Ultraviolet Limb Darkening and Spectra for Accretion Disks in Cataclysmic Variables

Marcos P. Diaz (1) - Richard A. Wade (1) - Ivan Hubeny (2)

(1) Department of Astronomy & Astrophysics, The Pennsylvania State University,
525 Davey Laboratory, PA 16802; mdiaz@astro.psu.edu, wade@astro.psu.edu
(2) NASA Goddard Space Flight Center, Greenbelt, MD 20771; hubeny@stars.gsfc.nasa.gov

Abstract:

Limb darkening is an important effect, more so for flat objects such as accretion disks (AD) than for stars, since no averaging over emergent angles occurs for disks. As with stars, limb darkening in AD is especially important in the ultraviolet, and at a given wavelength it is more important for low temperature atmospheres. We study the size of the limb darkening effect in the ultraviolet (925 Å to 1750 Å) spectra of AD in cataclysmic variables, using a grid of models and spectra of disk atmospheres. Radial emissivity (surface brightness) distributions in the ultraviolet are presented, along with a brief comparison of limb darkening in stars and disks. The changes in the absorption line profiles in the model disk spectra as the disk inclination is varied, due to both limb darkening and kinematic broadening, is also discussed. Limb darkening correction factors for the integrated disk brightness at 1448 Å are derived for a representative set of disk parameters and orbital inclinations.

cataclysmic variables, stars: accretion, stars: atmospheres

• Introduction
• The Disk Models
  • The Disk Structure and Spectrum Synthesis
  • Model Parameters
• Results
  • Continuum Radial Emissivity Profiles
  • The Absorption Line Spectrum
  • The Limb Darkening Correction Factors
• Discussion
• Summary
• Bibliography
• About this document ...