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L. Zaninetti

Publications and source records attributed to L. Zaninetti.

At least 37 records · Page 2Linked to original sources
arXiv2014

The physics of the optical light curve in supernovae

We present a new formula which models the rate of decline of supernovae (SN) as given by the light curve in various bands. The physical basis is the conversion of the flux of kinetic energy into radiation. The two main components of the model are a power law dependence for the radius--time relation and a decreasing density with increasing distance from the central point. The new formula is applied to SN 1993J, SN 2005cf, SN 1999ac, and SN 2001el in different bands.

astro-ph.HE↗
arXiv2014

The Luminosity Function of Galaxies as modeled by a left truncated beta distribution

A first new luminosity functions of galaxies can be built starting from a left truncated beta probability density function, which is characterized by four parameters. In the astrophysical conversion, the number of parameters increases by one, due to the addition of the overall density of galaxies. A second new galaxy luminosity function is built starting from a left truncated beta probability for the mass of galaxies once a simple nonlinear relationship between mass and luminosity is assumed; in this case the number of parameters is six because the overall density of galaxies and a parameter that regulates mass and luminosity are added. The two new galaxy luminosity functions with finite boundaries were tested on the Sloan Digital Sky Survey (SDSS) in five different bands; the results produce a "better fit" than the Schechter luminosity function in two of the five bands considered. A modified Schechter luminosity function with four parameters has been also analyzed.

astro-ph.CO↗
arXiv2014

The oscillating behavior of the pair correlation function in galaxies

The pair correlation function (PCF) for galaxies presents typical oscillations in the range 20-200 Mpc/h which are named baryon acoustic oscillation (BAO). We first review and test the oscillations of the PCF when the 2D/3D vertexes of the Poissonian Voronoi Tessellation (PVT) are considered. We then model the behavior of the PCF at a small scale in the presence of an auto gravitating medium having a line/plane of symmetry in 2D/3D. The analysis of the PCF in an astrophysical context was split into two, adopting a non-Poissonian Voronoi Tessellation (NPVT). We first analyzed the case of a 2D cut which covers few voids and a 2D cut which covers approximately 50 voids. The obtained PCF in the case of many voids was then discussed in comparison to the bootstrap predictions for a PVT process and the observed PCF for an astronomical catalog. An approximated formula which connects the averaged radius of the cosmic voids to the first minimum of the PCF is given.

astro-ph.CO↗
arXiv2014

A right and left truncated gamma distribution with application to the stars

The gamma density function is usually defined in interval between zero and infinity. This paper introduces an upper and a lower boundary to this distribution. The parameters which characterize the truncated gamma distribution are evaluated. A statistical test is performed on two samples of stars. A comparison with the lognormal and the four power law distribution is made.

astro-ph.IM↗
arXiv2013

Photometric Effects and Voronoi-diagrams as a mixed model for the spatial distribution of galaxies

We review the model of the Voronoi Diagrams which allows to reproduce the large-scale structures of our universe as given by the astronomical catalogs. The observed number of galaxies in a given solid angle with a chosen flux/magnitude versus the redshift presents a maximum that is a function of the flux/magnitude ; it can be explained by a detailed analysis of the standard luminosity function for galaxies as well by two new luminosity function for galaxies. The current status of the research on the statistics of the Voronoi Diagrams is reviewed.

astro-ph.CO↗
arXiv2013

Three dimensional evolution of SN 1987A in a self-gravitating disk

The introduction of a exponential or power law gradient in the interstellar medium (ISM) allows to produce an asymmetric evolution of the supernova remnant (SNR) when the framework of the thin layer approximation is adopted. Unfortunately both the exponential and power law gradients for the ISM do not have a well defined physical meaning. The physics conversely is well represented by an isothermal self-gravitating disk of particles whose velocity is everywhere Maxwellian. . We derived a law of motion in the framework of the thin layer approximation with a control parameter of the swept mass. The photon's losses ,that are often neglected in the thin layer approximation, are modeled trough a velocity dependence. The developed framework is applied to SNR 1987A and the three observed rings are simulated.

astro-ph.GA↗
arXiv2013

Chord distribution along a line in the local Universe

A method is developed to compute the chord length distribution along a line which intersects a cellular Universe. The cellular Universe is here modeled by the Poissonian Voronoi Tessellation (PVT) and by a non-Poissonian Voronoi Tessellation (NPVT). The distribution of the spheres is obtained from common approximations used in modeling the volumes of Voronoi Diagrams. We give analytical formulas for the distributions of the lengths of chords in both the PVT and NPVT. The astrophysical applications are made to the real Eso Slice Project and to an artificial slice of galaxies which simulates the 2dF Galaxy Redshift Survey.

astro-ph.CO↗
arXiv2013

The initial mass function modeled by a left truncated beta distribution

The initial mass function (IMF) for the stars is usually fitted by three straight lines, which means seven parameters. The presence of brown dwarfs (BD) increases to four the straight lines and to nine the parameters. Another common fitting function is the lognormal distribution, which is characterized by two parameters. This paper is devoted to demonstrating the advantage of introducing a left truncated beta probability density function, which is characterized by four parameters. The constant of normalization, the mean, the mode and the distribution function are calculated for the left truncated beta distribution. The normal-beta (NB) distribution which results from convolving independent normally distributed and beta distributed components is also derived. The chi-square test and the K-S test are performed on a first sample of stars and BDs which belongs to the massive young cluster NGC 6611 and on a second sample which represents the star's masses of the cluster NGC 2362.

