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Astron. Astrophys. 315, L249-L252 (1996)

ISOPHOT observations of R CrB: a star caught smoking*

H.J. Walker1, I. Heinrichsen2,3, P.J. Richards1, U. Klaas4,3, and I.L. Rasmussen5

1 CLRC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK
2 Max Planck Institut für Kernphysik, Saupfercheckweg, D-69117 Heidelberg, Germany
3 ISOPHOT IDT, Villafranca del Castillo Satellite Tracking Station, P.O. Box Apdo 50727, E-28080 Madrid, Spain
4 Max Planck Institut für Astronomie, Königstuhl, D-69117 Heidelberg, Germany
5 Danish Space Research Institute, Juliane Maries Vej 30, DK-2100 Copenhagen O, Denmark

Received 1 August 1996 / Accepted 3 September 1996

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 img1.gifm to 200 img1.gifm). The dust shell was observed using the low resolution spectrometer (from 2.5 img1.gifm to 5 img1.gifm and 5.8 img1.gifm to 11.6 img1.gifm). The energy distribution peaks around 6 - 8 img1.gifm, 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.

Key words: circumstellar matter - stars: individual - stars: variable - stars: AGB and post-AGB - infrared: stars

* Based on observations by the Infrared Space Observatory (ISO), an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

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Last change: December 16, 1996
© European Southern Observatory (ESO) 1996