In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants. In the following study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. Determination of atmospheric parameters is based on analyses of silicon ionisation balance.

Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral standards in our Galaxy.

We compare our results with the abundances expected from studies of H II regions.

We have started a project to observe and analyze Wolf-Rayet stars in the galaxies of the Local Group. The first observing run was marred with disastrous weather and therefore, we do not yet have any results to report. Instead, we briefly summarize the motivation of our project.

Results of follow-up multi-object spectroscopy of 173 blue stars with Hα emission in the galaxy M33, carried out on the 6-m telescope, are presented. The stars have been originally selected as candidates for LBV and SS 433-type stars. The spectra have been obtained in the region of Hα. All the objects have fallen into two groups – stars with probable intrinsic Hα emission and stars where this emission may belong to H II regions. A number of criteria have been used at the selection, the principal one being the width of Hα emission. 57 stars in whose spectra the Hα line was broad have been selected. Spectra of the most interesting stars are presented. On the basis of luminosity and spectral type, stars were selected which may be considered as hypergiants or LBV candidates (3 of them – N41, N512, N517 are the most reliable). Two stars (v532, N35) have spectra similar to MCA1-B (Ofpe/WN9). The object I 322 is discussed as a candidate for an SS 433-type star.

We present observations of the new Local Group galaxy candidates Cassiopeia dSph, Pegasus dSph = And VI and Camelopadalis A. Our deep color-magnitude diagrams show that the first two galaxies are certainly Local Group members, and likely dSph galaxies at a distance similar to that of the Andromeda galaxy. Cam A seems to be a star-forming galaxy situated considerably further away.

Local Group galaxies allow us to test some properties of massive star evolution which are inaccessible in our Galaxy, in particular the effects of different metallicities. Thus, after showing that we still do not know the exact process by which massive stars are formed, we examine the differences in the distributions of O-stars, blue and red supergiants and WR stars in the Local Group. The number ratios WR/O and WN/WC are well accounted for by stellar models in which the mass-loss rates depend on the metallicity, Z, as predicted by stellar wind theories. The number ratio of red supergiants to WR stars is growing for decreasing Z. Although this behaviour is qualitatively well explained, the models need some extra mixing to fit the observational data. The same is true for the explanation of the He- and N-excesses in O, B and A supergiants. Rotation and related mixing processes certainly play a major role in massive star evolution. The relative number of Be-stars is higher at lower Z, which suggests that rotation is faster, also with more mixing, in small, irregular low-metallicity galaxies.

Dwarf galaxies may play a key role in the formation and evolution of bigger systems. This makes knowing how they form and evolve and, in particular, how their star formation histories (SFHs) have proceeded since their birth, a topic of major interest. For nearby galaxies, the color-magnitude diagram (CMD) contains stars formed over all their lifetime. It is hence a fossil record of their SFHs. The analysis with synthetic CMDs provides a powerful tool to retrieve them.

In this paper, I discuss the critical issues related to the computation of synthetic CMDs, present a short summary of the currently available results for the SFH extending the full life of galaxies and make a few critical considerations about the powerfulness and draw-backs of the method.

For a sample of 16 Sb galaxies, disc scale lengths rD in B and I are investigated in order to study the dust content. The ratios rD(B)/rD(I) increase from 1.0 for face-on galaxies to 1.5 for edge-on galaxies. Scale length ratios derived from model images increase from face-on to edge-on view by ≤ 10% only, regardless of whether the model galaxies are optically thin or optically thick.

The study of gradients in the stellar populations of dwarf galaxies will give us necessary information to construct detailed models of their formation and evolution. We find clear traces of these gradients, in the sense of stars being older for larger galactocentric distances, in two interesting nearby dwarfs: Phoenix and Leo I.

We present SCUBA imaging observations of the nearby prototype starburst galaxy M82, in order to study large-scale outflows observed in such galaxies and associated with starburst phenomena. We use (1) deep 450 μm continuum maps to investigate the structure and details of the large-scale outflows and (2) 850 μm linear-polarization maps to investigate the relation between nuclei and halo magnetic fields.

The X-ray emission from M32 has been studied with ROSAT PSPC and HRI observations. A new analysis of the best available exposure with M32 in the central part of a PSPC frame improves on a previously published analysis and indicates only one source associated with M32. Our analysis of the dedicated HRI exposure of M32 also leads to different conclusions than published recently. At HRI resolution M32 appears as an extended source, probably a little offset from the optical nucleus. Possible interpretations are discussed, which are relevant to the question whether a low-level active nucleus may be present or not.

