共查询到10条相似文献，搜索用时 93 毫秒
1.
Precise fiber positioning is crucial to a wide field,multi-fiber spectroscopic survey such as the Guoshoujing Telescope(the Large Sky Area Multi-Object Fiber Spectroscopic Telescope,LAMOST).Nowadays,most position error measurements are based on CCD photographic and image processing techniques.These methods only work for measuring errors orthogonal to the telescope optical axis,but there are also errors that lie parallel to the optical axis of the telescope,such as defocusing,and errors caused by the existing deviation angle between the optical axes of a fiber and the telescope.Directly measuring the two latter types of position errors is difficult for an individual fiber,especially during observations.Possible sources of fiber position errors are discussed in brief for LAMOST.By constructing a model of magnitude loss due to the fiber position error for a point source,we propose an indirect method to calculate both the total and systematic position errors for each individual fiber from spectral data.Restrictions and applications of this method are also discussed. 相似文献
2.
In this paper we discuss a set of three consecutive VLBI observations of the binary system UX Arietis. The most interesting result is the variation with time of the source structure. The usual interpretation in terms of gyrosynchrotron emission from relativistic electrons trapped in a magnetic loop and undergoing collisional and radiative losses is not able, alone, to explain the observed variations. By using optical, radio and X-ray information we have produced a model of two giant loops anchored on a rotating star. As the star rotates, the loops change their relative position and orientation with respect to the line of sight, causing the observed variation of the source structure. The qualitative agreement found is consistent with our hypothesis and makes these observations a sort of a pilot experiment for a new way of using VLBI to observe radio-stars. In order to quantitatively test our model of evolving electrons confined in loops anchored on a rotating star, we plan in the near future a set of several phase-reference VLBI observations fully covering the 6.4 day rotational period. 相似文献
3.
We report results from two station, short-baseline (< 100 m) high resolution measurements of faint meteors (limiting meteor
magnitude +9) with the goal of measuring their optical trail widths. Meteors were observed using two 0.40 m Newtonian telescopes
(field of view ˜0.4 degrees) equipped with image intensifiers. Both telescopes were vertically oriented in a fixed mount and
pointed to the same field of view. One system used a gated image intensified camera allowing the transverse velocity component
to be measured. The widest trail captured, out of a total of 34 common events measured by both optical systems, had a full-width
to half-maximum of 1.37±0.71 m. The widest trail overall was captured by the gated system only, and was found to have a full-width
of ∼
∼10 m. The brightness variation across this trail was found to be best represented by a Lorentzian. Most trails were smaller
than our resolution limit and hence we could only place upper limits on their optical width. These were generally less than
1 m after correction for instrumental effects. Four meteors were found to have heights near 65 km and very low transverse
velocities. These may be indicative of a largely unreported high density asteroidal component at these faint meteor magnitudes. 相似文献
4.
一个巨型望远镜方案 总被引：4，自引：0，他引：4
提出一个有特色的巨型望远镜(FGT)方案．其主镜口径为30米，主焦比为1．2，由1095块圆环形子镜构成．采用地平式装置．光学系统包括Nasmyth系统、折轴(Coude)系统和一个大视场系统．提出一个由4个镜面组成的新的Nasmyth系统，在约10′的视场范围内像斑小于爱里斑，达到衍射极限．比传统的Nasmyth系统的衍射极限视场大得多．可在这样的大视场内同时作好几个小区域的衍射极限的观测．当由Nasmyth系统转换到折轴系统和大视场系统时，采用主动光学技术改变子镜的面形、倾斜和平移，产生一个新的主镜面形，使折轴系统和大视场系统都能得到很好的像质．大视场系统的视场直径25′，场曲轻微，并有可能校正大气色散．给出了子镜面形和位置的公差，并讨论了望远镜的装置和结构,方案中的特色和创新对未来大望远镜的研制有普遍意义． 相似文献
5.
