Lithium abundances have been determined in more than 100 metal-poor halo stars both in the field and in clusters. From these data we find trends of Li with both temperature and metallicity and a real dispersion in Li abundances in the Spite Li plateau. We attribute this dispersion primarily to Li depletion (presumably due to extra mixing induced by stellar rotation) and to Galactic chemical evolution. We derive a primordial Li of 2.44$\,{\pm}\,$0.18 for A(Li)$_p$ = log N(Li/H) + 12.00. This agrees with the Li abundances predicted by the WMAP results. For stars cooler than the Li plateau we have evidence that Li depletion sets in at hotter temperatures for the higher metallicity stars than for the low-metal stars. This is the opposite sense of predictions from stellar models. The smooth transition of the Li content from the Li plateau stars to the cool stars adds weight to the inference of Li depletion in the plateau stars.

The Chandra X-ray Observatory is providing remarkable new views of massive star-forming regions, revealing all stages in the life cycle of high-mass stars and their effects on their surroundings. We present a Chandra tour of several high-mass star-forming regions, highlighting physical processes that characterize the life of a cluster of high-mass stars, from deeply-embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. Along the way we see that X-ray observations reveal hundreds of stellar sources powering great HII region complexes, suffused by both hard and soft diffuse X-ray structures caused by fast O-star winds thermalized in wind-wind collisions or by termination shocks against the surrounding media. Finally, we examine the effects of the deaths of high-mass stars that remained close to their birthplaces, exploding as supernovae within the superbubbles that these clusters created. We present new X-ray results on W51 IRS2E and 30 Doradus and we introduce new data on Trumpler 14 in Carina and the W3 HII region complexes W3 Main and W3(OH).

We have observed with UVES@VLT 15 field Blue Straggler Stars for which kinematical attribution to the Halo or Thick Disk is available. We present here the first results of our detailed chemical analysis.

Stars with masses of $\gtsim 20$ $M_{odot}$ have short Kelvin times that enable them to reach the main sequence while still accreting from their natal clouds. The resulting nuclear burning produces a huge luminosity and a correspondingly large radiation pressure force on dust grains in the accreting gas. This effect may limit the upper mass of stars that can form by accretion. Indeed, simulations and analytic calculations to date have been unable to resolve the mystery of how stars of 50 $M_{odot}$ and up form. We present two new ideas to solve the radiation pressure problem. First, we use three-dimensional radiation hydrodynamic adaptive mesh refinement simulations to study the collapse of massive cores. We find that in three dimensions a configuration in which radiation holds up an infalling envelope is Rayleigh-Taylor unstable, leading radiation driven bubbles to collapse and accretion to continue. We also present Monte Carlo radiative transfer calculations showing that the cavities created by protostellar winds provides a valve that allow radiation to escape the accreting envelope, further reducing the ability of radiation pressure to inhibit accretion.

Massive protostars are generally enshrouded in dust, so that most of their radiation emerges in the far infrared. For protostars embedded in opaque, spherical cores, the spectral energy distribution (SED) is determined by two distance-independent parameters, the luminosity-to-mass ratio, $L/M_c$, and the surface density of the core, $\Sigma=M_c/(\pi R_c^2)$, where $R_c$ is the radius of the core. Chakrabarti & McKee (2005a) have derived an approximate analytic expression for the SED that agrees well with numerical results. It is generally not possible to infer the power-law of the density from the SED of a massive protostar. Masses and accretion rates are inferred for several well-studied sources.

We discuss the fraction of carbon stars (C-stars) and of C-enhanced stars among samples of candidate extremely metal poor (EMP: [Fe/H] $\le -3.0$ dex) stars selected from the Hamburg/ESO Survey (HES), obtaining a total for C-rich stars with [C/Fe] $\ge$ +1.0 dex of 14.4$\pm4$%. We also present the key results of detailed abundance analyses of a sample of 14 C-stars selected in this way.

Abundance variations in globular clusters have been observed for the light elements C, N, O, Na, Al, as well as sometimes Mg. Such variations can be understood as the result of H-burning. In particular for the globular cluster M4, anticorrelations of O with Na and Al have been established from previous studies. In this study, we discuss fluorine abundances in a sample of M4 red-giants derived from infrared high-resolution spectra obtained with Pheonix on Gemini South. Our results show that fluorine now can be added to the suite of elements that are shown to vary in M4: the abundance of 19F is found to be anti-correlated with the sodium and aluminium variations. These results provide further evidence that H-burning is indeed responsible for the observed chemical inhomegeneities. Moreover, from comparisons with stellar models, tighter constraints on the mass of the polluting star in this globular cluster are extablished.

I review selected results obtained using Chandra X-ray observations of high mass star forming regions. Discussed topics include diffuse X-ray emission; the mechanism of X-ray emission in stars from the highest to the lowest masses; the role of imaging X-ray observations in the identification of star forming region members and the implications for star formation studies. Special attention will be given to results recently obtained for the Orion Nebula Cluster by the Chandra Orion Ultradeep Project (COUP).

