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

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