Pulsations and Dust Formation in R Coronae Borealis Stars

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Session 84 -- Variable Stars
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[84.07] Pulsations and Dust Formation in R Coronae Borealis Stars

G.C. Clayton (U. Colorado), B.A. Whitney (CfA), W.A. Lawson (ADFA)

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. However, the nature of this relationship and the process of dust formation itself are not understood at all. We have shown that it is likely that dust is forming in close proximity ($< 2 R_*$ ) to the RCB star photosphere, based on time scales for acceleration of the dust, eclipse of the chromospheric region, and dispersal of the dust. 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 $C_{60}$. Shocks in the stellar atmosphere due to the pulsations may provide such a mechanism for containing the carbon. We will present a large amount of recently obtained observational data which document molecular, kinematic and geometrical variations related to RCB pulsations. These data include 7 years of spectroscopy and polarimetry of R Coronae Borealis, and high dispersion UV and visible spectroscopy of RY Sagittarii covering a complete pulsation cycle of that star. This work was carried out with the support of NASA grants NAGW-2338 and NAG5-87.

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