EDP Sciences
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Volume 434, Number 3, May II 2005
Page(s) 1077 - 1084
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20042116

A&A 434, 1077-1084 (2005)
DOI: 10.1051/0004-6361:20042116

Seismology of triple-mode classical Cepheids of the Large Magellanic Cloud

P. Moskalik1 and W. A. Dziembowski2, 1

1  Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
    e-mail: pam@camk.edu.pl
2  Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland

(Received 5 October 2004/ Accepted 23 December 2004)

We interpret the three periods detected in OGLE LMC Cepheids SC3-360128 and SC5-338399 as corresponding to the first three overtones of radial pulsations. This interpretation imposes stringent constraints on parameters of the stars and on their evolutionary status, which could only be the first crossing of the instability strip. Evolutionary models reproducing measured periods exist only in a restricted range of metallicities ( Z=0.004 - 0.007). The models impose an upper limit to the extent of overshooting from the convective core. Absolute magnitude of each star is confined to a narrow interval, which allows us to derive a new estimate of the distance to the LMC . We obtain the value of m-M ranging from $18\fm 34$ to $18\fm 53$ with a systematic difference between the two stars of about $0\fm 13$. The rates of period change predicted by the models are formally in conflict with the derived observational limits, though the uncertainties of measured $\dot{P}$ may have been underestimated. If this discrepancy is confirmed, it would constitute a significant challenge to the stellar evolution theory.

Key words: stars: variables: Cepheids -- stars: oscillations -- stars: evolution -- galaxies: Magellanic Clouds

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