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  • ASTROPHYSICS  (20)
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  • 1
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    The semicircular shell of CTB 109 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The radio and X-ray images of the supernova remnant CTB 109 have the morphology of a semicircular shell. It is shown that such a structure is a natural result of a supernova explosion that occurred 3,000 yr ago near an interface between the diffuse interstellar medium and a dense molecular cloud. The calculated X-ray, infrared, and radio fluxes agree fairly well with the observed values.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 388; 127-130
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  • 2
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    Bow shocks and bubbles are seen around hot stars by IRAS (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Examination of the IRAS all-sky imagery reveals extended, arcuate, and ringlike features associated with hot luminous stars. They fall into a number of classes: stellar wind bow shocks, stellar wind bubbles, dust shells, dust heated by isolated B stars, bright rims, and dust in H II regions. Here, some objects are discussed in which the star exercises structural control over the spatial distribution of dust: bow shocks, bubbles, and radiation pressure-driven shells. A list of the 15 most prominent objects is presented, a few prototypes are shown, and their characteristics are explained in terms of thermal emission processes and gasdynamics.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 329; L93-L96
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  • 3
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    Superbubble blowout dynamics (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Multiple supernovae and stellar winds from OB associations carve large holes filled with hot gas in the galactic disk. These superbubbles sweep up H I into cold, thin, dense shells and eventually grow large enough to blow completely out of the galactic H I disk. When superbubbles blow out of the disk, they vent hot gas and supernova energy into the galactic corona. In this paper ZEUS, a two-dimensional hydrodynamics code, is used to model the blowout of a superbubble from exponential and Gaussian models for the vertical density stratification. The results are compared to those from the Kompaneets (thin-shell) approximation. It is found that this approximation works very well, and that most of the mass of the shell remains in the plane, with 5 percent of it accelerating upward. The venting of the hot gas and the stability of the shell depends strongly on the model of the density distribution. It is suggested that the low galactic halo actually consists of a froth of merged superbubbles.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 337; 141-154
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  • 4
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    The Ca II emission lines of SN 1987A (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We study the evolution of the forbidden Ca II 7300 A and Ca II 8600 A emission lines in the spectrum SN 1987A. We can explain the observations with a model in which (1) the lines come from about 1.7 x 10 exp -4 solar mass of calcium distributed with filling factor about 0.1 in a sphere expanding with velocity 2500 km/s; (2) the electron number density is given by 4 x 10 exp 9/cu cm/(t/100d)-cubed; (3) the gas temperature decreases from T roughly 6400 K at 200 days to T roughly 3900 K at 500 days; and (4) ultraviolet pumping in the Ca II 3934 A, 3969 A (K, H) lines is required to explain the line ratios for t greater than about 350 days. The mass of calcium in our model is consistent with the LMC abundance of calcium in about 5 solar mass of hydrogen in the inner envelope of SN 1987A. If more calcium is produced by supernova nucleosynthesis, it must be in dense clumps that are too cool to emit the forbidden Ca II 7300 A and Ca II 8600 A lines.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 405; 2; p. 730-737.
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  • 5
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    Supernova 1987A revisited (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Updates on research on SN 1987A are provided, with emphasis on the aftermath of the explosion: the interpretation of the light curve and spectrum, the physics of the envelope, and the interaction of the supernova with its circumstellar envelope. UVOIR light curves, gamma rays and hard X-rays, and dust formation are examined, and explosion dynamics is explored. Attention is given to optical and IR spectrum development, with emphasis on the photospheric spectrum, nebular spectrum, ionization, emission-line profiles, line strengths, and iron, cobalt, and nickel. The circumstellar environment is discussed, with special reference to progenitor mass loss, circumstellar ring and nebulosity, radio emission, and soft X-rays.
    Keywords: ASTROPHYSICS
    Type: In: Annual review of astronomy and astrophysics. Vol. 31 (A94-12726 02-90); p. 175-216.
