scholarly journals The magnetic field of the Galaxy determined from the zeeman splitting of the 21-cm hydrogen line

1964 ◽  
Vol 20 ◽  
pp. 134-139
Author(s):  
R. D. Davies
Keyword(s):  
Magnetic Field ◽  
Zeeman Effect ◽  
Mean Field ◽  
Neutral Hydrogen ◽  
Zeeman Splitting ◽  
Longitudinal Component ◽  
Frequency Separation ◽  
Intensity Difference ◽  
Interstellar Clouds ◽  
The Magnetic Field

The Zeeman effect can be used to measure directly the longitudinal component of the magnetic field in interstellar neutral hydrogen clouds. The frequency separation between the two circularly polarized components is 28 c/s for 10–5 G and can be inferred from measurements of the intensity difference between left- and right-hand circular polarization as a function of frequency. Earlier experiments at Jodrell Bank showed that the mean field in the interstellar medium was less than 10–5 G (Davies et al. 1960). Recent work using more sensitive techniques has provided a positive measurement of a weak general magnetic field and of fields of varying intensity in different interstellar clouds.

Magnetic fields in dense interstellar clouds

1981 ◽  
Vol 303 (1480) ◽  
pp. 581-587 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Zeeman Effect ◽  
Neutral Hydrogen ◽  
Magnetic Field Direction ◽  
Strong Indication ◽  
Interstellar Gas ◽  
Interstellar Clouds ◽  
The Magnetic Field ◽  
Maser Sources

Evidence is presented that shows that magnetic fields pervade the entire interstellar medium including interstellar gas clouds of both low and high density. The magnetic field in the ‘seed’ gas from which the denser clouds form is 0.2-0.3 nT (1T — 10 4 G). Zeeman effect measurements of neutral hydrogen show that stronger fields occur in denser clouds. These data, taken with the microtesla fields found in OH maser sources, indicate that magnetic flux is conserved during gravitational collapse of interstellar clouds from densities of ca. 5 to ca. 10 7 cm -3 . Magnetic fields appear to play a major role in the formation of dense interstellar clouds. Furthermore there is a strong indication that the magnetic field direction is preserved during cloud collapse.

scholarly journals Modelling of the Magnetic Configuration of CP Stars from Polarimetric Observations

1998 ◽  
Vol 11 (2) ◽  
pp. 679-681
Author(s):  
M. Landolfi
Keyword(s):  
Magnetic Field ◽  
Stokes Parameter ◽  
Quadratic Field ◽  
Mean Field ◽  
Longitudinal Component ◽  
Stokes Parameters ◽  
Longitudinal Field ◽  
The Mean ◽  
The Magnetic Field ◽  
Polarized Radiation

The observational quantities commonly used to study the magnetic field of CP stars – the mean field modulus and the mean longitudinal field, as well as the ‘mean asymmetry of the longitudinal field’ and the ‘mean quadratic field’ recently introduced by Mathys (1995a,b) – are based either on the Stokes parameter / or on the Stokes parameter V. However, a complete description of polarized radiation requires the knowledge of the full Stokes vector: in other words, we should expect that useful information is also contained in linear polarization (the Stokes parameters Q and U); or rather we should expect the information contained in (Q, U) and in V to be complementary, since linear and circular polarization are basically related to the transverse and the longitudinal component of the magnetic field, respectively.

scholarly journals The magnetic field in the dense photodissociation region of DR 21

2020 ◽  
Author(s):  
Atanu Koley ◽  
Nirupam Roy ◽  
Karl M Menten ◽  
Arshia M Jacob ◽  
Thushara G S Pillai ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Zeeman Effect ◽  
Zeeman Splitting ◽  
Weak Field ◽  
Field Energy ◽  
Evolutionary Stage ◽  
Maser Emission ◽  
The Magnetic Field ◽  
Photodissociation Region

Abstract Measuring interstellar magnetic fields is extremely important for understanding their role in different evolutionary stages of interstellar clouds and of star formation. However, detecting the weak field is observationally challenging. We present measurements of the Zeeman effect in the 1665 and 1667 MHz (18 cm) lines of the hydroxyl radical (OH) lines toward the dense photodissociation region (PDR) associated with the compact H ii region DR 21 (Main). From the OH 18 cm absorption, observed with the Karl G. Jansky Very Large Array, we find that the line of sight magnetic field in this region is ∼0.13 mG. The same transitions in maser emission toward the neighbouring DR 21(OH) and W 75S-FR1 regions also exhibit the Zeeman splitting. Along with the OH data, we use [C ii] 158 μm line and hydrogen radio recombination line data to constrain the physical conditions and the kinematics of the region. We find the OH column density to be ∼3.6 × 1016(Tex/25 K) cm−2, and that the 1665 and 1667 MHz absorption lines are originating from the gas where OH and C+ are co-existing in the PDR. Under reasonable assumptions, we find the measured magnetic field strength for the PDR to be lower than the value expected from the commonly discussed density–magnetic field relation while the field strength values estimated from the maser emission are roughly consistent with the same. Finally, we compare the magnetic field energy density with the overall energetics of DR 21’s PDR and find that, in its current evolutionary stage, the magnetic field is not dynamically important.

scholarly journals Observability of the Magnetic Field in Molecular Clouds

1990 ◽  
Vol 140 ◽  
pp. 304-304
Author(s):  
N. Bel ◽  
B. Leroy
Keyword(s):  
Magnetic Field ◽  
Molecular Clouds ◽  
Diatomic Molecules ◽  
Zeeman Effect ◽  
Interstellar Clouds ◽  
The Magnetic Field

We have done detailed calculations of the Zeeman effect in the dozen diatomic molecules identified in interstellar clouds.

