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

Nonlinear model pulsations for long-period Cepheids

II. Magellanic Cloud 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, 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 , 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 d. The latter relation, however, gives better results when compared with observations for d.

The longest P of stable limit cycle is about 130 d; in a previous paper we obtained, for , 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 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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