Journal Article

Energy transfer and its effects on the secondaries in W Ursae Majoris type contact binaries

Dengkai Jiang, Zhanwen Han, Tianyu Jiang and Lifang Li

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 396, issue 4, pages 2176-2182
Published in print July 2009 | ISSN: 0035-8711
Published online July 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14852.x
Energy transfer and its effects on the secondaries in W Ursae Majoris type contact binaries

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Based on the physical parameters of 133 W Ursae Majoris (W UMa) type contact binaries, energy transfer and its effects on the secondaries in W UMa contact binaries are investigated. Relations are given between the mass ratio (q) for W UMa contact binaries and the relative energy transfer rates, i.e. U1, the ratio of the transferred luminosity to the surface luminosity of the primary, and U2, the ratio of the transferred luminosity to the nuclear luminosity of the secondary. The theoretical curves(U1 versus q and U2 versus q) are derived based on various assumptions: that the two components in each W UMa system are nearly identical in effective temperature and just fill their inner Roche lobes, and the primaries are zero-age main-sequence stars. Although these curves can reflect the distribution of U1 and U2 versus q, some observational systems deviate significantly from these curves. This results mainly from the difference in effective temperatures of the components of W UMa systems. The radius and the density of the secondary are related to the relative energy transfer rate U2: the higher U2, the greater the expansion and the lower the density of the secondary in a W UMa system. In addition, it is found that the temperature difference of W UMa binary components is correlated with the relative energy transfer rate U1 and decreases with increasing U1. This might suggest that there is a thermal coupling between the two components in W UMa contact binaries, and that the classification of W UMa contact binaries into A or W types depends on the energy transfer from the primary to the secondary. The temperature difference of W UMa binary components is poorly correlated with the mass of the primary. This suggests that the properties of the common envelope of a W UMa contact binary might not have a significant effect on the energy transfer between the two components.

Keywords: binaries: eclipsing; stars: evolution; stars: statistics

Journal Article.  4382 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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