OBSERVATIONS OF 13.5 MICRON ROTATION-VIBRATION LINES OF SIS IN IRC PLUS 10216

We report the first observations of the 13.5 mu m fundamental band of SiS in the spectrum of the heavily obscured carbon star IRC +10216. The lines are formed in the inner region of the circumstellar envelope where the gas is accelerating and where the temperature ranges from 800-500 K. We have carried out a detailed model of the observed line profiles. Our observations are best fit by a gradient in the abundance of SiS. We derive an abundance relative to molecular hydrogen of x(SiS) = 4.3 x 10(-6) ata distance of twelve stellar radii from the central star rising to x(SiS)= 4.3 x 10(-5) at a few Stellar radii from the surface of the star.