The BV Photometry of the RR Lyrae Star, BH Ursae Majoris: Light Curves and Period Study

Abstract

m 47 in V, and 0. m 11 in B-V and with a small hump between 0. p 82 and 0. p 86. We determined nine new times of minimum light and eight times of maximum light. We also analyzed all of the available unanalyzed minimum timings and found for the first time that the period of BH UMa has varied dramatically in at least three independent sinusoidal ways superposed on a secularly downward parabola over 66 years. The secular period decreasing rate was obtained as 6. d 684 × 10 -8 y -1 , corresponding to -0.58 s/century. The semi-amplitude and period for each of the three sinusoidal varia- tions were (0. d 058, 14. y 44), (0. d 044, 9. y 98), and (0. d 005, 0. y 97), respectively. It is uncertain whether the periodicity for the shortest period of 0. y 97 is real or spurious. The secular period decrease, well consistent with those of the other RRc stars, could be considered as a natural result of the evolution of the BH UMa system. The two possible sinusoidal terms were interpreted as both two light-time effects due to two additional bodies orbiting BH UMa and combinations of random fluctuations in the pulsation period of BH UMa. Two interpretations were shortly discussed with related parameters.