ϵ Sagittarii : an extreme rapid rotator with a decretion disk

J. Bailey, F. Lewis, I. D. Howarth, Daniel V. Cotton, J. P. Marshall, L. Kedziora-Chudczer

Research output: Contribution to journalArticlepeer-review

Abstract

We report high-precision, multiwavelength 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 ultraviolet polarimetry, any of which would allow its extreme rotation to be tested and its stellar properties to be refined.

Original languageEnglish
Article number103
Number of pages14
JournalAstrophysical Journal
Volume972
Issue number1
DOIs
Publication statusPublished - 1 Sept 2024

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Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence (https://creativecommons.org/licenses/by/4.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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