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        Polarization due to rotational distortion in the bright star Regulus

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        1804_06576v1.aam.pdf (PDF, 3Mb)
        Author
        Cotton, Daniel V.
        Bailey, Jeremy A.
        Howarth, Ian D.
        Bott, Kimberly
        Kedziora-Chudczer, Lucyna
        Lucas, P. W.
        Hough, J. H.
        Attention
        2299/20473
        Abstract
        Polarization in stars was first predicted by Chandrasekhar [1] who calculated a substantial linear polarization at the stellar limb for a pure electron-scattering atmosphere. This polarization will average to zero when integrated over a spherical star but could be detected if the symmetry is broken, for example by the eclipse of a binary companion. Nearly 50 years ago, Harrington and Collins [2] modeled another way of breaking the symmetry and producing net polarization - the distortion of a rapidly rotating hot star. Here we report the first detection of this effect. Observations of the linear polarization of Regulus, with two different high-precision polarimeters, range from +42 parts-per-million (ppm) at a wavelength of 741 nm to -22 ppm at 395 nm. The reversal from red to blue is a distinctive feature of rotation-induced polarization. Using a new set of models for the polarization of rapidly rotating stars we find that Regulus is rotating at 96.5(+0.6/-0.8)% of its critical angular velocity for breakup, and has an inclination greater than 76.5 degrees. The rotation axis of the star is at a position angle of 79.5+/-0.7 degrees. The conclusions are independent of, but in good agreement with, the results of previously published interferometric observations of Regulus [3]. The accurate measurement of rotation in early-type stars is important for understanding their stellar environments [4], and course of their evolution [5].
        Publication date
        2018-10-01
        Published in
        Nature Astronomy
        Published version
        https://doi.org/10.1038/s41550-017-0238-6
        Other links
        http://hdl.handle.net/2299/20473
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