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Astron. Astrophys. 363, 601-604 (2000)


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Nonlinear model pulsations for long-period Cepheids

II. Magellanic Cloud Cepheids

T. Aikawa 1 and E. Antonello 2

1 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, radiative models for long-period Cepheids in the Magellanic Clouds were constructed and the theoretical light and velocity curves were compared with observations. We assumed a metal content [FORMULA], and two mass-luminosity M-L relations: one was obtained from stellar evolution calculation with convective overshooting models, and the other, which gives an even larger L for the same M, was suggested by the study of a bump Cepheid in the Magellanic Clouds. Both relations produce results which are in rough agreement with the observed light and radial velocity curves of Cepheids with period [FORMULA] d. The latter relation, however, gives better results when compared with observations for [FORMULA] d.

The longest P of stable limit cycle is about 130 d; in a previous paper we obtained, for [FORMULA], a maximum P of about 70 d. This result compares reasonably well with Cepheids observed in Galaxy and Magellanic Clouds; in other words, the longest P of Cepheids should depend on the average metallicity of the parent galaxy.

The nonlinear P of more massive models with low metallicity tends to lengthen significantly for a very small increase of M, and this could explain the flattening of the PL relation for [FORMULA] d, which is observed in metal poor galaxies.

A discussion of the shortcomings of the models for a period as short as about 10 d and some comments on resonance effects are also reported.

Key words: stars: variables: Cepheids – stars: variables: general – stars: oscillations – hydrodynamics – galaxies: Magellanic Clouds

Send offprint requests to: T. Aikawa

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000

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