造父变星投影因子的观测校准。II。HST/FGS视差测量在九颗造父变星中的应用
Observational calibration of the projection factor of Cepheids. II. Application to nine Cepheids with HST/FGS parallax measurements
摘要：
脉动恒星的距离通常使用脉动松弛（PoP）方法来估计，该方法结合了光谱径向速度测量和角直径估计来推导恒星的距离。这种方法的一个重要应用是确定造父变星的距离，鉴于其距离尺度的校准。然而，在PoP方法中，径向速度到脉动速度的转换依赖于校准不良的参数，投影因子（p因子）。我们的目标是凭经验测量的P-因子的值的均匀样本的九个银河造父变星的三角函数的测量与哈勃太空望远镜精细制导传感器。我们使用的SPIPS算法，一个强大的实现的PoP方法，结合测光，干涉，径向速度测量的脉动的全球建模。我们获得了新的干涉角直径使用PIONIER仪器在甚大望远镜干涉仪，完成了从文献中的数据。使用已知的距离作为输入，我们推导出的p-因子的值，并研究其与脉动周期的依赖关系。我们发现以下P因子：1.20 $\pm$ 0.12，用于RT Aur，1.48 $\pm$ 0.18（T Vul），1.14 $\pm$ 0.10（FF Aql），1.31 $\pm$ 0.19（Y Sgr），1.39 $\pm$ 0.09（X Sgr），1.35 $\pm$ 0.13（对于W Sgr），1.36 $\pm$ 0.08对于$β$ Dor，1.41 $\pm$ 0.10用于$ζ$ Gem，1.23 $\pm$ 0.12用于$\ell$ Car。这些值始终接近p = 1.324 $\pm$ 0.024。我们观察到这个平均值周围的一些分散，但所观察到的分布是统计学上一致的一个常数的p-因子作为脉动周期的函数。我们确定p因子值的误差预算目前主要由视差的不确定性决定，盖亚很快就会放弃这一限制。
英文摘要：
The distance to pulsating stars is classically estimated using the parallax-of-pulsation (PoP) method, which combines spectroscopic radial velocity measurements and angular diameter estimates to derive the distance of the star. An important application of this method is the determination of Cepheid distances, in view of the calibration of their distance scale. However, the conversion of radial to pulsational velocities in the PoP method relies on a poorly calibrated parameter, the projection factor (p-factor). We aim to measure empirically the value of the p-factors of a homogeneous sample of nine Galactic Cepheids for which trigonometric parallaxes were measured with the Hubble Space Telescope Fine Guidance Sensor. We use the SPIPS algorithm, a robust implementation of the PoP method that combines photometry, interferometry, and radial velocity measurements in a global modeling of the pulsation. We obtained new interferometric angular diameters using the PIONIER instrument at the Very Large Telescope Interferometer, completed by data from the literature. Using the known distance as an input, we derive the value of the p-factor and study its dependence with the pulsation period. We find the following p-factors: 1.20 $\pm$ 0.12 for RT Aur, 1.48 $\pm$ 0.18 for T Vul, 1.14 $\pm$ 0.10 for FF Aql, 1.31 $\pm$ 0.19 for Y Sgr, 1.39 $\pm$ 0.09 for X Sgr, 1.35 $\pm$ 0.13 for W Sgr, 1.36 $\pm$ 0.08 for $β$ Dor, 1.41 $\pm$ 0.10 for $ζ$ Gem, and 1.23 $\pm$ 0.12 for $\ell$ Car. These values are consistently close to p = 1.324 $\pm$ 0.024. We observe some dispersion around this average value, but the observed distribution is statistically consistent with a constant value of the p-factor as a function of the pulsation period. The error budget of our determination of the p-factor values is presently dominated by the uncertainty on the parallax, a limitation that will soon be waived by Gaia.
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