This review covers a variety of topics related to the properties of Pre–Main Sequence stars in star forming regions, young clusters and associations. Some recent developments of theoretical models of PMS evolution are discussed, with emphasis on the role of magnetic fields in low-mass stars and their impact on observable quantities. Critical tests on the comparison between model predictions and observations are presented for stars across the mass spectrum. The issue of the formation and early evolution of massive stars is addressed, with emphasis on clustered versus isolated objects. After a brief historical background on the derivation of the Initial Mass Function, current representations of this quantity are discussed. The issue of the duration of the star formation process is dealt with using the results of age dating methods for young stars, mainly based on the property of Lithium depletion during PMS evolution. A recent analysis of the properties of the stellar population of the Orion Nebula Cluster is presented with the resulting IMF and age distributions. Finally, a discussion of recent determinations of the metallicity distribution of young stars in clusters and associations closes the review.

Due to the recent interest shown by astronomers towards the Antarctic Plateauas a potential site for large astronomical facilities, we assistedin the last years to a strengthening of site testing activities in this region, particularly at Dome C. Most of the results collected so far concern meteorologic parameters and optical turbulence measurements based on different principles using different instruments. At present we have several elements indicating that, above the first $20{-}30$ m, the quality of the optical turbulence above Dome C is better than above whatever other site in the world. The challenging question, crucial to know which kind of facilities to build on, is to establish how much better the Dome C is than a mid-latitude site. In this contribution we will provide some complementary elements and strategies of analysis aiming to answer to this question. We will try to concentrate the attention on critical points, i.e. open questions that still require explanation/attention.

Large amounts of invisible matter have been discovered back in 1933 when the Swiss astronomer Fritz Zwicky measured for the first time the velocity dispersion of individual galaxies inside the Coma cluster. Since then, this pioneering observation has been confirmed on scales ranging from galactic radii to cosmological distances. The existence of the so–called astronomical dark matter is now well established. The puzzle lies in the fact that this essential component of the universe is not made of ordinary atoms and electrons. The astronomical dark matter is indeed non–baryonic. Its nature is still an unresolved issue. Many theoretical ideas and proposals have flourished in the past thirty years and yet none of them provides a definite answer. I have the challenging task to introduce the cohort of these dark matter candidates to you. They make up a bestiary of exotic species which have been recently proliferating. Instead of a liste à la Prévert, I will present a tentative classification of the various models.

Feedback processes are now realized to hold the key to our understanding ofgalaxy formation and evolution, particularly during the early epochs that we commonly dub as the Cosmic Dawn. We propose and discuss a classification in which three broad feedback classes (radiative, chemical and mechanical) can be identified. We also discuss the underlying physics for each of these feedbacks and point outtheir importance in different cosmological contexts. Finally, the link between mechanical feedback and the heavy element transport is explored with the aim of understanding the cosmic metal budget and the enrichment history of the intergalactic medium.

We have chosen the name of GYES, one of the mythological giants with one hundred arms,offspring of Gaia and Uranus, for our instrument study of a multifibre spectrograph forthe prime focus of the Canada-France-Hawaii Telescope. Such an instrument could provide anexcellent ground-based complement for the Gaia mission and a northern complement to theHERMES project on the AAT. The CFHT is well known for providing a stable prime focusenvironment, with a large field of view, which has hosted several imaging instruments, buthas never hosted a multifibre spectrograph. Building upon the experience gained at GÉPIwith FLAMES-Giraffe and X-Shooter, we are investigating the feasibility of a highmultiplex spectrograph (about 500 fibres) over a field of view one degree in diameter. Weare investigating an instrument with resolution in the range 15 000 to 30 000, whichshould provide accurate chemical abundances for stars down to 16th magnitude and radialvelocities, accurate to 1 km s-1 for fainter stars. The study is led byGÉPI-Observatoire de Paris with a contribution from Oxford for the study of thepositioner. The financing for the study comes from INSU CSAA and Observatoire de Paris.The conceptual study will be delivered to CFHT for review by October 1st 2010.

