Herschel/HIFI observations of O-rich AGB stars: molecular inventory
Journal article, 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.
winds
infrared: stars
giant branch stars
stars: AGB and post-AGB
red supergiant stars
hifi
rotational line-profiles
w-hydrae
water-vapor
stars: late-type
mass-loss history
circumstellar matter
line: identification
emission
circumstellar envelopes
Author
Kay Justtanont
Chalmers, Earth and Space Sciences, Onsala Space Observatory
T. Khouri
University of Amsterdam
Matthias Maercker
University of Bonn
European Southern Observatory (ESO)
J. Alcolea
Spanish National Observatory (OAN)
L. Decin
KU Leuven
University of Amsterdam
Hans Olofsson
Chalmers, Earth and Space Sciences, Onsala Space Observatory
Fredrik Schöier
Chalmers, Earth and Space Sciences, Onsala Space Observatory
V. Bujarrabal
Spanish National Observatory (OAN)
A. P. Marston
European Space Astronomy Centre (ESAC)
D. Teyssier
European Space Astronomy Centre (ESAC)
J. Cernicharo
Agencia Estatal Consejo Superior de Investigaciones Científicas (CSIC)
C. Dominik
Radboud University
University of Amsterdam
A. de Koter
University of Amsterdam
Sterrekundig Instituut Utrecht
G. J. Melnick
Harvard-Smithsonian Center for Astrophysics
K. M. Menten
Max Planck Society
D. A. Neufeld
Johns Hopkins University
P. Planesas
Atacama Large Millimeter-submillimeter Array (ALMA)
Spanish National Observatory (OAN)
M. Schmidt
Polish Academy of Sciences
R. Szczerba
Polish Academy of Sciences
R. Waters
University of Amsterdam
KU Leuven
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 537 Article Number: A144 - A144Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201117524