Disk-Magnetosphere Interaction and Outflows: Conical Winds and Axial Jets

We investigate outflows from the disk-magnetosphere boundary of rotating magnetized stars in cases where the magnetic field of a star is bunched into an X-type configuration using axisymmetric and full 3D MHD simulations. Such configuration appears if viscosity in the disk is larger than diffusivity, or if the accretion rate in the disk is enhanced. Conical outflows flow from the inner edge of the disk to a narrow shell with an opening angle 30-45 degrees. Outflows carry 0.1-0.3 of the disk mass and part of the disk's angular momentum outward. Conical outflows appear around stars of different periods, however in case of stars in the "propeller" regime, an additional - much faster component appears: an axial jet, where matter is accelerated up to very high velocities at small distances from the star by magnetic pressure force above the surface of the star. Exploratory 3D simulations show that conical outflows are symmetric about rotational axis of the disk even if magnetic dipole is significantly misaligned. Conical outflows and axial jets may appear in different types of young stars including Class I young stars, classical T Tauri stars, and EXors.Comment: Invited review, conference proceedings of the meeting "Protostellar Jets in Context", 7-12 July 2008, island of Rhodes, Greece; editors: profs. Tom Ray and Kanaris Tsinganos; 10 pages, 10 figures, see animations at http://www.astro.cornell.edu/~romanova/conical.htm and http://www.astro.cornell.edu/~romanova/propeller.ht

Models of Star-Planet Magnetic Interaction

Magnetic interactions between a planet and its environment are known to lead to phenomena such as aurorae and shocks in the solar system. The large number of close-in exoplanets that were discovered triggered a renewed interest in magnetic interactions in star-planet systems. Multiple other magnetic effects were then unveiled, such as planet inflation or heating, planet migration, planetary material escape, and even modification of the host star properties. We review here the recent efforts in modelling and understanding magnetic interactions between stars and planets in the context of compact systems. We first provide simple estimates of the effects of magnetic interactions and then detail analytical and numerical models for different representative scenarii. We finally lay out a series of future developments that are needed today to better understand and constrain these fascinating interactions.Comment: 23 pages, 10 figures, accepted as a chapter in the Handbook of Exoplanet

Stellar Coronal and Wind Models: Impact on Exoplanets

Surface magnetism is believed to be the main driver of coronal heating and stellar wind acceleration. Coronae are believed to be formed by plasma confined in closed magnetic coronal loops of the stars, with winds mainly originating in open magnetic field line regions. In this Chapter, we review some basic properties of stellar coronae and winds and present some existing models. In the last part of this Chapter, we discuss the effects of coronal winds on exoplanets.Comment: Chapter published in the "Handbook of Exoplanets", Editors in Chief: Juan Antonio Belmonte and Hans Deeg, Section Editor: Nuccio Lanza. Springer Reference Work

Dynamics of Disks and Warps

This chapter reviews theoretical work on the stellar dynamics of galaxy disks. All the known collective global instabilities are identified, and their mechanisms described in terms of local wave mechanics. A detailed discussion of warps and other bending waves is also given. The structure of bars in galaxies, and their effect on galaxy evolution, is now reasonably well understood, but there is still no convincing explanation for their origin and frequency. Spiral patterns have long presented a special challenge, and ideas and recent developments are reviewed. Other topics include scattering of disk stars and the survival of thin disks.Comment: Chapter accepted to appear in Planets, Stars and Stellar Systems, vol 5, ed G. Gilmore. 32 pages, 17 figures. Includes minor corrections made in proofs. Uses emulateapj.st

eIF2B bodies and their role in the integrated stress response

Eukaryotic initiation factor 2 (eIF2) is a G protein comprised of 3 subunits (α, β and γ) that is critical for translation. It is tightly regulated in the integrated stress response (ISR) via the phosphorylation of its α subunit following the induction of cellular stress. In its phosphorylated form eIF2α inhibits the guanine nucleotide exchange factor (GEF) eukaryotic initiation factor 2B (eIF2B), resulting in the attenuation of global protein synthesis. eIF2B is a multisubunit protein comprised of regulatory and catalytic subunits. The catalytic subunits are responsible for the GEF activity whereas the regulatory subunits mediate inhibition by phosphorylated eIF2α. Through studying the localisation of eIF2B subunits, cytoplasmic eIF2B bodies were identified in mammalian cells. A relationship between body size and the eIF2B subunits localising to them exists; larger bodies contain all subunits and smaller bodies contain predominantly catalytic subunits. eIF2 localises to eIF2B bodies and moves through these bodies in a manner that correlates with eIF2B GEF activity. Upon the induction of cellular stress phosphorylated eIF2α localises predominately to larger eIF2B bodies which contain regulatory subunits and a decrease in the movement of eIF2 through these bodies is observed. Interestingly, drugs that inhibit the ISR can rescue the movement of eIF2 through these eIF2B bodies, in a manner that correlates to cellular levels of phosphorylated eIF2α. In contrast, smaller eIF2B bodies, which contain predominately catalytic subunits, show increased movement of eIF2 during cellular stress. This increase in movement is accompanied by an increase in the localisation of eIF2Bδ to these bodies, suggesting the formation of a novel eIF2B subcomplex. This response is mimicked by ISR-inhibiting drugs, providing insight into their potential mechanisms of action. This study provides the first evidence that the composition and function of mammalian eIF2B bodies is regulated by the ISR and the drugs that control it