Parkes full polarization spectra of OH masers - II. Galactic longitudes 240 to 350

Abstract

Full polarization measurements of 1665 and 1667-MHz OH masers at 261 sites of massive star formation have been made with the Parkes radio telescope. Here we present the resulting spectra for 157 southern sources, complementing our previously published 104 northerly sources. For most sites, these are the first measurements of linear polarization, with good spectral resolution and complete velocity coverage. Our spectra exhibit the well-known predominance of highly circularly polarized features, interpreted as $\sigma$ components of Zeeman patterns. Focusing on the generally weaker and rarer linear polarization, we found three examples of likely full Zeeman triplets (a linearly polarized $\pi$ component, straddled in velocity by $\sigma$ components), adding to the solitary example previously reported. We also identify 40 examples of likely isolated $\pi$ components, contradicting past beliefs that $\pi$ components might be extremely rare. These were recognised at 20 sites where a feature with high linear polarization on one transition is accompanied on the other transition by a matching feature, at the same velocity and also with significant linear polarization. Large velocity ranges are rare, but we find eight exceeding 25 km/s, some of them indicating high velocity blue-shifted outflows. Variability was investigated on timescales of one year and over several decades. More than 20 sites (of 200) show high variability (intensity changes by factors of four or more) in some prominent features. Highly stable sites are extremely rare.

63 pages including 35 figures

References in corpus (7)

• GASKAP -- The Galactic ASKAP Survey
• Full-Polarization Observations of OH Masers in Massive Star-Forming Regions: II. Maser Properties and the Interpretation of Polarization
• A String of Radio Emission Associated with IRAS 16562-3959: A Collimated Jet Emanating from a Luminous Massive YSO
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• MAGMO: Coherent magnetic fields in the star forming regions of the Carina-Sagittarius spiral arm tangent
• Variability monitoring of the hydroxyl maser emission in G12.889+0.489
• Intermittent maser flare around the high mass young stellar object G353.273+0.641 II: Detection of a radio and molecular jet

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