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  • 1
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    Ultraviolet, X-ray, and infrared observations of HDE 226868 equals Cygnus X-1 (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: During April, May, and July of 1978, HDE 226868, the optical counterpart of Cygnus X-1, was repeatedly observed in the ultraviolet with the IUE satellite. Some X-ray and infrared observations have been made during the same period. The general shape of the spectrum is that expected from a late O supergiant. Strong absorption features are apparent in the ultraviolet, some of which have been identified. The equivalent widths of the most prominent lines appear to be modulated with the orbital phase. This modulation is discussed in terms of the ionization contours calculated by Hatchett and McCray, for a binary X-ray source in the stellar wind of the companion.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 242
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  • 2
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    The 1981 outburst of the old nova GK Persei (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Old nova GK Per was observed in 1981 with the IUE, during its rise, maximum, and subsequent return to minimum. In outburst, GK Per is luminous but much redder than dwarf novae or standard model accretion disks. The observed spectrum can be explained qualitatively with the Ghosh and Lamb (1979) model for the interaction of an accretion disk with the magnetic field of the accreting white dwarf. The N V and He2 are enhanced relative to other emission lines during outburst. This can be understood with photoionization by very soft X-rays having a luminosity comparable to that of the hard X-rays.
    Keywords: ASTRONOMY
    Type: ESA, A Decade of UV Astronomy with the IUE Satellite, Volume 1; p 155-157
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  • 3
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    IUE observations of oxygen-rich supernova remnants (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The IUE observations were used to determine the composition of the ejecta (especially C and Si abundances) and to test models for the ionization and excitation of the ejecta of two oxygen-rich supernova remnants (N132D in the Large Magellanic Cloud and 1E 0102-7219 in the Small Magellanic Cloud). Time-dependent photoionization by the EUV and X-ray radiation from 1E 0102-7219 can qualitatively explain its UV and optical line emission, but the density and ionization structures are complex and prevent a unique model from being specified. Many model parameters are poorly constrained, including the time dependence and shape of the ionizing spectrum. Moreover, the models presented are not self-consistent in that the volumes and densities of the optically emitting gas imply optical depths of order unity in the EUV, but absorption of the ionizing radiation was ignored. It is possible that these shortcomings reflect a more fundamental limitation of the model assumptions. It is assumed that the electron velocity distribution is Maxwellian and that the energy deposited by photoionization heats the electrons directly. The 500 eV electrons produced by the Auger process may excite or ionize other ions before they slow down enough to share their energy with other electrons. Many of the excitations would produce photons that could ionize lower ionization stages.
    Keywords: ASTRONOMY
    Type: ESA, A Decade of UV Astronomy with the IUE Satellite, Volume 1; p 117-120
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  • 4
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    Ultraviolet emission of the Vela supernova remnant and the Cygnus Loop (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Ultraviolet emission spectra of several filaments in the Vela supernova remnant and the Cygnus Loop are compared with theoretical models of radiative shocks. Shock velocities range from 85 to 130 km/s. Little or no grain depletion is apparent. Several of the observed filaments deviate from the steady-flow models in the sense that much of the photoionization-recombination zone is absent. It is shown that resonance line scattering within the emitting region can account for the weakness of the C II 1335 and C IV 1550 lines. Evaporation fronts, which are basic to the McKee and Ostriker picture of supernova remnant evolution, do not contribute significantly to the observed emission. Some discrepancies in UV emission predicted by different sets of shock models are traced to differing atomic rates used in the calculations. A fluorescent emission line of H2 may be observable in some supernova remnants.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 246
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  • 5
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    Emissivities of strong ultraviolet lines (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Using atomic data published during the last few years for Li to Mg sequence ions, we have carried out multilevel calculations over a range of electron pressures to obtain absolute intensities for spectral lines in the UV and EUV regions of the electromagnetic spectrum. Both the pressure dependence of the ionization balance and the dependence of line emissivities on the populations of metastable levels are taken into account. These line emissivities may be used to obtain plane-parallel model atmospheres for different solar transition region structures, and in general for other late-type stars which have observable lines over a wide range of excitation potentials.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 245
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  • 6
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    Observations of Cygnus X-2 with IUE: Ultraviolet results from a multiwavelength campaign (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The observations of the low-mass x ray binary, Cyg X-2, taken with the International Ultraviolet Explorer (IUE) in a campaign conducted in June and October of 1988 are reported. A direct relationship between the strength of the UV continuum and line emission and the placement of the x ray spectrum in one of three branches of the so-called Z-shaped curve is found by comparison with simultaneous x ray observations. All three previously known x ray spectral states are detected; the UV continuum and line emission increase monotonically along the Z with the least emission in the horizontal branch, and the most in the flaring branch. Emission lines due to HeII, CIV, NIII, NIV, NV, SiIV, and MgII are observed.
