Anderson Caproni - NAT-Universidade Cruzeiro do Sul

Anderson Caproni
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Name
Anderson Caproni
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NAT-Universidade Cruzeiro do Sul
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Astrophysics (7)
 
Astrophysics of Galaxies (5)
 
High Energy Astrophysical Phenomena (4)
 
Cosmology and Nongalactic Astrophysics (3)
 
General Relativity and Quantum Cosmology (1)
 
Solar and Stellar Astrophysics (1)
 
Instrumentation and Methods for Astrophysics (1)

Publications Authored By Anderson Caproni

2017Mar
Affiliations: 1NAT-Universidade Cruzeiro do Sul, 2NAT-Universidade Cruzeiro do Sul, 3NAT-Universidade Cruzeiro do Sul, 4NAT-Universidade Cruzeiro do Sul, 5EACH-Universidade de São Paulo

We present results from a non-cosmological, three-dimensional hydrodynamical simulation of the gas in the dwarf spheroidal galaxy Ursa Minor. Assuming an initial baryonic-to-dark-matter ratio derived from the cosmic microwave background radiation, we evolved the galactic gas distribution over 3 Gyr, taking into account the effects of the types Ia and II supernovae. For the first time, we used in our simulation the instantaneous supernovae rates derived from a chemical evolution model applied to spectroscopic observational data of Ursa Minor. Read More

2015Apr
Affiliations: 1NAT-Universidade Cruzeiro do Sul, 2NAT-Universidade Cruzeiro do Sul, 3CDCC-Universidade de São Paulo, 4EACH-Universidade de São Paulo

As is usual in dwarf spheroidal galaxies, today the Local Group galaxy Ursa Minor is depleted of its gas content. How this galaxy lost its gas is still a matter of debate. To study the history of gas loss in Ursa Minor, we conducted the first three-dimensional hydrodynamical simulations of this object, assuming that the gas loss was driven by galactic winds powered only by type II supernovae (SNe II). Read More

Atomic line opacities play a crucial role in stellar astrophysics. They strongly modify the radiative transfer in stars, therefore impacting their physical structure. Ultimately, most of our knowledge of stellar population systems (stars, clusters, galaxies, etc. Read More

2014Apr
Affiliations: 1NAT-Universidade Cruzeiro do Sul, 2NAT-Universidade Cruzeiro do Sul, 3IAG/USP, 4UNIFEI, 5Institut d'Astrophysique de Paris

We present 23 interferometric images of parsec-scale jet of the quasar PKS 1741--03 at 15, 24 and 43 GHz spanning about 13 yr. We model the images as a superposition of discrete two--dimensional elliptical Gaussian components, with parameters determined by the cross--entropy technique. All the images present a spatially unresolved component (core) and usually two or three components receding from it. Read More

Theoretical $\Lambda$CDM cosmological models predict a much larger number of low mass dark matter haloes than has been observed in the Local Group of galaxies. One possible explanation is the increased difficulty of detecting these haloes if most of the visible matter is lost at early evolutionary phases through galactic winds. In this work we study the current models of triggering galactic winds in dwarf spheroidal galaxies (dSph) from supernovae, and study, based on 3D hydrodynamic numerical simulations, the correlation of the mass loss rates and important physical parameters as the dark matter halo mass and its radial profile, and the star formation rate. Read More

BL Lacertae is the prototype of the BL Lac class of active galactic nuclei, exhibiting intensive activity on parsec (pc) scales, such as intense core variability and multiple ejections of jet components. In particular, in previous works the existence of precession motions in the pc-scale jet of BL Lacertae has been suggested. In this work we revisit this issue, investigating temporal changes of the observed right ascension and declination offsets of the jet knots in terms of our relativistic jet-precession model. Read More

We present a new technique for obtaining model fittings to VLBI images of astrophysical jets. The method minimizes a performance function proportional to the sum of the squared difference between the model and observed images. The model image is constructed by summing elliptical Gaussian sources characterized by six parameters: two-dimensional peak position, peak intensity, eccentricity, amplitude and orientation angle of the major axis. Read More

