Magnetic fluxes of massive stars: statistics and evolution

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.

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Magnetic fields, winds and X-rays of massive stars in the Orion Nebula Cluster

Proceedings of the International Astronomical Union ◽

10.1017/s174392130903110x ◽

2008 ◽

Vol 4 (S259) ◽

pp. 449-452 ◽

Cited By ~ 2

Author(s):

Véronique Petit ◽

G. A. Wade ◽

L. Drissen ◽

T. Montmerle ◽

E. Alecian

Keyword(s):

Magnetic Fields ◽

Massive Stars ◽

Magnetic Confinement ◽

Stellar Winds ◽

X Rays ◽

Orion Nebula ◽

X Ray ◽

Ob Stars ◽

Complex Processes ◽

The Relationship

AbstractIn massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind, resulting in X-ray emission that is harder, more variable and more efficient than that produced by instability-generated shocks in non-magnetic winds. Although magnetic confinement of stellar winds has been shown to strongly modify the mass-loss and X-ray characteristics of massive OB stars, we lack a detailed understanding of the complex processes responsible. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars. In conjunction with a Chandra survey of the Orion Nebula Cluster, we carried out spectropolarimatric ESPaDOnS observations to determine the magnetic properties of massive OB stars of this cluster.

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X-rays from magnetic massive OB stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314002427 ◽

2013 ◽

Vol 9 (S302) ◽

pp. 330-333

Author(s):

V. Petit ◽

D. H. Cohen ◽

Y. Nazé ◽

M. Gagné ◽

R. H. D. Townsend ◽

...

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Massive Stars ◽

Magnetic Activity ◽

Magnetic Characteristics ◽

Driving Mechanism ◽

X Rays ◽

X Ray ◽

Ob Stars ◽

Strong Winds

AbstractThe magnetic activity of solar-type and low-mass stars is a well known source of coronal X-ray emission. At the other end of the main sequence, X-rays emission is instead associated with the powerful, radiatively driven winds of massive stars. Indeed, the intrinsically unstable line-driving mechanism of OB star winds gives rise to shock-heated, soft emission (~0.5 keV) distributed throughout the wind. Recently, the latest generation of spectropolarimetric instrumentation has uncovered a population of massive OB-stars hosting strong, organized magnetic fields. The magnetic characteristics of these stars are similar to the apparently fossil magnetic fields of the chemically peculiar ApBp stars. Magnetic channeling of these OB stars' strong winds leads to the formation of large-scale shock-heated magnetospheres, which can modify UV resonance lines, create complex distributions of cooled Halpha emitting material, and radiate hard (~2-5 keV) X-rays. This presentation summarizes our coordinated observational and modelling efforts to characterize the manifestation of these magnetospheres in the X-ray domain, providing an important contrast between the emission originating in shocks associated with the large-scale fossil fields of massive stars, and the X-rays associated with the activity of complex, dynamo-generated fields in lower-mass stars.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937098 ◽

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.

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The MiMeS project: first results

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309030798 ◽

2008 ◽

Vol 4 (S259) ◽

pp. 387-388

Author(s):

Jason H. Grunhut ◽

E. Alecian ◽

D. A. Bohlender ◽

J.-C. Bouret ◽

H. Henrichs ◽

...

Keyword(s):

Magnetic Fields ◽

Massive Star ◽

Massive Stars ◽

Chemical Elements ◽

Statistical Properties ◽

The Sun ◽

Large Program ◽

Stellar Component ◽

First Results ◽

The Universe

AbstractMassive stars are those stars with initial masses above about 8 times that of the sun, eventually leading to catastrophic explosions in the form of supernovae. These represent the most massive and luminous stellar component of the Universe, and are the crucibles in which the lion's share of the chemical elements are forged. These rapidly-evolving stars drive the chemistry, structure and evolution of galaxies, dominating the ecology of the Universe - not only as supernovae, but also during their entire lifetimes - with far-reaching consequences. Although the existence of magnetic fields in massive stars is no longer in question, our knowledge of the basic statistical properties of massive star magnetic fields is seriously incomplete. The Magnetism in Massive Stars (MiMeS) Project represents a comprehensive, multidisciplinary strategy by an international team of recognized researchers to address the “big questions” related to the complex and puzzling magnetism of massive stars. This paper present the first results of the MiMeS Large Program at the Canada-France-Hawaii Telescope.

