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  • Weitere Quellen  (16)
  • NASA Technical Reports  (16)
  • 2005-2009  (1)
  • 1985-1989  (15)
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  • 11
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    A possible solution to the Cepheid mass problem? (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: With new, smaller distances of the Cepheids, as determined recently by Schmidt (1984) and by Bohm-Vitense (1985), smaller pulsational masses are obtained than previously. Giant companions of Cepheids show that the luminosities of the Cepheids are too large in comparison with those of the giants. If increased mixing is responsible for this, then an increase in the luminosity of the Cepheids of a given mass by approximately a factor of 4 (as compared to conventional evolution calculations) is expected. Taking into account both of these effects good agreement is found between the corrected evolutionary masses, the pulsational masses, the dynamical masses, the giant companion masses, and the Wesselink masses. The bump masses are only slightly smaller than the other masses.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Stellar pulsation; Aug 11, 1986 - Aug 15, 1986; Los Alamos, NM; United States
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 12
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    The Cepheid mass problem and Cepheid binaries (1986)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Existing mass determinations for Cepheids with different periods are examined. Wesselink masses are independent of the adopted distance scale. For short periods (less than 6 days) they follow the sequence of evolutionary masses. For periods longer than 10 days they are lower by up to a factor of 2. The lower mass branch joins up with the bump masses. The new pulsational masses agree with the Wesselink masses for periods longer than 6 days. Cepheid masses determined by means of their giant companions also agree with the Wesselink masses and the new pulsational masses. While the error bars are large, the derived dynamical masses determined for S Mus and V636 Sco also agree with the low Wesselink and giant companion masses.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 303; 262-272
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 13
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    ISM chemical abundances in two intermediate-velocity clouds in the line of sight to SN 1987A (1988)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: The earliest IUE high-resolution spectra of SN 1987A have been studied and reveal the presence of several clouds in the line of sight to the LMC. In particular, there are two clouds with radial velocities of about 130 km/s and about 180 km/s. These clouds' velocities are between those of Galactic clouds at 0-80 km/s and those of LMC gas at about 270 km/s. Chemical-abundance determinations may help to determine the origin and location of these clouds. Curve-of-growth analysis and 21-cm observations show that they may be underabundant in heavy elements by about a factor of 2 as compared to solar abundances. No depletion indicative of grain formation can be seen.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal (ISSN 0004-6256); 96; 1373-138
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 14
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    A nonspherically symmetric model for the peculiar A star Alpha-2 (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Observations show that in the optical region the peculiar A star Alpha-2 CVn has a flatter energy distribution during maximum light than during minimum light. This indicates that during maximum light a lower-temperature region, but necessarily larger surface area, than during minimum light is seen. This suggests a nonspherically symmetric star, which is oblate with respect to the magnetic axis and which is cooler at the magnetic poles than at the magnetic equator. The light variations of such nonspherically symmetric oblique rotator models have been studied. It is found that, for an oblate ellipsoid with an axial ratio of 0.92 and a temperature difference of about 1000 K between the poles and the equator, the overall variations of the optical and the ultraviolet energy distributions can be well understood.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal (ISSN 0004-6256); 93; 1527-153
    Format: text
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  • 15
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    Are most short-period Cepheids overtone pulsators? (1988)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Data given and analyzed recently by Coulson et al. (1986) and Gieren (1982) provide a consistent set of Wesselink radii and Wesselink masses, for which the internal error bars appear to be small enough that a quantitative discussion appears to be warranted. When it is assumed that all Cepheids pulsate in the fundamental mode, a steep discontinuity in mass is found for periods around 6.5 days. When short-period Cepheids are interpreted as first-overtone pulsators as required theoretically (Christy, 1966; Stobie, 1969), the discontinuity disappears and the mass-period relation passes through the bump and beat masses for Cepheids.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 324; L27-L29
    Format: text
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  • 16
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    Theory of transition-layer emission measures and coronae (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: The basic equations describing the energy equilibria, the conductive heat flux, and the temperature stratifications for stellar transition layers and coronae with 'open' field lines are summarized. The temperature dependence of the emission measures for lines originating in different temperature regions of the transition zone is determined. It is found that the stellar transition regions consist of two basically different parts: the lower part where mechnical energy input is balanced by the radiative losses, and the upper part where the mechanical energy input is balanced by the divergence of the conductive flux and radiative losses. In the lower part, the temperature stratification is determined by an equilibrium between mechanical flux input and radiative energy losses. The coronal temperatures increase with increasing mechanical flux and damping length in the upper transition zone.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 750-759
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
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