Dynamical mass of a Cepheid

Very precise mass determination of the Cepheid OGLE-LMC-CEP-0227 in an eclipsing binary system.

The dynamical mass of a classical Cepheid variable star in an eclipsing binary system

G. Pietrzyński, I. Thompson, W. Gieren, D. Graczyk, G. Bono, A. Udalski, I. Soszyński, D. Minniti, B. Pilecki

2010, Nature, 468, 542-544

The two ways to determine the Cepheid mass – from stellar pulsation theory and from stellar evolution theory – yield the results different by 30% (the Cepheid mass discrepancy problem). The accuracy of previous efforts to establish a dynamical Cepheid mass from single-lined non-eclipsing binaries was approximately 15-30%, not good enough to resolve the mass discrepancy problem. The discovery of a classical Cepheid OGLE-LMC-CEP0227 in a well detached, double-lined eclipsing binary allowed to determine the mass of the pulsator to 4.165 M with a precision of 1%. This determination agrees with its pulsation mass, providing strong evidence that pulsa- tion theory correctly and precisely predicts the masses of classical Cepheids.

The period and brightness of the Cepheid component of our system confirm that it is a classical Cepheid.

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