arXiv 1202.28552012-02-13astro-ph.SR

关于经典造父变星的演化和脉动质量：III。在大麦云星云中食双星造父变星CEP0227的情况

On the evolutionary and pulsation mass of Classical Cepheids: III. the case of the eclipsing binary Cepheid CEP0227 in the Large Magellanic Cloud

P. G. Prada Moroni, M. Gennaro, G. Bono, G. Pietrzynski, W. Gieren, B. Pilecki, D. Graczyk, I. B. Thompson, .

备注：: Accepted for publication in ApJ. 17 pages, 9 figures
DOI：: 10.1088/0004-637X/749/2/108

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摘要：

提出了一种新的贝叶斯方法来约束LMC中食双星CEP0227的内禀参数（恒星质量、年龄）。我们计算的进化模型涵盖了广泛的化学成分和恒星质量。通过忽略或包括一个温和的对流核心过冲（β = 0.2）在中央H-燃烧阶段的模型构建独立的集。通过忽略或假设典型（eta = 0.4，0.8）或增强（eta = 4）质量损失率也构建了模型。在三个不同的平面上计算了这些解：光度-温度、质量-半径和重力-温度。通过使用贝叶斯因子，我们发现，最可能的解决方案是在重力-温度平面与高斯质量先验分布。在假设对流核适度过冲（β = 0.2）和正则质量损失率（eta = 0.4）的条件下，所建立的演化模型给出了造父变星的初始质量M = 4.14 ^{+0.04}-0.05} Msun和次级质量M = 4.15 ^{+0.04}-0.05} Msun，与动力学测量结果在1%的水平上一致。此外，我们还发现两个组分和组合系统的年龄t = 151 ^{+4}_{-3} Myr在5%水平上一致。基于忽略质量损失的进化模型的解决方案获得类似的参数，而那些基于考虑增强的质量损失或忽略对流核心过冲的模型的解决方案具有较低的贝叶斯因子和较大的置信区间。对质量损失率的依赖性可能是我们用来模拟这种现象的粗略近似的结果。利用最概然解的等时线和高斯先验，我们得到了距离模18.53 ^{+0.02}-0.02} mag和红化值E（B-V）= 0.142 ^{+0.005}-0.010} mag，与文献估计值吻合得很好。

英文摘要：

We present a new Bayesian approach to constrain the intrinsic parameters (stellar mass, age) of the eclipsing binary system CEP0227 in the LMC. We computed evolutionary models covering a broad range in chemical compositions and in stellar mass. Independent sets of models were constructed either by neglecting or by including a moderate convective core overshooting (beta=0.2) during central H-burning phases. Models were also constructed either by neglecting or by assuming a canonical (eta=0.4,0.8) or an enhanced (eta=4) mass loss rate. The solutions were computed in three different planes: luminosity-temperature, mass-radius and gravity-temperature. By using the Bayes Factor, we found that the most probable solutions were obtained in the gravity-temperature plane with a Gaussian mass prior distribution. The evolutionary models constructed by assuming a moderate convective core overshooting (beta=0.2) and a canonical mass loss rate (eta=0.4) give stellar masses for the primary Cepheid M=4.14^{+0.04}_{-0.05} M_sun and for the secondary M=4.15^{+0.04}_{-0.05} M_sun that agree at the 1% level with dynamical measurements. Moreover, we found ages for the two components and for the combined system t=151^{+4}_{-3} Myr that agree at the 5% level. The solutions based on evolutionary models that neglect the mass loss attain similar parameters, while those ones based on models that either account for an enhanced mass loss or neglect convective core overshooting have lower Bayes Factors and larger confidence intervals. The dependence on the mass loss rate might be the consequence of the crude approximation we use to mimic this phenomenon. By using the isochrone of the most probable solution and a Gaussian prior on the LMC distance, we found a distance modulus 18.53^{+0.02}_{-0.02} mag and a reddening value E(B-V)= 0.142^{+0.005}_{-0.010} mag that agree well with literature estimates.

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