MAGMO: polarimetry of 1720-MHz OH masers towards southern star-forming regions

ABSTRACT From targeted observations of ground-state hydroxyl (OH) masers towards 702 Methanol Multibeam survey 6.7-GHz methanol masers, in the Galactic longitude range from 186° through the Galactic Centre to 20°, made as part of the ‘MAGMO’ (Mapping the Galactic Magnetic field through OH masers) project, we present the physical and polarization properties of the 1720-MHz OH maser transition, including the identification of Zeeman pairs. We present 10 new and 23 previously catalogued 1720-MHz OH maser sources detected towards star-forming regions (SFRs). In addition, we also detected 16 1720-MHz OH masers associated with supernova remnants and two sites of diffuse OH emission. Towards the 33 star formation masers, we identify 44 Zeeman pairs, implying magnetic field strengths ranging from −11.4 to +13.2 mG, and a median magnetic field strength of |BLOS| ∼ 6 mG. With limited statistics, we present the in situ magnetic field orientation of the masers and the Galactic magnetic field distribution revealed by the 1720-MHz transition. We also examine the association statistics of 1720-MHz OH SFR masers with other ground-state OH masers, excited-state OH masers, class I and class II methanol masers, and water masers, and compare maser positions with mid-infrared images of the parent SFRs. Of the 33 1720-MHz star formation masers, 10 are offset from their central exciting sources, and appear to be associated with outflow activity.

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The Role of Magnetic Fields in Star Forming Regions

Symposium - International Astronomical Union ◽

10.1017/s0074180900190187 ◽

1990 ◽

Vol 140 ◽

pp. 259-267

Author(s):

L Mestel

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Fields ◽

The Self ◽

Galactic Magnetic Field ◽

Star Forming ◽

Star Forming Regions

The flux from the galactic magnetic field alters radically the appropriate description of the equilibrium, collapse and fragmentation of the self-gravitating gas clouds that are the locale of star formation.

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Submillimeter Array Observations of Magnetic Fields in Star Forming Regions

Proceedings of the International Astronomical Union ◽

10.1017/s174392131100024x ◽

2010 ◽

Vol 6 (S270) ◽

pp. 103-106

Author(s):

R. Rao ◽

J.-M. Girart ◽

D. P. Marrone

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Fields ◽

Computational Models ◽

Dominant Role ◽

Theoretical Models ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions ◽

Low Mass

AbstractThere have been a number of theoretical and computational models which state that magnetic fields play an important role in the process of star formation. Competing theories instead postulate that it is turbulence which is dominant and magnetic fields are weak. The recent installation of a polarimetry system at the Submillimeter Array (SMA) has enabled us to conduct observations that could potentially distinguish between the two theories. Some of the nearby low mass star forming regions show hour-glass shaped magnetic field structures that are consistent with theoretical models in which the magnetic field plays a dominant role. However, there are other similar regions where no significant polarization is detected. Future polarimetry observations made by the Submillimeter Array should be able to increase the sample of observed regions. These measurements will allow us to address observationally the important question of the role of magnetic fields and/or turbulence in the process of star formation.

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LBA observations of OH masers in the star-forming region OH 330.953–0.182

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307012811 ◽

2007 ◽

Vol 3 (S242) ◽

pp. 162-163

Author(s):

B. Hutawarakorn Kramer ◽

J. L. Caswell ◽

A. Sukom ◽

J. E. Reynolds

Keyword(s):

Magnetic Field ◽

Excited State ◽

Ground State ◽

State Transitions ◽

Star Forming ◽

Left Hand ◽

Physical Conditions ◽

Star Forming Regions ◽

Long Baseline ◽

Right And Left Hand

AbstractOH masers are sensitive probes of the kinematics, physical conditions, and magnetic fields in star-forming regions. The maser site OH 330.953-0.182 has been studied using the Long Baseline Array of the Australia Telescope National Facility. Simultaneous observations of the 1665- and 1667-MHz hydroxyl ground-state transitions yield a series of maps at velocity spacing 0.09kms−1, in both right- and left-hand circular polarization, with tenth-arcsec spatial resolution. Several clusters of maser spots have been detected within a five-arcsec region. Eight Zeeman pairs were found, and in one case, at 1665 MHz, there is a nearby 1667-MHz pair indicating a similar value of magnetic field and velocity. Over the whole site, all magnetic field estimates are toward us (negative), and range from -3.7 to -5.8 mG. We also compared the morphology and kinematics of the 1665- and 1667-MHz maser spots with those from the excited state of OH at 6035 MHz and from methanol at 6668 MHz.

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Class I methanol masers in low-mass star formation regions

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317010961 ◽

2017 ◽

Vol 13 (S336) ◽

pp. 33-36

Author(s):

S. Kalenskii ◽

S. Kurtz ◽

P. Hofner ◽

P. Bergman ◽

C.M. Walmsley ◽

...

Keyword(s):

Star Formation ◽

Class I ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions ◽

Brightness Temperatures ◽

Push Forward ◽

Low Mass ◽

Methanol Masers ◽

Star Formation Regions

AbstractWe present a review of the properties of Class I methanol masers detected in low-mass star forming regions (LMSFRs). These masers, henceforth called LMMIs, are associated with postshock gas in the lobes of chemically active outflows in LMSFRs NGC1333, NGC2023, HH25, and L1157. LMMIs share the main properties with powerful masers in regions of massive star formation and are a low-luminosity edge of the total Class I maser population. However, the exploration of just these objects may push forward the exploration of Class I masers, since many LMSFRs are located only 200–300 pc from the Sun, making it possible to study associated objects in detail. EVLA observations with a 0.2″ spatial resolution show that the maser images consist of unresolved or barely resolved spots with brightness temperatures up to 5 × 105 K. The results are “marginally” consistent with the turbulent model of maser emission.

