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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experimental astronomy 1 (1989), S. v 
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new solar γ-ray telescope is described which is intended to take advantage of current long-duration balloon facilities such as the RACOON system. The primary scientific objective is to detect and measure γ-ray lines from solar flares along with the associated low-energy continuum. The proposed instrument is centered on a multi-headed germanium system and is designed to operate over the energy range 50 keV to 200 MeV. In the nuclear transition energy region, the average energy resolution of the primary detectors is over 20 times better than that achieved with the γ-ray spectrometer onboard the Solar Maximum Mission satellite. A detailed description of the instrument and its expected performance will be given.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Based on monoenergetic proton beam tests of both NaI and CsI, a method for estimating the spallation background, due to the cosmic ray protons and trapped protons, has been developed. Comparisons between the calculated background noise and those measured by telescopes on board satellites are made. Good agreements of these comparisons demonstrate that the approach is capable of providing realistic estimates for specific space borne gamma-ray telescopes in well defined orbits.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The design of very high energy (VHE) gamma ray telescopes is discussed and it is shown that a triple-mirror telescope operating in threefold fast coincidence provides an effective instrument. The design, construction and operation of a large VHE gamma ray telescope with an energy threshold of 300 GeV (at the zenith) and incorporating several novel features is described. The use of a coincidence ‘guard ring’ technique is shown to result in the rejection of about 50% of the off-source (proton) events which form a high background and limit the sensitivity of such telescopes.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The minimum-norm least-squares solution of the phase-closure equations of an interferometric array is very stable. Furthermore, this canonical solution can be obtained by simple backprojection, each closure phase leaving its “algebraic” imprint on the corresponding baselines. More precisely, the generalized inverse of the phase-closure operator C of an n-point array is equal to its adjoint (its Hermitian transpose) divided by n: C + =C * /n. Likewise, the generalized inverse of the phase-aberration operator B is equal to B * /n. These remarkable properties, which have so far remained unnoticed, play an essential part in the algebraic analysis of phase-closure imaging, and thereby in the understanding and the treatment of the inverse problems of aperture synthesis. The applications presented in this paper concern the phase-factor restoration problem in optical interferometry and speckle imaging. We first propose a new iterative procedure for obtaining a particular least-squares solution. In the framework of this nonlinear technique, we then show how to initialize at each iteration the inner process of linear optimization. The backprojection method, which is the obvious choice in the case of weakly-redundant devices, is compared with the recursive techniques used in bispectral analysis for highly-redundant configurations. At the end of the restoration step under consideration, the phase indetermination reduces to a vector lying in the null space of the bispectral operator. The global reconstruction process is closely related to the regularization methods used for band-limited extrapolation. In this context, we outline the final hybrid procedure to be implemented, indicating how certain regularizing constraints can raise the intrinsic indeterminations related to the existence of the null space.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Experimental astronomy 1 (1989), S. 101-121 
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The present state of the art of acousto optical spectrometer (AOS) development for spectroscopy is reviewed with special emphasis given to the University of Cologne built systems. The underlying principles of acousto optical detection are discussed and are used for an in depth analysis of limitations and an optimal use of this powerful spectroscopic tool. The inherent instabilities were traced to arise from laser “speckles” which have been the primary cause of AOS instabilities, producing severe baseline problems and thus limiting its performance. The role of laser scatter is discussed and suitable techniques for removal of scattered background laser light are described. In addition, the influence of the various optical components on the performance of AOS is evaluated. Two examples of Cologne built AOS are described in detail. One is a low resolution AOS with 1.1 GHz bandwidth now in operation at the ESO SEST telescope at La Silla, Chile, and the other is a medium resolution AOS with 287 MHz bandwidth stationed at the KOSMA 3-m-radiotelescope at Gornergrat near Zermatt, Switzerland. Technical details of the high resolution AOS at Gornergrat are also given. The AOS are shown to be extremely stable so that they can be used for more than 100 sec integration time on each position in the position switch mode as proved by the spectroscopic Allan variance, specifically developed as a critical performance test procedure. Experimental results are presented and a future outlook for further AOS developments is given, i.e. array AOS or variable bandwidth AOS.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A sensitive spectrograph for rocket observations of celestial objects in the 910–1250Å band is described. The instrument incorporates a variety of new technologies that allow unprecedented sensitivity in this difficult, but scientifically rewarding, band. It includes a diamond-turned Wolter-Schwarzschild Type II telescope, a conventional Rowland Circle spectrograph, and resistive anode/micro-channel plate detectors. It has been launched twice from Woomera, Australia where it performed the only observations of SN1987a in its bandpass and discovered a new feature in the diffuse ultraviolet background.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Experimental astronomy 1 (1990), S. 145-163 
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Significance testing, parameter estimation and sensitivity calculations for γ-ray telescopes are discussed for single ‘on-off” astronomical observations. Four widely used significance test methods are examined by Monte-Carlo simulations. The Maximum Likelihood Ratio Method is found to consistently over-estimate the significance of an observation by a few percents whereas the Fisher's Exact Test is shown to be slightly conservative and always under-estimates the significance by about the same amount when the reported significance is about 3σ and therefore it is preferred for γ-ray astronomy applications. Two methods for constructing a confidence interval and an upper limit for γ-ray source counts are discussed. It is found that the method based on the Smooth Transformation provides slightly better estimations. A new formula for the calculation of the sensitivity of a γ-ray telescope is presented, in contrast to the widely accepted one, and their statistical meanings are explained in detail.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Lunar occultation can be considered of interest for future missions dedicated to X-ray astronomy only if instruments with a large enough collecting area are used. In this case, observations of the numerous, faint X-ray sources occulted by the moon during a typical satellite lifetime of several years, can, in principle, add good source positioning as a free bonus to a high-throughput, medium-imaging mission. In the practical case of the EPIC instrument aboard the XMM ESA satellite, a simple calculation shows the potential usefulness of this technique.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1572-9508
    Keywords: cryogenic equipmentelectro-optical instrumentation ; ground-based astronomy ; photon-countingdetectors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract S-Cam is a cryogenic camera for ground-basedastronomy using Superconducting Tunnel Junctions(STJs). It has been designed as a technologydemonstrator, aiming to prove the potential of a newgeneration of single photon counting detectors at aground-based telescope. The camera has a field of viewof about 4.0 × 4.0 arcsec2 and it is based on a6 × 6 array of Ta-Al Josephson junctions, operating atabout 350 mK and individually read-out. For eachdetected photon, the absorption position, the arrivaltime and the corresponding energy are measured. Inthis paper we provide an overview of the cryogenicdetector performance, a description of the S-Camsystem and a summary of the results obtained bothduring testing at ESTEC and during the firstobservations at the William Herschel Telescopein La Palma (Canary Islands, Spain). Initialastronomical results on the Crab pulsar are presentedalong with an outlook on future activities.
    Type of Medium: Electronic Resource
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