We present evolutionary synthesis modeling of the nuclear regions of the starburst galaxy M 82, based on near-infrared integral field spectroscopy and mid-infrared ISO spectroscopy. Our data indicate the occurrence of two distinct starburst episodes in the central 500 pc about 8 – 15 Myr and 5 Myr ago, each lasting a few million years only. The first burst was most intense within 50 pc of the nucleus while the second burst took place in a circumnuclear ring of radius ~ 85 pc and along the stellar bar at larger radii. These recent episodes succeeded earlier starburst activity ~ 1 kpc away from the nucleus and peaking 650 Myr ago, as traced by the luminous star clusters studied by de Grijs et al. (2001). The combined results of both studies reveal complex evolution of starburst activity in M 82 which is consistent with a tidally-induced bar-driven scenario.

We report the discovery of a population of Wolf-Rayet stars in the young Galactic open cluster Westerlund 1. In an incomplete shallow spectroscopic survey, we find six nitrogen-rich (WN) and five carbon-rich (WC) WR stars. We also confirm the presence of a large population of yellow supergiants, some of which are candidate hypergiants. Given this population, Westerlund 1 is likely to be one of the most massive young clusters in the Local Group.

Due to their high luminosity, the importance of understanding the massive star formation and evolution of giant Hii regions has become more and more evident in the last few years. A mayor scenario where giant H ii regions form and develop are the very inner parts of some galaxies. These bursts frequently are arranged in a ring-like pattern. We present a study of the stellar populations and gas physical conditions in circumnuclear star-forming regions (CNSFR) based on broad- and narrow-band photometry and spectrophotometric data, which have been analyzed with the use of evolutionary population synthesis and photo-ionization models. It is found that most CNSFRs show composite stellar populations of slightly different ages. They seem to have the highest abundances found in H ii region-like objects, showing also N/O overabundances and S/O underabundaces by a factor of about three. Also, CNSFRs as a class segregate from the disk H ii region family, clustering around higher ionizing temperatures.

We present the evolution of synthetic ultraviolet spectra of starburst regions having a significant fraction of binaries. The population synthesis program uses an extended library of stellar evolutionary tracks of single stars and binaries computed with 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. The most important synthesized line profiles are those of Si iv λ1400 and C iv λ1550, two P-Cygni lines prominent in O-type stars. The main effect of the close binaries is to extend the UV bright lifetime of the starburst due to the appearance of accretion stars. But more importantly, our computations show that a spectrum of a single star model of about 6 Myr old is effectively undistinguishable from that of a binary rich model of about 10 Myr old. This indicates a possible age degeneracy, reminiscent of the influence of binaries on the commonly used optical age indicator WHβ.

We have identified IRS 2b as the ionizing source of the Flame Nebula (NGC 2024). For several decades it has been clear that such a hot, massive star must be present in this heavily obscured region, and now it has been found. New J- and K-band photometry and a VLT-isaac K-band spectrum show that IRS 2b is an 08 - 09.7 V star, consistent with published radio continuum and recombination line observations. IRS 2b seems to be slightly evolved from the zero-age main sequence.

We present results of a new investigation (Carraro et al. 2002) aimed at clarifying the mutual relationship between the three most prominent young open clusters close to η Carinæ, namely Trumpler 16, Trumpler 14 and Collinder 232.

In this contribution, I present 90%-confidence limits on diagnostic diagrams of Wλ(WR-bump) and L(WR-bump)/L(Hβ) ratio vs.Wλ(Hβ) resulting from evolutionary synthesis models that include the statistical dispersion due to finite stellar populations in real star forming regions.

We present new narrow-band imaging and optical spectroscopy of Wolf-Rayet stars in the Local Group dwarf galaxy IC 10 (Gemini-N- gmos) and Sculptor group spiral galaxy NGC 300 (VLT fors2).

