A new type optical fiber T.V. adaptor-link between telescope and spectrography

A new type of optical fiber T.V. adaptor-link device is developed to bring a star image at the focus of a Schmidt telescope to the slit of a spectrograph located at the observing floor, as well as part of the field, to a T.V. monitor for acquisition and guiding purposes. The device is constructed by 60 000 thin glass fibers (18 micron in diameter and 1.2 m in length) used as the adaptor, and a single long (20 m) thicker (25 micron core diameter) fused silica fiber used as the link between the telescope and the spectrograph. The 60 000 thin fibers are arranged in a 4 by 5 mm rectangular array with the link built in the center of the field. With the adaptor-link the astronomer can easily acquire the star on the T.V. monitor, transfer the star image through the link to the slit of the spectrograph and guide the star during observation.     

Studying focal ratio degradation of optical fibres with a core size of 50 μm for astronomy

Along with the spectral attenuation properties, the focal ratio degradation (FRD) properties of optical fibres are the most important for instrumental applications in astronomy. We present a special study about the FRD of optical fibres with a core size of 50 μm to evaluate the effects of stress when mounting the fibre. Optical fibres like this were used to construct the Eucalyptus integral field unit. This fibre is very susceptible to the FRD effects, especially after the removal of the acrylate buffer. This operation is sometimes necessary to allow close packing of the fibres at the input to the spectrograph. Without the acrylate buffer, the protection of the cladding and core of the fibre may be easily damaged. In the near future, fibres of this size will be used to build the Southern Observatory for Astronomical Research (SOAR) integral field unit spectrograph (SIFS) and other instruments. It is important to understand the correct procedure which minimizes any increase in FRD during the construction of the instrument.     

观测天体光谱的纤维光学方法及2.16m望远镜实用系统

本文描述了近年来广泛发展起来的天体物理实测技术中的一项重要进展——纤维光学分光技术方法在天体光谱观测中的应用及2.16m望远镜实用系统的特点和初步应用结果     

光干涉与综合孔径技术发展

回顾了光干涉与综合孔径技术发展的历史和现状，分析了国际上用于天文观测的一些著名地基和空基光干涉仪的技术特点，介绍了光干涉与综合孔径技术的发展，以及在光学综合孔径技术领域所发展的光纤与集成光学等新技术，简要介绍了近年来我国开展光干涉与综合孔径技术的进展情况。针对光干涉与综合孔径技术的发展前景和国内外技术发展趋势，发出了加快发展我国光干涉与综合孔径技术的呼吁。     

The Atacama Large Millimeter/Submillimeter Array: overview & status

The Atacama Large Millimeter/Submillimeter Array (ALMA) is an international millimeter-wavelength radio telescope under construction in the Atacama Desert of northern Chile. ALMA will be situated on a high-altitude site at 5000 m elevation which provides excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will be comprised of two key observing components—a main array of up to sixty-four 12-m diameter antennas arranged in a multiple configurations ranging in size from 0.15 to ∼18 km, and a set of four 12-m and twelve 7-m antennas operating in a compact array ∼50 m in diameter (known as the Atacama Compact Array, or ACA), providing both interferometric and total-power astronomical information. High-sensitivity dual-polarization 8 GHz-bandwidth spectral-line and continuum measurements between all antennas will be available from two flexible digital correlators. At the shortest planned wavelength and largest configuration, the angular resolution of ALMA will be 0.005″. The instrument will use superconducting (SIS) mixers to provide the lowest possible receiver noise contribution, and special-purpose water vapor radiometers to assist in calibration of atmospheric phase distortions. A complex optical fiber network will transmit the digitized astronomical signals from the antennas to the correlators in the Array Operations Site Technical Building, and post-correlation to the lower-altitude Operations Support Facility where the array will be controlled, and initial construction and maintenance of the instrument will occur. ALMA Regional Centers in the US, Europe, Japan and Chile will provide the scientific portals for the use of ALMA; early science observations are expected in 2010, with full operations in 2012.     

Optical fibers in astronomical instruments

Summary This review is of current and projected applications of optical fibers to observational astronomy. The intent is to provide astronomers with a broad perspective on the subject, with the hope of encouraging productive use of optical fibers in the design of new instrumentation. The unique characteristics of fibers have been (or soon will be) exploited to advantage in several areas of astronomical instrumentation, including multiplexers for muti-object spectrographs, remote optical feeds for spectrographs and photometers, coherent beam recombiners for optical interferomety, and many miscellaneous applications. We discuss the most important such applications in detail, with reference to operational instruments wherever possible, and with emphasis on the optical properties of fibers and the engineering considerations encountered in their application to observational astronomy.     

