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).

Ihe triennial report from Commission 35 covers its organizational activities and highlights accomplishments in various topics of stellar interior physics.

We present evidence that FCC 046, a dE,N galaxy with an offset nucleus, suffered a counter-streaming instability. This instability may explain the presence of lopsided nuclei in other dE,Ns if these galaxies are weakly rotating. The counter-streaming needed for the instability may result from the destruction of box orbits during the assembly of the nucleus.

We present the detection of molecular oxygen with Odin toward the dense molecular core pOph A, which is part of a region of active star formation. The observed spectral line is the $(N_J=1_1-1_0)$ ground state transition of O2 at 119GHz ($\lambda$=2.5 mm). The line center is at the LSR velocity of a number of optically thin lines from other species in the region. The O2 line also has a very similar, narrow, line width. Within the $10^{\prime}$ beam, the line intensity is $\int\!T_{\rm A}\,{\rm d}v = 28$mK kms−1, which corresponds to $5\,\sigma$ of the rms noise. A standard LTE analysis results in an O2 abundance of $5 \times 10^{-8}$, with an uncertainty of at least a factor of two. We show that standard methods, however, do not apply in this case, as the coupling of the Odin beam to the source structure needs to be accounted for. Preliminary model results indicate O2 abundances to be higher by one order of magnitude than suggested by the standard case. This model predicts the 487GHz line of O2 to be easily detectable by the future Herschel-HIFI facility, but to be out of reach for observations on a shorter time scale with the Odin space observatory.

We build a sample of O VI absorption systems in the redshift range 2.0 $\lesssim z \lesssim$ 2.6 using high spectral resolution data of ten quasars from the VLT-UVES Large Programme. We investigate the existence of a metal-rich O VI population and define observational criteria for this class of absorbers under the assumption of photoionisation. The low temperatures of nearly half of all O VI absorbers, implied by their line widths, are too low for collisional ionisation to be a dominant process. We estimate the oxygen abundance under the assumption of photoionisation; a striking result is the bimodal distribution of [O/H] with median values close to 0.01 and 0.5 Solar for the metal-poor and metal-rich populations, respectively. Using the line widths to fix the temperature or assuming a constant, low gas density does not drastically change the metallicities of the metal-rich population. We present the first estimate of the O VI column density distribution. Assuming a single power-law distribution, $f$(N) $\propto$ N$^{-\alpha}$, yields $\alpha \sim 1.7$ and a normalisation of $f$(N) $=2.3\times 10^{-13}$ at log N(O VI) $\sim$ 13.5, both with a $\sim$30% uncertainty. The value of $\alpha$ is similar to that found for C IV surveys, whereas the normalisation factor is about ten times higher. We use $f$(N) to derive the number density per unit $z$ and cosmic density $\Omega_{\rm b}$(O VI), selecting a limited column density range not strongly affected by incompleteness or sample variance. Comparing our results with those obtained at $z\sim0.1$ for a similar range of column densities implies some decline of $dn/dz$ with $z$. The cosmic O VI density derived from $f$(N), $\Omega_{\rm b}$(O VI)$\approx (3.5\pm ^{3.2}_{0.9}) \times 10^{-7}$, is 2.3 times higher than the value estimated using the observed O VI sample (of which the metal-rich population contributes $\sim$35%), easing the problem of missing metals at high $z$ ($\sim$ 1/4 of the produced metals) but not solving it. We find that the majority of the metal-rich absorbers are located within $\sim$ 450 km s$^{-1}$ of strong Ly-$\alpha$ lines and show that, contrary to the metal-poor absorbers, this population cannot be in hydrostatic equilibrium. All of the O VI absorber properties imply that there are two distinct populations: metal-poor absorbers tracing the intergalactic medium and metal-rich absorbers associated with active sites of star formation and most probably linked to galactic winds.

Black hole (BH) theories predict the existence of an “intermediate” mass BH at the centers of dwarf elliptical (dE) galaxies. These intermediate mass black holes (IMBHs) are believed to bridge the observational gap between stellar-mass BHs ($M_{\rm BH} \lesssim 10^3{\rm M_\odot}$) and supermassive BHs ($M_{\rm BH} \gae 10^6{\rm M_\odot}$). Our project aims at finding tighter empirical constrains on the existence, location, and mass range of these hypothetical objects. For this purpose, we are conducting a deep IMBH search in a sample of $\sim$30 Local Volume dwarf galaxies. Using the Robert Stobie Spectograph (RSS) on the newly constructed Southern African Large Telescope (SALT), long-slit spectroscopic observations along the major-axis will be acquired for each galaxy to determine their kinematic and dynamical properties, particularly at their centers.

