Measuring surface magnetic fields of red supergiant stars

Abstract

RSG stars are very massive cool evolved stars. Recently, a weak magnetic field was measured at the surface of $\alpha$ Ori and this is so far the only M-type supergiant for which a direct detection of a surface magnetic field has been reported. By extending the search for surface magnetic field in a sample of late-type supergiants, we want to determine whether the surface magnetic field detected on $\alpha$ Ori is a common feature among the M-type supergiants. With the spectropolarimeter Narval at TBL we undertook a search for surface magnetic fields in a sample of cool supergiant stars, and we analysed circular polarisation spectra using the least-squares deconvolution technique. We detect weak Zeeman signatures of stellar origin in the targets CE Tau, ${\alpha }^1$ Her and $\mu$ Cep. For the latter star, we also show that cross-talk from the strong linear polarisation signals detected on this star must be taken into account. For CE Tau and $\mu$ Cep, the longitudinal component of the detected surface fields is at the Gauss-level, such as in $\alpha$~Ori. We measured a longitudinal field almost an order of magnitude stronger for ${\alpha }^1$ Her. We also report variability of the longitudinal magnetic field of CE Tau and ${\alpha }^1$ Her, with changes in good agreement with the typical atmospheric dynamics time-scales. We also report a non-detection of magnetic field at the surface of the yellow supergiant star $\rho$ Cas. The two RSG stars of our sample, CE Tau and $\mu$ Cep, display magnetic fields very similar to that of $\alpha$ Ori. The non-detection of a magnetic field on the post-RSG star $\rho$ Cas suggests that the magnetic field disappears, or at least becomes undetectable with present methods, at later evolutionary stages. Our analysis of ${\alpha }^1$ Her supports the proposed reclassification of the star as an AGB star.

Accepted for publication in Astronomy and Astrophysics (2017 April 19)

References in corpus (9)

• The evolution of surface magnetic fields in young solar-type stars I: the first 250 Myr
• Atmospheric dynamics and the mass loss process in red supergiant stars
• The Magnetic Fields at the Surface of Active Single G-K Giants
• Searching for Cool Dust in the Mid-to-Far Infrared: the Mass Loss Histories of The Hypergiants $\mu$ Cep, VY CMa, IRC+10420, and $\rho$ Cas
• Detection of ultra-weak magnetic fields in Am stars: beta UMa and theta Leo
• First detection of surface magnetic fields in Post-AGB stars : the cases of U Monocerotis and R Scuti
• The magnetic strip(s) in the advanced phases of stellar evolution - Theoretical convective turnover timescale and Rossby number for low- and intermediate-mass stars up to the AGB at various metallicities
• Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum
• The convection of close red supergiant stars observed with near-infrared interferometry

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