scholarly journals OH masers and magnetic fields in massive star-forming regions: ON1

2006 ◽  
Vol 2 (S237) ◽  
pp. 452-452
Author(s):  
S. Nammahachak ◽  
K. Asanok ◽  
B. Hutawarakorn Kramer ◽  
R. J. Cohen ◽  
O. Muanwong ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Massive Star ◽  
Zeeman Splitting ◽  
Young Stars ◽  
Star Forming ◽  
Physical Conditions ◽  
Bipolar Outflow ◽  
Star Forming Regions ◽  
The Magnetic Field

AbstractOH masers are sensitive probes of the kinematics and physical conditions, and give unique information on the magnetic field through their polarization. Zeeman splitting of the OH lines can give the magnetic field strength and direction. Observing OH masers with MERLIN we studied the bipolar outflow in the star-forming region ON1, which hosts one of the earliest known ultra-compact (UC) HII regions. The strongest masers lie near the southern edge of the UCHII region in an elongated distribution. The maser distribution is orthogonal to the bipolar outflow seen in HCO+, suggesting that the OH masers may be embedded in a molecular disk or torus around a young B0.3 star, most likely tracing a shock front. An isolated group of 1720-MHz masers is also seen to the East. The magnetic field deduced from Zeeman splitting of the OH maser lines shows a large-scale order, with field values ranging from -0.4 to -4.6 mG. These results add to the growing body of evidence for OH masers associated with molecular disks or tori at the centre of bipolar outflow from massive young stars, and for a significant role played by the magnetic field in generating or channeling the bipolar outflow. Further details are presented by Nammahachak et al. 2006.

scholarly journals 8.14. Magnetic fields in star-forming regions of our Galaxy

1998 ◽  
Vol 184 ◽  
pp. 371-372
Author(s):  
B. Hutawarakorn ◽  
R. J. Cohen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Zeeman Splitting ◽  
Theoretical Work ◽  
Field Configuration ◽  
Galactic Magnetic Field ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Magnetic Field

Masers provide a direct way of measuring magnetic fields in star-forming regions. OH ground-state masers at 18 cm wavelength exhibit strong circular polarization due to Zeeman splitting. The implied magnetic field strength is typically a few mG, which is sufficient for the field to be dynamically important, e.g. in channelling the observed bipolar outflows. Moreover there are indications that magnetic fields in maser regions are aligned with the large-scale Galactic magnetic field (Reid & Silverstein 1990), and that bipolar molecular outflows are also aligned with the local Galactic magnetic field (Cohen, Rowland & Blair 1984). Some theoretical work in fact suggests that the magnetic field is intimately connected with the origin of the molecular outflow (e.g. Pudritz & Norman 1983; Uchida & Shibata 1985). It is therefore important to investigate the magnetic field configuration in these regions in as much detail as possible.

scholarly journals A review of maser polarization and magnetic fields

2007 ◽  
Vol 3 (S242) ◽  
pp. 37-46 ◽  
Author(s):  
W. H. T. Vlemmings
Keyword(s):  
Magnetic Field ◽  
Supernova Remnants ◽  
Massive Star ◽  
Field Measurements ◽  
Star Forming ◽  
Physical Conditions ◽  
Evolved Stars ◽  
Star Forming Regions ◽  
Fields Of Study ◽  
The Magnetic Field

AbstractThrough polarization observations masers are unique probes of the magnetic field in a variety of different astronomical objects, with the different maser species tracing different physical conditions. In recent years maser polarization observations have provided insights in the magnetic field strength and morphology in, among others, the envelopes around evolved stars, Planetary Nebulae (PNe), massive star forming regions and supernova remnants. More recently, maser observations have even been used to determine the magnetic field in megamaser galaxies. This review will present an overview of maser polarization observations and magnetic field determinations of the last several years and discuss the implications of the magnetic field measurements for several important fields of study, such as aspherical PNe creation and massive star formation.

scholarly journals EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

2019 ◽  
Vol 623 ◽  
pp. A130 ◽  
Author(s):  
G. Surcis ◽  
W. H. T. Vlemmings ◽  
H. J. van Langevelde ◽  
B. Hutawarakorn Kramer ◽  
A. Bartkiewicz
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Massive Star ◽  
Zeeman Splitting ◽  
Limited Sample ◽  
Star Forming ◽  
Molecular Outflows ◽  
Star Forming Regions ◽  
The Magnetic Field

