scholarly journals A search for strong magnetic fields in massive and very massive stars in the Magellanic Clouds

2020 ◽  
Vol 635 ◽  
pp. A163
Author(s):  
S. Bagnulo ◽  
G. A. Wade ◽  
Y. Nazé ◽  
J. H. Grunhut ◽  
M. E. Shultz ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Longitudinal Magnetic Field ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Dipolar Field ◽  
Strong Magnetic Fields ◽  
Ob Stars ◽  
Stellar Magnetic Fields ◽  
The Universe

Despite their rarity, massive stars dominate the ecology of galaxies via their strong, radiatively-driven winds throughout their lives and as supernovae in their deaths. However, their evolution and subsequent impact on their environment can be significantly affected by the presence of a magnetic field. While recent studies indicate that about 7% of OB stars in the Milky Way host strong, stable, organised (fossil) magnetic fields at their surfaces, little is known about the fields of very massive stars, nor the magnetic properties of stars outside our Galaxy. We aim to continue searching for strong magnetic fields in a diverse set of massive and very massive stars (VMS) in the Large and Small Magellanic Clouds (LMC/SMC), and we evaluate the overall capability of FORS2 to usefully search for and detect stellar magnetic fields in extra-galactic environments. We have obtained FORS2 spectropolarimetry of a sample of 41 stars, which principally consist of spectral types B, O, Of/WN, WNh, and classical WR stars in the LMC and SMC. Four of our targets are Of?p stars; one of them was just recently discovered. Each spectrum was analysed to infer the longitudinal magnetic field. No magnetic fields were formally detected in our study, although Bayesian statistical considerations suggest that the Of?p star SMC 159-2 is magnetic with a dipolar field of the order of 2.4–4.4 kG. In addition, our first constraints of magnetic fields in VMS provide interesting insights into the formation of the most massive stars in the Universe.

scholarly journals The measurement of the energy of cosmic rays - II—The curvature measurements and the energy spectrum

1936 ◽  
Vol 154 (883) ◽  
pp. 573-587 ◽  
Keyword(s):  
Magnetic Field ◽  
Energy Spectrum ◽  
Cosmic Rays ◽  
Magnetic Fields ◽  
Strong Magnetic Fields ◽  
The Earth ◽  
Primary Particles ◽  
Curvature Measurements

Both the penetrating power of the cosmic rays through material ab­sorbers and their ability to reach the earth in spite of its magnetic field, make it certain that the energy of many of the primary particles must reach at least 10 11 e-volts. However, the energy measurements by Kunze, and by Anderson, using cloud chambers in strong magnetic fields, have extended only to about 5 x 10 9 e-volts. Particles of greater energy were reported, but the curvature of their tracks was too small to be measured with certainty. We have extended these energy measurements to somewhat higher energies, using a large electro-magnet specially built for the purpose and described in Part I. As used in these experiments, the magnet allowed the photography of tracks 17 cm long in a field of about 14,000 gauss. The magnet weighed about 11,000 kilos and used a power of 25 kilowatts.

scholarly journals Infrared Measurements of Stellar Magnetic Fields

1994 ◽  
Vol 154 ◽  
pp. 437-447 ◽  
Author(s):  
Steven H. Saar
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Pressure Support ◽  
Field Research ◽  
Future Directions ◽  
Rotation Rates ◽  
Infrared Measurements ◽  
Cool Stars ◽  
Rs Cvn Variables ◽  
Stellar Magnetic Fields

I review the advantages, techniques, and results of measurement of magnetic fields on cool stars in the infrared (IR). These measurements have generated several important results, including the following: the first data on the magnetic parameters of dMe and RS CVn variables; evidence for field strength confinement by photospheric gas pressure; support for the correlation between magnetic flux and rotation, with possible saturation at high rotation rates; indications of horizontal and/or vertical magnetic field structure; and evidence of spatial variations in B over a stellar surface. I discuss these results in detail, and suggest future directions for IR magnetic field research.

scholarly journals Magneto- and Tensoresistance of the p Ge Compensated Crystals in the Range of Weak, Intermediate and Classically Strong Magnetic Fields

