The ever-changing circumstellar nebula around UW Centauri

Geoffrey C. Clayton, Louisiana State University
F. Kerber, Space Telescope European Coordinating Facility
Karl D. Gordon, Louisiana State University
Warrick A. Lawson, University of New South Wales at Australian Defence Force Academy
Michael J. Wolff, Space Science Institute
D. L. Pollacco, Isaac Newton Group
E. Furlan, Universität Innsbruck


We present new images of the reflection nebula surrounding the R Coronae Borealis Star, UW Centauri. This nebula, first detected in 1990, has changed its appearance significantly. At the estimated distance of UW Cen, this nebula is approximately 0.6 lt-yr in radius, so the nebula cannot have physically altered in only 8 years. Instead, the morphology of the nebula appears to change as different parts are illuminated by light from the central star that is modulated by shifting thick dust clouds near its surface. These dust clouds form and dissipate at irregular intervals, causing the well-known declines in the R Coronae Borealis (RCB) stars. In this way, the central star acts like a lighthouse shining through holes in the dust clouds and lighting up different portions of the nebula The existence of this nebula provides clues to the evolutionary history of RCB stars, possibly linking them to the planetary nebulae and the final helium shell flash stars.