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  • 1
    Electronic Resource
    Electronic Resource
    Discovery of a massive equatorial torus in the η Carinae stellar system (1999)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 402 (1999), S. 502-504 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The enigmatic object η Carinae is believed to represent an important, but short-lived, unstable phase in the life of the most massive stars, occurring shortly before they explode as supernovae or collapse directly to black holes. The putative binary system believed to constitute η ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/990048
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Discovery of a corona around an early-type star and the problem of mass loss (1975)
    [s.l.] : Nature Publishing Group
    Nature 256 (1975), S. 190-190 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Apart from the numerous spectral features with a full width at half maximum (FWHM) of about 20 km s"1 which originate in the photosphere of the star, and the inter stellar absorption lines, the spectrum also shows a few very wide absorption lines. These lines are identified as belong ing to the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/256190a0
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  • 3
    Electronic Resource
    Electronic Resource
    The orbiting stellar ultraviolet spectrophotometer S59 in ESRO's TD-1A satellite (1974)
    Springer
    Astrophysics and space science 26 (1974), S. 207-262 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ultraviolet stellar spectrophotometer S59 of the Utrecht Astronomical Institute uses the stabilization properties of the ESRO TD-1A satellite. This spacecraft scans the sky along eliptic meridians with an orbital precession of one degree per day, thus covering the whole celestial sphere in half a year. This property is combined with a tracking system which points the spectrophotometer during four minutes at stars of sufficient brightness. During this time interval the ultraviolet stellar spectrum is scanned with a resolution of 1.7 Å in three bands of about 100 Å, around 2110, 2545 and 2825 Å. The optical, mechanical and electronic properties of the instrument and its tracking system are described in some detail, as well as the optical and technical performance in laboratory tests and in orbit. Some results obtained during the first half year of operation are briefly described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642637
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  • 4
    Electronic Resource
    Electronic Resource
    Progress in ultraviolet stellar spectrophotometry with S59 (1975)
    Springer
    Astrophysics and space science 38 (1975), S. 313-325 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A progress report is given of investigations related to observations of stellar spectra obtained with the ultraviolet stellar spectrophotometer S59 aboard the ESRO TD-1A satellite. We describe first the processing of the observations: intensity and wavelength calibration, identification of lines, classification of spectra. Thereafter some important groups of lines are dealt with: non-LTE computation of the Mgii lines are presented: apart from the peculiar emission line and shell stars they compare well with the observations; intensity ratios, of Feii and Feiii lines are an important temperature classification criterion. Interstellar UV lines indicate large deficiencies of some metals, as compared to solar values. A new ultraviolet continuous extinction curve is determined. We discuss the strong outstreaming motions observed in α Cygni, and the consequent mass loss of this star (〈 3 × 10−10 $$\mathfrak{M}_ \odot $$ yr−1and finally we describe the composite spectrum of the (WC8+09I) bnary γ2 Velorum; the ultraviolet continuous spectrum of the WC star is about one magnitude brighter than any theory predicts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647130
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  • 5
    Electronic Resource
    Electronic Resource
    Book reviews (1969)
    Springer
    Space science reviews 9 (1969), S. 617-620 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00212709
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  • 6
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    A prescription and fast code for the long-term evolution of star clusters - II. Unbalanced and core evolution (2013)
    Oxford University Press
    Details
    Publication Date: 2013-12-06
    Description: We introduce version two of the fast star cluster evolution code Evolve Me A Cluster of StarS ( emacss ). The first version (Alexander and Gieles) assumed that cluster evolution is balanced for the majority of the life cycle, meaning that the rate of energy generation in the core of the cluster equals the diffusion rate of energy by two-body relaxation, which makes the code suitable for modelling clusters in weak tidal fields. In this new version, we extend the model to include an unbalanced phase of evolution to describe the pre-collapse evolution and the accompanying escape rate such that clusters in strong tidal fields can also be modelled. We also add a prescription for the evolution of the core radius and density and a related cluster concentration parameter. The model simultaneously solves a series of first-order ordinary differential equations for the rate of change of the core radius, half-mass radius and the number of member stars N . About two thousand integration steps in time are required to solve for the entire evolution of a star cluster and this number is approximately independent of N . We compare the model to the variation of these parameters following from a series of direct N -body calculations of single-mass clusters and find good agreement in the evolution of all parameters. Relevant time-scales, such as the total lifetimes and core collapse times, are reproduced with an accuracy of about 10 per cent for clusters with various initial half-mass radii (relative to their Jacobi radii) and a range of different initial N up to N  = 65 536. The current version of emacss contains the basic physics that allows us to evolve several cluster properties for single-mass clusters in a simple and fast way. We intend to extend this framework to include more realistic initial conditions, such as a stellar mass spectrum and mass-loss from stars. The emacss code can be used in star cluster population studies and in models that consider the co-evolution of (globular) star clusters and large-scale structures.