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  • 1
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    The observations of the X-ray source HZ Herculis/Hercules X-1 (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The results of a campaign of monitoring HZ Her with the IUE satellite are presented. The spectrum and light variation outside of eclipse are consistent with the Milgrom and Salpeter model for emission from the X-ray heated photosphere of the primary. Near eclipse there is UV flux in excess of the prediction of the heated photosphere model, which shows significant 35 day variations and is consistent with an origin in a precessing disk, as described by Gerend and Boynton. The spectrum shows the strong emission lines of N V and C IV, which generally vary in the sense of the continuum. The N V/C IV ratio is greater than 2 near orbital phase 0.5 and approaches unity near eclipse. It is suggested that these emission lines are optically thick and arise from both the heated photosphere and the accretion disk.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 237
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  • 2
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    IUE observations of X-ray sources - HD153919 /4U1700-37/, HDE226868 /Cyg X-1/, HZ Her /Her X-1/ (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The first UV spectroscopic measurements of binary X-ray sources with IUE show highly variable emission from a photoionized plasma in the object HZ Her, and give evidence for localized circumsystem material in the binary source Cygnus X-1. In addition, a substantial stellar wind is found in one of the brightest identified X-ray sources HD153919. This system may be surrounded by an extensive H II region unusual in its content of high excitation ion species.
    Keywords: ASTROPHYSICS
    Type: Nature; 275; Oct. 5
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  • 3
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    Constraints on the inclination and masses of the HDE 226868/Cygnus X-1 system from the observations (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Analyses of two high-dispersions IUE spectra of HDE 226868 (the optical counterpart of Cygnus X-1) are combined with studies of low-dispersion IUE spectra to provide a more accurate determination of the variation of C IV stellar wind absorption as a function of orbital phase. By incorporating these observational results into an analysis of the structure of the X-ray ionization cavity in the stellar wind, it is found that the orbital inclination must lie between 36 and 67 deg, leading to a mass for the compact object between 5.7 and 11.2 solar masses.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 270; July 15
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  • 4
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    Simultaneous ultraviolet, optical, and X-ray observations of the X-ray source Vela X-1 /HD 77581/ (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: UV spectra (obtained by the IUE) of HD 77581, associated with the binary X-ray source Vela X-1, show a spectrum typical of an early B-type supergiant. However, the P Cygni profiles of strong resonance lines show substantial variations with orbital phase. These variations can be ascribed to the changing ionization state in the stellar wind caused by the X-ray emitting companion. X-ray and spectroscopic and photometric optical observations, simultaneous with the IUE observations, indicate behavior consistent with previous epochs.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 238
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  • 5
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    Chromospheres of the active dwarf binaries EQ Pegasi and Xi Bootis (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Ultraviolet spectroscopic measurements of the M dwarf binary EQ Peg and the G8 V star Xi Boo A have been made with the International Ultraviolet Explorer satellite. High-temperature emission lines (N V, C IV, Si IV) are present with similar strengths in both stars. The surface fluxes of chromospheric and transition-region lines are enhanced relative to those of normal main-sequence stars and are comparable to those observed in solar active regions. If inhomogeneities are present, the surface fluxes may be markedly higher than the derived values. It is likely that the emission observed from EQ Peg was not the result of major flare activity; however, the quiescent radiative losses observed in the ultraviolet are comparable to the time-averaged optical flare losses. The similarity of the line emissions of active dwarfs of diverse spectral types suggests that the character of the transition region is independent of the stellar effective temperature.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 233
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  • 6
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    Ultraviolet television data from the orbiting astronomical observatory. II - Stellar ultraviolet colors and interstellar extinction (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The results from the Celescope Catalog of Ultraviolet Stellar Observations (Davis, Deutschman, and Haramundanis 1973) are studied, emphasizing statistical groups and subgroups of stars. In spite of the rather large observational errors, the great number of Celescope observations make it possible to do that kind of study with reasonable accuracy. Some stars have ultraviolet colors that differ significantly from those of the group to which they have been assigned on the basis of ground-based observations. An attempt is made to describe the general properties of the ultraviolet colors of the stars as observed by the Celescope experiment on board NASA's Orbiting Astronomical Observatory (OAO-2). Besides the direct applicability of these results to the general study of stellar atmospheres and of interstellar extinction, they are also considered as a frame of reference for further studies of individual stars and groups of stars.
    Keywords: ASTROPHYSICS
    Type: vol. 28; Aug. 197
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  • 7
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    Chromospheres and coronae of late-type stars (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: IUE short wavelength (1150-2000 A) spectra of late-type dwarfs, giant, and supergiant stars show a variety of emission features varying in excitation from about 10,000 K to about 3 x 10 to the 5th K. High excitation species are found most strongly in main sequence stars. Dwarf stars with active chromospheres (e.g., Xi Boo) and flare stars (EQ Peg) show enhancement of surface flux as compared to the quiet sun; binary systems of W UMa and RS CVn types show even larger surface fluxes. The enhancement increases with temperature of formation much like a solar active region. The presence of high excitation species in the giant and supergiant stars suggests that parameters other than effective temperature and luminosity are important in establishing a transition region and corona.
    Keywords: ASTROPHYSICS
    Type: The first year of IUE; Apr 04, 1979 - Apr 06, 1979; London
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  • 8
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    Ultraviolet observations of AM Herculis with IUE (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Ultraviolet observations of the binary X-ray source AM Herculis from the IUE satellite show strong emission lines of ions from O I to N V, probably originating in photoionized gas, and a continuum which is partially eclipsed in phase with the X-ray eclipse. The emission lines have broad (about 600 km/s) and sharp (about 80 km/s) components at different velocities, as has been seen in optical lines. The continuum is interpreted as two components, a blackbody (blackbody kT of 25-30 eV) which accounts for the X-ray emission below 0.5 keV and the eclipsed part of the UV continuum, and a component which is never eclipsed, whose spectrum is roughly proportional to the inverse of frequency. Strong ultraviolet emission due to optically thick cyclotron emission, which has been predicted theoretically, is not observed. This presents a severe difficulty for the theory of accretion onto the magnetic pole of a white dwarf.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 230
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  • 9
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    Ultraviolet spectroscopic measurements of globular clusters (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Ultraviolet spectra of six globular clusters (M15, M92, NGC 1851, NGC 6624, 47 Tuc, and NGC 6752) have been taken with the International Ultraviolet Explorer satellite in order to investigate the surface brightness distributions in the central regions. The ultraviolet emission indicates composite stellar spectra. Short-wavelength emission (1200-1900 A) arises from blue horizontal-branch stars; long-wavelength emission (2100-3000 A) is characteristic of late-type horizontal-branch and giant stars. The surface brightness distribution is more compact at short wavelengths than at long wavelengths, suggesting a segregation of horizontal-branch stars. A dense core appears to be present in X-ray-emitting clusters and absent in those clusters without X-ray sources. The X-ray source in NGC 6624 may have been detected at short wavelengths (1300-1900 A).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 230
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  • 10
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    Seven poor clusters of galaxies (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The measurement of 83 new redshifts from galaxies in the region of seven of the poor clusters of galaxies identified by Morgan et al (1975) and Albert et al (1977) has been followed by an estimation of cluster masses through the application of both the virial theorem and the projected mas method. For each system, these two estimates are consistent. For the two clusters with highest X-ray luminosities, the line-of-sight velocity dispersions are about 700 km/sec, while for the five other clusters, the dispersions are of the order of less than about 370 km/sec. The D or cD galaxy in each poor cluster is at the kinematic center of each system.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 283; 33-49
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