2007May
Affiliations: 1Nucleo de Astrofisica Teorica-UNICSUL, IAG/USP, STScI, 2IAG/USP, 3STScI, 4ICRA-BR/CBPF
Category: Astrophysics

Strong evidence for the presence of a warped Keplerian accretion disc in NGC4258 (M 106) has been inferred from the kinematics of water masers detected at sub-parsec scales. Assuming a power-law accretion disc and using constraints on the disc parameters derived from observational data, we have analyzed the relativistic Bardeen-Petterson effect driven by a Kerr black hole as the potential physical mechanism responsible for the disc warping. We found that the Bardeen-Petterson radius is comparable to or smaller than the inner radius of the maser disc (independent of the allowed value for the black hole spin parameter). Read More

2006Aug

The Bardeen-Petterson general relativistic effect has been suggested as the mechanism responsible for precession in some accretion disk systems. Here we examine separately four mechanisms (tidally-induced, irradiation-induced, magnetically-induced and Bardeen-Petterson-induced) that can lead to warping and precession. We use a sample of eight X-ray binaries and four Active Galactic Nuclei (AGNs) that present signatures of warping and/or precession in their accretion disks to explore the viability of the different mechanisms. Read More

VLBA high spatial resolution observations of the disk structure of the active galactic nucleus NGC 1068 has recently revealed that the kinematics and geometry of this AGN is well characterized by an outer disk of H2O maser emission having a compact milliarcsecond (parsec) scale structure, which is encircling a thin rotating inner disk surrounding a ~10^7 M$_\sun$ compact mass, likely a black hole. A curious feature in this source is the occurrence of a misalignment between the inner and outer parts of the disk, with the galaxy's radio jet being orthogonal to the inner disk. We interpret this peculiar configuration as due to the Bardeen-Petterson effect, a general relativistic effect that warps an initially inclined (to the black hole equator) viscous disk, and drives the angular momentum vector of its inner part into alignment with the rotating black hole spin. Read More

We show that it is possible to explain the physical origin of jet precession in active galactic nuclei (AGNs) through the misalignment between the rotation axes of the accretion disk and of the Kerr black hole. We apply this scenario to quasars, Seyfert galaxies and also to the Galactic Center black hole Sgr A*, for which signatures of either jet or disk precession have been found. The formalism adopted is parameterized by the ratio of the precession period to the black hole mass and can be used to put constraints to the physical properties of the accretion disk as well as to the black hole spin in those systems. Read More

Optical variability of 3C 120 is discussed in the framework of jet precession. Specifically, we assume that the observed long-term periodic variability is produced by the emission from an underlying jet with a time-dependent boosting factor driven by precession. The differences in the apparent velocities of the different superluminal components in the milliarcsecond jet can also be explained by the precession model as being related to changes in the viewing angle. Read More

2003Nov
Affiliations: 1IAG/USP, 2IAG/USP
Category: Astrophysics

VLBI observations have shown that the parsec-jet of 3C 345 is formed by several components, ejected from the core with superluminal velocities and travelling along bent trajectories on the plane of the sky. We interpret the differences in velocity and position angle among the different features at formation time as the result of parsec-scale precession of the relativistic jet and calculate the aperture angle of the precession cone, the angle between the cone axis and the line of sight and the Lorentz factor associated with the jet bulk motion. We assumed a precession period of 10. Read More

2000Aug
Affiliations: 1IAG/USP, 2IAG/USP, 3CRAAE/INPE/MCT
Category: Astrophysics

The region centered in the NGC 6334 I(N) radio continuum source was surveyed in an extension of 6 arcmin in right ascension and 12 arcmin in declination, in the NH3(J,K) = (1,1) transition, using the Itapetinga radio telescope. The spectra show non-LTE behavior, and gradients of velocity and line-width were detected along the region. A detailed analysis of the spectra showed that the surveyed region is composed of at least three overlapped sources related to regions that are in different stages of star formation: NGC 6334 I, associated with an already known molecular bipolar outflow, NGC 6334 I(N)w, the brightest ammonia source, coincidental with the continuum source NGC 6334 I(N), and NGC 6334 I(N)e, weaker, more extended and probably less evolved than the others. Read More