Searcharxiv⌕ Search

arXiv subjects

Lorenzo Zaninetti

Publications and source records attributed to Lorenzo Zaninetti.

54 records · Page 3Linked to original sources
arXiv2010

New formulae for the Hubble Constant in a Euclidean Static Universe

It is shown that the Hubble constant can be derived from the standard luminosity function of galaxies as well as from a new luminosity function as deduced from the mass-luminosity relationship for galaxies. An analytical expression for the Hubble constant can be found from the maximum number of galaxies (in a given solid angle and flux) as a function of the redshift. A second analytical definition of the Hubble constant can be found from the redshift averaged over a given solid angle and flux. The analysis of two luminosity functions for galaxies brings to four the new definitions of the Hubble constant. The equation that regulates the Malmquist bias for galaxies is derived and as a consequence it is possible to extract a complete sample. The application of these new formulae to the data of the two-degree Field Galaxy Redshift Survey provides a Hubble constant of $( 65.26 \pm 8.22 ) \mathrm{\ km\ s}^{-1}\mathrm{\ Mpc}^{-1}$ for a redshift lower than 0.042. All the results are deduced in a Euclidean universe because the concept of space-time curvature is not necessary as well as in a static universe because two mechanisms for the redshift of galaxies alternative to the Doppler effect are invoked.

astro-ph.CO↗
arXiv2010

The Luminosity Function of Galaxies as modelled by the Generalized Gamma Distribution

Two new luminosity functions of galaxies can be built starting from three and four parameter generalized gamma distributions. In the astrophysical conversion, the number of parameters increases by one, due to the addition of the overall density of galaxies. A third new galaxy luminosity function is built starting from a three parameter generalized gamma distribution for the mass of galaxies once a simple nonlinear relationship between mass and luminosity is assumed; in this case the number of parameters is five because the overall density of galaxies and a parameter that regulates mass and luminosity are added. The three new galaxy luminosity functions were tested on the Sloan Digital Sky Survey (SDSS) in five different bands; the results always produce a "better fit" than the Schechter function. The formalism that has been developed allows to analyze the Schechter function with a transformation of location. A test between theoretical and observed number of galaxies as a function of redshift was done on data extracted from a two-degree field galaxy redshift survey.

astro-ph.CO↗
arXiv2010

A geometrical model for the catalogs of galaxies

The 3D network originated by the faces of irregular Poissonian Voronoi Polyhedrons may represent the backbone on which the galaxies are originated. As a consequence the spatial appearance of the catalogs of galaxies can be reproduced. The selected catalogs to simulate are the 2dF Galaxy Redshift Survey and the Third Reference Catalog of Bright Galaxies. In order to explain the number of observed galaxies for a given flux/magnitude as a function of the redshift, the photometric properties of the galaxies should be carefully examined from both the astronomical and theoretical point of view. The statistics of the Voronoi normalized volume is modeled by two distributions and the Eridanus super-void is identified as the largest volume belonging to the Voronoi Polyhedron. The behavior of the correlation function for galaxies is simulated by adopting the framework of thick faces of Voronoi Polyhedrons on short scales, while adopting standard arguments on large scales.

astro-ph.CO↗
arXiv2009

The Physics of turbulent and dynamically unstable Herbig-Haro jets

The overall properties of the Herbig-Haro objects such as centerline velocity, transversal profile of velocity, flow of mass and energy are explained adopting two models for the turbulent jet. The complex shapes of the Herbig-Haro objects, such as the arc in HH34 can be explained introducing the combination of different kinematic effects such as velocity behavior along the main direction of the jet and the velocity of the star in the interstellar medium. The behavior of the intensity or brightness of the line of emission is explored in three different cases : transversal 1D cut, longitudinal 1D cut and 2D map. An analytical explanation for the enhancement in intensity or brightness such as usually modeled by the bow shock is given by a careful analysis of the geometrical properties of the torus.

astro-ph.GA↗
arXiv2009

Scaling for the intensity of radiation in spherical and aspherical planetary nebulae

The image of planetary nebulae is made by three different physical processes. The first process is the expansion of the shell that can be modeled by the canonical laws of motion in the spherical case and by the momentum conservation when gradients of density are present in the interstellar medium. The second process is the diffusion of particles that radiate from the advancing layer. The 3D diffusion from a sphere as well as the 1D diffusion with drift are analyzed. The third process is the composition of the image through an integral operation along the line of sight. The developed framework is applied to A39, to the Ring nebula and to the etched hourglass nebula MyCn 18.

astro-ph.GA↗
arXiv2009

The relativistic equation of motion in turbulent jets

The turbulent jets are usually described by classical velocities. The relativistic case can be treated starting from the conservation of the relativistic momentum. The two key assumptions which allow to obtain a simple expression for the relativistic trajectory and relativistic velocity are null pressure and constant density.

astro-ph.HE↗
arXiv2009

A turbulent model for the surface brightness of extragalactic jets

This paper summarizes the known physics of turbulent jets observed in laboratory experiments. The formula, which gives the power released in turbulence describes the concentration of turbulence/relativistic particles in each point of the astrophysical jets. The same expression is also used to analyze the power released in turbulence in the case of pipe and non Newtonian fluids. Through an integral operation it is possible to deduce the intensity of synchrotron radiation for a profile perpendicular or not to a straight jet, a 2D map for a perpendicular, randomly oriented straight jet as well as a 2D map of complex trajectories such as NCC4061 and 3C31. Presented here is a simulation of the spectral index in brightness of 3C273 as well as a 2D map of the degree of linear polarization. The Sobel operator is applied to the theoretical 2D maps of straight perpendicular jets.

astro-ph.CO↗
arXiv2008

Semi-analytical formulas for the Hertzsprung-Russell Diagram

The absolute visual magnitude as function of the observed colour (B-V), also named Hertzsprung-Russell diagram can be described through five equations; that in presence of calibrated stars means eight constants. The developed framework allows to deduce the remaining physical parameters that are mass, radius and luminosity. This new technique is applied to the first 10 pc, the first 50 pc, the Hyades and to the determination of the distance of a cluster. The case of the white dwarfs is analysed assuming the absence of calibrated data: our equation produces a smaller $χ^2$ in respect to the standard colour-magnitude calibration when applied to the Villanova Catalog of Spectroscopically Identified White Dwarfs. The theoretical basis of the formulae for the colours and the bolometric correction of the stars are clarified through a Taylor expansion in the temperature of the Planck distribution.

astro-ph↗
arXiv2008

On the Truncated Pareto Distribution with applications

The Pareto probability distribution is widely applied in different fields such us finance, physics, hydrology, geology and astronomy. This note deals with an application of the Pareto distribution to astrophysics and more precisely to the statistical analysis of mass of stars and of diameters of asteroids. In particular a comparison between the usual Pareto distribution and its truncated version is presented. Finally a possible physical mechanism that produces Pareto tails for the distribution of the masses of stars is suggested.

astro-ph↗
arXiv2008

A new luminosity function for galaxies as given by the mass-luminosity relationship

The search for a luminosity function for galaxies both alternative or companion to a Schechter function is a key problem in the reduction of data from catalogs of galaxies. Two luminosity functions for galaxies can be built starting from two distributions of mass as given by the fragmentation. A first overall distribution function is the Kiang function that represents a useful description of the area and volume distribution of the Poisson Voronoi diagrams. The second distribution, that covers the case of low mass galaxies, is the truncated Pareto distribution : in this model we have a natural bound due to the minimum mass/luminosity observed and an upper bound (function of the considered environment) represented by the boundary with the observed mass/luminosity overall behaviour. The mass distribution is then converted into a luminosity distribution through a standard mass-luminosity relationship.

astro-ph↗
arXiv2007

X-rays profiles in symmetric and asymmetric supernova remnants

The non-thermal X-rays from the SN 1006 NE rim present characteristic scale lengths that are interpreted in the context of diffusion of a relativistic electron. The adopted theoretical framework is the mathematical diffusion in 3D, 1D and 1D with drift as well as the Monte Carlo random walk in 1D with drift. The asymmetric random walk with diffusion from a plane can explain the scale widths of 0.04 pc upstream and 0.2 pc downstream in the non thermal intensity of X-ray emission in SN 1006. A mathematical image of the non thermal X-flux from an supernova remnant as well as profiles function of the distance from the center can be simulated. This model provides a reasonable description of both the limbs and the central region of SN 1006. A new method to deduce the magnetic field in supernova remnant is suggested.

