scholarly journals Problems of modelization of circumstellar matter out of equilibrium

1994 ◽  
Vol 162 ◽  
pp. 431-433
Author(s):  
J-P. J. Lafon ◽  
E. Huguet
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Interstellar Medium ◽  
Circumstellar Matter ◽  
Solid Particles ◽  
Heavy Elements ◽  
Circumstellar Envelopes ◽  
Interstellar Gas ◽  
The Core ◽  
Evolved Stars

Circumstellar envelopes of young and evolved stars are responsible for many important phenomena concerning the exchange of matter, angular momentum, energy and maybe magnetic field between the core structure of stars and the interstellar medium. In particular, it is through them that matter enriched in heavy elements flows from evolved stars towards the interstellar gas, submitted to complex ordinary chemistry or photochemistry and condensation into solid particles.

scholarly journals Constraining the coherence scale of the interstellar magnetic field using TeV gamma-ray observations of supernova remnants

2020 ◽  
Vol 496 (2) ◽  
pp. 2448-2461 ◽  
Author(s):  
Matteo Pais ◽  
Christoph Pfrommer ◽  
Kristian Ehlert ◽  
Maria Werhahn ◽  
Georg Winner
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Galactic Cosmic Rays ◽  
Shock Acceleration ◽  
Interstellar Gas ◽  
Narrow Angle ◽  
Magnetohydrodynamic Simulations ◽  
Tev Gamma Rays

ABSTRACT Galactic cosmic rays (CRs) are believed to be accelerated at supernova remnant (SNR) shocks. In the hadronic scenario, the TeV gamma-ray emission from SNRs originates from decaying pions that are produced in collisions of the interstellar gas and CRs. Using CR-magnetohydrodynamic simulations, we show that magnetic obliquity-dependent shock acceleration is able to reproduce the observed TeV gamma-ray morphology of SNRs such as Vela Jr and SN1006 solely by varying the magnetic morphology. This implies that gamma-ray bright regions result from quasi-parallel shocks (i.e. when the shock propagates at a narrow angle to the upstream magnetic field), which are known to efficiently accelerate CR protons, and that gamma-ray dark regions point to quasi-perpendicular shock configurations. Comparison of the simulated gamma-ray morphology to observations allows us to constrain the magnetic coherence scale λB around Vela Jr and SN1006 to $\lambda _B \simeq 13_{-4.3}^{+13}$ pc and $\lambda _B \gt 200_{-40}^{+50}$ pc, respectively, where the ambient magnetic field of SN1006 is consistent with being largely homogeneous. We find consistent pure hadronic and mixed hadronic-leptonic models that both reproduce the multifrequency spectra from the radio to TeV gamma-rays and match the observed gamma-ray morphology. Finally, to capture the propagation of an SNR shock in a clumpy interstellar medium, we study the interaction of a shock with a dense cloud with numerical simulations and analytics. We construct an analytical gamma-ray model for a core collapse SNR propagating through a structured interstellar medium, and show that the gamma-ray luminosity is only biased by 30 per cent for realistic parameters.

scholarly journals Rotation and Stellar Evolution

1981 ◽  
Vol 93 ◽  
pp. 237-256
Author(s):  
R. Kippenhahn ◽  
H.-C. Thomas
Keyword(s):  
Magnetic Field ◽  
Stellar Evolution ◽  
Chemical Elements ◽  
Line Broadening ◽  
General Magnetic Field ◽  
The Core ◽  
Evolved Stars

Does rotation influence stellar evolution? Does it cause observational effects other than line broadening? Can rotation be responsible for mixing of chemical elements throughout the star? Do evolved stars have rapidly rotating cores? This, for instance, is of interest if one wants to compute the details of supernova events. We are not sure whether rotation has really important effects on the life of a star. There might be no rapidly rotating cores. If we think that a fossile general magnetic field couples core and envelope of an evolved star, the core will always be slowed down by the big inertial momentum of the outer regions.

scholarly journals The Physics of the Interstellar Matter

1974 ◽  
Vol 3 ◽  
pp. 37-49 ◽  
Author(s):  
G. B. Field
Keyword(s):  
Solar System ◽  
Interstellar Medium ◽  
The United States ◽  
Astronomical Observatory ◽  
Solid Particles ◽  
Heavy Elements ◽  
Interstellar Space ◽  
Interstellar Matter ◽  
Hydrogen Molecules ◽  
Long Time

