scholarly journals The magnetic field of β Cep and the Be phenomenon

2000 ◽  
Vol 175 ◽  
pp. 324-329 ◽  
Author(s):  
H.F. Henrichs ◽  
J.A. de Jong ◽  
J.-F. Donati ◽  
C. Catala ◽  
G.A. Wade ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Longitudinal Magnetic Field ◽  
Rotation Period ◽  
Spectral Lines ◽  
Be Stars ◽  
Full Paper ◽  
Rapid Rotation ◽  
Rotator Model ◽  
Maximum Field ◽  
The Magnetic Field

AbstractNew circular spectropolarimetric observations of the B1 IIIe star β Cep (υsini = 25 km s−1) show a sinusoidally varying weak longitudinal magnetic field (~ 200 G peak-to-peak). The period corresponds to the 12 day period in the stellar wind variations observed in ultraviolet spectral lines. Maximum field occurs at maximum emission in the UV wind lines. This gives compelling evidence for a magnetic-rotator model for this star, with an unambiguous rotation period of 12 days.The similarity between the Hα emission phases in β Cep and in Be stars suggests that the origin of the Be phenomenon does not have to be rapid rotation: we propose that in β Cep the velocity to bring material in (Keplerian) orbit is provided by the high corotation velocity at the Alfvén radius (~10 R*), whereas in Be stars this is done by the rapid rotation of the surface. In both cases the cause of the emission phases has still to be found. Weak temporary magnetic fields remain the strongest candidate.A full paper, with results including additional measurements in June and July 1999, will appear in A & A.

τ9 Eri: a bright pulsating magnetic Bp star in a 5.95-d double-lined spectroscopic binary

2021 ◽  
Vol 502 (4) ◽  
pp. 5200-5209
Author(s):  
K Woodcock ◽  
G A Wade ◽  
O Kochukhov ◽  
J Sikora ◽  
A Pigulski
Keyword(s):  
Magnetic Field ◽  
Longitudinal Magnetic Field ◽  
Rotation Period ◽  
Photometric Data ◽  
Spectral Lines ◽  
Eccentric Orbit ◽  
Typical Error ◽  
Spectroscopic Binary ◽  
Photometric Observations ◽  
Orbital Analysis

ABSTRACT τ9 Eri is a Bp star that was previously reported to be a single-lined spectroscopic binary. Using 17 ESPaDOnS spectropolarimetric (Stokes V) observations, we identified the weak spectral lines of the secondary component and detected a strong magnetic field in the primary. We performed orbital analysis of the radial velocities of both components to find a slightly eccentric orbit (e = 0.129) with a period of 5.95382(2) d. The longitudinal magnetic field (Bℓ) of the primary was measured from each of the Stokes V profiles, with typical error bars smaller than 10 G. Equivalent widths (EWs) of least-squares deconvolution profiles corresponding to only the Fe lines were also measured. We performed frequency analysis of both the Bℓ and EW measurements, as well as of the Hipparcos, SMEI, and TESS photometric data. All sets of photometric observations produce two clear, strong candidates for the rotation period of the Bp star: 1.21 and 3.82 d. The Bℓ and EW measurements are consistent with only the 3.82-d period. We conclude that HD 25267 consists of a late-type Bp star (M = $3.6_{-0.2}^{+0.1}~\mathrm{ M}_\odot$, T = $12580_{-120}^{+150}$ K) with a rotation period of 3.82262(4) d orbiting with a period of 5.95382(2) d with a late-A/early-F type secondary companion (M = 1.6 ± 0.1 M⊙, T = $7530_{-510}^{+580}$ K). The Bp star’s magnetic field is approximately dipolar with i = 41 ± 2°, β = 158 ± 5°, and Bd = 1040 ± 50 G. All evidence points to the strong 1.209912(3)-d period detected in photometry, along with several other weaker photometric signals, as arising from g-mode pulsations in the primary.

