Pulsational M_V versus [Fe/H] relation(s) for globular cluster RR Lyrae variables     

F. Caputo  V. Castellani  M. Marconi  V. Ripepi 《Monthly notices of the Royal Astronomical Society》2000,316(4):819-826

We use the results from recent computations of updated non-linear convective pulsating models to constrain the distance modulus of Galactic globular clusters through the observed periods of first-overtone (RR _c ) pulsators. The resulting relation between the mean absolute magnitude of RR Lyrae stars 〈 M _V (RR)〉 and the heavy element content [Fe/H] appears well in the range of several previous empirical calibrations, but with a non-linear dependence on [Fe/H] so that the slope of the relation increases when moving towards larger metallicities. On this ground, our results suggest that metal-poor ([Fe/H]<−1.5) and metal-rich ([Fe/H]>−1.5) variables follow two different linear 〈 M _V (RR)〉−[Fe/H] relations. Application to RR Lyrae stars in the metal-poor globular clusters of the Large Magellanic Cloud (LMC) provides an LMC distance modulus of the order of 18.6 mag, thus supporting the 'long' distance scale. The comparison with recent predictions based on updated stellar evolution theory is briefly presented and discussed.  相似文献   

Galactic globular clusters as a test for very-low-mass stellar models     

S. Cassisi  V. Castellani  P. Ciarcelluti  G. Piotto  M. Zoccali 《Monthly notices of the Royal Astronomical Society》2000,315(4):679-688

We make use of the 'Next Generation' model atmospheres of Allard et al. and Hauschildt, Allard & Baron to compute theoretical models for low- and very-low-mass stars for selected metallicities in the range Z =0.0002 to 0.002. On this basis, we present theoretical predictions covering the sequence of H-burning stars as observed in Galactic globulars from the faint end of the main sequence up to, and beyond, the cluster turn-off. The role played by the new model atmospheres is discussed, showing that present models appear in excellent agreement with models by Baraffe et al. as computed on a quite similar physical basis. One finds that the theoretical mass–luminosity relations based on this updated set of models are in good agreement with the empirical data provided by Henry & McCarthy. Comparison with HST observation discloses that the location on the colour–magnitude diagram of the lower main sequence in Galactic globular clusters appears again in good agreement with the predicted sensitive dependence of these sequences on the cluster metallicity.  相似文献   

Future dynamical evolution of the Neptune-Triton system. A new synthetic method of analysis     

Vittorio Banfi 《Earth, Moon, and Planets》1984,30(1):43-52

A new approach to the study of future dynamical evolution of the Neptune-Triton system is here presented. After the analytical development of the model, the final results are compared with those drawn by previous works on the same subject.  相似文献   

An investigation on H-R diagrams of globular clusters     

V. Castellani  P. Giannone  A. Renzini 《Astrophysics and Space Science》1969,3(4):518-529

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.

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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.

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- . . . q ₀ . q ₀ .

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Horizontal-branch star models     

V. Castellani  P. Giannone  A. Renzini 《Astrophysics and Space Science》1969,4(1):103-118

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.u 0,9M , 0,7M 0,6M . , 90% , . , .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.  相似文献   

Nuclear burning rates and Population II stellar models     

E. Brocato  V. Castellani  & F. L. Villante 《Monthly notices of the Royal Astronomical Society》1998,298(2):557-561

We discuss theoretical predictions concerning the evolution of globular cluster Population II stars with respect to current estimates of standard errors in the determination of nuclear burning rates. Numerical evaluations are given for the dependence of the turn-off and horizontal branch luminosities on the rate of the relevant nuclear reactions. We conclude that evolutionary predictions appear rather solid in this respect, with a maximum 3 σ error of about 1 Gyr in the evaluation of cluster ages derived from the calibration of the difference in luminosity between the horizontal branch and the turn-off. However, current evaluation of the original He content, as given on the basis of the R -parameter, will need to wait for a much better determination of the ¹²C(α, γ)¹⁶O reaction before reaching a satisfactory accuracy.  相似文献   

