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

一项使用伯克利独特的红外空间干涉仪(ISI)和三个可移动的60英寸望远镜的观测计划将被实施，以获得进化的晚型恒星的高分辨率图像。这将包括：以中红外(11微米)波长干涉测量狭窄光谱区域中老恒星的直径，以避免恒星直接大气层中气体产生的光谱线；利用这些基线在不同方向和具有相位闭合的情况下仔细检查恒星的形状；以及直接在光谱线上进行窄带测量，以确定恒星周围这类气体的空间分布。也可以使用多个基线和相位绘制恒星发出的尘埃的一些地图，但重点是测量恒星盘和形状。ISI可用的基线范围从4米到大约75米，可以准确测量旧恒星以及它们周围的尘埃和气体分布。在中红外和窄带宽的测量中，最大限度地减少了由于肢体变暗或周围气体光谱而造成的表观尺寸失真。ISI系统使用外差检测，其带宽约为0.2/cm；此外，所产生的信号可以被滤波以获得任意窄的频谱宽度。已经证明，恒星大小的测量精度为1%或更高。相位闭合测量的精度为1度，允许对包括不对称性在内的强度模式进行几乎完整的傅立叶分析。这次观测活动将着重检查木星和红巨星可能偏离球度的可能性，以及恒星大小随恒星振荡时间和相位的变化。之前的ISI测量显示，尘埃云在晚型恒星周围移动，以及云团偏离球对称。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个可移动望远镜功能良好，将能见度测量提高了三倍，并能够进行准确的相位闭合测量。这使得可以同时测量具有不同方向的三条基线的干涉测量，以及相位闭合。老星发射物质的不对称性和不规则时间似乎很常见，但恒星本身的不对称性尚不清楚。这个项目的总体目标是通过ISI和干涉技术的发展来实现详细的新测量，从而大幅增加我们对旧星特征的了解。将为年轻科学家(从本科生到博士后)提供光学、电子学、系统的计算机控制、望远镜操作、数据分析和科学解释方面的培训机会。

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.