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  • 1
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    Spectral evolution of the 5 March 1979 gamma burst (1981)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The spectral development of the intense gamma-ray burst observed on March 5, 1979 by nine spacecraft spaced on an interplanetary scale is discussed. As observed by the Pioneer Venus Orbiter detector, the hardness ratio of the burst, defined as the ratio between counts in the 100-1000 keV channels to those in the 50-100 keV channel, decreases during the very fast rise and subsequent 75 msec of the burst, consistent with a decrease in black-body temperature from 30 to 26 keV, and then increases during the shoulder on the gamma-ray burst light curve. Following the burst, the source was observed to exhibit many of the characteristics of a hard X-ray pulsar with a period of 8.0 sec and a hardness ratio varying in phase with the intensity. The observed characteristics of the pulsations are interpreted in terms of hot spots at the magnetic poles of a rotating neutron star, although it is shown that the simple cooling of residual hot spots does not completely explain the pulsations. Alternative explanations for the pulsation include accretion or an effect of beam geometry.
    Keywords: ASTROPHYSICS
    Type: Nature; 289; Jan. 8
    Format: text
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  • 2
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    Periodicity of the gamma-ray transient event of 5 March 1979 (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: An unusual gamma-ray burst event was observed on 5 March 1979 by nine different spacecraft. The position of the event has been accurately determined as r.a. = 5 h 25.95 min, dec = -66 deg 07.1 arcmin (epoch 1950.0), coincident with the location of the supernova remnant N49 in the Large Magellanic Cloud. The burst was of very high intensity, and if isotropic and located at the distance (approximately 55 kpc) of N49 had a peak luminosity of greater than 10 to the 44th erg/sec. Even more interesting is the obvious 8-s periodicity of the event, following the initial very intense outburst. The time history and power spectrum of this event as determined from Pioneer Venus Orbiter data is here reported.
    Keywords: ASTROPHYSICS
    Type: Nature; 285; June 5
    Format: text
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  • 3
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    Axisymmetric collapse of rotating, isothermal clouds (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The results of over 50 new models of the axisymmetric collapse of rotating, isothermal clouds are presented, with the following objectives: (1) to fully explore the initial conditions necessary for collapse from uniform density and uniform rotation, subject to constant volume and constant pressure boundary conditions; (2) to catalog the possible end states for cloud collapse from these initial conditions; and (3) to determine if there is a critical value of rotational energy/gravitational energy associated with ring formation, as appears to be the case for adiabatic clouds. Three end states are obtained: Bonnor-Ebert spheroids, rings and collapsing disks. The rings are formed with values of the ratio of rotational energy to the absolute value of the gravitational energy typically less than the Maclaurin spheroid value for dynamic instability to ring formation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 255
    Format: text
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  • 4
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    Mass loss from alpha Cyg /A2Ia/ derived from the profiles of low excitation Fe II lines (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The low-excitation Fe II lines in the spectral region 2000-3000 A are studied in the spectrum of alpha-Cyg. The profiles of the resonance lines are described by four representative parameters, and a preliminary model is derived from the dependence of these parameters on theoretical line strength, taking into account the influence of blending photospheric lines in an overall and qualitative way. At least 11% of all iron in the wind is once ionized, unless a non-thermal heating source enhances the fraction Fe(++) without destroying much Al(+). It is shown that the contribution of blending photospheric absorption lines to weaker P Cygni profiles has been previously largely underestimated. The mass loss rate corresponding to the model is derived, and is smaller by a factor of 500 than the one derived from the infrared excess by Barlow and Cohen (1977).
