Search Results - (Author, Cooperation:A. Renzini)
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1Latest Papers from Table of Contents or Articles in PressS. Tacchella ; C. M. Carollo ; A. Renzini ; N. M. Forster Schreiber ; P. Lang ; S. Wuyts ; G. Cresci ; A. Dekel ; R. Genzel ; S. J. Lilly ; C. Mancini ; S. Newman ; M. Onodera ; A. Shapley ; L. Tacconi ; J. Woo ; G. Zamorani
American Association for the Advancement of Science (AAAS)
Published 2015Staff ViewPublication Date: 2015-04-18Publisher: American Association for the Advancement of Science (AAAS)Print ISSN: 0036-8075Electronic ISSN: 1095-9203Topics: BiologyChemistry and PharmacologyComputer ScienceMedicineNatural Sciences in GeneralPhysicsPublished by: -
2Articles: DFG German National LicensesStaff View
ISSN: 1476-4687Source: Nature Archives 1869 - 2009Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsNotes: [Auszug] Direct spectroscopic determination of the abundance of helium in population II stars is quite difficult; and, because of the possibility of gravitational helium depletion caused by inward diffusion in the atmospheres of horizontal branch blue stars4, conclusions from spectroscopic determinations ...Type of Medium: Electronic ResourceURL: -
3Articles: DFG German National LicensesDaddi, E. ; Renzini, A. ; Cassata, P. ; Vanzella, E. ; Pozzetti, L. ; Cristiani, S. ; Fontana, A. ; Rodighiero, G. ; Mignoli, M. ; Zamorani, G. ; Cimatti, A.
[s.l.] : Macmillian Magazines Ltd.
Published 2004Staff ViewISSN: 1476-4687Source: Nature Archives 1869 - 2009Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsNotes: [Auszug] More than half of all stars in the local Universe are found in massive spheroidal galaxies, which are characterized by old stellar populations with little or no current star formation. In present models, such galaxies appear rather late in the history of the Universe as the culmination of a ...Type of Medium: Electronic ResourceURL: -
4Articles: DFG German National LicensesTacconi, L. J. ; Eisenhauer, F. ; Förster Schreiber, N. M. ; Cimatti, A. ; Daddi, E. ; Bouché, N. ; Davies, R. ; Lehnert, M. D. ; Lutz, D. ; Nesvadba, N. ; Verma, A. ; Abuter, R. ; Shapiro, K. ; Sternberg, A. ; Renzini, A. ; Kong, X. ; Arimoto, N. ; Mignoli, M. ; Genzel, R.
[s.l.] : Nature Publishing Group
Published 2006Staff ViewISSN: 1476-4687Source: Nature Archives 1869 - 2009Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsNotes: [Auszug] Observations and theoretical simulations have established a framework for galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark-matter haloes; mergers of haloes and galaxies then led to the hierarchical build-up of galaxy ...Type of Medium: Electronic ResourceURL: -
5Articles: DFG German National LicensesStaff View
ISSN: 0370-1573Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002Topics: PhysicsType of Medium: Electronic ResourceURL: -
6Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsDescription / Table of Contents: Со∂ерисанuе В работе рассчитаны эволюционные пути сдедуюшие за σтадией красных иγантов для моделей звёзд с массами 0,9M ⊙, 0,7M ⊙ и 0,6M ⊙ населения П типа. Исходние модели состгят из гелиевого ядра, содержащего 90% общей массы, и водородной ободочки. Их можно считать ‘остатками’ звезд, потерявших в акте предшествующей эволюции существенную частъ общей массы.Abstract: Riassunto È stata calcolata per modelli di stelle di 0,9M ⊙, 0,7M ⊙ e 0,6M ⊙ di Popolazione II l'evoluzione successiva allo stadio di gigante rossa. Inizialmente i modelli constano di un nucleo di elio contenente il 90% della massa totale e di un inviluppo idrogenico. Essi possono interpretarsi come i ‘resti’ di stelle che abbiano perso una frazione di massa considerevole in fasi evolutive precedenti, o all'innesco violento dell'elio al centro.Notes: Abstract Evolutionary tracks of 0.9M ⊙, 0.7M ⊙ and 0.6M ⊙ models for Population II stars have been computed in the post-red giant phase. The stars are initially composed of a helium core containing a mass fraction equal to 0.9 and of a hydrogen-rich envelope. They represent hypothetical remnants of stars after substantial mass loss in previous evolutionary phases or/and at the helium flash.Type of Medium: Electronic ResourceURL: -
7Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsDescription / 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 ResourceURL: -
8Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsDescription / Table of Contents: Содержание В работе указаны характерныы особенности диаграммы герцпрунга-рессела для шаровых скоплений. При этом уделено особое внимание положксеию и протяжению горизонтальной ветви. Приведено сравнение данных наблюдений со значениами параметров полученных из расчета тволюционных путей с потерей и без потера массы. Приведён также анализ моделей с большим значенмем отношенийq 0 массы гелиевото ядра к обшей массе. Равновесные моделы с двойным лсточнлком энергии расснитанн для значенийq 0 и общей массы псдхдлящих для звёзд горизонтальнои ветви.Abstract: Riassunto Sono indicate le principali caratteristiche dei diagrammi H-R degli ammassi globulari con particolare riferimento alla posizione ed alla estensione del ramo orizzontale. Sono esaminate relazioni tra la teoria ed i parametri indicati nei due casi di evoluzione con e senza perdita di massa. E' presentata infine una analisi di modelli con un'alta frazione di massa nel nucleo di elio (q 0). I modelli di equilibrio, non omogenei ed a doppia sorgente di energia, sono stati calcolati in un intervallo di valori diq 0 e della massa totale che sono in relazione alla regione delle stelle del ramo orizzontale.Notes: Abstract The most characteristic features of H-R diagrams of blobular clusters are summarized with particular regard to the position and the extension of the horizontal branch. A comparison of observations with theory in the two cases of evolution with and without mass loss is then shortly given. A preliminary approach to the evolution of models with large mass fractions (q 0) in the helium cores is presented. Inhomogeneous equilibrium models with double energy sources have been computed in a range of values ofq 0 and of the total mass referring to possible horizontal-branch stars.Type of Medium: Electronic ResourceURL: -
9Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsDescription / 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 ResourceURL: -
10Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsNotes: Abstract Results of calculations of main sequence stellar models for metal poor star are presented. A fictitious pre-main sequence evolution was computed in order to give the distribution of the primary elements H, He3, He4, C12, N14 and O16 in the stellar interior. The selected initial chemical composition wasX=.9,Z=.001. Comparison with previous results indicates a life-time of the main sequence phase shorter than it was believed before.Type of Medium: Electronic ResourceURL: -
11Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsNotes: Abstract A theoretical check is performed to determine for the horizontal-branch stars the zone (in the H-R diagram) in which the surface convection is acting. A possible experimental test of the efficiency of the depletion mechanism is also proposed.Type of Medium: Electronic ResourceURL: -
12Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsNotes: Abstract The actual knowledge on Horizontal Branch stars of the metal-poor Globular Clusters of our Galaxy suggests that these stars evolve along the Horizontal Branch from the very blue stars towards lower effective temperature. From this behaviour it follows that a substantial mass loss occurs at the He-flash. On the basis of a gravitational thermalization of Horizontal Branch stars any recent observational data concerning NGC 7006 are re-examined. It is pointed out that today it is not necessary to leave the hypothesis of a strong correlation between the metal and helium content for our Galaxy.Type of Medium: Electronic ResourceURL: -
13Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsDescription / 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 ResourceURL: -
14Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsDescription / 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 ResourceURL: -
15Articles: DFG German National LicensesStaff View
ISSN: 1572-946XSource: Springer Online Journal Archives 1860-2000Topics: PhysicsDescription / 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 ResourceURL: