The Vignetting Effect of a LAMOST-Type Schmidt Telescope

Optical vignetting of a Schmidt reflector is caused mainly by the spherical primary mirror not being big enough and by the effective light-collecting area of the corrector,which depends on the direction of the star light.Calculations of the vignetting of LAMOST,a special reflecting Schmidt telescope,are made by ray-tracing methods.The results show various features due to LAMOST's structure and observing modes.The un-vignetted field is small compared with its field of view.In the outmost portions of the field vignetting increases rapidly with the distance to the field center.The vignetting at a general position within the field of view is a function of both its distance to the field center and its position angle.Vignetting varies when the telescope points at different declinations and during observations.There is difference in vignetting between direct imaging and multi-fiber spectroscopy.Vignetting distorts the relative intensity of celestial objects at different positions in a field and also affects accurate sky-estimation and sky-subtraction.The determined vignetting functions may be used to correct the vignetting effect; alternatively flat-fielding may be adopted for the calibration.The effective apertures,which affect the signal-to-noise ratio of the observations,depend on the different declinations the telescope is pointing at and also different positions within a field due to vignetting.     

The development of the Schmidt telescope

Bernhard Schmidt (1879–1935) was born in Estonia. After a few years of studying engineering he ran an optical workshop in Mittweida, Saxonia, between 1901 and 1927. Astronomers appreciated the quality of his telescopes. Starting in 1925, on behalf of the Hamburg Observatory, he developed a short focal length optical system with a large field of view. For this purpose, Schmidt moved his workshop to the observatory. He succeeded in inventing the “Schmidt telescope” which allows the imaging of a large field of the sky without any distortions. Schmidt's first telescope (spherical mirror diameter 0.44 m, correction plate 0.36 m diameter, aperture ratio 1:1.75, and focal length 0.625 m) has been used since 1962 at the Boyden Observatory in Bloemfontein/South Africa. Apart from his 0.36m telescope, Schmidt produced a second larger one of 0.60m aperture. Shortly after Schmidt's death, the director of the observatory published details on the invention and production of the Schmidt telescope. After World War II, Schmidt telescopes have been widely used. The first large Schmidt telescope, the “Big Schmidt” (1.26 m), Mount Palomar, USA, was completed in 1948. The 0.80 m Schmidt telescope of Hamburg Observatory, planned since 1936, finished in 1954, is now on Calar Alto/Spain (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An experimental investigation of immersed gratings

A generic problem with spectrographs equipped with conventional diffraction gratings is that the maximum attainable spectral resolution scales inversely with the telescope aperture for a fixed grating dimension and angular slit width. It has long been realized that immersed gratings, where a prism is attached to the surface of a reflection grating, offer a means to bypass this limit. We show how, for the case of the Gemini Multiobject Spectrographs, the maximum spectral resolution may be approximately doubled, or, equivalently, how the same spectral resolution may be obtained with a wider slit, resulting in improved throughput when observing extended objects.
After reviewing the theory of immersed gratings, we present experimental verification of the theory and experimentally quantify two potential drawbacks: reduced throughput at blaze, and ghost images . We show that these effects are small and conclude that the benefits greatly outweigh the disadvantages.     

Exact optics – VI. Schmidt cameras and prime correctors

The methods of exact optics are here extended to cover the design of lens and mirror systems. Power series are given for the shapes of both Schmidt corrector plates and their complementary almost spherical mirrors. Their off-axis images are analysed.
A meniscus glass corrector extends the prime focus field of an f /3.333 reflector with subarcsecond images by a factor greater than 10.     

Field optimization and CCD data simulation for the antarctic International Concordia Explorer Telescope (ICE‐T)

We performed extensive data simulations for the planned ultra‐wide‐field, high‐precision photometric telescope ICE‐T (International Concordia Explorer Telescope). ICE‐T consists of two 60 cm‐aperture Schmidt telescopes with a joint field of view simultaneously in two photometric bandpasses. Two CCD cameras, each with a single 10.3k × 10.3k thinned back‐illuminated device, would image a sky field of 65 square degrees. Given a location of the telescope at Dome C on the East Antarctic Plateau, we searched for the star fields that best exploit the technical capabilities of the instrument and the site. We considered the effects of diurnal air mass and refraction variations, solar and lunar interference, interstellar absorption, overexposing of bright stars and ghosts, crowding by background stars, and the ratio of dwarf to giant stars in the field. Using NOMAD, SSA, Tycho‐2 and 2MASS‐based stellar positions and BVIJH magnitudes for these fields, we simulated the effects of the telescope's point‐spread‐function, the integration, and the co‐addition times. Simulations of transit light curves are presented for the selected star fields and convolved with the expected instrumental characteristics. For the brightest stars, we showed that ICE‐T should be capable of detecting a 2 R_Earth Super Earth around a G2 solar‐type star, as well as an Earth around an M0‐star – if these targets were as abundant as hot Jupiters. Simultaneously, the telescope would monitor the host star's surface activity in an astrophysically interpretable manner (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New Variable Stars Discovered as By-product of the Beijing Astronomical Observatory Supernova Survey

The Beijing Astronomical Observatory (BAO) 0.6 m telescope has been used for nearby supernova survey in more than 3000 fields, covering a total area of 235 deg2. More than 260000 CCD images have been collected since April 1996, with 45 supernovae discovered. We searched for variables in about 90000 images taken during 1996-1998. For the fields in which long period variables (LPVs) were discovered, we reduced further images taken from 1999 to 2000, for the period estimation. Among the 280000 stars selected from the survey fields, i.e., brighter than 18 mag, we discovered seven new LPVs and reconfirmed three known LPVs. Additionally, we found 146 variable star candidates, and reconfirmed about 20 previously known or suspected objects.     