The Zeeman effect in interstellar clouds

1967 ◽  
Vol 31 ◽  
pp. 385-389 ◽  
Author(s):  
G. L. Verschuur
Keyword(s):  
Magnetic Field ◽  
Uniform Magnetic Field ◽  
Zeeman Effect ◽  
Longitudinal Component ◽  
Interstellar Clouds ◽  
A Value ◽  
Upper Limit ◽  
The Mean ◽  
Cas A ◽  
Spiral Arm

The interpretation of Zeeman-effect measurements in terms of interstellar magnetic fields is strongly involved with the problems of the nature of interstellar clouds, and of their relationship to the structure of the field. The best measurements furnish, for the mean longitudinal component of the spectrum of Tau A, a value of + 1·1 ± 3·0 μG (micro-gauss), and for that in the Orion-Arm feature in Cas A, - 0·8 ± 3·5 μG. These values are consistent with an upper limit of 7 μG to a uniform magnetic field, pervading the absorbing clouds and directed parallel to the local spiral arm.

scholarly journals On the Orientation of Magnetic Fields in Quiescent Prominences

1971 ◽  
Vol 43 ◽  
pp. 656-662 ◽  
Author(s):  
Ulrich Anzer ◽  
E. Tandberg-Hanssen
Keyword(s):  
Magnetic Field ◽  
Distribution Function ◽  
Zeeman Effect ◽  
General Rule ◽  
Longitudinal Component ◽  
Spectral Lines ◽  
The Other ◽  
Relative Importance ◽  
Quiescent Prominence ◽  
The Magnetic Field

The longitudinal component of the magnetic field in quiescent prominences has been measured directly with magnetographs using the Zeeman effect on selected spectral lines (Rust, 1966; Ioshpa, 1968; Harvey, 1969). We know that as a general rule the magnetic field enters the, largely-vertical, sheet-like quiescent prominence on one side and exits on the other. The field traverses the prominence plasma with components both along and at right angles to the long axis of the prominence. It is the purpose of this paper to describe observations that may indicate the relative importance of the two components of the magnetic field, and to derive a distribution function for the magnetic field vectors.

scholarly journals Observations of Magnetic Fields in Quiescent Prominences

1971 ◽  
Vol 43 ◽  
pp. 192-200 ◽  
Author(s):  
Einar Tandberg-Hanssen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Component ◽  
Zeeman Effect ◽  
Mean Value ◽  
Longitudinal Component ◽  
The Other ◽  
Magnetic Field Component ◽  
The Magnetic Field

The longitudinal component of the magnetic field, B∥, has been recorded in about 135 quiescent prominences observed at Climax during the period 1968–1969. The measurements were obtained with the magnetograph which records the Zeeman effect on hydrogen, helium and metal lines. The following lines were used, Hα; He I, D3, He I, 4471 Å; Na I, D1 and D2, and the observed magnetic field component in these prominences was independent of the line. The overall mean value of the field B∥ for all the prominences was 7.3G. As a rule, the magnetic field enters the prominence on one side and exits on the other, but in traversing the prominence material, the field tends to run along the long axis of the prominence.

scholarly journals The magnetic field in luminous star-forming galaxies

2008 ◽  
Vol 4 (S259) ◽  
pp. 493-498
Author(s):  
Timothy Robishaw ◽  
Carl Heiles
Keyword(s):  
Magnetic Field ◽  
Emission Line ◽  
Zeeman Effect ◽  
Zeeman Splitting ◽  
Star Forming ◽  
The Magnetic Field

AbstractAn ongoing search for Zeeman splitting in the 1667 MHz OH megamaser emission from luminous star-forming galaxies has yielded numerous detections. These results, in addition to being the first extragalactic measurement of the Zeeman effect in an emission line, suggest that OH megamasers are excellent extragalactic magnetometers. We review the progress of our survey and discuss future observations.

ZEEMAN SPLITTING OF DONOR STATES IN GERMANIUM

1958 ◽  
Vol 36 (9) ◽  
pp. 1161-1167 ◽  
Author(s):  
R. R. Haering
Keyword(s):  
Magnetic Field ◽  
Effective Mass ◽  
Zeeman Effect ◽  
Zeeman Splitting ◽  
Energy Difference ◽  
Band Energy ◽  
Mass Approximation ◽  
Donor States ◽  
Energy Surfaces ◽  
The Magnetic Field

The linear Zeeman effect of the 2p m = ± 1 donor states is calculated in the effective mass approximation. The resulting level splitting is independent of the longitudinal mass characterizing the ellipsoidal conduction band energy surfaces. This result is valid as long as the Zeeman splitting of the m = ±1 states is small compared to the energy difference between the 2p m = 0 and the 2p m = ± 1 states. The Zeeman pattern to be expected in germanium is plotted as a function of the angle between the magnetic field and the (100) direction.

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