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: general

heterodyne instrument



circumstellar matter

planetary nebulae: individual: CRL 618



stars: AGB and post-AGB

molecular envelope

stars: mass-loss


V. Bujarrabal

J. Alcolea

R. Soria-Ruiz

P. Planesas

Atacama Large Millimeter-submillimeter Array (ALMA)

D. Teyssier

European Space Astronomy Centre (ESAC)

A. P. Marston

European Space Astronomy Centre (ESAC)

J. Cernicharo

Centro de Astrobiologia (CAB)

L. Decin

KU Leuven

University of Amsterdam

C. Dominik

Radboud University

University of Amsterdam

Kay Justtanont

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

A. de Koter

University of Amsterdam

Sterrekundig Instituut Utrecht

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- L3

Subject Categories

Astronomy, Astrophysics and Cosmology



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