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  • 1
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    In:  CASI
    Publication Date: 2013-08-31
    Description: The properties of stars showing Wolf-Rayet phenomena are outlined along with the direction of future work. Emphasis is placed on the characteristics of W-R spectra. Specifically the following topics are covered: the absolute visual magnitudes; the heterogeneity of WN spectra; the existence of transition type spectra and compositions the mass loss rates; and the existence of very luminous and possibly very massive W-R stars. Also, a brief overview of current understanding of the theoretical aspects of stellar evolution and stellar winds and the various scenarios that have been proposed to understand W-R spectra are included.
    Keywords: ASTRONOMY
    Type: NAS 1.26:169299 , NASA-CR-169299
    Format: application/pdf
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  • 2
    Publication Date: 2013-08-31
    Description: Spectra of very luminous, high temperature stars, the o-type stars with the largest masses among stars, and the Wolf-Rayet (W-R) stars are studied. These stars are characterized by strong stellar winds which produce signiicant mass loss. The nature and evolution of these winds are studied to learn the densities, velocity structue, ionization balance, and composition. The IUE satellite provides the best way to study these phenomena because many of the most important ground state and excited state lines of common highly ionized species are found in the spectral range.
    Keywords: ASTROPHYSICS
    Type: NAS 1.26:174288 , NASA-CR-174288
    Format: application/pdf
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  • 3
    Publication Date: 2017-06-27
    Description: Model stellar atmosphere abundance analysis of eight sharp-line A stars in Pleiades
    Keywords: SPACE SCIENCES
    Type: NASA-CR-93687 , REPT.-706-39
    Format: application/pdf
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  • 4
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    Unknown
    In:  CASI
    Publication Date: 2016-06-07
    Description: The mass loss rates are derived for a number of unevolved O-type stars and a few WN stars from high dispersion IUE spectra of their P Cygni profiles. When combined with other published mass loss rates, it is found that the relationship between log m and M sub BOL is a broad band rather than a linear relation, suggesting that the line radiation driven wind theory may not be sufficient to explain mass loss. The mass loss rates for the WN stars, while more uncertain, confirm that these stars lose mass about 100 times faster than O-stars.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 115-120
    Format: application/pdf
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  • 5
    Publication Date: 2011-08-17
    Description: Radial velocities are measured on coude spectrograms of over 200 O-type stars in both hemispheres. The selection of effective wavelengths for the stellar lines to be measured is reviewed, and the measured velocities are compared with those available in a catalog of O stars. The Trumpler (1935) effect (a reported anomalous redshift in certain O stars) is inconclusively reinvestigated, atmospheric motions in Of stars are examined, and some kinematic properties of O stars are discussed statistically. It is found that 58% of all O stars and 41% of all the Of stars considered are certain or probable binaries. A K-term in the range from 1 to 2 km/s is derived for the O stars, but the Of stars are shown to have a highly significant negative K-term. It is suggested that the systematically negative peculiar velocities of the Of stars are due to outflow of material beginning at the photospheric level.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 214
    Format: text
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  • 6
    Publication Date: 2011-08-16
    Description: Data from nine high-dispersion spectra of HDE 226868, the optical candidate for Cyg X-1, are presented. The line profiles at He II (4686 A) show marked changes from night to night. Our data are not compatible with models where the emission line arises from the unseen secondary component of the system, as has been suggested by other observers. We propose that the emission originates in a gas stream falling toward the secondary; this provides observational evidence that the X-ray source is powered by accretion. We also see changes in spectral type and luminosity class with phase, further complicating attempts to make mass estimates for the system.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 179; Feb. 1
    Format: text
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  • 7
    Publication Date: 2011-08-16
    Description: The ratio of the visual luminosities of the O and WC components of the binary system gamma (2) Vel has been derived by comparison of the emission-line strengths in the spectrum with those in the spectrum of a single WC8 star, HD 192103. The result is 1.4 mag, with the O star being brighter; the classification of the O star was found to be 09 I, so that the classification of gamma (2) Vel is WC8+09 I.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 172; Mar. 15
    Format: text
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  • 8
    Publication Date: 2011-08-12
    Description: Anomalously low Sc/Sr ratio in A zero stars of Pleiades cluster from model atmosphere abundance analysis
    Keywords: SPACE SCIENCES
    Type: ; YAL SOCIETY (
    Format: text
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  • 9
    Publication Date: 2011-08-18
    Description: It is demonstrated that absolute spectrophotometry of the continua of Wolf-Rayet stars may be obtained over the wavelength range 1200-7000 A using IUE and optical measurements. It is shown that the application of a 'standard' reddening law to the observed data gives spurious results in many cases. Additional UV extinction is apparently necessary and may well be circumstellar in origin. In such hot stars, the long-wavelength 'tail' of the emergent stellar continuum are measured. The inadequacy of previous attempts to determine intrinsic continua and effective temperatures of Wolf-Rayet stars is pointed out.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 278; 233-240
    Format: text
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  • 10
    Publication Date: 2011-08-18
    Description: R136 (HD 38268) is the brightest member of the compact cluster of stars at the center of the 30 Doradus Nebula, a massive H II region in the Large Magellanic Cloud (LMC). The far-ultraviolet luminosity is equivalent to at least 1000 ordinary O type stars. Optically, R136 is an unresolved patch corresponding to a linear extent of about 0.7 pc. Several components are known to be present, of which R136a is the brightest. A quantitative description of the optical spectrum of R136a has not been available in the literature. The present investigation is concerned with the analysis of spectrograms in the visible region. It is found that the optical spectrum of R136a shows broad but rather weak emission lines of ions which are frequently seen in early WN-type stars. The centroid of H-alpha is displaced by approximately 100 km/s redward of the nebular H-alpha emission. The Balmer series is visible, in absorption, up to H11.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 263
    Format: text
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