The cluster of galaxies Abell 376

We present a dynamical analysis of the galaxy cluster Abell 376 based on a set of 73 velocities, most of them measured at Pic du Midi and Haute-Provence observatories and completed with data from the literature. Data on individual galaxies are presented and the accuracy of the determined velocities is discussed as well as some properties of the cluster. We obtained an improved mean redshift value z=0.0478^{+0.005}_{-0.006} and velocity dispersion sigma=852^{+120}_{-76}km/s. Our analysis indicates that inside a radius of 900h_{70}^{-1}kpc (15 arcmin) the cluster is well relaxed without any remarkable feature and the X-ray emission traces fairly well the galaxy distribution. A possible substructure is seen at 20 arcmin from the centre towards the Southwest direction, but is not confirmed by the velocity field. This SW clump is, however, kinematically bound to the main structure of Abell 376. A dense condensation of galaxies is detected at 46 arcmin (projected distance 2.6h_{70}^{-1}Mpc) from the centre towards the Northwest and analysis of the apparent luminosity distribution of its galaxies suggests that this clump is part of the large scale structure of Abell 376. X-ray spectroscopic analysis of ASCA data resulted in a temperature kT = 4.3+/-0.4 keV and metal abundance Z = 0.32+/-0.08 Z_solar. The velocity dispersion corresponding to this temperature using the T_X-sigma scaling relation is in agreement with the measured galaxies velocities.Comment: 11 pages, 10 figures, accepted for publication in A&

Exact solutions for the spatial de Vaucouleurs and Sersic laws and related quantities

Using the Mathematica package, we find exact analytical expressions for the so-called de-projected De Vaucouleurs and Sersic laws as well as for related spatial (3D) quantities, such the mass, gravitational potential, the total energy and the central velocity dispersion, generally involved in astronomical calculations expressed in terms of the Meijer G functions.Comment: 11 pages, accepted in A

Gravo-thermal properties and formation of elliptical galaxies

We have analyzed a sample of galaxies belonging to three clusters: Coma, Abell 85, and Abell 496 (real galaxies) and a sample of simulated elliptical galaxies formed in a hierarchical merging scheme (virtual galaxies). We use the Sersic law to describe their light profile. The specific entropy (Boltzmann-Gibbs definition) is then calculated supposing that the galaxies behave as spherical, isotropic, one-component systems. We find that, to a good approximation (about 10%), both real and virtual galaxies have an almost unique specific entropy. Within this approximation the galaxies are distributed in a thin plane in the space defined by the three Sersic law parameters, which we call the Entropic Plane. A further analysis shows that both real and virtual galaxies are in fact located on a thin line, therefore indicating the existence of another - and yet unknown - physical property, besides the uniqueness of the specific entropy. A more careful examination of the virtual galaxies sample indicates a very small increase of their specific entropy with merging generation. In a hierarchical scenario, this implies a correlation between the specific entropy and the total mass, which is indeed seen in our data. The scatter and tilt of the Entropic Line, defined by Lima Neto et al. (1999a), are reduced when this correlation is taken into account. Although one cannot distinguish between various generations for real galaxies, the distribution of their specific entropy is similar to that in the virtual sample, suggesting that hierarchical merging processes could be an important mechanism in the building of elliptical galaxies

Mass-Luminosity Relation for White-Dwarf Stars

Recebido em 19 de Fevereiro de 1971 Improving the model of Milne in which the white-dwarf star is considered as consisting of an envelope of perfect gas and an interna1 part of degenerate electron gas, we investigated the relation between its mass and luminosity. In conclusion, we found thai, though the masses are the same, the luminosity of the white dwarfs which contain light elements in their interior is greater than that of those which contain heavier elements. Aperfeiçoando o modèlo de Milne em que a estrela anã branca é considerada como sendo constituida de um envelope de gás perfeito e de uma parte interna de gás de elétrons degenerado, investigamos a relação entre a sua massa e luminosidade. Como conclusão, achamos que, mesmo quando as massas sejam iguais, a luminosidade das anãs brancas que contenham elementos leves no seu interior é maior que a daquelas que contenham elementos pesados

Dissipationless Collapse of Spherical Protogalaxies and the Fundamental Plane

Following on from the numerical work of Capelato, de Carvalho & Carlberg (1995, 1997), where dissipationless merger simulations were shown to reproduce the "Fundamental Plane" (FP) of elliptical galaxies, we investigate whether the end products of pure, spherically symmetric, one-component dissipationless {\it collapses} could also reproduce the FP. Past numerical work on collisionless collapses have addressed important issues on the dynamical/structural characteristics of collapsed equilibrium systems. However, the study of collisionless collapse in the context of the nature of the FP has not been satisfactorily addressed yet. Our aim in this paper is to focus our attention on the resulting collapse of simple one-component spherical models with a range of different initial virial coefficients. We find that the characteristic correlations of the models are compatible with virialized, centrally homologous systems. Our results strengthen the idea that merging may be a fundamental ingredient in forming non-homologous objects.Comment: 9 pages, 4 Postscript figures, Astronomy & Astrophysics in press (2002). Abstract placement correcte