scholarly journals Maser polarization with ALMA

2012 ◽  
Vol 8 (S287) ◽  
pp. 64-68
Author(s):  
Andrés F. Pérez-Sánchez ◽  
Wouter Vlemmings
Keyword(s):  
Magnetic Field ◽  
Zeeman Splitting ◽  
Molecular State ◽  
Stimulated Emission ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Field Orientation ◽  
Maser Emission ◽  
Star Forming ◽  
The Magnetic Field

AbstractOnce ALMA full polarization capabilities are offered, (sub-)mm polarization studies will enter a new era. It will become possible to perform detailed studies of polarized maser emission towards for example massive star forming regions and late-type stars such as (post-) Asymptotic Giant Branch stars and young Planetary Nebulae. In these environments, SiO, H2O and HCN are molecules that can naturally generate polarized maser emission observable by ALMA. The maser polarization can then be used to derive the strength and morphology of the magnetic field in the masing regions. However, in order to derive, in particular, the magnetic field orientation from maser linear polarization, a number of conditions involving the rate of stimulated emission, molecular state decay and Zeeman splitting need to be satisfied. In this work, we discuss these conditions for the maser transitions in the ALMA frequency range and highlight the optimum transitions to further our understanding of star formation and evolved star magnetic fields.

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 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 Is the Magnetic Field Preserved During Core Formation?

2004 ◽  
Vol 221 ◽  
pp. 97-103
Author(s):  
Brenda C. Matthews ◽  
Shih-Ping Lai ◽  
Richard M. Crutcher ◽  
Christine D. Wilson
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Position Angle ◽  
Dark Cloud ◽  
Field Orientation ◽  
Nearby Star ◽  
Star Forming ◽  
Ordered Fields ◽  
Field Geometry ◽  
The Magnetic Field

We present recent JCMT and BIMA array polarimetry data of nearby star-forming regions in order to compare the core and cloud-scale magnetic field geometries in two regions of Orion. The similarity of the magnetic field geometry in these cores to that of their ambient clouds is contrasted with JCMT data toward the Barnard 1 dark cloud in Perseus, which reveal a different magnetic field orientation between the majority of the cores and the surrounding cloud; each of the cores exhibits a different mean polarization position angle. We conclude that the preservation of the magnetic field geometry is better in cores formed within clouds with ordered large scale structures. In Barnard 1, the cores may quickly exhibit a different polarization pattern if they have, for example, rotation which differs from the large scale cloud motions, or a weaker component of ordered fields. This could also explain why the cores exhibit such different geometries from each other in Barnard 1.

scholarly journals NGC 4631: The Unusual Star Forming Region Around CM67 — CO Observations with NMA and Pico Veleta

1994 ◽  
Vol 140 ◽  
pp. 363-365 ◽  
Author(s):  
M. Krause ◽  
G. Golla ◽  
K.-I. Morita ◽  
R. Wielebinski
Keyword(s):  
Magnetic Field ◽  
Central Region ◽  
Formation Rate ◽  
Radio Continuum ◽  
Field Orientation ◽  
Hii Region ◽  
Star Forming ◽  
Radio Halo ◽  
Star Forming Regions ◽  
The Magnetic Field

The late-type edge-on spiral galaxy NGC 4631 is known for its high star formation rate and extended radio halo with a uniform magnetic field component ordered predominantly perpendicular to the plane of the galaxy in the inner 6 kpc (assuming a distance of 7.5 Mpc, 1′ = 2.2 kpc) (Hummel et al. 1988; Golla, Ph.D., in preparation). The strongest radio continuum source of NGC 4631 is located at the eastern edge of the central region near a giant HII region complex CM67 (Crillon and Monnet 1969). The magnetic field orientation going out from the central region and especially from the region CM67 as well as the prominent north eastern low frequency radio spur (cf. Hummel et al. 1991) indicate a close connection between the synchrotron emission of the radio halo of NGC 4631 and star forming regions/CM67 in the disk (Golla and Hummel, in preparation). Probably cosmic rays from star forming regions in the disk propagate along the magnetic field Unes into the halo.

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.

