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

Nonlinear model pulsations for long-period Cepheids

I. Galactic Cepheids

T. Aikawa ¹ and E. Antonello <sup>2

1</sup> Tohoku Gakuin University, Izumi-ku, Sendai, 981-31, Japan (aikawa@ghi.tohoku-gakuin.ac.jp)
² Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy (elio@merate.mi.astro.it)

Received 4 April 2000 / Accepted 13 September 2000

Abstract

Nonlinear pulsation models for long-period Cepheids in Galaxy were constructed and their theoretical light and velocity curves were compared with observations. Two different mass-luminosity () relations were assumed, one for canonical evolutionary models and the other for models with overshooting. A model sequence was constructed by varying the masses and correspondingly the luminosities for both relations. The values of the effective temperatures of the models were assumed to be 200 K smaller than those of theoretical blue edge for the same masses and luminosities. Each sequence consisted of about 50 models with pulsation periods from about 10 to 100 days. Nonlinear hydrodynamic simulations were performed to get limit cycles. When nonlinear pulsation settled into limit cycles, light and velocity curves were Fourier decomposed and compared with observational results. It is concluded that the models with the overshooting-type are globally in better agreement with observations than those with the standard relation, while there are discrepancies for higher order Fourier components in both cases. Two additional model sequences were constructed by changing the value of artificial viscosity coefficients and of . Decreasing the artificial viscosity can produce a slightly better agreement between models and observations for the higher order Fourier components, while the effects of different on the same components are small.

The stability of the limit cycles are briefly discussed along with the lack of indications of modal resonance phenomena and the possible importance of the degree of nonadiabaticity.

Key words: stars: variables: Cepheids stars: variables: general stars: oscillations hydrodynamics

Send offprint requests to: T. Aikawa

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000

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