Infrared reflectance spectroscopy on thin films: Interference effects

Laboratory simulations of processes on astronomical surfaces that use infrared reflectance spectroscopy of thin films to analyze their composition and structure often ignore important optical interference effects which often lead to erroneous measurements of absorption band strengths and give an apparent dependence of this quantity on film thickness, index of refraction and wavelength. We demonstrate these interference effects experimentally and show that the optical depths of several absorption bands of thin water ice films on a gold mirror are not proportional to film thickness. We describe the method to calculate accurately band strengths from measured absorbance spectra using the Fresnel equations for two different experimental cases, and propose a way to remove interference effects by performing measurements with P-polarized light incident at Brewster's angle.     

Attempt to assess astronomical “seeing” using a model

The degradation of astronomic images by optical inhomogeneities in the earth's atmosphere is generally called seeing. It represents the angular diameter of the stellar images as seen through a turbulent medium. Several techniques can be used to determine this parameter. The knowledge of the optical strength of atmospheric turbulence, namely, the integrated structure coefficient of the atmospheric refractive index C_n ² allows to predict the atmospheric optical quality in terms of seeing. We tried in this study to assess an astronomical seeing using a model forecast using meteorological data collected in three stations in Latin America from 1958 to 1991. The efficiency of the model is tested by comparison with simultaneous seeing measurements, at Chiliean astronomical sites.     

Fine Structure of Solar Radio Bursts Observed at Decametric and Hectometric Waves

The analysis of WIND/WAVES RAD2 spectra with fine structure in the form of different fibers in 14 events covering 1997?–?2005 is carried out. A splitting of broad bands of the interplanetary (IP) type II bursts into narrow band fibers of different duration is observed. The instantaneous-frequency bandwidth of fibers is stable: 200?–?300 kHz for slow-drifting fibers in type II bursts, and 700?–?1000 kHz for fast-drifting fibers in type II?+?IV (continuum). Intermediate drift bursts (IDB or fiber bursts) and zebra patterns with variable frequency drift of stripes, typical for the metric range, were not found. Comparison of spectra with the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO C2) images shows a connection of the generation of the fiber structures with the passage of shock fronts through narrow jets in the wake of Coronal Mass Ejections (CME). Therefore the most probable emission mechanism of fibers in IP type II bursts appears to be resonance transition radiation (RTR) of fast particles at the boundary of two media with different refractive indices. The same mechanism is also valid for striae in the type III bursts. Taking into account a high-density contrast in the CME wake and the actually observed small-scale inhomogeneities, the effectiveness of the RTR mechanism in IP space must be considerably higher than in the meter or decimeter wavelengths. For the most part the fibers in the type IV continuum at frequencies of 14?–?8 MHz were seen as the direct expansion of similar fine structure (as fibers or “herringbone” structure) in the decametric range observed with the Nançay and IZMIRAN spectrographs.     

An investigation of collisions between fiber positioning units in LAMOST

The arrangement of fiber positioning units in the LAMOST focal plane may lead to collisions during the fiber allocation process. To avoid these collisions, a software-based protection system has to abandon some targets located in the overlapping field of adjacent fiber units. In this paper, we first analyze the probability of collisions between fibers and infer their possible reasons. It is useful to solve the problem of collisions among fiber positioning units so as to improve the efficiency of LAMOST. Based on this, a collision handling system is designed by using a master-slave control structure between the micro control unit and microcomputer. Simulated experiments validate that the system can provide real-time inspection and swap information between the fiber unit controllers and the main controller.     

30m环形干涉望远镜

简要介绍了云南天文台对下一代地面大型天文光学望远镜进行的初步研究，依据这些研究结果我们提出研制一个新概念的大型地面望远镜：30m环形干涉望远镜（Ringy Interferometric Telescope），它既有单口径望远镜那样的直接成像能力和分辨率，又可以进行综合孔径模式的高分辨率成像，该计划显著地不同于经典的地面大型望远镜，对其中关键技术的研究正在积极进行之中。     

Blind Deconvolution of Astronomical Images with a Constraint on Bandwidth Determined by the Parameters of the Optical System

