scholarly journals Observational tests of SiO maser polarisation models

2012 ◽  
Vol 8 (S287) ◽  
pp. 81-82
Author(s):  
L. L. Richter ◽  
A. J. Kemball ◽  
J. L. Jonas
Keyword(s):  
Magnetic Field ◽  
Zeeman Splitting ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Circumstellar Envelope ◽  
Late Type ◽  
High Luminosity ◽  
Component Level ◽  
Evolved Stars ◽  
The Magnetic Field

AbstractSiO masers are often observed in the near-circumstellar envelope of late-type evolved stars. The polarisation of the masers can be used as a probe of the magnetic field in this region, subject to maser polarisation radiative transfer model. Two main maser polarisation models have been developed for the weak Zeeman splitting case applicable to circumstellar SiO masers. Observational tests aimed at discriminating between these models were performed at maser component level, using VLBA observations of v=1 J=1-0, v=2 J=1-0 and v=1 J=2-1 SiO masers towards the high-luminosity source VY CMa.

scholarly journals The magnetic field of the evolved star W43A

2008 ◽  
Vol 4 (S259) ◽  
pp. 109-110
Author(s):  
Nikta Amiri ◽  
Wouter Vlemmings ◽  
Huib Jan van Langevelde
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Circular Polarization ◽  
Magnetic Field Strength ◽  
Large Scale ◽  
Zeeman Splitting ◽  
Density Region ◽  
Evolved Stars ◽  
Large Scale Magnetic Field ◽  
The Magnetic Field

AbstractPlanetary nebulae (PNe) often show large departures from spherical symmetry. The origin and development of these asymmetries is not clearly understood. The most striking structures are the highly collimated jets that are already observed in a number of evolved stars before they enter the PN phase. The aim of this project is to observe the Zeeman splitting of the OH maser of the W43A star and determine the magnetic field strength in the low density region. The 1612 MHz OH masers of W43A were observed with MERLIN to measure the circular polarization due to the Zeeman splitting of 1612 OH masers in the envelope of the evolved star W43A. We measured the circular polarization of the strongest 1612 OH masers of W43A and found a magnetic field strength of ~100μG. The magnetic field measured at the location of W43A OH masers confirms that a large scale magnetic field is present in W43A, which likely plays a role in collimating the jet.

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 The Magnetic Field Near the Local Bubble

1997 ◽  
Vol 166 ◽  
pp. 227-238
Author(s):  
Carl Heiles
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Zeeman Splitting ◽  
Relativistic Electrons ◽  
Local Bubble ◽  
Scale Field ◽  
Large Scale Field ◽  
Field Lines ◽  
Hi Shells ◽  
The Magnetic Field

AbstractThere are almost no direct observational indicators of the magnetic field inside the local bubble. Just outside the bubble, the best tracers are stellar polarization and HI Zeeman splitting. These show that the local field does not follow the large-scale Galactic field. Here we discuss whether the deformation of the large-scale field by the local HI shells is consistent with the observations. We concentrate on the Loop 1 region, and find that the field lines are well-explained by this idea; in addition, the bright radio filaments of Radio Loop 1 delineate particular field lines that are “lit up” by an excess of relativistic electrons.

scholarly journals Rapidly Evolving Structures in the Photosphere of the Mira Variable TX Cam

2001 ◽  
Vol 205 ◽  
pp. 252-255 ◽  
Author(s):  
P. J. Diamond ◽  
A. J. Kemball
Keyword(s):  
Magnetic Field ◽  
Gravitational Field ◽  
Shock Waves ◽  
Circumstellar Envelope ◽  
Structural Variations ◽  
Mira Variable ◽  
The Magnetic Field ◽  
Dynamical Mode

44 VLBA observations of the 43 GHz SiO masers in the circumstellar envelope surrounding the Mira variable TX Cam reveal dramatic structural variations over the 80 week stellar cycle. The dominant dynamical mode is one of expansion although other complex motions are visible. The gravitational field of the star does not have a significant effect on the dynamics observed, these are probably governed more by the magnetic field and the effects of the shock waves resulting from the pulsation of the Mira itself.

scholarly journals Environmental dependence of SFRs in late-type GAMA galaxies

2011 ◽  
Vol 7 (S284) ◽  
pp. 352-356
Author(s):  
Meiert W. Grootes ◽  
Richard J. Tuffs ◽  
Ellen Andrae ◽  
Lee S. Kelvin ◽  
Jochen Liske ◽  
...  
Keyword(s):  
Velocity Dispersion ◽  
Mass Function ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Late Type ◽  
Initial Application ◽  
Gas Consumption ◽  
Group Members ◽  
Attenuation Corrected ◽  
Environmental Dependence

