I review recent developments in the field of radio observations of ultracompact H II (UCHII) regions that have appeared in the literature since the last major review (Churchwell 2002). The morphology of UCHII regions continues to be a topic of research and recent studies of individual regions of star formation suggest modifications with respect to the results obtained from galactic plane surveys. I also briefly touch upon the question of the density structure of UCHII regions. Finally, I will also discuss the evidence of time variability in UCHII regions, and present examples of objects that are expanding, varying in flux density, or moving in the sky.

We present elemental abundance ratios for red giant stars in 9 old halo globular clusters based on the homogeneous data sample and analysis method. Our result suggests that [Si/Ti] ratios in old globular clusters decrease with Galactocentric distances, confirming the previous result by Lee & Carney (2002). We propose that contributions from different masses of the Type II suprenovae progenitors that enriched proto-globular clusters' clouds are responsible for this gradient.

We report on a survey of $^7$Li and $^6$Li isotopic abundances in metal-poor halo stars. The spectra of the 24 stars observed with VLT/UVES are of exceptionally high quality: $S/N>400$ and resolving power $R \simeq 120 000$. The $^7$Li abundances on our H$\alpha$$T_{\rm eff}$-scale show very small intrinsic scatter and a pronounced [Fe/H]-dependence. The resulting estimated primordial $^7$Li abundance is about 0.5 dex lower than predicted from Big Bang nucleosynthesis and the baryon density inferred by the cosmic microwave background. Nine of the stars yield a positive detection (${>}2\sigma$) of $^6$Li, which suggests the existence of a $^6$Li plateau for halo stars. The most interesting result is the presence of $^6$Li in the very metal-poor ([Fe/H]$=-2.74$) dwarf LP815-43 at the level of $^6$Li/$^7$Li${\simeq}\, 0.05\pm0.02$. According to models for stellar Li depletion due to diffusion or rotationally-induced mixing, a 0.5 dex $^7$Li depletion would require an unrealistic high initial $^6$Li abundance ($\log ^6{\rm Li} \ge 2.0$). Simultaneously, the observed high $^6$Li abundance at such low [Fe/H] can not be reconciled with existing models for Galactic cosmic ray spallation and $\alpha$-fusion reactions. This opens up exciting prospects of pre-Galactic $^6$Li production, possibly due to cosmological cosmic rays or late-decaying massive particles such as the gravitino or neutralino in the Big Bang.

The AMS-02 experiment is a large acceptance magnetic spectrometer which will operate on the International Space Station for more than 3 years. This will allow to perform high statistics studies of cosmic rays in space and the accurate determination of secondary-to-primary ratios such as B/C, and the ratio $^{10}$Be/$^{9}$B, thus allowing to discriminate among the possible propagation models and to infer other clues about the light elements production.

We present preliminary results on the chemical abundance patterns of extremely metal-poor stars obtained during an ongoing observing program with Subaru/HDS. High-resolution, high signal-to-noise spectra have been obtained for 14 stars with [Fe/H]$\lesssim -3$. Five of them exhibit clear overabundances of carbon, a remarkable characteristic found only in the most metal-poor range. One of the carbon-rich stars, HE 1327–2326, has [Fe/H]$_{\rm NLTE}=-5.4$, the lowest Fe abundance known. No stars with ${-}5\,{<}\,$[Fe/H]$\,{<}\,{-}4$ have yet been found in our program, suggesting that quite different enrichment processes were responsible for stars with [Fe/H]$\,{<}\,{-}5$ and [Fe/H]$\,{>}\,{-}4$. While neutron-capture elements are deficient in most of our stars, one star (BS 16550–087) exhibits large enhancements of its light neutron-capture elements (Sr, Y and Zr), providing a strong constraint on models for the production of such elements in the very early Galaxy.

We compute the evolution of the abundances of barium and europium in the Milky Way with a chemical evolution model which already reproduces the majority of observational constraints, and we compared our results with the observed abundances from the recent UVES Large Program “First Stars” (Cayrel et al. 2004, François et al. 2005).

We confirm that barium is a neutron capture element mainly produced in the low mass AGB stars, during the thermal-pulsing phase, by the 13C neutron source, in a slow neutron capture process. However, in order to reproduce the [Ba/Fe] vs. [Fe/H] as well as the Ba solar abundance, Ba should be also produced as a r-process element by massive stars in the range 10-30M[odot ]. On the other hand, europium should be only a r-process element produced in the same range of masses (10-30M[odot ]), at variance with previous suggestions indicating a smaller mass range for the Eu producers. As it is well known, there is a large spread in the [Ba/Fe] and [Eu/Fe] ratios at low metallicities, although smaller in the newest data. With our model we estimate ranges in the r-process yields from massive stars for both elements which better reproduce the trend of the data. We discuss several possibilities to explain the observed spread. We suggest that a peculiar behaviour of the neutron capture elements could be the responsible for the spread instead of invoking a strongly inhomogeneous early Galactic halo. We finally underline that the production ratio of [Ba/Eu] may be almost constant in the massive stars.