scholarly journals The magnetic field of the B1/B2V star σ Lup

2010 ◽  
Vol 6 (S272) ◽  
pp. 192-193
Author(s):  
Huib F. Henrichs ◽  
Katrien Kolenberg ◽  
Benjamin Plaggenborg ◽  
Stephen C. Marsden ◽  
Ian A. Waite ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Longitudinal Magnetic Field ◽  
Rotation Period ◽  
Uv Spectra ◽  
B Stars ◽  
Magnetic Period ◽  
Photometric Period ◽  
Magnetic Field Variations ◽  
The Magnetic Field ◽  
Chemical Peculiarity

AbstractThe ultraviolet stellar wind lines of the photometrically periodic variable early B-type star σ Lupi were found to behave very similarly to what has been observed in known magnetic B stars, although no periodicity could be determined. AAT spectropolarimetric measurements with SEMPOL were obtained. We detected a longitudinal magnetic field with varying strength and amplitude of about 100 G with error bars of typically 20 G. This type of variability supports an oblique magnetic rotator model. We fold the equivalent width of the 4 usable UV spectra in phase with the well-known photometric period of 3.019 days, which we identify with the rotation period of the star. The magnetic field variations are consistent with this period. Additional observations with ESPaDOnS attached to the CFHT strongly confirmed this discovery, and allowed to determine a precise magnetic period. Like in the other magnetic B stars the wind emission likely originates in the magnetic equatorial plane, with maximum emission occurring when a magnetic pole points towards the Earth. The 3.0182 d magnetic rotation period is consistent with the photometric period, with maximum light corresponding to maximum magnetic field. No helium or other chemical peculiarity is known for this object.

On the Configuration of the Magnetic Field of β CrB

1976 ◽  
Vol 32 ◽  
pp. 613-622
Author(s):  
I.A. Aslanov ◽  
Yu.S. Rustamov
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Radial Velocity ◽  
Magnetic Field Strength ◽  
Complex Shape ◽  
Rotation Period ◽  
Field Variation ◽  
Magnetic Field Variation ◽  
Secular Variations ◽  
The Magnetic Field

SummaryMeasurements of the radial velocities and magnetic field strength of β CrB were carried out. It is shown that there is a variability with the rotation period different for various elements. The curve of the magnetic field variation measured from lines of 5 different elements: FeI, CrI, CrII, TiII, ScII and CaI has a complex shape specific for each element. This may be due to the presence of magnetic spots on the stellar surface. A comparison with the radial velocity curves suggests the presence of a least 4 spots of Ti and Cr coinciding with magnetic spots. A change of the magnetic field with optical depth is shown. The curve of the Heffvariation with the rotation period is given. A possibility of secular variations of the magnetic field is shown.

scholarly journals Broadband Linear Polarization in Ap Stars

1993 ◽  
Vol 138 ◽  
pp. 305-309
Author(s):  
Marco Landolfi ◽  
Egidio Landi Degl’Innocenti ◽  
Maurizio Landi Degl’Innocenti ◽  
Jean-Louis Leroy ◽  
Stefano Bagnulo
Keyword(s):  
Magnetic Field ◽  
Circular Polarization ◽  
Linear Polarization ◽  
Rotation Axis ◽  
Spectral Lines ◽  
Line Of Sight ◽  
Long Time ◽  
Rotating Star ◽  
Ap Stars ◽  
The Magnetic Field

AbstractBroadband linear polarization in the spectra of Ap stars is believed to be due to differential saturation between σ and π Zeeman components in spectral lines. This mechanism has been known for a long time to be the main agent of a similar phenomenon observed in sunspots. Since this phenomenon has been carefully calibrated in the solar case, it can be confidently used to deduce the magnetic field of Ap stars.Given the magnetic configuration of a rotating star, it is possible to deduce the broadband polarization at any phase. Calculations performed for the oblique dipole model show that the resulting polarization diagrams are very sensitive to the values of i (the angle between the rotation axis and the line of sight) and β (the angle between the rotation and magnetic axes). The dependence on i and β is such that the four-fold ambiguity typical of the circular polarization observations ((i,β), (β,i), (π-i,π-β), (π-β,π-i)) can be removed.