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The evolution of the global stellar mass function of star clusters: an analytic description (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-04
    Description: The evolution of the global stellar mass function of star clusters is studied based on a large set of N -body simulations of clusters with a range of initial masses, initial concentrations, in circular or elliptical orbits in different tidal environments. Models with and without initial mass segregation are included. The depletion of low-mass stars in initially Roche-volume (tidal) filling clusters starts typically on a time-scale of the order of the core collapse time. In clusters that are initially underfilling their Roche-volume it takes longer because the clusters have to expand to their tidal radii before dynamical mass-loss becomes important. We introduce the concept of the differential mass function (DMF), which describes the changes with respect to the initial mass function (IMF). We show that the evolution of the DMF can be described by a set of very simple analytic expressions that are valid for a wide range of initial cluster parameters and for different IMFs. The agreement between this description and the models is very good, except for initially Roche-volume underfilling clusters that are severely mass segregated.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Early disc accretion as the origin of abundance anomalies in globular clusters (2013)
    Oxford University Press
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    Publication Date: 2013-11-17
    Description: Globular clusters (GCs), once thought to be well approximated as simple stellar populations (i.e. all stars having the same age and chemical abundance), are now known to host a variety of anomalies, such as multiple discrete (or spreads in) populations in colour–magnitude diagrams and abundance variations in light elements (e.g. Na, O, Al). Multiple models have been put forward to explain the observed anomalies, although all have serious shortcomings (e.g. requiring a non-standard initial mass function of stars and GCs to have been initially 10–100 times more massive than observed today). These models also do not agree with observations of massive stellar clusters forming today, which do not display significant age spreads nor have gas/dust within the cluster. Here we present a model for the formation of GCs, where low-mass pre-main-sequence stars accrete enriched material released from interacting massive binary and rapidly rotating stars on to their circumstellar discs, and ultimately on to the young stars. As was shown in previous studies, the accreted material matches the unusual abundances and patterns observed in GCs. The proposed model does not require multiple generations of star formation, conforms to the known properties of massive clusters forming today and solves the ‘mass budget problem’ without requiring GCs to have been significantly more massive at birth. Potential caveats to the model as well as model predictions are discussed.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    A prescription and fast code for the long-term evolution of star clusters - III. Unequal masses and stellar evolution (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-13
    Description: We present a new version of the fast star cluster evolution code Evolve Me A Cluster of StarS ( emacss ). While previous versions of emacss reproduced clusters of single-mass stars, this version models clusters with an evolving stellar content. Stellar evolution dominates early evolution, and leads to: (1) reduction of the mean mass of stars due to the mass loss of high-mass stars; (2) expansion of the half-mass radius; (3) for (nearly) Roche Volume filling clusters, the induced escape of stars. Once sufficient relaxation has occurred (~=10 relaxation times-scales), clusters reach a second, ‘balanced’ state whereby the core releases energy as required by the cluster as a whole. In this state: (1) stars escape due to tidal effects faster than before balanced evolution; (2) the half-mass radius expands or contracts depending on the Roche volume filling factor; and (3) the mean mass of stars increases due to the preferential ejection of low-mass stars. We compare the emacss results of several cluster properties against N -body simulations of clusters spanning a range of initial number of stars, mass, half-mass radius, and tidal environments, and show that our prescription accurately predicts cluster evolution for this data base. Finally, we consider applications for emacss , such as studies of galactic globular cluster populations in cosmological simulations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    A Search for HAeBe stars in the bar of the Large Magellanic Cloud based on optical variability (2002)
    EDP Sciences
    Details
    Publication Date: 2002-11-18
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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