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  • Weitere Quellen  (114)
  • ASTROPHYSICS  (114)
  • 1995-1999
  • 1980-1984  (114)
  • 1983  (114)
  • 1
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    The filaments of NGC 1275 - A collision between a galaxy and an accretion flow? (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Morphological evidence is presented (in the form of 3-A-bandpass Fabry-Perot images made with a CCD camera) that the two bright emission-line systems seen toward the galaxy NGC 1275 arise from a high-velocity impact of a foreground galaxy upon the accretion flow of gas cooling in the center of the Perseus cluster. The uniquely high optical-line luminosity of NGC 1275, in comparison with other central galaxies in clusters observed to have cooling flows, may be explained by energy deposited during the collision. Using additional information from 21-cm and extinction measurements, a rough model of the interaction is developed. Problems remain with this model - such as the likelihood of a gas-rich system penetrating to the cluster center. The kinematic structure of the optically emitting gas shows additional complex structure near the nucleus of NGC 1275.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 275; L27-L31
    Format: text
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  • 2
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    Coordinated Einstein and IUE observations of a disparitions brusques type flare event and quiescent emission from Proxima Centauri (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The Einstein Imaging Particle Counter observed a major X-ray flare in its entirety during a 5-hr period of simultaneous observations, with the IUE, of the dM5e flare star Proxima Centauri in August, 1980. The detailed X-ray light curve, temperature determinations during various intervals, and UV line fluxes obtained before, during, and after the flare indirectly indicate a 'two-ribbon flare' prominence eruption. The calculated ratio of coronal to bolometric luminosity for the event is about 100 times the solar ratio. The Proxima Cen corona is analyzed in the context of static loop models, in light of which it is concluded that less than 6% of the stellar surface seems to be covered by X-ray emitting active regions.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 267
    Format: text
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  • 3
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    NGC 315 - High-velocity H I in an active elliptical galaxy (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: The detection of high-velocity H I in absorption against the nuclear continuum source in the giant elliptical galaxy NGC 315 is reported. The absorption line is found to be highly blueshifted in the reference frame of the galaxy with a projected velocity toward the galaxy of 490 km/s. The absorption line is very strong (244 + or - 4 mJy), consisting of two components with very narrow velocity widths of 2.5 km/s (FWHM) each and peak optical depths of 0.9 and 0.2. The kinetic temperature must be 150 K if the line widths are due entirely to thermal broadening, while the neutral gas column densities implied are 2-5 x 10 to the 20th hydrogen atoms/sq cm. No OH in absorption was detected in these clouds to a limiting peak optical depth of 0.04, although this result is consistent with either a galactic or extragalactic origin of the clouds. It is suggested that these clouds may have condensed out of a large unobserved galactic halo of gas, or they may reside in or have been captured from the intracluster medium.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 266
    Format: text
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  • 4
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    2-165 keV observations of active galaxies and the diffuse background (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: HEAO 1 spectral observations of 12 active galaxies in the 12-165 keV and 2-50 keV ranges are reported. The spectra of these galaxies in the 2-165 keV range are well represented by a single power law model; within experimental uncertainties a narrow dispersion in power law index attributable to the individual galaxies is observed, while the 2-165 keV luminosities of these galaxies ranged from 3 x 10 to the 43rd to 3 x 10 to the 45th ergs/s. An apparent universality of the spectral form is found which can be interpreted as due to a common electron distribution with a temperature of tens of keV in the Compton scattering region or as a common nonthermal power-law distribution generating the observed flux through synchrotron-Compton processes. The data indicate that relativistic particles are likely to be responsible for the X-rays from cores of active galaxies through synchroton-Compton processes. In addition, it is noted that only weak number evolution, if any at all, is present in active galaxies.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 269; June 15
    Format: text
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  • 5
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    Gravitational waves and red shifts - A space experiment for testing relativistic gravity using multiple time-correlated radio signals (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: A two-step satellite mission for improving the accuracy of gravitational wave detection and for observing actual gravity waveforms is proposed. The spacecraft would carry both a highly stable hydrogen maser, which would control a transmitter sending signals to earth, and a Doppler transponder operating in the two-way mode. The use of simultaneous one- and two-way Doppler transmissions offers four time records of frequency pulsations, which can reveal gravitational radiation at 1-10 MHz with an amplitude accuracy of a factor of six. The first mission phase would consist of a Shuttle launch into a highly eccentric orbit to obtain measurements of the gravitational redshift using gravitational potentials of different earth regions to establish that gravity is describable by a metric theory. Then, after a boost into a heliocentric orbit at 6 AU, the earth-satellite system could detect gravitational waves in the solar system, as well as bursts emitted by the collisions of supermassive black holes.