scholarly journals Magnetic fields of rapidly oscillating Ap stars

1993 ◽  
Vol 139 ◽  
pp. 132-132
Author(s):  
G. Mathys
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Zeeman Effect ◽  
Rotation Frequency ◽  
Spectral Lines ◽  
Driving Mechanism ◽  
Line Splitting ◽  
Ap Stars ◽  
The Magnetic Field

Magnetic field appears to play a major role in the pulsations of rapidly oscillating Ap (roAp) stars. Understanding of the behaviour of these objects thus requires knowledge of their magnetic field. Such knowledge is in particular essential to interpret the modulation of the amplitude of the photometric variations (with a frequency very close to the rotation frequency of the star) and to understand the driving mechanism of the pulsation. Therefore, a systematic programme of study of the magnetic field of roAp stars has been started, of which preliminary (and still very partial) results are presented here.Magnetic fields of Ap stars can be diagnosed from the Zeeman effect that they induced in spectral lines either from the observation of line-splitting in high-resolution unpolarized spectra (which only occurs in favourable circumstances) or from the observation of circular polarization of the lines in medium- to high-resolution spectra.

scholarly journals Estimation of Electrical Conductivity and Magnetization Parameter of Neutron Star Crusts and Applied to the High-Braking-Index Pulsar PSR J1640-4631

Universe ◽  
2020 ◽  
Vol 6 (5) ◽  
pp. 63
Author(s):  
Hui Wang ◽  
Zhi-Fu Gao ◽  
Huan-Yu Jia ◽  
Na Wang ◽  
Xiang-Dong Li
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Neutron Stars ◽  
General Expression ◽  
Equations Of State ◽  
Rotation Period ◽  
Ohmic Dissipation ◽  
Hartree Fock ◽  
Induction Equation ◽  
The Magnetic Field

Young pulsars are thought to be highly magnetized neutron stars (NSs). The crustal magnetic field of a NS usually decays at different timescales in the forms of Hall drift and Ohmic dissipation. The magnetization parameter ω B τ is defined as the ratio of the Ohmic timescale τ O h m to the Hall drift timescale τ H a l l . During the first several million years, the inner temperature of the newly born neutron star cools from T = 10 9 K to T = 1.0 × 10 8 K, and the crustal conductivity increases by three orders of magnitude. In this work, we adopt a unified equations of state for cold non-accreting neutron stars with the Hartree–Fock–Bogoliubov method, developed by Pearson et al. (2018), and choose two fiducial dipole magnetic fields of B = 1.0 × 10 13 G and B = 1.0 × 10 14 G, four different temperatures, T, and two different impurity concentration parameters, Q, and then calculate the conductivity of the inner crust of NSs and give a general expression of magnetization parameter for young pulsars: ω B τ ≃ ( 1 − 50 ) B 0 / ( 10 13 G) by using numerical simulations. It was found when B ≤ 10 15 G, due to the quantum effects, the conductivity increases slightly with the increase in the magnetic field, the enhanced magnetic field has a small effect on the matter in the low-density regions of the crust, and almost has no influence the matter in the high-density regions. Then, we apply the general expression of the magnetization parameter to the high braking-index pulsar PSR J1640-4631. By combining the observed arrival time parameters of PSR J1640-4631 with the magnetic induction equation, we estimated the initial rotation period P 0 , the initial dipole magnetic field B 0 , the Ohm dissipation timescale τ O h m and Hall drift timescale τ H a l l . We model the magnetic field evolution and the braking-index evolution of the pulsar and compare the results with its observations. It is expected that the results of this paper can be applied to more young pulsars.

