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  • Other Sources  (6)
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  • 1
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    Stellar model chromospheres. XI - A survey of Ca II lambda 8542 line profiles in late-type stars of differing chromospheric activity (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: ASTROPHYSICS
    Type: PB80-144215 , Astrophysical Journal Supplement Series; 41; Nov. 197
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  • 2
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    Outer atmospheres of cool stars. VI - Models for Epsilon Eridani based on IUE spectra of C II, Mg II, Si II, and Si III (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Observations of the ultraviolet line spectrum of the active chromosphere star, Epsilon Eridani, obtained with the IUE satellite have been analyzed. The coupled statistical equilibrium and radiative transfer equations for the prominent transitions of C II, Mg II, Si II, and Si III. A satisfactory fit to all of the line strengths can be achieved with a model similar to that recently proposed to explain bright points on the quiet sun. A surface pressure at the base of the transition region of 0.5 dynes/sq cm is derived, which is a factor of 3 higher than the quiet sun value, but a factor of 3 smaller than predicted by scaling laws, assuming a conductively heated stellar transition region. It is found that the surface fluxes of the C II 1334, 1335 and Si III 1892 emission lines are good diagnostics of pressure at the base of the transition region, but line ratio techniques using the 1892 line for estimating electron densities may be valid.
    Keywords: ASTROPHYSICS
    Type: PB80-201270 , Astrophysical Journal; vol. 237
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  • 3
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    Stellar model chromospheres. IX - Chromospheric activity in dwarf stars (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: High-resolution Ca II K line profiles are used to model the upper photospheres and lower chromospheres of eight main-sequence stars ranging in spectral type from F0 to M0 and exhibiting different degrees of chromospheric activity. The model chromospheres are studied as a function of spectral type and activity for stars of similar spectral type in order to obtain evidence of enhanced nonradiative heating in the upper-photospheric models and in the ratio of minimum temperature at the base of the chromosphere to effective temperature, a correlation between activity and temperature in the lower chromospheres, and a correlation of the width at the base of the K-line emission core and at the K2 features with activity. Chromospheric radiative losses are estimated for the modelled stars and other previously analyzed main-sequence stars. The results obtained strengthen the argument that dMe flare stars exhibit fundamentally solar-type activity but on an increased scale.
    Keywords: ASTROPHYSICS
    Type: PB80-118086 , AD-A083858 , AFGL-TR-80-0106 , Astrophysical Journal; vol. 229
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  • 4
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    Physical properties of solar chromospheric plages. III - Models based on Ca II and Mg II observations (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Solar plages are modeled using observations of both the Ca II K and the Mg II h and k lines. A partial-redistribution approach is employed for calculating the line profiles on the basis of a grid of five model chromospheres. The computed integrated emission intensities for the five atmospheric models are compared with observations of six regions on the sun as well as with models of active-chromosphere stars. It is concluded that the basic plage model grid proposed by Shine and Linsky (1974) is still valid when the Mg II lines are included in the analysis and the Ca II and Mg II lines are analyzed using partial-redistribution diagnostics.
    Keywords: SOLAR PHYSICS
    Type: PB-289015 , Solar Physics; 58; June 197
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  • 5
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    Stellar model chromospheres. VIII - 70 Ophiuchi A /K0 V/ and Epsilon Eridani /K2 V/ (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Model atmospheres for the late-type active-chromosphere dwarf stars 70 Oph A and Epsilon Eri are computed from high-resolution Ca II K line profiles as well as Mg II h and k line fluxes. A method is used which determines a plane-parallel homogeneous hydrostatic-equilibrium model of the upper photosphere and chromosphere which differs from theoretical models by lacking the constraint of radiative equilibrium (RE). The determinations of surface gravities, metallicities, and effective temperatures are discussed, and the computational methods, model atoms, atomic data, and observations are described. Temperature distributions for the two stars are plotted and compared with RE models for the adopted effective temperatures and gravities. The previously investigated T min/T eff vs. T eff relation is extended to Epsilon Eri and 70 Oph A, observed and computed Ca II K and Mg II h and k integrated emission fluxes are compared, and full tabulations are given for the proposed models. It is suggested that if less than half the observed Mg II flux for the two stars is lost in noise, the difference between an active-chromosphere star and a quiet-chromosphere star lies in the lower-chromospheric temperature gradient.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 222
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  • 6
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    Stellar model chromospheres. VII - Capella /G5 III +/, Pollux /K0 III/, and Aldebaran /K5 III/ (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Data from high-resolution SEC vidicon spectroscopy with a ground-based telescope (for the Ca II K line) and from spectral scans made with the BUSS ultraviolet balloon spectrograph (for the Mg II h and k lines) are used to derive models of the chromospheres and upper photospheres of three G-K giants. The models are based on partial-redistribution analyses of the Ca II K line wings and cores and on the fluxes in the Mg II lines. The photospheres thus computed are hotter than predicted by radiative-equilibrium models. The minimum-to-effective temperature ratio is found to decrease with decreasing effective temperature, while the mass column density at the top of the chromosphere increases with decreasing stellar surface gravity. The computed pressure at the chromosphere top in the primary member of the Capella spectroscopic binary system is 70 times smaller than the transition-region pressure derived by Haisch and Linsky (1976), which suggests that additional terms must be included in the transition-region energy equations for giant stars. Estimates of the Ca II and hydrogen column densities are made for the circumstellar envelope of Aldebaran.
    Keywords: ASTROPHYSICS
    Type: PB-282120 , Astrophysical Journal; vol. 220
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