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  • 1
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    Ultraviolet continuum variability and visual flickering in the peculiar object MWC 560 (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: High-speed U-band photometry of the peculiar emission object MWC 560 obtained with the ground-based instrumentation, and V-band photometry obtained with the International Ultraviolet Explorer-Fine Error Sensor indicates irregular brightness variations are quasi-periodic. Multiple peaks of relative brightness power indicate statistically significant quasi periods existing in a range of 3-35 minutes, that are superposed on slower hourly varying components. We present a preliminary model that explains the minute and hourly time-scale variations in MWC 560 in terms of a velocity-shear instability that arises because a white dwarf magnetosphere impinges on an accretion disk. We also find evidence for Fe II multiplet pseudocontinuum absorption opacity in far-UV spectra of CH Cygni which is also present in MWC 560. Both CH Cyg and MWC 560 may be in an evolutionary stage that is characterized by strong UV continuum opacity which changes significantly during outburst, occurring before they permanently enter the symbiotic nebular emission phase.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 409; 2; p. L53-L56.
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  • 2
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    Observations of the peculiar object MWC 560 in outburst (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The results of ultraviolet spectroscopy, photoelectric photometry, and supplemental high-resolution H(alpha) spectroscopy of a photometric outburst of MWC 560 are discussed. Ultraviolet spectra are shown to be consistent with the ejection of an optically thick shell that produced strong absorption blends of Fe II and Cr II. The velocities reported exceed by far those previously found in symbiotic stars or recurrent novas. In addition to the variable high-velocity system of broad absorption features, a relatively stable system of Mg II, Mg I, Fe II, Cr II, and other ionic absorptions is observed. It is pointed out that the spectroscopic phenomena in MWC 560 resemble those found in XX Ophiuchi, but the velocities in the MWC 560 are an order of magnitude higher than those found in XX Oph.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 371; 761-771
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  • 3
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    A model of the pre-Sedov expansion phase of supernova remnant-ambient plasma coupling and X-ray emission from SN 1987A (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper examines the mechanism responsible for coupling supernova (SN) remnant to the ambient medium during the pre-Sedov or the so-called free expansion phase, immediately following the progenitor explosion. A theory is developed for the interaction of an SN piston with the ambient medium during the pre-Sedov phase. The possibility of X-ray production by the high-speed portion of the piston during this phase is investigated. The relevant observations of high-energy emissions from the SN 1987A, including the X-ray spectrum, luminosity, and temporal development, are considered. It is shown that the commonly assumed snowplow model for SNR evolution is valid, because of the action of a variety of collisionless two-stream instabilities that permit the coupling of the ambient plasma with SNR.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 356; 549-571
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  • 4
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    Planetary nebulae and stellar evolution (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Newly defined characteristics of planetary nebulae (PN) derived from analysis of a photometric survey of 57 PN are reported. The data were combined with measurements of 27 other PN made since 1918 and were found to indicate core masses ranging from 0.55-1.0 solar mass. N/O elemental abundance ratios observed were correlated with the planetary nuclei masses, and were in direct proportion. IUE data on PN that overlapped a large part of the survey indicated that the PN in the galactic disk are more massive than PN in the halo. It is suggested that PN evolve into white dwarfs, a hypothesis supported by astrometric solutions for three nearby visual binaries featuring white dwarfs with well-determined masses. It is noted, however, that PN with masses exceeding one solar mass have been sighted in the Magellanic Clouds.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 305; 670
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  • 5
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    IUE observations of the hot components in two symbiotic stars (1980)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Recent IUE observations reveal striking differences in the UV spectra of two symbiotic stars, R Aqr and RW Hya. RW Hya is found to be an unexpectedly intense source of UV radiation. The measurements reported demonstrate the presence of a hot component in each star, supporting the view that each is a binary system with a luminous red primary and a hot, subluminous companion. In one case, the hot companion manifests itself by exciting a compact nebulosity; in the other case the continuous spectrum of the hot star is directly detected, while the continuum of nebulosity excited by the hot star is detected at longer wavelengths.
