The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, x-ray binaries, and gamma-ray bursts. Unambiguous constraints on the fraction of massive stars affected by binary interaction were lacking. We simultaneously measured all relevant binary characteristics in a sample of Galactic massive O stars and quantified the frequency and nature of binary interactions. More than 70% of all massive stars will exchange mass with a companion, leading to a binary merger in one-third of the cases. These numbers greatly exceed previous estimates and imply that binary interaction dominates the evolution of massive stars, with implications for populations of massive stars and their supernovae.

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Binary Interaction Dominates the Evolution of Massive Stars

We report new precision measurements of the properties of our Galaxy's supermassive black hole. Based on astrometric (1995-2007) and radial velocity (RV; 2000-2007) measurements from the W. M. Keck 10m telescopes, a fully unconstrained Keplerian orbit for the short-period star S0-2 provides values for the distance (R_0) of 8.0±0.6 kpc, the enclosed mass (M_(bh)) of 4.1±0.6x10^6 M☉ and the black hole's RV, which is consistent with zero with 30 km/s uncertainty. If the black hole is assumed to be at rest with respect to the Galaxy (e. g., has no massive companion to induce motion), we can further constrain the fit, obtaining R_0 = 8.4±0.4kpc and M_(bh) 4.5±0.4x10^6 M☉. More complex models constrain the extended dark mass distribution to be less than 3-4x10^5 M☉ within 0.01 pc, ~100 times higher than predictions from stellar and stellar remnant models. For all models, we identify transient astrometric shifts from source confusion (up to 5 times the astrometric error) and the assumptions regarding the black hole's radial motion as previously unrecognized limitations on orbital accuracy and the usefulness of fainter stars. Future astrometric and RV observations will remedy these effects. Our estimates of R_0 and the Galaxy's local rotation speed, which it is derived from combining R_0 with the apparent proper motion of Sgr A*, (θ_0 = 229±18 km/s), are compatible with measurements made using other methods. The increased black hole mass found in this study, compared to that determined using projected mass estimators, implies a longer period for the innermost stable orbit, longer resonant relaxation timescales for stars in the vicinity of the black hole and a better agreement with the M_(bh)-σ relation.

/pdf/measuring-distance-and-properties-of-the-milky-way-s-central-533964sq63.pdf

Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits

Flattened, rotating disks of cool dust and gas extending for tens to hundreds of astronomical units are found around almost all low-mass stars shortly after their birth. These disks generally persist for several million years, during which time some material accretes onto the star, some is lost through outflows and photoevaporation, and some condenses into centimeter- and larger-sized bodies or planetesimals. Through observations mainly at IR through millimeter wavelengths, we can determine how common disks are at different ages; measure basic properties including mass, size, structure, and composition; and follow their varied evolutionary pathways. In this way, we see the first steps toward exoplanet formation and learn about the origins of the Solar System. This review addresses observations of the outer parts, beyond 1 AU, of protoplanetary disks with a focus on recent IR and (sub)millimeter results and an eye to the promise of new facilities in the immediate future.

http://www.ifa.hawaii.edu/users/cieza/WC2011_ARAA.pdf

Protoplanetary Disks and Their Evolution

The Galactic Center is an excellent laboratory for studying phenomena and physical processes that may be occurring in many other galactic nuclei. The Center of our Milky Way is by far the closest galactic nucleus, and observations with exquisite resolution and sensitivity cover 18 orders of magnitude in energy of electromagnetic radiation. Theoretical simulations have become increasingly more powerful in explaining these measurements. This review summarizes the recent progress in observational and theoretical work on the central parsec, with a strong emphasis on the current empirical evidence for a central massive black hole and on the processes in the surrounding dense nuclear star cluster. We present the current evidence, from the analysis of the orbits of more than two dozen stars and from the measurements of the size and motion of the central compact radio source, Sgr A*, that this radio source must be a massive black hole of about 4.4 \times 1e6 Msun, beyond any reasonable doubt. We report what is known about the structure and evolution of the dense nuclear star cluster surrounding this black hole, including the astounding fact that stars have been forming in the vicinity of Sgr A* recently, apparently with a top-heavy stellar mass function. We discuss a dense concentration of fainter stars centered in the immediate vicinity of the massive black hole, three of which have orbital peri-bothroi of less than one light day. This 'S-star cluster' appears to consist mainly of young early-type stars, in contrast to the predicted properties of an equilibrium 'stellar cusp' around a black hole. This constitutes a remarkable and presently not fully understood 'paradox of youth'. We also summarize what is known about the emission properties of the accreting gas onto Sgr A* and how this emission is beginning to delineate the physical properties in the hot accretion zone around the event horizon.

The galactic center massive black hole and nuclear star cluster

Young massive clusters are dense aggregates of young stars that form the fundamental building blocks of galaxies. Several examples exist in the Milky Way Galaxy and the Local Group, but they are particularly abundant in starburst and interacting galaxies. The few young massive clusters that are close enough to resolve are of prime interest for studying the stellar mass function and the ecological interplay between stellar evolution and stellar dynamics. The distant unresolved clusters may be effectively used to study the star-cluster mass function, and they provide excellent constraints on the formation mechanisms of young cluster populations. Young massive clusters are expected to be the nurseries for many unusual objects, including a wide range of exotic stars and binaries. So far only a few such objects have been found in young massive clusters, although their older cousins, the globular clusters, are unusually rich in stellar exotica. In this review we focus on star clusters younger than $\sim100$ Myr, more than a few current crossing times old, and more massive than $\sim10^4$ \Msun, irrespective of cluster size or environment. We describe the global properties of the currently known young massive star clusters in the Local Group and beyond, and discuss the state of the art in observations and dynamical modeling of these systems. In order to make this review readable by observers, theorists, and computational astrophysicists, we also review the cross-disciplinary terminology.

