9 research outputs found
Radiative Transfer and Limb Darkening of Accretion Disks
Transfer equation in a geometrically thin accretion disk is reexamined under
the plane-parallel approximation with finite optical depth. Emergent intensity
is analytically obtained in the cases with or without internal heating. For
large or infinite optical depth, the emergent intensity exhibits a usual
limb-darkening effect, where the intensity linearly changes as a function of
the direction cosine. For small optical depth, on the other hand, the
angle-dependence of the emergent intensity drastically changes. In the case
without heating but with uniform incident radiation at the disk equator, the
emergent intensity becomes isotropic for small optical depth. In the case with
uniform internal heating, the limb brightening takes place for small optical
depth. We also emphasize and discuss the limb-darkening effect in an accretion
disk for several cases.Comment: 7 pages, 4 figure
Relativistic Radiative Flow in a Luminous Disk II
Radiatively-driven transfer flow perpendicular to a luminous disk is examined
in the relativistic regime of , taking into account the gravity of the
central object. The flow is assumed to be vertical, and the gas pressure as
well as the magnetic field are ignored. Using a velocity-dependent variable
Eddington factor, we can solve the rigorous equations of the relativistic
radiative flow accelerated up to the {\it relativistic} speed. For sufficiently
luminous cases, the flow resembles the case without gravity. For less-luminous
or small initial radius cases, however, the flow velocity decreases due to
gravity. Application to a supercritical accretion disk with mass loss is
briefly discussed.Comment: 7 pages, 5 figure
Relativistic Radiation Hydrodynamical Accretion Disk Winds
Accretion disk winds browing off perpendicular to a luminous disk are
examined in the framework of fully special relativistic radiation
hydrodynamics. The wind is assumed to be steady, vertical, and isothermal. %and
the gravitational fields is approximated by a pseudo-Newtonian potential. Using
a velocity-dependent variable Eddington factor, we can solve the rigorous
equations of relativistic radiative hydrodynamics, and can obtain radiatively
driven winds accelerated up to the {\it relativistic} speed. For less luminous
cases, disk winds are transonic types passing through saddle type critical
points, and the final speed of winds increases as the disk flux and/or the
isothermal sound speed increase. For luminous cases, on the other hand, disk
winds are always supersonic, since critical points disappear due to the
characteristic nature of the disk gravitational fields. The boundary between
the transonic and supersonic types is located at around , where is the
radiative flux at the critical point normalized by the local Eddington
luminosity, is the enthalpy of the gas divided by the
rest mass energy, and is the Lorentz factor of the wind
velocity at the critical point. In the transonic winds, the final speed becomes
0.4--0.8 for typical parameters, while it can reach in the
supersonic winds.Comment: 6 pages, 5 figures; PASJ 59 (2007) in pres