Atmospheric turbulence severely restricts the spatial resolution of astronomical images obtained by a large ground-based telescope. In order to reduce effectively this effect, we propose a method of blind deconvolution, with a bandwidth constraint determined by the parameters of the telescope's optical system based on the principle of maximum likelihood estimation, in which the convolution error function is minimized by using the conjugate gradient algorithm. A relation between the parameters of the telescope optical system and the image's frequency-domain bandwidth is established, and the speed of convergence of the algorithm is improved by using the positivity constraint on the variables and the limited-bandwidth constraint on the point spread function. To avoid the effective Fourier frequencies exceed the cut-off frequency, it is required that each single image element (e.g., the pixel in the CCD imaging) in the sampling focal plane should be smaller than one fourth of the diameter of the diffraction spot. In the algorithm, no object-centered constraint was used, so the proposed method is suitable for the image restoration of a whole field of objects. By the computer simulation and by the restoration of an actually-observed image of α Piscium, the effectiveness of the proposed method is demonstrated.     

An Optical Intermediate Dispersion Spectrograph for the GTC

ODIN is an international consortium constituted to design and build a first-light multi-purpose optical intermediate dispersion spectrograph for the Gran Telescopio Canarias (GTC, 10-m) to be installed at the Observatorio del Roque de los Muchachos (La Palma). This instrument should fulfill an important fraction of the needs of the Spanish astronomical community in optical spectroscopy performed at large telescopes, and must be highly competitive in a variety of research fields. We are proposing a spectrograph that will be capable of providing multi-object observations by means of optical fibers, integral field spectroscopy, and also multi-integral fields. It will be mounted at the Nasmyth focus of the GTC. One of the main drivers of our proposal is to cover the whole visible range allowed by the atmospheric cut-off with the highest efficiency, particularly at the UV end. This revised version was published online in July 2006 with corrections to the Cover Date.     

A method to measure the mirror reflectivity of a prime focus telescope

We have developed a method to measure the mirror reflectivity of telescopes. While it is relatively easy to measure the local reflectivity of the mirror material, it is not so straightforward to measure the amount of light that it focuses in a spot of a given diameter. Our method is based on the use of a CCD camera that is fixed on the mirror dish structure and observes simultaneously part of the telescope’s focal plane and the sky region around its optical axis. A white diffuse reflecting disk of known reflectivity is fixed in the telescopes focal plane. During a typical reflectivity measurement the telescope is directed to a selected star. The CCD camera can see two images of the selected star, one directly and another one as a spot focused by the mirror on the white disk. The ratio of the reflected starlight integrated by the CCD from the white disk to the directly measured one provides a precise result of the product of (mirror area × mirror reflectivity).     

The Astrometric Telescope Facility

Summary The Astrometric Telescope Facility (ATF) proposed for use on NASA's planned Space Station is similar in form and data output to ground-based long focus astrometric instruments. With a focal plane scale of 12.7 arc seconds/mm, the strawman design has a field size of 10 arc min square and a limiting visual magnitude fainter than 16. Output from an observation includes the X and Y coordinates of each star and its relative brightness. The targeted precision for the AFT is 0.00001 arc seconds.Portions of the observing program will be made available to members of the astronomical community.     

天文光子学研究现状及其应用展望

天文学是一门观测学科, 其发展受观测技术及仪器进步所推动, 而天文科学发展同样不断对观测仪器提出新的要求. 天文学发展至今, 对观测仪器的要求逐渐走向极致和极端, 这在实现成本及难度两方面均带来极大挑战. 为应对上述挑战, 基于新原理、新技术的下一代天文光学技术及观测仪器已成为天文学发展的内在需要. 近年来, 集成光子学的发展为天文光学技术带来了新的变革性机遇, 在此基础上产生的新兴交叉学科天文光子学(Astrophotonics)可为天文观测提供低成本、高度集成化(芯片化)的新一代高性能光学终端仪器, 这类仪器将在空间天文观测、大规模光谱巡天、高分辨高精度光谱成像等应用中起到关键作用. 主要从仪器/器件功能出发介绍天文光子学主要研究内容及现状, 并简要讨论其发展所面临的主要问题, 最后对其发展趋势做出展望.     