/pdf/young-massive-star-clusters-1mlfusxprp.pdf

Young Massive Star Clusters

By matching infrared-selected, massive young stellar objects (MYSOs) and compact HII regions in the RMS survey to massive clumps found in the submillimetre ATLASGAL survey, we have identified ∼1000 embedded young massive stars between 280 ◦ <l< 350 ◦ and 10 ◦ <l< 60 ◦ with| b|< 1.5 ◦ . Combined with an existing sample of radio-selected methanol masers and compact HII regions, the result is a catalogue of∼1700 massive stars embedded within∼1300 clumps located across the inner Galaxy, containing three observationally distinct subsamples, methanol-maser, MYSO and HII-region associations, covering the most important tracers of massive star formation, thought to represent key stages of evolution. We find that massive star formation is strongly correlated with the regions of highest column density in spherical, centrally condensed clumps. We find no sig nificant di fferences between the three samples in clump structure or the relative location of the embedded stars, which suggests that the structure of a clump is set before the onset of s tar formation, and changes little as the embedded object evolves towards the main sequence. There is a strong linear correlation between clump mass and bolometric luminosity, with the most massive stars forming in the most massive clumps. We find that the MYSO and HII-regio n subsamples are likely to cover a similar range of evolutionary stages and that the majority are near the end of their main accretion phase. We find few infrared-bright MYSOs asso ciated with the most massive clumps, probably due to very short pre-main sequence lifetimes in the most luminous sources.

/pdf/atlasgal-towards-a-complete-sample-of-massive-star-forming-w56ll09cyr.pdf

ATLASGAL — towards a complete sample of massive star forming clumps ⋆

Aims. Most stars do not form in isolation but as part of a cluster comprising anywhere between a few dozen to several million stars with stellar densities ranging from 0.01 to several 10 5 Mpc −3 . The majority of these clusters dissolve within 20 Myr. The general assumption is that clusters are born more or less over this entire density range. Methods. A new analysis of cluster observations is presented. Results. It demonstrates that, in fact, clustered star formation works under surprisingly tight constraints with respect to cluster size and density. Conclusions. The observed multitude of cluster densities simply results from snapshots of two sequences evolving in time along pre-defined tracks in the density-radius plane. This implies that the cluster size can actually be used to determine its age.

/pdf/universality-of-young-cluster-sequences-3luybrcqm3.pdf

Universality of young cluster sequences

N-Particle-Simulations of Dust Growth: I. Growth Driven by Brownian Motion

1. Introduction 2. Basic structure of the hierarchical tree method 3. Open boundary problems 4. Optimisation of hierarchical tree codes 5. Periodic boundary conditions 6. Periodic boundary problems 7. The fast multipole method Appendices.

Many-Body Tree Methods in Physics

FUNDAMENTALS OF INERTIAL CONFINEMENT FUSION What happens in the sun? Can one produce energy on Earth like in the sun? The two approaches - Magnetic vs. Inertial Confinement Stages in inertial confinement fusion Outline of the Book LASER DRIVERS FOR ICF Basics of laser physics Lasers for ICF applications Nd-glass lasers for ICF Alternatives to Nd-glass lasers BASIC PLASMA PHYSICS Debye length and plasma frequency Particle description Fluid description Plasma waves Plasma heating The ponderomotive force Shock waves Equation of state for dense plasmas ABSORPTION OF LASER LIGHT Coupling of the laser energy to the target Inverse Bremsstrahlung absorption Resonance absorption Parametric instabilities Indirect drive: coupling laser energy to the hohlraum ii Energy transport HYDRODYNAMIC COMPRESSION AND BURN Implosion of solid target Foil target Rocket Model and Ablation Compression wave - Shock front - Shock wave Compression phase Spherically convergent shock waves Isentropic compression Multiple shocks Burn RAYLEIGH-TAYLOR INSTABILITIES Basic concept RT in the ablation phase RT instabilities in the deceleration phase Consequences for target design Idealized RT instabilities vs. ICF situation Other dynamic instabilities ENERGY REQUIREMENTS AND GAIN Power balance Energy requirements Gain TARGETS Basic considerations for target design Direct and indirect-drive targets Direct-drive targets Indirect-drive targets Target fabrication ICF POWER PLANT Power plant design Plant efficiency Target chamber Target fabrication for power plant Safety issues HEAVY-ION DRIVEN FUSION Heavy-ion drivers Ion beam energy deposition Target design for heavy-ion drivers Heavy-ion power plant Light-ion drivers FAST IGNITOR Fast-ignitor vs. hot-spot concept Hole boring or laser cone guiding? O_-center ignition Status and Future ABC OF ICF APPENDIX Predicted energy consumption and resources Constants Formulae Abbreviations Constants of the semiempirical mass formula List of Codes used for Numerical Modelling References Bibliography

Susanne Pfalzner

Papers

ATLASGAL — towards a complete sample of massive star forming clumps ⋆

Universality of young cluster sequences

N-Particle-Simulations of Dust Growth: I. Growth Driven by Brownian Motion

Many-Body Tree Methods in Physics

An Introduction to Inertial Confinement Fusion