2021/08/31 by T. Sarotsakulchai, Thawicharat Sarotsakulchai, Boonrucksar Soonthornthum +8
Engineering · Mathematics · Physics and Astronomy · #Arithmetic #Astronomical Observations and Instrumentation #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Binary number #Binary star #Contact binary #Geology #Light curve #Mass ratio #Mathematics #Period (music) #Physics #Stars #Stellar, planetary, and galactic studies #Term (time) #Type (biology) #astro-ph.SR
paper · pdf · doi:10.1093/pasj/psab090
27 pages, 11 figures
arxiv created 2021/08/31 · openalex publication_date 2021/09/08 · arxiv updated 2021/10/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Abstract In this study, all unpublished time series photometric data of BM UMa (q ∼ 2.0, P = 0.2712 d) from available archives were re-investigated together with new data taken from the 2.4-m Thai National Telescope of the Thai National Observatory. 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 dP/dt = −3.36(±0.02) × 10−8 d yr−1. This long-term period decrease can be explained by mass transfer from the more massive component (M2 ∼ 0.79M⊙) to the less-massive one (M1 ∼ 0.39M⊙), in combination with angular momentum loss. For photometric study, we found that the binary consists of K0 V stars and at the intermediate shallow of contact configuration with evolution of fill-out factor from 8.8% (in 2007) to 23.2% (in 2020). Those results suggest that the binary is at the pre-transition stage of evolution from W-type to A-type, agreeing with the results of statistical study of W-type contact binaries. The mass of M2 will be decreased close to or below M1 and the mass ratio will be decreased (q < 1.0). In this way, the binary will evolve into an A-type as a deeper normal over-contact system with period increase. Finally, the binary will become a merger or a rapid-rotating single star when the mass ratio meets the critical value (q < 0.094), and produce a red nova.