We use detailed modeling of stellar populations of nearby galaxies to calculate population parameters. Our sample of galaxies includes most galaxies of the Local Group and several more distant giant galaxies. Available data are sufficient to decompose galaxies into the nucleus, the metal rich core, the bulge, the halo, the young and old disks, and the dark halo. We compare mass-to-luminosity ratios and colors of bulges, disks and halos with results of models of galactic chemical evolution. The luminosity-weighted mean of the mass-to-luminosity ratio of visible stellar population is M/LB = 4 ± 1.4 in solar units. This ratio is surprisingly constant for galaxies of very different absolute magnitude.

Evolved AGB stars pass through a phase of heavy mass loss during which they become optically obscured. We describe an observational program to find and study such stars in the Magellanic Clouds. Many of the obscured stars are found to be luminous carbon stars, a population previously missing. We discuss the Mira PL relation, valid before the onset of the heaviest mass loss. We find that a number of semi-regulars fit this relation, based on Hipparcos parallaxes. No evidence is seen for a Z-dependence, giving a powerful potential distance indicator. We derive a distance modulus to the LMC of m − M = 18.63 ± 0.09 as well as a bright calibration for the Horizontal Branch in globular clusters.

Using Lester's version of the Kurucz codes, we have computed a set of models with and without “approximate overshooting”. Based on the new models, we have synthesized the spectra in the wavelength range 4800–5400 Å in order to investigate the role of overshooting and no-overshooting models on the Lick indices. Preliminary results show that the differences between the indices are significant in the case of Hβ and Mgb. We need to investigate further the importance of this convection parameter, by comparing model spectra with observed spectra.

We have built a new grid of synthetic spectra in the wavelength range λλ 4600-5600 Å for [α-elements/Fe] = 0.0, +0.2, +0.4 and +0.6. The Lick indices Mg2, Mgb, Fe5270 and Fe5335 are measured in all grid spectra, and their behaviour with stellar parameters is studied.

For the calculation of this new grid, the set of atomic and molecular constants was revised and model atmospheres with overshooting and mixing length parameters appropriate to reproduce the wings of the Hβ line (suitable to indicate temperatures) were computed. We also present a grid in the wavelength range λλ 6000 – 10200 Å. A computation of a high-resolution grid of spectra in the range λλ 3800–7000 Å, as well as a full grid in the range λλ 3000–10200 Å, to be further used in conjunction with evolutionary population synthesis models, are also underway.

Artificial neural networks have been applied to a catalog of spectral indices based on low-resolution spectra in the wavelength regions 3820–4500 Å and 4780–5450 Å. We classify the spectral indices using supervised neural networks. This project is in continuation of the previous efforts by one of us, applying new tools to determine basic properties of stars. We envisage the use of such methods for stellar contents studies of local stellar systems for which spectroscopic surveys are underway.

Using long slit spectroscopy, we investigate the stellar population and reddening gradients inside the central regions of the nearby spiral galaxy M81. Observational data are analyzed using a new mathematical method. The basic elements to construct the synthetic spectra are taken from a database of star spectra. We show the ability of this method to define detailed stellar populations and to differentiate between age and metallicity effects.

The initial chemical composition of stars is, besides the mass, another key factor in stellar evolution. Through stellar lifetimes and impact on radiation output and nucleosynthesis of stars it is controlling both the pace of evolution of galactic matter/light and changes in their integrated observables and spectra.

This talk reviews the internal dynamics of some of the different classes of Local Group galaxies. These include the dwarf spheroidal galaxies, the pure disk galaxy M33, the LMC and M31. The talk concludes with some general remarks about bulges and halos.

We report the discovery of hot horizontal branch stars in the nuclear bulge of the Milky Way. Spectra from the 2dF instrument of the Anglo-Australian Telescope allow us to confirm their membership in the bulge through radial velocities. We also review the current observational information on hot horizontal branch stars in Milky Way clusters and the Local Group, and discuss the relevance of star-by-star studies in the bulge for the ultraviolet-excess phenomenon seen in large ellipticals.

We investigate the dark matter (DM) content in the Local Group dwarf spheroidal galaxies (dSphs) by examining the correlations among their physical quantities. Two origins of the large velocity dispersions of the dSphs are possible: [1] the existence of DM and [2] tidal heating by the Galaxy. The correlation tests support both [1] and [2]. We finally mention circumstantial evidence for the existence of DM in the dSphs.