A Two‐armed Pattern in Flickering Maps of the Nova‐like Variable UU Aquarii1

  • Baptista R
  • Bortoletto A
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Abstract

We report the analysis of a uniform sample of 31 light curves of the nova-like variable UU Aqr with eclipse-mapping techniques. The data were combined to derive eclipse maps of the average steady-light component, the long-term brightness changes, and the low- and high-frequency flickering components. The long-term variability responsible for the ``low-brightness'' and ``high-brightness'' states is explained in terms of the response of a viscous disk to changes of 20%-50% in the mass transfer rate from the donor star. Low- and high-frequency flickering maps are dominated by emission from two asymmetric arcs reminiscent of those seen in the outbursting dwarf nova IP Peg, and they are similarly interpreted as manifestations of a tidally induced spiral shock wave in the outer regions of a large accretion disk. The asymmetric arcs are also seen in the map of the steady light aside from the broad brightness distribution of a roughly steady-state disk. The arcs account for 25% of the steady-light flux and are a long-lasting feature in the accretion disk of UU Aqr. We infer an opening angle of 10deg+/-3deg for the spiral arcs. The results suggest that the flickering in UU Aqr is caused by turbulence generated after the collision of disk gas with the density-enhanced spiral wave in the accretion disk. Based on observations made at the Laboratório Nacional de Astrofísica, CNPq, Brazil.

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Baptista, R., & Bortoletto, A. (2008). A Two‐armed Pattern in Flickering Maps of the Nova‐like Variable UU Aquarii1. The Astrophysical Journal, 676(2), 1240–1247. https://doi.org/10.1086/528706

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