The record-breaking rotational braking of the He strong CP star HD 37776

TL;DR

This study documents a record-breaking increase in the rotational period of the He-strong CP star HD 37776 over 31 years, indicating significant magnetic braking likely caused by magnetospheric processes.

Contribution

It provides the first long-term, multi-method observational confirmation of a continuously increasing rotational period in HD 37776, a phenomenon not previously documented in CP stars.

Findings

Confirmed ongoing period increase at 0.541 s/year

First long-term observational evidence of magnetic braking in a CP star

Period increase is among the fastest observed in chemically peculiar stars

Abstract

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.