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Investigating the origin of cyclical spectral variations in hot, massive stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314002439 ◽

2013 ◽

Vol 9 (S302) ◽

pp. 334-337

Author(s):

Alexandre David-Uraz ◽

Gregg A. Wade ◽

Véronique Petit ◽

Asif ud-Doula

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Massive Stars ◽

Physical Processes ◽

Corotating Interaction Regions ◽

Ob Stars ◽

Wind Variability ◽

Competing Hypotheses ◽

Interaction Regions ◽

Radial Pulsations

AbstractOB stars are known to exhibit various types of wind variability, as detected in their ultraviolet spectra, amongst which are the ubiquitous discrete absorption components (DACs). These features have been associated with large-scale azimuthal structures extending from the base of the wind to its outer regions: corotating interaction regions (CIRs). There are several competing hypotheses as to which physical processes may perturb the star's surface and generate CIRs, including magnetic fields and non radial pulsations (NRPs), the subjects of this paper with a particular emphasis on the former. Although large-scale magnetic fields are ruled out, magnetic spots deserve further investigation, both on the observational and theoretical fronts.

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Observations of magnetic fields in hot stars

Proceedings of the International Astronomical Union ◽

10.1017/s174392131101012x ◽

2010 ◽

Vol 6 (S272) ◽

pp. 106-117 ◽

Cited By ~ 2

Author(s):

Véronique Petit

Keyword(s):

Magnetic Properties ◽

Magnetic Fields ◽

Massive Stars ◽

Current Understanding ◽

High Mass ◽

Hot Stars ◽

Precise Information ◽

Ob Stars ◽

Modern Methods ◽

New Generation

AbstractThe presence of magnetic fields at the surfaces of many massive stars has been suspected for decades, to explain the observed properties and activity of OB stars. However, very few genuine high-mass stars had been identified as magnetic before the advent of a new generation of powerful spectropolarimeters that has resulted in a rapid burst of precise information about the magnetic properties of massive stars. During this talk, I will briefly review modern methods used to diagnose magnetic fields of higher-mass stars, and summarize our current understanding of the magnetic properties of OB stars.

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SGRs and AXPs: Evidence for Delayed Amplification of Magnetic Field after Neutron Star Formation?

Advances in Astronomy ◽

10.1155/2009/306821 ◽

2009 ◽

Vol 2009 ◽

pp. 1-8 ◽

Cited By ~ 7

Author(s):

Denis Leahy ◽

Rachid Ouyed

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Magnetic Fields ◽

Neutron Stars ◽

Birth Rate ◽

Massive Stars ◽

Robust Estimator ◽

High Magnetic Fields ◽

Field Amplification ◽

Kolmogorov Smirnov

We present new analysis of the birth rate of AXPs and SGRS and their associated SNRs. Using Kolmogorov-Smirnov statistics together with parametric fits based on a robust estimator, we find a birth rate of ∼1/(1000 years) for AXPs/SGRs and their associated SNRs. These high rates suggest that all massive stars (greater than ∼(23–32)M⊙) give rise to remnants with magnetar-like fields. Observations indicate a limited fraction of high magnetic fields in these progenitors; thus our study is suggestive of magnetic field amplification. Dynamo mechanisms during the birth of the neutron stars require spin rates much faster than either observations or theory indicate. We propose that massive stars produce neutron stars with normal (∼1012 G) magnetic fields, which are then amplified to1014-1015 G after a delay of hundreds of years. The amplification is speculated to be a consequence of color ferromagnetism and to occur with a delay after the neutron star core reaches quark deconfinement density (i.e., the quark-nova scenario). The delayed amplification allows one to interpret simultaneously the high birth rate and high magnetic fields of AXPs/SGRs and their link to massive stars.

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The B Fields in OB Stars (BOB) Survey

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314007054 ◽

2014 ◽

Vol 9 (S307) ◽

pp. 342-347 ◽

Cited By ~ 5

Author(s):

T. Morel ◽

N. Castro ◽

L. Fossati ◽

S. Hubrig ◽

N. Langer ◽

...

Keyword(s):

Theoretical Model ◽

Lower Bound ◽

Magnetic Fields ◽

Field Strength ◽

Massive Stars ◽

Occurrence Rate ◽

Early Type ◽

Ob Stars ◽

Early Type Stars ◽

Field Formation

AbstractThe B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects.

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Discussion – Winds and magnetic fields of active OB stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311010209 ◽

2010 ◽

Vol 6 (S272) ◽

pp. 172-175

Author(s):

Jean-Claude Bouret ◽

Lydia Cidale

Keyword(s):

Magnetic Fields ◽

Surface Brightness ◽

Large Scale ◽

Massive Stars ◽

Photometric Variability ◽

Ob Stars ◽

Star Surface

AbstractThe discussion on winds and magnetic fields of active OB stars was carried out by S. Owoki, G. Wade, M. Cantiello, O. Kochukhov, M. Smith, C. Neiner, T. Rivinius, H. Henrichs and R. Townsend. The topics were the ability to detect small and large scale magnetic fields in massive stars and the need to consider limits on photometric variability of the star surface brightness.

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