利用CHARA阵列干涉仪对经典造父变星的多色观测：表面亮度-颜色关系、投影因子和临边昏暗

中文摘要 AI 辅助

Baade-Wesselink（BW）方法通过比较造父变星的线性和角变化来推导其距离。然而，该方法受到投影因子的限制，投影因子将观测到的径向速度与恒星的真实脉动速度联系起来。利用CHARA阵列干涉仪在K、H和R波段分别使用MYSTIC、MIRC-X和SPICA组合器的同步观测，我们旨在更好地理解造父变星大气层的物理特性。通过对造父变星的多色同步干涉观测应用特定方法，我们推导出稳健的临边昏暗角直径，随后用于校准SBCR并研究投影因子。我们还开发了一种策略来测量造父变星在R、H和K波段的临边昏暗。这些测量随后被用于约束投影因子的几何分量。根据三颗造父变星的临边昏暗角直径曲线，我们将SBCR在$V-K$颜色中的离散度降低到0.0011星等，在$G_{BP}-G_{RP}$中的SBCR离散度降低到0.0040。这些SBCR特别稳健，因为它们基于多色直径且具有同质性，而之前的造父变星校准并非如此。我们首次推导了造父变星在R、H和K波段的临边昏暗。对于$\u03b4$ Cep，我们推导出基于R的投影因子为$1.275 \pm 0.051$，根据R波段测量的临边昏暗系数获得的几何部分估计为$1.420 \pm 0.016$（平均），正如恒星静态和流体动力学大气模型所预期的那样。在H和K波段获得的临边昏暗系数与模型一致。这些结果表明，多色干涉测量可以提高BW方法的精度。因此，在未来几年继续CHARA对造父变星的巡天至关重要。

英文摘要

The Baade-Wesselink (BW) method compares the linear and angular variations of Cepheids to derive their distance. This method is limited, however, by the projection factor, which relates the observed radial velocity to the true pulsation velocity of the star. Using simultaneous observations from the CHARA Array interferometer in the K, H, and R bands with the MYSTIC, MIRC-X, and SPICA combiners, respectively, we aim to understand the physics of Cepheid atmospheres better. Applying a specific method to multi-chromatic simultaneous interferometric observations of Cepheids, we derived robust limb-darkened angular diameters that were then used to calibrate the SBCR and study the projection factor. We also developed a strategy to measure the limb-darkening of Cepheids in R, H, and K bands. These measurements were then used to constrain the geometrical component of the projection factor. From the limb-darkened angular diameter curves of three Cepheids, we decreased the scatter of the SBCR in $V-K$ colour to 0.0011 magnitude and to 0.0040 for the SBCR in $G_{BP}-G_{RP}$. These SBCRs are particularly robust because they are based on multi-chromatic diameters and are homogeneous, which previous calibrations for Cepheids were not. For the very first time, we derived the limb-darkening of Cepheids in R, H, and K bands. For $δ$ Cep, we derived an R-based projection factor of $1.275 \pm 0.051$, and the geometrical part obtained from the measured limb-darkening coefficient in R band was estimated to $1.420 \pm 0.016$ (on average), as expected from stellar static and hydrodynamical atmosphere models. The limb-darkening coefficients obtained in H and K band are consistent with models. These results demonstrate that multi-chromatic interferometry can improve the accuracy of the BW method. It is therefore essential to continue the CHARA survey of Cepheids in the coming years.

发表机构

• Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学，蔚蓝海岸天文台）
• European Southern Observatory（欧洲南方天文台）
• LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台 LIRA 实验室，巴黎文理研究大学，索邦大学，巴黎西岱大学，CY 塞尔吉巴黎大学）
• French-Chilean Laboratory for Astronomy, IRL 3386, CNRS（中智天文学联合实验室）
• Instituto de Alta Investigación, Universidad de Tarapacá（塔拉帕卡大学高等研究院）
• Astronomy Department, University of Michigan（密歇根大学天文学系）

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