Accretion-disc precession in UX Ursae Majoris

• Published in: Monthly notices of the Royal Astronomical Society 2016-04, Vol.457 (2), p.1447-1455
• Main Authors: de Miguel, E., Patterson, J., Cejudo, D., Ulowetz, J., Jones, J. L., Boardman, J., Barret, D., Koff, R., Stein, W., Campbell, T., Vanmunster, T., Menzies, K., Slauson, D., Goff, W., Roberts, G., Morelle, E., Dvorak, S., Hambsch, F.-J., Starkey, D., Collins, D., Costello, M., Cook, M. J., Oksanen, A., Lemay, D., Cook, L. M., Ogmen, Y., Richmond, M., Kemp, J.
• Format: Article
• Language: English
• Subjects: Accretion disks; Astronomy; Photometry; Precession; Signatures; Slow waves; Stars; Stars & galaxies; Symbols; Time series
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stv3014

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 h 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 h. 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 ωorb + N and 2ωorb + N, where ωorb 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 yr of previous photometric studies.