Aperture masking observations for binary stars have been done with a 1.56-m telescope at Shanghai Astronomical Observatory(SHAO) during 2019-2024. In order to ensure ample light available to restore the high resolution images even at short exposure times and reach the diffraction limit of the 1.56-m telescope, we select some binary stars and reference stars nearby with magnitude 5-8 and angular distance 0.2-4 arcsec in the WDS catalog as observation targets. This article achieved high-resolution restoration of binary stars using a hybrid data processing method, including data reduction, a spatial domain method named ISA or a frequency domain method named SI to suppress atmospheric turbulence, and OS-EM to reduce image degradation caused by multi-aperture interference. The results show that this method can effectively obtain high-resolution images of binary stars, and the measured angular distance is basically consistent with the given value in WDS catalog.
The Fizeau type interferometric telescope forms an array of several sub telescopes for direct imaging on the image plane based on the principle of optical interferometry. Compared to the optical long baseline interferometer, this kind of telescope can be used for real time imaging of celestial body due to some excellent characteristics such as sufficient spatial frequencies coverage, single mounting avoiding outer optical delay lines and so on. We have built an interferometric imaging telescope with four apertures. Although each aperture size is 100mm, but this telescope can reach the higher angular resolution which is equivalent to a monolithic telescope of 280mm aperture size through optimal array configuration. Some novel opto-mechanical structure design and error control methods have been applied to this telescope successfully. For example, in order to enhance the rigidity of mechanical system, a unique C-shape structure to replace the traditional azimuth axis is adapted. Piston, tip/tilt errors between all apertures can be detected at the same time by extracting signals from Modulation Transfer Function (MTF), so some classical beam splitters can be removed which will reduce light loss significantly. At present, we have finished the final assembly, co-phasing calibration and verifying of dynamic co-phasing close-loop methods at laboratory. The FWHM of far field image spot is 0.43 arcsecond which is consistent with theoretical values. The out-door astronomical observation will be carried out soon.
Accurate piston error detection and closed-loop control are one of the key technologies to ensure the imaging quality of the interferometric imaging telescope. In this paper, we proposed a piston error detection and control scheme based on three computers and multithreading,which has been successfully applied to a four 0.1-m apertures interferometric telescope. This scheme adopts a kind of fringe contrast measurement and climbing method to achieve closed-loop control. The results implied that the fringe contrast can be raised through piston closed-loop correction. Compared with a single telescope with 0.1-m aperture, we can get a 2.63x improvement in resolution for the new interferometric telescope with four 0.1-m apertures. It is proved that the feasibility and effectiveness of this scheme. We will further carry out astronomical observation experiments and improve the piston error detection and control scheme, in order to provide technical guarantees for the implementation of interferometric imaging telescopes.
By placing a mask over the pupil of the optical telescope, the aperture masking technique transforms the telescope into a Fizeau interferometry telescope. Thanks to reasonable aperture configuration and baseline rotation techniques, it is possible to achieve almost the same imaging quality as a full aperture telescope. This technique has shown great potential in astrometry and astrophysics research, such as: exoplanet detection, protoplanetary disk, brown dwarf, etc. In order to verify the image restoration algorithm, we carried out binary stars observations on 1.56-m telescope. We presented the numerical simulation of aperture configuration and baseline rotation, and designed the mask and the experimental system. We select some binary stars with magnitude from 5 to 7 and angular distance from 0.2 to 2arcsec as observation targets. Combined with the short exposure observation, a two-step image restoration method is proposed, the results of high-resolution image reconstruction and angular distance measurement are verified. The above results will be applied to the first-generation Fizeau interferometry prototype at the Shanghai Astronomical Observatory (SHAO).
To achieve high-resolution image using optical synthesis aperture telescope, it’s necessary to co-phase accurately of all the telescopes so as to reduce the effect of co-phase errors including piston error, tip/tilt error, and mapping error, etc. Though simulation analysis of the optical system, error sources can be identified and thus save time of alignment. This paper introduces the Fizeau-type Y-4 prototype under development, including the layout of the Y-4 prototype, the layout of the reflective mirrors in the delayed light paths and the beam combiner. With the optical transfer function as the evaluation index, the actual equivalent diameter of Y-4 prototype is calculated. Furthermore, the effect of polarization introduced by coating and polarization differences on the contrast of interference fringe is analyzed. At present, the installation and alignment of the prototype in laboratory have been completed, and the interference synthesis of 4 light paths has been realized. One aim of this paper is to share some experiences in optical design and detection for the development of optical synthetic aperture telescopes. Another aim is to expand these new techniques to the larger optical synthesis aperture telescope project in the future.
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