Herschel/HIFI observations of O-rich AGB stars: molecular inventory
Artikel i vetenskaplig tidskrift, 2012

Aims. Spectra, taken with the heterodyne instrument, HIFI, aboard the Herschel Space Observatory, of O-rich asymptotic giant branch (AGB) stars which form part of the guaranteed time key program HIFISTARS are presented. The aim of this program is to study the dynamical structure, mass-loss driving mechanism, and chemistry of the outflows from AGB stars as a function of chemical composition and initial mass. Methods. We used the HIFI instrument to observe nine AGB stars, mainly in the H2O and high rotational CO lines. We investigate the correlation between line luminosity, line ratio and mass-loss rate, line width and excitation energy. Results. A total of nine different molecules, along with some of their isotopologues have been identified, covering a wide range of excitation temperature. Maser emission is detected in both the ortho-and para-H2O molecules. The line luminosities of ground state lines of ortho- and para-H2O, the high-J CO and NH3 lines show a clear correlation with mass-loss rate. The line ratios of H2O and NH3 relative to CO J = 6-5 correlate with the mass-loss rate while ratios of higher CO lines to the 6-5 is independent of it. In most cases, the expansion velocity derived from the observed line width of highly excited transitions formed relatively close to the stellar photosphere is lower than that of lower excitation transitions, formed farther out, pointing to an accelerated outflow. In some objects, the vibrationally excited H2O and SiO which probe the acceleration zone suggests the wind reaches its terminal velocity already in the innermost part of the envelope, i.e., the acceleration is rapid. Interestingly, for R Dor we find indications of a deceleration of the outflow in the region where the material has already escaped from the star.

circumstellar envelopes

stars: AGB and post-AGB


line: identification

rotational line-profiles

stars: late-type

circumstellar matter



red supergiant stars


mass-loss history

infrared: stars

giant branch stars



Kay Justtanont

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

T. Khouri

Universiteit Van Amsterdam

Matthias Maercker

European Southern Observatory

Universitat Bonn

J. Alcolea

Observatorio Astronomico Nacional

L. Decin

KU Leuven

Universiteit Van Amsterdam

Hans Olofsson

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

Fredrik Schöier

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

V. Bujarrabal

Observatorio Astronomico Nacional

A. P. Marston

European Space Astronomy Centre

D. Teyssier

European Space Astronomy Centre

J. Cernicharo

Consejo Superior de Investigaciones Científicas

C. Dominik

Universiteit Van Amsterdam

Radboud University Nijmegen

A. de Koter

Universiteit Van Amsterdam

Sterrekundig Instituut Utrecht

G. J. Melnick

Harvard-Smithsonian Center for Astrophysics

K. M. Menten

Max Planck-institutet

D. A. Neufeld

Johns Hopkins University

P. Planesas

Atacama Large Millimeter-submillimeter Array

Observatorio Astronomico Nacional

M. Schmidt

Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences

R. Szczerba

Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences

R. Waters

KU Leuven

Universiteit Van Amsterdam

Astronomy and Astrophysics

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

Vol. 537 Article Number: A144 - A144


Astronomi, astrofysik och kosmologi