We present the results and analysis of HST-wfpc2 imagery of the starburst galaxy NGC 1569 (d = 2.2 Mpc), which permit unprecedented resolution (~ 1pc) of the ionized gas and stellar population. The primary data in our analysis consists of images taken through narrow-band filters isolating Hβ, Hα, [O iii]λ5007, and [S ii]λλ6717+30, as part of go Program 8133. A variety of color-coded and grey-scaled maps of the morphology, ionization structure, and dust distribution are presented. Unsharp masks of the Hα images show a very chaotic structure for the ionized gas, with numerous filaments and arc-like bright rim features across the entire galaxy, but without significant large-scale ionization variations. Variations in the ionization and line-of-sight reddening occur on smaller scales (~ 10 – 50 pc), with numerous low-ionization semi-stellar knots seen throughout the main body of the galaxy, even within the ‘hole’ in the ionized gas distribution around the central super star clusters previously noted from H i maps. Several of these features have strong [S ii] emission indicative of being supernova remnants. We combine these data with archival wide-band HST-wfpc2 imagery to quantitatively evaluate the source(s) of the (largely photo-) ionized gas.

We report on two recent improvements to the library of stellar models from Padova. (i) A new set of massive stellar models has been computed for the metallicity Z = 0.001, thus filling an important gap in the previously existing library. (ii) We started a project aiming to convert the complete set of isochrones into a wide variety of photometric systems.

We present our results on high resolution imaging and spectroscopy using the HST of six high-excitation ‘blobs’ (HEB). HEBs constitute a rare class of compact H ii regions in the Magellanic Clouds. Contrary to the typical H ii regions of these galaxies, which are extended structures with sizes greater than 50 pc, the compact H ii regions are an order of magnitude smaller having diameters of less than about 3 pc. HEBs are believed to be the final stages in the evolution of the ultra-compact H ii regions, whose Galactic counterparts are detected only at infrared and radio wavelengths. We find that despite their small size, HEBs are in general excited by more than one newborn massive star. Color-magnitude diagrams of the exciting stellar population indicate that it is consistent with an O6-O8 type, and far-UV spectroscopy with HST-stis of several of these stars further confirms their youth. Surprisingly though, it also shows an astonishing weakness of their wind profiles and their sub-luminosity, up to ~ 2 mag fainter in MV than the corresponding dwarfs. Our analysis suggests that these stars are probably in the Hertzsprung-Russell diagram locus of a particularly young class of massive stars, the so-called Vz luminosity class, as they are arriving on the zero age main sequence.

Most of the Milky Way's evolved massive stellar population is hidden from view. We can attempt to remedy this situation with near-infrared observations, and in this paper we present our method for detecting Wolf-Rayet stars in highly extincted regions and apply it to the inner Galaxy. Using narrow-band filters at K-band wavelengths, we demonstrate how WR stars can be detected in regions where they are optically obscured. Candidates are selected for spectroscopic follow-up from our relative line and continuum photometry. The final results of applying this method with a near-IR survey in the Galactic plane will provide a more complete knowledge of the structure of the galactic disk, the role of metallicity in massive stellar evolution, and environments of massive star formation. In this paper we briefly describe the survey set-up and report on recent progress. We have discovered four emission-line objects in the inner Galaxy: two with nebular emission lines, and two new WR stars, both of late WC subtype.

This contribution reflects a detailed overall survey of the Carina Spiral Feature based on uvbyβ photometry of O- and B-type stars. New observations are combined with all data currently available, to collate a complete homogeneous magnitude-limited uvbyβ database. A uniform procedure is applied to obtain the photometry-derived stellar parameters. A homogeneous distance scale is established to the most prominent young structures in the field and the distribution of the visual extinction is analyzed.

The objective of this work is to generate a data base with the spectral classification, UV-to-IR photometry, and Hipparcos astrometry of a large number of Galactic O-type stars. Whenever possible, a single source will be used for each type of data, in order to ensure its uniformity and to allow accurate comparisons. This data base could be used for several purposes, such as the testing of atmospheric models or a study of the extinction law and its spatial variations. We present here the current status of this work as well as our plans for the following months. We plan to upgrade the data base in the future as more O-type stars are classified using the same procedure and more data are obtained from space and ground-based projects. The data base is available at http://www.stsci.edu/~jmaiz.