Enhanced α-elements and He-burning Population II stars     

D. Bencivenni  V. Castellani  A. Tornambé  A. Weiss 《Astrophysics and Space Science》1989,157(1-2):31-40

Spectroscopic analysis of Population II stars indicates that oxygen and other -elements appear to be overabundant with respect to iron (Sneden, 1985; Grattonet al., 1986; Gustafsson, 1987; Gratton, 1987; Gratton and Ortolani, 1989). By use of the Los Alamos Tapes Library, new opacities for Population II stars have been computed, including oxygen, neon, magnesium, and calcium enhanced by a factor five with respect to the solar ratios mixture. On this basis, a grid of evolutionary sequences of He-burning models has been computed for low-mass stars covering the He-burning phase from the Zero-Age Horizontal Branch (ZAHB) up to the onset of thermal pulses in an advanced phase of He-shell burning, for the following assumption on the stellar parameters: helium abundance in the envelopeY=0.20 and 0.25; intial chemical composition [Fe/H]=–2.3, and [Fe/H]=–1.3; initial helium-core massM _c=0.48 and 0.50 and total mass values fromM=0.56 up toM=0.76M . This choice of parameters was suggested by the opportunity of covering the range of values expected in galactic globular cluster HB stars, when an original abundance of heliumY=0.23 is assumed, as adopted throughout the recent literature. At this conference we present just a short overview of the main results while the large set of computed tracks and a detailed discussion on the topic will be presented elsewhere (Bencivenniet al., 1989).  相似文献   

Seismic performance evaluation of plasterboard partitions via shake table tests   总被引：1，自引：1，他引：0  

Gennaro Magliulo  Crescenzo Petrone  Vittorio Capozzi  Giuseppe Maddaloni  Pauline Lopez  Gaetano Manfredi 《Bulletin of Earthquake Engineering》2014,12(4):1657-1677

The damage of nonstructural components represents the largest contribution to the economic loss caused by an earthquake. Since nonstructural components are not amenable to traditional structural analysis, full-scale experimental testing is crucial to understand their behaviour under earthquake. For this reason, shaking table tests are performed to investigate the seismic behaviour of plasterboard partitions. A steel test frame is properly designed in order to simulate the seismic effects at a generic building storey. The tests are performed shaking the table simultaneously in both horizontal directions. To investigate a wide range of interstorey drift demand and seismic damage, the shakes are performed scaling the accelerograms at eleven different intensity levels. The tested plasterboard partitions from Siniat exhibit a good seismic behaviour, both in their own plane and out of plane, showing limited damage up to 1.1 % interstorey drift ratio. The correlation between the dynamic characteristics of the test setup and the recorded damage is evidenced. Finally, an interesting comparison between the experimental results and the analytical model is also performed.  相似文献   

Small‐scale experimental simulation of talus evolution     

Fabio Vittorio De Blasio  May‐Britt Sæter 《地球表面变化过程与地形》2009,34(12):1685-1692

We investigated a small‐scale laboratory model of a talus slope evolution. Five different size classes of basaltic rock were selected and marked with different colours. Homogenized mixtures of grains of different sizes were dropped from a fixed height onto a tilted experimental board covered with a loose granular layer. This was conducted in a series of regular sequences, and the resulting distribution on the board was studied after each sequence. At the beginning of the experiment, the grains developed a longitudinal gradation similar to natural talus slopes, where small grains settle at the top while the large ones roll down to the distal part. However, after a transient period dominated by single‐particle dynamics on the inert granular medium, the evolution proved to be more variable than expected. Due to the continuous shower of falling grains, the shear stress at the bottom of the upper granular layer increased. This resulted initially in a slow creep down slope that finally collapsed in large avalanches homogenizing the material. The slides occurred at the boundary between a weaker layer created by migration of small grains through the interstices, and marked by a vertical transition between small and large grains. We compare the experimental findings with observations from natural talus slopes, and suggest that similar experiments may be helpful in understanding the evolution of taluses. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Origin of salt giants in abyssal serpentinite systems     

Scribano  Vittorio  Carbone  Serafina  Manuella  Fabio C.  Hovland  Martin  Rueslåtten  Håkon  Johnsen  Hans-K. 《International Journal of Earth Sciences》2017,106(7):2595-2608

International Journal of Earth Sciences - Worldwide marine salt deposits ranging over the entire geological record are generally considered climate-related evaporites, derived from the...  相似文献