What is New with Landstreet Star HD 37776 (V901 Ori)?

TL;DR

This paper studies the unique magnetic and rotational properties of Landstreet's Star, a highly magnetic, complex, and rapidly rotating chemically peculiar star, using recent high-precision photometric and spectroscopic data.

Contribution

It provides the first detailed magnetic topology and rotational behavior analysis of Landstreet's Star, revealing its complex magnetic field and unexpected rotational acceleration.

Findings

Magnetic field is the strongest among He-strong mCP stars (~30 kG).

Surface magnetic field is dominated by high-order spherical harmonics.

The star exhibits an unexpected acceleration in its rotation over two decades.

Abstract

HD\,37776 (V901\,Ori, B2\,Vp), also known as Landstreet's Star, is possibly the most remarkable magnetic chemically peculiar (mCP) star known. Zeeman Doppler Imaging revealed this young, rapidly rotating star's surface magnetic field to be not only the strongest ($\sim 30$ kG) of the He-strong class of hot mCP stars but also by far the most topologically complex. In contrast to the overwhelming majority of mCP stars, which are well described by tilted dipoles, Landstreet's Star's non-axisymmetric surface magnetic field is entirely dominated by high-order spherical harmonics. It is one of the handful of stars for which rotational period change has been measured, and over the past two decades of monitoring, the object has demonstrated an unexpected acceleration in its rotation that so far defies explanation. Recently acquired TESS data have provided a photometric data set of unprecedented precision. These data have revealed a highly stable yet multi-featured light curve, making Landstreet's Star the prototype of hot mCP stars whose light curves are difficult to reproduce using the standard model of chemical/photometric spots modulated by solid-body rotation.