Confirmation of xi^1 CMa's ultra-slow rotation: magnetic polarity reversal and a dramatic change in magnetospheric UV emission lines

Abstract

The magnetic beta Cep pulsator xi^1 CMa has the longest rotational period of any known magnetic B-type star. It is also the only magnetic B-type star with magnetospheric emission that is known to be modulated by both rotation and pulsation. We report here the first unambiguous detection of a negative longitudinal magnetic field in xi^1 CMa (<Bz>=-87 +/- 2 G in 2019 and <Bz>=-207 +/- 3 G in 2020), as well as the results of ongoing monitoring of the star's Halpha variability. We examine evidence for deviation from a purely dipolar topology. We also report a new HST UV spectrum of xi^1 CMa obtained near magnetic null that is consistent with an equatorial view of the magnetosphere, as evidenced by its similarity to the UV spectrum of beta Cep obtained near maximum emission. The new UV spectrum of xi^1 CMa provides additional evidence for the extremely long rotation period of this star via comparison to archival data.

13 pages, Accepted 2021 May 14 to Monthly Notices of the Royal Astronomical Society 2021

References in corpus (20)

• The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
• Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: III. Angular Momentum Loss and Rotational Spindown
• The MiMeS survey of magnetism in massive stars: Magnetic analysis of the O-type stars
• Abundance analysis of prime B-type targets for asteroseismology I. Nitrogen excess in slowly-rotating beta Cephei stars
• Discovery of magnetic fields in the beta Cephei star xi^1 CMa and in several Slowly Pulsating B stars
• Magnetic massive stars as progenitors of "heavy" stellar-mass black holes
• The Magnetic Early B-type Stars I: Magnetometry and Rotation
• The effects of surface fossil magnetic fields on massive star evolution: I. Magnetic field evolution, mass-loss quenching and magnetic braking
• Modeling of Magneto-Rotational Stellar Evolution I. Method and first applications
• The Magnetic Early B-type Stars IV: Breakout or Leakage? H$\alpha$ emission as a diagnostic of plasma transport in centrifugal magnetospheres
• First magnetic field models for recently discovered magnetic beta Cephei and slowly pulsating B stars
• A new type of X-ray pulsar
• HD 156324: a tidally locked magnetic triple spectroscopic binary with a disrupted magnetosphere
• The pulsating magnetosphere of the extremely slowly rotating magnetic $\beta$ Cep star ${\xi }^1$ CMa
• The accelerating rotation of the magnetic He-weak star HD 142990
• New observations of NGC 1624-2 reveal a complex magnetospheric structure and underlying surface magnetic geometry
• The B Fields in OB Stars (BOB) Survey
• Evolving pulsation of the slowly rotating magnetic $\beta$ Cep star ${\xi }^1$ CMa
• Quantitative Modeling of the UV Line Profiles of Magnetic Massive Stars
• The magnetic variability of the $\beta$~Cep star ${\xi }^1$\,CMa

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• MOBSTER -- VII. Using light curves to infer magnetic and rotational properties of stars with centrifugal magnetospheres
• Stellar Magnetism