利用大视场测光系统评估观测天气质量

介绍一种利用大视场测光系统对观测天气质量进行评估的统计方法。此方法可以给出大气透明度、背景天光、视宁度和观测极限星等等多种与天观测有关的天气质量参数。通过检验证明,此方法可提供一处天气状况的实时监视方法,对北京天台施密特ＣＣＤ测光系统以及制定观测计划的评估观测质量有重要意义。     

兴隆60 cm望远镜主焦CCD系统测光性能的研究

对兴隆６０ｃｍ望远镜主焦ＣＣＤ系统的测光性能进行了测试和研究．测定了ＣＣＤ快门时间函数,讨论了快门延迟效应对短时间曝光观测的可能影响．通过观测大批Ｌａｎｄｏｌｔ标准星,较准确地定出了ＢＶＲＩ宽带测光的星等系统转换关系,结果表明本系统与标准ＢＶＲＩ系统很接近．对ＣＣＤ系统的天文测光精度作了仔细的检验和分析,并对ＰＳＦ拟合测光和孔径测光两种方法进行了比较     

兴隆60cm望远镜主焦CCD系统测光性能的研究

对兴隆６０ｃｍ望远镜主焦ＣＣＤ系统的测光性能进行了测试和研究,测定了ＣＣＤ快门时间函数,讨论了快门延迟效应对短时间曝光观测的可能影响,通过观测大批Ｌａｎｄｏｌｔ标准星,较准确地定出了ＢＶＲＩ宽带测光的星等系统转换关系,结果表明本系统与标准ＢＶＲＩ系统很接近,对ＣＣＤ系统的天文测光精度作了仔细的检验和分析,工对ＰＳＦ拟合测光和孔径测光两种方法进行了比较。     

吉林280mm全天区可转动光电阵测光精度评估研究

位于吉林天文观测基地的280 mm全天区可转动光电阵是一台用于空间碎片巡天观测的设备。为了研究该设备的光度测量性能,评估其测光精度,选择M67疏散星团中的测光标准星进行观测。首先,在IRAF(Image Reduction and Analysis Facility)中对观测图像进行预处理,之后进行较差测光;接着,提取测光数据并将整晚观测数据进行最小二乘直线拟合,拟合结果给出了主消光系数及相应的系统转换系数,并得到仪器星等至标准星等的转换公式;最后,利用计算得到的均方根误差对设备的测光精度进行大致评估。计算结果表明,在标准测光夜测量亮于13.8 mag时,280 mm全天区可转动光电阵的测光精度可达0.13 mag。同时将观测图像与UCAC2星表匹配识别,利用背景恒星中的UCAC2标准星做外符合精度的校验,结果与前者基本相同。本设备的测光精度基本满足空间碎片巡天观测的要求。     

彗星的CCD成像观测

近年来，对一系列彗星进行的宽带或带ＣＣＤ测光得到了许多有趣的结果，为深入地理解彗星的物理性质，结构，起源和演化等提供了丰富的信息。文中简要地介绍了利用ＣＣＤ成像观测在测量彗核的自转，大小，开头，质量和研究彗核的活动以及彗发的形成和演化等方面的进展。     

云南天文台1m望远镜卡焦(缩焦)CCD测光系统的初步研究

用云台１ｍ望远镜镜卡焦（缩焦）ＣＣＤ测光系统对测光标准星进行了ＢＶＲＩ四色测光,计算得到了该系统的转换方程及其转换结果,并对计算结果进行了分析讨论．     

空间碎片观测中拖长星像的测光

提出空间碎片观测中对拖长背景恒星的测光算法,介绍了该方法的基本原理.利用迭代法对目标图像进行局部阈值分割提取,得到的二值图像通常包含多个连通域.最后对各连通域块检测判断,计算出目标的星等,达到测光的目的.通过与天文图像和数据处理软件IRAF的测光结果对比,此算法的误差在0.02mag左右,可以达到测光的要求.     

恒星光电测光观测数据的处理

简要地阐述了恒星光电测光工作中的常规数据处理方法及应该注意的一些问题。对食双星光电测光这一领域的观测数据处理进行了概述,给出了ＢＶ双色光电测光观测数据处理软件包的编程思想及具体实现。最后介绍了这个软件包的使用情况和结果。     

Blazars天体的多波段的理论研究

在收集大量资料的基础上,较为全面的综述了Ｂｌａｚａｒｓ天体的基本观测特征,给出了目前较为完整的ＢＬＬａｃ天体总表。对该类天体的相关理论,多波段相关性,光变周期分析,Ｈｕｂｂｌｅ关系,ＢＬＬａｃ天体的偏振度的变化作了一定研究。并介绍了我们用ＣＣＤ测光和光谱对３Ｃ３４５作准同时性观测的结果,我们讨论了３Ｃ３４５的历史光变曲线和光变周期分析,研究结果表明：３Ｃ３４５具有（１０±０．８）ａ（年）的光变周期,其中心有一个１０６Ｍ⊙的黑洞。Ｊｕｒｋｅｖｉｃｈ方法是一种Ｂｌａｚａｒｓ天体的光变周期分析研究的好方法     

