Reviews latest star-disk interaction region in young stars for graduate students and researchers.

A complete record of the formal organisational and administrative proceedings of the XXVII General Assembly of the International Astronomical Union.

The star formation process usually proceeds with protoplanetary disks. These disks contain a mixture of gas, accounting for 99 % of the disk mass, and of solid particles called dust grains (1 % of the disk mass). These grains, initially at sub-micro metric sizes, gradually coagulate, grow, and potentially allow for the formation of planets about the star.The study of the dust and molecular composition of young disks is fundamental to constraint the physical and chemical initial conditions of planetary formation and the origins of the chemical composition of the planetary cores.The goal of this thesis was to build state-of-the-art models of typical young disks consisting of gas and of a population of grains of multiple sizes, then, in a new approach, to test with the use of numerical simulations the implication of the size and temperature distributions on the chemical evolution of disks.To achieve this, we have coupled the 3D Monte-Carlo radiative transfer code POLARIS to the time-dependent gas-grain code NAUTILUS. The radiative transfer code allowed us to finely compute the grain temperature as a function of the size and location as well as the UV flux within the disk. The gas-grain code was able to simulate the evolution of the chemical abundances in our disk models. Moreover, the computation of the UV flux by POLARIS coupled to a set of molecular cross-sections extracted from a comprehensive database allowed us to compute as a function of the frequency the rates of molecular photoabsorption, photodissociation, and photoionization.

Is the Sun and its planetary system special? How did the Solar system form? Are there similar systems in the Galaxy? How common are habitable planets? What processes take place in the early life of stars and in their surrounding circumstellar disks that could impact whether life emerges or not? This book is based on the lectures by Philip Armitage and Wilhelm Kley presented at 45th Saas-Fee Advanced Course „From Protoplanetary Disks to Planet Formation“ of the Swiss Society for Astrophysics and Astronomy. The first part deals with the physical processes occurring in proto-planetary disks starting with the observational context, structure and evolution of the proto-planetary disk, turbulence and accretion, particle evolution and structure formation. The second part covers planet formation and disk-planet interactions. This includes in detail dust and planetesimal formation, growth to protoplanets, terrestrial planet formation, giant planet formation, migration of planets, multi-planet systems and circumbinary planets. As Saas-Fee advanced course this book offers PhD students an in-depth treatment of the topic enabling them to enter on a research project in the field.

Recent discoveries of extrasolar planets and new direct evidence for protoplanetary disks around young stars have had a major impact on our understanding of star and planet formation. This volume provides a thorough, up-to-date, and concise overview of the physical processes involved in the formation of stars and their surrounding disks. The book traces the story of star formation from the fragmentation of cold molecular gas clouds, through the formation of protostars and rotating dusty disks to the subsequent accretion of material onto the central star. Lee Hartmann integrates state-of-the-art theoretical models with recent observations, highlighting important problems that remain to be solved.

Young stars have discs and are usually found in binary or multiple systems. In this thesis, we are interested in (a) the dynamical evolution of young stars in a multiple system and (b) the evolution of a circumprimary disc in a misaligned binary system. In a young multiple star system a close encounter between two stars may result in either an ejection of the least massive star or a collision. We perform N-body simulations to investigate the frequencies of both ejections and collisions in young coplanar triple systems. We find that the chance of a collision among the members is generally high, at least a few per cent in most configurations. From this finding, it is possible that collisions among young stars are responsible for some uncommon features found in young star systems such as an apparent non-coevality of members. The evolution of a circum primary disc in a misaligned binary system is, in several ways, affected by the companion. Dynamically. the disc is tilted by tidal effects from the companion. We perform SPH simulations to study the tilting process of the disc. We find that the disc precesses and, in most cases, is brought towards alignment with the binary orbit. The key findings include: (a) a significantly misaligned disc may not be aligned with the binary orbit within an estimated disc lifetime (~l06yr) and (b) the dispersal timescale of a misaligned disc could be of order the precession period of the disc. These findings would constrain the formation of planets in misaligned binary systems. For an alignment process that is driven by an alignment torque(s), our semi-analytic approach shows that the torque is mainly proportional to the change in the binary semi-major axis. In this work, we suggest a possible formation scenario for a spin-orbit misaligned planetary system around a single star that the system could form from a disc in a misaligned binary system which is later disrupted by dynamical interactions with other star in the cluster. Additionally, we also perform SPH simulations to study several properties of low-mass discs. We investigate the influence of resolution, temperature structure, and artificial viscosity on the stability of those low-mass discs. We find that our low-mass discs are all stable against gravitational instabilities.