On the Origin of the Ultraviolet Upturn in Elliptical Galaxies. II. Test of the Horizontal-Branch Hypothesis
On the Origin of the Ultraviolet Upturn in Elliptical Galaxies. II. Test of the Horizontal-Branch Hypothesis
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关于椭圆星系中紫外线上升的起源。
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
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.
富金属HB星是否是巨椭圆星系的主要紫外辐射源是当前天文学研究的一个重要问题。我们跟进我们以前的进化群体合成研究，在以下三个条件下进行定量测试，以肯定地回答这个问题：（1）Reimers的经验质量损失公式是正确的;（2）富金属星的质量损失效率参数η比贫金属星星研究的估计值稍大，（3）富氦参数（ΔY/ΔZ）的真值为正值。紫外线上升的所有三个重要的经验特征（即，强UV上升仅限于GE的事实、正的UV上升-金属丰度相关性以及UV源的Teff的窄范围）对于输入参数的合理范围被紧密地再现。我们讨论了模型中不确定性的主要来源，如热水平分支恒星在GE中的产生和作用，以及星系核合成的重要性。
Whether or not metal-rich HB stars are the dominant UV source in giant elliptical galaxies (GEs) is an important question in current astronomical research. We follow up our previous evolutionary population synthesis study with quantitative tests to answer this question affirmatively under the following three conditions: (1) Reimers's empirical mass-loss formula is proper, (2) the mass-loss efficiency parameter η in metal-rich stars is somewhat larger than the value estimated from the metal-poor star studies, and (3) the true value of the helium-enrichment parameter (ΔY/ΔZ) is positive. All three important empirical characteristics of the UV upturn (i.e., the fact that strong UV upturns are restricted to GEs, the positive UV upturn-metallicity correlation, and the narrow range of the Teff of the UV sources) are closely reproduced for reasonable ranges of input parameters. We discuss the major sources of uncertainties in the models, such as the production and role of hot horizontal-branch stars in GEs, and the importance of galactic nucleosynthesis.