On the incidence of magnetic fields in slowly pulsating B, β Cephei and B-type emission-line stars

Silvester, J.; Neiner, C.; Henrichs, H.F.; Wade, G. A.; Petit, Véronique; Alécian, E.; Huat, Anne-Laure; Martayan, Christophe; Power, J.; Thizy, O.

doi:10.1111/j.1365-2966.2009.15208.x

Cited by 76 publications

(102 citation statements)

References 28 publications

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“…β Cep itself was the first β Cephei star for which a Zeeman signature had been directly detected (Henrichs et al 2000). Since then, signatures have been reported for ξ 1 CMa (Hubrig et al 2006;Silvester et al 2009;FourtuneRavard et al 2011), 16 Peg (Henrichs et al 2009, and σ Lup (Henrichs et al 2011). Other magnetic β Cep stars have been suggested (e.g.…”

Section: Discussionmentioning

confidence: 95%

“…Hubrig et al 2009) but additional observations at higher signal-to-noise and resolution rejected those possible detections (e.g. Silvester et al 2009;Shultz et al 2011). In the same way, the detection of a magnetic field in the β Cephei star γ Peg claimed by Butkovskaya & Plachinda (2007) has been found to be spurious by the MiMeS collaboration (Neiner et al, in prep.).…”

Section: Discussionmentioning

confidence: 99%

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Detecting and modelling the magnetic field of theβ Cephei star V 2052 Ophiuchi

Neiner

Alécian

Briquet

et al. 2012

A&A

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Aims. Following the indirect detection of a magnetic field in the β Cephei star V 2052 Oph by Neiner and collaborators in 2003 with the Musicos spectropolarimeter, we remeasured the magnetic field of this star to attempt to directly confirm the detection of a magnetic field and study its configuration in greater detail. Methods. We used the Narval spectropolarimeter installed at TBL (Pic du Midi, France), which is about 20 times more efficient than the Musicos spectropolarimeter. We applied the least-squares deconvolution (LSD) technique to various groups of lines to measure the circular polarisation of the light coming from V 2052 Oph. We synthesized the measured Stokes V profiles with a centred and off-centred dipole model. Results. For the first time, we clearly detect the Zeeman signature in the Stokes V profiles of V 2052 Oph and thus directly prove the presence of a magnetic field in this star. The modulation with the rotation period is also confirmed and reflects an oblique dipole field. Thanks to the small error bars on the measurements, we are able to study the behaviour of different groups of lines and the centring of the dipole in the star. We find that the dipole is most likely off-centred along the magnetic axis and that He spots are present at the surface next to the magnetic axis. Conclusions. We conclude that V 2052 Oph is a magnetic He-strong β Cep star, with a dipole field, probably off-centred, with B pol ∼ 400 G and He patches close to the magnetic poles.

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Detecting and modelling the magnetic field of theβ Cephei star V 2052 Ophiuchi

Neiner

Alécian

Briquet

et al. 2012

A&A

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“…From the observed v rot sin i = 15 ± 2 km s −1 (NP12) we can reject the second solution of Aerts et al (2006) and conclude that the star is seen equator-on, with a rotational period of about 22 d (employing R from Table 1). Hubrig et al (2009) reported the detection of a magnetic field for this object based on spectropolarimetric observations with Fors1 on the VLT, which could not be confirmed by Bagnulo et al (2012) by reanalysis of the same observational data, and also by Silvester et al (2009) based on spectropolarimetry at high spectral resolution. The origin of the mixing of the surface with CN-cycled material is compatible with evolution models accounting for the effects of rotation.…”

