| 1. |
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| 2. |
- Bartel, N., et al.
(författare)
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The Compact Radio Source 2021+614 : Simultaneous 2.3 and 8.3 GHz Mark III VLBI Observations
- 1984
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Ingår i: Astrophysical Journal. - Philadelphia, PA : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 279:1, s. 116-121
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Tidskriftsartikel (refereegranskat)abstract
- Second-epoch VLBI observations of the flat-spectrum radio source 2021+614 made simultaneously at 2.3 and 8.3 GHz with the Mark III system are reported. The maps derived from these observations reveal a complex, frequency-dependent radio structure on the milliarcsecond scale. The object has four nearly collinear components oriented at a position angle of about 35 degrees and embedded in an extended region. Two of these are optically thin, one has a flat spectrum, and the other appears to be synchrotron self-absorbed in the frequency range 2.3-8.3 GHz. No significant structural variation is found at either frequency between epochs separated by about three years. The formal estimate of the transverse velocity between two components, one with a flat and the other with an inverted spectrum, is v/c = 0.7 + or - 2.3. Remarkable similarities between 2021+614 and the unusual source 0316+413 are discussed.
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| 3. |
- Bååth, L.B. 1948-, et al.
(författare)
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High Resolution Observations of the QSO 3C 345 at 1.3 centimeters
- 1981
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Ingår i: Astrophysical Journal. - Philadelphia, PA : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 243, s. L123-L126
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution VLBI observations made at a frequency of 22.235 GHz of the quasar 3C 345 are discussed. Antennas located at the Crimean Astrophysical Observatory, USSR; Onsala, Sweden; Effelsberg, West Germany; and the Haystack Observatory, Massachusetts were employed at 4-min integration times to provide baselines ranging up to 5.5 x 10 to the 8th wavelengths. About 40% of the total flux density of 7.85 Jy, observed in November 1977, and 8.05 Jy, observed in October 1978, is found to originate in an unresolved component of the quasar core in a region less than 0.1 milliarcsec in diameter. The elongated jet-like component of the quasar is observed to contain several peaks of emission extending up to 6 milliarsec from the core which decreased in extent between the two observations.
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| 4. |
- Clavel, J., et al.
(författare)
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Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. I. An 8 month campaign of monitoring NGC 5548 with IUE
- 1991
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 366:1, s. 64-8181
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Tidskriftsartikel (refereegranskat)abstract
- The authors present emission-line and ultraviolet continuum observations of a type I Seyfert galaxy in which the time resolution is adequate for describing the character of variability. Using the IUE satellite, the nucleus of NGC 5548 was observed every 4 days for a period of 8 months. Its mean properties-continuum shape, line ratios-are not unusual for type I Seyfert galaxies, but it was found to be strongly variable. The ultraviolet continuum flux and broad emission line fluxes varied significantly, going through three large maxima and three deep minima. The great majority of all variations were well resolved in time. The data lend qualitative support to the view that photoionization by the nuclear continuum is responsible for driving the emission lines
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| 5. |
- Cotton, W. D., et al.
(författare)
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High Resolution Observations of the Steep Spectrum Source 2147+145
- 1984
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Ingår i: Astrophysical Journal. - Philadelphia, PA : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 277, s. L41-L44
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Tidskriftsartikel (refereegranskat)abstract
- The results of an eight station, 18-cm intercontinental very long baseline interferometry for which the synthesized beam obtained was 0.008 x 0.003 arcsec are presented for the steep spectrum compact radio source 2147+145. These observations reveal a structure similar to flat spectrum compact sources and, if the source radiates due to the synchrotron process, a very weak magnetic field. The source consists of a line of knots 0.022 arcsec long along position angle of 38 deg dominated on one side by a component of size 0.0032 arcsec measured along a position angle of 38 deg. It is suggested that 2147+145 and, perhaps, related steep spectrum objects are similar to flat spectrum, optically active sources except that the magnetic field is much weaker.
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| 6. |
- Feltzing, Sofia, et al.
