Magnetic Field and Convection in the Cool Supergiant Betelgeuse

Petit, P.; Aurière, M.; Konstantinova-Antova, R.; Morgenthaler, A.; Perrin, G.; Roudier, T.; Donati, J.‐F.

doi:10.1007/978-3-642-30648-8_9

Cited by 25 publications

(24 citation statements)

References 30 publications

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“…In a parallel study, Aurière et al (2010) detect a weak magnetic field, at the Gauss-level, at the surface of α Ori and this is so far the only RSG star for which a direct detection has been obtained. A follow-up study also A&A 603, A129 (2017) shows that this surface magnetic field appears to vary on a monthly time-scale (Bedecarrax et al 2013;Petit et al 2013) in agreement with the convective patterns time-scale (Freytag et al 2002;Montargès et al 2015).…”

Section: Introductionmentioning

confidence: 58%

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Measuring surface magnetic fields of red supergiant stars

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Morin

et al. 2017

A&A

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Context. Red supergiant (RSG) stars are very massive cool evolved stars. Recently, a weak magnetic field was measured at the surface of α Ori and this is so far the only M-type supergiant for which a direct detection of a surface magnetic field has been reported. Aims. 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 α Ori is a common feature among the M-type supergiants. Methods. With the spectropolarimeter Narval at Télescope Bernard-Lyot 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. Results. We detect weak Zeeman signatures of stellar origin in the targets CE Tau, α 1 Her and µ 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 µ Cep, the longitudinal component of the detected surface fields is at the Gauss-level, such as in α Ori. We measured a longitudinal field almost an order of magnitude stronger for α 1 Her. We also report variability of the longitudinal magnetic field of CE Tau and α 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 ρ Cas. Conclusions. The two RSG stars of our sample, CE Tau and µ Cep, display magnetic fields very similar to that of α Ori. The nondetection of a magnetic field on the post-RSG star ρ Cas suggests that the magnetic field disappears, or at least becomes undetectable with present methods, at later evolutionary stages. Our analysis of α 1 Her supports the proposed reclassification of the star as an M-type asymptotic giant branch star.

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Section: Introductionmentioning

confidence: 58%

“…For active stars, emission can be seen in the core of these lines. Petit et al (2013) report no emission in the core of these lines for α Ori and no significant indication of activity. In our own study, we also found no sign of activity in these lines for µ Cep.…”

Section: µ Cepmentioning

confidence: 84%

Measuring surface magnetic fields of red supergiant stars

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Lèbre

Morin

et al. 2017

A&A

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“…Two 0.22 nm-wide rectangular bandpasses V Hα and R Hα , centred on 655.885 and 656.730 nm respectively, were used for the continuum flux in the red and blue sides of the Hα line. The TBL CaIRT-index, following Petit et al (2013), was determined using using Eqn. 3 .…”

Section: Tbl Activity Indices For Hd 35296mentioning

confidence: 99%

Magnetic fields on young, moderately rotating Sun-like stars – I. HD 35296 and HD 29615

Waite

Marsden

Carter

et al. 2015

Monthly Notices of the Royal Astronomical Society

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Observations of the magnetic fields of young solar-type stars provide a way to investigate the signatures of their magnetic activity and dynamos. Spectropolarimetry enables the study of these stellar magnetic fields and was thus employed at the Télescope Bernard Lyot and the Anglo-Australian Telescope to investigate two moderately rotating young Sun-like stars, namely HD 35296 (V119 Tau, HIP 25278) and HD 29615 (HIP 21632). The results indicate that both stars display rotational variation in chromospheric indices consistent with their spot activity, with variations indicating a probable long-term cyclic period for HD 35296. Additionally, both stars have complex, and evolving, large-scale surface magnetic fields with a significant toroidal component. High levels of surface differential rotation were measured for both stars. . Such a significant discrepancy in shear values between spot and magnetic features for HD 29615 is an extreme example of the variation observed for other lower-mass stars. From the extensive and persistent azimuthal field observed for both targets it is concluded that a distributed dynamo operates in these moderately rotating Sun-like stars, in marked contrast to the Sun's interface-layer dynamo.

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“…While local dynamos are probably active in all stars with convective zones, their direct observational signatures may only be detectable in the most evolved objects (cool supergiants), for which the larger pressure scale height results in much larger convective cells (Schwarzschild 1975). This last type of magnetism is presumably responsible for the weak magnetic field detected at the surface of the slowly rotating supergiant Betelgeuse Petit et al 2013). A&A 556, A43 (2013) Observations are obviously essential for deciding between these different scenarios (that may act independently or together, depending on the object) or unveil other possible physical explanations for the manifestations of atmospheric activity recorded in cool, evolved stars.…”

Section: Introductionmentioning

confidence: 99%

Magnetic field structure in single late-type giants:βCeti in 2010–2012

Tsvetkova

Petit

Aurière

et al. 2013

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Aims. We study the behavior of the magnetic field and the line activity indicators of the single late-type giant β Ceti. Using spectropolarimetric data, we aim to reconstruct the magnetic field structure on the star's surface and to present the first magnetic maps for β Ceti. Methods. The data were obtained using two spectropolarimeters -Narval at the Bernard Lyot Télescope, Pic du Midi, France, and ESPaDOnS at CFHT, Hawaii. Thirty-eight circularly-polarized spectra have been collected in the period June 2010-January 2012. The least square deconvolution method was applied for extracting high signal-to-noise ratio line profiles, from which we measured the surface-averaged longitudinal magnetic field B l . Chromospheric activity indicators CaII K, Hα, CaII IR (854.2 nm), and radial velocity were simultaneously measured, and their variability was analyzed along with the behavior of B l . The Zeeman Doppler imaging (ZDI) inversion technique was employed for reconstructing the large-scale magnetic field and two magnetic maps of β Ceti are presented for two periods (June 2010-December 2010 and June 2011-January 2012). Results. The B l stays with a same positive polarity for the whole observational period and shows significant variations in the interval 0.1-8.2 G. The behavior of the line activity indicators is in good agreement with the B l variations. Searching for periodic signals in the Stokes V time series, we found a possible rotation period of 215 days. The two ZDI maps show a mainly axisymmetric and poloidal magnetic topology and a simple surface magnetic field configuration dominated by a dipole. Little evolution is observed between the two maps, in spite of a 1 yr interval between both subsets. We also use state-of-the-art stellar evolution models to constrain the evolutionary status of β Ceti. We derive a mass of 3.5 M and propose that this star is already in the central helium-burning phase. Conclusions. Considering all our results and the evolutionary status of the star, we suggest that dynamo action alone may not be efficient enough to account for the high magnetic activity of β Ceti. As an alternate option, we propose that it is a descendant of an Ap star presently undergoing central helium-burning and still exhibiting a remnant of the Ap star magnetic field.

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Magnetic Field and Convection in the Cool Supergiant Betelgeuse

Cited by 25 publications

References 30 publications

Measuring surface magnetic fields of red supergiant stars

Measuring surface magnetic fields of red supergiant stars

Magnetic fields on young, moderately rotating Sun-like stars – I. HD 35296 and HD 29615

Magnetic field structure in single late-type giants:βCeti in 2010–2012

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