首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到11条相似文献，搜索用时 93 毫秒
1.
在大规模多波段成像和无缝光谱巡天中,无缝光谱巡天极限星等在一定程度上受无缝光谱效率和无缝光谱光栅衍射效率制约,针对无缝光谱仪中布置在焦面附近的光栅开展衍射效率优化设计研究.在光栅衍射效率的计算中采用严格耦合波分析方法,并在优化算法中综合采用模式搜索法和差分进化算法相结合的方法,得到了衍射效率高同时满足工程化要求的最优化槽型.模式搜索法能快速地收敛到局部最优值,差分进化算法具有全局择优的特点,两者结合提升了运算效率和结果的可靠性.针对无缝光谱仪中工作在不同波段、不同入射角和不同离面角的多块光栅优化衍射效率.优化结果表明,通过合理控制槽型,所有光栅在闪耀波长处的理论平均衍射效率均可达到0.83.  相似文献   

2.
  相似文献   

3.
A generic problem with spectrographs equipped with conventional diffraction gratings is that the maximum attainable spectral resolution scales inversely with the telescope aperture for a fixed grating dimension and angular slit width. It has long been realized that immersed gratings, where a prism is attached to the surface of a reflection grating, offer a means to bypass this limit. We show how, for the case of the Gemini Multiobject Spectrographs, the maximum spectral resolution may be approximately doubled, or, equivalently, how the same spectral resolution may be obtained with a wider slit, resulting in improved throughput when observing extended objects.
After reviewing the theory of immersed gratings, we present experimental verification of the theory and experimentally quantify two potential drawbacks: reduced throughput at blaze, and ghost images . We show that these effects are small and conclude that the benefits greatly outweigh the disadvantages.  相似文献   

4.
Future NASA X-ray Observatories will shed light on a variety of high-energy astrophysical phenomena. Off-plane reflection gratings can be used to provide high throughput and spectral resolution in the 0.3–1.5 keV band, allowing for unprecedented diagnostics of energetic astrophysical processes. A grating spectrometer consists of multiple aligned gratings intersecting the converging beam of a Wolter-I telescope. Each grating will be aligned such that the diffracted spectra overlap at the focal plane. Misalignments will degrade both spectral resolution and effective area. In this paper we present an analytical formulation of alignment tolerances that define grating orientations in all six degrees of freedom. We verify our analytical results with raytrace simulations to fully explore the alignment parameter space. We also investigate the effect of misalignments on diffraction efficiency.  相似文献   

5.
In this paper we simulate a deep multi-frequency zenith-field sky survey on RATAN-600 (the RZF survey). In our simulations we use the 1.4-GHz sky images obtained in the NVSS survey. We convolved NVSS images with the two-dimensional power beam pattern of RATAN-600 and obtain simulated 24-hour scans of sky transits at all wavelengths of the RZF survey. For the 7.6-cm wavelength we analyze the effect of the image area size on the results of the simulation. We estimate the accuracy of the determination of source fluxes on simulated scans and derive the distributions of the spectral indices of the sources. We use the simulated scans to clean real records of the RZF survey at 7.6 cm. The standard error of the residual noise at this wavelength is about 1 mJy.  相似文献   

6.
The Effelsberg‐Bonn H I survey (EBHIS) comprises an all‐sky survey north of Dec = –5° of the Milky Way and the local volume out to a red‐shift of z ≃ 0.07. Using state of the art Field Programmable Gate Array (FPGA) spectrometers it is feasible to cover the 100 MHz bandwidth with 16.384 spectral channels. High speed storage of H I spectra allows us to minimize the degradation by Radio Frequency Interference (RFI) signals. Regular EBHIS survey observations started during the winter season 2008/2009 after extensive system evaluation and verification tests. Until today, we surveyed about 8000 square degrees, focusing during the first all‐sky coverage of the Sloan‐Digital Sky Survey (SDSS) area and the northern extension of the Magellanic stream. The first whole sky coverage will be finished in 2011. Already this first coverage will reach the same sensitivity level as the Parkes Milky Way (GASS) and extragalactic surveys (HIPASS). EBHIS data will be calibrated, stray‐radiation corrected and freely accessible for the scientific community via a webinterface. In this paper we demonstrate the scientific data quality and explore the expected harvest of this new all‐sky survey (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
We present the observations and analysis of the spectral linewidths of neutral and ion species across the DR21(OH) core to investigate the cyclotron interaction as a probe of magnetic fields. It has been suggested that under average interstellar field strengths the cyclotron interaction between ions and magnetic fields is strong enough to narrow the linewidth and suppress the line wings in the ion spectra. We have obtained high spatial resolution spectral line images of H13CN and H13CO+ at 3 mm in DR21(OH) with the Millimeter Array of the Owens Valley Radio Observatory. Our results show that in the eastern parts of the DR21(OH) core the spectral linewidth of the ions is narrower than that of the neutrals. We use our results, along with the existing Zeeman and dust/CO polarization data on small scales, to derive the 3D magnetic field structure. We obtain a field strength of 0.44 ± 0.12 mG with inclination of 36° to the line of sight, directed toward the observer, and a position angle of ?75° in the plane of the sky.  相似文献   

