The Ever Changing Circumstellar Nebula Around UW Centauri

Abstract

We present new images of the reflection nebula surrounding the R Coronae Borealis Star, UW Cen. This nebula, first detected in 1990, has changed its appearance significantly. At the estimated distance of UW Cen, this nebula is approximately 0.6 ly 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 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.

To be published in ApJ Letters. 5 pages, 3 figures (2 in color)

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• The Double Dust Envelopes of R Coronae Borealis Stars
• Long-Slit Observations of Extended C II 1335 Emission Around V854 Centauri and RY Sagittarii
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• R Coronae Borealis: Radial-velocity and other observations, 1950-2007