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Pulsations and Dust Formation in R Coronae Borealis Stars

  • Geoffrey C. Clayton (a1), Barbara A. Whitney (a2) and Warrick A. Lawson (a3)

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The observed correlation between pulsational phase in RCB stars and the timing of their declines shows empirically that the stellar pulsations and dust formation are intimately connected (e.g., Lawson et al. 1992). However, the nature of this relationship and the process of dust formation itself are not well understood. We have shown that it is likely that dust is forming in close proximity (< 2 stellar radii) to the RCB star photosphere, based on time scales for acceleration of the dust, eclipse of the chromospheric region, and dispersal of the dust (Clayton et al. 1992, 1993; Whitney, Balm & Clayton 1993; Whitney et al. 1993). The temperature at which amorphous carbon forms can be as high as 4000 K, and can occur in conditions far removed from thermodynamic equilibrium, as long as a mechanism exists to contain carbon atoms within a given volume. A likely form of carbon condensate is fullerenes such as C60 (Whitney, Balm & Clayton 1993). Shocks in the stellar atmosphere due to the pulsations may provide such a mechanism for containing the carbon. However, no spectroscopic signature related to the dust formation has been seen. We have searched unsuccessfully for IR emission bands of C60 (Clayton et al. 1995a).

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References

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Clayton, G.C., Whitney, B.A., Stanford, S.A., & Drilling, J. 1992, ApJ, 397, 652
Clayton, G.C., Lawson, W.A., Whitney, B.A., & Pollacco, D.L. 1993, MNRAS, 264, L13
Clayton, G.C., Lawson, W.A., Cottrell, P.L., Whitney, B.A., Stanford, S.A., & de Ruyter, F. 1994, ApJ, 432, 785
Clayton, G.C., Kelly, D.M., Lacy, J.H., Little-Marenin, I.R., Feldman, P.A., & Bernath, P.F. 1995a, AJ, in press (May)
Clayton, G.C., Whitney, B.A., Meade, M.R., Babler, B., Bjorkman, K.S., & Nordsieck, K.H. 1995, PASP, in press
Lawson, W.A., Cottrell, P.L., Gilmore, A.C., & Kilmartin, P.M. 1992, MNRAS, 256, 339
Whitney, B.A., Clayton, G.C., Schulte-Ladbeck, R.E., Calvet, N., Hartmann, L., & Kenyon, S.J. 1993, ApJ, 417, 687
Whitney, B.A, Balm, S.P., & Clayton, G.C. 1993, Luminous High-Latitude Stars, ASP Conference Series No. 45, ed. Sasselov, D., p. 115

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