We study the long-term light and spectral variations in the He-strong magnetic chemically peculiar star HD 37776 (V901 Ori) to search for changes of its 1.5387 d period in 1976-2007. We analyze all published photometric observations and spectrophotometry in the HeI 4026 A line. The data were supplmented with 506 new (U)VB observations obtained during the last 2 observing seasons, 66 estimates of HeI equivalent widths on 23 CFHT spectrograms and 35 of the 6-m Zeeman spectrograms. All the 1895 particular observations heve been processed simultaneously. We confirm the previously suspected increase of the period in HD 37776 which is a record-breaking among CP stars. The mean rate of the period increase during the last 31 years is 0.541+-0.020 s per year. We interpret this ongoing period increase as the slowing down of the star's surface rotation due to momentum loss through events and processes in its magnetosphere.
Z. Mikulasek, J. Krticka, J. Zverko, G. W. Henry, J. Janik, I. I. Romanyuk, J. Ziznovsky, H. Bozic, M. Zejda, T. Graf, M. Netolicky "The record-breaking rotational braking of the He strong CP star HD 37776" Contrib. Astron. Obs. Skalnat ́e Pleso 38, 1 – 2, (2007)