I review the current state of knowledge regarding disk accretion in young brown dwarfs (BDs), and the interaction of the disk with the central object. In particular, I discuss (1) observations of accretion/outflow phenomena in BDs; (2) techniques for measuring accretion rates (Ṁacc ); (3) the dependence of Ṁacc on the central mass from stars to brown dwarfs; (4) the temporal evolution of Ṁacc ;...

In this lecture the basic theory of accretion disks is introduced, with emphasis on aspects relevant for X-ray binaries and Cataclysmic Variables.

Two pseudo-Newtonian potentials, which approximate the angular and epicyclic frequencies of the relativistic accretion disk around rotating (and counter rotating) compact objects, are presented. One of them, the Logarithmically Modified Potential, is a better approximation for the frequencies while the other, the Second-order Expanded potential, also reproduces the specific energy for circular ...

The disk-wind scenario for the broad-line region (BLR) and toroidal obscuration in active galactic nuclei predicts the disappearance of the BLR at low luminosities. In accordance with the model predictions, data from a nearly complete sample of nearby AGNs show that the BLR disappears at luminosities lower than 5 × 10 (M/107M⊙) 2/3 erg s, where M is the black hole mass. The radiative efficiency...

The dynamics of accretion onto a schwarzschild black hole is studied using Paczynski-Wiita pseudo newtonian potential. Steady state solution of the flow equations is obtained using thin disc approximation, including the effect of bremsstrahlung cooling in the energy equation. The topology of transonic solutions are got and the conditions for shock formation (Rankine-Hugoniot conditions) are che...

In this paper, the spectra of the persistent emission from anomalous X-ray pulsars (AXPs) and their variation with spin-down rate Ω̇ is considered. Firstly, based on an accretion-powered model, the influences of both magnetic field and mass accretion rate on the spectra properties of AXPs are addressed. Subsequently, the relation between the spectral property of AXPs and mass accretion rate Ṁ is...

We present numerical hydrodynamical modeling of the effects of a giant planet or brown dwarf companion orbiting within the extended atmosphere and wind formation zone of an approximately solar-mass Mira variable star. The large-scale, timedependent accretion flows within the radially oscillating and outflowing circumstellar gas around Miras are related to Bondi-Hoyle-Lyttleton flows, but have n...

We consider the radiative feedback processes that operate during the formation of the first stars, including the photodissociation of H2, Lyman-α radiation pressure, formation and expansion of an H II region, and disk photoevaporation. These processes may inhibit continued accretion once the stellar mass has reached a critical value, and we evaluate this mass separately for each process. Photod...

We study accretion induced collapse of magnetized white dwarfs as an origin of millisecond pulsars. We apply magnetized accretion disk models to the pre-collapse accreting magnetic white dwarfs and calculate the white dwarf spin evolution. If the pulsar magnetic field results solely from the flux-frozen fossil white dwarf field, a typical millisecond pulsar is born with a field strength ∼ 10 − ...

At present, there are two scenarios for the formation of massive stars: 1) The accretion scenario and 2) The coalescence scenario, which implies the merging of intermediate mass stars. We examine here some properties of the first one. Radio and IR observations by Churchwell (1999) and Henning et al. (2000) of mass outflows around massive Pre-Main Sequence (PMS) stars show an increase by several...