Context. Magnetohydrodynamical simulations show that the magnetic field can drive molecular outflows during the formation of massive protostars. The best probe to observationally measure both the morphology and the strength of this magnetic field at scales of 10–100 au is maser polarization. Aims. We measure the direction of magnetic fields at milliarcsecond resolution around a sample of massive star-forming regions to determine whether there is a relation between the orientation of the magnetic field and of the outflows. In addition, by estimating the magnetic field strength via the Zeeman splitting measurements, the role of magnetic field in the dynamics of the massive star-forming region is investigated. Methods. We selected a flux-limited sample of 31 massive star-forming regions to perform a statistical analysis of the magnetic field properties with respect to the molecular outflows characteristics. We report the linearly and circularly polarized emission of 6.7 GHz CH3OH masers towards seven massive star-forming regions of the total sample with the European VLBI Network. The sources are: G23.44−0.18, G25.83−0.18, G25.71−0.04, G28.31−0.39, G28.83−0.25, G29.96−0.02, and G43.80−0.13. Results. We identified a total of 219 CH3OH maser features, 47 and 2 of which showed linearly and circularly polarized emission, respectively. We measured well-ordered linear polarization vectors around all the massive young stellar objects and Zeeman splitting towards G25.71−0.04 and G28.83−0.25. Thanks to recent theoretical results, we were able to provide lower limits to the magnetic field strength from our Zeeman splitting measurements. Conclusions. We further confirm (based on ∼80% of the total flux-limited sample) that the magnetic field on scales of 10–100 au is preferentially oriented along the outflow axes. The estimated magnetic field strength of |B||| > 61 mG and >21 mG towards G25.71−0.04 and G28.83−0.25, respectively, indicates that it dominates the dynamics of the gas in both regions.

scholarly journals Zeeman splitting of OH masers and the galactic magnetic field

2002 ◽  
Vol 206 ◽  
pp. 371-374 ◽  
Author(s):  
Vincent L. Fish ◽  
Mark J. Reid ◽  
Alice L. Argon ◽  
Karl M. Menten
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Large Scale ◽  
Massive Star ◽  
Milky Way ◽  
Zeeman Splitting ◽  
Galactic Magnetic Field ◽  
Massive Star Formation ◽  
The Magnetic Field

Zeeman measurements of OH masers are used to probe the magnetic field around regions of massive star formation. Previous observations suggested that OH maser field directions were aligned in a clockwise sense in the Milky Way, but recent data from a large-scale VLA survey do not support this hypothesis. However, these observations suggest that the magnetic field of the Milky Way is correlated on kiloparsec scales.

scholarly journals Maser polarization and magnetic fields

2012 ◽  
Vol 8 (S287) ◽  
pp. 31-40 ◽  
Author(s):  
W. H. T. Vlemmings
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Supernova Remnants ◽  
Silicon Monoxide ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Theoretical Considerations ◽  
The Magnetic Field

AbstractMaser polarization observations can reveal unique information on the magnetic field strength and structure for a large number of very different astronomical objects. As the different masers for which polarization is measured, such as silicon-monoxide, water, hydroxil and methanol, probe different physical conditions, the masers can even be used to determine for example the relation between magnetic field and density. In particular, maser polarization observations have improved our understanding of the magnetic field strength in, among others, the envelopes around evolved stars, Planetary Nebulae (PNe), massive star forming regions, supernova remnants and megamaser galaxies. This review presents an overview of maser polarization observations and magnetic field determinations of the last several years and discusses some of the theoretical considerations needed for a proper maser polarization analysis.

scholarly journals Millimetre wavelength methanol masers survey towards massive star forming regions

2007 ◽  
Vol 3 (S242) ◽  
pp. 234-235
Author(s):  
T. Umemoto ◽  
N. Mochizuki ◽  
K. M. Shibata ◽  
D.-G. Roh ◽  
H.-S. Chung
Keyword(s):  
Detection Rate ◽  
Massive Star ◽  
Molecular Line ◽  
Maser Emission ◽  
Star Forming ◽  
Methanol Maser ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Methanol Masers ◽  
Maser Sources

