The luminous, compact star cluster R136 in the Large Magellanic Cloud is 300 times more spatially concentrated than a typical OB association and contains at least 39 O3 stars, the most massive of which is ~150 M⊙. Yet, the stellar IMF for 2.8–120 M⊙ is normal. The massive stars are 1–2 Myrs old, and Wolf-Rayet stars are not evolved.

We present a first analysis of our deep NICMOS/HST F160W images of the 30 Doradus cluster, aimed at detecting the low-mass stellar population (M ≤ 2 M⊙). We find that the infrared luminosity function keeps rising towards the faint end and that there is no indication of a low-mass IMF cut-off down to at least 1.5 M⊙. We also find a change of slope (steepening) in the luminosity function as a function of radial distance from the cluster center. The faintest stars we have detected have H=22.5 mag, corresponding to about M = 0.4 M⊙ at an age of 2 Myr.

Recent ROSAT and ASCA X-ray observations as well as HST images have provided new insights into the structure and evolution of the 30 Dor nebula. I review hot gas properties of the nebula and discuss related physical processes. The structure of the nebula can be understood as outflows of hot and HII gases from the parent giant molecular cloud of R136. The dynamic mixing between the two gas phases is likely a key mass loading process of the hot gas, providing a natural explanation of both temperature and density structure of the nebula.

Sk–67°105, a luminous O4f type stars in the Large Magellanic Cloud, is the exiting star of the H II region N 50 (DEM 193). Niemela & Morrell (1986) found this hot star to be a massive short period double lined spectroscopic binary. Because luminous OB stars are usually found in young stellar groups, we have searched for such an aggregate in the vicinity of Sk–67°105.

Here we report, as a result of our search, the discovery of a new OB association in the LMC. We also find that Sk–67°105 is the most luminous star of a small compact cluster inside this OB association.

We present an analysis of wide-field, far-ultraviolet images of the LMC and SMC obtained by the Ultraviolet Imaging Telescope. The photometric catalog of over 37,000 stars allows us to make large-scale, statistical studies of massive star formation in OB associations and in the field population. Our results show that: (1) the most probable slope for the initial mass function (IMF) of field stars is Γ = −1.80, slightly steeper than the Salpeter slope; and (2) there doesn't seem to be a single, unique IMF slope for stars in OB associations, with a range of values from Γ = −1.0 to −2.0. We also analyze the stellar vs. diffuse UV flux, and the population of OB star candidates in the field.

The supersoft X-ray sources are a distinct class of X-ray sources identified by ROSAT. They are characterized by very high luminosities (Lbol ~ 1038 ergs s−1) and black body temperatures of kT~ 30–60 eV. These sources are easily detected in the LMC and SMC because of the low column density of absorbing H gas. Thus, the samples found there are complete. They are much more difficult to find in the Galaxy due to soft X-ray absorption in the galactic plane.

Nine MC young globular cluster and field stars are analysed using fully line-blanketed LTE ATLAS 9 atmospheres and the DETAIL/SURFACE non-LTE line formation code. CNO mixing seems to occur much earlier than predicted by standard theory.

A photometric study of the 30 Doradus Nebula beyond the core is being carried out by means of HST/WFPC2 archival images, with special attention to the numerous multiple systems and compact clusterings found there.

On the basis of ample evidence accumulated during recent years for current star formation within the 30 Doradus Nebula, which appears to have been triggered by the massive central cluster (R136) in and just beyond the curved nebular filaments surrounding it, an HST/NICMOS survey of these regions was undertaken.

We are exploring the properties of obscured starburst galaxies, using observations of atomic fine structure lines taken with the Short Wavelength Spectrometer aboard ISO. However, it is important to ascertain how well our starburst models can recover the properties of the stellar populations in more distant starbursts. For this purpose, we use observations of a nebular “shell” in the 30 Doradus region, to show that our models reliably predict the presence of the very massive stars observed directly in the 30 Doradus region.

