基于OpenMP的并行图像相减算法实现与分析

图像相减是一种精确地获得密集星体区域中变星的相对光度变化的技术,其基本原理为通过同一区域不同时间的图像间差异来获得该区域的时间变化信息.传统上图像相减变源测光算法只有串行性算法,计算效率不高.讨论了图像相减测光算法的基本原理,在开源软件ISIS基础上提出了一个基于OpenMP技术的图像相减算法的可靠并行化实现,提高了程...     

基于图像相减和随机森林的AST3巡天暂现源及变源搜寻方法

AST3-2 (Antarctic Survey Telescopes)光学巡天望远镜位于南极大陆最高点冰穹A,其产生的大量观测数据对数据处理的效率提出了较高要求.同时南极通信不便,数据回传有诸多困难,有必要在南极本地实现自动处理AST3-2观测数据,进行变源和暂现源观测的数据处理,但是受到低功耗计算机的限制,数据的快速自动处理的实现存在诸多困难.将已有的图像相减方案同机器学习算法相结合,并利用AST3-2 2016年观测数据作为测试样本,发展一套的暂现源及变源的筛选方法成为可行的选择.该筛选方法使用图像相减法初步筛选出可能的变源,再用主成分分析法抽取候选源的特征,并选择随机森林作为机器学习分类器,在测试中对正样本的召回率达到了97%,验证了这种方法的可行性,并最终在2016年观测数据中探测出一批变星候选体.     

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。     

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.     

图像板图像高速读出方法

天文图像采集处理一直是天文观测领域的一个重要方面，普通的视频ＣＣＤ由于其本身所具有的物美价廉，快速简便等特点且能够满足大多数天文观测的需要而成为目前常用的终端探测设备，这样必不可免地要使用图像板进行视频信号的截取以及处理；在一段时间内获得尽可能多的观测图像无疑是提高观测质量的一个手段，而其中最关键的问题在于如何将图像板上的图像快速读出。本文对目前我台配备较多的Ｍ５４０图像板与ＣＡ６３００图像板的图     

银道面附近若干天区变星搜寻

对新疆天文台南山1 m大视场天文望远镜观测的历史数据进行细致的数据挖掘,发现了百余颗变源。数据处理流水线为新疆天文台时域巡天数据处理包,该处理包同时考虑了测光系统内部权重和相关性,并结合快速混合算法编写。除去已知的变源,又发现了很多新的变源。对新变源证认的过程中,将结果与LAMOST, GCVS, VSX, GaiaDR2等星表进行交叉。在讨论部分,对各星表的使用情况给出了说明。最后发现这些新变源绝大部分是食双星,少部分是脉动变星,并有一颗表现相对复杂的变源。     

1.26米红外望远镜测光处理管线设计与实现

1.26m红外望远镜是一台由国家天文台和广州大学联合建设的望远镜系统,测光观测是该望远镜的重要观测手段之一。但当前一直存在数据处理周期较长、处理过程需要人工处理等问题。为了提高广州大学合作团队的数据处理能力,提出了一种面向1.26 m红外望远镜半自动的测光处理管线,该管线在获取原始数据后,基于当日的观测记录重建FITS头文件信息,随后管线系统自动对图片进行预处理、定位目标星源、计算出目标星等相关操作,最后获得可利用的测光数据。这种方式高效、便捷,同时精度也得到了保证,它把当前主流测光模式中繁杂的、需要不断重复的步骤交由程序运行,从而节省了时间,显著提高了工作效率,解决了当前光学测光模式中图像数据的处理跟不上数据产出的难题,满足了广大科研工作者的需求。     

大天区望远镜中sCMOS相机的测光精度分析

与传统CCD (Charge Coupled Device)相机相比, s COMS (scientific Complementary Metal Oxide Semiconductor)相机被广泛装备于超大天区巡天设备,与传统CCD相机不同的是sCMOS相机采用卷帘式快门,因此对其进行测光精度的分析工作是很有意义的.首先,将s CMOS相机拍摄的图像与UCAC2 (The Second U.S. Naval Observatory CCD Astrograph Catalog)星表进行匹对,识别图像中的UCAC2标准星.接着对图中的标准星进行测光并提取测光数据进行最小二乘直线拟合,获得了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.然后,将转化后的仪器星等和标准星等做差并计算相应的均方根误差.最后,利用计算得到的均方根误差评估sCMOS相机的测光精度,并将标准星按星等划分后,分析了相应的测光误差.计算结果表明在标准测光夜测量亮度亮于14等的星时,测光精度优于0.15 mag.通过实测精度分析可知卷帘快门sCOMS相机具有较高的测光精度,基本满足空间碎片巡天观测的要求.     