2016 ◽  
Vol 17 (1) ◽  
pp. 43-47 ◽  
Author(s):  
G.P. Gaidar
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Mechanical Stress ◽  
Elastic Deformation ◽  
Crystallographic Orientation ◽  
Longitudinal Axis ◽  
Mechanical Stresses ◽  
Strong Magnetic Fields ◽  
Compensation Factor

On the crystalsof compensatedp‑Ge (with the compensation factor of k = NSb/NGa = 0.5) the transverse (Н ^ (J // X)) magnetoresistance (within the magnetic fields of 0 < Н £ 22.3 kOe) at fixed values of the mechanical stresses Хі = 0; 0.2; 0.4; 0.6; 0.9; 1.1; 1.5 GPa were measured at 77 K. These mechanical stresses X created the elastic deformation along the samples, the crystallographic orientation of which coincided with the direction of [100]. Also at fixed magnetic field intensities Ні = 2; 4; 8; 10; 15; 20; 22.3 kOe the dependencies of resistivity  on the mechanical stress X, which coincides with the longitudinal axis of the crystal (X // J // [100]) and changes in the range of 0 £ Х £ 1.5 GPa, were measured. Last dependences characterized by the presence of a minimum in the range of X ~ 0.5 ¸ 0.6 GPa at the minimal magnetic field intensities Н = 2 kOe, which was shifted to the values of X ~ 0.2 ¸ 0.3 GPa with increasing Н up to 22.3 kOe.

scholarly journals MOBSTER – III. HD 62658: a magnetic Bp star in an eclipsing binary with a non-magnetic ‘identical twin’

2019 ◽  
Vol 490 (3) ◽  
pp. 4154-4165 ◽  
Author(s):  
M E Shultz ◽  
C Johnston ◽  
J Labadie-Bartz ◽  
V Petit ◽  
A David-Uraz ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Light Curve ◽  
Line Profile ◽  
Longitudinal Magnetic Field ◽  
Stellar Structure ◽  
Line Profiles ◽  
Dipole Strength ◽  
Rotational Modulation ◽  
Brightness Modulation

ABSTRACT HD 62658 (B9p V) is a little-studied chemically peculiar star. Light curves obtained by the Kilodegree Extremely Little Telescope (KELT) and Transiting Exoplanet Survey Satellite (TESS) show clear eclipses with a period of about 4.75 d, as well as out-of-eclipse brightness modulation with the same 4.75 d period, consistent with synchronized rotational modulation of surface chemical spots. High-resolution ESPaDOnS circular spectropolarimetry shows a clear Zeeman signature in the line profile of the primary; there is no indication of a magnetic field in the secondary. PHOEBE modelling of the light curve and radial velocities indicates that the two components have almost identical masses of about 3 M⊙. The primary’s longitudinal magnetic field 〈Bz〉 varies between about +100 and −250 G, suggesting a surface magnetic dipole strength Bd = 850 G. Bayesian analysis of the Stokes V profiles indicates Bd = 650 G for the primary and Bd &lt; 110 G for the secondary. The primary’s line profiles are highly variable, consistent with the hypothesis that the out-of-eclipse brightness modulation is a consequence of rotational modulation of that star’s chemical spots. We also detect a residual signal in the light curve after removal of the orbital and rotational modulations, which might be pulsational in origin; this could be consistent with the weak line profile variability of the secondary. This system represents an excellent opportunity to examine the consequences of magnetic fields for stellar structure via comparison of two stars that are essentially identical with the exception that one is magnetic. The existence of such a system furthermore suggests that purely environmental explanations for the origin of fossil magnetic fields are incomplete.

scholarly journals On the stability of a general magnetic field topology in stellar radiative zones

2019 ◽  
Vol 82 ◽  
pp. 365-371
Author(s):  
K. Augustson ◽  
S. Mathis ◽  
A. Strugarek
Keyword(s):  
Magnetic Field ◽  
Global Change ◽  
Magnetic Fields ◽  
Potential Energy ◽  
Massive Stars ◽  
Spherical Geometry ◽  
Stable Region ◽  
Magnetic Field Topology ◽  
The Stability ◽  
The Magnetic Field

