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.
giant branch stars
w-hydrae
emission
stars: late-type
circumstellar matter
red supergiant stars
water-vapor
infrared: stars
rotational line-profiles
stars: AGB and post-AGB
circumstellar envelopes
hifi
line: identification
mass-loss history
winds
Author
Kay Justtanont
Chalmers, Earth and Space Sciences, Onsala Space Observatory
T. Khouri
University of Amsterdam
Matthias Maercker
European Southern Observatory (ESO)
University of Bonn
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 Agency (ESA)
D. Teyssier
European Space Agency (ESA)
J. Cernicharo
Agencia Estatal Consejo Superior de Investigaciones Científicas (CSIC)
C. Dominik
University of Amsterdam
Radboud University
A. de Koter
Sterrekundig Instituut Utrecht
University of Amsterdam
G. J. Melnick
Harvard-Smithsonian Center for Astrophysics
K. M. Menten
Max Planck Society
D. A. Neufeld
Johns Hopkins University
P. Planesas
Spanish National Observatory (OAN)
Atacama Large Millimeter-submillimeter Array (ALMA)
M. Schmidt
Polish Academy of Sciences
R. Szczerba
Polish Academy of Sciences
R. Waters
KU Leuven
University of Amsterdam
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