Ref: SCART-2021-0068

Polarimetric detection of nonradial oscillation modes in β Crucis

Cotton, D.V. ; Buzasi, D.L. ; Aerts, C. ; Bailey, J. ; Burssens, S. ; Pedersen, M.G. ; Stello, D. ; Kedziora-Chudczer, L. ; De Horta, A. ; De Cat, P. ; Lewis, F. ; Malla, S.P. ; Wright, D.J. ; Bott, K.

submitted to Nature Astronomy (2021)

Abstract: Asteroseismology has revolutionised our knowledge of low- and intermediate-mass stars across their entire evolution – determining fundamental parameters like mass, radius and age, and inferring interior rotation. High-mass stars in the range 8–25 M are also asteroseismically active and are known as β Cep stars. Their pulsation modes are of low radial order and lack recognisable frequency patterns, making mode assignment difficult. Identification of the mode degree, l, and azimuthal order, m, is a prerequisite for asteroseismic inferences of the stellar interior. Here we report the detection of polarization variations due to nonradial modes in the 14 M B-type star β Crucis. In so doing we confirm 40-year-old predictions of pulsation-induced polarization variability and its utility in mode identification. In an approach suited to other high-mass stars, we combine polarimetry with space-based photometry and archival spectroscopy to identify the dominant nonradial mode in polarimetry, f2, as l= 3, m = −3 and determine the stellar axis position angle as 25 (or 205) ± 8 deg. The rotation axis inclination to the line-of-sight was derived as 29 ± 2 deg from combined polarimetry and spectroscopy; this constraint was critical to enabling identification of additional modes, which in turn facilitated asteroseismic modelling. The modelling reveals a star about half way through its core hydrogen burning, with a convective core ∼28% of its total mass – making β Crucis the most massive star with an asteroseismic age.

The record appears in these collections:
Royal Observatory of Belgium > Astronomy & Astrophysics
Science Articles > Peer Reviewed Articles

 Record created 2021-02-10, last modified 2021-02-10