Related papers: Variability of young stellar objects: accretion, d…
Variability is a defining characteristic of young stellar systems, and optical variability has been heavily studied to select and characterize the photospheric properties of young stars. In recent years, multi-epoch observations sampling a…
In this work the most spectacular phenomena occurring during the formation of a star are briefly reviewed: accretion through a rotating disc of matter and outflow through the poles of the new stellar object. Magnetic fields have been…
Young stars exhibit short-term photometric variability caused by mass accretion events from circumstellar disks, the presence of dusty warps within the inner disks, starspots that rotate across the stellar surfaces, and flares. Long-term…
Variable accretion in young stellar objects reveals itself photometrically and spectroscopically over a continuum of timescales and amplitudes. Most dramatic are the large outbursts (e.g., FU Ori, V1647 Ori, and EX Lup type events), but…
Young stars show a variety of highly energetic phenomena, from accretion and outflow processes to hot coronal plasmas confined in their outer atmosphere, all regulated by the intense stellar magnetic fields. Many aspects on each of these…
Variability studies are an important tool to investigate key properties of stars and brown dwarfs. From photometric monitoring we are able to obtain information about rotation and magnetic activity, which are expected to change in the mass…
An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties…
Young stars accrete mass from a circumstellar disk, but at the same time disk and star eject outflows and jets. These outflows have an onion-like structure where the innermost and fastest layers are surrounded by increasingly lower velocity…
Recent observations have suggested that circumstellar disks may commonly form around young stellar objects. Although the formation of circumstellar disks can be a natural result of the conservation of angular momentum in the parent cloud,…
A detailed understanding of the physics of star and planet formation requires study of individual objects as well as statistical assessment of global properties and evolutionary trends. Observational investigations of circumstellar material…
The origin of disks surrounding young stars has direct implications for our understanding of the formation of planetary systems. In the interstellar clouds from which star form, angular momentum is regulated by magnetic fields, preventing…
Young stars exhibit variability due to changes in the gas accretion rate onto them, an effect that should be quite significant in the early stages of their formation. As protostars are embedded within their natal cloud, this variability may…
Space observatories have provided unprecedented depictions of the many variability behaviors typical of low-mass, young stars. However, those studies have so far largely omitted more massive objects ($\sim$2 $M_\odot$ to 4-5 $M_\odot$), and…
This summary talk aims at highlighting some of the remaining open issues regarding the physics of the magnetospheric accretion/ejection process in young stellar objects (YSOs). It lists a number of questions related to YSOs magnetic fields…
Young stars and planetary systems form in molecular clouds. For classical T Tauri stars (CTTS, F-K type precursors) the accretion disk does not reach down to the central star, but it is truncated near the co-rotation radius. The inner edge…
According to the magnetospheric accretion scenario, young low-mass stars are surrounded by circumstellar disks which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to…
Mass loss and variability are two linked, fundamental properties of evolved stars. In this paper I review our current understanding of these processes, with a particular focus on how observations and models are used to constrain reliable…
Interaction with possible fallback material, along with the magnetic fields and rotation rates at birth should determine the fates and categories of young neutron stars. This paper addresses some issues related to pure or hybrid accretion…
Context. A characteristic feature of young stellar objects is their variability, which is caused by a variety of different physical processes. High-resolution interferometric observations in the near- and mid-infrared wavelength ranges…
There is a growing number of observational indicators for the presence of bipolar outflows in massive, young stellar objects that are still accreting mass as part of their formation process. In particular, there is evidence that the…