Weak magnetic field, solid-envelope rotation, and wave-induced N-enrichment in the SPB star<i>ζ</i>Cassiopeiae

Briquet, Maryline; Neiner, C.; Petit, P.; Leroy, B.; Batz, B. de

doi:10.1051/0004-6361/201527751

Cited by 12 publications

(11 citation statements)

References 63 publications

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“…The detection of differentially rotating surfaces is common in cool active stars (Barnes et al 2005; Ammler-von Eiff & Reiners 2012). Similar searches have been so far unsuccessful when conducted on more massive, strongly magnetic stars (Donati et al 2006;Briquet et al 2016), while intermediate mass stars without strong surface magnetism seem to be differentially rotating (Balona & Abedigamba 2016). This lack of positive results is also consistent with the long-term stability of magnetic geometries of Ap stars (see e.g.…”

Section: Differential Rotationsupporting

confidence: 76%

Magnetic geometry and surface differential rotation of the bright Am star Alhena A

Blazère

Petit

Neiner

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Alhena A (γ Gem A) is a bright Am star, with the strongest disc-integrated magnetic field strength reported so far for an Am star. Its spectrum exhibits standard circularly polarized Zeeman signatures, contrary to all previously studied Am stars that display abnormal signatures dominated by a single-signed lobe.We present here the result of follow-up observations of Alhena, using very high signal-to-noise spectropolarimetric data obtained over 25 observing nights with NAR-VAL at Télescope Bernard Lyot, in the frame of the BRITE (BRIght Target Explorer) spectropolarimetric survey.We confirm that Alhena A is magnetic and we determine its surface magnetic properties using different methods. Inclined dipole models are used to reproduce the longitudinal field measurements, as well as the Stokes V line profiles themselves. In both cases, the model is consistent with a polar field strength of ∼ 30 G. This is confirmed by a Zeeman-Doppler Imaging (ZDI) model, which also unveils smaller scale magnetic structures. A rotational period of 8.975 days was identified using intensity line profile variations. The ZDI inversion suggests that the surface magnetic field is sheared by differential rotation, with a difference in rotation rate between high and low latitudes at about 15% of the solar value. This result challenges theories of the development of surface differential rotation in intermediate mass main sequence stars.

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Section: Differential Rotationsupporting

confidence: 76%

Magnetic geometry and surface differential rotation of the bright Am star Alhena A

Blazère

Petit

Neiner

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…On the other hand, the Ap component of HD 5550 has a higher temperature than the samples analysed in those works. Polar field strengths of 10-100 G have been recently found in early-B type stars (above B3) (Fossati et al 2015;Briquet et al 2016). While the limit of 100 G appears to be strict at temperatures lower than 10 000 K, it may decrease with increasing temperatures.…”

Section: Summary and Discussionmentioning

confidence: 94%

The magnetic field of the double-lined spectroscopic binary system HD 5550

Alécian¹,

Tkachenko²,

Neiner³

et al. 2016

A&A

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Context. The origin of fossil fields in intermediate-and high-mass stars is poorly understood, as is the interplay between binarity and magnetism during stellar evolution. Thus we have begun a study of the magnetic properties of a sample of intermediate-mass and massive short-period binary systems as a function of binarity properties. Aims. This paper specifically aims to characterise the magnetic field of HD 5550, a double-lined spectroscopic binary system of intermediate mass.Methods. We gathered 25 high-resolution spectropolarimetric observations of HD 5550 using the instrument Narval. We first fitted the intensity spectra using Zeeman/ATLAS9 LTE synthetic spectra to estimate the effective temperatures, microturbulent velocities, and the abundances of some elements of both components, as well as the light ratio of the system. We then applied the multi-line least-square deconvolution (LSD) technique to the intensity and circularly polarised spectra, which provided us with mean LSD I and V line profiles. We fitted the Stokes I line profiles to determine the radial and projected rotational velocities of both stars. We then analysed the shape and evolution of the V profiles using the oblique rotator model to characterise the magnetic fields of both stars. Results. We confirm the Ap nature of the primary, which has previously been reported, and find that the secondary displays spectral characteristics typical of an Am star. While a magnetic field is clearly detected in the lines of the primary, no magnetic field is detected in the secondary in any of our observations. If a dipolar field were present at the surface of the Am star, its polar strength must be below 40 G. The faint variability observed in the Stokes V profiles of the Ap star allowed us to propose a rotation period of 6.84 +0.61 −0.39 d, which is close to the orbital period (∼6.82 d), suggesting that the star is synchronised with its orbit. By fitting the variability of the V profiles, we propose that the Ap component hosts a dipolar field inclined with the rotation axis at an angle β = 156 ± 17• and a polar strength B d = 65 ± 20 G. The field strength is the weakest known for an Ap star.

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“…Asteroseismic modeling of the the magnetic β Cep pulsator V 2052 Ophiuchi by Briquet et al (2012) revealed that an internal magnetic field can suppress core overshoot. In addition, Briquet et al (2016) showed that the weakly magnetic B2 IV-V SPB star ζ Cas rotates rigidly with a magnetic field of strength 100-150 G inhibiting mixing in its envelope. The observed nitrogen enhancement was then attributed to transport by internal gravity waves.…”

Section: Summary Discussion and Conclusionmentioning

confidence: 99%

Sub-Inertial Gravity Modes in the B8v Star Kic 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing

Moravveji

Townsend

Aerts

et al. 2016

ApJ

164

273

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Thus far, KIC 7760680 is the richest slowly pulsating B star, exhibiting 36 consecutive dipole (ℓ = 1) gravity (g-) modes. The monotonically decreasing period spacing of the series, in addition to the local dips in the pattern, confirm that KIC 7760680 is a moderate rotator with clear mode trapping in chemically inhomogeneous layers. We employ the traditional approximation of rotation to incorporate rotational effects on g-mode frequencies. Our detailed forward asteroseismic modeling of this g-mode series reveals that KIC 7760680 is a moderately rotating B star with mass ∼3.25 M e . By simultaneously matching the slope of the period spacing and the number of modes in the observed frequency range, we deduce that the equatorial rotation frequency of KIC 7760680 is 0.4805 day −1 , which is 26% of its Roche break up frequency. The relative deviation of the model frequencies and those observed is less than 1%. We succeed in tightly constraining the exponentially decaying convective core overshooting parameter to f ov ≈ 0.024 ± 0.001. This means that convective core overshooting can coexist with moderate rotation. Moreover, models with exponentially decaying overshoot from the core outperform those with the classical step-function overshoot. The best value for extra diffusive mixing in the radiatively stable envelope is confined to »  D log 0.75 0.25 ext (with D ext in cm 2 s −1 ), which is notably smaller than theoretical predictions.

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Weak magnetic field, solid-envelope rotation, and wave-induced N-enrichment in the SPB starζCassiopeiae

Cited by 12 publications

References 63 publications

Magnetic geometry and surface differential rotation of the bright Am star Alhena A

Magnetic geometry and surface differential rotation of the bright Am star Alhena A

The magnetic field of the double-lined spectroscopic binary system HD 5550

Sub-Inertial Gravity Modes in the B8v Star Kic 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing

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