Abstract
Here we report the detection of polarization variations due to non-radial modes in the beta Cephei star beta Crucis. In so doing we confirm 40-year-old predictions of pulsation-induced polarization variability and its utility in asteroseismology for mode identification. In an approach suited to other beta Cephei stars, we combine polarimetry with space-based photometry and archival spectroscopy to identify the dominant non-radial mode in polarimetry, f(2), as mode degree l = 3, azimuthal order m = -3 (in the m-convention of Dziembowski) and determine the stellar axis position angle as 25 (or 205) +/- 8 degrees. The rotation axis inclination to the line of sight was derived as similar to 46 degrees from combined polarimetry and spectroscopy, facilitating identification of additional modes and allowing for asteroseismic modelling. This reveals a star of 14.5 +/- 0.5 M-circle dot and a convective core containing similar to 28% of its mass-making beta Crucis the most massive star with an asteroseismic age.