HD 164492C: a rapidly-rotating, H$\alpha$-bright, magnetic early B star associated with a 12.5d spectroscopic binary

Abstract

We employ high resolution spectroscopy and spectropolarimetry to derive the physical properties and magnetic characteristics of the multiple system HD 164492C, located in the young open cluster M20. The spectrum reveals evidence of 3 components: a broad-lined early B star (HD 164492C1), a narrow-lined early B star (HD 164492C2), and a late B star (HD 164492C3). Components C2 and C3 exhibit significant ($>100$ km/s) bulk radial velocity variations with a period of $12.5351(7)$ d that we attribute to eccentric binary motion around a common centre-of-mass. Component C1 exhibits no detectable radial velocity variations. Using constraints derived from modeling the orbit of the C2+C3 binary and from synthesis of the combined spectrum, we determine the approximate physical characteristics of the components. We conclude that a coherent evolutionary solution consistent with the published age of M20 implies a distance to the system of $0.9\pm 0.2$ kpc, corresponding to the smallest published values. We confirm the detection of a strong magnetic field in the combined spectrum. The field is clearly associated with the broad-lined C1 component of the system. Repeated measurement of the longitudinal magnetic field allows the derivation of the rotation period of the magnetic star, $P_{\mathrm{rot}}=1.36986(6)$ d. We derive the star's magnetic geometry, finding $i=63\pm 6$ deg, $\beta =33\pm 6$ deg and a dipole polar strength $B_{\mathrm{d}}=7.9_{-1.0}^{+1.2}$ kG. Strong emission - varying according to the magnetic period - is detected in the H$\alpha$ profile. This is consistent with the presence of a centrifugal magnetosphere surrounding the rapidly rotating magnetic C1 component.

Accepted by MNRAS

References in corpus (4)

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Cited by in corpus (13)

• The Magnetic Early B-type Stars I: Magnetometry and Rotation
• The Magnetic Early B-type Stars IV: Breakout or Leakage? H$\alpha$ emission as a diagnostic of plasma transport in centrifugal magnetospheres
• The Magnetic Early B-type Stars II: stellar atmospheric parameters in the era of Gaia
• HD 156324: a tidally locked magnetic triple spectroscopic binary with a disrupted magnetosphere
• $\epsilon$ Lupi: measuring the heartbeat of a doubly-magnetic massive binary with BRITE-Constellation
• Lucky spectroscopy, an equivalent technique to Lucky Imaging: II. Spatially-resolved intermediate-resolution blue-violet spectroscopy of 19 close massive binaries using the William Herschel Telescope
• The binary system of the spinning-top Be star Achernar
• B fields in OB stars (BOB): The magnetic triple stellar system HD 164492C in the Trifid nebula
• Detection of an extremely strong magnetic field in the double-degenerate binary merger product HD 144941
• The magnetic field and magnetosphere of Plaskett's star: A fundamental shift in our understanding of the system
• Photometric properties and stellar parameters of the rapidly rotating magnetic early-B star HD 345439
• The Young Stellar Population, Distance, and Cloud-Cloud Collision Induced Star Formation Scenario of the Trifid Nebula
• MOBSTER -- VII. Using light curves to infer magnetic and rotational properties of stars with centrifugal magnetospheres