The magnetic field and wind confinement of<i>β</i>Cephei: new clues for interpreting the Be phenomenon?

Donati, J.‐F.; Wade, G. A.; Babel, J.; Henrichs, H.F.; Jong, J.A. de; Harries, Tim J.

doi:10.1111/j.1365-2966.2001.04713.x

Cited by 127 publications

(169 citation statements)

References 23 publications

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“…New fiberfed spectropolarimeters avoid both instrumental polarization, with the polarimeter part placed at the Cassegrain focus of the telescope, and flexures, by the use of fiber optics to feed a fixed spectrograph (Donati et al 1999). However, fibers can produce other problems depending on how they are interfaced between the two instrumental components (Eversberg et al 1998).…”

Section: Discussionmentioning

confidence: 99%

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Detecting Magnetic Fields in Rotationally Perturbed, Hot Stellar Winds

Chesneau¹,

Moffat²

2002

PUBL ASTRON SOC PAC

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ABSTRACT. In this paper, we report on an attempt to optically detect localized and/or variable magnetic fields in the single O4 I(n)f star z Puppis and in the WC 8 star in the binary star g 2 Velorum with the spectropolarimeter Cassegrain echelle spectrograph mounted on the ESO 3.6 m telescope. The spectra cover 5700-6800 Å with resolution element 0.2 Å . These stars are sufficiently bright in principle to obtain Stokes V spectra with excellent signal-to-noise ratio and temporal resolution at this telescope. We discuss several procedures adapted to the extraction of the polarized signal from broad lines to put constraints on the global and local magnetic fields. Despite some instrumental difficulties, we report a null longitudinal component of the global magnetic field measurement in z Pup with G. We also find no significant activity in Stokes V above in10 minutes in z Puppis's observable photospheric lines, in a spectral bandpass of 0.2-3 Å . We also report a null detection above for the emission lines of g Vel. Spectral variability in natural light for these stars is 3j ∼ 0.3% V also discussed. Finally, we discuss the potential of such spectropolarimetric techniques in the context of newgeneration spectropolarimeters.

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Section: Discussionmentioning

confidence: 99%

“…Several physical processes are frequently invoked to be at the origin of the structures: wind instabilities, nonradial pulsations (NRPs), and rotating global or local magnetic fields. Some recent discoveries of Zeeman signatures in early-type stars, such as b Cep (B2 III, km s ; Donati et al 2001), show that even…”

Section: Introductionmentioning

confidence: 99%

Detecting Magnetic Fields in Rotationally Perturbed, Hot Stellar Winds

Chesneau¹,

Moffat²

2002

PUBL ASTRON SOC PAC

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“…A field was discovered in the prototype β Cep star, β Cep = HD 205021 itself (Henrichs et al 2000;Neiner et al 2001;Donati et al 2001). The field of this star appears to be very securely detected (see Sect.…”

Section: β Cephei Pulsators and Slowly Pulsating B Starsmentioning

confidence: 99%

“…On the basis of data from the MuSiCoS spectropolarimeter, Henrichs et al (2000), Neiner et al (2001) and Donati et al (2001) have reported the detection of a weak field in HD 205021 = β Cep, a double system composed of a Be star and a pulsating star -the latter being the proto-type of β Cep pulsating stars. Schnerr et al (2006) have shown that the primary star of the β Cep system is the pulsating and magnetic star, while the Be star is a non-magnetic companion that can be separated with speckle interferometry.…”

Section: Classical Be Starsmentioning

confidence: 99%

Magnetic field measurements and their uncertainties: the FORS1 legacy

Bagnulo

Landstreet

Fossati

et al. 2012

A&A

149

278

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Context. During the last decade, the FORS1 instrument of the ESO Very Large Telescope has been extensively used to study stellar magnetism. A number of interesting discoveries of magnetic fields in several classes of stars have been announced, many of which obtained at a ∼3σ level; some of the discoveries are confirmed by measurements obtained with other instruments, some are not. Aims. We investigate the reasons for the discrepancies between the results obtained with FORS1 and those obtained with other instruments. Methods. Using the ESO FORS pipeline, we have developed a semi-automatic procedure for magnetic field determination. We have applied this procedure to the full content of circular spectropolarimetric measurements of the FORS1 archive (except for most of the observations obtained in multi-object spectropolarimetric mode). We have devised and applied a number of consistency checks to our field determinations, and we have compared our results to those previously published in the literature. Results. We find that for high signal-to-noise ratio measurements, photon noise does not account for the full error bars. We discuss how field measurements depend on the specific algorithm adopted for data reduction, and we show that very small instrument flexures, negligible in most of the instrument applications, may be responsible for some spurious field detections in the null profiles. Finally, we find that we are unable to reproduce some results previously published in the literature. Consequently, we do not confirm some important discoveries of magnetic fields obtained with FORS1 and reported in previous publications. Conclusions. Our revised field measurements show that there is no contradiction between the results obtained with the low-resolution spectropolarimeter FORS1 and those obtained with high-resolution spectropolarimeters. FORS1 is an instrument capable of performing reliable magnetic field measurements, provided that the various sources of uncertainties are properly taken into account.

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“…This has been mainly in the context of early-type chemically peculiar (CP) stars with very strong magnetic fields (Havnes & Goertz 1984;Babel & Montmerle 1997a) but with ideas being extended recently toward applications to other hot stars and Be star phenomena (Babel & Montmerle 1997b;Donati et al 2001). Specifically, Havnes and Goertz (1984) discussed the effect of the growing '' magnetospheric '' density and mechanisms that might disrupt the field, releasing energy and producing X-rays.…”

Section: Introductionmentioning

confidence: 99%

A Magnetically Torqued Disk Model for Be Stars

Cassinelli

Brown

Maheswaran

et al. 2002

ApJ

105

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Despite extensive study, the mechanisms by which Be star disks acquire high densities and angular momentum while displaying variability on many timescales are still far from clear. In this paper, we discuss how magnetic torquing may help explain disk formation with the observed quasi-Keplerian (as opposed to expanding) velocity structure and their variability. We focus on the effects of the rapid rotation of Be stars, considering the regime where centrifugal forces provide the dominant radial support of the disk material. Using a kinematic description of the angular velocity, v ðrÞ, in the disk and a parametric model of an aligned field with a strength BðrÞ, we develop analytic expressions for the disk properties that allow us to estimate the stellar surface field strength necessary to create such a disk for a range of stars on the main sequence. The fields required to form a disk are compared with the bounds previously derived from photospheric limiting conditions. The model explains why disks are most common for main-sequence stars at about spectral class B2 V. The earlier type stars with very fast and high-density winds would require unacceptably strong surface fields (>10 3 G) to form torqued disks, while the late B stars (with their low mass-loss rates) tend to form disks that produce only small fluxes in the dominant Be diagnostics. For stars at B2 V the average surface field required is about 300 G. The predicted disks provide an intrinsic polarization and a flux at H comparable to observations. The radial extent of our dense quasi-Keplerian disks is compatible with typical estimates. We also discuss whether the effect on field containment of the time-dependent accumulation of matter in the flux tubes/disk can help explain some of the observed variability of Be star disks.

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The magnetic field and wind confinement ofβCephei: new clues for interpreting the Be phenomenon?

Cited by 127 publications

References 23 publications

Detecting Magnetic Fields in Rotationally Perturbed, Hot Stellar Winds

Detecting Magnetic Fields in Rotationally Perturbed, Hot Stellar Winds

Magnetic field measurements and their uncertainties: the FORS1 legacy

A Magnetically Torqued Disk Model for Be Stars

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