Spiral shock detection on eclipse maps: Simulations and Observations

Abstract

We perform simulations in order to reveal the effect of observational and physical parameters on the reconstruction of a spiral structure in an accretion disk, using eclipse mapping techniques. We show that a model spiral structure is smeared to a ``butterfly''-shape structure because of the azimuthal smoothing effect of the technique. We isolate the effects of phase resolution, signal-to-noise ratio and accurate centering of the eclipse at zero phase. We further explore disk emissivity factors such as dilution of the spiral structure by the disk light and relative spiral arm difference. We conclude that the spiral structure can be satisfactorily recovered in accretion disk eclipse maps with phase resolution |Δϕ| < 0.01, S/N>25 and zero phase uncertainty |Δϕ| < 0.005, assuming the two spiral arms have similar brightness and contribute > 30 % to the total disk light. Under the light of the performed simulations, we present eclipse maps of the IP Peg accretion disk reconstructed from eclipse light curves of emission lines and continuum during the outburst of August 1994, where spiral shocks were detected with the aid of Doppler tomography (Morales-Rueda et al. 2000). We discuss how the detection of spirals shocks with eclipse mapping is improved with the use of velocity-resolved eclipse light curves which do not include any contaminating low-velocity emission.