Precision Measurement of Stellar Sizes and Circumstellar Material with 10 Micron Interferometry and Narrow Frequency Bandwidths

利用伯克利独特的红外空间干涉仪（ISI）和三个可移动的60英寸望远镜，将进行一项观测计划，以获得进化后型恒星的高分辨率图像。这将包括在中红外（11微米）波长的窄光谱区域对老恒星的直径进行干涉测量，以避免由于恒星直接大气中的气体而选择谱线，使用这些基线在不同方向和相位闭合中仔细检查恒星的形状，以及直接在谱线上进行窄带测量以确定这些气体在恒星周围的空间分布。也可以使用多个基线和相位来绘制恒星发出的尘埃的一些地图，但将强调对恒星盘和形状的测量。ISI可用的基线范围从4米到大约75米，可以精确测量老恒星以及它们周围的尘埃和气体分布。中红外波段和窄波段的测量可以最大限度地减少由于边缘变暗或周围气体光谱造成的视尺寸畸变。ISI系统采用带宽约为0.2/cm的外差检测；此外，所得到的信号可以被滤波以获得任意窄的频谱宽度。恒星大小的测量精度达到1%或更高已经得到证实。相位闭合测量的精度为一度，允许几乎完整的傅立叶分析强度模式，包括不对称。观测活动将重点检查Miras和红巨星可能偏离球形的情况，以及恒星大小随时间和恒星振荡阶段的变化。ISI先前的测量显示了围绕晚型恒星的尘埃云的运动，以及云与球形对称的偏差。在接下来的一年里，重点将放在对恒星本身的测量上。最近安装在威尔逊山上的第三台可移动望远镜运行良好，将能见度测量增加了三倍，并允许精确的相位闭合测量。这允许干涉测量与三个不同方向的基线同时测量，以及相位闭合。老恒星发射物质的不对称性和不规则时间是很常见的，但恒星本身的不对称性尚不为人所知。该项目的总体目标是通过ISI和干涉测量技术的发展，通过详细的新测量，大大增加我们对老恒星特征的认识。在光学、电子学、计算机系统控制、望远镜操作、数据分析和科学解释等方面为青年科学家（从本科生到博士后）提供培训机会。

An observational program using Berkeley's unique Infrared Spatial Interferometer (ISI) with three movable 60 inch telescopes will be carried out to obtain high-resolution images of evolved late-type stars. This will include interferometric measurement of the diameters of old stars in narrow spectral regions at mid-infrared (11 micron) wavelengths chosen to avoid spectral lines due to gases in the immediate atmospheres of stars, careful examination of the shapes of stars using these baselines in different directions and with phase closure, and narrow-band measurements directly on spectral lines to determine the spatial distribution of such gases around the stars. Some mapping of dust emitted by stars using multiple baselines and phase also may be made, but measurement of stellar disks and shapes will be emphasized.Baselines available to the ISI range from four to approximately 75 meters and allow accurate measurements of old stars as well as the dust and gas distributions around them. Measurements in the mid-IR and with narrow bandwidths minimize the distortions in apparent size due to limb darkening or to spectra of surrounding gas. The ISI system uses heterodyne detection which has a bandwidth of about 0.2/cm; furthermore the resulting signals can be filtered to obtain arbitrarily narrow spectral widths. Stellar size measurements to a precision of 1% or better have been demonstrated. Phase closure measurements are made to an accuracy of one degree, allowing nearly complete Fourier analysis of intensity patterns, including asymmetries. The observing campaign will emphasize the examination of possible deviations from sphericity of Miras and red giants, and changes in stellar size with time and phase of stellar oscillation.Previous ISI measurements have shown movements of dust clouds surrounding late-type stars as well as deviations of the clouds from spherical symmetry. During the coming year focus will be placed on measurements of the stars themselves. The third movable telescope recently installed on Mt.Wilson functions well, and increases the visibility measurements by a factor of three as well as allowing accurate phase closure measurements. This allows interferometry with three baselines of various orientations to be measured simultaneously, along with phase closure. Asymmetries and irregular timing in emission of material by old stars appear common, but the asymmetries of stars themselves are not yet known.The overall goals of this project are to provide a substantial increase in our knowledge of the characteristics of old stars through the detailed new measurements which are made possible via ISI and the development of interferometric technology. Opportunities will be provided for the training of young scientists (from undergraduates to postdocs) in optics, electronics, computer control of systems, telescope operation, data analysis, and scientific interpretation.