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| Paper: |
V553 CEN and the Carbon Cepheids |
| Volume: |
135, A Half Century of Stellar Pulsation Interpretations: a Tribute to Arthur N. Cox |
| Page: |
36 |
| Authors: |
Wallerstein, G.; Gonzalez, G. |
| Abstract: |
During the 20th century a few cepheid variables have been gradually identified as showing C2 bands in their spectra. The class of Carbon Cepheids was recognized by Lloyd Evans (1983), who assembled a list of seven objects and described their properties. They seem to cover a wide range in period from 2 to 32 days and a substantial dispersion in galactic latitude indicating that they are probably disk stars of much greater age than are the Classical Cepheids of the spiral arms. In addition, they are likely to be of small mass. Their relationship to the CH stars of the halo population, the carbon-rich RV Tau stars, and the various subclasses of non-variable carbon stars is unclear, though their spectra and galactic distribution indicate a similarity to the early R stars. We have obtained high-resolution spectroscopic observations of V553 Cen, a short-period Type II Cepheid. We have confirmed the findings of previous investigators that V553 Cen is C- and N-rich. For the first time, we show that V553 Cen is also O-poor and Na-rich and that 12C/13C = 411. We do not see s-process element enhancements in this star. When compared to historical observations, our radial velocity measurements indicate that V553 Cen does not have a binary companion. Hence, the abundance peculiarities we observe on the surface are due to V553 Cen altering its own composition by nuclear reaction sequences and dredge-up episodes. These results imply that V553 Cen has experienced CN, ON, and triple-alpha processing and mixed the products of these reactions to its surface. The chemical composition of V553 Cen and the kinematics of the Carbon Cepheids indicate that they are of the same population as early R stars. The evolutionary processes that have produced such objects are not known but are suspected to be due to helium core flashing in small- mass stars of normal metallicity as suggested by both Lloyd Evans and Dominy (1984). |
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