CCD联合平差方法及其初步实例检验

在常规照相天体测量工作中，对暗天体的定位是采用逐级定标星过渡的方法实现的。由于星表系统差和局部差的存在，最终定位结果可能包含难以把握的误差积累。在CCD小视场观测情况下时常难以找到足够数量的定标星。鉴于此，推导了CCD观测联合平差方法的严格矢量表达式，以期通过共同星的过渡，实现大天区统一平差。原理上此方法可实现相对于河外天体的定位，以削弱星表系统差和局部差对定位结果的影响。讨论了CCD联合平差方法实现中的问题，包括底片常数模型选择、切点位置改正、共同星的较差改正和法方程解算方法等，并分析了具体的处理措施。用实例初步检验了CCD联合平差方法的效果，表明通过对多张CCD观测的联合平差，可以削弱单张CCD观测参考星数目过少、单张CCD观测参考星分布不均、个别参考星存在位置偏差和局部区域参考星存在系统性位置偏差等不利因素对归算结果的影响，进而达到扩大视场和提高归算精度的目的。     

整体平差方法在CCD天体测量中的应用

回顾了基于底片重叠观测的整体平差方法的发展历史和应用概况，分析了该方法应用于底片资料处理没有取得预期效果的原因，介绍了小视场CCD重叠观测的整体平差研究进展．分析与实测资料归算表明，整体平差方法可以在CCD资料处理中充分发挥作用，在保证长焦距、小底片比例尺的同时，通过对CCD重叠观测的整体平差(相当于扩大观测视场)，可覆盖更多的参考星，进而达到改善局部参考架、提高归算结果精度的目的。     

小视场CCD图像的几何定标

针对长焦距望远镜CCD观测天然卫星的情况,导出了用两颗亮星作为定标时,CCD视场几何参数(比例尺和指向)测量的误差公式,进而设计了多定标星定标时正确的归算方案。新方案不仅对天然卫星的位置测量,也对同类型的小视场CCD位置测量具有指导意义。     

CCD漂移扫描观测星表ACR和CMC13的系统误差研究

对2000年前后发表的两部用CCD漂移扫描观测的天体测量星表——ACR(As- trometric calibration regions along the celestial equator)和CMC13(Carlsberg Merid- ian Catalog 13)进行误差分析.通过与UCAC2(The second U.S.Naval Observatory CCD Astrograph Catalog)星表比较,采用数值法,分析了误差的形式和量级大小.并从星表观测方式和数据归算的角度,分析了误差的主要可能来源.发现ACR和CMC13在赤纬方向存在明显的星等差,位置差值随赤经存在与CCD视场大小相近的周期性变化,位置差值随赤纬存在与归算带尺寸大小相近的系统性变化.     

小视场CCD图像的几何定标

针对长焦距望远镜CCD观测天然卫星的情况，导出了用两颗亮星作为定标时，CCD视场几何参数(比例尺和指向)测量的误差公式，进而设计了多定标星定标时正确的归算方案。新方案不仅对天然卫星的位置测量，也对同类型的小视场CCD位置测量具有指导意义。     

土星主要卫星天体测量定标试验

在地面望远镜观测土星主要卫星的精确定位中,目前普遍采用CCD成像技术。为了测量视场中暗卫星的位置,常采用4颗主要卫星(土卫三-土卫六)进行定标。鉴于技术的进步,目前CCD视场正在逐步增加,如何精确定标图像值得研究。利用2010年1月20日在云南天文台1 m望远镜上观测的不同取向的105幅CCD图像进行了试验研究。采用了美国喷气推进实验室土星主要卫星历表和美国海军天文台的UCAC4恒星星表进行计算,相对于不同的参考对象进行定标。结果表明,采用4颗主要卫星进行定标并测量离卫星较近的观测对象时具有较好的测量准确度和内部精度。测量离定标星较远的卫星时,这种定标方法具有较大的不确定性。采用6颗主要卫星(土卫三-土卫八)进行定标,所有卫星的测量结果具有更好的外部和内部符合。即便如此,采用四常数模型和六常数模型定标的结果都不是令人满意,这揭示CCD视场存在明显的扭曲效应。如果采用视场中的恒星定标,卫星的外部符合和内部精度明显变差,这说明UCAC4恒星参考星表也不是理想的定标用参考星表。     

编制子午初始星表的满星平差方法

本文叙述了编制子午初始星表的满星平差方法。即先把所有星的中天观测记录时刻作岁差、章动、光行差和自行的修正后,采用不同观测夜之间的共同星观测值作连接过渡,消除钟差变化的影响;都归算到年首附近某一夜晚相对于年首平位置的观测,再取多次观测的平均、直接解算出对年首平位置的改正值。这种方法不需要采用传统的连锁观测,也不需要在白天进行观测,并打破了定组观测的惯例。     