We present ground-based disc resolved polarimetric imaging and spectropolarimetry of Uranus and Neptune in the wavelength range from 530 to 930 nm with the goal to constrain the expected polarization of extra-solar planets with similar atmospheric properties. We find for both planets a high limb polarization as expected for atmospheres with significant Rayleigh scattering layers. The limb polarization is enhanced in the strong methane absorption bands when compared to the adjacent continuum. From the observed polarization features we conclude that extra-solar planets with atmospheric properties similar to Uranus and Neptune are strongly polarized and well suited for polarimetric detection and investigation.

The Automated Patrol Telescope, operated by the University of New South Wales, has been undertaking a search for extrasolar planets using the transit method. We present lightcurves from two recent promising candidates; spectroscopic follow-up using the ANU 2.3m telescope shows that the companions are probably low mass stars rather than planets, although more data will be needed to be certain. Additionally, we outline future improvements to our transit search: a hardware upgrade scheduled for 2006, and the addition of a robust trend-filtering algorithm to the data reduction software.

The Submillimeter Wave Astronomy Satellite (SWAS) has recently completed 5.5 years of successful operation. Among the legacies of the mission has been a greater understanding of the abundance and spatial distribution of H2O and O2 within molecular clouds. We summarize SWAS results and discuss how the measured low abundance of water vapor and non-detections of molecular oxygen are suggestive of a general lack of atomic oxygen in the dense centers of molecular clouds. We also present a new more comprehensive model for the oxygen chemistry in the interstellar medium.

Radio-selected samples of quasars with complete optical identifications offer an ideal dataset with which to investigate dust bias associated with intervening absorption systems. Here, we review our work on the Complete Optical and Radio Absorption Line System (CORALS) survey whose aim is to quantify this bias and assess the impact of dust on absorber statistics. First, we review previously published results on the number density and gas content of high column density absorbers over the redshift range $0.6<z<3.5$. We then present the latest results from CORALS which focus on measuring the metal content of our unbiased absorber sample and an investigation of their optical–IR colours. Overall we find that although dust is unarguably present in absorption galaxies, the level appears to be low enough that the statistics of previous magnitude limited samples have not been severely affected and that the subsequent reddening of background QSOs is small.

I report X-ray features of young stage of intermediate and high mass stars. The giant molecular cloud Sagittarius B2 (Sgr B2) exhibits more than dozen X-ray sources, two are associated with the ultra compact (UC) HII complex, Sgr B2 Main. The sources show large absorption of $\gg$1023 Hcm−2, the largest among any known stellar X-ray sources.

The Arches cluster exhibits 3 extremely bright (a few $\times10^{33}$ ergs s−1) X-ray sources associated with the infrared (IR) massive stars. The X-ray spectra have 1-3 keV temperature in thin thermal model. Elongated diffuse 6.4 keV line emission is found.

The Monoceros R2 cloud exhibits half dozen X-ray sources associated with young high-mass IR stars. They show rapid time variability and a thin thermal spectrum of ${\sim }2$ keV temperature. Among 28 ASC A pointing on intermediate-mass pre-main-sequence stars, or Herbig Ae/Be stars (HAeBes), eleven are found to be plausible X-ray sources. The general X-ray properties of these HAeBes are; (1) the plasma temperature and time variability are higher than those of high mass main-sequence stars, and more similar to low mass stars; (2) the X-ray luminosities come to the upper end of low mass pre-main sequence stars, or in some cases exceed that; (3) the X-ray activity of HAeBe decreases at the age of about a few×106 years.

Using above observational facts, I propose a unified picture of X-ray activity of young stars in the wide mass range.

A tiny fraction (<1%) of very metal-deficient (12+log(O/H)≤7.6) blue compact dwarf (BCD) galaxies exhibits a nearly galaxy-wide starburst activity and no signatures of an old stellar host galaxy. The evolutionary status and formation history of these most metal-deficient BCDs are still a subject of debate. Various lines of evidence suggest, however, that these systems do not contain a substantial population of stars older than $\sim$1 Gyr and hence qualify as nearby young-galaxy candidates. Elaborated multiwavelength studies of these rare, most metal-deficient BCDs may therefore provide crucial insights into the formation and starburst-driven evolution of low-mass galaxies in the early universe.

