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| Paper: |
Limitations of Precise Radial-Velocity Measurements in Pulsating Stellar Atmospheres |
| Volume: |
185, Precise Stellar Radial Velocities, IAU Colloquium 170 |
| Page: |
223 |
| Authors: |
Vinkó, J.; Kaszás, G.; Kiss, L. L. |
| Abstract: |
We have studied the velocities of specific stellar absorption lines emerging from the atmospheres of Cepheid-type variable stars using newly obtained high-resolution echelle spectra. The spectra covered the interval 5860 - 6660 Angstroms with a resolution of 40,000. Both the cross-correlation method and the line bisector method using individual lines with specific excitation potential were applied to derive radial velocities. Our tests showed that these methods have internal accuracy of better than 100 m/s. Typical velocity differences of 3 - 5 km/s were found between photospheric lines having low- and high-excitation potentials in the case of long-period (P > 10 days) Cepheids. These differences are smaller, about 1 km/s or less, for the shorter period Cepheids. Furthermore, we have compared two very accurate techniques (Coravel and iodine-cell method) using recently published radial velocities. Systematic differences have been found between the shapes of these velocity curves, especially around the phase of velocity reversal. We conclude that these velocity differences could cause a few km/s ambiguity even in the best-quality Cepheid radial velocity curves that were obtained averaging the velocities of many lines. This may result in an uncertainty of Cepheid radii derived from Baade-Wesselink methods. |
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