N-band (10.8 μm) imaging of the blue compact starburst galaxy He 2-10 reveals the presence of four emission regions, which have no optical or near-IR counterparts. These sources correspond to the ‘ultradense H ii’ regions recently identified in 2cm and 6cm radio maps of this galaxy. We have used the N-band data to place constraints on the properties of the stellar clusters, that are deeply embedded within these dust-emitting regions.

We present the results of a study on the behaviour of the blue and red WR emission bumps (around 4650Å and 5808Å) and of the nebular contribution to He ii λ4686 in evolving young starburst regions (such as Wolf-Rayet galaxies), containing a non-negligible binary population. Calculations were made for solar metallicity and 1/20 solar. The population synthesis program uses an extended library of stellar evolutionary tracks of single stars and binaries, computed using the most recent stellar wind mass loss rates during RSG, LBV and WR stages. In the case of binaries, we account in detail for the effects of Roche lobe overflow, mass transfer and mass accretion, common envelope evolution, the spiral-in process, asymmetric kicks to neutron stars as a result of their supernova explosion, etc. This research is part of a more extensive project to explore every possible impact of massive binaries on stellar populations.

A HST-wfpc2 survey of Galactic Wolf-Rayet stars was undertaken over a five year period, in an effort to discover new close visual companions, tight clusters, and/or association memberships. In total, 61 Galactic WR stars were observed, with nine objects being members of the subclasses WC8 and WC9, which are associated with dust production. For these nine, we present images of WR 11, WR 48a, WR 69, WR 70, WR 81, and WR 92. We refer to Wallace et al. (2002) for discussion of WR 98a, WR 104, and WR 112. Overall, we find for separations of approximately ≥ 150 mas, that the binary/association properties of the WC8/WC9 sample are statistically indistinguishable from the overall WR population. These statistics are limited, however, by the small numbers of each WR subclass observed.

We have begun a census of various stellar groups in Local Group Galaxies, using the wide field camera on the Isaac Newton Telescope on La Palma. Here we present a preliminary color-magnitude diagram for the dwarf irregular galaxy IC-10. At present time, metallicity of IC-10 is measured to be Z = 0.005 (Garnett 1990). Comparison with recent literature values of reddening and distance suggest that IC-10's distance is ~ 1 Mpc. Our comprehensive wide-field survey encompasses both broad (g′, r′, i′) and narrow-band (O iii, He ii, Hα, S ii, Strömgren y) observations to look for emission-line objects, including Wolf-Rayet stars and Luminous Blue Variables. The analysis also yields the coordinates of massive stars to an accuracy sufficient for follow-up multi-object spectroscopic observations.

Massive stars evolve across the H-R diagram, losing mass along the way and forming a variety of ring nebulae. During the main sequence stage, the fast stellar wind sweeps up the ambient interstellar medium to form an interstellar bubble. After a massive star evolves into a red giant or a luminous blue variable, it loses mass copiously to form a circumstellar nebula. As it evolves further into a WR star, the fast WR wind sweeps up the previous mass loss and forms a circumstellar bubble. Observations of ring nebulae around massive stars not only are fascinating, but also are useful in providing templates to diagnose the progenitors of supernovae from their circumstellar nebulae. In this review, I will summarize the characteristics of ring nebulae around massive stars throughout the H-R diagram, show recent advances in X-ray observations of bubble interiors, and compare supernovae's circumstellar nebulae with known types of ring nebulae around massive stars.

We show radio continuum observations of the WR ring nebulae around WR 101 and WR 113 obtained using the VLA and H i 21 cm line data of the interstellar bubble around the O type stars BD +24° 3866 and BD+25° 3952 obtained with the DRAO Synthesis Telescope. We review previous radio continuum and H i line results toward WR and O-type stars.