活动星系核的测光——类星体3C 273的照相观测

1978年初,我们在云南天文台的SBG人造卫星跟踪照相望远镜上,对类星体3C 273进行照相观测.初步建立起一套包括照相、测量、归算以及结果验核在内的照相测光方法. 本文报道了观测类星体3C 273的照相测光结果以及对疏散星团NGC 2287中部分恒星的测光.     

光学相机FOC对黑洞双星高时间分辨测光性能研究

黑洞暂现双星MAXI J1820+070于2018年3月的明亮爆发为研究光学快速测光能力提供了重要机遇. 以快速光学相机(Fast Optical Camera, FOC)为终端设备分别在2018年4月22日、5月26日和8月31日(UTC)使用云南天文台丽江观测站2.4m望远镜对爆发中的黑洞双星MAXI J1820+070进行了亚秒时标的测光观测. 通过观测数据分析, 研究了相机的快速测光性能.对全帧和1/4帧两种观测模式的帧间间隔(frame time), 测得平均帧间间隔为(22.866 pm 0.679)ms和(5.868 pm 0.169)ms. 通过视场中多颗明亮参考源校准,提取了观测对象和参考源的光变曲线, 获得了光变曲线的傅里叶功率谱, 区分了观测对象本征光变和仪器或望远镜等观测因素带来的非本征光变, 成功探测到目标黑洞双星MAXI J1820+070中的光学波段低频准周期振荡信号, 并判别了观测中来自仪器设备或与观测条件相关的时变信号. 这成功验证了相机高速稳定的测光性能和对短至5ms时标光变信号的探测能力.     

An Automatic Method for Detecting Transients and Variable Sources in AST3 Survey Based on Image Subtraction and Random Forest

AST3-2 (the second Antarctic Survey Telescope) is located in Antarctic Dome A, the loftiest ice dome on the Antarctic Plateau. It produces a huge amount of observational data which require a more efficient data reduction program to be developed. Also the data transmission in Antarctica is much difficult, thus it is necessary to perform data reduction and detect variable and transient sources remotely and automatically in Antarctica, but this attempt is restricted by the unsatisfactory performance of the low power consumption computer in Antarctica. For realizing this purpose, to develop a new method based on the existing image subtraction method and random forest algorithm, taking the AST3-2 2016 dataset as the test sample, becomes an alternative choice. This method performs image subtraction on the dataset, then applies the principle component analysis to extract the features of residual images. Random forest is used as a machine learning classifier, and in the test a recall rate of 97% is resulted for the positive sample. Our work has verified the feasibility and accuracy of this method, and finally found out a batch of candidates for variable stars in the AST3-2 2016 dataset.     

Decomposing the host galaxy from high-z QSOs using principal component analysis

High resolution deep imaging from space and adaptive optics techniques with large ground-based facilities have enabled studies examining faint host galaxies of high redshift quasi-stellar objects(QSOs).However, the related image processing techniques, especially for a precise point-spread function(PSF) reconstruction and characterization of the host galaxy light profiles, have yet to be optimized. We present here the scientific performance of a principal component analysis(PCA) based PSF subtraction of the central bright point source of high redshift QSO images, as well as further characterization of the host galaxy profile by directly fitting a S`ersic model to the residual image using the Markov Chain Monte Carlo(MCMC)algorithm. With a set of reference PSF star images which represent interleaving exposures between the QSO imaging, we can create an orthogonal basis of eigen-images and restore the PSF of QSO images by projecting the QSO images onto the basis. In this way, we can quantify the modes in which the PSF varies with time by a basis function that characterizes the temporal variations of the reference star as well as the QSO images. To verify the algorithm, we performed a simulation and applied this method to one of the high-z QSO targets from Mechtley et al. We demonstrate that the PCA-based PSF subtraction and further modeling of the galaxy's light profile using MCMC fitting would sufficiently remove the effects from central dominating point sources, and improve characterization ability for the host galaxies of high-z QSOs to the background noise level which is much better than previous two-component fitting procedures.     

Research on scheduling of robotic transient survey for Antarctic Survey Telescopes(AST3)

Antarctic Survey Telescopes(AST3) are designed to be fully robotic telescopes at Dome A,Antarctica,which aim for highly efficient time-domain sky surveys as well as rapid response to special transient events(e.g.,gamma-ray bursts,near-Earth asteroids,supernovae,etc.).Unlike traditional observations,a well-designed real-time survey scheduler is needed in order to implement an automatic survey in a very efficient,reliable and flexible way for the unattended telescopes.We present a study of the survey strategy for AST3 and implementation of its survey scheduler,which is also useful for other survey projects.     

