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arXiv · 1804.07535

The pulsationally modulated radial crossover signature of the slowly rotating magnetic B-type star $\xi^1$ CMa

M. Shultz·O. Kochukhov·G. A. Wade·Th. Rivinius
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Abstract

We report the latest set of spectropolarimetric observations of the magnetic $\beta$ Cep star $\xi^1$ CMa. The new observations confirm the long-period model of Shultz et al.\ (2017), who proposed a rotational period of about 30 years and predicted that in 2018 the star should pass through a magnetic null. In perfect agreement with this projection, all longitudinal magnetic field $\langle B_z \rangle$ measurements are close to 0 G. Remarkably, individual Stokes $V$ profiles all display a crossover signature, which is consistent with $\langle B_z \rangle \sim 0$ but is {\em not} expected when $v\sin{i} \sim 0$. The crossover signatures furthermore exhibit pulsationally modulated amplitude and sign variations. We show that these unexpected phenomena can all be explained by a `radial crossover' effect related to the star's radial pulsations, together with an important deviation of the global field topology from a purely dipolar structure, which we explore via a dipole+quadrupole configuration as the simplest non-dipolar field.

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M. Shultz, O. Kochukhov, G. A. Wade, Th. Rivinius. 2018-04-20. The pulsationally modulated radial crossover signature of the slowly rotating magnetic B-type star $\xi^1$ CMa. https://doi.org/10.1093/mnrasl/sly070

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