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

• Published in: Nature (London) 2010-11, Vol.468 (7323), p.542-544
• Main Authors: Pietrzyński, G., Thompson, I. B., Gieren, W., Graczyk, D., Bono, G., Udalski, A., Soszyński, I., Minniti, D., Pilecki, B.
• Format: Article
• Language: English
• Subjects: 639/766/33/34/867; Astronomy; Astrophysics; Binary systems; Cepheid variables; Cepheids; Cepheids (delta cephei, w virginis); Detaching; Double stars; Earth, ocean, space; Eclipsing binaries; Eclipsing binary stars; Evolutionary; Exact sciences and technology; Humanities and Social Sciences; letter; Luminosity; Magellanic clouds; Masses; Measurement; multidisciplinary; Natural history; Pulsation; Science; Science (multidisciplinary); Stars; Stars & galaxies; Stellar characteristics and properties; Stellar evolution; Variable and peculiar stars (including novae)
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature09598

Cepheid variable mass Cepheid variable stars have been important in the development of modern astrophysics through their use in establishing cosmic distances, but despite extensive research they retain some of their mysteries. One is the mass discrepancy problem, the fact that the masses of classical Cepheid supergiants calculated from pulsation theory (it is pulsation that causes their luminosity to vary) are smaller than the masses calculated from stellar evolution models. The ideal system in which to make an accurate mass determination would be a well-detached double-lined eclipsing binary in which one of the components was a classical Cepheid. Pietrzynski et al . report the discovery of just such a system in the Large Magellanic Cloud. The resultant mass determination, to a precision of one per cent, is in agreement with the mass as predicted by pulsation theory. Masses of pulsating classical Cepheid supergiants derived from stellar pulsation theory are smaller than the masses derived from stellar evolution theory. An independent determination for a classical Cepheid in a binary system is needed to determine which is correct. These authors report the discovery of a classical Cepheid in the Large Magellanic Cloud. They determine the mass to a precision of one per cent and show that it agrees with its pulsation mass. 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 1 , 2 , for which a solution is missing 3 , 4 , 5 . 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 8 , 9 , 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 t