Optimising optimal image subtraction

Difference imaging is a technique for obtaining precise relative photometry of variable sources in crowded stellar fields and, as such, constitutes a crucial part of the data reduction pipeline in surveys for microlensing events or transiting extrasolar planets. The Optimal Image Subtraction (OIS) algorithm of Alard & Lupton (1998) permits the accurate differencing of images by determining convolution kernels which, when applied to reference images with particularly good seeing and signal‐to‐noise (S/N), provide excellent matches to the point‐spread functions (PSF) in other images of the time series to be analysed. The convolution kernels are built as linear combinations of a set of basis functions, conventionally bivariate Gaussians modulated by polynomials. The kernel parameters, mainly the widths and maximal degrees of the basis function model, must be supplied by the user. Ideally, the parameters should be matched to the PSF, pixel‐sampling, and S/N of the data set or individual images to be analysed. We have studied the dependence of the reduction outcome as a function of the kernel parameters using our new implementation of OIS within the IDL‐based TRIPP package. From the analysis of noise‐free PSF simulations of both single objects and crowded fields, as well as the test images in the ISIS OIS software package, we derive qualitative and quantitative relations between the kernel parameters and the success of the subtraction as a function of the PSF widths and sampling in reference and data images and compare the results to those of other implementations found in the literature. On the basis of these simulations, we provide recommended parameters for data sets with different S/N and sampling. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

同幅双速跟踪成像CCD相机模拟电路系统设计

讨论了同幅双速跟踪成像技术对CCD相机系统的特殊要求,详细地介绍了该相机前端模拟系统的设计思想、系统结构和主要的电路模块。对系统中一些关键电路模块进行了仿真和测试,并对仿真和测试结果进行比较分析,以检验电路系统设计的合理性。     

TRIFFID observations of the cores of the three globular clusters M15, M92 and NGC 6712

We present the results of TRIFFID simultaneous V - and B -band observations of the cores of the globular clusters M15, M92 and NGC 6712. A variability search of their dense centres was made feasible through performing post-exposure image sharpening on the images, increasing the image resolution by a factor of ∼2. The isis implementation of the image subtraction technique developed by Alard & Lupton was then used to detect flux variations in our image sets. We have obtained periods for all observable variables (in our field of view) in NGC 6712 and we have found two new RR Lyrae variables (an RRab and an RRc). We have confirmed three variables in our field of view of the M92. For M15, we detect 48 variables in our field of view, 23 of which are new discoveries. We obtain periods and amplitudes for all variables and classify new ones based on the light-curve shape, the most significant period and the mean magnitude in the V band. Among the detected RR Lyrae we find 19 RRc, 12 RRab and two RRd types. In the subsequent analysis we find a marked increase in RRc over RRab variables in the core. In a refined procedure to search for fainter objects we find no dwarf novae in our field of view of M15. Simulations performed on the data set to quantify our sensitivity to such objects indicate that an upper limit of 10 dwarf novae (at 92 per cent probability) exist in our field of view. The implications this result has on globular clusters are discussed.     

Reliability Analysis of Main-axis Control System of the Antarctic Equatorial Astronomical Telescope Based on Fault Tree

The Antarctic astronomical telescopes work chronically on the top of the unattended South Pole, and they have only one chance to maintain every year. Due to the complexity of the optical, mechanical, and electrical systems, the telescopes are hard to be maintained and need versatile expedition teams, which means that an excessive awareness is essential for the reliability of the Antarctic telescopes. Based on the fault mechanism and fault mode of the main-axis control system for the Antarctic equatorial astronomical telescope AST3-3 (Antarctic Schmidt Telescope 3-3), the method of fault tree analysis is introduced in this article, and we obtain the importance degree of the top event from the importance degree of the bottom event structure. From the above result, the hidden problems and weak links of the system can be effectively found out, which will indicate the direction for improving the stability of the system and optimizing the design of the system.     

同幅双速跟踪成像CCD相机数字控制器的设计

在介绍了同幅双速跟踪成像CCD相机的工作原理及其对相机数字控制器的要求之后,阐述了该数字控制器的设计思想,基本结构,并给出了仿真及测试结果。针对仿真及测试过程中出现的问题作了较为详细的分析,并提出了解决的方法。通过软件仿真及硬件测试,表明其设计是基本正确的。     

Radio images of four luminous blue variable stars

We have used the Australia Telescope Compact Array to image four southern luminous blue variable stars: AG Car, He3-519, HR Car and WRA 751, at wavelengths of 3 and 6 cm, and resolutions of 1 and 2 arcsec respectively. With the partial exception of HR Car, all radio images show an unresolved stellar core surrounded by a large ionized gaseous nebula, and agree well with published H α and [N  ii ] optical images. The image of WRA 751 shows a stellar torus or disc. HR Car's radio image is unusual, and seems best explained by the presence of a hot binary companion.