OPTICAL-ABSORPTION AND EMISSION BANDS OF SIC2 IN CARBON STARS

Observations of the Merrill-Sanford bands of SiC2 in the 4750-5050 Ang strom spectral region, seen in absorption in some carbon stars and in emission in IRAS 12311-3509, are reported. Vibrational band assignment s based on recent laser-based laboratory electronic spectroscopy of th is molecule constitute substantial revisions compared with earlier wor k. Vibrational hot bands are very strong when present in carbon stars, but were greatly weakened in T Mus for a time in 1994, indicating tha t the bands were then formed in a cooler region than that typical of c arbon star photospheres. Emission bands of SiC2, with intensities that are consistent with optical excitation of cool gas, appear in IRAS 12 311-3509 which is probably a J-type carbon star occulted by a dusty di sk so that the star is seen by reflection from material out of the pla ne of the disk.