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Tachoastrometry: astrometry with radial velocities

机译：测速天文法：具有径向速度的天文法

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Context. Spectra of composite systems (e.g., spectroscopic binaries) contain spatial information that can be retrieved by measuring the radial velocities (i.e., Doppler shifts) of the components in four observations with the slit rotated by 90 degrees in the sky. Aims. We aim at developing a framework to describe the method and to test its capabilities in a real case. Methods. By using basic concepts of slit spectroscopy we show that the geometry of composite systems can be reliably retrieved by measuring only radial velocity differences taken with different slit angles. The spatial resolution is determined by the precision with which differential radial velocities can be measured. Results. We use the UVES spectrograph at the VLT to observe the known spectroscopic binary star HD 188088 (HIP 97944), which has a maximum expected separation of 23 milli-arcseconds. We measure an astrometric signal in radial velocity of 276 ?m s-1?, which corresponds to a separation between the two components at the time of the observations of 18 ± 2 milli-arcseconds. The stars were aligned east-west. We describe a simple optical device to simultaneously record pairs of spectra rotated by 180 degrees, thus reducing systematic effects. We compute and provide the function expressing the shift of the centroid of a seeing-limited image in the presence of a narrow slit. Conclusions. The proposed technique is simple to use and our test shows that it is amenable for deriving astrometry with milli-arcsecond accuracy or better, beyond the diffraction limit of the telescope. The technique can be further improved by using simple devices to simultaneously record the spectra with 180 degrees angles. This device together with an optimized data analysis will further reduce the measurement errors. With tachoastrometry, radial velocities and astrometric positions can be measured simultaneously for many double line system binaries in an easy way. The method is not limited to binary stars, but can be applied to any astrophysical configuration in which spectral lines are generated by separate (non-rotational symmetric) regions.
机译：上下文。复合系统的光谱（例如，光谱双星）包含空间信息，这些信息可以通过在狭缝在天空中旋转90度的四个观测值中测量组件的径向速度（即多普勒频移）来获取。目的我们旨在开发一个框架来描述该方法并在实际情况下测试其功能。方法。通过使用狭缝光谱学的基本概念，我们表明可以通过仅测量在不同狭缝角度下获得的径向速度差来可靠地恢复复合系统的几何形状。空间分辨率取决于可以测量径向速度差的精度。结果。我们在VLT上使用UVES光谱仪观察了已知的光谱双星HD 188088（HIP 97944），其最大预期间隔为23毫秒。我们以276？m s-1？的径向速度测量了一个天体信号，这对应于观测18±2毫秒时两个分量之间的间隔。星星排列成东西方向。我们描述了一种简单的光学设备，可同时记录旋转180度的光谱对，从而减少系统影响。我们计算并提供了一个函数，该函数在出现窄缝的情况下表示观看受限图像质心的偏移。结论。所提出的技术易于使用，并且我们的测试表明，该技术可用于推导超出望远镜衍射极限的毫秒级或更高精度的天体测量。通过使用简单的设备同时记录180度角的光谱，可以进一步改善该技术。该设备与优化的数据分析一起将进一步减少测量误差。使用测速天文法，可以轻松地同时测量许多双线系统双星的径向速度和天文位置。该方法不限于双星，而是可以应用于通过分开的（非旋转对称）区域生成谱线的任何天体构造。

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