We have generated far-UV stellar libraries using spectra of hot stars in the Galaxy and the Large and Small Magellanic Clouds. These libraries were implemented into the stellar population synthesis codes starburst99 and lavalsb and used to compute synthetic spectra of star-forming galaxies. Model spectra for galaxies are presented and variations of the hot star photospheric and wind profiles are discussed. This poster summarizes the work of Robert et al. (2002).

We are undertaking various studies of primordial galaxies with the following main aims:

1. (i) synthesize the properties of rest-frame UV-optical spectra of Population III galaxies and ‘transition objects’ between Pop III and normal starbursts;

2. (ii) devise optimal search strategies for the detection of Pop III and related objects with ground-based and space observations;

3. (iii) simulate photometric and spectroscopic observations of Pop III galaxies to quantify the feasibility of such studies especially for future ground-based instruments; and

4. (iv) study the physics of Pop III and ‘transition’ galaxies and their implications on cosmology and the physics of galaxies

We consider the Orion Nebula (M 42) within a project aimed at studying the interaction between massive stars and their surrounding ISM. This is an H ii region ionized by θ1 Ori C, one of the four massive stars in the Trapezium Cluster. θ1 Ori C has the earliest spectral type (O7Vp) among them, emitting an ionizing flux several orders of magnitude larger than those of the other stars. We present a spectral analysis of the Trapezium Cluster stars to determine their stellar parameters. We use spectra between 4250 – 4750 Å and compare them with synthetic spectra obtained by means of an updated version of fastwind that includes an approximated treatment of metal-line blanketing.

We present an analysis of the Chandra observations of two dwarf starburst, Wolf-Rayet galaxies (NGC 4449 and NGC 5253). We have identified at least three different classes of objects within the X-ray point source populations, and we have found the diffuse emission, resulting from the stellar winds and supernova explosions of massive stars, to have a complex morphology and to consist of several components. Comparison with the Hα emission suggests the presence of ~ kpc-scale wind-blown bubbles and ruptured superbubbles.

Series of CCD long-slit spectra have been obtained in the 3600-10000 Å range, with the ESO 1.5m telescope, for the six brightest compact H ii regions in the LMC and SMC: N 11A, N 160 A1-A2 and N 88A, N 81 and N 26A-B, respectively. For each region the spectral type of its complex exciting source is given. From the emission-line intensities we have derived the gas electron density and temperature, and computed the chemical abundances of He, O, N, Ne, S, and Ar, which we compare with the ones found for other H ii regions in the Magellanic Clouds.

We report preliminary results from high-resolution UV spectroscopy of the super star cluster 1 in the nearby dwarf starburst galaxy NGC 1705, using HST-stis. These new observations can help us to quantify accurately the stellar content in this super cluster. Together with high quality spectra from SMC stars and the evolutionary synthesis code starburst99, we estimate an age for this cluster of 12±3 Myr, in agreement with previous studies. The measured dynamical mass and the theoretical L/M ratio suggest a normal IMF down to the hydrogen-burning limit.

The most massive evolved stars (above 50 M⊙) undergo a phase of extreme mass loss, in which their evolution is reversed from a redward to a blueward motion in the H-R diagram. In this phase, the stars are known as Luminous Blue Variables and they are located in the H-R diagram close to the Humphreys-Davidson limit. It is far from understood what causes the strong mass loss or what triggers the so-called giant eruptions, active events in which in a short time a large amount of mass is ejected. Here I present results from a larger project, devoted to better understand LBVs through studying the LBV nebulae. These nebulae are formed as a consequence of the strong mass loss. The analysis concentrates on the morphology and kinematics of these nebulae. Of special concern is the frequently observed bipolar nature of the LBV nebulae. Bipolarity seems to be a general feature and strongly constrains models of the LBV phase, especially of the formation of the nebulae. In addition, we find outflows from LBV nebulae, the first evidence for ongoing instabilities in the nebulae.

η Car is a very luminous and unstable evolved star. Outflowing material ejected during the star's giant eruption in 1843 surrounds it as a nebula, which consists of an inner bipolar region, coined the Homunculus, and the Outer Ejecta. The outer ejecta is very filamentary and shaped irregularly. Kinematic analysis, however, shows a regular bi-directional expansion, despite of the complex morphology. Radial velocities in the outer ejecta reach 2000 km s–1 and give rise to X-ray emission, as first detected by ROSAT. We will present a detailed study of the outer ejecta based on HST images, high-resolution echelle spectra for kinematic studies, images from Chandra-acis and HST-stis spectra.

I have put together a necessarily limited summary of the main threads of this Symposium.

This is a brief report on the highlights of this informal session attended by over 50 symposium participants for three hours on the day preceeding the symposium.

Nebular emission-line spectra offer fundamental tests for models of stellar atmospheres, and ultimately, they offer important probes of massive star properties in situations where the stars themselves are unresolved or obscured. Presentations in the first half of this special session focused on the impact of revised stellar properties for O-type and Wolf-Rayet stars on the effective temperature scale and on their Lyman continuum fluxes, whilst the second half emphasized the relationship of nebular diagnostics with stellar atmospheres.