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

Abstract

Stellar pulsation theory provides a means of determining the masses of pulsating classical Cepheid supergiants-it is the pulsation that causes their luminosity to vary. Such pulsational masses are found to be smaller than the masses derived from stellar evolution theory: this is the Cepheid mass discrepancy problem, for which a solution is missing. An independent, accurate dynamical mass determination for a classical Cepheid variable star (as opposed to type-II Cepheids, low-mass stars with a very different evolutionary history) in a binary system is needed in order to determine which is correct. The accuracy of previous efforts to establish a dynamical Cepheid mass from Galactic single-lined non-eclipsing binaries was typically about 15-30% (refs 6, 7), which is not good enough to resolve the mass discrepancy problem. In spite of many observational efforts, no firm detection of a classical Cepheid in an eclipsing double-lined binary has hitherto been reported. Here we report the discovery of a classical Cepheid in a well detached, double-lined eclipsing binary in the Large Magellanic Cloud. We determine the mass to a precision of 1% and show that it agrees with its pulsation mass, providing strong evidence that pulsation theory correctly and precisely predicts the masses of classical Cepheids.

The dependence of convective core overshooting on stellar mass

“…These objects were discovered in the course of the Optical Gravitational Microlensing Experiment (OGLE) 1 , and have served to establish a precise distance scale to those galaxies (e.g. Pietrzyński et al 2010Pietrzyński et al , 2013Graczyk et al 2012Graczyk et al , 2014. They are also ideal for our purposes because they are highly evolved.…”

The Ca ii triplet in red giant spectra: [Fe/H] determinations and the role of [Ca/Fe]

“…Using the reddening for the LMC disk field given by Van der Swaelmen et al (2013), E(B − V ) = 0.12 mag, and an LMC distance modulus (m-M)0 of 18.50 (Pietrzynski et al 2013), the adopted LMC VHB value of 19.26 corresponds to MV = 0.38 -a value that is ∼0.4 mag brighter than the red clump stars in Melotte 66 or M67, for example, which have MV ≈ 0.8. If a value of VHB value of 19.66 had been used instead for the LMC stars, then the resulting metallicities would have been lower by 0.4 × 0.66 × 0.528 = 0.14 dex, precisely the offset seen.…”

The impact of large-scale, long-term optical surveys on pulsating star research

“…Third, it is possible to precisely determine the so called p-factor -the crucial parameter in the Baade-Wesselink method of distance determinations to Cepheids. The Araucaria project ( [11]) specializes in the in-depth analysis of pulsating stars in eclipsing binary systems (e.g., [12,31,34]). …”