A new grid of ionizing fluxes for O-type and Wolf-Rayet stars is presented for use with evolutionary synthesis codes and analyses of single star H ii regions. A total of 230 expanding, non-LTE, line-blanketed model atmospheres have been calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 Z⊙). We have used the wm-basic code of Pauldrach et al. (2001) for O-type stars and the cmfgen code of Hillier & Miller (1998) for WR stars. The stellar wind parameters are scaled with metallicity for both O-type and WR stars. The ionizing fluxes of the new models, incorporated into the evolutionary synthesis code STARBURST99 (Leitherer et al. 1999), are compared with the predictions of the original starburst99 and Schaerer & Vacca (1998) for an instantaneous burst. We find large changes in the output ionizing fluxes as a function of age, especially below the He+ edge. In contrast to previous studies, nebular He ii λ4686 will be at, or just below, the detection limit in low metallicity starbursts during the WR phase. The new models have lower fluxes in the He i continuum for Z ≥ 0.4 Z⊙ and ages ≤ 7 Myr because of the increased line-blanketing. The accuracy of the new model atmosphere grid is tested by constructing photo-ionization models for an H ii region where the ionizing flux is provided by an instantaneous burst. The new models occupy the same region in nebular diagnostic diagrams as the observational data of Bresolin et al. (1999), particularly during the WR phase. The new model grid and updated starburst99 code can be downloaded from http://www.star.ucl.ac.uk/starburst.

In this contribution we present a few selected examples of how the latest generation of space-based instrumentation — NASA's Chandra X-ray Observatory and the Far-Ultraviolet Spectroscopic Explorer (FUSE) — are finally answering old questions about the influence of massive star feedback on the warm and hot phases of the ISM and IGM. In particular, we discuss the physical origin of the soft thermal X-ray emission in the halos of star-forming and starburst galaxies, its relationship to extra-planar Hα emission, and plasma diagnostics using FUSE observations of O vi absorption and emission.

The processes that disperse the products of massive stars from their birth sites play a fundamental role in determining the observed abundances. I discuss parameterizations for element dispersal and their roles in chemical evolution, with an emphasis on understanding present-day dispersion and homogeneity in metallicity. Turbulence dominates mixing processes, with characteristic timescales of order 108 yr, implying significant dilution of metals into the ISM. This permits a rough estimate of the metallicity distribution function of enrichment events. Many systems, including the Milky Way and nearby galaxies, show metallicity dispersions that as yet appear consistent with pure inhomogeneous evolution. There are also systems like I Zw 18 that show strong homogenization, perhaps tied to small galaxy size, high star formation rate, and/or superwinds.

Models of supernova (SN) driven galactic winds for ellipticals are presented. We assume that ellipticals formed at high redshift and suffered an intense burst of star formation. The role of supernovae of Type II and Type Ia in the chemical enrichment and in triggering galactic winds is studied. In particular, several recipes for SN feed-back together with detailed nucleosynthesis prescriptions are considered. It is shown that SNe of Type II have a dominant role in enriching the interstellar medium of elliptical galaxies whereas Type Ia SNe dominate the enrichment and the energetics of the intracluster medium.

N 51D (= DEM L 192) appears at first glance as a nearly circular, 120 pc diameter bubble of ionized gas around the LMC OB association LH 54. A deeper look reveals a complex web of filaments and deviations from radial expansion. Using a deep XMM-Newton pointing centered on N 51D we find that diffuse soft X-ray emitting gas fills the whole superbubble as delineated by the Hα filaments. Contrary to recent findings for galactic winds, the correlation between Hα and X-ray surface brightness is not good. The X-ray spectrum of this diffuse gas cannot be fitted with the LMC abundance pattern, but implies an overabundance of at least oxygen and neon, consistent with recent enrichment from supernovae Type II. Some indications for enhanced mixing at the brightest region of the Hα shell and for a beginning outflow of the hot gas were also detected.

We review our current knowledge on the IMF in nearby environments, massive star forming regions, super star clusters, starbursts and alike objects from studies of integrated light, and discuss the various techniques used to constrain the IMF. In most cases, including UV-optical studies of stellar features and optical-IR analysis of nebular emission, the data is found to be compatible with a ‘universal’ Salpeter-like IMF with a high upper mass cut-off over a large metallicity range. In contrast, near-IR observations of nuclear starbursts and LIRG show indications of a lower Mup and/or a steeper IMF slope, for which no alternate explanation has yet been found. Also, dynamical mass measurements of seven super star clusters provide so far no simple picture of the IMF. Finally, we present recent results of a direct stellar probe of the upper end of the IMF in metal-rich H ii regions, showing no deficiency of massive stars at high metallicity, and determining a lower limit of Mup ≳ 60 – 90 M⊙.

