title: Discovery of Time Variation of the Intensity of Molecular Lines in IRC+10216 in The Submillimeter and Far Infrared Domains.
abstract: We report on the discovery of strong intensity variations in the high rotational lines of abundant molecular species towards the archetypical circumstellar envelope of IRC+10216. The observations have been carried out with the HIFI instrument on boardHerscheland with the IRAM 30-m telescope. They cover several observing periods spreading over 3 years. The line intensity variations for molecules produced in the external layers of the envelope most probably result from time variations in the infrared pumping rates. We analyze the main implications this discovery has on the interpretation of molecular line emission in the envelopes of Mira-type stars. Radiative transfer calculations have to take into account both the time variability of infrared pumping and the possible variation of the dust and gas temperatures with stellar phase in order to reproduce the observation of molecular lines at different epochs. The effect of gas temperature variations with stellar phase could be particularly important for lines produced in the innermost regions of the envelope. Each layer of the circumstellar envelope sees the stellar light radiation with a different lag time (phase). Our results show that this effect must be included in the models. The sub-mm and FIR lines of AGB stars cannot anymore be considered as safe intensity calibrators.
authors.affiliation: Group of Molecular Astrophysics. ICMM. CSIC. C/Sor Juana Inés de La Cruz N3. E-28049, Madrid. Spain.
authors.forename: J
authors.initials: J
authors.lastname: Cernicharo
authors.affiliation: ESA. ESAC. P.O. Box 78, Villanueva de la Cañada E-28691 Madrid. Spain.
authors.forename: D
authors.initials: D
authors.lastname: Teyssier
authors.affiliation: Group of Molecular Astrophysics. ICMM. CSIC. C/Sor Juana Inés de La Cruz N3. E-28049, Madrid. Spain.
authors.forename: G
authors.initials: G
authors.lastname: Quintana-Lacaci
authors.affiliation: Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France CNRS, IPAG, F-38000 Grenoble, France.
authors.forename: F
authors.initials: F
authors.lastname: Daniel
authors.affiliation: Group of Molecular Astrophysics. ICMM. CSIC. C/Sor Juana Inés de La Cruz N3. E-28049, Madrid. Spain.
authors.forename: M
authors.initials: M
authors.lastname: Agúndez
authors.affiliation: Group of Molecular Astrophysics. ICMM. CSIC. C/Sor Juana Inés de La Cruz N3. E-28049, Madrid. Spain.
authors.forename: L Velilla
authors.initials: LV
authors.lastname: Prieto
authors.affiliation: Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Decin
authors.affiliation: Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, F-38406, St-Martin d'Hères, France.
authors.forename: M
authors.initials: M
authors.lastname: Guélin
authors.affiliation: LERMA, Observatoire de Paris, 61 Av. de l'Observatoire, F-75014 Paris, France.
authors.forename: P
authors.initials: P
authors.lastname: Encrenaz
authors.affiliation: ESA. ESAC. P.O. Box 78, Villanueva de la Cañada E-28691 Madrid. Spain.
authors.forename: P
authors.initials: P
authors.lastname: García-Lario
authors.affiliation: Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE 43992 Onsala, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: de Beck
authors.affiliation: Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Barlow
authors.affiliation: Koninklijke Sterrenwacht van België, Ringlaan 3, B-1180, Brussel, Belgium.
authors.forename: M A T
authors.initials: MA
authors.lastname: Groenewegen
authors.affiliation: Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.
authors.forename: D
authors.initials: D
authors.lastname: Neufeld
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA.
authors.forename: J
authors.initials: J
authors.lastname: Pearson
keywords: Stars: individual (IRC +10216); astrochemistry; stars: AGB and post-AGB; stars: carbon