Hydrodynamic simulations of flares on accretion disks

We have constructed a hydrodynamic simulation of flares on the accretion disks of cataclysmic variable stars. In these flares the disk photosphere is heated by a beam of suprathermal electrons. The beam energy flux, beam duration, position in the accretion disk, and accretion disk temperature were varied in 20 are simulations. All the are simulations show that above a site of maximum heating the gas is blown upward from the disk. Below this point the gas is compressed and heated. A non-LTE radiative transfer program calculates the resulting continuous emission and Balmer line radiation from the are. The temporal development of each are model is followed by calculating the radiation at 15-20 time steps. The Hbeta line flux from accretion disks is estimated for 20 dwarf novae and 12 nova and nova-like systems by using information gathered from the literature. We then use a simple approximation for the rate of flaring across an accretion disk to see whether flares can account for all the Hbeta emission. The rate of flickering observed in cataclysmic variables is used as a constraint on this model. Using flickering rates from one study we find that if each observed flicker is one magnetic are, then flares can account for only 1%-2% of the Hbeta emission. A much higher are rate can account for the observed Hbeta emission if flickering studies underestimate the true rate of flaring. A are avalanche model may account for both the observed Hbeta flux and the observed flickering.