scholarly journals The MiMeS project: first results

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.

scholarly journals The Formation of Massive Stars

2010 ◽  
Vol 6 (S270) ◽  
pp. 57-64
Author(s):  
Ian A. Bonnell ◽  
Rowan J Smith
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Massive Star ◽  
Massive Stars ◽  
Cluster Formation ◽  
High Mass ◽  
Prestellar Cores ◽  
Stellar Mergers ◽  
Massive Clusters ◽  
Viable Mechanism

AbstractThere has been considerable progress in our understanding of how massive stars form but still much confusion as to why they form. Recent work from several sources has shown that the formation of massive stars through disc accretion, possibly aided by gravitational and Rayleigh-Taylor instabilities is a viable mechanism. Stellar mergers, on the other hand, are unlikely to occur in any but the most massive clusters and hence should not be a primary avenue for massive star formation. In contrast to this success, we are still uncertain as to how the mass that forms a massive star is accumulated. there are two possible mechanisms including the collapse of massive prestellar cores and competitive accretion in clusters. At present, there are theoretical and observational question marks as to the existence of high-mass prestellar cores. theoretically, such objects should fragment before they can attain a relaxed, centrally condensed and high-mass state necessary to form massive stars. Numerical simulations including cluster formation, feedback and magnetic fields have not found such objects but instead point to the continued accretion in a cluster potential as the primary mechanism to form high-mass stars. Feedback and magnetic fields act to slow the star formation process and will reduce the efficiencies from a purely dynamical collapse but otherwise appear to not significantly alter the process.

scholarly journals The effects of surface fossil magnetic fields on massive star evolution – II. Implementation of magnetic braking in mesa and implications for the evolution of surface rotation in OB stars

2020 ◽  
Vol 493 (1) ◽  
pp. 518-535 ◽  
Author(s):  
Z Keszthelyi ◽  
G Meynet ◽  
M E Shultz ◽  
A David-Uraz ◽  
A ud-Doula ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Magnetic Fields ◽  
Massive Star ◽  
Massive Stars ◽  
Rotation Rates ◽  
Momentum Loss ◽  
Star Models ◽  
Surface Rotation ◽  
Angular Momentum Loss ◽  
Magnetic Braking

ABSTRACT The time evolution of angular momentum and surface rotation of massive stars are strongly influenced by fossil magnetic fields via magnetic braking. We present a new module containing a simple, comprehensive implementation of such a field at the surface of a massive star within the Modules for Experiments in Stellar Astrophysics (mesa) software instrument. We test two limiting scenarios for magnetic braking: distributing the angular momentum loss throughout the star in the first case, and restricting the angular momentum loss to a surface reservoir in the second case. We perform a systematic investigation of the rotational evolution using a grid of OB star models with surface magnetic fields (M⋆ = 5–60 M⊙, Ω/Ωcrit = 0.2–1.0, Bp = 1–20 kG). We then employ a representative grid of B-type star models (M⋆ = 5, 10, 15 M⊙, Ω/Ωcrit = 0.2, 0.5, 0.8, Bp = 1, 3, 10, 30 kG) to compare to the results of a recent self-consistent analysis of the sample of known magnetic B-type stars. We infer that magnetic massive stars arrive at the zero-age main sequence (ZAMS) with a range of rotation rates, rather than with one common value. In particular, some stars are required to have close-to-critical rotation at the ZAMS. However, magnetic braking yields surface rotation rates converging to a common low value, making it difficult to infer the initial rotation rates of evolved, slowly rotating stars.

scholarly journals Luminous Blue Variables, cool hypergiants and some impostors in the H-R diagram

2003 ◽  
Vol 212 ◽  
pp. 38-46
Author(s):  
Roberta M. Humphreys
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
Surface Activity ◽  
Massive Star ◽  
Massive Stars ◽  
High Mass ◽  
Luminous Blue Variables ◽  
Star Evolution ◽  
High Mass Loss ◽  
Massive Star Evolution

Current observations of the S Dor/LBVs and candidates and the implications for their important role in massive star evolution are reviewed. Recent observations of the cool hypergiants are altering our ideas about their evolutionary state, their atmospheres and winds, and the possible mechanisms for their asymmetric high mass loss episodes which may involve surface activity and magnetic fields. Recent results for IRC+10420, ρ Cas and VY CMa are highlighted. S Dor/LBVs in eruption, and the cool hypergiants in their high mass loss phases with their optically thick winds are not what their apparent spectra and temperatures imply; they are then ‘impostors’ on the H-R diagram. The importance of the very most massive stars, like η Carinae and the ‘supernovae impostors’ are also discussed.

Twinkle little stars: Massive stars are quenched in strong magnetic fields

2018 ◽  
Vol 14 (A30) ◽  
pp. 118-118
Author(s):  
Fatemeh S. Tabatabaei ◽  
M. Almudena Prieto ◽  
Juan A. Fernández-Ontiveros
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Massive Star ◽  
Massive Stars ◽  
Radio Continuum ◽  
Small Scale ◽  
Massive Star Formation ◽  
Low Mass ◽  
Formation Efficiency

AbstractThe role of the magnetic fields in the formation and quenching of stars with different mass is unknown. We studied the energy balance and the star formation efficiency in a sample of molecular clouds in the central kpc region of NGC 1097, known to be highly magnetized. Combining the full polarization VLA/radio continuum observations with the HST/Hα, Paα and the SMA/CO lines observations, we separated the thermal and non-thermal synchrotron emission and compared the magnetic, turbulent, and thermal pressures. Most of the molecular clouds are magnetically supported against gravitational collapse needed to form cores of massive stars. The massive star formation efficiency of the clouds also drops with the magnetic field strength, while it is uncorrelated with turbulence (Tabatabaei et al. 2018). The inefficiency of the massive star formation and the low-mass stellar population in the center of NGC 1097 can be explained in the following steps: I) Magnetic fields supporting the molecular clouds prevent the collapse of gas to densities needed to form massive stars. II) These clouds can then be fragmented into smaller pieces due to e.g., stellar feedback, non-linear perturbations and instabilities leading to local, small-scale diffusion of the magnetic fields. III) Self-gravity overcomes and the smaller clouds seed the cores of the low-mass stars.

