Polarization due to rotational distortion in the bright star Regulus

Daniel V. Cotton, Jeremy A. Bailey, Ian D. Howarth, Kimberly Bott, Lucyna Kedziora-Chudczer, P. W. Lucas, J. H. Hough

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17 Citations (Scopus)
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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].
Original languageEnglish
Pages (from-to)690–696
Number of pages7
JournalNature Astronomy
Issue number10
Early online date18 Sept 2017
Publication statusPublished - 1 Oct 2018


  • astro-ph.SR


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