Polarimetric detection of nonradial oscillation modes in the beta Cephei star beta Crucis

Abstract

Here we report the detection of polarization variations due to nonradial 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 Cep 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 (in the m-convention of Dziembowski) 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 approx. 46 deg. from combined polarimetry and spectroscopy, facilitating identification of additional modes and allowing for asteroseismic modelling. This reveals a star of 14.5 +/- 0.5 Solar masses and a convective core containing approx. 28% of its mass -- making beta Crucis the most massive star with an asteroseismic age.

33 pages, 11 figures, 8 tables (incl. Supplementary Information). Accepted version; published as Cotton et al. (2022), Nature Astro., Vol 6, pp 154-164. Data is available through VizieR as: J/other/NatAs/6.154. Two explainer articles are available: Cotton & Buzasi (2022), Nature Astro., Vol 6, pp 24-25; Baade (2022), Nature Astro., Vol 6, pp 20-21

References in corpus (13)

• Asteroseismology of solar-type stars
• Discovery of magnetic fields in the beta Cephei star xi^1 CMa and in several Slowly Pulsating B stars
• Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs
• Diverse Variability of O and B Stars Revealed from 2-minute Cadence Light Curves in Sectors 1 and 2 of the TESS Mission: Selection of an Asteroseismic Sample
• A new method for the spectroscopic identification of stellar non-radial pulsation modes. I. The method and numerical tests
• A high-sensitivity polarimeter using a ferro-electric liquid crystal modulator
• New magnetic field measurements of beta Cephei stars and Slowly Pulsating B stars
• HIPPI-2: A Versatile High Precision Polarimeter
• Recipes for bolometric corrections and Gaia luminosities of B-type stars: Application to an asteroseismic sample
• Tess asteroseismology of the known planet host star ${\lambda }^2$ Fornacis
• A high precision polarimeter for small telescopes
• Beta Cephei stars in the ASAS-3 data. I. Long-term variations of periods and amplitudes
• Polarization of hot Jupiter systems: a likely detection of stellar activity and a possible detection of planetary polarization

Cited by in corpus (5)

• Pulsating B stars in the Scorpius-Centaurus Association with TESS
• Multiples among B stars in the Scorpius-Centaurus association
• A study of the F-giant star $\theta$ Scorpii A: a post-merger rapid rotator?
• PICSARR: high-precision polarimetry using CMOS image sensors
• Polarization position angle standard stars: a reassessment of $\theta$ and its variability for seventeen stars based on a decade of observations