Section: #16: Hd 216916 (En Lac)mentioning

confidence: 99%

Fundamental properties of nearby single early B-type stars

Nieva

Przybilla

2014

A&A

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Aims. Fundamental parameters of a sample of 26 apparently slowly-rotating single early B-type stars in OB associations and in the field within a distance of 400 pc from the Sun are presented and compared to high-precision data from detached eclipsing binaries (DEBs). Together with surface abundances for light elements the data are used to discuss the evolutionary status of the stars in context of the most recent Geneva grid of models for core hydrogen-burning stars in the mass-range ∼6 to 18 M at metallicity Z = 0.014. Methods. The fundamental parameters are derived on the basis of accurate and precise atmospheric parameters determined earlier by us from non-LTE analyses of high-quality spectra of the sample stars, utilising the new Geneva stellar evolution models. Results. Evolutionary masses plus radii and luminosities are determined to better than typically 5%, 10%, and 20% uncertainty, respectively, facilitating the mass−radius and mass−luminosity relationships to be recovered for single core hydrogen-burning objects with a similar precision as derived from DEBs. Good agreement between evolutionary and spectroscopic masses is found. Absolute visual and bolometric magnitudes are derived to typically ∼0.15−0.20 mag uncertainty. Metallicities are constrained to better than 15−20% uncertainty and tight constraints on evolutionary ages of the stars are provided. Overall, the spectroscopic distances and ages of individual sample stars agree with independently derived values for the host OB associations. Signatures of mixing with CN-cycled material are found in 1/3 of the sample stars. Typically, these are consistent with the amount predicted by the new Geneva models with rotation. The presence of magnetic fields appears to augment the mixing efficiency. In addition, a few objects are possibly the product of binary evolution. In particular, the unusual characteristics of τ Sco point to a blue straggler nature, due to a binary merger. Conclusions. The accuracy and precision achieved in the determination of fundamental stellar parameters from the quantitative spectroscopy of single early B-type stars comes close (within a factor 2-4) to data derived from DEBs. While our fundamental parameters are in good agreement with those derived from DEBs as a function of spectral type, significant systematic differences with data from the astrophysical reference literature are found. Masses are ∼10−20% and radii ∼25% lower then the recommended values for luminosity class V, resulting in the stars being systematically fainter than assumed usually, by ∼0.5 mag in absolute visual and bolometric magnitude. Our sample of giants is too small to derive firm conclusions, but similar trends as for the dwarfs are indicated.

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“…Fields have recently been discovered in a variety of types of stars such as Of?p stars (Grunhut & Wade 2012, and references therein), β Cep and slowly pulsating B stars (Henrichs et al 2000;Neiner et al 2003;Silvester et al 2009), Herbig AeBe stars (Wade et al 2005(Wade et al , 2007Catala et al 2007;Alecian et al 2013), red giant (Aurière et al 2009) and AGB supergiant stars (Grunhut et al 2010), and many kinds of cool dwarfs (Donati & Landstreet 2009, and references therein). Fields in such stars have become detectable as a result of having new generation instrumentation of very high efficiency and broad wavelength coverage available on medium and large telescopes, and through advanced data reduction and treatment techniques that allow very small polarimetric signatures to be reliably detected.…”

Section: Introductionmentioning

confidence: 99%

The importance of non-photon noise in stellar spectropolarimetry

Bagnulo

Fossati

Kochukhov

et al. 2013

A&A

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Context. The low-resolution, Cassegrain mounted, FORS spectropolarimeter of the ESO Very Large Telescope is being extensively used for magnetic field surveys. Some of the new discoveries suggest that relatively strong magnetic fields may play an important role in numerous physical phenomena observed in the atmospheres as well as in the circumstellar environments of certain kinds of stars. Aims. We show in detail how small instabilities or data-reduction inaccuracies represent an alternative explanation for the origin of certain signals of circular polarisation published in recent years. Methods. With the help of analytical calculations we simulate the observation of a spectral line in spectropolarimetric mode, adding very small spurious wavelength shifts, which may mimic the effects of seeing variations, rapid variations of the stellar radial velocity, or instrument instabilities. As a case study, we then re-visit the FORS2 measurements that have been used to claim the discovery of a magnetic field in the A0 supergiant HD 92207. In addition, we present new observations of this star obtained with the HARPSpol instrument.Results. Both calibration and science data show compelling evidence that photon-noise is not the only source of error in magnetic field measurements, especially in sharp spectral lines. Non-photon noise may be kept under control by accurate data reduction and quality controls. Our re-analysis of FORS2 observations of HD 92207 shows no evidence of a magnetic field, and we are able to reproduce the previous FORS detection only by degrading the quality of our wavelength calibration. Our HARPSpol spectropolarimetric measurements show no evidence of a magnetic field at the level of 10 G. Conclusions. Our work contributes to a better understanding of the importance of accurate data treatment and instrument characterisation, and demonstrates that ultra-high signal-to-noise ratio measurements do not automatically translate into ultra-high accuracy.

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On the incidence of magnetic fields in slowly pulsating B, β Cephei and B-type emission-line stars

Cited by 76 publications

References 28 publications

Detecting and modelling the magnetic field of theβ Cephei star V 2052 Ophiuchi

Detecting and modelling the magnetic field of theβ Cephei star V 2052 Ophiuchi

Fundamental properties of nearby single early B-type stars

The importance of non-photon noise in stellar spectropolarimetry

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