Magnetically controlled circumstellar matter in the helium-strong stars

Shore, Steven N.; Brown, Douglas

doi:10.1086/169520

Cited by 127 publications

(120 citation statements)

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“…Together with a low v sin i, it suggests a low inclination angle i, as predicted by Shore & Brown (1990) from UV wind lines and determined spectroscopically (i ≤ 4 • ) by Zboril & North (1999).…”

Section: B Z Measurements and Stokes Profilessupporting

confidence: 62%

“…IUE spectra of HD 96446 revealed that the wind sensitive C iv lines at 1548, 1550 Å are always observed in emission with weak variability, while the Si iv lines at 1394, 1403 Å are only seen weakly in absorption (Shore & Brown 1990). In the framework of an oblique rotator with a magnetically confined radiative wind, Shore & Brown (1990) concluded that the inclination angle i of the rotation axis must be close to 0 • , while the obliquity angle β must be lower than 70 • .…”

Section: The Bp Star Hd 96446mentioning

confidence: 98%

“…In the framework of an oblique rotator with a magnetically confined radiative wind, Shore & Brown (1990) concluded that the inclination angle i of the rotation axis must be close to 0 • , while the obliquity angle β must be lower than 70 • . From the photometric variations, MB91 proposed i = 3 • and indicated in addition that β must be higher than 60 • .…”

Section: The Bp Star Hd 96446mentioning

confidence: 99%

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HD 96446: a puzzle for current models of magnetospheres?

Neiner

Landstreet

Alécian

et al. 2012

A&A

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Context. Oblique magnetic dipole fields have been detected in Bp stars for several decades, and more recently also in normal massive stars. In the past decade, it has been established that stellar magnetospheres form through the channelling and confinement of an outflowing stellar wind by the stellar magnetic field. This explains specific properties of magnetic massive stars, such as their rotationally modulated photometric light curve, Hα emission, UV spectra, and X-ray emission. Aims. In the framework of the MiMeS (Magnetism in Massive Stars) project, four HARPSpol observations of the magnetic Bp star HD 96446 have been obtained. HD 96446 is very similar to σ Ori E, the prototype of centrifugally supported rigidly rotating magnetospheres (CM) and is therefore a perfect target to study the validity of this model. Methods. We first updated the basic parameters of HD 96446 and studied its spectral variability. We then analysed the HARPSpol spectropolarimetric observations using the LSD (Least-Squares Deconvolution) technique to derive the longitudinal magnetic field and Zeeman signatures in various types of lines. With LTE spectrum modelling, we derived constraints on the field modulus, the rotational velocity, and the inclination angle, and measured non-solar abundances of several elements which we checked with NLTE modelling. Finally, we calculated the magnetic confinement and Alfvén and Kepler radii from the stellar magnetic field and rotation properties, and we examined the various types of magnetospheres that may be present around HD 96446. Results. We find radial velocity variations with a period around 2.23 h, that we attribute to β Cep-type p-mode pulsations. We detect clear direct magnetic Stokes V signatures with slightly varying values of the longitudinal magnetic field, typical of an oblique dipole rotator, and show that these signatures are not much perturbed by the radial velocity variations. The magnetic confinement parameter and Alfvén radius in the centrifugally supported, rigidly-rotating magnetosphere (CM) model points towards the presence of confined material in the magnetosphere. However, HD 96446 does not present signatures of the presence of such confined material, such as Hα emission. Conclusions. We conclude that, even though HD 96446 fulfills all criteria to host a CM with confined material, it does not. The rotation period must be significantly revised, or another model of magnetosphere with a leakage mechanism will need to be developed to explain the magnetic environment of this star.

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Section: B Z Measurements and Stokes Profilessupporting

confidence: 62%

Section: The Bp Star Hd 96446mentioning

confidence: 98%

Section: The Bp Star Hd 96446mentioning

confidence: 99%

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HD 96446: a puzzle for current models of magnetospheres?

Neiner

Landstreet

Alécian

et al. 2012

A&A

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“…The wind can fill stellar magnetospheres in the presence of the magnetic field, creating magnetospheric clouds (Landstreet & Borra 1978;Shore & Brown 1990;Smith & Groote 2001;.…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet and visual flux and line variations of one of the least variable Bp stars HD 64740

Krtička

Janík

Marková

et al. 2013

A&A

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Context. The light variability of hot magnetic chemically peculiar stars is typically caused by the flux redistribution in spots with peculiar abundance. This raises the question why some stars with surface abundance spots show significant rotational light variability, while others do not. Aims. We study the Bp star HD 64740 to investigate how its remarkable inhomogeneities in the surface distribution of helium and silicon, and the corresponding strong variability of many spectral lines, can result in one of the faintest photometric variabilities among the Bp stars. Methods. We used model atmospheres and synthetic spectra calculated for the silicon and helium abundances from surface abundance maps to predict the ultraviolet and visual light and line variability of HD 64740. The predicted fluxes and line profiles were compared with the observed ones derived with the IUE, HST, and Hipparcos satellites and with spectra acquired using the FEROS spectrograph at the 2.2 m MPG/ESO telescope in La Silla. Results. We are able to reproduce the observed visual light curve of HD 64740 assuming an inhomogeneous distribution of iron correlated with silicon distribution. The light variations in the ultraviolet are hardly detectable. We detect the variability of many ultraviolet lines of carbon, silicon, and aluminium and discuss the origin of these lines and the nature of their variations. Conclusions. The maximum abundances of helium and silicon on the surface of HD 64740 are not high enough to cause significant light variations. The detected variability of many ultraviolet lines is most likely of atmospheric origin and reflects the inhomogeneous elemental surface distribution. The variability of the C iv resonance lines of carbon is stronger and it probably results from the dependence of the wind mass-loss rate on the chemical composition and magnetic field orientation. We have not been able to detect a clear signature of the matter trapped in the circumstellar clouds.

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“…Among the Hestrong stars that appear not to show emission, many nevertheless exhibit variable UV Civ resonance lines consistent with trapped circumstellar material (see Shore & Brown 1990). Common to all of the He-strong stars is the presence of a strong (multi-kG), ordered (typically, dipole) magnetic field.…”

Section: Circumstellar Structurementioning

confidence: 99%

Modeling the winds and magnetospheres of active OB stars

Townsend

2010

Proc. IAU

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Abstract. After briefly reviewing the theory behind the radiative line-driven winds of OB stars, I examine the processes that can generate structure in them; these include both intrinsic instabilities, and surface perturbations such as pulsation and rotation. I then delve into wind channeling and confinement by magnetic fields as a mechanism for forming longer-lived circumstellar structures. With a narrative that largely follows the historical progression of the field, I introduce the key insights and results that link the first detection of a magnetosphere, over three decades ago, to the recent direct measurement of magnetic braking in a number of active OB stars.

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Magnetically controlled circumstellar matter in the helium-strong stars

Cited by 127 publications

References 0 publications

HD 96446: a puzzle for current models of magnetospheres?

HD 96446: a puzzle for current models of magnetospheres?

Ultraviolet and visual flux and line variations of one of the least variable Bp stars HD 64740

Modeling the winds and magnetospheres of active OB stars

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