Constraining the Limits of the Magnetic Confinement-Rotation Diagram: An Analysis of Two B-type Systems Hosting Recently Discovered Extreme Centrifugal Magnetospheres
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Following the detection in the late 70s of a strong magnetic field in the early B-type star sigma Ori E and, more recently with the results of the Magnetism In MassivE Stars (MiMeS) survey, an important and rare subclass of magnetic B-type stars has been emerging. Magnetic stars hosting so called "centrifugal magnetospheres" are characterized by rapid rotation and feature strong and broad emission lines in their spectra produced by a hot plasma co-rotating with the star well beyond the surface (at distances of several times the stellar radius). Since the first discovery of these properties in the magnetic B2Vp star sigma Ori E, the dense, rigidly-rotating circumstellar plasma has been understood as an accumulation of the star's wind in regions of closed magnetic loops above the surface. These objects serve as unique laboratories for studying how the fast winds emitted by all B-type stars interact with magnetic fields in extreme environments. In this study, the properties of two rapidly rotating stars, HD 23478 and HD 35502, hosts to centrifugal magnetospheres and exhibiting strong emission in their spectra, are derived. Our results establish new upper limits on the magnetic confinement-rotation diagram -- a diagnostic tool which is used to understand the magnetospheres of O- and B-type stars in a broader context. The derived rapid rotation and strong magnetic fields imply that these two stars occupy the most extreme region of the magnetic confinement-rotation diagram populated by known centrifugal magnetosphere-hosting stars such as sigma Ori E and HR 5907.