    Keywords: ASTRONOMY
    Type: Max-Planck-Inst. fuer Physik und Astrophysik, Observations of Cygnus X-2 at X Ray, UV, Optical and Radio Frequencies; p 46-88
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  • 7
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    The low state of AM Herculis - Observations from 0.12 to 10 microns (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Observations of AM Her during a low state over a wavelength range from 0.12 to 10 microns are reported. These include IUE ultraviolet spectra, light curves at U, B, V, R, J, H, K, and magnitudes at L, M, and N. The UV observations reveal a nearly Rayleigh-Jeans continuum spectral distribution and broad Lyman-alpha absorption from a hot (effective temperature = 50,000 K) white dwarf. Of the strong emission lines present in the high state, only weak C IV (1550 A) and Mg II (2800 A) features remain. The optical light curves are markedly different from the high state, while the infrared light curves are similar in appearance to the high state. The infrared variations cannot be explained solely by the ellipsoidal variations of a secondary star which is heated by an accretion column. The 10 micron flux is less than the high state, but it is not possible to tell if the excess noted during the high state is still present. The large available wavelength range is used to constrain the relative contributions of the white dwarf, the red dwarf, and the accretion columns.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 257
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  • 8
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    Combined ultraviolet studies of astronomical sources (1982)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Ultraviolet studies of astronomical sources are discussed. Some studies utilized IVE data. Non-radiative shock at the edge of the Cygnses Loop, stellar flares, local interestellar medium, hot galaxies, stellar mass ejection, contact binaries, double quasars, and stellar chromosphere and coronae are discussed.
    Keywords: ASTRONOMY
    Type: NASA-CR-168789 , NAS 1.26:168789 , SAR-3
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  • 9
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    An X-ray and optical study of the interaction of the Cygnus Loop supernova remnant with an interstellar cloud (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: We have used the ROSAT high-resolution imager and optical emission line data to study the structure of a bright optical knot on the southeastern rim of the Cygnus Loop supernova remnant. This knot has been identified as an encounter between the blast wave and a small isolated cloud. The knot appears in projection just behind the blast wave, which is traced by Balmer line filaments which bound the X-ray emission. The knot is a prominent X-ray feature, consisting of a numerb of filaments which are correlated with the optical line emission. These data permit a detailed view of the blast wave interaction. By combining the optical and X-ray data it is possible to trace the blast wave as a continuous surface from its southern edge around the western side of the cloud that then continues on to the north. The southeastern knot is an indentation on the surface of the blast wave. Thus the southeastern knot is not a small cloud that has been overrun by the blast wave, but the tip of a larger cloud. Bright X-ray emission is associated with bright radiative filaments. The location of this emission, upstream of the radiative shocks, implies that the enhanced X-rays come from a reverse shock. The presence of a reverse shock is further evidence that the southeastern knot represents an early stage of a blast wave encountering a large cloud. A consistent picture of the Cygnus Loop as an explosion within a preexisting cavity is emerging. These observations agree with that picture.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 444; 2; p. 787-795
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  • 10
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    New model of iron spectra in the extreme ultraviolet and application to SERTS and EUV observations: A solar active region and capella (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: We report new predictions for the EUV spectral emission of FeIX-FeXXIV, based on data now available from the Solar EUV Rocket Telescope and Spectrograph (SERTS) and the Extreme Ultraviolet Explorer (EUVE) spectrometers. The iron spectral emission model is the first result of a larger effort to revise the Raymond & Smith model and to update the atomic rates. We present here predicted emissivities for selected densities and temperatures applicable to various astrophysical plasmas. Comparisons of our predicted spectra with two recent observations provide important tests of the atomic data. They also test to some extent some basic assumptions of coronal emission codes: optically thin spectral lines and ionization equilibrium.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 97; 2; p. 551-571
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