Input Parameters
On the Origin of the UV Upturn in Elliptical Galaxies. I. Sensitivity of UV Population Synthesis to Various Input Parameters
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DOI：
10.1086/304498
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发表时间：
1997-05
期刊：
影响因子：
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通讯作者：
S. Yi;P. Demarque;Augustus Oemler, Jr.
中科院分区：
文献类型：
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作者：
S. Yi;P. Demarque;Augustus Oemler, Jr.
我们提出了恒星演化后期的模型，旨在解释椭圆星系中的“紫外线上升”现象。这样的模型对一些约束较差的物理参数的值很敏感，包括金属丰度、年龄、恒星质量损失、氦富集和恒星在零年龄水平分支（HB）上的分布。我们探讨了结果对这些参数值的敏感性，并得出以下结论。古老的、富含金属的星系，比如巨大的椭圆星系，在没有年轻恒星存在的情况下，会在合理的时间尺度内（小于哈勃时间）自然地产生紫外线上升。在这类恒星群中，最有可能主宰紫外线通量的恒星是低质量的核心氦燃烧（HB和演化的HB）恒星。由于不透明的影响，金属含量较低的恒星产生较高的UV- v通量比率，但只有富含金属的恒星产生紫外线上升，其中通量向较短的紫外波长增加。
We present models of the late stages of stellar evolution intended to explain the “UV upturn” phenomenon in elliptical galaxies. Such models are sensitive to values of a number of poorly constrained physical parameters, including metallicity, age, stellar mass loss, helium enrichment, and the distribution of stars on the zero-age horizontal branch (HB). We explore the sensitivity of the results to values of these parameters and reach the following conclusions. Old, metal-rich galaxies, such as giant ellipticals, naturally develop a UV upturn within a reasonable timescale—less than a Hubble time—without the presence of young stars. The most likely stars to dominate the UV flux of such populations are low-mass, core helium-burning (HB and evolved HB) stars. Metal-poor populations produce a higher ratio of UV-to-V flux, owing to opacity effects, but only metal-rich stars develop a UV upturn, in which the flux increases toward shorter UV wavelengths.