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  • 1970-1974  (10)
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Material
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Year
  • 1
    Electronic Resource
    Electronic Resource
    On the models of core-helium-burning stars (1972)
    Springer
    Astrophysics and space science 17 (1972), S. 80-86 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Sono presi in esame alcuni aspetti relativi all'aumento in massa del nucleo ed alla comparsa e sviluppo di una zona semiconvettiva intermedia in modelli di stelle con combustione centrale dell'elio. E'inoltre schematizzato il metodo iterativo di calcolo con particolare riferimento alle stelle di ramo orizzontale degli ammassi globulari.
    Notes: Summary Some aspects concerning the core-mass increase and the appearance and development of an intermediate semiconvective zone in helium-burning stars are discussed. An iterative method of computation of core increase and semiconvection is also presented. Details of this procedure are given with regard to the horizontal-branch stars of globular clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642544
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Self-accretion of matter, red subluminous stars and early evolution of low-mass stars (1972)
    Springer
    Astrophysics and space science 15 (1972), S. 462-466 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Sommario Stelle di bassa massa in fase di contrazione pre-sequenza sono con ogni probabilità circondate da abbondante gas. In queste condizioni al diminuire della luminosità può divenire efficiente il meccanismo di accrescimento, cosi da condurre la stella su una linea evolutiva del tutto peculiare. Una simile evoluzione può rendere conto di oggetti sottoluminosi e a bassa temperatura, come pure di alcune peculiarità negli spettri di stelle di bassa massa.
    Notes: Abstract Low-mass stars during their pre-main sequence contraction phase are expected to be surrounded by a certain amount of the primordial gas. At low luminosities, accretion of this gas can make the stars to follow a peculiar evolutionary course which can account for certain types of red subluminous stars. The efficiency of the accretion mechanism can also account for some peculiarities in the spectra of the stars of low mass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00649772
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Induced semi-convection in helium-burning horizontal-branch stars (1971)
    Springer
    Astrophysics and space science 10 (1971), S. 355-362 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Come conseguenza del progressivo aumento in massa per overshooting del nucleo convettivo nella fase iniziale di combustione centrale dell'elio in stelle di ramo orizzontale e per l'andamento del gradiente radiativo della temperatura al bordo del nucleo, viene raggiunto uno stadio nel quale una zona intermedia è instabile rispetto alla convezione. Dalla considerazione dei tempi caratteristici di propagazione della convezione e di combustione nucleare, si conclude che l'instabilità può indurre un mescolamento parziale (semiconvezione) in una regione esterna al nucleo.
    Notes: Abstract In the evolutionary phase of central helium burning, models of horizontal-branch stars reach a stage at which an intermediate region is unstable against convection. This feature is due to the progressive increase of the core mass by overshooting during the previous evolutionary stages and to the behaviour of the radiative temperature gradient at the core boundary. By consideration of the typical time scales of propagation of convection and nuclear burning, a partial mixing (semi-convection) can be induced in a region around the convective core.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00649680
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The structure of late type stars and the Hayashi track (1974)
    Springer
    Astrophysics and space science 28 (1974), S. 303-324 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A topological approach in the HR diagram is given for the occurrence and the characteristics of convective envelopes in population II stars. The location of the Hayashi track and of the Red Giants branch are both investigated for various assumed masses of the stars and chemical compositions of the convective layers. An analysis is performed on the influence of the assumed mixing length. The observational consequences of a possible mass loss is discussed for both the Red Giants and the Asymptotic branches. Possible causes for separation between these two branches are briefly examined. The case of the globular cluster ω Cen is investigated, in order to give some suggestions for a large dispersion in colours observed among the giants belonging to this cluster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00641930
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Physical conditions in the convective envelope of stars (1971)
    Springer
    Astrophysics and space science 10 (1971), S. 136-149 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Sommario Si mostra come il flusso cinetico originato negli inviluppi convettivi di una stella dipenda criticamente dalle assunzioni fatte nel trattamento della convezione superadiabatica. In particolare, sulla base della teoria della lunghezza di rimescolamento, a seconda che si assumal=H P o l=H ϱ i flussi cinetici passano dall'essere un fenomeno marginale a contributi determinanti. E' discussa una serie di possibili implicazioni riguardanti la microturbolenza atmosferica in stelle di sequenza principale, le stelleA p eA m, diversi tipi di variabili e la perdita di massa in fase di gigante.
    Notes: Summary The mechanical flux originating in the convective envelope of stars is shown to depend critically by the treatment of convection. In particular, in the framework of the mixing-length theory, in passing from a mixing lengthl=H P to a mixing lengthl=H ϱ the presence of mechanical fluxes shifts from being a marginal phenomenon to a dominant one. Possible implications concerning atmospheric microturbulence in Main Sequence stars, as so asA p andA m stars, several types of variables and mass loss are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00654612
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Overshooting of convective cores in helium-burning horizontal-branch stars (1971)
    Springer
    Astrophysics and space science 10 (1971), S. 340-349 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Nei primi stadi evolutivi di stelle di ramo orizzontale, la combustione di elio in carbonio aumenta l'opacità nel nucleo convettivo. Ne segue che il rimescolamento al bordo della convezione (overshooting) induce una progressiva instabilità convettiva negli strati contornanti il nucleo con conseguente incremento della massa del nucleo stesso. E' studiata l'efficienza di tale meccanismo al fine di ottenere indicazioni sui tempi scala caratteristici del processo di propagazione. Si mostra come il criterio di Schwarzschild risulti verificato entro qualche percento al bordo interno del nucleo convettivo.
