The R Coronae Borealis stars .2. Further inferences from the infrared data

The extensive infrared JHKL photometry of R Coronae Borealis (RCB) variables reported in Paper I is further discussed, especially in relation to the temperature and formation of circumstellar (carbon) particles. Evidence is given for a range of dust temperatures in the shell consistent with the random dust-puff model. The mean dust temperature is higher when the flux from the dust is increasing than when it is decreasing. This is also consistent with the puff model. There is no evidence from any of the stars that a significant proportion of the dust is at temperatures greater than similar to 1500 K. It is suggested that the dust forms at similar to 1500 K above the cool regions of large convection cells in a quasi-steady Eddington-driven outflow, Dust formation can then take place relatively close to the stellar surface, as appears necessary in order to explain the details of the RCB-type obscuration events, Enhanced C-2-band absorption seen occasionally at maximum light in RCB stars also finds a natural explanation in this model, Related data on the HdC stars are also discussed.