Maser Polarization

2017 ◽  
Vol 13 (S336) ◽  
pp. 27-32
Author(s):  
Gabriele Surcis ◽  
Wouter H. T. Vlemmings ◽  
Boy Lankhaar ◽  
Huib Jan van Langevelde
Keyword(s):  
Magnetic Field ◽  
Maser Emission ◽  
Circularly Polarized ◽  
Star Forming ◽  
Evolved Stars ◽  
Star Forming Regions ◽  
The Magnetic Field ◽  
G Factors

AbstractThrough the observations and the analysis of maser polarization it is possible to measure the magnetic field in several astrophysical environments (e.g., star-forming regions, evolved stars). In particular from the linearly and circularly polarized emissions we can determine the orientation and the strength of the magnetic field, respectively. In these proceedings the implications, on observed data, of the new estimation of the Landé g-factors for the CH3OH maser are presented. Furthermore, some example of the most recent results achieved in observing the polarized maser emission from several maser species will also be reported.

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 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 Relative alignment between dense molecular cores and ambient magnetic field: the synergy of numerical models and observations

2020 ◽  
Vol 494 (2) ◽  
pp. 1971-1987 ◽  
Author(s):  
Che-Yu Chen ◽  
Erica A Behrens ◽  
Jasmin E Washington ◽  
Laura M Fissel ◽  
Rachel K Friesen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Numerical Models ◽  
Field Orientation ◽  
Relative Significance ◽  
Star Forming ◽  
Ambient Magnetic Field ◽  
Core Field ◽  
Dense Cores ◽  
Background Magnetic Field ◽  
The Magnetic Field

ABSTRACT The role played by magnetic field during star formation is an important topic in astrophysics. We investigate the correlation between the orientation of star-forming cores (as defined by the core major axes) and ambient magnetic field directions in (i) a 3D magnetohydrodynamic simulation, (ii) synthetic observations generated from the simulation at different viewing angles, and (iii) observations of nearby molecular clouds. We find that the results on relative alignment between cores and background magnetic field in synthetic observations slightly disagree with those measured in fully 3D simulation data, which is partly because cores identified in projected 2D maps tend to coexist within filamentary structures, while 3D cores are generally more rounded. In addition, we examine the progression of magnetic field from pc to core scale in the simulation, which is consistent with the anisotropic core formation model that gas preferably flows along the magnetic field towards dense cores. When comparing the observed cores identified from the Green Bank Ammonia Survey and Planck polarization-inferred magnetic field orientations, we find that the relative core–field alignment has a regional dependence among different clouds. More specifically, we find that dense cores in the Taurus molecular cloud tend to align perpendicular to the background magnetic field, while those in Perseus and Ophiuchus tend to have random (Perseus) or slightly parallel (Ophiuchus) orientations with respect to the field. We argue that this feature of relative core–field orientation could be used to probe the relative significance of the magnetic field within the cloud.

Effect of a static magnetic field onEscherichia coliadhesion and orientation

2016 ◽  
Vol 62 (11) ◽  
pp. 944-952 ◽  
Author(s):  
Lotfi Mhamdi ◽  
Nejib Mhamdi ◽  
Naceur Mhamdi ◽  
Philippe Lejeune ◽  
Nicole Jaffrezic ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Bacterial Adhesion ◽  
Parallel Magnetic Field ◽  
Field Orientation ◽  
Static Magnetic Fields ◽  
Preliminary Study ◽  
The Difference ◽  
The Magnetic Field

This preliminary study focused on the effect of exposure to 0.5 T static magnetic fields on Escherichia coli adhesion and orientation. We investigated the difference in bacterial adhesion on the surface of glass and indium tin oxide-coated glass when exposed to a magnetic field either perpendicular or parallel to the adhesion surface (vectors of magnetic induction are perpendicular or parallel to the adhesion surface, respectively). Control cultures were simultaneously grown under identical conditions but without exposure to the magnetic field. We observed a decrease in cell adhesion after exposure to the magnetic field. Orientation of bacteria cells was affected after exposure to a parallel magnetic field. On the other hand, no effect on the orientation of bacteria cells was observed after exposure to a perpendicular magnetic field.

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