CCD用于建立惯性坐标系(Ⅴ)——河外星系与亮定标星相对位置的测量试验

本文介绍了试验观测的过程,给出了归算的程序,得到用CCD测定河外星系相对于两颗定标星位置的单次测定精度是±0″.050,中误差是±0″.022,外部符合是±0″.044。从而证明用CCD测量技术,并采用“底片重迭法”,通过两颗定标星来精确测定河外星系的相对位置是可行的。可望以相隔10年左右的两个历元的观测测定出岁差常数改正值。     

Astrometrica与MaxIm DL在天体测量中的应用与技术研究

为探究Astrometrica和MaxIm DL两个软件在天体测量中应用与处理的差异,从软件的总体情况、CCD图像的读写与变换、平场校正、参数设置、归算与堆叠等方面进行了详细的比较和研究。以中国科学院云南天文台1 m光学望远镜拍摄的M35星团的两组观测资料为例,探究了Astrometrica均值、中值和MaxIm DL均值、中值、标准差(Sigma Clip)、迭代标准差(SD Mask)6种图像堆叠方法的输出结果。对上述6种输出结果进行了数据归算,具体参考Gaia DR2星表,比较了6种堆叠方法星像的位置测量精度。研究发现,使用Astrometrica中值堆叠输出的图像在位置精度中存在异常。最后给出了两个软件在天体测量和巡天工作中配合使用的方法。     

CCD整体平差方法的FORTRAN语言归算程序

介绍了实现CCD整体平差的FORTRAN归算程序的详细流程,包括(a)数据收集、(b)预处理和(c)整体平差与结果输出共三个步骤,并给出了各步所调用的子程序名称及其功能说明。采用模拟数据对该程序进行了可靠性检验,并将该程序应用于4颗河外射电源的光学定位。结果表明, 由于利用整体平差方法参加归算的观测资料覆盖天区扩大,包含了较多的参考星,因而可以获得高于单底片归算的定位精度。     

Reduction of micrometer cometary observations to the PPM star catalogue

An adaptation of Bielicki's method of reduction of old cometary micrometer observations of the comet-minus-star type to the PPM star catalogue is presented. A fully automatic utility is described which reduces old positions of stars to the coordinates in the PPM star catalogue for comet-minus-star astrometric observations. The reduction clears observations from systematic errors in old catalogues and decreases the mean error of observations. That may have implications for orbit improvement. The utility predicts new positions of stars in the PPM catalogue as needed and can also restore observations which have been previously rejected due to a selection criterion. It helps to get all data in one, coherent reference frame with maximum possible precision when there are lots of old and new observations of the same object. As an illustration, results of application of the utility to observations of comets 122P/de Vico and 109P/Swift-Tuttle are presented.     

研制低纬子午环初衷的沿革

介绍了在低纬子午环研制过程中，如何跟踪国内外测量方法和科学技术的发展，调整该仪器的主要课题目标：开始时仅计划在低纬度地区进行天体位置的绝对测定，改善基本星表系统；在１ｍ望远镜试验ＣＣＤ底片重迭法成功后，打算把该仪器绝对测定的恒星位置与河外天体联系起来，间接地建立准惯性天球参考架；当国外传统子午环配备ＣＣＤ测微器作相对测量后，提出了在该仪器上配备ＣＣＤ测微器作绝对测定的方法，用其观测数据直接建立实用的准惯性天球参考架，并为太阳系和银河系研究提供有用数据的总体目标。     

Star catalogue in the fields of axial meridian circle of the Nikolaev observatory

On the base of CCD-observations made with the axial meridian circle of the Nikolaev Observatory from 2008 to 2009, we compiled a catalogue for astrometric positions and proper motions for 140321 stars located in an ecliptic zone and around high proper motion stars. The root-meansquare error for a star position is 20–65 mas in right ascension and 30–70 mas in declination. The UCAC2 catalogue is used as a reference for astrometric reductions. To derive stars’ proper motion and to estimate systematic errors of the compiled catalogue, cross-identification of the obtained data with modern astronomic catalogues Tycho2, 2MASS, CMC14, LSPM, PPMX, USNO-A2, and XPM-1.0 is performed. In addition to star position and proper motion, our catalogue contains photometric values B, V, r’, J, H, and K taken from other catalogues.     

Astrometric observations of visual binaries using 26-inch refractor during 2007–2014 at Pulkovo

We present the results of 15184 astrometric observations of 322 visual binaries carried out in 2007–2014 at Pulkovo observatory. In 2007, the 26-inch refractor (F = 10413 mm, D = 65 cm) was equipped with the CCD camera FLI ProLine 09000 (FOV 12′ × 12′, 3056 × 3056 pixels, 0.238 arcsec pixel^?1). Telescope automation and weather monitoring system installation allowed us to increase the number of observations significantly. Visual binary and multiple systems with an angular distance in the interval 1.?1–78.?6 with 7.?3 on average were included in the observing program. The results were studied in detail for systematic errors using calibration star pairs. There was no detected dependence of errors on temperature, pressure, and hour angle. The dependence of the 26-inch refractor’s scale on temperature was taken into account in calculations. The accuracy of measurement of a single CCD image is in the range of 0.?0005 to 0.?289, 0.?021 on average along both coordinates. Mean errors in annual average values of angular distance and position angle are equal to 0.?005 and 0.°04 respectively. The results are available here http://izmccd.puldb.ru/vds.htmand in the Strasbourg Astronomical Data Center (CDS). In the catalog, the separations and position angles per night of observation and annual average as well as errors for all the values and standard deviations of a single observation are presented. We present the results of comparison of 50 pairs of stars with known orbital solutions with ephemerides.     

