INFRARED AND OPTICAL VELOCITIES OF CARBON STARS

We present radial velocities of 2 mu m infrared photospheric lines obs erved in 46 bright carbon stars. The velocities were measured by cross correlation from FTS observations of a spectral region dominated by t he Delta nu = -2 bands of the CN red system. In addition, for 37 of th ese stars we have measured velocities of 9 infrared Ti I lines. We als o present velocities of CO second overtone (Delta nu = 3) lines in 28 of these stars and of high excitation first overtone of CO (Delta nu = 2) lines in 27 stars. These velocities are compared with optical velo cities from both cross-correlation measurements of the optical bands o f the CN red system and individual atomic absorption lines. We find th e following: (1) In Miras (large pulsational amplitude variables), vel ocities of the same molecule at different wavelengths can be different by tens of kilometers per second. However, optical and infrared veloc ities are in relatively good agreement for the lower amplitude variabl es (SR and Lb) and are within a few kilometers per second of the cente r-of-mass velocity. (2) Velocities in SR and Lb variables show no syst ematic redshift or blueshift. (3) The resonance line of K I is the exc eption with a systematic blueshift that is consistent with the outflow velocity of the circumstellar shell in the SR variables, yet there is no such correlation in the Lb variables. (4) As found previously, the mean optical velocity of carbon star Miras over a pulsational period is systematically redshifted from the center-of-mass velocity. However , we find that the infrared cross-correlation velocities do not show a redshift bias when observed throughout a photometric period, but rath er are equally distributed about center-of-mass motion. We suggest tha t infrared spectroscopy would be a better way to measure center-of-mas s motion in carbon stars than optical spectra if the photometric perio d is well sampled. (C) 1995 American Astronomical Society.