astro-ph.SR↗
arXiv2012

Revisiting the Cosmological Principle in a Cellular Framework

The Cosmological Principle in it's various versions states that: (i) the Galaxy does not occupy a particular position, (ii) the Universe is homogeneous and isotropic. This statement does not agree with the recent astronomical observations in the range z lower than 0.05 which are in agreement with a cellular structure of the Universe. Here we present a local analysis of the inhomogeneity of the Universe. When z is greater than 0.05 our analysis cannot be applied because the astronomical sample of galaxies here processed is not complete. The two tools of the Poisson Voronoi tessellation (PVT) and the luminosity function for galaxies allow of building a new version of the local Cosmological Principle.

astro-ph.CO↗
arXiv2012

The intergalactic Newtonian gravitational field and the shell theorem

The release of the 2MASS Redshift Survey (2MRS), with it's 44599 galaxies allows the deduction of the galaxy's masses in nearly complete sample. A cubic box with side of 37 Mpc containing 2429 galaxies is extracted and the Newtonian gravitational field is evaluated both at the center of the box as well in 101 x 101 x 101 grid points of the box. The obtained results are then discussed at the light of the shell theorem which states that at the internal of a sphere the gravitational field is zero.

astro-ph.CO↗
arXiv2012

Asteroids dimensions and the Truncated Pareto distribution

In this chapter first the statistics of the standard and truncated Pareto distributions are derived and used to fit empirical values of asteroids diameters from different families, namely, Koronis, Eos and Themis, and from the Astorb database. A theoretical analysis is then carried out and two possible physical mechanisms are suggested that account for Pareto tails in distributions of asteroids diameter.

astro-ph.EP↗
arXiv2012

New Analytical Results for Poissonian and non-Poissonian Statistics of Cosmic Voids

Stereology allows shifting from the 3D distribution of the volumes of Poissonian Voronoi Diagrams to their 2D cross-sections. The basic assumption is that the 3D statistics of the volumes of the voids in the local Universe has a distribution function of the gamma-type. The standard rule of conversion from 3D volumes to 2D circles, adopting the standard rules of stereology, produces a new probability density function of the radii which contains the Meijer $G$-function. A non-Poissonian distribution of volumes is also considered. The distribution of the 3D radii of the Sloan Digital Sky Survey Data Release 7 is best fitted by a non-Poissonian distribution in volumes as given by the Kiang function with argument of about two.

astro-ph.CO↗
arXiv2012

Interaction of planetary nebulae, Eta-Carinae and supernova remnants with the Interstellar Medium

The image of planetary nebulae (PN), supernova remnant (SNR) and Eta-Carinae 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 quality of the simulations is introduced along one direction as well along many directions. The second process is the diffusion of particles that radiate from the advancing layer. The 3D diffusion from a sphere, the 1D diffusion with drift and 1D random walk 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 three PN which are A39, the Ring nebula and the etched hourglass nebula MyCn 18, the hybrid object Eta-Carinae, and to two SNR which are SN 1993J and SN 1006. In all the considered cases a careful comparison between the observed and theoretical profiles in intensity is done.

astro-ph.GA↗
arXiv2012

Evolution of superbubbles in a self-gravitating disk

The expansion of a superbubble is investigated both analytically and numerically. Our model implements the thin layer approximation in a vertical profile of density as given by an isothermal self-gravitating disk. A precise comparison with the results of numerical hydro-dynamics is given. Analogies are drawn with the Kompaneets equation that includes the quadratic hyperbolic-secant law in the list of the plane-parallel stratified media. An astrophysical application is made to the superbubble connected with the two worms 46.4+5.5 and 39.7+5.7. The effects of the rotation of the galaxy on the simulated radius and on the velocity are introduced. The worms with their strong limb-brightening visible on astronomical maps are explained in the framework of image theory.

astro-ph.GA↗
arXiv2012

On the statistics of area size in two-dimensional thick Voronoi Diagrams

Cells of Voronoi diagrams in two dimensions are usually considered as having edges of zero width. However, this is not the case in several experimental situations in which the thickness of the edges of the cells is relatively large. In this paper, the concept of a thick Voronoi tessellation, that is with edges of non-zero width, is introduced and the the statistics of cell areas, as thickness changes, are analyzed.

cond-mat.stat-mech↗
arXiv2012

Direct conversion of the flux of kinetic energy into radiation in gamma-ray burst

The time evolution of a Gamma-ray burst (GRB) is associated with the evolution of a supernova remnant (SNR). The time evolution of the flux of a GRB is modeled introducing a law for the density of the medium in the advancing layer. The adopted radiative model for the GRB in the various e.m. frequencies is synchrotron emission. The X-ray ring which appears a few hours after a GRB is simulated.

astro-ph.HE↗
arXiv2012

Analytical and Monte Carlo results for the surface-brightness diameter relationship in supernova remnants

The surface brightness diameter relationship for supernovae remnants (SNRs) is explained by adopting a model of direct conversion of the flux of kinetic energy into synchrotron luminosity. Two laws of motion are adopted, a power law model for the radius-time relationship, and a model which uses the thin layer approximation. The fluctuations on the log-log surface diameter relationship are modeled by a Monte Carlo simulation. In this model a new probability density function for the density as function of the galactic height is introduced.

astro-ph.GA↗