The evolutionary status of W Ursae Majoris-type systems

Abstract

Well-determined physical parameters of 130 W UMa systems have been collected from the literature. Based on these data, the evolutionary status and dynamical evolution of W UMa systems are investigated. It is found that there is no evolutionary difference between W- and A-type systems in $M-J$ diagram which is consistent with the results derived from the analysis of observed spectral type, $M-R$ and $M-L$ diagrams of W UMa systems. $M-R$ and $M-L$ diagrams of W- and A-type systems indicate that a large amount of energy should be transferred from the more massive to the less massive component so that they are not in thermal equilibrium and undergo thermal relaxation oscillation (TRO). Meanwhile, the distribution of angular momentum, together with the distribution of mass ratio, suggests that the mass ratio of the observed W UMa systems is decreased with the decrease of their total mass. This could be the result of the dynamical evolution of W UMa systems which suffer angular momentum loss (AML) and mass loss due to magnetic stellar wind (MSW). Consequently, the tidal instability forces these systems towards the lower q values and finally to fast rotating single stars.Comment: 8 pages, 5 figures, accepted for publication in MNRA

Photometric study of W UMa type binaries in the old open cluster Berkeley 39

“…No third body is found in any of the four systems. We found a correlation between the period and mass-ratio as well as temperature and mass-ratio for the respective variables which is similar to the relationship between mass ratio and total mass of the contact binaries as shown by van't Veer (1996) and Li et al (2008). …”

“…Be 39 are similar to the relationship between mass ratio and total mass of the contact binaries as shown by van't Veer (1996) and Li et al (2008). To confirm the photometric mass ratio of the variables in Be 39, …”

Contribution of Primordial Binary Evolution to the Two Blue-straggler Sequences in Globular Cluster M30

“…Webbink 2003;Jiang et al 2009). Considering the luminosity transfer between two components and the primaries still in the main sequence (Yakut & Eggleton 2005;Li et al 2008), we can obtain these luminosities and effective temperatures of two components of contact binaries, and then their combined magnitudes when these binaries are observed as one point. Figure 9 shows the distribution of contact binaries with mass ratios q = 0.1, 0.3, 0.5, 0.7, 0.9 in the color-magnitude diagram, while the primary masses range from 0.91 M ⊙ to 1.44 M ⊙ .…”

“…Moreover, we suggest that W UMa contact binaries could evolve from the red sequence to the blue sequence, when they evolve into systems with smaller mass ratios due to dynamical evolution (Li et al 2008). At present, there are about a dozen W UMa systems with known mass ratios in globular clusters (e.g.…”

Absolute Parameters and Physical Nature of the Low-Amplitude Contact Binary Hi Draconis

“…The data are taken from the compilations of Yakut & Eggleton (2005), Li et al (2008), and Christopoulou et al (2012). As can be seen in the figure, the location of the binary components favors the general pattern of A subtype W UMa systems.…”