astro-ph↗
arXiv2007

Models of diffusion of galactic Cosmic Rays from Super-bubbles

Super-bubbles are shells in the interstellar medium produced by the simultaneous explosions of many supernova remnants. The solutions of the mathematical diffusion and of the Fourier expansion in 1D, 2D and 3D were deduced in order to describe the diffusion of nucleons from such structures. The mean number of visits in the the case of the Levy flights in 1D was computed with a Monte Carlo simulation. The diffusion of cosmic rays has its physical explanation in the relativistic Larmor gyro-radius which is energy dependent. The mathematical solution of the diffusion equation in 1D with variable diffusion coefficient was computed. Variable diffusion coefficient means magnetic field variable with the altitude from the Galactic plane. The analytical solutions allow us to calibrate the code that describes the Monte Carlo diffusion. The maximum energy that can be extracted from the super-bubbles is deduced. The concentration of cosmic rays is a function of the distance from the nearest super-bubble and the selected energy. The interaction of the cosmic rays on the target material allows us to trace the theoretical map of the diffuse Galactic continuum gamma-rays. The streaming of the cosmic rays from the Gould Belts that contains the sun at it's internal was described by a Monte Carlo simulation. Nine new formulas are derived.

astro-ph↗
arXiv2006

Physical mechanisms that shape the morphologies of extragalactic jets

In order to find a law characterising the decrease of velocity along a jet, five analytical methods are suggested. The first two simple models examine the variation of velocity in the presence of Newton's or Stoke's resistance. The equation that represents the conservation of the momentum along a pyramidal sector is solved from an analytical point of view (third model). The application of the conservation of the total momentum flux allows us to deduce the velocity of the galaxy as a function of time for classical velocities (fourth model) and relativistic velocities (fifth model). The variation of velocity along the jet combined with an adequate composition of jet precession velocity, rotational velocity of the galaxy, and galaxy dispersion velocity in the cluster allows us to trace the geometrical pattern of the head-tail radio sources. Application of the developed theory/code to the radio galaxies NGC1265,NGC4061,NGC326, and Cygnus A gives the central galaxy's approximate dispersion velocities in the direction perpendicular to the jet. A transition from head--tails to classical double radio galaxies as a function of the increasing jet's mechanical power is introduced.

astro-ph↗
arXiv2006

On the Large-Scale Structure of the Universe as given by the Voronoi Diagrams

The size distributions of 2D and 3D Voronoi cells and of cells of $V_p(2,3)$,--2D cut of 3D Voronoi diagram--are explored, with the single-parameter (re-scaled) gamma distribution playing a central role in the analytical fitting. Observational evidence for a cellular universe is briefly reviewed. A simulated $V_p(2,3)$ map with galaxies lying on the cell boundaries is constructed to compare, as regards general appearance, with the observed CFA map of galaxies and voids, the parameters of the simulation being so chosen as to reproduce the largest observed void size.

astro-ph↗
arXiv2005

The Initial Mass Function as given by the fragmentation

The dichotomy between a universal mass function (IMF) and a variable IMF which depends on local physical parameters characterises observational and theoretical stellar astronomy. In this contribution the available distributions of probability are briefly reviewed. The physical nature of two of them, gamma variate and lognormal, is then explained once the framework of the fragmentation is introduced. Interpolating techniques are then applied to the sample of the first 10 pc and to the open cluster NGC6649: in both cases lognormal distribution produces the best fit. The three power law function has also been investigated and visual comparison with an artificially generated sample of 100000 stars suggests that the variations in the spectral index are simply due to the small number of stars available in the observational sample. In order to derive the sample of masses, a new formula that allows us to express the mass as a function of the absolute magnitude and (B-V) for MAIN V, GIANTS III and SUPERGIANTS I is derived.

astro-ph↗
arXiv2005

On the shape of Superbubbles evolving in the Galactic Plane

The galactic supershells are cavities in the interstellar medium. These shells can be explained by introducing the concept of superbubbles, the theoretical result of multiple supernova. The superbubbles can be analytically described if the ambient medium has a constant density both in the so-called bursting phase and in the subsequent adiabatic expansion. In order to solve the expansion of superbubbles in the ISM, which is a non-homogeneous medium, a numerical technique is used that divides the sphere into many sectors. By varying the time of the bursting phenomenon and the time over which the phenomenon is followed, elliptical and hour-glass shapes or vertical walls can be obtained. Application of the developed theory/code to the super-shell associated with GW~46.4+5 and with GSH 238 allows us to say that the suggested physical parameters are consistent with our theory. The map of the expanding superbubble's velocity can be tentatively traced by generating random points on the expanding surface. The structure of the galactic plane as a result of the evolution of many super-bubbles was simulated by adopting the percolation theory in order to generate new OB associations.

astro-ph↗
arXiv2005

The cubic period-distance relation for the Kater reversible pendulum

We describe the correct cubic relation between the mass configuration of a Kater reversible pendulum and its period of oscillation. From an analysis of its solutions we conclude that there could be as many as three distinct mass configurations for which the periods of small oscillations about the two pivots of the pendulum have the same value. We also discuss a real compound Kater pendulum that realizes this property.

physics.class-ph↗