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 106; 1, Fe; Feb. 198
    Format: text
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  • 5
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    New insight into the physics of atmospheres of early type stars (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The phenomenon of mass loss and stellar winds from hot stars are discussed. The mass loss rate of early type stars increases by about a factor of 100 to 1000 during their evolution. This seems incompatible with the radiation driven wind models and may require another explanation for the mass loss from early type stars. The winds of early type stars are strongly variable and the stars may go through active phases. Eclipses in binary systems by the stellar winds can be used to probe the winds. A few future IUE studies are suggested.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 93-103
    Format: application/pdf
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  • 6
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    CCD photometry of Abell clusters. II - Surface photometry of 249 cluster galaxies (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The luminosity of the brightest cluster galaxies remains the best standard candle for observational cosmology. Studies of over 250 relatively nearby clusters show that the luminosity of these objects within an aperture of constant metric diameter has a dispersion of only 0.35 mag. The observations considered by Schneider et al. (1983) were acquired to measure the aperture luminosities of the brightest cluster galaxies. However, the data base, because of its high signal-to-noise ratio and large spatial coverage, allows several other investigations to be performed. In the present investigation, surface photometry of the brightness three galaxies within approximately 250 kpc of the cluster center is presented, taking into account the cores of 83 Abell clusters. The relevance of the photometry to cosmological studies is also discussed. It is found that dynamical friction does play an extremely important role in determining properties of brightest cluster galaxies and cluster morphology.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 268; May 15
    Format: text
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  • 7
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    Observations of Of-star wind variability (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Nightly variations in He II 4686 A have been observed in four Of stars, HD 152408, HD 151804, 9 Sge, and Lambda Cep. Three of the stars were not previously known to show such variations. In one case, Lambda Cep, simultaneous observations with IUE showed variations in ultraviolet (UV) resonance-line profiles during the same time period as those in He II 4686 A. This implies that the perturbations causing the He II 4686 A variability affect the entire wind acceleration zone.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 271; Aug. 15
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  • 8
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    Accreting X-ray pulsar atmospheres heated by Coulomb deceleration of protons (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Results are presented from detailed self-consistent models of accreting magnetized neutron star atmospheres, heated by the gradual deceleration of infalling protons via Coulomb encounters. The temperature and density gradients are calculated assuming momentum and energy balance, coupled with the radiative transfer for two polarizations. The cyclotron resonance effects were treated approximately. These models are characterized by power-law energy spectra, with single pulses at higher frequencies and multiple pulses at lower ones for some aspect angles, as well as a phase-dependent spectral index.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 266
    Format: text
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  • 9
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    The depletion of calcium in the Rho Ophiuchi cloud (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Data on the interstellar Ca II H and K lines toward HD 147889, a star deeply embedded in the rho Ophiuchi dark cloud, were obtained at the Mauna Kea Observatory of the University of Hawaii, using a multi-anode microchannel array (MAMA) detector. An upper limit on the Ca II column density of 1.7 x 10 to the 11th/sq cm was derived, which, together with ionization considerations and an estimated lower limit on the total hydrogen column density, implies that the calcium-to-hydrogen ratio in this line of sight is 0.00000795 or less, relative to the solar value. The logarithmic depletion is up to -5.10, the largest yet measured, and implies that gas-grain interaction in this region has proceeded to a much greater degree than is typical of diffuse clouds.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 265
    Format: text
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  • 10
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    CCD photometry of Abell clusters. I - Magnitudes and redshifts for 84 brightest cluster galaxies (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The way in which the luminosity of brightest cluster galaxy varies with cluster parameters is investigated in a sample of 84 Abell clusters of moderate redshift and of richness classes in the zero-to-5 range. A photometric system is used which is well matched with the low noise CCD detector employed, as well as to the arrangement of galaxies with different redshifts on a standard system. The data, together with measurements from earlier work which forms a low redshift sample of the 199 brightest cluster galaxies, confirm that the luminosity dispersion in first-rank cluster galaxies is about 0.34 mag. The colors of giant ellipticals have not changed since redshifts of 0.25, and the richness correction is well established at 0.10 mag/Abell richness class. Application of these corrections reduces the luminosity dispersion to 0.29 mag.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 264
    Format: text
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