Effects of Chaos in the Galactic Halo

To study the way in which the principal periodic orbits in a Galactic potential determine orbital structure, horizontal and vertical surfaces of section, i.e. (dR/dt, R) and (dz/dt, z), are being used to explore the potential of Allen & Santillán (1991) and to investigate possible vertical structure in the Galactic halo. The chaotic “scattering” process due to the nearly spherical mass distribution close to the Galactic center in conjunction with the confinement of the chaotic orbits produces a vertical segregation of both chaotic and non-chaotic orbits in the halo. Certain zmax, zmin are preferred by the chaotic orbits over others as a result of the conservation of the total orbital energy and of the interaction and confinement of the chaotic orbits by the principal families of periodic orbits (Figure 1). Some of these periodic orbits have been identified. Correlations between the structure found in the observed W distribution and that of the numerically determined zmax, zmin histograms are shown for our sample of 280 halo stars (Schuster et al. 1993). W is the star's velocity perpendicular to the Galactic plane and zmax, zmin the maximum distances above or below the Galactic plane, respectively, reached by the star in the course of its orbit. This vertical structure may explain certain puzzling observations of the galactic halo, such as conflicting c/a values for the shape of the halo, and unusual velocity dispersions and/or distributions near the Galactic poles. These results are in good agreement with Hartwick's (1987) two component model for the halo.

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The magnetic structure of our Galaxy: a review of observations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309031123 ◽

2008 ◽

Vol 4 (S259) ◽

pp. 455-466 ◽

Cited By ~ 8

Author(s):

JinLin Han

Keyword(s):

Magnetic Fields ◽

Magnetic Structure ◽

Large Scale ◽

Galactic Halo ◽

Galactic Center ◽

Galactic Plane ◽

Galactic Disk ◽

Dust Emission ◽

Measure Data ◽

Radio Sources

AbstractThe magnetic structure in the Galactic disk, the Galactic center and the Galactic halo can be delineated more clearly than ever before. In the Galactic disk, the magnetic structure has been revealed by starlight polarization within 2 or 3 kpc of the Solar vicinity, by the distribution of the Zeeman splitting of OH masers in two or three nearby spiral arms, and by pulsar dispersion measures and rotation measures in nearly half of the disk. The polarized thermal dust emission of clouds at infrared, mm and submm wavelengths and the diffuse synchrotron emission are also related to the large-scale magnetic field in the disk. The rotation measures of extragalactic radio sources at low Galactic latitudes can be modeled by electron distributions and large-scale magnetic fields. The statistical properties of the magnetized interstellar medium at various scales have been studied using rotation measure data and polarization data. In the Galactic center, the non-thermal filaments indicate poloidal fields. There is no consensus on the field strength, maybe mG, maybe tens of μG. The polarized dust emission and much enhanced rotation measures of background radio sources are probably related to toroidal fields. In the Galactic halo, the antisymmetric RM sky reveals large-scale toroidal fields with reversed directions above and below the Galactic plane. Magnetic fields from all parts of our Galaxy are connected to form a global field structure. More observations are needed to explore the untouched regions and delineate how fields in different parts are connected.

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Large scale magnetic fields of our Galaxy

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310010239 ◽

2009 ◽

Vol 5 (H15) ◽

pp. 450-451

Author(s):

JinLin Han

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

Large Scale ◽

Galactic Halo ◽

Galactic Center ◽

Galactic Plane ◽

Galactic Disk ◽

Zeeman Splitting ◽

Radio Sources ◽

Star Formation Regions

AbstractLarge-scale magnetic fields in the Galactic disk have been revealed by distributions of pulsar rotation measures (RMs) and Zeeman splitting data of masers in star formation regions, which have several reversals in arm and interarm regions. Magnetic fields in the Galactic halo are reflected by the antisymmetric sky distribution of RMs of extragalactic radio sources, which have azimuthal structure with reversed directions below and above the Galactic plane. Large-scale magnetic fields in the Galactic center probably have a poloidal and toroidal structure.

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Mapping the Galactic Center

Symposium - International Astronomical Union ◽

10.1017/s0074180900232889 ◽

1996 ◽

Vol 171 ◽

pp. 369-369

Author(s):

W.J. Duschl ◽

S. von Linden ◽

T. Walter ◽

M. Wittkowski

Keyword(s):

Angular Momentum ◽

Molecular Clouds ◽

Vertical Structure ◽

Galactic Center ◽

Galactic Plane ◽

The Galaxy ◽

Sgr A ◽

Celestial Sphere ◽

Inner Region ◽

Galactic Longitude

Gas and dust in the inner region of the Galaxy are distributed in a flat, disklike structure. We model the dynamics of this material in the framework of an accretion disk approach, and thus determine the efficiency of the radial transport of mass and angular momentum in the inner ∼ 200 pc of the Galactic Plane. Moreover, this allows us to establish the location (coordinates: galactic longitude l and depth normal to the celestial sphere) of molecular clouds from the observed positions (l) and radial velocities (currently, we neglect details of the vertical structure). Ultimately this will yield a map of the distribution of molecular clouds about Sgr A∗.

