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  • 1
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    Anisotropy of the neutral gas distribution of Comet Halley deduced from NGE/Vega 1 measurements (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The neutral gas density profile of comet Halley measured by the Neutral Gas Experiment on Vega 1 showed an asymmetry between the inbound and the outbound legs during the fly-by on 6 March 1986. The implications of this asymmetry are discussed, and it is shown how the asymmetry detected by NGE on Vega 1 can be traced back to regions on or near the nucleus to obtain their relative gas production activities at specific times of emission.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 417-421
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  • 2
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    On the structure of the outer layers of cool carbon stars (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Exposures on the spectra of four late C-type stars have been made with the IUE satellite in the wavelength range of the LWR camera (1900-3200 A). Two Mira variables near maximum light and two semiregular variables were observed. Although the exposure times used, which range up to 240 min in the low-resolution mode, were more than sufficient to record the continuum and emission lines of Mg II, Fe II, and Al II in normal M stars of similar magnitude and temperature, no light was recorded. It is concluded that the far-ultraviolet continuum is strongly depressed in these cool carbon stars. The absence of UV emission lines implies either that the chromospheric lines observed in M stars require an ultraviolet flux for their excitation, or that cool carbon stars have no chromosphere at all or that the opacity source is located above even the emission-line-forming region. This opacity source, which is probably some carbon condensate since it is weak or absent in M stars while absorbing strongly in C stars, is discussed both in terms of the chromospheric interpretation of the emission lines and in terms of their shock-wave interpretation.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 111; 1, Ju; July 198
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  • 3
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    Giotto-IMS observations of ion flow velocities and temperatures outside the contact surface of Comet Halley (1986)
    In:  Other Sources
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    Publication Date: 2013-08-29
    Description: Fluid parameters for He(++) ions obtained from the Giotto ion mass spectrometer are presented. Proton densities and velocities and thermal speeds of protons, alpha particles, and heavy ions in the hour before closest approach are discussed. A region of enhanced He(++) ion densities, and velocity, and decreased temperature is observed from 20:26 to 21:45. Sharp decreases in the proton density are observed at 23:30 and at 23:41. There is a relative flow velocity between alpha particles and oxygen ions of 30 km/sec during a period from 22:55 to 23:30; the difference in flow velocity is less than the experimental uncertainities. The flow properties of protons observed during this period are also discussed.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 229-233
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  • 4
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    An interpretation of the ion pile-up region outside the ionospheric contact surface (1986)
    In:  Other Sources
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    Publication Date: 2013-08-29
    Description: The possibility that the formation of the plasma pile-up region at comet Halley as observed by Giotto could be the combined result of field-aligned transport and recombination process is discussed. Giotto measurements support the hypothesis.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 219-223
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  • 5
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    Comet Halley neutral gas density profile along the Vega 1 trajectory measured by NGE (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Data from the Vega 1 permitted the determination of the total neutral gas density profile along the spacecraft trajectory. Discounting small fluctuations, the field ionization source instrument measured a density profile which varied approximately as the inverse radial distance squared. Data from the electron impact ionization instrument yielded a series of calibration points; e.g., the neutral density at 100,000 km is 10,000/cc. The combined data provide a calibrated total density profile, and imply a neutral production rate of 10 to the 30th power molecules/sec.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 391-395
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  • 6
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    Ion temperature and flow profiles in Comet Halley's close environment (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The Giotto high intensity spectrometer identified the contact surface 4800 km from the comet nucleus. This boundary is clearly seen by a drastic drop in the temperatures of different ion species from 2000 K outside to values as low as 300 K inside. Inside the contact surface outflow speed = 〉 1 km/sec, in contrast to a value around 0 right outside. These numbers might be affected by a potential charge-up of the spacecraft. Outside the contact surface, the ion temperature rises gradually with increasing distance. Between 9000 and 10,000 km distance the ion density increases by a factor of 4. At 27,000 km distance there is again a rather abrupt jump to significantly higher temperatures, higher outflow speeds, and lower densities.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 225-227
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  • 7
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    Mira variables: An informal review (1980)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: The structure of the Mira variables is discussed with particular emphasis on the extent of their observable atmospheres, the various methods for measuring the sizes of these atmospheres, and the manner in which the size changes through the cycle. The results obtained by direct, photometric and spectroscopic methods are compared, and the problems of interpretation are addressed. Also, a simple model for the atmospheric structure and motions of Miras based on recent observations of the doubling of infrared molecualr times is described. This model, consisting of two atmospheric layers plus a circumstellar shell, provides a physically plausible picture of the atmosphere which is consistent with the photometrically measured magnitude and temperature variations as well as the spectroscopic data.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Current Probl. in Stellar Pulsation Instabilities; p 533-566
    Format: application/pdf
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  • 8
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    Notes on the early-type components of W Cep, o Cet, CH Cyg, AR Mon, and BL Tel (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Low resolution IUE spectra in both spectral regions are used to clarify the nature of the warmer components of several binary systems. The W Cep, the primary of which is a luminous K-type supergiant, shows an ultraviolet absorption spectrum of type B0 or B1; this system is heavily reddened. The hot companion of Mira (o Cet) is surprisingly faint in the short wavelength region, but it excites a rich emission spectrum from the surrounding gas. The ultraviolet active M7 giant CH Cyg is shown to be a binary with a hot companion. This system was also observed at high resolution and shows variable Fe II emission and well-separated circumstellar and interstellar absorptions within the broad Mg II emission profiles. The eclipsing binaries AR Mon and BL Tel are shown not to have hot companions.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 341-347
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  • 9
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    Density sensitive C II lines in cool stars of low gravity (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is shown that the relative intensities of emission lines within the multiplet UV 0.01 of C II, around 2325 A, are sensitive to electron density in the range 10 to the 9th to 10 to the 7th per cu cm. The lines therefore offer a valuable method for measuring electron densities in the chromospheres of late-type giants and supergiants. Calculated line ratios are compared with those observed in a range of objects.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society; vol. 196
    Format: text
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  • 10
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    Chromospheres of the active dwarf binaries EQ Pegasi and Xi Bootis (1979)
    In:  Other Sources
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    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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