共查询到20条相似文献,搜索用时 15 毫秒
1.
Biao Du Yang Wu Yuan-Peng Zheng Xiao-Ming Chai Guo-Xi Liu Hai-Dong Wang Yi-Fan Zhang Sheng-Hua Yu Bin Liu Ye-Zhao Yu Hong-Wei Xi Long Chen Lei Yu Dong-Liang Liu Cheng-Jin Jin Bo Peng 《天文和天体物理学研究(英文版)》2019,(6):97-108
The Square Kilometre Array(SKA) will be the world’s largest synthesis radio telescope, which is designed to answer major scientific questions such as those relating to the cosmic origin and fundamental forces in the universe. With the SKA entering into the phase of pre-construction, more than 100 institutes in about 20 countries including China have been involved in the associated key technology development.The Dish Verification Antenna China(DVA-C) is a concept prototype which has been built to meet the requirements of the SKA’s scientific goals. It utilizes a unique skin-and-rib structure with single-piece panel reflectors. This paper presents details on the design and measured performances of DVA-C, as well as the preliminary observational results. Current applications of the DVA-C are also introduced. 相似文献
2.
Wim Brouw 《Astrophysics and Space Science》2001,278(1-2):205-208
The next generation radio telescope being planned is the Square Kilometer Array (SKA): an international project which is currently
in the research and development phase. Australia is one of the partner countries in the SKA consortium; here I describe some
of the SKA research being undertaken in Australia.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
The sensitivity and versatility of SKA will provide microarcsec astrometric precision and high quality milliarcsec-resolution images by simultaneously detecting calibrator sources near the target source. To reach these goals, we suggest that the long-baseline component of SKA contains at least 25% of the total collecting area in a region between 1000 and 5000 km from the core SKA. We also suggest a minimum of 60 elements in the long-baseline component of SKA to provide the necessary (u–v) coverage. For simultaneous all-sky observations, which provide absolute astrometric and geodetic parameters, we suggest using 10 independent subarrays each composed of at least six long-baseline elements correlated with the core SKA. We discuss many anticipated SKA long-baseline astrometric experiments: determination of distance, proper motion and orbital motion of thousands of stellar objects; planetary motion detections; mass determination of degenerate stars using their kinetics; calibration of the universal distance scale from 10 to 107 pc; the core and inner-jet interactions of AGN. With an increase by a factor of 10 in absolute astrometric accuracy using simultaneous all sky observations, the fundamental quasar reference frame can be defined to <10 μas and tied to the solar-system dynamic frame to this accuracy. Parameters associated with the earth rotation and orientation, nutation, and geophysical parameters, can be accurately monitored. Tests of fundamental physics include: solar and Jovian deflection experiments, the sky frame accuracy needed to interpret the gravity wave/pulsar-timing experiment, accurate monitoring of spacecraft orbits that impact solar system dynamics. 相似文献
4.
We describe a SKA hardware component model that includes various concepts for achieving a wide field-of-view (FoV) as desired for survey speed. Costs for each of the components in the model are derived and in some cases optimum parameters are estimated. The model identifies components of major cost and allows comparison of the relative costs of the wide FoV concepts. 相似文献
5.
In this paper, we investigate how the Square Kilometre Array (SKA) can aid in determining the evolutionary history of active galactic nuclei (AGN) from redshifts z = 0 → 6. Given the vast collecting area of the SKA, it will be sensitive to both ‘radio-loud’ AGN and the much more abundant ‘radio-quiet’ AGN, namely the radio-quiet quasars and their ‘Type-II’ counterparts, out to the highest redshifts. Not only will the SKA detect these sources but it will also often be able to measure their redshifts via the Hydrogen 21-cm line in emission and/or absorption. We construct a complete radio luminosity function (RLF) for AGN, combining the most recent determinations for powerful radio sources with an estimate of the RLF for radio-quiet objects using the hard X-ray luminosity function of [ApJ 598 (2003) 886], including both Type-I and Type-II AGN. We use this complete RLF to determine the optimal design of the SKA for investigating the accretion history of the Universe for which it is likely to be a uniquely powerful instrument. 相似文献
6.