This paper provides a brief overview of the formation of stellar fossil magnetic fields and what potential instabilities may occur given certain configurations of the magnetic field. One such instability is the purely magnetic Tayler instability, which can occur for poloidal, toroidal, and mixed poloidal-toroidal axisymmetric magnetic field configurations. However, most of the magnetic field configurations observed at the surface of massive stars are non-axisymmetric. Thus, extending earlier studies in spherical geometry, we introduce a formulation for the global change in the potential energy contained in a convectively-stable region for both axisymmetric and non-axisymmetric magnetic fields.

scholarly journals Magnetic fields, winds and X-rays of massive stars in the Orion nebula cluster

2010 ◽  
Vol 6 (S272) ◽  
pp. 208-209 ◽  
Author(s):  
Véronique Petit ◽  
Gregg A. Wade ◽  
Evelyne Alecian ◽  
Laurent Drissen ◽  
Thierry Montmerle ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Massive Stars ◽  
Theoretical Models ◽  
Magnetic Star ◽  
X Rays ◽  
Orion Nebula ◽  
X Ray ◽  
Ob Stars ◽  
The Impact ◽  
The Relationship

AbstractIn some massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind. Although theoretical models and MHD simulations are able to illustrate the dynamics of such a magnetized wind, the impact of this wind-field interaction on the observable properties of a magnetic star - X-ray emission, photometric and spectral variability - is still unclear. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars, by providing empirical observations and confronting theory. In conjunction with the COUP survey of the Orion Nebula Cluster, we carried out spectropolarimatric ESPaDOnS observations to determine the magnetic properties of massive OB stars of this cluster.

scholarly journals Modelling the photometric variability of magnetic massive stars with the Analytical Dynamical Magnetosphere model

2019 ◽  
Author(s):  
M S Munoz ◽  
G A Wade ◽  
Y Nazé ◽  
J Puls ◽  
S Bagnulo ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Scattering ◽  
Massive Star ◽  
Massive Stars ◽  
Mass Density ◽  
Magellanic Clouds ◽  
Light Curves ◽  
Photometric Variability ◽  
P Type ◽  
The Magnetic Field

Abstract In this paper, we investigate the photometric variability of magnetic O-type stars. Such stars possess oblique, predominantly dipolar magnetic fields that confine their winds roughly axisymmetrically about the magnetic equator, thus forming a magnetosphere. We interpret their photometric variability as phase-dependent magnetospheric occultations. For massive star winds dominated by electron scattering opacity in the optical and NIR, we can compute synthetic light curves from simply knowing the magnetosphere’s mass density distribution. We exploit the newly-developed Analytical Dynamical Magnetosphere model (ADM) in order to obtain the predicted circumstellar density structures of magnetic O-type stars. The simplicity in our light curve synthesis model allows us to readily conduct a parameter space study. For validation purposes, we first apply our algorithm to HD 191612, the prototypical Of?p star. Next, we attempt to model the photometric variability of the Of?p-type stars identified in the Magellanic Clouds using OGLE photometry. We evaluate the compatibility of the ADM predictions with the observed photometric variations, and discuss the magnetic field properties that are implied by our modelling.

scholarly journals Oscillatory convection in strong magnetic fields and origin of active regions

1968 ◽  
Vol 35 ◽  
pp. 127-130 ◽  
Author(s):  
S. I. Syrovatsky ◽  
Y. D. Zhugzhda
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Active Regions ◽  
Oscillatory Convection ◽  
Strong Magnetic Fields ◽  
Various Boundary Conditions ◽  
Convective Cells ◽  
The Magnetic Field ◽  
Polytropic Atmosphere

The convection in a compressible inhomogeneous conducting fluid in the presence of a vertical uniform magnetic field has been studied. It is shown that a new mode of oscillatory convection occurs, which exists in arbitrarily strong magnetic fields. The convective cells are stretched along the magnetic field, their horizontal dimensions are determined by radiative cooling. Criteria for convective instability in a polytropic atmosphere are obtained for various boundary conditions in the case when the Alfvén velocity is higher compared with the velocity of sound.The role of oscillatory convection in the origin of sunspots and active regions is discussed.

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