IRAS observations reveal a ≡18arcmin diameter, nearly symmetrical 60 and 100 μm emission region centered on the extreme hydrogen-deficient supergiant, R CrB. If R CrB is at a distance of 1.6 kpc, the shell has a linear extent of ≡8 pc, and luminosity of about 28 L_sun;. The dust temperature is 25 - 30K, and the radiating dust mass is 0.1×10-2M_sun; to 2.4×10-2M_sun;, depending on the assumed grain optical properties. The corresponding total shell mass, for solar abundances, is at least 0.25 M_sun;. The dust shell is tentatively identified as a fossil remnant of R CrB's hydrogen-rich envelope. The ejection process appears to have occurred with a nearly constant mass loss rate and expansion velocity over a period of about 1.5×105yr, terminating about 2.6×104yr ago.
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Gillett et al. (1986) studied this question.