UBV光电测光系统的转换方程和精度比较

根据对鬼星团中Ｊｏｈｎｓｏｎ测光标准星的观测，我们研究了北京天文台６０ｃｍ望远镜直流光电光度计ＵＢＶ测光系统的转换方程．应用该方程推算了对三颗变星观测得到的ＵＢＶ星等，讨论了所得光变曲线的精度，并与较差方法所得结果进行了比较     

Sky subtraction for LAMOST

Sky subtraction is a key technique in data reduction of multi-fiber spectra. Knowledge of characteristics related to the instrument is necessary to determine the method adopted in sky subtraction.In this study, we describe the sky subtraction method designed for the Large sky Area Multi-Object fiber Spectroscopic Telescope(LAMOST) survey. The method has been integrated into the LAMOST 2D Pipeline v2.6 and applied to data from LAMOST DR3 and later. For LAMOST, calibration using sky emission lines is used to alleviate the position-dependent(and thus time-dependent) ~ 4% fiber throughput uncertainty and small wavelength instability(0.1 A) during observation. Sky subtraction using principal component analysis(PCA) further reduces 25% of the sky line residual from OH lines in the red part of LAMOST spectra after the master sky spectrum, which is derived from a B-spline fit of 20 sky fibers in each spectrograph. Using this approach, values are adjusted by a sky emission line and subtracted from each fiber. Further analysis shows that our wavelength calibration accuracy is about 4.5 km s~(-1), and the averages of residuals after sky subtraction are about 3% for sky emission lines and 3% for the continuum region. The relative sky subtraction residuals vary with moonlight background brightness, and can reach as low as 1.5% for regions that have sky emission lines during a dark night.Tests on F stars with both similar sky emission line strength and similar object continuum intensity show that the sky emission line residual of LAMOST is smaller than that of the SDSS survey.     

一种基于主分量分析的减天光方法

天光是天体观测中的一种重要噪声源.减天光问题是制约多目标光纤光谱观测深度的重要因素.主分量分析(PCA)是统计学的一种分析方法,它可以用来寻找各个天光谱之间的关系,以进一步获得目标光谱中含有的天光成分.为了研究LAMOST的减天光方法,用SDSS的一组原始观测数据进行了仿真实验,实验结果表明,采用PCA方法比SDSS处理程序能够更有效地减天光.最后对PCA方法在LAMOST中的应用前景进行了展望.     

Eigenvector Sky Subtraction

We develop a new method for estimating and removing the spectrum of the sky from deep spectroscopic observations. Our method does not rely on simultaneous measurement of the sky spectrum with the object spectrum. The technique is based on the iterative subtraction of continuum estimates and eigenvector sky models derived from singular value decompositions of sky spectra and sky spectra residuals. Using simulated data derived from small-telescope observations, we demonstrate that the method is effective for faint objects on large telescopes. We discuss simple methods to combine our new technique with the simultaneous measurement of sky to obtain sky subtraction very near the Poisson limit.     

Wavelength calibration by combining arc and night sky lines for LAMOST

A novel method is presented for the wavelength calibration of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). The proposed method combines the arc lines and night sky lines, and can achieve high performance. Firstly, the initial wavelength calibration is performed by employing arc lines. Afterwards, the centroids of sky lines are calculated by the initial calibration results and adjusted by the gravity method iteratively. Finally, the ultimate wavelength calibration is obtained by fitting the centroids of arc lines and sky lines with their corresponding wavelengths. Experiments are performed on the data observed by LAMOST, and the results of the proposed method are more accurate than that of the calibration only by arc lines or sky lines. The calibration sky lines are dense in the red channel (5,700–9,000 Å) of LAMOST, but only a few ones are in the blue channel (3,700–5,900 Å). The new method achieves excellent results in the red channel as the substantial sky lines are employed, and the calibration accuracy of the blue channel is also enhanced in some degree by the scare sky lines.     

Detection of Leonids meteoric dust in the upper atmosphere by polarization measurements of the twilight sky

A new method for the meteoric dust detection in the upper atmosphere based on the polarimetric observations of the twilight sky is proposed. Polarization measurements are effective for detection of the meteoric dust scattering on the background consisting basically of troposphere multiple scattering. The method is based on the observed and explained polarization properties of the sky background during different stages of twilight. It is used to detect the mesosphere dust after the Leonids maximum in 2002, estimate its altitude range and to investigate its evolution—slow decrease of the altitude. The polarization method takes into account the multiple scattering and sufficient contribution of moonlight scattering background and turns out to be more sensitive than existing analogs used in the present time.     

