Herschel/HIFI observations of high-J CO transitions in the protoplanetary nebula CRL 618
Artikel i vetenskaplig tidskrift, 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.



molecular envelope


planetary nebulae: individual: CRL 618

heterodyne instrument

circumstellar matter

stars: AGB and post-AGB

stars: mass-loss

planetary nebulae: general



V. Bujarrabal

J. Alcolea

R. Soria-Ruiz

P. Planesas

Atacama Large Millimeter-submillimeter Array

D. Teyssier

European Space Astronomy Centre

A. P. Marston

European Space Astronomy Centre

J. Cernicharo

CSIC-INTA - Centro de Astrobiologia (CAB)

L. Decin

Universiteit Van Amsterdam

KU Leuven

C. Dominik

Radboud University Nijmegen

Universiteit Van Amsterdam

Kay Justtanont

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

A. de Koter

Universiteit Van Amsterdam

Sterrekundig Instituut Utrecht

G. J. Melnick

Harvard-Smithsonian Center for Astrophysics

K. M. Menten

Max Planck-institutet

D. A. Neufeld

Johns Hopkins University

Hans Olofsson

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

M. Schmidt

Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences

Fredrik Schöier

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

R. Szczerba

Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences

Lbfm Waters

Universiteit Van Amsterdam

KU Leuven

G. Quintana-Lacaci

Instituto de Radioastronomia Milimetrica

R. Güsten

Max Planck-institutet

J. D. Gallego

Centro Astronomico de Yebes

M. C. Diez-Gonzalez

Centro Astronomico de Yebes

A. Barcia

Centro Astronomico de Yebes

I. Lopez-Fernandez

Centro Astronomico de Yebes

K. Wildeman

SRON Netherlands Institute for Space Research

Aggm Tielens

Leiden Observatory Research Institute

K. Jacobs

Universitat zu Koln

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 521 Article Number: L3- L3


Astronomi, astrofysik och kosmologi