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44 GHz Methanol Maser Surveys

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312006795 ◽

2012 ◽

Vol 8 (S287) ◽

pp. 133-140

Author(s):

S. E. Kurtz

Keyword(s):

Star Formation ◽

Formation Process ◽

Class Ii ◽

Class I ◽

High Mass ◽

Mass Star ◽

Star Forming ◽

Methanol Maser ◽

Star Forming Regions ◽

Methanol Masers

AbstractClass I 44 GHz methanol masers are not as well-known, as common, or as bright as their more famous Class II cousins at 6.7 and 12.2 GHz. Nevertheless, the 44 GHz masers are commonly found in high-mass star forming regions. At times they appear to trace dynamically important phenomena; at other times they show no obvious link to the star formation process. Here, we summarize the major observational efforts to date, including both dedicated surveys and collateral observations. The principal results are presented, some that were expected, and others that were unexpected.

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900085272 ◽

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.

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Polarisation properties of methanol masers

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039149 ◽

2020 ◽

Vol 644 ◽

pp. A122

Author(s):

D. Dall’Olio ◽

W. H. T. Vlemmings ◽

B. Lankhaar ◽

G. Surcis

Keyword(s):

Magnetic Field ◽

Resonant Scattering ◽

Stimulated Emission ◽

Emission Rates ◽

Circular Polarisation ◽

Star Forming ◽

Methanol Maser ◽

Hyperfine Transitions ◽

Star Forming Regions ◽

Methanol Masers

Context. Astronomical masers have been effective tools in the study of magnetic fields for years. Observations of the linear and circular polarisation of different maser species allow for the determination of magnetic field properties, such as morphology and strength. In particular, methanol can be used to probe different parts of protostars, such as accretion discs and outflows, since it produces one of the strongest and the most commonly observed masers in massive star-forming regions. Aims. We investigate the polarisation properties of selected methanol maser transitions in light of newly calculated methanol Landé g-factors and in consideration of hyperfine components. We compare our results with previous observations and evaluate the effect of preferred hyperfine pumping and non-Zeeman effects. Methods. We ran simulations using the radiative transfer code, CHAMP, for different magnetic field values, hyperfine components, and pumping efficiencies. Results. We find a dependence between the linear polarisation fraction and the magnetic field strength as well as the hyperfine transitions. The circular polarisation fraction also shows a dependence on the hyperfine transitions. Preferred hyperfine pumping can explain some high levels of linear and circular polarisation and some of the peculiar features seen in the S-shape of observed V-profiles. By comparing a number of methanol maser observations taken from the literature with our simulations, we find that the observed methanol masers are not significantly affected by non-Zeeman effects related to the competition between stimulated emission rates and Zeeman rates, such as the rotation of the symmetry axis. We also consider the relevance of other non-Zeeman effects that are likely to be at work for modest saturation levels, such as the effect of magnetic field changes along the maser path and anisotropic resonant scattering. Conclusions. Our models show that for methanol maser emission, both the linear and circular polarisation percentages depend on which hyperfine transition is masing and the degree to which it is being pumped. Since non-Zeeman effects become more relevant at high values of brightness temperatures, it is important to obtain good estimates of these quantities and the maser beaming angles. Better constraints on the brightness temperature will help improve our understanding of the extent to which non-Zeeman effects contribute to the observed polarisation percentages. In order to detect separate hyperfine components, an intrinsic thermal line width that is significantly smaller than the hyperfine separation is required.

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Variability of Class II methanol masers in massive star forming regions

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312006709 ◽

2012 ◽

Vol 8 (S287) ◽

pp. 85-92

Author(s):

Sharmila Goedhart ◽

Mike Gaylard ◽

Johan van der Walt

Keyword(s):

Time Series ◽

Star Formation ◽

Massive Star ◽

Class Ii ◽

Star Forming ◽

Star Forming Regions ◽

Methanol Masers ◽

Long Term Monitoring ◽

Term Monitoring

AbstractClass II methanol masers are known to be tracers of an early phase of massive star formation. The 6.7- and 12.2-GHz methanol maser transitions can show a significant amount of variability, including periodic variations. Studying maser variability can lead to important insights into conditions in the maser environment but first the maser time-series need to be characterised. The results of long-term monitoring of 8 regularly-varying sources will be presented and methods of period-search discussed.

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Linear polarisation of Class I methanol masers in massive star formation regions

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317010195 ◽

2017 ◽

Vol 13 (S336) ◽

pp. 243-246

Author(s):

Ji-hyun Kang ◽

Do-Young Byun ◽

Kee-Tae Kim ◽

Aran Lyo ◽

Jongsoo Kim ◽

...

Keyword(s):

Star Formation ◽

Massive Star ◽

Star Forming ◽

Methanol Maser ◽

Follow Up Study ◽

Star Forming Regions ◽

Methanol Masers ◽

Star Formation Regions ◽

Linear Polarisation

AbstractWe present the results of the linear polarisation observations of methanol masers at 44 and 95 GHz towards 39 massive star forming regions (Kanget al.2016). These two lines are observed simultaneously with the 21-m Korean VLBI Network (KVN) telescope in single dish mode. About 60% of the observed showed fractional polarisation of a few percents at least at one of the two transition lines. We note that the linear polarisation of the 44 GHz methanol maser is first detected in this study including single dish and interferometer observations. We find the polarisation properties of these two lines are similar as expected, since they trace similar regions. As a follow-up study, we have carried out the VLBI polarisation observations toward some 44 GHz maser targets using the KVN telescope. We present preliminary VLBI polarisation results of G10.34-0.14, which show consistent polarisation properties in multiple epoch observations.

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