2024/07/16 by Jeremy Bailey, Bailey, Jeremy, F. Lewis +9 · 2 citations
Engineering · #FOS: Physical sciences #Instrumentation and Methods for Astrophysics (astro-ph.IM) #Mechanics and Biomechanics Studies #Solar and Stellar Astrophysics (astro-ph.SR)
paper · pdf · doi:10.48550/arxiv.2407.11352
openalex publication_date 2024/07/16 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We report high-precision multi-wavelength linear-polarization observations of the bright B9 (or A0) star ε Sagittarii. The polarization shows the distinctive wavelength dependence expected for a rapidly rotating star. Analysis of the polarization data reveals an angular rotation rate ω (= Ω/Ωcrit) of 0.995 or greater, the highest yet measured for a star in our galaxy. An additional wavelength-independent polarization component is attributed to electron scattering in a low-density edge-on gas disk that also produces the narrow absorption components seen in the spectrum. Several properties of the star (polarization due to a disk, occasional weak Hα emission, and multiple periodicities seen in space photometry) resemble those of Be stars, but the level of activity in all cases is much lower than that of typical Be stars. The stellar properties are inconsistent with single rotating-star evolutionary tracks, indicating that it is most likely a product of binary interaction. The star is an excellent candidate for observation by interferometry, optical spectropolarimetry to detect the Öhman effect, and UV polarimetry; any of which would allow its extreme rotation to be tested and its stellar properties to be refined.