A 16-yr photometric campaign on the eclipsing novalike variable DW Ursae Majoris

Abstract

We present an analysis of photometric observations of the eclipsing novalike\nvariable DW UMa made by the CBA consortium between 1999 and 2015. Analysis of\n372 new and 260 previously published eclipse timings reveals a 13.6 year period\nor quasi-period in the times of minimum light. The seasonal light curves show a\ncomplex spectrum of periodic signals: both positive and negative superhumps,\nlikely arising from a prograde apsidal precession and a retrograde nodal\nprecession of the accretion disc. These signals appear most prominently and\nfamously as sidebands of the orbital frequency but the precession frequencies\nthemselves, at 0.40 and 0.22 cycles per day, are also seen directly in the\npower spectrum. The superhumps are sometimes seen together and sometimes\nseparately. The depth, width and skew of eclipses are all modulated in phase\nwith both nodal and apsidal precession of the tilted and eccentric accretion\ndisc. The superhumps, or more correctly the precessional motions which produce\nthem, may be essential to understanding the mysterious SW Sextantis syndrome.\nDisc wobble and eccentricity can both produce Doppler signatures inconsistent\nwith the true dynamical motions in the binary, and disc wobble might boost the\nmass-transfer rate by enabling the hot white dwarf to directly irradiate the\nsecondary star.\n