The Sun has typical abundances of both oxygen and sulphur for its metallicity, age and galactic orbit, when compared to the nearby solar-type stars. This result favors a solution of the old riddle of the solar overabundance in oxygen with respect to the local interstellar medium as caused by the recent infall of metal-poor gas over the disk, rather than the competing explanations of an outward migration of the Sun from a inner, and metal richer, birthplace in the disk, or a last-minute supernova which might have enriched the proto-solar nebula.

We summarize the results of recent model computation for massive Asymptotic Giant Branch stars of low metallicity, whose winds are thought to be the matter from which second generation stars are born in Globular Clusters (GCs) showing abundance anomalies. The yields of these ejecta are highly uncertain, but our models in the range of masses 3.5–4.5M[odot ] can reasonably explain some of the chemical anomalies of Globular Cluster stars.

Eight cool giants in the unusual globular cluster NGC 6388 have been investigated in order to derive their elemental abundances. Average relative-to-solar abundance of iron is about –0.8. We have found that oxygen abundance is reduced as compared to most stars of a similar metallicity. The reduced carbon as compared to oxygen is at the level to be expected for red giant tip stars. Abundance of the rest of investigated elements are within the expected limits for the globular cluster stars.

We present numerical investigations into the formation of massive stars from turbulent cores of density gradient $\rho \propto r^{-1.5}$. The results of five hydrodynamical simulations are described, following the collapse of the core, fragmentation and the formation of small clusters of protostars. We generate two different initial turbulent velocity fields corresponding to power-law spectra $P \propto k^{-4}$ and $P \propto k^{-3.5}$, and apply two different initial core radii. Calculations are included for both completely isothermal collapse, and a non-isothermal equation of state above a critical density ($10^{-14}$gcm$^{-3}$). Our calculations reveal the preference of fragmentation over monolithic star formation in turbulent cores. Fragmentation was prevalent in all the isothermal cases. Although disc fragmentation was largely suppressed in the non-isothermal runs due to the small dynamic range between the initial density and the critical density, our results show that some fragmentation still persisted. This is inconsistent with previous suggestions that turbulent cores result in the formation of a single massive star. We conclude that turbulence cannot be measured as an isotropic pressure term.

The physical parameters of HII regions span orders of magnitude in scale. The classes most closely linked to star formation are the smallest, densest, and, presumably, youngest stages: compact, ultracompact, and hypercompact HII regions.

Although hypercompact HII regions have been known for over ten years, until recently only a very small number of these regions were known. Moreover, it is only in the past several years that these regions have come to be recognized as a distinct class of HII region and that attempts have been made to understand their place in the scheme of massive star formation.

Here we present a summary of the observational studies to date. We give special emphasis to radio continuum studies, which indicate density gradients within the ionized gas, and to radio spectral line studies, which show unusually broad recombination line profiles. Possible interpretations of these aspects of hypercompact HII regions are discussed, and their implications for the interpretation of hypercompact HII regions as an evolutionary stage in the high-mass star formation process.

Attempts are made to summarize some main points and results discussed at the IAU Symposium No. 228 in Paris, May 2005. It is concluded that, although the situation in areas pioneered by F. and M. Spite is nowdays rather complex, some important progress has recently been made, and more is expected to occur within the next few years if the level of ambition in the astronomical community is kept at the high level set by the pioneers.

Molecular outflows in the form of wide-angle winds and/or well-collimated jets are associated with young stellar objects of all luminosities. Independent studies have established that the mass outflow rate is proportional to L$_{bol}^{0.6}$ for L$_{bol} = 0.3$ to $10^5$ L$_{\odot}$, suggesting that there is a strong link between accretion and outflow for a wide range of source luminosity and there is reasonable evidence that accretion-related processes are responsible for generating massive molecular flows from protostars up to spectral type B0. Beyond L$_{bol} \sim 10^4$ L$_{\odot}$, O stars generate powerful wide-angle, ionized winds that can dramatically affect outflow morphology and even call into question the relationship between outflow and accretion.

Recently Beuther & Shepherd 2005 have proposed an evolutionary scenario in which massive protostellar flows (up to early B spectral type) begin collimated. Once the star reaches the Main Sequence, ionizing radiation may affect the balance between magnetic and plasma pressure, inducing changes in the flow morphology and energetics. Here I review the properties of outflows from young OB stars, discuss implications and observational tests of this proposed evolutionary scenario, and examine differences between low-mass and massive star formation.

Globular cluster stars exhibit abundance anomalies which are not shared by their field counterparts. Two global scenarii have been proposed in the past to explain these differences: The primordial enrichment scenario and the evolutionary (or intrinsic) one. Recent observations well below the bump luminosity in globular clusters have raised the weight of the primordial solution. However the stellar sources responsible for these abundance variations have not yet been indubitably identified. In this review we discuss the possible stellar culprits as well as their pros and cons.

