Using Spitzer Space Telescope photometric observations of the eclipsing, interacting binary WZ Sge, we have discovered that the accretion disk is far more complex than previously believed. Our 4.5 and 8 micron time series observations reveal that the well known gaseous accretion disk is surrounded by an asymmetric disk of dusty material with a radius approximately 15 times larger than the gaseo...

Quasi-periodic oscillations (QPOs) in the X-ray lightcurves of accreting neutron star and black hole binaries have been widely interpreted as being due to standing wave modes in accretion disks. These disks are thought to be highly turbulent due to the magnetorotational instability (MRI). We study wave excitation by MRI turbulence in the shearing box geometry. We demonstrate that axisymmetric s...

We present a high spatial resolution submillimeter continuum survey of 24 circumstellar disks in the Taurus-Auriga and Ophiuchus-Scorpius star formation regions using the SMA. In the context of a simple model, we use broadband spectral energy distributions and submillimeter visibilities to derive constraints on some basic parameters that describe the structure of these disks. For the typical di...

The structure of magnetic fields within protostellar disks may be studied via polarimetry provided that grains are aligned in respect to magnetic field within the disks. We explore alignment of dust grains by radiative torque in T Tauri disks and provide predictions for polarized emission for disks viewed at different wavelengths and viewing angles. We show that the alignment is especially effi...

We present a simple analytical formula for the Thomson depth of the X-ray heated skin of accretion disks valid at any radius and for a broad range of spectral indices of the incident X-rays, accretion rates and black hole masses. We expect that this formula may find useful applications in studies of geometry of the inner part of accretion flows around compact objects, and in several other astro...

The observed iron Kα fluorescence lines in Seyfert I galaxies provide strong evidence for an accretion disk near a supermassive black hole as a source of the line emission. These lines serve as powerful probes for examining the structure of inner regions of accretion disks. Previous studies of line emission have considered geometrically thin disks only, where the gas moves along geodesics in th...

We describe 2D hydrodynamic simulations of the migration of low-mass planets (≤ 30M⊕) in nearly laminar disks (viscosity parameter α < 10 ) over timescales of several thousand orbit periods. We consider disk masses of 1, 2, and 5 times the minimum mass solar nebula, disk thickness parameters of H/r = 0.035 and 0.05, and a variety of α values and planet masses. Disk selfgravity is fully included...

A fraction of the radiation produced by an accretion disk may be Thomson scattered by a wind flowing away from the disk. Employing a simple plane-parallel model of the wind, we calculate the polarization of the scattered radiation and find that its sign depends on the wind velocity, β = v/c. In the case, 0.12 < β < 0.78, the polarization is parallel to the disk normal, i.e., it is orthogonal to...

Ultraluminous X-ray sources fed by Wolf-Rayet star winds and X-ray bursters in ultracompact binaries with He or C white dwarfs have accretion disks, whose properties may significantly differ from those of pure H α-accretion disks. We have therefore included the dependence on charge number Z and mean molecular weights μe/I into the Shakura and Sunyaev (1973) scaling relations for the key paramet...

The magnetic Prandtl number PrM is the ratio of viscosity to resistivity. In astrophysical disks the diffusion of angular momentum (viscosity) and magnetic fields (resistivity) are controlled by turbulence. Phenomenological models of the evolution of large scale poloidal magnetic fields in disks suggest that the turbulent magnetic Prandtl number PrM,T controls the rate of escape of vertical fie...