Issue |
A&A
Volume 545, September 2012
|
|
---|---|---|
Article Number | A99 | |
Number of page(s) | 14 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/201219545 | |
Published online | 13 September 2012 |
Herschel/HIFI observations of red supergiants and yellow hypergiants
I. Molecular inventory⋆,⋆⋆,⋆⋆⋆
1
European Space Astronomy Centre, Urb. Villafranca del Castillo, PO Box
50727,
28080
Madrid,
Spain
e-mail: David.Teyssier@esa.int
2
Instituto de Radio Astronomía Milimétrica (IRAM),
Avenida Divina Pastora 7, Local
20, 18012
Granada,
Spain
3
Observatorio Astronómico Nacional (IGN),
Ap 112, 28803
Alcalá de Henares,
Spain
4
Observatorio Astronómico Nacional (IGN),
Alfonso XII
N° 3, 28014
Madrid,
Spain
5
CAB, INTA-CSIC, Ctra de Torrejón a Ajalvir, km 4, 28850 Torrejón
de Ardoz, Madrid,
Spain
6
Instituut voor Sterrenkunde, Katholieke Universiteit
Leuven, Celestijnenlaan
200D, 3001
Leuven,
Belgium
7
Sterrenkundig Instituut Anton Pannekoek, University of
Amsterdam, Science Park 904,
1098
Amsterdam, The
Netherlands
8
Department of Astrophysics/IMAPP, Radboud University
Nijmegen, Nijmegen,
The Netherlands
9
Onsala Space Observatory, Dept. of Radio and Space Science,
Chalmers University of Technology, 43992
Onsala,
Sweden
10
Astronomical Institute, Utrecht University,
Princetonplein 5, 3584 CC
Utrecht, The
Netherlands
11
Harvard-Smithsonian Center for Astrophysics,
Cambridge, MA
02138,
USA
12
Max-Planck-Institut für Radioastronomie,
Auf dem Hügel 69, 53121
Bonn,
Germany
13
The Johns Hopkins University, 3400 North Charles St, Baltimore, MD
21218,
USA
14
Department of Astronomy, AlbaNova University Center, Stockholm
University, 10691
Stockholm,
Sweden
15
N. Copernicus Astronomical Center, Rabiańska 8,
87-100
Toruń,
Poland
16
SRON Netherlands Institute for Space Research,
Sorbonnelaan 2, 3584 CA
Utrecht, The
Netherlands
Received: 4 May 2012
Accepted: 26 July 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 13CO 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%.
Key words: stars: AGB and post-AGB / supergiants / circumstellar matter / submillimeter: stars
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendix A is available in electronic form at http://www.aanda.org
FITS files of the spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/545/A99
© ESO, 2012
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