The magnetic fields of the AP stars

Borra, E. F.; Landstreet, J. D.

doi:10.1086/190656

Cited by 249 publications

(286 citation statements)

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“…(when the limb-darkening coefficient is 0.4, see Borra & Landstreet 1980). The B pol values we obtained for the three groups of lines are shown in Table 3.…”

Section: Geometry Of the Fieldmentioning

confidence: 90%

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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“…(when the limb-darkening coefficient is 0.4, see Borra & Landstreet 1980). The B pol values we obtained for the three groups of lines are shown in Table 3.…”

Section: Geometry Of the Fieldmentioning

confidence: 90%

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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“…Numerous investigations of magnetism in such stars (e.g. Borra & Landstreet 1980;Glagolevskij et al 1985;Shorlin et al 2002;Aurière et al 2010;Makaganiuk et al 2011) have found no convincing evidence for fields in this class of stars with uncertainties often in the range of a few G up to a few tens of G. Furthermore, α And has been specifically investigated with the MuSiCoS (13 observations, typical σ ∼ 30-60 G) and ESPaDOnS (5 observations, typical σ ∼ 6-19 G) spectropolarimeters without any significant detection of a nonzero longitudinal field or of any Stokes V signature indicative of a non-zero field ).…”

Section: Repeated Observations Of Non-magnetic Starsmentioning

confidence: 99%

Magnetic field measurements and their uncertainties: the FORS1 legacy

Bagnulo

Landstreet

Fossati

et al. 2012

A&A

Self Cite

147

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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“…The T eff determination for HD 32633 with a relative age of 26% is very uncertain, ranging from our photometric estimate of 12 819 K to 10 250 K using the (B2-G) index (Sokolov 1999). We assumed T eff = 10 500 K, which corresponds to the spectral type B9 given by Borra & Landstreet (1980). The reddening A V = 0.16 was adopted following Lucke's maps, instead of the initial A V = 0.411 obtained from the X and Y Geneva parameters.…”

Section: The Distribution Of the Magnetic Ap And Bp Stars In The H-r mentioning

confidence: 99%

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

Hubrig¹,

North

Schöller

2007

Astron Nachr

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We re-discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the study of Ap and Bp stars with accurate measurements of the mean magnetic field modulus and mean quadratic magnetic fields that magnetic stars of mass M < 3 M are concentrated towards the centre of the main-sequence band. In contrast, stars with masses M > 3 M seem to be concentrated closer to the ZAMS. The study of a few known members of nearby open clusters with accurate Hipparcos parallaxes confirms these conclusions. Stronger magnetic fields tend to be found in hotter, younger and more massive stars, as well as in stars with shorter rotation periods. The longest rotation periods are found only in stars which spent already more than 40% of their main sequence life, in the mass domain between 1.8 and 3 M and with log g values ranging from 3.80 to 4.13. No evidence is found for any loss of angular momentum during the main-sequence life. The magnetic flux remains constant over the stellar life time on the main sequence. An excess of stars with large obliquities β is detected in both higher and lower mass stars. It is quite possible that the angle β becomes close to 0 • in slower rotating stars of mass M > 3 M too, analog to the behaviour of angles β in slowly rotating stars of M < 3 M . The obliquity angle distribution as inferred from the distribution of r-values appears random at the time magnetic stars become observable on the H-R diagram. After quite a short time spent on the main sequence, the obliquity angle β tends to reach values close to either 90 • or 0 • for M < 3 M . The evolution of the obliquity angle β seems to be somewhat different for low and high mass stars. While we find a strong hint for an increase of β with the elapsed time on the main sequence for stars with M > 3 M , no similar trend is found for stars with M < 3 M . However, the predominance of high values of β at advanced ages in these stars is notable. As the physics governing the processes taking place in magnetised atmospheres remains poorly understood, magnetic field properties have to be considered in the framework of dynamo or fossil field theories.

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The magnetic fields of the AP stars

Cited by 249 publications

References 0 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

Magnetic field measurements and their uncertainties: the FORS1 legacy

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

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