Polarisation observations of VY Canis Majoris H2O 532-441 620.701 GHz maser emission with HIFI
Journal article, 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 fur 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.
outflows
late-type stars
stars: winds
polarimeter
sharp
circumstellar matter
supergiants
millimeter
line
reference systems
masers
water masers
stars: AGB and post-AGB
evolved stars
Author
M. Harwit
Cornell University
M. Houde
Western University
P. Sonnentrucker
Johns Hopkins University
A. Boogert
California Institute of Technology (Caltech)
J. Cernicharo
Agencia Estatal Consejo Superior de Investigaciones Científicas (CSIC)
Elvire De Beck
KU Leuven
L. Decin
University of Amsterdam
KU Leuven
C. Henkel
Max Planck Society
R. Higgins
Maynooth University
W. Jellema
Netherlands Institute for Space Research (SRON)
A. Kraus
Max Planck Society
C. McCoey
University of Waterloo
Western University
G. J. Melnick
Harvard-Smithsonian Center for Astrophysics
K. M. Menten
Max Planck Society
C. Risacher
Netherlands Institute for Space Research (SRON)
D. Teyssier
European Space Agency (ESA)
J. E. Vaillancourt
Universities Space Research Association
J. Alcolea
V. Bujarrabal
C. Dominik
University of Amsterdam
Radboud University
Kay Justtanont
Chalmers, Earth and Space Sciences, Onsala Space Observatory
A. de Koter
Utrecht University
University of Amsterdam
A. P. Marston
European Space Agency (ESA)
Hans Olofsson
Chalmers, Earth and Space Sciences, Onsala Space Observatory
P. Planesas
Atacama Large Millimeter-submillimeter Array (ALMA)
M. Schmidt
Polish Academy of Sciences
Fredrik Schöier
Chalmers, Earth and Space Sciences, Onsala Space Observatory
R. Szczerba
Polish Academy of Sciences
Lbfm Waters
KU Leuven
University of Amsterdam
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 521 1 Article Number: L51- L51Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201015042