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Herschel observations of gas and dust in comet C/2006 W3 (Christensen) at 5 AU from the Sun

de Val-Borro, M. and Bockelée-Morvan, D. and Jehin, E. and Hartogh, P. and Opitom, C. and Szutowicz, S. and Biver, N. and Crovisier, J. and Lis, D. C. and Rezac, L. and de Graauw, T. and Hutsemékers, D. and Jarchow, C. and Kidger, M. and Küppers, M. and Lara, L. M. and Manfroid, J. and Rengel, M. and Swinyard, B. M. and Teyssier, D. and Vandenbussche, B. and Waelkens, C. (2014) Herschel observations of gas and dust in comet C/2006 W3 (Christensen) at 5 AU from the Sun. Astronomy and Astrophysics, 564 . Art. No. A124. ISSN 0004-6361.

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Context. Cometary activity at large heliocentric distances is thought to be driven by outgassing of molecular species more volatile than water that are present in the nucleus. The long-period comet C/2006 W3 (Christensen) was an exceptional target for a detailed study of its distant gaseous and dust activity. Aims. We aimed to measure the H_2O and dust production rates in C/2006 W3 (Christensen) with the Herschel Space Observatory at a heliocentric distance of ~5 AU and compared these data with previous post-perihelion Herschel and ground-based observations at ~3.3 AU from the Sun. Methods. We have searched for emission in the HO and NH_3 ground-state rotational transitions, J_K_(a)K_(c) (1_(10)–1_(01)) at 557 GHz and JK (1_(0)–0_(0)) at 572 GHz, simultaneously, toward comet C/2006 W3 (Christensen) with the Heterodyne Instrument for the Far Infrared (HIFI) onboard Herschel on UT 1.5 September 2010. Photometric observations of the dust coma in the 70 μm and 160 μm channels were acquired with the Photodetector Array Camera and Spectrometer (PACS) instrument on UT 26.5 August 2010. Results. A tentative 4σ H_2O line emission feature was found in the spectra obtained with the HIFI wide-band and high-resolution spectrometers, from which we derive a water production rate of (2.0 ± 0.5) × 1027 molec s^(-1). A 3σ upper limit for the ammonia production rate of <1.5 × 10^(27) molec s^(-1) is obtained taking into account the contribution from all hyperfine components. The dust thermal emission was detected in the 70 μm and 160 μm filters, with a more extended emission in the blue channel. We fit the radial dependence of the surface brightness with radially symmetric profiles for the blue and red bands. The dust production rates, obtained for a dust size distribution index that explains the fluxes at the photocenters of the 70 μm and 160 μm PACS images, lie in the range 70 kg s^(-1) to 110 kg s^(-1). Scaling the CO production rate measured post-perihelion at 3.20 AU and 3.32 AU, these values correspond to a dust-to-gas production rate ratio in the range 0.3–0.4. Conclusions. The blueshift of the water line detected by HIFI suggests preferential emission from the subsolar point. However, it is also possible that water sublimation occurs in small ice-bearing grains that are emitted from an active region on the nucleus surface at a speed of ~0.2 km s^(-1). The dust production rates derived in August 2010 are roughly one order of magnitude lower than in September 2009, suggesting that the dust-to-gas production rate ratio remained approximately constant during the period when the activity became increasingly dominated by CO outgassing.

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Lis, D. C.0000-0002-0500-4700
Additional Information:© 2014 ESO. Received: 15 January 2014; accepted: 26 February 2014. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada, and the United States under the leadership of SRON, Netherlands Institute for Space Research, Groningen, The Netherlands, and with major contributions from Germany, France, and the US. Consortium members are: Canada: CSA, U.Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri-INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiología (CSIC-INTA). Sweden: Chalmers University of Technology – MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University – Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAFIFSI /OAA/OAP/OAT, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT /MCYT (Spain). Support for this work was provided by NASA through an award issued by JPL/Caltech. We thank M. Sánchez-Portal from the Herschel Science Center, and H. Linz from the PACS Instrument Control Center (ICC) for their help with the reduction and analysis of the Herschel data. The anonymous referee is thanked for providing constructive comments and help in improving the contents of the paper. M.dV.B. acknowledges partial support from grants NSF AST-1108686 and NASA NNX12AH91H. E.J. is FNRS Research Associate, D.H. is Senior Research Associate and J.M. is Research Director FNRS. C.O. thanks the Belgian FNRS for funding her PhD thesis. S.S. acknowledges support from Polish MNiSW under grant 181/N-HSO/2008/0. L.R. was supported by the Special Priority Program 1488 (PlanetMag, of the German Science Foundation.
Funding AgencyGrant Number
Bundesministerium für Verkehr, Innovation und Technologie (BMVIT)UNSPECIFIED
Commissariat à l’Energie Atomique (CEA)UNSPECIFIED
Deutsches Zentrum für Luft- und Raumfahrt (DLR)UNSPECIFIED
Agenzia Spaziale Italiana (ASI)UNSPECIFIED
Fonds de la Recherche Scientifique (FNRS)UNSPECIFIED
Ministerstwo Nauki i Szkolnictwa Wyższego (MNiSW)181/N-HSO/2008/0
Deutsche Forschungsgemeinschaft (DFG)1488
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Subject Keywords:comets: individual: C/2006 W3 (Christensen); submillimeter: planetary systems; techniques: photometric; techniques: spectroscopic
Record Number:CaltechAUTHORS:20140530-105609658
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Official Citation:Herschel observations of gas and dust in comet C/2006 W3 (Christensen) at 5 AU from the Sun M. de Val-Borro, D. Bockelée-Morvan, E. Jehin, P. Hartogh, C. Opitom, S. Szutowicz, N. Biver, J. Crovisier, D. C. Lis, L. Rezac, Th. de Graauw, D. Hutsemékers, C. Jarchow, M. Kidger, M. Küppers, L. M. Lara, J. Manfroid, M. Rengel, B. M. Swinyard, D. Teyssier, B. Vandenbussche and C. Waelkens A&A 564 A124 (2014) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46006
Deposited By: Jason Perez
Deposited On:30 May 2014 19:46
Last Modified:30 Aug 2017 21:32

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