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Eclipse mapping of the cataclysmic variable DW Ursae Majoris
Received 5 January 2000 / Accepted 11 September 2000
Broad-band VR-photometry of the nova-like variable DW UMa is presented. The observations reveal a quickly changing nature of the variable, with the out-of-eclipse brightness and eclipse depth having increased monotonically during the observing period. Maximum entropy eclipse mapping techniques were applied to groups of light curves corresponding to different states of the variable. The reconstructed maps show a bright spot feature lying along the theoretical stream trajectory and disappearing gradually as the system was brightening. Photometric disk radii varied between 0.55 and 0.7 with a mean of 0.6 . They agree well with the radial distance of the bright spot. Colour-magnitude diagrams of the reconstructed disk stages suggest that the inner disk region can be approximated to be optically thick. Fitting main-sequence and blackbody relations to the data tentatively gives a distance estimate of pc to the system. The brightness temperature profiles of the disk were found to be much flatter than the theoretical prediction for a steady-state, optically thick accretion disk. Tests show that the discrepancy is too high to be explained as an artifact of the reconstruction method or by large uncertainties in the system parameters. A thick accretion disk model did not help in explaining the flat profiles. However, a disrupted flat disk, expected in intermediate polars, brings the brightness temperature profiles in agreement with the theoretical model for inner disk radii of depending on various system parameters. This suggests an intermediate polar (IP) nature of DW UMa. Although current data cannot disclose the presence of a nonsteady or optically thin accretion disk, the IP model is in the advantage of having some observational support.
Key words: stars: binaries: eclipsing stars: novae, cataclysmic variables accretion, accretion disks stars: individual: DW UMa, GSC 3822 1056, GSC 3822 0070
© European Southern Observatory (ESO) 2000
Online publication: January 29, 2001