A 16-Year Photometric Campaign on the Eclipsing Novalike Variable DW Ursae Majoris

TL;DR

This 16-year photometric study of DW UMa reveals complex periodic signals, including superhumps and precession, with implications for understanding accretion disc dynamics and the SW Sextantis syndrome.

Contribution

The paper provides a long-term observational analysis identifying multiple precession frequencies and their effects on eclipse characteristics in DW UMa.

Findings

Detection of a 13.6-year quasi-period in eclipse timings.

Identification of positive and negative superhumps and their relation to disc precession.

Modulation of eclipse properties by disc precession.

Abstract

We present an analysis of photometric observations of the eclipsing novalike variable DW UMa made by the CBA consortium between 1999 and 2015. Analysis of 372 new and 260 previously published eclipse timings reveals a 13.6 year period or quasi-period in the times of minimum light. The seasonal light curves show a complex spectrum of periodic signals: both positive and negative superhumps, likely arising from a prograde apsidal precession and a retrograde nodal precession of the accretion disc. These signals appear most prominently and famously as sidebands of the orbital frequency but the precession frequencies themselves, at 0.40 and 0.22 cycles per day, are also seen directly in the power spectrum. The superhumps are sometimes seen together and sometimes separately. The depth, width and skew of eclipses are all modulated in phase with both nodal and apsidal precession of the tilted and eccentric accretion disc. The superhumps, or more correctly the precessional motions which produce them, may be essential to understanding the mysterious SW Sextantis syndrome. Disc wobble and eccentricity can both produce Doppler signatures inconsistent with the true dynamical motions in the binary, and disc wobble might boost the mass-transfer rate by enabling the hot white dwarf to directly irradiate the secondary star.