scholarly journals Magnetic Massive Stars

2007 ◽  
Vol 3 (S250) ◽  
pp. 577-586 ◽  
Author(s):  
Rich Townsend ◽  
David H. Cohen ◽  
Luc Dessart ◽  
Swetlana Hubrig ◽  
Yaël Nazé ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Significant Influence ◽  
Massive Star ◽  
Massive Stars ◽  
Structure Evolution ◽  
Special Session ◽  
The Past ◽  
Recent Developments ◽  
Circumstellar Environments ◽  
Theoretical Developments

AbstractMagnetic fields are unexpected in massive stars, due to the absence of a sub-surface convective dynamo. However, advances in instrumentation over the past three decades have led to their detection in a small but growing subset of these stars. Moreover, complementary theoretical developments have highlighted their potentially significant influence over the structure, evolution and circumstellar environments of massive stars. Here, we summarize a special session convened prior to the main conference, focused on presenting recent developments in the study of massive-star magnetic fields.

scholarly journals Asteroseismology and spectropolarimetry: opening new windows on the internal dynamics of massive stars

2014 ◽  
Vol 9 (S307) ◽  
pp. 420-425 ◽  
Author(s):  
S. Mathis ◽  
C. Neiner
Keyword(s):  
Angular Momentum ◽  
Magnetic Fields ◽  
Massive Star ◽  
State Of The Art ◽  
Massive Stars ◽  
The State ◽  
Internal Dynamics ◽  
Dynamical Processes ◽  
Internal Mixing ◽  
Mixing And Transport

AbstractIn this article, we show how asteroseismology and spectropolarimetry allow to probe dynamical processes in massive star interiors. First, we give a summary of the state-of-the-art. Second, we recall the MHD mechanisms that take place in massive stars. Next, we show how asteroseismology gives strong constraints on the internal mixing and transport of angular momentum while spectropolarimetry allows to unravel the role played by magnetic fields.

scholarly journals Links between surface magnetic fields, abundances, and surface rotation in clusters and in the field

2014 ◽  
Vol 9 (S307) ◽  
pp. 404-413
Author(s):  
Norbert Przybilla
Keyword(s):  
Magnetic Fields ◽  
Massive Stars ◽  
Chemical Elements ◽  
Relevant Information ◽  
Transport Processes ◽  
Observational Constraints ◽  
Comprehensive Description ◽  
Surface Rotation ◽  
The Many ◽  
Further Development

AbstractTheory predicts that hydrodynamical instabilities transport angular momentum and chemical elements in rotating massive stars. An interplay of rotation and a magnetic field affects these transport processes. The complexity of the problem imposes that a comprehensive description cannot be developed on theoretical grounds alone, progress in the understanding of the evolution of massive stars has to be guided by observations. The challenge lies both in the derivation of accurate and precise observational constraints as well as in the extraction of the relevant information for identifying possible correlations – like between surface magnetic fields, abundances, and surface rotation – from a multivariate function of the many parameters involved. I review the most important steps recently made based on detailed studies of massive stars both in the field and in clusters towards finding such links that ultimately may guide the further development of the models.

scholarly journals Evidence for ram-pressure stripping in a cluster of galaxies at z = 0.7

2019 ◽  
Vol 631 ◽  
pp. A114 ◽  
Author(s):  
A. Boselli ◽  
B. Epinat ◽  
T. Contini ◽  
V. Abril-Melgarejo ◽  
L. A. Boogaard ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Massive Star ◽  
Observational Evidence ◽  
Star Forming ◽  
Cluster Of Galaxies ◽  
Stellar Component ◽  
Ram Pressure ◽  
The Galaxy ◽  
The Universe ◽  
Projected Distance

Multi-Unit Spectroscopic Explorer (MUSE) observations of the cluster of galaxies CGr32 (M200 ≃ 2 × 1014 M⊙) at z = 0.73 reveal the presence of two massive star-forming galaxies with extended tails of diffuse gas detected in the [O II]λλ3727–3729 Å emission-line doublet. The tails, which have a cometary shape with a typical surface brightness of a few 10−18 erg s−1 cm−2 arcsec−2, extend up to ≃100 kpc (projected distance) from the galaxy discs, and are not associated with any stellar component. All this observational evidence suggests that the gas was removed during a ram-pressure stripping event. This observation is thus the first evidence that dynamical interactions with the intracluster medium were active when the Universe was only half its present age. The density of the gas derived using the observed [O II]λ3729/[O II]λ3726 line ratio implies a very short recombination time, suggesting that a source of ionisation is necessary to keep the gas ionised within the tail.

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 Magnetic fluxes of massive stars: statistics and evolution

2010 ◽  
Vol 6 (S272) ◽  
pp. 198-199
Author(s):  
Alexander F. Kholtygin ◽  
Sergei N. Fabrika ◽  
Natalia A. Drake ◽  
Andrei P. Igoshev
Keyword(s):  
Magnetic Fields ◽  
Neutron Stars ◽  
Massive Stars ◽  
Statistical Properties ◽  
Ob Stars ◽  
The Mean

AbstractThe statistical properties of magnetic fields and magnetic fluxes of OB stars were investigated. The mean magnetic fluxes of massive OB stars appear to be 3 order larger than those for neutron stars.

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