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  • ASTRONOMY  (12)
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  • 1
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    The 1985 May superoutburst of the dwarf nova OY Carinae. II - IUE and Exosat observations (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Ultraviolet (IUE) and X-ray (Exosat) observations of the eclipsing dwarf nova OY Carinae during the superoutburst of May 1985 are presented. From the lack of X-ray eclipse and UV behavior, it is deduced that the X-ray flux originates in an optically thin corona comparable in size to the Roche lobe, and not directly from the white dwarf or boundary layer. The asymmetric UV line emission originates partly in the accretion disk and partly in a wind. There is a strong modulation of the UV continuum flux that is thought to be caused by extended vertical disk structure shadowing the inner regions.
    Keywords: ASTRONOMY
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 231; 237-255
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  • 2
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    The dwarf nova dippers (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Previous papers have shown that the dwarf nova OY Car has an extensive vertical disk structure during its superoutbursts. This structure is analogous to that seen in the low mass X-ray binaries (LMXBs), in that the whole disk flares toward its edge, and there is a bulge or 'dark spot' where the mass transfer stream meets the disk edge. The paper presents evidence suggesting that two more dwarf novae may have such a stream impact bulge, which manifests itself as a dip in the UV light curve, analogous to those seen in the X-ray light curves of the LMXB dippers.
    Keywords: ASTRONOMY
    Type: Advances in Space Research (ISSN 0273-1177); 8; 2-3,
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  • 3
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    IUE observations of the 1987 superoutburst of the dwarf nova Z Cha (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Low resolution IUE observations of the dwarf nova Z Cha during superoutburst are presented. These cover most of the development of the outburst and have sufficient time resolution to probe continuum and line behavior on orbital phase. The observed modulation on this phase is very similar to that observed in the related object OY Car. The results imply the presence of a cool spot on the edge of the edge of the accretion disk, which periodically occults the brighter inner disk. Details of the line behavior suggest that the line originated in an extended wind-emitting region. In contrast to archive spectra obtained in normal outburst, the continuum is fainter and redder, indicating that the entire superoutburst disk may be geometrically thicker than during a normal outburst.
    Keywords: ASTRONOMY
    Type: ESA, A Decade of UV Astronomy with the IUE Satellite, Volume 1; p 187-190
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  • 4
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    IUE observations of the dwarf novae OY Car in superoutburst (1986)
    In:  Other Sources
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    Publication Date: 2013-08-29
    Description: The May 1985 superoutburst of OY Car, an eclipsing member of the SU UMa subclass of dwarf novae, was observed extensively with IUE to obtain phase-resolved spectra throughout several orbital cycles, when the superhump was well developed and lay close in phase to the eclipse. The UV lines and continuum vary with orbital phase and show a strong UV eclipse coincident with the optical eclipse. This implies that the superhump source at eclipse is not a strong contributor in the ultraviolet. The UV emission line spectrum and lack of X-ray eclipse suggest the presence of an extended coronal region. The flux evolution observed is unusual in that gross changes occur during the decline from superoutburst. The later spectra actually appear hotter than spectra earlier in the decline, and suggest that, early on, the inner disk is obscured from view.