We present the first comparison between high resolution echelle velocity fields and a mosaic of all Hubble Space Telescope narrowband observations of 30 Doradus.

30 Doradus is a giant H II region in the Large Magellanic Cloud (Bode 1801). It is the nearest extragalactic giant H II region and the location of active star formation. The complex nature of this extended region provides an excellent opportunity to investigate the impact of massive stars on the structure of the interstellar medium. Specifically the presence of supernova remnants (SNRs) is expected to play an important role.

Multiple images of the R136 cluster in the Large Magellanic Cloud taken with the HST/WFPC2 and the F555W and F814W filters were combined to obtain very deep images of the cluster, with total exposure times of 1240 and 760 sec respectively. The objective of the study was to extend the luminosity function below the limit of 2.8 M⊙ published by Hunter et al. (1995, 1996).

The overall stellar metallicity scale as a function of age for both Magellanic Clouds reveals that they have followed a different pattern of enrichment when compared to each other as well as to the Galactic disk. In addition, an investigation into the abundances of two key elements, oxygen and europium, shows that the detailed nucleosynthesis history of these systems is unique in comparison to any Galactic population yet studied.

I review measurements of heavy element abundances within H II regions in the Magellanic Clouds, highlighting in particular improved determinations of carbon abundances based on UV spectroscopy with Hubble Space Telescope. In general, the Magellanic Cloud H II regions show average underabundances in O, Ne, and S (relative to their Galactic counterparts) that are similar to those measured in Magellanic Cloud stars. However, comparison of stars and ionized gas shows discrepancies in C and N abundances that may be related to recently recognized mixing processes that may be operating in massive stars.

The re-cycling of gas between stars and the interstellar medium (ISM) leads to a gradual metal-enrichment of a galaxy. Accordingly, information on the chemical evolution of a galaxy, e.g., its star-formation history (SFH), is contained in the chemical composition of the ISM. In this context, the abundance ratio of the rare oxygen isotopes, 18O/17O (usually taken as the C18O/C17O column density ratio), appears to be a particularly promising probe of the SFH. According to present understanding of stellar nucleosynthesis, 17O is mainly produced in intermediate-mass stars (say a few to ten M⊙) while 18O is synthesised in massive stars (say >10M⊙) (e.g., Prantzos et al. 1996). Thus, the 18O/17O abundance ratio possibly reflects the relative number of massive stars compared to intermediate-mass stars, and thereby (qualitatively) constrains the SFH in terms of the average star-formation rate (SFR) and the initial mass-function (IMF). However, it should be remembered that the stellar nucleosynthesis of 17,18O is not yet fully understood, leaving room for other interpretations of the 18O/17O ratio.

We discuss the relative gas-phase abundances found for the predominantly neutral interstellar clouds — located in the Galactic disk and halo, in the LMC or SMC, and (perhaps) in between — along the lines of sight to Sk 108 in the SMC and to SN 1987A in the LMC.

In radio astronomy, interstellar isotope ratios have been measured for more than two decades towards different parts of the Milky Way and central regions of some star-burst galaxies. While signals are often too weak to detect rare isotopic species in relatively distant extragalactic sources, our Galaxy only provides an environment with limited metallicity range. Obviously, this constraint can be removed by observing isotopic species in the Magellanic Clouds, located only 50–60 kpc away from us. We thus observed isotope ratios of hydrogen, carbon, nitrogen, oxygen, and sulfur and the results are given in Table 1.

I present the results of the photoionization modeling of eleven H II regions in the Magellanic Clouds (MCs). A comparison of their abundances with other systems are also presented.

The stellar populations in the LMC, the SMC, and the Bridge region are discussed and shown to be composed of a number of well separated generations. Asymmetries are seen in the distributions of the intermediate-age and youngest generations. The possibility is considered that all generations, apart from the oldest one, have been produced by bursts of star formation.