It is now well established that young brown dwarfs harbor accretion disks –and thus undergo a T Tauri phase– similar to their low-mass stellar counterparts. The supporting evidence includes infrared and millimeter observations of the dust component as well as optical and infrared spectra with signatures of gas accretion and outflow. Recent findings suggest that disks are common even around young planetary mass objects. The ubiquity of circum-sub-stellar disks not only hints at a common formation scenario for PMOs, brown dwarfs and stars, but also offers a new regime for investigating processes such as episodic accretion, grain growth and disk clearing.

Diffuse gas in the Galaxy is observed to exist as cold (T ~ 100 K) neutral atomic gas (CNM) and warm neutral atomic (T ~ 8000 K) gas (WNM). In addition to these “thermal” phases, gas can also exist as warm (T ~ 8000 K) ionized gas, cold (T ~ 10 K) molecular gas and in warm (T ~ 100 - 500 K) interface regions or Photodissociation Regions (PDRs) on the surfaces of molecular clouds. The same chemical and thermal processes that dominate in the PDRs associated with molecular clouds are also at work in the diffuse neutral gas. Two additional “phases” are gas associated with GMCs that has H2 but no or little CO, and short lived or transient phases such as shocks, shears, and turbulence. I will first review the different gas phases in the Galaxy, their physical conditions and their dominant cooling lines. I will also discuss the observations and theoretical modeling in support of turbulence versus thermal instability as the driving force in producing the “thermal” gas phase distributions. Rough estimates for the distribution of phases in the Galaxy and the origin of the dominant emission lines has been conducted by previous telescopes (e.g., COBE, BICE) but with low velocity and low spectral resolution. The distribution and mass of the various gas phases is important for sorting out the role of SN in setting ISM pressures and in driving ISM turbulence. In addition, understanding the Galactic phase distribution is important in interpreting observations of extragalactic systems in which beams encompass several emission components. I will review the potential for future observations by e.g., STO, SOFIA, and Herschel to detect and separate phases in Galactic and extragalactic systems.

We review our knowledge about the spiral structure of the disk of our Galaxy using tracers of star formation. These tracers reveal a 4-arm picture of the Galaxy.

Connections between observations of the lithium abundance in various types of red giants and stellar evolution are discussed here. The emphasis is on three main topics; 1) the depletion of Li as stars ascend the red giant branch for the first time, 2) the synthesis of 7Li in luminous and massive asymptotic giant branch stars via the mechanism of hot-bottom burning, and 3) the possible multiple sources of excess Li abundances found in a tiny fraction of various types of G and K giants.

Oscillation frequencies were determined for a number of rapidly rotating main sequence stars. However, real seismic probing is still ahead of us. I review here tools that we have for modeling pulsation in rotating stars and their potential application to seismic sounding.

Microwave and far infrared (FIR) spectra of atoms and molecules are in general more sensitive to the variation of the fundamental constants than optical spectra. For example, FIR transitions between levels of the ground state multiplet 3PJ of Carbon-like ions are sensitive to α-variation, (Levshakov et al. (2008)). Moreover, sensitivities of the transitions (1-0) and (2-1) are different, (Kozlov et al. (2008)). This allows to study α-variation by comparing apparent redshifts for these two transitions of the same ion and significantly reduce systematic errors from the Doppler noise.

We recall the concepts and nomenclature associated with the IAU 2000 definition of UT1 as function of the Earth rotation angle (ERA). We comment on the complications that arise when UT1 is regarded as both an angle and a time scale. We review the IAU 2006 expressions for the position of the celestial intermediate origin (CIO) and the equation of the origins, and the associated CIO and equinox based procedures for the celestial-to-terrestrial transformation.

The atmospheres of Brown Dwarfs (BDs) are the site of molecular opacities and cloud formation, and control their cooling rate, radius and brightness evolution. Brown dwarfs evolve from stellar-like properties (magnetic activity, spots, flares, mass loss) to planet-like properties (electron degeneracy of the interior, cloud formation, dynamical molecular transport) while retaining, due to their fully convective interior, larger rotational velocities (≤ 30 km/s i.e. P < 4 hrs versus 11 hrs for Jupiter). Model atmospheres treating all this complexity are therefore essential to understand the evolution properties, and to interpret the observations of these objects. While the pure gas-phase based NextGen model atmospheres (Allard et al. 1997, Hauschildt et al. 1999) have allowed the understanding of the several populations of Very Low Mass Stars (VLMs), the AMES-Dusty models (Allard et al. 2001) based on equilibrium chemistry have reproduced some near-IR photometric properties of M and L-type brown dwarfs, and played a key role in the determination of the mass of brown dwarfs and Planetary Mass Objects (PMOs) in the eld and in young stellar clusters. In this paper, we present a new model atmosphere grid for VLMs, BDs, PMOs named BT-Settl, which includes a cloud model and dynamical molecular transport based on mixing information from 2D Radiation Hydrodynamic (RHD) simulations (Freytag et al. 2009). We also present the status of our 3D RHD simulations including rotation (Coriolis forces) of a cube on the surface of a brown dwarf. The BT-Settl model atmosphere grid will be available shortly via the Phoenix web simulator (http://phoenix.ens-lyon.fr/simulator/).

