A mid-infrared search for C60 in R coronae borealis stars and IRC+10216

Geoffrey C. Clayton, University of Colorado Boulder
Douglas M. Kelly, The University of Texas at Austin
J. H. Lacy, The University of Texas at Austin
Irene R. Little-Marenin, University of Colorado Boulder
P. A. Feldman, National Research Council Canada
P. F. Bernath, University of Waterloo


Buckminsterfullerene (C60) is suspected to be an important constituent of the Interstellar Medium but to date no certain detection of C60 has been made in an astronomical context. Dust-forming material around R Coronae Borealis (RCB) stars may be ideal sites for the formation of C60. The high-temperature, hydrogen-deficient, carbon-rich environment around RCB stars closely mimics the laboratory conditions under which C60 forms. It is believed that dust is being formed continually in the atmospheres of the RCB stars during their pulsation cycles. The temperature at which this dust forms could 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 C60. Low Resolution Spectra from IRAS show the apparent presence of an emission feature near 8.6 μm in three RCB stars which could possibly be associated with C60. However, the low resolution and poor S/N of these spectra do not permit identification of the features. Therefore, we obtained new observations using the Irshell mid-infrared spectrograph at the NASA Infrared Telescope Facility. We searched the 8.6 μm spectral region of the RCB stars, R CrB, RY Sgr, and V854 Cen. No narrow features were found at a level of 2% of the continuum. However, the carbon star, IRC+10216 did show a possible emission feature centered at 8.6 μm.