    Keywords: ASTRONOMY
    Type: ESA Proceedings of an International Symposium on New Insights in Astrophysics. Eight Years of UV Astronomy with IUE; p 467-470
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  • 5
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    Soft X-ray spectrum and structure of the supernova remnant G65.2+5.7 (1979)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The HEAO 1 low energy detectors have observed the supernova remnant G65.2+5.7 in the energy range 0.2-2.5 keV. A strong, extended source of X-ray emission is observed coincident with the eastern side of the optical filamentary structure. The characteristic temperature of the emission is in the range 2-3.8 x 10 to the 6th K, and evidence is found for line emission at about 0.8 keV in the X-ray spectrum. These observations imply a shock velocity (425 km/s) and age (about 20,000 yr) that markedly disagree with the estimates from optical and radio observations.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 230
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  • 6
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    Low energy X-ray emission from five galaxy cluster sources (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: We report the detection of soft (0.2-2.5 keV) X-ray emission from several known cluster X-ray sources using the low energy detectors of the HEAO 1 A-2 experiment. Soft X-ray emission was observed from five clusters - the Centaurus cluster, Abell 2147, SC 1329-314, Abell 2319, and Abell 133. Spectral parameters estimated from the soft X-ray fluxes are inconsistent with those reported at higher energies for the Centaurus cluster, Abell 2147, and SC 1329-314, indicating the presence of more than one spectral component in these clusters. No evidence for more than one component was found for either Abell 2319 or Abell 133. The temperature of Abell 133 is constrained to be less than 2 x 10 to the 7th K, making it the coolest X-ray cluster yet detected.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 247
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  • 7
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    Low-energy X-ray line emission from IC 443 (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: HEAO 1 observations of the spectrum of the supernova remnant IC 443 in the energy range of 0.4-3 keV reveal the presence of a complex structure suggestive of emission from Fe XVIII-XX, S XV-XVI, and Si XIII-XIV ions. The best electron temperature in the band for simple model fits is about (6-11) x 10 to the 6th K. Raymond and Smith collisional equilibrium emission models do not adequately fit the data. These results are discussed in terms of possible nonequilibrium effects in the remnant.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 246
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  • 8
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    Einstein observations of the confused 2A 2315-428 region (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Four distinct X-ray sources have been detected by the Einstein Observatory imaging proportional counter in the 2A2315-428 field. The strongest source in the 0.2-3.8 keV band is associated with the Sersic 159-03 cluster, which contains a cD galaxy, and may account for as much as 40% of the observed 2A flux. The rest of the flux is suspected to issue from the weaker but more heavily cut-off galaxy NGC 7582. It is suggested that such a large X-ray absorption column density in NGC 7582 may account for the absence of a broad H-alpha emission component, as has been observed in other narrow-line X-ray galaxies. The weak X-ray flux from NGC 7552 shows together with a reanalysis of previous observations, that the source is not variable, that its X-ray emission is not likely to result from a compact nucleus, and that it may be a starburst galaxy.
    Keywords: ASTRONOMY
    Type: Royal Astronomical Society; vol. 200
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  • 9
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    Discovery of X-ray emission from two southern supernova remnants (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Two soft X-ray sources positionally coincident with the supernova remnants PKS 1209-52 and RCW 103 have been discovered by using the A-2 experiment on HEAO 1. Their measured fluxes are, respectively, about 1.4 x 10 to the -10th erg/cm-sec (0.2-1.0 keV) and about 1.8 x 10 to the -10th erg/cm-sec (0.6-2.0 keV). Spectral data are used to derive physical parameters for each remnant. For PKS 1209-52 the parameters are suggestive of the remnant's being in an advanced evolutionary phase, with shock-heated interstellar material producing the soft X-ray emission. RCW 103, in contrast, is known from radio and optical data to be in an earlier evolutionary phase, and the soft X-ray flux is most likely due to emission originating in a reflected shock wave or in plasma evaporated from shock-heated interstellar clouds.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 230
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  • 10
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    Simultaneous X-ray and optical observations of the flaring X-ray source, Aquila A-1 (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: During the summer of 1978 the recurrent transient X-ray source, Aquila X-1, underwent its first major outburst in two years. The results of extensive observations at X-ray and optical wavelengths throughout this event, which lasted for approximately two months are presented. The peak X-ray luminosity was approximately 1.3 times that of the Crab and exhibited spectral dependent flickering on timescales approximately 5 minutes. The observations are interpreted in terms of a standard accretion disk model withparticular emphasis on the similarities to Sco X-1 and other dward X-ray systems, although the transient nature of the system remains unexplained. It was found that Aquila X-1 can be described adequately by the semi-detached Roche lobe model and yields a mass ratio of less than or approximate to 3.5.
    Keywords: ASTRONOMY
    Type: NASA-CR-158849 , UCBSSL-SER-20-ISSUE-34
    Format: application/pdf
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