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Register a new userBM UMa: a middle shallow contact binary at pre-transition stage of evolution from W-type to A-type
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Added by
Thawicharat Sarotsakulchai Mr.
Publication date
2021
fields
Physics
and research's language is
English
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In this study, all unpublished time series photometric data of BM UMa ($q sim$ 2.0, P = 0.2712,d) from available archives were re-investigated together with new data taken from the TNT-2.4m of the Thai National Observatory (TNO). Based on period analysis, there is a short-term variation superimposed on the long-term period decrease. The trend of period change can be fitted with a downward parabolic curve indicating a period decrease at a rate of $mathrm{d}P/mathrm{d}t = -3.36(pm 0.02)times10^{-8}$ d $textrm{yr}^{-1}$. This long-term period decrease can be explained by mass transfer from the more massive component ($M_2 sim 0.79 M_{odot}$) to the less massive one ($M_1 sim 0.39 M_{odot}$), combination with AML. For photometric study, we found that the binary consists of K0,V stars and at the middle shallow contact phase with evolution of fill-out factor from 8.8,% (in 2007) to 23.2,% (in 2020). Those results suggest that the binary is at pre-transition stage of evolution from W-type to A-type, agreeing to the results of statistical study of W-type contact binaries. The mass of $M_2$ will be decreased close to or below $M_1$ and the mass ratio will be decreased ($q < 1.0$). By this way, the binary will evolve into A-type as a deeper normal over-contact system with period increase. Finally the binary will end as a merger or a rapid-rotating single star when the mass ratio meet the critical value ($q < 0.094$), as well as produce a red nova.
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The first four-color light curves of V868 Mon in the $B$ $V$ $R_c$ and $I_c$ bands are presented and analyzed by using the Wilson-Devinney method of the 2013 version. It is discovered that V868 Mon is an A-subtype contact binary (f=$58.9,%$) with a large temperature difference of 916$K$ between the two components. Using the eight new times of light minimum determined by the authors together with those collected from literatures, the authors found that the general trend of the observed-calculate ($O$-$C$) curve shows a upward parabolic variation that corresponds to a long-term increase in the orbital period at a rate of $dP/dt=9.38times{10^{-7}}daycdot year^{-1}$. The continuous increase may be caused by a mass transfer from the less massive component to the more massive one.
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