Accretion-disc precession in UX Ursae Majoris

TL;DR

This study presents a comprehensive photometric analysis of UX Ursae Majoris, revealing accretion disc precession, negative superhumps, and their effects on eclipse timings, suggesting long-term disc wobble behavior.

Contribution

First detection of accretion disc precession and negative superhumps in UX Ursae Majoris through extensive time-series photometry.

Findings

Detected a 3.680-day precession period of the accretion disc.

Observed a 33-second wobble in eclipse timings linked to disc precession.

Identified persistent negative superhumps at specific frequencies.

Abstract

We report the results of a long campaign of time-series photometry on the nova-like variable UX Ursae Majoris during 2015. It spanned 150 nights, with ~1800 hours of coverage on 121 separate nights. The star was in its normal `high state' near magnitude V=13, with slow waves in the light curve and eclipses every 4.72 hours. Remarkably, the star also showed a nearly sinusoidal signal with a full amplitude of 0.44 mag and a period of 3.680 +/- 0.007 d. We interpret this as the signature of a retrograde precession (wobble) of the accretion disc. The same period is manifest as a +/-33 s wobble in the timings of mid-eclipse, indicating that the disc's centre of light moves with this period. The star also showed strong `negative superhumps' at frequencies w_orb+N and 2w_orb+N, where w_orb and N are respectively the orbital and precession frequencies. It is possible that these powerful signals have been present, unsuspected, throughout the more than 60 years of previous photometric studies.