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59 results on '"Di Fazio, A."'

13. Physical Processes in Fragmentation and Star Formation

Author

R. Capuzzo-Dolcetta, Cesare Chiosi, and Alberto di Fazio

Subjects
Physics, Stellar mass, Fragmentation (mass spectrometry), Star formation, Molecular cloud, Astrophysics, Galactic nuclei, Exoplanet
Published
1990

14. Fragmentation and Supersonic Turbulence in Self-Gravitating Gas Clouds

Author

V. A. Urpin, A. Soloviev, A. di Fazio, and S. V. Vereshchagin

Subjects
Physics, Orbital speed, Gravitational field, Turbulence, Molecular cloud, Orbital motion, Velocity dispersion, Astrophysics, Magnetohydrodynamic turbulence, Astrophysics::Galaxy Astrophysics, Virial theorem
Abstract

We test three different hypotheses to explain the Δv-L correlation between the velocity dispersion deduced from the line broadening in molecular clouds and the cloud sizes, namely: i) that the clouds are born essentially due to turbulence, with negligible evolutionary effects on the above spectrum, and that the relation is the universal specrum of turbulence, in the fashion of Kolmogorov; ii) that the clouds are born through some fragmentation process, and that the relation is nothing else than the virial correlation; iii) that both fragmentation and turbulence are present, and that the observed correlation is actually the superposition of the velocity dispersion of fragments’ orbits and the velocity dispersion of turbulence. The virial slope in the LogΔv − Log L (0.5 − 0.62) is closer to that of the data (0.56) than that of Kolmogorov spectrum (0.33), although the quality of the data does not allow a net decision between the two extreme hypotheses. Nevertheless, the use of the model with turbulence and fragmentation shows that the obtained (at virialization) orbital velocity dispersion of fragments is always significatively larger than the turbulent velocity dispersion. If this model (see [10]) were correct, then the observed velocity dispersion would be mainly due to random orbits of sub-condensated globules or fragments, and not to turbulence. The latter seems to be the most plausible case.

Published
1990

15. A MultiFluid Hydrodynamical Radiative Model for the Evolution of a Spherical Protogalaxy

Author

A. di Fazio, A. B. Men’shchikov, and R. Capuzzo-Dolcetta

Subjects
Shock wave, Physics, protogalaxies - star:formation- hydrodynamics, Radiative cooling, Stellar mass, Protogalaxy, Metallicity, Globular cluster, Bremsstrahlung, Radiative transfer, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

In this paper we present a new radiative, multifluid, hydrodynamical model of protogalactic evolution, using the fragmentation law by Di Fazio (1986). A treatment for radiation transport suitable for non-equi1ibrium conditions was included. The most important results are : strong shock waves are formed at the time of the bounce of the system, causing a mass loss from the protogalaxy both in fragments and gas; the initial quasi-isothermal phase at ≈ 300 °K is abruptly abandoned when the collapse heating overwhelms the molecular hydrogen radiative cooling, and the second quasi-isothermal phase at ≈ 3500 °K is also abandoned when the center of the system reaches a bremsstrahlung phase. The X-luminosity is, in this phase, similar to that of QSO’s. After this transient violent radiative phase, the protogalaxy’s radiation activity seems to slowly decline and degrade towards longer wavelengths. In the stellar mass range, two peaks are attained in the IMF at ≈ 20 and ≈ 100 M⊙. The slopes of the declining part of the IMF in that range is similar to Salpeter’s. Globular clusters seem to form in two bursts, in regions r > 7 Kpc and r > 20 Kpc. with radial metallicity distribution implications. The slope of the globular cluster family IMF is ≈ −1.8.

Published
1990

16. Turbulence in the Frame of the Evolution of a Self-Gravitating Protocloud

Author

V. A. Urpin, A. di Fazio, P. Battinelli, S. V. Vereshchagin, and R. Capuzzo-Dolcetta

Subjects
Physics, SUPERSONIC FLOW, Orbital speed, GALACTIC EVOLUTION, GRAVITATIONAL FIELDS, MAGNETOHYDRODYNAMIC TURBULENCE, MOLECULAR CLOUDS, ASTRONOMICAL MODELS, CHEMICAL EVOLUTION, COSMOCHEMISTRY, FRAGMENTATION, STAR FORMATION, TURBULENT WAKES, Turbulence, Molecular cloud, Velocity dispersion, Mechanics, Dissipation, Magnetohydrodynamic turbulence, Physics::Fluid Dynamics, Classical mechanics, Supersonic speed, Choked flow, Astrophysics::Galaxy Astrophysics
Abstract

This paper studies the influence of turbulence generated by the supersonic motion of fragments formed during the collapse of a self-gravitating cloud. We investigate the dependence of the results upon the physical parameters, needed to describe turbulence. The results are given for three values of the gas cloud mass. The presence of turbulence with consequent dissipation is shown to raise appreciably the gas temperature. The results show that the turbulent velocity dispersion is sistematically smaller than the fragments’ orbital velocity dispersion.

Published
1990

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