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| Paper: |
The Dynamical and Beat Masses of the Beat Cepheid Y Carinae |
| Volume: |
135, A Half Century of Stellar Pulsation Interpretations: a Tribute to Arthur N. Cox |
| Page: |
280 |
| Authors: |
Bohm-Vitense, E.; Evans, N. R.; Carpenter, K.; Winchatz, B. Beck-; Morgan, S.; Robinson, R. |
| Abstract: |
The mass-luminosity relation for Cepheids depends on the degree of excess mixing in their main sequence progenitors. The mass determination for Cepheids with their known luminosities therefore determines the degree of excess mixing in massive main sequence stars. We have determined the dynamical mass of several Cepheids with blue companions. Here we discuss the beat Cepheid Y Carinae. By means of HST, GHRS spectra we measured the radial velocity of the B9.5 V companion Y Car B at phases near minimum and maximum orbital radial velocities. The orbital velocity amplitude ratio between the Cepheid and the hot companion and thereby the mass ratio comes out to be 1.51 0.5, leading to a mass of 3.8 1 1.2 solar masses. Taking the 3.8 solar masses at face value this indicates excess mixing corresponding to convective overshoot by about 1 pressure scale height, (see Bertelli et al.1986), but the error limits are too large for a firm conclusion. The beat masses, determined from the period ratios for the beat Cepheids, have puzzled astronomers for a long time (see Cox 1980) because they came out around 1 to 2 solar masses, when the Cox-Tabor opacities were used for the model calculations. Moskalik et al.(1992) showed that beat masses around 4 to 5 solar masses can now be derived, if the new OPAL opacities are used instead. With the determination of the dynamical mass for Y Car A we can now check the validity of the OPAL opacities more quantitatively than was possible before. Using the model calculations incorporating the OPAL opacities, and the observed effective temperature of Y Carinae we determine for its beat mass a possible range of 3.75 < M/Ms < 4.0, in very good agreement with the dynamical mass. This supports the validity of the OPAL opacities, and also supports the conclusion about the high degree of excess mixing in the main sequence progenitor of Y Carinae A. |
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