We review the statistical properties of stars and brown dwarfs obtained from the first hydrodynamical simulation of star cluster formation to produce more than a thousand stars and brown dwarfs while simultaneously resolving the lowest mass brown dwarfs (those with masses set by the opacity limit for fragmentation), binaries with separations down to ~ 1 AU, and discs with radii greater than ~ 10 AU. In particular, we present the eccentricity distribution of the calculation's very-low-mass and brown dwarf binaries which has not been previously published.

Efforts to determine the primordial helium abundance via observations of metal poor HII regions have been limited by significant uncertainties. Because of a degeneracy between the solutions for density and temperature, the precision of the helium abundance determinations is limited. Spectra from the literature are used to show the effects of new atomic data and to demonstrate the challenges of determining precise He abundances. Several suggestions are made for meeting these challenges.

This article summarises the subject matter of Special Session 3 at IAU General Assembly XXVII in Rio de Janeiro, Brazil, which took place on August 6-7, 2009. In it, we overview the state of Astronomy in Antarctica as it is in 2009. Significant astronomical activity is now taking place at four stations on the Antarctic plateau (South Pole, Domes A, C & F), as well as at the coastal station of McMurdo.

Thermohaline mixing has been recently identified as the dominating process that governs the photospheric composition of low-mass bright giant stars (Charbonnel & Zahn 2007a). Here we present the predictions of stellar models computed with the code STAREVOL that takes into account this mechanism together with rotational mixing and atomic diffusion. We compare our theorical predictions with recent observations and discuss how the corresponding yields for 3He are compatible with the observed behaviour of this light element in our Galaxy.

Large-scale magnetic fields in the Galactic disk have been revealed by distributions of pulsar rotation measures (RMs) and Zeeman splitting data of masers in star formation regions, which have several reversals in arm and interarm regions. Magnetic fields in the Galactic halo are reflected by the antisymmetric sky distribution of RMs of extragalactic radio sources, which have azimuthal structure with reversed directions below and above the Galactic plane. Large-scale magnetic fields in the Galactic center probably have a poloidal and toroidal structure.

The influence of post-Newtonian effects in the rotation of Earth on UT1 are investigated and found to be negligible.

Atmospheric parameters and Li abundances have been determined for 162 stars observed at high resolution, high signal to noise ratio with the ELODIE echelle spectrograph (OHP, France). Among them, about 70 stars are active stars with a large fraction of BY Dra type stars. For all stars, rotational velocities were obtained with a calibration of the cross-correlation function, effective temperatures by the line depth ratio method, surface gravities by the parallaxe method and by the ionization balance of iron. The frequency of stars with observed lithium is significantly higher in active stars than in non active stars. Among active stars, no clear correlation has been found between different indicators of activity for our sample stars, but some correlation of an index R′H K and vsini is observed.

Early-type galaxies (ETGs) satisfy a now classic scaling relation Re ∝ σ1.2eI−0.8e, the Fundamental Plane (FP; Djorgovski & Davis 1987; Dressler et al. 1987), between their size, stellar velocity dispersion and mean surface brightness. A significant effort has been devoted in the past twenty years to try to understand why the coefficients of the relation are not the ones predicted by the virial theorem Re ∝ σ2eI−1e.

We present new maps of the distribution of both dust and stars across the Galactic disk, based largely on an improved analysis of 2MASS and Spitzer-IRAC data. The infrared extinction law is rederived throughout the disk and we found strong longitudinal variations in both diffuse and dense environments that we incorporate in our analysis.

Stellar rotation at young ages: new results from Corot's Angular momentum is one of the driving forces in the early evolution of stars. Issues such as the coupling between the star and the accretion disk (the so-called disk regulation paradigm), are traced by the evolution of rotational momentum, but affect the star-forming process as a whole. One of the features observed in star-forming regions (e.g. ONC and NGC 2264) of age between 1 and few Myr, for masses above 0.25 solar masses, is a bimodality of the rotational period distribution, with a peak around 1 day and the other at around 4 to 7 days. This bimodality has been interpreted as the smoking gun of the disk-locking mechanism (with the fast rotators having lost their disk and the slow ones still being regulated by their disks).

Observations of light elements in hot massive stars are limited to few transitions of boron in the satellite-ultraviolet; lithium and beryllium are not observable at all. But because of its high sensitivity to the effects of rotational mixing, boron abundance determinations in massive stars have excelled as the definite test for evolutionary models with rotation. In this paper the observational evidence for rotational mixing in massive stars is reviewed and alternative interpretations are discussed.

Historically, low luminosity stars have attracted very little attention, in part because they are difficult to see except with large telescopes, however, by neglecting to study them we are leaving out the vast majority of stars in the Universe. Low mass stars evolve very slowly, it takes them trillions of years to burn their hydrogen, after which, they just turn into a He white dwarf, without ever going through the red giant phase. This lack of observable evolution partly explains the lack of interest in them. The search for the “missing mass” in the galactic plane turned things around and during the 60s and 70s the search for large M/L objects placed M-dwarfs and cool WDs among objects of astrophysical interest. New fields of astronomical research, like BDs and exoplanets appeared as spin-offs from efforts to find the “missing mass”. The search for halo white dwarfs, believed to be responsible for the observed microlensing events, is pursued by several groups. The progress in these last few years has been tremendous, here I present highlights some of the great successes in the field and point to some of the still unsolved issues.