scholarly journals Some Properties of Magnetic Variables

1971 ◽  
Vol 15 ◽  
pp. 59-62 ◽  
Author(s):  
Karl D. Rakoš
Keyword(s):  
Magnetic Field ◽  
Light Curve ◽  
Spectral Lines ◽  
Light Curves ◽  
Magnetic Pole ◽  
Yellow Light ◽  
The Past ◽  
Oblique Rotator ◽  
Ap Stars ◽  
The Magnetic Field

It is certain, that the mechanism causing variations of the magnetic field and spectral lines in Ap stars must also cause variations in their luminosities. The light curves are synchronous with the magnetic variations and usually the maximum of the positive magnetic field strength coincides with the minimum of the light curve. In the past the oblique rotator theory was not able to explain easily such brightness change. There is no simple reason to suppose, that the brightness of the surface of a star would increase or decrease at one magnetic pole only. Since that time a few stars were found with some indications for secondary minima and maxima in the light curves, but the first established double wave in a light curve was recently found by H. M. MAITZEN and K. D. RAKOš in HD 125 248 (1970), see Figure 1. It is a very exciting result, only the light curve in yellow light shows two maxima and two minima. The light curves in blue and ultraviolet are very smooth and show no evidence for secondary waves.

scholarly journals A short and sudden increase of the magnetic field strength and the accompanying spectral variability in the O9.7 V star HD 54879

2019 ◽  
Vol 484 (4) ◽  
pp. 4495-4506 ◽  
Author(s):  
S Hubrig ◽  
M Küker ◽  
S P Järvinen ◽  
A F Kholtygin ◽  
M Schöller ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Longitudinal Magnetic Field ◽  
Sudden Increase ◽  
Spectral Variability ◽  
Dipole Strength ◽  
Large Program ◽  
Short And Long Term ◽  
The Magnetic Field

Abstract Only 11 O-type stars have been confirmed to possess large-scale organized magnetic fields. The presence of a −600 G longitudinal magnetic field in the O9.7 V star HD 54879 with a lower limit of the dipole strength of ∼2 kG was discovered a few years ago in the framework of the ESO large program ‘B-fields in OB stars’. Our FORS 2 spectropolarimetric observations from 2017 October 4 to 2018 February 21 reveal the presence of short- and long-term spectral variability and a gradual magnetic field decrease from about −300 G down to about −90 G. Different scenarios are discussed in an attempt to interpret our observations. Our FORS 2 radial velocity measurements indicate that HD 54879 is a member of a long-period binary.

scholarly journals Modeling Oblique Rotators: Magnetospheres and Winds

1999 ◽  
Vol 169 ◽  
pp. 178-186
Author(s):  
Steven N. Shore
Keyword(s):  
Main Sequence ◽  
Rotational Axis ◽  
Be Stars ◽  
Polar Caps ◽  
Rotator Model ◽  
Peculiar Stars ◽  
Oblique Rotator ◽  
Circumstellar Gas ◽  
Nonthermal Radio Emission ◽  
The Magnetic Field

AbstractThe upper main sequence chemically peculiar (CP) stars display evidence of trapped circumstellar gas and nonspherical outflows. These stars are also known to possess strong magnetic fields that are often highly inclined to the rotational axis. Their phenomenology can be understood by using the oblique rotator model, which has successfully accounted for the observed behavior of the cooler CP stars. This paper reviews some features of the oblique rotator model, in which the magnetic field is assumed to provide a rigid framework for the structuring of the stellar and circumstellar gas. Corotation of circumstellar plasma is enforced out to the Alfven radius in the magnetic equatorial plane, while for the hotter stars, a radiatively driven wind emerges from the magnetic polar caps. Some observable consequences of the model are discussed, especially the Hα and ultraviolet resonance line absorption and emission periodic variability that has been observed in the He-peculiar stars and nonthermal radio emission. Magnetospheres may also be present in O stars, e.g. θ1 Ori C, and in the Herbig Ae/Be stars.

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