Volume 574, February 2015
|Number of page(s)||6|
|Section||Stellar structure and evolution|
|Published online||15 January 2015|
The occurrence of classical Cepheids in binary systems
Department of Astronomy and Astrophysics, University of
Toronto, 50 St. George
Street, Toronto, ON
2 Department of Physics and Astronomy, East Tennessee State University, Box 70652, Johnson City, 37614 Tennessee, USA
3 Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
4 Smithsonian Astrophysical Observations, MS 4, 60 Garden Street, Cambridge, MA 02138, USA
Received: 16 June 2014
Accepted: 11 December 2014
Classical Cepheids, like binary stars, are laboratories for stellar evolution and Cepheids in binary systems are especially powerful ones. About one-third of Galactic Cepheids are known to have companions and Cepheids in eclipsing binary systems have recently been discovered in the Large Magellanic Cloud (LMC). However, there are no known Galactic binary Cepheids with orbital periods less than one year. We compute population synthesis models of binary Cepheids to compare to the observed period and eccentricity distributions of Galactic Cepheids as well as to the number of observed eclipsing binary Cepheids in the LMC. We find that our population synthesis models are consistent with observed binary properties of Cepheids. Furthermore, we show that binary interaction on the red giant branch prevents some red giant stars from becoming classical Cepheids. Such interactions suggest that the binary fraction of Cepheids should be significantly less than that of their main-sequence progenitors, and that almost all binary Cepheids have orbital periods longer than one year. If the Galactic Cepheid spectroscopic binary fraction is about 35%, then the spectroscopic binary fraction of their intermediate mass main sequence progenitors is about 40−45%.
Key words: binaries: general / stars: variables: Cepheids
© ESO, 2015
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