Cepheid Models and Distances in the Age of Interferometry

Sasselov、DimitarCepheid变星是天文学上主要的距离指示星。 造父变星的周期光度关系所设定的距离刻度，目前的校准不确定度约为10%。 径向速度测量加上来自长基线光学和红外干涉仪的新数据，将提供可直接估计恒星距离的线直径和角直径。 在这个项目中，时间和波长依赖的亮度分布的造父变星样本将使用动态非LTE大气模型，包括平面平行和球面几何计算。 这些模型的结果将比较观察到的造父变星径向速度测量和集成的方式与海军原型光学干涉仪收集的角尺寸数据一致。 径向速度和脉动速度之间的适当变换将使用相应的线形成区域的谱线的选择来应用。该计划的目标是将造父变星距离标尺的绝对精度提高大约两倍。

ABSTRACTAST-9876734Sasselov, DimitarCepheid variable stars are primary distance indicators in astronomy. The current calibration of the distance scale set by the Cepheid period-luminosity relation is uncertain by about 10%. Radial velocity measurements combined with new data from long baseline optical and infrared interferometers will provide linear and angular diameters from which stellar distances can be directly estimated. In this project time- and wavelength-dependent brightness distributions for a sample of Cepheid variables will be computed using dynamical non-LTE atmosphere models that incorporate both plane-parallel and spherical geometry. The results of these models will be compared to observed Cepheid radial velocities measured and integrated in a manner consistent with the angular size data collected by the Navy Prototype Optical Interferometer. Appropriate transformations between the radial and pulsational velocities will be applied using a selection of spectral lines of corresponding line-forming regions. The goal of this program is to improve the absolute precision of the Cepheid distance scale by roughly a factor of two.