(författare)
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The production of beryllium in the early Galaxy
- 1994
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 423:1, s. 68-72
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Tidskriftsartikel (refereegranskat)abstract
- The formation of beryllium in the early Galaxy is discussed. It is shown that if spallation occurs predominantly in regions rich in heavy elements, i.e., close to supernovae, the linear relation recently obtained by Gilmore et al. (1992) between beryllium and oxygen abundances for Population II stars may be reproduced. Estimates of relevant timescales for mixing show that the decisive factor, the ratio of the timescale of cosmic-ray diffusion out of the locally enriched regions to the decay time of cosmic rays in the Galaxy as a whole, admits this scenario. Although energetically possible, it requires, however, very high local cosmic-ray fluxes (greater than or equal to 105/sq cm/s), which predicts gamma-ray fluxes above those observed from supernova remnants and the Galaxy. We therefore consider other models, such as those given by Duncan et al. (1992) or Prantzos et al. (1993), more probable.
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| 7. |
- Johansson, S. G, et al.
(författare)
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Comparison of New Experimental and Astrophysical F-values For Some Ru-ii Lines, Observed In Hst Spectra of Chi-lupi
- 1994
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 421:2, s. 809-815
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Tidskriftsartikel (refereegranskat)abstract
- We report on experimental absolute oscillator strengths for 18 UV lines of Ru II, obtained by combining laser-induced fluorescence measurements of radiative lifetimes and branching fractions from line intensities in a calibrated Fourier-transform spectrum. HST/GHRS observations of the spectrum of the sharp-lined B star chi Lupi contain six of these lines, for which ''astrophysical'' relative f-values have been determined. The agreement is within 0.10 dex for a Ru abundance of log N(Ru)/N(H) = -7.90, which is 2.3 dex above the solar abundance.
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| 8. |
- Jones, D. L., et al.
(författare)
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High dynamic range VLBI observations of NGC 6251
- 1986
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Ingår i: Astrophysical Journal. - Philadelphia, United States : Institute of Physics Publishing, Inc. - 0004-637X .- 1538-4357. ; 305:2, s. 684-697
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Tidskriftsartikel (refereegranskat)
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| 9. |
- Jönsson, Per, et al.
(författare)
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Accurate Calculation of the Isotope Shift and Hyperfine-structure In the Boron (b-ii) Line At 1362 Angstrom
- 1994
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 429:1
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Tidskriftsartikel (refereegranskat)abstract
- An extensive multiconfiguration Hartree-Fock (MCHF) calculation of the isotope shift and hyperfine structure in the resonance line of B II at 1362 angstrom has been performed. The calculated B-11-B-10 isotope shift is 13.3 mangstrom with an estimated uncertainty of 1%. The calculated interaction constants A and B give a hyperfine structure splitting of less than 0.45 mangstrom for both isotopes. The size of the isotope shift in the B II line is similar to the limit of detection in high-resolution observations with the Goddard High Resolution Spectrograph aboard the Hubble Space Telescope when side A becomes operational after the service mission.
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| 10. |
- Mundy, Lee G., et al.
(författare)
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High-resolution images of the Orion molecular ridge in the CS J = 2-1 transition
- 1988
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Ingår i: Astrophysical Journal. - Philadelphia, PA : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 325:1, s. 382-388
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Tidskriftsartikel (refereegranskat)abstract
- The authors have constructed 7arcsec.5 resolution images of the CS J = 2-1 emission from a 3arcmin.5 section of the Orion molecular ridge using a maximum entropy algorithm to combine Owens Valley Millimeter-Wave Interferometer and Onsala Space Observatory 20 m data. The resulting images include all of the flux and have positional accuracy of 1arcsec-2arcsec on the small-scale features. The observed section of the ridge includes four condensations. The condensations have dimensions from 0.03 to 0.11 pc and virial massses from 30 to 80 M_sun;. Approximately 70% of the total mass within the 3arcmin region is contained in these condensations.
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