基于光学辅助指向测量的太赫兹望远镜指向误差模型研究

针对太赫兹波段天文点源目标较少, 指向测量相对困难的特点, 研究了利用与太赫兹天线共轴的小型光学望远镜来辅助太赫兹望远镜指向测量以及建立指向误差修正模型的方法. 依托紫金山天文台1.2 m斜轴式太赫兹天线开展了光学辅助指向测量的实验研究, 利用一台安装在天线背架上的100mm口径折射式光学望远镜获得了优于2$''$的指向测量精度. 此外, 通过对斜轴天线的结构分析以及大气折射和本地恒星时(Local Sidereal Time, LST)偏差等误差来源的分析, 建立了包含23个误差项的斜轴式光学指向修正模型, 实现了约3$''$的拟合精度. 最后, 借助高精度数字摄影测量对光电轴一致性进行了标定, 并针对其对指向模型精度的影响进行了讨论. 研究成果将为南极5 m太赫兹望远镜(The 5m Dome A Terahertz Explorer, DATE5)及其他太赫兹望远镜提供指向测量和指向修正模型方面的技术参考.     

Research Status and Application Prospects of Astrophotonics

Astronomy is an observational discipline, and its improvement is driven by the progress of observation technology and instruments. The advancement of astronomy also constantly puts forward new requirements for observation instruments. Since the development of astronomy, the requirements for observing instruments have gradually become extreme, which brings great challenges in both cost and difficulty. In order to tackle the challenges, a future generation of astronomical optical technology and observation instruments based on new principles and technologies has become an inherent need to promote the advancement of astronomy. In recent years, the growth of integrated photonics has presented revolutionary opportunities for that of astronomical optical technology. On the basis, astrophotonics, an emerging interdisciplinary subject, can provide a new generation of high-performance optical terminal instruments with low cost and high integration (chip-based) for astronomical observation. Such instruments will play a vital role in space astronomical observation, large-scale spectral survey, high-resolution and high-precision spectral imaging, and other applications. This paper mainly introduces the main research contents and status quo of astronomical photonics starting from the instruments/device functions, briefly discusses the major problems in its development, and eventually forecasts its development prospect.     

IFU Unit in Scorpio-2 Focal Reducer for Integral-Field Spectroscopy on the 6-m Telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences

We describe the scheme and design features of the new IFU unit (Integral Field Unit) meant to perform integral-field spectroscopy as a part of SCORPIO-2 focal reducer, which is mounted in the prime focus of the 6-m telescope of the Special Astrophyscial Observatory of the Russian Academy of Sciences. The design of the unit is based on the principle of the formation of array spectra using a lens raster combined with optical fibers. The unit uses a rectangular raster consisting of 22×22 square 2-mm diameter lenses. The image of the object is transferred by an optical system with a 23^× magnification from the focal plane of the telescope to the plane of the lens raster. The image scale is —0.″75/lens and the field of view of the instrument has the size of 16.″5 × 16.—5². The raster also contains two extra 2 × 7 lens arrays to acquire the night-sky spectra whose images are offset by ±3′from the center. Optical fibers are used to transform micropupil images into two pseudoslits located at the IFU collimator entrance. When operating in the IFU mode a set of volume phase holographic gratings (VPHG) provides a spectral range of 4600–7300 Å and a resolution λ/δλ of 1040 to 2800. The quantum efficiency of SCORPIO-2 field spectroscopy is 6–13% depending on the grating employed.We describe the technique of data acquisition and reduction using IFU unit and report the results of test observations of the Seyfert galaxyMrk 78 performed on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences.     

Development of the Automatic Seeing Monitor for the Site Testing of Dome A

The Antarctic site-testing campaigns have shown that Dome C is an excellent astronomical site on the earth, it is better than any of existing mid-latitude astronomical sites in the world, because of its cold and dry weather, low infrared background radiation, continuously observable time as long as 3–4 months, clear and highly transparent atmosphere, low wind speed, and the absence of dust and light pollution. And in the international astronomical community it is generally believed that Dome A with a higher altitude may be better than Dome C as a potential excellent astronomical site. In the past 3 years, although held by the Center for Antarctic Astronomy of Chinese Academy of Sciences, the site testing at Dome A has preliminarily con?rmed the many advantages of Dome A as an excellent astronomical site, but the data about the atmospheric seeing, which is an important parameter for assessing the site quality for optical observations, have not been obtained until now. Hence, on the basis of a commercial telescope with the diameter of 35 cm, we have made the hardware reformation and software development to have it operate as a DIMM (Differential Image Motion Monitor), which can simultaneously monitor both the seeing and isoplanatic angle at Dome A automatically. At present this instrument has been shipped to Antarctica by the “Xuelong” exploration ship, and will be installed at Dome A, and begin to work in early 2011. Before the shipment, by through the comparative measurements together with an existing seeing monitor at the Xinglong astronomical station, the software, hardware, as well as the installation and adjustment of the instrument, are further veri?ed by testing.