135 citations · 984 across the 46 of their papers we have counts for
21 papers · 1 filter
Dynamics of Nearby Groups of Galaxies: the role of the cosmological constant
Sébastien Peirani, José Antonio De Freitas Pacheco
(context) Different cosmological data are consistent with an accelerated expansion produced by an exotic matter-energy component, dubbed "dark-energy''. A cosmological constant is…
Evolution of the Phase-Space Density of Dark Matter Halos and Mixing Effects in Merger Events
Sébastien Peirani, Fabrice Durier, José Antonio De Freitas Pacheco
Cosmological N-body simulations were performed to study the evolution of the phase-space density Q = rho/sigma^3 of dark matter halos. No significant differences in the scale relat…
Mass Determination of Groups of Galaxies: Effects of the Cosmological Constant
Sébastien Peirani, José Antonio De Freitas Pacheco
The spherical infall model first developed by Lemaître and Tolman was modified in order to include the effects of a dark energy term. The resulting velocity-distance relation was e…
New insights on the complex planetary nebula Hen 2-113
Eric Lagadec, Olivier Chesneau, Mikako Matsuura +5
We report infrared observations of the planetary nebula Hen 2-113 obtained with VLT/NACO, VLTI/MIDI, VLT/ISAAC and TIMMI at the ESO 3.6m. Hen 2-113 exhibits a clear ring-like struc…
Indirect Search for Dark Matter
José Antonio De Freitas Pacheco, Sébastien Peirani
Possible dark matter candidates are reviewed as well as indirect search methods based on annihilation or decay channels of these particles. Neutralino is presently the best particl…
A Search for Very Active Stars in the Galaxy
G. Tsarevsky, J. A. De Freitas Pacheco, N. Kardashev +7
We report the first results of a systematic search near the plane of the Galaxy for the so called very active stars (VAS), which are characterized by a hard X-ray spectrum and acti…
Einstein's gravitational lensing and nonlinear electrodynamics
Herman J. Mosquera Cuesta, Jose' A. de Freitas Pacheco, Jose' M. Salim
In 1936 Einstein predicted the phenomenon presently known as gravitational lensing (GL). A prime feature of GL is the magnification, because of the gravitational field, of the star…
Phase Transitions in Neutron Stars and Gravitational Wave Emission
G. F. Marranghello, C. A. Z. Vasconcellos, J. A. de Freitas Pacheco
We review the detectability of gravitational waves generated by oscillations excited during a phase transition from hadronic matter to deconfined quark-gluon matter in the core of…
New UBVRI colour distributions in E-type galaxies I.The data
T. P. Idiart, R. Michard, J. A. de Freitas Pacheco
New colour distributions have been derived from wide field UBVRI frames for 36 northern bright elliptical galaxies and a few lenticulars. The classical linear representations of co…
Limits on the early afterglow phase of gamma-ray burst sources from TAROT-1
M Boer, J-L Atteia, M Bringer +5
The Télescope à Action Rapide pour les Objets Transitoires (TAROT-1) has as prime objective the observation of the prompt and delayed emission of cosmic gamma-ray bursts (GRBs). We…
A nuclear many-body theory at finite temperature applied to protoneutron star
Guilherme F. Marranghello, Cesar A. Z. Vasconcellos, Manfred Dillig
Thermodynamical properties of nuclear matter are studied in the framework of an effective many-body field theory at finite temperature, considering the Sommerfeld approximation. We…
Cosmic Background of Gravitational Waves from Rotating Neutron Stars
T. Regimbau, J. A. de Freitas Pacheco
The extragalactic background of gravitational waves produced by tri-axial rotating neutron stars was calculated, under the assumption that the properties of the underlying pulsar p…
Population Synthesis of Pulsars: Magnetic Field Effects
T. Regimbau, J. A. de Freitas Pacheco
New results based on methods of population synthesis, concerning magnetic field effects on the evolution of pulsars are reported. The present study confirms that models with timesc…
VLT Observations of Turnoff stars in the Globular Cluster NGC 6397
F. Thévenin, C. Charbonnel, J. A. de Freitas Pacheco +4
VLT-UVES high resolution spectra of seven turnoff stars in the metal-poor globular cluster NGC 6397 have been obtained. Atmospheric parameters and abundances of several elements (L…
H-dibaryons and Primordial Nucleosynthesis
J. A. de Freitas Pacheco, S. Stoica, F. Thevenin +1
The apparent discrepancy between abundances of light nuclides predicted by the standard Big-Bang and observational data is explained, by assuming the presence of metastable H dibar…
TAROT: A status report
Michel Boër, J. L. Atteia, M. Bringer +11
TAROT-1 is an automatic, autonomous ground based observatory whose primary goal is the rapid detection of the optical counterparts of cosmic gamma-ray burst sources. It will be abl…
Gravitational Wave Emission from Galactic Radio Pulsars
J. A. de Freitas Pacheco, J. E. Horvath
We consider in this work continuous gravitational wave (GW) emission from non-axisymmetric radio pulsars. We treat in some detail the observational issues related to the known radi…
Equilibrium configurations for quark-diquark stars and the problem of Her X-1 mass
J. E. Horvath, J. A. de Freitas Pacheco
We report new calculations of the physical properties of a quark-diquark plasma. A vacuum contribution is taken into account and is responsible for the appearance of a stable state…
The role of thermal instabilities on the theoretical mass function of MACHOs
E. M. de Gouveia Dal Pino, J. E. Horvath, J. A. de Freitas Pacheco
We analyze the primordial protogalactic gas to investigate the role of thermal instabilities in the formation of condensations that could contribute to the MACHO mass function. We…
The Helium-Core Mass at the Helium Flash in Low-Mass Red Giant Stars: Observations and Theory
M. Catelan, J. A. de Freitas Pacheco, J. E. Horvath
The method developed by Raffelt (1990a,b,c) to estimate a possible increase in the standard values of the helium-core mass at the tip of the red giant branch, $\Mc$, from propertie…
Gravitational Waves from Wobbling Pulsars
J. C. N. de Araújo, J. A. de Freitas Pacheco, J. E. Horvath +1
The prospects for detection of gravitational waves from precessing pulsars have been considered by constructing fully relativistic rotating neutron star models and evaluating the e…