We report the algorithms used in the software of the upgraded SBG camera. Fast-moving satellites are observed in the “rotated” coordinate system where one of the axes points towards the pole of the object’s orbit. The ephemeris for this coordinate system is computed based on the ephemeris for the equatorial coordinate system using special transition matrices. The parameters of the matrices are the coordinates of the orbital pole, which are found by averaging the vector products of the radius vectors of the consecutive positions of the satellite. The position angle of the image is computed as the difference between the hour angles of the orbital and celestial poles in the coordinate system, the pole of which coincides with the optical center of the frame. The speed of object tracking is computed via quadratic interpolation of the ephemeris in the “rotated” coordinate system. 相似文献
6.
Ronald J. Kroll 《Solar physics》1994,152(1):105-110
In an effort to monitor solar limb-darkening variability, the continuum radiation intensity at 550 nm over the outermost 32 arcseconds of the limb is measured at various solar latitudes. Using the Finite Fourier Transform Definition, the edge location of the Sun is determined for a series of scan amplitudes at each of the observed positions. The differential radius is the difference between edge locations for a fixed pair of scan amplitudes, and is a quantity which characterizes the slope of the solar limb-darkening function. Utilizing the differential radius, such observations offer the possibility of revealing a latitudinal variation of the photospheric temperature gradient and could provide clues to the mechanisms and variability of energy transport out of the Sun. These observations began in 1988 with measurements at 24 separate limb positions and include observations since 1990 when 36 positions were observed. The daily differential radius measurements for each position that is free of contamination from solar active regions are weighted according to the corresponding daily variance and averaged to obtain an overall value at each position for the observing season. The results indicate that during the 1991 observing season, there were regions near 20°N latitude and 30°S latitude on the Sun where the differential radius values were significantly greater than surrounding regions. This suggests that perturbations to the temperature gradient occur in latitudinally localized regions and persist for at least several months. It is shown that this phenomenon could have the same origin as the observed latitudinal variations of surface temperature and could also speak to the question of a lag time between the cycles of irradiance and magnetic variation. 相似文献
7.
8.
Atmospheric turbulence severely restricts the spatial resolution of astronomical images obtained by a large ground-based telescope. In order to reduce effectively this effect, we propose a method of blind deconvolution, with a bandwidth constraint determined by the parameters of the telescope's optical system based on the principle of maximum likelihood estimation, in which the convolution error function is minimized by using the conjugate gradient algorithm. A relation between the parameters of the telescope optical system and the image's frequency-domain bandwidth is established, and the speed of convergence of the algorithm is improved by using the positivity constraint on the variables and the limited-bandwidth constraint on the point spread function. To avoid the effective Fourier frequencies exceed the cut-off frequency, it is required that each single image element (e.g., the pixel in the CCD imaging) in the sampling focal plane should be smaller than one fourth of the diameter of the diffraction spot. In the algorithm, no object-centered constraint was used, so the proposed method is suitable for the image restoration of a whole field of objects. By the computer simulation and by the restoration of an actually-observed image of α Piscium, the effectiveness of the proposed method is demonstrated. 相似文献
9.
In this paper we present current progress in development of new observational instruments for the double station video experiment.
The Meteor Automatic Imager and Analyser (MAIA) system is based on digital monochrome camera JAI CM-040 and well proved image
intensifier XX1332. Both the observations as well as the data processing will be fully automatic. We are expecting the recorded
data of better quality and both spatial and time resolution in comparison with currently used analogue system. The main goal
of the MAIA project is to monitor activity of the meteor showers and sporadic meteor each night for the period of at least
3 years. First version of the system was already assembled and has been intensively tested in the optical laboratory. Optical
properties were measured and the result confirmed our expectations according to image quality and resolution. First night
sky observation was already carried out. 相似文献
10.
In order to improve the ability to find the faint and small celestial bodies in the solar system, a method of shifting and stacking images which improves the detection efficiency of faint moving objects is applied to process the sequential optical images. This method determines the existence of moving objects by using the method of false position to pre-estimate the apparent velocities of moving objects, then determines iteratively the accurate positions of moving objects based on the SNR (Signal-to-Noise Ratio) and elongation of stellar image. Using the sequential images of the China Near Earth Object Survey Telescope (CNEOST), we carry out an experiment and succeed in detecting asteroids fainter than 21 magnitude which are invisible on a single image. Thus, the feasibility of this method is verified. 相似文献