8.
This paper describes the Wide Field Spectrograph (WiFeS) under construction at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) for the ANU 2.3 m telescope at the Siding Spring Observatory. WiFeS is a powerful integral field, double-beam, concentric, image-slicing spectrograph designed to deliver excellent throughput, wavelength stability, spectrophotometric performance and superb image quality along with wide spectral coverage throughout the 320–950 nm wavelength region. It provides a 25×38 arcsec field with 0.5 arcsec sampling along each of twenty five 38×1 arcsec slitlets. The output format is optimized to match the 4096×4096 pixel CCD detectors in each of two cameras individually optimized for the blue and the red ends of the spectrum, respectively. A process of “interleaved nod-and-shuffle” will be applied to permit quantum noise-limited sky subtraction. Using VPH gratings, spectral resolutions of 3000 and 7000 are provided. The full spectral range is covered in a single exposure at R=3000, and in two exposures in the R=7000 mode. The use of transmissive coated optics, VPH gratings and optimized mirror coatings ensures a throughput (including telescope atmosphere and detector) >30% over a wide spectral range. The concentric image-slicer design ensures an excellent and uniform image quality across the full field. To maximize scientific return, the whole instrument is configured for remote observing, pipeline data reduction, and the accumulation of calibration image libraries.  相似文献   

9.
The power beam pattern and antenna effective area of the RATAN-600 radio telescope are analyzed based on source samples observed during the 7.6-cm sky surveys preformed in 1980, 1988, 1990, 1991, 1993, 1994, and 1999. The surveys were made with the Northern sector of the RATAN-600 at the same declination as the COLD experiment (δ ∼ 5°). Experimental power beam patterns derived from the survey data are compared with the computed patterns. The r.m.s. deviation of the experimental data from the corresponding computed values averaged over all years is (0.19 − 0.23) ± 0.02. The vertical pattern of the 1980 survey is offset by about 1t’ with respect to the central horizontal section. The patterns obtained from the data for other years are symmetric within the measurement errors. The mean antenna effective area averaged over all years except 1993 is 803 ± 88 m2. The behavior of both the beam pattern and effective telescope surface areas was stable from 1980 through 1999  相似文献   

10.
A model is constructed for the magnetic field of the star HD 187474, which has a very long axial rotation period P = 2345d. It turns out that the structure of the magnetic field is best described by a model of a displaced (Δα = 0.1) dipole inclined to the axis of rotation by an angle β = 24°. The star is inclined to the line of sight by an angle i = 86°. Because of the displaced dipole the magnitude of the magnetic field differs at the poles: Bp = +6300 and 11600 G. A Mercator map of the distribution of the magnetic field over the surface is obtained. The 7 slowly rotating CP stars studied thus far have an average angle β = 62°, which equals the average value for a random orientation of dipoles. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 575–583 (November 2005).  相似文献   

11.
We present the catalogue, mask, redshift data and selection function for the PSC z survey of 15 411 IRAS galaxies across 84 per cent of the sky. Most of the IRAS data are taken from the Point Source Catalog, but this has been supplemented and corrected in various ways to improve the completeness and uniformity. We quantify the known imperfections in the catalogue, and we assess the overall uniformity, completeness and data quality. We find that overall the catalogue is complete and uniform to within a few per cent at high latitudes and 10 per cent at low latitudes. Ancillary information, access details, guidelines and caveats for using the catalogue are given.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号