We present initial results from a survey of the Orion A and B molecular clouds made with the InfraRed Array Camera (IRAC) onboard the Spitzer Space Telescope. This survey encompasses a total of 5.6 square degrees with the sensitivity to detect objects below the hydrogen burning limit at an age of 1 Myr. These observations cover a number of known star forming regions, from the massive star forming clusters in the Orion Nebula and NGC 2024, to small groups of low mass stars in the L1641. We combine the IRAC photometry with photometry from the 2MASS point source catalog and use the resulting seven band data to identify stars with infrared excesses due to dusty disks and envelopes. Using the presence of an infrared excess as an indicator of youth, we show the distribution of young stars and protostars in the two molecular clouds. We find that roughly half of the stars are found in dense clusters surrounding the two regions of recent massive star formation in the Orion clouds, NGC 2024 and the Orion Nebula.

A detailed abundance analysis of four giants in the metal-rich bulge globular cluster NGC 6553 is carried out, based on optical high resolution échelle spectra obtained with UVES at the ESO VLT-UT2 Kueyen telescope. A mean radial heliocentric velocity of −1.86 km s−1 is found. Stellar parameters are derived from spectroscopic data based on Fe I and Fe II lines. Enhanced abundance ratios for the α-elements Mg and Si with respect to Ca and Ti are obtained. The odd-Z elements are typically solar. A solar value for the r-process element Eu ([Eu/Fe] = +0.05 ±0.06) was also found.

We have recently obtained moderate resolution (R${\sim}$8,000–12,000) high signal-to-noise H- and K-band spectroscopy of a number of optically visible, well studied OB stars (Hanson et al. 2005) to test the reliability of a pure near-infrared quantitative analysis (Repolust et al. 2005). The analysis of 25 of these OB stars via near-infrared spectra alone using the NLTE line-blanketed model atmosphere code FASTWIND (Puls et al. 2005) has proved successful at constraining stellar and wind parameters, consistent with results from previous optical analyses of these stars. This opens the door to quantitative analysis of OB stars at an extraordinarily young age, while they are still heavily enshrouded in their birth cocoons. Because the analysis requires good quality spectra at both H and K band, present 8-m class telescopes limit us to sources which are not extremely embedded ($A_V < 30$). As a first example, we present a preliminary analysis of the heavily reddened ($A_V = 25$), early-O star ionizing the UCHII region, G29.96-0.02. Challenges facing such an analysis include contributions from excess thermal emission from circumstellar material (disks, etc.) which weaken or even eliminate photospheric lines used in the analysis, nebular contamination in several of the principle H and He lines and crowding or general confusion in these very young and typically complex regions. Spectrographs coupled with state of the art adaptive optics will be extremely useful in minimizing these challenges, and may allow even fairly complex regions to be directly studied.

The presence of ices along the line of sight of high mass star forming regions is clearly evidenced by infrared observations. In dense molecular clouds icy grain mantles form after direct freeze out of gas phase species and after surface reactions of atoms and radicals on grains. Thus chemical composition of icy mantles differs from that of the gas phase. Due to the presence of the protostar and of cosmic radiation, icy mantles suffer from ion bombardment, UV photolysis and thermal annealing. Most of our knowledge on the physical and chemical properties of ices is based on the comparison between observations and laboratory experiments performed at low temperature (10-80 K). Experimental results show that after ion irradiation and UV photolysis the chemical composition and the structure of the sample is modified. Both more volatile and less volatile species are formed and if a C-bearing species is present in the original sample a refractory residue is left over after warm-up to room temperature. After thermal annealing, segregation, crystallization, and sublimation take place. Thus molecular species are released to the gas phase which could be enriched by species formed in the solid phase. Here I will discuss some recent laboratory experiments relevant to our knowledge of the physico-chemical properties of ices in star forming regions.

We have derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Ni and Ba for 43 metal-poor field stars, mostly stars at the turn-off point and on the subgiant branch, in the interval ${-}3.0{<}$[Fe/H]${<}{-}0.4$. The analysis is differential relative to the Sun. Oxygen abundances, with consideration of NLTE effects, were derived from the OI 777.4 nm triplet lines. We find [O/Fe] to gradually increase with decreasing [Fe/H], though considerably slower than has earlier been obtained from OH lines in the UV. A scatter in [O,Mg,Ca,Ti/Fe] at a given [Fe/H] is found and we argue that this scatter is partly real. The deviations from the mean trends of abundance ratios vs [Fe/H] are found to correlate in non-trivial ways for different abundances. Similar trends are found from results of accurate studies by other groups. This seems to give further evidence for the hypothesis that the stars once formed in different subsystems, with different star-formation rates.

The paper is in press in A&A, may be obtained as astro-ph/0505118.

