The circumstellar environment of R Coronae Borealis: White dwarf merger or final-helium-shell flash?
In 2007, R Coronae Borealis (RCrB) went into a 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 μm with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around RCrB 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 RCrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4pc away from the star containing cool 25K dust that is detected all the way out to 500 μm. The spectral energy distribution of RCrB can be well fitted by a 150AU 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⊙, 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 RCrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that RCrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of RCrB and its high fluorine abundance support a white dwarf merger. © 2011. The American Astronomical Society. All rights reserved.
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Clayton, G., Sugerman, B., Adam Stanford, S., Whitney, B., Honor, J., Babler, B., Barlow, M., Gordon, K., Andrews, J., Geballe, T., Bond, H., De Marco, O., Lawson, W., Sibthorpe, B., Olofsson, G., Polehampton, E., Gomez, H., Matsuura, M., Hargrave, P., Ivison, R., Wesson, R., Leeks, S., Swinyard, B., & Lim, T. (2011). The circumstellar environment of R Coronae Borealis: White dwarf merger or final-helium-shell flash?. Astrophysical Journal, 743 (1) https://doi.org/10.1088/0004-637X/743/1/44