AbstractPresent and past gas-fuelling of galaxies is expected to depend upon both the properties of the galaxies themselves, as well as their larger-scale environments. In the case of galaxies in groups the environment, i.e the group mass, can be probed by measuring the velocity dispersion of the group members, as done with the GAMA Galaxy Group catalogue (Robotham et al. 2011), probing the halo mass function all the way to small groups. The gas-fuelling rate of normal late-type galaxies can be traced by the SFR under the assumption of a steady state between gas-fuelling and gas-consumption by SF. We present a method to estimate disk opacities from UV/optical photometric characteristics, calibrated using the radiative transfer model of Popescu et al. (2011), applied to UV-Opt-FIR GAMA/H-ATLAS photometry for a subset of GAMA galaxies. We use the method to extract attenuation corrected SFRs for a large sample of late-type GAMA galaxies, which we use in an initial application to constrain the dependency of star formation/gas-fuelling in late-type galaxies on mass of parent DMH, and compactness of galaxy group.

scholarly journals Magnetic Fields in OH Maser Clouds

1974 ◽  
Vol 60 ◽  
pp. 275-292 ◽  
Author(s):  
R. D. Davies
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Field Data ◽  
Zeeman Splitting ◽  
Galactic Rotation ◽  
Magnetic Field Data ◽  
The Magnetic Field ◽  
Maser Sources

Observations of Class I OH maser sources show a range of features which are predicted on the basis of Zeeman splitting in a source magnetic field. Magnetic field strengths of 2 to 7 mG are derived for eight OH maser sources. The fields in all the clouds are directed in the sense of galactic rotation. A model of W3 OH is proposed which incorporates the magnetic field data. It is shown that no large amount of magnetic flux or angular momentum has been lost since the condensation from the interstellar medium began.

scholarly journals Optical and Radio Surface Photometry of NGC 891

1990 ◽  
Vol 140 ◽  
pp. 223-224
Author(s):  
R.J. Allen ◽  
S. Sukumar ◽  
F.X. Hu ◽  
P. C. Van Der Kruit
Keyword(s):  
Magnetic Field ◽  
Spatial Distribution ◽  
Surface Brightness ◽  
Relativistic Electrons ◽  
Synchrotron Emission ◽  
Surface Photometry ◽  
Star Forming ◽  
Evolved Stars ◽  
Optical Continuum ◽  
The Magnetic Field

A general correlation between the radio and optical continuum surface brightness has been found in the edge-on galaxy NGC 891. This suggests that the relativistic electrons are produced/accelerated in the vicinity of evolved stars or stellar remnants which have a spatial distribution similar to old disk stars. In this picture, the magnetic field required for the synchrotron emission is carried up from the disk to high Z through instabilities and star-forming activity in the plane.

scholarly journals First detection of Zeeman splitting of water masers in circumstellar shells

2002 ◽  
Vol 206 ◽  
pp. 375-378
Author(s):  
Wouter Vlemmings ◽  
Phil Diamond ◽  
Huib Jan van Langevelde
Keyword(s):  
Zeeman Splitting ◽  
Central Star ◽  
Rotational Transition ◽  
Circumstellar Envelope ◽  
Circumstellar Envelopes ◽  
First Results ◽  
Circumstellar Shells ◽  
Water Masers ◽  
The Magnetic Field ◽  
Density Regime

The strength and structure of the magnetic fields in circumstellar envelopes have been measured through polarization observations of OH and SiO masers. Here we present the first results obtained by observing the circular polarization of the H2O masers using VLBI. SiO masers are probes of the high temperature and density regime close to the central star. OH masers are found at much lower densities and temperatures, generally much further out in the circumstellar envelope. The detection of the Zeeman splitting of the (616-523) rotational transition of the H2O maser allows us to determine the magnetic field strength in the intermediate temperature and density regime.

VALLEY SPLITTING AND g-FACTOR IN AlAs QUANTUM WELLS

2009 ◽  
Vol 23 (12n13) ◽  
pp. 2948-2954
Author(s):  
C. A. DUARTE ◽  
G. M. GUSEV ◽  
T. E. LAMAS ◽  
A. K. BAKAROV ◽  
J.-C. PORTAL
Keyword(s):  
Magnetic Field ◽  
Quantum Wells ◽  
Quantum Confinement ◽  
Zeeman Splitting ◽  
Exchange Contribution ◽  
G Factor ◽  
Valley Splitting ◽  
Perpendicular Component ◽  
Magneto Resistance ◽  
The Magnetic Field

Here we present the results of magneto resistance measurements in tilted magnetic field and compare them with calculations. The comparison between calculated and measured spectra for the case of perpendicular fields enable us to estimate the dependence of the valley splitting as a function of the magnetic field and the total Landé g -factor (which is assumed to be independent of the magnetic field). Since both the exchange contribution to the Zeeman splitting as well as the valley splitting are properties associated with the 2D quantum confinement, they depend only on the perpendicular component of the magnetic field, while the bare Zeeman splitting depends on the total magnetic field. This information aided by the comparison between experimental and calculated gray scale maps permits to obtain separately the values of the exchange and the bare contribution to the g -factor.

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