    Notes: Abstract In helium-burning horizontal-branch stars, transformation of helium into carbon increases opacity in the convective core. Such a situation can drive an increase of the core-mass extension via the mixing by overshooting. The efficiency of this mechanism is investigated in order to obtain an indication of the time scale for the propagation of the convective boundary. Schwarzschild's criterion is shown to be fulfilled within a few percent at the innermost interface of the core boundary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00704092
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Photometric information on globular cluster stars from the Palomar Sky Survey prints (1973)
    Springer
    Astrophysics and space science 22 (1973), S. 71-78 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photometric information that can be taken from the Palomar Sky Survey prints can be used to discriminate among the various evolutionary stages of stars that are members of globular clusters, as well as to obtain some idea of the HR diagram for vary faint stars. For a test case, it is shown that in a check analysis forM3 the known turn-off luminosity is given to within about 0.5 mag. The globular cluster NGC 5466 is examined and it is concluded that no turn-off occurs beforeP≈20 mag.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642823
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Current problems on horizontal branch stars (1973)
    Springer
    Astrophysics and space science 22 (1973), S. 213-225 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In the light of our present knowledge on stellar evolution, it is shown that red ZAHB will not develop for very low metal Globular Clusters ifY is appreciably greater than 0.1. Recent determinations of the mass-sizes of the He-cores at the time of the He-flash support independently conclusion that, if no increase in surface He-abundance occurs between the turn-off evolutionary phase and the H.B. stages,Y-values lower than 0.2 imply ages of the clusters larger than 20 b.y. By comparing evolutionary paths with the observed populations of the Horizontal Branches we find evidence for mass loss in blue H.B., and evidence for mass dispersion in red H.B. not depopulated in RR Lyrae. A few clusters (M3, M15) have their H.B. dominated by mass dispersion. Finally the expected correlations between mass loss and spatial distribution of H.B. stars are briefly discussed in order to point out some observational possibilities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642835
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Current problems on horizontal branch stars (1973)
    Springer
    Astrophysics and space science 22 (1973), S. 199-211 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract After a short historical survey (Section 1), present available informations on the location of H.B. stars in the colour-magnitude diagram are collected. A general agreement is found between observations and theoretical predictions as deduced from the available B.C.- and (B-V)-logT e relations. It is shown that some peculiarities or differences in the shapes of the blue branch — if real — can be ascribed to differences in the He content and/or in the efficiency of gravitational sedimentation, whereas the discrepancies in the maximum colour index of red H.B. stars is perhaps related with present indeterminacy of the treatment of superadiabacity (Section 2). Finally (Section 3) a comparison among presently available evaluations of the B.C.-logT e and (B-V)-logT e relations is made in order to derive informations about the range of reliability, as well as in order to emphasize some possible peculiarities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642834
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    A multidimensional classification of globular clusters (1970)
    Springer
    Astrophysics and space science 9 (1970), S. 418-439 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Sommario 42 ammassi globulari galattici sono stati classificati sulla base di cinque parametri osservativi: (B-V)o, g edS, usati da Hartwick,P ab (periodo medio delle variabili RR Lyrae di tipoab),n c/n ab (rapporto tra i numeri delle variabili di tipoc e di tipoab) eQ=(U-B)−0.72 (B-V). Sono state così selezionate sette classi e si è ottenuta una concordanza tra la classificazione basata sulle proprietà delle variabili RR Lyrae e quella di Hartwick. Resta in particolare confermato che gli ammassi globulari formano una famiglia di oggetti dipendente da due parametri, ciò che implica come probabilmente un solo ulteriore parametro in aggiunta all'abbondanza metallica vari da ammasso ad ammasso. Sono esaminate in dettaglio le caratteristiche evolutive di modelli stellari in relazione con le osservazioni di stelle di ramo orizzontale. Vengono infine discusse le implicazioni relative alla iniziale struttura galattica ed al problema dell'elio.
    Notes: Abstract Forty-two galactic globular clusters are classified according to the five observational parameters:S and (B-V)o, g, used by Hartwick,P ab, the mean period of theab-type RR Lyrae variables,n c/n ab, the relative number of thec-type to theab-type RR Lyrae variables and the red-dening-free parameterQ=(U-B)−0.72(B-V). Seven groups are isolated; a consistency between the Hartwick classification and a subdivision based on the RR Lyrae properties is shown. Globular clusters are confirmed to form a two parametric family of objects, what means that probably only another parameter in addition to the metal abundance must vary from a cluster to another. Evolutionary considerations in relation to the HB characteristics are given in detail. Implications concerning the initial galactic structure and the belium problem are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00649581
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    Paper (German National Licenses)
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