The UVES Paranal Observatory Project (POP), is an ESO public database of about 400 stars whose high quality spectra were obtained with UVES, the high resolution spectrometer of the VLT. All stars were observed with two instrument modes, in order to cover almost completely the optical region (300–1000 nm). The resolving power is about 80000, and for most of the spectra, the typical S/N ratio is 300–500 in the V band. Program stars fall into two groups, stars belonging to open clusters IC2391 and NGC6475, and bright field stars. For field stars, the only selection criterion applied was to cover the largest possible variety of spectral types in the HR diagram, including peculiar objects, e.g., Ap and Bp stars, Wolf-Rayet stars, Be stars, carbon stars and metal poor stars. The spectra have been reduced, coadded and merged and various products can be downloaded from a public area. For each star the final spectrum may be displayed through a dedicated user-friendly Spectral Preview Interface. The database is accessible at http://www.eso.org/uvespop

While the origin of r-process nuclei remains a long-standing mystery, recent spectroscopic studies of extremely metal-poor stars in the Galactic halo strongly suggest that it is associated with core-collapse supernovae. In addition, recent comprehensive analysis of such stars implies the presence of the “weak” r-process that is responsible for only lighter nuclei with A <130. In this study, we show that the weak r-process nuclei can be produced in the neutrino winds from a typical proto-neutron star of $1.4 M_\odot$. This suggests that the significant fraction of weak r-process elements (Sr, Y, Zr, etc.) originate from typical core-collapse supernovae with the progenitor mass range of ∼ 10–$20 M_\odot$

Super star clusters are one of the most extreme star forming environments in the universe, and the most massive and dense of these may be proto globular clusters. Like individual massive stars, the earliest stages of super star cluster evolution are deeply obscured, and therefore our knowledge about their birth environments is currently very incomplete. However, the study of natal super star clusters has become somewhat of a cottage industry in recent years, and the sample of such objects has been growing rapidly with high-quality long-wavelength data now available from a number of observatories. The natal super star clusters identified in thermal-infrared and radio observations represent the youngest stage of massive star cluster evolution yet observed. Their properties appear to be similar to those of ultracompact hII regions in the milky way, but scaled up in total mass and luminosity. I will overview what we think we know about these objects based on existing observations, discuss their relationship to ultracompact hII regions, present new models of their spectral energy distributions based on 3-d simulations, and outline some of the most significant gaps in our current understanding.

The Spitzer Space Telescope has delivered impressive infrared images of numerous low-mass star forming regions at unprecedented sensitivity. In this paper we focus on their high-mass counterparts, the most massive HII regions in the Local Group: NGC3603 (MW), W49A (MW), 30 Doradus (LMC), NGC346 (SMC), and NGC604 (M33). The deep mid-IR images, taken with IRAC show the complex structure of the ISM, the interplay between ISM and stellar clusters, and reveal new sites of star formation. We compare the IRAC data with observations from Chandra and find good anti-correlations between the mid-IR and soft X-ray emission regions. We also investigate the commonalities and differences between the giant HII regions NGC604 and 30 Doradus.

We present a discovery of a giant stellar halo in NGC 6822, a dwarf irregular galaxy in the Local Group. This halo is mostly made of old red giants, showing striking features: 1) it is several times larger than the main body of the galaxy seen in the optical images, and 2) it is elongated in the direction almost perpendicular to the HI disk of NGC 6822. The structure of this stellar halo looks similar to the shape of dwarf elliptical galaxies, indicating that the halos of dwarf irregular galaxies share the same origin with those of the dwarf elliptical galaxies.

We use recent observations of the HI mass function to constrain the amount of cold gas in dark matter halos. It is found that the cold gas mass in a halo decreases rapidly with decreasing halo mass for low-mass halos with $M<10^{12} h^{-1}{\rm M_\odot}$. This result is in conflict with the standard model, in which most of the gas in a low-mass halo is assumed to settle into a gaseous disk, and the cold gas is depleted by star formation and supernova-driven outflow until the disk becomes gravitationally stable. Heating by the UV background can reduce the amount of cold gas in halos with masses $<10^{10} h^{-1}{\rm M}_\odot$, but is insufficient to explain the observational result. A consistent model can be found if low-mass halos are embedded in a preheated medium, with a specific gas entropy $\sim 10\,{\rm keV\,cm^{2}}$. Such a model can also explain why the faint-end slope of the galaxy luminosity function is flat. We propose a preheating model in which the medium around low-mass halos is preheated by gravitational pancaking. Since large-scale tidal fields tend to suppress the formation of low-mass virialised halos while promoting the formation of pancakes, the formation of massive pancakes may precede that of low-mass dark halos at the present time. ‘Previrialisation’ of such pancakes can heat the intergalactic medium. The preheated gas has a cooling time longer than the age of the Universe at $z\lesssim 2$, and has a specific entropy comparable to that required to reduce the amount of cold gas and star formation activity in galaxy halos.