摘要
本文通过恒星子午光子计数观测过程的分析,给出了观测输出信号所满足的解析关系式。利用该关系式,采用实际信号的期望值加上Poisson随机噪声的办法得到输出信号的模拟值。通过对中星仪子午光子计数观测的模拟办法,得到恒星中天时光子计数模拟观测信号。利用模拟方法,讨论和解决了一个子午观测中的实际问题。
Simulating the stellar observation is a sort of very useful implement for the analysis and the reduction of photon counting data on Transit Instrument. In some cases, it is difficult to estimate the errors directly from the observed data because the data noise and the function of real signals is complicated. With the method of simulating observation, this problem would be solved. And the simulated data can be used to compare with the observed data in order to find out an experiential method for estimations. The simulated data can be also used to study the reduction methods from a various number of methods and to determine the optimal one in order to get the best precision. The simulating observation is also worthy to study the instrumental accuracy and the influence of the hardware upon the precision of the observed data and their determinations. It has been found that the slit micrometer is very important to the precision. The optimal size of the slit is existed. With the method of simulation, the optimal slit size can be calculated. So that, better precision of the stellar observation will be achieved and fainter stars can be observed. In this paper, the simulating principle and process of photon counting data of meridian observations with one or muitislit micrometer will be discussed. In general, the output signal of meridian photon counting observation can be expressed as a convolution of the image profile function plus the background photon counts and their noise signal(cf.equation <1>)with a trapezoid weighting function.Because the atmospheric agitation is a random process, the image profile will be a gaussian function. The weighting function is determined by the constants of the slit, δ and the time interval of sampling. Asume Am is the amplitude of starlight counts with magnitude m_v, in order to get Am., we can observe the stars with magnitude m_0, and get their amplitude A_0. Am will be calculated from A_0. The background counts b can not only be experientially but also analytically determined. Using a Poisson random noise generator, the noise signal will be got. When the constants of the slit, the time interval of sampling,the variance of the image profile,the magnitude of the observed star and its declination are known, we can therefore simulate the meridian photon counting observation of the star. As an exaple, the application of the simulating method will be discussed. First, we analyse the image profile of a star, Simulated data will be used to find an experiential equation for the meridian observation on the Transit Instrument at Shaanxi Astronomical Observatory. This equation expresses a relation of an estimated parameter to the variance of a gaussian distribution. In comparison with the simulated data, the variance σ~2 of image profile can be calculated from the observed data of a star. By means of this method, we got σ=0″.7～1″.9. The second example is to discuss the influence of the slit width on the determining precision of meridian time. By experiences, we come to. the conclusion that the slit width of 20.6265 (used in the Transit Instrument at Shaanxi Astronomical Observatory) is not ideal one for stellar meridian observation. If the slit with 5″.width of the transparent part and with 15″ width of the reflective part were used, the determined precision of meridian time would be better,and fainter stars would be observed.
出处
《陕西天文台台刊》
CSCD
1989年第1期43-49,共7页
Publications of The Shaanxi Astronomical Observatiory
