Polarization due to rotational distortion in the bright star Regulus

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$\begin{array}{c}+0.6-0.8\end{array}$% 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$\pm$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].

arXiv commentThis is the full published article including the Methods and Supplementary Information sections: 33 pages, 10 figures, 8 tables

References in corpus (13)

• Validation of the new Hipparcos reduction
• Be-star rotation: how close to critical?
• Gravity darkening in rotating stars
• Rotational velocities of A-type stars IV. Evolution of rotational velocities
• First Results from the CHARA Array. I. An Interferometric and Spectroscopic Study of the Fast Rotator alpha Leonis (Regulus)
• Colder and Hotter: Interferometric imaging of β Cassiopeiae and α Leonis
• New limb-darkening coefficients and synthetic photometry for model-atmosphere grids at Galactic, LMC, and SMC abundances
• A high-sensitivity polarimeter using a ferro-electric liquid crystal modulator
• Polarization measurements of hot dust stars and the local interstellar medium
• The linear polarisation of southern bright stars measured at the parts-per-million level
• A High Precision, Optical Polarimeter to Measure Inclinations of High Mass X-Ray Binaries
• The intrinsic and interstellar broadband linear polarization of nearby FGK dwarfs
• Rapid rotators revisited: absolute dimensions of KOI-13

Cited by in corpus (23)

• A Chip-scale, Full-Stokes Polarimeter
• Polarized Radiative Transfer in Planetary Atmospheres and the Polarization of Exoplanets
• The wavelength dependence of interstellar polarization in the Local Hot Bubble
• The polarization of the planet-hosting WASP-18 system
• RefPlanets: Search for reflected light from extra-solar planets with SPHERE/ZIMPOL
• Ultraviolet Spectropolarimetry: on the origin of rapidly rotating B stars
• The Rotationally Modulated Polarization of $\xi$ Boo A
• The Polstar High Resolution Spectropolarimetry MIDEX Mission
• Polarization of hot Jupiter systems: a likely detection of stellar activity and a possible detection of planetary polarization
• The rotation of alpha Oph investigated using polarimetry
• Polarimetric detection of nonradial oscillation modes in the beta Cephei star beta Crucis
• Polarimetric and radiative transfer modelling of HD 172555
• Phase-locked polarization by photospheric reflection in the semidetached eclipsing binary ${\mu }^1$ Sco
• Photo-polarimetric characteristics of brown dwarfs, Part I: uniform cloud decks
• Detection of polarization neutral points in observations of the combined corona and sky during the 21 August 2017 total solar eclipse
• A study of the F-giant star $\theta$ Scorpii A: a post-merger rapid rotator?
• The evolved fast rotator Sargas. Stellar parameters and evolutionary status from VLTI/PIONIER and VLT/UVES
• A study of the rapid rotator $\zeta$ Aql: differential surface rotation?
• PICSARR: high-precision polarimetry using CMOS image sensors
• Multi-wavelength aperture polarimetry of debris disc host stars
• The polarization of the binary system Spica, and the reflection of light from stars
• Polarization position angle standard stars: a reassessment of $\theta$ and its variability for seventeen stars based on a decade of observations
• Fundamental properties of two rapidly rotating stars: Rasalhague and Alkaid