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| Paper: |
Velocity Differences in Cepheid Atmospheres |
| Volume: |
135, A Half Century of Stellar Pulsation Interpretations: a Tribute to Arthur N. Cox |
| Page: |
182 |
| Authors: |
Vinko, J.; Kaszas, G.; Balog, Z.; Kiss, L. L. |
| Abstract: |
We have obtained high-resolution spectroscopic observations in the 6200 - 6700 A spectral region including H-alpha in order to extend the observational basis of the problem of Cepheid atmospheres and to look for possible similarities andor differences between the spectral features of different kinds of Cepheids. The Cassegrain- and echelle spectrograph of David Dunlap Observatory were used during this project. Our observational sample contains 13 classical and 12 Type II Cepheids in the galactic field. It is well known that Type II Cepheids seem to be much more affected by shock waves than classical Cepheids which is indicated by the presence/absence of strong H-alpha emission. Such kind of emission and strong line-splitting was observed in BL Her during the outward acceleration phases which is in good agreement with recent results of Gillet et al. No similar phenomenon was found in any other cases which confirm the earlier results that the shocks in shorter period Cepheids do not have enough strength to produce H-alpha emission. Line profiles of H-alpha and photospheric metals have been investigated computing the Sasselov-Lester asymmetry parameter. It is shown that the asymmetries of metallic lines have essentially the same phase dependence as it was recently given by Sabbey et al. for 4 Cepheids. However, the asymmetry of H-alpha varies less smoothly during the pulsation. Finally, radial velocities of metallic and H-alpha lines were determined and the velocity differences have been studied during the pulsation. We show how the maximum velocity difference depends on the pulsational period and amplitude. It is concluded that at certain periodamplitude regions classical and Type II Cepheids seem to be separated which may mean that atmospheric motions are different in the two classes. This parameter could also be used for classification purposes, which, however, require further observations. |
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