AbstractWe present the results of a mm wavelength methanol maser survey towards massive star forming regions. We have carried out Class II methanol maser observations at 86.6 GHz, 86.9 GHz and 107.0 GHz, simultaneously, using the Nobeyama 45 m telescope. We selected 108 6.7 GHz methanol maser sources with declinations above −25 degrees and fluxes above 20 Jy. The detection limit of maser observations was ~3 Jy. Of the 93 sources surveyed so far, we detected methanol emission in 25 sources (27%) and “maser” emission in nine sources (10%), of which thre “maser” sources are new detections. The detection rate for maser emission is about half that of a survey of the southern sky (Caswell et al. 2000). There is a correlation between the maser flux of 107 GHz and 6.7 GHz/12 GHz emission, but no correlation with the “thermal” (non maser) emission. From results of other molecular line observations, we found that the sources with methanol emission show higher gas temperatures and twice the detection rate of SiO emission. This may suggest that dust evaporation and destruction by shock are responsible for the high abundance of methanol molecules, one of the required physical conditions for maser emission.

scholarly journals Magnetic Field Structure of Star Forming Regions: VLBI Spectral Line Results

1984 ◽  
Vol 110 ◽  
pp. 333-334
Author(s):  
J.A. Garcia-Barreto ◽  
B. F. Burke ◽  
M. J. Reid ◽  
J. M. Moran ◽  
A. D. Haschick
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Aperture Synthesis ◽  
Stokes Parameters ◽  
Hii Region ◽  
Star Forming ◽  
Star Forming Regions ◽  
Vlbi Observations ◽  
The Magnetic Field ◽  
Synthesis Experiment

Magnetic fields play a major role in the general dynamics of astronomical phenomena and particularly in the process of star formation. The magnetic field strength in galactic molecular clouds is of the order of few tens of μG. On a smaller scale, OH masers exhibit fields of the order of mG and these can probably be taken as representative of the magnetic field in the dense regions surrounding protostars. The OH molecule has been shown to emit highly circular and linearly polarized radiation. That it was indeed the action of the magnetic field that would give rise to the highly polarized spectrum of OH has been shown by the VLBI observations of Zeeman pairs of the 1720 and 6035 MHz by Lo et. al. and Moran et. al. VLBI observations of W3 (OH) revealed that the OH emission was coming from numerous discrete locations and that all spots fell within the continuum contours of the compact HII region. The most detailed VLBI aperture synthesis experiment of the 1665 MHz emission from W3 (OH) was carried out by Reid et. al. who found several Zeeman pairs and a characteristic maser clump size of 30 mas. In this work, we report the results of a 5 station VLBI aperture synthesis experiment of the 1665 MHz OH emission from W3 (OH) with full polarization information. We produced VLBI synthesis maps of all Stokes parameters of 16 spectral features that showed elliptical polarization. The magnitude and direction of the magnetic field have been obtained by the detection of 7 Zeeman pairs. The three dimensional orientation of the magnetic field can be obtained, following the theoretical arguments of Goldreich et. al., from the observation of π and σ components.

scholarly journals The atomic hydrogen/molecular cloud association: an unavoidable relationship

1991 ◽  
Vol 147 ◽  
pp. 37-40
Author(s):  
G. Joncas
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Clouds ◽  
Large Scale ◽  
Young Stars ◽  
Physical Processes ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
The Impact

The presence of HI in the interstellar medium is ubiquitous. HI is the principal actor in the majority of the physical processes at work in our Galaxy. Restricting ourselves to the topics of this symposium, atomic hydrogen is involved with the formation of molecular clouds and is one of the byproducts of their destruction by young stars. HI has different roles during a molecular cloud's life. I will discuss here a case of coexisting HI and H2 at large scale and the origin of HI in star forming regions. For completeness' sake, it should be mentionned that there are at least three other aspects of HI involvement: HI envelopes around molecular clouds, the impact of SNRs (see work on IC 443), and the role of HI in quiescent dark clouds (see van der Werf's work).

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.

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