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Distribution of R- and S-Process Elements in the Galactic Halo

Symposium - International Astronomical Union ◽

10.1017/s0074180900035555 ◽

1988 ◽

Vol 132 ◽

pp. 501-506

Author(s):

C. Sneden ◽

C. A. Pilachowski ◽

K. K. Gilroy ◽

J. J. Cowan

Keyword(s):

Heavy Element ◽

Galactic Halo ◽

Low Noise ◽

Heavy Elements ◽

Process Synthesis ◽

Element Abundances ◽

Halo Stars ◽

Abundance Patterns ◽

R Process ◽

Process Elements

Current observational results for the abundances of the very heavy elements (Z>30) in Population II halo stars are reviewed. New high resolution, low noise spectra of many of these extremely metal-poor stars reveal general consistency in their overall abundance patterns. Below Galactic metallicities of [Fe/H] Ã −2, all of the very heavy elements were manufactured almost exclusively in r-process synthesis events. However, there is considerable star-to-star scatter in the overall level of very heavy element abundances, indicating the influence of local supernovas on element production in the very early, unmixed Galactic halo. The s-process appears to contribute substantially to stellar abundances only in stars more metal-rich than [Fe/H] Ã −2.

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Constructing the natural families of periodic orbits near irregular bodies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stv1784 ◽

2015 ◽

Vol 453 (3) ◽

pp. 3270-3278 ◽

Cited By ~ 10

Author(s):

Yang Yu ◽

Hexi Baoyin ◽

Yu Jiang

Keyword(s):

Periodic Orbits ◽

Families Of Periodic Orbits ◽

Natural Families

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The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars

Nature ◽

10.1038/nature03645 ◽

2005 ◽

Vol 435 (7046) ◽

pp. 1203-1205 ◽

Cited By ~ 63

Author(s):

Nicolas Dauphas

Keyword(s):

Milky Way ◽

Galactic Halo ◽

Halo Stars ◽

Production Ratio

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Remarkable Symmetries in the Milky Way Disc's Magnetic Field

Publications of the Astronomical Society of Australia ◽

10.1071/as10045 ◽

2011 ◽

Vol 28 (2) ◽

pp. 171-176 ◽

Cited By ~ 15

Author(s):

P. P. Kronberg ◽

K. J. Newton-McGee

Keyword(s):

Magnetic Structure ◽

Large Scale ◽

Milky Way ◽

Galactic Center ◽

Galactic Plane ◽

Galactic Disk ◽

Field Structure ◽

Field Pattern ◽

Close Coupling ◽

Sign Change

AbstractWe apply a new, expanded compilation of extragalactic source Faraday rotation measures (RM) to investigate the broad underlying magnetic structure of the Galactic disk at latitudes ∣b∣ ≲15° over all longitudes l, where our total number of RMs is comparable to those in the combined Canadian Galactic Plane Survey (CGPS) at ∣b∣ < 4° and the Southern Galactic Plane (SGPS) ∣b∣<1.5°. We report newly revealed, remarkably coherent patterns of RM at ∣b∣≲15° from l∼270° to ∼90° and RM(l) features of unprecedented clarity that replicate in l with opposite sign on opposite sides of the Galactic center. They confirm a highly patterned bisymmetric field structure toward the inner disc, an axisymmetic pattern toward the outer disc, and a very close coupling between the CGPS/SGPS RMs at ∣b∣≲3° (‘mid-plane’) and our new RMs up to ∣b∣∼15° (‘near-plane’). Our analysis also shows the vertical height of the coherent component of the disc field above the Galactic disc's mid-plane—to be ∼1.5 kpc out to ∼6 kpc from the Sun. This identifies the approximate height of a transition layer to the halo field structure. We find no RM sign change across the plane within ∣b∣∼15° in any longitude range. The prevailing disc field pattern and its striking degree of large-scale ordering confirm that our side of the Milky Way has a very organized underlying magnetic structure, for which the inward spiral pitch angle is 5.5°±1° at all ∣b∣ up to ∼12° in the inner semicircle of Galactic longitudes. It decreases to ∼0° toward the anticentre.

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