标题： 多相PC/PL关系：理论与观测的比较 显示英文标题

标题： Multiphase PC/PL Relations: Comparison between Theory and observations

摘要： 造父变星在天体物理上是基本的天体，因为它们掌握了独立于宇宙微波背景（CMB）估算哈勃常数的关键。 许多研究者指出，如果存在一个精确到百分之几的独立于CMB的距离尺度，可以在Omega_Matter和H0之间打破退化关系（Hu 2005）。 目前距离尺度的不确定性约为10%，但未来的观测，例如使用詹姆斯·韦伯太空望远镜（JWST），将能够以百分之几的精度估算H0。 这一过程中的关键步骤是造父变星的周光关系。 最近有证据表明，至少在光学波段，周光关系是非线性的，并且忽略这种非线性可能导致估算H0的误差高达2%。 因此，批判性地考察这种可能的非线性，无论是观测还是理论上都是重要的。 现有的PC/PL关系完全依赖于平均光强度下评估这些关系。 然而，由于这些关系是不同相位关系的平均值。 在这里，我们报告了最近尝试在多相位PC/PL平面上比较理论与观测的结果。 我们构建适合大麦哲伦云/银河系的最先进的造父变星脉动模型，并将由此得到的PC/PL关系与观测结果按相位进行比较。 对于大麦哲伦云，最小光度下的(V-I)周期-颜色关系可以具有相当窄的离散度（0.2-0.3个星等），因此可能有助于对模型施加约束。 在更长周期的情况下，模型预测的V-I颜色明显更红（约0.2-0.3个星等）。 我们讨论了造成这种情况的可能原因，并且比较了脉动各个阶段的PL关系，发现在理论和观测中都清楚地存在非线性的PL关系。 显示英文摘要

摘要： Cepheids are fundamental objects astrophysically in that they hold the key to a CMB independent estimate of Hubble's constant. A number of researchers have pointed out the possibilities of breaking degeneracies between Omega_Matter and H0 if there is a CMB independent distance scale accurate to a few percent (Hu 2005). Current uncertainties in the distance scale are about 10% but future observations, with, for example, the JWST, will be capable of estimating H0 to within a few percent. A crucial step in this process is the Cepheid PL relation. Recent evidence has emerged that the PL relation, at least in optical bands, is nonlinear and that neglect of such a nonlinearity can lead to errors in estimating H0 of up to 2 percent. Hence it is important to critically examine this possible nonlinearity both observationally and theoretically. Existing PC/PL relations rely exclusively on evaluating these relations at mean light. However, since such relations are the average of relations at different phases. Here we report on recent attempts to compare theory and observation in the multiphase PC/PL planes. We construct state of the art Cepheid pulsations models appropriate for the LMC/Galaxy and compare the resulting PC/PL relations as a function of phase with observations. For the LMC, the (V-I) period-color relation at minimum light can have quite a narrow dispersion (0.2-0.3 mags) and thus could be useful in placing constraints on models. At longer periods, the models predict significantly redder (by about 0.2-0.3 mags) V-I colors. We discuss possible reasons for this and also compare PL relations at various phases of pulsation and find clear evidence in both theory and observations for a nonlinear PL relation.