Dynamical studies of cluster pairs in the Magellanic Clouds

We performed N -body simulations of star cluster encounters with Hernquist's TREECODE in a CRAY YMP-2E computer under different initial conditions (relative positions and velocities, cluster sizes, masses and concentration degrees). The total number of particles per simulation ranged from 1024 to 20480. These models are compared with a series of isodensity maps of cluster pairs in the Magellanic Clouds. Evidence is found that during the interactions, transient morphological effects such as an expanded halo, isophotal deformation and isophotal twisting can occur as a result of tidal effects and dynamical friction. The simulations also show that different outcomes are possible depending on the initial parameters: (i) long-standing changes of concentration degree can occur after the collision; (ii) one member can disaggregate; or (iii) the pair can coalesce into a single cluster with a distinct structure compared with the original ones. These simulations can reproduce a wide range of morphological structures in observed cluster pairs.     

A comparative study of the stellar content in normal and active nuclei of spiral galaxies

We present spectrophotometry andUBV photometry of the central region of spiral galaxies. The sample consists of the Seyfert galaxies NGC 1566, 3783 and IC 4329A; NGC 1097, 2997, and 5236 containing peculiar nucleus and NGC 5530, 5643, and 6699 with normal nucleus.The stellar composition of the nuclei was derived by treating the equivalent widths of a sample of absorption lines with the method of constrained nonlinear optimization. The observed continua and theUBV colours were compared with the theoretical results in order to obtain the internal reddening and the contribution of the hot gas or non-thermal radiation. The age of the last cycle of star formation, the internal absorption and the theoretical relations M/L and H/K Caii present differences among the three types of nuclei.     

The response of the Sao Paulo Continental Shelf, Brazil, to synoptic winds

The response of the Sao Paulo Continental Shelf (SPCS) to synoptic wind forcing has been analyzed. Two different methods are used for this purpose, one based on hydrographic data, bottom topography, and geographical characteristics, and a second on analyzing currentmeter data directly and using empirical orthogonal functions. Both methods show similar results for an essentially barotropic shelf. The SPCS response in the subinertial frequency band appears to be trapped on the continental shelf. Numerical experiments have also been carried out showing results that qualitatively agree with the observations, including the velocity component parallel to the coastline. Supported by CAPES.     

The equivalent width of the Hβ emission line and the evolution of the Hii regions

The synthetic equivalent width (W _H) of the line H in emission is obtained for Hii regions opaque to the Lyman photon flux, with embedded OB associations with different initial chemical compositions and initial mass functions. The variation ofW _H as a function of the evolution of the ionizing stars is analysed. The observations ofW _H for M33, M101, and M51 by Searle (1971) are discussed.     

A minimization procedure applied to population synthesis in galaxy nuclei using a star cluster library: M31, M32

We apply the MINOS optimization system to the population synthesis of galactic nuclei, using a grid of star cluster equivalent widths as a function of age and metallicity. For some classes of red galaxy nuclei, this observational approach to population synthesis produces results similar to those predicted by the theoretical approach of Arimoto and Yoshii (1987). The synthesis results for blue nuclei tend to scatter more in the age vs metallicity plane, probably because we use only visible and near-infrared spectral data. Additional information at shorter wavelengths will possibly produce better-focused solutions in the plane. However, strong bursts of star formation can easily be identified. We provide in this contribution population synthesis for the central regions of M31 and M32. The bulge and the semi-stellar nucleus of M31 are dominated by the old metal-rich population: the semi-stellar nucleus has reached up [Z/Z ]0.6 and the bulge [Z/Z ]0.3. In the central region of M32, a metallicity up to the solar value has been reached and the synthesis indicates that the intermediate age component is not dominant.     

3D NIR spectroscopy at subarcsecond resolution

We present a scientific case approached through high quality 3D NIR spectroscopy performed with CIRPASS, attached to the Gemini South telescope. A binary mass concentration at the nucleus of the galaxy M 83 was suggested by Thatte et al. [A&A 364 (2000) L47] and Mast et al. [BAAA 45 (2002) 98. Astroph#0505264] determined the possible position of the hidden secondary mass concentration with 2D H-alpha kinematics. The preliminary results of the NIR study presented here are based in almost 1500 spectra centered in the wavelength 1.3 μm, with a spectral resolving power of 3200. They allow us to unveil, with 0.36″ (6.4 pc) sampling and subarcsecond resolution, the velocity field in a region of 13″ × 9″ around the optical nucleus. We confirm that the optical nucleus is not located at the most important center of symmetry of the ionized gas velocity field. The largest black hole that could fit to the circular motion in this kinematic center should have a mass not larger than 3 × 10⁶(sin i)⁻¹ M solar masses.     

Burst of star formation in detached extragalactic Hii regions: A qualitative analysis

A calibration previously determined for the evolution of the equivalent width of the emission line H with age for Hii regions (Dottori, 1981) is applied to detached extragalactic Hii regions. The frequency distribution of ages seems to indicate that some of these regions had other bursts of star formation so important as the observed last one.     

Lyman continuum photons emission from hot stars

The number of Lyman continuum photons emitted from stars with temperatures between 15 000K and 50 000K for several values of the surface gravity are calculated on the basis of Kurucz's new models of stellar atmospheres. Results are compared with previous data.     

DifferentialUBV photometry in the central regions of spiral galaxies

The differential color indices in the central bulk of spiral SA, SAB and SB galaxies were analyzed. A comparison of the data derived for the three families do not show any systematical difference among them, within the most probable error of the sample.