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  • 1
    Publication Date: 2013-08-31
    Description: Random process models phased in the time domain are used to analyze astrophysical time series data produced by random processes. A moving average (MA) model represents the data as a sequence of pulses occurring randomly in time, with random amplitudes. An autoregressive (AR) model represents the correlations in the process in terms of a linear function of past values. The best AR model is determined from sampled data and transformed to an MA for interpretation. The randomness of the pulse amplitudes is maximized by a FORTRAN algorithm which is relatively stable numerically. Results of test cases are given to study the effects of adding noise and of different distributions for the pulse amplitudes. A preliminary analysis of the optical light curve of the quasar 3C 273 is given.
    Keywords: NUMERICAL ANALYSIS
    Type: NASA-TM-81148 , A-7959
    Format: application/pdf
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  • 2
    Publication Date: 2018-12-01
    Description: The advent of the Space Station Program has provided an unexpected opportunity for the Astrometric Telescope Facility (ATF) study program by providing a potential long-duration on-orbit serviceable platform. It required a concept change for ATF from a free-flyer observatory to a Space-Station-based Observatory. The program was sent in this new direction at the start of fiscal year 1985, and program plans including study schedules and science and technical requirements are being revised and defined. The facility is designed to be versatile and capable of fulfilling the primary goal of planet detection, and to be highly useful for other astrophysics observations. Basically the ATF observing program is a long-duration plan requiring repetitive observations of single stars over a one to two decade period. These repetitive observations are needed to provide data necessary to conclusively determine the existence (or nonexistence) of planets of the Uranus and Neptune class in extrasolar planetary systems.
    Keywords: ASTRONOMY
    Type: AIAA PAPER 86-0540
    Format: text
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  • 3
    Publication Date: 2019-01-25
    Description: If gamma-ray bursters are at cosmological distances-a possibility suggested by their isotropic distribution and spatial inhomogeneity-then the temporal profiles and spectra of more distant sources will be time dilated compared to those of relatively nearby sources. Analyses of bright and dim Burst and Transient Source Experiment (BATSE) gamma-ray bursts yield a relative time-dilation factor of 2.3 on timescales of pulses and event durations. We redshift the spectra of time intervals near the intensity peaks of the bright sample on a trial grid and compare with spectra of the dim sample. A redshift factor of order two-with wide latitude permitted-brings the spectra of the two brightness groups into alignment. Thus there is coarse agreement with the time-dilation factor found in the temporal domain.
    Keywords: Astrophysics
    Type: Gamma ray astronomy; E2 Symposium of COSPAR Scientific Commission E, COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994 . (ISSN 0273-1177); 15; 5; p. (5)135-(5)138
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  • 4
    Publication Date: 2011-08-17
    Description: The infrared spectrum of the Kleinmann-Low nebula in M42 has been measured from 80 to 350 kaysers (approximately 29 to 125 microns) with a Michelson interferometer aboard the NASA Kuiper Airborne Observatory. The frequency spectrum peaks at about 185 kaysers. A simple model of the emission implies that the temperature is in the range 70-95 K and that the optical depth is at least 0.2 at the peak frequency. A possible absorption is seen at about 176 kaysers. Thermal emission by dust at a temperature of 71 K, with the absorption cross section proportional to frequency, provides a good fit to the data. Other thermal-emission models can also fit the spectrum. The data are compared with previous broad-band measurements. Upper limits are placed on expected line emission from the surrounding H II region at the position of the nebula.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 212
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  • 5
    Publication Date: 2011-08-16
    Description: A Monte Carlo method is given for analyzing the transfer of resonance radiation in a rapidly and differentially expanding nebula. Coherence in the frame of the atom is shown to lead to interesting modifications of the emergent radiation field, as compared with the other more usual assumptions of coherence or redistribution in the fluid frame. Results are presented in tabular form suitable for further use. Sample line profiles produced by pure scattering out of the continuum are generated, and it is shown that an arbitrarily high peak can be obtained. This conclusion is independent of the coherence assumption used. The distribution of the number of scatterings is found in all cases. An analytic solution is presented for the case of coherence in the fluid frame.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 176; Sept. 1
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  • 6
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: Crab Nebula pulsar magnetic field structure, discussing linear polarization modifications and wisps
    Keywords: SPACE SCIENCES
    Type: ; ADEMIE DES SCIENCES
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  • 7
    Publication Date: 2011-08-16
    Description: Quasars PHL 5200 and RS 23 spectra absorption lines, examining resonance line transfer of radiation through differentially expanding atmosphere
    Keywords: SPACE SCIENCES
    Type: ; 47 (
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  • 8
    Publication Date: 2011-08-17
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 228
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  • 9
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: It is shown that application of standard MHD arguments to hydromagnetic waves observed in the Crab Nebula dramatically improves the upper bound on photon rest mass. The standard argument that massive photons are governed by the Phoca field equations is outlined and applied to wisp features (identified as hydromagnetic waves) observed in the Crab. The results imply an upper limit for the photon rest mass of between 3 by 10 to the -54th power and 3 by 10 to the -53rd power gram, which is smaller than the best previous limits by a factor of 10,000 to 100,000. It is noted that although the present limit is probably valid in order of magnitude, some doubt remains since there are inconsistencies in the standard arguments.
    Keywords: ASTROPHYSICS
    Type: Physical Review Letters; 35; Oct. 27
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  • 10
    Publication Date: 2011-08-16
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 184; Aug. 15
    Format: text
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