    Keywords: ASTROPHYSICS
    Type: Nature; 284; Mar. 13
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  • 6
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    Millimeter-wave experiments for cometary space missions (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Predicted brightness temperatures, computed by means of radiative transfer techniques adapted from the modeling of terrestrial ice and snow fields, are given for cometary nucleus models consisting of homogeneous layers of water ice and refractory grain mixtures presented as functions of wavelength. The computed millimeter-wave spectra are sensitive to the values of such physically significant nucleus parameters as (1) crust thickness, (2) subsurface temperature gradient, and (3) sublimating surface boundary temperature. Although antenna beam dilution is a major obstacle for ground-based molecular spectral line radio observations of comets, a millimeter-wave radiometer in the vicinity of the comet would be immune to this effect and able to make observations of several candidate parent molecules in the gas phase.
    Keywords: ASTROPHYSICS
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  • 7
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    Relativistic astrophysics - The view from Texas in Baltimore /Review/ (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Recent observational and theoretical work presented at the Tenth Texas Symposium on Relativistic Astrophysics held in Baltimore, Maryland from December 15-19, 1980, is outlined. Areas covered include the theoretical foundations of relativistic astrophysics in general relativity, quantum gravitational theory and the association of grand unification with astronomical and cosmological issues, the cosmic microwave, X-ray, gamma-ray, UV, cosmic ray and gravitational wave backgrounds, the current expansion rate and average mass-energy density of the universe, and mechanisms of galaxy formation. Also discussed are the characteristics of active galaxies and clusters emitting in the gamma-ray and X-ray regions, and compact objects formed from supernova explosions, including pulsars, X-ray-emitting neutron stars, Sco X-1 and SS 433, gamma-ray sources, and X-ray and gamma-ray bursters.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Letters; 22; 1, 19; 1981
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  • 8
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    The origin of OB associations and extended regions of high-energy activity in the Galaxy through supernova cascade processes (1976)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: A number of observed characteristics of OB associations, including their positive total energies and subgroup structure, are explained by the hypothesis that an association is composed of stars formed by compression of interstellar clouds in blast waves of several generations of supernovae. The later-generation supernovae are simply the most massive stars formed by this mechanism in the earlier generations. This supernova cascade process may also be responsible for giant loops such as the North Polar Spur. Enhanced high-energy gamma-ray emission is expected from the loops.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 209; Oct. 1
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  • 9
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    Microwave continuum radiation from comet Kohoutek 1973f - Emission from the icy-grain halo (1975)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: Cometary emission was measured at 3.71 cm on January 10-11, 1974. A possible detection at 2.8 cm and an upper limit at 11.1 cm are also reported. Interferometer measurements at 3.71 cm show that the angular diameter is less than 1.4 arc sec or less than 850 km at the comet. The corresponding disk brightness temperature is greater than 313 + or - 80 K. The radiation presumably originates in the icy-grain halo postulated by Delsemme.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 201; Nov. 1
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  • 10
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    Microwave continuum radiation from comet West 1975n (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Continuum emission at wavelength 3.71 cm was observed from the nuclear region of comet West 1975n on March 5, 1976. The flux density was 0.040 Jy, which is uncertain by 25% due to calibration. Assuming that the source was a uniformly illuminated disk, the diameter was no more than about 1100 km and the brightness temperature was at least 330 + or - 85 K. On March 4, 1976, similar observations yielded only an upper limit (two standard deviations) to the flux density of 0.010 Jy. Thus it appears that the source turned on with a time scale of 1 day or less, at about the time that the short-lived cometary daughter nucleus 'C' split from the main nucleus 'A'. Similar emission was observed from comet Kohoutek 1973f. In each case, it appears that the microwave emission can be interpreted as thermal radiation from a temporarily enhanced icy-grain halo (IGH). If this interpretation is correct, then the actual temperature (which is assumed to be approximately equal to the nuclear surface temperature) must be in the range 200-250 K, roughly compatible with the observations, in order to satisfy the IGH models of Delsemme (1973).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 218
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