The variability of Betelgeuse explained by surface convection

Abstract

Context. Betelgeuse is a red supergiant (RSG) that is known to vary semi-regularly on both short and long timescales. The origin of the short period of Betelgeuse has often been associated to radial pulsations but could also be due to the convection motions present at the surface of RSGs. Aims. We investigate the link between surface activity and the variability of the star. Methods. Linear polarization in Betelgeuse is a proxy of convection which is unrelated to pulsations. Using 10 years of spectropolarimetric data of Betelgeuse, we seek for periodicities in the least-squares deconvolution profiles of Stokes I, Q, U and the total linear polarization using Lomb-Scargle periodograms. Results. We find similar periods in linear polarization signals than in photometric variability. The 400 d period is too close to a peak of the window function of our data. But the two periods of 330 d and 200 d are present in the periodogram of Stokes Q and U, showing that the variability of Betelgeuse can be interpreted as due to surface convection. Conclusions. Since linear polarization in the spectrum of Betelgeuse is not known to vary with pulsations, but is linked to surface convection, and since similar periods are found in time series of photometric measurements and spectropolarimetry, we conclude that the photometric variability is due to the surface convective structures, and not to any pulsation phenomenon.

6 pages, 7 figures, accepted for publication in A&A

References in corpus (21)

• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Magnetic fields of non-degenerate stars
• Least squares deconvolution of the stellar intensity and polarization spectra
• Variability in red supergiant stars: pulsations, long secondary periods and convection noise
• Atmospheric dynamics and the mass loss process in red supergiant stars
• Magnetic fields of M dwarfs
• A dusty veil shading Betelgeuse during its Great Dimming
• Standing on the shoulders of giants: New mass and distance estimates for Betelgeuse through combined evolutionary, asteroseismic, and hydrodynamical simulations with MESA
• The Photospheric Temperatures of Betelgeuse during the Great Dimming of 2019/2020: No New Dust Required
• The close circumstellar environment of Betelgeuse. IV. VLTI/PIONIER interferometric monitoring of the photosphere
• The Great Dimming of Betelgeuse: a Surface Mass Ejection (SME) and its Consequences
• The period-luminosity relation of red supergiants with Gaia DR2
• Atmosphere of Betelgeuse before and during the Great Dimming event revealed by tomography
• Tomography of cool giant and supergiant star atmospheres II. Signature of convection in the atmosphere of the red supergiant star $\mu$ Cep
• Convective cells in Betelgeuse: imaging through spectropolarimetry
• Evolution of the magnetic field of Betelgeuse from 2009 - 2017
• Three-dimensional imaging of convective cells in the photosphere of Betelgeuse
• Probing Red Supergiant dynamics through photo-center displacements measured by Gaia
• Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum
• Analysis of photometric and spectroscopic variability of red supergiant Betelgeuse
• The height of convective plumes in the red supergiant $\mu$ Cep

Cited by in corpus (1)

• Betelgeuse, the Prototypical Red Supergiant