Herschel/HIFI observations of high-J CO transitions in the protoplanetary nebula CRL 618
Journal article, 2010
Aims. We aim to study the physical conditions, particularly the excitation state, of the intermediate-temperature gas components in the protoplanetary nebula CRL 618. These components are particularly important for understanding the evolution of the nebula. Methods. We performed Herschel/HIFI observations of several CO lines in the far-infrared/sub-mm in the protoplanetary nebula CRL 618. The high spectral resolution provided by HIFI allows measurement of the line profiles. Since the dynamics and structure of the nebula is well known from mm-wave interferometric maps, it is possible to identify the contributions of the different nebular components (fast bipolar outflows, double shells, compact slow shell) to the line profiles. The observation of these relatively high-energy transitions allows an accurate study of the excitation conditions in these components, particularly in the warm ones, which cannot be properly studied from the low-energy lines. Results. The (CO)-C-12 J = 16-15, 10-9, and 6-5 lines are easily detected in this source. Both (CO)-C-13 J = 10-9 and 6-5 are also detected. Wide profiles showing spectacular line wings have been found, particularly in (CO)-C-12 J = 16-15. Other lines observed simultaneously with CO are also shown. Our analysis of the CO high-J transitions, when compared with the existing models, confirms the very low expansion velocity of the central, dense component, which probably indicates that the shells ejected during the last AGB phases were driven by radiation pressure under a regime of maximum transfer of momentum. No contribution of the diffuse halo found from mm-wave data is identified in our spectra, because of its low temperature. We find that the fast bipolar outflow is quite hot, much hotter than previously estimated; for instance, gas flowing at 100 km s(-1) must have a temperature higher than similar to 200 K. Probably, this very fast outflow, with a kinematic age < 100 yr, has been accelerated by a shock and has not yet cooled down. The double empty shell found from mm-wave mapping must also be relatively hot, in agreement with the previous estimate.
planetary nebulae: individual: CRL 618
apex
circumstellar matter
crl-618
dynamics
stars: AGB and post-AGB
stars: mass-loss
planetary nebulae: general
heterodyne instrument
facility
molecular envelope
Author
V. Bujarrabal
J. Alcolea
R. Soria-Ruiz
P. Planesas
Atacama Large Millimeter-submillimeter Array (ALMA)
D. Teyssier
European Space Agency (ESA)
A. P. Marston
European Space Agency (ESA)
J. Cernicharo
Centro de Astrobiologia (CAB)
L. Decin
University of Amsterdam
KU Leuven
C. Dominik
Radboud University
University of Amsterdam
Kay Justtanont
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
A. de Koter
Utrecht University
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
M. Schmidt
Polish Academy of Sciences
Fredrik Schöier
Chalmers, Earth and Space Sciences, Onsala Space Observatory
R. Szczerba
Polish Academy of Sciences
Lbfm Waters
University of Amsterdam
KU Leuven
G. Quintana-Lacaci
Institut de Radioastronomie Millimétrique (IRAM)
R. Güsten
Max Planck Society
J. D. Gallego
Yebes Observatory
M. C. Diez-Gonzalez
Yebes Observatory
A. Barcia
Yebes Observatory
I. Lopez-Fernandez
Yebes Observatory
K. Wildeman
Netherlands Institute for Space Research (SRON)
Aggm Tielens
Leiden University
K. Jacobs
University of Cologne
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 521 1 Article Number: L3- L3Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201015068