7.
A. Van Ardenne P. N. Wilkinson P. D. Patel J. G. Bij De Vaate 《Experimental Astronomy》2004,17(1-3):65-77
ASTRON has demonstrated the capabilities of a 4 m2, dense phased array antenna (Bij de Vaate et al., 2002) for radio astronomy, as part of the Thousand Element Array project (ThEA). Although it proved the principle, a definitive answer related to the viability of the dense phased array approach for the SKA could not be given, due to the limited collecting area of the array considered. A larger demonstrator has therefore been defined, known as “Electronic Multi-Beam Radio Astronomy Concept”, EMBRACE, which will have an area of 625 m2, operate in the band 0.4–1.550 GHz and have at least two independent and steerable beams. With this collecting area EMBRACE can function as a radio astronomy instrument whose sensitivity is comparable to that of a 25-m diameter dish. The collecting area also represents a significant percentage area (∼10%) of an individual SKA “station.” This paper presents the plans for the realisation of the EMBRACE demonstrator. 相似文献
8.
Andrew H. Jaffe 《New Astronomy Reviews》2004,48(11-12):1483
We discuss the ability of the SKA to observe QSO proper motions induced by long-wavelength gravitational radiation. We find that the SKA, configured for VLBI with multiple beams at high frequency (8 GHz), is sensitive to a dimensionless characteristic strain of roughly 10−13, comparable to (and with very different errors than) other methods in the 1/yr frequency band such as pulsar timing. 相似文献
9.
In this paper we examine the possibility of adopting standards within the context of radio astronomy and the benefits to be derived thereby. In particular we consider the application of standards within the three areas of the receiver hardware, the control and communication between different parts of the observing system, and the interface with the astronomer. The adoption of such standards will increase flexibility of observing systems, allow the easy interchange of equipment between observatories and greatly simplify guest observing. In this paper we will only consider the application of standards within the field of millimetre-wave and sub-millimetre-wave single dish astronomy. However, the principle can be easily extended to other astronomical wavebands. We describe some current developments at the Onsala Space Observatory which illustrate the proposed philosophy and show how such standards may be implemented. Naturally, the detailed definition of such standards would have to be agreed in conjunction with other interested astronomical institutions. 相似文献
10.
The λ21-cm line is an excellent tracer of the neutral interstellar medium (ISM). Atomic hydrogen (HI) is found in a variety of environments, from dense clouds to the diffuse galactic halo, and its filling factor is often high, so structures with sizes over a wide range of scales can be mapped with this line. Galactic HI surveys show small scale structure that is consistent with a spectrum of interstellar turbulence similar to what is measured in the ionized component of the ISM. But our sampling of the spectrum of this turbulence is limited to a few size ranges, based on the sensitivities of existing telescopes for emission and absorption studies. The Square Kilometer Array (SKA) will provide the sensitivity and resolution to give continuous coverage of the turbulence spectrum from hundreds of parsecs to a few tens of Astronomical Units. By showing us the full spectrum of interstellar turbulence in the neutral medium, the physical processes driving hydrodynamic and magneto-hydrodynamic instabilities will be illuminated. Ultimately the turbulence governs the passage of the gas from the warm phases of the medium to the cold phases where gravitational collapse can initiate star formation. The SKA is needed to fill in this missing link in the cycle of star formation and chemical enrichment that drives the evolution of galaxies. In the Milky Way halo, SKA mapping of HI high velocity clouds will trace the structure and motion of both the warm phase gas and the hot medium. The interaction between these two phases of halo gas is a great unsolved problem in Galactic astrophysics. 相似文献
11.
Germán Cortés-Medellín 《Experimental Astronomy》2004,17(1-3):111-118
The frequency specifications of the Square Kilometre Array (SKA) call for an optimum operation of the antenna elements from 25 down to 100 MHz. The current 12 m diameter US-SKA design is specified from 500 up to 25 GHz, with an upper goal of 35 GHz. At the low frequency end of the band (i.e., 100 MHz), a 12 m reflector antenna is about four wavelengths in diameter. Then, the question is: how well can you do, at this low frequency end of the specified band of operation for the SKA, with a symmetric reflector configuration using an ultra-wide-band prime focus feed? This paper presents the analysis of the antenna performance, in terms of A eff/T A, of three symmetric configurations of the 12 m US-SKA antenna design between 100 and 200 MHz. 相似文献
12.
