The influence of chemical composition on the properties of Cepheid stars. II - The iron content ⋆
The influence of chemical composition on the properties of Cepheid stars. II - The iron content ⋆
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DOI：
10.1051/0004-6361:20065661
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发表时间：
2008-07
影响因子：
6.5
通讯作者：
M. Romaniello;F. Primas;M. Mottini;S. Pedicelli;B. Lemasle;G. Bono;G. Bono;P. Francois;
中科院分区：
文献类型：
--
作者：
M. Romaniello;F. Primas;M. Mottini;S. Pedicelli;B. Lemasle;G. Bono;G. Bono;P. Francois;
上下文造父变星的周期-光度（PL）关系无疑是我们所掌握的确定河外距离尺度的最有力的工具之一。虽然在过去的几年里，在观测和理论方面都取得了重大进展，但关于化学成分对PL关系的影响的争论仍然没有解决。目标。为了评估恒星铁含量对V带和K带光致发光关系的影响，我们将Freedman等（2001，ApJ，553，47）和Fredson等（2004，AJ，128，2239）的标准光致发光关系中的V带和K带残差分别与[Fe/H]联系起来。方法.我们使用直接测量的铁丰度的68银河系和麦哲伦造父变星的FEROS和UVES高分辨率和高信噪比的光谱。结果我们发现银河系样品（32颗星）的平均铁丰度（[Fe/H]）约为太阳的（σ = 0.10），大麦哲伦云（LMC）样品（22颗星）约为-0.33dex（σ = 0.13），小麦哲伦云（SMC）样品（14颗星）约为-0.75dex（σ = 0.08）。我们对麦哲伦造父变星的丰度测量使迄今为止在高分辨率下研究的恒星数量增加了一倍。金属丰度影响V波段造父变星的PL关系，富金属造父变星似乎比贫金属造父变星系统地暗淡。这些发现既不依赖于银河造父变星的距离尺度，也不依赖于大麦哲伦星系的距离模数。目前的数据不允许我们得出一个坚定的结论，关于K带PL关系的金属丰度的依赖。新的银河系距离表明影响很小，而旧的则支持边际效应。结论.最近对LMC距离的稳健估计和目前的结果表明，造父变星PL关系不是普适的。
Context. The Cepheid period-luminosity (PL) relation is unquestionably one of the most powerful tools at our disposal for determining the extragalactic distance scale. While significant progress has been made in the past few years towards its understanding and characterization both on the observational and theoretical sides, the debate on the influence that chemical composition may have on the PL relation is still unsettled. Aims. With the aim to assess the influence of the stellar iron content on the PL relation in the V and K bands, we have related the V -band and the K -band residuals from the standard PL relations of Freedman et al. (2001, ApJ, 553, 47) and Persson et al. (2004, AJ, 128, 2239), respectively, to [Fe/H]. Methods. We used direct measurements of the iron abundances of 68 Galactic and Magellanic Cepheids from FEROS and UVES high-resolution and high signal-to-noise spectra. Results. We find a mean iron abundance ([Fe/H]) about solar ($\sigma $= 0.10) for our Galactic sample (32 stars), ~-0.33 dex ( σ = 0.13) for the Large Magellanic Cloud (LMC) sample (22 stars) and ~-0.75 dex ( σ = 0.08) for the Small Magellanic Cloud (SMC) sample (14 stars). Our abundance measurements of the Magellanic Cepheids double the number of stars studied up to now at high resolution. The metallicity affects the V -band Cepheid PL relation and metal-rich Cepheids appear to be systematically fainter than metal-poor ones. These findings depend neither on the adopted distance scale for Galactic Cepheids nor on the adopted LMC distance modulus. Current data do not allow us to reach a firm conclusion concerning the metallicity dependence of the K -band PL relation. The new Galactic distances indicate a small effect, whereas the old ones support a marginal effect. Conclusions. Recent robust estimates of the LMC distance and current results indicate that the Cepheid PL relation is not Universal.