Volume 567, July 2014
|Number of page(s)||7|
|Section||Interstellar and circumstellar matter|
|Published online||07 July 2014|
Polarisation observations of H2O JK-1 K1 = 532 − 441 620.701 GHz maser emission with Herschel/HIFI in Orion KL ⋆,⋆⋆
1 University of Western Ontario, Department of Physics and Astronomy, London, Ontario, N6A 3K7, Canada
2 Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
3 Cornell University, Center for Radiophysics & Space Research, 511 H Street, SW, Washington, DC 20024-2725, USA
4 Herschel Science Centre, ESAC, European Space Agency, 28691 Villanueva de la Cañada, Madrid, Spain
5 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
6 University of Waterloo, Department of Physics and Astronomy, Waterloo, Ontario, N2L 3G1, Canada
7 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 66, Cambridge, MA 02138, USA
8 Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, California, USA
Received: 17 December 2013
Accepted: 4 June 2014
Context. The high intensities and narrow bandwidths exhibited by some astronomical masers make them ideal tools for studying star-forming giant molecular clouds. The water maser transition JK-1K1 = 532−441 at 620.701 GHz can only be observed from above Earth’s strongly absorbing atmosphere; its emission has recently been detected from space.
Aims. We sought to further characterize the star-forming environment of Orion KL by investigating the linear polarisation of a source emitting a narrow 620.701 GHz maser feature with the heterodyne spectrometer HIFI on board the Herschel Space Observatory.
Methods. High-resolution spectral datasets were collected over a thirteen month period beginning in 2011 March, to establish not only the linear polarisation but also the temporal variability of the source.
Results. Within a 3σ uncertainty, no polarisation was detected to an upper limit of approximately 2%. These results are compared with coeval linear polarisation measurements of the 22.235 GHz JK-1K1 = 616 − 523 maser line from the Effelsberg 100-m radio telescope, typically a much stronger maser transition. Although strongly polarised emission is observed for one component of the 22.235 GHz maser at 7.2 km s-1, a weaker component at the same velocity as the 620.701 GHz maser at 11.7 km s-1 is much less polarised.
Key words: magnetic fields / masers / polarisation / ISM: magnetic fields
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with significant participation from NASA.
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2014
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