As part of a program of abundance studies of old open clusters, we present an analysis of high-dispersion echelle spectra of three giant stars in the 10 Gyr old cluster Berkeley 17. Abundances were determined relative to the disk giant Arcturus. Be 17 is found to have a mean [Fe/H] = −0.10 ±0.05 (mean error). Oxygen abundances, determined from the forbidden [O I] lines, show solar abundance ratios. The α-elements Mg, Ca, and Ti also show scaled solar abundance ratios, with suggestions that the Si abundance is slightly enhanced. The odd-Z elements Na and Al are significantly enhanced relative to scaled solar abundances. These abundance patterns are similar to those in two other 8-10 Gyr old open clusters, Cr261 and NGC 6791, and suggest that the Galactic disk was enriched to solar abundance levels at very early times.

We report on the distribution of metallicities, [Fe/H], for very metal-poor stars in the halo of the Galaxy. Although the primary information on the nature of the Metallicity Distribution Function (MDF) is obtained from the two major recent surveys for metal-poor stars, the HK survey of Beers and collaborators, and the Hamburg/ESO Survey of Christlieb and collaborators, we also discuss the MDF derived from the publicly available database of stellar spectra and photometry contained in the third data release of the Sloan Digital Sky Survey (SDSS DR-3). Even though the SDSS was not originally planned as a stellar survey, significant numbers of stars have been observed to date – DR-3 contains spectroscopy for over 70,000 stars, at least half of which are suitable for abundance determinations. There are as many very metal-poor ([Fe/H] $< -2.0$) stars in DR-3 as have been obtained from all previous survey efforts combined. We also discuss prospects for significant expansion of the list of metal-poor stars to be obtained from the recently funded extension of the SDSS, which includes the project SEGUE: Sloan Extension for Galactic Understanding and Evolution.

We describe a programme that aims to increase the known sample of massive young stellar objects (MYSOs) by an order of magnitude. About 2000 candidates colour-selected from the MSX survey are being followed up at radio, mm and IR wavelengths to identify genuine MYSOs from the UCHII regions and other contaminants. Results so far indicate that the strategy does indeed deliver a significant fraction of luminous YSOs that will provide the basis for future galaxy-wide systematic studies.

Our mid-infrared and near-infrared surveys over the last five years have helped to strengthen and clarify the relationships between water, methanol, and OH masers and the star formation process. Our surveys show that maser emission seems to be more closely associated with mid-infrared emission than cm radio continuum emission from UC HII regions. We find that masers of all molecular species surveyed trace a wide variety of phenomena and show a proclivity for linear distributions. The vast majority of these linear distributions can be explained by outflows or shocks, and in general do not appear to trace circumstellar disks as was previously thought. Some water and methanol masers that are not associated with radio continuum emission appear to trace infrared-bright hot cores, the earliest observable stage of massive stellar life before the onset of a UC HII region.

Effective temperatures of 30 turnoff stars with $-3.2 {<}$[Fe/H]${<}{-}1.5$ have been derived from the profiles of Balmer lines in high S/N, VLT/UVES spectra. While the systematic error of $T_{\rm eff}$ may be of the order of 100K, the differential values of $T_{\rm eff}$ are determined with a one-sigma precision of ${\sim}25$K. These precise $T_{\rm eff}$ values are used in a study of the slope and dispersion of the Li abundance as a function of [Fe/H]. A small, but significant cosmic dispersion in $A$(Li) appears to be present exemplified by the two very metal-poor stars G64-12 and G64-37.

We calculate evolution, explosion and nucleosynthesis of 1000$M_{\odot}$ stars. Even such massive stars may explode at the end of their lives if they rotate. We use a 2 dimensional hydrodynamical code to take aspherisity by the effect of rotation into account. Our results show that (1) abundance pattern of ejected matter by explosion is consistent with observational data of intracluster medium gas and M82 hot gas, (2) such massive stars can supply more efficient UV photons to re-ionize HI, HeI and HeII than ordinary massive stars (less than 100 solar-masses) and (3) final black hole mass is 500 solar-mass, which is consistent of the mass scale of intermediate-mass black hole (IHBH) found in M82.

This review discusses near- and mid- infrared observations of Ultracompact (UC) HII regions. The importance of ISO mid-IR fine-structure nebular lines is emphasised, since only a small fraction of UCHII regions are observed directly in the near-IR. The reliability of contemporary atmospheric models for such indirect diagnostics is discussed, whilst a revised spectral type-temperature calibration is presented for Galactic O3 to B3 dwarfs. In particular, fine-structure line derived properties of G29.96–0.02 differ from the direct near-IR spectroscopic result and represents a serious discrepancy which needs to be addressed. Mid-IR MSX and Spitzer imaging permits the identification of those UCHII regions for which far-IR IRAS fluxes are reliable, relevant to the single versus cluster nature of individual sources. High spatial resolution imaging with ground-based 8m telescopes allows more direct tests, as recently applied to G70.29+1.60. Finally, recent Spitzer mid-IR observations of Giant HII regions are briefly discussed.