Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....110..805b&link_type=abstract
Astronomical Journal v.110, p.805
Astronomy and Astrophysics
Astronomy
18
Stars: Late-Type, Stars: Interiors
Scientific paper
We present radial velocities of 2 μm infrared photospheric lines observed in 46 bright carbon stars. The velocities were measured by cross correlation from FTS observations of a spectral region dominated by the Δυ=-2 bands of the CN red system. In addition, for 37 of these stars we have measured velocities of 9 infrared Ti I lines. We also present velocities of CO second overtone (Δυ=3) lines in 28 of these stars and of high excitation first overtone of CO (Δυ=2) lines in 27 stars. These velocities are compared with optical velocities from both cross-correlation measurements of the optical bands of the CN red system and individual atomic absorption lines. We find the following: (1) In Miras (large pulsational amplitude variables), velocities of the same molecule at different wavelengths can be different by tens of kilometers per second. However, optical and infrared velocities are in relatively good agreement for the lower amplitude variables (SR and Lb) and are within a few kilometers per second of the center-of-mass velocity. (2) Velocities in SR and Lb variables show no systematic redshift or blueshift. (3) The resonance line of K I is the exception 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 rather are equally distributed about center-of-mass motion. We suggest that infrared spectroscopy would be a better way to measure center-of-mass motion in carbon stars than optical spectra if the photometric period is well sampled.
Barnbaum Cecilia
Hinkle Kenneth H.
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