Some of the most striking recent discoveries about interstellar matter involve molecules. It has been known for a long time that there are atoms and ions in space - mainly hydrogen and helium, of course - but also heavier elements like sodium and calcium. In addition, there are solid particles of dust, about 10-5cm across, which must be composed of heavier elements, as hydrogen and helium cannot condense under interstellar conditions.In 1972, the Orbiting Astronomical Observatory-3, which employs an 80-cm telescope at wavelengths between 1000Å and 3000Å, was launched in the United States and put into operation. In the ensuing year, it has demonstrated that much of the interstellar medium is composed of hydrogen molecules. This result, based upon the observation of Lyman-band absorption in the spectrum of early-type stars, had been anticipated by a rocket observation of H2 by Carruthers in 1970.The same OAO-3 instrument observed resonance lines of many cosmically abundant elements, and found that these elements often appear to be less abundant in interstellar space than in the solar system, relative to hydrogen. As young stars born recently from the interstellar medium do not show this effect, the heavy elements must in fact be present in some other form. Here I will argue that the heavy elements are largely locked up in the form of the dust and, further, that dust is critical for the formation of the molecules in interstellar space.It is appropriate that the Orbiting Astronomical Observatory-3 which made these discoveries has been named in honor of Copernicus, the Polish astronomer we honor here on the 500th anniversary of his birth. Just as his discoveries were revolutionary for the understanding of the solar system, those made using the Observatory named in his honor have been revolutionary for the understanding of the Galaxy.

scholarly journals Cosmic Rays and the Parker Instability

1985 ◽  
Vol 107 ◽  
pp. 361-363
Author(s):  
A.H. Nelson
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Interstellar Medium ◽  
Galactic Halo ◽  
Cosmic Ray ◽  
Interstellar Gas ◽  
Horizontal Magnetic Field ◽  
Magnetic Buoyancy ◽  
Field Lines ◽  
Gas Layer

Parker (1966, 1969, 1979) has shown that the magnetic buoyancy of a uniform horizontal magnetic field will destabilize the Galactic gas layer. Perturbations of the form shown in Fig. 1 will grow in time with the magnetic loops ballooning up into the Galactic halo, and the interstellar gas draining down the field lines to collect in the mid-plane. Parker also showed that if the dynamical effect of the cosmic ray component of the interstellar medium is included, using an isotropic cosmic ray pressure, then the instability is enhanced.

scholarly journals Stability of an interstellar medium with curved magnetic field lines

1979 ◽  
Vol 84 ◽  
pp. 321-322
Author(s):  
Catherine J. Cesarsky
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Equilibrium State ◽  
Galactic Plane ◽  
Interstellar Gas ◽  
Gravitational Pull ◽  
Rayleigh Taylor Instability ◽  
Field Lines ◽  
The Stability ◽  
The Magnetic Field

Parker (1966) has considered a simple equilibrium state of the interstellar gas and fields system, such that the magnetic field lines are parallel to the galactic plane; he has shown that this state is subject to the Rayleigh-Taylor instability. The gravitational pull of the stars on the gas and the buoyancy of the magnetic field tend to bend the field lines, allowing the gas to slide down towards the plane. The stability of equilibria with curved magnetic field lines remained to be considered.

scholarly journals A VLBI polarization study of SiO masers towards VY CMa

2007 ◽  
Vol 3 (S242) ◽  
pp. 328-329
Author(s):  
L. L. Richter ◽  
A. J. Kemball ◽  
J. L. Jonas
Keyword(s):  
Magnetic Field ◽  
Late Type ◽  
Circumstellar Envelopes ◽  
Maser Emission ◽  
Evolved Stars ◽  
Polarization Study ◽  
Wide Range ◽  
Supergiant Star

AbstractMaser emission from the SiO molecule has been widely observed in the near-circumstellar envelopes of late-type, evolved stars. VLBI images can resolve individual SiO maser spots, providing information about the kinematics and magnetic field in the extended atmospheres of these stars. This poster presents full polarization images of several SiO maser lines towards the supergiant star VY CMa. VY CMa is a particularly strong SiO maser source and allows observations of a wide range of maser transitions. We discuss implications of these observations for VY CMa morphology, polarization, and pumping models.

Investigation of the Structure and Magnetic Properties of Bulk Amorphous FeCoYB Alloy

2017 ◽  
Vol 68 (9) ◽  
pp. 2162-2165 ◽  
Author(s):  
Katarzyna Bloch ◽  
Mihail Aurel Titu ◽  
Andrei Victor Sandu
Keyword(s):  
Magnetic Field ◽  
Magnetic Properties ◽  
Hyperfine Field ◽  
Irreversible Processes ◽  
Magnetization Process ◽  
Casting Method ◽  
The Core ◽  
Injection Casting ◽  
Core Losses ◽  
Microstructural Studies

The paper presents the results of structural and microstructural studies for the bulk Fe65Co10Y5B20 and Fe63Co10Y7B20 alloys. All the rods obtained by the injection casting method were fully amorphous. It was found on the basis of analysis of distribution of hyperfine field induction that the samples of Fe65Co10Y5B20 alloy are characterised with greater atomic packing density. Addition of Y to the bulk amorphous Fe65Co10Y5B20 alloy leads to the decrease of the average induction of hyperfine field value. In a strong magnetic field (i.e. greater than 0.4HC), during the magnetization process of the alloys, where irreversible processes take place, the core losses associated with magnetization and de-magnetization were investigated.

scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

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