Three-micron absorption band of carbon stars.

Narrow-band spectrophotometric observations have been carried out for 22 carbon stars and 23 M-type stars between 2.85 and 4.1 m with a resolution of J2/ 0.02. It is shown that all the carbon stars exhibit a broad absorption feature centered at about 3.05 m, while no trace of absorption was found in the M-type stars. It is found that the band depth correlates with color indices U- V, B- V as well as the abundance ratio CN/C2. Certain kinds of dust particles and molecules are examined as the absorbing agent. Key words: Carbon stars; Spectrophotometry; Three-micron band.