STK: A new CCD camera at the University Observatory Jena

The Schmidt‐Teleskop‐Kamera (STK) is a new CCD‐imager, which is operated since begin of 2009 at the University Observatory Jena. This article describes the main characteristics of the new camera. The properties of the STK detector, the astrometry and image quality of the STK, as well as its detection limits at the 0.9 m telescope of the University Observatory Jena are presented (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Methods and statistics of TV observations of telescopic meteors

A review of TV and telescopic methods of meteor observations and of the problems of meteor astronomy addressed using these methods is presented. A meteor patrol developed at the Astronomical Observatory of Odessa National University and based on a Schmidt telescope and a TV detector is described. The meteor patrol allows meteor events to be recorded with a time resolution of 0.04 s. The investigated characteristics of the patrol are reported, and some aspects of the methods of observations and reduction employed are considered. The results of observations made during the period 2003–2004 are reported. A total of 368 meteors were recorded on 1093 individual frames during a total patrol time of 679 hours within a 36′ × 48′ field of view. The statistical data for meteor observations are reported, and classification of meteor images is presented. The specific features of some recorded meteor events are analyzed.     

基于大视场反卷积的天文图像叠加方法

地基望远镜在成像过程中,由于受大气湍流、望远镜静态像差、跟踪误差、指向误差及视场变化的影响,不同视场区域的PSF (Point Spread Function)具有差异;同时,不同望远镜获取的图像PSF也存在差异.将多个望远镜获取的星象直接叠加至相同的区域后,图像质量受像质最差的望远镜限制,最终观测分辨率和灵敏度均会受到影响.通过图像复原,可以提高图像质量,进而提高叠加效果.根据该思路提出了1种基于PSF分区的迭代图像复原方法:该方法首先通过SOM (Self-organizing Maps)对PSF进行聚类分析,利用同类别PSF的平均PSF进行反卷积,再将反卷积结果按PSF聚类结果分割为不同大小的子图,最后将子图进行拼接.图像复原在提高图像质量的同时,降低了PSF不一致性对图像叠加带来的影响.将几个望远镜在同一时刻获取的图像经反卷积处理之后利用图像配准算法进行矫正并叠加,可获得高信噪比图像.对实际望远镜获取的数据处理后的结果表明:图像在进行复原和叠加过程中,星象目标信噪比不断提升,提高了成像系统对暗星的探测能力.     

Faint UBVRI CCD sequences for wide-field surveys – II. UBVR sequences at δ=−30°

We present results from a continuing campaign to secure deep multi-colour CCD sequences for photometric calibration in UK Schmidt fields with galactic latitudes | b |>50°. In this paper we present UBVR photometry in 12 fields and BR photometry in a further 14 fields observed within UK Schmidt survey fields centred at δ =−30°. Photometric errors are at the 0.05 level at 20.2, 21, 20.5 and 20 mag for UBVR sequences respectively. Our observations were carried out with the 0.9-m telescope at the Cerro-Tololo Inter-American Observatory. These data are not intended for use as highly accurate individual photometric standards, but rather for use as sequences, using a large number of stars to calibrate wide-area data such as photographic plates. The data are available electronically at http://icstar5.ph.ic.ac.uk/~scroom/phot/photom.html .     

Optical monitoring of the quasar 4C 38.41

The results of a photometric monitoring of the quasar 4C 38.41, performed at the optical R and B bands in 2002 February–March, are presented. With a 60/90 cm Schmidt telescope at the Xinglong station of the National Astronomical Observatories of China, we observed the source exhibiting amplitude variations of up to 0.78 mag in both bands during the whole campaign. Intraday and even intranight variations are detected as well. A typical variability time-scale of about 36 d is derived from our 2-month observations at the optical bands, which is identical to that found at a radio wavelength of 92 cm, suggesting a common origin for the variations in 4C 38.41 from optical to radio bands.     

四颗射电源在依巴谷和PPM星表中的光学定位

利用北京天文台施密特望远镜的CCD巡天资料（BATC）中的20次观测,用IRAF软件处理得到星象中心位置,以依巴谷星表和PPM星表作为参考星表,用底片常数法进行处理,得到4颗河外射电源0851 202,1228 126,1442 101,1749 701的光学位置。文中还对所得到的位置与射电位置作了比较。     

Discovery of Three Variable Stars in Direction toward NGC 4565

We present the results of a variable star search in a field next to the edge-on galaxies NGC 4565 from the archive data of Beijing-Arizona-Taibei-Connecticut Multicolor Sky Survey. Three new variable stars were discovered. Based on spectra obtained from the 2.16 m NAOC telescope, we identify two of these as RR Lyr stars and one as a special T Tauri star.     

