Astron. Astrophys. 363, 593-600 (2000)

5. Conclusions

Sequences of nonlinear pulsation models for long period Cepheids in Galaxy have been constructed for comparison purposes with observations, in terms of weighted phases and amplitude ratios of Fourier components of light and radial velocity curves. The sequence of more luminous models are in better agreement with observations, and we pointed out that a slightly overluminous M-L relation than the overshooting-type one is necessary to explain a considerable drop of low order amplitude ratios at the end of long-period Cepheid sequence. Simon (1995) suggested that the M-L relation for bump Cepheids should be intermediate between the canonical and overshooting-type one; however we suggest that the degree of overshooting may be a function of pulsation periods, i.e. it depends on the stellar mass.

The characteristics of nonlinear pulsations in longer period Cepheids are intermediate between the slightly nonadiabatic behavior of short-period Cepheids and the strong nonadiabaticity in less-massive supergiant stars. Antonello & Aikawa (1998) suggested that a lower degree of nonadiabaticity may favor modal resonant phenomena and permanent double-mode pulsation. Modal resonant phenomena may be ineffective in long-period Cepheids due to strong nonadiabaticity; however the question is whether a different metallicity could affect this behavior.

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000
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