Is there a mass discrepancy in the Cepheid binary OGLE-LMC-CEP0227?

Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
e-mail: hneilson@astro.uni-bonn.de

Received: 5 August 2011
Accepted: 25 October 2011

Abstract

Context. The Cepheid mass discrepancy, the difference between masses predicted from stellar evolution and stellar pulsation calculations, is a challenge for the understanding of stellar astrophysics. Recent models of the eclipsing binary Cepheid OGLE 0227 have suggested that the discrepancy may be resolved.

Aims. We explore for what physical parameters do stellar evolution models agree with the measured properties of OGLE-LMC-CEP0227 and compare to canonical stellar evolution models assuming no convective core overshooting.

Methods. We construct state-of-the-art stellar evolution models for varying mass, metallicity, and convective core overshooting and compare the stellar evolution predictions with the observed properties.

Results. The observed mass, effective temperature, and radius of the two stars in the binary system are well fit by numerous combinations of physical parameters, suggesting a Cepheid mass discrepancy of 10−20% relative to canonical stellar evolution models.

Conclusions. The properties of the observed binary Cepheid suggest that the Cepheid mass discrepancy is still a challenge and requires more specific observations, such as the rate of period change, to better constrain and understand the necessary physics for stellar evolution models to resolve the discrepancy.