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تسجيل مستخدم جديدThe accelerating rotation of the magnetic He-weak star HD 142990
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HD 142990 (V 913 Sco; B5 V) is a He-weak star with a strong surface magnetic field and a short rotation period ($P_{rm rot} sim 1$ d). While it is clearly a rapid rotator, recent determinations of $P_{rm rot}$ are in formal disagreement. In this paper we collect magnetic and photometric data with a combined 40-year baseline in order to re-evaluate $P_{rm rot}$ and examine its stability. Both period analysis of individual datasets and $O-C$ analysis of the photometric data demonstrate that $P_{rm rot}$ has decreased over the past 30 years, violating expectations from magnetospheric braking models, but consistent with behaviour reported for 2 other hot, rapidly rotating magnetic stars, CU Vir and HD 37776. The available magnetic and photometric time series for HD 142990 can be coherently phased assuming a spin-up rate $dot{P}$ of approximately $-0.6$ s/yr, although there is some indication that $dot{P}$ may have slowed in recent years, possibly indicating an irregular or cyclic rotational evolution.
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