An overview of some key results related to hot, massive stars and starbursts in the infrared is given. The wavelength range covers the ground- and space-based near-infrared, the mid- and far-IR as probed by several space missions, and the sub-millimeter regime. I discuss how these observations permit an unbiased view of dust-obscured stars and how they are related to data at optical and ultraviolet wavelengths.

I summarize the method commonly used to estimate the current star formation rate per unit volume as a function of redshift from various star formation diagnostics, as well as the often conflicting results from the various multi-wavelength datasets collected in recent years. Combined together, and with the help of theoretical and empirical models, these results allow us to address the issues of excitation, reddening, metallicity, and star formation history in individual galaxies at low redshift. They seem to point to the fact, that a lot of the star formation in the local universe, and potentially at all redshift, occurs in burst mode rather than continuously.

Massive stars provide most of our current knowledge of the first star forming galaxies in the universe via their ultraviolet and optical spectra redshifted into the visible and near-infrared bands. Here I briefly review the growing body of data on these early stellar populations from which star formation rates, the initial mass function, chemical abundances, ages, and dust reddenings are being deduced. New evidence also shows the dramatic impact which massive stars have on their galactic and intergalactic environments.

The close similarities in the spectra of the Lyα absorption forests in separate images of gravitationally lensed QSOs at high redshifts provide upper limits for the filling factor of the universe for gas that has undergone recent hydrodynamic disturbances. Strong winds blowing for a substantial fraction of the local Hubble time do not significantly affect the low density regions which fill a large fraction of the volume of the universe. Many of the higher density absorbers appear to be photo-ionized and show some heavy element enrichment. They also contain a cosmologically significant fraction of the baryons and the heavy elements in the universe at that stage of its evolution.

In popular cold dark matter cosmological scenarios, stars may have first appeared in significant numbers around a redshift of 10 or so, as the gas within protogalactic halos with virial temperatures Tvir ≃ 20 000 K (corresponding to masses comparable to those of present-day dwarf ellipticals) cooled rapidly due to atomic processes and fragmented. It is this ‘second generation’ of subgalactic stellar systems, aided perhaps by an early population of accreting black holes in their nuclei, which may have generated the ultraviolet radiation and mechanical energy that ended the cosmic ‘dark ages’ and reheated and re-ionized most of the hydrogen in the universe by a redshift of z = 6. The detailed history of the universe during, and soon after these crucial formative stages, depends on the power-spectrum of density fluctuations on small scales and on a complex network of poorly understood feedback mechanisms, and is one of the missing links in galaxy formation and evolution studies.

We report here the first results of an extensive optical/near-infrared imaging and spectroscopic study of massive stellar clusters in Wolf-Rayet (WR) galaxies using observations obtained from KPNO (USA), OAN (Mexico), the HST and the 2MASS data archive. We have collected spectra, B-imagery and 2MASS JHK imagery of approximately 60 prominent stellar clusters in 23 WR galaxies. One-third of the clusters have a WR stellar signature at He ii λ4686. In this poster, we present the comparison of the derived ages and masses of clusters with WR stars (WRCs) against clusters not containing WR stars (nWRCs). The results show that the mean age of the WRCs distribution is 5.2 ± 1.8 Myr and 6.4 ± 2 Myr for the nWRCs. The mean ages of the two cluster groups are not statistically different. The WRCs masses appear to be more evenly distributed than the nWRC masses and one typically finds that the WRC mass in a particular galaxy is larger than the nWRC mass.

In recent years, the detection of Wolf-Rayet stars in Giant Extragalactic H ii Regions (GEHRs) has yielded several questions about our current understanding of massive stars evolution and hot expanding atmospheres, the age of the ionizing populations and their impact onto the physical properties of GEHRs. Here, we present spectrophotometric observations of four extragalactic GEHRs which show WR features in their spectra. Our goal is to reproduce simultaneously the observed WR properties and the emission-line spectra with the help of current evolutionary synthesis models.

The structure and dynamics of the interstellar medium (ISM) are strongly affected by the action of massive stars. They deposit in the ISM a huge number of ionizing photons and transfer to it vast amounts of mechanical energy via their powerful stellar winds. As a consequence, massive stars create what is known as an interstellar bubble, i.e., a minimum in the gas distribution characterized by a low volume density and a high temperature, surrounded by an expanding envelope (Weaver et al. 1977). The star should be seen projected onto, or close to, the centre of the H i minimum.