The magnetic field and magnetosphere of Plaskett's star: A fundamental shift in our understanding of the system

Abstract

Plaskett's "star" appears to be one of a small number of short-period binary systems known to contain a hot, massive, magnetic star. Building on the 2013 discovery investigation, we combine an extensive spectropolarimetric (Stokes $V$) dataset with archival photometry and spectropolarimetry to establish the essential characteristics of the magnetic field and magnetosphere of the rapidly rotating, broad-line component of the system. We apply Least-Squares Deconvolution (LSD) to infer the longitudinal magnetic field from each Stokes $V$ spectrum. Using the timeseries of longitudinal field measurements, in combination with CoRoT photometry and equivalent width measurements of magnetospheric spectral lines, we infer the rotation period of the magnetic star to be equal to $1.21551_{-0.00034}^{+0.00028}$ d. Modeling the Stokes $V$ LSD profiles with Zeeman Doppler Imaging, we produce the first {reliable} magnetic map of an O-type star. We find a magnetic field that is predominantly dipolar, but with an important quadrupolar component, and weak higher order components. The dipolar component has an obliquity near 90 deg and a polar strength of about 850 G, while the average field strength over the entire surface is 520 G. We update the calculations of the theoretical magnetospheric parameters, and in agreement with their predictions we identify clear variability signatures of the H$\alpha$, H$\beta$, and He II $\lambda 4686$ lines confirming the presence of a dense centrifugal magnetosphere surrounding the star. Finally, we report a lack of detection of radial velocity (RV) variations of the observed Stokes $V$ profiles, suggesting that historical reports of the large RV variations of the broad-line star's spectral lines may be spurious. This discovery may motivate a fundamental revision of the historical model of the Plaskett's star as a near-equal mass O+O binary system.

25 pages, accepted by MNRAS

References in corpus (29)

• The Transiting Exoplanet Survey Satellite
• Binary interaction dominates the evolution of massive stars
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• Pre-Supernova Evolution of Massive Single and Binary Stars
• The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit
• The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
• Weak magnetic fields in Ap/Bp stars: Evidence for a dipole field lower limit and a tentative interpretation of the magnetic dichotomy
• How mergers magnetise massive stars
• Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: II. The Effects of Field-Aligned Rotation
• The MiMeS survey of magnetism in massive stars: Magnetic analysis of the O-type stars
• Binary Star Origin of High Field Magnetic White Dwarfs
• The evolution of surface magnetic fields in young solar-type stars II: The early main sequence (250-650 Myr)
• The Magnetic Early B-type Stars I: Magnetometry and Rotation
• Mass segregation in very young open clusters -- A case study of NGC 2244 and NGC 6530
• High resolution optical spectroscopy of Plaskett's star
• The Magnetic Early B-type Stars IV: Breakout or Leakage? H$\alpha$ emission as a diagnostic of plasma transport in centrifugal magnetospheres
• Exploring the photometric signatures of magnetospheres around Helium-strong stars
• How the breakout-limited mass in B-star centrifugal magnetospheres controls their circumstellar H-alpha emission
• The BinaMIcS project: understanding the origin of magnetic fields in massive stars through close binary systems
• Properties of six short-period massive binaries: a study of the effects of binarity on surface chemical abundances
• The accelerating rotation of the magnetic He-weak star HD 142990
• A JVLA survey of the high frequency radio emission of the massive magnetic B- and O-type stars
• HD 164492C: a rapidly-rotating, H$\alpha$-bright, magnetic early B star associated with a 12.5d spectroscopic binary
• Search for magnetic fields in particle-accelerating colliding-wind binaries
• A search for weak or complex magnetic fields in the the B3V star iota Herculis
• NGC 6611 601: A hot pre-main sequence spectroscopic binary containing a centrifugal magnetosphere host star
• Short-term spectroscopic variability of Plaskett's star
• Magnetic fields in early-type stars
• Mapping Stellar Magnetic Fields

Cited by in corpus (7)

• Are magnetic fields universal in O-type multiple systems?
• Ultraviolet Spectropolarimetry: Investigating stellar magnetic field diagnostics
• Ultraviolet Spectropolarimetry With Polstar: Using Polstar to test Magnetospheric Mass-loss Quenching
• Detection of extragalactic magnetic massive stars
• MOBSTER -- VII. Using light curves to infer magnetic and rotational properties of stars with centrifugal magnetospheres
• Stellar Magnetism
• A magnetic field detection in the massive O-type bright giant 63 Oph