Polarisation observations of VY Canis Majoris H2O 532-441 620.701 GHz maser emission with HIFI
Artikel i vetenskaplig tidskrift, 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.

circumstellar matter



stars: winds




evolved stars



water masers

reference systems

stars: AGB and post-AGB

late-type stars


M. Harwit

Cornell University

M. Houde

Western University

P. Sonnentrucker

Johns Hopkins University

A. Boogert

Caltech Infrared Processing and Analysis Center

J. Cernicharo

Consejo Superior de Investigaciones Científicas

Elvire De Beck

KU Leuven

L. Decin

Universiteit Van Amsterdam

KU Leuven

C. Henkel

Max Planck-institutet

R. Higgins

Maynooth University

W. Jellema

SRON Netherlands Institute for Space Research

A. Kraus

Max Planck-institutet

C. McCoey

University of Waterloo

Western University

G. J. Melnick

Harvard-Smithsonian Center for Astrophysics

K. M. Menten

Max Planck-institutet

C. Risacher

SRON Netherlands Institute for Space Research

D. Teyssier

European Space Astronomy Centre

J. E. Vaillancourt

Universities Space Research Association

J. Alcolea

V. Bujarrabal

C. Dominik

Radboud University Nijmegen

Universiteit Van Amsterdam

Kay Justtanont

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

A. de Koter

Sterrekundig Instituut Utrecht

Universiteit Van Amsterdam

A. P. Marston

European Space Astronomy Centre

Hans Olofsson

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

P. Planesas

Atacama Large Millimeter-submillimeter Array

M. Schmidt

Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences

Fredrik Schöier

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

R. Szczerba

Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences

Lbfm Waters

Universiteit Van Amsterdam

KU Leuven

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 521 Article Number: L51- L51


Astronomi, astrofysik och kosmologi