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arXiv · 1110.3235

The Circumstellar Environment of R Coronae Borealis: White Dwarf Merger or Final Helium Shell Flash?

Geoffrey C. Clayton·Ben E. K. Sugerman·S. Adam Stanford·B. A. Whitney·J. Honor·B. Babler·M. J. Barlow·K. D. Gordon·J. E. Andrews·T. R. Geballe·Howard E. Bond·O. De Marco·W. A. Lawson·B. Sibthorpe·G. Olofsson·E. Polehampton·H. L. Gomez·M. Matsuura·P. C. Hargrave·R. J. Ivison·R. Wesson·S. J. Leeks·B. M. Swinyard·T. L. Lim
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Abstract

In 2007, R Coronae Borealis (R CrB) went into an historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 micron with Gemini/GMOS, HST/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 micron. The SED of R CrB can be well fit by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10^-4 and 2 M(Sun), respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white-dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant Lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white-dwarf merger.

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Geoffrey C. Clayton, Ben E. K. Sugerman, S. Adam Stanford, B. A. Whitney, J. Honor, B. Babler, M. J. Barlow, K. D. Gordon, J. E. Andrews, T. R. Geballe, Howard E. Bond, O. De Marco, W. A. Lawson, B. Sibthorpe, G. Olofsson, E. Polehampton, H. L. Gomez, M. Matsuura, P. C. Hargrave, R. J. Ivison, R. Wesson, S. J. Leeks, B. M. Swinyard, T. L. Lim. 2011-10-14. The Circumstellar Environment of R Coronae Borealis: White Dwarf Merger or Final Helium Shell Flash?. https://doi.org/10.1088/0004-637x%2F743%2F1%2F44

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