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arXiv · 1504.07062

Excited-state hydroxyl maser polarimetry: Who ate all the πs?

James A Green·James L Caswell·Naomi M McClure-Griffiths
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Abstract

We present polarimetric maser observations with the Australia Telescope Compact Array (ATCA) of excited-state hydroxyl (OH) masers. We observed 30 fields of OH masers in full Stokes polarization with the Compact Array Broadband Backend (CABB) at both the 6030 and 6035 MHz excited-state OH transitions, and the 6668-MHz methanol maser transition, detecting 70 sites of maser emission. Amongst the OH we found 112 Zeeman pairs, of which 18 exhibited candidate π components. This is the largest single full polarimetric study of multiple sites of star formation for these frequencies, and the rate of 16% π components clearly indicates the π component exists, and is comparable to the percentage recently found for ground-state transitions. This significant percentage of π components, with consistent proportions at both ground- and excited-state transitions, argues against Faraday rotation suppressing the π component emission. Our simultaneous observations of methanol found the expected low level of polarisation, with no circular detected, and linear only found at the less than or equal to 10% level for the brightest sources.

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James A Green, James L Caswell, Naomi M McClure-Griffiths. 2015-04-27. Excited-state hydroxyl maser polarimetry: Who ate all the πs?. https://doi.org/10.1093/mnras%2Fstv936

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