This is one of two chapters that describe the methods used to extract closure phase from CLIMB data and visibility amplitude from both the CLASSIC and CLIMB beam combiners. In this, the second chapter, I describe the pipeline software.

We discuss the various post-main sequence phases of massive stars,focusing on Wolf-Rayet stars, Luminous Blue Variables, plus connectionswith other early-type and late-type supergiants. End states for massive stars are also investigated, emphasising connections between Supernovae originating fromcore-collapse massive stars and Gamma Ray Bursts.

We present the results of an all sky survey for binary systems among the massive stars that we made with the HST Fine Guidance Sensors. The sample of 225 stars is comprised mainly of Galactic O- and B-type stars and Luminous Blue Variables, plus a few luminous stars in the LMC. The FGS TRANS mode observations are sensitive to detection of companions with an angular separation of 0.01–1 arcsec and brighter than △m = 5 mag. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets, yielding a companion detection frequency of 29%. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample. These results confirm the high multiplicity fraction. The period distribution is essentially flat in increments of log P, although there remains an observational gap in detections for periods of years and decades.

This report aims to provide a summary of the status of our Antarctic Submillimetre Telescope (AST) project up to date. It is a very new project for Antarctic astronomy. Necessary prerequisites for a future deployment of a large size telescope infrastructure have been tested in years 2007 and 2008. The knowledge of the transmission, frost formation and temperature gradient were fundamental parameters before starting a feasibility study. The telescope specifications and requirements are currently discussed with the industrial partnership.

Abundances anomalies and helioseismology provideconstraints on the turbulent transport of chemical species in stellar radiativezone. We use these constraints to derive upper bounds on thevelocity and lengthscale of the vertical turbulent motions.We also present numerical simulations showingthat a strong anisotropy between horizontal and vertical motionscould help understand the observed transport.

The Large Magellanic Cloud (LMC) is the closest large satellite of the Milky Way (MW) and the first step of the extragalactic distance scale, hence knowing the distance to the LMC and its three-dimensional structure contributes to the definition of the entire cosmic distance ladder. RR Lyrae stars are old objects which trace the halo of the LMC. They can be used as distance indicators because they follow a period-luminosity-metallicity (PLKsZ) relation in the Ks passband. The purpose of this study was the derivation of a new PLKsZ relation for RR Lyrae stars in the LMC based on the multi-epoch Ks photometry obtained by the VISTA survey of the Magellanic Clouds system (VMC, Cioni et al. 2011).

Astronomy is in a golden age of discovery of the new, with a growingappreciation from astrophysics that physics has studied so far analmost insignificant fraction of reality. This golden age is enabledby technology, with next generation technologies approaching theGiga-euro/dollar investment level. This forces a strategic view of relativestrengths in the past, and strategies for future developments. Some ofthese may transcend traditional wavelength classifications.


One of the key aspects of the upcoming Ultra-Fast Flash Observatory (UFFO) pathfinder forGamma Ray Bursts (GRBs) identification is the UFFO Burst Alert & Trigger Telescope(UBAT). The scientific propose of UBAT is to detect and locate as fast as possible theGRBs in the sky. This is achieved by using a coded mask aperture camera scheme with a widefield of view (FOV) and selecting a X-ray detector of high quantum efficiency and largedetection area. This X-ray detector of high quantum efficiency and large detection area iscalled the UBAT detector. The UBAT detector consists of 48 × 48 Yttrium Oxyorthosilicate(YSO) scintillator crystal arrays and Multi Anode Photomultiplier Tubes (MAPMTs), analogelectronics equipped with ASIC chips, digital electronics equipped with Field ProgrammableGate Array (FPGA) chips, and a mechanical structure that supports all components of theUBAT detector. The total number of the pixels in the UBAT detector is 2304, and the totaleffective detection area is 191 cm2. We will present the design andconstruction, and performance of the UBAT detector including the responses of the UBATdetector to X-ray sources.