The artificial night sky brightness mapped from DMSP satellite Operational Linescan System measurements

We present a method to map the artificial sky brightness across large territories in astronomical photometric bands with a resolution of approximately 1 km. This is of use in quantifying the situation regarding night sky pollution, recognizing potential astronomical sites and allowing future monitoring of trends. The artificial sky brightness present in the chosen direction at a given position on the surface of the Earth is obtained by the integration of the contributions produced by every surface area in the surroundings . Each contribution is computed via detailed models for the propagation in the atmosphere of the upward light flux emitted by the area. The light flux is measured with top-of-atmosphere radiometric observations made by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System.
We have applied the described method to Europe, obtaining maps of artificial sky brightness in the V and B bands.     

Near-infrared sky background fluctuations at mid- and low latitudes

The emission of the upper atmosphere introduces an additional variable component into observations of astronomical objects in the NIR 700–3,000 nm range. The subtraction of this component is not easy because it varies during the night by as much as 100% and it is not homogeneous over the sky. A program aimed at measuring and understanding the main characteristics of the atmospheric NIR emission was undertaken. A 512?×?512 CCD camera equipped with a RG780/2 mm filter is used to obtain images of the sky in a 36°?×?36° field of view. The intensities of a given star and of the nearby region devoid of star in a 439 arcmin² area are monitored during periods of time of several hours. The sky intensity measured in the 754–900 nm bandpass, reduced to zenith and zero airmass is comprised between mag20 and mag18.5 per arcsecond². A diminution by a factor of two during the night is frequently observed. Intensity fluctuations having an amplitude of 15% and periods of 5–40 min are present in the images with a structure of regularly spaced stripes. The fluctuations of the NIR sky background intensity are due to (1) the chemical evolution of the upper atmosphere composition during the night and (2) dynamical processes such as tides with periods of 3–6 h or gravity waves with periods of several tens of minutes. We suggest that a monitoring of the sky background intensity could be set up when quantitative observations of astronomical objects require exposure times longer than ~10 min. The publication is illustrated with several video films accessible on the web site http://www.obs-besancon.fr/nirsky/. Enter username: nirsky and password: skynir.     

Using a New Sky Brightness Monitor to Observe the Annular Solar Eclipse on 15 January 2010

For the future development of Chinese Giant Solar Telescope (CGST) in Western China, a new sky brightness monitor (SBM) has been produced for the site survey for CGST. To critically examine the performance and sensitivity of SBM, we used it in the observation of the annular solar eclipse in Dali City, Yunnan, on 15 January 2010. The observation met good weather conditions with an almost clear sky during the eclipse. The SBM measurement translates into the solar illuminance changes at a level of 2.4×10^?4 I?s^?1 during the eclipse. The time of the minimal sky brightness in the field of view (FOV) is found consistent with the time of maximum eclipse. Two local sky regions in the FOV are chosen to make a time series of the calibrated skylight profiles. The evolution of the sky brightness thus calibrated also shows good consistency with the eclipse, particularly between the second and the third contacts. The minimal sky brightness in each local sky region took place within half a minute from the corresponding predicted contact time. Such small time delays were mainly caused by occasional cirri. The minimal sky brightness measured during the eclipse is a few millionths of I _?? with standard deviation of 0.11 millionths of I _??. The observation supports that the single-scattering process (optically thin conditions) is the main contributor to the atmospheric scattering. We have demonstrated that many important aerosol optical parameters can be deduced from our data. We conclude that the new SBM is a sensitive sky photometer that can be used for our CGST and coronagraph site surveys.     

A hybrid Fast Multipole Method for cosmological N-body simulations

We investigate a hybrid numerical algorithm aimed at large-scale cosmological N-body simulation for on-going and future high precision sky surveys.It makes use of a truncated Fast Multiple Method(FMM)for short-range gravity,incorporating a Particle Mesh(PM)method for long-range potential,which is applied to deal with extremely large particle number.In this work,we present a specific strategy to modify a conventional FMM by a Gaussian shaped factor and provide quantitative expressions for the interaction kernels between multipole expansions.Moreover,a proper Multipole Acceptance Criterion for the hybrid method is introduced to solve potential precision loss induced by the truncation.Such procedures reduce the amount of computation compared to an original FMM and decouple the global communication.A simplified version of code is introduced to verify the hybrid algorithm,accuracy and parallel implementation.     

全天相机在多设备巡天中的应用

天文观测站夜天空星像星等信息和天区分布信息可用于指导多设备巡天观测.建立全天相机监测系统(Monitoring all-sky system)对本地天区夜天空实时监测,获取的监测图像需要有效的方法进行处理以提取全天图像星像信息.由于全天图像视场大和高阶扭曲的影响,采用天顶等距投影与多项式函数组合的方法计算图像的底片常数.天文定位的均方根残差约为0.15个像素.通过对图像中亮星部分测光得到的星等差,改正大气消光误差.最后使用HEALPix (Hierarchical Equal Area isoLatitude Pixelation)方法实现天区划分和每个天区可观测极限星等值的存储.