On the Change of the Inner Boundary of an Optically Thick Accretion Disk around White Dwarfs Using the Dwarf Nova SS Cyg as an Example

TL;DR

This study uses high-time-resolution optical observations of SS Cyg to analyze how the inner boundary of its accretion disk changes with accretion rate, revealing the disk's truncation near the white dwarf during low states.

Contribution

It demonstrates that power spectral analysis of optical flux variability can trace the inner boundary of accretion disks around white dwarfs, providing a new method to estimate the mass of the accreting object.

Findings

Inner disk boundary approaches the white dwarf at accretion peak.

Disk truncation occurs at about 8.5e9 cm (~10 R_{WD}) in low state.

Power spectra can be used to estimate white dwarf mass.

Abstract

We present the results of our studies of the aperiodic optical flux variability for SS Cyg, an accreting binary systemwith a white dwarf. The main set of observational data presented here was obtained with the ANDOR/iXon DU-888 photometer mounted on the RTT-150 telescope, which allowed a record(for CCD photometers) time resolution up to 8 ms to be achieved. The power spectra of the source's flux variability have revealed that the aperiodic variability contains information about the inner boundary of the optically thick flow in the binary system. We show that the inner boundary of the optically thick accretion disk comes close to the white dwarf surface at the maximum of the source's bolometric light curve, i.e., at the peak of the instantaneous accretion rate onto the white dwarf, while the optically thick accretion disk is truncated at distances 8.5e9 cm ~10 R_{WD} in the low state. We suggest that the location of the inner boundary of the accretion disk in the binary can be traced by studying the parameters of the power spectra for accreting white dwarfs. In particular, this allows the mass of the accreting object to be estimated.