This article is intended to be used as an introduction to the problem of protoplanetary dust aggregation. The basic concept of dust aggregation and its description by Smoluchowski's equation are presented. Analytic solutions to Smoluchowski's equation are explored which show some characteristics of the more general solutions, such as self-similarity and scaling behavior. The physics of dust aggregation is treated through interaction forces between the particles and empirical data on sticking efficiencies and particle morphologies in dust-dust collisions. Aggregate morphologies are described by the fractal concept, and its implications for collision cross sections and collision velocities are discussed. Theoretical and experimental work on collision-induced restructuring and fragmentation of fractal and non-fractal dust aggregates is presented. Finally, the latest modelling approaches for protoplanetary dust growth are discussed.

Recent ultra-high precision observations of eclipsing binaries, especially data acquired by the Kepler satellite, have made accurate light curve modelling increasingly challenging but also more rewarding. In this contribution, we discuss low-amplitude signals in light curves that can now be used to derive physical information about eclipsing binaries but that were unaccessible before the Kepler era. A notable example is the detection of Doppler beaming, which leads to an increase in flux when a star moves towards the satellite and a decrease in flux when it moves away. Similarly, Rømer delays, or light travel time effects, also have to taken into account when modelling the supreme quality data that is now available. The detection of offsets between primary and secondary eclipse phases in binaries with extreme mass ratios, and the observation of Rømer delays in the signals of pulsators in binary stars, have allowed us to determine the orbits of several binaries without the need for spectroscopy. A third example of a small-scale effect that has to be taken into account when modelling specific binary systems, are lensing effects. A new binary light curve modelling code, PHOEBE 2.0, that takes all these effect into account is currently being developed.

We discuss the impact of the inclusionof both mass loss and rotation in massive star models at different metallicities.Rotation much improves the agreement between theory and observation. In particular rotational mixing allows to produce variations of the surface abundances already during the Main-Sequence phase. The changes of the surface abundances are more important when, for a given initial velocity, the initial mass increases, and/or the initial metallicity decreases. Alsothe observed high number of red supergiants at low metallicity can be accounted for by rotating stellar models, as well asthe observed variation of the number ratioof Wolf-Rayet to O-type stars as a function of the metallicity and the variation with themetallicity of the number ratio of type Ibc to type IIsupernovae. In all these questionsnon-rotating models give unsatisfactory fits. Rotating models can also give interestinginsights on questions as the origin of the Be stars, themechanisms responsible for thehuge mass loss rates undergone by the Luminous Blue Variables, the sources of primary nitrogen at low metallicity, the rotation rateof pulsars and the progenitors of the collapsars.

With the first light of COROT, the preparation of KEPLER and the future helioseismology spatial projects such as GOLF-NG, a coherent picture of the evolution of rotating stars from their birth to their death is needed. We describe here the modelling of the macroscopic transport of angular momentum and matter in stellar interiors that we have undertaken to reach this goal. First, we recall in detail the dynamical processes that are driving these mechanisms in rotating stars and the theoretical advances we have achieved. Then, we present our new results of numerical simulations which allow us to follow in 2D the secular hydrodynamics of rotating stars, assuming that anisotropic turbulence enforces a shellular rotation law. Finally, we show how this work is leading to a dynamical vision of the Hertzsprung-Russel diagram with the support of asteroseismology and helioseismology, seismic observables giving constraints on the modelling of the internal transport and mixing processes. In conclusion, we present the different processes that should be studied in the near future to improve our description of stellar radiation zones.

The accuracy with which it is possible to calculate theoretically the positions ofenergy levels and the low density (in frequency) of the grid on which opacity sampling is calculated bothlimit the accuracy with which the effect ofblends can be determined. For species such as Fe for which a large number of transitionsare involved in calculations, this leads to a small effect since, statistically, cancellations occur. However the effect can be large for an element such as Li with only a few transitions contributing to its radiative acceleration, grad(Li), at any given stellar radius. In particular, the Fe lines are shown to modify grad(Li) in and below the Fe convection zone but the modification depends on Fe level positions.This is analyzed quantitatively here using the OPAL data base. The grad(Li) are found to be uncertain by a factor of 2 in Pop I stars but of 1.03 in Pop II stars.