We have carried out a search for emission line pre-main sequence (PMS) stars in the area of the star-forming young open cluster NGC 1893 by means of slitless spectroscopy. We find 19 emission line stars with spectral types spanning the range from early B-type to G-type. All the PMS stars are confined to two small regions: the outer rim of the molecular cloud associated with the H ii region IC 410 and the vicinity of the bright emission cometary nebulae Sim 129 and Sim 130. The overall spatial distribution of PMS stars strongly suggests, that present day star formation in NGC 1893 is triggered by the O-type stars in the cluster.

We present the first results of a spectroscopic study of young massive stars in the SMC high excitation blob N 81. These stars have Mv values which are ~ 2 mag smaller than those of normal dwarf stars. Their UV HST-stis spectra reveal features typical of O-type stars, but surprisingly weak wind components. The preliminary modeling of these spectra with the code cmfgen (Hillier & Miller 1998) indicates mass loss rates of the order of 10–9 M⊙ yr–1. If confirmed, such a weak wind may indicate either a breakdown of the wind-momentum luminosity relation at low luminosity, or a steeper slope of this relation at low metallicity.

Median values of the fwhm and equivalent width Wλ of the C iv 581 nm, O v 559 nm and 465 nm emission lines were derived from an extended statistical analysis of WC and WO stars (Norci et al. 2002; see Table 1). We find that the C iv equivalent width shows an increasing trend towards earlier WC subtypes, reaching a maximum value of 95 nm (± 32 %) for the Galactic WC4-6 stars, and decreases by about a factor of three in the hotter WO stars (Figure 1, left). The line appears about twice as strong in the LMC than in the Galactic WC4 stars, and the difference is particularly evident in the non-Galactic WO stars. Such an effect is absent in the O v 559 nm line, which smoothly increases towards WCE and WO stars, with no significant difference between Galactic and non-Galactic WC4 and WO stars. Thus this C anomaly is not an ionization effect; it is, therefore, probably due to a cause that selectively operates on C rather than on O. Different physical conditions in the winds of Galactic and non-Galactic stars, possibly related to the different initial metallicity Z, could be responsible for the anomaly.

We have used a population synthesis programme to calculate the soft X-ray emission from the 30 Dor cluster. Contributions from the single and binary stellar population are included. The intended future use of the programme is the simulation of extra-galactic starbursts. Nearby clusters with violent star-formation activity provide suitable training grounds. Using our programme, we confirm that the stellar population of 30 Dor cannot by itself produce the totality of the observed soft X-ray emission.

Recent advances in atmosphere codes now permit the calculation of realistic grids of hot star atmospheres. Here we use the new O and WR star atmosphere of Smith, Norris & Crowther (2002) with an updated version of the evolutionary synthesis code starburst99 to predict the population of WR stars in a variety in astrophysical conditions. We present a series of synthetic starburst spectra in the optical region which shows the time evolution of the WR-bumps at ~ 4650 Å and ~ 5800 Å.

NGC 595 is, after NGC 604, the second most luminous H ii region in the Milky Way's neighbouring spiral galaxy M 33. Its Wolf-Rayet star content has mainly been unveiled by two different channels. On the one hand, the stellar population of NGC 595 has been resolved and its WR stars identified through online/off-line H ii λ4686 observations realised with the HST. Nevertheless, due to the limited number of filters used, this did not give any information on the WR spectral subtypes. On the other hand, spectroscopic observations of NGC 595, realised at optical and ultraviolet wavelengths, have enabled the determination of some spectral subtypes, but this time, the lack of angular resolution did not allow to resolve the whole population. Thanks to our photometric technique, based on five dedicated narrow-band filters, we present here a determination of the spectral subtypes of NGC 595 WR stars which for the first time combines high-angular resolution and high-‘spectroscopic’ discrimination capabilities.