    Schlagwort(e): ASTROPHYSICS
    Materialart: General Relativity and Gravitation; 15; Feb. 198
    Format: text
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  • 6
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    Chromospheric and coronal emissions from the giants in the Hyades (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The visible Ca II K and International Ultraviolet Explorer spectra from the four K0 III stars (theta-1, gamma, delta, and epsilon Tau) in the Hyades, along with a field giant of similar spectral type, beta Gem, have been measured. Among the Hyades giants, the range of the high-temperature emissions can be a factor of 6 or more for C IV and an order of magnitude in the X-ray luminosity measured by Stern et al. (1981). For these presumably coeval cluster giants with similar macroscopic parameters, such as age, mass, effective temperature, gravity, and projected rotational velocity, the observed range in chromospheric and coronal emissions is not easily explained by the dominant factors thought to control these emissions in cool stars. It is possible that the emissions are time variable, on a time scale longer than six months. This would be the first evidence that giants undergo magnetic activity cycles similar to those of dwarf stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 271; Aug. 15
    Format: text
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  • 7
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    Orbital period changes in Centaurus X-3 (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Two new times of mid-X-ray eclipse for Cen X-3 are presented on the basis of pulse arrival time analyses of pointed observations with SAS 3. When combined with all other published eclipse times based on Doppler delay measurements, the results show that the 2.1d binary period is decreasing at an average rate of 1.8 x 10 to the -6th/yr. The decrease, however, is seen as having significant fluctuations about a smooth, linear decrease. The changes observed in the orbital period can be accounted for by mass loss from the system through the L2 point, although the rates required are implausibly high. It is also shown that the long-term overall orbital decay can readily be interpreted as the result of torques exerted by the tidally distorted companion star (Krzeminski's star) on the orbiting neutron star. It is noted that the inferred asynchronism between the orbital frequency and the rotation frequency of the companion star may be maintained by mass and angular momentum loss in a stellar wind or by a tidal instability related to the Darwin effect. However, this would not provide a natural explanation for any short-term deviations from a constant rate of orbital decay.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 268; May 15
    Format: text
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  • 8
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    On the possibility of detecting very hot gas through absorption-line studies (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The possibility of detecting hot (T greater than or approximately equal to 10 to the 6th K) diffuse interstellar and intergalactic gas through absorption-line studies is assessed. Optical studies of semiforbidden lines are shown to be just beyond feasibility. X-ray absorption-line studies are concluded to be within the capability of future soft X-ray spectrographs, however. In particular, it is shown that the Bragg crystal spectrometer aboard Einstein could possibly have been used to detect O VII and O VIII lines against the Crab if they are present at plausible levels. Improvement of instrument parameters by only a small factor could make this the most important method available for studying hot interstellar, galactic halo and possibly even intergalactic gas.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 264
    Format: text
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  • 9
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    Radial variations of large-scale magnetohydrodynamic fluctuations in the solar wind (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Two time periods are studied for which comprehensive data coverage is available at both 1 AU using IMP-8 and ISEE-3 and beyond using Voyager 1. One of these periods is characterized by the predominance of corotating stream interactions. Relatively small scale transient flows characterize the second period. The evolution of these flows with heliocentric distance is studied using power spectral techniques. The evolution of the transient dominated period is consistent with the hypothesis of turbulent evolution including an inverse cascade of large scales. The evolution of the corotating period is consistent with the entrainment of slow streams by faster streams in a deterministic model.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-TM-85116 , NAS 1.15:85116
    Format: application/pdf
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  • 10
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    A far-infrared study of the N/O abundance ratio in galactic H II regions (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: New measurements are presented for W43 (G30.8-0.0), Orion A, and G75.84+0.4, which are located at widely varying distances from the galactic center. The combination of the forbidden N III 57.3 microns and forbidden O III 88.4 and 51.8 microns yields measurements of N(++)/O(++) that are for the most part insensitive to electron temperature and density uncertainties and to clumping of the ionized gas. This is due to the similarity of the critical densities for these transitions. It is contended that for the observed nebulae, N(++)/O(++) should be indicative of N/O, a ratio that is of signal importance in nucleosynthesis theory. The measurements are compared with previous measurements of M17 and W51, which lie at intermediate galactocentric distances. For nebulae in the solar circle, it is found that N(++)/O(++) is greater than the N/O values derived from optical studies of N(+)/O(+) in low-ionization zones of the same nebulae. Possible sources of this discrepancy are considered. It is found that N(++)/O(++) in W43 is significantly higher than for the other H II regions in the sample. Since W43 is located at R = 5 kpc, which is the smallest galactocentric distance in the sample, the data are seen as consistent with the presence of a negative abundance gradient d(N/O)/dR.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 271; Aug. 15
    Format: text
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