Herschel/HIFI observations of red supergiants and yellow hypergiants I. Molecular inventory
Journal article, 2012
Context. Red supergiant stars (RSGs) and yellow hypergiant stars (YHGs) are believed to be the high-mass counterparts of stars in the asymptotic giant branch (AGB) and early post-AGB phases. As such, they are scarcer and the properties and evolution of their envelopes are still poorly understood. Aims. We study the mass-loss in the post main-sequence evolution of massive stars, through the properties of their envelopes in the intermediate and warm gas layers. These are the regions where the acceleration of the gas takes place and the most recent mass-loss episodes can be seen. Methods. We used the HIFI instrument on-board the Herschel Space Observatory to observe sub-millimetre and far-infrared (FIR) transitions of CO, water, and their isotopologues in a sample of two RSGs (NML Cyg and Betelgeuse) and two YHGs (IRC + 10420 and AFGL 2343) stars. We present an inventory of the detected lines and analyse the information revealed by their spectral profiles. A comparison of the line intensity and shape in various transitions is used to qualitatively derive a picture of the envelope physical structure. On the basis of the results presented in an earlier study, we model the CO and (CO)-C-13 emission in IRC + 10420 and compare it to a set of lines ranging from the millimetre to the FIR. Results. Red supergiants have stronger high-excitation lines than the YHGs, indicating that they harbour dense and hot inner shells contributing to these transitions. Consequently, these high-J lines in RSGs originate from acceleration layers that have not yet reached the circumstellar terminal velocity and have narrower profiles than their flat-topped lower-J counterparts. The YHGs tend to lack this inner component, in line with the picture of detached, hollow envelopes derived from studies at longer wavelengths. NH3 is only detected in two sources (NML Cyg and IRC + 10420), which are also observed to be the strongest water-line emitters of the studied sample. In contrast, OH is detected in all sources and does not seem to correlate with the water line intensities. We show that the IRC + 10420 model derived solely from millimetre low-J CO transitions is capable of reproducing the high-J transitions when the temperature in the inner shell is simply lowered by about 30%.
submillimeter
circumstellar envelopes
rotational line-profiles
AGB and post-AGB
nml-cygni
supergiants
evolved
stars
alpha-orionis
nebulae
circumstellar matter
emission
giant branch stars
afgl-2343
mass-loss history
protoplanetary
Author
D. Teyssier
European Space Astronomy Centre (ESAC)
G. Quintana-Lacaci
Centro de Astrobiologia (CAB)
Institut de Radioastronomie Millimétrique (IRAM)
A. P. Marston
European Space Astronomy Centre (ESAC)
V. Bujarrabal
Spanish National Observatory (OAN)
J. Alcolea
Spanish National Observatory (OAN)
J. Cernicharo
Centro de Astrobiologia (CAB)
L. Decin
KU Leuven
University of Amsterdam
C. Dominik
University of Amsterdam
Radboud University
Kay Justtanont
Chalmers, Earth and Space Sciences, Onsala Space Observatory
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
Hans Olofsson
Chalmers, Earth and Space Sciences, Onsala Space Observatory
P. Planesas
Spanish National Observatory (OAN)
M. Schmidt
Polish Academy of Sciences
R. Soria-Ruiz
Spanish National Observatory (OAN)
Fredrik Schöier
Chalmers, Earth and Space Sciences, Onsala Space Observatory
R. Szczerba
Polish Academy of Sciences
Lbfm Waters
University of Amsterdam
Netherlands Institute for Space Research (SRON)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 545 A99 (article no.)- A99Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201219545