ULAS J234311.93-005034.0: a gravitational lens system selected from UKIDSS and SDSS

We report the discovery of a new gravitational lens system. This object, ULAS J234311.93-005034.0, is the first to be selected by using the new UKIRT Infrared Deep Sky Survey (UKIDSS), together with the Sloan Digital Sky Survey (SDSS). The ULAS J234311.93-005034.0 system contains a quasar at redshift 0.788 which is doubly imaged, with separation 1.4 arcsec. The two quasar images have the same redshift and similar, though not identical, spectra. The lensing galaxy is detected by subtracting point spread functions from R -band images taken with the Keck telescope. The lensing galaxy can also be detected by subtracting the spectra of the A and B images, since more of the galaxy light is likely to be present in the latter. No redshift is determined from the galaxy, although the shape of its spectrum suggests a redshift of about 0.3. The object's lens status is secure, due to the identification of two objects with the same redshift together with a lensing galaxy. Our imaging suggests that the lens is found in a cluster environment, in which candidate arc-like structures, that require confirmation, are visible in the vicinity. Further discoveries of lenses from the UKIDSS survey are likely as part of this programme, due to the depth of UKIDSS and its generally good seeing conditions.     

Herbig-Haro objects—tracers of the formation of low-mass stars and sub-stellar objects

Herbig-Haro objects (HHOs) are caused by outflows from young objects. Since the outflow relies on mass accretion from a circumstellar disk, it indicates ongoing growth. Recent results of infrared observations yielded evidence for disks around brown dwarfs. This suggests that at least a certain fraction of brown dwarfs forms like stars. Thus, young sub-stellar objects might cause HHOs as well. We present selected results of a general survey for HHOs based on DSS-II plates and CCD images taken with the Tautenburg Schmidt telescope. Numerous young objects could be identified due to their association with newly detected HHOs. In some cases the luminosity is consistent with very low-mass stars or close to sub-stellar values. This holds for L1415-IRS and a few infrared sources embedded in other dark clouds (e.g., GF9, BHR111). The question on the minimum mass for outflow activity is addressed.     

图像移位堆叠方法用于暗天然卫星的天体测量

暗弱天然卫星与主带小行星相比,具有亮度低、速度变化快的特点.在观测这类天体时,不能简单地延长曝光时间来提高其信噪比.尝试观测多幅短曝光的CCD (chargecoupled device)图像,采用移位堆叠(shift-and-add)方法,希望提高目标成像的信噪比,获得暗弱天然卫星的精确测量结果.使用2018年4月9—12日夜间,中国科学院云南天文台1 m望远镜(1 m望远镜)拍摄的木星5颗暗卫星的229幅CCD图像,实施了移位堆叠试验.为了验证结果的正确性,与相近日期中国科学院云南天文台2.4 m望远镜(2.4 m望远镜)观测的相同木卫图像的测量结果进行了比较和分析.位置归算采用了JPL (Jet Propulsion Laboratory)历表.结果表明,对CCD图像使用移位堆叠方法,通过叠加约10幅曝光时间100 s的图像, 1 m望远镜能观测暗至19等星的不规则天然卫星,而且测量的准确度与2.4 m望远镜的测量结果有良好的一致性.     

Verwendbarkeit des Prismas auf der Korrektionsplatte des Tautenburger Schmidt-Spiegels bei Positionsbestimmungen

To overcome a possible magnitude equation a weakly refracting prism fitted on the correcting plate of the Tautenburg Schmidt telescope was used, forming a secondary image of every object 3.8 mag weaker than the primary one. Because the distances between these two images are not constant, a polynomial was searched which could reflect these variation in dependence on the magnitude of a star and its position on the plate. For each of the 11 plates tested we have got another polynomial, therefore this way to tide over large magnitude differences is unefficient for astrometric investigations.     

Submillimetre observations of luminous z>4 radio-quiet quasars and the contribution of AGN to the submm source population

We present polarization observations of the gravitational lens system B1422+231 made at 8.4 GHz using the VLBA and the 100-m telescope at Effelsberg. All four images of the quasar show structure on the milliarcsec scale. The three bright images show tangential stretching as expected from lens models. Some basic properties of gravitational lensing are exhibited by this system. The surface brightness of images A and B are the same and the parity reversal expected in image B is revealed, for the first time, by polarization observations. There is a large differential Faraday rotation between images A and B.     

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.     

A photometric study of poor clusters of galaxies

Sixteen poor clusters of galaxies with suspected cD galaxies are studied usingV-band photographs taken with the 105 cm Kiso Schmidt telescope. Galaxian images were automatically detected using an image detection software developed for the present study. It is found from the luminosity functions that the richness of the clusters are well correlated with the optical properties of central galaxies and the X-ray luminosities of the clusters.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.