Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks scale strongly with the central stellar mass, approximately Ṁ ∝ M ∗ . No dependence of accretion rate on stellar mass is predicted by the simplest version of the layered disk model of Gammie (1996), in which non-thermal ionization of upper disk layers allows accretion to occur via the magnetorot...

Close pre-main-sequence binary stars are expected to clear central holes in their protoplanetary disks, but the extent to which material can flow from the circumbinary disk across the gap onto the individual circumstellar disks has been unclear. In binaries with eccentric orbits, periodic perturbation of the outer disk is predicted to induce mass flow across the gap, resulting in accretion that...

We consider a class of steady-state self-gravitating accretion disks for which efficient cooling mechanisms are assumed to operate so that the disk is self-regulated at a condition of approximate marginal Jeans stability. In an earlier paper, this scenario had been shown to lead naturally, in the absence of a central point mass, to a self-similar solution characterized by a flat rotation curve....

Radiation dominated accretion disks are likely to be subject to the “photon bubble” instability, which may lead to strong density inhomogeneities on scales much shorter than the disk scale height. Such disks – and magnetized, radiation-dominated atmospheres in general – could radiate well above the Eddington limit without being disrupted. When density contrasts become large over distances of or...

Thus far our impressions regarding the evolutionary time scales for young circumstellar disks have been based on small number statistics. Over the past decade, however, in addition to precision study of individual star/disk systems, substantial observational effort has been invested in obtaining less detailed data on large numbers of objects in young star clusters. This has resulted in a pletho...

We report first results from a series of N-body/gasdynamical simulations designed to study the origin of galaxy morphologies in a cold dark matter-dominated universe. The simulations include star formation and feedback and have numerical resolution sufficiently high to allow for a direct investigation of the morphology of simulated galaxies. We find, in agreement with previous theoretical work,...

Context. Transitional disks are thought to be a late evolutionary stage of protoplanetary disks whose inner regions have been depleted of dust. The mechanism responsible for this depletion is still under debate. To constrain the various models it is mandatory to have a good understanding of the properties of the gas content in the inner part of the disk. Aims. Using X-Shooter broad band − UV to...

We examine the consequences of radiatively driven warping of accretion disks surrounding pre-main-sequence stars. These disks are stable against warping if the luminosity arises from a steady accretion flow, but are unstable at late times when the intrinsic luminosity of the star overwhelms that provided by the disk. Warps can be excited for stars with luminosities of around 10L⊙ or greater, wi...

X-ray illumination of accretion disks is an invaluable diagnostic of the structure of these disks because of the associated iron Kα emission. Here we point out that the resulting reflected spectra depend very sensitively on the geometry of the X-ray source, and that this fact can be efficiently used to test these models observationally. In particular, we discuss three different accretion disk g...

We predict the existence of dusty disks and possibly CO planets around massive white dwarfs. We show that the thermal emission from these disks should be detectable in the infrared. The planets may also be detectable either by direct IR imaging, spectroscopy, or using the pulsations of the white dwarfs. Subject headings: white dwarfs—stars: planetary systems—accretion disks