N. Razavi-Ghods E. de Lera Acedo A. El-Makadema P. Alexander A. Brown 《Experimental Astronomy》2012,33(1):141-155
The new generation of radio telescopes, such as the proposed Square Kilometer Array (SKA) and the Low-Frequency Array (LOFAR) rely heavily on the use of very large phased aperture arrays operating over wide band-widths at frequency ranges up to approximately 1.4?GHz. The SKA in particular will include aperture arrays consisting of many thousands of elements per station providing un-paralleled survey speeds. Currently two different arrays (from nominally 70?MHz to 450?MHz and from 400?MHz to 1.4?GHz) are being studied for inclusion within the overall SKA configuration. In this paper we aim to analyze the array contribution to system temperature for a number of regular and irregular planar antenna array configurations which are possible geometries for the low-frequency SKA (sparse disconnected arrays). We focus on the sub-500?MHz band where the real sky contribution to system temperature (T sys ) is highly significant and dominants the overall system noise temperature. We compute the sky noise contribution to T sys by simulating the far field response of a number of SKA stations and then convolve that with the sky brightness temperature distribution from the Haslam 408?MHz survey which is then scaled to observations at 100?MHz. Our analysis of array temperature is carried out by assuming observations of three cold regions above and below the Galactic plane. The results show the advantages of regular arrays when sampled at the Nyquist rate as well as their disadvantages in the form of grating lobes when under-sampled in comparison to non-regular arrays. 相似文献
13.
R. M. Hueckstaedt S. H. Batha M. M. Balkey N. D. Delamater J. R. Fincke R. L. Holmes N. E. Lanier G. R. Magelssen J. M. Scott J. M. Taccetti C. J. Horsfield K. W. Parker S. D. Rothman 《Astrophysics and Space Science》2005,298(1-2):255-259
Observations of the interstellar medium reveal a dynamic realm permeated by shocks. These shocks are generated on a large
range of scales by galactic rotation, supernovae, stellar winds, and other processes. Whenever a shock encounters a density
interface, Richtmyer-Meshkov instabilities may develop. Perturbations along the interface grow, leading to structure formation
and material mixing. An understanding of the evolution of Richtmyer-Meshkov instabilities is essential for understanding galactic
structure, molecular cloud morphology, and the early stages of star formation. An ongoing experimental campaign studies Richtmyer-Meshkov
mixing in a convergent, compressible, miscible plasma at the Omega laser facility. Cylindrical targets, consisting of a low
density foam core and an aluminum shell covered by an epoxy ablator, are directly driven by fifty laser beams. The aluminum
shell is machined to produce different perturbation spectra. Surface types include unperturbed (smooth), single-mode sinusoids,
multi-mode (rough), and multi-mode with particular modes accentuated (specified-rough). Experimental results are compared
to theory and numerical simulations. 相似文献
14.
Sk. Saiyad Ali Somnath Bharadwaj Samir Choudhuri Abhik Ghosh Nirupam Roy 《Journal of Astrophysics and Astronomy》2016,37(4):35
The Diffuse Galactic Syncrotron Emission (DGSE) is the most important diffuse foreground component for future cosmological 21-cm observations. The DGSE is also an important probe of the cosmic ray electron and magnetic field distributions in the turbulent interstellar medium (ISM) of our galaxy. In this paper we briefly review the Tapered Gridded Estimator (TGE) which can be used to quantify the angular power spectrum C ? of the sky signal directly from the visibilities measured in radio-interferometric observations. The salient features of the TGE are: (1) it deals with the gridded data which makes it computationally very fast, (2) it avoids a positive noise bias which normally arises from the system noise inherent to the visibility data, and (3) it allows us to taper the sky response and thereby suppresses the contribution from unsubtracted point sources in the outer parts and the side lobes of the antenna beam pattern. We also summarize earlier work where the TGE was used to measure the C ? of the DGSE using 150 MHz GMRT data. Earlier measurements of C ? are restricted to \(\ell \le \ell _{\max } \sim 10^{3}\) for the DGSE, the signal at the larger ? values is dominated by the residual point sources after source subtraction. The higher sensitivity of the upcoming SKA1 Low will allow the point sources to be subtracted to a fainter level than possible with existing telescopes. We predict that it will be possible to measure the C ? of the DGSE to larger values of \(\ell _{\max }\) with SKA1 Low. Our results show that it should be possible to achieve \(\ell _{\max }\sim 10^{4}\) and ~105 with 2 minutes and 10 hours of observations respectively. 相似文献
15.