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  • 6
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    Supernovae and the interstellar medium (1987)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Repeated supernovae from an OB association will, in a few 10s of Myr, create a cavity of coronal gas in the interstellar medium, with radius greater than 100 pc, surrounded by a dense expanding shell of cool interstellar gas. Such a cavity will likely burst through the gas layer of a disk galaxy. Such holes and 'supershells' have been observed in optical and H I radio emission maps of the Galaxy and other nearby galaxies. The gas swept up in supershell is likely to become gravitationally unstable, providing a mechanism for propagating star formation that may be particularly effective in irregular galaxies.
    Keywords: ASTROPHYSICS
    Type: Physical processes in interstellar clouds; Aug 18, 1986 - Aug 28, 1986; Irsee; Germany
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  • 7
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    On the origin of the soft X-ray background (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The angular autocorrelation function and spectrum of the soft X-ray background is studied below a discrete source detection limit, using two deep images from the Rosat X-ray satellite. The average spectral shape of pointlike sources, which account for 40 to 60 percent of the background intensity, is determined by using the autocorrelation function. The background spectrum, in the 0.5-0.9 keV band (M band), is decomposed into a pointlike source component characterized by a power law and a diffuse component represented by a two-temperature plasma. These pointlike sources cannot contribute more than 60 percent of the X-ray background intensity in the M band without exceeding the total observed flux in the R7 band. Spectral analysis has shown that the local soft diffuse component, although dominating the background intensity at energies not greater than 0.3 keV, contributes only a small fraction of the M band background intensity. The diffuse component may represent an important constituent of the interstellar or intergalactic medium.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 409; 2; p. L37-L40.
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  • 8
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    Supernova remnant 1987 A (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A dense circumstellar shell, with radius of about 0.5 lt-yr, surrounds SN 1987 A. In 16 yr or less after outburst, the expanding debris of SN 1987 A will strike this shell. When it does, the hot gas and relativistic electrons resulting from the forward and reverse shocks will radiate X-rays, infrared radiation, and nonthermal radio waves. The remnant of SN 1987 A will then become one of the brightest X-ray and radio sources in the LMC.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 372; 194-198
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  • 9
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    The circumstellar shell of SN 1987A (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: An hourglass-shaped circumstellar shell, with radius about 0.65 lt-yr at the equator and about 2.4 lt-yr at the poles, surrounds SN 1987A. The shell is a bubble blown by the wind of the blue giant progenitor of SN 1987A into an equatorially concentrated wind of a prior red giant stage. The bubble was ionized by the initial UV flash of the supernova, and the emission-line region is concentrated in a ring at the waist of the hourglass. In about 2002 AD the supernova envelope will strike the shell. The resulting young supernova remnant will become a luminous source of soft X-rays and broad optical and ultraviolet emission lines.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 379; 659-662
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  • 10
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    The impact of SN 1987A with its circumstellar ring (1994)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The envleope of SN 1987A will strike its circumstellar ring in 12 +/- 3 yr after explosion (A.D. 1999+/-3), the exact time depending weakly on the uncertain density of diffuse gas between the supernova and the ring. The impact will drive a radiative shock into the ring with velocity approximatley 200-400 km s(exp -1). The shocked ring will become a bright optical and ultraviolet emsiison-line source. A bright arc will suddenly appear at the near side of the ring and grow into an entire ring about 11 months later. The luminosities of the brightest lines, H-alpha H-alpha, N v lambda lambda 1238, 1242, and O VI lambda lambda 1032, 1038 will rise rapidly to approxminately 10(exp 36)-10(exp 37) ergs s(exp -1) and remain bright for several years after impact. The emission lines from the shocked ring will have FWHM approximatley 300-600 km s(exp -1) and complex profiles that will depend on position and will be sensitive to the details of the density distribution of gas in the ring. Strong EUV radiation from the shock will photoionize the unshocked ring, causing emission of narrow FWHM equivalent to 15 km s(exp -1) H-alpha, H-beta and (O III) lambda lambda 4959, 5007 lines with luminosities approximatley 10(exp 35) ergs s(exp -1).The EUV radiation will probably cause the nebulosity beyond the ring to become visable again. The EUV radiation may also illuminate the unshocked outer supernova envelope, causing visible emission of broad FWHM equivalent to 10(exp 4) km s(exp -1) H-alpha and H-beta lines.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 430; 1; p. 264-276
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