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  • 1
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    The ultraviolet continuous and emission-line spectra of the Herbig-Haro objects HH 2 and HH 1 (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Recent studies of the continuous spectrum of Herbig-Haro (HH) objects at optical and near-infrared wavelengths and the observation of continuous radiation in the ultraviolet have shown an unexpectedly steep increase of the flux toward shorter wavelengths. The present investigation provides the results of ultraviolet observations of HH 2. The obtained data are compared with the HH 1 data. It is found that HH 2 has an ultraviolet continuous and emission-line spectrum which is similar to that of HH 1. The UV line spectrum of HH 2H indicates an even somewhat larger ionization than does the HH 1 spectrum. As in HH1, the UV emission-line spectrum shows a much higher degree of ionization than that derived from the optical spectrum. Consequently, the same difficulty arises as in the case of HH 1. The complete UV plus optical spectrum cannot be explained by a single plane-parallel shock-wave model.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 262
    Format: text
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  • 2
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    Herbig-Haro objects (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The IUE (International Ultraviolet Explorer) spectra of Herbig-Haro (HH) objects and their relation to the very detailed optical spectra available for these objects are studied. Useful information about the physics of HH objects in general and especially about their hydrodynamic models which are contained in these IUE observations is outlined. The merged spectra of high excitation, low excitation HH objects (like HH43 and HH47), and peculiar HH objects are discussed. Results of the spatial variation of lines and continua in HH objects are discussed. Their compatibility with predictions for aerodynamic and especially bow shock models is discussed. The problems arising in the interpretation of the continuous energy distribution in the short wavelength range are discussed. They require the presence of other emission mechanisms in addition to the collisionally enhanced two photon continuum. In HH43 the fluorescent H2 line emission comes from a surprisingly small spatial region. Implications of these results are discussed.
    Keywords: ASTROPHYSICS
    Type: ESA, Evolution in Astrophysics: IUE Astronomy in the Era of New Space Missions; p 23-31
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  • 3
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    The white dwarf companion of the B a 2 star zeta Cap (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Ba II star zeta Cap has a white dwarf companion. Its T (sub eff) is determined to be 22000 K, its mass is approximately one solar mass. The importance of this finding for the explanation of abundance peculiarities is discussed.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 455-458
    Format: application/pdf
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  • 4
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    Outlook for ultraviolet astronomy (1981)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: A brief overview of galactic and extragalactic research is given with emphasis on the problems of temperature determination, chemical abundance determination, and the question about the energy sources for the high temperature regions. Stellar astronomy, stellar winds, and the interstellar medium are among the topics covered.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 3-17
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  • 5
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    The ultraviolet spectrum of Herbig-Haro Object 1 (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Continuum and emission line fluxes for HH 1 in the range of 1200-1300 A have been determined using IUE spectra, and it is found that the luminosity of HH 1 in this wavelength interval is slightly larger than 1 solar luminosity, or 20 times greater than for the wavelength range 3200-11,000 A. If averaged over intervals of 100 A, it is shown that the UV continuum rises almost monotonically toward shorter wavelengths over the entire interval 1300-3000 A. The UV continuum energy distribution cannot be explained by a T Tauri stellar continuum that is scattered by dust. Emission line identifications and flux measurements strongly confirm the statement that the high-ionization emission lines are too strong to be explained by shock-wave models derived from the emission line spectrum in the interval 3700-11,000 A. A possible explanation for this fact is discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 245
    Format: text
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  • 6
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    On the energy distribution in Sirius B (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A spectrum of Sirius B in the wavelength region 1100-1900 A taken with the IUE satellite shows an absolute flux and spectral energy distribution in the continuum in agreement with theoretical white-dwarf models with T(eff) of 26,000 K plus or minus 1000 K for log g equals 8.65 and R equals 5.08 x 10 to the 8th cm. The Lyman-alpha profile is also in agreement with these parameters. No obvious emission lines in the spectrum of Sirius B or A which could indicate the presence of a chromosphere or corona in either of the stars are observed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 232
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  • 7
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    The Mg II resonance line emission at 2800 A in stars with different rotational velocities and different metal abundances (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In many investigations, a study of the Mg II 2800 A emission was conducted in order to derive more information about the correlation of chromospheric emission with the properties of the convection zone. It has been suggested by Ayres and Linsky (1980) that there is a positive correlation between rotation and chromospheric emission at least for binary stars. The present investigation is concerned with such a correlation between rotation and chromospheric emission. Since large differences in rotational velocities are observed for F stars for which also strong chromospheric emission is observable, this particular study deals mainly with F stars. On the basis of observations of the Mg II emission in F and G stars, it is found that the emission is abnormally strong in close binary F stars. This may be explained by the generation of a large differential rotation due to tidal effects which may give very efficient dynamo generation of a surface magnetic field.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 258
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  • 8
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    Far-ultraviolet energy distributions of the metal-poor A stars HD 109995 and HD 161817 (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Low-resolution IUE spectra at wavelengths between 1300 and 3400 A of the metal-poor stars HD 109995 (A1p) and HD 161817 (A4p) have been compared with model-atmosphere energy distributions computed by Kurucz (1979). Good overall agreement is found. Effective temperatures, metal abundances, and angular diameters could be determined. Assuming an absolute visual magnitude of 0.7, the previously determined gravity log = 3 yields masses of 0.5 solar masses for both stars. It is found that the theoretical UBV colors calculated earlier agree reaonably well with the ones observed for these stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 243
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  • 9
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    The chromospheric and transition layer emission of stars with different metal abundances (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Preliminary results on observations of chromospheric and transition layer emission of stars with different metal abundances are reported. Metal deficient stars generally show reduced emission in the Mg II resonance lines and also in the other chromospheric and transition layer emission lines. This is interpreted as showing that energy fluxes other than acoustic fluxes must at least be coresponsible for the coronal and transition layer heating.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 303-309
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  • 10
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    The ultraviolet spectra of the O and B stars in the young galactic cluster NGC 6530 (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The UV spectra between 1200 and 3000 A of stars in the young galactic cluster NGC 6530 and the surrounding association are studied. From the UBV colors and empirical as well as theoretical calibrations, the T(eff) and L for those stars which follow a sequence in the H-R diagram corresponding to the main sequence are determined. From a comparison with theoretical evolutionary tracks, the age of the cluster is estimated to be 5 + or - 2 x 10 to the 6th yr, with a very small scatter for the different stars. The UV extinction is determined for the stars from a comparison of theoretical model energy distributions for the stellar T(eff)s and the observed energy distributions. The stellar wind lines are studied, and strong stellar winds are found for bolometric magnetidues less than -8.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 287; 825-839
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