“Falling Star”: Software for Processing of Double-Station TV Meteor Observations

Software named “Falling Star” has been developed for digital processing of double-station TV meteor observations. It was designed for measurement and calculation of both kinematic and photometric parameters of faint meteors observed with any video system. Data from video recordings are first digitized as standard AVI files, and then converted into the software’s TVS (TV sequence) format. Additional astronomical information like date, time of observations, geographic position of point of the observation and horizontal coordinates of TV camera optical axis orientation are added to the files. These parameters allow the right ascension and declination of the optical center of camera for the moment of meteor flight to be calculated. “Falling Star” includes a range of automated procedures for the identification of frame stars with star catalogues, search of movable meteor-like objects inside frame, calculation of equatorial coordinates and photometry. Finally, meteor trajectory parameters, orbital elements and brightness curves are calculated. Errors of calculations are determined using Monte-Carlo method.     

International program of observations of selected minor planets: first results

International programs of observations of selected minor planets have lasted about 50 years and the last one comes to the end in 2000. The main aim of these observational programs consists in obtaining the orientation of the stellar reference frame with respect to the dynamical one using observations of the bright minor planets. The observations are also useful for the orbital improvements of the asteroids themselves. They are available from the author via e-mail at the address .During the above mentioned period more than 23 000 observations of minor planets, referred to different reference star catalogues, have been obtained. The reduction procedure of observations to the PPM star catalogue is described. The orientation parameters are given and discussed.     

人卫观测中拖长星像的中心定位

提出应用于人造卫星观测中确定拖长星像中心的平均几何中心法 ,介绍了该方法的基本原理与实现步骤。将中值滤波应用于CCD数据的预处理并收到较好的效果。利用实际观测资料初步验证了平均几何中心法 ,结果表明 ,与通常采用的重心法相比 ,此方法对人卫观测中的拖长星像进行中心定位的精度较高。     

Comparison of the four catalogues by pairs,the Hipparcos,new Hipparcos,EOC‐2 and IL,by using μδ for the common 1120 stars

We present comparison results of our Independent Latitude (IL) catalogue of μ_δ determinations for 1120 bright stars with the Hipparcos, new Hipparcos and Earth Orientation Catalogue (EOC‐2) values. Also, we took into consideration the EOC3 and EOC4 (recent versions of EOC catalogues). Our μ_δ values are based on zenith telescope observations from seven Independent Latitude (IL) observatories. The IL measures are spanning a time baseline of up to 90 years which is the key advantage to the accurate determination of μ_δ. The short interval of the Hipparcos satellite observations is a disadvantage for a good accuracy of stellar proper motion, especially in the case of double and multiple stars. For this reason many astrometric catalogues have appeared after the publication of the Hipparcos including our IL catalogue. These catalogues are an appropriate combination of the Hipparcos satellite and ground‐based data which yields more accurate stellar coordinates and/or their proper motions. Among various types of ground‐based observations the latitude and universal time variations obtained from several million observations of stars reduced to the Hipparcos reference system were used for this purpose. These observations were obtained during almost the entire last century and were originally used to determine the Earth Orientation Parameters. It is also possible to use these data in the inverse task of checking the accuracy of stellar coordinates and/or their proper motions listed in the Hipparcos Catalogue. Such latitude and universal time variations data are the basis of the EOC and IL catalogues. In this paper, we computed the differences in μ_δ values between pairs of catalogues and analyzed the results to characterize the μ_δ errors for the four catalogues with a special focus on our IL catalogue. The standard errors of μ_δ for IL stars observed over more than 20 years are mostly smaller than or equal to the Hipparcos errors, and close to the accuracy level of the EOC‐2 (EOC‐3, EOC‐4) and the new Hipparcos. The resulting investigations of errors of differences of μ_δ, show that all four catalogues have relatively small random and systematic errors which are close to each other meaning that the corresponding μ_δ values have a high accuracy. Our sample also contains detected double and multiple stars for which the effects of the orbital and proper motions are difficult to separate. The differences of μ_δ values for these stars generally exceed those obtained for single stars. Also, these discrepancies could be attributed to effect of possible, still unrecognized, astrometric binaries. These investigations about the proper motions and double stars are in line with the activity of the IAU Working Group on Astrometry by Small Ground‐Based Telescopes. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)