Issue |
A&A
Volume 521, October 2010
|
|
---|---|---|
Article Number | L51 | |
Number of page(s) | 5 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361/201015042 | |
Published online | 01 October 2010 |
Polarisation observations of VY Canis Majoris H2O 532–441 620.701 GHz maser emission with HIFI *,**
1
Cornell University, Center for Radiophysics & Space Research,
511 H street, SW, Washington, DC 20024-2725, USA e-mail: harwit@verizon.net
2
University of Western Ontario, Department of Physics and Astronomy,
London, Ontario, N6A 3K7, Canada e-mail: houde@astro.uwo.ca
3
Johns Hopkins University, Department
of Physics and Astronomy, Baltimore, MD 21218, USA
4
IPAC, Caltech, Pasadena, CA 91925, USA
5
Consejo Superior de Investigaciones Cientificas, 28006 Madrid, Spain
6
Katolieke
Universiteit Leuven, Institut voor Sterrenkunde, Heverlee 3001, Belgium
7
Sterrenkundig Instituut Anton Pannekoek,
University of Amsterdam, Science Park 904, 1098 Amsterdam, The
Netherlands
8
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn,
Germany
9
National University of Ireland, Maynooth, Department
of Experimental Physics, County Kildare, Ireland
10
Space Research
Organization of the Netherlands (SRON), 9700 AV Groningen, The Netherlands
11
University of Waterloo, Department of Physics and Astronomy, Waterloo,
Ontario, N2L 3G1, Canada
12
Harvard-Smithsonian Center for Astrophysics
Cambridge, MA 02138, USA
13
European Space Astronomy Centre, Urb.
Villafranca del Castillo, PO Box 50727, 28080 Madrid, Spain
14
SOFIA Science Center, Universities Space Research Association, NASA
Ames Research Center, Moffett Field, CA 94035-0001, USA
15
Observatorio
Astronómico Nacional (IGN), Alfonso XII N3, 28014 Madrid,
Spain
16
Observatorio Astronómico Nacional (IGN), Ap 112, 28803
Alcalá de Henares, Spain
17
Department of Astrophysics/IMAPP, Radboud University
Nijmegen, Nijmegen, The Netherlands
18
Onsala Space Observatory,
Dept. of Radio and Space Science, Chalmers University of Technology,
43992 Onsala, Sweden
19
The Netherlands and Astronomical Institute,
Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
20
Department of Astronomy, AlbaNova University Center, Stockholm University,
10691 Stockholm, Sweden
21
Joint ALMA Observatory, El Golf 40,
Las Condes, Santiago, Chile
22
N. Copernicus Astronomical Center,
Rabiańska 8, 87–100 Toruń, Poland
Received:
26
May
2010
Accepted:
3
September
2010
Context. Water vapour maser emission from evolved oxygen-rich stars remains poorly understood. Additional observations, including polarisation studies and simultaneous observation of different maser transitions may ultimately lead to greater insight.
Aims. We have aimed to elucidate the nature and structure of the VY CMa water vapour masers in part by observationally testing a theoretical prediction of the relative strengths of the 620.701 GHz and the 22.235 GHz maser components of ortho H2O.
Methods. In its high-resolution mode (HRS) the Herschel Heterodyne Instrument for the Far Infrared (HIFI) offers a frequency resolution of 0.125 MHz, corresponding to a line-of-sight velocity of 0.06 km s-1, which we employed to obtain the strength and linear polarisation of maser spikes in the spectrum of VY CMa at 620.701 GHz. Simultaneous ground based observations of the 22.235 GHz maser with the Max-Planck-Institut für Radioastronomie 100-m telescope at Effelsberg, provided a ratio of 620.701 GHz to 22.235 GHz emission.
Results. We report the first astronomical detection to date of H2O maser emission at 620.701 GHz. In VY CMa both the 620.701 and the 22.235 GHz polarisation are weak. At 620.701 GHz the maser peaks are superposed on what appears to be a broad emission component, jointly ejected from the star. We observed the 620.701 GHz emission at two epochs 21 days apart, both to measure the potential direction of linearly polarised maser components and to obtain a measure of the longevity of these components. Although we do not detect significant polarisation levels in the core of the line, they rise up to approximately 6% in its wings.
Key words: stars: AGB and post-AGB / stars: winds, outflows / supergiants / circumstellar matter / masers / reference systems
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendix (page 5) is only available in electronic form at http://www.aanda.org
© ESO, 2010
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