We present a study of the evolution of late-type field dwarfs over the last 1.5 Gyr, based on HST ACS observations carried out as part of the GEMS survey. This study is amongst the first to probe the evolution of dwarfs over such a large timescale. The comparison of structural properties, particularly size and scale length, indicates that the dwarfs in the redshift range $z \sim$ 0.01 to 0.15 (look-back times up to 1.8 Gyr) are more extended than local dwarfs. We argue that this difference is due to the star formation activity becoming more centrally concentrated in late-type dwarfs over the last ${\sim} 1.5$ Gyr. We discuss several possible causes for this evolution. We also find a lack of blue compact dwarfs in the GEMS sample and interpret this as indication of the fact that strong, centrally concentrated star formation is a feature of evolved dwarfs that are entering their final stages of evolution.

High energy gamma-ray astronomy has recently made significant progresss through ground-based instruments like the H.E.S.S. array of imaging atmospheric Cherenkov telescopes. The unprecedented angular resolution and the large field of view has allowed to spatially resolve for the first time the morphology of gamma-ray sources in the TeV energy range. The experimental technique is described and the types of sources detected and still expected are discussed. Selected results include objects as different as a Galactic binary Pulsar, the Galactic Center and Supernova Remnants but they also concern the diffuse extragalactic optical/infrared radiation field. Finally, a scan of the Galactic plane in TeV gamma rays is described which has led to a significant number of new TeV sources, many of which are still unidentified in other wavelengths. The field has a close connection with X-ray astronomy which allows the study of the synchrotron emission from these very high energy sources.

Rotating massive stars at $Z=10^{-8}$ and $10^{-5}$ lose a great part of their initial mass through stellar winds. The chemical composition of the rotationally enhanced winds of very low $Z$ stars is very peculiar. The winds show large CNO enhancements by factors of $10^3$ to $10^7$, together with large excesses of $^{13}$C and $^{17}$O and moderate amounts of Na and Al. The excesses of primary N are particularly striking. When these ejecta from the rotationally enhanced winds are diluted with the supernova ejecta from the corresponding CO cores, we find [C/Fe], [N/Fe],[O/Fe] abundance ratios very similar to those observed in the C–rich extremely metal poor stars (CEMP). We show that rotating AGB stars and rotating massive stars have about the same effects on the CNO enhancements. Abundances of s-process elements and the $^{12}$C/$^{13}$C ratio could help us to distinguish between contributions from AGB and massive stars. On the whole, we emphasize the dominant effects of rotation for the chemical yields of extremely metal poor stars.

Commission 36 covers all the physics of stellar atmospheres. The scientific activity in this large field has been very intense during the last triennium and led to the publication of a large number of papers which makes an exhaustive report practically not feasible. As a consequence we decided to keep the format of the preceding report: first a list of areas of current research, then web links for obtaining further information.

Theoretical estimates of nucleosynthesis yields are widely used to infer the meaning of abundance trends, and to predict behavior of abundances in the first stars. We show that the standard prescriptions are incomplete, and illustrate some simple improvements. We consider the effects of internal gravity waves (induced in radiative regions by convective zones) on the evolution of slowly rotating (nonrotating) stars. We demonstrate that such modifications to the standard evolutionary algorithms give better agreement with observation. They imply new phenomena: interations between carbon and oxygen burning shells, detached flames in convective layers, and intermittency, for example. We argue that such hydrodynamic behavior must be part of realistic stellar evolution. Some preliminary results for the Sun and Sirius are discussed.

The field of ground based gamma-ray astronomy has seen rapid growth over the past thirty years with the development of the Imaging Atmospheric Cherenkov Technique to search for Very High Energy (VHE; E > 100 GeV) gamma radiation. This growth continues with the construction of four third generation telescope systems in Namibia, Australia, La Palma and the USA. These systems will search for VHE gamma radiation from such objects as AGN, SNRs, microquasars, dark matter and the galactic centre.

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 summarise recent results assessing the carbon and silicon abundances of the intergalactic medium (IGM) using the ‘pixel optical depth’ technique. We briefly discuss the implications of these results for models of intergalactic enrichment, focusing on distinguishing ‘early’ $z \gg 4$ enrichment by the first generations of stars and objects from ‘late’ enrichment by $2 \lesssim z\lesssim 5$ Ly-break galaxies. We then discuss the comparison of observed QSO spectra to simulated spectra generated from cosmological simulations that self-consistently include enrichment, and draw qualitative implications for the general picture of intergalactic enrichment at $z \gtrsim 2$.