ISOPHOT observations of R CrB: a star caught smoking
H. J. Walker , I. Heinrichsen, P. J. Richards, U. Klaas and I. L. Rasmussen
Abstract:
R CrB is a very unusual star, being extremely hydrogen deficient and
undergoing irregular deep minima in its visible light.
R CrB started to undergo a fading episode in October 1995. The Infrared
Space Observatory (ISO) observed the star after it had faded by 7 magnitudes.
The inner, warm dust shell has been observed by ISOPHOT, using the long
wavelength camera mode (from 60 
m to 200 m). The dust shell
was observed using the low resolution spectrometer (from 2.5 m to 5 m
and 5.8 m to 11.6 m). The energy distribution peaks around
6 - 8 m, indicative of a 650K dust shell with an unusual shape
to the observed spectrum.
The long wavelength photometry, when compared to IRAS data, shows the
temperature of the warm dust shell is unaffected by the ejection
of a new cloud of carbon from the central star. The dust cloud is
probably composed of pure carbon, but other materials cannot be excluded.
There is no evidence of hydrogenated carbon molecules.
Keywords:
Circumstellar matter - Stars:individual - Stars:variable -
Stars:AGB and post-AGB - Infrared:stars