Herschel/HIFI observations of molecular emission in protoplanetary nebulae and young planetary nebulae
Journal article, 2012

Aims. We aim to study the physical conditions, particularly the excitation state, of the intermediate-temperature gas in protoplanetary nebulae and young planetary nebulae (PPNe, PNe). The information that the observations of the different components deliver is of particular importance for understanding the evolution of these objects. Methods. We performed Herschel/HIFI observations of intermediate-excitation molecular lines in the far-infrared/submillimeter range in a sample of ten nebulae. The high spectral resolution provided by HIFI allows the accurate measurement of the line profiles. The dynamics and evolution of these nebulae are known to result from the presence of several gas components, notably fast bipolar outflows and slow shells (that often are the fossil AGB shells), and the interaction between them. Because of the diverse kinematic properties of the different components, their emissions can be identified in the line profiles. The observation of these high-energy transitions allows an accurate study of the excitation conditions, particularly in the warm gas, which cannot be properly studied from the low-energy lines. Results. We have detected FIR/sub-mm lines of several molecules, in particular of (CO)-C-12, (CO)-C-13, and H2O. Emission from other species, like NH3, OH, (H2O)-O-18, HCN, SiO, etc., has been also detected. Wide profiles showing sometimes spectacular line wings have been found. We have mainly studied the excitation properties of the high-velocity emission, which is known to come from fast bipolar outflows. From comparison with general theoretical predictions, we find that CRL 618 shows a particularly warm fast wind, with characteristic kinetic temperature T-k greater than or similar to 200 K. In contrast, the fast winds in OH 231.8+4.2 and NGC 6302 are cold, T-k similar to 30 K. Other nebulae, like CRL 2688, show intermediate temperatures, with characteristic values around 100 K. We also discuss how the complex structure of the nebulae can affect our estimates, considering two-component models. We argue that the differences in temperature in the different nebulae can be caused by cooling after the gas acceleration (that is probably caused by shocks); for instance, CRL 618 is a case of very recent acceleration, less than similar to 100 yr ago, while the fast gas in OH 231.8+4.2 was accelerated similar to 1000 yr ago. We also find indications that the densest gas tends to be cooler, which may be explained by the expected increase of the radiative cooling efficiency with the density.

stars: AGB and post-AGB

stars: mass-loss

circumstellar matter

planetary nebulae: general


V. Bujarrabal

Spanish National Observatory (OAN)

J. Alcolea

Spanish National Observatory (OAN)

R. Soria-Ruiz

Spanish National Observatory (OAN)

P. Planesas

Spanish National Observatory (OAN)

Atacama Large Millimeter-submillimeter Array (ALMA)

D. Teyssier

European Space Astronomy Centre (ESAC)

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, Onsala Space Observatory

A. de Koter

University of Amsterdam

Sterrekundig Instituut Utrecht

A. P. Marston

European Space Astronomy Centre (ESAC)

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

KU Leuven

University of Amsterdam

Astronomy and Astrophysics

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

Vol. 537 Article Number: A8- A8

Subject Categories

Astronomy, Astrophysics and Cosmology



More information

Latest update