Chen-Hui Niu Qun-Xiong Wang David MacMahon Feng-Quan Wu Xue-Lei Chen Ji-Xia Li Hai-Jun Tian Guillaume Shippee Dan Werthimer Xiao-Ping Zheng 《天文和天体物理学研究(英文版)》2019,(7)
A digital correlator is a crucial element in a modern radio telescope. In this paper, we describe a scalable design for the correlator system of the Tianlai pathfinder array, which is an experiment dedicated to testing key technologies for conducting a 21 cm intensity mapping survey. The correlator implements the FX design, which firstly performs a fast Fourier transform(FFT) including polyphase filter bank(PFB) computation using a Collaboration for Astronomy Signal Processing and Electronics Research(CASPER) Reconfigurable Open Architecture Computing Hardware-2(ROACH2) board, then computes cross-correlations by employing Graphics Processing Units(GPUs). The design has been tested both in laboratory and in actual observation. 相似文献
16.
《天文和天体物理学研究(英文版)》2021,(6)
A space-borne hard X-ray collimator, comprising 91 pairs of grids, has been developed for the Hard X-ray Imager(HXI). The HXI is one of the three scientific instruments onboard the first Chinese solar mission: the Advanced Space-based Solar Observatory(ASO-S). The HXI collimator(HXI-C) is a spatial modulation X-ray telescope designed to observe hard X-rays emitted by energetic electrons in solar flares.This paper presents the detailed design of the HXI-C for the qualification model that will be inherited by the flight model. Series tests on the HXI-C qualification model are reported to verify the ability of the HXI-C to survive the launch and to operate normally in on-orbit environments. Furthermore, results of the X-ray beam test for the HXI-C are presented to indirectly identify the working performance of the HXI-C. 相似文献
17.
Lazarus E. Kopilovich 《Experimental Astronomy》2010,28(1):1-9
Estimates for the maximum number of elements of non-redundant configurations on integer square and hexagonal grids of given
sizes are derived (a “non-redundant” configuration implies that the vector differences between its elements are all distinct).
When projecting a large 2-D interferometer or a telescope, such an estimate can be used as a guide for evaluating the maximum
possible number of antennas in a non-redundant configuration that can be arranged within a given area. The suggested estimates
are empirical and based on the available data. They are obtained by reducing the problem to the linear case and by generalizing
the method applied therein. Examples of applying the method are presented. 相似文献
18.
《天文和天体物理学研究(英文版)》2020,(4)
This paper describes the establishment and verification of an accurate pointing model for a1.2 m aperture slant-axis terahertz antenna. A new analytical pointing model for the slant-axis antenna is presented based on an analogy to that of the alt-azimuth antennas. Furthermore, extra error terms are added to the pointing model based on the structure and mechanical analysis of the slant-axis antenna. To verify the pointing model experimentally, a pointing error measurement method based on photogrammetric techniques is proposed. Using this method, pointing behaviors of the antenna are accurately measured without the aid of astronomical observations, and major sources of the pointing errors are measured individually by photogrammetry and their respective coefficients are compared with those in the analytical pointing model.The results show that an extended pointing model consisting 21 error terms can significantly reduce the residual systematic errors compared with the traditional model, more details are given in the following sections. 相似文献
19.
The article presents the results of the development of a directional microstrip antenna array with small mass-dimensional characteristics as a directional antenna of the transmitting channel of a small spacecraft. 相似文献