HD 142990 ( V 913 Sco ; B5 V ) is a He-weak star with a strong surface magnetic field and a short rotation period ( P _ { rot } \sim 1 d ) .
While it is clearly a rapid rotator , recent determinations of P _ { 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 _ { rot } and examine its stability .
Both period analysis of individual datasets and O - C analysis of the photometric data demonstrate that P _ { 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 .