Vol 12, No 1

A newly discovered active contact binary in the field of NGC 1348

Xiang-Song Fang, Sheng-Hong Gu, Ho-Keung Hui, Chi-Tai Kwok, Bill Yeung, Kam-Cheung Leung


Abstract We present a CCD photometry study of a newly discovered active eclipsing binary in the field of open cluster NGC 1348 based on the first time-series photometric observation. From the minimum times, we determined an orbital period of P = 0.691363 d. Among our datasets, the BV(RI)c light curves obtained in November 2008 were analyzed using the Wilson-Devinney light curve modeling technique. Because of the uncertainty of the membership of this binary in open cluster NGC 1348, we have analyzed the photometric data in two cases with different primary effective temperatures: Case A (T1 = 7750 K) and Case B (T1 = 5250 K). Our analyses reveal that, for Case A, it is a deep (f > 70%), very low mass ratio (q ≃ 0.096) binary system, indicating that it is now in the late evolution stage of a contact binary; while for Case B, it is a red system with extraordinarily long orbital period with respect to the period-color relation for normal contact binaries, which suggests that this binary has evolved off the main sequence. The well known O’Connell effect (e.g., ∆B ≃ 0.03 mag) was found in the dataset obtained in November 2008, which could be due to the existence of starspots on the components, therefore the corresponding spot properties (for Case A: hot spot; for Case B: dark spot) were determined using the Wilson-Devinney code. With the purpose of analyzing the dark spot activity for Case B, we compared the light curves derived in different observing runs, and found that a slight change appeared from November to December, 2008, which indicates the evolution of spot activity on at least one component over a time scale of about one month.


Keywords stars: binaries: close — stars: binaries: eclipsing — stars: spots

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